JP2797699B2 - Catalyst temperature control device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a catalyst temperature control device for an internal combustion engine.

[Conventional technology]

At the time of engine low load operation, a mixture is formed in a limited area within the combustion chamber, and the other area is ignited by an ignition plug with only air as the other area, and when the engine load becomes high, a limited area within the combustion chamber is increased. There is known an internal combustion engine in which an air-fuel mixture ignitable by an ignition plug is formed, and other regions are filled with a lean air-fuel mixture thinner than this air-fuel mixture (see JP-A-2-169834). In this internal combustion engine, when the engine is under low load operation, the mixture is burned in the presence of a large amount of air, so that the exhaust gas temperature is low, and when the engine load is high, the lean mixture that occupies most of the mixture is Is burned, so that the exhaust gas temperature is similarly lowered.

[Problems to be Solved by the Invention] By the way, an exhaust gas purifying catalytic converter is usually arranged in an engine exhaust passage. However, this catalyst does not perform the exhaust gas purifying action unless the temperature rises to a certain extent, that is, unless the catalyst is activated. Therefore, when the catalyst temperature is low, such as when the engine is started, or when the catalyst temperature becomes low even after the warm-up is completed, the exhaust gas cannot be purified by the catalyst. In particular, when the exhaust gas temperature is low as in the case of the internal combustion engine described in Japanese Patent Application Laid-Open No. 2-169834, it takes time for the catalyst temperature to rise when the engine is started, and the catalyst temperature decreases after the warm-up is completed. However, there is a problem that it takes time for the catalyst temperature to rise again.

[Means for solving the problem]

According to the present invention, in order to solve the above-mentioned problems, the cylinder is set to the first position.
Is divided into a cylinder group and a second cylinder group, an intake shut-off valve is arranged in an intake passage of the first cylinder group, a catalytic converter is arranged in an engine exhaust passage, and a temperature representative of the temperature of the catalyst is set. When the temperature detected by the temperature sensor is higher than a predetermined set temperature, the air intake shutoff valve is fully opened and fuel is supplied to all cylinders, and the temperature detected by the temperature sensor is set. When the temperature is lower than the temperature, the intake shutoff valve is fully closed to stop the supply of fuel to the first cylinder group and to supply the fuel to the second cylinder group so as to obtain an engine output torque substantially equal to that in the full cylinder operation. I try to increase the amount of fuel.

[Action]

When the temperature representative of the temperature of the catalyst becomes lower than the set temperature, the first cylinder group is deactivated and only the second cylinder group is operated, and at this time, an engine output torque substantially equal to that during all-cylinder operation is obtained. Thus, the amount of fuel supplied to the second cylinder group is increased. When the amount of fuel supplied to the second cylinder group is increased so as to obtain an engine output torque substantially equal to that during all-cylinder operation, the heat energy of the exhaust gas discharged into the exhaust passage per unit time increases, and Temperature rises rapidly.

〔Example〕

Referring to FIG. 1, 1 is the engine body, # 1, # 2, # 3, #
Reference numeral 4 denotes a first cylinder, a second cylinder, a third cylinder, and a fourth cylinder, respectively. The first cylinder # 1 and the fourth cylinder # 4 constitute a first cylinder group, and the second cylinders # 2 and # 3. Cylinder # 3 constitutes a second cylinder group. Each of the cylinders # 1, # 2, # 3, # 4 is connected to a common surge tank 3 via a corresponding intake branch pipe 2, and the surge tank 3 is connected to an air cleaner 5 via an intake duct 4. A throttle valve 7 driven by a step motor 6 is arranged in the intake duct 4. The throttle valve 7 is closed to some extent only when the engine load is extremely low, and is kept fully open when the engine load is slightly increased. Inside the intake branch pipe 2 of the first cylinder # 1 and the fourth cylinder # 4
Each of the intake branch pipes 2 has an intake cutoff valve 8 which is connected to an actuator 10 via a common shaft 9. On the other hand, each of the cylinders # 1, # 2, # 3, # 4 is connected to a common exhaust manifold 11, and this exhaust manifold 11 is connected to a three-way catalytic converter 12. The three-way catalytic converter 12 has a temperature sensor 13 for detecting the temperature of the three-way catalyst.
Is attached. Further, a fuel injection valve 14 is attached to each of the cylinders # 1, # 2, # 3, and # 4, and the fuel injection valve 14 is controlled based on an output signal of the electronic control unit 20.

The electronic control unit 20 is composed of a digital computer, and a RAM (random access memory) 22, a ROM (read only memory) 23, a CPU (microprocessor) 24, and an input port 25 interconnected via a bidirectional bus 21.
And an output port 26. The temperature sensor 13 generates an output voltage proportional to the temperature of the three-way catalyst, and this output voltage
The signal is input to the input port 25 via the AD converter 27. The accelerator pedal 15 is connected to a load sensor 16 that generates an output voltage proportional to the amount of depression of the accelerator pedal 15, and
The output voltage of 16 is input to the input port 25 via the AD converter 27. The input port 25 is connected to a rotation speed sensor 17 that generates an output pulse representing the engine rotation speed. On the other hand, the output port 26 is connected to the step motor 6, the actuator 10, and each fuel injection valve 14 via the corresponding drive circuit 29.

FIG. 2 and FIG. 3 show the combustion chamber structures of the cylinders # 1, # 2, # 3, and # 4.

2 and 3, reference numeral 30 denotes a cylinder block, 31 denotes a piston that reciprocates in the cylinder block 30, 32 denotes a cylinder head fixed on the cylinder block 30, and 33 denotes a piston 31 and a cylinder head 32. Each shows a combustion chamber formed between them. Although not shown in the drawing, an intake valve and an exhaust valve are arranged on the inner wall surface of the cylinder head 32, and the intake port is provided so that air flowing into the combustion chamber 33 generates a swirling flow around the cylinder axis. Is configured.
As shown in FIG. 2, an ignition plug 34 is disposed at the center of the inner wall surface of the cylinder head 32, and the fuel injection valve 14 is disposed at a peripheral portion of the inner wall surface of the cylinder head 32. As shown in FIGS. 2 and 3, on the top surface of the piston 31, a shallow plate portion 35 having a substantially circular contour extending from below the fuel injection valve 14 to below the spark plug 34 is formed. A deep dish portion 36 having a substantially hemispherical shape is formed at the center of the dish portion 35. Also,
A substantially spherical concave portion 37 is formed at a connection portion between the shallow plate portion 35 and the deep plate portion 36 below the ignition plug 34.

FIG. 4 shows a combustion method at the time of engine low load operation, and FIG. 5 shows a combustion method at the time of engine medium load operation.

At the time of engine low load operation, as shown in FIGS. 4A and 4B, at the end of the compression stroke, fuel injection F is performed toward the peripheral wall surface of the deep dish portion 36, and in the embodiment shown in FIG. Will be This fuel is diffused while being vaporized by the swirling flow S, whereby an air-fuel mixture G is formed in the concave portion 37 and the deep dish portion 36 as shown in FIG. 4 (C). At this time, the inside of the combustion chamber 33 other than the concave portion 37 and the deep dish portion 36 is filled with air. Next, the mixture G is ignited by the spark plug 34. On the other hand, during the engine middle load operation, fuel injection is performed in two stages, the initial stage of the intake stroke and the final stage of the compression stroke.
That is, first, as shown in FIGS. 5 (A) and 5 (B), fuel injection F is performed toward the shallow plate portion 35 at the beginning of the intake stroke, and the injected fuel causes the lean mixture into the entire combustion chamber 33. Qi is formed. Next, as shown in FIG. 5 (C), fuel injection F is performed toward the peripheral wall surface of the deep dish portion 36 at the end of the compression stroke, and as shown in FIG. An ignitable air-fuel mixture G serving as a fire is formed in the deep dish portion 36. The mixture G is ignited by an ignition plug 34, and the ignition flame causes the lean mixture in the entire combustion chamber 33 to burn.

During the high engine load operation, the fuel injection is performed in two stages, the initial stage of the intake stroke and the final stage of the compression stroke, as in the engine middle load operation, or the fuel injection is performed only once at the beginning of the intake stroke.

When the air-fuel mixture G is burned in the presence of a large amount of air as shown in FIG. 4, the combustion gas is cooled by the surrounding air, so that the temperature of the exhaust gas becomes low.
As shown in the figure, even when most of the mixture is a lean mixture, the exhaust gas temperature is low. If the exhaust gas temperature is low as described above, it takes time to raise the catalyst temperature of the catalytic converter 12. Therefore, in the embodiment according to the present invention, when the catalyst temperature becomes lower than the set temperature, the intake cutoff valve 8 is fully closed and the first cylinder # 1 and the fourth cylinder # 4.
The fuel injection into the second cylinder # 2 and the third cylinder # 3 is increased almost twice so that the engine output torque does not change. As described above, when the first cylinder # 1 and the fourth cylinder # 4 are deactivated, the amount of exhaust gas discharged into the exhaust manifold 11 per unit time is reduced. However, even if the number of operating cylinders is reduced in this manner, operation is continued. If the combustion shown in FIG. 4 is performed before and after the number of cylinders is reduced, the combustion gas temperature in the second cylinder # 2 and the third cylinder # 3 rises and the air-fuel mixture region widens, so that the air region narrows. If the combustion shown in FIG. 5 is performed before and after the number of working cylinders is reduced, the combustion temperature rises because the air-fuel mixture becomes thicker before and after the number of working cylinders is reduced. When the number of cylinders is reduced and the combustion shown in FIG. 4 shifts to the combustion shown in FIG. 5, the combustion temperature rises, and in any case, the thermal energy of the exhaust gas passing through the catalyst per unit time is increased. There is increased. As a result, the temperature of the catalyst can be rapidly increased.

Next, a method for controlling the temperature of the catalyst will be described with reference to a main routine shown in FIG.

Referring to FIG. 6, first, at step 40, the fuel injection amount Q is calculated. The fuel injection amount Q is stored in advance in the ROM 23 as a function of the depression amount L of the accelerator pedal 15 and the engine speed N as shown in FIG. Next, at step 41, it is determined whether or not the fuel injection amount Q is smaller than the fuel injection amount Q1, which is almost half of the maximum injection amount. Q
If Q1, the process proceeds to step 47, and if Q <Q1, the process proceeds to step. Or lower or not than the set temperature T ₀ of the catalyst temperature T is a predetermined detected by the temperature sensor 13 in step 42 is determined, the process proceeds to any or step 47 in TT _0.

In step 47, the intake cutoff valve 8 is fully opened, and then the fuel injection amount Qa to be actually injected is set to Q. Next, at step 49, the fuel injection amount Qa is reduced to a predetermined injection amount Q2.
It is determined whether the number is smaller than the number. When the ratio of Qa <Q2 is reached, the routine proceeds to step 50 where the single injection shown in FIG.
In the case of Q2, the routine proceeds to step 51, where two injections shown in FIG. 5 are performed. At this time, in all cases, all cylinders # 1,
Fuel injection is performed at # 2, # 3, and # 4.

On the other hand, the intake shutoff valve 8 is completely closed proceeds to step 43 when it is judged that T <T ₀ in step 42. Next, at step 44, the supply of fuel to the first cylinder # 1 and the fourth cylinder # 4 is stopped. Next, at step 45, a correction coefficient α for the fuel injection amount is calculated. The correction coefficient α is stored in advance in the ROM 23 as a function of the engine speed N as shown in FIG. Then step 46
Then, the fuel injection amount Qa to be actually injected into the second cylinder # 2 and the third cylinder # 3 is calculated based on the following equation.

Qa = 2 · Q + α This fuel injection amount Qa is determined so that the output torque of the engine does not fluctuate even when shifting from full cylinder operation to partial cylinder operation in which only half of the cylinders operate. In other words, the first cylinder # 1 and the fourth cylinder # 4 that are at rest do not cause much pumping loss because the intake cutoff valve 8 is closed, but drive to move the piston up and down as the engine speed increases. The torque increases. Therefore, in order to prevent the engine output torque from changing when shifting to the partial cylinder operation, it is necessary to gradually increase the correction coefficient α as the engine speed N increases as shown in FIG. Next, the routine proceeds to step 49, and then proceeds to step 50 or 51 to perform single injection or double injection.

In the embodiment shown in FIG. 1, the temperature of the catalyst is directly detected by the temperature sensor 13. However, the temperature sensor 13 detects a temperature representative of the temperature of the catalyst, for example, the temperature of the housing of the three-way catalytic converter 12, the temperature of the exhaust gas flowing into the three-way catalytic converter 12, or the temperature of the exhaust gas flowing out of the three-way catalytic converter 12. You may.

Further, the intake branch pipes 2 of the first cylinder # 1 and the fourth cylinder # 4 located on the outermost sides are easily cooled by the outside air, and the second cylinder # 2 and the third cylinder # 3 sandwiched by the intake branch pipes 2. Is hardly cooled by the outside air.
Accordingly, the first cylinder # 1 having the intake cutoff valve 8 located at the outermost position
And when the first and fourth cylinders # 1 and # 4 are deactivated,
Relatively warm air can be supplied to the cylinder # 2 and the cylinder # 3. As a result, the temperature of the catalyst can be more rapidly increased because the exhaust gas temperature is further increased.

Further, the present invention can be applied to an internal combustion engine in which fuel is supplied into an intake passage. In this case, when half of the cylinders are operated, the amount of air supplied to the operating cylinders is almost doubled. Therefore, even when the operation shifts from the full cylinder operation to the partial cylinder operation, the exhaust gas amount does not change so much. Since the combustion temperature in the cylinder increases, the heat energy of the exhaust gas increases.

〔The invention's effect〕

When the catalyst temperature is low, the catalyst temperature can be rapidly increased, so that the exhaust gas purifying performance of the catalyst can be improved.

[Brief description of the drawings]

1 is an overall view of an internal combustion engine, FIG. 2 is a side sectional view of a combustion chamber, FIG. 3 is a plan view of a piston top face, FIG. 4 is a view for explaining a combustion method at the time of low load operation, FIG. 5 is a diagram for explaining a combustion method at the time of medium load operation, and FIG.
FIG. 7 is a flowchart showing a main routine, FIG. 7 is a diagram showing a fuel injection amount, and FIG. 8 is a diagram showing a correction coefficient. 2 ... intake branch pipe, 8 ... intake shutoff valve, 12 ... three-way catalytic converter, 13 ... temperature sensor, 14 ... fuel injection valve.

Claims (1)

(57) [Claims] A first cylinder group and a second cylinder group, and an intake shutoff valve disposed in an intake passage of the first cylinder group;
A catalyst converter is disposed in the engine exhaust passage, and a temperature sensor for detecting a temperature representative of the temperature of the catalyst is provided. When the temperature detected by the temperature sensor is higher than a predetermined set temperature, the intake cutoff valve is turned on. When the temperature is lower than the set temperature, the intake shutoff valve is fully closed to stop the supply of fuel to the first cylinder group and to supply fuel to all cylinders. A catalyst temperature control device for an internal combustion engine configured to increase the amount of fuel supplied to a second cylinder group so as to obtain an engine output torque substantially equal to that during operation.