INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2018-177654 filed on Sep. 21, 2018 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The disclosure relates to a braking and driving force control device that is mounted on a vehicle to control a braking and driving force of the vehicle.

2. Description of Related Art

A control device that is mounted on a vehicle, acquires a request for a braking and driving force (a braking force and a driving force) that has to be generated on the vehicle, from a driving assistance device or the like, and integratedly controls a driving device, such as a powertrain, that can generate both a braking force and a driving force, and a braking device, such as a brake, that can generate a braking force, based on the acquired request, has been proposed.

Japanese Unexamined Patent Application Publication No. 2008-024027 (JP 2008-024027 A) discloses a control device that causes a driving device to generate a braking and driving force and causes a braking device to generate a braking force, based on a requested braking and driving force and availability that represents the range of the braking and driving force that the driving device can currently generate. In JP 2008-024027 A, contradictory operations are avoided by integratedly controlling the driving device and the braking device, and low fuel consumption, electric power saving, and part consumption suppression are achieved by generating a braking and driving force by the driving device as much as possible to reduce the use frequency of the braking device.

In general, the braking and driving force is expressed by a force that makes a traveling direction of the vehicle a positive direction, and for example, in a case where a value is positive, it represents a driving force, and in a case where a value is negative, it means a braking force. The availability of the driving device is represented, for example, by the range of the braking and driving force. In the control device of JP 2008-024027 A, in a case where the requested braking and driving force is within the availability, the requested braking and driving force is generated by the driving device. In a case where the requested braking and driving force is less than a lower limit value of the availability, the driving device generates a braking and driving force that is the lower limit value of the availability, and the braking device generates a braking force corresponding to the difference between the lower limit value of the availability and the requested braking and driving force.

SUMMARY

For example, in the case of engine traveling, the lower limit value of the availability of the driving device is determined by adding an amount corresponding to an amplification or an amount corresponding to a loss by a transmission or a torque converter to an engine torque when a throttle is fully closed. In this manner, the lower limit value of the availability of the driving device generally includes a non-linear element, and changes discontinuously while the vehicle is traveling. For this reason, in the control device of JP 2008-024027 A described above, when the lower limit value of the availability at each point in time is used for control, variation in the braking force that is generated by the braking device is severe according to discontinuous variation in the lower limit value, and thus there is a possibility that an influence of the deterioration of the feeling that an occupant receives may occur in the behavior of the vehicle.

For this reason, JP 2008-024027 A discloses achieving the stabilization of control by retaining and using the lower limit value of the availability at the point in time when the braking device operates, as the lower limit value of the availability, in the calculation of the braking force that is generated by the braking device. However, for example, in the case of engine traveling, when a speed of the vehicle becomes smaller than a speed in a range of 8 km/h to 10 km/h, a driving force corresponding to creep torque becomes dominant over a braking force corresponding to the engine brake in the driving device, and thus a state where the driving force is generated is created. In the calculation of the braking force that is generated by the braking device, when a constant value is retained and used as the lower limit value of the availability, it is not possible to cope with the variation in the actual availability of such a driving device, and the braking and driving force that is actually generated greatly deviates from the requested braking and driving force. Therefore, in a case where the speed of the vehicle is equal to or lower than a predetermined value, it is conceivable to correct a requested value of the braking and driving force according to the speed of the vehicle.FIG. 6shows an example of a variation pattern of the lower limit value of the availability of the driving device according to the speed of the vehicle, and an example of a map of correction values that has to be subtracted from the requested value of the braking and driving force according to the speed of the vehicle. However, this method uniformly applies the correction value, based on a predetermined model, and does not reflect the variation in the lower limit value of the actual availability. In a case where the speed of the vehicle has already become equal to or lower than a predetermined value at the point in time when the braking device has operated, there is a possibility that overcorrection may occur.

The disclosure provides a braking and driving force control device capable of coping with a characteristic change of a driving device and realizing accurate control, while stabilization of control is attained.

A first aspect of the disclosure relates to a braking and driving force control device mounted on a vehicle and configured to control a driving device configured to generate a braking and driving force and a braking device configured to generate a braking force. The braking and driving force control device includes: a target braking and driving force calculation unit configured to calculate a target braking and driving force that is a target value of the braking and driving force, based on at least a requested value of acceleration; and a braking and driving force distribution unit configured to cause the driving device to generate the braking and driving force and cause the braking device to generate the braking force, based on the target braking and driving force and availability that represents a range of the braking and driving force currently generable by the driving device. The braking and driving force distribution unit is configured to, in a case where the target braking and driving force is within the availability, cause the driving device to generate the target braking and driving force, and in a case where the target braking and driving force is less than a lower limit value of the availability, cause the driving device to generate a braking and driving force corresponding to the lower limit value of the availability, perform arithmetic processing of suppressing time variation on the lower limit value of the availability, and cause the braking device to generate a braking force corresponding to a difference between the lower limit value of the availability after the arithmetic processing and the target braking and driving force.

In the braking and driving force control device according to the first aspect, the arithmetic processing may include a low-pass filter arithmetic operation.

In the braking and driving force control device according to the first aspect, the arithmetic processing may include change amount guard processing of causing a calculated value to follow the lower limit value of the availability while variation is suppressed such that a difference between the calculated value and a previous calculated value is within a predetermined allowable value.

In the braking and driving force control device according to the first aspect, the braking and driving force distribution unit may be configured to change a degree of suppressing the time variation according to a variation characteristic of the lower limit value of the availability with respect to a speed of the vehicle in the arithmetic processing.

In the braking and driving force control device according to the first aspect, the braking and driving force distribution unit may be configured to, in a case where the speed of the vehicle is less than a predetermined speed, relax the degree of suppressing the time variation, compared to a case where the speed of the vehicle is equal to or higher than the predetermined speed, in the arithmetic processing.

A second aspect of the disclosure relates to a braking and driving force control device mounted on a vehicle and configured to control a driving device configured to generate a braking and driving force and a braking device configured to generate a braking force. The braking and driving force control device includes: a target braking and driving force calculation unit configured to calculate a target braking and driving force that is a target value of the braking and driving force by performing processing using feedback of acceleration of the vehicle, based on at least a requested value of acceleration, acceleration of the vehicle, and a speed of the vehicle; and a braking and driving force distribution unit configured to cause the driving device to generate the braking and driving force and cause the braking device to generate the braking force, based on the target braking and driving force and availability that represents a range of the braking and driving force currently generable by the driving device. The target braking and driving force calculation unit is configured to set a gain of the feedback according to a variation characteristic of the lower limit value of the availability with respect to the speed of the vehicle. The braking and driving force distribution unit is configured to, in a case where the target braking and driving force is within the availability, cause the driving device to generate the target braking and driving force, and in a case where the target braking and driving force is less than the lower limit value of the availability, cause the driving device to generate a braking and driving force corresponding to the lower limit value of the availability, and cause the braking device to generate a braking force corresponding to a difference between the target braking and driving force and the lower limit value of the availability at a point in time when the target braking and driving force has become less than the lower limit value of the availability.

In the braking and driving force control device according to the second aspect, the target braking and driving force calculation unit may be configured to, in a case where the speed of the vehicle is equal to or lower than a predetermined speed, set the gain of the feedback to be large, compared to a case where the speed of the vehicle is higher than the predetermined speed.

In the braking and driving force control device according to the second aspect, the target braking and driving force calculation unit may be configured to, in a case where the speed of the vehicle is equal to or lower than a predetermined speed and the braking device generates the braking force, set the gain of the feedback to be large, compared to a case where the speed of the vehicle is higher than the predetermined speed.

According to the aspects of the disclosure, it is possible to provide a braking and driving force control device capable of coping with a characteristic change of a driving device and realizing accurate control, while stabilization of control is attained.

