JP4704891B2 - Liquid state detection device - Google Patents

Description

  The present invention relates to a liquid state detection device that detects the concentration of a liquid stored in a liquid storage container.

  In recent years, for example, an NOx selective reduction (SCR) catalyst may be used in an exhaust gas purification device that reduces nitrogen oxide (NOx) discharged from a diesel vehicle to a harmless gas, and an aqueous urea solution is used as the reducing agent. It is known that an aqueous urea solution having a urea concentration of 32.5 wt% may be used to efficiently perform this reduction reaction. However, the urea concentration stored in a urea water tank mounted on an automobile may change in its urea concentration due to changes over time. Further, there is a possibility that a different liquid or water may be mistakenly mixed into the urea water tank. Therefore, a concentration sensor for detecting the urea concentration is attached to the urea water tank so that the urea concentration of the urea aqueous solution can be managed, and the concentration detection is performed.

  Incidentally, it is known that the thermal conductivity varies depending on the concentration of urea contained in the aqueous urea solution. Therefore, a concentration sensor provided with two temperature sensors (sensor elements) whose resistance values change in proportion to the temperature in parallel is attached to the urea water tank, and one of the temperature sensors is heated by energization. If the concentration of the urea aqueous solution is affected during heat conduction to the other temperature sensing element, the urea concentration of the urea aqueous solution can be detected from the difference between the measured resistance values (see, for example, Patent Document 1). ). If the detected urea concentration is not within the normal concentration range, it is possible to make an abnormality determination such as determination that a different liquid or water is mixed in the urea water tank or determination that the urea aqueous solution is empty.

On the other hand, as the diesel vehicle travels, the vehicle body may vibrate and the aqueous urea solution stored in the urea water tank may be shaken or stirred. In the concentration sensor of Patent Document 1, the concentration of the urea aqueous solution is uneven due to the flow of the aqueous urea solution (flow caused by shaking or stirring), or the sensor element is deprived of heat and the resistance value of the sensor element is not proportional to the urea concentration. And the detected urea concentration may show a value significantly different from the original value. For this reason, in Patent Document 1, it is determined whether or not the urea aqueous solution is in a stationary state based on the traveling state of the diesel vehicle (specifically, the vehicle speed). Density abnormality is determined by weighting different from that in a stationary state.
Japanese Patent No. 3686672

  However, in Patent Document 1, since the determination as to whether or not the urea aqueous solution in the urea water tank is in a stationary state is made based on prediction based on the vehicle speed of the diesel vehicle, what is the actual state of the flow due to the shaking of the urea aqueous solution? In some cases, the density abnormality may not be accurately determined.

  The present invention has been made to solve the above problems, and determines a stationary state based on the current concentration value of the liquid stored in the liquid storage container and the concentration value detected immediately before, It is an object of the present invention to provide a liquid state detection device capable of more accurately determining an abnormal concentration.

  In order to achieve the above object, a liquid state detection device according to a first aspect of the present invention includes a detection element that outputs a signal related to the concentration of a specific component in a liquid stored in a liquid storage container, and the detection element Based on a signal from the concentration detection means for detecting the concentration value of the specific component, and on the basis of a signal from the detection element and a threshold value set corresponding to a specific abnormal state related to the liquid, An abnormality detection means for detecting whether or not the liquid is in the specific abnormal state, and an abnormality count value is added by a predetermined count value each time the liquid is detected to be in the specific abnormal state by the abnormality detection means. And a liquid state detection unit that determines that the liquid is in the specific abnormal state when the abnormal count value obtained by the counter unit reaches an abnormal fixed value. The apparatus calculates a difference value between the current density value detected by the density detection means and the previous density value detected immediately before or a ratio between the two as a stillness determination value, and determines the stillness determination. Based on a value, a stationary state determining means for determining whether or not the liquid is in a stationary state in the liquid container, and a case in which the liquid is determined to be stationary by the stationary state determining means; Setting value changing means for setting at least one of the predetermined count value and the abnormality confirmed value to a different value when it is determined that the liquid is not in a stationary state.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect of the invention, the detection element has a heating resistor that generates heat when energized, and the concentration detection means A first corresponding value corresponding to the first resistance value of the heating resistor acquired after the energization of the heating resistor is started, and a second resistance value corresponding to the second resistance value acquired after the heating resistor is energized for a predetermined time. 2 to obtain a difference value with respect to the corresponding value, and detect a concentration value of a specific component contained in the liquid corresponding to the difference value, and the abnormality detection means includes at least the difference value and the current concentration value. One value is compared with a threshold value set corresponding to a specific abnormal state related to the liquid to detect whether or not the liquid is in the specific abnormal state. The stationary judgment value is a judgment criterion of the stationary state If greater than that reference threshold, wherein the liquid and judging that no stationary.

  According to a third aspect of the present invention, in addition to the configuration of the first or second aspect of the invention, the abnormality determination unit determines that the liquid is in the specific abnormal state. In addition, an informing means for informing the external circuit of the abnormality is provided.

  In addition to the configuration of the invention according to any one of claims 1 to 3, the liquid state detection device according to the invention according to claim 4 provides a signal corresponding to the level of the liquid contained in the liquid container. A level detection unit for outputting, and the stationary state determination means determines whether or not the liquid is stationary in the liquid container based on the stationary determination value and a signal from the level detection unit. It is characterized by determining.

  According to a fifth aspect of the present invention, in addition to the configuration of the fourth aspect of the invention, the level detection unit includes a first electrode and a second electrode extending in a longitudinal direction, A capacitor whose capacitance changes in accordance with the level of the liquid stored in the liquid storage container between one electrode and the second electrode is formed, and the level detection unit is connected to the liquid storage container When the liquid storage container is installed in a posture for use, and the liquid is stored, the detection element has at least a part of the detection element from a tip of the level detection unit facing the liquid level lowering direction. Is also located on the tip side and is integrated with the level detection unit in an insulated state.

  In addition to the configuration of the invention according to any one of claims 1 to 5, the liquid state detection device according to a sixth aspect of the invention is configured so that a specific abnormal state related to the liquid is caused by the liquid in the liquid container. It is one of a state in which the liquid is empty, a state in which a different kind of liquid is mixed into the liquid container, and a state in which the concentration of the specific component contained in the liquid is abnormal.

  According to a seventh aspect of the present invention, in addition to the configuration of the first aspect, the liquid is a urea aqueous solution, and the specific component is urea. Features.

  When a liquid with an appropriate concentration is stored in the liquid container, the two concentration values detected continuously by the concentration detecting means are usually greatly different values if the liquid is in a stationary state. There is no indication. However, when the liquid is not in a stationary state and a flow occurs in the liquid around the detection element, it is detected continuously due to the influence of unevenness in the concentration of a specific component in the liquid around the detection element. The inventors of the present application have found that the two density values are greatly different values. Therefore, in the liquid state detection device according to the first aspect of the present invention, the concentration value of the specific component in the liquid stored in the liquid storage container is detected, and the current concentration value and the immediately preceding detected value are detected. A difference value from the concentration value or a ratio between the two is obtained as a stillness determination value, and based on the stillness determination value, it is determined whether or not the liquid is in a still state. As described above, according to the present invention, since it is directly determined whether or not the liquid is in a stationary state based on the variation of the detected concentration value, the reliability of the determination result of the stationary state is high.

  Furthermore, by reflecting the determination result of the stationary state on at least one of a predetermined count value and an abnormality confirmation value, weighting based on whether or not the liquid is stationary is detected in the detection of the abnormal state of the liquid. It can be carried out. Thereby, even if an abnormality is detected in the concentration of the specific component in the liquid, it is not immediately determined as an abnormal state. Therefore, if the liquid is not in a stationary state, it is possible to increase the chance of detecting an abnormal state before determining that the liquid is in a specific abnormal state, so that the reliability of the determination of the abnormal state can be improved. it can.

  By the way, since the thermal conductivity of the liquid varies depending on the concentration of the specific component contained in the liquid, when the surrounding liquid is heated for a certain period of time using a heating resistor, the temperature increase rate differs for liquids with different concentrations. Become. Therefore, in the invention according to claim 2, the heating resistor is energized for a certain period of time, the first corresponding value corresponding to the first resistance value after the energization of the heating resistor is started, and after the energization to the heating resistor for a certain period of time. Based on the difference value from the second corresponding value corresponding to the second resistance value, it is possible to grasp the degree of temperature rise of the heating resistor and to detect the concentration of the specific component contained in the liquid. Using at least one of the difference value obtained when detecting the concentration and the detected current concentration value, and comparing the value with a threshold set corresponding to a specific abnormal state related to the liquid It is possible to detect whether the liquid is in a specific abnormal state.

  The first corresponding value may be a value corresponding to the first resistance value of the heating resistor, and specifically includes a voltage value, a current value, a temperature converted value, and the like. Similarly, the second corresponding value may be a value corresponding to the second resistance value of the heating resistor. However, in the invention according to claim 2, since it is necessary to obtain a difference value between the second corresponding value and the first corresponding value, for example, when the first corresponding value is a voltage value, the second corresponding value is also Similarly, it is necessary to set the voltage value.

  Furthermore, in the invention according to claim 2, the timing for acquiring the first corresponding value is within a period in which the temperature of the heating resistor itself is substantially the same as the temperature of the surrounding liquid after the energization of the heating resistor is started. What is necessary is just to acquire, and specifically, a 1st corresponding value should just be acquired within 100 msec after the energization start to a heating resistor. At the start of energization of the heating resistor, the current applied to the heating resistor tends to be difficult to stabilize. Therefore, after the energization of the heating resistor has started, 2 msec has elapsed and within 100 msec (more preferably It is preferable to acquire the first corresponding value within 50 msec).

  In the invention according to claim 3, the abnormality can be notified to the external circuit only when it is determined that the liquid is in a specific abnormal state. That is, even if a temporary abnormal state of the liquid is detected internally, it is not determined that a specific abnormal state has occurred in the liquid unless it is a continuous abnormal state. For this reason, it is possible to notify the external circuit of an abnormal state with high reliability.

  In the invention according to claim 4, the determination as to whether or not the liquid is in a stationary state in the liquid storage container is performed using a signal from a level detection unit that can detect the level of the liquid. Yes. That is, since the state of the liquid in the liquid container can be detected directly from the fluctuation of the level, the determination of the stationary state of the liquid can be performed with higher accuracy. The stationary state may be determined based on the difference between the maximum value and the minimum value of the signal from the level detection unit acquired a plurality of times within a predetermined period, that is, the difference in the vertical movement of the liquid level.

  In the invention according to claim 5, the level detection unit for detecting the level of the liquid and the detection element for detecting the concentration of the liquid are integrated in an insulated state. With this configuration, the device for detecting the liquid level and the device for detecting the concentration of the liquid occupy the liquid storage container of the liquid state detection device as compared with the case where the device is separately provided and disposed in the liquid storage container. The volume can be made relatively small, and the maximum amount of liquid that can be stored in the liquid storage container can be increased. Furthermore, since the mounting portion for mounting the liquid state detection device to the liquid container is only required in one place, the structure for maintaining the airtightness and watertightness between the liquid container and the mounting portion is simplified. Can be. In addition, since at least a part of the detection element is located on the tip side of the level detection unit rather than the tip that faces the liquid level lowering direction, the state where the detection element is immersed in the liquid even if the level of the liquid is lowered. The liquid can be maintained longer, and the liquid concentration can be detected stably.

  Further, as in the invention according to claim 6, the specific abnormal state relating to the liquid includes a state in which the liquid is empty in the liquid storage container, a state in which a different kind of liquid is mixed in the liquid storage container, and the liquid. One of the states in which the concentration of the specific component is abnormal can be mentioned.

  In the invention according to claim 7, by detecting a signal related to the concentration of urea contained in the urea aqueous solution from the detection element, it is possible to accurately detect and determine a specific abnormal state related to the urea aqueous solution.

  Hereinafter, an embodiment of a liquid state detection device embodying the present invention will be described with reference to the drawings. First, the structure of a liquid state detection sensor 100 as an example of a liquid state detection device will be described with reference to FIGS. FIG. 1 is a partially cutaway longitudinal sectional view of the liquid state detection sensor 100. FIG. 2 is a schematic diagram showing the heater pattern 115 of the ceramic heater 110. In the liquid state detection sensor 100, the longitudinal direction of the level detection unit 70 (capacitor constituted by the outer cylinder electrode 10 and the internal electrode 20) is the axis O direction, and the side on which the liquid property detection unit 30 is provided is the front end side and attached. The side where the portion 40 is provided is the rear end side. The outer cylinder electrode 10 and the inner electrode 20 correspond to the “first electrode” and the “second electrode” in the present invention, respectively.

  The liquid state detection sensor 100 of the present embodiment is a state of an aqueous urea solution used for reduction of nitrogen oxide (NOx) contained in exhaust gas of a diesel vehicle, that is, the level (liquid level) and temperature of the aqueous urea solution. And a sensor for detecting the concentration of urea as a specific component contained in the solution. As shown in FIG. 1, the liquid state detection sensor 100 includes a cylindrical outer cylinder electrode 10 and a cylindrical shape provided along the axis O direction of the outer cylinder electrode 10 inside the outer cylinder electrode 10. Mounting for attaching the level detection unit 70 constituted by the internal electrode 20, the liquid property detection unit 30 provided on the tip side of the internal electrode 20, and the liquid state detection sensor 100 to the urea water tank 98 (see FIG. 3). Unit 40.

  The outer cylinder electrode 10 is made of a metal material and has a long and thin cylindrical shape extending in the axis O direction. A plurality of narrow slits 15 are intermittently opened along each bus bar on three bus bars that are equally spaced in the circumferential direction on the outer periphery of the outer cylindrical electrode 10. Further, at the distal end portion 11 of the outer cylinder electrode 10, an opening portion 16 for preventing a rubber bushing 80 interposed between the inner electrode 20 (described later) from coming off is formed on each bus bar where the slit 15 is formed. Each is provided. Furthermore, one air vent hole 19 is formed on a bus bar different from each bus bar where the slits 15 are formed at a position close to the base end portion 12 on the rear end side of the outer cylinder electrode 10. Further, the distal end portion 11 of the outer cylindrical electrode 10 is formed so as to surround the periphery of the ceramic heater 110 in the radial direction of the liquid property detection unit 30 described later together with the protector 130 that covers and protects the ceramic heater 110. It extends further to the front end side in the axis O direction than the position. And the most advanced part (the lowest part in the figure) is opened, and the protector 130 constituting the liquid property detecting unit 30 is visible from the opening side.

  Next, the outer cylinder electrode 10 is welded in a state in which the base end portion 12 is engaged with the outer periphery of the electrode support portion 41 of the metal attachment portion 40. The attachment portion 40 functions as a base for fixing the liquid state detection sensor 100 to the urea water tank 98 as a liquid container, and an attachment hole (not shown) for inserting an attachment bolt is formed in the flange portion 42. Yes. Further, on the opposite side of the electrode support portion 41 across the flange portion 42 of the mounting portion 40, a circuit for detecting the level, temperature, urea concentration, etc. of the urea aqueous solution, which will be described later, or an external circuit (not shown) A housing portion 43 for housing a circuit board 60 on which an input / output circuit for electrical connection with the engine control device (ECU) is mounted is formed. The outer cylinder electrode 10 is grounded through the mounting portion 40.

  The circuit board 60 is placed on a board placement portion (not shown) protruding from the four corners of the inner wall surface of the housing portion 43. The accommodating portion 43 is covered and protected by a cover 45, and the cover 45 is fixed to the flange portion 42. A connector 62 is fixed to the side surface of the cover 45, and a connection terminal (not shown) of the connector 62 and a pattern (an input / output circuit unit 290 described later) on the circuit board 60 are connected by the wiring cable 61. Yes. The circuit board 60 and the ECU are connected via the connector 62.

  A hole 46 penetrating into the accommodating portion 43 is opened in the electrode support portion 41 of the attachment portion 40, and the base end portion 22 of the internal electrode 20 is inserted into the hole 46. The internal electrode 20 of the present embodiment is made of a long and thin cylindrical metal material extending in the direction of the axis O. On the outer peripheral surface of the internal electrode 20, an insulating coating 23 made of a fluorine resin such as PTFE, PFA, ETFE, an epoxy resin, a polyimide resin or the like is formed. The insulating coating 23 is formed in the form of a resin coating layer by applying such a resin onto the outer surface of the internal electrode 20 by dipping or electrostatic powder coating and heat-treating it. Between the internal electrode 20 and the outer cylinder electrode 10, a level detection unit 70 is formed, in which a capacitor whose capacitance changes according to the level of the urea aqueous solution is formed.

  A pipe guide 55 and an inner case 50 for fixing the internal electrode 20 to the mounting portion 40 are engaged with the base end portion 22 on the rear end side in the axis O direction of the internal electrode 20. The pipe guide 55 is an annular guide member joined near the end edge of the base end portion 22 of the internal electrode 20. The inner case 50 is a flanged cylindrical resin member that positions and supports the inner electrode 20 so that the inner electrode 20 and the outer cylinder electrode 10 are reliably insulated, and the tip side of the inner case 50 is the electrode support portion 41 of the mounting portion 40. Engage with hole 46. The inner case 50 is formed with a flange portion 51 that protrudes radially outward. When the inner case 50 is engaged with the electrode support portion 41, a hole in the electrode support portion 41 is formed from the housing portion 43 side. 46 is inserted. Then, the flange portion 51 abuts against the bottom surface in the housing portion 43, thereby preventing the inner case 50 from passing through the hole 46. In addition, the internal electrode 20 is inserted into the inner case 50 from the accommodating portion 43 side, but the pipe guide 55 is brought into contact with the flange portion 51 so that the inner electrode 20 is prevented from falling off the inner case 50.

  Further, an O-ring 53 and an O-ring 54 are provided on the outer periphery and the inner periphery of the inner case 50, respectively. The O-ring 53 seals a gap between the outer periphery of the inner case 50 and the hole 46 of the mounting portion 40, and the O-ring 54 is formed between the inner periphery of the inner case 50 and the outer periphery of the base end portion 22 of the internal electrode 20. The gap between them is sealed. Thereby, when the liquid state detection sensor 100 is attached to the urea water tank 98 (see FIG. 3), the water tightness and the inside of the urea water tank 98 are prevented from communicating with each other through the housing portion 43. Airtightness is maintained. A plate-like sealing member (not shown) is attached to the front end surface of the flange portion 42 of the attachment portion 40, and when the liquid state detection sensor 100 is attached to the urea water tank 98, the flange portion 42 and urea water are attached. Watertightness and airtightness with the tank are maintained.

  When the internal electrode 20 is assembled to the mounting portion 40, the pipe guide 55 is pressed against the flange portion 51 of the inner case 50 by the two pressing plates 56 and 57. The insulating pressing plate 56 is fixed in the accommodating portion 43 with screws 58 in a state where the pressing plate 57 is sandwiched between the insulating guide plate 56 and the pipe guide 55. Thereby, the internal electrode 20 joined to the pipe guide 55 is fixed to the electrode support portion 41. A hole 59 is opened in the center of the holding plates 56 and 57, and two lead wires 90 (in FIG. 1) for electrically connecting the electrode lead wire 52 of the internal electrode 20 and a ceramic heater 110 described later. Only one of the lead wires 90 is shown.) A two-core cable 91 containing the lead wire 90 is inserted and electrically connected to the pattern on the circuit board 60, respectively. An electrode (not shown) on the ground side of the circuit board 60 is connected to the mounting portion 40, whereby the outer cylinder electrode 10 welded to the mounting portion 40 is electrically connected to the ground side.

  Next, the liquid property detection unit 30 provided at the distal end portion 21 of the internal electrode 20 includes a ceramic heater 110 as a detection element that detects the temperature of the urea aqueous solution and the concentration of urea contained in the present embodiment, In addition to supporting the ceramic heater 110, a holder 120 made of an insulating resin attached to the tip portion 21 of the internal electrode 20 and a protector 130 covering and protecting the periphery of the ceramic heater 110 exposed from the holder 120 are provided. Composed.

  As shown in FIG. 2, the ceramic heater 110 is formed by forming a heater pattern 115 mainly composed of Pt on a plate-like ceramic base 111 made of an insulating ceramic and sandwiching it between a pair of ceramic bases (not shown). In this state, the heater pattern 115 is embedded. Heat generation is performed mainly in the heating resistor 114 during energization so that the cross-sectional area of the pattern constituting the heating resistor 114 is made smaller than the pattern of the lead portions 112 and 113 serving as both poles for voltage application. I am doing so. In addition, through holes (not shown) penetrating the surface of the ceramic base 111 are provided at both ends of the lead portions 112 and 113, respectively, and two connectors 119 (relaying connections between the two lead wires 90) In FIG. 1, only one of them is displayed). The ceramic heater 110 corresponds to the “detection element” in the present invention.

  Next, as shown in FIG. 1, the holder 120 that supports the ceramic heater 110 has a cylindrical shape in which the outer diameter is configured to be two steps in a stepped shape, and the heating resistor 114 of the heating resistor 114 is formed on the distal end side having a small diameter. The ceramic heater 110 in a state where the embedded side (see FIG. 2) is exposed is fixed by fixing members 125 and 126 made of an adhesive. The rear end side, which is the large diameter side, is attached to the distal end portion 21 of the internal electrode 20, and a seal ring 140 is interposed between the outer peripheral surface of the internal electrode 20 and the inner peripheral surface of the holder 120. The water-tightness and air-tightness of the interior of the are secured.

  By the way, before the holder 120 is mounted, the core wires of the two lead wires 90 of the cable 91 are joined to the connector 119 of the ceramic heater 110 by caulking or soldering, respectively. Further, the insulating protection member 95 covers and protects the connector 119 and the lead wire 90 together with the joint portion. The two lead wires 90 are inserted through the cylindrical internal electrode 20 and connected to the circuit board 60.

  Next, the protector 130 is a metal protective member formed in a bottomed cylindrical shape. The opening side is fitted to the outer periphery of the small diameter portion of the holder 120. Further, a liquid circulation hole (not shown) is opened on the outer periphery of the protector 130, and the urea aqueous solution is exchanged inside and outside the protector 130.

  The liquid property detection unit 30 having such a configuration is attached to the distal end portion 21 of the internal electrode 20 via the holder 120 and is elastically supported in the outer cylindrical electrode 10 by the rubber bush 80. The rubber bush 80 has a cylindrical shape, and a protrusion 87 formed on the outer peripheral surface thereof is engaged with and fixed to the opening 16 of the outer cylinder electrode 10. A plurality of grooves (not shown) along the axis O direction are provided in each of the outer peripheral surface and the inner peripheral surface of the rubber bush 80. When the liquid state detection sensor 100 is attached to the urea water tank 98, liquid exchange and bubble removal between the urea aqueous solution flowing into the front end side of the rubber bush 80 and the urea aqueous solution flowing into the rear end side through this groove are performed. Is done. By the rubber bush 80, the liquid property detection unit 30 and the level detection unit 70 are integrally configured in an insulated state.

  Next, the electrical configuration of the liquid state detection sensor 100 will be described with reference to FIGS. FIG. 3 is a block diagram showing an electrical configuration of the liquid state detection sensor 100. FIG. 4 is a diagram showing a conceptual configuration of the storage area of the RAM 300. As shown in FIG.

  As shown in FIG. 3, the liquid state detection sensor 100 is attached to a urea water tank 98 as a liquid container, and includes a level detection unit 70 including a pair of electrodes (the outer cylinder electrode 10 and the internal electrode 20), and a heating resistance. The liquid property detection unit 30 including the ceramic heater 110 in which the body 114 is embedded is immersed in a urea aqueous solution as a state detection target liquid stored in the urea water tank 98. The liquid state detection sensor 100 includes a microcomputer 220 mounted on the circuit board 60, a level detection circuit unit 250 that controls the level detection unit 70, and a liquid property detection circuit unit 280 that controls the liquid property detection unit 30. An input / output circuit unit 290 that communicates with the ECU is connected.

  The microcomputer 220 includes a CPU 221, a ROM 222, and a RAM 300 having a known configuration. The CPU 221 controls the liquid state detection sensor 100. The ROM 222 is provided with various storage areas not shown, and a state detection program, expressions (1) to (5) described later, initial values of various variables, threshold values, and the like are stored in a predetermined storage area. Similarly, various storage areas shown in FIG. 4 to be described later are also provided in the RAM 300, and a part of the program, various variables, a timer count value, and the like are temporarily stored when the state detection program is executed.

  The input / output circuit unit 290 controls the communication protocol in order to input and output signals between the liquid state detection sensor 100 and the ECU. Further, the level detection circuit unit 250 applied an AC voltage between the outer cylinder electrode 10 and the internal electrode 20 of the level detection unit 70 based on an instruction from the microcomputer 220, and flowed through a capacitor forming the level detection unit 70. This is a circuit unit that converts a current into a voltage, performs A / D conversion, and outputs the result to the microcomputer 220.

  Next, the liquid property detection circuit unit 280 applies a constant current to the ceramic heater 110 of the liquid property detection unit 30 based on an instruction from the microcomputer 220, and supplies the detection voltage generated at both ends of the heating resistor 114 to the microcomputer 220. It is the circuit part which outputs. The liquid property detection circuit unit 280 includes a differential amplifier circuit unit 230, a constant current output unit 240, and a switch 260.

  The constant current output unit 240 outputs a constant current that flows through the heating resistor 114. The switch 260 is provided on the energization path to the heating resistor 114 and opens / closes the switch according to the control of the microcomputer 220. The differential amplifier circuit unit 230 outputs a difference between the potential Pin appearing at one end of the heating resistor 114 and the potential Pout appearing at the other end to the microcomputer 220 as a detection voltage.

  Next, the storage area of the RAM 300 will be described. As shown in FIG. 4, the RAM 300 has a level fluctuation value storage area 301, a voltage value storage area 302, a voltage difference value storage area 303, a normal voltage difference value storage area 304, a density conversion value storage area 305, and a timer count value storage. An area 306, a flag storage area 307, a counter value storage area 308, and the like are provided.

  In the level fluctuation value storage area 301, a detection value (A / D conversion value) indicating the level of the urea aqueous solution obtained by A / D converting the output from the level detection unit 70 in the level detection circuit unit 250 is stored. The output of the liquid property detection unit 30 (that is, the difference between the potential Pin and the potential Pout) is input to the microcomputer 220 via the differential amplifier circuit unit 230 as a detection voltage. The voltage value Vm after 10 msec and the voltage value Vn after 700 msec are stored after the start of concentration measurement. The storage area of the voltage value Vm is provided with five storage areas, and the latest five voltage values among the voltage values repeatedly detected according to the state detection program described later are stored and detected before that. The discarded voltage value is discarded.

  In the voltage difference value storage area 303, a difference value ΔVmn between the latest voltage value Vm and the voltage value Vn stored in the voltage value storage area 302 is stored. The normal voltage difference value storage area 304 stores the voltage difference value ΔVmn when it is determined by the state detection program that there is no abnormality in the detected concentration of the aqueous urea solution. The normal voltage difference value storage area 304 is also provided with five storage areas, and the latest five voltage difference values ΔVmn are stored as described above. In the density conversion value storage area 305, a density conversion value Cn calculated from the voltage difference value ΔVmn is stored. Two storage areas are provided in the storage area of the density conversion value Cn, the latest two density conversion values Cn are stored, and the density conversion values calculated before that are discarded.

  The timer count value storage area 306 is provided with an initial value storage area for two types of timers T1 and T2 used in the state detection program, and a timer program (not shown) that is executed separately when the timer is reset. The count value is stored. In the state detection program to be described later, when confirmation of elapse of a predetermined time (for example, 1 sec) is performed, the initial values of the timers T1 and T2 stored at the time of resetting and the count value of the timer program at that time This is done by determining whether or not the difference is greater than a value corresponding to the predetermined time.

  The flag storage area 307 stores values of a normal detection flag and a stationary state flag used in the state detection program. The counter value storage area stores the count values of the concentration abnormality counter, the empty counter, and the different liquid counter.

  The RAM 300 is provided with various storage areas (not shown), and a state detection program that uses the above parameters is read into a predetermined storage area and executed.

  Next, the principle of detecting the level, temperature, and urea concentration of the urea aqueous solution by the liquid state detection sensor 100 of the present embodiment will be described. First, the principle of detecting the level of the urea aqueous solution in the level detection unit 70 will be described with reference to FIG. FIG. 5 is an enlarged cross-sectional view of the vicinity of the water surface of the urea aqueous solution filled in the gap between the outer cylinder electrode 10 and the inner electrode 20.

  The liquid state detection sensor 100 (see FIG. 1) is assembled in a urea water tank 98 (see FIG. 3) containing a urea aqueous solution in a state where the front end side of the outer cylinder electrode 10 and the inner electrode 20 faces the bottom wall side. It is done. That is, the level detection unit 70 of the liquid state detection sensor 100 sets the direction of displacement of the urea aqueous solution whose capacity changes in the urea water tank 98 (the level of the urea aqueous solution level) as the axis O direction, and the outer cylinder electrode 10 and the internal electrode. 20 is assembled to the urea water tank 98 so that the tip side of 20 is the side (low level side) where the volume of the urea aqueous solution is small. And the electrostatic capacitance between the gaps of the outer cylinder electrode 10 and the inner electrode 20 is measured, and it is detected to what level the urea aqueous solution existing between the two is present in the axis O direction. As is well known, this is based on the fact that the capacitance increases as the difference in diameter between two points having different potentials in the radial direction decreases.

  That is, as shown in FIG. 5, in the portion not filled with the urea aqueous solution, the distance of the portion where the potential difference occurs between the gaps is the air interposed between the inner peripheral surface of the outer cylinder electrode 10 and the insulating coating 23. This is the total distance (indicated by distance X) of the distance corresponding to the thickness of the layer (indicated by distance Y) and the distance corresponding to the thickness of the insulating coating 23 (indicated by distance Z). On the other hand, in the portion filled with the urea aqueous solution, the potential of the potential difference between the gaps is such that the potential of the outer cylinder electrode 10 and the urea aqueous solution becomes substantially equal because the urea aqueous solution exhibits conductivity. The distance Z is equivalent to the thickness of.

  In other words, the capacitance between the gaps in the portion not filled with the aqueous urea solution is such that the distance between the electrodes is Y and air is a dielectric (non-conductor) and the distance between the electrodes is It can be said that this is the combined capacitance of a capacitor in which a capacitor having the insulating coating 23 as a dielectric is connected in series with Z. Further, the capacitance between the gaps in the portion filled with the aqueous urea solution can be said to be the capacitance of a capacitor in which the distance between the electrodes is Z and the insulating coating 23 is a dielectric. And the electrostatic capacitance of the capacitor | condenser which connected both in parallel will be measured as an electrostatic capacitance of the level detection part 70 whole.

  Here, since the distance Y is configured to be larger than the distance Z, the electrostatic capacity per unit between the electrodes using air as a dielectric is the electrostatic capacity per unit between the electrodes using the insulating coating 23 as a dielectric. Smaller than. For this reason, the change in the capacitance of the portion filled with the urea aqueous solution is larger than the change in the capacitance of the portion not filled with the urea aqueous solution. Is proportional to the level of the aqueous urea solution.

  Such measurement of the level of the aqueous urea solution is performed by the microcomputer 220 connected to the level detection unit 70 via the level detection circuit unit 250, and the obtained level information signal is illustrated from the input / output circuit unit 290. Output to an external ECU.

  Next, the principle of detecting the temperature of the urea aqueous solution and the concentration of urea as a specific component contained in the urea aqueous solution in the ceramic heater 110 constituting the liquid property detection unit 30 will be described with reference to FIGS. . FIG. 6 shows an example of an aqueous urea solution having a urea concentration of 32.5 wt% and a temperature of 25 ° C. As the temperature of the heating resistor itself increases with the lapse of time since the start of constant current supply to the heating resistor. It is a graph which shows a mode that the voltage value corresponding to the resistance value rises. FIG. 7 is a graph showing that the voltage value change ΔV of the heating resistor and the urea concentration of the urea aqueous solution are in a proportional relationship and have temperature dependence. FIG. 8 shows that when the relationship between the voltage value change ΔV of the heating resistor and the urea concentration of the urea aqueous solution is corrected by the temperature of the urea aqueous solution, the corrected concentration (converted concentration) and the urea concentration almost coincide. It is a graph to show.

  The temperature of the heating resistor itself at a short time after energization is almost the same as the temperature of the liquid existing around the heating resistor because the heat generation is not yet large. Then, as shown in the graph of FIG. 6, after the constant current has started to flow to the heating resistor (however, it takes about 10 msec until the current value becomes stable after the start of energization), the heating resistor with the passage of time. It shows that its temperature rises continuously.

Therefore, if the correlation between the voltage value corresponding to the resistance value after energization of the heating resistor and the temperature of the urea aqueous solution existing in the surroundings is confirmed in advance, the temperature of the urea aqueous solution can be measured. Is possible. Below, the formula showing the relationship between the resistance value after the energization to the heating resistor and the temperature of the urea aqueous solution existing around the resistance value is shown.
R _T = R ₀ (1 + α ₀ T) (1)
Note that _RT represents the resistance value of the heating resistor at T ° C. When the energization of the heating resistor is started, the temperature of the liquid around the heating resistor is also T ° C. R ₀ represents the resistance value (Ω) of the heating resistor at 0 ° C. α ₀ indicates a temperature coefficient based on 0 ° C., but is determined by the material constituting the heating resistor. Therefore, it can be seen from the equation (1) that the resistance value of the heating resistor is proportional to the ambient temperature.

From Ohm's law,
R _T = V _T / I (2)
Although a constant current flows through the heating resistor, the current value I (A) is constant. That is, the voltage value V _T of the heating resistor (in this embodiment, the voltage value (V) output from the differential amplifier circuit unit 230) is proportional to the resistance value R _T (Ω) from the equation (2). From the equation (1), it can be seen that it is proportional to the ambient temperature.

  Next, when energization to the heating resistor is continued, the temperature of the heating resistor itself is taken away by the liquid present around, but the amount of heat taken away by the heating resistor varies depending on the thermal conductivity of the liquid. That is, the rate of temperature rise of the heating resistor varies depending on the thermal conductivity of the liquid present around. Further, it is known that the thermal conductivity of the liquid varies depending on the concentration of the specific component contained in the liquid. From this, when the heating resistor is immersed in the liquid and the liquid is heated for a certain period of time, if the degree of change in the resistance value of the heating resistor is obtained, the difference in the thermal conductivity of the surrounding liquid can be found, A liquid concentration can be obtained.

  This is shown in the graph of FIG. For example, when a heating resistor immersed in a urea aqueous solution at a temperature of 25 ° C. is energized for 700 msec, when the urea concentration of the urea aqueous solution is 0 wt%, the voltage value change corresponding to the resistance value change of the heating resistor is 1220 mV, 16.25 wt. % And 32.5 wt% are 1262 mV and 1298 mV, respectively. That is, as the urea concentration of the urea aqueous solution increases, the thermal conductivity decreases, and the heating resistor becomes difficult to take heat, so the rate of temperature rise increases, and as a result, the resistance value change of the heating resistor increases. It is shown that the voltage value change (indicated by ΔV in the figure) corresponding to the resistance value change increases.

Thus, it can be seen that there is a proportional relationship as shown in FIG. 7 between the urea concentration of the urea aqueous solution and the resistance value change (voltage value change) of the heating resistor. Below, an equation representing the relationship between the urea concentration of the urea aqueous solution around the heating resistor and the voltage value change ΔV corresponding to the resistance value change of the heating resistor is shown.
ΔV = a _T C + b _T (3)
ΔV represents the difference (mV) between the voltage value corresponding to the resistance value after the energization start of the heating resistor and the voltage value corresponding to the resistance value after a certain detection time (eg, 700 msec) has elapsed after energization. . C represents the urea concentration (wt%) in the urea aqueous solution. a _T represents the slope of the ΔV-C line at a temperature T ° C. of the urea aqueous solution, and b _T represents the intercept of the ΔV-C line at the temperature T ° C. of the urea aqueous solution.

  On the other hand, even if the concentration of urea contained in the urea aqueous solution is the same, if the temperature of the urea aqueous solution is different, the temperature increase rate (that is, voltage value change ΔV) of the heating resistor is different. That is, the temperature rise rate of the heating resistor depends on the temperature of the urea aqueous solution.

  This is shown in the graph of FIG. For example, when a heating resistor is energized for 700 msec and a urea solution having a urea concentration of 32.5 wt% and a temperature of 25 ° C. is heated, the voltage value change ΔV corresponding to the resistance value change of the heating resistor becomes 1298 mV. On the other hand, when a heating resistor is energized for 700 msec with respect to an aqueous urea solution having the same concentration and a temperature of 80 ° C., the voltage value change ΔV is 1440 mV. That is, when the urea concentration of the urea aqueous solution is constant, the resistance value change of the heating resistor is reduced as the temperature of the urea aqueous solution is lower, and the voltage value change ΔV corresponding to the resistance value change is reduced.

Thus, it can be seen that the relationship between the urea concentration of the urea aqueous solution and the resistance value change (voltage value change ΔV) of the heating resistor is dependent on the temperature of the urea aqueous solution. Therefore, by correcting (calibrating) the equation (3) according to the temperature of the urea aqueous solution obtained from the equations (1) and (2), it is possible to accurately calculate the urea concentration. The equation for performing correction according to the temperature of the urea aqueous solution is shown below.
a _T = a ₂₅ + x (T−25) (4)
b _T = b ₂₅ + y (T−25) (5)
Incidentally, a _25, the temperature of the urea aqueous solution shows the slope of [Delta] V-C lines in the case of 25 ° C., x is a temperature correction coefficient for the slope of the straight line. Similarly, b ₂₅ represents the intercept of the ΔV-C line when the temperature of the urea aqueous solution is 25 ° C., and y is the temperature correction coefficient of the intercept of the straight line.

When correction values corresponding to the equations shown in the above (3), (4), and (5) were obtained by experiments and the like, a ₂₅ = 2.3, b ₂₅ = 1.223, x = 0.015 , Y = 2.45 was obtained. FIG. 8 shows that using these values, the concentration (converted concentration) of the urea aqueous solution obtained by the correction and the actual urea concentration substantially coincide.

  In the liquid state detection sensor 100 of the present embodiment, the level, temperature, and urea concentration of the urea aqueous solution are detected based on such a principle. Hereinafter, the state detection program will be described with reference to FIGS. 3, 4, and 9 to 14. 9 to 12 are flowcharts of the main routine of the state detection program. FIG. 13 is a flowchart of the stationary state determination subroutine. FIG. 14 is a graph for explaining the threshold values Q and R for discriminating between the empty and different liquids. Each step in the flowchart is abbreviated as “S”.

  When the state of the urea aqueous solution is detected based on an instruction from the ECU, the state detection program stored in the ROM 222 is read into a predetermined storage area of the RAM 300 and executed. As shown in FIG. 9, first, initialization is performed (S1), and all variables, count values, and the like in each storage area of the RAM 300 shown in FIG. 4 are reset. Next, initial values are set (S 2), and the detected values in the level fluctuation value storage area 301 of the RAM 300, the voltage values Vn in the voltage value storage area 302, and the difference values ΔVmn in the voltage difference value storage area 303 are stored in the ROM 222. Written initial values are written. In the state detection program, after the start of execution, the processing of S2 to S90 is repeatedly executed. However, variables and count values other than the above-described variables are continuously maintained during the execution of the state detection program. Become.

  Next, the timer T1 is reset (S3), the count value of a timer program (not shown) that is separately executed is referred to, and the value is stored in the timer count value storage area 306 as the initial value of the timer T1. Remembered. Similarly, the timer T2 is reset (S4), and the count value of the timer program is stored in the timer count value storage area 306 as the initial value of the timer T2.

  In S5, the process waits until 1 sec elapses after the timer T2 is reset (S5: NO). In this determination process, the count value of the timer program is referred to, and 1 sec has elapsed depending on whether or not the difference between the count value and the initial value of the timer T2 stored in S4 is greater than a value corresponding to 1 sec. It is confirmed whether or not. When 1 sec elapses (S5: YES), the output from the level detection unit 70 that is A / D converted and input to the microcomputer 220 via the level detection circuit unit 250 based on the principle of level detection described above is urea. The detected value of the aqueous solution level is stored in the level fluctuation value storage area 301 of the RAM 300 (S6).

  Next, using a conversion formula or a table that is created in advance by experiments or the like and stored in the ROM 222, the detected value of the level stored in the level fluctuation value storage area 301 in S6 is an output value indicating the actual level of the urea aqueous solution. Converted. This level conversion value is output from the liquid state detection sensor 100 to the ECU (S15).

  Then, it is confirmed whether 59 sec has elapsed since the timer T1 was reset in S3 (S16). If not, the process returns to S4 (S16: NO), and S4 to S15 are repeatedly executed. When 59 seconds have elapsed since the timer T1 was reset (S16: YES), the process proceeds to S21 shown in FIG.

  In S21, the timer T2 is reset as in S4 (S21), and the count value of the timer program at that time is stored as the initial value of the timer T2. Then, a control signal is transmitted from the microcomputer 220 to the switch 260, the switch 260 is closed, and energization from the constant current output unit 240 to the heating resistor 114 is started (S22). As described above, 10 msec is set as the time for the current value to become stable after the energization of the heating resistor 114 is started. In the next S23, whether 10 msec has elapsed since the timer T2 was reset in S21. Is confirmed, and waiting is performed before the time elapses (S23: NO). When 10 msec as the standby time has elapsed (S23: YES), the differential amplifier circuit 230 measures the detection voltage of the heating resistor 114, and the detection voltage is input to the microcomputer 220 to obtain a voltage value. Vm is stored in the voltage value storage area 302 (S24).

  In the next S25, the storage area of the voltage value Vm in the voltage value storage area 302 is referred to, and it is confirmed whether or not the number of stored voltage values is five, that is, whether or not the detection voltage measurement in S24 has been performed five times or more ( S25). If the sampling of the voltage value is less than 5 times (S25: NO), the process proceeds to S27 as it is, and temperature conversion described later is performed based on the voltage value Vm.

  On the other hand, in S25 after the fifth round, since the number of voltage values stored in the voltage value Vm storage area of the voltage value storage area 302 is five, it is determined that sampling has been performed five times or more (S25). : YES), the process proceeds to S26. As described above, since the measured detection voltage values are stored in the storage area of the voltage value Vm up to the latest five voltage values, the oldest voltage value is obtained in S24 after the sixth lap of the state detection program. Will be overwritten. In S26, a process of calculating an average value of three voltage values excluding the maximum value and the minimum value from the latest five voltage values stored in the voltage value storage area 302 of the voltage value storage area 302 is performed (S26). ).

In S27, the average value of the voltage value Vm calculated in S26 if the processing of S26 is been performed and V _T, also, the voltage value of the voltage value storage area 302 in the case where the processing of S26 is not performed the latest voltage value stored in the storage area of Vm and V _T, (1), is performed calculation based on equation (2), the temperature T around the urea solution heating resistor 114 is determined. The calculated temperature is transmitted from the input / output circuit unit 290 to the ECU as a temperature information signal (S27).

  Next, in S34 shown in FIG. 11, it is confirmed whether or not 700 msec has elapsed since the time when the timer T2 was reset in S21 (S34), and a standby is performed before the elapse of time (S34: NO). When 700 msec has elapsed (S34: YES), the detection voltage of the heating resistor 114 is measured and stored in the voltage value storage area 302 as the voltage value Vn (S35) as described above. When this voltage measurement is completed, a control signal for the switch 260 is output from the microcomputer 220, and energization to the heating resistor 114 is stopped (S36). Similarly to S33, the difference between this voltage value Vn and the latest value of the voltage value Vm stored in S24 is calculated, and stored in the voltage difference value storage area 303 as a difference value ΔVmn (S37).

  Using the difference value ΔVmn calculated in this way, concentration conversion is performed based on the principle of urea concentration detection described above. That is, the difference value ΔVmn is calculated based on the equations (3) to (5) using the temperature T of the urea aqueous solution obtained in S27, and the concentration conversion value Cn of urea contained in the urea aqueous solution is obtained. . Then, each is stored in the storage area of the converted density value Cn of the converted density value storage area 305 (S38). The CPU 221 that calculates the concentration conversion value Cn in S38 based on ΔVmn calculated in S37 corresponds to the “concentration detection means” in the present invention.

  Then, each determination process of S51, S52, and S71 shown in FIG. 12 is performed to determine whether or not the state of the urea aqueous solution is abnormal. The CPU 221 that determines whether or not the state of the urea aqueous solution is abnormal by performing the determination processes of S51, S52, and S71 corresponds to the “abnormality detection unit” in the present invention.

  First, in S51, the maximum value of the voltage value change ΔV based on the difference value ΔVmn stored in the voltage difference value storage area 303 and the value that can be taken by the urea concentration of the urea aqueous solution that is determined in advance by experiments or the like and stored in the ROM 222. (Threshold value Q shown as an example in FIG. 14) is compared (S51). If the difference value ΔVmn is greater than or equal to the threshold value Q, the process proceeds to S71 (S51: NO).

  In S71, the difference value ΔVmn and the minimum value of the voltage value change that can be taken when the surroundings of the heating resistor 114 are air, which is determined in advance by experiments or the like and stored in the ROM 222 (the threshold value R shown as an example in FIG. 14). ) Is performed (S71). If the difference value ΔVmn is larger than the threshold value R (S71: YES), it is detected that the urea water tank 98 is empty, that is, an empty state, and the processing of S72 to S77 is performed. In this case, the difference value ΔVmn takes a value larger than the threshold value R, for example, a magnitude G, as illustrated in FIG.

  In S72, a stationary state determination subroutine shown in FIG. 13 is executed (S72). First, 0 is set to the normal detection flag in the flag storage area 307 (S101), and then the density fluctuation range is calculated (S102). In this process, a difference value between the previous value and the latest value of the density conversion value Cn stored in the density conversion value storage area 305 is obtained. That is, the fluctuation range of the concentration between the urea concentration of the urea aqueous solution detected 60 msec before and the current urea concentration is obtained as a difference value. Then, the difference value (concentration fluctuation range) and the maximum value (threshold value) of the urea concentration fluctuation range of the urea aqueous solution that can be taken when the urea aqueous solution can be regarded as being in a stationary state, which is determined in advance by experiments or the like and stored in the ROM 222. L) is compared (S103). At this time, if the concentration fluctuation range is larger than the threshold value L (S103: YES), 0 is set to the stationary state flag assuming that the urea aqueous solution is not in the stationary state (S111). If the concentration fluctuation range is equal to or less than the threshold value L (S103: NO), 1 is set to the stationary state flag assuming that the urea aqueous solution is in the stationary state (S112). Then, the process returns to the main routine. The CPU 221 that determines whether or not the urea aqueous solution is in a static state by executing the static state determination subroutine corresponds to the “static state determination unit” in the present invention, and the concentration fluctuation range is “ This corresponds to “stillness determination value”.

  Returning to the main routine of the state detection program shown in FIG. 12, in S73, it is determined whether or not the camera is stationary. If the stationary flag is 1 and it is determined that the camera is stationary (S73: YES) ), 2 is added to the empty counter in the counter value storage area (S75). On the other hand, when it is determined that the stationary state flag is 0 and not in the stationary state (S73: NO), 1 is added to the empty counter (S74). Thereafter, the process proceeds to S76, the value of the empty counter is referred to, and if it is less than a threshold value H (for example, 10) preset and stored in the ROM 222, the process proceeds to S90 as it is (S76: NO), and the timer in S3 Waiting is performed until 60 seconds have elapsed since the time of resetting T1 (S90: NO), and when 60 seconds have elapsed (S90: YES), the process returns to S2. The CPU 221 that adds the count values of the empty counter, the concentration abnormality counter, and the different liquid counter by performing the processes of S74, S75 and S63, S64, S83, and S84 described later is the “counter means” in the present invention. Equivalent to. Note that the CPU 221 that sets the count value added to each counter to a different value depending on whether the urea aqueous solution is in a stationary state or not by performing the determination processing of S73 and S62 and S82 described later is the present invention. This corresponds to “setting value changing means”.

  Then, as the main routine of the state detection program is repeatedly executed, an empty counter is incremented. If the value exceeds the threshold value H (S76: YES), it is determined that an empty state has occurred. Then, a notification signal for notifying of airing is transmitted to the ECU via the input / output circuit unit 290 (S77). Thereafter, similarly to the above, the process returns to S2 via S90. It should be noted that the CPU 221 that determines whether or not there is a state in which emptying occurs, a state in which the concentration is abnormal, or a state in which a different kind of liquid is mixed by performing the determination processing in S76 and S65 and S85 described later, This corresponds to “abnormality determination means” in the present invention. Further, in the processing of S77 and S66 and S86 described later, the CPU 221 that transmits a notification signal of an empty state, a state in which a different kind of liquid is mixed, and a state in which the concentration is abnormal is sent to the ECU. Is equivalent to.

  Next, in S71 described above, when the difference value ΔVmn is a value equal to or less than the threshold value R (S71: NO), it is detected that the liquid around the heating resistor 114 is not a urea aqueous solution (for example, light oil). Then, the processing of S81 to S86 is performed. In this case, the difference value ΔVmn takes a value of, for example, a magnitude F that is not less than the threshold value Q and not more than the threshold value R, as illustrated in FIG.

  In S81, the stationary state determination subroutine described in FIG. 13 is executed, and the stationary state flag is set to 1 or 0 (S81). Similarly, in S82, it is determined whether or not it is stationary. If it is stationary (S82: YES), 2 is added to the different liquid counter in the counter value storage area (S84), and if it is not stationary (S84). S82: NO), 1 is added to the different liquid counter (S83). Thereafter, the process proceeds to S85, the value of the different liquid counter is referred to, and if it is less than the threshold value H described above, the process proceeds to S90 as it is (S85: NO). On the other hand, if the value of the different liquid counter is equal to or greater than the threshold value H (S85: YES), it is determined that a state in which the different liquid is mixed in the urea water tank 98 has occurred, and a notification signal that notifies the different liquid. Is transmitted to the ECU via the input / output circuit unit 290 (S86). Thereafter, similarly to the above, the process returns to S2 via S90.

  On the other hand, when the difference value ΔVmn is less than the threshold value Q in S51 described above (S51: YES), the process proceeds to S52. Note that the difference value ΔVmn in this case takes a value smaller than the threshold value Q, for example, a magnitude E, as illustrated in FIG.

  In S52, the latest value of the converted concentration value Cn stored in the converted concentration value storage area 305 in S38 and the liquid around the heating resistor 114, which is determined in advance through experiments or the like and stored in the ROM 222, is water. Comparison is made with the maximum density value (threshold value W not shown) that can be taken (S52). If the concentration conversion value Cn is equal to or less than the threshold value W (S52: NO), it is detected that the urea concentration of the urea aqueous solution stored in the urea water tank 98 is abnormal, and the processing of S61 to S66 is performed. Is called.

  In S61, the stationary state determination subroutine described in FIG. 13 is executed, and 1 or 0 is set in the stationary state flag (S61). Similarly, in S62, it is determined whether or not it is stationary. If it is stationary (S62: YES), 2 is added to the concentration abnormality counter in the counter value storage area (S64), and if it is not stationary (S64). S62: NO), 1 is added to the concentration abnormality counter (S63). Thereafter, the process proceeds to S65, the value of the density abnormality counter is referred to, and if it is less than the above threshold value H, the process proceeds to S90 as it is (S65: NO). On the other hand, when the value of the concentration abnormality counter is equal to or greater than the threshold value H (S65: YES), the urea concentration in the urea aqueous solution is abnormal (for example, the water is put into the urea water tank 98). And a notification signal for notifying the concentration abnormality is transmitted to the ECU via the input / output circuit unit 290 (S66). Thereafter, similarly to the above, the process returns to S2 via S90.

  In S52 described above, when the concentration conversion value Cn is larger than the threshold value W (S52: YES), the urea aqueous solution stored in the urea water tank 98 is in a specific abnormal state, that is, an empty state, a different type, or the like. It is determined that the liquid is not mixed or the urea concentration is abnormal. At this time, the normal detection flag is confirmed (S53), but when this determination process is performed for the first time, the normal detection flag is 0 (S53: NO), so 1 is set in the normal detection flag. (S54), the process proceeds to S56.

  When it is determined that the urea aqueous solution is in a specific abnormal state (S51: NO or S51: YES, S52: NO), the normal detection flag is set to 0 in S101 of the stationary state determination subroutine of FIG. Is done. For this reason, when the main routine of the state detection program is repeatedly executed, if it is determined twice consecutively that the aqueous urea solution is not in a specific abnormal state (S51: YES, S52: YES), the previous line 1 is stored in the normality detection flag by the process of S54 (S53: YES). In this case, the concentration abnormality counter, empty counter, and different liquid counter stored in the counter value storage area 308 are reset (S55). Since the value of the normal detection flag is stored even if the state detection program is repeatedly executed, each counter is reset if it is determined that the urea aqueous solution is not in a specific abnormal state both in the previous time and this time.

  Next, assuming that the urea concentration in the urea aqueous solution is normal, the difference value ΔVmn that is the basis of the concentration conversion is stored in the normal voltage difference value storage area 304 (S56). In the next S57, the storage area of the difference value ΔVmn in the normal voltage difference value storage area 304 is referred to, and the number of stored voltage difference values is 5, that is, the normal difference value ΔVmn in S56 has been stored five times or more. It is confirmed whether or not (S57). If the difference value ΔVmn is sampled less than 5 times (S57: NO), the process proceeds to S59 as it is, and concentration conversion based on the normal difference value ΔVmn stored in S56 is performed.

  In S56, as described above, up to the five latest values of the normal difference value ΔVmn are stored in the storage area of the normal difference value ΔVmn. When the state detection program is repeatedly executed and the urea concentration in the urea aqueous solution is determined to be normal six times or more, the oldest voltage difference value is overwritten.

  On the other hand, when the number of stored voltage difference values is 5 or more, the latest five differences in the normal voltage difference value storage area 304 are assumed to have been sampled five times or more at normal difference values ΔVmn (S57: YES). A process of calculating an average value of three voltage difference values excluding the maximum value and the minimum value from the value ΔVmn is performed (S58).

  In S59, when the process of S58 is performed, the average value of the difference values ΔVmn calculated in S58 is set to ΔV. When the process of S58 is not performed, the difference in the normal voltage difference value storage area 304 is determined. The latest difference value stored in the storage area of the value ΔVmn is set to ΔV, and concentration conversion is performed based on the above-described principle of urea concentration detection as in S38. That is, for the normal difference value ΔVmn, the calculation based on the equations (3) to (5) is performed using the temperature T of the urea aqueous solution obtained in S27, and the concentration converted value of urea contained in the urea aqueous solution is obtained. It is done. The urea concentration calculated as the converted value is transmitted as a concentration information signal from the input / output circuit unit 290 to the ECU (S59). Thereafter, the process returns to S2 via S90, and the state detection program is repeatedly executed.

  Needless to say, the present invention can be modified in various ways. For example, in the state detection program, the temperature of the urea aqueous solution is calculated based on the equations (1) and (2) in S27, and the urea concentration is calculated based on the equations (3) to (5) in S38 and S59. However, a table may be created in advance by experiments or the like, stored in a predetermined storage area of the ROM 222, and obtained by referring to S27, S38, and S59, respectively.

  In addition, the respective standby times in S5, S16, S23, S34, and S90 are merely examples, and an optimal standby time may be obtained and set by experiments or the like. Further, the threshold value W of the concentration abnormality counter, the empty counter, and the different liquid counter is set to 10 as an example in the present embodiment, but an optimal threshold value may be set by experiment or the like. In addition, the counter is incremented by 2 when it is in a stationary state, and it is incremented by 1 when it is not in a resting state. It is good to set. Of course, the setting of the threshold value and the added value of the counter may be changed together so that a more appropriate abnormal state can be determined.

  Further, in S51 and S71, the difference value ΔVmn is compared with the threshold values Q and R to determine the state in which emptying occurs or a state in which a different kind of liquid is mixed, but the concentration conversion value Cn calculated in S38. May be used for comparison with a threshold. Similarly, in S52, the difference value ΔVmn may be used for comparison with a threshold value to determine whether or not the urea concentration in the urea aqueous solution is abnormal.

  In the stationary state determination subroutine, based on the concentration fluctuation range obtained as a difference value between the current urea concentration (concentration converted value Cn) calculated in S38 and the urea concentration calculated in the previous execution of the processing in S38. Thus, it is determined whether the urea aqueous solution is in a stationary state. The ratio of the current urea concentration to the previous urea concentration is obtained as a concentration fluctuation range, and the magnitude of the ratio is compared with a threshold value to determine whether the urea aqueous solution is stationary. You may determine whether it is in a state.

  Further, in the stationary state determination subroutine, determination based on the fluctuation range of the level of the urea aqueous solution, or a concentration fluctuation range in a shorter time than the present embodiment may be obtained, and determination based on this may be performed. An example of the determination method is shown in FIGS. 15 and 16 are flowcharts showing a series of processes added to the main routine as a modification of the state detection program. FIG. 17 is a flowchart showing a modification of the stationary state determination subroutine. Note that the same processing numbers as those of the main routine and the stationary state determination subroutine of the state detection program of the present embodiment are shown with the same step numbers.

  Although not shown, the level fluctuation value storage area 301 of the RAM 300 is provided with storage areas for maximum and minimum levels, and the voltage value storage area 302 is provided with a storage area for the voltage value Vp. Further, it is assumed that the voltage difference value storage area 303 is provided with a storage area for the difference value ΔVmp, and the density conversion value storage area 305 is provided with a storage area for the density conversion value Cp. In the process of S2 (see FIG. 9) of the state detection program, the minimum value of the possible values is set as the maximum value of the level fluctuation value storage area 301 as an initial value. Is set to the maximum possible value. As an example, if the level of the urea aqueous solution to be measured is converted into a digital value indicating the liquid level in 65536 stages by A / D conversion, 0 is stored as the maximum level value and 65535 as the minimum level value. Is memorized.

  The series of processing shown in FIG. 15 is inserted between S6 and S15 (see FIG. 9) of the state detection program, and in order to determine a stationary state based on the level fluctuation range in a stationary state determination subroutine shown in FIG. Used for. As shown in FIG. 15, first, in S <b> 11, the level detection value stored in the level fluctuation value storage area 301 in S <b> 6 of FIG. 9 is compared with the level maximum value in the level fluctuation value storage area 301. If the detected value is greater than the maximum level value (S11: YES), the detected maximum value is stored by storing the detected value as the maximum level value (S12), and the process proceeds to S13. Even when the detected value is equal to or lower than the maximum level value, the process proceeds to S13 (S11: NO), and then, similarly to S11, the detected level value is compared with the minimum level value. If the detected value is not less than the minimum level value, the minimum level value is not updated. If the detected value is smaller than the minimum level value (S13: YES), the detected minimum value is stored as the minimum level value. The update is performed (S14), and the process proceeds to S15 in FIG. As described above, the processing of S4 to S16 is repeatedly performed until 59 seconds elapse from the time when the timer T1 is reset, and thus the maximum level value and the minimum value are updated.

  Next, the series of processing shown in FIG. 16 is inserted between S27 (see FIG. 10) and S34 (see FIG. 11) of the state detection program, and the short-term density fluctuation range in the stationary state determination subroutine shown in FIG. It is used to determine the stationary state based on. As shown in FIG. 16, first, in S31, it is confirmed whether or not 500 msec has elapsed since the time when the timer T2 was reset in S21 of FIG. 10 (S31), and a standby is performed before the time elapses (S31: NO). When 500 msec has elapsed (S31: YES), the detection voltage of the heating resistor 114 is measured and stored in the voltage value storage area 302 as the voltage value Vp (S32), as described above. Then, the difference between the voltage value Vp and the latest value of the voltage value Vm stored in S24 is calculated and stored in the storage area of the difference value ΔVmp in the voltage difference value storage area 303 (S33), FIG. The process proceeds to S34. By this series of processing, sampling of the urea concentration is performed at a timing slightly before the timing when the liquid state detection sensor 100 detects the urea concentration of the urea aqueous solution (200 msec before this modification).

  In S38 of FIG. 11, the converted density value Cn is obtained using the difference value ΔVmn as described above. Furthermore, the converted density value Cp is obtained using the difference value ΔVmp, and is stored in the converted density value storage area 305. It is stored in the storage area of the density conversion value Cp.

  In the modified example of the stationary state determination subroutine shown in FIG. 17, when the density fluctuation range is equal to or smaller than the threshold L in S103 (S103: NO), the stationary state flag is not immediately set to 1 and the levels in S104 and S105 are set. The stationary state determination based on the fluctuation range and the stationary state determination based on the short-term density fluctuation range in S106 and S107 are performed.

  First, in S104, the level fluctuation range is calculated (S104). In this process, the difference value between the maximum level value and the minimum value updated in S12 and S14 in FIG. 15 and stored in the level fluctuation value storage area 301 is obtained. Then, the difference value (level fluctuation range) and the maximum value (threshold value J) of the level fluctuation range that can be taken when the urea aqueous solution can be regarded as being in a stationary state, which is determined in advance by experiments or the like and stored in the ROM 222. Comparison is performed (S105). At this time, if the level fluctuation range is larger than the threshold value J (S105: YES), 0 is set to the stationary state flag assuming that the urea aqueous solution is not in the stationary state (S111).

  On the other hand, if the level fluctuation range is equal to or less than the threshold value J (S105: NO), the short-term density fluctuation range is further calculated (S106). In this process, the difference value between the density conversion values Cn and Cp stored in the density conversion value storage area 305 in S38 of FIG. 11 is obtained. That is, the density fluctuation range in a short period between 500 msec after the start of energization of the heating resistor 114 and 700 msec is obtained as a difference value. Then, the difference value (short-term concentration fluctuation range) and the fluctuation range of the urea concentration of the urea aqueous solution that can be taken when the urea aqueous solution can be considered to be stationary in a short period of time, which is determined in advance by experiments or the like and stored in the ROM 222. Comparison with the maximum value (threshold value K) is performed (S105). At this time, if the short-term concentration fluctuation range is larger than the threshold value K (S105: YES), 0 is set to the stationary state flag because the urea aqueous solution is not in the stationary state (S111). Thereafter, the process may return to the main routine.

  The above-described modification of the static state determination subroutine shows an example in which the static state determination based on the density fluctuation range, the static state determination based on the level fluctuation range, and the static state determination based on the short-term density fluctuation range are performed in this order. However, the order of determination may be arbitrarily changed.

  The circuit board 60 is provided as a circuit board for relaying the outputs from the level detection unit 70 and the liquid property detection unit 30, and is connected to an external circuit on which the microcomputer 220 or the like is mounted, and the level detection is performed by controlling the external circuit. Further, temperature / concentration detection may be performed.

  In S25 and S57, the sampling of the voltage value Vm for obtaining the average value and the normal difference value ΔVmn is set to 5 times, but the sampling is not limited to 5 times. Further, in the process for obtaining the average value, the process for removing the maximum value and the minimum value may be omitted.

  The present invention can be applied to a liquid state detection sensor that can detect the concentration of a liquid.

4 is a partially cutaway longitudinal sectional view of the liquid state detection sensor 100. FIG. It is a schematic diagram which shows the heater pattern 115 of the ceramic heater 110. FIG. 2 is a block diagram showing an electrical configuration of a liquid state detection sensor 100. FIG. 3 is a diagram illustrating a conceptual configuration of a storage area of a RAM 300. FIG. FIG. 3 is an enlarged cross-sectional view of the vicinity of the water surface of a urea aqueous solution filled between the gap between the outer cylinder electrode 10 and the inner electrode 20. As an example of a urea aqueous solution having a urea concentration of 32.5 wt% and a temperature of 25 ° C., the resistance value of the heating resistor itself increases with the passage of time since the start of energization of a constant current to the heating resistor. It is a graph which shows a mode that the voltage value corresponding to is going up. It is a graph which shows that voltage value change (DELTA) V of a heating resistor and the urea concentration of urea aqueous solution have a proportional relationship, and have temperature dependence. FIG. 6 is a graph showing that when the relationship between the voltage value change ΔV of the heating resistor and the urea concentration of the urea aqueous solution is corrected by the temperature of the urea aqueous solution, the corrected concentration (converted concentration) and the urea concentration substantially coincide. . It is a flowchart of the main routine of a state detection program. It is a flowchart of the main routine of a state detection program. It is a flowchart of the main routine of a state detection program. It is a flowchart of the main routine of a state detection program. It is a flowchart of a stationary state determination subroutine. It is a graph for demonstrating the threshold values Q and R for discriminating an airing and a dissimilar liquid. It is a flowchart which shows a series of processes added to a main routine as a modification of a state detection program. It is a flowchart which shows a series of processes added to a main routine as a modification of a state detection program. It is a flowchart which shows the modification of a stationary state determination subroutine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Outer cylinder electrode 20 Internal electrode 70 Level detection part 98 Urea water tank 100 Liquid state detection sensor 110 Ceramic heater 114 Heating resistor 221 CPU

Claims (7)

A detection element that outputs a signal related to the concentration of a specific component in the liquid contained in the liquid container;
A concentration detection means for detecting a concentration value of the specific component based on a signal from the detection element;
An abnormality detecting means for detecting whether or not the liquid is in the specific abnormal state based on a signal from the detection element and a threshold set in correspondence with the specific abnormal state relating to the liquid;
Counter means for adding an abnormal count value by a predetermined count value every time the abnormality detection means detects that the liquid is in the specific abnormal state;
A liquid state detection device comprising: an abnormality determination unit that determines that the liquid is in the specific abnormal state when the abnormality count value obtained by the counter unit reaches an abnormality determination value;
While calculating the difference value between the current density value detected by the density detection means and the previous density value detected immediately before it, or the ratio between the two as a static determination value, based on the static determination value, A stationary state determining means for determining whether or not the liquid is stationary in the liquid container;
A value when at least one of the predetermined count value and the abnormality determination value is determined when the liquid is determined to be stationary by the stationary state determination unit and when the liquid is determined not to be stationary. And a set value changing means for setting the values to different values. The detection element has a heating resistor that generates heat when energized,
The concentration detecting means acquires a first corresponding value corresponding to the first resistance value of the heating resistor obtained after the energization of the heating resistor is started, and a first value obtained after energizing the heating resistor for a predetermined time. Obtaining a difference value from a second corresponding value corresponding to two resistance values, and detecting a concentration value of a specific component contained in the liquid corresponding to the difference value;
The abnormality detection means compares at least one of the difference value and the current concentration value with a threshold value set corresponding to a specific abnormal state related to the liquid, and the liquid has the specific abnormality. Detect whether it is in a state,
2. The liquid state according to claim 1, wherein the stationary state determination unit determines that the liquid is not in a stationary state when the stationary determination value is greater than a reference threshold value that is a criterion for determining the stationary state. Detection device.   3. The liquid state according to claim 1, further comprising an informing unit that informs an external circuit of an abnormality when the abnormality determining unit determines that the liquid is in the specific abnormal state. Detection device. A level detection unit that outputs a signal corresponding to the level of the liquid stored in the liquid container;
2. The stationary state determining means determines whether or not the liquid is in a stationary state in the liquid container based on the stationary determination value and a signal from the level detection unit. The liquid state detection device according to any one of 1 to 3. The level detection unit includes a first electrode and a second electrode extending in a longitudinal direction, and according to a level of the liquid stored in the liquid storage container between the first electrode and the second electrode. It forms a capacitor whose capacitance changes,
When the level detection unit is attached to the liquid storage container and the liquid storage container is installed in a posture to be used and the liquid is stored, the detection element receives at least a part of itself from the liquid of the level detection unit. The liquid state detection device according to claim 4, wherein the liquid state detection device is integrated with the level detection unit in a state where the level detection unit is insulated from the tip of the level detection direction.   The specific abnormal state relating to the liquid includes a state where the liquid is empty in the liquid container, a state where a different kind of liquid is mixed in the liquid container, and a concentration of a specific component contained in the liquid. 6. The liquid state detection device according to claim 1, wherein the liquid state detection device is in one of the following states. The liquid state detection device according to claim 1, wherein the liquid is an aqueous urea solution, and the specific component is urea.

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