JPH11107806A - Engine control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize regenerative control without incurring a torque variation and an emission increase by installing the second fuel injection means to spray fuel at an engine expansion stroke so as to keep up oxygen content or air-fuel ratio in front of a catalyzer to the specified value. SOLUTION: An air-fuel ratio sensor 8 is installed in space between an exhaust valve 7 and a NOx catalyzer 2. This air-fuel ratio signal 105 is inputted into a controller 9 and it is used for a catalyzer regenerative control 202. A fuel injection quantity determined for regeneration by this catalyzer regenerative control 202 is added to a signal proportioned to torque by operation 203, and an injection signal 104 is outputted to an injector 5. In brief, the fuel injection quantity for this regenerative control 202 is made into a closed loop by means of output value of the air-fuel ratio sensor 8. Fuel for the regeneration control is spray at the latter period of an expansion stroke of a cylinder injection engine 1 so as not to exert any influence to the engine torque. Since this unbernt hydrocarbon is burned in the exhaust pipe, an exhaust temperature goes up. Thus, the NOx catalyzer 2 is regenerable owing to this reducing atmosphere and the rising of exhaust temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of regenerating a catalytic converter for purifying engine exhaust during operation when the performance of the catalytic converter is reduced.

[0002]

2. Description of the Related Art In order to improve the fuel efficiency of an engine, a technique of increasing the amount of air in excess of the stoichiometric air-fuel ratio, that is, performing lean combustion, is becoming widespread. In a gasoline engine, a method of injecting fuel directly into a cylinder to shift to a method of achieving leaner combustion has been shifted from a conventional method of injecting fuel through an intake pipe. In this in-cylinder injection engine, pumping loss and heat diffusion can be reduced by extremely lean combustion such as an air-fuel ratio of 40 to 50 to improve fuel efficiency. However, when looking at the exhaust gas, HC and CO are reduced, but the concentration of NOx is at a high level. A three-way catalyst has been widely used as a device for purifying exhaust gas of a gasoline engine.
This catalyst removes HC, NOx, and CO contained in the exhaust gas. However, it is necessary to keep the air-fuel ratio at the stoichiometric air-fuel ratio in order to sufficiently exhibit this function. It cannot be applied to NOx purification in combustion. On the other hand, a catalyst having an adsorption function has been proposed for purifying NOx in such lean combustion. This catalyst can be used to reduce the amount of NOx
To prevent the release to the atmosphere. Hereinafter, this adsorption type catalyst is referred to as a NOx catalyst.

When using a NOx catalyst, it is necessary to maintain the performance in consideration of the following three points.

(1) When an amount of NOx that is full of the adsorption capacity of the NOx catalyst is adsorbed, it is necessary to immediately reduce the amount of oxygen in the exhaust gas to promote the reduction reaction.

(2) Since SOx contained in fuel is more easily adsorbed than NOx, if operation is continued as it is, NOx
The performance as a catalyst decreases. To prevent this, it is necessary to promote the reduction reaction by setting the exhaust gas in a state of insufficient oxygen.

(3) In order to further promote the NOx reduction reaction, it is necessary to raise the temperature of the catalyst.

[0007] Such an operation for maintaining the performance of the NOx catalyst is hereinafter referred to as regeneration control.

In order to promote the regeneration control, the temperature of the catalyst is first raised by taking the characteristics of the NOx catalyst into account, and the state is shifted quickly from a lean burn state to an excessive fuel state, that is, a rich state. As this means, in the conventional method, the fuel injection amount, the intake air amount, and the ignition timing are changed.

[0009]

In the regeneration control method as in the prior art, when the NOx adsorbed on the NOx catalyst is reduced, the amount of fuel injection, the amount of intake air, and the ignition timing are changed. There is a practical problem that the driving performance is impaired due to the fluctuation of the engine torque or the air-fuel ratio fluctuates, which easily causes the deterioration of the exhaust gas.

SUMMARY OF THE INVENTION The present invention has been made to solve such a conventional problem, and provides a method capable of realizing regeneration control and maintaining the performance of a NOx catalyst without causing torque fluctuation and emission increase. The purpose is to do.

The present invention is suitable when the present invention is applied to a catalyst having both a three-way catalytic function and a NOx adsorbing function as disclosed in Japanese Patent Application No. 9-13655 as a NOx catalyst.

[0012]

The present invention utilizes the fact that a direct injection engine has the characteristic that it can inject fuel not only in the intake stroke but also in any stroke. That is, an air-fuel ratio control system as shown in FIG. 1 is constructed for the direct injection engine. The present invention is conceived to separate the control means for generating torque by combustion, which is the mission of the engine, from the control means for regenerating the performance of the catalyst.

FIG. 2 shows the characteristics of the in-cylinder injection engine during lean combustion, which outputs a predetermined torque, when fuel injection is added in the expansion stroke (stroke from the late stage of the explosion to the exhaust). The torque is constant in spite of the increase in the total fuel, and at this time, the HC and the exhaust gas temperature increase. Based on these findings,
According to the present invention, the torque control and the catalyst regeneration control are executed separately and independently by using the control means shown in FIG. FIG.
In the compression stroke, the intake valve lift 3
A means for outputting the fuel injection pulse Tp1 at the timing of the crank angle θt at which 01 has decreased, and a means for separately outputting the fuel injection pulse Tp2 at a timing of the crank angle θc before and after the exhaust valve lift 302 rises.

[0014]

FIG. 1 shows a system configuration of an embodiment. The control system for the in-cylinder injection engine 1 and the NOx catalyst 2 includes an air amount sensor 4, an engine speed signal 10
2, a crank angle signal 103, an air-fuel ratio sensor 8, a control device 9, and an injector 5. In the control device 9, all processing is performed by a single-chip microcomputer having an A / D converter. The operation will be described below. Air amount signal 101, engine speed signal 10
2 is determined by the torque control 102. The specific ratio of this engine torque is output to the injector 5 as a fuel injection amount. Here, although not shown, when determining the torque, a signal of the accelerator opening may be used. The injected fuel burns in the direct injection engine 1,
The exhaust flows through the exhaust valve 7 to the NOx catalyst 2. An air-fuel ratio sensor 8 is provided between the exhaust valve 7 and the NOx catalyst 2. The air-fuel ratio signal 105 is input to the control device 9 and used for the catalyst regeneration control 202. The fuel injection amount determined for regeneration in the catalyst regeneration control 202 is added to a signal proportional to the torque in operation 203, and an injection signal 1
04 is output to the injector 5. That is, the fuel injection amount for the regeneration control is closed-loop by the output value of the air-fuel ratio sensor 8. In this case, the amount of fuel used for this regeneration control has little to do with engine torque,
The fuel is injected into the in-cylinder injection engine 1. As a result, the engine torque becomes the value determined by the torque control 201, and is not affected by the regeneration control.

Here, the fuel for the regeneration control does not affect the engine torque, so that the direct injection engine 1
Will be injected later or later in the expansion stroke. In this case, the fuel amount for determining the engine torque is to be injected before the ignition timing. That is, injection is performed twice in one cycle. FIG. 2 shows the relationship between the fuel injection pulse width Tc, engine torque, HC (unburned hydrocarbon), and exhaust gas temperature in the case of the second expansion stroke injection. When the injection pulse increases and the injection amount increases, the amount of HC discharged to the exhaust pipe without burning increases. That is, the ratio of the cylinder filling air weight to the pre-ignition injected fuel weight + the fuel injection weight during the expansion stroke may be greater than 14.7. The overall air-fuel ratio will be lean. However, when the amount of HC is increased by injection during the expansion stroke, the exhaust pipe becomes a reducing atmosphere with less oxygen. Further, the exhaust gas temperature rises because the HC is burned in the exhaust pipe. The NOx catalyst 2 can be regenerated by the reduction atmosphere and the increase in the exhaust gas temperature. Closed loop control is performed based on the signal of the air-fuel ratio sensor so that the exhaust gas before the catalyst becomes a reducing atmosphere.

FIG. 3 shows the relationship between the operation timing of the intake and exhaust valves, the fuel injection pulse, and the crank angle. Fuel for torque control is injected at a crank angle θt. This θt is the ignition timing or the crank angle before the compression top dead center. Fuel for regeneration control is injected at the crank angle θc. This θt is injected during the expansion (explosion) stroke of the engine. Note that the respective fuel injection pulse widths are Tp1 and Tp2. Here, the engine torque is determined by Tp1,
The air-fuel ratio in the exhaust pipe for the regeneration control is determined by Tp2. That is, the pulse width of Tp2 is closed-loop controlled based on the signal of the air-fuel ratio sensor 8.

Next, FIG. 4 shows an operation flow of the torque control 201. In step 211, the engine speed Ne
And the intake air flow rate Qa, and in step 212 (1),
According to the equation (2), the target torque To and the fuel injection pulse width T
Find p1.

To = (Qa / Ne) / (A / F) o (1) Tp1 = kTo (2) Next, in steps 213 and 215, the injection timing is delayed until the crank angle reaches θt. And step 21
At 6, a fuel injection signal is transmitted to the injector 5. Here, only the engine speed Ne and the intake air flow rate Qa are used to determine the engine torque, but the engine torque may be determined using other parameters.
The effects of the present invention can be implemented. For example, the accelerator opening may be used to determine the engine torque, or the pressure in the intake pipe or the pressure in the cylinder may be used.

FIG. 5 shows an operation flow of the catalyst regeneration control 202. At step 221, the air-fuel ratio signal 105 is input. In step 222, it is determined that a predetermined time has elapsed since the previous catalyst regeneration control, and
At 3, it is determined whether or not the target air-fuel ratio for regeneration has exceeded the target. Here, the target air-fuel ratio for regeneration is set at or around the stoichiometric air-fuel ratio. In steps 224 and 225, according to the equations (3) and (4), the fuel is increased when the engine is lean, and the fuel is decreased when the engine is rich.

Tp2 = Tp2 + ΔTp2 (3) Tp2 = Tp2-ΔTp2 (4) Next, in steps 216 and 217, the injection timing is delayed until the crank angle reaches θc. And step 21
At 8, a fuel injection signal is transmitted to the injector 5.

In this case, the air-fuel ratio sensor may be a sensor that detects a stoichiometric air-fuel ratio or a sensor that detects the air-fuel ratio in an analog manner. Further, the timing for performing the reproduction control is determined based on the elapsed time from the previous time, but may be determined based on the traveling distance. In addition, traveling distance, traveling air-fuel ratio,
It may be based on the result of the performance degradation judging means in consideration of the temperature and the like.

The effect of the present invention will be described with reference to FIG. This shows characteristics during steady operation, and the throttle opening is constant. The air-fuel ratio before the catalyst is usually in a lean state (A / F = 40 to 5
0), but during regeneration, stoichiometry is controlled by adding fuel or before or after stoichiometry. As a result, the NOx purification rate is restored, but there is no influence on the torque because the fuel injection is performed during the expansion stroke, and the torque is kept substantially constant during the regeneration control. The lower part of FIG. 6 shows the NOx values before and after the catalyst. Before the catalyst, the NOx value is constant.
The value of NOx after the x catalyst gradually increases as the purification rate decreases. However, after the regeneration control is performed, the NOx value again increases.
Is decreased, and it can be seen that purification is performed.

As the NOx catalyst used in the present invention, for example, an adsorption and reduction type catalyst as disclosed in Japanese Patent Application No. 9-13655 is suitable.

[0024]

According to the present invention, while reducing the pumping loss due to the lean burn and the heat diffusion loss due to the increase in the intake air, at the same time, the exhaust to the catalyst is accurately maintained at the target air-fuel ratio to reduce the emission during regeneration. Deterioration can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to a claim.

FIG. 2 is a characteristic diagram of a direct injection engine.

FIG. 3 is a timing chart in the embodiment.

FIG. 4 is a processing flowchart of one embodiment.

FIG. 5 is a processing flowchart of one embodiment.

FIG. 6 is a characteristic diagram for explaining the effect of the present invention.

[Explanation of symbols]

Qa: intake air flow rate, Ne: engine speed, Tp: fuel injection pulse width, (A / F) o ... set air-fuel ratio, 1 ... cylinder injection engine, 2 ... NOx catalyst, 4 ... air amount sensor, 5
... Injector, 8 ... Air-fuel ratio sensor, 9 ... Control device, 2
01: torque control, 202: catalyst regeneration control.

Continued on the front page (72) Inventor Toshiharu Nogi 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Takuya Shiraishi 7-1-1, Omikamachi, Hitachi City, Ibaraki Prefecture Inside Hitachi Research Laboratory, Hitachi, Ltd.

Claims (5)

[Claims] In a gasoline engine for injecting fuel into a cylinder, first fuel injection means for injecting fuel in an intake or compression stroke according to a required torque, and detecting an oxygen concentration or an air-fuel ratio of engine exhaust. Means for injecting fuel during an expansion stroke of the engine so as to maintain the oxygen concentration or the air-fuel ratio in front of the catalyst at a predetermined value. 2. The engine control method according to claim 1, wherein the oxygen concentration or the air-fuel ratio in front of the catalyst is set such that the exhaust gas in front of the catalyst or in the catalyst section has a reducing atmosphere. 3. The method according to claim 1, wherein the means for detecting the oxygen concentration or the air-fuel ratio of the engine exhaust is a sensor for detecting a stoichiometric air-fuel ratio or a sensor for outputting a signal proportional to the air-fuel ratio. Engine control method. 4. The engine control method according to claim 1, wherein when the purification performance of the catalyst is reduced, a second fuel injection for injecting fuel during an expansion stroke of the engine is performed. 5. The method according to claim 4, wherein the purifying performance of the catalyst is reduced when a predetermined time has elapsed since the previous execution of the second injection means, when a predetermined traveling distance has been reached, or An engine control method, wherein the purification rate deterioration determining means determines that deterioration has occurred.