JPH11241626A - Knocking control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a combustion temperature, and effectively suppress knocking by supplying fuel having a large rate toward a more lean condition of a target air-fuel ratio, at least at either one side of a compression stroke and a combustion stroke of an engine, according to an output of a knocking detecting means for detecting knocking of the engine. SOLUTION: A target air-fuel ratio is set in a target air-fuel ratio setting unit 34 according to an engine parameter detected by an operating condition detecting unit 33. A real air-fuel ratio is detected by an air-fuel ratio feed back unit 32 for inputting an output detected by an all rage air-fuel ratio sensor 22, and a feed back correcting coefficient is calculated in a fuel injection control unit 35 according to a deviation between the real air-fuel ratio and the target air-fuel ratio. When knocking of an engine is detected by a knocking sensor 21, control is carried out in such a way that flue having a large rate toward a more lean condition of the target air-fuel ratio is supplied at least at either one side of a compression stroke and a combustion stroke of an engine. It is thus possible to reduce a combustion temperature by vaporization latent heat of fuel and increase of molar numbers, and knocking is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a so-called in-cylinder direct injection engine which injects fuel directly into a combustion chamber, and more specifically to control for suppressing knocking.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. 9-126028 discloses an in-cylinder direct injection engine in which fuel is injected separately from an injection valve into a front stage and a rear stage. It is described that the fuel is supplied and burned at the stoichiometric air-fuel ratio as a whole. In a high compression ratio direct injection engine having a compression ratio of 10 or more, in the operating range where knocking is relatively likely to occur as compared with other operating ranges, the fuel injection is divided into the former stage and the latter stage, and the occurrence of knocking is reduced. In order to suppress this, at least the fuel of the subsequent stage is supplied after the fuel of the preceding stage is ignited, and the two-stage fuel injection is not performed except in the knocking occurrence operation range.

[0003] Knocking is a phenomenon caused by abnormal combustion of an engine. An unburned air-fuel mixture present at the end of a cylinder is compressed by the combustion pressure and reacts, and a flame generated and propagated by ignition by a spark plug arrives. It is a phenomenon that causes self-ignition before. As a result, the terminal gas burns rapidly, generating an unbalanced pressure, generating a strong pressure wave of several KHz, and generating a sound that knocks the door by exciting the engine.
This pressure wave destroys the temperature boundary layer on the wall of the combustion chamber, and the high-temperature combustion gas directly contacts the surface to increase the wall temperature, and also reduces or evaporates the viscosity of the lubricating oil film formed on the cylinder wall. Or As a result, seizure and melting of moving parts such as pistons may occur. Further, knocking is further promoted by a rise in the temperature of the wall surface.

[0004] Knocking and ignition timing are closely related. When the ignition timing is advanced, the maximum combustion pressure increases and knocking occurs. In addition, the ignition timing at which the engine produces maximum torque (MBT: Minimum spark advance for Best Torqu
e) is near the ignition timing at which knocking occurs (knocking limit). Therefore, when setting the normal ignition timing, it is necessary to take a margin from the knocking limit, so that the ignition timing is set at a position delayed from the MBT, so that the torque is reduced accordingly.

In general, a knock sensor is attached to an appropriate position of an engine block to detect the acceleration of a pressure wave when vibrated by knocking, or a method of directly detecting a pressure wave in a cylinder. Is detected, and when knocking occurs, the ignition timing is immediately delayed. When knocking does not occur, feedback control for advancing the ignition timing gradually is performed, and control at the very end of the knocking limit is performed.

On the other hand, as one type of lean burn type engine, an in-cylinder direct injection engine in which a fuel injection valve is disposed in a combustion chamber and fuel is directly supplied to the combustion chamber has attracted attention. This engine can be operated at a lean air-fuel ratio by providing a recess at the top of the piston and collecting fuel spray injected from the injector near the spark plug. The form of combustion is spray combustion and includes diffusion combustion. It is said that since the knocking resistance is improved, a higher compression ratio can be achieved.

[0007]

The technique disclosed in the above publication only proposes suppression of knocking during operation at a stoichiometric air-fuel ratio and a high compression ratio on the assumption that the engine is operated at a stoichiometric air-fuel ratio. Since the cylinder direct injection engine can operate at a leaner air-fuel ratio than the intake pipe injection engine, knocking measures during lean operation are required.

[0008]

According to a first aspect of the present invention, there is provided an engine for directly injecting fuel into a combustion chamber, comprising: operating state detecting means for detecting an operating state of the engine; Target air-fuel ratio setting means for setting a target air-fuel ratio in accordance with the output of the operating state detection means, knocking detection means for detecting engine knocking,
A fuel supply means is provided which supplies a larger amount of fuel as the target air-fuel ratio is leaner in accordance with the output of the knocking detection means in at least one of the compression step and the combustion step of the engine.

According to the present invention, when knocking is detected, the larger the target air-fuel ratio is the leaner the ignition timing is advanced in accordance with the output of the knocking detection means, the larger the amount of fuel is supplied to the engine during the compression step and the combustion step. At least one of them is directly supplied to the combustion chamber, so that the combustion temperature decreases due to the latent heat of vaporization of the fuel and the increase in the number of moles, and knocking can be suppressed without lowering the engine torque.

[0010]

Embodiments of the present invention will now be described with reference to the drawings. First, the structure of a direct injection engine to which the present invention is applied will be described. As shown in FIG. 1, an engine 1 comprises a piston 2, a combustion chamber 3, a spark plug 4, an intake valve 5, an intake port 6, an exhaust valve 7. , An exhaust port 8, and a fuel injection device, ie, an injector 11, for directly injecting (supplying) fuel into the combustion chamber. A recess is provided at the top of the piston 2 to change the direction of fuel injected from the injector 11 and collect the fuel around the spark plug 4.

The intake port 6 is connected to the corresponding manifold 9
Is connected to the surge tank 10. The surge tank 10 is connected to an air cleaner 14 via an intake duct 12.
It is connected to the. A pressure sensor 13 for measuring an intake pipe pressure is connected to the surge tank 10.

A throttle valve 15 is disposed in the intake duct 12, and an opening sensor 23 is provided with a throttle valve.
It detects the opening of the valve 15 and outputs a signal corresponding to the opening. On the other hand, an exhaust gas manifold 16 is connected to an all-range air-fuel ratio sensor 22 and generates a voltage output that is substantially proportional to the air-fuel ratio over a wide air-fuel ratio region. The exhaust pipe 17 is provided with a casing 19 containing a catalytic converter 18.

A knock sensor 21 is attached to the engine 1. In this embodiment, a piezoelectric knock sensor using a piezoelectric element is used, but a magnetostrictive or electromagnetic knock sensor can also be used. Knock sensor 2
1 outputs a signal corresponding to the vibration of the engine.

The electronic control unit ECU 30 is constituted by a computer, a ROM (Read Only Memory) for storing programs and data to be executed by the computer,
A RAM (random access memory) that retrieves and stores programs and data necessary for execution and provides a work area for operations, a CPU (processor) that executes programs, and a circuit that processes input signals from various sensors And a drive circuit for sending a control signal to each part of the engine. FIG. 1 shows the ECU 30 as functional blocks based on such a hardware configuration.

The output of the pressure sensor 13 for detecting the intake pipe pressure and the output of the throttle opening sensor 23 for detecting the opening of the throttle valve are input to an operating state detecting section 33 (operating state detecting means) of the ECU 30. . The driving state detection unit 33 receives a signal indicating the vehicle speed from the vehicle speed sensor 26 and a signal indicating the engine speed Ne from the engine speed sensor 25.

The operating state detector 33 processes these input signals to detect the intake pipe pressure PB, the throttle valve opening θ, the vehicle speed V, and the engine speed Ne.
Further, the operating state detection unit 33 outputs parameters such as exhaust gas temperature, engine cooling water temperature, intake air temperature, and atmospheric pressure (hereinafter collectively referred to as engine operating parameters) from the output of a sensor (not shown) together with the above parameters. The detection is sent to the fuel injection control unit 35 and the ignition timing control unit 36.

The target air-fuel ratio setting unit 34 (target air-fuel ratio setting means) determines the target air-fuel ratio in the range of, for example, 13 to 40 in air-fuel ratio based on the engine parameters from the operating state detection unit 33.

The fuel injection control unit 35 (fuel supply means)
The basic fuel injection time Tp is obtained based on the intake pipe pressure PB and the engine speed Ne sent from the operating state detection unit 33. Fuel is supplied to the injector 11 at a constant pressure, and the amount of fuel supplied to the engine is determined by the time during which the valve of the injector 11 is opened. This time, that is, the fuel injection time Tr is represented by Tr = Tp × Km. Km is a correction coefficient determined in accordance with a target air-fuel ratio, a correction coefficient for obtaining an appropriate air-fuel ratio in an engine state at that time, such as during cold or acceleration, based on a signal from each sensor, and an air-fuel ratio feedback correction described later. Indicates a coefficient or the like.

Further, the fuel injection control unit 35 determines a fuel injection method (broadly classified into an intake process injection and a compression process injection) according to the target air-fuel ratio set by the target air-fuel ratio setting unit 34.

The detection output from the full range air-fuel ratio sensor 22 is E
It is input to the air-fuel ratio feedback section 32 of the CU 30, and the actual air-fuel ratio of the engine is detected. The detected air-fuel ratio is sent to the fuel injection control unit 35, and a feedback correction coefficient for correcting a deviation from the target air-fuel ratio is calculated.

On the other hand, a signal indicating the vibration of the engine from the knock sensor 21 attached to the engine body is an EC signal.
Knock detection unit 31 of U30 (knock detection means)
And the occurrence of knocking is detected. FIG. 2 is a block diagram illustrating an example of a configuration of the knocking detection unit 31.
A signal corresponding to the vibration of the engine from the knock sensor 21 attached to the engine is output from the bandpass filter 311.
To extract a signal component in the frequency domain that includes a unique vibration component at the time of knocking.
At 12, the peak value is detected. On the other hand, the reference level calculation circuit 313 monitors the output signal of the filter 311 over a certain period, and calculates a reference value used for knocking determination based on the average level. This reference value may be a fixed value set in advance. Knocking determination circuit 314
Compares the peak value obtained by the peak detection circuit 312 with the reference level obtained by the reference level calculation circuit 313,
When the peak value exceeds the reference level, a knock signal indicating the occurrence of knocking is output. The knock signal is sent to fuel injection control unit 35 and ignition timing control unit 36.

The fuel injection control unit 35 may correct the fuel injection time Tr in response to the knock signal so as to increase the fuel injection amount as the target air-fuel ratio is leaner than the stoichiometric air-fuel ratio. After supplying the fuel for the injection time Tr (main injection), it is preferable to supply a larger amount of fuel as the target air-fuel ratio is leaner as the second injection (sub injection) in the compression step or the combustion step.

In order to enhance the effect of suppressing knocking,
The knocking suppression injection is preferably performed in the vicinity of the maximum in-cylinder pressure. FIG. 3 is a diagram showing the relationship between the crank angle and the combustion pressure (curve a, left scale), and curve b shows the heat release rate (right scale). The rising position of the curve b is the ignition timing. In general, since the in-cylinder pressure becomes maximum after entering the combustion process, it is preferable that the injection for suppressing knocking is executed separately from the main injection by a sub-injection method in the combustion process.

The fuel injection control unit 35 estimates the timing at which the combustion pressure reaches a maximum from the ignition timing based on the relationship shown in FIG. 3, and at this timing, the fuel injection device 11 performs the fuel injection for suppressing knocking. Control. In this case, the leaner the target air-fuel ratio, the larger the auxiliary injection amount for knocking suppression. This is because the leaner the air-fuel ratio is, the more advanced the ignition timing is, so that more fuel injection is required to suppress knocking.

In the above embodiment, when the occurrence of knocking is detected, the knocking is suppressed by controlling the fuel injection without delaying the ignition timing. However, the ignition timing may be delayed together with the fuel injection for suppressing knocking. .
Further, knocking may be suppressed for each cylinder. Further, the fuel injection amount may be determined according to the knocking intensity. That is, the fuel injection amount may be increased as the knocking intensity increases.

FIG. 4 is a flowchart showing the above-described knocking suppression process. The operating state detecting unit 33 shown in FIG. 1 measures engine operating parameters (S101), and the target air-fuel ratio setting unit 34 applies these parameters to these parameters. The target air-fuel ratio is calculated based on the calculated value (S102). The knocking detection unit 31 processes the signal from the knock sensor 21 (S103), and determines whether knocking has occurred (S104). When it is determined that knocking has occurred, the fuel injection control unit 35 sends a signal to the fuel injection device 11 to perform fuel injection for suppressing knocking as described above. The occurrence of knocking is checked again (S106). If knocking still occurs, fuel injection for suppressing knocking is continued (S105). At this time, the fuel injection time may be further extended to suppress knocking, or the ignition timing may be controlled to be delayed. Step S1
When knocking has not occurred in 04 and S106, the process for suppressing knocking ends, and after a certain time,
Alternatively, the process is restarted when a knock signal is sent from knocking detection unit 31.

[0027]

According to the present invention, when knocking is detected, a larger amount of fuel is provided as the target air-fuel ratio is leaner in accordance with the output of the knocking detecting means, at least in one of the compression step and the combustion step of the engine. , The combustion temperature decreases due to the latent heat of vaporization of the fuel and the increase in the number of moles, and knocking can be suppressed without lowering the torque of the engine.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of a system according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating an example of a knocking determination circuit.

FIG. 3 is a diagram showing a relationship between combustion pressure and ignition timing.

FIG. 4 is a flowchart showing the flow of processing for suppressing knocking.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine 11 Fuel injection device (fuel supply means) 21 Knock sensor (knock detection means) 31 Knock detection section (knock detection means) 33 Operating state detection section (operation state detection means) 34 Target air-fuel ratio setting section (target air-fuel ratio setting) Means) 35 fuel injection control unit (fuel supply means)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Takashi Kiyomiya 1-4-1 Chuo, Wako City, Saitama Prefecture Inside Honda R & D Co., Ltd. (72) Inventor Hironao Fukuchi 1-4-1 Chuo Wako City, Saitama Prefecture No. In Honda R & D Co., Ltd.

Claims (1)

[Claims] 1. An engine for directly injecting fuel into a combustion chamber, wherein: an operating state detecting means for detecting an operating state of the engine; and a target air-fuel ratio setting for setting a target air-fuel ratio in accordance with an output of the operating state detecting means. Means, knocking detection means for detecting knocking of the engine, and at least one of a compression step and a combustion step of the engine, in which a larger amount of fuel is provided as the target air-fuel ratio is leaner in accordance with an output of the knocking detection means. A knocking control device for an engine, comprising: