JP2008256723A - Output correction device of cylinder internal pressure sensor and cylinder internal pressure detecting device having device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an output correction device capable of correcting an offset drift of a cylinder internal pressure sensor, and a cylinder internal pressure detecting device capable of accurately detecting cylinder internal pressure of an internal combustion engine by using this device. <P>SOLUTION: This cylinder internal pressure detecting device 12 has a detecting circuit part 200 for detecting a change in resistance of a piezoresistance element 138 as an electric signal, an amplification circuit part 201 for amplifying and outputting this electric signal, and a correction circuit part 202 correcting this output value. The correction circuit part 202 is composed of a reset control part 205 for resetting the output value of the amplification circuit part 201 to a reference value, and a reset timing detecting part 206 for determining its timing. The reset timing detecting part 206 measures its waveform period based on an output waveform outputted from the amplification circuit part 201, and calculates the reset timing based on this waveform period, and outputs a reset signal to the reset control part 205 in this timing. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an output correction device for an in-cylinder pressure sensor that detects an in-cylinder pressure of an internal combustion engine and an in-cylinder pressure detection device including the same.

  In recent years, in an internal combustion engine such as a diesel engine, in order to respond to demands such as improvement of fuel consumption and reduction of emissions in exhaust gas, precise operation control according to the combustion state such as control of fuel injection amount by electronic control is performed. It has become common.

  One method for grasping the combustion state of the internal combustion engine is to detect the pressure in the cylinder (hereinafter referred to as in-cylinder pressure). Therefore, the internal combustion engine is provided with an in-cylinder pressure sensor, and an electric signal corresponding to the in-cylinder pressure is output.

  However, in an environment where an abrupt temperature change occurs as in an internal combustion engine, the drift of the output voltage of the in-cylinder pressure sensor due to factors such as temperature, the so-called offset drift, cannot be avoided. Correction is essential.

As a technique for correcting such a drift, for example, a technique (for example, refer to Patent Document 1) in which correction is performed from the value of a separately installed temperature sensor based on the temperature characteristics of an in-cylinder pressure sensor, or a crank angle sensor provided in an internal combustion engine Is detected from the outside, and the output voltage of the in-cylinder pressure sensor is reset to a reference value at a timing corresponding to a predetermined crank angle (for example, see Patent Document 2).
JP 2004-257888 A JP-A-7-280686

  When correcting using a temperature sensor, it is necessary to accurately detect the temperature of the drift generation factor, but in reality, the accurate temperature cannot be adjusted due to various factors such as the inability to install a temperature sensor near the drift generation factor. In many cases, it cannot be measured. Therefore, the measurement error is reflected in drift correction and may appear as a correction error. In addition, when there are multiple factors that cause drift, it is necessary to install multiple temperature sensors corresponding to all the factors, which complicates the configuration and correction processing, and increases the circuit scale associated with this. There is a risk.

  On the other hand, when the correction is performed using the crank angle sensor, a terminal for inputting a signal from the crank angle sensor must be separately provided on the output correction device side, which may increase the size of the device.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an output correction device that can correct an offset drift of an in-cylinder pressure sensor, and an in-cylinder pressure detection device that can accurately detect the in-cylinder pressure of an internal combustion engine. Is to provide.

  Hereinafter, each configuration suitable for solving the above-described problems will be described in terms of items. In addition, the effect etc. peculiar to the structure to respond | correspond as needed are added.

Configuration 1. The output correction device of this configuration is
An output correction device for an in-cylinder pressure sensor that outputs an electrical signal in accordance with the in-cylinder pressure of the internal combustion engine or the rate of change of the in-cylinder pressure of the internal combustion engine,
Period measuring means for measuring the period of the output waveform based on the output waveform of the in-cylinder pressure sensor;
Reset timing calculating means for calculating reset timing based on the waveform period measured by the period measuring means;
And reset means for resetting the output value of the in-cylinder pressure sensor to a reference value at the reset timing calculated by the reset timing calculation means.

  According to the configuration 1, since the timing for performing the reset process is obtained from the output waveform cycle of the in-cylinder pressure sensor corresponding to the combustion cycle of the internal combustion engine, a predetermined cycle of the combustion cycle is obtained without using the information of the crank angle sensor. The offset drift of the sensor output can be eliminated at the timing. Therefore, it is not necessary to separately provide a terminal for signal input from the crank angle sensor, and the size of the output correction device can be suppressed. In particular, when an in-cylinder pressure detection device in which an in-cylinder pressure sensor and an output correction device are integrated is installed in an internal combustion engine, the effect of the device must be reduced in consideration of vibration durability and the like. In the above configuration, since the sensor output is corrected by resetting the output value of the in-cylinder pressure sensor to the reference value without grasping the temperature, there is no need to provide a separate temperature sensor. As a result, the in-cylinder pressure of the internal combustion engine can be accurately detected without complicating the configuration and the correction process.

  Note that the reset timing calculation means calculates the reset timing based on a preset arithmetic expression using the waveform period of the sensor output as a variable. For example, the timing t + nΔt at which the time nΔt calculated by multiplying the waveform period Δt by a predetermined coefficient n elapses from a predetermined base point t (such as when the previous sensor output value exceeds a predetermined threshold or when the previous reset is performed). Set as reset timing Rt. In this case, the arithmetic expression necessary for calculating the reset timing from the waveform period of the sensor output, such as Rt = t + nΔt, has the lowest in-cylinder pressure of the internal combustion engine so that the offset drift of the sensor output is properly eliminated. The reset timing is adjusted to the desired timing of the combustion cycle. Therefore, by adopting a measurement value (variable) having a relatively long measurement time, such as the waveform period Δt of the sensor output, as a variable for obtaining a reset timing that matches the desired timing of one combustion cycle of the internal combustion engine. The ratio of the measurement error to the measured value (variable) can be reduced. As a result, the measurement error of the measured value (variable) hardly affects the calculation error of the reset timing, the deviation between the actual reset timing and the desired timing can be suppressed relatively small, and the sensor output can be improved at a better timing. Correction can be performed.

Configuration 2. The output correction apparatus of this configuration is the above-described configuration 1,
The period measuring means comprises:
A time interval from the time when the output value of the in-cylinder pressure sensor exceeds a predetermined threshold in a predetermined direction until the time when the threshold exceeds the predetermined direction is measured as the waveform period. .

  According to the configuration 2, the waveform period of the sensor output is actually measured by a relatively simple process in which one threshold is set in advance and a time exceeding the threshold is detected. As a result, the circuit configuration and correction processing can be further simplified.

Configuration 3. The output correction device of this configuration is the above-described configuration 2,
When the output value of the in-cylinder pressure sensor exceeds the threshold value in the predetermined direction, the threshold value is changed to increase or decrease in a direction opposite to the predetermined direction.

  In general, the output waveform of the in-cylinder pressure sensor may be accompanied by a noise waveform with a shorter cycle due to the influence of vibrations from the internal combustion engine. For this reason, when the threshold value used as the determination reference value in the period measurement is always fixed to one value, the output value of the in-cylinder pressure sensor continues from the predetermined time when the output value of the in-cylinder pressure sensor exceeds the threshold value in the predetermined direction as in the above configuration 2. In the method of measuring the time interval until the time point exceeding the predetermined direction, there is a risk that the cycle of the noise waveform is erroneously measured as the output waveform cycle of the in-cylinder pressure sensor. On the other hand, according to the configuration 3, for example, when the output value of the in-cylinder pressure sensor exceeds the first threshold value, the threshold value is changed to the second threshold value that is lower than the first threshold value, and the output of the in-cylinder pressure sensor. It can be configured such that the value is changed to the first threshold again when the value falls below the second threshold. In this case, the time interval from the predetermined time point when the output value of the in-cylinder pressure sensor exceeds the first threshold value to the next time point when the output value exceeds the first threshold value is measured as the output waveform cycle of the in-cylinder pressure sensor. In other words, the output correction device of the configuration 3 described above is “in the configuration 2, the threshold value has a first threshold value and a second threshold value that are different from each other, and the output value of the in-cylinder pressure sensor sets the first threshold value to the predetermined threshold value. When the threshold value is exceeded, the threshold value is changed to the second threshold value that is increased or decreased in the direction opposite to the predetermined direction with respect to the first threshold value, and the output value of the in-cylinder pressure sensor is In other words, when the second threshold value is exceeded in the direction opposite to the predetermined direction, the threshold value is changed from the second threshold value to the first threshold value. In this way, if the threshold value can be changed to a binary value and the difference between the two threshold values is set to an extent exceeding the assumed noise waveform amplitude, the in-cylinder pressure is not affected by noise. The output waveform cycle of the sensor can be measured appropriately. As a result, the accuracy of period measurement can be improved.

Configuration 4. The output correction device of this configuration is the above configuration 2 or 3,
The period measuring means includes
The time interval from the first time point when the output value of the in-cylinder pressure sensor exceeds the threshold value in the predetermined direction to the second time point when the output value exceeds the threshold value in the predetermined direction, and the second time point And then measuring the amount of change in the waveform period from the difference from the time interval until the third time point that exceeded the threshold in the predetermined direction,
The reset timing calculating means includes
The reset timing is calculated in consideration of the change amount of the waveform period.

  In the process in which the rotational speed of the internal combustion engine is changing (acceleration / deceleration), it is difficult to calculate the optimum reset timing only by the waveform period of the sensor output. In this regard, according to the configuration 4, the reset timing is calculated by taking into account not only the waveform period of the sensor output but also the change amount of the waveform period, so that it is more optimal than considering the change in the rotational speed of the internal combustion engine. Reset timing can be obtained. As a result, the deviation between the actual reset timing and the desired timing can be further reduced.

Configuration 5. The output correction device of this configuration is any one of the above configurations 2 to 4,
The threshold value is set within a range in which an in-cylinder pressure of the internal combustion engine can take in a compression stroke of one combustion cycle of the internal combustion engine.

  The output waveform of the in-cylinder pressure sensor takes various modes depending on the type of the internal combustion engine and its rotational speed. Among them, the output waveform in the compression stroke (the period from when the intake valve of the internal combustion engine closes until combustion starts) Even when the type and the rotational speed of the internal combustion engine are different, the individual difference is small, and a relatively similar waveform is taken and is stable. Therefore, the versatility of the output correction device is enhanced by setting the threshold value within a range that the in-cylinder pressure of the internal combustion engine can take in the compression stroke.

Configuration 6. The output correction device of this configuration is any one of the above configurations 1 to 5,
One time measurement means performs at least time measurement when measuring the waveform period and time measurement for managing whether or not the reset timing has been reached.

  Normally, if you want to perform multiple types of time measurement, such as time measurement when measuring the waveform period or time measurement to manage whether or not the reset timing has been reached, multiple time measurement means (timer circuits) )Is required. However, the integrated circuit of the output correction device for the in-cylinder pressure sensor is extremely small, and installing a plurality of time measuring means therein may increase the circuit scale and increase the manufacturing cost. On the other hand, if the configuration is such that at least the two time measurements are performed by one time measurement means as in the configuration 6, the circuit scale can be reduced and the manufacturing cost can be reduced. In addition to the above two time measurements, if there is a target for time measurement, the effect can be further enhanced by performing this measurement together with the one time measurement means. For example, in addition to the reset process at the reset timing calculated based on the waveform period, a configuration in which the reset process is forcibly performed when the output value of the in-cylinder pressure sensor cannot be recognized as exceeding a predetermined threshold within a set time. In the configuration, the time measurement (measurement of the set time) for managing whether or not the forced reset timing has been reached may be performed by the one time measurement unit together with the two time measurements.

Configuration 7. The in-cylinder pressure detection device of this configuration is
An in-cylinder pressure sensor that outputs an electric signal in accordance with the in-cylinder pressure of the internal combustion engine or the change rate of the in-cylinder pressure of the internal combustion engine;
The output correction apparatus according to any one of the configurations 1 to 6 is provided.

  According to the configuration 7, by integrating the in-cylinder pressure sensor and the output correction device, it is possible to effectively use a limited installation space of the internal combustion engine and improve convenience. In addition, when this in-cylinder pressure detecting device is integrated with a glow plug or the like, the operational effect can be further enhanced.

[First Embodiment]
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, a schematic configuration of an internal combustion engine to which an in-cylinder pressure detecting apparatus according to the present invention is attached will be described with reference to FIG. 2 taking a four-cycle diesel engine (hereinafter simply referred to as an engine) as an example. FIG. 2 is a schematic diagram showing the configuration of the engine control system.

  An intake pipe 3 and an exhaust pipe 4 are connected to the cylinder 2 of the engine 1. An intake valve 5 is provided in the intake port 3 a of the cylinder 2 connected to the intake pipe 3, and an exhaust valve 6 is provided in the exhaust port 4 a of the cylinder 2 connected to the exhaust pipe 4.

  A piston 7 is accommodated in the cylinder 2, and the piston 7 is connected to a crankshaft 9 via a connecting rod 8. In addition to the intake valve 5 and the exhaust valve 6, the tip of the glow plug 10 and the fuel injection nozzle 11 faces the space surrounded by the upper part of the piston 7 and the wall surface of the cylinder 2, that is, the combustion chamber 2a.

  The glow plug 10 incorporates an in-cylinder pressure detecting device 12 for detecting a pressure in the combustion chamber 2a of the cylinder 2 (hereinafter referred to as an in-cylinder pressure) as will be described later. The crankshaft 9 is provided with a crank angle sensor 15 that detects its rotation angle (crank angle). Detection signals from various sensors including the in-cylinder pressure detection device 12 and the crank angle sensor 15 are input to an engine control electronic control unit (hereinafter referred to as “ECU”) 18. The ECU 18 controls the fuel injection amount from the fuel injection nozzle 11 and the like based on these detection signals and a detection signal proportional to the movement of the accelerator pedal input from the throttle sensor 19.

  When fuel is injected from the fuel injection nozzle 11 with the glow plug 10 energized to generate heat, the fuel 1 is ignited and the engine 1 is started.

  Next, the structure of the glow plug 10 incorporating the in-cylinder pressure detecting device 12 according to the present invention and its mounting mode will be described with reference to FIG. FIG. 1 is a partial cross-sectional view of a cylinder head 2b to which a glow plug 10 is attached.

  The glow plug 10 is mounted in a plug mounting hole 2c formed in the cylinder head 2b, and is positioned so that the tip side protrudes into the combustion chamber 2a.

  The glow plug 10 is disposed on the distal end side of the central shaft 101, a cylindrical metallic shell 100 extending along the axis C direction, a conductive rod-shaped middle shaft 101 held in the metallic shell 100, and a main body. And a rod-shaped heater member 102 protruding outward from the tip of the metal fitting 100.

  On the outer peripheral surface on the base end side of the metal shell 100, a male thread portion 111 for fixing the glow plug 10 to the plug mounting hole 2c of the cylinder head 2b, and a hexagonal shape for engaging a tool such as a wrench when the screw is fixed. The tool engaging portion 112 is formed.

  A cylindrical heater holding member 114 in which the heater member 102 is press-fitted and held, and a seal member 115 that closes the gap between the heater holding member 114 and the tip of the metal shell 100 are provided on the front end side of the metal shell 100. ing.

  The proximal end portion of the heater member 102 is connected to the distal end portion of the middle shaft 101 by a cylindrical electrode member 116 having conductivity.

  The heater member 102 includes a base body 120 made of an insulating ceramic and a heating element 121 embedded in the base body 120. One end of the heating element 121 is electrically connected to the central shaft 101 via the electrode member 116, and the other end is electrically connected to the metal shell 100 via the heater holding member 114. Thus, when the temperature of the heater member 102 is raised, the current supplied to the heating element 121 through the middle shaft 101 flows to the cylinder head 2b through the metal shell 100.

  The heater holding portion 114 is held in a state displaceable in the direction of the axis C by a holding member 119 made of self-lubricating graphite. As a result, the heater holding member 114 and the heater member 102 press-fitted into the heater holding member 114 are displaced in the direction of the axis C according to the change in the in-cylinder pressure in the combustion chamber 2a.

  A cylindrical slide pipe 126 is slidably disposed in the shaft hole 125 of the metal shell 100. The front end of the slide pipe 126 is connected to the proximal end portion of the heater holding member 114, and the push pipe 127 is connected to the rear end. Therefore, when the heater holding member 114 is displaced, the slide pipe 126 and the push pipe 127 are also displaced in the axis C direction.

  The push pipe 127 protrudes from the base end portion of the metal shell 100, and an O-ring 129 that closes the gap with the base end portion of the metal shell 100 is fitted around the push pipe 127.

  The above-described in-cylinder pressure detecting device 12 is provided on the base end side of the metal shell 100. The outer shell of the in-cylinder pressure detecting device 12 includes a cylindrical housing 131 surrounding the periphery thereof and a grommet 132 that closes the proximal end side of the housing 131. A plurality of connecting wires 133 are drawn into the in-cylinder pressure detecting device 12 through the grommet 132.

  The in-cylinder pressure detecting device 12 includes an annular base 135 attached to the base end portion of the metal shell 100 so as to surround the push pipe 127 and a base 135 in contact with the base end portion of the push pipe 127. And a diaphragm member 136 mounted on the substrate.

  The diaphragm member 136 has a thin diaphragm portion 136a, and is deformed by being pushed by the push pipe 127. Further, a piezoresistive element 138 is affixed to the diaphragm portion 136a, and the resistance value of the piezoresistive element 138 changes due to the deformation of the diaphragm member 136.

  A printed circuit board 140 is disposed on the base end side of the diaphragm member 136. On the printed circuit board 140, electronic components such as an IC are mounted, and various electronic circuits are formed. Then, when the pressure received by the heater member 102 is transmitted to the piezoresistive element 138 due to the change in the in-cylinder pressure in the combustion chamber 2a, the pressure on the printed circuit board 140 connected to the piezoresistive element 138 via the bonding wire 143 is increased. The detection circuit unit detects a change in resistance of the piezoresistive element 138 as an electric signal. The detected electrical signal is amplified by the amplification circuit unit and output to the outside as a detection signal proportional to the in-cylinder pressure. However, since a drift due to factors such as temperature occurs in the detection signal, a correction circuit section for eliminating this drift is also provided on the printed circuit board 140. Since the process of eliminating this drift is performed by resetting the output value of the amplifier circuit unit to the reference value as will be described later, this process is hereinafter referred to as “reset (reset process)”.

  One of the plurality of connection lines 133 described above is electrically connected to the proximal end portion of the central shaft 101 for supplying power to the heater member 102. The other connection lines 133 are electrically connected to the printed circuit board 140 and are used for outputting detection signals or supplying power to the printed circuit board 140.

  Here, the circuit configuration of the in-cylinder pressure detecting device 12 will be described with reference to FIG. FIG. 3 is a functional block diagram showing a circuit configuration.

  The in-cylinder pressure detection device 12 includes a detection circuit unit 200 that detects a change in resistance of the piezoresistive element 138 as an electrical signal, an amplification circuit unit 201 that amplifies and outputs the electrical signal, and a correction circuit that corrects the output value. Part 202. Among these, the piezoresistive element 138, the detection circuit unit 200, and the amplification circuit unit 201 constitute an in-cylinder pressure sensor in the present embodiment, and the correction circuit unit 202 constitutes an output correction device.

  The correction circuit unit 202 includes a reset control unit 205 as a reset unit that resets the output value of the amplification circuit unit 201 to a reference value, and a reset timing detection unit 206 that obtains the timing.

  The reset timing detection unit 206 functions as a period measuring unit that measures the waveform period based on the output waveform (in-cylinder pressure waveform) output from the amplification circuit unit 201 and resets based on the waveform period measured thereby. It has a function as a reset timing calculation means for calculating timing and a function as a reset signal output means for outputting a reset signal to the reset control unit 205 at the calculated timing.

  Then, based on the input of the reset signal, the reset control unit 205 turns on the switch element, for example, and discharges the charge of the capacitor connected in parallel to the amplifier of the amplifier circuit unit 201, and calculates the potential difference between the input and output of the amplifier. The above reset process is performed by eliminating them.

  Next, the flow of correction processing performed by the correction circuit unit 202 will be described with reference to FIGS. FIG. 4 is a flowchart showing the flow of the correction process, and FIG. 5 is a diagram showing the output waveform of the amplifier circuit unit 201. However, for the sake of convenience, FIG. 5 shows the output waveform when there is no drift, and in order to make it easier to understand the relationship between the combustion cycle of the engine 1 and the in-cylinder pressure, the horizontal axis represents the crank angle instead of the time, and the vertical axis represents Shows the in-cylinder pressure corresponding to the output value of the amplifier circuit unit 201.

  As shown in FIG. 4, the reset process is first executed in step S <b> 1, such as immediately after the engine 1 is started, and the output value of the amplifier circuit unit 201 is set as the reference value O. The reset process executed in step S1 is hereinafter referred to as “forced reset”.

  In subsequent step S <b> 2, it is determined whether or not the output value of the amplification circuit unit 201 has exceeded the pressure threshold P within the set time (exceeded the pressure threshold P). Thereby, it is determined whether or not the forced reset timing in step S1 is appropriate. For example, when the forced reset is performed in the combustion stroke of one combustion cycle (combustion / exhaust / intake / compression) of the engine 1, the output value of the amplification circuit unit 201 becomes the pressure threshold value P within the set time. May not be detected. In such a case, it is considered that the timing of the forced reset is not appropriate. Therefore, if it is not detected in step S2 that the output value of the amplification circuit unit 201 has exceeded the pressure threshold P within the set time, the process returns to step S1 to perform a forced reset again. That is, these processes are repeated until it can be detected that the output value of the amplification circuit unit 201 exceeds the pressure threshold value P within the set time.

  In the present embodiment, as the set time, the slowest engine 1 that is assumed within a specification range (for example, a range of the rotational speed of the engine 1 from 600 rpm to 4000 rpm) in which the in-cylinder pressure detection device 12 can maintain a specified accuracy. A time corresponding to one combustion cycle (for example, 0.2 seconds) is set in accordance with the number of rotations (for example, 600 rpm). Further, the pressure threshold P is the in-cylinder pressure (the output value of the amplification circuit unit 201) in the compression stroke of one combustion cycle of the engine 1, that is, in the period from when the intake valve 5 of the engine 1 is closed until combustion is started. Is set within the possible range. This is because the output waveform in the compression stroke is stable even when the type and speed of the internal combustion engine are different and the individual difference is small and relatively similar. Therefore, versatility is enhanced by using such a setting.

  If it is detected in step S2 that the output value of the amplification circuit unit 201 has exceeded the pressure threshold value P, it is considered that the timing of forced reset is appropriate, and the time t1 when the pressure threshold value P has been exceeded in step S3. Remember.

  In the subsequent step S4, it is determined whether or not the output value of the amplifier circuit unit 201 has again exceeded the pressure threshold P within the set time from the time t1. Even when the timing of the forced reset in step S1 is appropriate, for example, when the drift amount is large, the output value of the amplifier circuit unit 201 may not exceed the pressure threshold P again within the set time. In such a case, the process returns to step S1 according to the determination in step S4, and the forced reset is performed again. That is, the processing of step S1 to step S4 is repeated until it can be detected that the output value of the amplification circuit unit 201 has appropriately exceeded the pressure threshold P twice.

  If it is detected in step S4 that the output value of the amplification circuit unit 201 has exceeded the pressure threshold P again within the set time from the time t1, the time t2 when the pressure threshold P has been exceeded in step S5. Remember.

  In the subsequent step S6, the period Δt of the output waveform of the amplifier circuit 201 is calculated from the difference t2−t1 between the times t1 and t2 exceeding the two-degree pressure threshold P, and reset based on the following equation (1). Timing Rt is calculated.

Rt = nΔt + t2
= N (t2-t1) + t2 (1)
That is, the timing at which the time nΔt calculated by multiplying the waveform period Δt by the predetermined coefficient n from the time t2 when the output value of the amplifier circuit 201 exceeds the pressure threshold P is the reset timing Rt. Here, the coefficient n is a coefficient arbitrarily set in the range of 0 <n <1. The reset timing Rt is less affected by combustion and compression, and it is desirable that the in-cylinder pressure be close to atmospheric pressure. Therefore, in this embodiment, the reset timing Rt is the intake stroke immediately before switching to the compression stroke in one combustion cycle of the engine 1. Thus, the coefficient n = 0.65 is set so that the reset process is performed.

  In step S7, the reset process is executed at the reset timing Rt calculated in step S6. The reset process executed in step S7 is hereinafter referred to as “normal reset”.

  Thereafter, in step S8, the value of the time t2 stored as the time exceeding the pressure threshold P for the second time is shifted as the value of time t1 exceeding the pressure threshold P for the first time, and the process returns to step S4. As a result, when the output value of the amplifier circuit unit 201 newly exceeds the pressure threshold value P within the set time, a new time t2 is stored, and the processing after step S5 is repeatedly executed as described above. On the other hand, when the pressure threshold value P is not newly exceeded, it returns to step S1 according to determination of step S4, and forced reset is performed. Therefore, while the output value of the amplification circuit unit 201 is properly reset, the processes in steps S4 to S8 are repeatedly performed, and the normal reset is executed for each combustion cycle of the engine 1.

  As described above in detail, in the present embodiment, the timing for performing the reset process is obtained from the output waveform cycle of the in-cylinder pressure detecting device 12 (amplifying circuit unit 201) corresponding to the combustion cycle of the engine 1. Without using the information of the sensor 15, the offset drift of the amplification circuit unit 201 can be eliminated at a predetermined timing of the combustion cycle. Therefore, it is not necessary to separately provide a terminal for inputting a signal from the crank angle sensor 15, and the increase in the cylinder pressure detection device 12 (correction circuit unit 202) can be suppressed. Further, in this embodiment, output correction is performed by resetting the output value of the amplifier circuit unit 201 to the reference value without grasping the temperature, so there is no need to provide a separate temperature sensor. As a result, the in-cylinder pressure of the engine 1 can be detected with high accuracy without complicating the configuration and the correction process.

  Further, as a variable for obtaining the reset timing Rt that matches the desired timing of one combustion cycle of the engine 1, a measurement value (variable) having a relatively long measurement time is employed, such as the output waveform period Δt of the amplification circuit unit 201. By doing so, the ratio of the measurement error to the measured value (variable) can be reduced. As a result, the measurement error of the measurement value (variable) hardly affects the calculation error of the reset timing Rt, the deviation between the actual reset timing and the desired timing can be suppressed relatively small, and the amplifier circuit at a better timing The output of the unit 201 can be corrected.

[Second Embodiment]
Hereinafter, a second embodiment different from the first embodiment will be described. However, since the structure and circuit configuration of the glow plug 10 and the in-cylinder pressure detection device 12 are the same as those in the first embodiment, description thereof is omitted. In the present embodiment, the correction processing performed in the correction circuit unit 202 has a feature different from that of the first embodiment, and the flow of the correction processing will be described with reference to FIGS. FIG. 6 is a flowchart showing the flow of the correction process, and FIG. 7 is a diagram showing the output waveform of the amplifier circuit unit 201 as in FIG.

  As shown in FIG. 6, in the process of steps S11 to S17 of the correction process in the present embodiment, the same process as the process of steps S1 to S7 of the first embodiment is performed. That is, in step S11, a forced reset is first executed, and the output value of the amplifier circuit unit 201 is set to the reference value O.

  In step S12, it is determined whether or not the output value of the amplifier circuit unit 201 has exceeded the pressure threshold P within the set time. If it is not detected that the pressure threshold value P has been exceeded, the process returns to step S11 to perform a forced reset again. On the other hand, if it is detected that the pressure threshold P has been exceeded, the time t1 when the pressure threshold P has been exceeded is stored in step S13.

  In step S14, it is determined whether or not the output value of the amplification circuit unit 201 has again exceeded the pressure threshold value P within the set time from the time t1. If it is not detected that the pressure threshold value P has been exceeded, the process returns to step S11 to perform a forced reset again. On the other hand, if it is detected that the pressure threshold P has been exceeded, the time t2 when the pressure threshold P has been exceeded is stored in step S15.

  In step S16, the period of the output waveform of the amplifier circuit unit 201 is calculated from the difference t2-t1 between the times t1 and t2 exceeding the two-degree pressure threshold P, and the arithmetic expression (1) shown in the first embodiment ( Based on 1), the reset timing Rt is calculated. The coefficient n is an arbitrarily set coefficient, but here, the coefficient n = 0.65 is set for the same reason as in the first embodiment (the same applies to the arithmetic expression (2) described later).

  In step S17, a normal reset is executed at the reset timing Rt calculated in step S16.

  In step S18, it is determined whether or not the output value of the amplification circuit unit 201 has again exceeded the pressure threshold value P within the set time from the time t2. This process is performed for the same reason as in step S14. Therefore, if it is not detected that the pressure threshold value P has been exceeded, the process returns to step S11 to perform a forced reset again. On the other hand, if it is detected that the pressure threshold P has been exceeded, the time t3 when the pressure threshold P has been exceeded is stored in step S19.

  In the subsequent step S20, the first waveform period Δt1 is determined from the difference t2-t1 between the times t1 and t2 when the pressure threshold P is exceeded, and the second waveform period is determined from the difference t3-t2 between the times t2 and t3 when the pressure threshold P is exceeded. Δt2 is calculated, and the change amount Δt2−Δt1 is calculated, and the reset timing Rt is calculated based on the following equation (2).

Rt = n {n (Δt2−Δt1) + Δt2} + t3
= N2 (Δt2-Δt1) + nΔt2 + t3
= N2 (t3-2.t2 + t1) + n (t3-t2) + t3 (2)
That is, from the time t3 when the output value of the amplifier circuit 201 exceeds the pressure threshold value P, the coefficient n2 is calculated for the time nΔt2 calculated by multiplying the waveform period Δt2 by the predetermined coefficient n and the change amount Δt2−Δt1 of the waveform period. The timing at which the time n2 (Δt2−Δt1) calculated by multiplying is the reset timing Rt.

  In step S21, reset processing (normal reset) is executed at the reset timing Rt calculated in step S20. Thereafter, in step S22, the value of the time t2 stored as the time exceeding the pressure threshold P at the second time is shifted as the value of the time t1 exceeding the pressure threshold P at the first time, and the pressure threshold P is set at the third time. The value of the time t3 stored as the exceeded time is shifted as the value of the time t2 when the pressure threshold P is exceeded for the second time, and the process returns to step S18. Thereby, when the output value of the amplification circuit unit 201 newly exceeds the pressure threshold value P within the set time, a new time t3 is stored, and the processing after step S19 is repeatedly executed as described above. On the other hand, if the pressure threshold value P is not newly exceeded, the process returns to step S11 in accordance with the determination in step S18 to perform a forced reset. Therefore, while the output value of the amplification circuit unit 201 is properly reset, the processing of step S18 to step S22 is repeated, and normal reset is executed for each combustion cycle of the engine 1.

  As described above in detail, in this embodiment, the reset timing Rt is calculated not only by the output waveform period Δt2 (or Δt1) of the amplifier circuit unit 201 but also by the change amount Δt2−Δt1 of the waveform period. . In the process in which the rotation speed of the engine 1 is changing (acceleration / deceleration), it is difficult to calculate the optimum reset timing Rt only with the output waveform period Δt2 (or Δt1) of the amplification circuit unit 201. Accordingly, it is possible to obtain a more optimal reset timing Rt in consideration of the change in the rotational speed of the engine 1. As a result, the deviation between the actual reset timing and the desired timing can be further reduced.

  In addition, it is not limited to the description content of embodiment mentioned above, For example, you may implement as follows.

  (A) In each of the above-described embodiments, the in-cylinder pressure detection device 12 in which the in-cylinder pressure sensor including the piezoresistive element 138 and the like and the output correction device including the correction circuit unit 202 and the like are integrated is illustrated. Not limited to this, the output correction device may be provided separately from the in-cylinder pressure sensor. For example, the output correction device for the in-cylinder pressure sensor may be provided in the electronic control unit (ECU) 18. The in-cylinder pressure detecting device 12 may be provided separately from the glow plug 10.

  (B) In each of the above embodiments, the piezoresistive element 138 is adopted as a pressure-sensitive means for detecting the in-cylinder pressure of the engine 1, but the present invention is not limited thereto, and offset drift such as a piezoelectric element or a metal resistance strain gauge occurs. Even in a configuration that employs other pressure-sensitive means, the present invention has the same effects as the above-described embodiment.

  (C) In each of the above embodiments, by measuring the time interval from the time when the output value of the amplification circuit unit 201 exceeds the predetermined pressure threshold P to the next time when the pressure threshold P is exceeded, the amplification circuit The output waveform period of the unit 201 is obtained. The method for obtaining the waveform period is not limited to this. For example, the time interval from the time when the output value of the amplifier circuit 201 falls below a predetermined pressure threshold P to the next time when the pressure threshold P falls below is measured. You may make it ask by doing. In this case, in one combustion cycle of the engine 1, for example, at the later stage of the combustion stroke or the start period of the exhaust stroke, it is determined whether or not the output value of the amplification circuit unit 201 is lower than the pressure threshold value P. . However, during such a period, the output waveform of the amplifier circuit unit 201 changes variously due to the difference in the rotational speed of the engine 1 and the like, so that the measurement error of the waveform period may increase. For this reason, the method of calculating | requiring a waveform period based on the output waveform (output value) of the amplifier circuit part 201 in a compression process like said each embodiment is more preferable.

  (D) The arithmetic expression for calculating the reset timing Rt is not limited to the arithmetic expressions (1) and (2). For example, if more accuracy is required, the number of calculation terms may be increased. Further, the reset timing Rt may not be adjusted to the intake stroke as in the above embodiment, but may be set to the timing at which the in-cylinder pressure is close to the atmospheric pressure at the end of the exhaust stroke or the start of the compression stroke. Therefore, the coefficient n can be arbitrarily set according to a desired timing in one combustion cycle of the engine 1. Further, the time point that is the base point for obtaining the reset timing Rt may be the time point when the previous reset is executed, that is, the previous reset timing Rt, instead of the time t2 when the pressure threshold P is exceeded.

  (E) In implementing the first and second embodiments, the following configuration may be adopted. This configuration is characterized by the configuration of the correction circuit unit 202, in particular, the reset timing detection unit 206, and hence the correction processing executed thereby.

  First, the circuit configuration of the reset timing detection unit 206 will be described with reference to the functional block diagram shown in FIG.

  The reset timing detection unit 206 of this configuration compares the output value of the amplifier circuit unit 201 with the pressure threshold value P, and outputs a rectangular wave signal whose output level is switched according to the magnitude comparison result. A memory 502 that stores two types of values as P, a threshold value switching unit 503 that switches between the two values stored in the memory 502 and outputs the result to the comparator 501, and a rising edge of the rectangular wave signal output from the comparator 501 And a calculation unit 505 that calculates a reset timing Rt based on the detection result of the rise detection unit 504 and outputs a reset signal to the reset control unit 205 at the timing Rt.

  The comparator 501 has a non-inverting input terminal (+) connected to the amplifier circuit unit 201 and an inverting input terminal (−) connected to the threshold switching unit 503. When the output value of the amplifier circuit unit 201 does not exceed the pressure threshold value P, a low level signal is output, and when the output value of the amplifier circuit unit 201 exceeds the pressure threshold value P, a high level signal is output. [Refer to FIG. 9B].

  The memory 502 includes a first threshold data storage area 502a and a second threshold data storage area 502b. In both storage areas 502a and 502b, a first threshold value P1 and a second threshold value P2 are stored as pressure threshold values P, respectively. As the values of the threshold values P1 and P2, any value satisfying at least the relationship of P1> P2 can be set. For example, in this configuration, 0.5 MPa is stored as the first threshold value P1, and 0.4 MPa is stored as the second threshold value P2. However, as described later, in order not to be affected by noise, it is necessary to set the difference between the two threshold values P1 and P2 so as to exceed the assumed amplitude of the noise waveform.

  On the other hand, the threshold switching unit 503 outputs a signal having a level corresponding to the first threshold P1 or the second threshold P2 according to the output level of the comparator 501. Thereby, the value of the pressure threshold value P used as a determination reference is changed to the first threshold value P1 or the second threshold value P2 depending on whether the output value of the amplifier circuit 201 exceeds the pressure threshold value P or not. It will be.

  Under the above-described configuration, as shown in FIGS. 9A and 9B, in a situation where the output value of the amplifier circuit unit 201 is lower than the pressure threshold P and the output level of the comparator 501 is low. The pressure threshold value P is the first threshold value P1. FIG. 9A is a diagram showing an output waveform of the amplifier circuit unit 201, as in FIG. 5, and FIG. 9B is a diagram showing an output waveform of the comparator 501 corresponding thereto.

  Then, at the time point t1 when the output value of the amplification circuit unit 201 exceeds the first threshold value P1 and the output level of the comparator 501 switches to a high level (when the rising edge of the rectangular wave signal is detected), the value of the pressure threshold value P is the first threshold value P1. To the second threshold value P2 lower than that. In this state, while the output value of the amplifier circuit unit 201 is higher than the pressure threshold P and the output level of the comparator 501 is high, the value of the pressure threshold P is maintained at the second threshold P2.

  Thereafter, at the time when the output value of the amplifier circuit 201 falls below the second threshold value P2 and the output level of the comparator 501 switches to the low level (at the falling edge of the rectangular wave signal) s1, the value of the pressure threshold value P again becomes the first threshold value. It is changed to P1.

  Thereafter, such switching of the pressure threshold value P is repeatedly performed in accordance with one combustion cycle of the engine 1.

  As a result, the time interval from the predetermined time point t1 when the output value of the amplification circuit unit 201 exceeds the first threshold P1 (at the time of rising detection) to the time point t2 when it next exceeds (at the time of rising detection) t2 is the output of the amplification circuit unit 201. It is measured as a waveform period Δt. For example, in the case of corresponding to the first embodiment, a reset signal is output to the reset control unit 205 at the reset timing Rt calculated from the arithmetic expression (1) based on this, and the amplifier circuit unit 201 Is reset to the reference value.

  As shown in FIG. 10, the output waveform of the amplification circuit unit 201 may be generally subjected to a noise waveform with a shorter cycle due to the influence of vibration or the like from the engine 1. FIG. 10 is a partially enlarged view schematically showing a range surrounded by a broken line W in FIG. For this reason, if the pressure threshold value P is always fixed to the first threshold value P1, the time interval from the predetermined time point t1 when the output value of the amplifier circuit 201 exceeds the first threshold value P1 to the next time point k1 is exceeded. That is, there is a possibility that the period Δk of the noise waveform is erroneously measured as the output waveform period Δt of the amplifier circuit unit 201.

  On the other hand, according to this configuration, at the time point t1 when the output value of the amplification circuit unit 201 exceeds the first threshold value P1, the value of the pressure threshold value P is changed to the second threshold value P2 that is not affected by the noise waveform. Therefore, it is possible to appropriately measure the time intervals t1 to t2 that are originally desired to be measured as the output waveform period Δt of the amplifier circuit unit 201. As a result, the accuracy of period measurement can be improved.

  Note that, based on the falling edge of the rectangular wave signal, a time interval from a predetermined time point s1 when the output value of the amplifier circuit 201 falls below the pressure threshold value P to a time point s2 when the output value falls below the pressure threshold value P is measured. The configuration for obtaining the output waveform period of the amplifier circuit unit 201 can also be realized by the same procedure as described above.

  (F) When implementing each of the above-described embodiments, at least a timer for measuring the period Δt of the output waveform of the amplifier circuit unit 201, whether or not the reset timing Rt (normal reset timing) has been reached is managed. Three timers are necessary, that is, a timer for managing whether or not the timing for forced reset has been reached. However, the integrated circuit of the in-cylinder pressure detecting device 12 built in the glow plug 10 is extremely small, and installing three timer circuits therein may increase the circuit scale and increase the manufacturing cost.

  Therefore, here, a configuration capable of realizing each of the above embodiments with only one timer circuit is shown below. First, the circuit configuration of the reset timing detection unit 206 will be described with reference to the functional block diagram shown in FIG.

  The reset timing detection unit 206 of this configuration includes a rise detection unit 601 that detects a rise of a rectangular wave signal generated by comparing the output value of the amplification circuit unit 201 and the pressure threshold value P, and a timer 602 as a time measurement unit. A memory 603 for storing time data obtained from the timer 602 and various numerical data set in advance, a reset timing calculator 604 for calculating a reset timing based on the data stored in the memory 603, and a timer 602 The first comparison unit 605 and the second comparison unit 606 that compare the time data obtained from the predetermined time data stored in the memory 603 and the output signal from the first comparison unit 605 or the second comparison unit 606 An output unit 607 that outputs a reset signal to the reset control unit 205 is provided.

  In the memory 603, a cycle data storage area 603a for storing cycle data of the output waveform of the amplifier circuit unit 201 (for example, the cycle Δt) and coefficient data (for example, the above-described) A coefficient data storage area 603b for storing the coefficient n and the like, and a normal reset time data storage area for storing time interval data (for example, nΔt and the like) up to the reset timing Rt calculated by the reset timing calculation unit 604 603c and a forced reset time data storage area 603d for storing time interval data for executing the forced reset (for example, the set time of 0.2 seconds or the like).

  Among these, the data stored in the periodic data storage area 603a and the normal reset time data storage area 603c are rewritten as needed. On the other hand, arbitrary values are set in advance in the coefficient data storage area 603b and the forced reset time data storage area 603d.

  Under the above configuration, when the rising edge detection unit 601 detects the rising edge of the rectangular wave signal, the value of the timer 602 at this time is written to the periodic data storage area 603a of the memory 603 and the value of the timer 602 is set to 0. Reset. This process is performed every time the rising edge detection unit 601 detects the rising edge of the rectangular wave signal. By repeating this process, the periodic data storage area 603a has a time interval from the previous detection time t1 of the rectangular wave signal to the current detection time t2 of the rectangular wave signal as periodic data (for example, period Δt = 0.1 second).

  Subsequently, the reset timing calculation unit 604 is based on the periodic data stored in the periodic data storage area 603a of the memory 603 and the coefficient data (for example, coefficient n = 0.5) stored in advance in the coefficient data storage area 603b. In addition, for example, the reset timing Rt (= nΔt + t2) of the normal reset is calculated from the arithmetic expression (1) of the first embodiment, and is stored in the normal reset time data storage area 603c. However, since the time point t2 serving as the base point is the time point when the timer 602 is reset to 0, the time interval data from the base point to the reset timing Rt (eg, nΔt = 0.05 seconds) is the normal reset time data. The data is written in the storage area 603c.

  Further, the first comparison unit 605 compares the value of the timer 602 with the value stored in the normal reset time data storage area 603c as needed, and outputs a low level signal if the two values do not match, If both values match, a high level signal is output.

  On the other hand, the second comparison unit 606 compares the value of the timer 602 with the value stored in the forced reset time data storage area 603d as needed, and outputs a low level signal if the two values do not match, If both values match, a high level signal is output.

  When the high level signal is input from the first comparison unit 605 or the second comparison unit 606, the output unit 607 formed of an OR circuit outputs a reset signal to the reset control unit 205.

  Thereby, the rising edge of the rectangular wave signal is periodically detected by the rising edge detection unit 601 and normal reset is executed every time a predetermined time elapses. On the other hand, when the rising edge of the rectangular wave signal is not detected by the rising edge detection unit 601 within the set time stored in the forced reset time data storage area 603d and the value of the timer 602 has passed that time. The forced reset is executed.

  According to the above configuration, time measurement when measuring the waveform period of the amplification circuit unit 201, time measurement for managing whether or not the normal reset timing has been reached, and management of whether or not the forced reset timing has been reached The time measurement for this can be performed by one timer 602. As a result, it is not necessary to provide a plurality of timer circuits, and an increase in circuit scale and an increase in manufacturing cost can be suppressed. Of course, in the configuration in which the forced reset is not performed, the above-described components related to the forced reset can be omitted.

It is a fragmentary sectional view of the cylinder head to which the glow plug was attached. It is the schematic which shows the structure of an engine control system. It is a functional block diagram which shows the circuit structure of a cylinder pressure detection apparatus. It is a flowchart which shows the flow of a correction process. It is the figure which showed the output waveform of the amplifier circuit part. It is a flowchart which shows the flow of the correction process in another embodiment. It is the figure which showed the output waveform of the amplifier circuit part in another embodiment. It is a functional block diagram which shows the circuit structure of a reset timing detection part. (A) is the figure which showed the output waveform of the amplifier circuit part, (b) is the figure which showed the output waveform of the comparator corresponding to it. FIG. 10 is a partially enlarged view schematically showing a range surrounded by a broken line W in FIG. 9. It is a functional block diagram which shows the circuit structure of a reset timing detection part.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Engine, 10 ... Glow plug, 12 ... In-cylinder pressure detection apparatus, 138 ... Piezoresistive element, 201 ... Amplifier circuit part, 202 ... Correction circuit part, 205 ... Reset control part, 206 ... Reset timing detection part, O ... Reference | standard Value, P: Pressure threshold, Δt: Waveform cycle, Rt: Reset timing.

Claims (7)

An output correction device for an in-cylinder pressure sensor that outputs an electrical signal in accordance with the in-cylinder pressure of the internal combustion engine or the rate of change of the in-cylinder pressure of the internal combustion engine,
Period measuring means for measuring the period of the output waveform based on the output waveform of the in-cylinder pressure sensor;
Reset timing calculating means for calculating reset timing based on the waveform period measured by the period measuring means;
An output correction apparatus comprising: reset means for resetting an output value of the in-cylinder pressure sensor to a reference value at a reset timing calculated by the reset timing calculation means.   The period measuring means measures, as the waveform period, a time interval from the time when the output value of the in-cylinder pressure sensor exceeds a predetermined threshold in a predetermined direction to the next time when the threshold exceeds the predetermined direction. The output correction apparatus according to claim 1, wherein:   When the output value of the in-cylinder pressure sensor exceeds the threshold value in the predetermined direction, the threshold value is changed to be a value that is increased or decreased in a direction opposite to the predetermined direction. Item 3. The output correction device according to Item 2. The period measuring means includes
The time interval from the first time point when the output value of the in-cylinder pressure sensor exceeds the threshold value in the predetermined direction to the second time point when the output value exceeds the threshold value in the predetermined direction, and the second time point And then measuring the amount of change in the waveform period from the difference from the time interval until the third time point that exceeded the threshold in the predetermined direction,
The reset timing calculating means includes
The output correction apparatus according to claim 2, wherein the reset timing is calculated in consideration of a change amount of the waveform period.   The said threshold value is set in the range which can take the cylinder pressure of the said internal combustion engine in the compression stroke of the one combustion cycle of the said internal combustion engine, The any one of Claim 2 thru | or 4 characterized by the above-mentioned. Output correction device.   6. The time measurement for measuring at least the waveform period and the time measurement for managing whether or not the reset timing has been reached are performed by one time measurement means. The output correction apparatus of any one of Claims. An in-cylinder pressure sensor that outputs an electric signal in accordance with the in-cylinder pressure of the internal combustion engine or the change rate of the in-cylinder pressure of the internal combustion engine;
An in-cylinder pressure detecting device comprising the output correcting device according to any one of claims 1 to 6.

Images