HYBRID ELECTRIC VEHICLE

The hybrid electric vehicle includes an engine, a motor, a clutch, an accelerator operation amount detecting unit, and a control device. The control device is configured to include: a determination unit configured to determine whether or not the accelerator operation amount is equal to or greater than a threshold value when there is a start request for the engine; and an ignition timing control unit configured to advance an ignition timing of the engine, when an affirmative determination is made by the determination unit, than when a negative determination is made by the determination unit.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2022-041614 filed on Mar. 16, 2022, incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a hybrid electric vehicle.

2. Description of Related Art

There is a hybrid electric vehicle including an engine, a motor provided on a power transmission path from the engine to drive wheel, and a clutch provided on the power transmission path between the engine and the motor. In such a hybrid electric vehicle, when a start request of the engine is given in a state where the clutch is released, combustion in the engine is started while the engine is cranked by the motor via the clutch, and the clutch is engaged. Thus, the engine is started (see, for example, Japanese Unexamined Patent Application Publication No. 2021-054165 (JP 2021-054165 A)).

SUMMARY

When an accelerator operation amount operated by a driver at the time of starting the engine is large, that is, when the degree of an acceleration request by the driver is large and an increase speed of engine torque is low, there is a possibility that acceleration responsiveness to the request by the driver decreases.

An object of the present disclosure is to provide a hybrid electric vehicle in which the acceleration responsiveness has improved at the time of starting the engine.

A hybrid electric vehicle according to a first aspect of the present disclosure includes:an engine;a motor provided on a power transmission path from the engine to a drive wheel;a clutch provided on the power transmission path between the engine and the motor;an accelerator operation amount detecting unit for detecting an accelerator operation amount; anda control device that starts combustion in the engine while cranking the engine by the motor via the clutch and engages the clutch when a start request of the engine is given in a release state of the clutch.Here, the control device is configured to include:a determination unit configured to determine whether the accelerator operation amount is equal to or larger than a threshold value when the start request of the engine is given; and an ignition timing control unit configured to advance an ignition timing of the engine when an affirmative determination is made by the determination unit than when a negative determination is made by the determination unit.

In the hybrid electric vehicle according to the first aspect, the control device may further include a predicting unit that predicts a rotational speed of the motor when the clutch is engaged, andthe ignition timing control unit may be configured to advance the ignition timing as the predicted rotational speed of the motor increases.

The hybrid electric vehicle according to the first aspect may further include a motor rotational speed detecting unit configured to detect a rotational speed of the motor. Here, the ignition timing control unit may be configured to advance the ignition timing as the rotational speed of the motor increases.

The hybrid electric vehicle according to the first aspect may further include a temperature detecting unit configured to detect a temperature of the engine. Here, the ignition timing control unit may be configured to advance the ignition timing as the temperature of the engine decreases.

The hybrid electric vehicle according to the first aspect may further include an engine speed detecting unit configured to detect a speed of the engine. Here, the ignition timing control unit may be configured to advance the ignition timing as the speed of the engine increases.

In the hybrid electric vehicle according to the first aspect, the ignition timing control unit may be configured to advance the ignition timing as the accelerator operation amount increases.

According to the present disclosure, it is possible to provide a hybrid electric vehicle in which the acceleration responsiveness has improved at the time of starting the engine.

DETAILED DESCRIPTION OF EMBODIMENTS

Schematic Configuration of the Hybrid Electric Vehicle

FIG.1is a schematic configuration diagram of a hybrid electric vehicle1. In the hybrid electric vehicle1, a K0 clutch14, a motor15, a torque converter18, and a transmission19are provided in this order in a power transmission path from the engine10to the drive wheels13. The engine10and the motor15are mounted as a driving source for traveling of the hybrid electric vehicle1. The engine10is, for example, a V-type 6-cylinder gasoline engine, but the number of cylinders is not limited thereto. The engine10may be a series type gasoline engine or a diesel engine. K0 clutch14, the motor15, the torque converter18, and the transmission19are provided in the transmission unit11. The transmission unit11and the left and right drive wheels13are drivingly connected to each other via a propeller shaft12aand a differential12.

K0 clutch14is provided between the motor15and the engine10on the same power transmission path. K0 clutch14is supplied with hydraulic pressure from the released state to be brought into an engaged state, and connects the power transmission between the engine10and the motor15. K0 clutch14is released in response to the stoppage of the hydraulic pressure supply and shuts off the power transmission between the engine10and the motor15. The engagement state is a state in which both engagement elements of K0 clutch14are coupled to each other, and the engine10and the motor15have the same rotational speed. The disengaged state is a state in which both engagement elements of K0 clutches14are separated from each other.

The motor15is connected to the battery16via an inverter17. The motor15functions as a motor that generates a driving force of the vehicle in response to power supply from the battery16. The motor15also functions as a generator that generates electric power to charge the battery16in response to power transmission from the engine10and the drive wheels13. The electric power exchanged between the motor15and the battery16is adjusted by the inverter17.

The inverters17are controlled by an ECU100which will be described later. The inverter17converts a DC voltage from the battery16into an AC voltage, or converts an AC voltage from the motor15into a DC voltage. In the case of power running operation in which the motor15outputs torque, the inverter17converts the DC voltage of the battery16into an AC voltage and adjusts the electric power supplied to the motor15. In the case of the regenerative operation generated by the motor15, the inverter17converts the AC voltage from the motor15into a DC voltage and adjusts the electric power supplied to the battery16.

The torque converter18is a fluid coupling having a torque amplification function. The transmission19is a stepped automatic transmission in which the gear ratio is switched in multiple stages by switching the gear stages, but the present disclosure is not limited thereto, and may be a continuously-type automatic transmission. The transmission19is provided between the motor15and the drive wheels13on the power transmission path. The motor15and the transmission19are coupled to each other via the torque converter18. The torque converter18is provided with a lock-up clutch20that receives a supply of hydraulic pressure and is in an engaged state to directly couple the motor15and the transmission19.

The transmission unit11is further provided with an oil pump21and a hydraulic control mechanism22. Hydraulic pressure generated by the oil pump21is supplied to K0 clutch14, the torque converter18, the transmission19, and the lockup clutch20via the hydraulic control mechanism22. The hydraulic control mechanism22is provided with hydraulic circuits of K0 clutch14, the torque converter18, the transmission19, and the lockup clutch20, and various hydraulic control valves for controlling the hydraulic pressures. A wet clutch may be provided instead of the torque converter18.

The hybrid electric vehicle1is provided with an Electronic Control Unit (ECU)100as a control device of the vehicle. ECU100is an electronic control unit including an arithmetic processing unit that performs various arithmetic processing related to travel control of vehicles, and a memory that stores control programs and data. ECU100is an exemplary control device for a hybrid electric vehicle, and functionally realizes a determination unit, an ignition timing control unit, and a predicting unit, which will be described later.

ECU100controls driving of the engine10and the motor15. Specifically, ECU100controls the rotational speed and torque of the engine10by controlling the throttle valve opening degree, the ignition timing, and the fuel injection amount of the engine10. ECU100controls the rotational speed and torque of the motor15by controlling the inverters17to adjust the amount of transfer of electric power between the motor15and the battery16. ECU100controls driving of K0 clutch14, the lock-up clutch20, and the transmission19through control of the hydraulic control mechanism22.

Signals from the ignition switch71, the crank angle sensor72, the motor rotational speed sensor73, the accelerator operation amount sensor74, the air flow meter75, and the water temperature sensor76are inputted to ECU100. The crank angle sensor72detects the rotational speed of the crankshaft of the engine10. The crank angle sensor72is an example of an engine speed detecting unit. The motor rotational speed sensor73detects the rotational speed of the output shaft of the motor15. The motor rotational speed sensor73is an example of a motor rotational speed detecting unit. The accelerator operation amount sensor74detects an accelerator pedal operation amount that is a depression amount of the accelerator pedal of the driver. The accelerator operation amount sensor74is an example of an accelerator operation amount detecting unit. The air flow meter75detects an intake air amount of the engine10. The water temperature sensor76detects the temperature of the coolant for cooling the engine10. The temperature of the coolant correlates with the temperature of the engine10. The water temperature sensor76is an example of an engine temperature detecting unit. The engine temperature detecting unit may be, for example, an oil temperature sensor that detects the temperature of the lubricating oil that lubricates the engine10correlated with the temperature of the engine10.

ECU100causes the hybrid electric vehicles to travel in either the motor mode or the hybrid mode. In the motor mode, ECU100releases K0 clutch14, and the hybrid electric vehicle1travels by the power of the motor15. In the hybrid mode, ECU100switches K0 clutch14to the engaged condition, and the hybrid electric vehicle1is driven by at least the power of the engine10. Note that the hybrid mode includes a mode in which the engine10is driven by power only, and a mode in which the motor15is driven by power to drive both the engine10and the motor15as power sources.

The driving mode is switched based on the required driving force of the vehicle obtained from the vehicle speed and the accelerator operation amount, the state of charge of the battery16, and the like. For example, when the required driving force is relatively small and state of charge (SOC) indicating the storage capacity of the battery16is relatively large, the motor mode in which the engine10is stopped is selected in order to improve the fuel efficiency. When the required driving force is relatively large or SOC of the battery16is relatively low, a hybrid mode for driving the engine10is selected.

In the hybrid mode, ECU100automatically stops the engine10when a predetermined stop condition is satisfied, and executes intermittent operation control for starting the engine10that has automatically stopped when a predetermined start condition is satisfied. For example, ECU100automatically stops the engine10when the accelerator operation amount becomes zero in the hybrid mode. When the accelerator operation amount is greater than zero, ECU100automatically starts the engine10on the assumption that the starting condition is satisfied. When the engine10is automatically stopped, ECU100releases K0 clutch14to stop the fuel-injection. When the engine10is automatically started, ECU100cranks the engine10by the motor15via K0 clutch14, starts fuel injection and ignition, and then engages K0 clutch14.

Schematic Configuration of the Engine

FIG.2is a schematic configuration diagram of the engine10. The engine10includes a cylinder30, a piston31, a connecting rod32, a crankshaft33, an intake passage35, an intake valve36, an exhaust passage37, and an exhaust valve38. InFIG.2, only one of the plurality of cylinders30of the engine10is displayed. In the cylinder30, combustion of the air-fuel mixture is performed. The piston31is reciprocally accommodated in each cylinder30, and is connected to a crankshaft33, which is an output shaft of the engine10, via a connecting rod32. The connecting rod32converts the reciprocating motion of the piston31into a rotational motion of the crankshaft33.

The intake passage35is connected to an intake port of each cylinder30via an intake valve36. The exhaust passage37is connected to an exhaust port of each cylinder30via an exhaust valve38. The intake passage35is provided with an air flow meter75and a throttle valve40for adjusting an amount of intake air. A catalyst43for exhaust gas purification is provided in the exhaust passage37.

The cylinder30is provided with an in-cylinder injection valve41. The in-cylinder injection valve41injects fuel directly into the cylinder30. Instead of the in-cylinder injection valve41or in addition to the in-cylinder injection valve41, a port injection valve that injects fuel toward the intake port may be provided. Each cylinder30is provided with an ignition device42that ignites an air-fuel mixture of the intake air introduced through the intake passage35and the fuel injected by the in-cylinder injection valve41by spark discharge.

When the engine10configured as described above is requested to start with K0 clutch14released, ECU100controls the engine10, K0 clutch14, and the motor15as follows. ECU100causes the motor15to crank the engine10via K0 clutch14by slipping K0 clutch14to increase the torque of the motor15. When the engine speed becomes equal to or higher than the predetermined value, ECU100starts burning in the engine10and engages K0 clutch14in synchronization with the engine speed and the motor speed. In this way, the start of the engine10is completed. Here, when the accelerator operation amount operated by the driver at the time of starting the engine10is large, that is, when the degree of the acceleration request by the driver is large, when the increase speed of the engine torque is slow, there is a possibility that the acceleration responsiveness decreases with respect to the driver's request. Therefore, ECU100advances the ignition timing of the engine10to increase the engine torque at an early stage when the engine10is requested to start and the accelerator operation amount is large. Details will be described below.

Engine Start Control

FIG.3is a flow chart illustrating an exemplary engine-start control executed by ECU100. This control is repeatedly executed at predetermined intervals in a state where the ignition is on. ECU100determines whether or not there is a need to start the engine10(step S1). If S1of steps is No, this control ends. If Yes in step S1, ECU100determines whether or not the accelerator operation amount is equal to or greater than the threshold a (step S2). The threshold value α is set to a minimum value in which the degree of acceleration request by the driver is large and the advance angle of the ignition timing is required. Step S2is an exemplary process executed by the determination unit.

When the step S2is No, ECU100executes the normal ignition start control (step S3) by considering that the degree of the acceleration demand by the driver is small. In the normal ignition start control, the ignition timing is controlled based on the temperature of the coolant, the engine speed, and the predicted motor speed, which will be described in detail later, to start the engine10.

When the step S2is Yes, ECU100executes the advance ignition start control (step S4) on the assumption that the degree of the acceleration demand by the driver is large. In the advance ignition start control, the ignition timing is set to the advance side rather than the normal ignition start control, and the engine10is started. Similarly to the normal ignition start control, the ignition timing of the advance ignition start control is controlled based on the temperature of the coolant, the engine speed, and the predicted motor speed. The step S4is an exemplary process executed by the ignition timing control unit.

In the normal ignition start control and the advance ignition start control, ECU100refers to the map of theFIG.4CfromFIG.4Ato control the ignition timing.FIG.4A,FIG.4B, andFIG.4Care exemplary maps that define the ignition timing. FromFIGS.4A to4C, the ignition timing when the accelerator operation amount is less than the threshold value α and the ignition timing when the accelerator operation amount is equal to or greater than the threshold value α are shown.

FIG.4Ais an example of a map that defines a relation between an ignition timing and a coolant temperature. The vertical axis indicates the ignition timing [deg], and the horizontal axis indicates the coolant temperature [° C.]. As shown in4A, when the accelerator operation amount is either less than the threshold value α or greater than or equal to the threshold value α, the ignition timing is defined to be advanced as the temperature of the coolant detected by the water temperature sensor76is lower. This is because the lower the temperature of the coolant, the more likely the engine torque is to decrease, and it is preferable to advance the ignition timing so as to compensate for the decrease in the engine torque. Further, when the accelerator operation amount is equal to or greater than the threshold value α, the ignition timing is defined to be on the advance side as compared with the case where the accelerator operation amount α is less than the accelerator operation amount α. When the accelerator operation amount is equal to or greater than the threshold value α, the degree of acceleration request by the driver is large, and it is preferable to increase the engine torque at an early stage from the viewpoint of acceleration responsiveness.

In the map ofFIG.4A, the rate of increase in the advance angle of the ignition timing with respect to the decrease in the temperature of the coolant is defined to be larger when the accelerator operation amount is equal to or larger than the threshold value α than when the accelerator operation amount is equal to or larger than the threshold value α. This is because, even when the amount of decrease in the coolant temperature is the same, the influence on the decrease in the engine torque is larger than that in the case where the accelerator operation amount is larger than that in the case where the accelerator operation amount is smaller.

FIG.4Bis an exemplary map that defines the relation between the ignition timing and the engine-speed. The vertical axis indicates the ignition timing [deg], and the horizontal axis indicates the engine speed [rpm]. As shown in4B, when the accelerator operation amount is less than the threshold value α or greater than or equal to the threshold value α, the ignition timing is defined to be advanced as the engine speed detected by the crank angle sensor72is higher. This is because, by advancing the ignition timing when the engine speed is high, the combustion speed can be increased, and the timing at which the in-cylinder pressure is maximized can be made to correspond to the optimum timing with high torque efficiency. In addition, inFIG.4B, when the accelerator operation amount is equal to or greater than the threshold value α, the ignition timing is defined to be on the advance side as compared with when the accelerator operation amount α is less than the accelerator operation amount α. In this case as well, it is preferable to increase the engine torque at an early stage from the viewpoint of acceleration responsiveness.

In the map shown in4B, when the engine speed is less than the predetermined value, the ignition timing is constant regardless of the accelerator operation amount. This is because, when the engine speed is low, even if the ignition timing is advanced, the combustion speed is less likely to increase and the engine torque is less likely to increase. When the engine speed is equal to or higher than the predetermined value, the rate of increase in the advance angle amount of the ignition timing with respect to the increase in the engine speed is defined to be larger when the accelerator operation amount is equal to or larger than the threshold value α than when the accelerator operation amount is equal to or larger than the threshold value α. Further, when the engine speed becomes higher than a predetermined value, the ignition timing is limited to be constant. This is because if the ignition timing is excessively controlled to the advance angle side, knocking may occur.

FIG.4Cis an exemplary map that defines the relation between the ignition timing and the predicted motor rotational speed. The vertical axis indicates the ignition timing [deg], and the horizontal axis indicates the predicted motor rotational speed [rpm]. The predicted motor rotational speed is a motor rotational speed at the time of engagement of K0 clutch14in the engine-start control, which is predicted based on the accelerator operation amount, which will be described in detail later. As shown in4C, when the accelerator operation amount is either less than the threshold value α or greater than or equal to the threshold value α, the ignition timing is defined to be advanced as the predicted motor rotational speed is higher than or equal to the predetermined value. This is because the higher the predicted motor rotational speed, the larger the difference from the engine rotational speed prior to the engagement of K0 clutch14, and it is preferable to secure the engine torque at the time of starting the engine10. InFIG.4Cas well, when the accelerator operation amount is equal to or greater than the threshold value α, the ignition timing is defined to be on the advance side as compared with the case where the accelerator operation amount α is less than the accelerator operation amount α. In this case as well, it is preferable to increase the engine torque at an early stage from the viewpoint of acceleration responsiveness.

In the map ofFIG.4C, with respect to the rate of increase in the advance angle of the ignition timing with respect to the increase in the predicted motor rotational speed, when the accelerator operation amount is equal to or greater than the threshold value α, the accelerator operation amount is defined to be larger than when the accelerator operation amount is less than the threshold value α. This is because even when the amount of increase in the predicted motor rotational speed is the same, it is necessary to secure a larger increase rate of the engine torque than when the accelerator operation amount is larger than when the accelerator operation amount is smaller.

As described above, in the advance ignition start control, ECU100controls the ignition timing closer to the advance than the normal ignition start control. As a result, the engine torque at the time of starting the engine can be increased at an early stage in response to the driver's acceleration request, and the acceleration responsiveness is improved.

In the map ofFIGS.4A to4C, the ignition timing changes linearly, but the present disclosure is not limited thereto, and may change in a curved shape or a stepped shape. Further, the present disclosure is not limited to the above-described map, and the ignition timing may be calculated by an arithmetic expression using the accelerator operation amount, the coolant temperature, the engine speed, and the predicted motor speed as arguments. Further, in the above-described map, when the accelerator operation amount is equal to or greater than the threshold value α, the ignition timing is defined regardless of the accelerator operation amount, but the present disclosure is not limited thereto. When the accelerator operation amount is equal to or larger than the threshold value α, the ignition timing may be defined so as to be on the advance side as the accelerator operation amount is larger.

Motor Rotational Speed Prediction Control

Next, the motor rotational speed prediction control for calculating the predicted motor rotational speed described above will be described. The motor rotational speed prediction control is an example of a process executed by the predicting unit.FIG.5is a flowchart illustrating an example of the motor rotational speed prediction control. The motor rotational speed prediction control is executed when there is a start request of the engine10and the accelerator operation amount is equal to or greater than the threshold value α.

First, ECU100calculates an accelerator operation amount and an accelerator operation amount change rate per unit-time when the engine10is requested to start based on the accelerator operation amount sensor74(step S11). Next, ECU100predicts the accelerator operation amount when K0 clutch14is engaged (step S12). Specifically, the accelerator operation amount at the time of engagement of K0 clutch14is predicted by multiplying the accelerator operation amount change rate by the time required for engagement of K0 clutch14after the start of the engine10is requested and adding the accelerator operation amount at the current time to the value obtained by the multiplication.

Next, ECU100predicts the required torque to the engine10when K0 clutch14is engaged based on the predicted accelerator operation amount (step S13). Specifically, the required torque to the engine10at the time of engagement of K0 clutch14is predicted as follows.

ECU100calculates a required torque (hereinafter, referred to as a vehicle required torque) to the hybrid electric vehicle1from the predicted accelerator operation amount by referring to the map ofFIG.6A.FIG.6Ais a map that defines a relation between a propeller shaft torque and a propeller shaft rotational speed for each accelerator operation amount. The vertical axis indicates the propeller axis torque [Nm], and the horizontal axis indicates the propeller axis rotational speed [rpm]. The propeller shaft torque and the number of revolutions of the propeller shaft are the torque and the number of revolutions of the propeller shaft12a.The propeller shaft torque corresponds to the required vehicle torque. InFIG.6A, the accelerator operation amounts of 0%, 50%, and 100% are shown as exemplary cases. In the memories of ECU100, such maps for the respective gear stages are stored.

As shown in6A, as the accelerator operation amount increases, the propeller shaft torque, that is, the required vehicle torque increases. ECU100calculates a required torque of the vehicle on the basis of the predicted accelerator operation amount and the shift stage at the present time. Next, the required vehicle torque is multiplied by the current motor rotational speed to calculate a required output to the hybrid electric vehicle1(hereinafter, referred to as a vehicle required output).

Next, an output based on the charge/discharge request of the battery16(hereinafter, referred to as a charge/discharge request output) is added to the vehicle request output to calculate a request output to the engine10(hereinafter, referred to as an engine request output). The charge/discharge request output is calculated as a positive value when there is a charge request to the battery16, as a negative value when there is a discharge request to the battery16, and as0when there is no charge/discharge request to the battery16. Next, the required engine torque (hereinafter, referred to as the required engine torque) to the engine10is calculated by dividing the required engine output by the current engine speed.

Next, ECU100calculates the predicted motor rotational speed based on the engine-required torque calculated in this manner (step S14). Specifically, ECU100refers to the map ofFIG.6Band predicts the motor speed at the time of engagement of K0 clutch14from the required engine torque.6B is a map that defines the relation between the required torque and the motor rotational speed. The vertical axis indicates the required torque [N m], and the horizontal axis indicates the motor rotational speed [rpm].

InFIG.6B, the iso-output line is indicated by a dotted line, the relation between the rotational speed and the torque according to the gear stage is indicated by a thin line, and the actual operation line of the hybrid electric vehicle1is indicated by a thick line. For example, when the operating condition of the hybrid electric vehicle1indicates the operating point P1and the gear stage is the third gear and the engine required torque T2, the predicted gear stage at the time of engagement of K0 clutch14is the fourth gear, and the predicted motor rotational speed is the rotational speed R2. In this way, the motor rotational speed at the time of engagement of K0 clutch14can be predicted based on the accelerator operation amount.

Since the ignition timing is advanced on the basis of the predicted motor rotational speed calculated as described above, the engine torque can be increased at an early stage corresponding to the predicted motor rotation speed, and the acceleration responsiveness is improved.

Next, a modification will be described. In the above embodiment, ECU100calculates the advance angle of the ignition timing according to the predicted motor rotational speed. In contrast, in the modification, ECU100calculates the advance angle of the ignition timing in accordance with the motor rotational speed detected by the motor rotational speed sensor73when the engine10is requested to start. Specifically, ECU100refers to the map ofFIG.7to calculate the advance angle of the ignition timing.FIG.7is a map that defines the relationship between the ignition timing and the motor rotational speed. The vertical axis indicates the ignition timing [deg], and the horizontal axis indicates the motor rotational speed [rpm].FIG.7corresponds toFIG.4C. In this case as well, in the same manner as in the map ofFIG.4C, in any case where the accelerator operation amount is less than the threshold value α and is equal to or greater than the threshold value α, the ignition timing is defined to be advanced as the motor rotational speed is higher. In the present modification, unlike the above-described embodiment, the motor rotational speed does not need to be predicted, so that ECU100process load is reduced.

In the above embodiment, the hybrid electric vehicle is controlled by a single ECU100, but the present disclosure is not limited thereto. For example, the above-described control may be executed by a plurality of ECU such as an engine ECU for controlling the engine10, a clutch ECU for controlling the motor ECU, K0 clutch14for controlling the motor15, and a hybrid ECU for integrally controlling these ECU. For example, the above-described step51and S2may be executed by the hybrid ECU, and the engine S3and S4may be executed by the engine ECU.

Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present disclosure described in the claims.