JPH02193773A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To secure running stability in a high speed region and steering stability in a low speed region by constructing the title device in such a way as to inhibit the control performed by a rear wheel steering means based on the equation of the rear wheel target angle when the speed is detected to be lower than the fixed speed by the output signal of a speed detecting means. CONSTITUTION:The title device is provided with a rear wheel steering control means for steering rear wheels based on an equation 1 in which TGthetaR signifies the target steering angle of the rear wheel, thetaF: the steering angle of a front wheel, V: speed, psi: a yaw-rate, and KF.KR: coefficients determined according to the characteristic of a vehicle. In order to perform this control, a control unit U is provided with a steering control means for steering the rear wheels based on the equation 1 as well as an inhibiting means 102 for inhibiting the control performed by the rear wheel steering control means based on the equation 1 if the speed is detected to be lower than the specified speed by the signal from a speed sensor 31. That is to say, the control performed by the rear wheel steering control means 101 based on the equation 1 is suitable at the time of high speed running over the fixed speed, but not so suitable at the time of low speed running under the fixed speed, thereby inhibiting the control.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a rear wheel steering device for a vehicle.

(Prior Art) Conventionally, as a four-wheel steering device for a vehicle, one that steers the rear wheels according to the vehicle speed and the front wheel steering angle is known.

At low speeds, they are controlled in opposite phases depending on the steering angle, and at high speeds, they are controlled in the same phase depending on the steering angle.

However, with this type of control, at the beginning of a turn,
When turning the steering wheel slowly while turning a corner, the amount of steering angle between the front and rear wheels is different, so the necessary yaw rate will occur and no problem will occur, but if you turn the steering wheel suddenly Since the rear wheels are in the same phase at high speed, the vehicle moves diagonally, the yaw rate is suppressed, and the slip angle β between the vehicle's direction and the direction of travel is not 0, and the driver wants to change direction. Requests are not met.

That is, at the time of initial steering, it is desirable to first change the direction and then become in phase and stabilize, so that the slip angle β-0 is always achieved.

Therefore, in order to satisfy the above requirements, TGθR--KP-θp+KR'V"ψTGθR: Rear wheel target steering angle θF = Front wheel steering angle V: Vehicle speed φ: Yaw rate KP, KR: Constant determined by vehicle characteristics Rear wheel It is proposed to steer the coefficient KP Kl? on the basis of which is determined by the following formula: where:

I (P-CI/C2 KR-WV/g-' = W/ C2g CI+ (C212-C+ I+)/V C2: Cornering power W: m: 11: Distance between the center of gravity of the vehicle and the front wheel axle 12: The distance between the center of gravity of the vehicle and the front wheel axle In other words, at low speeds, the distance between the center of gravity and the rear wheel axle, V is small and the influence of the second term is small, resulting in an opposite phase, but at high speeds, both the vehicle speed, v5, and the yaw rate increase, and the influence of the second term becomes large. However, at the beginning of the turn, the yaw rate is still small, so the influence of the second term is not so large, and the phases are opposite.

By the way, as described in, for example, Japanese Unexamined Patent Publication No. 57-44568, a vehicle is known in which the rear wheels are steered in accordance with the output of a yaw rate sensor in order to correct the influence of external disturbances such as crosswinds.

(Problem to be Solved by the Invention) However, when such a device is actually applied to a rear wheel steering system of a vehicle, it is desirable to control the slip angle to form a slip angle β-0 at high speeds, but at low speeds If the influence of the second term is large, the turning radius will not be very effective, the vehicle will wobble, and the vehicle will become unstable.

The present invention has been made in view of the above, and an object of the present invention is to provide a rear wheel steering device for a vehicle that can achieve both running stability at a slip angle β-0 and steering stability in a low speed range. be.

(Means for Solving the Problem) In order to achieve the above object, the invention of claim (1) uses the formula % formula % TGθR: Target steering angle of the rear wheels θF: Steering angle of the front wheels ■Second vehicle speed φ: Yaw rate KP, KR: In a vehicle having a rear wheel steering control means for steering the rear wheels based on a coefficient determined by the characteristics of the vehicle, a vehicle speed detection means for detecting the vehicle speed, and a vehicle receiving the output of the vehicle speed detection means are configured to control the vehicle speed at a predetermined vehicle speed. Hereinafter, the present invention is characterized in that it includes a prohibition means for prohibiting control of the rear wheel steering control means using the above formula.

That is, the control of the rear wheel steering control means using the above formula is as follows:
This control is suitable at high speeds exceeding a predetermined vehicle speed, but is not so suitable at low speeds below a predetermined vehicle speed, so its control is prohibited.

(Operation) When the vehicle speed is below a predetermined speed, the control of the rear wheel steering control means based on the above formula is prohibited by the prohibition means.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

In FIG. 1 showing the overall configuration of a rear wheel steering device of a vehicle,
ILllR is the left and right front wheels, respectively, 2L.

2R is the left and right rear wheels, and the left and right front wheels IL and IR are linked by the front wheel steering mechanism A, and the left and right rear wheels 2L and 2R are linked by the front wheel steering mechanism A.
are linked by rear wheel steering mechanism B.

The front wheel steering mechanism A includes a pair of left and right knuckle arms 3L, 3R and a tie rod 4L4R, and a relay rod 5 that connects the pair of left and right tie rods 4L, 4R. A steering mechanism C is linked to the front wheel steering device fMA, and the steering mechanism C is of a rack and pinion type, and a pinion 6, which is a component thereof, is connected to a handle 8 via a shaft 7. .

As a result, when the handle 8 is operated to the right, the relay rod 5 is displaced to the left in FIG. is steered clockwise in the same figure. Similarly, when the steering wheel 8 is turned to the left, the left and right front wheels IL and IR are
will be steered to the left.

Similarly to the front wheel steering mechanism B, the rear wheel steering mechanism A also includes a pair of left and right knuckle arms IOL, 10R and tie rods IIL, IIR, and a pair of left and right tie rods IIL.
, and a relay rod 12 that connects the IIRs, and a neutral holding means 13 is attached to the relay rod 12.

The neutral holding means 13 has a casing fixed to the vehicle body 14, as shown in detail in FIG. If compressed between 16b. 17 is provided. The relay rod 12 extends through the casing 15, and a pair of flanges 12a, 12b are formed on the relay rod 12 at a distance from each other.
The relay rod 12 is always biased in the neutral direction by a compression spring 17. The compression spring 17 is designed to have a spring force sufficient to overcome side forces during cornering.

The rear wheel steering device tlB is linked to a servo motor 20 as a drive source for steering the rear wheels 2L and 2R. A clutch 22 is interposed in the linkage mechanism between the relay rod 12 and the servo motor 20. As a result, the clutch 22 appropriately controls the servo motor 20 and the rear wheel steering mechanism B.
It is designed to be able to mechanically disconnect the connection.

With the above configuration, when the clutch 22 is in the connected state, the servo motor 20 rotates in the forward or reverse direction.
The relay rod 12 is displaced to the left or right in FIG. 1, and the knuckle arm 10L.

10R rotates the servo motor 2 around its rotation center.
The steering wheel is steered clockwise or counterclockwise in the figure by an amount corresponding to the amount of rotation at zero.

On the other hand, when the clutch 22 is in the connected state, the rear wheels 2L, 2R are forcibly returned to the neutral position by the neutral holding means 13, and are held at this neutral position. In other words, when the clutch 22 is disengaged, only the front wheels IL and IR are steered, resulting in a so-called 2WS vehicle.

Rear wheel steering control is performed based on the following equation.

Formula % Formula % TGθR: Rear wheel target steering angle θF: Front wheel steering angle V Second vehicle speed tjp: Yaw rate Note that the coefficients KP and KR are constants determined by the characteristics of the vehicle, but they are variables that change based on the vehicle speed. Good too.

In order to carry out the above control, the control unit U has a steering control means 101 that steers the rear wheels based on the above mathematical formula, and furthermore, receives a signal from the vehicle speed sensor 31, and when the vehicle speed is below a predetermined vehicle speed, the steering control means 101 steers the rear wheels based on the above mathematical formula. The vehicle has prohibition means 102 for prohibiting control of the rear wheel steering means by the vehicle (see FIG. 4).

When the vehicle speed is below the predetermined speed at which the control using the above formula is prohibited by the prohibition means 102, the vehicle is controlled by TGθR−−KP2・θP (KP2≦1), and the control is in the opposite phase, making small turns effective and controlling the vehicle in the low speed range. Stability is ensured.

Specifically, as shown in FIG. 1, signals from a steering wheel angle sensor 30, a vehicle speed sensor 31, an encoder 32 that detects the rotational position of the servo motor 20, a front lateral G sensor 33, and a rear lateral G sensor 34 are Based on the steering wheel steering angle θF (front wheel steering angle) and vehicle speed V, the control unit U calculates the target rear wheel steering angle using the above formula, taking into account the yaw rate φ, except when the vehicle speed is below a predetermined vehicle speed. T
GθR is calculated and a control signal corresponding to the required rear wheel steering amount is output to the servo motor 20. Thus, the encoder 32 constantly monitors whether or not the servo motor 20 is operating properly, that is, the rear wheels 2L and 2R are steered under feedback control.

The control system described above has a dual configuration for fail-safe purposes.

In other words, as shown in FIG.
A front wheel steering angle sensor 35 is added to the vehicle speed sensor 3.
1, a vehicle speed sensor 36 is added to the encoder 32, and a rear wheel steering angle sensor 37 that detects mechanical displacement of a member closer to the relay rod 12 than the clutch 22 is added, and these sensors 30, 31, 32 In .35, 36.37, rear wheel steering is performed only when both corresponding sensors detect the same value. That is,
In the sensors 30 to 32, 35 to 37, for example, when the vehicle speed detected by the vehicle speed sensor 31 and the vehicle speed detected by another vehicle speed sensor 36 are different, it means that an enemy camp has occurred, and the rear wheels 2L and 2R are controlled in the fail mode. is designed to hold it in a neutral position.

The above-mentioned both lateral G sensors 3B and 34 are respectively disposed on the center axis of the vehicle body in front and behind the center of gravity to detect the magnitude of the lateral G, and are used to detect the yaw rate tjt.
The current yaw rate φn is calculated from the outputs of the sensors 33 and 34 using the following equation.

tjtn-φn-+ +(GF-GR) t/i)φn
-1: Previous yaw rate GF: Output of front lateral G sensor 33 GR: Output of rear lateral G sensor 34 t: DJ fixed interval J7 = Interval between both lateral G sensors Note that instead of using the lateral G sensor, the yaw rate ψ can be directly calculated. It is also possible to add a yaw rate sensor for detection.

In addition, for various controls, the control unit U includes a vehicle height sensor 39, a raindrop sensor 40, a brake switch 41, a reverse switch 42, and an accelerator switch 4.
3, and a signal representing the presence or absence of power generation is input from the alternator terminal, although not shown.

The vehicle height sensor 39 detects the vehicle height, and thereby indirectly detects the loaded weight. The raindrop sensor 40 detects raindrops, thereby indirectly detecting the friction coefficient μ of the road surface. The brake switch 41 outputs an on signal when the brake pedal is depressed, the reverse switch 42 outputs an on signal when the shift lever is in the reverse position, and the accelerator switch 43 outputs an on signal when the shift lever is in the reverse position. It outputs an on signal when the rate of change exceeds a predetermined value.

Control is performed by two interconnected main controllers 5OA and sub-controllers 50B, and each controller 50A, 50B is equipped with various sensors 30, 37.
, 39.40 and the alternator's terminals are inputted to the sensors 31, 35.36 via the analog buffer 51 and the A/D converter 52, respectively.
Signals from the switches 41, 42, and 43 are input to each via a digital buffer 53, and signals from both lateral G sensors 33, 34 are input via another analog buffer 54 and an A/D converter 55 to the main It is manually operated by the controller 50A.

On the other hand, the signal generated in the main controller 50A is output to the servo motor 20 via the servo amplifier 61 and the servo driver 62, and is set as the target rear wheel steering angle. The rotation amount of the servo motor 20 is determined by the encoder 32.
A signal from the encoder 32 is input to the main controller 50A via the servo amplifier 61, and the servo motor 20 is feedback-controlled.

Also, only when the signals from both controllers 50A and 50B are compared in AND circuits 71 and 72 and match,
Clutches 73 and 74 are connected to enable steering of the rear wheels. Further, an OR circuit 75 is also compared, and when the two signals do not match, a warning lamp 76 is turned on.

Note that this rear wheel steering control is started on the condition that the signal from the alternator terminal becomes high (Hi).

In addition, 77 has a 5V regulator and a voltage control circuit that resets the main controller 5OA in the event of an abnormality, 78 is a battery, 79 is an ignition switch,
80 is a fuse. Therefore, according to the above configuration, when the vehicle speed exceeds a predetermined speed (for example, 40 cm/h),
Control is performed according to the above formula, and the slip angle β-0 is achieved even transiently.

On the other hand, below a predetermined vehicle speed, control using the above formula is prohibited, and control is performed using TGθR--KF2·θP (K1'2≦1), resulting in reverse phase control. Therefore, the amount of steering does not become too large in the low speed range, and steering stability is ensured.

(Effects of the Invention) As described above, the present invention prohibits control based on the above formula below a predetermined vehicle speed, thereby improving running stability by realizing a slip angle β-0 in a high speed range and improving running stability in a low speed range. Maneuvering stability is ensured.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, in which Fig. 1 is a rear wheel steering system of a vehicle, Fig. 2 is an enlarged sectional view of a neutral holding means, Fig. 3 is a block diagram of a control system, and Fig. 4 is a diagram of a control unit. It is a block diagram. U...Control unit 30...Handle steering angle sensor 31.36...Vehicle speed sensor 33.34...Lateral G sensor 35... Front wheel steering angle sensor search 101...Steering angle control means 102...Prohibition means

Claims (1)

[Claims] (1) Formula TGθR = -KF・θF+KR・V・ψ ΥGθR: Rear wheel target steering angle θF: Front wheel steering angle V: Vehicle speed ψ: Yaw rate KF, KR: Rear wheel steering angle based on coefficients determined by vehicle characteristics. In the vehicle having a rear wheel steering control means for steering, a vehicle speed detection means detects the vehicle speed, and a prohibition means receives the output of the vehicle speed detection means and prohibits control of the rear wheel steering means according to the above formula when the vehicle speed is below a predetermined vehicle speed. A rear wheel steering device for a vehicle, comprising: