Vehicle control system

Abstract

To provide a vehicle control device that can achieve the vehicle behavior intended by the driver. [Solution] The rear-wheel steering mechanism and the rear-wheel differential limiting mechanism are controlled in coordination. When the rear-wheel steering mechanism is controlled in phase, the rear-wheel differential limiting mechanism is controlled in such a way that the differential action in the differential gear mechanism is easily restricted. This aligns the function of not wanting to generate a yaw moment due to the in-phase control of the rear-wheel steering mechanism with the function of not wanting to generate a yaw moment due to the operation (restriction of differential) of the rear-wheel differential limiting mechanism. When the rear-wheel steering mechanism is controlled in reverse phase, the rear-wheel differential limiting mechanism is controlled in such a way that the differential action in the differential gear mechanism is not easily restricted. This aligns the function of wanting to generate a yaw moment due to the reverse phase control of the rear-wheel steering mechanism with the function of wanting to generate a yaw moment due to the non-operation (allowing differential) of the rear-wheel differential limiting mechanism. Therefore, the vehicle behavior intended by the driver can be realized.

Description

Technical Field

[0001] The present invention relates to a control device for a vehicle having a rear-wheel steering mechanism and a rear-wheel differential limiting mechanism.

Background Art

[0002] A vehicle including a power source, left and right front wheels whose steering angles are changed according to a steering operation, left and right rear wheels, a differential gear mechanism that distributes the power from the power source to the left and right of the rear wheels and allows differential rotation between the left and right of the rear wheels, and a rear-wheel differential limiting mechanism that is operated to limit the differential action in the differential gear mechanism, and a control device for the vehicle are well known. For example, a connection device between the left and right wheels of a vehicle described in Patent Document 1 is such a device. Patent Document 1 discloses that by restricting the differential rotation between the left and right rear wheels, when a yaw moment is applied to the vehicle due to an external disturbance or the like, a moment that resists this is generated, and the straight-ahead stability and high-speed turning stability are improved.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, a rear-wheel steering mechanism that is operated to change the steering angle of the rear wheels is also well known. Both the rear-wheel differential limiting mechanism and the rear-wheel steering mechanism have a function of controlling the yaw moment. By the way, if the operations of the rear-wheel differential limiting mechanism and the rear-wheel steering mechanism are not coordinated and both are independently operated under their respective driving conditions, the respective effects may cancel each other out, and there is a risk that the vehicle behavior intended by the driver cannot be realized. The effects here are, for example, the performance of realizing a function for which a yaw moment is desired and the performance of realizing a function for which a yaw moment is not desired.

[0005] This invention was made against the above circumstances, and its objective is to provide a vehicle control device that can realize the vehicle behavior intended by the driver. [Means for solving the problem]

[0006] The gist of the first invention is a control device for a vehicle comprising: (a) a power source; left and right front wheels whose steering angle can be changed in accordance with steering operation; left and right rear wheels; a rear wheel steering mechanism that is operated to change the steering angle of the rear wheels; a differential gear mechanism that distributes power from the power source to the left and right of the rear wheels and allows differential rotation between the left and right rear wheels; and a rear wheel differential limiting mechanism that is operated to limit the differential action in the differential gear mechanism, wherein (b) the rear wheel steering mechanism and the rear wheel differential limiting mechanism are controlled in coordination; and (c) when in-phase control is performed to steer the rear wheels in the same direction as the front wheels, the rear wheel differential limiting mechanism is controlled so that the differential action in the differential gear mechanism is easily limited, while when out-of-phase control is performed to steer the rear wheels in the opposite direction to the front wheels, the rear wheel differential limiting mechanism is controlled so that the differential action in the differential gear mechanism is not easily limited. [Effects of the Invention]

[0007] According to the first invention described above, the rear-wheel steering mechanism and the rear-wheel differential limiting mechanism are controlled in coordination. When the rear-wheel steering mechanism is controlled in phase, the rear-wheel differential limiting mechanism is controlled in such a way that the differential action in the differential gear mechanism is easily restricted. This aligns the function of not wanting to generate a yaw moment due to the in-phase control of the rear-wheel steering mechanism with the function of not wanting to generate a yaw moment due to the operation (restriction of differential action) of the rear-wheel differential limiting mechanism. When the rear-wheel steering mechanism is controlled in reverse phase, the rear-wheel differential limiting mechanism is controlled in such a way that the differential action in the differential gear mechanism is not easily restricted. This aligns the function of wanting to generate a yaw moment due to the reverse phase control of the rear-wheel steering mechanism with the function of wanting to generate a yaw moment due to the non-operation (allowing differential action) of the rear-wheel differential limiting mechanism. Therefore, the vehicle behavior intended by the driver 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 flowchart explains the key aspects of the control operation of an electronic control unit, and describes the control operation required to achieve the vehicle behavior intended by the driver. [Figure 3] This figure shows an example of the operating state when the control operation shown in the flowchart in Figure 2 is performed. [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 comprises a power source 12, left and right front wheels 14, left and right rear wheels 16, and a power transmission device 18 provided in the power transmission path between the power source 12 and the rear wheels 16. The front wheels 14 are driven wheels and include the left front wheel 14l and the right front wheel 14r. The rear wheels 16 are drive wheels and include the left rear wheel 16l and the right rear wheel 16r. Note that "left and right" above refers to left and right with respect to the forward direction of the vehicle 10.

[0011] The power source 12 is, for example, a known internal combustion engine. Alternatively, an electric motor may be used instead of the engine. The output torque of the power source 12 is controlled by an electronic control device 90, which will be described later.

[0012] The power transmission device 18 includes an automatic transmission 20 connected to the power source 12, a propeller shaft 22 connected to the automatic transmission 20, a differential gear 24 connected to the propeller shaft 22, and left and right drive shafts 26, etc. The drive shafts 26 include a left rear axle 26l that connects the differential gear 24 to the left rear wheel 16l, and a right rear axle 26r that connects the differential gear 24 to the right rear wheel 16r. The differential gear 24 is a differential gear mechanism that distributes power from the power source 12 to the left and right rear wheels 16 and allows differential rotation between the left and right rear wheels 16.

[0013] The power transmission device 18 further includes a differential limiting clutch (LSD) 30 provided on the differential gear 24. The differential limiting clutch 30 has, for example, a plurality of first friction plates 32 mounted on the differential case 24a of the differential gear 24 so as not to rotate relative to each other, and a plurality of second friction plates 34 mounted on the right rear axle 26r so as not to rotate relative to each other, stacked alternately. The differential limiting clutch 30 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 32 and the second friction plates 34 against each other. The larger the pressing load, the larger the torque capacity of the differential limiting clutch 30, and the easier it is to limit the differential action of the differential gear 24. The torque capacity of the differential limiting clutch 30 is synonymous with the differential limiting torque that limits the differential action of the differential gear 24. When the pressing load is increased and the differential limiting clutch 30 is fully engaged, the differential gear 24 is locked and unable to operate. The differential limiting clutch 30 is a rear-wheel differential limiting mechanism that operates to limit the difference in rotation between the left and right rear wheels 16, that is, to limit the differential action of the differential gear 24.

[0014] Vehicle 10 is further equipped with a steering wheel 40 and a front steering mechanism 50. The front steering mechanism 50 includes a steering shaft 52, a steering gearbox 54, a front tie rod 56, a front knuckle arm 58, and the like. The steering gearbox 54, for example, uses a rack and pinion type steering gear mechanism. Since the front steering mechanism 50 is based on known technology, the specific structure and operation of the front steering mechanism 50 will be omitted. The rotation of the steering wheel 40 is mechanically transmitted to the front wheels 14 via the front steering mechanism 50. The steering angle of the front wheels 14 is changed according to the steering operation by the driver. The steering angle of the front wheels 14 is synonymous with the front wheel steering angle.

[0015] Vehicle 10 is further equipped with a rear steering mechanism 60. The rear steering mechanism 60 includes an electric actuator 62 including a motor, a rear tie rod 64, a rear knuckle arm 66, and the like. The rear steering mechanism 60 is controlled by an electronic control device 90 (described later) which controls the electric actuator 62, causing the rear tie rod 64 to slide (stroke) in the left-right direction, thereby steering the rear wheels 16. The rear steering mechanism 60 is a rear-wheel steering mechanism that is operated to change the steering angle of the rear wheels 16. The steering angle of the rear wheels 16 is synonymous with the rear wheel steering angle.

[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 a steering sensor 70, an accelerator pedal position sensor 72, a brake sensor 74, an acceleration sensor 76, a yaw rate sensor 78, a vehicle speed sensor 80, a gradient sensor 82, a surrounding information sensor 84, a position sensor 86, and a navigation system 88. Examples of these signals include steering angle θsw, steering direction Dsw, accelerator pedal position θacc, brake on signal Bon, brake operation amount Bra, longitudinal acceleration Gx, lateral acceleration Gy, yaw rate Ryaw, vehicle speed V, road surface gradient Φ, surrounding vehicle information Iard, position information Ivp, and navigation information Inavi.

[0018] The steering angle θsw is the steering angle of the steering wheel 40. The steering direction Dsw is the steering direction of the steering wheel 40. The road surface gradient Φ is the estimated gradient of the road the vehicle 10 is traveling on. The surrounding information sensor 84 includes at least one of the following: LiDAR, radar, and onboard camera. The surrounding information sensor 84 directly acquires information about the road being traveled and information about objects present around the vehicle, and outputs the acquired information as vehicle surrounding information Iard. The position sensor 86 includes a GPS (Global Positioning System) antenna, etc. Position information Ivp is information indicating the current position of the vehicle 10 on the ground or on a map based on GPS signals (orbital signals) transmitted by GPS satellites, etc. Navigation information Inavi includes map information such as road information and facility information based on map data pre-stored in the navigation system 88, for example. The electronic control unit 90 acquires an estimated value of the road surface friction coefficient μ based on imaging information of the road from the surrounding information sensor 84, etc.

[0019] The electronic control unit 90 outputs various command signals to each device installed in the vehicle 10. These devices include, for example, the differential limiting clutch 30 and the electric actuator 62. The various command signals include, for example, the differential limiting control command signal Slsd for controlling the torque capacity of the differential limiting clutch 30, and the rear wheel steering control command signal Sdrs for controlling the rear wheel steering angle.

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

[0021] The traveling state determination unit 92 determines the driver's intention to turn based on, for example, the steering wheel angle θsw, the steering direction Dsw, the accelerator opening θacc, the brake operation amount Bra, the longitudinal and lateral acceleration Gx, the vehicle speed V, the road surface gradient Φ, an estimated value of the road surface friction coefficient μ, the navigation information Inavi, etc. That is, the traveling state determination unit 92 discriminates whether the driver wants to go straight or turn. When the driver has no intention to turn, for example, it is assumed that the driver has an intention to go straight or is stopped.

[0022] The traveling state determination unit 92 determines, for example, whether the vehicle speed V is a low vehicle speed less than a predetermined vehicle speed or a medium to high vehicle speed of a predetermined vehicle speed or more. The traveling state determination unit 92 determines, for example, whether the steering wheel angle θsw is larger than a predetermined steering angle.

[0023] When it is determined by the traveling state determination unit 92 that the driver has no intention to turn, for example, the rear-wheel differential control unit 94 executes yaw anti (stability) control that increases the differential limiting torque of the differential limiting clutch 30 to limit the differential action in the differential gear 24. The yaw anti (stability) control is a control that makes it easy to generate an anti-yaw moment for canceling the yaw moment caused by a crosswind or a rough road and stabilizing the vehicle 10 in preparation for the generation of the yaw moment due to a crosswind or the like. The control for operating the differential limiting clutch 30 (increasing the differential limiting torque) is a control that makes it difficult to generate a yaw moment. A rough road is a traveling road on which the vehicle 10 straddles a high μ road and a low μ road on the left and right of the vehicle 10.

[0024] The rear wheel differential limiting control unit 94, for example, if the driving state determination unit 92 determines that the driver intends to turn, that the vehicle speed V is a low vehicle speed below a predetermined vehicle speed, and that the steering angle θsw is greater than a predetermined steering angle, will execute turning yaw control to make it easier to turn the vehicle 10 by reducing the differential limiting torque of the differential limiting clutch 30. Turning yaw control is a control that makes it easier to generate a yaw moment. When the steering angle θsw is large during low-speed driving, for example, when performing a parking operation or a U-turn operation of the vehicle 10 is expected. Therefore, the predetermined vehicle speed is a predetermined threshold for determining whether the vehicle speed V is a slow vehicle speed such as when performing a parking operation or a U-turn operation. Similarly, the predetermined steering angle is a predetermined threshold for determining whether the steering angle θsw is a large steering angle such as when performing a parking operation or a U-turn operation.

[0025] The rear wheel steering control unit 96 performs reverse-phase control to steer the rear wheels 16 in the opposite direction to the front wheels 14 if, for example, the driving state determination unit 92 determines that the driver intends to turn, the vehicle speed V is a low vehicle speed below a predetermined vehicle speed, and the steering angle θsw is greater than a predetermined steering angle. The reverse-phase control of the rear steering mechanism 60 is a control that makes it easier to generate a yaw moment.

[0026] The rear wheel steering control unit 96 performs in-phase control, steering the rear wheels 16 in the same direction as the front wheels 14, if, for example, the driving state determination unit 92 determines that the driver intends to turn, the vehicle speed V is above a predetermined speed, and the turn is one in which yaw moment is undesirable. Examples of turns in which yaw moment is undesirable during medium-to-high speed driving include lane changes, entering a main road, and exiting a main road. The in-phase control of the rear steering mechanism 60 is a control that makes it difficult to generate yaw moment.

[0027] The rear-wheel steering control unit 96 performs reverse-phase control of the rear steering mechanism 60 if, for example, the driving state determination unit 92 determines that the driver intends to turn, the vehicle speed V is above a predetermined vehicle speed, and the turn is intended to generate a yaw moment. Examples of turns intended to generate a yaw moment during medium-to-high speed driving include performing a tuck-in maneuver while cornering. Tuck-in is a maneuver that shifts a vehicle behavior that tends towards understeer towards oversteer, and is considered a vehicle behavior between understeer and oversteer.

[0028] However, if the driver intends to turn and the vehicle speed V is above a predetermined speed, activating the differential limiting clutch 30 (increasing the differential limiting torque) in conjunction with the activation of the rear steering mechanism 60 may prevent the driver from achieving their intended vehicle behavior. For example, if the driver intends to turn and the vehicle speed V is above a predetermined speed, the rear steering mechanism 60 performs both in-phase control and out-of-phase control, which result in opposite yaw moment states. When the rear steering mechanism 60 performs out-of-phase control, activating the differential limiting clutch 30 may cause interference between the control that makes it easier to generate yaw moment and the control that makes it harder to generate yaw moment, potentially reducing stability.

[0029] The rear-wheel differential limiting control unit 94 controls the differential limiting clutch 30 so that the differential action in the differential gear 24 is more easily limited when the rear-wheel steering control unit 96 is performing in-phase control of the rear steering mechanism 60. For example, if the driving state determination unit 92 determines that the driver intends to turn, the vehicle speed V is above a predetermined vehicle speed, and in-phase control of the rear steering mechanism 60 is being performed, the rear-wheel differential limiting control unit 94 increases the differential limiting torque of the differential limiting clutch 30 to perform turning anti-yaw control, which limits the differential action in the differential gear 24. Turning anti-yaw control is a control that makes it easier to generate an anti-yaw moment when turning and you do not want to generate a yaw moment.

[0030] The rear-wheel differential limiting control unit 94 controls the differential limiting clutch 30 so that the differential action in the differential gear 24 is not easily restricted when the rear-wheel steering control unit 96 is performing reverse-phase control of the rear steering mechanism 60. If, for example, the driving state determination unit 92 determines that the driver intends to turn, the vehicle speed V is above a predetermined vehicle speed, and reverse-phase control of the rear steering mechanism 60 is performed, the rear-wheel differential limiting control unit 94 performs turning tuck-in control by lowering the differential limiting torque of the differential limiting clutch 30 to make it easier to turn the vehicle 10. Turning tuck-in control is a control that makes it easier to generate yaw moment.

[0031] In this manner, the electronic control unit 90 coordinates the control of the rear steering mechanism 60 and the differential limiting clutch 30.

[0032] Figure 2 is a flowchart illustrating the essential parts of the control operation of the electronic control device 90, and is a flowchart illustrating the control operation to achieve the vehicle behavior intended by the driver, which is, for example, repeatedly executed.

[0033] In Figure 2, first, in step S10, which corresponds to the function of the driving state determination unit 92 (the step will be omitted hereafter), it is determined whether or not the driver intends to turn. If the determination in S10 is affirmative, then in S20, which corresponds to the function of the driving state determination unit 92, it is determined whether or not the vehicle speed V is a medium-to-high speed above a predetermined vehicle speed. If the determination in S20 is negative, then in S30, which corresponds to the function of the driving state determination unit 92, it is determined whether or not the steering angle θsw is greater than a predetermined steering angle. If the determination in S10 is negative, or if the determination in S30 is negative, then in S40, which corresponds to the function of the rear wheel differential limit control unit 94, it is determined whether or not the differential limit clutch 30 should be operated, and the amount of differential limit torque increase is set. Next, in S50, which corresponds to the function of the rear wheel differential limit control unit 94, turning anti-yaw (stabilization) control is performed, and the differential limit torque of the differential limit clutch 30 is increased. If the judgment in S30 is affirmed, then in S60, which corresponds to the function of the rear wheel differential limiting control unit 94, cornering yaw control is performed and the differential limiting torque of the differential limiting clutch 30 is reduced. If the judgment in S20 is affirmed, then in S70, which corresponds to the function of the driving state determination unit 92, it is determined whether or not in-phase control of the rear steering mechanism 60 is performed. If the judgment in S70 is affirmed, then in S80, which corresponds to the function of the rear wheel differential limiting control unit 94, it is determined whether or not the differential limiting clutch 30 is activated and the amount of the differential limiting torque increase is set. Next, in S90, which corresponds to the function of the rear wheel differential limiting control unit 94, cornering anti-yaw control is performed and the differential limiting torque of the differential limiting clutch 30 is increased. If the judgment in S70 is denied, that is, if it is determined that reverse-phase control of the rear steering mechanism 60 is performed, then in S100, which corresponds to the function of the rear wheel differential limiting control unit 94, cornering tuck-in control is performed and the differential limiting torque of the differential limiting clutch 30 is reduced.

[0034] Figure 3 shows an example of the operating state when the control operation shown in the flowchart of Figure 2 is performed. Figure 3(a) shows an example when the in-phase control of the rear steering mechanism 60 and the operation of the differential limiting clutch 30 are performed in conjunction. In Figure 3(a), for example, when changing lanes, the function of not generating yaw moment is performed by both the rear steering mechanism 60 and the differential limiting clutch 30. Figure 3(b) shows an example when the reverse-phase control of the rear steering mechanism 60 is performed and the differential limiting clutch 30 is not operated. In Figure 3(b), as shown in the dashed comparative example, when the differential limiting clutch 30 is operated, an anti-yaw moment is generated that cancels out the yaw moment of left turns. As shown in the solid line embodiment, when the differential limiting clutch 30 is not operated, for example, when driving around a curve, the function of not generating yaw moment is performed by both the rear steering mechanism 60 and the differential limiting clutch 30.

[0035] As described above, according to this embodiment, the rear steering mechanism 60 and the differential limiting clutch 30 are controlled in coordination. When the rear steering mechanism 60 is in phase control, the differential limiting clutch 30 is controlled so that the differential action in the differential gear 24 is easily restricted. This aligns the function of not wanting to generate a yaw moment due to the in-phase control of the rear steering mechanism 60 with the function of not wanting to generate a yaw moment due to the operation (restriction of differential action) of the differential limiting clutch 30. When the rear steering mechanism 60 is in reverse phase control, the differential limiting clutch 30 is controlled so that the differential action in the differential gear 24 is not easily restricted. This aligns the function of wanting to generate a yaw moment due to the reverse phase control of the rear steering mechanism 60 with the function of wanting to generate a yaw moment due to the non-operation (allowing differential action) of the differential limiting clutch 30. Therefore, the vehicle behavior intended by the driver can be realized.

[0036] Although embodiments of the present invention have been described in detail above with reference to the drawings, 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]

[0037] 10: Vehicle 12: Power source 14 (14l, 14r): Front wheels (left and right) 16 (16l, 16r): Rear wheels (left and right) 24: Differential gear (differential gear mechanism) 30: Differential limiting clutch (rear wheel differential limiting mechanism) 60: Rear steering mechanism (rear wheel steering mechanism) 90: Electronic control unit (control unit)

Claims

[Claim 1] A control device for a vehicle comprising: a power source; left and right front wheels whose steering angle can be changed in accordance with steering operation; left and right rear wheels; a rear wheel steering mechanism that is operated to change the steering angle of the rear wheels; a differential gear mechanism that distributes power from the power source to the left and right rear wheels and allows differential rotation between the left and right rear wheels; and a rear wheel differential limiting mechanism that is operated to limit the differential action in the differential gear mechanism, The rear wheel steering mechanism and the rear wheel differential limiting mechanism are controlled in coordination. A vehicle control device characterized in that, when in-phase control is performed to steer the rear wheels in the same direction as the front wheels, the rear wheel differential limiting mechanism is controlled so that the differential action in the differential gear mechanism is easily restricted, while when out-phase control is performed to steer the rear wheels in the opposite direction to the front wheels, the rear wheel differential limiting mechanism is controlled so that the differential action in the differential gear mechanism is not easily restricted.

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