JP2002242710A - Lean-burn engine for automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent variation in torque due to variation in air/fuel ratio if the air/fuel ratio is varied depending on whether the engine is old or hot. SOLUTION: In this engine, the air/fuel ratio in a low-speed and low-load region of the engine is lean when the engine is hot; when the engine is cold, the air/fuel ratio is rich so that it is equal to or less than a stoichiometric air/fuel ratio. The engine is provided with valve timing changers 13 and 14 and a valve timing control means 44 for controlling the changers. Valve timing is controlled so that the closing timing of an intake valve in the low-speed and low-load region when the engine is cold is set at a delay side where the efficiency of charging intake decreases, in relation to the closing timing of the intake valve when the engine is hot.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lean burn for an automobile in which a set air-fuel ratio in a low-speed low-load region of an engine is set to be larger than a stoichiometric air-fuel ratio when the engine is warm and is equal to or lower than the stoichiometric air-fuel ratio when the engine is cold. It is about the engine.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Unexamined Patent Publication No.
As disclosed in Japanese Patent Application Publication No. 6-64, the air-fuel ratio is controlled so as to be leaner than the stoichiometric air-fuel ratio in a low-speed low-load range in order to improve fuel efficiency, and NOx is generated in the exhaust passage even when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio. Providing a NOx catalyst having purification performance,
There is known an engine capable of performing lean burn operation while reducing NOx emission.

Further, as disclosed in Japanese Patent Application Laid-Open No. 10-274085, for example, NOx which absorbs NOx in an oxygen-excess atmosphere and releases NOx as the oxygen concentration decreases.
In a lean burn engine having a catalyst in an exhaust passage and an injector for directly injecting fuel into a combustion chamber, when a NOx storage amount of a NOx catalyst increases, CO as a reducing agent in exhaust gas is increased. By controlling the fuel injection to the NOx catalyst,
2. Description of the Related Art There is known an exhaust gas purifying apparatus that emits x and reduces x.

[0004]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. Hei 8-12
In a lean-burn engine such as that disclosed in Japanese Patent No. 8346, the air-fuel ratio is usually lean in a low-speed low-load region when the engine is warm, but when the engine is poorly vaporized and atomized, the combustion is stable when the engine is cold. The air-fuel ratio is set to the stoichiometric air-fuel ratio or richer in the low-speed low-load region in order to avoid deterioration of the performance. Therefore, if the intake air amount is the same at the same accelerator opening at the same accelerator opening between the cold time and the warm time, a difference occurs in the torque due to the difference in the fuel supply amount according to the difference in the air-fuel ratio. Even when driving with the accelerator opening, there is a problem that the driver feels a drop in torque when the vehicle shifts from cold to warm.

To solve such a problem, if the throttle valve provided in the intake passage is electrically controllable, the throttle valve is controlled to change according to the difference in the air-fuel ratio. Although it is conceivable to adjust the torque, such a method cannot be adopted with a throttle valve mechanically connected to an accelerator pedal.

When the NOx storage amount of the NOx catalyst increases, CO as a reducing agent in the exhaust gas is increased to perform a process of releasing NOx from the NOx catalyst (release and reduction of NOx). In the case where the air-fuel ratio is changed during the NOx release processing, a problem of torque fluctuation also occurs.
As described in Japanese Patent Application Laid-Open Publication No. H10-209, if a method of performing fuel injection in the expansion stroke is adopted, fuel economy is likely to deteriorate.

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention is to effectively prevent a torque difference due to a difference in air-fuel ratio when the air-fuel ratio is changed between when the engine is cold and when the engine is warm. It is intended to provide a lean burn engine for an automobile which can perform the following.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to an automotive vehicle in which a set air-fuel ratio in a low-speed low-load region of an engine is set to be larger than a stoichiometric air-fuel ratio when the engine is warm and lower than the stoichiometric air-fuel ratio when the engine is cold. In lean burn engines,
A variable valve timing device capable of changing the opening / closing timing of the intake valve; and a variable valve timing control means for controlling the variable valve timing device in accordance with an operating state and a temperature state of the engine. The intake valve closing timing when the engine is cold in the low load range is set to a delay side where the intake charging efficiency decreases with respect to the intake valve closing timing when the engine is warm with the same accelerator opening degree. It is.

According to the present invention, in the low-speed and low-load region of the engine, the fuel efficiency is improved by making the air-fuel ratio lean when the engine is warm, while the air-fuel ratio is made lower than the stoichiometric air-fuel ratio when the engine is cold. The intake valve closing timing is adjusted so that the intake charge efficiency is reduced while ensuring combustion stability. This allows
The intake air amount is adjusted so as to reduce the torque difference with respect to the difference in the air-fuel ratio between the cold state and the warm state.

[0010] In the present invention, it is preferable that the intake valve opening timing when the engine is cold in the low-speed low-load region is delayed with respect to the intake valve opening timing when the engine is warm with the same accelerator opening degree. In this way, the overlap of the valve opening periods of the intake and exhaust valves does not increase when the engine is cold, and the combustion stability during cold is ensured.

In addition to the above configuration, a NOx catalyst that absorbs NOx in an oxygen-excess atmosphere and releases NOx as the oxygen concentration decreases is provided in the exhaust passage. At the time of transition from a value larger than the air-fuel ratio to a value equal to or less than the stoichiometric air-fuel ratio, the intake valve closing timing is changed to a delay side where the intake charging efficiency is reduced, and
At least during this transition, it is preferable to set the exhaust valve closing timing defined at the transition point from the acceleration section to the constant velocity section in the exhaust valve cam lift characteristic before the intake top dead center.

In this manner, when the lean operation state is established, NOx in the exhaust gas is absorbed by the NOx catalyst, and when the air-fuel ratio is changed from a value larger than the stoichiometric air-fuel ratio to a value equal to or lower than the stoichiometric air-fuel ratio. NOx from NOx catalyst
Is released and reduced to refresh the NOx catalyst. When the air-fuel ratio is changed from a value greater than the stoichiometric air-fuel ratio to a value equal to or lower than the stoichiometric air-fuel ratio, the action of adjusting the torque by delaying the intake valve closing timing is obtained. Is set before the intake top dead center, NOx is reduced by so-called internal EGR, and N
The effect of promoting the release and reduction of NOx from the Ox catalyst is obtained.

Further, a variable valve timing device is provided for each of the intake valve and the exhaust valve, and the valve timing control means controls the variable valve timing device for the exhaust valve in addition to controlling the variable valve timing device for the intake valve. It is preferable to perform control and set the exhaust valve closing timing after the intake top dead center in a low-speed low-load region when the engine is cold.

With this configuration, when the engine is cold, the internal EGR is reduced, and the combustion stability is improved.

Further, the present invention provides a method for producing NOx in an oxygen-excess atmosphere.
In the exhaust passage, a NOx catalyst that releases NOx as the oxygen concentration is reduced by absorbing oxygen is provided, and the air-fuel ratio is made larger than the stoichiometric air-fuel ratio in a low-speed low-load region to perform a lean operation, and at a specific time. Valve opening / closing timings for an intake valve and an exhaust valve in a vehicle lean burn engine that performs a NOx release process of releasing NOx from a NOx catalyst by changing an air-fuel ratio from a lean operation state to a stoichiometric air-fuel ratio or less. And a valve timing control means for controlling the variable valve timing apparatus. The valve timing control means is provided with a cam valve lift for the exhaust valve when starting the NOx release process from the lean operation. The emission defined at the point of transition from the acceleration section to the constant speed section in the characteristics The valve timing is variable so that the valve closing timing is a predetermined period before the intake top dead center, and the intake valve opening timing defined by the transition point from the constant speed section to the acceleration section in the intake valve cam lift characteristic is after the intake top dead center. The device is controlled.

According to the present invention, when the NOx releasing process is performed, the so-called internal EGR is increased by the control of the valve timing, so that the NOx is reduced, and the action of promoting the release and reduction of the NOx from the NOx catalyst is obtained.

In the present invention, at least the variable valve timing device for the intake valve is a phase type variable valve timing device capable of changing the opening / closing timing while keeping the valve opening period constant. When it is set to be after the point, it is preferable that the intake valve closing timing be a late timing that causes a decrease in the intake charging efficiency.

In this way, at the start of the NOx release process, the air-fuel ratio is enriched from lean to the stoichiometric air-fuel ratio, but the intake air amount is adjusted so as not to cause a sudden change in the silk.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 schematically shows the overall structure of a four-stroke engine for an automobile to which the present invention is applied.
In this figure, reference numeral 1 denotes an engine body, which has a plurality of cylinders, each of which has a combustion chamber 5 formed above a piston 4 inserted into a cylinder bore. An intake port 7 and an exhaust port 8 are opened in the combustion chamber 5, and these ports 7, 8 are opened and closed by an intake valve 9 and an exhaust valve 10.

The intake valve 9 and the exhaust valve 10 are opened and closed by a valve operating mechanism including camshafts 11 and 12 and the like. The valve mechanism for the intake valve 9 and the valve mechanism for the exhaust valve 10 are respectively provided with variable valve timing devices 13 and 14 that can change the valve opening / closing timing. The variable valve timing devices 13 and 14 are provided between a cam pulley and a camshaft interlocking with the crankshaft, and change the phase of the camshaft with respect to the crankshaft, thereby keeping the valve opening period constant and the opening timing and time. The closing time can be changed. Since various types of such variable valve timing devices 13 and 14 have been conventionally known, illustration and description of a specific structure will be omitted.

At the center of the combustion chamber 5, a spark plug 16
And the plug tip faces the combustion chamber. Further, the tip of the injector 18 faces the combustion chamber 5 from the side, and fuel is directly injected from the injector 18 into the combustion chamber 5.

An intake passage 20 and an exhaust passage 30 are connected to the engine body 1. In the intake passage 20, an air cleaner 21, an air flow sensor 22, a throttle valve 23 and a surge tank 24 are arranged in this order from the upstream side.
Is provided. The throttle valve 23 is mechanically connected to an accelerator pedal (not shown), and is opened to an opening corresponding to the accelerator pedal depression amount. A throttle opening sensor 25 for detecting the opening of the throttle valve 23 is provided.

The exhaust passage 30 is provided with an O ₂ sensor 31 for detecting the air-fuel ratio by detecting the concentration of oxygen in the exhaust gas.
2 are provided. The NOx catalyst 32 has NOx purification performance even in a lean operation state in which the air-fuel ratio is larger than the stoichiometric air-fuel ratio. The NOx catalyst 32 absorbs NOx in exhaust gas in an oxygen-excess atmosphere, and the air-fuel ratio shifts from lean to rich. NOx absorbed when oxygen concentration decreased due to change
And NOx is reduced by a reducing agent such as CO present in the atmosphere.

More specifically, the NOx catalyst 3
Reference numeral 2 denotes a structure in which a NOx absorbent layer and a catalyst layer are formed in layers on a support made of, for example, a cordierite honeycomb structure.
Component and a Ba component as a NOx absorbent are composed as a main component, and the catalyst material layer is mainly composed of a catalyst material obtained by supporting a Pt component and a Rh component on a zeolite as a supporting base material. Is configured as

Reference numeral 40 denotes a control unit (ECU) for controlling the engine. The ECU 40 includes the air flow sensor 22, the throttle opening sensor 25, and O _2.
A signal from the sensor 31 is input, a crank angle signal for detecting an engine rotation speed and the like is input from a crank angle sensor 35, and a signal from a water temperature sensor 36 and the like for detecting the temperature of engine cooling water is also input. ing.

The ECU 40 outputs a signal for controlling the fuel injection to the injector 18 and outputs a signal for controlling the same to the variable valve timing devices 13 and 14.

The above-mentioned ECU 40 is provided with an operating state determining means 4.
1. It includes a temperature state determination unit 42, a fuel injection control unit 43, and a valve timing control unit 44. The operating state determining means 41 includes an engine speed detected by measuring a cycle of a crank angle signal from the crank angle sensor 35, the air flow sensor 22, the throttle opening sensor 2 and the like.
The operating state of the engine is determined on the basis of the engine load checked by a signal from 5 or the like.

The temperature state discriminating means 42 includes a water temperature sensor 36
, It is determined whether the engine cooling water temperature is lower than the predetermined temperature or not.

The fuel injection control means 43 controls the fuel injection amount and the injection timing according to the engine operating state determined by the operating state determining means 41 and the engine temperature determined by the temperature state determining means 42. When the engine is cold, control is performed based on the cold map shown in FIG. 2A, and when the engine is warm, control is performed based on the warm map shown in FIG. 2B.

That is, when the engine is warm, FIG.
As shown in (b), a low-speed and low-load region where the load is equal to or lower than a predetermined load and equal to or lower than a predetermined engine speed is defined as a lean operation region A. In this lean operation region A, the air-fuel ratio is set to be leaner than the stoichiometric air-fuel ratio (excess air ratio). While λ is set to λ> 1), the fuel injection amount and the injection timing are controlled such that the fuel is injected in the latter half of the compression stroke, so that the air-fuel mixture is unevenly distributed around the ignition plug 16 to perform stratified combustion. On the other hand, in the region B other than the lean operation region, the air-fuel ratio is set to be equal to or lower than the stoichiometric air-fuel ratio (the excess air ratio λ is λ ≦ 1).
= 1) and inject fuel in the intake stroke to diffuse the air-fuel mixture and perform uniform combustion.
The fuel injection amount and the injection timing are controlled.

Also, when the engine is cold, as shown in FIG. 2 (a), the air-fuel ratio is kept below the stoichiometric air-fuel ratio (λ
.Ltoreq.1), the fuel injection amount and the injection timing are controlled such that the fuel mixture is diffused by injecting fuel in the intake stroke to perform uniform combustion.

The valve timing control means 44 changes the opening / closing timing of the intake valve and the exhaust valve according to the engine operating state determined by the operating state determining means 41 and the engine temperature determined by the temperature state determining means 42. The variable valve timing devices 13 and 14 are controlled as described above. The outline of the control of the valve timing will be described with reference to FIGS.

FIG. 3 shows a cam lift curve for indicating the opening / closing timing of the intake / exhaust valve.
ExV means an exhaust valve. InO and InC are the opening and closing times of the intake valve, and ExO and ExC are the opening and closing times of the exhaust valve. Here, the opening timings InO and ExO of the intake valve and the exhaust valve are defined by a transition point from a constant speed section to an acceleration section in the cam lift characteristic,
The closing timings InC and ExC of the intake valve and the exhaust valve are defined at the transition point from the acceleration section to the constant speed section in the cam lift characteristic (see FIG. 4).

In FIG. 3, when the intake valve is advanced most in the opening / closing timing variable range, the opening timing InO is slightly before the intake top dead center TDC and the closing timing InC is as shown by the broken line.
Is a little later than the intake bottom dead center BDC, and this is a timing advantageous for increasing the intake charging efficiency in the low speed range. on the other hand,
When the intake valve is most retarded within the opening / closing timing variable range, as shown by the solid line, the opening timing InO is after the intake top dead center TDC (preferably 30 ° or more after the intake top dead center), and the closing timing InC. Is much later than the intake bottom dead center BDC, and the timing at which the charging efficiency is reduced due to the occurrence of the blowback of the intake air.

When the exhaust valve is most advanced within the opening / closing timing variable range, the closing timing ExC is much earlier than the intake top dead center TDC as shown by the solid line (preferably, the intake top dead center TD).
C at least 20 ° before C), and when the valve is most retarded, the closing timing ExC is slightly after the intake top dead center TDC as shown by the broken line. Therefore, when the exhaust valve is retarded and the intake valve is advanced as indicated by the broken line, the exhaust valve closing timing ExC and the intake valve opening timing I
nO is near the intake top dead center TDC, and there is a slight overlap in the opening period of the intake and exhaust valves, but in the state where the exhaust valve is advanced and the intake valve is retarded as shown by the solid line. There is no overlap between both valve opening periods, and the exhaust valve closing timing E
There is a considerable period from xC to the intake valve opening timing InO. The period from the exhaust valve closing timing ExC to the intake valve opening timing InO without such overlap is referred to as minus overlap (minus O / L) for convenience in the description of the embodiment.

For the variable valve timing devices 13 and 14 having such a variable range of the valve timing, the valve timing control means 44 operates based on a preset valve timing map for the warm state when the engine is warm. In this case, at least in the low-speed and low-load region within the lean operation region A, as shown in FIG.
The opening and closing timing of the intake valve is set on the advance side within the variable range, and the opening and closing timing of the exhaust valve is set on the retard side within the variable range.

Further, when the engine is cold, control is performed based on a preset map of valve timing for a cold time. In this case, at least in a low-speed and low-load region, FIG.
As shown in the figure, the intake valve opening / closing timing is corrected to the retard side compared to when the engine is warm with the same accelerator opening degree, and the intake valve is closed to the extent that the intake recharging efficiency is reduced due to the return of intake air. The period InC is delayed. However, the opening and closing timing of the exhaust valve is substantially the same as in the warm state, and the exhaust valve closing timing ExC is set to be after the intake top dead center TDC.

Further, the valve timing control apparatus further includes a control circuit for controlling the air-fuel ratio from lean (λ> 1) to rich side (λ ≦ 1) during a warm state due to NOx purging, which will be described later, as shown in FIG. ), The exhaust valve closing timing ExC is set before the intake top dead center TDC by setting the opening and closing timing of the exhaust valve to the advance side, and the intake valve opening and closing timing is set to the retard side by setting the opening and closing timing of the intake valve to the retard side. The opening timing InO is after the intake top dead center TDC.

A specific example of such valve timing control and fuel injection control will be described with reference to the flowchart of FIG.

When the processing shown in the flowchart starts, first, signals from the respective sensors are input (step S1), and then the operating state is determined based on the engine speed and the engine load (step S2). Further, it is determined whether or not the engine is cold based on a signal from the water temperature sensor 36 (step S3).

If it is a cold time, the opening and closing timings of the intake valve and the exhaust valve are set based on a map of the valve timing for the cold time (step S4). The setting is made as shown in FIG. Further, the air-fuel ratio is equal to or less than the stoichiometric air-fuel ratio (λ ≦
1), the fuel injection amount is calculated so as to achieve this air-fuel ratio (step S5), and the injection timing is calculated so as to perform uniform combustion by the intake stroke injection (step S6). Then, the process proceeds to steps S7 and S8, and the control of the variable valve timing device and the control of the fuel injection are performed based on the settings and calculations in steps S4 to S6.

If the engine is warm (NO in step S3), the opening / closing timing of the intake valve and the exhaust valve is set based on a map of the valve timing for the warm time (step S9). In this case, at least in the low speed and low load range, the setting is made as shown in FIG.

Next, it is determined whether or not the engine is in the lean operation area (step S10). If it is in the lean operation area, it is further determined whether or not the NOx purge processing condition is satisfied (step S11). The determination in step S11 is performed by, for example, accumulating the NOx absorption amount estimated from the operation state or the like in order to perform the NOx purge (NOx release process) when the NOx storage amount of the NOx catalyst 32 increases during the lean operation. It is checked whether or not the obtained NOx storage amount has increased to a predetermined value or more.

When the NOx purging condition is not satisfied in the lean operation region, the air-fuel ratio is set to a lean air-fuel ratio (λ> 1) larger than the stoichiometric air-fuel ratio, and the fuel is set to this air-fuel ratio. The injection amount is calculated (step S12), and the injection timing is calculated so that stratified combustion is performed by the compression stroke injection (step S1).
3). Then, the process proceeds to steps S7 and S8.

When the NOx purge processing condition is satisfied in the lean operation region (when the determination in step S11 is YES), the air-fuel ratio is set to be equal to or lower than the stoichiometric air-fuel ratio (λ ≦ 1), and the air-fuel ratio is set to this value. The fuel injection amount is calculated (step S14), and the injection timing is calculated so as to perform uniform combustion by the intake stroke injection (step S15). Further, the intake valve opening timing InO is set at the top dead center TD.
C, the intake valve opening / closing timing is changed to the retard side, and the exhaust valve opening / closing timing is changed to the advance side so that the exhaust valve closing timing ExC is before the top dead center TDC (step S16). ). Then, the process proceeds to steps S7 and S8.

When the engine is not in the lean operation range when the engine is warm (when the determination in step S10 is NO), the air-fuel ratio is set to be equal to or lower than the stoichiometric air-fuel ratio (λ ≦ 1), and the fuel is set so as to become this air-fuel ratio. The injection amount is calculated (step S
At the same time, the injection timing is calculated so that uniform combustion is performed by the intake stroke injection (step S18).
Further, when shifting from the lean operation region A to the region B where λ ≦ 1, the intake valve opening / closing timing is changed to the retard side so that the intake valve opening timing InO is after the top dead center TDC, and the exhaust valve is closed. The exhaust valve opening / closing timing is changed to the advanced side so that the timing ExC is before the top dead center TDC (steps S19 and S20). Then, the process proceeds to steps S7 and S8.

According to the engine of the present embodiment as described above, when the engine is in the warm state, the air-fuel ratio is lean (λ> 1) when the engine is in the lean operation region A on the low-speed, low-load side, and the engine is stratified. Combustion occurs, and when the engine is cold, fuel vaporization and atomization are poor and combustion stability is likely to be impaired in lean operation, so the air-fuel ratio is less than the stoichiometric air-fuel ratio even at low speed and low load. (Λ ≦ 1), and uniform combustion is performed. As described above, while the air-fuel ratio is changed between the cold state and the warm state, the valve timing is changed between the cold state and the warm state as shown in FIGS.
The torque difference between the cold state and the warm state at the same accelerator opening is corrected.

That is, when the throttle valve 23 is mechanically connected to the accelerator pedal as in the present embodiment, since the correspondence between the accelerator opening and the throttle opening is always constant, the valve timing must be changed. For example, since the same intake air amount is obtained at the same accelerator opening between the cold state and the warm state, when the set air-fuel ratio changes, the fuel injection amount changes accordingly, and during the warm state where λ> 1 Λ ≦
The fuel injection amount is larger in the cold state set to 1.

In response to this tendency, the valve timing control means 44 delays the opening / closing timing of the intake valve when the engine is cold, compared to the opening / closing timing when the engine is warm at the same accelerator opening, so that the intake air is changed. Accordingly, the intake valve closing timing InC is delayed so that the intake charging efficiency is reduced. Accordingly, when the engine is cold, the valve timing is adjusted such that the air-fuel ratio becomes richer than when the engine is hot, while the intake charge efficiency is reduced.
The difference in fuel injection amount and the difference in torque based on the difference are reduced. For this reason, for example, even when the air-fuel ratio is changed to lean by increasing the water temperature and moving from cold to warm while operating at a constant accelerator opening, there is no sharp decrease in torque, A decrease in running feeling is prevented.

Further, by setting the valve timing as described above at the time of cold, deterioration of the combustion stability at the time of cold is prevented.

That is, as a method of using the variable valve timing device to lower the intake charging efficiency at the time of cold, the opening and closing timing of the intake valve is advanced so that the intake valve closing timing is optimized for the intake charging efficiency. It is conceivable to reduce the intake amount of fresh air by increasing the internal EGR, which will be described later, by increasing the valve-opening overlap period of the intake / exhaust valves, and increasing the valve overlap overlap period. As described above, it is conceivable to increase the internal EGR by setting the exhaust valve closing timing earlier than the intake top dead center so as to reduce the fresh air amount by that amount. Internal EGR
The combustion stability is likely to be impaired due to an increase in (residual burned gas). On the other hand, in the present embodiment, the intake valve opening / closing timing is delayed, and the opening / closing timing of the exhaust valve is set such that the closing timing ExC is set to be after the intake top dead center TDC during the cold period. While the charging efficiency is reduced, the internal EGR is not increased, and the combustion stability during cold operation is not impaired.

When the lean operation is being performed in the lean operation region A during the warm period, NOx in the exhaust gas becomes NO.
x is absorbed by the x-catalyst 32, and this operating state continues to be NOx
When the NOx storage amount of the catalyst 32 increases to a predetermined value or more, the air-fuel ratio becomes rich (λ ≦ 1) by the processing of steps S14 and S15 following the determination of YES in step S11 in FIG.
As a result, NOx purge, that is, release and reduction of NOx from the NOx catalyst are performed. The NOx purge is also performed at the time of transition from the lean operation region A to the other operation region B.

At the time of these NOx purging, as shown in FIG. 5C, the intake valve closing timing In is set so that the intake valve opening / closing timing is retarded to reduce the intake charging efficiency.
With the delay of C, the intake valve opening timing InO is after the intake top dead center TDC, and the exhaust valve closing timing ExC is made earlier than the intake top dead center TDC by advancing the opening and closing timing of the exhaust valve. . As a result, the burned gas remains in the combustion chamber 5 because the exhaust valve closes before the burned gas in the combustion chamber is completely exhausted in the exhaust stroke.
An external EG that provides the effect and recirculates exhaust gas from outside
NOx is reduced similarly to R.

At the time of NOx purging, the NOx from the NOx catalyst 32 is reduced by a reducing agent such as CO contained in the exhaust gas.
Ox is released and reduced. In this case, the larger the ratio of the amount of CO to the amount of NOx in the exhaust gas, the more NO
Although the release and reduction of x are promoted, the ratio of the amount of CO to the amount of NOx is quickly increased by enriching the air-fuel ratio and reducing NOx by the internal EGR as described above. Performance is enhanced.

Further, as described above, the intake valve closing timing InC is delayed so that the intake charging efficiency is reduced, and the internal EGR is performed, so that the intake amount of fresh air is reduced. A sudden increase in torque due to a rich fuel ratio is suppressed, and torque shock is reduced.

[0057]

As described above, in an engine in which the set air-fuel ratio in the low-speed low-load region of the engine is lean when the engine is warm and rich below the stoichiometric air-fuel ratio when the engine is cold. And the valve timing control means shifts the intake valve closing timing when the engine is cold in the low-speed low-load range to the lag side where the intake charging efficiency decreases with respect to the intake valve closing timing when the engine is warm with the same accelerator opening degree. According to the invention that is set, the intake air amount can be adjusted so as to reduce the torque difference with respect to the difference in the air-fuel ratio between the cold state and the warm state.

Therefore, it is possible to avoid a torque difference between a cold state in which the air-fuel ratio is rich and a warm state in which the air-fuel ratio is lean so as to improve fuel efficiency so as not to impair the combustion stability. The adjustment of the amount of intake air for that purpose can be effectively performed by using the variable valve timing device without maintaining a means for electrically controlling the throttle valve while maintaining a good feeling.

Further, in an engine in which a NOx catalyst is provided in an exhaust passage and a NOx release process is performed by changing an air-fuel ratio from a lean operation state to a stoichiometric air-fuel ratio or less, a variable valve timing apparatus and a variable valve timing control apparatus are provided. According to the invention, when the NOx release process is started from the lean operation, the exhaust valve closing timing is set to a predetermined period before the intake top dead center and the intake valve opening timing is set to be after the intake top dead center. By controlling the valve timing, the so-called internal EGR is increased to reduce NOx, and the release and reduction of NOx from the NOx catalyst can be promoted.

[Brief description of the drawings]

FIG. 1 is a schematic view of a lean burn engine for an automobile according to an embodiment of the present invention.

FIG. 2 is a diagram showing a map for fuel injection control for a cold time and for a warm time.

FIG. 3 is a diagram showing a cam lift curve for indicating the opening / closing timing of an intake valve and an exhaust valve.

FIG. 4 is a partially enlarged view of a cam lift curve.

FIG. 5 is a diagram showing opening / closing timings of an intake valve and an exhaust valve in a cold state, a warm state, and a NOx purge.

FIG. 6 is a flowchart showing a specific example of control of fuel injection and valve timing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 5 Combustion chamber 9 Intake valve 10 Exhaust valve 13 and 14 Variable valve timing device 32 NOx catalyst 40 ECU 41 Operating state determination means 42 Temperature state determination means 43 Fuel injection control means 44 Valve timing control means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/06 320 F02D 41/06 320 45/00 301 45/00 301G 312 312B F-term (Reference) 3G084 AA04 BA09 BA13 BA15 BA23 CA02 CA03 CA06 CA09 DA10 DA11 EA11 EB08 EC01 FA10 FA18 FA20 FA29 FA33 3G091 AA12 AA17 AA24 AB06 BA14 CB02 CB03 CB07 EA01 EA02 EA16 EA34 FA04 FA08 FA09 FA13 FA14 FB10 GB10 AGB11 GB03 AGB11 GB03 AGB11 GB03 GB03 BB06 DA01 DA02 DA10 DA12 DC15 EA03 EA04 EA05 EA07 EC01 FA04 FA17 GA02 GA05 GA06 GA17 GA18 HA00Z HA11Z HA13X HD00Z HE01Z HE08Z 3G301 HA16 HA19 JA04 JA25 KA05 KA08 KA16 KB04 LA07 MA01 MA11 MA19 NA08 PE02Z

Claims (6)

[Claims] 1. A set air-fuel ratio in a low-speed low-load region of an engine is made larger than a stoichiometric air-fuel ratio when the engine is warm,
A variable valve timing device that can change the opening and closing timing of an intake valve in an automotive lean-burn engine that has a stoichiometric air-fuel ratio or less when the engine is cold, and controls the variable valve timing device according to the operating state and temperature state of the engine Valve timing control means for controlling the intake valve closing timing when the engine is cold in a low-speed low-load range with respect to the intake valve closing timing when the engine is warm in the same accelerator opening state. A lean-burn engine for an automobile, wherein the lean-burn engine is set on a delay side where intake air charging efficiency is reduced. 2. An intake valve opening timing in a low-speed low-load region when the engine is cold is delayed with respect to an intake valve opening timing in a case where the engine is warm with the same accelerator opening degree. Lean burn engine for automobiles. 3. An exhaust passage having a NOx catalyst that absorbs NOx in an oxygen-excess atmosphere and releases NOx as the oxygen concentration decreases, and the air-fuel ratio is larger than the stoichiometric air-fuel ratio when the engine is warm. At the time of the transition to be changed to the stoichiometric air-fuel ratio or less, the intake valve closing timing is changed to the delay side where the intake charging efficiency is reduced, and at least at this transition, the acceleration section in the exhaust valve cam lift characteristic is changed from the acceleration section to the constant speed section. 2. The exhaust valve closing timing defined at the transition point is set before the intake top dead center.
Or a lean burn engine for an automobile according to 2. 4. A variable valve timing device for each of the intake valve and the exhaust valve, wherein the valve timing control means controls the variable valve timing device for the exhaust valve in addition to controlling the variable valve timing device for the intake valve. 4. The lean burn engine according to claim 3, wherein the control is performed to set the exhaust valve closing timing after the intake top dead center in a low-speed low-load region when the engine is cold. 5. An exhaust passage having a NOx catalyst that absorbs NOx in an oxygen-excess atmosphere and releases NOx as the oxygen concentration decreases, and makes the air-fuel ratio larger than the stoichiometric air-fuel ratio in a low-speed low-load region. NOx that releases NOx from the NOx catalyst by performing lean operation at a specific time and changing the air-fuel ratio from the lean operation state to a stoichiometric air-fuel ratio or less at the time of specific operation
In a vehicle lean burn engine that performs a release process, a valve timing variable device that can change a valve opening / closing timing for each of an intake valve and an exhaust valve is provided, and a valve timing that controls these valve timing variable devices is provided. Control means for controlling the NOx from the lean operation.
At the start of the discharge process, the exhaust valve closing timing defined by the transition point from the acceleration section to the constant speed section in the exhaust valve cam lift characteristic is a predetermined period before the intake top dead center, the constant velocity section to the acceleration section in the intake valve cam lift characteristic. A lean-burn engine for an automobile, characterized in that the variable valve timing device is controlled so that the opening timing of the intake valve defined at the time of the transition to (i) is after the intake top dead center. 6. A variable valve timing device for at least the intake valve is a phase-type variable valve timing device capable of changing the opening / closing timing while keeping the valve opening period constant, wherein the intake valve opening timing is after the intake top dead center. 6. The lean burn engine for an automobile according to claim 5, wherein the intake valve closing timing is set so as to be late so as to cause a decrease in intake air charging efficiency.