Vehicle control device and vehicle control method

A vehicle control device includes a control unit configured to execute free-run traveling in which an engine is stopped and a clutch that transmits power of the engine to a drive wheel is disengaged, at a time acceleration is not requested during traveling. The control unit is configured to prohibit upshifting of a continuously variable transmission at least during execution of the free-run traveling, drive the engine from the free-run traveling state in response to an acceleration request, and upshift the continuously variable transmission at a time of returning to a normal traveling state in which the clutch is engaged.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2014-144147 filed in Japan on Jul. 14, 2014.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicle control device and a vehicle control method for a vehicle that can execute free-run traveling.

2. Description of the Related Art

In a hybrid vehicle, when acceleration is requested during EV traveling in which an engine is stopped and a clutch is disengaged, the engine is re-started and the clutch is engaged. At this time, to promptly increase a rotation speed of the engine, a part of drive torque of a motor is used. Therefore, when the clutch is engaged, a driver might have difficulty in feeling the sense of acceleration and drivability may be deteriorated due to lack of the drive torque. In view of the circumstances, Japanese Patent Application Laid-open No. 2012-201194 has proposed a technique in which an output torque is transmitted to a drive wheel by upshifting of continuously variable transmission, the output torque being obtained such that inertia torque of the continuously variable transmission is added to the drive torque of the motor, so that the deterioration of the drivability is suppressed.

By the way, a vehicle is conventionally known, which can execute free-run traveling in which the engine is stopped and the clutch is disengaged when the acceleration is not requested during traveling. Suppression of the deterioration of the drivability can be considered by applying of the technique disclosed in Japanese Patent Application Laid-open No. 2012-201194 to such a vehicle, when the vehicle returns from the free-run traveling state to a normal traveling state in which the engine is started and the clutch is engaged, in response to an acceleration request. However, at this time, when the vehicle does not include a motor, the vehicle cannot increase the rotation speed of the engine using the drive torque of the motor, and thus requires a lot of time to start the engine, compared with a hybrid vehicle. Accordingly, when the vehicle returns from the free-run traveling state to the normal traveling state, a lot of time is required to re-accelerate the vehicle by the engine. Therefore, when the vehicle that can execute the free-run traveling does not include the motor, the deterioration of the drivability cannot be suppressed when the vehicle returns from the free-run traveling state to the normal traveling state even if the technique disclosed in Japanese Patent Application Laid-open No. 2012-201194 is applied to the vehicle.

There is a need for a vehicle control device and a vehicle control method, which can suppress the deterioration of the drivability when the vehicle returns from the free-run traveling state to the normal traveling state.

SUMMARY OF THE INVENTION

A vehicle control device includes: a control unit configured to execute free-run traveling in which an engine is stopped and a clutch that transmits power of the engine to a drive wheel is disengaged, at a time acceleration is not requested during traveling, and the control unit is configured to prohibit upshifting of a continuously variable transmission at least during execution of the free-run traveling, drive the engine from the free-run traveling state in response to an acceleration request, and upshift the continuously variable transmission at a time of returning to a normal traveling state in which the clutch is engaged.

A vehicle control method includes: a control step of executing free-run traveling in which an engine is stopped and a clutch that transmits power of the engine to a drive wheel is disengaged, at a time acceleration is not requested during traveling, and the control step includes: prohibiting upshifting of a continuously variable transmission at least during execution of the free-run traveling; driving the engine from the free-run traveling state in response to an acceleration request; and upshifting the continuously variable transmission at a time of returning to a normal traveling state in which the clutch is engaged.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a configuration of a vehicle control device and a vehicle control method according to an embodiment of the present invention will be described in detail with reference to the drawings.

Configuration of Vehicle

First, a configuration of a vehicle to which a vehicle control device according to the embodiment is applied will be described with reference toFIG. 1.

FIG. 1is a schematic diagram illustrating a configuration of a vehicle to which a vehicle control device according to the embodiment is applied. As illustrated inFIG. 1, a vehicle1to which a vehicle control device according to the embodiment is applied includes an engine2, a torque converter3, and a continuously variable transmission (CVT)4, as principal configuration elements.

The engine2functions as a power source of the vehicle1, and is coupled with the continuously variable transmission4through the torque converter3. An output torque of the engine2is input from an output shaft5of the engine2to the continuously variable transmission4through the torque converter3, and is transmitted from the continuously variable transmission4to a drive wheel6of the vehicle1through a differential mechanism and the like (not illustrated). In this way, a power transmission path is formed between the engine2and the drive wheel6.

The torque converter3includes a pump impeller3aconnected to the output shaft5of the engine2, and a turbine runner3bconnected to an input shaft7of the continuously variable transmission4. The pump impeller3ais an input member to which the output torque of the engine2is input, and the turbine runner3bis an output member that outputs the output torque of the engine2. The torque converter3can transmit the output torque of the engine2between the pump impeller3aand the turbine runner3bthrough a differential fluid.

The torque converter3includes a lock-up (L/U) clutch3c. The L/U clutch3cis a friction engagement-type clutch device arranged in the power transmission path of between the engine2and the drive wheel6. The L/U clutch3ccan connect the output shaft5of the engine2and the input shaft7without through the differential fluid.

When the L/U clutch3cis disengaged, the torque converter3transmits the output torque of the engine2to the continuously variable transmission4with the output shaft5and the input shaft7through the differential fluid. Meanwhile, when the L/U clutch3cis engaged, the torque converter3directly connects the pump impeller3aand the turbine runner3b, and transmits the output torque of the engine2to the continuously variable transmission4with the output shaft5and the input shaft7without through the differential fluid.

The continuously variable transmission4is configured with a known belt-type continuously variable transmission. The continuously variable transmission4includes a primary pulley4aprovided at a side near the engine2, and a secondary pulley4bprovided at a side near the drive wheel6, a belt4c, and a C1 clutch4d. The primary pulley4ais coupled with the input shaft7. The secondary pulley4bis coupled with an output shaft (not illustrated). The belt4cis stretched between the primary pulley4aand the secondary pulley4b.

The C1 clutch4dis provided on the input shaft7, and is arranged in series with the L/U clutch3cin the power transmission path of between the engine2and the drive wheel6. The C1 clutch4dincludes an engine-side engagement element coupled with an engine2side of the input shaft7, and a drive wheel-side engagement element coupled with a drive wheel6side of the input shaft7.

The C1 clutch4dconnects the power transmission path of between the engine2and the drive wheel6by engaging the engine-side engagement element and the drive wheel-side engagement element. Meanwhile, the C1 clutch4dcuts the power transmission path of between the engine2and the drive wheel6by disengaging the engine-side engagement element and the drive wheel-side engagement element. In other words, the C1 clutch4dfunctions as a switch device that switches a state of the power transmission path of between the engine2and the drive wheel6to between a power transmittable state, and a power non-transmittable state.

Configuration of Vehicle Control Device

Next, a configuration of a vehicle control device according to the embodiment will be described with reference toFIG. 2.

FIG. 2is a block diagram illustrating a configuration of a vehicle control device according to the embodiment. As illustrated inFIG. 2, a vehicle control device10according to the embodiment includes an accelerator position sensor11, an engine rotation speed sensor12, a vehicle speed sensor13, an electronic control unit (ECU)14, and a hydraulic control device15. The ECU14functions as a control unit according to the present invention.

The accelerator position sensor11detects an operation amount of an acceleration pedal (the accelerator opening degree) of the vehicle1, and outputs a signal that indicates a detected accelerator opening degree to the ECU14.

The engine rotation speed sensor12detects a rotation speed of the engine2, and outputs a signal that indicates a detected engine rotation speed to the ECU14.

The vehicle speed sensor13detects a speed of the vehicle1(vehicle speed), and outputs a signal that indicates a detected vehicle speed to the ECU14.

The ECU14is configured with a CPU, a RAM, a ROM, and an electronic circuit mainly including a known microcomputer including an interface and the like. A function of the ECU14is realized such that the CPU executes a control program loaded from the ROM to the RAM to operate various devices in the vehicle1, and to perform reading and writing of data in the RAM or the ROM, under control of the CPU.

The ECU14comprehensively controls the engine2, the torque converter3, and the hydraulic control device15, based on information of various sensors in the vehicle1including the above-described configuration elements. To be specific, the ECU14determines a fuel injection amount, injection timing, ignition timing, and the like, based on operation states of the engine2, such as the engine rotation speed, an intake air amount, and the throttle opening degree, and controls an injector, an ignition plug, and the like, based on determined information.

The ECU14stores, in the ROM, data of a variable speed diagram (variable speed map) that describes relationship between the accelerator opening degree and the vehicle speed of the vehicle1, and a variable speed ratio (a value obtained by dividing the rotation speed of the primary pulley4aby the rotation speed of the secondary pulley4b) of the continuously variable transmission4. The ECU14determines the variable speed ratio of the continuously variable transmission4from the variable speed diagram based on the accelerator opening degree and the vehicle speed respectively detected by the accelerator position sensor11and the vehicle speed sensor13, and controls the hydraulic control device15so as to establish the determined variable speed ratio.

Here, examples of variable speed lines illustrated in the variable speed diagram include: an upshift line that defines relationship between the accelerator opening degree and the vehicle speed, at which the speed should be changed toward a side into which the variable speed ratio of the continuously variable transmission4is decreased, that is, upshifting should be performed; and a downshift line that defines the accelerator opening degree and the vehicle speed, at which the speed should be changed toward a side into which the variable speed ratio of the continuously variable transmission4is increased, that is, downshifting should be performed. These variable speed lines serve as boundaries of regions of combinations of the accelerator opening degree and the vehicle speed, at which different variable speed ratios are selected, in the variable speed diagram.

When the acceleration pedal is not operated during traveling, that is, when the acceleration is not requested during the traveling, the ECU14executes free-run traveling. The free-run traveling is control for causing the vehicle1to travel in a state where driving of the engine2is stopped and the C1 clutch4dis disengaged. By execution of the free-run traveling, an inertia travel distance of the vehicle1can be increased, and the fuel efficiency can be improved. When the acceleration pedal is operated during the execution of the free-run traveling, that is, when the acceleration is requested during the execution of the free-run traveling, the ECU14returns the state of the vehicle1from the free-run traveling state to a normal traveling state by driving the engine2and engaging the C1 clutch4d. In the normal traveling state, the vehicle1becomes able to perform acceleration by the power of the engine2.

The hydraulic control device15has a function to supply oil pressure to the torque converter3, the primary pulley4a, the secondary pulley4b, and the C1 clutch4d. The hydraulic control device15changes the variable speed ratio of the continuously variable transmission4according to a variable speed ratio change instruction input from the ECU14. To be specific, the hydraulic control device15controls the variable speed ratio and a variable speed by controlling inflow and outflow of the oil pressure to a primary pulley-side actuator. Further, the hydraulic control device15changes a pulley ratio by adjusting the oil pressure of the primary pulley-side actuator to continuously change the variable speed ratio of the continuously variable transmission4.

The vehicle control device10having such a configuration suppresses the deterioration of the drivability when returning from the free-run traveling state to the normal traveling state by executing variable speed control processing described below. Hereinafter, an operation of the vehicle control device10that executes the variable speed control processing will be described with reference toFIGS. 3 to 5.

Variable Speed Control Processing

FIG. 3is a flowchart illustrating a flow of the variable speed control processing according to the embodiment.FIG. 4is a timing chart for describing a flow of the variable speed control processing according to the embodiment.FIG. 5is a diagram illustrating temporal change of the acceleration, the engine rotation speed, the turbine rotation speed, and the input rotation speed, of a vehicle of when the vehicle returns from the free-run traveling state to the normal traveling state.

The flowchart illustrated inFIG. 3is started at timing when an ignition switch of the vehicle1is switched from an OFF state to an ON state, and the variable speed control processing proceeds to step S1. The variable speed control processing is repeatedly executed in every predetermined control cycle while the ignition switch of the vehicle1is in the ON state.

In step S1, the ECU14determines whether a current operation point of the continuously variable transmission4on the variable speed diagram is in a region where the speed can be changed toward the side into which the variable speed ratio is decreased, that is, the upshifting can be performed, based on the signal that indicates the accelerator opening degree output from the accelerator position sensor11and the signal that indicates the vehicle speed output from the vehicle speed sensor13. As a result of the determination, when the operation point of the continuously variable transmission4is not in the region where the upshifting can be performed (No at step S1), the ECU14terminates the series of the variable speed control processing. Meanwhile, when the operation point of the continuously variable transmission4is in the region where the upshifting can be performed (Yes at step S1), the ECU14advances the variable speed control processing to step S2.

In step S2, the ECU14determines whether the acceleration is OFF (the accelerator pedal is not operated), based on the signal that indicates the accelerator opening degree output from the accelerator position sensor11. When the accelerator opening degree is a predetermine value or more, the ECU14determines that the accelerator pedal has been operated (acceleration ON) (No at step S2), and terminates the series of the variable speed control processing. Meanwhile, when the accelerator opening degree is less than the predetermined value, the ECU14determines that the accelerator pedal has not been operated (acceleration OFF) (Yes at step S2), and advances the variable speed control processing to step S3.

In step S3, the ECU14stops the engine2, and fixes the variable speed ratio of the continuously variable transmission4to a current variable speed ratio. Further, the ECU14disengages the C1 clutch4dby controlling the hydraulic control device15. Accordingly, the ECU14completes the processing of step S3, and advances the variable speed control processing to step S4.

In step S4, the ECU14determines whether the accelerator pedal is operated, based on the signal that indicates the accelerator opening degree output from the accelerator position sensor11. Then, the ECU14determines that the accelerator pedal has been operated (acceleration ON) (Yes at step S4) at timing when the accelerator opening degree is determined to be the predetermined value or more, and advances the variable speed control processing to step S5.

In step S5, the ECU14re-starts the engine2. Accordingly, the ECU14completes the processing of step S5, and advances the variable speed control processing to step S6.

In step S6, the ECU14upshifts the continuously variable transmission4by controlling the hydraulic control device15. Typically, at the time of start of the free-run traveling (a time T illustrated inFIG. 4=T1), the variable speed ratio of the continuously variable transmission4is decreased, as illustrated by the curved line L4ofFIG. 4(b). That is, the continuously variable transmission4is upshifted. Therefore, the inertia torque of the continuously variable transmission4, which occurs in association with the upshifting, is wastefully consumed at the time of the free-run traveling. Accordingly, when the vehicle1returns from the free-run traveling state to the normal traveling state (the time T illustrated inFIG. 4=T2), the torque is not transmitted to the drive wheel6until the C1 clutch4dis engaged.

In contrast, in the variable speed control processing according to the embodiment, at the time of start of the free-run traveling (the time T illustrated inFIG. 4=T1), the ECU14fixes the variable speed ratio of the continuously variable transmission4, as illustrated by the curved line L3ofFIG. 4(b). Therefore, when the vehicle1returns from the free-run traveling state to the normal traveling state (the time T illustrated inFIG. 4=T2), the ECU14upshifts the continuously variable transmission4, thereby to transmit the inertia torque of the continuously variable transmission4to the drive wheel6without waste. Note that the curved line L6illustrated inFIG. 4(a)indicates the engine rotation speed, and the curved lines L1and L2illustrated inFIG. 4(c)respectively indicate the acceleration of the vehicle in the variable speed control processing of the present embodiment and of a conventional case. Accordingly, the ECU14completes the processing of step S6, and advances the variable speed control processing to step S7.

In step S7, the ECU14determines whether the engine2has performed complete explosion, based on the signal that indicates the engine rotation speed output from the engine rotation speed sensor12. Here, the complete explosion indicates that the engine2moves onto a state in which the engine2is continuously rotated without auxiliary power such as a starter. In other words, the complete explosion indicates that the engine2moves onto a self-operable state. When the engine rotation speed becomes a rotation speed or more, the rotation speed being a threshold of the complete explosion determination, the ECU14determines that the engine2has performed the complete explosion. Note that the ECU14may determine that the engine2has performed the complete explosion at timing when the engine rotation speed is decreased after increased to a peak value at the time of start of the engine2. The ECU14then advances the variable speed control processing to step S8at timing when the engine2is determined to have performed the complete explosion.

In step S8, the ECU14starts the engagement of the C1 clutch4dby increasing engagement oil pressure of the C1 clutch4dby controlling the hydraulic control device15. By the engagement of the C1 clutch4d, the vehicle1becomes in the normal traveling state in which the vehicle1can perform acceleration by the power of the engine2. Accordingly, the ECU14completes the processing of step S8, and terminates the series of the variable speed control processing.

As is clear from the above description, in the variable speed control processing according to the embodiment, the ECU14fixes the variable speed ratio of the continuously variable transmission4during execution of the free-run traveling, and upshifts the continuously variable transmission4when the vehicle1returns from the free-run traveling state to the normal traveling state. Therefore, when the vehicle1returns from the free-run traveling state to the normal traveling state, the inertia torque of the continuously variable transmission4can be transmitted to the drive wheel6without waste.

Further, in the conventional variable speed control processing, the continuously variable transmission4is upshifted according to a normal variable speed line at the time of execution of the free-run traveling, and the continuously variable transmission4is downshifted when the vehicle returns from the free-run traveling state to the normal traveling state (the curved line L4illustrated inFIG. 4(b)). Therefore, in the conventional variable speed control processing, the rotation speed (input rotation speed) NIN (the curved line L8illustrated inFIG. 5(a)) of the C1 clutch4dof the drive wheel6side is increased without input torque, at the time of return from the free-run traveling state (the time T illustrated inFIG. 5=T2). As a result, the sense of drawing of deceleration (the curved line L2illustrated inFIG. 5(b)) due to downshifting occurs, and a difference between the rotation speed (turbine rotation speed) NT of the C1 clutch4dof the engine2side (the curved line L7illustrated inFIG. 5(a)) and the input rotation speed NIN is expanded, and a lot of time is required to engage the C1 clutch4d. Accordingly, a time (T4−T2) from the time of return from the free-run traveling state (the time T=T2) to a point of time when the vehicle1is re-accelerated by the engine2(the time T=T4) becomes long. Note that the curved line L6illustrated inFIG. 5(a)indicates the engine rotation speed.

In contrast, in the variable speed control processing according to the embodiment, the continuously variable transmission4is upshifted when the vehicle1returns from the free-run traveling state to the normal traveling state. Therefore, the sense of drawing of deceleration due to downshifting does not occur when the vehicle1returns from the free-run traveling state (the curved line L1illustrated inFIG. 5(b)). Further, the input rotation speed NIN (the curved line L5illustrated inFIG. 5(a)) is decreased by the upshifting of the continuously variable transmission4. Therefore, the difference between the turbine rotation speed NT and the input rotation speed NIN is smaller than that in the conventional variable speed control processing. As a result, the time required from the time of return from the free-run traveling to when the C1 clutch4dis engaged becomes short, and a time (T3−T2) from the time of return from the free-run traveling state (the time T=T2) to a point of time when the vehicle1is re-accelerated by the engine2(the time T=T3) becomes short.

As described above, according to the variable speed control processing according to the embodiment, when the vehicle1returns from the free-run traveling state to the normal traveling state, the inertia torque of the continuously variable transmission4can be transmitted to the drive wheel6without waste, and the time required to re-accelerate the vehicle1by the engine2can be shortened. Therefore, the difficulty of the driver in feeling the sense of acceleration and the deterioration of the drivability can be suppressed.

Further, according to the variable speed control processing according to the embodiment, the ECU14upshifts the continuously variable transmission4before starting the engagement of the C1 clutch4d. Therefore, the inertia torque of the continuously variable transmission4can be transmitted to the drive wheel6before the output torque of the engine2is transmitted to the drive wheel6.

As described above, an embodiment to which the invention made by the inventors of the present application is applied has been described. However, the present invention is not limited by the description and the drawings that are a part of the disclosure of the present invention by the present embodiment. For example, in the present embodiment, the ECU14fixes the variable speed ratio of the continuously variable transmission4at the time of the free-run traveling. However, the ECU14may be configured as long as it is does not upshift the continuously variable transmission4. That is, the ECU14may change the speed toward a side into which the variable speed ratio of the continuously variable transmission4is increased, that is, may downshift the continuously variable transmission4, instead of fixing the variable speed ratio of the continuously variable transmission4at the time of the free-run traveling. When the ECU14downshifts the continuously variable transmission4, the sense of drawing due to deceleration of the downshifting occurs at the time of execution of the free-run traveling. However, the inertia torque of the continuously variable transmission4transmitted to the drive wheel6becomes larger when the vehicle1returns from the free-run traveling state to the normal traveling state. Therefore, the deterioration of the drivability can be further suppressed. Further, in the present embodiment, the present invention is applied to a vehicle without a motor that can execute the free-run traveling. However, the present invention may be applied to a vehicle that includes a motor and can execute the free-run traveling, such as a hybrid vehicle. As described above, all of other embodiments, examples, operation technologies, and the like, which are made by a person skilled in the art and the like, on the basis of the present embodiment, are included in the scope of the present invention.

According to the vehicle control device and the vehicle control method of the embodiment, when the vehicle returns from the free-run traveling state to the normal traveling state, inertia torque of the continuously variable transmission can be transmitted to the drive wheel without waste, and time required to accelerate the vehicle by the engine can be shortened. Therefore, the difficulty of the driver in feeling the sense of acceleration and the deterioration of the drivability can be suppressed.