JP2000314334A - Cylinder fuel injection type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cylinder fuel injection type internal combustion engine, which can switch the operation mode following the change of a combustion form without generating excessive torque shocks. SOLUTION: When an internal combustion engine can select a proper operation mode in response to the operation state (step S10), especially the switch of selection following the change of a combustion form is carried out (step S12), prior to the execution of a new operation mode, a fuel injection is carried out in a combustion stroke and a compression stoichiometric mode, carrying out the stratified combustion in the stoichiometric vicinity is executed (steps S22-S24). Meantime, as the intake air quantity and EGR gas amount of the internal combustion engine dissolve the response delay, the torque shock generated at the switching time of the operation mode (step S26) is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-cylinder injection type internal combustion engine which injects fuel directly into a combustion chamber and switches between uniform combustion and stratified combustion in accordance with the engine operating state.

[0002]

Related Background Art This type of in-cylinder injection type internal combustion engine has already been put into practical use, and a high output and a low fuel consumption are achieved by using operation modes having different combustion modes according to the operation state. ing. On the other hand, in order to prevent a torque shock occurring at the time of switching the operation mode, for example, Japanese Patent Application Laid-Open No. H10-68344 discloses a control technique suitable for switching the operation mode in a direct injection internal combustion engine. .

More specifically, as is more apparent with reference to FIG. 5 in the above publication, in the known control technique, the operation mode is switched from stratified combustion (compression stroke injection) to uniform combustion (intake stroke injection). When a signal is output, exhaust gas recirculation (E
(GR) A tailing process is performed to throttle the valve and gradually enrich the air-fuel ratio, and when the air-fuel ratio reaches the smoke generation limit in stratified combustion, the air-fuel ratio is switched stepwise to an air-fuel ratio suitable for uniform combustion. I have. Further, at this time, the air-fuel ratio at the time of switching is temporarily set to the rich air-fuel ratio in order to compensate for the shortage of the combustion torque due to the EGR gas remaining in the cylinder.

[0004]

However, even when the above-mentioned known control method is applied at the time of switching the operation mode, the combustion mode and the air-fuel ratio are switched stepwise, and the throttle valve opening degree and the control in the control are changed. Since the actual intake air amount and the change in the EGR gas introduction amount have a response delay with respect to the response of the EGR valve opening, the change characteristic of the engine torque intended in control cannot be sufficiently obtained, and The torque shock at the time of mode switching cannot be reliably suppressed.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an in-cylinder injection type internal combustion engine capable of suppressing a torque shock at the time of switching operation modes.

[0006]

The direct injection internal combustion engine of the present invention has first and second operation modes selectively executed according to the operation state of the internal combustion engine. In the first operation mode, fuel is mainly injected during the intake stroke to cause uniform combustion near the stoichiometric air-fuel ratio, while in the second operation mode, fuel is mainly injected during the compression stroke. Perform stratified combustion at a lean air-fuel ratio. In particular, in the internal combustion engine of the present invention, when the selection is switched between the above-mentioned operation modes, the fuel is injected during the compression stroke and the stoichiometric air-fuel ratio is set prior to the operation mode newly executed by the selection. , A transition mode in which stratified combustion is performed is executed.

According to the above-described in-cylinder injection type internal combustion engine, for example, when the selection is switched from the second operation mode to the first operation mode, the above-mentioned transition mode is executed before the execution of the first operation mode. Then, the engine performs the stoichiometric air-fuel ratio operation while maintaining the stratified combustion mode. Thereafter, even if the first operation mode is executed and the combustion mode is switched to the uniform combustion, the air-fuel ratio of the engine has already shifted to the vicinity of the stoichiometric air-fuel ratio, and the combustion mode at the substantially same air-fuel ratio is obtained. Since the switching is performed, the torque shock at the time of switching the operation mode is effectively suppressed. On the other hand, from the first operation mode to the second operation mode
When the selection is switched to the operation mode, the engine shifts from the uniform combustion to the stratified combustion while maintaining the stoichiometric air-fuel ratio operation (substantially the same air-fuel ratio state). After that, even if the second operation mode is executed to perform the lean air-fuel ratio operation, the air-fuel ratio is changed in the same combustion mode, so that the torque shock can be reduced in this case as well.

Preferably, in the case of switching from the first operation mode to the second operation mode described above, the above-mentioned transition mode is executed immediately after the switching is selected. On the other hand, in the case of switching from the second operation mode to the first operation mode, the rich air-fuel ratio is shifted from the time point when the switching is selected to the vicinity of the air-fuel ratio at which combustion becomes unstable in the second operation mode. After performing the tailing process, the transition mode is executed.

Further, the in-cylinder injection type internal combustion engine of the present invention includes control means for appropriately controlling the ignition timing and the fuel injection timing according to the combustion mode in each operation mode. In particular, in order to prevent the generation of smoke during exhaust in the above-described transition mode, the means controls the ignition timing to the retard side and the injection timing to the advance side as viewed from the second operation mode, and controls the fuel. It is preferable to extend the time from injection to ignition.

Further, the in-cylinder injection type internal combustion engine of the present invention includes a device (EGR device) for recirculating the exhaust gas to an intake system.
This EGR device is generally equipped with N2
Although a large amount of exhaust gas recirculation is introduced into the cylinder in order to reduce Ox, it is preferable to stop the introduction of exhaust gas recirculation in order to prevent deterioration of combustion, particularly in the above-described transition mode.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a gasoline engine 1 for a vehicle is schematically shown as one embodiment of a direct injection internal combustion engine of the present invention. The engine 1 shown in FIG. 1 has, for example, an in-line four-cylinder cylinder layout, and an ignition plug 4 and a fuel injection valve 6 are attached to a cylinder head 2 for each cylinder. Each fuel injection valve 6 is arranged to inject fuel directly into the combustion chamber 8.

The engine 1 has an intake manifold 10 in an intake system, and a surge tank 12 is formed at a start end thereof. An electric opening / closing type throttle valve 14 is attached to the inlet of the surge tank 12, and an intake pipe (not shown) is connected to the throttle valve 14. Further, the engine 1 has an exhaust gas recirculation (EGR).
The exhaust system is equipped with an EGR passage 16
Is connected. One end of the EGR passage 16 opens into the exhaust port, and the other end opens into the surge tank 12. An EGR valve 18 of an electromagnetic opening and closing type is inserted in the EGR passage 16 in the middle thereof.

The engine 1 of the embodiment is equipped with an electronic control unit (ECU) 20, and the operation of various devices can be controlled using the ECU 20. That is,
The ECU 20 determines the rotational speed Ne of the engine 1 based on the crank angle pulse CA supplied from the crank angle sensor 22.
Is detected, and each spark plug 4 is synchronized with the pulse CA.
In addition, by controlling the operation of the fuel injection valve 6, the ignition timing and the injection timing can be controlled for each cylinder.

The above-described adjustment of the opening of the throttle valve 14 and the opening / closing operation of the EGR valve 18 are both controlled by the ECU 20. Note that a throttle opening sensor 24 is attached to the throttle valve 14,
U20 can detect the throttle opening TPS based on the sensor signal. Further, as a function of the ECU 20 relating to the operation control of the engine 1, the ECU 20 obtains a target average effective pressure Pe correlated to the engine load based on the detected throttle opening TPS and the engine rotation speed Ne. A predetermined operation mode can be selected based on the pressure Pe and the engine rotation speed Ne (mode selection means).

For more details on the selection of the operation mode,
The ECU 20 prepares, for example, a mode selection map (not particularly shown) defined in advance from the relationship between the target average effective pressure Pe and the engine rotation speed Ne, and the operation mode corresponding to the determination region defined on this map. Select
Specifically, when one of the target average effective pressure Pe and the engine rotation speed indicates a large value on the map,
The intake stroke injection mode (first operation mode) is selected as the operation mode. On the other hand, if any one of them shows a relatively small value, the compression stroke injection mode (second operation mode)
Is selected.

The above-described intake stroke injection mode is shown on a map.
It is further divided into a plurality of determination areas. Specifically, the intake lean mode, intake stoichiometric feedback (SF /
B) Each area of the mode and the open loop mode is included. Each of these determination regions is classified according to the air-fuel ratio to be set. In the intake lean mode, the lean air-fuel ratio (for example, 18 to 23), the stoichiometric feedback mode, the stoichiometric air-fuel ratio, and the open loop In the mode, the rich air-fuel ratio is set.

On the other hand, the air-fuel ratio in the compression stroke injection mode (compression lean mode) is an ultra-lean air-fuel ratio (for example, 25
In this compression lean mode, fuel is mainly injected during the compression stroke, and stratified combustion is performed at a lean air-fuel ratio. In addition to the function of selecting each operation mode described above, the ECU 20 actually smoothly switches the operation mode of the engine 1 when the selection is switched between these operation modes while the vehicle is running. It also has a mode switching function for operating the engine 1 in a new operation mode (mode switching means). This mode switching function is incorporated in the form of a control program in the ECU 20, and the ECU 20 switches the operation mode of the engine 1 according to the control program.

Referring to FIGS. 2 and 3, there is shown an example of a mode switching control routine executed by the ECU 20 as the above-described control program, and each mode switching procedure will be specifically described below. The control routine of FIG. 2 shows a control procedure when switching from the compression stroke injection mode to the intake stroke injection mode. Specifically, first,
In step S10, the various sensor signals described above are read, and when the target average effective pressure Pe and the engine rotation speed Ne are obtained from these sensor signals, the ECU 20 selects an operation mode from the above-described setting map.

Next, in step S12, step S10
It is determined whether or not the selection of the operation mode performed in the above corresponds to, for example, switching from the compression lean mode to the intake stoichiometric feedback mode. As a result, if the above-mentioned mode switching is not particularly satisfied (No), the ECU 20
Returns the control routine here without executing step S14. On the other hand, if the above-mentioned mode switching is applicable (Yes), the ECU 20 proceeds to step S14 and performs a predetermined mode switching process.

More specifically, in the case of switching from the compression lean mode to the intake stoichiometric feedback mode as described above, prior to the execution of a new intake stoichiometric feedback operation, the compression stroke In, a compression stoichiometric mode (transition mode) in which stratified combustion is performed at an air-fuel ratio (for example, 14 to 15) near stoichiometry including stoichiometry is executed.

The above-described compression stoichiometric mode as the mode switching process is programmed to be executed at step S22 in the control routine. In the present embodiment, however, steps S14 to S18 are preferable.
The parallel processing described above is also executed together. Referring to FIG. 4, there is shown a timing diagram of the mode switching process and its parallel process. Specifically, step S
When the above-described mode switching determination is established at 12, the ECU 2
0 performs tailing processing closed and the air-fuel ratio of the EGR valve from that point t ₁ (step S14, S16).

As shown in FIG. 4, the air-fuel ratio is gradually enriched from the time point t _{1 of the} mode switching.
GR valve 18 is closed at the time t _1. Moreover, tailing processing of the air-fuel ratio is performed until the loop of steps S16~S18 reaches a predetermined air-fuel ratio af _1. Incidentally, the specific value of the predetermined air-fuel ratio af ₁ at step S18, is set to the limit air-fuel ratio smoke generated in the exhaust (e.g., about 24) by combustion deterioration in the compression stroke injection.

The tailing process described above is completed (step S
18 = True) Then, ECU 20 proceeds to step S20, squeeze the throttle valve 14 at this time t ₂ (small throttle opening). The air-fuel ratio is switched stoichiometric or near at time t ₂ reaches a predetermined limit air-fuel ratio af _1,
Then, the time t ₂ from the above compression stoichiometric mode (Fig. 4 in one-dot chain line) is started (step S22).
At this time, it is preferable that the ECU 20 controls the operation timings of the ignition plug 4 and the fuel injection valve 6, respectively, to retard the ignition timing more than in the compression lean mode, and to advance the injection timing.

As shown in the drawing, in the above-described compression stoichiometric mode, the compression stroke injection is continuously performed, and the combustion mode is maintained in stratified combustion following the compression lean mode. At the same time as the execution of step S22, the EC
U20 activates the built-in timer counter and executes the compression stoichiometric mode until the elapse of a predetermined time is counted (loop of steps S22 to S24).

FIG. 4 shows the change in the actual EGR gas amount from the time point t ₁ when the EGR valve 18 is closed and the throttle valve 1.
The changes in the actual intake air amount from the point in time t ₂ when the throttle valve 4 is reduced are indicated by two-dot chain lines. Up to ₃ have been continued. Therefore, the predetermined time to be counted in step S24 is appropriately set in consideration of the transient characteristics of the actual EGR gas amount and the actual intake air amount.

[0026] elapse of the predetermined time is confirmed in step S24 (Yes), ECU20 is terminated compression stoichiometric mode proceeds to step S26, it executes the new intake stoichiometric feedback mode from the time t _3. Further, the injection timing is switched to the intake stroke injection. Thereafter, when the engine 1 completely shifts to the intake stoichiometric feedback operation, the ECU 20 completes all the procedures of the mode switching control routine and restarts the control routine.

Next, the control routine of FIG. 3 shows a control procedure when switching from the intake stroke injection mode to the compression stroke injection mode. In this case, the determination of the mode switching described above is performed in step S32.
It is determined whether or not the selection of the operation mode at 10 corresponds to switching from the intake stoichiometric feedback mode to the compression lean mode.

When the above-mentioned mode switching is applied (Ye
s), the ECU 20 proceeds to step S34, and at that time t
Immediately after step ₄ , the injection timing is switched to the compression stroke injection to execute the above-described compression stoichiometric mode (see FIG. 4). At this time, the operations of the ignition plug 4 and the fuel injection valve 6 are controlled in consideration of the suppression of smoke as in the case described above. In the case of the control routine of FIG. 3, when executing the mode switching process, steps S38 to S40 and step S44 are incorporated as preferable modes.

[0029] Specifically, first, at time t ₄ when started compression stoichiometric mode, ECU 20 is also executed in parallel step S36 and step S38, the performing a predetermined air-fuel ratio tailing process causes opening the throttle valve 14 .
In this case, the air-fuel ratio as shown in FIG. 4 are progressively leaner from stoichiometric, the tailing processing is performed by the loop of steps S38~S40 to reach a predetermined air-fuel ratio af _2. Further, specific values of the predetermined air-fuel ratio af ₂ is set to the limit air-fuel ratio combustion is deteriorated at the intake stroke injection (for example, about 16).

[0030] tailing process described above is completed (step S40 = true), the time t ₅ in ECU20 is terminated compression stoichiometric mode, to perform the compression lean mode proceeds to step S42. Further, the air-fuel ratio at this time t ₅ is switched to the lean air-fuel ratio. At this time, the ECU
20 executes simultaneously a step S44, to open the EGR valve 18 in switching time point t ₅ to the compression lean mode. Therefore, during execution of the compression stoichiometric mode, the EGR valve 18 is closed, and no EGR gas is introduced during this time. However, considering that there is actually a response delay of the EGR gas flow rate (two-dot chain line in FIG. 4), the mode switching time t ₅
The control routine may be modified so that step S44 is executed earlier.

Thereafter, when the engine 1 shifts to the compression lean operation, the ECU 20 completes the procedure of the switching control routine and restarts the routine. According to the mode switching process described above, in the case of switching from the compression lean mode to the intake stoichiometric feedback mode, the compression stoichiometric operation is performed within a period in which there is a response delay of the residual EGR gas amount and the intake air amount in the intake system. By executing the mode, the engine 1 realizes the stoichiometric combustion while maintaining the stratified combustion mode. Since the EGR valve 18 has already been closed at the time point t ₁ of the mode switching determination, the residual E
The GR gas does not deteriorate the combustion in the compression stoichiometric mode. Thereafter, the residual EGR gas is almost purged from the intake system, by executing the intake stoichiometric feedback mode from the time t ₃ when the amount of intake air is recovered sufficient responsive to the throttle opening degree, the engine 1 is extreme The switching of the operation mode can be completed smoothly without any torque shock.

Further, in the case of the present embodiment, by performing the tailing process of the air-fuel ratio before the start of the compression stoichiometric mode (steps S16 to S18), the torque shock when executing the compression stoichiometric mode can be reduced. When the tailing process is performed in the compression stoichiometric mode, the tailing speed may be appropriately changed according to the required operation state of the engine 1 (for example, the throttle opening, the target load Pe, the accelerator opening, and the like). At this time, by extending the time from fuel injection to ignition in accordance with the tailing process, generation of smoke is effectively suppressed.

On the other hand, when the mode is switched from the intake stoichiometric mode to the compression lean mode, the compression stoichiometric mode is immediately executed from the time point t ₄ at which the mode switching is determined, so that the engine 1 can perform an extreme change in the air-fuel ratio. It shifts to the form of stratified combustion without accompanying. Thereafter, the engine 1 can shift to the compression lean mode in a combustion mode suitable for lean air-fuel ratio combustion, and can complete the switching of the operation mode without an extreme torque shock.

[0034] In the present embodiment, the compressed air from the start t ₄ stoichiometric mode gradually by causing lean (step S38～S40), reduction and exhaust emissions deteriorate suppression of torque shock can be reduced. At this time, E
If the introduction of the GR gas is also performed, the exhaust gas characteristics can be further improved. In the above-described embodiment, only the case of switching between the compression lean mode and the intake stoichiometric feedback mode is described. However, even when switching to another mode included in the intake stroke injection mode, The invention can work effectively.

In addition, the present invention may function only when switching from one of the two operation modes to the other.

[0036]

As described above, according to the in-cylinder injection type internal combustion engine of the present invention (claim 1), the combustion mode can be switched smoothly without causing an extreme torque shock regardless of the operating conditions. Can be realized. Therefore, for example, in the case of an internal combustion engine for a vehicle, an uncomfortable feeling given to a driver is extremely reduced, and the drivability of the vehicle can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of a direct injection gasoline engine according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating an example of a mode switching control routine.

FIG. 3 is a flowchart showing a mode switching control routine different from that of FIG. 2;

FIG. 4 is a timing chart of various processes accompanying the execution of the mode switching control routine of FIGS. 2 and 3;

[Explanation of symbols]

 Reference Signs List 1 engine 6 fuel injection valve 20 ECU (mode selection means, mode switching means)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroki Tamura 5-33-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation (72) Inventor Shigeo Yamamoto 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi F-term (reference) in Automobile Industry Co., Ltd. 3G301 HA04 HA13 HA16 JA04 JA11 LA03 LB04 MA01 MA18 PA11Z PC02Z PE03Z

Claims (1)

[Claims] 1. A first operation mode in which fuel is mainly injected during an intake stroke to perform uniform combustion near a stoichiometric air-fuel ratio, and a second operation mode in which fuel is mainly injected during a compression stroke to perform stratified combustion at a lean air-fuel ratio. A mode selection unit having an operation mode, wherein one of the first and second operation modes is selected and executed according to an operation state of the internal combustion engine; and the mode selection unit mutually selects between the operation modes. Mode switching means for executing a transition mode for injecting fuel during the compression stroke and performing stratified combustion near the stoichiometric air-fuel ratio when the switching is performed, prior to the execution of the newly selected operation mode. Direct injection type internal combustion engine.