JP2009120017A - Vehicle behavior control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicle behavior control device capable of reducing a braking distance of a vehicle while using braking force of a wheel on the low μ side to the maximum in braking on a split μ road. <P>SOLUTION: This vehicle behavior control device is furnished with a rear wheel toe angle control device to independently control each of toe angles of the right and left rear wheels 2L, 2R, and the rear wheel toe angle control device controls only the rear wheel on the side of a high friction coefficient to change its direction to the toe-out side when it detects a difference of a friction coefficient between road surfaces of the right and left rear wheels 2L, 2R on a rear wheel axis in braking the vehicle. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a vehicle behavior control device including a rear wheel toe angle control device that independently controls toe angles of left and right wheels on a rear wheel shaft of a four-wheel vehicle.

Conventionally, various four-wheel steering devices for controlling the toe angle of the rear wheels have been proposed in order to improve the turning performance of a four-wheel vehicle (hereinafter simply referred to as a vehicle). For example, as a technology of a rear wheel toe angle control device that independently controls the toe angle of the left and right rear wheels of a vehicle, an actuator using a hydraulic mechanism or an actuator using a feed screw mechanism instead of the hydraulic mechanism is used. Have been proposed (see, for example, Patent Document 1).
On roads with different friction coefficients (μ) between the left and right wheels of the vehicle (hereinafter referred to as split μ road), a braking force control device (ABS: Antilock Brake System) performs braking on the split μ road (hereinafter referred to as “split μ road”). When performing split μ braking), the braking force of the wheel on the high μ side is matched to the braking force of the wheel on the low μ side, with an emphasis on stability. Further, a technique of a four-wheel steering control device that obtains a yaw rate at the time of braking while traveling on a split μ road of a four-wheel steering vehicle and performs optimum four-wheel steering control is also known (for example, Patent Document 2). reference).
Japanese Patent Publication No. 6-47388 (see FIGS. 2 to 4) JP-A-5-305874 (see paragraph numbers 0011 to 0015 and FIGS. 2 to 6)

  However, when split μ braking is performed by ABS, the braking force of the wheels on the high μ side is reduced in accordance with the braking force of the wheels on the low μ side, resulting in an increase in the braking distance of the vehicle. Therefore, in order to avoid an increase in the braking distance on the split μ road, it is conceivable to ensure stability during braking by 4WS (four-wheel steering). However, in the case of this technology, when braking is performed on the split μ road, the direction of the low μ side wheel is changed (that is, the low μ side wheel is also steered), and as a result, the low μ side wheel is changed. It is not possible to make full use of the braking force at.

  The present invention has been made in view of such circumstances, and vehicle behavior that can reduce the braking distance of the vehicle while maximally utilizing the braking force of the wheels on the low μ side in braking on the split μ road. An object is to provide a control device.

  In order to solve the above problems, the vehicle behavior control device of the present invention is a vehicle behavior control device including a rear wheel toe angle control device capable of independently controlling the toe angles of the left and right wheels on the rear wheel shaft, When the rear wheel toe angle control device detects a difference in friction coefficient with the road surface of the left and right wheels on the rear wheel shaft during braking of the vehicle, only the rear wheel on the high friction coefficient side changes direction to the toe-out side. It is characterized by controlling.

  According to the present invention, when a difference in friction coefficient (μ) between the left and right wheel road surfaces on the rear wheel shaft is detected, the rear wheel toe angle control device determines that only the rear wheel on the high friction coefficient side is on the toe out side (vehicle Control to change direction to outside. As a result, when a braking force is applied on the split μ road, a counter-rotating moment that cancels the yaw moment generated in the vehicle is generated, so that it is possible to ensure straight traveling performance.

  Further, the present invention further includes a braking force control device that independently controls the braking force of the left and right wheels on the rear wheel shaft, and when the limit of changing the direction of the rear wheel to the toe-out side has reached, The braking force control device reduces the braking force of the rear wheel on the high friction coefficient side.

  According to the present invention, when the rear wheel toe angle control device reaches the limit for changing the direction of the rear wheel to the toe-out side, the braking force control device reduces the braking force of the rear wheel having the higher friction coefficient. When the braking force is applied on the split μ road, the yaw moment generated in the vehicle can be reduced. Thereby, it is possible to ensure straight traveling performance.

  According to the present invention, it is possible to obtain a vehicle behavior control device that can reduce the braking distance of a vehicle while maximally utilizing the braking force of a low μ wheel in braking on a split μ road.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an overall conceptual diagram of a four-wheeled vehicle including a steering system 100 including a rear wheel toe angle control device as a vehicle behavior control device according to an embodiment of the present invention.

As shown in FIG. 1, the steering system 100 corresponds to the electric power steering device 110 that assists the steering by the steering handle 3 that steers the front wheels 1L and 1R by the electric motor 4, the operation angle of the steering handle 3, and the vehicle speed. The rear wheel toe angle changing devices 120L and 120R for controlling the toe angles of the rear wheels 2L and 2R independently by the actuator 30 and the rear wheel toe angle changing control ECU for controlling the rear wheel toe angle changing devices 120L and 120R (RTC) ECU) 37, steering control ECU 130 for controlling electric power steering apparatus 110 and RTC / ECU 37, braking force control apparatus (ABS) 41, ABS / ECU 42 for controlling ABS 41, operation angle sensor S _H , vehicle speed sensor S _V , a yaw rate sensor _{S Y,} lateral acceleration sensor _{S GS,} steering angle sensor _{S D,} the hydraulic pressure sensor S It is configured to include a like.

Of these components, ABS41 is the left and right rear wheels 2L, on the basis of the hydraulic signal from the hydraulic pressure sensor _{S E} installed in each 2R, the braking force control by controlling the ABS · ECU 42. The rear wheel toe angle changing devices 120L and 120R are controlled by the RTC / ECU 37 based on the steering angle signals from the steering angle sensors _SD installed on the left and right rear wheels 2L and 2R, respectively. Toe angle control of the wheels 2L and 2R is performed. The control range of the toe angles of the left and right rear wheels 2L and 2R by the rear wheel toe angle changing devices 120L and 120R is about 2 ° at the maximum. Since the operation of the ABS 41 is a known technique, a detailed description thereof will be omitted, and the operation of the rear wheel toe angle changing devices 120L and 120R will be described in detail below.

(Rear wheel toe angle control device)
First, the configuration of the rear wheel toe angle control device will be described with reference to FIGS. 2 and 3. FIG. 2 is a plan view of the rear wheel toe angle changing device 120L on the left rear wheel side in the steering system 100 shown in FIG. 3 is a schematic cross-sectional view showing the structure of the actuator 30 of the rear wheel toe angle changing device 120L shown in FIG.
The rear wheel toe angle changing devices 120L and 120R (see FIG. 1) constituting the rear wheel toe angle control device are respectively attached to the left and right rear wheels 2L and 2R of the vehicle. In FIG. As an example, a rear wheel toe angle changing device 120L is shown. The rear wheel toe angle changing device 120L includes an actuator 30 and an RTC / ECU 37. Note that FIG. 2 shows only the left rear wheel 2L, but the right rear wheel 2R is attached in the same manner (symmetrical).

  In FIG. 2, the vehicle width direction end of the cross member 12 extending substantially in the vehicle width direction is elastically supported by the rear side frame 11 of the vehicle body. The front end of the trailing arm 13 extending substantially in the longitudinal direction of the vehicle body is supported near the end of the cross member 12 in the vehicle width direction. The rear wheel 2L is supported at the rear end of the trailing arm 13. The trailing arm 13 is configured by connecting a vehicle body side arm 13a attached to the cross member 12 and a wheel side arm 13b supported by the rear wheel 2L via a substantially vertical rotation shaft 13c. Yes. Thereby, the trailing arm 13 can be displaced in the vehicle width direction.

  One end of the actuator 30 is attached to the front end of the wheel side arm 13b on the front side of the rotating shaft 13c via the ball joint 16, and the other end is attached to the cross member 12 via the ball joint 17.

  As shown in FIG. 3, the actuator 30 includes an electric motor 31, a speed reduction mechanism 33, a feed screw portion 35, and the like. The electric motor 31 is configured by a brush motor, a brushless motor, or the like that can rotate in both forward and reverse directions. The speed reduction mechanism 33 is configured by combining, for example, a two-stage planetary gear (not shown).

  The feed screw portion 35 is engaged with the rod 35a formed in a cylindrical shape, a nut 35c inserted into the rod 35a to have a cylindrical shape, and a screw groove 35b formed on the inner peripheral side, and the screw groove 35b. The screw shaft 35d supports the rod 35a so as to be movable in the axial direction. The feed screw portion 35 is accommodated in an elongated, substantially cylindrical case main body 34 together with the speed reduction mechanism 33 and the electric motor 31. A boot 36 is attached to the feed screw portion 35 side of the case body 34 so as to cover between the end of the case body 34 and the end of the rod 35a, and the rod 35a exposed from the end of the case body 34. This prevents dust and foreign matter from adhering to the outer peripheral surface of the case, and prevents dust, foreign matter and water from entering the case main body 34 from the outside.

  One end of the speed reduction mechanism 33 is connected to the output shaft of the electric motor 31, and the other end is connected to the screw shaft 35d. The power from the electric motor 31 is transmitted to the screw shaft 35d via the speed reduction mechanism 33 and the screw shaft 35d rotates, so that the rod 35a operates to expand and contract in the horizontal direction (axial direction) in the figure with respect to the case body 34. It is supposed to do. The toe angle of the rear wheel is kept constant even when the motor 31 is not energized and driven by the frictional force of engagement between the screw shaft 35d and the screw groove 35b of the nut 35c.

  Further, the actuator 30 is provided with a stroke sensor 38 for detecting the position (expansion / contraction amount) of the rod 35a. The stroke sensor 38 includes, for example, a magnet and can detect the position using magnetism. Thus, by detecting the position using the stroke sensor 38, the steering angles (toe angles) of the toe-in and toe-out of the rear wheels 2L and 2R can be detected individually with high accuracy.

  In the actuator 30 configured in this manner, the ball joint 16 provided at the distal end of the rod 35a is rotatably connected to the wheel side arm 13b (see FIG. 2) of the trailing arm 13, and the base end of the case main body 34 is connected. A ball joint 17 provided on the right end in FIG. 3 is rotatably connected to the cross member 12 (see FIG. 2). When the screw shaft 35d is rotated by the power of the electric motor 31 and the rod 35a extends (left direction in FIG. 2), the wheel side arm 13b is pressed outward in the vehicle width direction (left direction in FIG. 2), and the rear wheel 2L ( 1) turns leftward and the rod 35a contracts (right direction in FIG. 3), the wheel side arm 13b is pulled inward in the vehicle width direction (right direction in FIG. 2), and the rear wheel 2L ( Turns right).

  The place where the ball joint 16 of the actuator 30 is attached is not limited to the wheel side arm 13b as long as the toe angle of the rear wheel 2L such as a knuckle can be changed. Further, in this embodiment, the rear wheel toe angle changing devices 120L and 120R are shown as examples applied to a semi-trailing arm type independent suspension type suspension, but are not limited thereto, and other suspension types It can be applied to other suspensions. For example, it can be realized by incorporating the actuator 30 into a side rod of a double wishbone suspension or a side rod of a strut suspension.

  In addition, an RTC / ECU 37 is integrally attached to the actuator 30. The RTC / ECU 37 is fixed to the case body 34 of the actuator 30 and is connected to the stroke sensor 38 via a connector or the like. The left and right RTC / ECUs 37 and 37 and the RTC / ECUs 37 and 37 and the steering control ECU 130 are connected by a communication line. Electric power is supplied to the RTC / ECU 37 from a power source such as a battery (not shown) mounted on the vehicle. The steering control ECU 130 and the electric motor drive circuit 23 are also supplied with electric power from a power source such as a battery (not shown) in a separate system.

(Split μ braking)
Next, the operation of split μ braking when a four-wheeled vehicle (vehicle) configured as shown in FIG. 1 performs braking by the ABS system on the split μ road will be described. FIG. 4 is a conceptual diagram showing a braking operation when a general vehicle applies a brake while traveling on a split μ road. As shown in FIG. 4, the road 51 is a dry μ road surface with a high μ road surface, and the right road is a wet road surface with a low μ road surface, which is a split μ road.

  The left rear wheel 2L of the vehicle 52 travels on a dry road surface, and the right rear wheel 2R travels on a wet road surface. At this time, when the vehicle 52 brakes by the ABS system, a large braking force such as a vector indicated by an arrow a in the left side acts on the left rear wheel 2L, and an arrow b in the figure indicates the right rear wheel 2L. A small braking force like a vector works. Therefore, the vehicle 52 has a yaw moment C in the counterclockwise direction of turning to the dry side (left side) of the road 51. As a result, when the vehicle 52 brakes on the road 51 on the split μ road, the vehicle 52 turns in the direction of the arrow d.

  FIG. 5 is a conceptual diagram showing a braking operation when a vehicle equipped with the rear wheel toe angle control device according to the present embodiment applies a brake while traveling on a split μ road. As described above, the road 51 is a road surface state where the left side is a dry road surface and the road surface is high μ, and the right side is a road surface state where the road surface is a low μ and a wet road surface, and is a split μ road. Further, the vehicle 52a includes rear wheel toe angle changing devices 120L and 120R (see FIG. 1, the same applies hereinafter) capable of independently controlling the toe angle of the left rear wheel 2L and the toe angle of the right rear wheel 2R. . Therefore, when the vehicle 52a detects a difference in friction coefficient between the left rear wheel 2L and the right rear wheel 2R (hereinafter referred to as a μ difference) during braking, the rear wheel toe angle changing devices 120L and 120R have a higher friction coefficient side. Only the wheels on the (high μ side) are turned in the direction of the arrow e1 toward the toe-out side (that is, the outside of the vehicle 52a).

  That is, in FIG. 5, when the vehicle 52a detects the μ difference between the left rear wheel 2L and the right rear wheel 2R during braking, the rear wheel toe angle changing devices 120L and 120R Only the wheel on the high μ side of the road surface (left rear wheel 2L) performs toe angle control in the direction as indicated by arrow e1, and changes the direction of rear wheel 2L to the toe-out side. As a result, the braking force of the left rear wheel 2L becomes a vector in the direction indicated by the arrow a1. Therefore, the vehicle 52a has a counterclockwise (right rotation) moment C2 that cancels the counterclockwise yaw moment C1 that acts during split μ braking.

  Accordingly, since the left turn by the left rotation yaw moment C1 is canceled by the right rotation moment C2, the traveling direction of the vehicle 52a is corrected to the straight traveling direction closer to the center of the road 51 as indicated by the arrow d1. As a result, the vehicle 52a can travel substantially straight even when the brake is applied on the split μ road.

  FIG. 6 is a characteristic diagram showing a change in brake fluid pressure when a vehicle including the rear wheel toe angle control device according to the present embodiment performs braking by the ABS 41 (see FIG. 1, the same applies hereinafter) on a split μ road. The horizontal axis represents time t, and the vertical axis represents the brake fluid pressure. FIG. 7 is a characteristic diagram showing the operation of rear wheel toe angle control corresponding to the brake hydraulic pressure operation according to FIG. 6, with the horizontal axis indicating time t and the vertical axis indicating the toe angle on the toe-out side.

  Hereinafter, the operation of rear wheel toe angle control during braking will be described with reference to FIGS. 6 and 7 while referring to the traveling state of the vehicle 52a on the split μ road as shown in FIG. As shown in FIG. 6, when braking is started at time t1 on the split μ road (see FIG. 5), the brake fluid pressure of the rear wheel 2L on the high μ side (left side) of the dry road surface and the low μ of the wet road surface The brake fluid pressure of the rear (right) rear wheel 2R increases, and braking force acts on both the left rear wheel 2L and the right rear wheel 2R. At this time, the ABS 41 has not detected the brake fluid pressure difference between the left rear wheel 2L on the high μ side and the right rear wheel 2R on the low μ side, so the brake fluid pressure control is not performed. Therefore, the ABS 41 does not perform split μ braking but performs equal braking on the left and right rear wheels 2L, 2R.

  Thereafter, when the brake fluid pressure rises (time t2) and a slip occurs on the right rear wheel 2R on the low μ side, the brake fluid pressure on the right rear wheel 2R on the low μ side is reduced by the ABS 41. On the other hand, the rear wheel 2L on the left side on the high μ side further increases the brake fluid pressure in accordance with the friction coefficient of the dry road surface to increase the braking force, and the brake fluid pressure difference between the left and right rear wheels 2L, 2R. Produce. Then, the steering control ECU 130 detects that the brake hydraulic pressure difference is generated, and determines that the road surface of the road 51 that is running is a split μ road, and performs split μ braking.

  At this time, as shown in FIG. 7, the rear wheel toe angle control device determines the toe angle of the left rear wheel 2L on the high μ side based on the determination result that the road is a split μ road after time t2. While changing to the toe-out side (the direction of the arrow e1 on the high μ side as shown in FIG. 5), the toe angle of the right rear wheel 2L on the low μ side is maintained unchanged.

  As a result, after time t2, as shown in FIG. 6, the brake control for reducing the brake fluid pressure of the rear wheel 2R on the right side on the low μ side is continued by the ABS 41, and the rear wheel toe angle control device. However, control is performed to change the toe angle of the left rear wheel 2L on the high μ side to the toe-out side (the direction of the arrow e1 in FIG. 5). Therefore, as shown in FIG. 5, the yaw moment C of the left rotation by the split μ road is canceled by the right rotation moment C2 by changing the toe angle of the left rear wheel 2L to the toe out side, and braking on the split μ road is performed. Thus, turning of the vehicle is preferably avoided and straight running is maintained.

  Next, when time t3 is reached, as shown in FIG. 7, the rear wheel toe angle control device detects the limit value of the change range of the toe angle of the left rear wheel 2L on the high μ side. The limit value of the change range of such a toe angle is, for example, about 2 °. When the rear wheel toe angle control device detects the limit value of the change range of the toe angle at time t3, the toe angle of the left rear wheel 2L on the high μ side is kept at a constant angle (limit value) after time t3. Keep it fixed on the toe-out side.

  On the other hand, the steering control ECU 130 receives the detection of the limit value by the rear wheel toe angle control device at time t3, and performs control to reduce the brake fluid pressure of the left rear wheel 2L on the high μ side, as shown in FIG. To the ABS 41. Thus, after time t3, the brake fluid pressure of the left rear wheel 2L on the high μ side is reduced, and the braking force of the rear wheel 2L is reduced. Therefore, after time t3, the braking force of the rear wheel 2L is reduced while the toe angle of the left rear wheel 2L on the high μ side is maintained at the limit value, and the left-rotating yaw shown in FIG. The moment C1 is reduced. As a result, turning of the vehicle is preferably avoided and straight running is maintained.

FIG. 8 is a flowchart showing the flow of processing when the ABS 41 and the rear wheel toe angle control device cooperate to perform split μ braking in this embodiment.
First, when braking is performed during travel (step S1), it is detected whether there is a brake hydraulic pressure difference between the left and right rear wheels 2L, 2R (step S2). It is determined that the road is a split μ road (step S3).

  Then, the rear wheel toe angle control device performs control to change the toe angle of the wheel on the high μ side, for example, the left rear wheel 2L to the toe-out side (step S4). Thereafter, the rear wheel toe angle control device determines whether or not the limit value for changing the toe angle has been reached (step S5), and if the limit value for changing the toe angle has not yet been reached (No in step S5). ), Returning to step S4, the toe angle of the wheel on the higher μ side is further changed to the toe-out side.

  On the other hand, if the limit value for changing the toe angle is reached in step S5 (Yes in step S5), the brake fluid pressure on the rear wheel on the high μ side is reduced (step S6). As a result, after reaching the limit value for changing the toe angle, the braking force of the rear wheel on the high μ side is reduced, so that turning of the vehicle on the split μ road is avoided.

  In step S2, if there is no difference in μ on the road that is running (No in step S2), the road is not a split μ road (step S7), and normal braking is performed (step S8).

(Modification)
As described above, in this embodiment, when the brake fluid pressure is detected and the slit μ road is detected, the toe angle of the rear wheel (2L) on the high μ side is controlled. Split μ braking is performed by reducing the hydraulic pressure of the rear wheel (2L) on the high μ side by controlling the hydraulic pressure, but the present invention is not limited to this. The yaw rate may be detected by a sensor or the like, and when the yaw rate value is equal to or greater than a predetermined value, it is determined that the road is a split μ road and split μ braking is performed.

1 is an overall schematic diagram of a four-wheel vehicle including a steering system including a rear wheel toe angle control device as a vehicle behavior control device according to an embodiment of the present invention. FIG. 2 is a plan view showing a rear wheel toe angle changing device on the left rear wheel side in the steering system shown in FIG. 1. FIG. 3 is a schematic sectional view showing a structure of an actuator of the rear wheel toe angle changing device shown in FIG. 2. It is a conceptual diagram which shows the braking operation | movement when a general vehicle applies a brake during driving | running | working on split micro road. It is a conceptual diagram which shows the braking operation | movement when the vehicle provided with the toe angle control apparatus which concerns on this embodiment applies a brake during driving | running | working on split micro road. FIG. 6 is a characteristic diagram showing a change in brake fluid pressure when a vehicle equipped with a toe angle control device according to the present embodiment applies a brake while traveling on a split μ road. FIG. 7 is a characteristic diagram showing an operation of rear wheel toe angle control corresponding to the brake hydraulic pressure operation according to FIG. 6. It is a flowchart explaining an effect | action.

Explanation of symbols

1L, 1R Front wheel 2L Rear wheel (Left rear wheel)
2R rear wheel (right rear wheel)
3 Steering handle 30 Actuator 31 Electric motor 31a Temperature sensor 33 Deceleration mechanism 35 Feed screw part 37 Rear wheel toe angle change control ECU (RTC / ECU)
38 Stroke sensor 41 Braking force control device (ABS)
42 ABS / ECU
51 Road 52, 52a Vehicle 120L, 120R Rear wheel toe angle changing device 130 Steering control ECU
_SH Operation angle sensor S _GS lateral acceleration sensor S _V vehicle speed sensor S _Y yaw rate sensor S _E hydraulic pressure sensor S _D rudder angle sensor

Claims (2)

A vehicle behavior control device including a rear wheel toe angle control device for independently controlling the toe angles of the left and right wheels on the rear wheel axis,
When the rear wheel toe angle control device detects a difference in friction coefficient with the road surface of the left and right wheels on the rear wheel shaft during braking of the vehicle, only the rear wheel on the high friction coefficient side changes direction to the toe-out side. A vehicle behavior control device characterized by controlling. A braking force control device for independently controlling the braking forces of the left and right wheels on the rear wheel shaft;
The braking force control device reduces the braking force of the rear wheel on the high friction coefficient side when the limit of changing the direction of the rear wheel toward the toe-out side is reached. Vehicle behavior control device.

Images