JP4826300B2 - Control device and control method for internal combustion engine - Google Patents

Description

  The present invention relates to a control technique for an internal combustion engine provided with a high-pressure fuel pipe.

  In an internal combustion engine, particularly a direct injection type spark ignition internal combustion engine that directly injects fuel into a combustion chamber, a high pressure boosted by a high-pressure fuel pump mechanically driven by the engine output in order to stably obtain a high fuel injection pressure. There is known a fuel system that supplies fuel to a high-pressure fuel pipe connected to a plurality of fuel injection valves via a check valve. In such a fuel system, at the start of a fuel cut recover operation (hereinafter also referred to simply as a recover) that restarts fuel injection from a fuel cut operation that temporarily stops fuel injection, such as during engine deceleration or idle stop, Even if the fuel injection period is minimized, the amount of fuel injection cannot be sufficiently reduced, and the engine output torque temporarily increases, causing unpleasant torque fluctuations.

In order to reduce and eliminate such torque fluctuations, Patent Document 1 proposes the following three methods. In the first method, a relief valve for releasing fuel in the fuel pressure chamber of the high-pressure fuel pipe is added, and the fuel pressure in the high-pressure fuel pipe is lowered by opening the relief valve at the time of fuel cut recovery. In the second method, in an internal combustion engine capable of realizing both stratified combustion operation and homogeneous combustion operation, performing the homogeneous combustion operation of reducing the intake air amount and injecting fuel during the intake stroke at the time of the fuel cut recovery. As a result, the fuel pressure in the high-pressure fuel pipe is reduced. In the third technique, in the internal combustion engine including both an intake passage injection fuel injection valve for injecting fuel into the intake passage and an in-cylinder injection fuel injection valve for injecting fuel into the combustion chamber, the fuel cut recovery is performed. Sometimes, the fuel pressure in the high-pressure fuel pipe is lowered by reducing the amount of intake air and performing fuel injection from the fuel injection valve for intake passage injection.
Japanese Patent No. 3170974

  However, the above first and third methods require additional parts such as a relief valve, an intake passage injection fuel injection valve, and an in-cylinder injection fuel injection valve, leading to an increase in size, weight, and cost. End up. Further, the second method can be used only for an internal combustion engine that can realize both stratified combustion operation and homogeneous combustion operation. Further, in the second and third methods, when the operation condition after the fuel cut recovery is an operation state in which the intake air amount is originally low like the idle operation, it is extremely possible to further reduce the intake air amount by the throttle valve. Have difficulty. Moreover, if the intake air amount at the time of recovery is reduced as in the second and third methods, the air-fuel ratio of the exhaust gas may become rich, and the exhaust performance may be hindered.

The present invention has been made in view of such a problem, and is provided with a fuel injection valve for injecting fuel into a combustion chamber or an intake system of an internal combustion engine, and high-pressure fuel via a check valve, and the fuel Regarding control of an internal combustion engine having a high-pressure fuel pipe for supplying fuel to an injection valve, the control is preset at the start of a fuel cut recovery operation for restarting fuel injection from a fuel cut operation for temporarily stopping the fuel injection . The efficiency reduction operation is performed for a predetermined period. In this efficiency reduction operation, while correcting the combustion efficiency to be reduced, the fuel injection amount is corrected so as to increase compared to the required fuel injection amount, and the intake air amount is adjusted. It is characterized by correcting so as to increase compared to the required intake air amount .

  According to the present invention, the fuel pressure of the high-pressure fuel pipe is reduced after the start of the fuel cut recovery operation with a simple configuration that does not require any additional parts, without deteriorating the exhaust performance and without causing torque fluctuation. It can be quickly reduced.

  FIG. 1 is a configuration diagram schematically showing a fuel system of a direct injection type spark ignition internal combustion engine according to an embodiment of the present invention. The fuel system includes a plurality of high-pressure fuel injection valves 11 that directly inject fuel into a combustion chamber (not shown) of each cylinder of an internal combustion engine, and a high-pressure fuel pump that is mechanically driven by engine output. 12 and a high-pressure fuel pipe 13 that is supplied with high-pressure fuel boosted by the high-pressure fuel pump 12 via a check valve 15 and supplies the high-pressure fuel to a plurality of fuel injection valves 11.

  The high-pressure fuel pump 12 is driven in a reciprocating manner against the spring force of the return spring 12C by a cam shaft 12A of a camshaft that is rotationally driven by a crankshaft (not shown) that is an engine output shaft. It is mechanically driven in conjunction with the rotation of the crankshaft. The high-pressure fuel pipe 13 is provided with a high-pressure fuel rail 14 connected to the plurality of fuel injection valves 11 and a check valve 15 for preventing a back flow from the high-pressure fuel rail 14 to the high-pressure fuel pump 12 side. . A fuel pressure sensor 16 that detects the fuel pressure in the high-pressure fuel rail 14 (fuel pressure chamber) is also provided.

  The fuel tank 17 in which the fuel is stored and the high pressure fuel pump 12 are connected by a low pressure fuel pipe 18. The low-pressure fuel pipe 18 is provided with a low-pressure fuel pump 19 driven by a pump drive motor 20, a fuel pressure regulator 21, fuel filters 22 and 23, and an electromagnetic valve 24. The fuel pressure regulator 21 returns a part of the fuel discharged from the low-pressure fuel pump 19 to the fuel tank 17 when the fuel pressure of the fuel discharged from the low-pressure fuel pump 19 becomes higher than a predetermined set fuel pressure. Thus, the fuel pressure supplied to the high-pressure fuel pump 12 is kept constant. The solenoid valve 24 adjusts the amount of fuel supplied from the high pressure fuel pump 12 to the high pressure fuel pipe 13 side by intermittently supplying fuel from the low pressure fuel pump 19 to the high pressure fuel pump 12 side.

  As is well known, the control unit 25 is a digital computer having a function of storing and executing various control processes, and in addition to the fuel pressure sensor 16, a water temperature sensor 27 for detecting the engine water temperature and an intake air temperature sensor for detecting the intake air temperature. Based on detection signals from various sensors such as 28, control is made to the fuel injection valve 11, the pump drive motor 20 and the electromagnetic valve 24 as well as an electrically controlled throttle valve 26 which opens and closes an intake passage (not shown). A signal is output to control its operation.

  This fuel system is a returnless system having no return line from the high-pressure fuel pipe 13 to the fuel tank 17. Such a returnless system simplifies piping and can be reduced in size and weight, and high-pressure and high-temperature fuel is not returned to the fuel tank 17, so that evaporated fuel is generated in the fuel tank 17. There is an advantage that can be suppressed.

  FIG. 2 is a flowchart schematically showing the control flow of this embodiment. At the time of engine deceleration or idle stop in an idle stop vehicle, a fuel cut operation for temporarily stopping fuel injection from the fuel injection valve 11 is performed. At the start P0 (see FIG. 3) of such fuel cut operation, the process proceeds from step 11 to step 12, and the engine operating state such as fuel pressure, water temperature, intake air temperature detected by the various sensors 16, 27, 28, etc. At the same time, the measurement of the duration T of the fuel cut operation is started in step 13. In step 14, it is determined whether or not to perform a fuel cut recovery operation for restarting fuel injection based on the engine operating state. For example, it is determined that the fuel cut recovery operation should be started when the vehicle stops from the deceleration state or when the vehicle restarts from the idle stop, and the process proceeds to step 15 to start the fuel cut recovery operation.

  In this embodiment, when the predetermined determination condition of Steps 16 to 18 is satisfied at the start P1 of the fuel cut recovery operation (see FIG. 3), the combustion efficiency is reduced in Step 20 or Step 21. Then, the fuel injection amount is increased, and the combustion efficiency decreasing operation is performed to increase the intake air amount. Specifically, in step 16, it is determined whether the duration T of the fuel cut operation is equal to or shorter than a predetermined first determination time TTW set based on the water temperature or intake air temperature corresponding to the engine temperature. The first determination time TTW corresponds to a time during which the catalyst disposed in the exhaust passage is lowered to the inactive temperature due to a decrease in the exhaust temperature due to the fuel cut operation. In step 17, an upper limit value A of fuel pressure is calculated based on the required fuel injection amount after recovery. This upper limit value A corresponds to an upper limit value of the fuel pressure that can stably realize the required fuel injection amount. In step 18, it is determined whether the fuel pressure detected by the fuel pressure sensor 16 is equal to or higher than the fuel pressure upper limit A. Only when the duration time T is equal to or shorter than the first determination time TTW and the fuel pressure is less than the upper limit value A, the routine proceeds to step 19 and normal operation is performed. Otherwise, the routine proceeds to step 20 or 21. Then, the above efficiency reduction operation is performed.

  In the normal operation of step 19, normal control, that is, the throttle opening is set to the required throttle opening after recovery, the fuel injection timing is set to the intake stroke once in one cycle, and the fuel injection amount is The required fuel injection amount after recovery is set, and the ignition timing is set to the optimal ignition timing during the compression stroke.

  On the other hand, in the efficiency reduction operation in steps 20 and 21, in order to reduce the combustion efficiency, as shown in FIG. 4, fuel injection in one cycle is performed in a plurality of times. More specifically, fuel injection is performed in two steps, a compression stroke and an expansion stroke. In this case, the fuel injection amount is the sum of each injection in one cycle. Typically, the ratio between the first half and the second half is about 6: 4. In addition, in this efficiency reduction operation, the ignition timing is retarded as shown in FIG. 5 in order to reduce the combustion efficiency. More specifically, the ignition timing is retarded to the compression top dead center side than the normal required ignition timing. Then, the fuel injection amount and the intake air amount are increased as compared with the normal control (see FIG. 3).

  When the duration T exceeds the first determination time TTW, in step 22, the elapsed time after recovery, that is, the elapsed time TR of the combustion efficiency lowering operation is set based on the first determination time TTW. Until the second determination time TTR is reached. This second determination time TTR corresponds to a time sufficient to activate the catalyst provided in the exhaust passage.

  FIG. 3 is a time chart showing changes in the fuel injection amount (fuel flow rate), the intake air amount (throttle opening), and the like in an operation state in which the fuel cut recovery operation is performed after the fuel cut operation by engine deceleration. In the figure, the solid line characteristic corresponds to the present embodiment in which the efficiency reduction operation is performed, and the broken line characteristic corresponds to a comparative example in which the efficiency reduction operation is not performed.

  At the start P0 of the fuel cut operation, the fuel injection is stopped to set the fuel injection amount to 0 (zero), and according to the required intake air amount in the operation state after recovery (typically idle operation). Reduce the intake air amount (throttle opening). Even during such a fuel cut operation, the fuel pressure in the high-pressure fuel pipe 13 is maintained high in the above-described returnless fuel system.

  In this embodiment, when the fuel pressure at the start P1 of the fuel cut recovery operation is higher than the upper limit value A and cannot be suppressed to the required fuel injection amount, the efficiency reduction operation is performed. That is, while reducing the combustion efficiency, the fuel injection amount is increased from the original required fuel injection amount after the recovery (see the comparative example), and the intake air amount is the original required intake air amount after the recovery (the comparative example) Than see). Therefore, it is possible to absorb and cancel the torque increase corresponding to the increase in the fuel injection amount due to the decrease in the combustion efficiency, and sufficiently reduce or eliminate the torque fluctuation due to the increase in the fuel injection amount. be able to. In addition, by increasing the intake air amount, the expected combustion stability can be ensured by offsetting the decrease in combustion stability caused by retarding the ignition timing (decreasing combustion efficiency), and fuel. It is possible to suppress and avoid the richness of the air-fuel ratio of the exhaust gas accompanying the increase, and to prevent the exhaust performance from being deteriorated during the efficiency reduction operation. In addition, the combustion efficiency is reduced by multiple fuel injections and retarded ignition timing, and there is no need for additional parts as in the above-described conventional example. Cost reduction and the like can be achieved. The fuel pressure in the high-pressure fuel pipe 13 can be quickly increased after recovering the fuel cut without reducing exhaust performance and causing torque fluctuations with a simple configuration that does not require additional parts. Therefore, the fuel injection valve can be selected to an appropriate size, and variations in flow rate can be suppressed to improve exhaust, fuel consumption, and output.

  Since the exhaust temperature decreases during the fuel cut operation, if the fuel cut operation is prolonged, the temperature of the catalyst (not shown) disposed in the exhaust passage excessively decreases, and the exhaust after the fuel cut recovery is performed. May reduce emissions. In this embodiment, when the duration T of the fuel cut operation exceeds the first determination time TTW, the combustion efficiency reduction operation is forcibly performed, and the exhaust temperature rises due to the fuel efficiency reduction, and consequently the catalyst temperature rises. The combustion efficiency decreasing operation is continued until the elapsed time TR of the combustion efficiency operation exceeds a predetermined second determination time TTR. Accordingly, it is possible to avoid an excessive decrease in the catalyst temperature due to the fuel cut operation, and to quickly raise the temperature of the catalyst after the recovery, effectively reducing and avoiding a decrease in exhaust emission associated with the fuel cut operation. be able to.

  As described above, the present invention has been described based on the specific embodiments. However, the present invention is not limited to the above-described embodiments, and includes various modifications and changes without departing from the spirit of the present invention. . For example, the present invention can be applied to a port injection type internal combustion engine that injects fuel into an intake port of an intake system. Further, in the above embodiment, as a method for reducing the combustion efficiency, a plurality of fuel injections and retarding the ignition timing are used in combination, but either one of the methods may be used, and the other The methods may be combined or used alone.

The block diagram which shows simply the fuel system of the internal combustion engine which concerns on one Example of this invention. The flowchart which shows the flow of control of a present Example. The time chart which shows the mode of a change of the fuel injection quantity, the amount of intake air, etc. in the driving | running condition which performs a fuel cut recovery driving | operation after a fuel cut driving | operation. Explanatory drawing for demonstrating the method of dividing | segmenting fuel injection into multiple times in order to reduce combustion efficiency. Explanatory drawing for demonstrating the method of retarding ignition timing in order to reduce combustion efficiency.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Fuel injection valve 12 ... High pressure fuel pump 13 ... High pressure fuel piping 15 ... Check valve 25 ... Control part

Claims (8)

An internal combustion engine having a fuel injection valve that injects fuel into a combustion chamber or an intake system of an internal combustion engine, and a high-pressure fuel pipe that is supplied with high-pressure fuel through a check valve and supplies fuel to the fuel injection valve. In the control device,
At the start of the fuel cut recovery operation in which the fuel injection is resumed from the fuel cut operation in which the fuel injection is temporarily stopped , the efficiency reduction operation is performed for a predetermined period, and in this efficiency reduction operation, the combustion efficiency is reduced. while correcting such, with correction for to increase the fuel injection amount compared to the required fuel injection amount, and correcting to increase compared to the required intake air amount of intake air quantity internal combustion Engine control device. An internal combustion engine having a fuel injection valve that injects fuel into a combustion chamber or an intake system of an internal combustion engine, and a high-pressure fuel pipe that is supplied with high-pressure fuel through a check valve and supplies fuel to the fuel injection valve. In the control device,
While starting the fuel cut recovery operation in which the fuel injection is restarted from the fuel cut operation in which the fuel injection is temporarily stopped and when it is determined that the fuel pressure is greater than a predetermined value, the combustion efficiency is reduced. A control device for an internal combustion engine that performs an efficiency reduction operation that increases the fuel injection amount and increases the intake air amount. 3. The control device for an internal combustion engine according to claim 1, wherein in the efficiency reduction operation, in order to reduce combustion efficiency, fuel injection is performed in a plurality of times during one cycle. The control apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein , in the efficiency reduction operation, the ignition timing is retarded in order to reduce the combustion efficiency. If the duration of the fuel cut operation at the start of the fuel cut recovery operation exceeds the first determination time given, according to any one of claims 1 to 4, characterized in that the efficiency decreasing operation Control device for internal combustion engine. 6. The control device for an internal combustion engine according to claim 5 , wherein the efficiency reduction operation is continued until an elapsed time of the efficiency reduction operation exceeds a predetermined second determination time. A fuel pressure detecting means for detecting the fuel pressure in the high-pressure fuel pipe;
The control apparatus for an internal combustion engine according to any one of claims 1 to 6 , wherein the efficiency reduction operation is performed when a fuel pressure at the start of the fuel cut recovery operation is equal to or greater than a predetermined upper limit value. An internal combustion engine having a fuel injection valve that injects fuel into a combustion chamber or an intake system of an internal combustion engine, and a high-pressure fuel pipe that is supplied with high-pressure fuel through a check valve and supplies fuel to the fuel injection valve. In the control method,
At the start of the fuel cut recovery operation in which the fuel injection is resumed from the fuel cut operation in which the fuel injection is temporarily stopped , the efficiency reduction operation is performed for a predetermined period, and in this efficiency reduction operation, the combustion efficiency is reduced. while correcting such, with correction for to increase the fuel injection amount compared to the required fuel injection amount, and correcting to increase compared to the required intake air amount of intake air quantity internal combustion How to control the engine.

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