Engine System

Abstract

To provide an engine system capable of improving emissions while stabilizing a combustion state when an engine is restarted.SOLUTION: An engine system comprises an engine provided with first and second cylinders and a control device which executes automatic stop and restart of the engine. The control device has: an acquisition section which acquires an engine temperature and duration of the automatic stop of the engine; a fuel cut control section which executes specific cylinder fuel cut processing where fuel is supplied to the second cylinder with fuel supply to the first cylinder stopped when a request is made for restarting the engine; and an injection amount control section which increases an amount of fuel injected into the second cylinder with increasing duration of the automatic stop of the engine or with a decreasing engine temperature while the specific cylinder fuel cut processing is in execution.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an engine system. [Background technology]

[0002] BACKGROUND ART When restarting an automatically stopped engine, it is known to cut fuel to specific cylinders among a plurality of cylinders of the engine, while supplying fuel to the remaining cylinders (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-106391 Summary of the Invention [Problem to be solved by the invention]

[0004] When the engine is restarted in this manner, the combustion state in the cylinders to which fuel is supplied may become unstable, which may result in a deterioration in emissions.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an engine system that stabilizes the combustion state when the engine is restarted while improving emissions. [Means for solving the problem]

[0006] The above object can be achieved by an engine system including an engine having first and second cylinders, and a control device that executes automatic stopping and restarting of the engine, wherein the control device includes an acquisition unit that acquires the temperature of the engine and the time during which the engine is automatically stopped, a fuel cut control unit that executes a specific cylinder fuel cut process that stops the supply of fuel to the first cylinder and supplies fuel to the second cylinder when there is a request to restart the engine, and an injection amount control unit that increases the amount of fuel injected into the second cylinder while the specific cylinder fuel cut process is being executed, the longer the time during which the engine is automatically stopped and the lower the temperature of the engine.

[0007] The injection amount control unit may calculate the increase in the fuel injection amount in the second cylinder using a correction coefficient related to non-contributing fuel that does not contribute to combustion.

[0008] The injection amount control unit may calculate an increase in the fuel injection amount in the second cylinder using a correction coefficient for suppressing NOx emissions.

[0009] The control device may include an ignition timing control unit that controls the ignition timing of the engine, and a throttle opening control unit that controls the throttle opening of the engine, wherein the ignition timing control unit controls the ignition timing of the second cylinder in accordance with the amount of fluctuation per unit time in at least one of the engine speed and torque while the specific cylinder fuel cut process is being executed, and the throttle opening control unit controls the throttle opening in accordance with the ignition timing of the engine while the specific cylinder fuel cut process is being executed.

[0010] The engine may further include a motor that assists the torque of the engine while the specific cylinder fuel cut process is being executed. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an engine system that stabilizes the combustion state when the engine is restarted and improves emissions. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of the engine system. [Figure 2] FIG. 2 is a schematic diagram of the engine. [Figure 3] FIG. 3 is a flowchart illustrating the intermittent operation control executed by the ECU. [Figure 4] FIG. 4A is an example of a map that defines a correction coefficient K1 for increasing the non-contributing fuel amount, and FIG. 4B is an example of a map that defines a correction coefficient K2 for increasing the fuel amount required to suppress NOx emissions. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Engine system overview] FIG. 1 is a schematic diagram of an engine system 1 according to this embodiment. In this embodiment, the engine system 1 is mounted on a hybrid vehicle. The engine system 1 includes an ECU (Electronic Control Unit) 100, an engine 10, a first motor generator (hereinafter referred to as the "first MG (Motor Generator)") 14, a second motor generator (hereinafter referred to as the "second MG") 15, a PCU (Power Control Unit) 17, a battery 18, a power split mechanism 50, a transmission mechanism 51, a transmission 52, a drive shaft 53, a differential 54, and drive wheels 55. In this embodiment, the engine 10 has four cylinders #1 to #4. The number of cylinders in the engine 10 is not limited to four, as long as the engine 10 has multiple cylinders. The engine 10 is a gasoline engine, but may be a diesel engine. The engine 10, the first MG 14, and the second MG 15 are power sources for driving the engine system 1.

[0014] Each of the first MG 14 and the second MG 15 functions as a motor that outputs torque when supplied with electric power, and as a generator that generates regenerative power when torque is applied to it. The first MG 14 and the second MG 15 are electrically connected to a battery 18 via a PCU 17. The PCU 17 supplies electric power from the battery 18 to the first MG 14 or the second MG 15. The PCU 17 causes the battery 18 to receive the regenerative power generated in the first MG 14 or the second MG 15.

[0015] The power split mechanism 50 mechanically couples the crankshaft of the engine 10, the rotating shaft of the first MG 14, and the output shaft of the power split mechanism 50. The output shaft of the power split mechanism 50 is coupled to a transmission mechanism 51. The rotating shaft of the second MG 15 is coupled to the transmission mechanism 51. The transmission mechanism 51 is coupled to a transmission 52. The transmission 52 is coupled to a drive shaft 53. The driving forces of the engine 10, the first MG 14, and the second MG 15 are transmitted to drive wheels 55 via the transmission mechanism 51, the transmission 52, the drive shaft 53, and the differential 54.

[0016] The transmission 52 is a stepped automatic transmission provided between the second MG 15 and the drive shaft 53. The transmission 52 changes its gear ratio under the control of the ECU 100.

[0017] The ECU 100 is an electronic control unit that includes a processing circuit that performs various types of calculations related to vehicle driving control and a memory that stores control programs and data. The ECU 100 is an example of a control device. The ECU 100 functionally realizes an acquisition unit, a fuel cut control unit, an injection amount control unit, an ignition timing control unit, and a throttle opening control unit, which will be described later.

[0018] The ECU 100 receives signals from an ignition switch 71, a water temperature sensor 72, a crank angle sensor 73, an air flow meter 74, and an accelerator position sensor 75. The ignition switch 71 detects the on / off state of the ignition. The water temperature sensor 72 detects the temperature of the coolant for the engine 10. The crank angle sensor 73 detects the engine rotation speed, which is the rotation speed of the crankshaft of the engine 10. The air flow meter 74 detects the amount of intake air introduced into the engine 10. The accelerator position sensor 75 detects the operating position of the accelerator pedal.

[0019] [Engine outline] FIG. 2 is a schematic diagram of engine 10. Engine 10 has cylinder #1, piston 31, connecting rod 32, crankshaft 33, intake passage 35, intake valve 36, exhaust passage 37, and exhaust valve 38. FIG. 2 illustrates cylinder #1 of four cylinders #1 to #4 of engine 10. Because cylinders #1 to #4 have the same configuration, only cylinder #1 will be described below. Combustion of an air-fuel mixture occurs in cylinder #1. Piston 31 is accommodated in cylinder #1 so as to be able to reciprocate, and is connected to crankshaft 33, which is the output shaft of engine 10, via connecting rod 32. Connecting rod 32 and crankshaft 33 convert the reciprocating motion of piston 31 into rotational motion of crankshaft 33.

[0020] Cylinder #1 is provided with an in-cylinder injection valve 41d. The in-cylinder injection valve 41d injects fuel directly into cylinder #1. The intake passage 35 is provided with a port injection valve 41p that injects fuel toward the intake port 35p. Cylinder #1 is provided with an ignition device 42 that ignites, by spark discharge, an air-fuel mixture of intake air introduced through the intake passage 35 and fuel injected by the in-cylinder injection valve 41d and the port injection valve 41p. It is sufficient that at least one of the in-cylinder injection valve 41d and the port injection valve 41p is provided.

[0021] The intake passage 35 is connected to an intake port 35p of cylinder #1 via an intake valve 36. The exhaust passage 37 is connected to an exhaust port 37p of cylinder #1 via an exhaust valve 38. The intake passage 35 is provided with the air flow meter 74 and a throttle valve 40 that controls the amount of intake air.

[0022] A catalyst 43 and a gasoline particulate filter (GPF) 44 are provided in the exhaust passage 37 from the upstream side. The catalyst 43 contains a catalytic metal such as platinum (Pt), palladium (Pd), or rhodium (Rh), has oxygen storage capacity, and purifies NOx, HC, and CO. The GPF 44 is a porous ceramic structure that captures exhaust particulates (hereinafter referred to as PM (Particulate Matter)) in the exhaust gas.

[0023] The throttle valve 40 can increase or decrease the amount of intake air introduced into the cylinder #1 by increasing or decreasing the opening degree thereof. The opening degree of the throttle valve 40 is controlled in accordance with the opening degree required by the ECU 100.

[0024] [Intermittent operation control] 3 is a flowchart illustrating the intermittent operation control executed by the ECU 100. This control is repeatedly executed at predetermined intervals while the ignition is on. The ECU 100 determines whether or not there is a request to restart the engine 10 (step S1). If the answer is No in step S1, this control ends.

[0025] If the answer is Yes in step S1, the ECU 100 executes a specific cylinder fuel cut process (step S2). The specific cylinder fuel cut process is a process in which fuel supply to one of cylinders #1 to #4 is stopped and fuel is supplied to the remaining cylinders. In this embodiment, fuel supply to cylinder #1 is stopped and fuel is supplied to cylinders #2 to #4. Since fuel supply to a specific cylinder is stopped in this manner, fuel economy and emissions are improved. Note that while the specific cylinder fuel cut process is being executed, feedback control that controls the fuel injection amount and intake air amount based on the exhaust air-fuel ratio is stopped. Step S2 is an example of a process executed by a fuel cut control unit. Cylinder #1 is an example of a first cylinder. Cylinder #2 is an example of a second cylinder.

[0026] Next, the ECU 100 acquires the automatic stop time, which is the time during which the engine 10 is automatically stopped, and the temperature of the coolant of the engine 10 (step S3). The automatic stop time is the time from when the engine 10 is automatically stopped until when it is restarted. The ECU 100 measures the time from when the engine 10 is automatically stopped until when it is restarted. The ECU 100 acquires the temperature of the coolant of the engine 10 based on the detection value of the water temperature sensor 72. Step S3 is an example of processing executed by the acquisition unit.

[0027] Next, the ECU 100 determines whether the automatic stop time is longer than a threshold value (step S4). If the answer is Yes in step S4, the ECU 100 performs a correction to increase the fuel injection amount for each of the cylinders #2 to #4 that are not subject to fuel cut (step S5). This correction is a correction to increase the basic fuel injection amount to compensate for the non-contributing fuel that adheres to the inner cylinder surface and the top surface of the piston 31 and does not contribute to combustion. The longer the automatic stop time is, the more the fuel adhering to the bore wall surface in the cylinder progresses to vaporize. Therefore, at restart, some of the injected fuel may adhere to the inner cylinder wall surface, etc., increasing the amount of non-contributing fuel. This may result in an unstable combustion state. Therefore, the threshold value in step S4 is set to the shortest automatic stop time at which the combustion state becomes unstable at restart. Therefore, the longer the automatic stop time is compared to the threshold value, the more the fuel injection amount at restart is increased. Specifically, the ECU 100 performs a correction to increase the fuel injection amount by referring to the map shown in FIG. 4A. Step S5 is an example of a process executed by the injection amount control unit.

[0028] FIG. 4A is an example diagram of a map defining a correction coefficient K1 for increasing the non-contributing fuel amount. The correction coefficient K1 is a correction coefficient for increasing the basic fuel injection amount to compensate for the non-contributing fuel amount. As shown in FIG. 4A, the correction coefficient K1 is defined to be larger as the coolant temperature decreases. FIG. 4A also illustrates the case of an automatic stop time T1 and the case of an automatic stop time T2 that is longer than the automatic stop time T1. The correction coefficient K1 is defined to be larger for the automatic stop time T2 than for the automatic stop time T1. The correction coefficient K1 is a value greater than or equal to 1 and less than 2. The target injection amount is calculated by multiplying the calculated correction coefficient K1 by the basic injection amount. The ECU 100 controls the valve opening time of at least one of the direct injection valve 41d and the port injection valve 41p so that the fuel injection amount becomes the target injection amount. Increasing the fuel injection amount in this manner stabilizes the combustion state of the engine 10.

[0029] If the answer is No in step S4 or after executing step S5, the ECU 100 determines whether the automatic stop time is greater than a threshold (step S6). If the answer is Yes in step S6, the ECU 100 performs a correction to increase the fuel injection amount for each of the cylinders #2 to #4 that are not subject to fuel cut (step S7). This correction is a correction to increase the basic fuel injection amount so as to suppress an increase in NOx emissions at the time of restart. The longer the automatic stop time, the greater the oxygen storage amount of the catalyst 43. If exhaust gas with an air-fuel ratio having a high oxygen concentration flows into the catalyst 43 with a large oxygen storage amount, the NOx purification ability of the catalyst 43 decreases. Therefore, the threshold in step S6 is set to the shortest automatic stop time at which the NOx purification ability of the catalyst 43 decreases at the time of restart. The threshold in step S6 may be the same as or different from the threshold in step S4. Specifically, the ECU 100 performs a correction to increase the fuel injection amount by referring to the map shown in FIG. 4B. Step S7 is an example of processing executed by the injection amount control unit.

[0030] FIG. 4B is an example of a map that defines a correction coefficient K2 for increasing the amount of fuel required to suppress NOx emissions. The correction coefficient K2 is a correction coefficient for increasing the basic fuel injection amount so as to suppress NOx emissions. As shown in FIG. 4B, the correction coefficient K2 is defined to be larger as the coolant temperature decreases. Furthermore, the correction coefficient K2 is defined to be larger for the automatic stop time T2 than for the automatic stop time T1. The correction coefficient K2 is, for example, a value greater than or equal to 1 and less than 2. For example, when the above-described correction coefficient K1 and correction coefficient K2 are calculated, the target injection amount is calculated by adding the correction coefficient K2 to the correction coefficient K1 and subtracting 1 from the result, and multiplying the result by the basic injection amount. When only the correction coefficient K2 is calculated, the target injection amount is calculated by multiplying the basic injection amount by the correction coefficient K2. Increasing the fuel injection amount in this manner improves emissions when the engine 10 is restarted.

[0031] Next, the ECU 100 causes the first MG 14 to assist the torque of the engine 10 accompanying the execution of the specific cylinder fuel cut process (step S8). The torque of the engine 10 temporarily decreases during a period corresponding to the explosion stroke of the cylinder for which fuel cut is being executed. The torque of the first MG 14 is controlled to compensate for this decrease in torque of the engine 10. For example, the ECU 100 determines the explosion stroke of the cylinder for which fuel cut is being executed based on the detection value of the crank angle sensor 73. The ECU 100 controls the PCU 17 so that the torque of the first MG 14 temporarily increases during this explosion stroke. This ensures drivability.

[0032] Next, the ECU 100 determines whether the amount of fluctuation in the rotation speed of the engine 10 per unit time is greater than a threshold value (step S9). The rotation speed of the engine 10 is calculated based on the detection value of the crank angle sensor 73. In this case, the threshold value is set to, for example, an upper limit value of the amount of fluctuation in the rotation speed of the engine 10 that does not affect drivability. If the result of step S9 is No, the ECU 100 determines whether the amount of fluctuation in the torque of the engine 10 per unit time is greater than a threshold value (step S10). In this case, the threshold value is also set to, for example, an upper limit value of the amount of fluctuation in the torque of the engine 10 that does not affect drivability. The torque of the engine 10 may be calculated based on, for example, the value of the current supplied to the first MG 14 connected to the engine 10 and the rotation speed of the engine 10. Alternatively, the torque of the engine 10 may be calculated from various state quantities, such as the rotation speed of the engine 10 and the opening degree of the throttle valve 40. If the result of step S10 is No, this control ends.

[0033] If the answer is Yes in step S9 or S10, the ECU 100 controls the ignition timing and the throttle opening (step S11). Specifically, the ECU 100 retards the ignition timing more than when the answer is No in steps S9 and S10. Furthermore, the ECU 100 retards the ignition timing more as the coolant temperature decreases. This stabilizes the combustion state of the engine 10 and increases the torque of the engine 10. Furthermore, the ECU 100 controls the throttle opening according to the ignition timing thus controlled. Specifically, the ECU 100 reduces the throttle opening more than when the answer is No in steps S9 and S10. This reduces the intake air amount and correspondingly reduces the fuel injection amount. Therefore, fuel economy is improved. As a result, fuel economy is improved while suppressing fluctuations in the rotation speed and torque of the engine 10. Step S11 is an example of processing executed by the ignition timing control unit and the throttle opening control unit.

[0034] It is to be noted that only one of steps S9 and S10 may be executed. The contents of this embodiment may be applied to an engine system of an engine vehicle that is equipped with only an engine as a driving power source.

[0035] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0036] 1 Engine System 10 Engine 14 First motor generator 100 ECU (control device, acquisition unit, fuel cut control unit, injection amount control unit, ignition timing control unit, throttle opening control unit)

Claims

[Claim 1] An engine system mounted on a hybrid vehicle, an engine having first and second cylinders; a catalyst provided in an exhaust passage of the engine, having an oxygen storage capacity, and purifying NOx, HC, and CO; a control device that executes automatic stopping and restarting of the engine, Fuel is injected into each of the first and second cylinders by at least one of a cylinder injection valve and a port injection valve, The control device an acquisition unit that acquires the temperature of the engine and the time during which the engine is automatically stopped; a fuel cut control unit that, when a restart of the engine is requested, executes a specific cylinder fuel cut process that stops the supply of fuel to the first cylinder and supplies fuel to the second cylinder; an injection amount control unit that increases the fuel injection amount in the second cylinder as the time during which the engine is automatically stopped becomes longer and as the temperature of the engine becomes lower during execution of the specific cylinder fuel cut process, the injection amount control unit calculates a target fuel injection amount for the second cylinder during execution of the specific cylinder fuel cut process, using a first correction coefficient for increasing a basic fuel injection amount so as to compensate for a non-contributing fuel amount that does not contribute to combustion and a second correction coefficient for increasing the basic fuel injection amount so as to suppress NOx emissions; The control device an ignition timing control unit that controls the ignition timing of the engine; a throttle opening control unit that controls a throttle opening of the engine, the ignition timing control unit, when a fluctuation amount per unit time of at least one of the engine speed and torque during execution of the specific cylinder fuel cut process is greater than a threshold, retards the ignition timing in the second cylinder more than when the fluctuation amount during execution of the specific cylinder fuel cut process is equal to or less than the threshold, the throttle opening control unit reduces the throttle opening when the fluctuation amount during execution of the specific cylinder fuel cut process is greater than the threshold value, more than when the fluctuation amount during execution of the specific cylinder fuel cut process is equal to or less than the threshold value; the threshold value is set to an upper limit value of the amount of fluctuation that does not affect drivability, a motor that assists the torque of the engine while the specific cylinder fuel cut process is being executed; The engine system is configured such that the motor torque is temporarily increased during the power stroke of the first cylinder while the specific cylinder fuel cut process is being performed.

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