Front-rear wheel driving power distribution control device for four-wheel drive vehicle

Abstract

To provide a front-rear wheel driving power distribution control device for four-wheel drive vehicle by which electric mileage of the four-wheel drive vehicle is further improved.SOLUTION: When a four-wheel drive vehicle 10 is an unmanned autonomous vehicle, the four-wheel drive vehicle 10 is travelled by using a driving system with lesser loss exclusively among a front wheel driving system SF and a rear wheel driving system SR by a front-rear wheel driving power distribution control part 44. That is, driving power is distributed to a wheel of the driving system with lesser loss among the front wheel driving system SF and the rear wheel driving system SR. Since the four-wheel drive vehicle 10 is travelled by such driving power distribution, electric mileage of the four-wheel drive vehicle 10 is further improved.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a front and rear wheel drive force distribution control device for a four-wheel drive vehicle, and particularly to a technology for improving the driving efficiency during unmanned automatic driving.

Background Art

[0002] For example, as described in Patent Document 1, there has been proposed a four-wheel drive vehicle including a first wheel and a second wheel arranged separately in the front-rear direction of the vehicle, and capable of traveling in a first direction from the second wheel to the first wheel and a second direction from the first wheel to the second wheel. In this four-wheel drive vehicle, there is no description regarding the change in the drive force distribution between the front and rear wheels during traveling.

[0003] On the other hand, it is conceivable to control the drive force distribution between the front and rear wheels, giving priority to the drivability of the driver who rides on the front wheel side of the vehicle and the riding comfort of the passenger who rides on the rear wheel side of the vehicle.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in the above conventional four-wheel drive vehicle, since the front and rear wheel drive force distribution control that always gives priority to the riding comfort of the driver and the passenger is performed, the fuel consumption or electricity cost is not necessarily good, and there is room for improvement when performing automatic driving in an unmanned driving mode where there is no need to give priority to the riding comfort.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a front and rear wheel drive force distribution control device for a four-wheel drive vehicle that further improves the fuel consumption or electricity cost of the four-wheel drive vehicle.

Means for Solving the Problem

[0007] The gist of the present invention is a front-rear wheel driving force distribution control device for a four-wheel drive vehicle having a front-wheel drive system for driving front wheels and a rear-wheel drive system for driving rear wheels, which includes: (a) a loss estimation unit that estimates the loss of the front-wheel drive system for driving the front wheels and the loss of the rear-wheel drive system for driving the rear wheels respectively; and (c) when the four-wheel drive vehicle is in unmanned automatic driving, a front-rear wheel driving force distribution control unit that causes the vehicle to travel using only the drive system with the smaller loss among the front-wheel drive system and the rear-wheel drive system.

Effect of the Invention

[0008] According to such a front-rear wheel driving force distribution control device for a four-wheel drive vehicle, when the four-wheel drive vehicle is in unmanned automatic driving, the front-rear wheel driving force distribution control unit causes the vehicle to travel using only the drive system with the smaller loss among the front-wheel drive system and the rear-wheel drive system. That is, the driving force is distributed to the wheels of the drive system with the smaller loss among the front-wheel drive system and the rear-wheel drive system. Since the four-wheel drive vehicle is caused to travel with such a driving force distribution, the fuel consumption or electricity cost of the four-wheel drive vehicle is further improved.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0010] The present invention is applicable to a four-wheel drive electric vehicle including a common forward electric motor or a pair of forward electric motors (wheel motors) that drive the left and right front wheels respectively, and a common rear-wheel electric motor or a pair of rear-wheel electric motors (wheel motors) that drive the left and right rear wheels respectively. It may also be a four-wheel drive vehicle having a drive source consisting of only an internal combustion engine or an internal combustion engine and an electric motor, and in which the output from the single drive source is distributed to the front and rear wheels.

Embodiment

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 1, a four-wheel drive vehicle (hereinafter referred to as a vehicle) 10 includes left and right front wheels 12L and 12R, left and right rear wheels 14L and 14R, a battery 16, a front-wheel electric motor MGf that drives the left and right front wheels 12L and 12R using the electric power stored in the battery 16, a rear-wheel electric motor MGr that drives the left and right rear wheels 14L and 14R using the electric power stored in the battery 16, a front-wheel inverter 18 that controls the supply of the electric power stored in the battery 16 to the front-wheel electric motor MGf or the storage of the regenerative electric power output from the front-wheel electric motor MGf in the battery 16, a rear-wheel inverter 20 that controls the supply of the electric power stored in the battery 16 to the rear-wheel electric motor MGr or the storage of the regenerative electric power output from the rear-wheel electric motor MGr in the battery 16, and an electronic control device 30 corresponding to a front and rear wheel driving force distribution control device that controls the front-wheel inverter 18 and the rear-wheel inverter 20 to adjust the driving force or braking force of the front-wheel electric motor MGf and the rear-wheel electric motor MGr.

[0012] Front-wheel wheel brakes 22L and 22R for applying braking force to the front wheels 12L and 12R are provided on the front wheels 12L and 12R, and rear-wheel wheel brakes 24L and 24R for applying braking force to the rear wheels 14L and 14R are provided on the rear wheels 14L and 14R. The front-wheel wheel brakes 22L and 22R and the rear-wheel wheel brakes 24L and 24R preferably include electric actuators controlled by commands from the electronic control device 30, and are composed of electric brakes that generate braking force by the operation of the electric actuators.

[0013] The vehicle 10 has a front-wheel drive system SF from the front-wheel motor MGf to the left and right front wheels 12L and 12R, and a rear-wheel drive system SR from the rear-wheel motor MGr to the left and right rear wheels 14L and 14R. The front-wheel drive system SF is provided with a steering angle changing mechanism (not shown) for changing the steering angles of the left and right front wheels 12L and 12R. Between these front-wheel drive system SF and rear-wheel drive system SR, the transmission losses of the driving force are different due to differences in the capacity of the motor, the structure of the reduction gear, the type of constant velocity joint provided on the drive shaft, etc. And, for example, the transmission efficiency (transmission loss) of a reduction gear depends on the rotational speed and transmission torque of the reduction gear.

[0014] The electronic control device 30 is supplied with a signal representing the actual accelerator opening Acc from an accelerator opening sensor 34 that detects the accelerator opening Acc (%) of the accelerator pedal 32, a signal representing the actual brake operation amount Bra from a brake operation amount sensor 38 that detects the brake operation amount Bra (%) of the brake pedal 36, a signal representing the speed of the vehicle 10, that is, the vehicle speed V (km / h), from a vehicle speed sensor (not shown), and an automatic driving command signal SAD indicating that the automatic driving mode has been selected from an automatic driving selection switch 40 operated by the driver.

[0015] The electronic control unit 30 includes a so-called microcomputer, processes input signals according to a pre-stored program, and controls the driving torque or regenerative braking torque of the front-wheel motor MGf and the rear-wheel motor MGr. For example, regarding the acceleration running of the vehicle 10, the electronic control unit 30 calculates a required driving force based on the actual accelerator opening Acc (%) of the accelerator pedal 32 and the vehicle speed V (km / h) from a pre-stored relationship, and adjusts the driving forces of the front-wheel motor MGf and the rear-wheel motor MGr using the electric power stored in the battery 16 so as to obtain the required driving force. Also, for example, regarding the deceleration running of the vehicle 10, the electronic control unit 30 calculates a regenerative target braking force and a wheel target braking force based on the actual braking operation amount Bra (%) of the brake pedal 36 from a pre-stored relationship, and adjusts the regenerative braking torque of the front-wheel motor MGf and the rear-wheel motor MGr, and the braking forces of the front-wheel wheel brakes 22L, 22R and the rear-wheel wheel brakes 24L, 24R so as to obtain the regenerative target braking force and the wheel target braking force.

[0016] The electronic control unit 30 functionally includes an automatic driving control unit 42 that runs the vehicle 10 in an automatic driving mode, a front-rear wheel driving force distribution control unit 44 that controls the driving force distribution of the left and right front wheels 12L, 12R and the left and right rear wheels 14L, 14R, and a loss estimation unit 46 that estimates the losses of the front-wheel drive system SF and the rear-wheel motor MGr. When the automatic driving mode is selected, the automatic driving control unit 42 automatically performs the acceleration and braking operations of the vehicle 10, and runs the vehicle at a preset vehicle speed in a constant-speed running or following running mode without requiring the driver's acceleration / deceleration operation or steering operation.

[0017] The front and rear wheel drive force distribution control unit 44 controls the distribution of the drive force between the front wheels 12L and 12R driven by the front wheel motor MGf and the drive force of the rear wheel motor MGr that drives the rear wheels 14L and 14R. For example, when the vehicle 10 is driving off-road on rough roads, sandy roads, muddy roads, snow-packed roads, etc., or when making a sudden start, in order to avoid wheel slip, the front and rear wheel drive force distribution control unit 44 adjusts the drive force distribution between the front wheels 12L and 12R driven by the front wheel motor MGf and the rear wheels 14L and 14R driven by the rear wheel motor MGr to, for example, 50:50, so as to control four-wheel drive driving.

[0018] Also, in relatively light-load steady driving, in order to prioritize the drivability of the driver sitting on the front wheel side of the vehicle 10 and the riding comfort of the passengers sitting on the rear wheel side of the vehicle 10, the front and rear wheel drive force distribution control unit 44 controls the drive force distribution to drive only the drive system on the side farther from the driver in the front seat or the passengers in the rear seat among the front wheel drive system SF and the rear wheel drive system SR, driving the left and right front wheels 12L, 12R or the left and right rear wheels 14L, 14R.

[0019] The loss estimation unit 46 repeatedly calculates, during front-wheel driving and rear-wheel driving, the loss LF of the front-wheel drive system SF when the drive force of the vehicle 10 is provided only by the front-wheel motor MGf and the loss LR of the rear-wheel drive system SR when the drive force of the vehicle 10 is provided only by the rear-wheel motor MGr. The loss LF of the front-wheel drive system SF is calculated, for example, based on the drive power supplied to the front-wheel motor MGf and the rotational acceleration of the left and right front wheels 12L, 12R. The loss LR of the rear-wheel drive system SR is calculated, for example, based on the drive power supplied to the rear-wheel motor MGr and the rotational acceleration of the left and right rear wheels 14L, 14R. The relationships between the loss LF of the front-wheel drive system SF, the loss LR of the rear-wheel drive system SR, and the driving conditions of the vehicle 10 (transmission torque (drive torque) and rotational speed of the drive shaft (vehicle speed)) are stored in advance.

[0020] When the vehicle 10 is traveling in unmanned automatic driving and there is no need to prioritize the driver's drivability or the passenger's riding comfort, in order to increase the electricity cost of the vehicle 10, among the loss LF of the front-wheel drive system SF and the loss LR of the rear-wheel drive system SR estimated by the loss estimation unit 46, the vehicle 10 is made to travel using only the drive system with the smaller loss. For example, when the loss LF of the front-wheel drive system SF is smaller than the loss LR of the rear-wheel drive system SR among the loss LF of the front-wheel drive system SF and the loss LR of the rear-wheel drive system SR, the driving force distribution between the driving forces of the front wheels 12L and 12R driven by the front-wheel motor MGf and the driving forces of the rear wheels 14L and 14R driven by the rear-wheel motor MGr is set to 100:0. Conversely, when the loss LR of the rear-wheel drive system SR is smaller, the driving force distribution between the driving forces of the front wheels 12L and 12R driven by the front-wheel motor MGf and the driving force of the rear-wheel motor MGr that drives the rear wheels 14L and 14R is set to 0:100.

[0021] Figure 2 is a time chart for explaining the operation of the front and rear wheel driving force distribution control unit 44 when the vehicle 10 is traveling in unmanned automatic driving. When it is determined at time t1 that it is unmanned automatic driving, at low vehicle speeds, since the loss LF of the front-wheel drive system SF is smaller than the loss LR of the rear-wheel drive system SR among the loss LF of the front-wheel drive system SF and the loss LR of the rear-wheel drive system SR, the vehicle 10 starts to travel using only the front-wheel drive system SF. When the vehicle speed increases due to traveling using only the front-wheel drive system SF, both the loss LF of the front-wheel drive system SF and the loss LR of the rear-wheel drive system SR increase, but when the loss LF of the front-wheel drive system SF exceeds the loss LR of the rear-wheel drive system SR in the same driving state (time t2), the vehicle switches from traveling using only the front-wheel drive system SF to traveling using only the rear-wheel drive system SR, and thereafter, traveling using only the rear-wheel drive system SR continues.

[0022] FIG. 3 is a flowchart for explaining the main part of the control operation of the front and rear wheel driving force distribution control unit 44 and the loss estimation unit 46 of the electronic control device 30. In FIG. 3, in step S1 (hereinafter, steps are omitted), it is determined whether or not the vehicle is in the state of autonomous driving without a driver. Whether or not the vehicle is driverless is determined, for example, by a signal from a seat switch provided on the seat. When the determination in S1 is negative, in S2, the conventional driving force distribution control is performed. However, when the determination in S1 is affirmative, in S3 corresponding to the loss estimation unit 46, the loss LF of the front wheel drive system SF during traveling by the front wheel drive system SF only while the rear wheel drive system SR is non-driven is estimated. Also, in S4 corresponding to the loss estimation unit 46, the loss LR of the rear wheel drive system SR during traveling by the rear wheel drive system SR only while the front wheel drive system SF is non-driven is estimated. Next, S5 to S7 corresponding to the front and rear wheel driving force distribution control unit 44 are executed. That is, in S5, it is determined whether or not the loss LF of the front wheel drive system SF is larger than the loss LR of the rear wheel drive system SR. When the determination in S5 is affirmative, in S6, the driving force of the front wheel drive system SF is set to zero, and the driving force distribution between the front wheels 12L and 12R driven by the front wheel motor MGf and the rear wheels 14L and 14R driven by the rear wheel motor MGr is set to 0:100. However, when the determination in S5 is negative, in S7, the driving force of the rear wheel drive system SR is set to zero, and the driving force distribution between the front wheels 12L and 12R driven by the front wheel motor MGf and the rear wheels 14L and 14R driven by the rear wheel motor MGr is set to 100:0.

[0023] As described above, according to the electronic control device 30 of the present embodiment, when the vehicle 10 is in autonomous driving without a driver, the front and rear wheel driving force distribution control unit 44 causes the vehicle 10 to travel using only the drive system with the smaller loss among the front wheel drive system SF and the rear wheel drive system SR. That is, the driving force is distributed to the wheels of the drive system with the smaller loss among the front wheel drive system SF and the rear wheel drive system SR. Since the vehicle 10 is caused to travel with such a driving force distribution, the electricity cost of the vehicle 10 is further improved.

[0024] As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, this is merely one embodiment, and the present invention can be implemented in various modified and improved forms based on the knowledge of those skilled in the art.

[0025] For example, in the above-described embodiment, positive torque is output from the front-wheel motor MGf, and negative torque is output from the rear-wheel motor MGr. However, the reverse may also be possible. In short, it may be controlled such that only positive torque is output from one of the front-wheel motor MGf and the rear-wheel motor MGr, and only negative torque is output from the other.

[0026] Note that what has been described above is merely one embodiment of the present invention, and the present invention can be implemented in various forms without departing from the gist thereof.

Explanation of Reference Numerals

[0027] 10: Vehicle (four-wheel drive vehicle), 12L, 12R: Front wheels, 14L, 14R: Rear wheels, 30: Electronic control unit, 40: Automatic driving selection switch, 42: Automatic driving control unit, 44: Front and rear wheel drive force distribution control unit, 46: Loss estimation unit, MGf: Front-wheel motor, MGr: Rear-wheel motor

Claims

【Claim 1】 A front-rear wheel drive force distribution control device for a four-wheel drive vehicle having a front-wheel drive system for driving front wheels and a rear-wheel drive system for driving rear wheels, a loss estimation unit that estimates the loss of the front-wheel drive system for driving the front wheels and the loss of the rear-wheel drive system for driving the rear wheels respectively, and when the four-wheel drive vehicle is in unmanned automatic driving, a front-rear wheel drive force distribution control unit that causes the vehicle to travel using only the drive system with the smaller loss among the front-wheel drive system and the rear-wheel drive system. A front-rear wheel drive force distribution control device for a four-wheel drive vehicle, characterized by the above.

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