Control device of four-wheel drive vehicle

Abstract

To provide a control device of a four-wheel drive vehicle which can suppress vehicle behavior change when slip occurs.SOLUTION: A control device of a four-wheel drive vehicle is given in which: when occurrence of slip is determined, power source is controlled so that one wheel among four wheels selected based on traveling state is to be driving force not affecting traveling; a drive state is made by three wheels when slip occurs to suppress slipping of four wheels; an estimation value of vehicle body speed is acquired based on rotational speed of one wheel which is the driving force that does not affect traveling; the vehicle body speed is hardly missed when slip occurs so that vehicle behavior change can be suppressed when slip occurs.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a control device for a four-wheel drive vehicle capable of independently controlling the driving forces of the front, rear, left, and right wheels.

Background Art

[0002] Control devices for four-wheel drive vehicles are well known. For example, the vehicle body speed estimation device described in Patent Document 1 is one such device. Patent Document 1 discloses obtaining an estimated value of the vehicle body speed of a four-wheel drive vehicle using the minimum value among the rotational speeds of the four front, rear, left, and right wheels.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, even if slip occurs in one wheel, an estimated value of the vehicle body speed can be obtained by using the rotational speed of the slowest rotating wheel. By the way, when slip occurs in all the wheels, the estimated value of the vehicle body speed becomes higher than the actual vehicle body speed, and there is a phenomenon of the estimated vehicle body speed rising, and as a result, there is a possibility of losing the vehicle body speed. On the other hand, in the technique described in Patent Document 1, when slip occurs in all the wheels, the driving force of some wheels is reduced to reduce the wheel speed of some wheels, thereby eliminating the rise of the estimated vehicle body speed. However, the technique described in Patent Document 1 is control after four-wheel slip occurs. When four-wheel slip occurs, it may become difficult to estimate the running state. Or, in the process leading to four-wheel slip, the driving force distribution control to the wheels where no slip has occurred may be delayed, and there is a possibility that the suppression of vehicle behavior change may be delayed. On the other hand, in terms of tire characteristics, more driving force can be obtained before slip than after slip. Or, by suppressing the occurrence of slip itself, it becomes easier to suppress unintended vehicle behavior changes. Therefore, a process for preventing four-wheel slip is desired.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a control device for a four-wheel drive vehicle that can suppress changes in vehicle behavior when slip occurs.

Means for Solving the Problem

[0006] The gist of the first invention is as follows: (a) a control device for a four-wheel drive vehicle including four wheels on the front, rear, left, and right, and four power sources provided independently for each of the wheels to generate power serving as the driving force of the wheels; (b) a vehicle body speed acquisition unit that acquires an estimated value of the vehicle body speed of the four-wheel drive vehicle using the lowest value among the rotational speeds of the wheels; (c) a drive control unit that controls the driving force of the wheels independently for each of the wheels; and (d) a slip determination unit that determines whether slip has occurred in any of the wheels. (e) When the slip determination unit determines that slip has occurred, the drive control unit controls the power source so that one of the wheels selected based on the driving state has a driving force that does not affect driving. (f) The vehicle body speed acquisition unit acquires an estimated value of the vehicle body speed using the rotational speed of the one wheel that has a driving force that does not affect driving by the drive control unit.

Advantages of the Invention

[0007] According to the first invention, when it is determined that slip has occurred, the power source is controlled so that one of the four wheels selected based on the driving state has a driving force that does not affect driving. Thereby, when slip occurs, a driving state is created by three wheels, and the occurrence of four-wheel slip is suppressed. In addition, an estimated value of the vehicle body speed is acquired using the rotational speed of the one wheel that has a driving force that does not affect driving. Thereby, it is difficult to lose sight of the vehicle body speed when slip occurs. Therefore, changes in vehicle behavior when slip occurs can be suppressed.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Embodiment

[0010] FIG. 1 is a diagram for explaining the schematic configuration of a vehicle 10 to which the present invention is applied. In FIG. 1(a), the vehicle 10 includes four wheels 12 on the front, rear, left, and right, and four electric motors MG provided independently for each wheel 12. The electric motor MG is a power source that generates power to become the driving force Fw, which is the force in the wheel 12. The electric motor MG is a known rotary electric machine, which is a so-called motor generator. The wheels 12 include a left front wheel 12fl, a right front wheel 12fr, a left rear wheel 12rl, and a right rear wheel 12rr. The electric motors MG include a left front electric motor MGfl, a right front electric motor MGfr, a left rear electric motor MGrl, and a right rear electric motor MGrr. The vehicle 10 is a four-wheel drive vehicle (= all-wheel drive vehicle) capable of adjusting the distribution of the driving force to the four wheels 12 on the front, rear, left, and right. Note that the above "left and right" are the left and right with respect to the forward direction of the vehicle 10.

[0011] Furthermore, the vehicle 10 includes a drive shaft 14 and a gear mechanism 16. The gear mechanism 16 is, for example, a reduction gear. The drive shaft 14 includes a left front axle 14fl, a right front axle 14fr, a left rear axle 14rl, and a right rear axle 14rr. The gear mechanism 16 includes a left rear gear mechanism 16rl and a right rear gear mechanism 16rr.

[0012] One side of the left front axle 14fl is connected to the rotor shaft of the left front motor MGfl, and the other side is connected to the left front wheel 12fl. One side of the right front axle 14fr is connected to the rotor shaft of the right front motor MGfr, and the other side is connected to the right front wheel 12fr. One side of the left rear axle 14rl is connected to the left rear motor MGrl via the left rear gear mechanism 16rl, and the other side is connected to the left rear wheel 12rl. One side of the right rear axle 14rr is connected to the right rear motor MGrr via the right rear gear mechanism 16rr, and the other side is connected to the right rear wheel 12rr.

[0013] Furthermore, the vehicle 10 includes a battery 20 and a power control unit 22. The power control unit 22 includes a left front PCU (Power Control Unit) 22fl, a right front PCU 22fr, a left rear PCU 22rl, and a right rear PCU 22rr.

[0014] The battery 20 is a rechargeable DC power source and is a high-voltage battery for driving. The battery 20 is connected to the power control unit 22. The stored power from the battery 20 is supplied to the motor MG via the power control unit 22. Also, the power generated by the motor MG through regenerative braking is supplied to the battery 20 via the power control unit 22.

[0015] The power control unit 22 includes an inverter and the like. The power control unit 22 is connected to the motor MG. The power control unit 22 converts the DC power from the battery 20 into AC power and supplies it to the motor MG, or converts the AC power generated by the motor MG through regenerative braking into DC power and supplies it to the battery 20.

[0016] Vehicle 10 is a vehicle capable of independently controlling the change amount of the driving force Fw of the front, rear, left, and right wheels, and is a front-rear-left-right wheel independently driven electric vehicle, that is, a BEV (Battery Electric Vehicle). In vehicle 10, as shown in Fig. 1(b), the driving force distribution to the front, rear, left, and right wheels can be controlled according to the driving state, and an electronic control drive system that controls the vehicle behavior with the driving force distribution according to the tire friction circle and weight distribution is provided. Fig. 1(b) shows an example of the driving state during a right turn.

[0017] Fig. 2 is a diagram for explaining the main parts of the control functions and control systems for various controls in vehicle 10. Vehicle 10 is provided with an electronic control device 50 (refer to "ECU" in the figure) including the control device of vehicle 10. The electronic control device 50 is configured to include a so-called microcomputer equipped with, for example, a CPU, RAM, ROM, input / output interface, etc.

[0018] Various signals (for example, MG rotation speed Nm, wheel speed Nw, accelerator opening θacc, steering wheel angle θsw, longitudinal acceleration Gx, lateral acceleration Gy, yaw rate Ryaw, etc.) based on the detection values by various sensors (MG rotation sensor 30, wheel speed sensor 32, accelerator opening sensor 34, steering sensor 36, G sensor 38, yaw rate sensor 40, etc.) provided in vehicle 10 are respectively supplied to the electronic control device 50. The MG rotation sensor 30 includes a left front MG rotation sensor 30fl, a right front MG rotation sensor 30fr, a left rear MG rotation sensor 30rl, and a right rear MG rotation sensor 30rr. The wheel speed sensor 32 includes a left front wheel speed sensor 32fl, a right front wheel speed sensor 32fr, a left rear wheel speed sensor 32rl, and a right rear wheel speed sensor 32rr.

[0019] The MG rotational speed Nm is the rotational speed of the motor MG and includes the left front MG rotational speed Nmfl, the right front MG rotational speed Nmfr, the left rear MG rotational speed Nmrl, and the right rear MG rotational speed Nmrr. The wheel speed Nw is the rotational speed of the wheel 12 and includes the left front wheel speed Nwfl, the right front wheel speed Nwfr, the left rear wheel speed Nwrl, and the right rear wheel speed Nwrr. The accelerator opening θacc is a signal corresponding to the acceleration demand amount representing the magnitude of the driver's acceleration operation and is the accelerator operation amount by the driver. The steering wheel angle θsw is the steering angle of the steering wheel. The longitudinal acceleration Gx is the longitudinal acceleration of the vehicle 10. The lateral acceleration Gy is the lateral acceleration of the vehicle 10. The yaw rate Ryaw is the rotational angular velocity of the vehicle 10 around the vertical axis.

[0020] From the electronic control unit 50, various command signals (such as the MG control command signal Sm, etc.) are output to each device (such as the power control unit 22, etc.) provided in the vehicle 10. The MG control command signal Sm is a torque instruction value for controlling the MG torque Tm, which is the torque of the motor MG. The MG control command signal Sm includes the left front motor control command signal Smfl, the right front motor control command signal Smfr, the left rear motor control command signal Smrl, and the right rear motor control command signal Smrr. The left front motor control command signal Smfl is a torque instruction value for controlling the left front motor torque Tmfl, which is the torque of the left front motor MGfl, and is output to the left front PCU 22fl. The right front motor control command signal Smfr is a torque instruction value for controlling the right front motor torque Tmfr, which is the torque of the right front motor MGfr, and is output to the right front PCU 22fr. The left rear motor control command signal Smrl is a torque instruction value for controlling the left rear motor torque Tmrl, which is the torque of the left rear motor MGrl, and is output to the left rear PCU 22rl. The right rear motor control command signal Smrr is a torque instruction value for controlling the right rear motor torque Tmrr, which is the torque of the right rear motor MGrr, and is output to the right rear PCU 22rr.

[0021] The electronic control unit 50 includes a vehicle body speed acquisition unit 52, a drive control unit 54, and a slip determination unit 56 in order to realize various controls in the vehicle 10.

[0022] The vehicle body speed acquisition unit 52 acquires the vehicle body speed Vv of the vehicle 10 based on the wheel speeds Nw. For example, the vehicle body speed acquisition unit 52 acquires an estimated vehicle body speed Vve, which is an estimated value of the vehicle body speed Vv, using the minimum value among the respective wheel speeds Nw (Nwfl, Nwfr, Nwrl, Nwrr).

[0023] The drive control unit 54 calculates the drive request amount for the vehicle 10 by the driver, for example, by applying the accelerator opening θacc and the estimated vehicle body speed Vve to a predetermined drive request amount map. This drive request amount uses, for example, a required drive torque Twdem [Nm] as a required value of the drive torque Tw at the wheels 12, a required drive force Fwdem [N] as a required value of the drive force Fw, and the like. The required drive torque Twdem is a combined value of a required left front wheel torque Twfldem as a required value of the left front wheel torque Twfl, a required right front wheel torque Twfrdem as a required value of the right front wheel torque Twfr, a required left rear wheel torque Twrldem as a required value of the left rear wheel torque Twrl, and a required right rear wheel torque Twrrdem as a required value of the right rear wheel torque Twrr. The same applies to the required drive force Fwdem. Note that when not particularly distinguished, torque and force (drive force) are synonymous.

[0024] The drive control unit 54 sets the torque distribution ratio γfrlr of the front, rear, left, and right wheels by applying a plurality of driving force-related values such as the accelerator opening θacc, the estimated vehicle body speed Vve, the longitudinal acceleration Gx, and the yaw rate Ryaw to a predetermined torque distribution ratio map, for example. The drive control unit 54 calculates the required left front wheel torque Twfldem, the required right front wheel torque Twfrdem, the required left rear wheel torque Twrldem, and the required right rear wheel torque Twrrdem based on the required driving torque Twdem and the torque distribution ratio γfrlr. The drive control unit 54 outputs a left front motor control command signal Smfl for controlling the left front motor MGfl so as to achieve the required left front wheel torque Twfldem. The drive control unit 54 outputs a right front motor control command signal Smfr for controlling the right front motor MGfr so as to achieve the required right front wheel torque Twfrdem. The drive control unit 54 outputs a left rear motor control command signal Smrl for controlling the left rear motor MGrl so as to achieve the required left rear wheel torque Twrldem. The drive control unit 54 outputs a right rear motor control command signal Smrr for controlling the right rear motor MGrr so as to achieve the required right rear wheel torque Twrrdem. Thus, the drive control unit 54 independently controls the driving torque Tw (synonymous with the driving force Fw) of the wheel 12 for each wheel 12.

[0025] The slip determination unit 56 determines whether slip has occurred in any of the wheels 12. For example, the slip determination unit 56 compares the left front wheel speed Nwfl, the right front wheel speed Nwfr, the left rear wheel speed Nwrl, and the right rear wheel speed Nwrr, and determines whether slip has occurred in any of the wheels 12 based on whether one value deviates from the other three values. Alternatively, the slip determination unit 56 determines whether slip has occurred in any of the wheels 12 based on whether the required acceleration Gxdem estimated from the required driving torque Twdem and the estimated acceleration Gxe based on the differential value of the wheel speed Nw deviate from each other.

[0026] When the drive control unit 54 determines that slip has occurred in any of the wheels 12 by the slip determination unit 56, it executes slip suppression control to set the torque distribution ratio γfrlr so as to increase the distribution of the drive torque Tw to the wheels where no slip is occurring. As a result, it becomes easier to ensure starting performance and turning performance. In the slip suppression control, the greater the slip, the greater the distribution of the drive torque Tw to the wheels where no slip is occurring (also referred to as the slip feedback (=F / B) function).

[0027] By the way, depending on the driving situation, if slip occurs in the wheel where the drive torque Tw has been increased by the slip F / B function and four-wheel slip occurs, there is a possibility that the estimated vehicle body speed Vve will increase and the vehicle body speed Vv will be lost. Losing the vehicle body speed Vv means losing the target wheel speed Nwtgt of the four wheels, and there is a possibility that the slip F / B function for suppressing vehicle behavior changes cannot be properly activated.

[0028] Therefore, when one-wheel slip occurs, the electronic control unit 50 creates the vehicle body speed Vv by stopping four-wheel drive and creating a wheel with a drive force Fw of zero. At this time, while performing slip suppression control, the electronic control unit 50 acquires the estimated vehicle body speed Vve using the rotational speed of the wheel with a drive force Fw of zero. Even in a four-wheel drive vehicle, a three-wheel drive state is deliberately created to realize the required drive force Fwdem.

[0029] Making the drive force Fw zero may mean idling the wheel by making the drive force distribution zero, or it may mean making the difference between the force corresponding to the running resistance and the force from the power source zero in consideration of the running resistance and the like in the wheel. That is, making the drive force Fw zero means making a drive force that does not affect running.

[0030] For example, when the drive control unit 54 determines that slip has occurred in any of the wheels 12, that is, when it determines that one-wheel slip has occurred, it selects a torque suppression wheel, which is a wheel that has a driving force that does not affect driving, based on the driving state. The drive control unit 54 selects, for example, the wheel in which slip has occurred as the torque suppression wheel. Alternatively, the drive control unit 54 selects, for example, one of the front wheels, which has the smallest dynamic load distribution during starting, acceleration, or straight running, as the torque suppression wheel. Alternatively, the drive control unit 54 selects, for example, the wheel with the slowest rotational speed or the wheel with the smallest contribution to the generation of yaw moment, such as the inner front wheel, as the torque suppression wheel during turning. Alternatively, the drive control unit 54 selects, for example, a wheel with little change in vehicle behavior as the torque suppression wheel during climbing, when VSC is activated, or during deceleration. When selecting a wheel other than the wheel in which slip has occurred as the torque suppression wheel, a three-wheel drive state is created including the wheel in which slip has occurred. For example, in a driving state where it is better to apply the driving force Fw even when slip has occurred, a three-wheel drive state is created including the wheel in which slip has occurred.

[0031] Then, the drive control unit 54 controls the electric motor MG so that one of the wheels 12 selected based on the driving state, that is, the torque suppression wheel, has a driving force Fw that does not affect driving.

[0032] When the vehicle body speed acquisition unit 52 determines that slip has occurred in any of the wheels 12 by the slip determination unit 56, it acquires an estimated vehicle body speed Vve using the rotational speed of one of the wheels, that is, the torque suppression wheel, which has a driving force Fw that does not affect driving by the drive control unit 54.

[0033] FIG. 3 is a flowchart for explaining the main part of the control operation of the electronic control device 50, and is a flowchart for explaining the control operation for suppressing changes in vehicle behavior when slip occurs, and is repeatedly executed, for example.

[0034] In FIG. 3, first, in step S10 corresponding to the function of the slip determination unit 56 (hereinafter, steps are omitted), it is determined whether or not one-wheel slip has occurred. At this time, in order to specify that the vehicle 10 is in a driving state, it may be determined whether or not the longitudinal acceleration Gx is equal to or greater than a predetermined value. If the determination in this S10 is affirmative, in S20 corresponding to the function of the drive control unit 54, a torque suppression wheel is selected based on the running state. Next, in S30 corresponding to the function of the drive control unit 54, it is determined whether or not it is possible to control the torque suppression wheel so that the driving force Fw does not affect running, that is, whether or not it is possible to reduce the driving force. For example, when the driver continues to step on the accelerator, since it is desired to maintain the required driving force Fwdem, it is determined that the driving force can be reduced. Or, when it is likely that a low-μ road continues based on external recognition, since it is desired to avoid four-wheel slip, it is determined that the driving force can be reduced. Or, when the steering wheel angle θsw is on the cutting side and it is likely that turning continues, it is determined that the driving force can be reduced. Or, when it is predicted that the vehicle behavior change generation (longitudinal acceleration Gx, lateral acceleration Gy, yaw rate Ryaw, vehicle body speed Vv, etc.) that will occur next by reducing the driving force Fw and it is determined that four-wheel slip will occur, it is determined that the driving force cannot be reduced. If the determination in this S30 is affirmative, in S40 corresponding to the functions of the drive control unit 54 and the vehicle body speed acquisition unit 52, the torque suppression wheel is controlled so that the driving force Fw does not affect running. In addition, the estimated vehicle body speed Vve is obtained using the rotational speed of the torque suppression wheel, that is, the slowest wheel. If the determination in the above S10 is negative or the determination in the above S30 is negative, in S50 corresponding to the function of the vehicle body speed acquisition unit 52, the estimated vehicle body speed Vve is obtained using the lowest value among the wheel speeds Nw of each wheel.

[0035] As described above, according to this embodiment, when it is determined that slip has occurred, the electric motor MG is controlled such that the torque suppression wheel selected based on the running state has a driving force Fw that does not affect running. Thereby, when slip occurs, a driving state is created by three wheels, and the occurrence of four-wheel slip is suppressed. In addition, the estimated vehicle speed Vve is obtained using the rotational speed of the torque suppression wheel that has a driving force Fw that does not affect running. Thereby, it becomes difficult to lose the vehicle speed Vv when slip occurs. Therefore, it is possible to suppress changes in vehicle behavior when slip occurs.

[0036] As described above, the embodiments of the present invention have been described in detail with reference to the drawings, but the present invention is also applicable in other aspects.

[0037] For example, in the above-described embodiment, the electric motor MG is exemplified as the power source, but it may include a known internal combustion engine (engine). In short, the present invention can be applied to a vehicle with independent front, rear, left, and right wheel drive.

[0038] Note that the above 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.

Explanation of Reference Numerals

[0039] 10: Vehicle (four-wheel drive vehicle) 12: Wheel 12fl: Left front wheel 12fr: Right front wheel 12rl: Left rear wheel 12rr: Right rear wheel 50: Electronic control unit (control unit) 52: Vehicle speed acquisition unit 54: Drive control unit 56: Slip determination unit MG: Electric motor (power source) MGfl: Left front electric motor MGfr: Right front electric motor MGrl: Left rear electric motor MGrr: Right rear electric motor

Claims

[Claim 1] A control device for a four-wheel drive vehicle including four wheels (front, rear, left, and right) and four power sources provided independently for each wheel to generate power to drive the wheels, comprising: a vehicle speed acquisition unit that acquires an estimated vehicle speed of the four-wheel drive vehicle using a minimum value among the rotational speeds of the wheels; a drive control unit that controls a drive force of each of the wheels independently; a slip determination unit that determines whether or not slip has occurred in any of the wheels; and the drive control unit controls the power source so that, when the slip determination unit determines that the slip has occurred, one of the wheels selected based on a running state provides a driving force that does not affect running, A control device for a four-wheel drive vehicle, characterized in that the vehicle speed acquisition unit acquires an estimated value of the vehicle speed using the rotational speed of the one wheel that has been converted by the drive control unit into a driving force that does not affect the driving.

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