JP5326019B2 - Rear wheel toe angle controller - Google Patents

Description

  The present invention relates to a rear wheel toe angle control device that is used to control a rear wheel toe angle in a rear wheel toe angle variable vehicle that changes a toe angle of a rear wheel, and more particularly to a rear wheel toe angle according to a yaw rate and a lateral acceleration. The present invention relates to a technique for controlling a corner.

  Since the automobile does not go straight if it receives a crosswind or a tire external force on an irregular road during straight running, the driver continues driving while slightly correcting the steering wheel. As a means to solve this problem, one that generates a correction reaction force in the power steering to assist the driving operation, one that improves straightness by active steering of the front wheels and rear wheel steering, 4WS, and combinations thereof, etc. Has been proposed.

  For front wheel active steering, in a vehicle equipped with a variable transmission ratio control device that variably controls the transmission ratio in the steering system from the steering wheel to the steering gear box, the lateral acceleration calculated based on the turning angle and the actual vehicle body are calculated. It has been proposed that a variable transmission rate control device is operated so as to perform a correction steering that obtains a lateral acceleration due to a disturbance from the lateral acceleration, predicts a change in vehicle behavior due to the lateral acceleration due to the disturbance, and cancels this (Patent) Reference 1).

  Various control methods have been proposed for rear wheel steering.For example, when a driver steers a front wheel to ensure traveling stability immediately after steering, the vehicle tends to become unstable. By changing only the rear wheels to toe-in and then steering only the rear wheels inside the turn to the toe-in, it has been proposed to improve the running stability immediately after turning and to prevent the understeer characteristics from becoming too strong. (See Patent Document 2).

Japanese Patent Laid-Open No. 05-77751 Japanese Patent Laid-Open No. 08-25482

  However, the applied point of the disturbance that disturbs the straight-line stability is not always constant, and the reaction of the vehicle due to the disturbance is complicated with lateral movement and rotational movement. Therefore, the operation for suppressing this is complicated, and the driver's reaction is complicated. Increase the burden. And since the behavior control of the prior art basically suppresses the rotational motion or lateral motion of the vehicle, the driver needs to correct the steering for the actual disturbance, and completely ensure straight running stability. It was not a thing.

  Further, in the steering control device described in Patent Literature 1, if the driver does not have a power steering that cancels the steering reaction force generated when the variable transmission rate control device is driven, the driver may feel uncomfortable due to increase or decrease of the steering torque, If the driver does not hold the steering wheel securely, the tire side is not steered and only the steering wheel side rotates, making it difficult to control the behavior of the vehicle. Even if this problem is solved by providing a power steering, a control error during straight traveling causes the vehicle behavior to be unstable as it is because control for generating lateral force is performed.

  Further, in the toe angle variable control device described in Patent Document 2, since the rear wheel toe angle is controlled based on the turning state of the vehicle, the control device does not function during straight traveling, and is subject to disturbance such as cross wind during straight traveling. If this happens, the behavior of the vehicle becomes unstable.

  The present invention has been made in view of such a background, and an object of the present invention is to provide vehicle behavior control that can effectively improve straight traveling performance against disturbance even during straight traveling.

  In order to solve the above problems, the present invention provides a rear wheel toe angle control device provided in a rear wheel toe angle variable vehicle in which a rear wheel toe angle is variably controlled, and used for controlling the rear wheel toe angle. A yaw rate detecting means for detecting the lateral acceleration, and a lateral acceleration detecting means for detecting the lateral acceleration. It is determined whether or not an external force is acting on the vehicle body. Is determined to be in front of or behind the vehicle body center of gravity, and when the applied point of the external force is in front of the vehicle body center of gravity, the detection result of the yaw rate detection means and the detection result of the lateral acceleration detection means The rear wheel toe angle is controlled to the toe-in side, and when the applied point of the external force is behind the center of gravity of the vehicle body, the detection result of the yaw rate detection means and the detection result of the lateral acceleration detection means Based on before The rear wheel toe angle be configured to control the toe-out side.

  In the rear wheel toe angle control device having the above configuration, the detection result of the yaw rate detection means and the detection result of the lateral acceleration detection means with respect to the auxiliary torque of the power steering device applied to the steering system in accordance with steering by the driver. Based on the above, it is preferable to set the additional torque.

  According to the present invention, it is possible to perform steering that cancels both rotational motion and lateral motion, as well as both of them, so that the straight running stability can be dramatically improved as compared with the conventional straight running stability control device. Since the behavior is controlled for both the rotational motion and the lateral motion, straight traveling is maintained with little correction steering, and the burden on the driver is reduced. Even if a control error occurs, a turning force is not generated from an error in the toe-in amount or toe-out amount during straight traveling, so that the control error does not directly disturb the vehicle behavior.

  In addition, by setting an additional torque for the auxiliary torque of the power steering device, the driver's steering (steering force) is inappropriate and the straight running stability cannot be exhibited effectively, or the driver's steering error is caused by a control error during turning. Even when steering becomes necessary, the driver can easily hold the steering, or can easily perform the correction steering.

Schematic configuration diagram of an automobile equipped with a rear wheel toe angle control device Vehicle motion model with rear wheel toe angle controller Rear wheel toe angle control flowchart

<< Configuration of Embodiment >>
<Overall configuration of automobile>
DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment of a rear wheel toe angle variable vehicle including a rear wheel toe angle control device 11 according to the present invention will be described in detail with reference to the drawings. In the description, for the wheels and members arranged for them, such as tires and electric actuators, suffixes l or r indicating left and right are attached to the numerals respectively, for example, left rear wheel 5l, right rear wheel For example, the rear wheel 5 or the rear wheels 5l and 5r are denoted as 5r.

  FIG. 1 is a plan view showing a schematic configuration of an automobile V provided with a rear wheel toe angle control device 11 according to the embodiment. The vehicle V includes front wheels 3l and 3r fitted with tires 2l and 2r, and rear wheels 5l and 5r fitted with tires 4l and 4r. The front wheels 3l and 3r and the rear wheels 5l and 5r are It is suspended from the vehicle body 1 by left and right front suspensions 6l and 6r and rear suspensions 7l and 7r.

  The vehicle V also includes an electric power steering device 21 (EPS) that applies an auxiliary torque to the steering system to reduce manual steering force, and directly steers the front wheels 3 as steering wheels by steering the steering wheel 22. The toe angles θl and θr of the left and right rear wheels 5l and 5r are individually changed by extending and contracting the front wheel steering device 20 and the left and right electric actuators 12l and 12r provided to the left and right rear suspensions 7l and 7r. And a rear wheel toe angle control device 11.

  The front wheel steering device 20 includes a pinion 24 that is integrally connected to the steering wheel 22 via the steering shaft 23, and both ends that are connected to the front wheels 3 on the left and right front wheels via the tie rods 25 and the like. Then, a rack and pinion mechanism comprising a rack shaft 26 reciprocating in the vehicle width direction, and an electric motor 27 provided coaxially with the rack shaft 26 to generate an auxiliary steering force for reducing manual steering force. The main component is an electric power steering device 21 including

  A steering angle sensor 29 that detects the steering angle of the steering wheel 22 is provided on the steering shaft 23, and a steering torque sensor (not shown) that detects manual steering torque that acts on the pinion 24 is provided in the vicinity of the pinion 24. When the output signals of these sensors are input to an EPS / ECU (Electronic Control Unit) 28, the EPS / ECU 28 variably controls the current flowing through the electric motor 27 and causes the electric motor 27 to generate an auxiliary steering force.

  On the other hand, although not shown in detail, the electric actuator 12 includes a housing connected to the vehicle body 1 side, a motor housed in the housing, a speed reducer, a feed screw mechanism using a trapezoidal screw, and a female screw of the feed screw mechanism. It constitutes a member and is composed of an output rod or the like connected to the rear wheel 5 side, and linearly expands and contracts by converting the rotational motion of the motor into a thrust motion by a feed screw mechanism. The feed screw mechanism has a self-locking function depending on the relationship between the lead angle and the friction angle of the screw, and has a structure that does not reverse-differentiate even if there is an input from the output rod side.

  In addition, the automobile V includes a main ECU 8 that performs overall control of various systems, a yaw rate sensor 9 that detects a yaw rate generated in the vehicle body 1, a lateral acceleration sensor 10 that detects lateral acceleration acting on the vehicle body 1, a vehicle speed sensor 30, Various sensors (not shown) are installed at appropriate positions, and detection signals from the sensors are input to the main ECU 8 to be used for vehicle control.

The main ECU 8 is composed of a microcomputer, ROM, RAM, peripheral circuit, input / output interface, various drivers, and the like. The sensors 9, 10, 29, 30 and the EPS / ECU 28, an MCU to be described later, are connected via a communication line. (Motor Control Unit) 13 is connected. The main ECU 8 calculates the target toe angle θ _RTC of the rear wheels 5 based on the detection results of the sensors 9, 10, etc., calculates the stroke amount of each electric actuator 12, and then sends a drive control signal to the MCU 13. , The toe control of the rear wheels 5l and 5r can be performed separately on the left and right.

The left and right electric actuators 12 are provided with stroke sensors 16l and 16r that detect the stroke amounts of the electric actuators 12 by detecting the positions of magnets arranged close to each other from the differential transformer. The drive control of the electric actuator 12 is performed based on the drive control signal output from the control signal, and the feedback control of the electric actuator 12 is performed based on the stroke amount detected by the stroke sensor 16, so that only the stroke amount calculated by the main ECU 8 is obtained. The rear wheels 5l and 5r are expanded and contracted to change to a desired toe angle θ _RTC .

  According to the vehicle V configured in this way, the left and right electric actuators 12l and 12r are simultaneously symmetrically displaced to freely control the toe-in / to-out of the left and right rear wheels 5l and 5r under appropriate conditions. In addition, if one of the left and right electric actuators 12l and 12r is extended and the other is contracted, the left and right rear wheels 5l and 5r can be steered left and right. For example, the vehicle V changes the rear wheel 5 to toe-out during acceleration, the rear wheel 5 to to-in during braking, and the rear wheel 5 during high-speed turning, based on the vehicle motion state grasped by various sensors in order to improve steering stability. The wheel 5 is in phase with the front wheel rudder angle, and the rear wheel 5 is toe-changed (turned) in phase opposite to the front wheel rudder angle during low-speed turning.

<< Vehicle Movement of Embodiment >>
Next, the movement of the vehicle when the external force Fp is applied to the automobile V will be described. FIG. 2 is a plan view showing a motion model of the automobile V provided with the rear wheel toe angle control device 11. As shown in FIG. 2, when an external force Fp caused by a cross wind or the like is applied at a distance Lp from the vehicle body center of gravity CG, the lateral force F of the tire before and after balancing the lateral force and the rotational force is expressed by the following equation. The
Fp = −Ff−Fr (1)
Lp · Fp = −Lf · Ff + Lr · Fr (2)
In addition,
L = Lf + Lr (3)
It is.
Where Fp: external force, Ff: lateral force of front wheel tire, Fr: lateral force of rear wheel tire, Lp: distance from vehicle body center of gravity CG, L: wheelbase, Lf: distance from vehicle body center of gravity CG to front wheel axle, Lr : Distance from the vehicle body center of gravity CG to the rear wheel axle. When this is modified, it becomes as follows.
Ff = − (1 / L) · Lp · Fp− (Lr / L) · Fp (4)
Fr = + (1 / L) · Lp · Fp− (Lf / L) · Fp (5)

Further, the differential value γ ′ and the lateral acceleration αy of the yaw rate γ can be sensed as the following equations.
(Lp · Fp) / I = γ ′ (6)
Fp / m = αy (7)
Here, I: vehicle yaw inertial rotation mass, γ: yaw rate, γ ′: differential value of yaw rate, m: vehicle mass, αy: lateral acceleration.

The lateral force Fr generated on the rear wheel 5 by the toe angle θ _RTC of the rear wheel 5 is expressed by the following equation. For the basis of the following formula, refer to Japanese Patent Application No. 2006-231543 filed by the applicant of the present application.
Fr = −K · Kr · αy · θ _RTC (8)
However, K: Roll rigidity coefficient, Kr: Cornering power of the rear wheel 5.
Therefore, the toe angle θ _RTC of the rear wheel 5 needs to satisfy the following expression.
−K · Kr · αy · θ _RTC = (1 / L) · (I · γ′−Lf · m · αy) (9)
This can be organized as follows:

の場合、すなわち、Ｌｐ＞０の場合、後輪５をトーイン側に制御し、

の場合、すなわち、Ｌｐ＜０の場合、後輪５をトーアウト側に制御すれば外乱に対する車両挙動の変化を抑制することができる。また、積分制御としてγ’をγに、αｙを∇βに置き換えて制御することも可能である。 Therefore,

In this case, that is, when Lp> 0, the rear wheel 5 is controlled to the toe-in side,

In this case, that is, when Lp <0, if the rear wheel 5 is controlled to the toe-out side, the change in the vehicle behavior with respect to the disturbance can be suppressed. Further, it is also possible to perform control by replacing γ ′ with γ and αy with ∇β as integral control.

From the above formulas (6) and (7), the power steering additional torque T _EPS is expressed as the following formula.
T _EPS = −K _EPS (I · γ ′ + Lr · m · αy) (11)
However, K _EPS : a proportional constant determined from the caster rail and the wheel base L. In a normal automobile, Lf <Lr is often satisfied, and in this case, the direction of Ff is opposite to αy.

<< Control Flow of Embodiment >>
Next, the control flow of this embodiment will be described. FIG. 3 is a flowchart showing a rear wheel toe angle control procedure by the rear wheel toe angle variable vehicle V according to the embodiment. When the vehicle V starts to start, that is, when the vehicle speed V> 0, the following rear wheel toe angle setting process is performed at predetermined intervals.

  First, the main ECU 8 determines whether or not the external force Fp is acting on the vehicle body 1 (step 1). Whether or not the external force Fp is working is determined by monitoring the difference between the standard yaw rate calculated from the steering angle sensor 29, the vehicle speed sensor 30, and the like and the actual yaw rate detected by the yaw rate sensor 9.

If it is determined in step 1 that there is no external force (No), the main ECU 8 sets the toe angle θ _RTC of the rear wheel 5 to 0 degrees (step 2), and sets the additional torque T _EPS of the electric power steering device 21 according to equation (11). Set. If it is determined that there is no external force, the additional torque _TEPS is zero. Then, the main ECU 8 repeats the above procedure. On the other hand, if it is determined in step 1 that there is an external force (Yes), the main ECU 8 next calculates a distance Lp from the vehicle body center of gravity CG to the applied point of the external force Fp, and whether or not Lp is greater than 0, that is, external force It is determined whether the force point of Fp is ahead of the vehicle body center of gravity CG (step 3).

When Lp is larger than 0 in step 3 (when the applied force point of the external force Fp is ahead of the vehicle body center of gravity CG) (Yes), the main ECU 8 sets the toe angle θ _RTC of the rear wheel 5 to the toe-in side according to Equation 10. (Step 4) When Lp is smaller than 0 in Step 3 (when the point of application of the external force Fp is behind the vehicle body center of gravity CG) (No), the main ECU 8 determines the toe angle θ _RTC of the rear wheel 5 according to Equation 10. Set to toe-out side (step 5). Then, as in the case where it is determined in Step 1 that there is no external force (No), the additional torque T _EPS is set according to Equation 11 (Step 6), and the above procedure is repeated.

As described above, by setting the toe angle θ _RTC of the rear wheel 5 and the additional torque T _EPS of the electric power steering device 21 according to the above-described formula, the rotational motion (yaw rate γ) and lateral motion (lateral acceleration αy) by the external force Fp are set. Since not only one of the two, but both of them are canceled out, significantly higher straight-line stability is realized as compared with the conventional straight-line stability control device. And if the driver holds the steering wheel 22 securely, the additional torque T _EPS of the electric power steering device 21 does not affect the behavior of the vehicle. However, since no turning force is generated during straight traveling, the control error during straight traveling does not directly disturb the vehicle behavior. Then, the behavior is controlled for both the rotational motion and the lateral motion, and it is unnecessary to perform corrective steering and the straight traveling is maintained, so the burden on the driver is reduced.

Also, by adding the torque T _EPS is set to the assist torque of the electric power steering device 21, and if inappropriate and straight running stability steering (Hokajiryoku) of the driver is not effectively exhibited, upon turning Even when the driver needs to steer due to a control error, the driver can easily hold the steering wheel 22 or can easily perform corrective steering.

  Although the description of the specific embodiment is completed as described above, the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

V Car 1 Car body 2, 4 Tire 3 Front wheel 5 Rear wheel 8 ECU
9 Yaw Rate Sensor 10 Lateral Acceleration Sensor 11 Rear Wheel Toe Angle Control Device 12 Electric Actuator 13 MCU
20 Front wheel steering device 21 Electric power steering device

Claims (2)

A rear wheel toe angle control device provided in a rear wheel toe angle variable vehicle in which a rear wheel toe angle is variably controlled and used for controlling the rear wheel toe angle,
A yaw rate detection means for detecting the yaw rate;
Lateral acceleration detection means for detecting the lateral acceleration,
It is determined whether or not an external force is applied to the vehicle body. If it is determined that an external force is applied, it is determined whether the external force application point is ahead or behind the vehicle body center of gravity, and the external force application force is determined. When the point is ahead of the center of gravity of the vehicle body, the rear wheel toe angle is controlled to the toe-in side based on the detection result of the yaw rate detection means and the detection result of the lateral acceleration detection means, and the point of application of the external force Rear wheel toe angle is controlled to the toe-out side based on the detection result of the yaw rate detection means and the detection result of the lateral acceleration detection means when the vehicle is behind the center of gravity of the vehicle body. Toe angle control device.   An additional torque is set based on the detection result of the yaw rate detection means and the detection result of the lateral acceleration detection means for the auxiliary torque of the power steering device applied to the steering system in accordance with steering by the driver. The rear wheel toe angle control device according to claim 1, wherein the rear wheel toe angle control device is characterized.

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