JPH1047172A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control emission of HC by making switching to the total area mixture layer when the storage quantity of the evaporated fuel exceeds the prescribed value during the operation by the limited layer in an engine provided with a mixture layer forming means to selectively switch the limited mixture layer and the total mixture layer according to the operational condition. SOLUTION: In a control unit 19 while an engine is in operation, the engine speed, the load, the cooling water temperature, etc., are read to judge the condition of stratification by the limited mixture layer based on the read data. For example, when the engine is operated in the relatively low speed and load, and after warming-up of the engine, it is judged that the condition of stratification of the mixture is established, while the homogeneous mixture layer by the total mixture layer is formed when the condition is not established. When the condition of stratification is established, the estimated value of the quantity of the evaporated fuel stored in a canister 43 is read, and compared with the set level. When the estimated value is smaller, the limited mixture layer is formed. When the estimated value is higher, the pre-mixing combustion is performed by forming homogeneous mixture layer totally in the combustion chamber without performing the stratified combustion when the estimated value is higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control apparatus for an internal combustion engine that stratifies an air-fuel mixture in a combustion chamber according to an operation state and performs lean combustion.

[0002]

2. Description of the Related Art A combustible air-fuel mixture layer is provided around an ignition plug in a combustion chamber.
A stratified combustion internal combustion engine that forms an air layer containing almost no fuel around it, that is, forms a mixture in a part of the combustion chamber and enables stable combustion even with an extremely lean mixture as a whole. For example, it is proposed in Japanese Patent Application Laid-Open No. 4-241754.

[0003] In this case, stratification of the air-fuel mixture, which is performed in a low-to-medium load region under operating conditions, involves injecting only air into the combustion chamber during an intake stroke and injecting fuel near the spark plug in the latter half of the compression stroke. This is achieved by:

In such an internal combustion engine, when fuel evaporated from a fuel tank or the like is stored in a canister so as not to diffuse into the atmosphere, and the fuel is returned from an intake passage to a combustion chamber, the evaporated fuel is premixed with air. Since the fuel is sucked into the combustion chamber, the evaporated fuel also exists in the air layer.

However, since the air-fuel ratio of this air layer far exceeds the flammability limit to the lean side, the combustion flame extinguishes without propagating to the vaporized fuel in the air layer, and the air containing the vaporized fuel remains unchanged. Is discharged outside,
This will increase the HC in the exhaust gas.

According to Japanese Patent Application Laid-Open No. Hei 5-223017, when the operating condition of the internal combustion engine is in a low / medium load region where stratified combustion is performed, the recirculation of the evaporated fuel into the intake air is stopped.
That is, a proposal has been made not to purge the fuel vapor.

[0007] By doing so, the evaporated fuel is recirculated into the intake air in a high load region where stratified combustion is not performed, and is combusted and removed.

[0008]

However, the adsorption of fuel to the canister is continued during operation, and if the operation at low / medium load where the recirculation of the evaporated fuel into the intake air is stopped is long as described above. If it takes place over time,
The fuel vapor in the canister becomes saturated, causing a problem that a part of the fuel flows back into the intake system or leaks to the outside.

In this case, even if the purging is stopped during stratified combustion, the function of suppressing the emission of HC is weakened.

According to the present invention, in order to solve such a problem, when the amount of adsorbed fuel vapor reaches a saturated state, stratified combustion with a limited mixture of fuel is temporarily stopped to temporarily stop the stratified combustion. It is an object of the present invention to switch over to combustion using a mixture (premixed combustion) and to recirculate the evaporated fuel to suppress the emission of HC.

[0011]

According to a first aspect of the present invention, there is provided a limited air-fuel mixture layer in which an air-fuel mixture is present in a partial area of a combustion chamber, and a global air-fuel mixture layer in which an air-fuel mixture is entirely present in a combustion chamber. A means for selectively switching either one of the above according to the operation state, a means for returning the fuel vapor from the fuel tank or the like to the intake system via the adsorption storage means, and a limited gas mixture layer. In an internal combustion engine having a means for stopping the return of the evaporated fuel to the intake system during operation, a means for calculating the storage amount of the evaporated fuel; And control means for switching from the limited gas mixture layer to the entire gas mixture layer when the pressure exceeds the limit.

In a second aspect of the present invention, the evaporative fuel calculating means calculates an initial value of the stored amount from at least the fuel temperature condition when the engine is stopped.

In a third aspect of the present invention, the evaporative fuel calculating means subtracts the amount of change from the stored amount when the evaporative fuel is recirculated to the intake system, and adds it when the recirculation is stopped.

According to a fourth aspect of the present invention, the switching control means for the mixture layer adjusts the amount of intake air when the mixture layer is switched, and adjusts the air-fuel ratio so as to maintain the same output torque.

According to a fifth aspect of the present invention, when the switching control means for the gas mixture layer switches from the limited gas mixture layer to the global gas mixture layer, the intake air amount is temporarily reduced to a value larger than the target value.

According to a sixth aspect of the present invention, the switching control means for the gas mixture layer determines whether or not the operating condition at the time of switching is in a region where stable combustion can be performed by any of the gas mixture layers while maintaining the same torque. And means for switching the air-fuel mixture only when in the stable combustion region.

According to a seventh aspect of the present invention, the means for forming an air-fuel mixture layer includes a fuel injection valve for directly injecting fuel into a combustion chamber, and an injection timing of the fuel injection valve between an intake stroke and a compression stroke. Switching means.

[0018]

According to the first aspect of the present invention, an air-fuel mixture layer is limitedly formed in the combustion chamber, such as in a low-to-medium-load region of the engine. As a result, stable combustion is ensured and fuel efficiency can be improved. During the operation by the stratified charge combustion, the recirculation of the fuel vapor from the fuel tank to the intake system is stopped, and the HC generated when the fuel vapor is mixed with the air layer containing almost no fuel in the stratified air-fuel mixture layer. Control emissions.

However, when the storage amount of the fuel vapor exceeds a predetermined value, the stratification of the air-fuel mixture is stopped, and the air-fuel mixture layer is formed so that the air-fuel mixture exists throughout the combustion chamber. By returning the evaporated fuel to the intake system, eliminating the saturated state of the evaporated fuel storage means, preventing the divergence of the evaporated fuel, and reliably burning the recirculated evaporated fuel as a part of the air-fuel mixture,
Reduces the production of HC.

In the second aspect of the present invention, the fuel vapor from the fuel tank is mainly stored in the storage means when the engine is stopped, and the amount of the fuel vapor increases substantially in proportion to the fuel temperature. By estimating the amount, the storage amount can be accurately calculated.

In the third aspect of the present invention, when calculating the stored amount, the fuel amount is reduced when the fuel vapor is recirculated to the intake system and is increased when the fuel recirculation is stopped. Can be calculated.

In the fourth aspect of the invention, the amount of intake air is adjusted at the time of switching the air-fuel mixture and the air-fuel ratio is adjusted so as to maintain the same output torque. Sex is maintained.

In the fifth invention, when switching from the limited air-fuel mixture layer to the entire air-fuel mixture layer, the intake air amount is temporarily reduced to a value larger than the target value, so that the switching response of the intake air amount is improved. The air-fuel ratio can converge to the target value with good response.

In the sixth aspect, the switching of the air-fuel mixture layer is performed only in a region where stable combustion is performed while maintaining the same torque, so that there is no change in combustion characteristics at the time of switching and smooth operability is ensured. .

[0025] In the seventh invention, the formation of the air-fuel mixture layer is as follows.
Switching can be achieved simply and reliably by switching the injection timing of the fuel injection valve.

[0026]

1, a throttle valve 4 for adjusting the amount of intake air is provided downstream of an air flow meter 1 for measuring the amount of intake air flowing through an intake passage 6. Is provided, and an auxiliary air control valve 3 for controlling the flow rate of the auxiliary air is interposed in the auxiliary air passage 2. Therefore, the amount of intake air taken into the engine is controlled in proportion to the opening of the throttle valve 4 and the auxiliary air control valve 3. The opening degree of the auxiliary air control valve 3 is controlled by a control unit (ECU) 19 described later in accordance with the driving situation.

A combustion chamber 10 is defined by the cylinder head 9, the cylinder block 8, and the piston 11. The combustion chamber 10 is provided with a fuel injection valve 15 for directly injecting fuel toward the vicinity of an ignition plug 16. .

Reference numeral 13 denotes an intake valve, 14 denotes an exhaust valve, and an exhaust passage 7 is provided with an air-fuel ratio sensor 17 for detecting an air-fuel ratio in exhaust gas.

The control unit 19 receives an intake air amount signal from the air flow meter 1, a rotation angle signal from a crank angle sensor 21 attached to a crankshaft, and the like. Then inject the fuel. As will be described in detail later, fuel is injected in the compression stroke of the engine in the low / medium load region of the engine operating condition, the fuel is mainly concentrated near the spark plug 16, and the combustible mixture layer near the ignitability and its surroundings With the air layer containing almost no fuel, the air-fuel mixture is limitedly present in the combustion chamber to perform stratified combustion. On the other hand, in a high load region where high output is required, fuel is injected during the intake stroke, and air and fuel are mixed and stirred in advance from the intake stroke to the compression stroke, thereby forming a mixed gas layer having a uniform concentration throughout the combustion chamber. It forms and performs premix combustion.

On the other hand, in order to guide the fuel evaporated from the fuel tank 41 to the intake passage 6, a canister 43 for temporarily storing the evaporated fuel is provided through an evaporated fuel pipe 42, and the canister 43 is evaporated to an activated carbon layer 44 of the canister 43. Adsorb fuel. The vaporized fuel adsorbed on the activated carbon layer 44 is discharged (purged) via the pipe 46 to the downstream of the throttle valve 4 together with the air taken in from the upstream of the throttle valve 4 via the pipe 45. A purge control valve 47 for adjusting the flow passage area and controlling the purge amount is provided in the middle of the passage 46.

The purge control valve 47 is operated by a signal from the control unit 19 as will be described later, and basically closes and stops purging in a low / medium load region, and opens and purges in a high load region. , Control unit 19
Is the amount of fuel vapor stored in the canister 43 (estimated value)
Exceeds a predetermined value, the purge control valve 47 is opened even in the low / medium load region to perform purging. At this time, the fuel injection timing of the fuel injection valve 15 is switched from the compression stroke to the intake stroke, and the limited mixture It switches from stratified combustion by stratified combustion to premixed combustion by a global mixture layer.

The control operations performed by the control unit 19 will be described with reference to the flowcharts of FIGS.

First, FIG. 2 shows a state where the fuel is stored in the canister 43.
A routine for estimating the amount of evaporated fuel,
In step 11, after starting the internal combustion engine, this process is executed.
Judge whether it is the first (first time), and if
If there is, in step 12 the initial value of the stored amount of fuel vapor
Is set to Qevap (Qevap = Qevap in
t). This initial value corresponds to the fuel temperature at the time of the previous engine stop.
Or as a function of its estimate. Evaporative fuel
The estimated amount is, for example, the cooling water temperature when the engine is stopped,
From the engine operation continuation time.
It is estimated that the amount of evaporated fuel will increase.

In step 13, it is determined whether or not the purge control valve 47 for discharging the fuel vapor is closed. When the purge control valve 47 is closed, it is assumed that the storage amount Qevap increases. In step 14, the increase amount ΔQevap (positive value) is used. Is estimated. The estimated amount is obtained as a function of the fuel temperature or an estimated value of the fuel temperature, and the increased amount is estimated so as to increase as the temperature increases.

On the other hand, when the purge control valve 47 is open, the stored amount decreases due to the purge. Therefore, at step 15, the purge decrease amount ΔQevap (negative value) is estimated. As this estimation method, ΔQevap is given as a function of the opening of the purge control valve 47 and the suction negative pressure, and the amount of decrease increases as the control valve opening increases and the suction negative pressure increases.

In step 16, the initial value Qev of the storage amount
The change amount ΔQevap, which is the increase or decrease amount thus obtained, is added to ap to estimate the current storage amount of the fuel vapor (Qevap = Qevap + ΔQev).
ap).

From the above, the amount of fuel vapor stored in the canister at the current stage is estimated.

Next, based on the flow chart of FIG. 3, the operation of switching the formation of the mixture layer between the case where the mixture is limited in the combustion chamber and the case where the mixture is substantially uniform over the entire area is performed. explain.

In step 21, operating conditions such as engine speed, load, cooling water temperature, etc. are read, and based on these, in step 22, the stratification condition by the limited gas mixture layer is determined. For example, if the engine is relatively slow,
And, after the engine is warmed up, it is determined that the stratification condition of the air-fuel mixture is satisfied. When the stratification condition is not satisfied, for example, in a high load region, the process proceeds to step 23, and a homogeneous mixture layer is formed by the entire mixture layer.

If the stratification condition is satisfied, step 2
In step 4, the estimated value of the amount of evaporated fuel Qevap stored in the canister 43 obtained as described above is read or estimated. Then, in step 25, this evaporated fuel amount Qevap is set to a predetermined level Lev.
If it is smaller than the predetermined level as compared with el1, the routine proceeds to step 26, where a limited mixture layer is formed.

On the other hand, when the fuel vapor amount is higher than the predetermined level, the process proceeds to step 23, even though the stratification condition of the air-fuel mixture is satisfied, and the stratified combustion is performed without performing the stratified combustion. Premixed combustion is performed by forming a homogeneous mixture layer throughout the chamber.

Here, the overall operation will be described.

Generally, as the air-fuel ratio of the air-fuel mixture burned in the combustion chamber becomes leaner, the amount of intake air required to obtain the same torque relatively increases, and the resulting reduction in pumping loss improves fuel efficiency.

In a normal gasoline engine of a type in which fuel and air are premixed and burned, the lean limit is set at around 25 in the air-fuel ratio from the viewpoint of combustion stability.
However, in the case of a type in which a combustible air-fuel mixture layer is formed in the vicinity of the spark plug and only the air layer exists around the layer, the air-fuel mixture is stratified and burned, the actual air-fuel ratio is above the lean limit. , And can be operated even at an air-fuel ratio of around 40, further improving fuel efficiency.

Therefore, in the low / medium load region, the fuel injection valve 1
By performing the fuel injection from the engine 5 in the compression stroke of the engine, most of the injected fuel is retained only in the vicinity of the ignition plug 16 to form a combustible mixture layer only in a partial region in the combustion chamber, and stratified combustion is performed. It does.

However, in the stratified combustion, even if the intake air amount is increased to the maximum, for example, during a high output operation, the generated torque is insufficient because the fuel amount is relatively small due to the relationship with the cylinder volume. I do. Therefore, in the operation region where the required load is large, the stratified charge combustion is stopped, the fuel injection from the fuel injection valve 15 is performed in the intake stroke, and in the subsequent compression stroke, the fuel is sufficiently mixed and stirred with the intake air, so that the combustion chamber 10
In the entire region, a uniform air-fuel mixture layer having an air-fuel ratio of about 22, for example, is formed, and premixed combustion is performed to secure a sufficient output.

Incidentally, most of the evaporated fuel adsorbed by the canister 43 is generated after the engine is stopped, but increases with an increase in the fuel temperature even during normal running. The fuel vapor is introduced from the canister 43 into the intake passage 6 via the purge control valve 47. Since the air-fuel ratio varies depending on the introduced state, the amount of the introduced fuel is controlled by controlling the opening degree of the purge control valve 47 by the control unit 19. By controlling according to the conditions, it is controlled appropriately.

However, in a low / medium load region where stratified combustion of the air-fuel mixture is performed, the mixing of such evaporated fuel into the intake air causes the outside of the combustible air-fuel mixture layer in the vicinity of the ignition plug 16. Evaporated fuel also exists in the air layer. However, during stratified combustion, the combustion flame does not propagate to the extremely lean air layer containing the evaporated fuel, and the amount of unburned HC emission increases. Therefore, at the time of such stratified combustion, the purge control valve 47 is closed by a signal from the control unit 19, the introduction of the evaporated fuel is stopped, and the emission amount of HC is reduced.

However, when the operating conditions for performing stratified combustion continue for a long time, the fuel vapor stored in the canister 43 cannot be released, and a saturated state is reached.
Backflow may occur during intake via the line 42. In this case, if stratified combustion is maintained, the same problem as described above occurs.

Therefore, the amount of fuel vapor stored in the canister 43 is estimated from the operating conditions and the like at that time. If the estimated value exceeds a predetermined value, even if the operating condition is a stratified combustion condition, the fuel-air mixture Is stopped, and the purge control valve 47 is opened to introduce the evaporated fuel into the intake air.

FIG. 4 shows the state at this time. The fuel vapor amount Qev stored in the canister 43 is shown in FIG.
When ap exceeds a predetermined level, the operation is switched from the operation with the limited gas mixture to the operation with the entire homogeneous gas mixture.
However, in this case, if the output torque fluctuates due to the switching, a sense of incongruity occurs in the driving characteristics.

Therefore, the opening degree of the throttle valve 4 is reduced so that the air supply ratio is switched from 40 to 22, for example, while maintaining the same fuel supply amount so that torque fluctuation does not occur before and after the switching. Alternatively, the opening degree of the auxiliary air control valve 3 is reduced. By doing so, the cylinder intake air amount decreases with a first-order lag according to the dynamics of the intake system, and the air-fuel ratio changes from 40 to 22.

Then, when the air-fuel ratio becomes 22, the fuel injection timing from the fuel injection valve 15 is advanced from the compression stroke to the intake stroke, and from the limited gas mixture layer to the entire homogeneous gas mixture layer. It is switched.

Since the fuel and air are sufficiently mixed and stirred in the combustion chamber 10, the fuel vapor introduced into the intake air from the purge control valve 47 is also sufficiently mixed, and a uniform air-fuel mixture is obtained throughout the combustion chamber. It will be surely burned. In addition, since the air-fuel ratio becomes relatively rich due to the purge of the evaporated fuel, the amount of fuel injection necessary to maintain the same air-fuel ratio may be reduced by that amount.

As described above, even if the stratified combustion operation condition is satisfied, when the storage amount of the evaporated fuel in the canister 43 exceeds a predetermined value, the stratified combustion is stopped, and the evaporated fuel is returned to the intake system. Since the premixed combustion is performed by the homogeneous mixture, the recirculated evaporative fuel is reliably burned, the HC is reduced, the saturated state of the canister 43 is eliminated, and the proper function can always be maintained.

When it is determined that the evaporated fuel stored in the canister 43 has been sufficiently purged in this way, the same fuel injection amount is maintained while the operating conditions satisfy the stratified combustion conditions. By switching the fuel injection timing at the same time as opening the throttle valve 4 (or the auxiliary air control valve 3), the mixture is switched from a homogeneous gas mixture layer over the entire area to a limited gas mixture layer, and stratified combustion at an air-fuel ratio of 40 is performed. Return to

In the above description, when switching from stratified combustion with a limited mixture mixture to premixed combustion with a homogeneous mixture, the air-fuel ratio that fluctuates during this switch is not necessarily in a favorable state from the viewpoint of exhaust performance. . Therefore,
It is desirable that the switching of the air-fuel ratio be performed as quickly as possible.

FIG. 5 shows that the opening degree of the throttle valve 4 (or the auxiliary air control valve 3) at the time of the switching is temporarily reduced as compared with FIG. The amount of air is immediately reduced, and then the opening of the throttle valve 4 is returned to the opening direction so as to reach the target amount of air.

By doing so, the response to the decrease in the intake air amount is improved, and the air-fuel ratio is switched more rapidly from the state of 40 to 22, and the time during which the air-fuel ratio is maintained at a value between these becomes shorter. The exhaust performance can be improved accordingly.

In order to perform this more accurately,
Based on the dynamics of the intake system, the throttle valve 4
It is advisable to apply phase lead compensation to the opening degree control.

In the above control, the air-fuel ratio is from 40 to 2
When the fuel injection timing is switched to 2, the fuel injection timing is switched,
Although the method of forming the air-fuel mixture layer is switched, the air-fuel ratio band that enables stable combustion based on the operating conditions is set programmatically for each of the entire air-fuel mixture layer and the limited air-fuel mixture layer. Alternatively, the mixture formation method can be switched only when there is an overlapping air-fuel ratio on that zone.

In this case, the fuel injection timing is switched based on the fact that the operating condition has shifted to the air-fuel ratio band in which stable combustion can be performed by the changed air-fuel mixture forming method.

In this way, the switching of the air-fuel mixture formation method is performed only in a state in which stable combustion occurs regardless of the air-fuel mixture.
The output torque does not fluctuate and the smooth running characteristics are maintained.

In the above description, the method of forming the air-fuel mixture is switched by changing the injection timing from the fuel injection valve 15 provided in the combustion chamber 10. However, the present invention is not limited to this. It does not prevent adoption of a known method such as controlling the intake air flow and stratifying the air-fuel mixture in the combustion chamber.

As for the formation of the entire mixture layer, the mixture may be stratified such that a rich mixture exists near the spark plug and a lean mixture exists around the spark plug.
It is not always necessary to form a homogeneous mixture in the entire combustion chamber.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart showing an operation for estimating the amount of evaporated fuel.

FIG. 3 is a flowchart showing a switching control operation of the air-fuel mixture forming method.

FIG. 4 is a timing chart showing operation characteristics of the control operation.

FIG. 5 is a timing chart showing operation characteristics of a control operation according to another embodiment.

[Explanation of symbols]

 Reference Signs List 3 auxiliary air control valve 4 throttle valve 6 intake passage 10 combustion chamber 15 fuel injection valve 16 spark plug 19 control unit 41 fuel tank 43 canister 47 purge control valve

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location F02D 41/02 330 F02D 41/02 330J 330F

Claims (7)

[Claims] An air-fuel mixture layer in which a mixture is present in a partial area of a combustion chamber and a gas-air mixture layer in which an air-fuel mixture is present in a whole area of a combustion chamber are selected according to operating conditions. Means for selectively switching the mixture gas layer; means for returning the fuel vapor from the fuel tank or the like to the intake system via the adsorption storage means; and means for returning the fuel vapor to the intake system when operating with the limited gas mixture layer Means for calculating the storage amount of the evaporative fuel, and when the storage amount of the evaporative fuel exceeds a predetermined value during operation with the limited air-fuel mixture layer, a limited air-fuel mixture layer And a control means for switching from an air-fuel mixture to an entire air-fuel mixture layer. 2. The control device for an internal combustion engine according to claim 1, wherein said evaporative fuel calculating means calculates an initial value of the storage amount from at least a fuel temperature condition when the engine is stopped. 3. The control device for an internal combustion engine according to claim 1, wherein said evaporative fuel calculating means subtracts the amount of change from the stored amount when the evaporative fuel is recirculated, and adds it when the evaporative fuel is stopped. 4. The internal combustion engine according to claim 1, wherein the switching control of the air-fuel mixture layer adjusts the amount of intake air at the time of switching the air-fuel mixture and adjusts the air-fuel ratio so as to maintain the same output torque. Control device. 5. The air-fuel mixture switching control means according to claim 1 or 4, wherein when switching from the limited air-fuel mixture layer to the entire air-fuel mixture layer, the intake air amount is temporarily reduced to a value larger than the target value. Internal combustion engine control device. 6. A means for controlling the switching of the air-fuel mixture to determine whether the operating condition at the time of the switching is in a region where stable combustion can be performed by any of the air-fuel mixtures while maintaining the same torque. Means for switching the gas mixture only when in the stable combustion region.
3. The control device for an internal combustion engine according to claim 1. 7. A fuel supply system comprising: a fuel injection valve for directly injecting fuel into a combustion chamber; and means for switching the injection timing of the fuel injection valve between an intake stroke and a compression stroke. The control device for an internal combustion engine according to any one of claims 1 to 6, including: