JP2005308665A - Heating resistor type flow meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for detecting the breakdown of an air flowrate detecting element with a simple way, capable deciding even during normal operation, and also to provide a means of self-calibrating against a very small change in characteristics not leading to a breakdown, without adding a special element. <P>SOLUTION: The voltage of a heating current applying section or the duty of pulse-width modulation for controlling the temperature of a heater to detect a breakdown and failures in normal operation are detected, and then the method decides as the breakdown when a maximum or a minimum value lasts for a fixed time or longer. the method detects whether detected signals from an air flowrate converting circuit are within a specified value to decide the presence of the failures or to self-calibrate, in a state that the operation of a constant temperature control circuit for controlling the heating temperature of the heater is stopped. A heater resistor for self-diagnostics is added near the temperature difference detecting resistor of the air flowrate converting circuit, and then the presence of failures is diagnosed by the difference between detected signals at the on-off action of the heater. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a flow meter for measuring a gas flow rate, and more particularly to an air flow meter suitable for detecting an air flow rate taken into an automobile engine.

  As a conventional example of an automobile engine intake air flow meter, a method of detecting an overheat control current value of a heating resistor as described in Patent Document 1 and converting it to an air flow rate, A system is known in which a thermal effect on a temperature-sensitive resistor disposed downstream is detected as a temperature difference signal and captured as a voltage of a bridge circuit.

  In addition, as a failure diagnosis method of the air flow rate detection element, a resistor for detecting that the diaphragm is broken as described in Patent Document 2 is arranged, and a method of diagnosing the failure from the resistance value, , A method of connecting a fixed resistor in parallel to a detection element as described in Patent Document 3 and changing the output in a pseudo manner, and a method of diagnosis in an engine system as described in Patent Document 4 Has been proposed.

  However, in these conventional examples, it is necessary to newly arrange a resistor for diagnosing a failure of the sensor, which is not a satisfactory method in terms of cost. Further, the detection characteristic for converting the temperature of the detection element into the resistance value cannot be diagnosed, and the consideration for the slight characteristic change that does not lead to destruction is not sufficient. Furthermore, the self-diagnosis can be performed only when the air flow rate is not flowing, and a failure occurring during normal operation cannot be determined by the flow meter itself.

JP 2003-185481 A Japanese Patent Laid-Open No. 11-118571 JP-A-3-33619 JP 11-295125 A

  The problem to be solved is to present a first simple method and a method for detecting the breakage of the air flow rate detecting element that can be determined even during normal operation. Secondly, a means for self-calibration without adding a special element to a slight characteristic change that does not cause destruction is presented. Thirdly, the resistance change characteristic with respect to temperature, which is the detection characteristic of the air flow rate detection element, can be confirmed.

  In order to solve the first problem, the present invention detects the voltage of the heating current application unit for controlling the temperature of the heater unit or the pulse width modulation duty in order to detect a breakdown failure during normal operation. When the maximum or minimum value continues for a certain time or more, it is determined that the device is broken.

  In order to solve the second problem, it is confirmed that the detection signal from the air flow rate conversion circuit is within a specified value while the operation of the constant temperature control circuit for controlling the heating temperature of the heater is stopped. It is detected and judged whether there is a failure, or self-calibrated.

  Furthermore, in order to solve the third problem, a heater resistance for self-diagnosis is added in the vicinity of the temperature difference detection resistance of the air flow rate detection element, and the presence or absence of a failure is diagnosed from the detection signal difference when the heater is turned on and off. It is what you do.

  The air flow meter of the present invention can always make a self-diagnosis during operation by a simple method for a breakdown failure of the detection element. In addition, a slight characteristic change that does not cause destruction can be self-calibrated, and detection accuracy can be improved.

  Hereinafter, it demonstrates using drawing.

FIG. 1 shows a block configuration of an air flow rate detector according to the present invention. A heater 9 as a heating resistor, a cold film resistor 10 for detecting the air temperature, and fixed resistors 11 and 12 are connected as a heater bridge circuit 1 and are arranged in an air flow passage of the measured object. The temperature difference bridge circuit 3 configured to detect the air flow rate from the resistance change of the temperature sensitive resistors 13, 14, 15, 16 disposed adjacent to the heater bridge circuit 1 and upstream and downstream of the heater 9 is also air. It is arranged in the passage.

  The heater bridge circuit 1 is heated and controlled by a constant temperature control circuit 2 so that the heater temperature becomes a constant value. The detection signal of the temperature difference bridge circuit 3 is amplified and adjusted to a predetermined input / output characteristic by the signal amplification output adjustment circuit 4 and output from the output terminal 6. This air flow meter is driven by a power supply terminal 5 and a ground terminal 7.

  FIG. 2 shows a cross-sectional structure of the air flow meter of the present invention in a mounted state. The air flow meter of the present invention is inserted into the passage tube 28 and secured to the passage tube by the flange 20. A sealed chamber 21 in which a part of the circuit board 25 is accommodated in the passage pipe and a bypass passage 22 that divides the air in the passage pipe bend and the air is discharged from the bypass passage outlet 24 through the passage pipe 23. The air flow rate in the bypass passage passes around the air flow rate detection element 27 mounted on the circuit board 25, and the flow rate is detected by being converted into a resistance change. The detected flow rate signal is amplified and output by the circuit element 26 on the circuit board. Normally, air flows in the flow direction 29, but air also flows in the reverse direction 30 primarily due to the pulsation of the engine. The air flow meter of the present invention can measure air in both forward and reverse directions.

  FIG. 3 shows a specific circuit configuration for realizing the block configuration shown in the first embodiment of the present invention. In the heater bridge circuit 1, a heater 9 controlled to a constant temperature, a cold film resistor 10 for detecting air temperature, and fixed resistors 11 and 12 are connected in a bridge shape. The bridge circuit signal is feedback controlled so that the temperature of the heater becomes constant by a constant temperature control circuit 2 constituted by an operational amplifier 32 and a transistor 31 for supplying a heating current.

  The temperature sensitive resistors 13, 14, 15, 16 arranged on the upstream and downstream sides of the heater form a temperature difference bridge circuit 3, and a voltage signal corresponding to the air flow rate is output. This temperature difference output signal is buffered by operational amplifiers 33, 34 and resistors 36, 37, 38, 39, respectively, and is input to a predetermined input by a signal amplification adjusting circuit comprising an operational amplifier 35 and resistors 40, 41, 42, 43, 44. The output characteristic is adjusted and output from the output terminal 6.

  Here, it is assumed that the diaphragm 67 of the air flow rate detection element 27 described later with reference to FIG. The control voltage V1 of the constant temperature control circuit operates within a predetermined voltage when normal. However, at the time of failure such as breakage, the V1 voltage sticks to a voltage that is higher or lower than the normal operating voltage. This abnormal voltage is detected by a determination circuit including resistors 53, 56a, 56b, 58, transistors 55a, 56b, and an OR circuit 57 in the failure diagnosis circuit 17, and a diagnosis signal D is output. Since the output terminal 6 is always fixed to 0 V by this diagnostic signal, the system can be notified of the abnormality.

  FIG. 4 shows the operation when the diaphragm is broken. Although the control voltage V1 and the output voltage Vout (the voltage at the terminal 7) change according to the detected air flow rate, the control voltage V1 sticks out of the normal operating range when a failure occurs. The output D of the self-diagnosis circuit that detects this voltage becomes a high voltage (for example, 5 V), and therefore the output voltage is fixed to 0 V, and an abnormality can be transmitted to the system.

  Furthermore, by applying a self-calibration / diagnosis signal, automatic calibration of the zero point and diagnosis on the temperature difference bridge circuit side can be realized. This can be realized by applying a diagnostic signal from a terminal 52 to an active diagnostic circuit comprising transistors 45 and 48, resistors 46, 47 and 49, and a capacitor 50 in the self-diagnosis circuit 17 of FIG.

  The active self-diagnosis operation will be described using the diagnosis diagram of FIG.

  The power VCC supplied from the control unit when the engine key of the automobile is off is kept supplied for key-off diagnosis. Thereafter, when a self-diagnosis start signal DIAG is input from the system after a certain period of time, the operation of the heater control circuit stops and the output of the air flow meter changes up to the zero point output of the temperature difference bridge signal. Here, the zero point output is a state in which no heater current flows (a state in which the heater current is not heated), and a state in which intake air does not flow because the engine is in a stopped state. Thereafter, the control unit samples the zero point voltage, calculates the amount of deviation from the initial zero point, and if it has changed, stores the amount of deviation in a memory in the unit for correction at the next key-on. At the next key-on, calibration can be performed by subtracting the zero point correction data in this memory from the output signal of the air flow meter. Further, when the amount of deviation is abnormally large, it is possible to determine that a failure has occurred and shift to the fail-safe mode so that the driver is notified at the next key-on.

  When the time further elapses, the self-diagnosis heater 51 disposed in the vicinity of the temperature-sensitive resistor of the temperature difference bridge circuit is turned on, causing a temperature imbalance in the temperature difference bridge circuit. From the output signal change amount A at this time, it is detected that the temperature sensor is operating correctly, and it can be determined in the control unit on the system side whether or not it is normal.

  FIG. 6 shows details of the air flow rate detecting element used in the present invention. The air flow rate detecting element 60 includes a heater 9 made of platinum or polysilicon, temperature sensitive resistors 14, 15, 13, 16, which are arranged on the upstream and downstream sides of the heater and change in resistance value due to the heat effect from the heater. It is comprised by the cold film resistor 10 which detects air temperature, and the connection pad 65 for transmitting them to the exterior electrically. Further, a self-diagnosis heater 51 is disposed adjacent to one side (left side in the drawing) of the temperature sensitive resistor. All elements other than the cold film resistor and the connection pad are arranged on the diaphragm 67 whose back surface is etched. With the above configuration, an air flow meter having a self-diagnosis function can be realized.

  FIG. 7 shows another circuit embodiment of the present invention.

The configurations of the heater bridge circuit 1 and the temperature difference bridge circuit 3 are the same as those in FIG. 3, but an example in which the heater constant temperature control circuit 2, the output adjustment circuit 4, and the self-diagnosis circuit 17 are configured by digital circuits is shown. . In the heating control of the heater, the detection signal of the control bridge circuit is input to the comparator 70 and changed to a digital signal. This is input to the PI control circuit 71, converted into a pulse width signal by the PWM circuit, and controlled to be turned on / off by the driver 73, so that the heating temperature of the heater is controlled to a constant value.

  On the other hand, the signal from the temperature difference bridge circuit is converted into a digital signal by the A / D converter 74, is subjected to arithmetic processing by the DSP 75, converted back to an analog signal by the D / A converter 76, and output from the output terminal 6. . In the DSP, a correction calculation is performed to a predetermined characteristic based on a program and correction data stored in the ROM.

  Self-diagnosis of the digital correction type air flow meter having such a configuration can be realized as follows. First, if a diaphragm breakage or the like occurs, the PWM signal, which is the heating control signal of the heater, is judged by the self-diagnosis circuit 78. If it is judged abnormal, the signal is sent to the DSP to fix the output to the fail-safe voltage. By doing so, you can tell the unit about the abnormality.

  In the active calibration and temperature difference signal diagnosis, when the self-diagnosis signal 52 is applied, the transistor 80 is turned off via the resistor 79 and the transistors 83 and 84, and the heating current of the heater is shut down. By monitoring the output signal at this time, self-calibration and self-diagnosis can be performed in the same manner as in the case of an analog circuit. After that, the diagnostic signal delayed by the FF circuit 81 drives the driver 82 and overheats one side of the temperature-sensitive resistor of the temperature difference bridge circuit. Can be calibrated. Further, in the case of a digital circuit, the calibration calculation of the air flow meter performed in the unit can be realized in the air flow meter relatively easily. This is because a DSP and a memory are provided inside the flow meter.

  The present invention can be used for a device that detects air flow rate, for example, an airplane, a ship, or a medium other than air, for example, a flow rate detection device for hydrogen or the like that requires high reliability.

The block structure of the air flowmeter of this invention. The air flow meter mounting structure of the present invention. The circuit diagram of the air flowmeter of this invention. Explanatory operation explanatory drawing of the air flowmeter of this invention. The self-diagnosis operation explanatory drawing of the air flowmeter of this invention. The schematic diagram of the flow volume detection element of the air flowmeter of this invention. The other circuit diagram of the air flowmeter of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Heater bridge circuit, 2 ... Constant temperature control circuit, 3 ... Temperature difference bridge circuit, 4 ... Signal amplification output adjustment circuit, 5 ... Power supply terminal, 6 ... Output terminal, 7 ... Ground terminal, 9 ... Heater,
10 ... Cold film resistor, 11, 12 ... Resistance.

Claims (3)

A heater that generates heat due to an electric current and a resistor that detects the ambient temperature, a constant temperature control circuit that controls the temperature of the heater to a constant value, and a resistance of a temperature sensing element arranged on the upstream and downstream sides of the heater A signal that has a flow rate conversion circuit that converts a flow rate signal into an electrical signal, and that amplifies the output signal of the flow rate conversion circuit to a predetermined signal level, capturing that the thermal effect from the heater changes according to the gas flow rate A flow meter with an amplifier circuit,
A flowmeter comprising a self-calibration circuit that detects and determines a PWM (pulse width modulation) signal or a control voltage value of a constant temperature control circuit. A heater that generates heat due to an electric current and a resistor that detects the ambient temperature, a constant temperature control circuit that controls the temperature of the heater to a constant value, and a resistance of a temperature sensing element arranged on the upstream and downstream sides of the heater A signal that has a flow rate conversion circuit that converts a flow rate signal into an electrical signal, and that amplifies the output signal of the flow rate conversion circuit to a predetermined signal level, capturing that the thermal effect from the heater changes according to the gas flow rate A flow meter with an amplifier circuit,
A flowmeter characterized in that the self-calibration of the flow rate conversion circuit uses the output of the flow rate conversion circuit in a state where the operation of the constant temperature control circuit is stopped. A heater that generates heat due to an electric current and a resistor that detects the ambient temperature, a constant temperature control circuit that controls the temperature of the heater to a constant value, and a resistance of a temperature sensing element arranged on the upstream and downstream sides of the heater A signal that has a flow rate conversion circuit that converts a flow rate signal into an electrical signal, and that amplifies the output signal of the flow rate conversion circuit to a predetermined signal level, capturing that the thermal effect from the heater changes according to the gas flow rate A flow meter with an amplifier circuit,
The flowmeter is characterized in that self-calibration of the flow rate conversion circuit is performed by energizing a self-diagnostic overheating element arranged adjacent to the temperature-sensitive element.

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