JP2003129848A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine which carries out a spark ignition operation by the spark-ignition combustion in the high-speed high-load operation range and a compression ignition operation by the compression ignition combustion in the low-speed low-load driving range, wherein a switch from the spark ignition operation to the compression ignition operation can be executed without deteriorating the combustibility. SOLUTION: The switch from the spark ignition operation to the compression ignition operation is carried out in the operating range whose required temperature in a cylinder to the compression ignition is lower than that at the switch from the compression ignition operation to the spark ignition operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine capable of switching between operation by spark ignition combustion and operation by compression ignition combustion.

[0002]

2. Description of the Related Art An internal combustion engine capable of switching between compression ignition combustion, which provides excellent fuel efficiency and exhaust composition by lean combustion, and spark ignition combustion, which easily obtains high output, is provided.
For example, it is proposed by Japanese Patent Laid-Open No. 2000-220458. An issue in operation control in such a combined combustion engine is how to smoothly switch between different combustion states of spark ignition combustion and compression ignition combustion, or how to make these combustion systems compatible.

It is necessary to secure a certain compression ratio for compression ignition, but a high compression ratio causes abnormal combustion such as knocking in premixed combustion. As a measure against this, suppression of the intake air amount and retardation of the ignition timing result in a decrease in specific output and diminish the characteristics of the spark ignition system. on the other hand,
In order to enable compression ignition while setting a relatively low compression ratio that allows appropriate spark ignition combustion, as disclosed in JP-A-10-252512, a variable valve operating device is disclosed. Therefore, it is conceivable to apply the method of advancing the exhaust valve closing timing to maintain the in-cylinder temperature high by the internal EGR.

However, since the variable valve operating device generally operates mechanically by a hydraulic or electromagnetic drive system, it takes several cycles to switch the valve opening / closing timing, and this delay causes the combustion system. It becomes a problem when trying to switch. That is, if the internal EGR amount is increased in advance before combustion switching as a countermeasure against this delay, there is a possibility that knocking may occur due to spark ignition combustion during that period. On the contrary, if the increase of the internal EGR amount is delayed,
When the transition to compression ignition combustion occurs, the in-cylinder temperature becomes insufficient and combustion becomes unstable, resulting in a significant inoperability.

The present invention has been made by paying attention to such a conventional problem, and an object thereof is combustion instability when switching from spark ignition combustion operation to compression self-ignition combustion operation in a low load operation region. Another object is to provide an internal combustion engine that can switch stably while suppressing the occurrence of knocking. It is another object of the present invention to provide an internal combustion engine that can stably switch to compression self-ignition combustion while suppressing the occurrence of knocking even when a variable valve mechanism having a high responsiveness is used.

[0006]

According to a first aspect of the present invention, a rotational speed and a load are detected as an engine operating state, a spark ignition operation by spark ignition combustion is performed in a relatively high speed and high load operating region, and a relatively low speed operation is performed. In an internal combustion engine that performs compression ignition operation by compression ignition combustion in a low load operation region, switching from spark ignition operation to compression ignition operation is more efficient than switching from compression ignition operation to spark ignition operation. It was designed to be performed in the operating region where the temperature required for in-cylinder ignition is lower.

In a second aspect of the invention, the cooling water temperature of the engine is detected as the operating state, and when the detected water temperature is equal to or higher than a predetermined value, switching from the spark ignition operation to the compression ignition operation is allowed. .

In a third aspect of the present invention, the lubricating oil temperature of the engine is detected as the operating state, and when the detected oil temperature is a predetermined value or more, switching from the spark ignition operation to the compression ignition operation is allowed. did.

A fourth invention is the same as the first invention,
A variable valve operating device for controlling the opening / closing state of the intake valve or the exhaust valve of the engine is provided, and the valve opening / closing timing is controlled at the time of transition from the spark ignition operation to the compression ignition operation.

A fifth aspect of the invention is the same as the fourth aspect of the invention.
At the time of transition to compression ignition operation, by the variable valve device,
By controlling the closing timing of the exhaust valve and delaying the opening timing of the intake valve to set a minus overlap, control is performed so that the residual gas in the cylinder increases. The internal combustion engine according to claim 4.

In a sixth aspect of the invention, the minus overlap amount of the fifth aspect of the invention is set to be larger as the engine load is lower.

A seventh invention is the same as the first invention,
Depending on the operating state, a period during which spark ignition is continued even after the transition to compression ignition operation is provided.

[0013]

According to each of the following inventions,
Since the switching from the spark ignition operation to the compression ignition operation is performed in the operation region in which the required temperature is relatively low in the compression ignition combustion, it is possible to avoid the problem that the combustion becomes unstable during the switching. On the other hand, the transition from the compression ignition operation to the spark ignition operation is performed in the operating region where the in-cylinder required temperature is higher,
That is, since it is possible to operate from a lower speed or a lower load operation range, it is possible to sufficiently secure output performance during acceleration or the like.

According to the second or third aspect of the present invention, by determining whether or not the compression ignition operation is possible based on the water temperature or the oil temperature in the spark ignition operation area, the compression ignition operation is started from the spark ignition operation area even when the engine is started. When moving to the operating area,
It is possible to switch the combustion method without causing unstable combustion.

According to the fourth aspect of the invention, the temperature in the cylinder can be controlled by controlling the opening / closing timing of the intake / exhaust valve in the compression ignition operation region, that is, the required temperature for stabilizing the compression ignition operation is controlled by the valve. It can be adjusted by controlling the opening and closing timing. Further, according to the fifth aspect of the invention, since the minus overlap region is set for the opening / closing timing of the intake / exhaust valve, the temperature in the cylinder can be made extremely high by the internal EGR, whereby the compression ignition combustion is performed. It becomes possible to switch the combustion system from spark ignition to compression ignition under conditions where the required temperature for stable operation is extremely high. Further, according to the sixth aspect of the present invention, when shifting to the compression ignition operation, the minus overlap amount of the intake and exhaust valves is set to be larger as the load is lower, so that the compression ignition is performed at a low load. When the required temperature for stable combustion is extremely high,
Appropriate in-cylinder temperature control can be performed corresponding to the case where the required temperature for stably operating the compression ignition combustion at a high load is low. In addition, since the minus overlap amount can be minimized, that is, the valve variable amount when shifting from spark ignition operation to compression ignition operation can be minimized, the combustion method can be switched in a state where combustion stability is further enhanced. You can

According to the seventh aspect of the invention, the spark ignition is continued for a certain period of time, for example, at an extremely low temperature when it is judged that the compression ignition becomes unstable after the transition from the spark ignition operating region to the compression ignition operating region. It is possible to assist the start of combustion, which makes it possible to stably continue the subsequent operation by compression ignition combustion.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an embodiment of an internal combustion engine according to the present invention. 1 in the figure is a piston,
2 is a combustion chamber, 3 is a fuel injection valve for directly injecting fuel into the cylinder, 4 is an intake passage, 5 is an intake valve, 6 is an exhaust passage, 7 is an exhaust valve, 8 is an ignition plug, 9 is an intake valve 6 Or exhaust valve 7
The variable valve device 10 for controlling the opening / closing operation of the fuel injection valve 10 controls the fuel injection by the fuel injection valve 3, the ignition by the spark plug 8, and the opening / closing operation of the intake valve 5 or the exhaust valve 7 by the variable valve device 9 according to the operating state. It is a controller that controls. 1
Reference numerals 1, 12, and 13 are a rotation speed sensor, a load sensor, and a temperature sensor, respectively, which output an engine speed signal, a load signal, and a cooling water temperature (or lubricating oil temperature) signal to the controller 10 as operation state signals. The load detected by the load sensor 12 is an accelerator pedal operation amount, a throttle valve opening degree, a fuel supply amount, or the like.

The fuel injection valve 3 receives fuel from a fuel injection pump (not shown) and injects it into the combustion chamber 2.
The fuel injection is performed during the intake stroke during the spark ignition operation, and the injected fuel at this time forms a combustible mixture together with the fresh air from the intake passage 4 to perform premixed combustion by spark ignition. In addition, during compression ignition operation, injection is started at the end of the compression stroke, and the injected fuel at this time undergoes diffusion combustion by compression self-ignition.

The controller 10 is constructed as a microcomputer including a CPU and its peripheral devices, and switches between the spark ignition operation and the compression ignition operation described above in accordance with the detected operation state. For this reason, the controller 10 determines the combustion pattern determination unit 10a that determines whether to perform the spark ignition operation or the compression ignition operation according to the operation conditions, and the control parameters for the spark ignition operation. Spark ignition combustion control unit 10b, and compression ignition combustion control unit 1 that determines control parameters during compression ignition operation
0c and.

Combustion pattern determination unit 1 of controller 10
At 0a, the operating region is determined from the engine speed and the load by referring to a map in which the spark ignition operating region and the compression ignition operating region are allocated as shown in FIG. In this case, as shown in the figure, the compression ignition operation is basically performed in the operation range of medium speed to medium load or less, and the spark ignition operation is performed in the operation range in which the load or the rotation speed is higher than that. However, as will be described later in detail, in the process of shifting from spark ignition operation to compression ignition operation, the in-cylinder required temperature for compression ignition is low, that is, the combustion state is switched in an operating region where self-ignition is easier, and then Change the opening / closing timing of the intake / exhaust valve to ensure combustion stability after the transition to compression ignition operation.

The spark ignition combustion control unit 10b is used in the spark ignition operation region, and the compression ignition combustion control unit 1 is used in the compression ignition operation region.
0c calculates the fuel injection amount, the injection timing, and the opening / closing timing of the intake valve 5 and the exhaust valve 7 according to the operating state, and controls the injection valve 3 and the variable valve operating device 9 based on the result. The calculation method of the fuel injection amount and the injection timing is arbitrary. For example, for the injection amount, a basic fuel injection amount is determined by a map search based on the intake air amount and the engine speed, and the basic fuel injection amount is determined by the cooling water temperature and the start correspondence. The control amount is corrected if necessary.

FIG. 3 is a flow chart showing a combustion control processing routine executed by the controller 10. This processing routine is repeatedly executed at regular intervals. In the following description and the figures, the numbers with the reference symbol S represent processing step numbers. Hereinafter, this control will be described step by step.

First, in S1, various parameters are detected as the engine operating state, in this case, the engine speed signal from the speed sensor 11, the load signal from the load sensor 12, and the temperature signal from the temperature sensor 13. In S2, the engine cooling water temperature or the lubricating oil temperature is determined from the temperature signal, and when it is less than the reference value, the process proceeds to S3 regardless of the operating region, and the spark ignition combustion operation is performed. During the spark ignition combustion operation, as described above, the premixed air is supplied to the engine to be ignited and burned by the spark plug 8. The opening / closing timing of the intake valve 5 and the exhaust valve 7 at this time is set by the variable valve operating device 9 so as to appropriately cause the valve overlap as shown in FIG.

When it is determined in S2 that the detected temperature is equal to or higher than the reference value, the operation proceeds to S4 and the operating region is determined. This determination is made based on the detected rotation speed N and load T by referring to a map set in advance as shown in FIG. At this time, if it is in the compression ignition region, the process proceeds to S5 and the compression ignition operation is performed. During the compression ignition operation, fuel is injected and supplied from the injection valve 3 during the compression stroke to cause self-ignition combustion. At this time, the opening / closing timing of the intake valve 5 and the exhaust valve 7 is set to a minus overlap as shown in FIG. 4, in which the intake valve 5 is opened after the exhaust valve 7 is closed. The minus overlap amount is set to increase as the load or the rotation speed decreases, as shown in the figure. Thus, the residual gas is appropriately secured in the combustion chamber 2, the combustion temperature is kept high, and stable compression ignition combustion with a relatively low compression ratio is possible.

On the other hand, when it is determined in S4 that it is in the spark ignition region, it is then determined in S6 whether or not the change amount of the rotation speed N or the load T is moving to the compression ignition region. This is determined to shift to the compression ignition region when, for example, the amount of reduction in the number of revolutions or the load near the boundary of the operating region in FIG. 2 is equal to or greater than a predetermined reference value. When the transition to the compression ignition region is not determined in the determination of S6, the spark ignition of S3 is continued, while when the transition to the compression ignition region is determined, the control of the compression ignition of S5 is performed at that time. To do.

According to the above-described control, the transition from the spark ignition operation to the compression ignition operation is started in a region where the required temperature is low in which the fuel easily self-ignites, so that the compression ignition combustion during the transition is stably started. It is possible to compensate for the time delay required for switching the timing of the intake and exhaust valves during this time, and to smoothly shift to the compression ignition operation. FIG. 5 shows the relationship between the engine load or engine speed and the in-cylinder required temperature for compression ignition. As shown in the figure, the lower the load and the lower the engine speed, the higher the required temperature, that is, the fuel is self-contained. It becomes difficult to ignite. Therefore, as shown in FIG. 6, the combustion unstable region due to compression ignition is omnipresent on the low speed / low load side. In the present invention, as described above, the spark ignition is switched to the compression ignition during the operation state in which the required temperature is low, and since the compression ignition operation is performed before entering the unstable combustion region, the compression ignition operation is performed. Combustion deterioration due to the transition can be avoided. However, since the transition from compression ignition operation to spark ignition operation can be performed from a lower load or engine speed range as necessary, it is sufficient to quickly transition to spark ignition operation during sudden acceleration. It is possible to exert output performance.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of an internal combustion engine according to the present invention.

FIG. 2 is an explanatory diagram of a spark ignition region and a compression ignition region.

FIG. 3 is a flowchart showing the control contents of the embodiment.

FIG. 4 is an explanatory diagram related to switching of opening / closing timings of intake / exhaust valves according to operating regions.

FIG. 5 is an explanatory diagram showing a relationship between a load or a rotation speed of an engine and a required temperature in a cylinder for compression ignition.

FIG. 6 is an explanatory diagram regarding a combustion unstable region during compression ignition operation.

[Explanation of symbols]

1 piston 2 combustion chamber 3 Fuel injection valve 4 Intake passage 5 intake valve 6 exhaust passage 7 exhaust valve 8 spark plugs 9 Variable valve device 10 controller 11 Speed sensor 12 Load sensor 13 Temperature sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02D 43/00 F02D 43/00 301Z 45/00 312 45/00 312H 312Q F term (reference) 3G023 AA01 AA02 AA06 AB06 AC02 AC04 AG02 3G084 BA11 BA16 BA23 CA03 CA04 CA09 DA04 EB08 EC01 EC03 FA18 FA20 FA33 3G092 AA01 AA02 AA06 AA09 AA11 AB02 BA08 DA08 EA03 EA04 EA16 LA08 KA08 KA08 KA08 KA08 ZA08 HO08Z0824 NC02 PA17Z PE01Z PE08Z

Claims (7)

[Claims] Claim: What is claimed is: 1. The engine speed is detected as the engine speed and the load. The spark ignition operation is performed by spark ignition combustion in a relatively high speed and high load operation area, and the compression ignition combustion is performed in a relatively low speed and low load operation area. In an internal combustion engine that is designed to perform compression ignition operation, switching from spark ignition operation to compression ignition operation is performed in a region where the cylinder temperature required for compression ignition is lower than when switching from compression ignition operation to spark ignition operation. An internal combustion engine characterized by being carried out in. 2. The internal combustion engine according to claim 1, wherein a cooling water temperature of the engine is detected as the operating state, and when the detected water temperature is equal to or higher than a predetermined value, switching from the spark ignition operation to the compression ignition operation is permitted. . 3. The lubricating oil temperature of the engine is detected as the operating state, and when the detected oil temperature is equal to or higher than a predetermined value, switching from the spark ignition operation to the compression ignition operation is permitted. Internal combustion engine. 4. A variable valve device for controlling the opening / closing state of an intake valve or an exhaust valve of an engine, wherein the valve opening / closing timing is controlled at the time of transition from the spark ignition operation to the compression ignition operation. Internal combustion engine described. 5. A residual gas in a cylinder is set by setting the minus overlap by advancing the closing timing of the exhaust valve and delaying the opening timing of the intake valve by the variable valve operating device when shifting to the compression ignition operation. The internal combustion engine according to claim 4, wherein the internal combustion engine is controlled so as to increase. 6. The internal combustion engine according to claim 5, wherein the minus overlap amount is set to be larger as the engine load is lower. 7. The internal combustion engine according to claim 1, wherein a period during which spark ignition is continued after the transition to the compression ignition operation is provided in accordance with the operating state.