JP2009229329A - Output correction device for cylinder pressure sensor and cylinder pressure detecting device provided therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an output correction device which can correct the offset drift of a cylinder pressure sensor and a cylinder pressure detecting device which uses it and can detect the cylinder pressure of an internal combustion engine with high precision. <P>SOLUTION: The cylinder pressure detecting device 12 includes a detection section 203 for detecting a change in the resistance of a piezoelectric element 138 as an electric signal, a correction circuit section 204 for correcting it and outputting it to the outside, and a temperature detection element 201 for detecting the temperature of the piezoelectric element 138. The correction circuit section 204 includes a temperature detection element 210 for detecting the temperature of the correction circuit section 204, a reset circuit section 215 for resetting the output value of the electric signal output from the detection section 203 to be a standard value, and a span correction section 217 for adjusting the amplification factor of an electric signal output from the reset circuit section 215 in accordance with the output values of the temperature detection elements 201, 210. <P>COPYRIGHT: (C)2010,JPO&amp;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) that corrects from a value of a temperature sensor that is separately installed based on a temperature characteristic 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.

  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,
Reset means for calculating a reset timing based on an output signal of the in-cylinder pressure sensor, and resetting an output value of the in-cylinder pressure sensor to a reference value at the reset timing;
Based on temperature information detected from the temperature sensor, comprising a span correction means for adjusting the amplification factor of the output signal of the in-cylinder pressure sensor,
The span correction by the span correction unit is executed on the signal after the reset process by the reset unit.

  According to the configuration 1, the offset drift of the sensor output can be eliminated without relying on the temperature information by providing the reset means for resetting the output value of the in-cylinder pressure sensor to the reference value. Further, by including a span correction means for adjusting the amplification factor of the output signal of the in-cylinder pressure sensor, it is possible to correct the sensitivity of the in-cylinder pressure sensor that changes depending on the temperature environment. As a result, the in-cylinder pressure of the internal combustion engine can be detected with better accuracy.

  Further, the reset means obtains the timing for performing the reset process based on the output signal of the in-cylinder pressure sensor that changes corresponding to the combustion cycle of the internal combustion engine. For this reason, the reset process can be performed at a predetermined timing of the combustion cycle without using information of the crank angle sensor. As a result, it is not necessary to separately provide a terminal for signal input from the crank angle sensor, and it is possible to suppress an increase in the size and manufacturing cost of the output correction device. 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.

  However, in the configuration including both the reset function and the span correction function as described above, the correction accuracy may be lowered unless the circuit configuration is performed so as to follow an appropriate processing procedure. For example, when span correction is performed on the output signal (in-cylinder pressure waveform) of the in-cylinder pressure sensor as shown in FIG. 5A before the drift is eliminated by the reset process, as shown in FIG. 5B. A part of the in-cylinder pressure waveform reaches a peak at the circuit power supply voltage Vt and becomes saturated. Therefore, even if the reset process is performed on the reference value Vo thereafter, there is a concern that the in-cylinder pressure waveform may deteriorate as shown in FIG.

  In this regard, if the configuration is such that the span correction is performed on the signal after the reset processing as in the present configuration 1, the deterioration of the in-cylinder pressure waveform due to the span correction can be suppressed, and the detection accuracy of the in-cylinder pressure of the internal combustion engine is improved. can do.

Configuration 2. The output correction apparatus of this configuration is the above-described configuration 1,
The reset means calculates the reset timing based on the signal after the span correction.

  When calculating the reset timing based on the output signal (in-cylinder pressure waveform) of the in-cylinder pressure sensor, first, as shown in FIG. 5C, for example, as shown in FIG. For example, it is determined whether or not the sensor output value has exceeded the pressure threshold value Vc. Thus, it is determined at which timing of the combustion cycle of the internal combustion engine this corresponds.

  However, as described above, the output value of the in-cylinder pressure sensor changes depending on the temperature environment. For this reason, if the reset timing is calculated from a signal before fine adjustment such as reset processing or span correction is performed, the timing at which the sensor output value exceeds the predetermined pressure threshold value Vc as shown in FIG. There is a risk of deviating from the desired timing. As a result, there is a possibility that the calculation accuracy of the reset timing is lowered and a correction error occurs. In this regard, according to the present configuration 2, it is possible to suppress the occurrence of such a problem.

Configuration 3. The output correction apparatus of this configuration is the above configuration 1 or 2,
A signal amplifying means for amplifying the output signal of the in-cylinder pressure sensor is provided before the reset process by the reset means.

  The output signal of the in-cylinder pressure sensor is as small as several mV to several tens of mV, and the output correction device needs to increase the amplification factor. However, if all of the amplification is performed by span correction after the reset process, the reference value error that may occur in the reset process may be greatly amplified. The influence of the reference value error on the detection accuracy increases in proportion to the amplification factor after the reset process, and as a result, the detection accuracy may be significantly reduced.

  On the other hand, by performing appropriate amplification in advance before the reset process as in the present configuration 3, it is not necessary to increase the amplification factor in span correction after the reset process more than necessary. In other words, in the third configuration, the necessary amplification factor is ensured and the influence of the reference value error on the detection accuracy is reduced by the stepwise process of the coarse adjustment by the signal amplification unit and the fine adjustment by the span correction unit. The detection accuracy can be improved.

  Further, in a configuration in which an analog signal, which is an output signal of the in-cylinder pressure sensor, is converted into a digital signal before the reset processing and various signal processing is performed, the signal amplification is performed before the analog / digital conversion processing. If the signal amplification processing is performed by the means, the number of bits (resolution) necessary for analog / digital conversion can be suppressed, and the processing load can be reduced and the cost can be reduced.

Configuration 4. The output correction device of this configuration is the above-described configuration 3,
An offset voltage adjusting means for adjusting an offset voltage of the output signal of the in-cylinder pressure sensor is provided in a stage prior to the signal amplification processing by the signal amplifying means.

  If the output signal (cylinder pressure waveform) of the in-cylinder pressure sensor is directly amplified by the signal amplifying means without adjusting the offset voltage (output voltage when no pressure is applied), the offset voltage is amplified. As in the case of the operation and effect of the configuration 1, the in-cylinder pressure waveform may be deteriorated due to saturation.

  In this regard, as in the present configuration 4, if the offset adjustment is performed prior to the signal amplification processing by the signal amplification means, the deterioration of the in-cylinder pressure waveform in the signal amplification processing can be suppressed, and the detection accuracy is reduced. Can be suppressed. As a result, the amplification factor by the signal amplification unit can be further increased and the amplification factor by the span correction unit can be suppressed. As a result, the influence of the reference value error on the detection accuracy can be reduced, and the detection accuracy can be further improved. .

  The magnitude of the offset voltage varies depending on the manufacturing variation of the in-cylinder pressure sensor. For this reason, it is assumed that an extremely large offset voltage such as tens or hundreds of times the sensor sensitivity (span) is generated. In this case, there is a possibility that it cannot be handled without using an extremely large circuit power supply.

  However, as in the present configuration 4, it is not necessary to provide an excessively large circuit power supply by performing an appropriate offset adjustment in advance before the signal amplification processing by the signal amplification means, and further in the reset processing. It is not necessary to increase the offset adjustment amount (reset amount) more than necessary. That is, in the present configuration 4, finer offset adjustment can be performed in a wider range by stepwise processing of coarse adjustment by the offset adjustment unit and fine adjustment by the reset unit, and further improvement in detection accuracy can be achieved. Can do.

Configuration 5. The output correction device of this configuration is the above configuration 3 or 4,
In a stage after signal amplification processing by the signal amplification means and in a stage before reset processing by the reset means,
Analog / digital conversion means for converting an analog signal output from the in-cylinder pressure sensor into a digital signal;
Filter means comprising an FIR filter for attenuating a frequency component of a predetermined frequency or higher from the digital signal.

  When an in-cylinder pressure detecting device having an in-cylinder pressure sensor is installed in an internal combustion engine, a noise component may be superimposed on an output signal of the in-cylinder pressure sensor due to the influence of vibration or the like. Although it is conceivable to provide a filter circuit as a method of coping with this, some types of filters have nonlinear phase characteristics. This nonlinear phase characteristic causes distortion in the in-cylinder pressure waveform, and this waveform distortion greatly affects the calculation accuracy related to the calculation of the average effective pressure of the internal combustion engine, which is one of the uses of the in-cylinder pressure detection device, for example.

  In this respect, the FIR (Finite Impulse Response) type filter employed as the filter means of the configuration 5 has a linear phase characteristic in which the phase is constant in the entire frequency band to be passed. Accordingly, a signal delay occurs, but the delay is constant and waveform distortion hardly occurs, so that a decrease in detection accuracy can be suppressed.

  Further, the FIR type filter has a steep cut-off characteristic as compared with an analog filter such as a general low-pass filter composed of a resistor and a capacitor. For this reason, it is possible to efficiently attenuate even noise having a frequency component close to the frequency component to be passed as a detection signal of the in-cylinder pressure, and the detection accuracy can be further improved.

Configuration 6. The output correction apparatus of this configuration is the above-described configuration 5,
At least digital / analog conversion means for converting a digital signal after filtering by the filter means into an analog signal is provided.

  The configuration in which the in-cylinder pressure detection signal is externally output as a digital signal may prevent a desired output speed from being secured. However, as in the above configuration 6, if the configuration is such that the analog signal is converted again after noise removal, such a configuration is possible. Problems can be suppressed.

Configuration 7. The output correction device of this configuration is any one of the above configurations 1 to 6,
It is characterized by comprising failure detecting means for detecting a failure by determining whether or not the output value of each sensor is within a preset setting range.

  According to the configuration 7, it is possible to detect a failure of each sensor without complicating the circuit configuration, and it is possible to improve convenience and versatility.

Configuration 8. The output correction device of this configuration is the above-described configuration 7,
An output terminal electrically connected to a predetermined external device;
An output adjustment means capable of adjusting an output value of a signal output from the output terminal within a preset set output range;
The output adjusting means is
When the failure detecting means determines that there is no failure, the signal output is within an output limit range in which the upper limit is smaller than the maximum value of the set output range and the lower limit is limited to be larger than the minimum value of the set output range. And
When the failure detection means determines that there is a failure, a failure detection signal having a value larger than the upper limit value of the output restriction range or a value smaller than the lower limit value of the output restriction range is output. To do.

  According to the configuration 8, for example, the set output range is ± 0 (V) to +5 (V) depending on a predetermined circuit power supply voltage, whereas the output adjustment means restricts this when normal, Adjustment is made so that the output value falls within the output limit range of +0.5 (V) to +4.5 (V). That is, the output adjusting means adjusts with an appropriate amplification factor so that the detection signal of the in-cylinder pressure does not saturate within the output limit range even when the maximum / minimum pressure is applied. When a failure is detected, a failure detection signal having a value smaller than +0.5 (V) that is outside the limit range or a value larger than +4.5 (V) is output.

  Usually, an output correction device for an in-cylinder pressure sensor includes an output terminal for outputting a detection signal of the in-cylinder pressure sensor to an external device such as an electronic control unit (hereinafter referred to as “ECU”) for controlling an internal combustion engine. Yes.

  On the other hand, when trying to output an output signal from the failure detection means to the outside such as an ECU, it is conceivable to newly provide a terminal for signal output in the output correction device. However, in this case, the device becomes larger or complicated. There is a concern that the manufacturing cost will increase.

  On the other hand, according to the configuration 8, since the failure detection signal can be output to the outside through the existing output terminal, it is not necessary to separately provide a terminal for signal output and the like. Increase and the like can be suppressed.

Configuration 9 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;
A temperature sensor;
The output correction apparatus according to any one of the configurations 1 to 8 is provided.

  According to the configuration 9, by integrating the in-cylinder pressure sensor, the temperature 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.

  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 connection lines 133 a, 133 b, 133 c 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 board 140, electronic components such as an IC and a memory 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 unit detects a change in resistance of the piezoresistive element 138 as an electric signal. The detected electrical signal is amplified 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 for eliminating the drift is performed by resetting the output value of the detection unit to the reference value as described later, this process is hereinafter referred to as “reset (reset process)”.

  Note that the connection line 133 a among the plurality of connection lines 133 a to 133 c 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 133b and 133c are electrically connected to the printed circuit board 140, and are used for outputting a detection signal (connection line 133b) and for supplying power to the printed circuit board 140 (connection line 133c).

  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 detecting device 12 includes the piezoresistive element 138 as a pressure detecting element, a temperature detecting element 201 that detects the temperature of the piezoresistive element 138, an element control unit 202 that controls both the elements 138 and 201, A detection unit 203 that detects a change in resistance of the piezoresistive element 138 as an electric signal, and a correction circuit unit 204 that corrects the electric signal detected by the detection unit 203 and outputs the correction to the outside. Among these, the piezoresistive element 138 and the detection unit 203 constitute an in-cylinder pressure sensor in the present embodiment, and the correction circuit unit 204 constitutes this output correction device.

  The correction circuit unit 204 includes a temperature detection element 210 that detects the temperature of the correction circuit unit 204, and an offset voltage adjustment unit 211 that serves as an offset voltage adjustment unit that adjusts an offset voltage of an electrical signal output from the detection unit 203. As a signal amplifying unit 212 as a signal amplifying unit for amplifying the electric signal output from the offset voltage adjusting unit 211, and an analog / digital converting unit for converting the analog signal output from the signal amplifying unit 212 into a digital signal. A / D converter 213, a noise filter 214 as filter means for removing noise from the digital signal output from the A / D converter 213, and an output of an electric signal output through the noise filter 214 A reset circuit unit 215 for appropriately resetting the value to the reference value, and the reset circuit A reset timing calculation unit 216 that gives a reset timing to the unit 215, and a span correction unit that adjusts the amplification factor of the electric signal output from the reset circuit unit 215 according to the output values of the temperature detection elements 201 and 210. A span correction unit 217, a D / A conversion unit 218 as a digital / analog conversion means for converting a digital signal output from the span correction unit 217 into an analog signal, and an electric output output from the D / A conversion unit 218 An output circuit unit 219 as an output adjustment unit that amplifies and adjusts a signal and outputs the signal to the outside; a failure detection unit 220 as a failure detection unit that detects a failure of the piezoresistive element 138 and the temperature detection elements 201 and 210; It has. Note that the temperature detection element 210 is also controlled by the element control unit 202 as in the temperature detection element 201. These temperature detection elements 201 and 210 constitute a temperature sensor in the present embodiment.

  Next, the flow of correction processing performed in the correction circuit unit 204 will be described. 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 piezoresistive element 138 is deformed and the resistance value changes. This resistance change is converted into a voltage change by electrically controlling the piezoresistive element 138 by the element control unit 202. Then, the voltage change is detected by the detection unit 203 and output to the offset voltage adjustment unit 211 as an electrical signal.

  On the other hand, the electrical characteristics of the temperature detection elements 201 and 210 change due to the temperature change of the piezoresistive element 138 and the correction circuit unit 204, respectively. This change is converted into a voltage change under the control of the element control unit 202 and output to the span correction unit 217 as an electrical signal.

  The offset voltage adjustment unit 211 adjusts the offset voltage of the electrical signal output from the detection unit 203. Thereby, rough adjustment of a relatively large offset voltage generated due to manufacturing variation or the like is performed.

  The subsequent signal amplifying unit 212 adjusts the offset voltage with an appropriate amplification factor (for example, about one fifth of the amplification factor of the in-cylinder pressure detection device 12 as a whole) that does not saturate due to the circuit power supply voltage even when the maximum / minimum pressure is applied. The electric signal output from the unit 211 is amplified.

  The analog signal amplified by the signal amplifier 212 is converted into a digital signal by the A / D converter 213, and noise is removed by the noise filter 214.

  In the present embodiment, an FIR type filter is employed as the noise filter 214. Since the FIR type filter has a steep cut-off characteristic, it is possible to efficiently attenuate even noise having a frequency component close to a frequency component to be passed as a detection signal for in-cylinder pressure. As a result, resonance noise or the like due to vibration of the in-cylinder pressure detection device 12 can be effectively removed. Further, since the FIR type filter has a linear phase characteristic in which the phase is constant in the entire frequency band to be passed, the output in-cylinder pressure waveform is hardly distorted, and the in-cylinder pressure can be detected with better accuracy.

  The reset circuit unit 215 performs fine adjustment of the offset voltage by reset processing when receiving a reset signal from the reset timing calculation unit 216. Upon receiving the reset signal, the reset circuit unit 215 discharges the charge of the capacitor connected in parallel with its amplifier, for example, by turning on the switch element, thereby eliminating the potential difference between the input and output of the amplifier, thereby performing the reset processing. I do. By the reset process, the sensor output value becomes the reference value, and the drift is eliminated. However, when there is no reset signal, the signal is passed as it is without performing reset processing.

  The subsequent span correction unit 217 finely adjusts the amplification factor of the electric signal output from the reset circuit unit 215 according to the output values of the temperature detection elements 201 and 210.

  The reset timing calculation unit 216 calculates the reset timing based on the electrical signal output from the span correction unit 217. For example, based on the output waveform (in-cylinder pressure waveform) output from the span correction unit 217, the time interval from when the output value exceeds a predetermined threshold to the next time when the output value exceeds the threshold is determined as the in-cylinder pressure waveform. The measurement is performed as a cycle, and the reset timing is calculated by substituting the waveform cycle into a predetermined arithmetic expression.

  The reset timing calculation unit 216 temporarily stores the reset timing calculated in this manner in a memory or the like, and outputs a reset signal to the reset circuit unit 215 at the reset timing by timer management. Accordingly, the reset circuit in the present embodiment is configured by the reset circuit unit 215 and the reset timing calculation unit 216.

  The electrical signal output from the span correction unit 217 is converted again to an analog signal by the D / A conversion unit 218 and is externally output from the in-cylinder pressure detection device 12 through the output circuit unit 219 as a detection signal of the in-cylinder pressure. An output terminal 219a of the correction circuit unit 204 (output circuit unit 219) is electrically connected to the ECU 18 via an output line including the detection signal output connection line 133b and the like. Is input.

  In the present embodiment, for example, external output is possible within a range of ± 0 (V) to +5 (V) by a predetermined circuit power supply voltage, while the output value of the output circuit unit 219 is +0 in normal times. The signal is output so as to be within the output restriction range of .5 (V) to +4.5 (V). That is, the output is adjusted with an appropriate amplification factor that does not saturate within the output limit range even when the maximum and minimum pressures are applied.

  The failure detection unit 220 has a function of detecting a failure in the piezoresistive element 138 and the temperature detection elements 201 and 210 and informing the output circuit unit 219 of the failure.

  For example, as shown in FIG. 4, the failure detection unit 220 includes two comparison units 220 a and 220 b electrically connected to the piezoresistive element 138 and a comparison unit electrically connected to the temperature detection elements 201 and 210. 220c and 220d, and an output unit 220e composed of an OR circuit electrically connected to the comparison units 220a to 220d.

  Each of the comparison units 220a to 220d determines whether or not the output value D of each sensor element such as the piezoresistive element 138 is within a preset setting range (−Vz to + Vz) (−Vz). <D <+ Vz), a low level signal is output when the output value D is within the set range, and a high level signal is output when the output value D is outside the set range. The output unit 220e outputs a failure detection signal to the output circuit unit 219 when a high level signal is input from any one of the comparison units 220a to 220d.

  In response to this, the output circuit unit 219 externally outputs a failure detection signal amplified to a value larger than +4.5 (V) outside the output limit range, for example, the maximum value +5.0 (V) of the set output range. Output. Alternatively, the failure detection signal may be output with a value smaller than +0.5 (V). Thereby, ECU18 can grasp | ascertain generation | occurrence | production of a failure.

  As described above in detail, in this embodiment, the offset drift is eliminated by resetting the output value from the piezoresistive element 138 (detector 203) to the reference value without grasping the temperature. Furthermore, the sensitivity which changes with temperature environments is corrected by performing span correction for adjusting the amplification factor of the output signal. As a result, the in-cylinder pressure of the engine 1 can be detected with high accuracy.

  Moreover, when performing the said reset process, in this embodiment, the timing is calculated | required from the period of the output waveform of the detection part 203 corresponded to the combustion cycle of the engine 1. FIG. For this reason, the reset process can be executed at a desired timing of the combustion cycle without using the information of the crank angle sensor 15. As a result, it is not necessary to separately provide a terminal for inputting a signal from the crank angle sensor 15, and the increase in the size of the in-cylinder pressure detection device 12 (correction circuit unit 204), an increase in manufacturing cost, and the like can be suppressed. In addition, in the present embodiment, the reset timing is calculated from the signal after the correction such as the reset process and the span correction is performed, so that the calculation accuracy of the reset timing is improved, and thus the occurrence of the correction error is suppressed. Can do.

  Furthermore, by performing the span correction after the reset process, a part of the in-cylinder pressure waveform reaches a peak at the circuit power supply voltage, prevents saturation, and suppresses deterioration of the in-cylinder pressure waveform. Further improvement can be achieved.

  Further, in this embodiment, the reset voltage adjustment by the offset voltage adjustment unit 211 and the signal amplification process by the signal amplification unit 212 are performed in advance before the reset processing by the reset circuit unit 215 and the span correction by the span correction unit 217. By performing coarse adjustment, it is possible to perform finer correction over a wider range, and further improve detection accuracy.

  Furthermore, in this embodiment, since the failure detection unit 220 that detects a failure of each sensor element such as the piezoresistive element 138 is provided, convenience and versatility are high. Moreover, since the failure detection unit 220 has a relatively simple configuration in which it is determined whether or not the output value of each sensor element is within a preset setting range, the size of the correction circuit unit 204 can be increased and the manufacturing cost can be reduced. Increase and the like can be suppressed.

  The output circuit unit 219 normally limits the output value within the output limit range of +0.5 (V) to +4.5 (V), while the failure detection unit 220 detects a failure. A failure detection signal having a value larger than +4.5 (V) that is outside the output limit range is output to the outside.

  As a result, a failure detection signal can be externally output via the output terminal 219a of the correction circuit unit 204, so that it is not necessary to provide a signal output terminal separately, and the cylinder pressure detection device 12 (correction circuit unit 204) is increased in size. And an increase in manufacturing cost can be suppressed.

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

  (A) In the above-described embodiment, 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 204 and the like are integrated is illustrated. However, the configuration is not limited to this, and the output correction device may be provided separately from the in-cylinder pressure sensor and the temperature 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 the above-described embodiment, the piezoresistive element 138 is employed as the pressure-sensitive means for detecting the in-cylinder pressure of the engine 1, but the present invention is not limited to this, and offset drift such as a piezoelectric element or a metal resistance strain gauge occurs. Even in a configuration employing other pressure-sensitive means, the present invention has the same effects as the above-described embodiment.

  For example, when a piezoelectric element that outputs an electrical signal in accordance with the rate of change in the in-cylinder pressure of an internal combustion engine is used, the electric charge generated by the pyroelectric characteristics of the piezoelectric element and stored in a predetermined capacitor or the like is converted into a voltage. It becomes the structure provided with the function and the function to discharge the said electric charge. This discharge function serves as a reset means.

  (C) The reset timing calculation unit 216 in the above embodiment calculates the reset timing based on the waveform period of the output signal of the span correction unit 217. The reset timing calculation method is not limited to this, and may be another method. Further, the reset timing may be calculated from the output signal of the detection unit 203 instead of the output signal of the span correction unit 217, for example.

  (D) In the above embodiment, the noise is removed by the noise filter 214 after the detection signal is once converted into a digital signal by the A / D converter 213. Then, after reset processing and span correction, the D / A converter 218 converts the signal again into an analog signal before output. For example, when the noise filter 214 is not a digital filter such as an FIR filter or when noise removal is not performed, the A / D conversion unit 213 is omitted, and the signal processing is performed with the analog signal as it is. Also good. Alternatively, the D / A conversion unit 218 may be omitted and the digital signal may be output externally.

  (E) In the above-described embodiment, the failure detection unit 220 that detects the failure of each sensor element such as the piezoresistive element 138 is provided. However, this may be omitted.

  In the above embodiment, when the failure detection unit 220 detects a failure, the output circuit unit 219 outputs a failure detection signal having a value outside the normal output limit range to the outside via the output terminal 219a. ing. However, the present invention is not limited to this, and a configuration in which an output terminal for a failure detection signal is separately provided may be employed.

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 functional block diagram which shows the circuit structure of a failure detection part. (A) is a figure which shows an in-cylinder pressure waveform, (b) is a figure which shows the state which the amplified in-cylinder pressure waveform was saturated, (c) shows the state which reset it to the reference value FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Engine, 10 ... Glow plug, 12 ... In-cylinder pressure detection apparatus, 138 ... Piezoresistive element, 201, 210 ... Temperature detection element, 203 ... Detection part, 204 ... Correction circuit part, 211 ... Offset voltage adjustment part, 212 ... Signal amplification unit, 213... A / D conversion unit, 214... Noise filter, 215... Reset circuit unit, 216... Reset timing calculation unit, 217. ... Fault detection unit.

Claims (9)

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,
Reset means for calculating a reset timing based on an output signal of the in-cylinder pressure sensor, and resetting an output value of the in-cylinder pressure sensor to a reference value at the reset timing;
Based on temperature information detected from the temperature sensor, comprising a span correction means for adjusting the amplification factor of the output signal of the in-cylinder pressure sensor,
An output correction apparatus that performs span correction by the span correction means on a signal after reset processing by the reset means.   The output correction apparatus according to claim 1, wherein the reset unit calculates the reset timing based on the signal after the span correction.   3. The output correction device according to claim 1, further comprising a signal amplifying unit that amplifies an output signal of the in-cylinder pressure sensor at a stage prior to a reset process by the reset unit.   4. The output correction apparatus according to claim 3, further comprising an offset voltage adjusting unit that adjusts an offset voltage of an output signal of the in-cylinder pressure sensor at a stage prior to a signal amplification process by the signal amplifying unit. In a stage after signal amplification processing by the signal amplification means and in a stage before reset processing by the reset means,
Analog / digital conversion means for converting an analog signal output from the in-cylinder pressure sensor into a digital signal;
5. The output correction apparatus according to claim 3, further comprising: a filter unit including an FIR filter that attenuates a frequency component of a predetermined frequency or more from the digital signal.   6. The output correction apparatus according to claim 5, further comprising a digital / analog conversion unit that converts at least the digital signal after the filter processing by the filter unit into an analog signal.   7. The apparatus according to claim 1, further comprising a failure detection unit configured to detect a failure by determining whether or not an output value of each sensor is within a preset setting range. The output correction apparatus as described. An output terminal electrically connected to a predetermined external device;
An output adjustment means capable of adjusting an output value of a signal output from the output terminal within a preset set output range;
The output adjusting means is
When the failure detecting means determines that there is no failure, the signal output is within an output limit range in which the upper limit is smaller than the maximum value of the set output range and the lower limit is limited to be larger than the minimum value of the set output range. And
When the failure detection means determines that there is a failure, a failure detection signal having a value larger than the upper limit value of the output restriction range or a value smaller than the lower limit value of the output restriction range is output. The output correction device according to claim 7. 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;
A temperature sensor;
An in-cylinder pressure detection apparatus comprising the output correction apparatus according to claim 1.

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