JP2007077856A - Combustion condition judgment device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a combustion condition judgment device for an internal combustion engine capable of accurately judging a combustion condition by eliminating influence of change of an engine operation condition and variation of characteristics of a cylinder pressure sensor. <P>SOLUTION: A judgment threshold DPTH(k) is calculated by multiplying a predetermined value α and a previous value of the maximum pressure change rate dpdθmax (k-1) which is the maximum value of pressure change rate dpdθ detected by the cylinder pressure sensor 2 (S11) together. Limiting processing of the judgment threshold DPTH(k) is performed (S12-S16) and an error counter CERR is incremented when the maximum pressure change rate dpdθ(k) is the judgment threshold DPTH(k) or less (S17, S18). An error rate RERR is calculated based on a value of the error counter CERR, and the occurrence of a misfire is judged (S21-S23) if the error rate RERR exceeds a predetermined reference value RERTH. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a combustion state determination device that determines a combustion state of an air-fuel mixture in a combustion chamber of an internal combustion engine, and more particularly to a device that determines a combustion state by detecting pressure fluctuations in the combustion chamber.

  Japanese Patent Application Laid-Open No. 2005-228561 discloses an apparatus that includes a cylinder pressure sensor that detects a pressure in a combustion chamber (cylinder pressure) and determines a combustion state based on the cylinder pressure detected by the cylinder pressure sensor. According to this apparatus, the differential pressure between the in-cylinder pressure at the timing of 30 degrees after the top dead center in the expansion stroke and the in-cylinder pressure at the timing of 30 degrees after the bottom dead center in the compression stroke is calculated. When it exceeds a predetermined level, it is determined as normal combustion, and when the differential pressure falls below a predetermined level, it is determined as misfire.

JP-A-10-231740

  In the above-described conventional apparatus, the predetermined level for misfire determination is fixed, and therefore the predetermined level is inappropriate due to a problem that erroneous determination is likely to occur when the engine operating state changes or due to characteristic variations of the in-cylinder pressure sensor. There was a problem that it was easy to make an erroneous determination.

  The present invention has been made paying attention to this point, and can determine the combustion state of an internal combustion engine that can accurately determine the combustion state, excluding the influence of changes in the engine operating state and variations in characteristics of the in-cylinder pressure sensor. An object is to provide an apparatus.

In order to achieve the above object, the invention described in claim 1 includes pressure fluctuation detecting means (2) for detecting pressure fluctuation in the combustion chamber of the internal combustion engine (1), and is detected by the pressure fluctuation detecting means (2). In the combustion state determination device for an internal combustion engine that determines the combustion state of the air-fuel mixture in the combustion chamber based on the pressure fluctuation value (dpdθ), the previous pressure fluctuation value detected by the pressure fluctuation detection means (2) Threshold calculation means for calculating a threshold value (DPTH (k)) based on the maximum value (dpdθmax (k−1)) is provided, the threshold value (DPTH (k)) calculated by the threshold value calculation means, and the detected pressure It is characterized by comparing the maximum value (dpdθmax (k)) of the fluctuation value and determining the combustion state based on the result of the comparison.
Specifically, it is desirable that the threshold value calculation means calculates the determination threshold value by multiplying the maximum value of the pressure fluctuation value by a predetermined value smaller than “1”. The combustion state determination device includes a counting unit that counts the number of times that the maximum value of the detected pressure fluctuation value is less than or equal to the determination threshold and the number of executions of the comparison, and is counted by the counting unit. It is desirable to determine that a misfire has occurred when the ratio of the number of errors to the number of executions exceeds a predetermined reference value above a predetermined reference value.

  According to the first aspect of the present invention, the threshold value is output based on the maximum value of the previous pressure fluctuation value detected by the pressure fluctuation detection means, and the comparison result between this threshold value and the detected pressure fluctuation value is obtained. Based on this, the combustion state is determined. The threshold calculated based on the previous maximum value of the pressure fluctuation value reflects the influence of changes in engine operating conditions and variations in the characteristics of the sensors constituting the pressure fluctuation detection means. By comparing these, it is possible to accurately determine the combustion state.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of an internal combustion engine and a control device thereof according to an embodiment of the present invention. An internal combustion engine (hereinafter simply referred to as “engine”) 1 having four cylinders is a diesel engine that directly injects fuel into a cylinder, and a fuel injection valve 6 is provided in each cylinder.

  Each cylinder of the engine 1 is provided with an in-cylinder pressure sensor 2 that detects an in-cylinder pressure (combustion pressure). In the present embodiment, the in-cylinder pressure sensor 2 is configured integrally with a glow plug provided in each cylinder. A detection signal from the in-cylinder pressure sensor 2 is supplied to the ECU 4. The detection signal of the in-cylinder pressure sensor 2 actually corresponds to a differential signal with respect to the crank angle (time) of the in-cylinder pressure PCYL, and the in-cylinder pressure PCYL is obtained by integrating the in-cylinder pressure sensor output. .

  The engine 1 is provided with a crank angle position sensor 3 that detects a rotation angle of a crankshaft (not shown). The crank angle position sensor 3 generates a pulse every crank angle, and the pulse signal is supplied to the ECU 4. The crank angle position sensor 3 further generates a cylinder identification pulse at a predetermined crank angle position of the specific cylinder and supplies it to the ECU 4.

  The ECU 4 includes an accelerator sensor 33 that detects an operation amount AP of an accelerator pedal of a vehicle driven by the engine 1, a cooling water temperature sensor 34 that detects a cooling water temperature TW of the engine 1, and an intake air that detects an intake air temperature TA of the engine 1. An air temperature sensor 35 is connected, and detection signals from these sensors are supplied to the ECU 4.

  The ECU 4 supplies a control signal for the fuel injection valve 6 provided in the combustion chamber of each cylinder of the engine 1 to the drive circuit 5. The drive circuit 5 is connected to the fuel injection valve 6, and supplies a drive signal corresponding to the control signal supplied from the ECU 4 to the fuel injection valve 6. Thus, at the fuel injection timing corresponding to the control signal output from the ECU 4, fuel is injected into the combustion chamber of each cylinder by the fuel injection amount corresponding to the control signal.

  The ECU 4 includes an amplifier 10, an A / D converter 11, a pulse generator 13, a CPU (Central Processing Unit) 14, a ROM (Read Only Memory) 15 that stores a program executed by the CPU 14, and a CPU 14. A RAM (Random Access Memory) 16 for storing calculation results and the like, an input circuit 17, and an output circuit 18 are provided. A detection signal of the in-cylinder pressure sensor 2 is input to the amplifier 10. The amplifier 10 amplifies an input signal. The signal amplified by the amplifier 10 is input to the A / D converter 11. The pulse signal output from the crank angle position sensor 3 is input to the pulse generator 13.

  The A / D conversion unit 11 includes a buffer 12, converts the in-cylinder pressure sensor output input from the amplifier 10 into a digital value (hereinafter referred to as “pressure change rate”) dpdθ, and stores the converted value in the buffer 12. More specifically, the A / D converter 11 is supplied with a pulse signal PLS1 (hereinafter referred to as “1 degree pulse”) PLS1 having a crank angle of 1 degree from the pulse generator 13, and this 1 degree pulse PLS1. The in-cylinder pressure sensor output is sampled at a period of ## EQU2 ## and converted into a digital value and stored in the buffer 12.

  On the other hand, the pulse signal PLS6 with a crank angle of 6 degrees is supplied from the pulse generator 13 to the CPU 14, and the CPU 14 performs a process of reading the digital value stored in the buffer 12 with the period of the 6 degrees pulse PLS6. . That is, in this embodiment, the A / D conversion unit 11 does not issue an interrupt request to the CPU 14, but the CPU 14 performs a reading process at a cycle of the 6-degree pulse PLS6.

  The input circuit 17 converts detection signals from various sensors into digital values and supplies them to the CPU 14. The engine speed NE is calculated from the cycle of the 6-degree pulse PLS.

  FIG. 2 is a flowchart of a process for determining misfire, and this process is executed by the CPU 14 every time the crankshaft rotates 180 degrees.

In step S11, by multiplying the previous value dpdθmax (k−1) of the maximum value (hereinafter referred to as “maximum pressure change rate”) dpdθmax of the pressure change rate dpdθ in the ignition cylinder by a predetermined value α (for example, 0.6), A determination threshold DPTH (k) is calculated. The maximum pressure change rate dpdθmax (k) is calculated by monitoring the pressure change rate dpdθ obtained from the output signal of the in-cylinder pressure sensor 2 of the cylinder in the expansion stroke in a process (not shown). Here, “k” indicates a discretization time discretized in the combustion cycle (a period required for the crankshaft to rotate 720 degrees).
In step S12, the threshold value change amount DDPTH is calculated by subtracting the previous value DPTH (k-1) from the current value DPTH (k) of the determination threshold value.

  In step S13, it is determined whether or not the absolute value of the threshold change amount DDPTH is greater than a predetermined change amount DDPLMT. If the answer is negative (NO), the process immediately proceeds to step S17. If the answer is positive (YES), it is determined whether or not the threshold change amount DDPTH is larger than “0” (step S14). When DDPTH> 0, the determination threshold DPTH (k) is set to a value obtained by adding the predetermined change amount DDPLMT to the previous value DPTH (k−1) (step S15). On the other hand, when DDPTH <0, the determination threshold DPTH (k) is set to a value obtained by subtracting the predetermined change amount DDPLMT from the previous value DPTH (k-1) (step S16). By steps S12 to S16, a sudden change in the determination threshold value DPTH is prevented.

  In step S17, it is determined whether or not the maximum pressure change rate dpdθmax (k) is larger than a determination threshold value DPTH (k). When the answer is affirmative (YES), the process immediately proceeds to step S19, and when it is negative (NO), that is, when the maximum pressure change rate dpdθmax (k) is equal to or less than the determination threshold DPTH (k), the error counter CERR. Is incremented by "1" (step S18), and the process proceeds to step S19.

  In step S19, the operation counter n is incremented by “1”, and then it is determined whether or not the value of the operation counter n has reached a predetermined value N0 (for example, 10) (step S20). Since this answer is negative (NO) at first, this processing is immediately terminated.

Thereafter, when the value of the operation counter n reaches a predetermined value N0, the process proceeds from step S20 to step S21, and an error rate RERR is calculated by the following equation.
RERR = CERR / N0
In step S22, it is determined whether or not the error rate RERR is equal to or greater than a predetermined reference value RERTH (for example, 0.1). If RERR <RERTH, it is determined to be normal (step S24). On the other hand, when the error rate RERR is equal to or greater than the predetermined reference value RERTH, it is determined that a misfire has occurred (step S23).

  FIG. 3 is a waveform diagram (time chart) showing the transition of the pressure change rate dpdθ, in which the solid line indicates the maximum pressure change rate dpdθmax, and the broken line is a determination calculated from the previous value of the maximum pressure change rate dpdθmax. The threshold value DPTH is indicated. FIG. 5A shows a waveform when no misfire has occurred. In the example shown in FIG. 4B, the error rate is detected because the maximum pressure change rate dpdθmax falls below the determination threshold value DPTH at time ter. The counter CERR is incremented.

  FIG. 4 is a diagram showing the relationship between the fluctuation rate of the indicated mean effective pressure (hereinafter referred to as “Pmi fluctuation rate”) RDPM and the error rate RERR calculated in step S20 of FIG. 2, and an increase in the Pmi fluctuation rate RDPM. As a result, the error rate RERR increases almost linearly. Therefore, the combustion state in each cylinder of the engine 1 can be determined relatively accurately by calculating the error rate RERR instead of calculating the Pmi variation rate from the in-cylinder pressure sensor output. The calculation of the Pmi fluctuation rate RDPM considerably increases the calculation load of the CPU 14, so that the calculation load of the CPU 14 is increased by determining the combustion state (misfire) using the error rate RERR instead of the Pmi change rate RDPM. It is possible to perform accurate determination while suppressing.

  As described above in detail, in the present embodiment, the determination threshold value DPTH (k) is calculated by multiplying the previous value dpdθmax (k−1) of the maximum pressure change rate by a predetermined value α smaller than “1”. The combustion state of the engine is determined using the determination threshold value DPTH (k). Specifically, when the maximum pressure change rate dpdθ (k) is equal to or less than the determination threshold DPTH, the error counter CERR is incremented, and when the value of the operation counter n indicating the number of executions of the process of FIG. 2 reaches the predetermined value N0. When the error rate RERR is calculated and the error rate RERR is equal to or greater than a predetermined reference value RERTH, it is determined that a misfire has occurred. Therefore, the influence of the change in the engine operating state and the characteristic variation of the in-cylinder pressure sensor 2 is reflected in the determination threshold value DPTH (k), and the accurate combustion state determination can be performed.

  In the present embodiment, the in-cylinder pressure sensor 2 and the ECU 4 constitute a combustion state determination device. Specifically, the in-cylinder pressure sensor 2 corresponds to a pressure fluctuation detection unit, and steps S11 to S16 in FIG. 2 correspond to a threshold value calculation unit.

  The present invention is not limited to the embodiment described above, and various modifications can be made. For example, in the above-described embodiment, “10” is shown as an example of setting the predetermined value N0. However, it is set to a number larger than “10” (for example, “100” or a value between “10” and “100”). May be. As the value of the predetermined value N0 is increased, the time until the determination result is obtained becomes longer, but the determination accuracy can be improved.

  In the above-described embodiment, an example of a four-cylinder diesel internal combustion engine has been described. However, the present invention is not limited to this, and a ship such as a diesel internal combustion engine having a different number of cylinders, an outboard motor having a crankshaft in a vertical direction, or the like. The present invention can also be applied to a combustion state determination of a propulsion engine or a gasoline internal combustion engine.

It is a figure which shows the structure of the internal combustion engine and its control apparatus concerning one Embodiment of this invention. It is a flowchart of the process which determines a combustion state (misfire). It is a time chart which shows transition of the pressure change rate detected by a cylinder pressure sensor. It is a figure which shows the relationship between Pmi fluctuation rate (RDPM) and the error rate (RERR) calculated by the process of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 In-cylinder pressure sensor (pressure fluctuation detection means)
3 Crank angle position sensor 4 Electronic control unit (threshold detection means)
6 Fuel injection valve

Claims (1)

Combustion of the internal combustion engine comprising pressure fluctuation detection means for detecting pressure fluctuation in the combustion chamber of the internal combustion engine, and determining the combustion state of the air-fuel mixture in the combustion chamber based on the pressure fluctuation value detected by the pressure fluctuation detection means In the state determination device,
Threshold value calculating means for calculating a threshold value based on the maximum value of the previous pressure fluctuation value detected by the pressure fluctuation detecting means;
A combustion state determination device for an internal combustion engine, wherein the threshold value calculated by the threshold value calculation means is compared with the maximum value of the detected pressure fluctuation value, and the combustion state is determined based on the comparison result. .

Images