Vehicle control device

A vehicle control device includes an engine, and a motor that is driven by power to be supplied from a battery, the vehicle control device controlling a vehicle that uses at least one of engine output and motor output as a driving force. The vehicle control device includes a regeneration control and a downhill-acceleration control unit. The regeneration control unit causes the motor to perform regeneration on a downhill. The downhill-acceleration control unit performs downhill acceleration control for causing, in a specific zone on the downhill, the vehicle to travel at increased speed without allowing the vehicle to use the engine output as drive output, and without causing the motor to perform the regeneration.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No. 2015-231393 filed on Nov. 27, 2015, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to vehicle control in a vehicle that performs regeneration using with a motor.

BACKGROUND ART

Causing a motor to be rotated by rotation of the wheels such that the motor is utilized as a power generator has become known as regeneration. Electrical energy generated by the regeneration is used for charging a rechargeable battery. Further, the regeneration is controlled by a vehicle control device installed in the vehicle, and is performed when a predetermined driving condition is satisfied.

When the vehicle performs the regeneration while traveling downhill, potential energy based on a height difference of the downhill can be recovered as the electrical energy. However, when the rechargeable battery is fully charged while the vehicle is traveling downhill, the energy generated by the regeneration needs to be discharged, for example, as heat. As a countermeasure, in the configuration disclosed in Patent Literature 1, a charge level of the rechargeable battery is reduced before the downhill so as to increase efficiency of the regeneration.

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

During the regeneration, loss that is caused by generation of the heat caused by the rotation of the motor is inevitable. In addition, loss is caused also when the electrical energy stored in the rechargeable battery is used as kinetic energy of the motor. As a result, there arises a problem in that energy efficiency is degraded by the losses that are caused during these conversions.

The present disclosure has been made to solve this problem, and it is an object thereof to provide a vehicle control device capable of increasing energy efficiency of a vehicle while traveling downhill.

According to an aspect of the present disclosure, there is provided a vehicle control device including an engine, and a motor that is driven by power to be supplied from a rechargeable battery. The vehicle control device controls a vehicle that uses at least one of engine output and motor output as a driving force. The vehicle control device includes a regeneration control unit and a downhill-acceleration control unit. The regeneration control unit causes the motor to perform regeneration on a downhill. The downhill-acceleration control unit performs downhill acceleration control for causing, in a specific zone on the downhill in which the regeneration is performed, the vehicle to travel at increased speed without allowing the vehicle to use the engine output as drive output, and without causing the motor to perform the regeneration.

With this configuration, the vehicle is accelerated by the downhill acceleration control in the specific zone on the downhill in which the regeneration is performed. In this downhill acceleration control, in the specific zone on the downhill, the vehicle is caused to travel without using the engine output as the drive output, and without performing regeneration. In other words, in this specific zone, potential energy from the downhill is directly converted to kinetic energy. As a result, a proportion in which the potential energy at the time when the vehicle travels on the downhill is converted to electric energy by the regeneration can be reduced, and energy efficiency of the vehicle can be increased.

DESCRIPTION OF EMBODIMENTS

Embodiments according to the present disclosure are described with reference to the drawings. In the following description, a vehicle control device according to the embodiments is applied to a hybrid vehicle that obtains a vehicle driving force from an engine and a drive motor. Note that, the hybrid vehicle may be abbreviated as a vehicle. In addition, parts that are the same as or equivalent to each other among the embodiments described below are denoted by the same reference symbols in the drawings, and redundant description of the parts denoted by the same reference symbols is omitted.

FIG. 1is a diagram showing a configuration of a vehicle100as an example. The vehicle100mainly includes an engine31, a motor32being a motor generator, a clutch33, a transmission34, a drive shaft35, drive wheels37, an inverter unit39, a battery (rechargeable battery)40, and a vehicle control device50. Further, the vehicle100also includes a navigation device60, and the vehicle control device50is capable of acquiring geographic information from this navigation device60.

The engine31is a well-known internal combustion engine that generates a desired engine output by combusting, in combustion chambers, a mixture of air and fuel that is injected from fuel injection valves. As examples of the engine31, there may be mentioned a gasoline engine that uses gasoline as fuel and a diesel engine that uses, for example, light oil as fuel.

The motor32generates motor output by being rotated with power from the battery40, and also functions as a power generator that generates power for the battery40. The motor32, which is an AC motor that is driven by AC power, includes a rotor as a rotary element, and a stator that is arranged around the rotor and generates an induction voltage. The rotor is connected, via the transmission34, to the drive shaft35that rotates the drive wheels37. The stator is connected to the battery40via the inverter unit39.

The inverter unit39functions as a power conversion device that performs power conversion between DC power that is supplied from the battery40and AC power that is generated by the motor32. For example, the inverter unit39includes a converter that converts the AC power to the DC power, and an inverter that converts the DC power to the AC power. When the motor32is driven, the stator generates the induction voltage in a different phase with use of the AC power supplied from the battery40via the inverter unit39so as to rotate the rotor. Further, when the motor32performs regeneration, the rotor is rotated by rotation of the drive wheels37. With this, the AC power is generated in the stator. This generated power is rectified by the inverter unit39, and then supplied to the battery40. The battery40is charged with this supplied power.

The clutch33functions as a transmission switching unit that disconnects the engine output being a part of the driving force of the vehicle100. The engine31is drive-coupled to an output shaft of the motor32via the clutch33. Thus, in an HV drive mode, the engine31and the motor32are coupled to each other via the clutch33, and the vehicle100travels by obtaining the driving force from both the engine output and the motor output. Meanwhile, in an EV drive mode, the engine31is disconnected from the motor32by the clutch33, and the vehicle100travels by obtaining the driving force only from the motor output.

The vehicle control device50refers collectively to devices that control units in the vehicle100, specifically, an engine ECU51, a motor ECU52, an HVECU53, and an ACCECU54. The engine ECU51controls and drives the engine31. The motor ECU52controls and drives the motor32and the inverter unit39. The HVECU53performs cooperative control between the engine ECU51and the motor ECU52so as to control the drive modes of the vehicle100. The ACCECU54develops a travel plan for the vehicle100in a cruise control mode (under constant-speed control) based on the geographic information that is supplied from the navigation device60.

These ECUs51to54each mainly include a well-known microcomputer including a CPU, ROM, and RAM. Further, the ECUs51to54are electrically connected to each other via a bus so as to be capable of performing bidirectional communication. With this, the ECUs51to54are capable of controlling the driving, in response to a detected signal or an operation signal input to any of the ECUs, of various devices connected to outputs of other ones of the ECUs.

The navigation device60provides geographic information to the vehicle100. The navigation device60is, for example, a car navigation system or a smartphone, and is connected to the ACCECU54in a wired or wireless manner. The geographic information includes map information items such as a latitude, longitude, and altitude, and relevant information items of, for example, facilities related to the map information items. The geographic information is managed by a database (not shown). From the geographic information acquired via the navigation device60, the ACCECU54can acquire information items necessary for traveling of and regeneration in the vehicle100.

Next, operations during the regeneration in the vehicle100are described with reference toFIGS. 2.FIG. 2Ais a chart showing a travel route of the vehicle100and a gradient of the travel route.FIG. 2Bis an explanatory chart showing changes in a target vehicle speed under the cruise control.FIG. 2Cis an explanatory chart showing changes in a charge level SOC of the battery40.FIG. 2Dis an explanatory chart showing changes in the driving force of the vehicle100.

On a downhill satisfying a predetermined condition, the vehicle100starts regeneration for charging the battery40. InFIG. 2A, the regeneration is started while traveling downhill, and the regeneration is continued even after traveling downhill by utilizing a low-load state as a result of traveling downhill. During regeneration, the battery40is charged with the power generated by the motor32, and the charge level SOC is increased (FIG. 2C).

When the vehicle100travels on a long downhill or a downhill with a high gradient, the charge level SOC of the battery40may exceed its upper limit value during the regeneration that utilizes traveling downhill. An excess of the power over the upper limit value needs to be discharged, for example, as heat, and hence efficiency of the regeneration is degraded. As a countermeasure, before starting the regeneration, the vehicle100performs deceleration control for reducing the charge level SOC of the battery40. In the deceleration control, the vehicle100is decelerated (FIG. 2B) such that the charge level SOC of the battery40is reduced (FIG. 2C). This deceleration control is performed by reducing the driving force of the vehicle100to a range corresponding to the EV drive mode. The charge level SOC is reduced by the deceleration control before the start of the regeneration (FIG. 2C), and then the battery40is charged by the regeneration that utilizes traveling downhill. With this, the charge level SOC can be increased.

Next, specific processes by the vehicle control device50for performing the drive control of the vehicle100, which is shown inFIG. 2AtoFIG. 2D, are described with reference to the other drawings.FIG. 3is an explanatory flowchart showing processes when developing a travel plan for the vehicle100. The travel planning process shown inFIG. 3is implemented, for example, in the cruise control mode (constant vehicle speed mode) for causing the vehicle100to travel at a vehicle speed in a certain range. Note that, the ACCECU54executes processes of Steps S11to S13so that the vehicle control device50functions as a search unit. Further, the ACCECU54executes processes of Steps S14and S15so that the vehicle control device50functions as a deceleration position search unit.

In Step S11, the ACCECU54acquires the geographic information necessary for the travel plan. The geographic information to be acquired in Step S11is acquired, for example, based on the travel route selected via the navigation device60by a driver or another passenger. The geographic information includes a latitude, longitude, a gradient information item, and a downhill gradient distance at each point on the travel route. The ACCECU54requests the navigation device60to supply this geographic information.

In Step S12, the ACCECU54searches for a downhill on which the regeneration can be performed. The downhill on which the regeneration can be performed is selected based, for example, on the acquired gradient information items from among downhills each having a predetermined gradient angle or higher and a predetermined gradient distance or longer. The ACCECU54searches for any appropriate downhill based on the geographic information acquired in Step S11.

When an appropriate downhill is detected (YES at Step S12), in Step S13, the ACCECU54acquires a gradient start position Dd of the downhill. For example, the ACCECU54sets, as the gradient start position Dd, a latitude and longitude of a position where a gradient of the downhill starts. Note that, when no appropriate downhill is detected (NO at Step S12), the travel planning process is ended.

In Step S14, the ACCECU54acquires a deceleration start position Dc where the deceleration control is started. The deceleration start position Dc refers to a position where the deceleration control of the vehicle100is started. The deceleration start position Dc to be acquired is a position before the registered gradient start position Dd on the travel route, the position Dd being set in Step S13.

FIG. 4is an explanatory flowchart showing in detail an example of how the deceleration start position Dc is acquired in Step S14. Further,FIG. 5AandFIG. 5Bare explanatory charts showing how a vehicle speed or the driving force is controlled in the deceleration control. In this embodiment, the deceleration start position Dc is acquired by calculation based on the target vehicle speed V and a driving-force upper limit value MD in the deceleration control.

First, in Step S141, the ACCECU54sets a target vehicle speed V1. The target vehicle speed V1refers to a speed that the vehicle100finally reaches by the deceleration control of the vehicle100. The ACCECU54sets the target vehicle speed V1such that, as shown inFIG. 5A, a reduction rate of the vehicle speed by the deceleration control increases according to a vehicle speed before the deceleration control.

In Step S142, the ACCECU54sets the driving-force upper limit value MD. The driving-force upper limit value MD refers to a value for setting an upper limit of the driving force that the vehicle100is allowed to output. As shown inFIG. 5B, the drive modes of the vehicle100are switched by changing a ratio of the engine output and the motor output in the driving force. The ACCECU54sets the driving-force upper limit value MD to be within a driving-force range corresponding to the EV drive mode. With this, in the deceleration control, driving of the engine31(engine output) is limited, and only the output from the motor32(motor output) is used as the driving force of the vehicle100.

In Step S143, based on the target vehicle speed set in Step S141and on the driving-force upper limit value MD set in Step S142, the ACCECU54calculates the deceleration start position Dc. For example, first, the ACCECU54calculates a distance necessary for the vehicle100to reach the target vehicle speed V1based on the set driving-force upper limit value MD. Then, the ACCECU54uses the calculated distance as a point-to-point distance L from the gradient start position Dd acquired in Step S13to the deceleration start position Dc. In this way, the deceleration start position Dc on the travel route is calculated.

Referring back toFIG. 3, in Step S15, the ACCECU54acquires an acceleration start position Da. The acceleration start position Da refers to a position before the deceleration start position Dc acquired in Step S14, that is, a position where the vehicle100starts acceleration control. In the acceleration control, the vehicle100is accelerated before the start of the deceleration control such that the vehicle-speed reduction rate of the vehicle100in the deceleration control is secured. The acceleration start position Da to be acquired by the ACCECU54is, for example, a position at predetermined distance before the deceleration start position Dc.

When the acceleration start position Da is acquired, the travel planning process is ended.

Next, drive control with use of the positions (Dd, Dc, and Da) acquired in the travel plan and during the regeneration in the vehicle100is described.FIG. 6is an explanatory flowchart showing the drive control of the vehicle100. The HVECU53executes processes of Steps S24to S28inFIG. 6so that the vehicle control device50functions as a charge level control unit.

In Step S21, the HVECU53acquires a current vehicle position Dp. The vehicle position Dp refers to a current position of the vehicle100in motion, which is acquired from the navigation device60via the ACCECU54.

In Step S22, the HVECU53determines whether the vehicle100has reached the gradient start position Dd where the regeneration is started. The HVECU53compares the vehicle position Dp acquired in Step S21and the gradient start position Dd acquired in the travel plan to each other, and determines whether the vehicle100has reached the gradient start position Dd.

In the case where the vehicle100has not yet reached the gradient start position Dd (NO at Step S22), in Step S24, the HVECU53determines whether the vehicle100has reached the deceleration start position Dc where the vehicle100starts the deceleration control. The HVECU53compares the vehicle position Dp and the deceleration start position Dc acquired in the travel plan to each other, and determines whether the vehicle100has reached the deceleration start position Dc.

In the case where the vehicle100has not yet reached the deceleration start position Dc (NO at Step S24), in Step S27, the HVECU53determines whether the vehicle100has reached the acceleration start position Da where the acceleration control is performed. The HVECU53compares the vehicle position Dp and the acceleration start position Da acquired in the travel plan, and determines whether the vehicle100has reached the acceleration start position Da.

In the case where the vehicle100has not yet reached the acceleration start position Da (NO at Step S27), in Step S29, the HVECU53sets a target vehicle speed V0. The target vehicle speed V0refers to a vehicle speed of the vehicle100within a range set by the cruise control. In other words, in Step S29, the HVECU53keeps the vehicle speed within a range of the target vehicle speed V0set by the cruise control.

Meanwhile, in the case where the vehicle position Dp has reached the acceleration start position Da (YES at Step S27), in Step S28, the HVECU53starts the acceleration control. In the acceleration control, the HVECU53sets a target vehicle speed V2to cause the vehicle speed to be higher than a current vehicle speed (V0). In accordance with the target vehicle speed V2set in Step S28, the engine ECU51and the motor ECU52increase driving forces of the engine31and the motor32so as to accelerate the vehicle100.

FIG. 7AandFIG. 7Bare explanatory charts showing an example of how the vehicle speed is controlled in the acceleration control. The HVECU53sets the target vehicle speed V2in the acceleration control such that, as shown inFIG. 7A, an increased amount of the vehicle speed becomes higher as a current vehicle speed Vp becomes higher. Further, the HVECU53sets acceleration in the acceleration control such that, as shown inFIG. 7B, the acceleration becomes lower as the current vehicle speed Vp becomes higher.

Referring back toFIG. 6, in the case where the vehicle100has reached the deceleration start position Dc (YES at Step S24), in Step S25, the HVECU53starts the deceleration control. In the deceleration control, the HVECU53causes the vehicle speed to be lower than the vehicle speed V0before the acceleration so as to reduce the charge level SOC of the battery40. At this time, the HVECU53limits the driving force to be within a range in which the driving-force upper limit value MD set in the travel plan (FIG. 5B) is not exceeded. Thus, the vehicle100is switched to the EV drive mode, and starts to travel at reduced speed.

In Step S26, the HVECU53performs lower-limit avoidance control. The lower-limit avoidance control refers to control for preventing extreme reduction of the charge level SOC of the battery40as a result of performing the deceleration control. When the charge level SOC of the battery40significantly decreases in the deceleration control, the HVECU53performs the lower-limit avoidance control so as to stop the deceleration control, and to restore the vehicle speed to the vehicle speed V0set in the cruise control.

FIG. 8is an explanatory flowchart showing in detail the lower-limit avoidance control that is performed in Step S26.FIG. 9is an explanatory chart showing the lower-limit avoidance control.

In Step S261, the HVECU53compares the charge level SOC to a threshold Sa. As shown inFIG. 9, the threshold Sa refers to a maximum value of the charge level SOC after the reduction that is required in the deceleration control. In other words, when the deceleration control is performed, the vehicle speed is controlled such that the charge level SOC of the battery40is equal to or less than the threshold Sa.

When the charge level SOC is more than the threshold Sa (NO at Step S261), the HVECU53ends the lower-limit avoidance control. This is because it can be determined that, when the charge level SOC is more than the threshold Sa, the battery40is sufficiently charged, and the charge level SOC is not excessively reduced even when the deceleration control is continued.

When the charge level SOC is equal to or less than the threshold Sa (YES at Step S261), in Step S262, the HVECU53compares the charge level SOC to a threshold Sb. The threshold Sb refers to an allowable lower limit value of the charge level SOC in the deceleration control. The threshold Sb is experimentally acquired based, for example, on at which charge level SOC the battery40starts to be deteriorated. Thus, in the deceleration control, the charge level SOC of the battery40is reduced within a range from the threshold Sa to the threshold Sb (FIG. 9).

When the charge level SOC is more than the threshold Sb (NO at Step S262), in Step S264, the HVECU53reduces a reduction rate of the charge level SOC in the deceleration control. In this case, the HVECU53sets a vehicle-speed target value higher than the vehicle speed V1that is set in the deceleration control (sets a target vehicle speed V3), and reduces the driving-force upper limit value MD. As described above, the driving-force upper limit value MD is set within the driving-force range in which the vehicle100is in the EV drive mode. Thus, when the driving-force upper limit value MD is reduced, the reduction rate of the charge level SOC is reduced despite continuation of the deceleration control.

When the charge level SOC is equal to or less than the threshold Sb (YES at Step S262), in Step S263, the HVECU53stops the deceleration control. When the deceleration control is continued in this case, there arises a risk that the charge level SOC may fall below the threshold Sb. As a countermeasure, the HVECU53resets the vehicle-speed target value to V0, and resets the driving-force upper limit value MD into a range in which the engine31is driven.

Referring back toFIG. 6, in the case where the vehicle100has reached the gradient start position Dd (YES at Step S22), in Step S23, the HVECU53starts the regeneration. Thus, the power, which is generated by the motor32through the regeneration that is started by the vehicle100while traveling downhill, is supplied to the battery40via the inverter unit39, and the battery40starts to be charged.

As described above in this first embodiment, the vehicle control device50performs the deceleration control for reducing the charge level SOC of the battery40before the regeneration on the downhill so as to increase the efficiency of the regeneration by the vehicle100while traveling downhill. In this deceleration control, the engine31is stopped by reducing the driving force of the vehicle100to a level at which only the motor output is used as the driving force. With this, degradation in engine efficiency is restrained. As a result, both the efficiency of the regeneration and the engine efficiency can be increased, and energy efficiency of the vehicle100can be increased.

In order to increase the driving force, the vehicle100is switched from a mode of using only the motor output to a mode of using the engine output and the motor output in combination with each other. In the deceleration control, the upper limit value of the driving force of the vehicle100is set within the range in which only the motor output is used. With this configuration, in the deceleration control, the driving force is set within the range in which only the motor output is used. As a result, the degradation in engine efficiency can be restrained irrespective of the drive modes of the vehicle100.

The charge level control unit monitors changes in the charge level of the battery40during the deceleration control. When the reduction rate of the charge level SOC is high, the charge level control unit stops the deceleration control. With this configuration, the charge level SOC can be prevented from being excessively reduced by the deceleration control before the start of the regeneration. As a result, deterioration of the battery40can be reduced.

The deceleration position search unit searches for the deceleration start position based on the vehicle speed after the deceleration of the vehicle100, which is set in the deceleration control. With this configuration, the deceleration start position can be searched for based on the target vehicle speed of the vehicle100, which is set in the deceleration control. As a result, a deceleration start position appropriate for performing the vehicle speed reduction necessary in the deceleration control can be set.

The deceleration position search unit sets the vehicle speed after the deceleration such that the vehicle-speed reduction rate becomes higher as the vehicle speed of the vehicle100before the deceleration control becomes higher. With this setting, during low-speed traveling, the vehicle speed can be restrained from being excessively reduced by the deceleration control. As a result, degradation in drivability can be reduced.

The charge level control unit performs the acceleration control for accelerating the vehicle100before performing the deceleration control. With this configuration, the vehicle speed can be increased before the deceleration. As a result, even when the vehicle100is traveling at low speed, the vehicle-speed reduction rate can be secured. In addition, the vehicle speed can be prevented from being excessively reduced by the deceleration control, and hence degradation in drivability can be restrained.

The charge level control unit increases the increased amount of the vehicle speed in the acceleration control as the vehicle speed of the vehicle100before the acceleration control becomes higher. With this configuration, a sense of discomfort to the driver and the other passengers, which is caused as a result of the acceleration of the vehicle by the acceleration control, can be alleviated.

The charge level control unit performs the deceleration control when the vehicle100is in the cruise control mode (constant-speed control mode). With this configuration, in the constant-speed control mode at a preset speed, vehicle speed control can be performed without causing the driver to feel a sense of discomfort.

A configuration of this second embodiment is the same as the configuration of the first embodiment in performing regeneration on a downhill, but is different from the configuration of the first embodiment in that downhill acceleration control for accelerating the vehicle100is performed in a specific zone on the downhill in which the regeneration is performed.

FIGS. 10are explanatory charts showing processes for regeneration in the second embodiment.FIG. 10Ais a chart showing a travel route of the vehicle100and a gradient of the travel route.FIG. 10Bis an explanatory chart showing changes in the target vehicle speed.FIG. 10Cis an explanatory chart showing changes in the charge level SOC of the battery40.FIG. 10Dis an explanatory chart showing changes in the driving force of the vehicle100.

Also in this second embodiment, as shown inFIGS. 10A to 10D, the vehicle100performs the regeneration on a downhill satisfying a predetermined condition. Also in this embodiment, the ACCECU54searches for a downhill satisfying the condition for performing regeneration, and the regeneration is started when the vehicle100reaches this downhill. Further, also in the drive control shown inFIGS. 10, the deceleration control is performed before the regeneration is performed. Note that, also in this second embodiment, the acceleration control may be performed before the deceleration control.

In addition, in a specific zone on the downhill in which the regeneration is performed, the vehicle100performs the downhill acceleration control for increasing its vehicle speed. In the downhill acceleration control, in the specific zone on the downhill, the vehicle100is accelerated by converting some of potential energy while traveling downhill to kinetic energy of the vehicle without using the engine output as the driving force (FIGS. 10B and 10D). As a result, loss in the regeneration is reduced. In addition, the kinetic energy of the vehicle100while traveling downhill is increased, and hence the energy efficiency of the vehicle is increased.

Next, specific processes by the vehicle control device50for performing the drive control of the vehicle100, which is shown inFIGS. 10A to 10D, are described with reference to the other drawings.FIG. 11is an explanatory flowchart showing processes when developing a travel plan for the vehicle100. The travel plan shown inFIG. 11is implemented, for example, when the vehicle is in the cruise control mode.

In Step S31, the ACCECU54acquires geographic information necessary for the travel plan. Also in Step S31, as in Step S11, the geographic information is acquired based on a travel route selected via the navigation device60by the driver or the other passenger.

In Step S32, the ACCECU54searches for the downhill that satisfies the condition for performing regeneration. Also in Step S32, the same process as that of Step S12inFIG. 3is executed. When an appropriate downhill is detected (YES at Step S32), the ACCECU54proceeds to Step S33. Meanwhile, when no appropriate downhill is detected (NO at Step S32), the ACCECU54ends the travel planning process.

In Step S33, the ACCECU54determines a curvature of the downhill detected in Step S32. In the case where the curvature of the downhill is large, when the speed of the vehicle100is changed, there is a risk that the driver will feel a sense of discomfort. As a countermeasure, when the curvature of the downhill is equal to or larger than a preset threshold Ta (NO at Step S33), the ACCECU54ends the travel planning process. As a result, the deceleration control is not performed in the vehicle100. The HVECU53executes the process of Step S33so that the vehicle control device50functions as a curvature acquisition unit.

When the curvature of the downhill is smaller than the threshold Ta (YES at Step S33), the ACCECU54proceeds to Step S34. In Step S34, the ACCECU54acquires the gradient start position Dd of the downhill on which the regeneration is performed.

In Step S35, the ACCECU54determines whether the charge level SOC may still be reduced. When the charge level SOC may still be reduced, the ACCECU54turns the deceleration control ON (Step S36). When the charge level SOC may not still be reduced, the ACCECU54turns the deceleration control OFF (Step S37). Whether the charge level SOC may still be reduced is determined based on the energy efficiency of the vehicle100that travels on the downhill. Specifically, in the case where the vehicle speed when the vehicle100travels on the downhill while performing regeneration including the deceleration control is lower than the vehicle speed before traveling downhill, the ACCECU54determines that the charge level SOC is not allowed to be further reduced.

FIG. 12is a flowchart showing processes of Step S35in detail. Further,FIGS. 13A and 13Bare explanatory charts showing the processes of Step S35for determining whether to perform the deceleration control. Also inFIG. 12, processes from Steps5351to5353may be the same as the processes from Steps S141to S143inFIG. 4.

First, in Step S351, the ACCECU54sets the target vehicle speed V1in the deceleration control. Next, in Step S352, the ACCECU54sets the driving-force upper limit value MD in the deceleration control. Further, in Step S353, based on the target vehicle speed set in Step S351and on the driving-force upper limit value MD set in Step S352, the ACCECU54calculates the deceleration start position Dc.

In Step S354, the ACCECU54acquires gradient information items of the downhill on which the regeneration is performed. For example, the ACCECU54acquires, as the gradient information items of the downhill, a gradient angle and a gradient distance.

In Step S355, the ACCECU54calculates an estimated vehicle speed Ve of the vehicle100assuming that the vehicle100finishes traveling downhill after the deceleration control is performed. The estimated vehicle speed Ve refers to a speed of the vehicle100at an end point of the downhill in the case where the vehicle100travels on this downhill after the deceleration control is performed. The ACCECU54calculates the estimated vehicle speed Ve based, for example, on potential energy that is obtained when the vehicle100travels on the detected downhill, the target vehicle speed V1of the vehicle100in the deceleration control, and a weight of the vehicle100.

In Step S356, the ACCECU54compares the estimated vehicle speed Ve and the current vehicle speed Vp to each other. As shown inFIGS. 13A and 13B, if an estimated vehicle speed (Vel) is equal to or more than the current speed Vp, even when the deceleration control is performed, the speed of the vehicle100can be restored by using, during the downhill acceleration control, the potential energy that is obtained by traveling downhill. Thus, the ACCECU54proceeds to Step S357, and determines that the charge level SOC may still be reduced. Meanwhile, if an estimated vehicle speed (Ve2) is less than the current speed Vp, when the deceleration control is performed, the speed of the vehicle100cannot be restored even by using the potential energy that is obtained by traveling downhill. Thus, the ACCECU54proceeds to Step S358, and determines that the charge level SOC is not allowed to be further reduced.

Referring back toFIG. 11, when the charge level SOC may still be reduced (YES at Step S35), in Step S36, the ACCECU54turns the deceleration control ON. Thus, in Step S38, the ACCECU54acquires the deceleration start position Dc. At the time of acquiring the deceleration start position Dc in Step S38, for example, the value calculated in Step5353may be used. When the deceleration control is turned ON, before the downhill on which the regeneration is performed, the vehicle100reduces its vehicle speed so as to reduce the charge level SOC of the battery.

When the charge level SOC is not allowed to be further reduced (NO at Step S35), in Step S37, the ACCECU54turns the deceleration control OFF. In other words, a higher priority is given to increasing the energy efficiency while traveling downhill over increasing the regeneration efficiency by the deceleration control.

Next, with reference to the positions (Dd and Dc) acquired in the travel plan in the second embodiment, the processes during the regeneration in the vehicle100are described.FIG. 14is an explanatory flowchart showing drive control of the vehicle100. Processes of Steps S41, S42, S44, S47, and S48shown inFIG. 14may similarly be the same as the processes shown inFIG. 6. The HVECU53executes the process of Step S44inFIG. 14so that the vehicle control device50functions as a regeneration control unit, and the HVECU53executes the process of Step S43so that the vehicle control device50functions as a downhill-acceleration control unit.

In Step S41, the HVECU53acquires the current vehicle position Dp. In Step S42, the HVECU53determines whether the vehicle100has reached the gradient start position Dd of the downhill on which the regeneration is performed. In the case where the vehicle100has not yet reached the gradient start position Dd (NO at Step S42), in Step S45, the HVECU53determines whether the deceleration control has been set to ON. In the case where the deceleration control has not been set to ON (NO at Step S45), in Step S48, the HVECU53sets the target vehicle speed V0.

Further, in the case where the deceleration control has been set to ON (YES at Step S45), in Step S46, the HVECU53determines whether the vehicle100has reached the deceleration start position Dc. In the case where the vehicle100has not yet reached the deceleration start position Dc (NO at Step S46), in Step S48, the HVECU53sets the target vehicle speed to V0.

In the case where the vehicle100has reached the deceleration start position Dc (YES at Step S46), in Step S47, the HVECU53performs the deceleration control. In the deceleration control, the HVECU53causes the vehicle100to be switched to the EV drive mode such that the vehicle100is decelerated to the vehicle speed (V1). With this, the charge level SOC of the battery40is reduced.

In the case where the vehicle100has reached the gradient start position Dd of the downhill (YES at Step S42), in Step S43, the HVECU53performs the downhill acceleration control. In this downhill acceleration control, in a specific zone while traveling downhill, the vehicle100is accelerated without performing regeneration.

FIG. 15is a flowchart showing the downhill acceleration control that is performed in Step S43.

In Step S431, the HVECU53sets a target vehicle speed V4. The target vehicle speed V4refers to an upper limit value of the vehicle speed of the vehicle100in the downhill acceleration control. For example, the HVECU53sets, as the target vehicle speed V4, a speed that is higher than the current vehicle speed Vp (or higher than a vehicle speed after the deceleration control) within a range of the increased amount of the vehicle speed set by the cruise control.

In Step S432, the HVECU53disconnects transmission of the engine output. For example, the HVECU53issues an instruction to the clutch33to disconnect the engine31and the motor32from each other. In response thereto, the clutch33enters a disengaged state, and stops transmitting the driving force from the engine31.

In Step S433, the HVECU53stops the engine31. For example, the HVECU53issues an instruction to the engine ECU51to stop the engine31. In response to this instruction, the engine ECU51stops internal combustion of the engine31.

In Step S434, the HVECU53monitors acceleration of the vehicle100. When the acceleration of the vehicle100while traveling downhill is increased by the potential energy, there is a risk that the driver and the other passengers feel a sense of discomfort. As a countermeasure, when the acceleration is equal to or more than a threshold Ta (YES at Step S434), in Step S435, the HVECU53performs negative torque control for decelerating the vehicle100. In this negative torque control, the HVECU53issues an instruction to the motor ECU52to generate a torque in a direction opposite to a rotational direction of the rotor of the motor32. In response to this instruction, the motor ECU52applies to a stator so as to generate a negative torque.

In Step S436, the HVECU53determines whether the vehicle100has satisfied a condition for starting the regeneration. The condition for starting the regeneration is satisfied, for example, when the vehicle100travels by a predetermined distance on the downhill. In the case where the vehicle100has not yet satisfied the condition for starting the regeneration (NO at Step S436), the HVECU53returns to Step S434, and continues to monitor the acceleration. Meanwhile, in the case where the vehicle100has satisfied the condition for starting the regeneration (YES at Step S436), the HVECU53ends the processes for the downhill acceleration control.

Referring back toFIG. 14, in Step S44, the HVECU53performs the regeneration. The power generated by the motor32through the regeneration is supplied to the battery40via the inverter unit39. With this, the battery40is charged.

Note that, performing the downhill acceleration control from a gradient start point of the downhill is merely an example. Alternatively, the downhill acceleration control may be performed a plurality of times while traveling downhill. Still alternatively, the downhill acceleration control may be performed after the regeneration.

In order to perform the downhill acceleration control, the vehicle100need not necessarily include the navigation device60. For example, the vehicle100may include a gradient detection sensor (not shown) such that the HVECU53determines that the vehicle100is traveling downhill based on an output from this gradient detection sensor. With this configuration, the downhill acceleration control and the regeneration may be performed. In this case, the HVECU53specifies the gradient start position of the downhill in response to the output from the gradient detection sensor in Step S41inFIG. 14, and then executes the series of processes (Steps S42to S48). Further, detection of the deceleration start position Dc is performed in this Step S41.

As described above in this second embodiment, the vehicle100is accelerated by the downhill acceleration control in a specific zone on the downhill in which the regeneration is performed. In this downhill acceleration control, in the specific zone on the downhill, the vehicle100is caused to travel without using the engine output as its driving force, and without performing regeneration. In other words, in this zone, potential energy from the downhill is directly converted to kinetic energy. As a result, a proportion in which the potential energy at the time when the vehicle100travels on the downhill is converted to electric energy by the regeneration can be reduced, and the energy efficiency of the vehicle can be increased.

The vehicle100includes the clutch33(transmission switching unit) that switches whether to perform the transmission of the engine output to the driving force, and the downhill-acceleration control unit causes the transmission switching unit to disconnect the transmission of the engine output in the downhill acceleration control. With this configuration, in the downhill acceleration control, loss that is caused, for example, by engine braking can be reduced, and hence the energy efficiency can be increased.

In the downhill acceleration control, the downhill-acceleration control unit stops the engine. With this configuration, in the downhill acceleration control, degradation in fuel efficiency of the engine under low load can be suppressed. As a result, the energy efficiency can be increased.

In the downhill acceleration control, when the acceleration of the vehicle100is equal to or more than a threshold, the downhill-acceleration control unit causes the motor32to generate negative torque. With this configuration, a sense of discomfort to the driver and the other passengers, which is caused as a result of the acceleration of the vehicle100, can be reduced.

The curvature acquisition unit acquires a curvature of the downhill based on the geographic information that is supplied from the navigation device60. The downhill-acceleration control unit does not perform the downhill acceleration control when the curvature is equal to or more than a threshold. With this configuration, the downhill acceleration control is not performed on a downhill having a large curvature, and hence a sense of discomfort to the driver and the other passengers can be reduced.

The charge level control unit (S47) performs, before the downhill acceleration control is performed, the deceleration control for reducing the charge level of the battery40by reducing the vehicle speed. With this configuration, the vehicle can be accelerated after being once decelerated to a preset speed. As a result, the vehicle speed can be reduced from extremely increasing by the downhill acceleration control.

The downhill-acceleration control unit performs the downhill acceleration control under the state in which the vehicle is in the constant-speed control mode. With this configuration, in the constant-speed control mode at a preset speed, vehicle speed control can be performed without causing the driver to feel a sense of discomfort.

Setting the deceleration start position Dc based on the target vehicle speed V1is merely an example. For example, the deceleration start position Dc may be set based on a reduction target value of the charge level SOC.FIG. 16is a flowchart showing how the deceleration start position Dc is set in a third embodiment. The flowchart ofFIG. 16shows processes that are executed, for example, in Step S14ofFIG. 3. Further,FIG. 17is a map showing a relationship between the reduction target value of the charge level SOC (SOC reduction target value) and the distance (point-to-point distance) L from the gradient start position Dd of the downhill to the deceleration start position Dc.

InFIG. 16, in Step S144, the ACCECU54sets the SOC reduction target value. As inFIG. 9, the SOC reduction target value is set within the range from the thresholds Sa to Sb.

In Step S145, the ACCECU54sets the driving-force upper limit value MD. As in the first embodiment, the driving-force upper limit value MD is set within the driving-force range in which the vehicle100is driven in the EV drive mode.

In Step S146, the ACCECU54calculates the deceleration start position Dc based on the SOC reduction target value set in Step S144. At this time, the ACCECU54sets the deceleration start position Dc so as to establish a relationship in which the point-to-point distance L become longer as the SOC reduction target value becomes larger.

For example, the ACCECU54includes a map that defines the relationship shown inFIG. 17between the SOC reduction target value and the point-to-point distance L. As defined in this map, the relationship between the SOC reduction target value and the point-to-point distance varies in accordance with the driving-force upper limit value MD set in Step S145. Thus, with respect to the same SOC reduction target value, the point-to-point distance L becomes shorter as the driving-force upper limit value MD becomes larger. In contrast, with respect to the same SOC reduction target value, the point-to-point distance L becomes longer as the driving-force upper limit value MD becomes smaller.

As described above in this third embodiment, the deceleration start position Dc in the deceleration control is set in accordance with the reduction target value of the charge level SOC of the battery40. With this, intended reduction of the charge level SOC can be performed in the deceleration control.

Performing the deceleration control only once before traveling downhill as in the first to the third embodiments described above is merely an example. The deceleration control may be repeated a plurality of times before traveling downhill. Alternatively, when the acceleration control is performed before the deceleration control is performed, the acceleration control and the deceleration control may each be repeated a plurality of times before the downhill.

FIG. 18is an explanatory flowchart showing production of a travel plan according to a fourth embodiment. The deceleration start position Dc and the acceleration start position Da acquired in this travel plan are used, for example, in the drive control shown inFIG. 6.

In Step S51, the ACCECU54acquires geographic information. Further, in Step S52, the ACCECU54searches for a downhill on which the regeneration can be performed. The ACCECU54searches for any appropriate downhill within a range of a search distance QD1from a current position of a vehicle. When the downhill is detected (YES at Step S52), in Step S53, the ACCECU54acquires the gradient start position Dd.

In Step S54, the ACCECU54acquires a reference position Ds(i) for setting the acceleration start position and the deceleration start position. The reference position Ds(i) refers to a variable for setting a position as a reference for searching for an acceleration start position Da(i) and a deceleration start position Dc(i). For example, in a first search, a value of the reference position Ds(i) corresponds to the gradient start position Dd of the downhill acquired in Step S51.

In Step S55, the ACCECU54acquires the deceleration start position Dc(i) being a start position of the deceleration control. In Step S56, the ACCECU54acquires the acceleration start position Da(i) being a start position of the acceleration control. The positions that are acquired in Steps S55and S56are set, for example, within a range of a search distance QD2(QD2<QD1) from the reference position Ds(i). In a travel plan to cause the vehicle100to perform the deceleration control and the acceleration control N times each (N is an integer number equal to or greater than 1) before the vehicle100reaches the gradient start position Dd, the search distance QD2is shorter than a distance obtained by dividing the search distance QD1by N. In addition, the positions may be acquired by the same methods as those in the other embodiments described above.

In Step S57, the ACCECU54determines whether the position of the vehicle100has reached the gradient start position Dd. In the case where the position of the vehicle100has not yet reached the gradient start position Dd (NO at Step S57), in Step S58, the ACCECU54determines whether the position of the vehicle100has reached the acceleration start position Da(i) acquired in Step S56.

In the case where the vehicle100has not yet reached the acceleration start position Da(i) (NO at Step S58), in Step S59, the ACCECU54increments a counter i for identifying a search target. When the counter i is incremented (i+1), in Steps S54to S56, the search range is changed before a range that is searched based on the counter i in an advancing direction of the vehicle100. Specifically, when the ACCECU54inputs the acceleration start position Da(i) acquired in Step S58as a reference position Ds(i+1), a deceleration start position Dc(i+1) and an acceleration start position Da(i+1) are searched for before this updated reference position Ds(i+1) in the advancing direction of the vehicle100. Note that, in this embodiment, the deceleration start position Dc(i+1) and the acceleration start position Da(i+1) are searched for within a similar range of the search distance QD2from the reference position Ds(i+1).

In the case where the vehicle100has reached the acceleration start position Da(i) (YES at Step S58), the ACCECU54proceeds to Step S60. The vehicle100has reached the acceleration start position Da(i), and hence the HVECU53needs to perform the acceleration control. Thus, in Step S60, first, the ACCECU54acquires the position Dp of the vehicle100.

In Step S61, by using the vehicle position Dp acquired in Step S60, the ACCECU54searches for a counter i that satisfies the acceleration start position Da(i). For example, the ACCECU54searches for a counter i that satisfies a relationship of Da(i)≤Dp<Ds(i) from among the counters i updated by the series of processes of Steps S54to S59.

In Step S62, based on the counter i specified in Step S61, the ACCECU54acquires an acceleration start position Da(i) and a deceleration start position Dc(i).

Then, with use of the acceleration start position Da(i) and the deceleration start position Dc(i) set inFIG. 18, the drive control of the vehicle100, which is shown inFIG. 6, is performed. As a matter of course, the processes shown inFIG. 18are repetitively performed in a predetermined cycle. Further, as another example of the second embodiment, when the downhill acceleration control is performed, the drive control of the vehicle100, which is shown inFIG. 14, is performed with use of the acceleration start position Da(i) and the deceleration start position Dc(i) set inFIG. 18.

As described above in this fourth embodiment, before the vehicle enters the downhill, the ACCECU54performs each of the acceleration control and the deceleration control a plurality of times. Thus, the charge level SOC can be reduced a plurality of times, and hence the reduction rate of the charge level SOC can be increased in a period before traveling downhill.

In the vehicle100, the engine and the motor are coupled to each other with the single clutch with respect to the drive shaft. However, this configuration is merely an example. As another example of the configuration of the vehicle100, there may be mentioned a configuration in which the engine and the motor are coupled to each other with double clutches with respect to the drive shaft. In addition, instead of the clutch, a power division mechanism that uses planetary gears may be employed as the driving-force transmission mechanism. In the configuration of the vehicle100in this case, the engine and double motors may be used with respect to the drive shaft, and the engine output and the motor output may be obtained via the power division mechanism. Alternatively, instead of the configuration including the driving-force transmission mechanism that couples the engine and the motor to each other, the vehicle100may have a configuration in which the engine and the motor are coupled directly to each other through intermediation of the output shaft, or a configuration in which the engine is connected to an output shaft on a front wheel side and in which the motor is connected to an output shaft on a rear wheel side.

The deceleration control and the downhill acceleration control of the vehicle100need not necessarily be performed when the vehicle100is under the cruise control. For example, the deceleration control and the downhill acceleration control described above may be performed under a state in which the vehicle100travels in modes other than the cruise control.

In the deceleration control, instead of setting only one target vehicle speed V1, the speed before reaching the target vehicle speed V1may be set in a plurality of stages on a travel route on which the deceleration control is performed. With this configuration, the vehicle speed in the deceleration control can be reduced in a stepwise manner, and hence the vehicle100can be decelerated without causing the driver and the other passengers to feel a sense of discomfort.

It should be understood that the present disclosure, which has been described with reference to the embodiments, is not limited to these embodiments and the structures. The present disclosure also encompasses various modifications and equivalents. In addition, various combinations and modes, and other combinations and modes that additionally include only a single or more or fewer elements are also encompassed within the scope and the technical idea of the present disclosure.