Vehicle control system

Abstract

The present invention provides a vehicle control device that can achieve sprung mass attitude control that takes driving conditions into consideration. [Solution] When the vehicle is turning and accelerating, the drive state is set to rear-wheel drive, and the differential action is made less restrictive. As a result, an anti-squat force, which suppresses the rearward tilt of the vehicle body during starting or acceleration, is generated by the rear-wheel drive state, and the sprung mass posture during starting or acceleration is stabilized. On the other hand, when the vehicle is turning and decelerating, the drive state is set to rear-wheel drive, and the differential action is made more restrictive. As a result, an anti-dive force, which suppresses the forward tilt of the vehicle body during deceleration or braking, i.e., an anti-lift force that suppresses the lifting of the rear wheels, is generated by the rear-wheel drive state, and changes in the sprung mass posture during deceleration or braking are suppressed. Therefore, sprung mass posture control that takes driving conditions into account can be achieved.

Description

Technical Field

[0001] The present invention relates to a control device for a vehicle including a power distribution device and a rear-wheel differential limiting device that are operated by electronic control.

Background Art

[0002] A control device for a vehicle equipped with a differential limiting device that is operated by electronic control so as to limit the differential action that allows differential rotation between the left and right wheels at the drive wheels is well known. For example, the control device of the left and right driving force adjustment device for a vehicle described in Patent Document 1 is such a device. Patent Document 1 discloses that by using a target rotational speed difference calculated from the vehicle speed and the steering angle, a torque difference for differential limiting is caused to act by the amount by which the actual vehicle body posture deviates from the target vehicle body posture.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, the control described in Patent Document 1 mainly functions to improve the turning performance (turning posture, turning behavior) that becomes planar motion, and is not control that focuses on the movement above the spring. On the other hand, control for switching the driving state of the vehicle between an all-wheel drive state in which the front and rear wheels are driven and a rear-wheel drive state in which only the rear wheels are driven is also well known. There is room for improvement in the posture above the spring that can be controlled by power distribution from the viewpoint of driving conditions including acceleration / deceleration states and turning states.

[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 vehicle that can realize on-spring posture control in consideration of driving conditions.

Means for Solving the Problems

[0006] The gist of the first invention is a control device for a vehicle comprising: (a) a power distribution device that is operated by electronic control to switch the drive state between an all-wheel drive state in which the front and rear wheels are driven and a rear-wheel drive state in which only the rear wheels are driven; and a rear-wheel differential limiting device that is operated by electronic control to limit the differential action that allows for differential rotation between the left and right rear wheels, wherein (b) when it is determined that the vehicle is in a turning state and the vehicle is in an accelerating state, the power distribution device is operated so that the drive state is the rear-wheel drive state and the rear-wheel differential limiting device is operated so that the differential action is not easily limited, and (c) when it is determined that the vehicle is in a turning state and the vehicle is in a deceleration state, the power distribution device is operated so that the drive state is the rear-wheel drive state and the rear-wheel differential limiting device is operated so that the differential action is easily limited. [Effects of the Invention]

[0007] According to the first invention, when the vehicle is turning and accelerating, the drive state is set to rear-wheel drive, and the differential action is made less restrictive. As a result, turning performance is ensured while only the rear wheels, which bear a large load during acceleration, are driven. In addition, an anti-squat force, which suppresses the rearward tilt of the vehicle body during starting or acceleration, is generated by the rear-wheel drive state, stabilizing the sprung mass posture during starting or acceleration. On the other hand, when the vehicle is turning and decelerating, the drive state is set to rear-wheel drive, and the differential action is made less restrictive. As a result, turning during deceleration is stabilized. In addition, an anti-dive force, which suppresses the forward tilt of the vehicle body during deceleration or braking, i.e., an anti-lift force that suppresses the lifting of the rear wheels, is generated by the rear-wheel drive state, suppressing changes in the sprung mass posture during deceleration or braking. Therefore, sprung mass posture control that takes driving conditions into account can be realized. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram illustrates the schematic configuration of a vehicle to which the present invention is applied, as well as the main components of the control functions for various types of control in the vehicle. [Figure 2] This is a schematic diagram illustrating the relationship between driving force and the sprung mass. (a) shows the case of acceleration, and (b) shows the case of deceleration. [Figure 3] This flowchart explains the key aspects of the control operation of an electronic control unit, specifically the control operation required to achieve sprung mass attitude control considering driving conditions. [Modes for carrying out the invention]

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

[0010] Figure 1 is a diagram illustrating the schematic configuration of a vehicle 10 to which the present invention is applied, and also illustrates the main parts of the control functions for various controls in the vehicle 10. In Figure 1, the vehicle 10 is equipped with left and right front wheels 12, a front wheel drive unit 20 that drives the front wheels 12, left and right rear wheels 14, and a rear wheel drive unit 30 that drives the rear wheels 14, all spaced apart from each other. The front wheels 12 include the left front wheel 12L and the right front wheel 12R. The rear wheels 14 include the left rear wheel 14L and the right rear wheel 14R. The vehicle 10 is also equipped with a battery 60, which is a rechargeable DC power source. Note that "left and right" above refers to left and right with respect to the forward direction of the vehicle 10.

[0011] Vehicle 10 is an all-wheel drive vehicle in which the drive torque distribution between the front wheels 12 and the rear wheels 14 can be adjusted. Since vehicle 10 has two front wheels 12 and two rear wheels 14, and thus has four wheels in total, it is also a four-wheel drive vehicle. In this embodiment, all-wheel drive (AWD) and four-wheel drive (4WD) are synonymous. In addition to driving in AWD control (AWD state is also synonymous) which drives both the front wheels 12 and the rear wheels 14, vehicle 10 can also drive in two-wheel drive (=2WD) control (2WD state is also synonymous) which drives only one of the front wheels 12 or the rear wheels 14. Furthermore, for vehicle 10 to which the present invention is applied, it is sufficient that in addition to driving in AWD mode, it is possible to drive in rear-wheel drive (RWD) control (RWD state is also synonymous) which drives only the rear wheels 14, among the 2WD modes. The front wheels 12 and the rear wheels 14 are the drive wheels of vehicle 10, respectively.

[0012] The front-wheel drive system 20 comprises a front motor 22, a front-wheel power transmission system 24, and a front-wheel PCU (Power Control Unit) 26. The rear-wheel drive system 30 comprises a rear motor 32, a rear-wheel power transmission system 34, and a rear-wheel PCU 36. The front motor 22 and the rear motor 32 each function as a power source for the vehicle 10. The front-wheel power transmission system 24 is a power transmission system that transmits power from the front motor 22 to the front wheels 12. The rear-wheel power transmission system 34 is a power transmission system that transmits power from the rear motor 32 to the rear wheels 14. The front-wheel PCU 26 controls the front motor 22. The rear-wheel PCU 36 controls the rear motor 32.

[0013] The front motor 22 is a known rotating electric machine (a so-called motor generator) and is connected to the battery 60 via the front wheel PCU 26. The front wheel power transmission device 24 includes a gear mechanism (not shown) connected to the front motor 22, a differential gear (not shown) connected to the gear mechanism, and left and right front drive shafts 28 connected to the differential gear. The front drive shafts 28 include a left front drive shaft 28L and a right front drive shaft 28R. The front wheel PCU 26 is a power control device that controls the power exchanged between the battery 60 and the front motor 22, and includes, for example, an inverter.

[0014] The rear motor 32 is a known rotating electric machine (a so-called motor generator) and is connected to the battery 60 via the rear wheel PCU 36. The rear wheel power transmission device 34 includes a gear mechanism (not shown) connected to the rear motor 32, a rear differential gear 40 (hereinafter referred to as the rear differential 40) connected to the gear mechanism, and left and right rear drive shafts 38 connected to the rear differential 40. The rear drive shafts 38 include a left rear drive shaft 38L that connects the rear differential 40 to the left rear wheel 14L, and a right rear drive shaft 38R that connects the rear differential 40 to the right rear wheel 14R. The rear wheel PCU 36 is a power control device that controls the power exchanged between the battery 60 and the rear motor 32, for example, by including an inverter. The rear differential 40 is a differential gear mechanism that distributes power from the rear motor 32 to the left and right rear wheels 14 and allows differential rotation between the left and right rear wheels 14.

[0015] The rear-wheel power transmission device 34 further includes a differential limiting clutch 50 provided on the rear differential 40 (see section A enclosed by the dashed line in Figure 1). The differential limiting clutch 50 has, for example, a plurality of first friction plates 52 mounted on the differential case 40a of the rear differential 40 so as not to rotate relative to each other, and a plurality of second friction plates 54 mounted on the right rear drive shaft 38R so as not to rotate relative to each other, stacked alternately. The differential limiting clutch 50 has, for example, an electric actuator (not shown), and the electric actuator is controlled by an electronic control device 90 (described later), thereby applying a pressing load that presses the first friction plates 52 and the second friction plates 54 against each other. The larger the pressing load, the larger the torque capacity of the differential limiting clutch 50, and the easier it is to limit the differential action of the rear differential 40. The torque capacity of the differential limiting clutch 50 is synonymous with the differential limiting torque that limits the differential action of the rear differential 40. When the pressing load is increased and the differential limiting clutch 50 is fully engaged, the rear differential 40 is locked, rendering it unable to perform differential action. The differential limiting clutch 50 is an electronically controlled rear-wheel differential limiting device (eLSD) in this embodiment, which is operated to limit the differential action that allows for differential rotation between the left and right rear wheels 14, that is, to limit the differential action in the rear differential 40.

[0016] Vehicle 10 is further equipped with an electronic control unit 90, which serves as a controller for the vehicle 10. The electronic control unit 90 is composed of a so-called microcomputer, which includes, for example, a CPU, RAM, ROM, input / output interfaces, etc.

[0017] The electronic control unit 90 is supplied with various signals based on detection values ​​from various sensors installed in the vehicle 10. Examples of these sensors include the MGF rotation sensor 70, the MGR rotation sensor 72, each wheel speed sensor 74, accelerator opening sensor 76, brake sensor 78, steering sensor 80, G sensor 82, and yaw rate sensor 84. Examples of these signals include the MGF rotation speed Nmgf, the MGR rotation speed Nmgr, the left front wheel rotation speed Nwfl, the right front wheel rotation speed Nwfr, the left rear wheel rotation speed Nwrl, the right rear wheel rotation speed Nwrr, the accelerator opening θacc, the brake operation amount θbp, the steering angle θsw, the steering direction Dsw, longitudinal acceleration Gx, lateral acceleration Gy, and yaw rate Ryaw. The electronic control unit 90 acquires the vehicle speed V based on, for example, the left front wheel rotation speed Nwfl, the right front wheel rotation speed Nwfr, the left rear wheel rotation speed Nwrl, and the right rear wheel rotation speed Nwrr.

[0018] The MGF rotation speed Nmgf is the rotation speed of the front motor 22. The MGR rotation speed Nmgr is the rotation speed of the rear motor 32. The accelerator opening θacc is a signal that represents the magnitude of the driver's acceleration operation and is the amount of accelerator operation by the driver. The brake operation amount θbp is a signal that represents the state in which the brake pedal for activating the wheel brakes is operated by the driver, and is also a signal that represents the magnitude of the brake pedal depression operation. The steering angle θsw is the steering angle of the steering wheel. The steering direction Dsw is the steering direction of the steering wheel.

[0019] From the electronic control unit 90, various command signals and the like are output to each device and the like provided in the vehicle 10. Each device and the like are, for example, the front-wheel PCU 26, the rear-wheel PCU 36, the differential limit clutch 50, and the like. The various command signals and the like are, for example, the MGF control command signal Smgf, the MGR control command signal Smgr, the differential limit control command signal Slsd, and the like. The MGF control command signal Smgf is a torque instruction value for controlling the MGF torque Tmgf, which is the torque of the front motor 22. The MGR control command signal Smgr is a torque instruction value for controlling the MGR torque Tmgr, which is the torque of the rear motor 32. The differential limit control command signal Slsd is a torque instruction value for controlling the torque capacity of the differential limit clutch 50.

[0020] The electronic control unit 90 includes a drive control unit 92, a rear-wheel differential limit control unit 94, and a running state determination unit 96 in order to realize various controls in the vehicle 10.

[0021] The drive control unit 92 controls the front-wheel drive device 20 and the rear-wheel drive device 30 respectively. The drive control unit 92 calculates the drive demand amount for the vehicle 10 by the driver, for example, by applying the accelerator opening θacc and the vehicle speed V to a predetermined drive demand amount map. The drive demand amount is, for example, the required driving force as a required value of the driving force at the wheels (front wheels 12, rear wheels 14) and the like. The drive control unit 92 performs drive control to control the front motor 22 and the rear motor 32 so as to realize the required driving force. Incidentally, when not particularly distinguished, torque and force (driving force) are synonymous.

[0022] The drive control unit 92 sets the drive force distribution ratio between the front and rear wheels by applying a plurality of drive force related values such as the accelerator opening θacc, vehicle speed V, longitudinal acceleration Gx, yaw rate Ryaw, etc. to a predetermined drive force distribution ratio map, for example. The drive control unit 92 calculates the required front drive force and the required rear drive force based on the required drive force and the drive force distribution ratio. The drive control unit 92 outputs an MGF control command signal Smgf for controlling the front motor 22 so as to realize the required front drive force to the front wheel PCU 26. The drive control unit 92 outputs an MGR control command signal Smgr for controlling the rear motor 32 so as to realize the required rear drive force to the rear wheel PCU 36. By the above-described control, the drive control unit 92 can switch the drive state of the vehicle 10 between the AWD state and the RWD state. The front-wheel drive device 20 and the rear-wheel drive device 30 function as the power distribution device of the present invention, which are operated by electronic control so as to switch the drive state between the AWD state and the RWD state.

[0023] The rear differential restriction control unit 94 operates the differential restriction clutch 50 so that the differential action in the rear differential 40 is easily restricted, for example, by increasing the differential restriction torque of the differential restriction clutch 50. The rear differential restriction control unit 94 operates the differential restriction clutch 50 so that the differential action in the rear differential 40 is hardly restricted, for example, by decreasing the differential restriction torque of the differential restriction clutch 50. The control in which the torque capacity of the differential restriction clutch 50 is made greater than zero and the differential action in the rear differential 40 is restricted is referred to as "eLSD ON control". The control in which the torque capacity of the differential restriction clutch 50 is made zero and the differential action in the rear differential 40 is not restricted is referred to as "eLSD OFF control".

[0024] The driving state determination unit 96 determines whether the vehicle 10 is in a turning state, for example, based on the steering angle θsw, the left-right acceleration Gy, etc. For example, the driving state determination unit 96 determines whether the vehicle 10 is in a turning state based on whether the steering angle θsw exceeds a certain value, or whether the left-right acceleration Gy exceeds a certain value. The driving state determination unit 96 may also determine whether the vehicle 10 is in a turning state based on whether the difference between the left front wheel rotation speed Nwfl and the right front wheel rotation speed Nwfr exceeds a certain value, or whether the difference between the left rear wheel rotation speed Nwrl and the right rear wheel rotation speed Nwrr exceeds a certain value.

[0025] The driving state determination unit 96 determines whether the vehicle 10 is in an accelerating state, for example, based on the accelerator opening θacc, longitudinal acceleration Gx, etc. For example, the driving state determination unit 96 determines whether the vehicle 10 is in an accelerating state based on whether the accelerator opening θacc exceeds a certain value, or whether the longitudinal acceleration Gx exceeds a certain value. The driving state determination unit 96 may also determine whether the vehicle 10 is in an accelerating state based on whether the amount of change in the accelerator opening θacc exceeds a certain value, or whether the amount of change in the driving force exceeds a certain value.

[0026] The driving state determination unit 96 determines whether the vehicle 10 is in a deceleration state, for example, based on longitudinal acceleration Gx, brake operation amount θbp, etc. For example, the driving state determination unit 96 determines whether the vehicle 10 is in a deceleration state based on whether the longitudinal acceleration Gx is below a certain value, or whether the brake pedal is being pressed down.

[0027] The driving state determination unit 96 determines whether or not inner wheel slip is occurring in the vehicle 10 when it is turning, based on, for example, the left front wheel rotation speed Nwfl, the right front wheel rotation speed Nwfr, the left rear wheel rotation speed Nwrl, and the right rear wheel rotation speed Nwrr. For example, the driving state determination unit 96 determines whether or not inner wheel slip is occurring based on whether or not the rotation speed of one of the front and rear inner wheels deviates significantly towards the higher rotation speed relative to the rotation speed of the other three wheels.

[0028] Figure 2 is a schematic diagram illustrating the relationship between driving force and the sprung mass. Figure 2(a) shows the case of acceleration, and Figure 2(b) shows the case of deceleration. In Figure 2(a), when driving force acts on the rear wheels 14, the rear suspension is rotated instantaneously around a virtual center. This generates an anti-squat force that moves the vehicle body. The anti-squat force is a force that reduces the downward sinking of the rear of the vehicle in response to the backward tilt of the vehicle body caused by load transfer during acceleration, and is a force that lifts the vehicle body. In Figure 2(b), when braking force acts on the rear wheels 14, the rear suspension is rotated instantaneously around a virtual center. This generates an anti-dive force that moves the vehicle body. The anti-dive force is a force that reduces the phenomenon called nose dive, in which the vehicle body tilts forward due to the braking force acting on the rear wheels 14 during braking or the load transfer to the front wheels 12, through the characteristics of the suspension, and is a force that lifts the vehicle body. In particular, the force that suppresses the lifting of the rear wheels 14 is called the anti-lift force. Anti-squat and anti-dive forces are increased as the load increases.

[0029] Here, the control of the differential limiting clutch 50 focuses on the movement of the vehicle 10's sprung mass. The function of the differential limiting clutch 50 in controlling the sprung mass attitude varies greatly depending on the driving conditions and the front-to-rear torque distribution. Each function that operates simultaneously recognizes the conditions of the others and operates in a coordinated manner. The function of the differential limiting clutch 50, along with the suspension stroke, such as anti-dive and anti-squat, makes it possible to control the sprung mass attitude of the vehicle 10. Rather than correction by feedback control such as vibration damping control or electronically controlled suspension, feedforward control is performed to prevent changes in attitude. The differential limiting clutch 50 is controlled in accordance with the driving conditions and the front-to-rear torque distribution while maintaining driving performance.

[0030] The drive control unit 92 performs RWD control by operating the front wheel drive unit 20 and the rear wheel drive unit 30 so that the drive state is RWD when the driving state determination unit 96 determines that the vehicle 10 is in a turning state and the vehicle 10 is in an accelerating state. The rear wheel differential limiting control unit 94 operates the differential limiting clutch 50 so that the differential action in the rear differential 40 is not easily restricted when the driving state determination unit 96 determines that the vehicle 10 is in a turning state and the vehicle 10 is in an accelerating state. For example, the rear wheel differential limiting control unit 94 performs eLSD OFF control. However, if inner wheel slip occurs when the vehicle 10 is in a turning state and accelerating state, the driving force of the inner wheel will be lost. Therefore, if the driving state determination unit 96 determines that inner wheel slip is occurring, the drive control unit 92 performs AWD control by operating the front wheel drive unit 20 and the rear wheel drive unit 30 so that the driving state becomes AWD state, and the rear wheel differential limit control unit 94 performs eLSD ON control.

[0031] The drive control unit 92 performs RWD control when the driving state determination unit 96 determines that the vehicle 10 is in a turning state and that the vehicle 10 is in a deceleration state. The rear wheel differential limiting control unit 94 operates the differential limiting clutch 50 so that the differential action in the rear differential 40 is more easily limited when the driving state determination unit 96 determines that the vehicle 10 is in a turning state and that the vehicle 10 is in a deceleration state. For example, the rear wheel differential limiting control unit 94 performs eLSD ON control.

[0032] Figure 3 is a flowchart illustrating the main parts of the control operation of the electronic control device 90, and is a flowchart illustrating the control operation for realizing sprung mass attitude control that takes driving conditions into consideration, and is, for example, executed repeatedly.

[0033] In Figure 3, first, in step S10, which corresponds to the function of the driving state determination unit 96 (the step will be omitted hereafter), it is determined whether or not the vehicle 10 is in a turning state. If the determination in S10 is affirmative, then in S20, which corresponds to the function of the driving state determination unit 96, it is determined whether or not the vehicle 10 is in an accelerating state. If the determination in S20 is negative, then in S30, which corresponds to the function of the driving state determination unit 96, it is determined whether or not the vehicle 10 is in a deceleration state. If the determination in S30 is affirmative, then in S40, which corresponds to the functions of the drive control unit 92 and the rear wheel differential limit control unit 94, RWD control and eLSD ON control are performed, and braking attitude control is performed. If the determination in S10 is negative, or if the determination in S30 is negative, then in S50, which corresponds to the functions of the drive control unit 92 and the rear wheel differential limit control unit 94, normal control is performed. If the determination in S20 is affirmative, then in S60, which corresponds to the function of the driving state determination unit 96, it is determined whether or not inner wheel slip is occurring. If the judgment in S60 is affirmed, AWD control and eLSD ON control are performed in S70, which corresponds to the functions of the drive control unit 92 and the rear wheel differential limit control unit 94, and limit driving control is performed. If the judgment in S60 is denied, RWD control and eLSD OFF control are performed in S80, which corresponds to the functions of the drive control unit 92 and the rear wheel differential limit control unit 94, and acceleration attitude control is performed.

[0034] As described above, according to this embodiment, when the vehicle 10 is turning and accelerating, the drive state is set to RWD and the differential action is less restricted. As a result, turning performance is ensured while only the rear wheels 14, which bear a large load during acceleration, are driven. In addition, an anti-squat force, which suppresses the rearward tilt of the vehicle body during starting or acceleration, is generated by the RWD state, stabilizing the sprung mass posture during starting or acceleration. On the other hand, when the vehicle 10 is turning and decelerating, the drive state is set to RWD and the differential action is more easily restricted. As a result, turning during deceleration is stabilized. In addition, an anti-dive force, that is, an anti-lift force that suppresses the lifting of the rear wheels 14, which suppresses the forward tilt of the vehicle body during deceleration or braking, is generated by the RWD state, suppressing changes in the sprung mass posture during deceleration or braking. Therefore, sprung mass posture control that takes driving conditions into account can be realized.

[0035] Although embodiments of the present invention have been described in detail above with reference to the drawings, the present invention is also applicable to other embodiments.

[0036] For example, in the above-described embodiment, the present invention can be applied even if the vehicle 10 is an AWD vehicle, for example, which is based on rear-wheel drive and also distributes power to the front wheels by an electronically controlled coupling or the like.

[0037] It should be noted that the above-described embodiment is merely one example, 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 Symbols]

[0038] 10: Vehicle 12 (12L, 12R): Front wheels 14 (14L, 14R): Rear wheels 20: Front wheel drive system (power distribution system) 30: Rear wheel drive system (power distribution system) 50: Differential limiting clutch (rear wheel differential limiting system) 90: Electronic control unit (control unit)

Claims

[Claim 1] A control device for a vehicle comprising: a power distribution device operated by electronic control to switch between an all-wheel drive state in which the front and rear wheels are driven and a rear-wheel drive state in which only the rear wheels are driven; and a rear-wheel differential limiting device operated by electronic control to limit the differential action that allows for differential rotation between the left and right rear wheels, If it is determined that the vehicle is in a turning state and is also in an accelerating state, the power distribution device is activated so that the drive state becomes the rear-wheel drive state, and the rear-wheel differential limiting device is activated so that the differential action is not easily restricted, A vehicle control device characterized in that, when it is determined that the vehicle is in a turning state and is also determined that the vehicle is in a deceleration state, it operates the power distribution device so that the drive state becomes the rear-wheel drive state and operates the rear-wheel differential limiting device so that the differential action is easily limited.

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