JP2004036626A - Control method of direct injection engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control method of an engine to prevent deterioration of exhaust air emission because of a catalyst not at activating temperature at the time of restarting as wall temperature of a cylinder and temperature of the exhaust air purifying catalyst are lowered during temporary stopping of the engine on a hybrid vehicle assembling a direct injection engine using gasoline as fuel and an electric motor. <P>SOLUTION: An ECU 7 stops the engine after raising the temperature of the exhaust gas purifying catalyst 5 up to a heat resistance limit of the catalyst by previously changing injection timing of the fuel over to an early stage of a suction process from an intermediate stage of the suction process so that the exhaust air temperature becomes higher in advance of stopping of the engine. Consequently, it is possible to prevent deterioration of emission after restarting because an exhaust air purifying function of the catalyst 5 is displayed after the restarting or in a short period of time after restart since the temperature of the catalyst 5 is high at restarting. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an in-cylinder direct injection engine (in-cylinder direct injection engine) applied to a vehicle (HV = Hybrid Vehicle, hybrid vehicle) having both an electric motor as a power source and an internal combustion engine (engine) using gasoline as fuel. It relates to a control method.

多 様 Various power sources have been devised to meet the demand for lower fuel consumption of automobiles. A so-called HV system using an electric motor and an internal combustion engine in combination is one of them. As an internal combustion engine combined with an electric motor in the HV system, a gasoline engine, a diesel engine, and the like can be mentioned, and an attempt has been made to use a gasoline in-cylinder direct injection engine having excellent specific power.

In a gasoline direct injection engine, a control mode is used in which stratified combustion is performed by injecting fuel in the compression stroke at low load, and premixed uniform combustion by injecting fuel in the intake stroke at high load, according to the required load. Is known.

In the HV, when the required load of the vehicle is small, the engine is stopped and the vehicle is driven by the electric motor. Therefore, the required load of the engine is limited to a high load. Limited to

As described above, in the HV, the engine is stopped when the load is low, so that the engine is frequently started and stopped during normal running. Therefore, there is a problem that the temperature of the cylinder wall surface and the temperature of the exhaust gas purifying catalyst tend to decrease.

Even during normal running, if the temperature of the exhaust gas purifying catalyst is lowered to the activation temperature or lower by stopping the engine, the exhaust gas is not purified immediately after restarting, so that the exhaust emission is deteriorated. . The present invention has been made to solve such a problem.

This invention employs the technical means described in claim 1 in order to solve the above problems. That is, by raising the temperature of the catalyst to the endurance limit in advance when the engine is stopped, the catalyst temperature at the time of restart is increased, and the time required for warming up the catalyst is reduced or eliminated, and the exhaust gas purification performance of the catalyst is reduced. This makes it possible to prevent the occurrence of a break in the exhaust gas, thereby preventing an increase in exhaust emission during warm-up of the catalyst.

According to this technical means, in the warming-up process, not only can the catalyst temperature rise be promoted, but also the oil dilution can be reduced, and low fuel consumption can be realized after the warming-up.

According to the technical means described in claim 2, when the engine is temporarily stopped such as at a light load, the same effect as that of the technical means of claim 1 is obtained, and the vehicle is continuously stopped. At times, the driver can turn off the main switch (ignition key) of the HV to immediately stop the engine, so that the driver does not feel uncomfortable.

According to the technical means described in claim 3, prior to the temporary stop of the engine, the fuel injection timing is changed to a point at which the exhaust gas temperature increases, that is, the fuel injection timing is changed from the middle stage of the intake stroke to the intake stroke. The same effect as the technical means of claims 1 and 2 can be obtained by changing early.

FIG. 1 is a system configuration diagram showing a first embodiment of only an engine portion to be controlled by a control method of the present invention in an HV system in which a gasoline direct injection engine is one of the power sources. In the in-cylinder direct injection engine of the first embodiment, a cylinder wall temperature sensor 3 is provided at a position on the wall surface of the cylinder 1 facing the injection hole of the fuel injection valve 2 where fuel spray adheres, and exhaust gas is discharged. A catalyst temperature sensor 6 is provided in the catalyst 5 provided in the passage 4, and output signals of these sensors 3 and 6 are input to an ECU (electronic control device) 7 having a built-in microcomputer.

In addition, the ECU 7 includes an accelerator position sensor 9 for detecting the amount of depression of an accelerator pedal 8 operated by the driver, an air flow sensor 10 for detecting the amount of intake air, and an empty space provided in the exhaust passage 4 for detecting the oxygen concentration. Output signals from a crank angle sensor 13 and the like, which are provided to face the fuel ratio sensor 11 and the crankshaft 12 and detect the rotation position and the number of rotations, are input. Then, the ECU 7 determines the fuel injection timing of the fuel injection valve 2, the ignition timing for energizing the ignition plug 14, and the like based on these signals. The opening and closing of the throttle valve 16 provided in the intake passage 15 is controlled directly by the accelerator pedal 8 or indirectly via the ECU 7. 17 is a fuel tank, 18 is a high-pressure fuel pump, and 19 is a piston.

FIG. 2 shows changes in the fuel consumption rate, the amount of fuel adhering to the cylinder wall surface, and the exhaust gas temperature when the intake stroke injection is performed in the gasoline cylinder direct injection engine shown in FIG. As shown in FIG. 3, when the fuel is injected in the middle stage of the intake stroke (around point A in FIG. 2), the fuel consumption rate decreases, but the amount of fuel adhering to the cylinder wall increases, and the exhaust temperature decreases. . On the other hand, when fuel is injected at the beginning of the intake stroke (around point B in FIG. 2) as shown in FIG. 4, the amount of fuel adhering to the cylinder is reduced and the exhaust temperature is increased.

FIG. 5 is a flowchart illustrating a control method of the present invention utilizing the properties shown in FIG. Next, this control example will be described with reference to FIGS. 1 to 5.

When the control program shown in the flowchart of FIG. 5 starts, first, in step 101, the output signal of the cylinder wall temperature sensor 3 is read by the ECU 7 and compared with a predetermined temperature. In step 102, the output signal of the catalyst temperature sensor 6 is read and compared with the activation temperature of the catalyst. If the cylinder wall temperature is high and the catalyst temperature is equal to or higher than the activation temperature of the catalyst 5, the routine proceeds to step 103, and the fuel injection timing is set to the point A in FIG. 2, that is, the middle point of the intake stroke at which the fuel consumption rate becomes the best. Is selected.

At this time, a part of the fuel spray injected from the fuel injection valve 2 collides with and adheres to the wall surface of the cylinder 1 as shown in FIG. Therefore, as shown in FIG. 2, the amount of fuel adhering to the cylinder is about to increase. However, since the cylinder wall temperature is high, the adhering fuel is immediately vaporized by the heat of the wall surface, and does not lead to an increase in oil dilution. Further, the emission discharged from the engine is sufficiently purified by the activated catalyst 5 and reduced.

However, in the HV, when the required load on the power source of the vehicle is small, the engine is temporarily stopped, so that the cylinder wall temperature and the catalyst temperature may decrease even during running.

When the wall temperature of the cylinder 1 is low, the fuel adhering to the cylinder 1 is hard to vaporize, so it is mixed with the oil forming the lubricating oil film on the wall, and is scraped off by the piston ring together with the oil. Oil stored in the oil pan in the crankcase causes dilution. In this case, in the control method illustrated in FIG. 5, the process proceeds from step 101 to step 104, and the fuel injection timing is controlled to the point B in FIG. 2, which is the early injection point in the intake stroke. When the injection timing reaches point B, the fuel spray is injected toward the top surface of the piston 19 as shown in FIG. 4, so that the adhesion to the wall surface of the cylinder 1 is reduced as shown in FIG. Solution can be prevented.

(4) If the temperature of the catalyst 5 is lower than the activation temperature of the catalyst, sufficient purification performance cannot be obtained, so that emission emissions from the vehicle deteriorate. In this case, the process proceeds from step 102 to step 104 in FIG. 5, and the fuel injection timing is changed from the point A to the point B as in the case described above. As is clear from FIG. 2, the injection temperature at the point B is higher than the injection temperature at the point A, so that the temperature rise of the catalyst 5 is promoted.

Fig. 6 shows an outline of the system of the entire HV. When the engine is stopped in the HV, the main CU (main control device) 21 depends on the continuous stop of the engine (eg, by turning off the ignition key switch 20) accompanying the stop of the vehicle by the driver's will, and the running state or load state. There is a temporary stop when it is determined that the in-cylinder direct injection engine 22 is temporarily stopped. A control program for stopping the engine will be described with reference to a flowchart of FIG.

When a stop command for the engine 22 is issued from the main CU 21 in step 201, and it is found in step 202 that the command is due to the driver's will (ignition key OFF or the like), the process immediately proceeds to step 203 and the engine ECU 23 22 is stopped. However, when it is determined in step 202 that the engine stop is not due to the driver's intention, the process proceeds to step 204. In this case, that is, even when the main CU 21 determines that the torque of the engine 22 is unnecessary from the running state of the vehicle, in step 204, until the catalyst temperature detected by the sensor 6 reaches the heat resistance limit, the fuel injection valve The control of moving the fuel injection timing of No. 2 to the point B is performed to continue the operation of the engine 22. When the heat limit is reached, the routine proceeds to step 203, where the engine ECU 23 temporarily stops the engine 22. In this case, the operation control of the motor 25 by the motor ECU 24 is continued.

(4) By this control, the catalyst temperature at the time of restart can be increased, and the warm-up time of the catalyst 5 can be shortened or substantially eliminated, so that the emission in the warm-up process of the catalyst 5 can be reduced.

FIG. 8 shows another embodiment of a gasoline direct injection engine for HV to which the control method of the present invention is applied. In this embodiment, an output signal of a cooling water temperature sensor 26 conventionally provided in an engine cooling water passage and used for detecting a cooling water temperature is input to an engine ECU 7 without installing a cylinder wall temperature sensor. This determines the vaporization state of the fuel adhering to the cylinder 1, and the other controls are the same as in the above-described example. In FIG. 8, reference numeral 27 denotes a radiator, and reference numeral 28 denotes a cooling water passage. Other reference numerals are the same as those shown in FIG.

FIG. 1 is a system configuration diagram showing a first embodiment of a direct injection engine to which a control method of the present invention is applied. FIG. 4 is a graph showing changes in various characteristics of an in-cylinder direct injection engine with changes in injection timing during intake stroke injection. FIG. 3 is a cross-sectional view showing a middle-stage injection in an intake stroke of a direct injection engine. FIG. 3 is a cross-sectional view illustrating an initial injection in an intake stroke of a direct injection engine. 5 is a flowchart illustrating a control example according to the present invention. 1 is a system configuration diagram schematically illustrating the entire HV system. 5 is a flowchart illustrating an example of control for stopping the engine in the HV system. It is a system configuration diagram showing a second embodiment of a direct injection engine to which a control method of the present invention is applied.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... Cylinder of gasoline in-cylinder direct injection engine 2 ... Fuel injection valve 3 ... Cylinder wall temperature sensor 5 ... Exhaust purification catalyst 6 ... Catalyst temperature sensor 7 ... Electronic control device 20 for in-cylinder direct injection engine 20 ... Main switch (ignition Key switch)
21: Main control unit (Main CU) for HV (Hybrid Vehicle)
22 ... gasoline cylinder direct injection engine 25 ... motor 26 ... cooling water temperature sensor

Claims (3)

For direct injection engines in gasoline cylinders applied to vehicles that have both an electric motor and an internal combustion engine as power sources, switch to a control mode in which the exhaust gas temperature rises before the engine stops, and set the temperature of the exhaust gas purification catalyst to the heat resistance limit of the catalyst. A method for controlling an in-cylinder direct injection engine, wherein the engine is stopped after the temperature is raised to the maximum. The control method according to claim 1 is executed at the time of a temporary engine stop peculiar to an engine used in a vehicle having both an electric motor and an internal combustion engine as a power source, other than a continuous engine stop by shutting off a main switch. Characteristic control method. A control method according to claim 1 or 2, wherein the control mode for increasing the exhaust gas temperature is to change the fuel injection timing from a middle stage of the intake stroke to an early stage of the intake stroke.

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