JP2000352349A - Control system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify structure of an inner-cylinder pressure detection section for an internal combustion engine and reduce cost and output fluctuation depending on temperature by calculating inner-cylinder pressure from a digitized value of an output signal from inner-cylinder pressure detection means and controlling the engine utilizing the inner-cylinder pressure. SOLUTION: An inner-cylinder pressure sensor 3 for detecting pressure in a combustion chamber (inner-cylinder pressure) is provided in a combustion chamber 2 of an internal combustion engine 1. The detected signal is input into an ECU 4. Also, a crank angle sensor 7 for detecting a rotation angle of a crankshaft is provided and an output signal therefrom is input into the ECU 4. In the ECU 4, the inner-cylinder pressure signal is converted into a digital one by an AD converter 5. Based on the signal after the AD conversion and engine operation parameters (throttle valve opening, intake pipe absolute pressure, engine cooling water temperature and the like) detected by other sensors, the engine control parameters are calculated in a calculation unit 6. Then fuel injection valves and ignition plugs are controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a control device for detecting an in-cylinder pressure of an internal combustion engine and controlling the internal combustion engine based on the detected in-cylinder pressure.

[0002]

2. Description of the Related Art A piezoelectric element type in-cylinder pressure sensor is known as a sensor for detecting an in-cylinder pressure of an internal combustion engine.
FIG. 9 is a diagram illustrating a configuration of a conventional example of a control device using the sensor. In this figure, a piezoelectric element type in-cylinder pressure sensor 10
1 is a differential waveform of the in-cylinder pressure PCYL, that is, the in-cylinder pressure PCYL.
In order to output a signal proportional to the YL change rate dPCYL / dt, a charge amplifier 102 having a function as an integrating circuit and a function as an amplifier circuit is conventionally provided on the output side of the sensor. The output of 102 is converted into a digital signal by the AD converter 103,
The calculation unit 104 is configured to calculate a control parameter of the internal combustion engine, for example, a fuel supply amount and an ignition timing based on the digitized in-cylinder pressure, and to output a control signal SCTL.

[0003]

However, in the conventional apparatus, since the charge amplifier 102 which is an analog circuit is used, in addition to the cost increase due to the provision of the amplifier, there are the following problems. Was.

That is, although it is possible to change the integration time constant of the charge amplifier 102 or to add a circuit for resetting the integration output, it is necessary to provide a plurality of resistors or capacitors in advance and select and use them. As a result, output variations due to temperature, cost increases, and mounting space increase. Therefore, it has been difficult to increase the degree of freedom of change.

The present invention has been made in view of this point. The structure of the detecting unit for detecting the in-cylinder pressure of the internal combustion engine is simplified to reduce the cost, reduce the output variation due to temperature, and improve the design flexibility. It is an object of the present invention to provide a control device capable of enhancing the control.

[0006]

According to a first aspect of the present invention, there is provided an in-cylinder pressure detecting means for outputting a differential waveform of an in-cylinder pressure of an internal combustion engine. A control device for an internal combustion engine that controls the engine based on the A / D conversion means for converting an output signal of the in-cylinder pressure detection means into a digital signal, and calculates an in-cylinder pressure from the output signal of the A / D conversion means by digital signal processing. And a control means for controlling the engine using the in-cylinder pressure calculated by the in-cylinder pressure calculating means.

According to this configuration, the output signal of the in-cylinder pressure detecting means for outputting a differential waveform of the in-cylinder pressure is directly converted into a digital signal, and the in-cylinder pressure is calculated by digital signal processing. It is not necessary to use the above, the structure of the in-cylinder pressure detecting unit can be simplified, cost can be reduced, output variation due to temperature can be reduced, and design flexibility can be increased.

According to a second aspect of the present invention, the control means corrects the phase of the in-cylinder pressure calculated by the in-cylinder pressure calculating means, and controls the engine based on the corrected in-cylinder pressure. Features. According to this configuration, the phase correction of the in-cylinder pressure calculated by the in-cylinder pressure calculation means is performed, and the engine is controlled based on the corrected in-cylinder pressure. It is possible to improve the control accuracy when the crank angle at which the in-cylinder pressure is maximized is obtained and the fuel supply amount and the exhaust gas recirculation amount are controlled in accordance with those parameters.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a diagram showing a main part of an internal combustion engine according to an embodiment of the present invention and a configuration of a control device thereof. A combustion chamber 2 of an internal combustion engine (hereinafter referred to as “engine”) 1 is shown.
Is provided with an in-cylinder pressure sensor 3 as in-cylinder pressure detecting means for detecting a pressure in the combustion chamber, that is, an in-cylinder pressure PCYL, and a detection signal of the in-cylinder pressure sensor 3 is provided by an electronic control unit (hereinafter “EC”).
U ”). The in-cylinder pressure sensor 3 is a piezoelectric element type pressure sensor that outputs a signal DPCYL proportional to the rate of change of the in-cylinder pressure PCYL.

A crank angle position sensor 7 for detecting a rotation angle of a crankshaft (not shown) of the engine 1 is provided, and a signal corresponding to the rotation angle of the crankshaft is provided by the ECU 4.
Supplied to The crank angle position sensor 7 outputs a signal pulse (hereinafter referred to as a “CYL signal pulse”) at a predetermined crank angle position of a specific cylinder of the engine 1, and a top dead center (TDC) at the start of an intake stroke of each cylinder. )
The TDC sensor that outputs a TDC signal pulse at a crank angle position before a predetermined crank angle (every 180 degrees of crank angle in a four-cylinder engine) and a constant crank angle cycle shorter than the TDC signal pulse (for example, a cycle of 1 to 30 degrees) is 1
A CRK sensor that generates a pulse (hereinafter referred to as a “CRK signal pulse”) is provided, and a CYL signal pulse, a TDC signal pulse, and a CRK signal pulse are supplied to the ECU 4.
These signal pulses are used for various timing controls such as fuel injection timing, ignition timing, and the like, and detection of the engine speed NE.

The ECU 4 includes an AD converter 5 as AD conversion means for converting an input signal DPCYL into a digital signal, and a calculation unit 6 to which an output signal of the AD converter 5 is input. The ECU 4 includes an amplifier circuit (not shown) and the like, and the CYL signal pulse, the TDC signal pulse, and the CRK signal pulse are amplified and waveform-shaped and supplied to the arithmetic unit 6. The arithmetic unit 6 of the ECU 4 receives the digitized in-cylinder pressure detection signal DPCYL and the engine operating parameters (for example, the throttle valve opening θTH, the intake pipe absolute pressure PBA, and the engine coolant temperature TW) detected by other sensors (not shown). , Etc.) to calculate an engine control parameter (for example, fuel supply amount, ignition timing, etc.) and output a control signal SCTL corresponding to the calculation result to a fuel injection valve or a spark plug (not shown).

FIG. 2 is a flow chart of the processing executed by the arithmetic unit 6, and this processing is performed by the in-cylinder pressure detection signal DPCY.
The calculated mean effective pressure PMI is calculated based on L, and control according to the mean effective pressure PMI is performed. In step S11, it is determined whether or not the detection of the in-cylinder pressure PCYL and the control based on the detected in-cylinder pressure are permitted. If not, the process is immediately terminated. If it is permitted, first, noise removal processing is performed (step S12). This process is, for example, a low-pass filter process in which the cutoff frequency is set relatively high.

In the following step S13, the in-cylinder pressure P is calculated by performing an integral operation on the in-cylinder pressure detection signal DPCYL.
CYL is calculated, and then a phase shift correction process of the in-cylinder pressure PCYL is performed (step S14). This is a process for correcting a phase delay Δθ of the detected in-cylinder pressure PCYL as shown in FIG. 4 due to the noise removal process and the integration operation process. That is, the calculated value of the in-cylinder pressure PCYL (the value obtained in step S13) is the crank angle θC
The curve L2 in FIG. 4 is used as a function RK function PCYL (θCRK).
The actual in-cylinder pressure is Δ at crank angle.
Since the curve L1 is like the curve L1 preceding by θ, the curve L2 is corrected to match the curve L1. Specifically, the correction is performed by converting the delay time TD in the arithmetic processing into a phase delay Δθ in accordance with the detected engine speed NE and moving the crank angle θCRK in the direction in which the crank angle θCRK decreases by the phase delay Δθ. .

In the following step S15, the indicated mean effective pressure PMI is calculated based on the corrected in-cylinder pressure PCYL.
Specifically, data obtained by sampling the in-cylinder pressure PCYL at every predetermined crank angle (for example, 1 degree) is integrated during the compression stroke and the explosion stroke of the cylinder, and according to the integrated value thus obtained, Calculate the average effective pressure PMI.

The indicated mean effective pressure PMI is obtained by dividing the area on the PV diagram by the stroke volume VH, and is defined by the following equation (1).

(Equation 1) Since the volume V is a function of the crank angle θCRK, if there is a phase shift in the detected in-cylinder pressure PCYL (θCRK), the indicated mean effective pressure PM calculated by the above equation (1)
I will be incorrect. In the present embodiment, step S
Since the indicated mean effective pressure PMI is calculated using the in-cylinder pressure PCYL whose phase shift has been corrected by the step 14, an accurate PMI value can be obtained.

In step S16, control parameters of the engine 1 are calculated according to the indicated mean effective pressure PMI calculated in step S15. Specifically, for example, during a lean operation in which the air-fuel ratio is set leaner than the stoichiometric air-fuel ratio, a standard deviation σ is calculated from a plurality of calculated values of the indicated mean effective pressure PMI, and fuel supply is performed in accordance with the standard deviation σ. Correct the amount. That is, the standard deviation σ of the indicated mean effective pressure PMI
Indicates that the larger the value is, the more unstable the combustion state of the engine is. Therefore, when the standard deviation σ increases, the fuel supply amount is corrected in the increasing direction, while when the standard deviation σ decreases, The fuel supply amount is corrected in a decreasing direction. As a result, it is possible to improve fuel efficiency while avoiding extreme deterioration of the combustion state.

As described above, in the present embodiment, the output of the piezoelectric element type in-cylinder pressure sensor 3 is directly input to the ECU 4 without passing through a charge amplifier and is converted into a digital signal. Since the in-cylinder pressure PCYL is obtained by executing the method, there is no need to use a charge amplifier as in the prior art, and the integration time constant can be changed by changing the numerical value on a program. The configuration of the unit can be simplified to reduce costs and reduce output variations due to temperature, and increase the degree of freedom in design.

In the present embodiment, the calculating section 6 of the ECU 4 corresponds to the in-cylinder pressure detecting means and the control means. (Second Embodiment) In the present embodiment, the processing shown in FIG. 3 is executed by the arithmetic unit 6, and the detected in-cylinder pressure PCYL becomes the maximum crank angle (θPMAX1 shown in FIG. 4, hereinafter referred to as the “maximum in-cylinder pressure crank angle”). )) To control the engine 1. Except for the points shown in FIG. 3, the configuration is the same as that of the first embodiment.

Steps S11 to S14 in FIG. 3 are the same processing as the corresponding steps in FIG. Step S21
Then, the maximum in-cylinder pressure crank angle θPMAX is obtained based on the data of the in-cylinder pressure PCYL (θCRK) after the phase shift correction. As shown in FIG. 4, in the data before the phase shift correction, θPMAX = θPMAX2, but by using the corrected data, θPMAX = θPMAX1, and the original correct maximum in-cylinder pressure crank angle θPMAX1
Can be obtained.

In step S22, an engine control parameter is calculated according to the maximum in-cylinder pressure crank angle θPMAX. Specifically, for example, as shown in JP-A-6-42409, during execution of exhaust gas recirculation, a target value of the maximum in-cylinder pressure crank angle θPMAX is set, and the target value and the crank angle θPMAX calculated in step S21 are compared with the target value. The valve opening command value of the exhaust gas recirculation valve is calculated in accordance with the deviation of. This makes it possible to increase the exhaust gas recirculation amount to a limit that does not deteriorate the operability, and obtain good exhaust gas characteristics.

As described above, in the present embodiment, the detected value PCYL of the in-cylinder pressure is calculated in the same manner as in the first embodiment, the phase shift is corrected, and then the maximum in-cylinder pressure crank angle θPMAX is calculated. As a result, an accurate maximum in-cylinder pressure crank angle θPMAX can be obtained, and θPM
The accuracy of control based on the AX value can be improved.
As in the present embodiment, the maximum in-cylinder pressure crank angle θPMAX
When the control is performed according to the above, the effect of the phase shift of the in-cylinder pressure detection value directly appears, so that a significant control accuracy improvement effect can be obtained by the phase shift correction in step S14.

(Third Embodiment) In this embodiment, the processing shown in FIG. 5 is executed by the arithmetic unit 6, the output of the piezoelectric element type in-cylinder pressure sensor 3 is directly converted into a digital signal, and the in-cylinder pressure is obtained by integration processing. Without calculating PCYL, occurrence of knocking is detected based on the digitized detection signal DPCYL, and when knocking is detected, the ignition timing is corrected in the retard direction. Except for the points shown in FIG. 5, the third embodiment is the same as the first embodiment.

Steps S41 and S42 are the same as steps S11 and S12 in FIG.
At 43, a knocking detection process is performed. This detection processing is more specifically bandpass filter processing. When knocking occurs, a specific frequency component is extracted, and when the level is equal to or higher than a predetermined value, knocking is determined. In the subsequent step S44, when it is determined that knocking has occurred, a correction is made so that the ignition timing is retarded from the optimum ignition timing set according to the engine operating state, and the process ends.

In this embodiment, the output of the piezoelectric element type in-cylinder pressure sensor is directly converted into a digital signal, and the differential waveform signal D
Since the knocking detection process is directly performed without performing the process of converting PCYL to the in-cylinder pressure PCYL,
As in the first embodiment, a charge amplifier is not required, cost can be reduced, and arithmetic processing after digitization can be simplified.

[0025]

As described in detail above, according to the first aspect of the present invention, the output signal of the in-cylinder pressure detecting means for outputting the differential waveform of the in-cylinder pressure is directly converted into a digital signal, and the digital signal is processed by digital signal processing. Since the internal pressure is calculated, there is no need to use a charge amplifier as in the conventional case, and the configuration of the in-cylinder pressure detection unit is simplified to reduce costs and reduce output variations due to temperature, and increase design flexibility. Can be.

According to the second aspect of the invention, the phase correction of the in-cylinder pressure calculated by the in-cylinder pressure calculating means is performed, and the control of the engine is performed based on the corrected in-cylinder pressure. It is possible to obtain the crank angle at which the indicated mean effective pressure and the in-cylinder pressure are maximized from the in-cylinder pressure and improve the control accuracy when controlling the fuel supply amount and the exhaust gas recirculation amount according to those parameters.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a main part of an internal combustion engine and a control device according to an embodiment of the present invention.

FIG. 2 is a flowchart (first embodiment) of a process executed by a calculation unit shown in FIG. 1;

FIG. 3 is a flowchart (second embodiment) of a process executed by the calculation unit shown in FIG. 1;

FIG. 4 is a diagram for explaining a phase shift of a calculated in-cylinder pressure.

FIG. 5 is a flowchart (third embodiment) of a process executed by a calculation unit shown in FIG. 1;

FIG. 6 is a diagram showing a configuration of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Combustion chamber 3 In-cylinder pressure sensor (in-cylinder pressure detection means) 4 Electronic control unit 5 AD conversion part (AD conversion means) 6 Operation part (in-cylinder pressure calculation means, control means)

Claims (2)

[Claims] 1. A control device for an internal combustion engine, comprising: an in-cylinder pressure detecting means for outputting a differential waveform of an in-cylinder pressure of an internal combustion engine; and controlling the engine based on a value detected by the in-cylinder pressure detecting means. AD conversion means for converting an output signal of the means into a digital signal, in-cylinder pressure calculation means for calculating an in-cylinder pressure from the output signal of the A / D conversion means by digital signal processing, and an in-cylinder pressure calculated by the in-cylinder pressure calculation means A control unit for controlling the engine by using the control unit. 2. The apparatus according to claim 1, wherein the control means performs a phase correction of the in-cylinder pressure calculated by the in-cylinder pressure calculating means, and controls the engine based on the corrected in-cylinder pressure. A control device for an internal combustion engine according to claim 1.