Hybrid vehicle

Abstract

To provide a technique for achieving braking torque corresponding to a braking command, while protecting a catalysis arranged in an exhaust pipe of an internal combustion engine.SOLUTION: A hybrid vehicle is provided with a power train having an internal combustion engine and a motor, which drives wheels, a battery connected to the motor, and a control unit that controls the power train. The control unit executes processing for executing fuel-cut in response to a barking command and processing for stopping the fuel-cut and then resuming combustion operation of the internal combustion engine when a predetermined time elapses after starting the fuel-cut and when output of the braking command is continued. In the resumed combustion operation, the control unit adjusts an air-fuel mixture to be supplied to the internal combustion engine to rich, and when an upper limit value of electric power that can be supplied to the battery is below regenerated energy of the motor corresponding to the braking command, lowers a degree of the rich as rotation speed of the internal combustion engine increases.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] This specification discloses a hybrid vehicle. [Background technology]

[0002] Patent Document 1 describes a hybrid vehicle. This hybrid vehicle includes a control unit that executes fuel cut in response to a braking command. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-070891 A Summary of the Invention [Problem to be solved by the invention]

[0004] When fuel cut is performed, a large amount of oxygen is supplied to the catalyst arranged in the exhaust pipe of the internal combustion engine. At this time, if a large amount of particulate matter accumulates on the catalyst, the oxidation reaction of the particulate matter is promoted within the catalyst, and the catalyst may become hot. In order to protect the catalyst from such a temperature rise, it is possible to stop the fuel cut when a predetermined time has passed since the start of the fuel cut.

[0005] When the fuel cut is stopped, the internal combustion engine resumes combustion operation. The torque generated by the internal combustion engine combustion operation can hinder the braking of the vehicle. In this regard, in the powertrain of a hybrid vehicle, the required braking torque can be realized by adjusting the regenerative braking by the motor. However, if the power that can be supplied to the battery is limited due to the battery condition (temperature, etc.), the regenerative braking by the motor will also be limited, and there is a risk that the required braking torque cannot be realized.

[0006] This specification provides a technique for realizing a braking torque according to a braking command while protecting a catalyst disposed in an exhaust pipe of an internal combustion engine. [Means for solving the problem]

[0007] The hybrid vehicle disclosed in this specification comprises a powertrain having an internal combustion engine and a motor to drive wheels, a battery connected to the motor, and a control unit to control the powertrain, wherein the control unit executes a process of performing a fuel cut in response to a braking command, and a process of canceling the fuel cut and resuming combustion operation of the internal combustion engine when a predetermined time has elapsed since the start of the fuel cut and the braking command is continuing, and during the resumption of combustion operation after the restart, the mixture supplied to the internal combustion engine is adjusted to be rich, and when the upper limit value of the power that can be supplied to the battery falls below the regenerative energy of the motor corresponding to the braking command, the degree of richness is reduced in accordance with an increase in the rotation speed of the internal combustion engine.

[0008] In the above configuration, when the combustion operation of the internal combustion engine is resumed after the fuel cut is stopped, the mixture supplied to the internal combustion engine is adjusted to be rich. This consumes oxygen in the catalyst, and the temperature rise of the catalyst is suppressed. On the other hand, when the internal combustion engine is operated with a rich mixture, the torque generated by the internal combustion engine increases compared to the combustion operation at the theoretical air-fuel ratio. Therefore, it is necessary to increase the rotation speed of the internal combustion engine, but an excessive increase in the rotation speed leads to a deterioration of the NV ratio. Therefore, in the above configuration, the ratio of fuel contained in the mixture (i.e., the degree of richness) is reduced according to the increase in the rotation speed of the internal combustion engine, thereby suppressing a further increase in the rotation speed of the internal combustion engine. This makes it possible to suppress the deterioration of the NV ratio. Note that the ratio of fuel contained in the mixture is reduced on the condition that the upper limit value of the power that can be supplied to the battery falls below the regenerative energy required according to the braking command. This is because, under this condition, it is not expected that the necessary braking torque can be secured by regeneration by the motor.

[0009] Details and further improvements of the technology disclosed in this specification are described in the following "Forms for Carrying Out the Invention". [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a block diagram showing a configuration of a hybrid vehicle. [Diagram 2] FIG. 4 is a flowchart of a process executed by a control unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The hybrid vehicle 2 includes wheels 10, a power train 20, a power conversion device 30, a battery 40, a control unit 50, and an accelerator pedal 60. The power train 20 drives the wheels 10. The power train 20 includes an internal combustion engine 22, a first motor 24, and a second motor 26.

[0012] An intake pipe 22a and an exhaust pipe 22b are connected to the internal combustion engine 22. The intake pipe 22a supplies a mixture of fuel and air to the internal combustion engine 22. The exhaust pipe 22b exhausts exhaust gas generated from the mixture burned in the internal combustion engine 22 to the outside of the internal combustion engine 22. A catalyst 22c is disposed in the exhaust pipe 22b. The catalyst 22c is, for example, a three-way catalyst that purifies particulates (CO, HC, NOx, etc.) contained in the exhaust gas.

[0013] The powertrain 20 distributes the output torque of the internal combustion engine 22 to the wheels 10 and the second motor 26 using a power distribution mechanism (not shown). The second motor 26 mainly functions as a generator, and the electric power generated by the second motor 26 is supplied to a battery 40. The first motor 24 is connected to the axle of the wheels 10, and the output torque of the first motor 24 is transmitted to the wheels 10. Note that the configuration of the powertrain 20 in FIG. 1 is merely an example. For example, the powertrain 20 may be configured with one motor and one internal combustion engine 22.

[0014] The power conversion device 30 is connected to the first motor 24 and the second motor 26. The power conversion device 30 converts the output power of the battery 40 into power suitable for driving the first motor 24. Furthermore, the power conversion device 30 converts the power generated by the second motor 26 into power suitable for charging the battery 40.

[0015] The battery 40 is connected to the power conversion device. The battery 40 is, for example, a lithium ion battery.

[0016] The control unit 50 controls the power train 20 and the power conversion device 30. The control unit 50 operates according to various instructions from a user. For example, the user supplies an acceleration command to the control unit 50 to accelerate the hybrid vehicle 2 by depressing the accelerator pedal 60. The user also supplies a braking command to the control unit 50 to brake the hybrid vehicle 2 by releasing the accelerator pedal 60 from its depressed state.

[0017] The control unit 50 executes a fuel cut in response to a braking command. The fuel cut is a process for stopping the supply of fuel to the intake pipe 22a. When the fuel cut is executed, a large amount of oxygen is supplied to the catalyst 22c. At this time, if a large amount of particulate matter is accumulated in the catalyst 22c, the oxidation reaction of the particulate matter is promoted in the catalyst 22c, and the catalyst 22c may become hot. In order to protect the catalyst 22c from such a temperature rise, it is considered to stop the fuel cut when a predetermined time has elapsed since the start of the fuel cut.

[0018] When the fuel cut is stopped, the combustion operation of the internal combustion engine 22 is resumed. In a situation where the braking command continues, the torque generated by the combustion operation of the internal combustion engine 22 may hinder the braking of the hybrid vehicle 2. In this regard, the powertrain 20 can realize the required braking torque by adjusting the regenerative braking by the second motor 26. However, if the power that can be supplied to the battery 40 is limited due to the state of the battery 40 (temperature, etc.), the regenerative braking by the second motor 26 is also limited. In this case, there is a risk that the required braking torque cannot be realized.

[0019] In order to address the above problem, the control unit 50 executes the process of Fig. 2. In S10, the control unit 50 monitors whether a braking command is provided from the user. If a braking command is provided from the user (YES in S10), the control unit 50 executes the process from S12 onwards.

[0020] In S12, the control unit 50 executes fuel cut. In S14, the control unit 50 judges whether a predetermined time has passed since the start of fuel cut in S12 and the braking command in S10 is still being issued. When the control unit 50 judges that a predetermined time has passed since the start of fuel cut in S12 and the braking command in S10 is still being issued (YES in S14), the control unit 50 proceeds to S16.

[0021] In S16, the control unit 50 judges whether the amount of particulate matter deposited in the catalyst 22c exceeds a predetermined amount. Here, the amount of deposition is estimated based on various parameters, such as the flow rate of exhaust gas flowing through the exhaust pipe 22b and the temperature of the catalyst 22c. Each parameter is measured by various sensors mounted on the hybrid vehicle 2. When the control unit 50 judges that the amount of deposition exceeds the predetermined amount (YES in S16), the process proceeds to S18.

[0022] In S18, the control unit 50 stops the fuel cut started in S12. In S20, the control unit 50 adjusts the mixture supplied to the internal combustion engine 22 to be rich, and resumes the combustion operation of the internal combustion engine 22. Here, the mixture being rich means that the ratio of fuel contained in the mixture is higher than the theoretical air-fuel ratio. As described above, by executing the fuel cut, a lot of oxygen is supplied to the catalyst 22c. By performing the combustion operation with a rich mixture, even if a lot of particulates are accumulated in the catalyst 22c, the oxygen in the catalyst 22c is consumed, and the temperature rise of the catalyst 22c is suppressed.

[0023] In the next step S22, the control unit 50 determines whether or not the upper limit of the power that can be supplied to the battery 40 exceeds the regenerative energy of the second motor 26 corresponding to the braking command in S10. The upper limit is determined based on various parameters such as the current temperature of the battery 40. For example, if the upper limit is lower than the regenerative energy, it means that the regenerative energy cannot be charged to the battery 40. In this case, it is not expected that the necessary braking torque can be secured by the regenerative braking by the second motor 26. On the other hand, if the upper limit is lower than the regenerative energy, it means that the regenerative energy can be charged to the battery 40. In this case, it is expected that the necessary braking torque can be secured by the regenerative braking by the second motor 26.

[0024] When the control unit 50 determines that the upper limit value exceeds the regenerative energy (YES in S22), the control unit 50 proceeds to S24. In S24, the control unit 50 determines to continue the combustion operation by fixing the rich degree determined in S20.

[0025] Moreover, when the control unit 50 determines that the upper limit value falls below the regenerative energy (NO in S22), the control unit 50 proceeds to S26. In S26, the control unit 50 decides to reduce the degree of richness determined in S20 according to the rotation speed of the internal combustion engine 22. Specifically, the control unit 50 reduces the degree of richness, i.e., the ratio of fuel contained in the mixture, so as to approach the theoretical air-fuel ratio as the rotation speed of the internal combustion engine 22 increases. Here, the reduction in the degree of richness may be stepwise or continuous. When the processing of S24 or S26 is completed, the control unit 50 terminates the processing of FIG. 2.

[0026] Furthermore, if the braking command is withdrawn before a predetermined time has elapsed since the start of fuel cut (NO in S14), and if the control unit 50 determines that the amount of particulate matter deposited in the catalyst 22c is below a predetermined amount (NO in S16), it skips the processes from S18 onwards and ends the process in Fig. 2. Although not shown, if NO is determined in S14, the fail cut is discontinued and combustion in the internal combustion engine 22 is resumed at the theoretical air-fuel ratio. If NO is determined in S16, the fail cut is continued until the braking command is withdrawn.

[0027] (Effects of this embodiment) When the internal combustion engine 22 is operated to burn a rich mixture, the torque generated by the internal combustion engine 22 increases compared to when the internal combustion engine 22 is operated to burn at a theoretical air-fuel ratio. Therefore, in order to realize the braking torque according to the braking command, it is necessary to increase the rotation speed of the internal combustion engine 22, but an excessive increase in the rotation speed leads to a deterioration of the NV ratio. In response to this, in S24 of FIG. 3, the control unit 50 reduces the degree of richness according to an increase in the rotation speed of the internal combustion engine 22. If the degree of richness is reduced, the torque generated by the internal combustion engine 22 also decreases, and as a result, a further increase in the rotation speed of the internal combustion engine 22 is suppressed. As described above, it is possible to realize the braking torque according to the braking command while suppressing the deterioration of the NV ratio.

[0028] (Correspondence) The hybrid vehicle 2 and the wheels 10 are examples of a "hybrid vehicle" and "wheels". The powertrain 20 and the internal combustion engine 22 are examples of a "powertrain" and an "internal combustion engine". The second motor 26 is an example of a "motor". The battery 40 and the control unit 50 are examples of a "battery" and a "control unit", respectively. [Explanation of symbols]

[0029] 2: hybrid vehicle, 10: wheels, 20: power train, 22: internal combustion engine, 22a: intake pipe, 22b: exhaust pipe, 22c: catalyst, 24: first motor, 26: second motor, 30: power conversion device, 40: battery, 50: control unit, 60: accelerator pedal

Claims

[Claim 1] A hybrid vehicle, a power train having an internal combustion engine and a motor for driving wheels; a battery connected to the motor; A control unit for controlling the powertrain; Equipped with The control unit A process of cutting fuel in response to a braking command; When a predetermined time has elapsed since the start of the fuel cut and the braking command is still being issued, a process of stopping the fuel cut and restarting the combustion operation of the internal combustion engine is executed; In the combustion operation after the restart, the mixture supplied to the internal combustion engine is adjusted to be rich, and when an upper limit value of the electric power that can be supplied to the battery falls below the regenerative energy of the motor corresponding to the braking command, the degree of the richness is reduced in accordance with an increase in the rotation speed of the internal combustion engine. Hybrid car.

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