Crawl control system for four-wheel drive electric vehicles

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 particularly to a technique for suppressing noise and vibration caused by backlash in a power transmission system.

Background Art

[0002] For example, as described in Patent Document 1, for 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, by controlling the torques of the front-wheel motor and the rear-wheel motor respectively, the driving force and braking force of the vehicle can be controlled 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 occur due to backlash of gears constituting a speed reducer or the like.

[0006] The present invention was made against the above circumstances, and its objective is to provide a crawl control device for a four-wheel drive electric vehicle that suppresses the generation of noise and vibration caused by backlash in the power transmission system. [Means for solving the problem]

[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 front wheel motors and drives the left and right rear wheels using rear wheel motors, and (b) a crawl control unit that controls the driving force and braking force of the four-wheel drive electric vehicle by controlling one of the front wheel motors and the rear wheel motors to output exclusively positive torque and the other to output exclusively negative torque. [Effects of the Invention]

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

[0009] [Figure 1] This diagram illustrates a schematic configuration of a four-wheel drive electric vehicle equipped with a control device that is one embodiment of the present invention, as well as a diagram illustrating the main parts of the control function for crawl control. [Figure 2] Figure 1 is a time chart illustrating the key control functions of the crawl control unit in this embodiment. [Figure 3]This is a time chart illustrating the key control functions of a comparative example of the crawl control unit. [Figure 4] Figure 1 is a flowchart illustrating the key aspects of the control operation of the crawl control unit. [Modes for carrying out the invention]

[0010] The present invention is also applicable to electric vehicles equipped with a pair of forward motors that drive the left and right front wheels, and a pair of rear-wheel motors that drive the left and right rear wheels, respectively. These forward motors and rear-wheel motors may be wheel motors. [Examples]

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

[0012] The front wheels 12L and 12R are equipped with front wheel brakes 22L and 22R that apply braking force to them, and the rear wheels 14L and 14R are equipped with rear wheel brakes 24L and 24R that apply braking force to them. Preferably, the front wheel brakes 22L and 22R and the rear wheel brakes 24L and 24R consist of electric brakes that are equipped with electric actuators controlled by commands from an electronic control unit 30 and generate braking force through 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 vehicle speed V (km / h) from a vehicle speed sensor (not shown), and a crawl control operation 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 and processes input signals according to a pre-stored program, controlling the driving torque or regenerative braking torque of the front wheel motor MGf and the rear wheel motor MGr. For example, in the case of accelerating the vehicle 10, the electronic control unit 30 calculates the required driving force based on the actual accelerator pedal opening Acc(%) and vehicle speed V(km / h) of the accelerator pedal 32 from a pre-stored relationship, and adjusts the driving force of the front wheel motor MGf and the rear wheel motor MGr using the power stored in the battery 16 so that the required driving force is obtained. Furthermore, the electronic control unit 30, for example, in the case of deceleration driving of the vehicle 10, calculates the regenerative target braking force and the wheel target braking force based on the actual brake 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 force of the front wheel brakes 22L, 22R and the rear wheel brakes 24L, 24R so that the regenerative target braking force and the wheel target braking force are obtained.

[0015] The electronic control unit 30 also functions as a crawl control unit and is functionally equipped with a crawl control unit 42 that performs crawl control in response to the operation of the crawl control switching operation switch 40. The crawl control unit 42 performs crawl control that automatically controls the driving force and braking force of the vehicle 10 to maintain the vehicle speed V within a predetermined low speed range, without requiring the driver to operate the accelerator or brakes, in order to travel at extremely low vehicle speeds of, for example, a few to a dozen km / h, without requiring delicate accelerator or brake operation when driving on rough or undulating roads, sandy or muddy roads.

[0016] In this embodiment, the crawl control unit 42 controls one of the motors, the front wheel motor MGf and the rear wheel motor MGr, to output a positive torque exclusively, and the other motor to output a negative torque exclusively. The unit then uses the difference between these positive and negative torques to automatically control the driving force and braking force of the vehicle 10. Figure 2 shows the torque output from the front wheel motor MGf (front motor torque MT1) and the torque output from the rear wheel motor MGr (rear motor torque MT2) when the vehicle 10 crosses a protrusion H on the road surface, with the one motor being the front wheel motor MGf and the other being the rear wheel motor MGr. In Figure 2, the rear-wheel motor MGr continuously outputs a constant negative torque -α, while the front-wheel motor MGf outputs a positive torque greater than the positive torque α that cancels out the negative torque -α until the vehicle crosses over a bump H in the road surface. The difference torque ΔT1 between the front motor torque MT1 and the rear motor torque MT2 drives the vehicle 10 at a predetermined low speed. Once the vehicle crosses over a bump H in the road surface, the front-wheel motor MGf outputs a positive torque smaller than the positive torque α that cancels out the negative torque -α. The difference torque ΔT2 between the front motor torque MT1 and the rear motor torque MT2 brakes the vehicle 10 at a predetermined low speed. 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 interposed in these power transmission systems, and no noise or vibration is generated due to gear backlash.

[0017] Incidentally, Figure 3 shows the front motor torque MT1 and rear motor torque MT2 when the vehicle 10 crosses over a bump H on the road surface in the comparative example of crawl control. 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 vehicle crosses over the bump H on the road surface, and the difference torque ΔT1 between the front motor torque MT1 and the rear motor torque MT2 drives the vehicle 10 at a predetermined low speed. Once the vehicle crosses over the bump H on the road surface, the front wheel motor MGf outputs a negative torque, and the difference torque ΔT2 between the front motor torque MT1 and the rear motor torque MT2 drives the vehicle 10 in a braking state at a predetermined low speed. In this crawl control system, when crossing a bump H on the road surface at an extremely low speed, the torque of the power transmission system from the front wheel electric motor MGf to the front wheels 12L and 12R crosses zero. As a result, noise and vibration are generated due to the backlash caused by the switching of the power transmission direction of the gears intervening in that power transmission system.

[0018] Figure 4 is a flowchart illustrating the main parts of the control operation of the crawl control unit 42 of the electronic control device 30. In Figure 4, in step S1 (the step will be omitted hereafter), it is determined whether or not crawl control, which automatically controls the driving force and braking force of the vehicle 10 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 positive, 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 device 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

[0021] As described above, according to the electronic control device 30 of this 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 backlash of gears and the like intervening in each power transmission system is always packed, so that running can be performed, and the generation of noise and vibration due to backlash is suppressed.

[0022] Furthermore, according to the electronic control device 30 of this 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 outputs a positive torque from the front wheel motor MGf and a negative torque from the other rear wheel motor MGr. When the vehicle is climbing a slope, the positive torque is set to have a larger absolute value than the negative torque, and when the vehicle is descending a slope, the positive torque is set to have a smaller absolute value than the negative torque. As a result, the vehicle 10 can be controlled to ascend or descend a slope by generating a control force from the rear wheels 14L and 14R using the other rear wheel motor MGr, while generating a driving force from the front wheels 12L and 12R using the one front wheel motor MGf.

[0023] Furthermore, according to the electronic control device 30 of this embodiment, the crawl control unit 42 provides feedback control of the torque (front motor torque MT1) output from the front motor MGf so that the rotational speed N1 of the front motor MGf matches the target rotational speed (command rotational speed) NT corresponding to the target vehicle speed during crawl control. As a result, the vehicle speed can be controlled to match the target vehicle speed during crawl control, regardless of whether the vehicle is going uphill or downhill, and the vehicle 10 can be moved at the target vehicle speed during crawl control.

[0024] Although embodiments of the present invention have been described in detail above with reference to the drawings, 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 embodiment described above, a positive torque was output from the front wheel motor MGf and a negative torque from the rear wheel motor MGr, but the reverse is also acceptable. In short, it is sufficient to control the motors so that a positive torque is output exclusively from one of the front wheel motors MGf and the rear wheel motors MGr, and a negative torque is output exclusively from the other.

[0026] It should be noted that the above-described example is merely one embodiment of the present invention, and the present invention can be implemented in various forms without departing from its spirit. [Explanation of Symbols]

[0027] 10: Vehicle (four-wheel drive electric vehicle), 12L, 12R: Front wheels, 14L, 14R: Rear wheels, 16: Battery, 18: Front wheel inverter, 20: Rear wheel inverter, 30: Electronic control unit (crawl control unit), 40: Crawl control switching operation switch, 42: Crawl control unit, MGf: Front wheel motor, MGr: Rear wheel motor

Claims

1. A crawl control device for a four-wheel drive electric vehicle that drives the left and right front wheels using electric motors for the front wheels and drives the left and right rear wheels using electric motors for the rear wheels, The crawl control unit controls the driving force and braking force of the four-wheel drive electric vehicle by controlling one of the front wheel motors and the rear wheel motors to output a positive torque exclusively, and the other to output a negative torque exclusively, in order to perform crawl control. A crawl control device for a four-wheel drive electric vehicle, characterized by the following features.

2. When the front wheel power transmission system from the front wheel motor to the front wheel and the rear wheel power transmission system from the rear wheel motor to the rear wheel have the same gear ratio, the crawl control unit outputs a positive torque from one of the front wheel motors and a negative torque from the other, and sets the positive torque to a value greater in absolute value than the negative torque when the vehicle is going uphill, and sets the positive torque to a value less in absolute value than the negative torque when the vehicle is going downhill. A crawl control device for a four-wheel drive electric vehicle according to feature 1.

3. The crawl control unit provides feedback control to the torque output from one of the motors, such that the rotational speed of one of the motors (either the front or rear wheel motor) matches the target rotational speed corresponding to the target vehicle speed during crawl control. A crawl control device for a four-wheel drive electric vehicle according to feature 1 or 2.

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