Engine System

Abstract

To provide an engine system capable of heating a catalyst while curbing degradation of an engine operation state.SOLUTION: An engine system comprises: an engine provided with first and second cylinders; a catalyst installed in an exhaust passage of the engine; and a control device of the engine. The control device has: 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 heating the catalyst; an injection amount control section which makes an amount of the fuel injected into the second cylinder larger than an amount when the specific cylinder fuel cut processing is stopped at a predetermined increase rate while the specific cylinder fuel cut processing is in execution; and an injection timing control section which advances fuel injection timing in a compression stroke of the second cylinder compared to fuel injection timing when the specific cylinder fuel cut processing is stopped 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] Fuel is cut off for specific cylinders among a plurality of cylinders of an engine, and the amount of fuel injected into the remaining cylinders is increased, thereby warming up the catalyst (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-167585 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a risk that the combustion condition will deteriorate in the cylinder where the fuel injection amount has been increased, resulting in unstable engine operation.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an engine system that can warm up a catalyst while suppressing deterioration of the engine's operating condition. [Means for solving the problem]

[0006] The above object can be achieved by an engine system including an engine having first and second cylinders, a catalyst provided in an exhaust passage of the engine, and a control device for the engine, wherein the control device includes 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 warm up the catalyst, an injection amount control unit that increases the fuel injection amount in the second cylinder by a predetermined increase rate while the specific cylinder fuel cut process is being executed, compared to when the specific cylinder fuel cut process is stopped, and an injection timing control unit that advances the fuel injection timing in the compression stroke of the second cylinder while the specific cylinder fuel cut process is being executed, compared to when the specific cylinder fuel cut process is stopped.

[0007] The control device may include an injection ratio control unit that controls the intake stroke injection rate and the compression stroke injection rate in the second cylinder, and 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 value, the injection ratio control unit may increase the intake stroke injection rate and decrease the compression stroke injection rate compared to when the fluctuation amount during execution of the specific cylinder fuel cut process is equal to or less than the threshold value.

[0008] When the increase rate is greater than a threshold value, the injection timing control unit may advance the fuel injection timing more than when the increase rate is equal to or less than the threshold value.

[0009] The engine system 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]

[0010] According to the present invention, it is possible to provide an engine system that can warm up a catalyst while suppressing deterioration of the engine operating condition. [Brief explanation of the drawings]

[0011] [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 showing an example of catalyst warm-up control executed by the ECU. DETAILED DESCRIPTION OF THE INVENTION

[0012] [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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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 a fuel cut control unit, an injection amount control unit, an injection timing control unit, and an injection ratio control unit, which will be described later.

[0017] 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.

[0018] [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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] [Catalyst warm-up control] 3 is a flowchart showing an example of catalyst warm-up 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 catalyst warm-up request (step S1). If the answer is No in step S1, this control ends.

[0024] If the answer to step S1 is Yes, 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. In this embodiment, split injection is performed by the in-cylinder injection valve 41d in each of cylinders #2 to #4. Specifically, fuel is injected during the intake stroke and the compression stroke, respectively. During the specific cylinder fuel cut process, feedback control that controls the fuel injection amount and intake air amount based on the air-fuel ratio of the exhaust gas 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.

[0025] The ECU 100 increases the fuel injection amount for each of the cylinders #2 to #4 that are not subject to fuel cut compared to when the specific cylinder fuel cut process is not being executed (step S3). This makes it possible to suppress a decrease in torque of the engine 10 that accompanies the stop of fuel supply to the cylinder #1. Furthermore, by increasing the fuel injection amount, it is possible to complete the warm-up of the catalyst 43 early.

[0026] The upper limit of the increase rate of the fuel injection amount can be expressed as (total number of cylinders / number of injection cylinders) [%]. The number of injection cylinders is the number of cylinders that are not subject to fuel cut. In this embodiment, the increase rate of each fuel injection amount for cylinders #2 to #4 is approximately 133 [%] at maximum. By setting the upper limit of the increase rate in this manner, the total fuel injection amount when the specific cylinder fuel cut process is being executed can be kept below the total fuel injection amount when the specific cylinder fuel cut process is stopped. This makes it possible to suppress deterioration of fuel efficiency while also suppressing deterioration of emissions. Note that the increase rate may be a variable value depending on the engine speed and intake air amount of engine 10, or may be a fixed value. In this embodiment, the increase rate will be described as a variable value. Step S3 is an example of processing executed by the injection amount control unit.

[0027] 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 S4). 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.

[0028] The ECU 100 determines whether the increase rate of the fuel injection amount is greater than a threshold value (step S5). The threshold value is set to an upper limit of the increase rate that ensures time for the air-fuel mixture to be formed and does not affect the combustion state. If the increase rate is greater than the threshold value, the injection period may become longer, which may worsen the combustion state. The threshold value is determined in advance based on experimental results or simulation results. If the answer is No in step S5, this control ends.

[0029] If the answer to step S5 is Yes, the ECU 100 advances the start timing of fuel injection during the compression stroke by a predetermined advance amount (step S6). This ensures time for the formation of the air-fuel mixture and stabilizes the combustion state. Step S6 is an example of processing executed by the injection timing control unit.

[0030] 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 S7). 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 S7 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 S8). 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 S8 is No, this control ends.

[0031] If step S7 or S8 returns "Yes," the ECU 100 increases the intake stroke injection rate and decreases the compression stroke injection rate (step S9). Split injection refers to injecting fuel multiple times within one combustion cycle. In this embodiment, fuel is injected in the first half of the intake stroke, the second half of the intake stroke, and the compression stroke. Specifically, the ECU 100 increases the intake stroke injection rate and decreases the compression stroke injection rate. For example, if the injection ratio for the first half of the intake stroke, the second half of the intake stroke, and the compression stroke is 6:2:2, the ratio is changed to 6.5:2.5:1. By decreasing the compression stroke injection rate, the degree of stratification of the air-fuel mixture is weakened, preventing the air-fuel ratio near the ignition device 42 from becoming excessively rich. This suppresses fluctuations in the engine speed and torque, thereby ensuring drivability. Step S9 is an example of processing executed by the injection ratio control unit.

[0032] It is to be noted that only one of steps S7 and S8 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.

[0033] 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]

[0034] 1 Hybrid vehicle 10 Engine 14 First motor generator 43 Catalyst 100 ECU (controller, fuel cut control unit, injection amount control unit, injection timing control unit, injection ratio control unit)

Claims

[Claim 1] An engine system mounted on a hybrid vehicle, an engine having first, second, third, and fourth 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 for the engine, Fuel is injected into each of the first, second, third, and fourth cylinders by a direct injection valve, The control device a fuel cut control unit that, when there is a request to warm up the catalyst, executes a specific cylinder fuel cut process that stops the supply of fuel to the first cylinder and supplies fuel to the second, third, and fourth cylinders; an injection amount control unit that increases the fuel injection amounts of the second, third, and fourth cylinders by a predetermined increase rate during execution of the specific cylinder fuel cut process compared to when the specific cylinder fuel cut process is stopped; an injection timing control unit that advances the fuel injection timing in the compression stroke of each of the second, third, and fourth cylinders during execution of the specific cylinder fuel cut process compared to when the specific cylinder fuel cut process is stopped, The upper limit of the predetermined increase rate is a value obtained by dividing the total number of cylinders (4) by the number of injection cylinders (3), the control device includes an injection ratio control unit that controls an intake stroke injection rate and a compression stroke injection rate for each of the second, third, and fourth cylinders, 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 value, the injection ratio control unit increases the intake stroke injection rate and decreases the compression stroke injection rate compared to 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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