Crawl control device for four-wheel drive type electric vehicle

Abstract

To provide a crawl control device for a four-wheel drive type electric vehicle that is able to prevent generation of noise and vibration caused by backlash of a power transmission system.SOLUTION: A crawl control unit 42 performs control such that a front-wheel electric motor MGf exclusively outputs positive torque and the rear-wheel electric motor MGr exclusively outputs negative torque. As a result, transmission torque in a front-wheel power transmission path from a front-wheel motor MGf to front wheels 12L, 12R and a rear-wheel power transmission path from a rear-wheel motor MGr to rear wheels 14L, 14R does not change between positive and negative during crawl control, and the vehicle can travel in a state where backlashes of gears, etc. interposed in the respective power transmission systems are constantly reduced; and, therefore, generation of noise and vibration caused by the backlashes of the power transmission systems is prevented.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a crawl control device for a four-wheel drive electric vehicle, and more particularly to a technique for suppressing noise and vibration generated due to backlash in a power transmission system.

Background Art

[0002] For example, as described in Patent Document 1, as driving assistance on road surfaces that require delicate speed adjustment such as sandy roads, rocky roads, paved roads, and snow-packed roads, crawl control that maintains the vehicle speed within a predetermined low speed range without requiring accelerator and brake operations by the driver is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, when the above-described crawl control is applied to a four-wheel drive electric vehicle that drives the left and right front wheels using a front-wheel motor and drives the left and right rear wheels using a rear-wheel motor, braking force can be applied to the vehicle by making the output torque of the motor negative. Therefore, when executing crawl control, the driving force and braking force of the vehicle can be controlled by controlling the torques of the front-wheel motor and the rear-wheel motor, respectively.

[0005] However, when the transmission torque changes between positive and negative in the power transmission system from the motor to the drive wheels, there is a problem that noise and vibration are generated due to backlash of gears constituting a speed reducer or the like.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a crawl control device for a four-wheel drive electric vehicle in which the generation of noise and vibration caused by backlash in the power transmission system is suppressed.

Means for Solving the Problems

[0007] The gist of the present invention is a crawl control device for a four-wheel drive electric vehicle that drives the left and right front wheels using a front-wheel motor and drives the left and right rear wheels using a rear-wheel motor, wherein (b) in executing crawl control, the front-wheel motor and one of the rear-wheel motors are controlled to exclusively output positive torque, and the other is controlled to exclusively output negative torque, and a crawl control unit that controls the driving force and braking force of the four-wheel drive electric vehicle is provided.

Effects of the Invention

[0008] According to such a crawl control device for a four-wheel drive electric vehicle, the crawl control unit controls so that only positive torque is output from one of the front-wheel motor and the rear-wheel motor, and only negative torque is output from the other. As a result, the transmission torque in the front-wheel power transmission path from the front-wheel motor to the front wheels and the rear-wheel power transmission path from the rear-wheel motor to the rear wheels does not change between positive and negative during crawl control, and each power transmission system can run with the backlash always tightened, so the generation of noise and vibration caused by the backlash of the power transmission system is suppressed.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0010] The present invention is also applicable to an electric vehicle including a pair of front electric motors that drive the left and right front wheels respectively, and a pair of rear electric motors that drive the left and right rear wheels respectively. These front electric motors and rear electric motors may be wheel motors.

Example

[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 electric vehicle (hereinafter referred to as a vehicle) 10 includes a pair of left and right front wheels 12L and 12R, a pair of left and right rear wheels 14L and 14R, a battery 16, a front electric motor MGf that drives the pair of left and right front wheels 12L and 12R using the electric power stored in the battery 16, a rear electric motor MGr that drives the pair of left and right rear wheels 14L and 14R using the electric power stored in the battery 16, a front inverter 18 that controls the supply of the electric power stored in the battery 16 to the front electric motor MGf or the storage of the regenerative electric power output from the front electric motor MGf in the battery 16, a rear inverter 20 that controls the supply of the electric power stored in the battery 16 to the rear electric motor MGr or the storage of the regenerative electric power output from the rear electric motor MGr in the battery 16, and an electronic control unit 30 that controls the front inverter 18 and the rear inverter 20 to adjust the driving force or braking force of the front electric motor MGf and the rear electric motor MGr.

[0012] The front wheels 12L and 12R are provided with front-wheel wheel brakes 22L and 22R that apply braking force to those front wheels 12L and 12R, and the rear wheels 14L and 14R are provided with rear-wheel wheel brakes 24L and 24R that apply braking force to those rear wheels 14L and 14R. The front-wheel wheel brakes 22L and 22R and the rear-wheel wheel brakes 24L and 24R preferably comprise electric actuators controlled by commands from the electronic control unit 30, and are constituted by electric brakes that generate braking force by the operation of the electric actuators.

[0013] The electronic control unit 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 V (km / h) of the vehicle 10 from a vehicle speed sensor (not shown), and a crawl control activation command signal Crw from a crawl control switching operation switch 40 operated by the driver.

[0014] The electronic control unit 30 includes a so-called microcomputer, processes input signals according to a program stored in advance, 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 relationship stored in advance, 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. Further, 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 brake operation amount Bra (%) of the brake pedal 36 from a relationship stored in advance, and adjusts the regenerative braking torques of the front-wheel motor MGf and the rear-wheel motor MGr, and the braking forces of the front-wheel wheel brakes 22L and 22R and the rear-wheel wheel brakes 24L and 24R so as to obtain the regenerative target braking force and the wheel target braking force.

[0015] The electronic control device 30 also functions as a crawl control device, and functionally includes a crawl control unit 42 that executes crawl control in response to an operation of a crawl control switch 40. The crawl control unit 42 performs crawl control to automatically control the driving force and braking force of the vehicle 10 so as to maintain the vehicle speed V within a predetermined low speed range without requiring an accelerator operation or a brake operation by the driver in order to travel at an extremely low vehicle speed of, for example, several to a dozen or so km / h without requiring a delicate accelerator operation or brake operation when driving on a severely uneven road surface, a wavy road surface, a sandy road, or a muddy road.

[0016] Then, when executing crawl control, the crawl control unit 42 of this embodiment controls to output only positive torque to one of the front-wheel motor MGf and the rear-wheel motor MGr, and controls to output only negative torque to the other motor, and automatically controls the driving force and braking force of the vehicle 10 using the differential torque between the positive torque and the negative torque. FIG. 2 shows the torque (front motor torque MT1) output from the front-wheel motor MGf and the torque (rear motor torque MT2) output from the rear-wheel motor MGr when the vehicle 10 crosses the convex portion H on the road surface, where the one motor is the front-wheel motor MGf and the other motor is the rear-wheel motor MGr. In FIG. 2, a constant negative torque -α is continuously output from the rear-wheel motor MGr, while from the front-wheel motor MGf, until crossing the convex portion H on the road surface, a positive torque larger than the positive torque α that cancels out the negative torque -α is output, and the vehicle 10 is driven at a predetermined low speed by the differential torque ΔT1 between the front motor torque MT1 and the rear motor torque MT2. When crossing the convex portion H on the road surface, from the front-wheel motor MGf, a positive torque smaller than the positive torque α that cancels out the negative torque -α is output, and the vehicle 10 is braked at a predetermined low speed by the differential torque ΔT2 between the front motor torque MT1 and the rear motor torque MT2. Since the torque of the power transmission system from the front-wheel motor MGf to the front wheels 12L and 12R and the torque of the power transmission system from the rear-wheel motor MGr to the rear wheels 14L and 14R do not cross zero, there is no switching of the power transmission direction of the gears intervening in those power transmission systems, and no noise or vibration is generated due to the backlash of the gears.

[0017] Incidentally, FIG. 3 shows the front motor torque MT1 and the rear motor torque MT2 when the vehicle 10 crosses the convex portion H of the road surface in the crawl control of the comparative example. In this case, the torque of the rear-wheel motor MGr is maintained at a constant zero value, while the front-wheel motor MGf outputs a positive torque until the convex portion H of the road surface is crossed, and the vehicle 10 is driven at a predetermined low speed by the differential torque ΔT1 between the front motor torque MT1 and the rear motor torque MT2. When the convex portion H of the road surface is crossed, the front-wheel motor MGf outputs a negative torque, and the vehicle 10 is braked at a predetermined low speed by the differential torque ΔT2 between the front motor torque MT1 and the rear motor torque MT2. In the case of this crawl control, when crossing the convex portion H of the road surface at an extremely low vehicle speed, the torque of the power transmission system from the front-wheel motor MGf to the front wheels 12L and 12R crosses zero, so noise and vibration occur due to the backlash of the switching of the power transmission direction of the gears intervening in the power transmission system.

[0018] FIG. 4 is a flowchart for explaining the main part of the control operation of the crawl control unit 42 of the electronic control unit 30. In FIG. 4, in step S1 (hereinafter, steps are omitted), it is determined whether or not crawl control for automatically controlling the driving force and braking force of the vehicle 10 so as to maintain the vehicle speed V within a predetermined low speed range is selected. If the determination in S1 is negative, this routine is terminated. However, if the determination in S1 is affirmative, in S2, the torque of the front-wheel motor MGf (front motor torque MT1) is set to a positive torque of a predetermined value α, and the torque of the rear-wheel motor MGr (rear motor torque MT2) is set to a negative torque of a predetermined value -α.

[0019] In subsequent S3, the torque (front motor torque MT1) output from the front-wheel motor MGf is feedback-controlled so that the commanded rotational speed NT from the electronic control unit 30 matches the rotational speed N1 of the front-wheel motor MGf. The commanded rotational speed NT is the target rotational speed corresponding to the target vehicle speed during crawl control. Also, the rotational speed N1 of the front-wheel motor MGf is the actual rotational speed relative to the target rotational speed. For example, a feedback command torque MT1fb is calculated according to the following feedback control formula (1), and the front motor torque MT1 is feedback-controlled by adding the feedback command torque MT1fb to a predetermined value α.

[0020] [Number] Here, in Equation (1), Cp is a proportionality constant (proportional gain), and Ci is an integral constant (integral gain).

[0021] As described above, according to the electronic control unit 30 of the present embodiment, the crawl control unit 42 controls so that only positive torque is output from the front-wheel motor MGf and only negative torque is output from the rear-wheel motor MGr. Thereby, the transmission torque in the front-wheel power transmission path from the front-wheel motor MGf to the front wheels 12L and 12R and in the rear-wheel power transmission path from the rear-wheel motor MGr to the rear wheels 14L and 14R does not change between positive and negative during crawl control, and the vehicle can travel with the backlash of gears and the like intervening in each power transmission system always filled, so the generation of noise and vibration caused by the backlash is suppressed.

[0022] Further, according to the electronic control device 30 of the present embodiment, when the front-wheel power transmission system and the rear-wheel power transmission system have the same gear ratio, the crawl control unit 42 causes the front-wheel motor MGf to output positive torque, and the other rear-wheel motor MGr to output negative torque. When the vehicle is going uphill, the absolute value of the positive torque is made larger than that of the negative torque, and when the vehicle is going downhill, the absolute value of the positive torque is made smaller than that of the negative torque. Thereby, while the other rear-wheel motor MGr generates a control force by the rear wheels 14L and 14R, one front-wheel motor MGf generates a driving force by the front wheels 12L and 12R, and the uphill and downhill of the vehicle 10 can be controlled.

[0023] Further, according to the electronic control device 30 of the present embodiment, the crawl control unit 42 performs feedback control on the torque (front motor torque MT1) output from the front-wheel motor MGf so that the rotational speed N1 of the front-wheel motor MGf matches the target rotational speed (command rotational speed) NT corresponding to the target vehicle speed during crawl control. Thereby, regardless of going uphill or downhill, the vehicle speed can be controlled to be the target vehicle speed during crawl control, and the vehicle 10 can be moved at the target vehicle speed during crawl control.

[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, but the reverse may also be possible. In short, it is only necessary to control so that positive torque is exclusively output from one of the front-wheel motor MGf and the rear-wheel motor MGr, and negative torque is exclusively output from the other.

[0026] Note that the above description is merely one embodiment of the present invention, and the present invention is implemented in various forms without departing from the spirit thereof.

Description of Reference Numerals

[0027] 10: Vehicle (Four-wheel drive electric vehicle), 12L, 12R: Front wheels, 14L, 14R: Rear wheels, 16: Battery, 18: Inverter for front wheels, 20: Inverter for rear wheels, 30: Electronic control unit (Crawl control unit), 40: Crawl control switchover operation switch, 42: Crawl control section, MGf: Electric motor for front wheels, MGr: Electric motor for rear wheels

Claims

1. A crawl control device for a four-wheel drive electric vehicle that drives the left and right front wheels using a front-wheel motor and drives the left and right rear wheels using a rear-wheel motor, In performing crawl control, it is controlled to output only positive torque to one of the front-wheel motor and the rear-wheel motor, and to output only negative torque to the other, and includes a crawl control unit that controls the driving force and braking force of the four-wheel drive electric vehicle. A crawl control device for a four-wheel drive electric vehicle, characterized by the above.

2. When the front-wheel power transmission system from the front-wheel motor to the front wheels and the rear-wheel power transmission system from the rear-wheel motor to the rear wheels have the same gear ratio, the crawl control unit outputs positive torque from one of the front-wheel motor and the rear-wheel motor, and outputs negative torque from the other. When the vehicle is going uphill, the absolute value of the positive torque is set to be larger than that of the negative torque, and when the vehicle is going downhill, the absolute value of the positive torque is set to be smaller than that of the negative torque. The crawl control device for a four-wheel drive electric vehicle according to Claim 1, characterized by the above.

3. The crawl control unit feedback-controls the torque output from one of the front-wheel motor and the rear-wheel motor so that the rotational speed of the one motor matches the target rotational speed corresponding to the target vehicle speed during crawl control. The crawl control device for a four-wheel drive electric vehicle according to Claim 1 or 2, characterized by the above.

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