JP2022063431A - Signal processing circuit for cylinder internal pressure sensor - Google Patents

Abstract

To realize a signal processing circuit for a cylinder internal pressure sensor with which it is possible to more suitably correct the offset of a sensor unit and the signal processing circuit.SOLUTION: A signal processing circuit 40 includes an arithmetic unit. The arithmetic unit performs, in a latest prescribed period for updating the amplification rate setting, first processing of calculating an output value on the basis of a pressure signal, a previous amplification rate and a previous correction value, and second processing of calculating an amplification value on the basis of a latest amplification rate. A correction value setting unit determines a correction value that corresponds to the latest amplification rate on the basis of the output value calculated in the latest first processing and the amplification value calculated in the latest second processing.SELECTED DRAWING: Figure 3

Description

The present invention relates to a signal processing circuit of an in-cylinder pressure sensor.

Patent Document 1 discloses a pressure sensor used in an internal combustion engine, and further discloses a method for correcting offset drift. The pressure sensor disclosed in Patent Document 1 has a circuit that identifies a target value of voltage between sensing cycles, and confirms a difference between a measured voltage value and a target value and a duration between sensing cycles. This circuit calculates the difference in the number of stages to obtain the target value from the above measured value using the above difference and the above duration, and adjusts and adjusts the output so as to substantially match the target value. Provides the corrected output as a corrected output.

Japanese Unexamined Patent Publication No. 2016-701279

In a device that detects pressure by a plurality of resistors, such as the pressure sensor disclosed in Patent Document 1, a voltage change that occurs at the potential of two midpoints of the Wheatstone bridge circuit when pressure is applied to the pressure sensor (hereinafter, , This is also referred to as pressure sensitivity), and a signal processing circuit may be configured to amplify and output this pressure signal. However, in this type of pressure sensor, the rate of change in resistance when pressure is applied depends on the temperature, so the pressure sensitivity also changes depending on the temperature. Therefore, in order to detect the pressure with high accuracy, it is necessary to correct the temperature dependence of the pressure sensitivity. As an example of this temperature-dependent correction, the fact that the combined resistance value of the entire pressure sensor changes with temperature is used, and a value corresponding to the combined resistance value of the entire pressure sensor, specifically, a constant current is passed through the pressure sensor. The voltage value that occurs at times or the current value that flows when a constant voltage is applied to the pressure sensor is detected, the amplification factor is set based on this voltage value or current value, and the pressure signal is amplified using this amplification factor. The method can be considered. In the signal processing circuit to which this method is applied, the temperature dependence can be continuously corrected by periodically performing such an amplification factor setting operation.

However, in this type of signal processing circuit, in the process of amplifying and outputting the pressure signal generated by the pressure sensor, the offset included in the pressure signal and the offset included in the processing process in the signal processing circuit are included. It ends up. Since these offsets cause a decrease in detection accuracy, the signal processing circuit is required to correct such offsets so as to cancel them as much as possible.
In the in-cylinder pressure sensor that measures the pressure of the internal combustion engine, the offset is canceled repeatedly aiming at zero pressure. However, if an excessive offset occurs due to a sudden temperature change or the like and the offset is canceled, the step caused by the cancellation also leads to a decrease in the accuracy of the combustion analysis. Therefore, it is necessary not to cancel a large number of offsets at one time.
Further, when the setting of the amplification factor is changed, the offset appearing at the output of the signal processing circuit also changes according to the setting change, which also leads to a decrease in the accuracy of the combustion analysis. Therefore, in the signal processing circuit, it is required to appropriately correct the offset even if the amplification factor changes.

In order to solve at least one of the above-mentioned problems, the present invention realizes a signal processing circuit of an in-cylinder pressure sensor that can better correct the offset of the sensor unit and the signal processing circuit.

The signal processing circuit of the in-cylinder pressure sensor, which is one of the present inventions, is
A signal for processing the pressure signal in an in-cylinder pressure sensor having a plurality of resistors and having a sensor unit arranged in the cylinder of the internal combustion engine and the sensor unit outputting a pressure signal corresponding to the pressure in the cylinder. It ’s a processing circuit,
A detection unit that detects the voltage value generated when a constant current is passed through the sensor unit, or the current value that flows when a constant voltage is applied to the sensor unit.
An amplification factor setting unit that sets the amplification factor based on the voltage value or the current value detected by the detection unit and repeatedly updates the amplification factor setting.
An amplification value calculation unit that calculates an amplification value obtained by amplifying the value of the pressure signal based on the amplification factor in each period in which the amplification factor setting unit repeatedly sets the amplification factor, and an amplification value calculation unit in each period. A calculation unit having a correction value setting unit for setting a correction value for correcting the amplification value calculated by the above-mentioned method, and an output value calculation unit for calculating an output value obtained by correcting the amplification value by the correction value in each period. When,
A signal output unit that outputs a signal of the output value calculated by the output value calculation unit, and a signal output unit.
Have,
The correction value setting unit is updated to the correction value corresponding to the updated amplification factor in response to the amplification factor setting unit repeatedly updating the amplification factor.
The calculation unit calculates the output value based on the pressure signal, the previous amplification factor, and the previous correction value in a predetermined period after the amplification factor setting unit calculates the amplification factor this time. The first process and the second process of calculating the calculated value according to the amplification value based on the amplification factor of this time are performed.
The correction value setting unit corresponds to the amplification factor of the present time based on the output value calculated in the first process of the present time and the calculated value calculated in the second process of the present time. Determine the correction value.

Since the above signal processing circuit can set the amplification factor based on the voltage value or current value detected by the detection unit, the temperature dependence of the pressure sensitivity can be corrected by reflecting the temperature of the sensor unit. .. Further, this signal processing circuit is based on the output value obtained based on the previous amplification factor and the correction value in the first processing, and reflects the calculated value according to the amplification value based on the current amplification factor in the second processing. The correction value of this time can be determined. Moreover, this signal processing circuit can perform both the first processing and the second processing in the above-mentioned predetermined period after the current amplification factor is calculated. Therefore, this signal processing circuit can suppress the time lag from the first process to the second process as compared with the method of performing the first process before calculating the amplification factor this time. Therefore, this signal processing circuit suppresses the influence of changes in the state of the sensor signal due to EMC noise, pressure fluctuation, etc. from the time when the first processing is performed to the time when the second processing is performed, and the correction value this time is more accurate. Can be decided.

In the signal processing circuit, the arithmetic unit may perform the first processing a plurality of times and the second processing a plurality of times in the predetermined period. Then, the correction value setting unit calculates an average value obtained by averaging a plurality of the output values calculated in the first process a plurality of times, and a plurality of the calculated values calculated in the second process a plurality of times. The correction value corresponding to the amplification factor of the present time may be determined based on the averaged average value.

Since this signal processing circuit averages the output value based on the first processing (output value based on the previous amplification factor and correction value) in the predetermined period, the representative value of the output value is suppressed from the influence of noise. It can be calculated with high accuracy. Further, since this signal processing circuit averages the calculated value based on the second processing (calculated value according to the amplification value based on the amplification factor this time) in the predetermined period, the representative value of the calculated value is affected by noise. Can be calculated with high accuracy. Therefore, this signal processing circuit can easily obtain a more appropriate correction value.

In the signal processing circuit, the arithmetic unit may operate so as to alternately perform the first process and the second process during the predetermined period.

In this signal processing circuit, the timing of the first processing and the timing of the second processing can be substantially the same. Therefore, this signal processing circuit can further suppress the error of the correction value caused by the large difference between the timing of the first processing and the timing of the second processing, and can further optimize the correction value.

In the above signal processing circuit, the correction value setting unit may include a first correction value calculation unit for calculating a first correction value and a second correction value calculation unit for calculating a second correction value. , The correction value may be set based on the value obtained by adding the first correction value and the second correction value. Further, the calculation unit adds the amplification value obtained by amplifying the value of the pressure signal this time based on the amplification factor of the previous time, the first correction value of the previous time, and the second correction value of the previous time. The third process for calculating the first addition value may be performed. Then, the first correction value calculation unit amplifies the value of the pressure signal this time based on the amplification factor of this time, the first correction value of the previous time, and the second correction value of the previous time. Based on the second addition value obtained by adding The first correction value of the above may be calculated. Then, in the first process, the calculation unit amplifies the value of the pressure signal of the present time in the predetermined period based on the amplification factor of the previous time, the first correction value of the previous time, and the previous time. The third addition value obtained by adding the second correction value of the above is calculated as the output value, and in the second processing, the value of the pressure signal in the predetermined period of the present time is amplified based on the amplification factor of the present time. The fourth addition value obtained by adding the above amplification value and the current first correction value may be calculated as the above calculation value. Then, the second correction value calculation unit may calculate the second correction value based on the third addition value and the fourth addition value.

In this signal processing circuit, the first correction value calculation unit calculates the first correction value this time so as to bring the second addition value closer to the first addition value calculated in the third processing. The first addition value calculated in the third process is an amplification value obtained by amplifying the value of the current pressure signal based on the previous amplification factor, the previous first correction value, and the previous second correction value. It is the added value. On the other hand, the second addition value is a value obtained by adding the amplification value obtained by amplifying the value of the pressure signal this time based on the amplification factor of the present time, the first correction value of the previous time, and the second correction value of the previous time. be. If the first correction value of this time is calculated so that the increase / decrease value that brings this second addition value closer to the first addition value is reflected in the first correction of the previous time, the amplification factor of this time has changed from the amplification factor of the previous time. The resulting change in offset (change in offset due to change in amplification factor) can be canceled to some extent by the first correction value this time.
Further, the calculation unit calculates the second correction value based on the third addition value and the fourth addition value. The third addition value is a value obtained by amplifying the value of the current pressure signal for a predetermined period based on the previous amplification factor, and correcting the amplification value by the previous first correction value and the previous second correction value. .. On the other hand, the fourth addition value is a value obtained by amplifying the value of the pressure signal of this time in a predetermined period based on the amplification factor of this time and correcting the amplification value by the first correction value of this time. If this fourth addition value is evaluated based on the third addition value, the third addition value of the amplification value obtained by amplifying the pressure signal value based on the current amplification factor and correcting it with the first correction value this time. Excess or deficiency based on (output value when the amplification factor, the first correction value, and the second correction value are not changed from the previous time) can be appropriately evaluated. Then, if the second correction value calculation unit calculates the second correction value based on the third addition value and the fourth addition value, and not only the first correction value but also the second correction value is added as the correction value, the second correction value is obtained. It is possible to correct an offset that cannot be completely corrected by one correction value. Therefore, even if the adjustment step of the first correction value has to be rough in order to widen the correction range, by making fine adjustments with the second correction value, a wide range and finely adjustable offset correction can be easily configured. Can be realized with.

In the signal processing circuit, the detection unit uses the current value or the voltage value only in the intake stroke and the exhaust stroke of the four strokes of the internal combustion engine, the intake stroke, the compression stroke, the combustion stroke, and the exhaust stroke. May be detected. Then, the amplification factor setting unit may set the amplification factor in the target period which is at least one of the intake stroke and the exhaust stroke in one cycle in which the four strokes are performed.

This signal processing circuit uses the current value or voltage value detected only in the intake stroke and the exhaust stroke of the four strokes of the internal combustion engine in correcting the temperature dependence of the pressure sensitivity by reflecting the temperature of the sensor unit. be able to. That is, the variable amplification unit can set the amplification factor based on the voltage value or the current value detected in a stable state where the in-cylinder pressure is relatively low. Therefore, the above signal processing circuit can correct the temperature dependence of the pressure sensitivity with higher accuracy.

The correction value setting unit changes the output value calculated by the output value calculation unit to a predetermined output value which is the output value corresponding to a low pressure state, and sets the amount of change in the range of the upper limit value and the lower limit value. The above correction value may be set so as to be within.

Since this signal processing circuit can suppress the amount of change in the output signal generated by each offset correction within the range between the upper limit value and the lower limit value, the amount of change in the output signal generated by one correction is large. It does not become too much, and it is possible to suppress a decrease in the accuracy of combustion analysis.

According to the present invention, it is possible to realize a signal processing circuit of an in-cylinder pressure sensor that can better correct the offset of the sensor unit and the signal processing circuit.

FIG. 1 is a cross-sectional view schematically illustrating the in-cylinder pressure sensor of the first embodiment. FIG. 2 is a block diagram conceptually illustrating the electrical configuration of the in-cylinder pressure sensor of the first embodiment. FIG. 3 is a block diagram that schematically illustrates the details of the variable amplification unit. FIG. 4 is a flowchart illustrating the flow of signal processing in the signal processing circuit of the first embodiment. FIG. 5 is an explanatory diagram conceptually explaining an example of a method of specifying the timing of the intake stroke or the exhaust stroke in the in-cylinder pressure sensor of the first embodiment. FIG. 6 is an explanatory diagram illustrating changes in the amplification factor, the first correction value, the second correction value, and the output hold state during the target period. FIG. 7 is an explanatory diagram conceptually explaining an example of a method of specifying the timing of the intake stroke or the exhaust stroke in the in-cylinder pressure sensor of the second embodiment.

1. 1. First Embodiment 1-1. Configuration of In-Cylinder Pressure Sensor 1 The in-cylinder pressure sensor 1 shown in FIG. 1 is a sensor attached to an internal combustion engine (not shown). The in-cylinder pressure sensor 1 is a sensor that can detect the in-cylinder pressure of the combustion cylinder of an internal combustion engine and output a signal indicating the value of the in-cylinder pressure. The combustion cylinder of an internal combustion engine is a part that constitutes a combustion chamber in the cylinder. The pressure inside the cylinder is the pressure inside the combustion cylinder and is the pressure inside the combustion chamber.

The internal combustion engine includes a 4-stroke engine. A 4-stroke engine is an engine that periodically repeats an operation in which four strokes of an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke are set as one cycle. The intake stroke is a stroke of taking in air (or a mixture of vaporized fuel and air) into the cylinder of the combustion cylinder. The compression stroke is a stroke of compressing the gas taken into the cylinder of the combustion cylinder. The combustion stroke is a stroke in which a compressed gas is burned and expanded. The exhaust stroke is a stroke in which the combustion gas is exhausted.

As shown in FIG. 1, the in-cylinder pressure sensor 1 includes a housing 2, a connector case 3, a metal stem 4, a bonded glass 5, a sensor portion 6, and a plurality of terminal fittings 7.

The housing 2 is a hollow case in which a metal material such as stainless steel is processed by cutting or the like. The housing 2 is a portion attached to the internal combustion engine. A connector case 3 is connected to the housing 2 on the side opposite to the combustion chamber side of the housing 2. The connector case 3 closes the opening on the inner space of the housing 2 opposite to the combustion chamber side.

The metal stem 4 is a hollow tubular metal member provided with a pressure introduction hole 10. The metal stem 4 is fixed to the combustion chamber side of the housing 2 so as to close the combustion chamber side in the inner space of the housing 2. The metal stem 4 is arranged so that the pressure introduction hole 10 is connected to the combustion chamber. The space in the pressure introduction hole 10 leads to the space in the combustion chamber. The metal stem 4 has a diaphragm 11 that is distorted by the pressure of a pressure medium (for example, gas, gas-liquid mixture, etc.) introduced into the pressure introduction hole 10 from the combustion chamber side.

The sensor unit 6 is a device having a plurality of resistors and arranged in a cylinder of an internal combustion engine to output a pressure signal according to the pressure in the cylinder. The sensor unit 6 is attached to the surface of the diaphragm 11 opposite to the combustion chamber side via the bonded glass 5. The bonded glass 5 is an insulator, and the diaphragm 11 and the sensor unit 6 are bonded to each other. The sensor unit 6 has a silicon substrate, and a strain gauge as a resistor is formed on the silicon substrate by ion implantation or the like. The sensor unit 6 is electrically connected to the terminal fitting 7 via the bonding wire 12 and the substrate 13.

The plurality of terminal fittings 7 are all made of metal, and all of them are arranged so as to penetrate the connector case 3. The terminal fitting 7 is arranged in a state where one end is electrically connected to the sensor unit 6 via the bonding wire 12 and the substrate 13, and the other end is exposed in the space outside the in-cylinder pressure sensor 1. The pressure signal output by the sensor unit 6 is output to the outside of the in-cylinder pressure sensor 1 via, for example, the terminal fitting 7.

As shown in FIG. 2, the in-cylinder pressure sensor 1 further includes a signal processing circuit 40. The in-cylinder pressure sensor 1 supplies the electric power supplied from the input terminal Ti to the sensor unit 6, processes the pressure signal output from the sensor unit 6 by the signal processing circuit 40, and then outputs the pressure signal from the output terminal To.

One end of the sensor unit 6 is electrically connected to the conductive path 31. The conductive path 31 is a conductive path to which an output current is supplied from the drive circuit 41. In the example of FIG. 2, a portion having the same potential as the conductive path 31 is regarded as one end of the sensor unit 6. The other end of the sensor unit 6 is electrically connected to the reference conductive path 90 via the conductive path 32. In the example of FIG. 2, the portion having the same potential as the conductive path 32 is the other end of the sensor portion 6.

The sensor unit 6 has a first series unit 25 in which the first resistor 21 and the second resistor 22 are connected in series, and a second unit in which the third resistor 23 and the fourth resistor 24 are connected in series. The series portion 26 is provided. The sensor unit 6 has a bridge circuit 27 in which the first series unit 25 and the second series unit 26 are connected in parallel between the “one end of the sensor unit 6” and the “other end of the sensor unit 6”. The first series portion 25 and the second series portion 26 may be formed on separate silicon substrates or may be formed on the same silicon substrate.

Both the first resistor 21 and the third resistor 23 are connected to the side of the "one end of the sensor unit 6", and one end of the first resistor 21 and the third resistor 23 is connected to the conductive path 31. It is considered to be the same potential. Both the second resistor 22 and the fourth resistor 24 are connected to the side of the "other end of the sensor unit 6", and the other end of the second resistor 22 and the fourth resistor 24 is a conductive path 32. Is the same potential as. The first resistor 21 and the fourth resistor 24 are N-type elements (for example, N-type piezo resistance elements) whose element resistance value decreases when pressure is applied. Therefore, as the pressure in the pressure introduction hole 10 increases, the resistance values of the first resistor 21 and the fourth resistor 24 decrease. The second resistor 22 and the third resistor 23 are P-type elements (for example, P-type piezo-resistance elements) whose element resistance value increases when pressure is applied. Therefore, as the pressure in the pressure introduction hole 10 increases, the resistance values of the second resistor 22 and the third resistor 23 increase. The first resistor 21 and the fourth resistor 24 have the same resistance value, for example, when the diaphragm 11 has a reference shape. The second resistor 22 and the third resistor 23 have the same resistance value, for example, when the diaphragm 11 has a reference shape. The diaphragm 11 has a reference shape, for example, when the pressure in the pressure introduction hole 10 is the standard atmospheric pressure.

The sensor unit 6 corresponds to the potential difference between the first potential between the first resistor 21 and the second resistor 22 and the second potential between the third resistor 23 and the fourth resistor 24. Generates and outputs a pressure signal. The pressure signal is a voltage signal input to the first terminal 43A and the second terminal 43B of the variable amplification unit 43, and the voltage applied between the first terminal 43A and the second terminal 43B is an example of the pressure signal. Corresponds to. As shown in FIG. 2, the potential of the conductive path interposed between the first resistor 21 and the second resistor 22 is input to the first terminal 43A of the variable amplification unit 43 as the first potential. Further, the potential of the conductive path interposed between the third resistor 23 and the fourth resistor 24 is input to the second terminal 43B of the variable amplification unit 43 as the second potential.

The signal processing circuit 40 is a circuit that is electrically connected to the sensor unit 6 of the in-cylinder pressure sensor 1 and receives a pressure signal output from the sensor unit 6, and is a circuit that processes the pressure signal. The signal processing circuit 40 includes a drive circuit 41, a detection unit 42, a variable amplification unit 43, a filter circuit 45, and an output circuit 46.

The drive circuit 41 is arranged between the input terminal Ti and the sensor unit 6, and supplies driving power to the sensor unit 6 based on the electric power supplied from the input terminal Ti. The drive circuit 41 is composed of, for example, a known constant current circuit, and causes a predetermined constant value constant current (hereinafter referred to as constant current) to flow through the conductive path 31. Therefore, a constant current flows from one end to the other end of the sensor unit 6. Further, the constant current is adjusted to a current such that the potential difference between the conductive path 31 and the reference conductive path 90 becomes a predetermined voltage when the potential difference between the conductive path 31 and the reference conductive path 90 is set to a predetermined temperature at the time of product shipment inspection or the like. The constant current value flowing through the sensor unit 6 is stored in advance in a non-volatile memory such as EEPROM.

The detection unit 42 is configured as, for example, a sensor voltage measuring circuit for measuring a voltage value generated in a resistor constituting the sensor unit 6. Specifically, the detection unit 42 uses the voltage value corresponding to the combined resistance value between the above-mentioned "one end of the sensor unit 6" and the "other end of the sensor unit 6" as the "voltage value of the sensor unit 6". To detect. More specifically, the voltage value of the sensor unit 6 is the potential difference between the potential of the conductive path 31 and the potential of the reference conductive path 90.

The resistors (first resistor 21, second resistor 22, third resistor 23, fourth resistor 24) constituting the sensor unit 6 are temperature-dependent, and the first resistor 21 and the second resistor are present. The resistance values of the body 22, the third resistor 23, and the fourth resistor 24 are values according to the temperature. Therefore, the "voltage value of the sensor unit 6" also becomes a value according to the temperature.

The detection unit 42 is connected to one end side of the sensor unit 6 and measures the "voltage value of the sensor unit 6" when a constant current is passed through the sensor unit 6. The input line 42A of the detection unit 42 is electrically connected to one end of the conductive path 31 and the sensor unit 6. The current flowing through the sensor unit 6 is a constant current adjusted for each individual sensor, and the voltage value measured by the detection unit 42 does not depend on the variation in the combined resistance of the bridge circuit 27 and changes only according to the temperature characteristics of the combined resistance. Therefore, the "voltage value of the sensor unit 6" can be used for correcting the pressure sensitivity as a signal indicating the resistance change rate of the sensor unit 6. The detection unit 42 gives a signal indicating the voltage value of the sensor unit 6 to the variable amplification unit 43. The signal given from the detection unit 42 to the variable amplification unit 43 may be a signal that can specify the voltage value of the sensor unit 6, and may be a digital signal or an analog signal.

The variable amplification unit 43 is configured as a circuit that amplifies and outputs a pressure signal input from the sensor unit 6. The first terminal 43A of the variable amplification unit 43 is electrically connected between the first resistor 21 and the second resistor 22, and is conductive between the first resistor 21 and the second resistor 22. A voltage signal indicating the potential V1 of the road is input. The second terminal 43B of the variable amplification unit 43 is electrically connected between the third resistor 23 and the fourth resistor 24, and the potential between the third resistor 23 and the fourth resistor 24 is reached. A voltage signal indicating V2 is input. That is, the potential difference V1-V2 between the first terminal 43A and the second terminal 43B is the input voltage Vin input to the variable amplification unit 43. The input voltage Vin corresponds to an example of the pressure signal output by the sensor unit 6.

Further, the variable amplification unit 43 is configured as a sensitivity correction circuit that sets the amplification factor based on the voltage value detected by the detection unit 42, for example, and generates an amplification signal obtained by amplifying the pressure signal based on the amplification factor. There is. The amplification signal output from the variable amplification unit 43 is output to the output terminal To via the filter circuit 45 and the output circuit 46.

The filter circuit 45 is, for example, a low-pass filter, which may be an analog filter such as an RC circuit, or a digital filter such as FIR (finite impulse response). The filter circuit 45 attenuates the high frequency component in the amplification signal given from the variable amplification unit 43, and outputs the attenuated signal.

The output circuit 46 is for stably outputting the corrected amplification signal (specifically, the corrected amplification signal in which the high frequency component is attenuated by the filter circuit 45) via the filter circuit 45 to the outside. It is a circuit. In this configuration, during the operation of the signal processing circuit 40, the corrected amplification signal is continuously output from the output terminal To via the filter circuit 45 and the output circuit 46.

1-2. Variable amplification unit 43
The following description relates to the details of the variable amplification unit 43. As shown in FIG. 3, the variable amplification unit 43 is configured as a circuit that amplifies and outputs a pressure signal given from the sensor unit 6. The variable amplification unit 43 mainly includes an amplification factor setting unit 61 and a calculation unit 62. The calculation unit 62 includes an amplification unit 63, a first correction value setting unit 64, a second correction value calculation unit 65, an output value calculation unit 66, and a DA conversion unit 67. The calculation unit 62 has a calculation function of calculating an output value based on the pressure signal given from the sensor unit 6 and the amplification factor set by the amplification factor setting unit 61.

The amplification factor setting unit 61 mainly includes an amplification factor calculation unit 61A and an amplification factor switching unit 61B. The amplification factor calculation unit 61A calculates the amplification factor based on the voltage value detected by the detection unit 42. The amplification factor calculation unit 61A has a function of holding the latest amplification factor calculated most recently and the previous amplification factor calculated last time before the calculation of the latest amplification factor. The amplification factor switching unit 61B has a function of selecting either the latest amplification factor held by the amplification factor calculation unit 61A or the previous amplification factor. In the example of FIG. 3, the amplification factor selected by the amplification factor switching unit 61B is given to the amplification signal generation unit 63A. In the example of FIG. 3, the amplification factor calculation unit 61A and the amplification factor switching unit 61B are configured by, for example, a digital circuit.

The amplification unit 63 includes an amplification signal generation unit 63A and an AD conversion unit 63B. The amplification signal generation unit 63A has a function of calculating the amplification value obtained by amplifying the value of the pressure signal (analog voltage signal) input from the sensor unit 6 based on the amplification factor given by the amplification factor switching unit 61B. The amplification signal generation unit 63A corresponds to an example of the amplification value calculation unit, and calculates the amplification value obtained by amplifying the pressure signal value based on the amplification factor in each period in which the amplification factor setting unit 61 sets the amplification factor. Works on.

Further, the amplification unit 63 has a function of outputting an added value obtained by adding the first correction value given by the first correction value setting unit 64 to the amplification value. The amplified signal generation unit 63A is composed of, for example, an analog circuit. The method of setting the first correction value by the first correction value setting unit 64 will be described in detail later. The AD conversion unit 63B is configured by a known AD converter and has a function of converting an input analog signal into a digital signal and outputting it. The AD conversion unit 63B converts an analog signal given from the amplification unit 63 (specifically, an analog signal indicating an addition value of the amplification value and the first correction value), and outputs a digital signal indicating the addition value. do.

The first correction value setting unit 64 includes a first correction value calculation unit 64A and a first correction value switching unit 64B. The first correction value calculation unit 64A has a function of calculating the first correction value based on the output value output by the output value calculation unit 66. The first correction value calculation unit 64A has a function of holding the latest first correction value calculated most recently and the previous first correction value calculated last time before the calculation of the latest first correction value. Have. The first correction value switching unit 64B has a function of selecting either the latest first correction value held by the first correction value calculation unit 64A or the previous first correction value. The first correction value selected by the first correction value switching unit 64B is given to the amplification signal generation unit 63A. The first correction value calculation unit 64A and the first correction value switching unit 64B are configured by, for example, a digital circuit.

The second correction value calculation unit 65 has a function of calculating the second correction value based on the value output from the amplification unit 63 and the value calculated by the output value calculation unit 66. The method of calculating the second correction value by the second correction value calculation unit 65 will be described in detail later. The second correction value calculation unit 65 is configured by, for example, a digital circuit capable of performing digital calculation. The first correction value setting unit 64 and the second correction value calculation unit 65 correspond to an example of the correction value setting unit.

The output value calculation unit 66 has a function of calculating an output value based on the value output from the amplification unit 63 and the second correction value calculated by the second correction value calculation unit 65. The output value calculation unit 66 is configured by, for example, a digital circuit capable of performing digital calculation.

The DA conversion unit 67 is configured by a known DA converter, converts an input digital signal into an analog signal, and outputs the signal. The DA conversion unit 67 converts the digital signal indicating the output value calculated by the output value calculation unit 66 into an analog signal, and outputs the analog signal indicating the output value. The DA conversion unit 67 corresponds to an example of the signal output unit, and has a function of outputting a signal of the output value calculated by the output value calculation unit 66.

1-3. Signal processing The following description relates to signal processing by the signal processing circuit 40.
In the signal processing circuit 40, the plurality of resistors constituting the sensor unit 6 may vary in the amount of change in the resistance value when pressure is applied. Specifically, when the pressure applied to the sensor unit 6 increases significantly, the amount of change in the resistance values of the first resistor 21 and the fourth resistor 24 becomes −ΔRA, and the second resistor 22 and the third resistor 23 The amount of change in the resistance value of is ΔRB, and it is assumed that ΔRA and ΔRB are different. The degree of such variation can vary depending on the magnitude of the pressure applied to the sensor unit 6. When such a variation occurs, the combined resistance value of the bridge circuit 27 changes due to the variation, so that the signal processing circuit 40 cannot accurately detect the temperature of the sensor unit 6, and the pressure sensitivity. It becomes impossible to properly correct the temperature. Therefore, the signal processing circuit 40 takes the following measures.

The signal processing circuit 40 performs signal processing when a predetermined start condition is satisfied. The signal processing is a process of amplifying and outputting the pressure signal detected by the sensor unit 6, and is a process of correcting so as to suppress the influence of the temperature characteristic of the sensor unit 6 when amplifying the pressure signal. The establishment of the predetermined start condition may be, for example, "the start switch (for example, the ignition switch) not shown in the automobile has been switched to the ON state" or "the operation of the specific device has started". It may also be "that other conditions have been met". When the start condition is satisfied, the signal processing circuit 40 repeats the signal processing.

In the signal processing circuit 40, the variable amplification unit 43 performs signal processing according to the flow chart illustrated in FIG. The signal processing shown in FIG. 4 ends after step S6 or when No in step S1, but is repeated so as to start immediately after the end. The signal processing of FIG. 4 is realized by a plurality of circuits.

After starting the signal processing of FIG. 4, the variable amplification unit 43 (FIG. 3) determines in step S1 whether or not the target period has been reached. The target period is a period for which the amplification factor change process and the correction value change process are performed, and is a period after a predetermined condition is satisfied. In making the determination in step S1, the variable amplification unit 43 may set the period of the exhaust stroke as the target period, the period of the intake stroke as the target period, or the period of the intake stroke and the exhaust stroke as the target period. In the typical example described below, the "period of the intake stroke and the exhaust stroke" is the target period. In FIG. 5, the target period (the period of the intake stroke and the exhaust stroke) of this representative example is shown as TM.

In this specification, the period from the start time of the combustion stroke to the end time of the compression stroke is one cycle of four steps in the combustion period. The variable amplification unit 43 sets the time for completing the update in step S6 after determining Yes in step S1 to be sufficiently shorter than the above one cycle, and completes the processing in steps S1 to S6 within the target period TM.

As shown in FIG. 5, the internal combustion engine to which the in-cylinder pressure sensor 1 (FIG. 2) is applied has an exhaust stroke after the combustion stroke, an intake stroke after the exhaust stroke, and a compression stroke after the intake stroke. The signal processing circuit 40 (FIG. 2) receives, for example, a signal indicating that it is an exhaust stroke or an intake stroke from another control device (for example, an ECU (Engine Control Unit) that controls the operation of the engine), and is based on this signal. It is determined whether or not the target period has been reached (that is, whether or not it is an exhaust stroke or an intake stroke). This signal may be a signal that is continuously output during the period of the exhaust stroke or the intake stroke, or is temporarily output at the start of the exhaust stroke or the intake stroke or at a predetermined timing in the exhaust stroke or the intake stroke. It may be a signal to be generated. In this example, receiving a signal indicating that it is an exhaust stroke or an intake stroke from another control device satisfies the above-mentioned "predetermined condition", and in "step S1 (FIG. 4)". The condition for determining Yes is satisfied. "

As shown in FIG. 4, when the variable amplification unit 43 (FIG. 3) determines in step S1 that the target period TM (FIG. 5) has been reached after starting signal processing (step S1: Yes), in step S2. Performs reference value calculation processing. The reference value calculation process corresponds to an example of the third process. In the following description, the period from t1 when the condition determined to be Yes in step S1 is satisfied to the time when the condition determined to be Yes in step S1 is satisfied is defined as the "current period". The period immediately before the "current period" is referred to as the "previous period". Further, the entire period from the time t1 to the time t2 when the update is completed (described later) is within the target period TM.

The variable amplification unit 43 (FIG. 3) performs the reference value calculation process in step S2 in the first period immediately after the time point t1 when it is determined that the target period TM has been reached (see FIG. 6). The reference value calculation process is performed by the amplification factor setting unit 61 (FIG. 3) and the calculation unit 62 (FIG. 3). In the following description, the amplification factor of the "current period" is gain (n), and the amplification factor of the "previous period" is gain (n-1). The first correction value of the "current period" is ofsr (n), and the first correction value of the "previous period" is ofsr (n-1). Further, the second correction value of the "current period" is ofsf (n), and the second correction value of the "previous period" is ofsf (n-1). The amplification value Va (n-1) is a value obtained by amplifying the pressure signal based on the amplification factor of the “previous period”. The amplification value Va (n) is a value obtained by amplifying the pressure signal based on the amplification factor of the “current period”.

The amplification factor setting unit 61 (FIG. 3) gives the amplification factor gain (n-1) of the “previous period” to the amplification signal generation unit 63A (FIG. 3) in the first period in which the reference value calculation process is performed. The amplification unit 63 (FIG. 3) performs an operation of multiplying the value Vp of the pressure signal input to the amplification signal generation unit 63A in the first period of this period by the amplification factor gain (n-1) of the previous period. The amplified amplification value Va (n-1) is obtained. Then, the amplification unit 63 adds an addition value (Va (n-1) + ofsr (n-1)) which is the sum of the amplification value Va (n-1) and the first correction value ofsr (n-1) in the previous period. ) Is output. Then, the output value calculation unit 66 adds the first addition value Z1 which is the sum of the addition value (Va (n-1) + ofsr (n-1)) and the second correction value ofsf (n-1) of the previous period. Is calculated as a reference value. The method of calculating the first correction value and the method of calculating the second correction value will be described in detail later. Z1 corresponds to an example of the first addition value in this period. Z1 can be expressed by the following equation.
Z1 = Va (n-1) ＋ ofsr (n-1) ＋ ofsf (n-1)

As described above, the arithmetic unit 62 (FIG. 3) has the amplification value Va (n-1) in the first period of the current period, the first correction value ofsr (n-1) in the previous period, and the previous period. The reference value calculation process (third process) is performed so as to calculate the first addition value Z1 in this period by adding the second correction value ofsf (n-1) of. The output value calculation unit 66 repeats the calculation of the first addition value Z1 a plurality of times in the first period of this period, and the average value Av1 of the first addition value Z1 calculated a plurality of times is a representative value of the first addition value Z1. Ask as. In the first period, an analog signal indicating the latest first addition value Z1 calculated by the output value calculation unit 66 is output from the DA conversion unit 67.

Since the value Vp of the pressure signal given from the sensor unit 6 (FIG. 3) to the amplified signal generation unit 63A (FIG. 3) includes the true value Press of the pressure signal of the sensor unit 6 and the offset Offss of the sensor unit 6 alone. , Can be expressed by the following equation.
It can be expressed as Vp = Press + Offss.

Further, when the amplification unit 63 (FIG. 3) multiplies the amplification factor, an offset occurs in the circuit of the amplification unit 63. Assuming that this offset is Offsa, the above-mentioned amplification value Va (n-1) generated by the amplification signal generation unit 63A can be expressed by the following equation.
Va (n-1) = (Press + Offss + Offsa) x gain (n-1)

Therefore, the above-mentioned first addition value Z1 can be expressed by the following equation.
Z1 = (Press + Offss + Offsa) x gain (n-1) + ofsr (n-1) + ofsf (n-1)

As shown in FIG. 4, the variable amplification unit 43 (FIG. 3) performs the amplification factor setting process in step S3 after the reference value calculation process in step S2. The amplification factor setting process is performed by the amplification factor setting unit 61 (FIG. 3). The amplification factor setting unit 61 calculates the amplification factor gain (n) in the current period in the second period after the first period in which the reference value calculation process is performed (see FIG. 6). The second period is a period after the first period in which the above-mentioned reference value calculation process is performed and before the third period in which the first correction value calculation process described later is performed, and is a partial period of the target period. Is. The amplification factor setting unit 61 calculates the amplification factor gain (n) in the current period based on the voltage value of the sensor unit 6 (FIG. 3) detected by the detection unit 42 (FIG. 3) in the second period. Specifically, the variable amplification unit 43 stores in advance an arithmetic expression for obtaining the amplification factor gain (n) using the voltage value of the sensor unit 6 as a variable, and the amplification factor calculation unit 61A (FIG. 3) stores. , The amplification factor gain (n) is obtained by substituting the above voltage value given by the detection unit 42 into this calculation formula. When the amplification factor calculation unit 61A calculates the amplification factor gain (n) of the current period in step S3 (second period), the amplification factor gain (n) of the current period is set as the latest amplification factor, and the previous period is set. The amplification factor gain (n-1) of is held so as to be the previous amplification factor. Although an example of obtaining gain (n) by an arithmetic expression has been described here, the variable amplification unit 43 stores and detects in advance a table in which each voltage value of the sensor unit 6 and each amplification factor are associated with each other. The amplification factor gain (n) corresponding to the voltage value detected by the unit 42 may be obtained from the table.

As described above, when the amplification factor setting unit 61 (FIG. 3) generates the amplification factor gain (n), the detection unit 42 (FIG. 3) has 4 of the intake stroke, the compression stroke, the combustion stroke, and the exhaust stroke of the internal combustion engine. The voltage value used for calculating the amplification factor gain (n) is detected only in the intake stroke and the exhaust stroke in the stroke. Then, the amplification factor setting unit 61 sets the amplification factor gain (n) in the target period (specifically, the second period) based on this voltage value. Then, the amplification factor setting unit 61 repeatedly updates the setting of the amplification factor gain (n) every time a new target period arrives. During the amplification factor setting process (second period), the output of the analog voltage signal from the DA conversion unit 67 is held by the analog voltage signal having the average value Av1 obtained in the first period by a holding circuit (not shown). Will be done. As a result, even if the amplification factor of the variable amplification unit 43 is changed from the amplification factor gain (n-1) to the amplification factor gain (n) in the second period, the output of the DA conversion unit 67 does not change, and the output waveform. Does not cause distortion.

As shown in FIG. 4, the variable amplification unit 43 (FIG. 3) performs the amplification factor calculation process in step S3, and then performs the first correction value (coarse adjustment value) calculation process in step S4. The first correction value calculation process is performed by the amplification factor setting unit 61 and the calculation unit 62 in the third period (FIG. 6). The third period is a period after the second period in which the above-mentioned amplification value calculation process is performed and before the fourth period in which the second correction value calculation process described later is performed, and is a partial period of the target period. be. In the third period, the amplification factor setting unit 61 is set to the current amplification factor gain (n) calculated in the second period immediately before. The first correction value setting unit 64 sets the first correction value ofsr (n-1) of the previous period in the third period. In the third period, the amplification unit 63 has an amplification value Va (n) based on the current amplification factor gain (n) given by the amplification factor setting unit 61 and a first correction value ofsr (n-1) in the previous period. And the added value (Va (n) + ofsr (n-1)) is output. The amplification value Va (n) here is a value obtained by multiplying the value of the pressure signal in the third period of this period by the amplification factor gain (n) of this period. The second correction value calculation unit 65 sets the second correction value ofsf (n-1) of the previous period in the third period. The output value calculation unit 66 adds the above addition value (Va (n) + ofsr (n-1)) and the second correction value ofsf (n-1) of the previous period in the third period, and this time. The second addition value Z2 for the period of is calculated. That is, Z2 is a value such that Z2 = Va (n) + ofsr (n-1) + ofsf (n-1). The second addition value Z2 is an output value set by the output value calculation unit 66 in the third period. Then, the first correction value calculation unit 64A calculates an increase / decrease value X that brings the second addition value Z2 closer to the first addition value Z1 calculated by the reference value calculation process (third process) in this period. The increase / decrease value X is reflected in the first correction value ofsr (n-1) in the previous period to calculate the first correction value ofsr (n) in the current period. That is, ofsr (n) = ofsr (n-1) + X, which is the value at which the difference between Z1 and Z2 + X is the smallest in the circuit of the first correction value calculation unit 64A. In the circuit of the first correction value calculation unit 64A, if the adjustment step for increasing / decreasing ofsr (n) must be rough in order to widen the offset adjustment range, even if the increase / decrease value X is added, Z1 and Z2 + X are displayed. It is highly possible that the difference between the two cannot be reduced to zero. In this case, even if the first correction value ofsr (n) is set to ofsr (n) = ofsr (n-1) + X, the offset remains.

In the present embodiment, the first correction value setting unit 64 and the second correction value calculation unit 65 function as an example of the correction value setting unit. The first correction value setting unit 64 (specifically, the first correction value calculation unit 64A) sets the first correction value ofsr (n) in this period in each period for updating the amplification factor gain (n). It has a function to calculate. The second correction value calculation unit 65 has a function of calculating the second correction value ofsf (n) in the current period in each period in which the amplification factor gain (n) is updated. Then, the first correction value setting unit 64 and the second correction value calculation unit 65 have the amplification value Va calculated by the amplification signal generation unit 63A (amplification value calculation unit) in each period for updating the amplification factor gain (n). It has a function to set a correction value to correct (n). Specifically, the first correction value setting unit 64 and the second correction value calculation unit 65 are a value obtained by adding the first correction value ofsr (n) and the second correction value ofsf (n) (ofsr (n) + ofsf). (n)) is set as the correction value. Then, in the first correction value setting unit 64 and the second correction value calculation unit 65, the amplification factor gain after the update is obtained in response to the amplification factor setting unit 61 repeatedly updating the amplification factor gain (n) in the current period. Update to the correction value (ofsr (n) + ofsf (n)) for this period corresponding to (n). In the period (third period) of the first correction value (coarse adjustment value) calculation process, the output of the analog voltage signal from the DA conversion unit 67 is an average value obtained in the first period by a holding circuit (not shown). It is held by the analog voltage signal of Av1.

As shown in FIG. 4, the variable amplification unit 43 (FIG. 3) performs the second correction value (fine adjustment value) calculation process in step S5 after the first correction value calculation process in step S4. The second correction value calculation process is performed in the fourth period (FIG. 6) by the amplification factor setting unit 61 (FIG. 3) and the calculation unit 62 (FIG. 3). The fourth period is a period after the third period in which the first correction value calculation process is performed, and before the normal period after the correction value is updated. The calculation unit 62 alternately performs the first process and the second process in the predetermined period (fourth period) of this period. The amplification factor setting unit 61 sets the amplification factor to the amplification factor gain (n-1) of the previous period in each period of the first processing, and sets the amplification factor to the current period in each period of the second processing. The amplification factor gain (n) is set to (see FIG. 6). The first correction value setting unit 64 sets the first correction value to the first correction value ofsr (n-1) in the previous period in each period of the first process, and sets the first correction value to the first correction value ofsr (n-1) in each period of the second process. The first correction value is set to the first correction value ofsr (n) in this period (see FIG. 6). The second correction value calculation unit 65 uses the second correction value ofsf (n-1) of the previous period as the second correction value in both the first process and the second process. ..

In each period of the first process, the calculation unit 62 includes the pressure signal output from the sensor unit 6 in the fourth period, the amplification factor gain (n-1) of the previous period, and the correction value of the previous period (ofsr (ofsr (ofsr)). The output value (Va (n-1) + ofsr (n-1) + ofsf (n-1)) is calculated based on n-1) + ofsf (n-1)). Va (n-1) is a value obtained by amplifying the value of the pressure signal in the fourth period (predetermined period) based on the amplification factor gain (n-1) in the previous period. Specifically, the value obtained by the amplification signal generation unit 65A performing an operation of multiplying the value of the pressure signal output from the sensor unit 6 during the first processing of the fourth period by gain (n-1). Is Va (n-1). Then, in the first process, the output value calculation unit 66 includes the above amplification value Va (n-1), the first correction value ofsr (n-1) in the previous period, and the second correction value in the previous period. The third addition value Z3 obtained by adding ofsf (n-1) and is calculated as the above output value. Since Va (n-1) can be expressed by the formula of Va (n-1) = (Press + Offss + Offsa) × gain (n-1), the above output value (first) in each period in which the first process is performed. 3 Addition value) Z3 can be expressed by the formula Z3 = (Press + Offss + Offsa) × gain (n-1) + ofsr (n-1) + ofsf (n-1). However, Press, Offss, and Offsa are values in each period in which the first process is performed.

In each period of the second process, the calculation unit 62 calculates a calculated value according to the amplification value Va (n) based on the amplification factor gain (n) of the current period. Va (n) is a value obtained by amplifying the value of the pressure signal in the fourth period (predetermined period) based on the amplification factor gain (n) in the current period. Specifically, the value obtained by multiplying the value of the pressure signal output from the sensor unit 6 by the gain (n) by the amplification signal generation unit 65A during the second processing of the fourth period is Va. (n). In the second process, the amplification unit 63 outputs the fourth addition value Z4, which is the sum of the above amplification value Va (n) and the first correction value ofsr (n) in the current period, as the above calculated value. .. Since Va (n) can be expressed by the formula of Va (n) = (Press + Offss + Offsa) × gain (n), the above-mentioned calculated value (fourth addition value) Z4 in each period in which the second processing is performed is , Z4 = (Press + Offss + Offsa) × gain (n-1) + ofsr (n). However, Press, Offss, and Offsa are values in each period in which the second process is performed.

At the time immediately before the end of the fourth period, the calculation unit 62 uses the third addition value Z3 (output value) calculated in the first process of the current period and the second process calculated in the second process of the current period. 4 Based on the added value Z4 (calculated value), the correction value (ofsr (n) + ofsf (n)) corresponding to the amplification factor gain (n) in this period is determined. As shown in FIG. 6, the calculation unit 62 is based on the first process (process based on the amplification factor gain (n-1)) and the second process (amplification rate gain (n)) in the fourth period (predetermined period). The process) is performed alternately, and the first process is performed a plurality of times and the second process is performed a plurality of times. Then, the second correction value calculation unit 65 calculates the average value Av3 obtained by averaging the plurality of third addition values Z3 (output values) calculated in the first processing a plurality of times. Further, the second correction value calculation unit 65 calculates an average value Av4 obtained by averaging a plurality of fourth addition values Z4 (calculated values) calculated in the second processing a plurality of times. The method of calculating the average values Av3 and Av4 may be a method of calculating a general arithmetic mean, a method of calculating an arithmetic mean of values excluding the maximum value and the minimum value, and others. The known method for calculating the average value may be used. The average value Av3 is a representative value of the third addition value Z3. The average value Av4 is a representative value of the fourth addition value Z4. The second correction value calculation unit 65 calculates the difference Df (Df = Av3-Av4) between the average value Av3 of the third addition value Z3 and the average value Av4 of the fourth addition value Z4, and based on this difference Df, The second correction value ofsf (n) corresponding to the amplification factor gain (n) in this period is determined. The calculation by the second correction value calculation unit 65 is a digital calculation performed by a digital circuit, and the second correction value ofsf (n) can be finely adjusted more than the first correction value ofsr (n). ..

The second correction value calculation unit 65 may use the above difference Df (Df = Av3-Av4) as the second correction value ofsf (n). If this difference Df is the second correction value ofsf (n), the amplification factor gain (n-1) of the previous period at the time of the fourth period and the correction value of the previous period (ofsr (n-1), The second correction value ofsf (n) required to maintain the output value when ofsf (n-1)) can be obtained. Even if the above-mentioned Press changes due to noise or the like between the first period and the fourth period, if the above-mentioned average values Av3 and Av4 of the fourth period are used, the deviation of the correction value due to such a change in Press can be obtained. It can be suppressed. Further, since the average values Av3 and Av4 are used as the representative values of the third addition value Z3 and the fourth addition value Z4, it is possible to suppress an error due to noise.

In the second correction value (fine adjustment value) calculation process, when the output value of the previous period is maintained, the above difference Df (Av3-Av4) itself may be used as the second correction value ofsf (n) of the current period. However, if the output signal of the signal processing circuit deviates from the expected output level in the zero pressure state due to temperature drift of the offset, it must be further corrected for the ideal zero point voltage. Further, in order to prevent the output waveform from being distorted, it is necessary to set a limit so that the amount of change in the output signal generated by each correction does not become too large. Therefore, the second correction value calculation unit 65 compares the average value Av3 with the ideal zero point voltage Vzero, and the difference Dfzero (Dfzero = | Av3) which is the absolute value of the difference between the average value Av3 and the ideal zero point voltage Vzero. -Vzero |) is calculated. Further, the difference Dfzero and the constant value γ are compared. When the average value Av3 is higher than the predetermined ideal zero point voltage and the difference Dfzero is larger than the constant value γ, the value Df−γ obtained by subtracting the constant value γ from the difference Df is used as the second correction value ofsf. Defined as (n). When the average value Av3 is higher than the predefined ideal zero point voltage and the difference Dfzero is smaller than the constant value γ, the value Df-Dfzero obtained by subtracting the difference Dfzero from the difference Df is the second correction value ofsf (n). Determined as. When the average value Av3 is lower than the ideal zero point voltage and the difference Dfzero is larger than the constant value γ, the value (Df + γ) obtained by adding the constant value γ to the difference Df is the second correction value ofsf (n). Determined as. When the average value Av3 is lower than the ideal zero point voltage and the difference Dfzero is smaller than the constant value γ, the value (Df + Dfzero) obtained by adding the difference Dfzero to the difference Df is defined as the second correction value ofsf (n). The constant value γ may be, for example, 1LSB (Least Significant Bit) or any other value (2LSB, 3LSB, etc.). By doing so, the correction value setting unit can keep the amount of change in the output signal generated by each correction within the range of the upper limit value and the lower limit value.

In each period in which the first process is performed in the fourth period, the output of the analog voltage signal from the variable amplification unit 43 is an analog voltage signal having a third addition value Z3 obtained in the first process in each period. .. In each period in which the second process is performed in the fourth period, the output of the analog voltage signal from the DA conversion unit 67 is the third addition obtained in the first process immediately before each second process by a holding circuit (not shown). It is held by an analog voltage signal with the value Z3. As a result, even if the amplification factor gain (n-1) is changed to the amplification factor gain (n) in each second process, the output of the DA conversion unit 67 does not change and the output waveform is not distorted.

The variable amplification unit 43 performs the update process of step S6 at the end of the fourth period after the second correction value calculation process of step S5. In the update process, the amplification factor set by the amplification factor setting unit is fixed to the amplification factor gain (n) of the current period calculated in step S3, and the first correction value set by the first correction value setting unit 64 is stepped. The second correction value (the second correction value given by the second correction value calculation unit 65) used by the output value calculation unit 66 is fixed to the first correction value ofsr (n) of the current period calculated in S4. It is fixed to the second correction value ofsf (n) of this period calculated in S5. The time t2 in FIG. 6 is the time when the update of step S6 is completed, and the normal period after the time t2 is the amplification factor gain (n) of the current period until it is determined to be Yes in the next step S1. It is maintained at the 1st correction value ofsr (n) and the 2nd correction value ofsf (n). During the normal period, a signal with an output value of Va (n) + ofsr (n) + ofsf (n) is output from the variable amplification unit 43 according to the pressure signal input from the sensor unit 6. This output value can be expressed as (Press + Offss + Offsa) × gain (n) + ofsr (n) + ofsf (n), and Press, Offss, and Offsa in this case are each value at each timing for calculating the output value.

In this way, the output value calculation unit 66 operates so as to calculate the output value obtained by correcting the amplification value Va (n) by the correction value (ofsr (n) + ofsf (n)) in each period. Then, the DA conversion unit 67 (signal output unit) operates so as to output a signal of the output value calculated by the output value calculation unit 66.

The following description relates to an example of the effect of the first embodiment.
Since the signal processing circuit 40 can set the amplification factor based on the voltage value detected by the detection unit 42, the temperature dependence of the pressure sensitivity can be corrected by reflecting the temperature of the sensor unit 6. Further, this signal processing circuit 40 is obtained in the first processing based on the amplification factor gain (n-1) and the correction value (ofsr (n-1), ofsf (n-1)) of the “previous period”. Based on the output value, the calculated value (amplification value Va (n) + ofsr (n)) according to the amplification value Va (n) based on the amplification factor gain (n) of the "current period" is reflected in the second processing. The correction value (ofsr (n) + ofsf (n)) for the "current period" can be determined. Moreover, the signal processing circuit 40 can perform both the first processing and the second processing in a predetermined period (fourth period) after the amplification factor gain (n) is calculated in the "current period". Therefore, this signal processing circuit 40 suppresses the time lag from the first process to the second process as compared with the method of performing the first process before calculating the amplification factor gain (n) of the "current period". Be done. Therefore, this signal processing circuit 40 suppresses the influence of changes in the state of the sensor signal due to EMC noise, pressure fluctuation, etc. from the time when the first processing is performed to the time when the second processing is performed, and corrects the "current period". The value (ofsr (n) + ofsf (n)) can be determined with higher accuracy.

In the predetermined period (fourth period), the signal processing circuit 40 has an output value based on the first processing (amplification rate gain (n-1) and correction value (ofsr (n-1), ofsf (n) in the previous period). -1) Average the output value) based on). Therefore, the representative value of the above output value can be calculated with high accuracy while suppressing the influence of noise. Similarly, the signal processing circuit 40 has a calculated value based on the second processing in the predetermined period (fourth period) (calculated value according to the amplification value Va (n) based on the amplification factor gain (n) in this period (n). Va (n) + ofsr (n))) is averaged. Therefore, the representative value of the above calculated value can be calculated with high accuracy while suppressing the influence of noise. Therefore, this signal processing circuit can easily obtain a more appropriate correction value.

By alternately performing the first processing and the second processing in the signal processing circuit 40, the timing of the first processing and the timing of the second processing can be set to substantially the same timing. Therefore, the signal processing circuit 40 can perform the first processing and the second processing in a more equivalent state, and further suppresses an error in the correction value caused by a large difference in timing between the first processing and the second processing. This makes it possible to further optimize the correction value.

The signal processing circuit 40 may use the voltage values detected only in the intake stroke and the exhaust stroke out of the four strokes of the internal combustion engine in correcting the temperature dependence of the pressure sensitivity by reflecting the temperature of the sensor unit 6. can. That is, the variable amplification unit 43 can set the amplification factor based on the voltage value detected in a stable state where the in-cylinder pressure is relatively low. Therefore, the signal processing circuit 40 can correct the temperature dependence of the pressure sensitivity with higher accuracy.

On the other hand, the first correction value calculation unit 64A calculates the first correction value ofsr (n) in this period so that the second addition value Z2 approaches the first addition value Z1 calculated in the third process. .. The first addition value Z1 calculated in the third process is an amplification value Va (n-1) obtained by amplifying the value of the pressure signal in the target period in the current period based on the amplification factor gain (n-1) in the previous period. ), The first correction value ofsr (n-1) in the previous period, and the second correction value ofsf (n-1) in the previous period. On the other hand, the second addition value Z2 is the amplification value Va (n) obtained by amplifying the value of the pressure signal in the target period based on the amplification factor gain (n) in the current period, and the first correction value ofsr (n) in the previous period. It is a value obtained by adding n-1) and the second correction value ofsf (n-1) of the previous period. The first correction value ofsr (n) of this period is calculated so that the increase / decrease value that brings this second addition value Z2 closer to the first addition value Z1 is reflected in the first correction value ofsr (n-1) of the previous period. Then, the change in offset due to the change from the amplification factor gain (n-1) in the previous period to the amplification factor gain (n) in this period (change in offset due to the change in amplification factor), It can be canceled to some extent by the first correction value ofsr (n) in this period.

Further, the calculation unit 62 calculates the second correction value ofsf (n) based on the third addition value Z3 and the fourth addition value Z4. The third addition value Z3 amplifies the value of the pressure signal in the target period of the current period and the predetermined period based on the amplification factor gain (n-1) of the previous period, and obtains the amplification value Va (n-1). It is a value corrected by the first correction value ofsr (n-1) of the previous period and the second correction value ofsf (n-1) of the previous period. On the other hand, the fourth addition value Z4 amplifies the value of the pressure signal in the target period and the predetermined period of this period based on the amplification factor gain (n) of this period, and the amplification value Va (n) of this time is used. It is a value corrected by the first correction value ofsr (n) of the period. If the fourth addition value Z4 is evaluated based on the third addition value Z3, the amplification value Va (n) obtained by amplifying the pressure signal value based on the amplification factor gain (n) in the current period is obtained in the current period. Excess or deficiency of the value corrected by the first correction value ofsr (n) based on the third addition value Z3 (output value when the amplification factor, the first correction value, and the second correction value are not changed from the previous period). Can be evaluated appropriately. Then, the second correction value calculation unit 65 calculates the second correction value ofsf (n) based on the third addition value Z3 and the fourth addition value Z4, and not only the first correction value ofsr (n) but also the first correction value ofsr (n) as the correction value. If the second correction value ofsf (n) is also added, it is possible to correct an offset that cannot be completely corrected by the first correction value ofsr (n). Therefore, even if the adjustment step of the first correction value has to be rough in order to widen the correction range, by making fine adjustments with the second correction value, a wide range and finely adjustable offset correction can be easily configured. Can be realized with.

Since the signal processing circuit 40 can suppress the amount of change in the output signal generated by each offset correction within the range between the upper limit value and the lower limit value, the amount of change in the output signal generated by the correction in one period. Does not become too large, and it is possible to suppress a decrease in the accuracy of combustion analysis.

2. 2. Second Embodiment The following description relates to the second embodiment.
The signal processing circuit 40 of the first embodiment is configured to be able to receive a signal that can identify that it is in the target period from another control device, and is configured to determine whether or not it is in the target period based on this signal. there were. However, the signal processing circuit 40 of the second embodiment determines by itself whether or not it is the target period. The in-cylinder pressure sensor 1 in which the signal processing circuit 40 of the second embodiment is used is the in-cylinder pressure sensor 1 (FIGS. 1 to 3 and the like) in which the signal processing circuit 40 of the first embodiment is used except for the signal processing circuit 40. Is the same as. Further, the signal processing circuit 40 of the second embodiment differs from the signal processing circuit 40 of the first embodiment only in the determination method of step S1 in FIG. 4 (method of determining whether or not the target period has been reached), and other signals are processed. The points are the same as the signal processing circuit 40 of the first embodiment.

The signal processing circuit 40 of the second embodiment also has the configuration shown in FIGS. 2 and 3, and the variable amplification unit 43 performs signal processing according to the flow shown in FIG. Then, also in this signal processing circuit 40, the variable amplification unit 43 determines in step S1 whether or not the target period (the period of the intake stroke and the exhaust stroke) has been reached.

In making the determination in step S1 of FIG. 4, the variable amplification unit 43 peaks the in-cylinder pressure (specifically, the pressure detected by the sensor unit 6) in each period, and then the in-cylinder pressure is equal to or less than the threshold pressure Pth. The period TA from the time when the pressure is changed to the time when the threshold pressure Pth is exceeded is calculated. FIG. 7 conceptually shows the period TA. After calculating the period TA, the variable amplification unit 43 calculates the period TB by multiplying this period TA by the coefficient β. The period TB is a value for determining the target period of the next period of the period for which the period TA is calculated (the period for which the period TA is calculated), and TB is TB = TA × β. The coefficient β is a coefficient set so that the intake stroke or the exhaust stroke occurs when the TA × β period elapses after the in-cylinder pressure becomes the threshold pressure Pth or less. The coefficient β may be fixed to a specific value such as half, or may be adjusted according to the engine speed or the like.

As shown in FIG. 7, in the signal processing circuit 40, when the in-cylinder pressure becomes equal to or less than the threshold pressure Pth after the in-cylinder pressure peaks after the above period TA, the in-cylinder pressure becomes equal to or less than the threshold pressure Pth. It is determined whether or not the period TB has elapsed from the time point. That is, in this example, the timing at which the period TB has elapsed from the time when the in-cylinder pressure peaked and then became the threshold pressure Pth or less is the timing at which it can be determined that the target period (either the exhaust stroke or the intake stroke) is the target period. .. The target period is from this timing to a predetermined period (for example, a period of TA × γ). In the signal processing circuit 40 of the second embodiment, when the variable amplification unit 43 reaches the threshold pressure Pth after such a determination (in-cylinder pressure peaks) in step S1 (FIG. 4) executed in each period. (Determining whether or not the period TB has elapsed) is performed. Then, when the variable amplification unit 43 determines in step S1 that "the period TB has elapsed from the time when the in-cylinder pressure peaked and then became the threshold pressure Pth or less", the variable amplification unit 43 performs the processing after step S2.

After determining that the target period has been reached in step S1, the signal processing circuit 40 of the second embodiment also performs the processing of steps S2 and S2 in the same manner as the signal processing circuit 40 of the first embodiment.

The signal processing circuit 40 of the second embodiment can determine whether or not it is an intake stroke or an exhaust stroke without receiving a signal indicating that it is an intake stroke or an exhaust stroke from another control device.

<Other embodiments>
The present invention is not limited to the embodiments described above and the drawings, and for example, the following embodiments are also included in the technical scope of the present invention. Moreover, various features of the above-described embodiment and the later-described embodiment may be combined in any combination as long as they are consistent combinations.

In the representative example of the first and second embodiments, the "period of the intake stroke and the exhaust stroke" is the target period, but only the period of the intake stroke may be the target period, and only the period of the exhaust stroke is the target period. May be.

In the first and second embodiments, the amplification factor is updated every one cycle of the four steps, and one cycle of the four steps corresponds to one cycle of the amplification factor, but the amplification factor is every multiple cycles of the four steps. May be updated. For example, in the process of FIG. 4, the process after step S2 may be performed every time the target period reaches a predetermined number of times.

The signal processing circuit of the first and second embodiments is a full-bridge circuit in which the sensor unit 6 is a full-bridge circuit, but it does not have to be a full-bridge circuit as long as it is composed of a plurality of resistors. Further, the resistor for pressure detection and the resistor for temperature detection may be separate resistors.

The signal processing circuit of the first and second embodiments has a configuration in which the amplification factor is set based on the voltage value of the entire bridge circuit 27, but the amplification factor is set based on the information indicating the temperature of the sensor unit 6. Any configuration may be used. For example, the amplification factor setting unit of the signal processing circuit may set the amplification factor based on the voltage value of a part of the resistor of the sensor unit 6.

The signal processing circuit of the first and second embodiments has a configuration in which the voltage value is detected and the amplification factor is set every one cycle (four steps) described above, but it is not performed every cycle described above. May be good. For example, the signal processing circuit may be configured to detect the voltage value and / or set the amplification factor every a plurality of cycles of the above-mentioned four steps.

In the signal processing circuit of the first and second embodiments, the amplification factor setting unit 61 repeatedly sets the amplification factor, but the amplification factor setting unit 61 sets the amplification factor periodically (every fixed period). May be good.

The internal combustion engine to which the in-cylinder pressure sensor 1 is attached may be a diesel engine or a gasoline engine.

In the signal processing circuit of the first and second embodiments, the value of the current supplied to the sensor unit 6 is constant, but the value of the voltage applied to the sensor unit 6 (specifically, the conductive paths 31 and 32). The voltage between them) may be constant. In this case, a constant voltage value may be stored in advance in a non-volatile memory such as EEPROM. In this case, the signal processing circuit 40 can detect the resistance change value of the sensor unit 6, for example, by detecting the value of the current flowing through the sensor unit 6 by the detection unit 42. In this case, the amplification factor calculation unit 61A replaces the calculation method of the above-described embodiment (method of calculating the amplification factor based on the voltage value of the sensor unit 6) with the value of the current flowing through the sensor unit 6 (detection unit 42). A method of calculating the amplification factor based on the current value detected by) may be adopted. Then, also in this example, the amplification factor setting unit 61 may repeatedly update the amplification factor in the same manner as in the above-described embodiment. In this example, it can be the same as the first embodiment except for the method of calculating the amplification factor by the amplification factor calculation unit 61A.

The signal processing circuit of the first and second embodiments has a configuration in which the value of the current supplied to the sensor unit 6 is stored in advance, but the value of the current supplied to the sensor unit 6 is detected by the current detection circuit. It may be a configuration or a configuration obtained by another method.

In the method in which the amplification factor setting unit calculates the amplification factor, an arithmetic expression for obtaining the amplification factor using the current value of the sensor unit 6 as a variable is stored in advance, and the current value given by the detection unit 42 is substituted into this arithmetic expression. It may be a method in which the amplification factor can be obtained by the above. Alternatively, in the method in which the amplification factor setting unit calculates the amplification factor, a table in which each current value of the sensor unit 6 and each amplification factor are associated with each other is stored in advance, and amplification corresponding to the current value detected by the detection unit 42 is performed. The rate may be obtained from the table.

In the first and second embodiments, the correction value is divided into a first correction value and a second correction value, but only the second correction value may be used without using the first correction value. In this case, the first correction value setting unit 64 can be omitted, and the first correction value may be excluded from the operation.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is not limited to the embodiments disclosed here, but includes all modifications within the scope indicated by the claims or within the scope equivalent to the claims. Is intended.

1 ... In-cylinder pressure sensor 6 ... Sensor unit 40 ... Signal processing circuit 42 ... Detection unit 61 ... Amplification rate setting unit 62 ... Calculation unit 63A ... Amplification signal generation unit (amplification value calculation unit)
64 ... First correction value setting unit (correction value setting unit)
64A ... 1st correction value calculation unit 65 ... 2nd correction value calculation unit (correction value setting unit)
66 ... Output value calculation unit 67 ... DA conversion unit (signal output unit)

Claims (6)

A signal for processing the pressure signal in an in-cylinder pressure sensor having a plurality of resistors and having a sensor unit arranged in the cylinder of the internal combustion engine and the sensor unit outputting a pressure signal corresponding to the pressure in the cylinder. It ’s a processing circuit,
A detection unit that detects the voltage value generated when a constant current is passed through the sensor unit, or the current value that flows when a constant voltage is applied to the sensor unit.
An amplification factor setting unit that sets the amplification factor based on the voltage value or the current value detected by the detection unit and repeatedly updates the amplification factor setting.
An amplification value calculation unit that calculates an amplification value obtained by amplifying the value of the pressure signal based on the amplification factor in each period in which the amplification factor setting unit repeatedly sets the amplification factor, and an amplification value calculation unit in each period. A calculation unit having a correction value setting unit for setting a correction value for correcting the amplification value calculated by the above-mentioned method, and an output value calculation unit for calculating an output value obtained by correcting the amplification value by the correction value in each period. When,
A signal output unit that outputs a signal of the output value calculated by the output value calculation unit, and a signal output unit.
Have,
The correction value setting unit is updated to the correction value corresponding to the updated amplification factor in response to the amplification factor setting unit repeatedly updating the amplification factor.
The calculation unit calculates the output value based on the pressure signal, the previous amplification factor, and the previous correction value in a predetermined period after the amplification factor setting unit calculates the amplification factor this time. The first process and the second process of calculating the calculated value according to the amplification value based on the amplification factor of this time are performed.
The correction value setting unit corresponds to the amplification factor of the present time based on the output value calculated in the first process of the present time and the calculated value calculated in the second process of the present time. The signal processing circuit of the in-cylinder pressure sensor that determines the correction value. The calculation unit performs the first process a plurality of times and the second process a plurality of times in the predetermined period.
The correction value setting unit averages the average value obtained by averaging the plurality of output values calculated in the first process a plurality of times, and the calculated values calculated in the second process a plurality of times. The signal processing circuit of the in-cylinder pressure sensor according to claim 1, wherein the correction value corresponding to the amplification factor of the present time is determined based on the average value obtained. The signal processing circuit for an in-cylinder pressure sensor according to claim 2, wherein the calculation unit alternately performs the first process and the second process during the predetermined period. The correction value setting unit includes a first correction value calculation unit for calculating a first correction value and a second correction value calculation unit for calculating a second correction value, and the first correction value and the second correction value are provided. The correction value is set based on the value obtained by adding the value to the value.
The calculation unit adds the amplification value obtained by amplifying the value of the pressure signal this time based on the amplification factor of the previous time, the first correction value of the previous time, and the second correction value of the previous time. 1 Perform the third process to calculate the added value,
The first correction value calculation unit includes the amplification value obtained by amplifying the value of the pressure signal this time based on the amplification factor of this time, the first correction value of the previous time, and the second correction value of the previous time. Based on the second addition value obtained by adding, the increase / decrease value that brings the second addition value closer to the first addition value calculated by the third process of this time is reflected in the first correction value of the previous time. Calculate the first correction value,
The arithmetic unit
In the first process, the amplification value obtained by amplifying the value of the pressure signal of the present time in the predetermined period based on the amplification factor of the previous time, the first correction value of the previous time, and the second correction value of the previous time. , Is added to calculate the third addition value as the output value.
In the second process, the fourth addition value obtained by adding the amplification value obtained by amplifying the value of the pressure signal of the present time in the predetermined period based on the amplification factor of the present time and the first correction value of the present time is added. Calculated as the above calculated value,
The in-cylinder pressure sensor according to any one of claims 1 to 3, wherein the second correction value calculation unit calculates the second correction value based on the third addition value and the fourth addition value. Signal processing circuit. The detection unit detects the current value or the voltage value only in the intake stroke and the exhaust stroke out of the four strokes of the intake stroke, the compression stroke, the combustion stroke, and the exhaust stroke of the internal combustion engine.
The amplification factor setting unit is any one of claims 1 to 4, which sets the amplification factor in a target period which is at least one of the intake stroke and the exhaust stroke in one cycle in which the four strokes are performed. The signal processing circuit for the in-cylinder pressure sensor according to item 1. The correction value setting unit changes the output value calculated by the output value calculation unit to a predetermined output value which is the output value corresponding to a low pressure state, and sets the amount of change in the range of the upper limit value and the lower limit value. The signal processing circuit of the in-cylinder pressure sensor according to any one of claims 1 to 5, wherein the correction value is set so as to be inside.

Images