JPH02204178A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To select each mode of stable/sporty in the steering characteristic according to necessity by reducing the insensitive band of the yaw rate, together with the increase of the car speed, in the constitution in which rear wheels are steered according to the specific equation on the basis of the yaw rate, car speed, steering angle, etc. CONSTITUTION:As for a control unit U which receives the output signals of a car speed sensor 31 for detecting the car speed V, steering angle sensor 35 for detecting the front wheel steering angle thetaF, lateral G sensors 33 and 34, etc., the yaw rate psi is calculated by integration-calculating the output difference of the both lateral G sensors 33 and 34. The aimed steering angle TGthetaR for a rear wheel is calculated from the equation TGthetaR = - KF.thetaF + KR.V.psi (In this case, KF and KR are coefficients determined according to the characteristic of a vehicle), and the rear wheel is steered by drive-controlling servomotor 20 on the basis of the calculation value. In this case, an insensitive body varying means for varying the insensitive band of the yaw rate to the less value together with the increase of the car speed V is provided, and the proper disposal of the variation of the yaw rate due to the external turbulence, etc. in a high speed region is permitted.

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,
If you turn the steering wheel slowly while turning the corner, the steering angle of the front and rear wheels will be different, so the required yaw rate will occur and there will be no problem, 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 O, 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, TGθII−-KP・θp+KR”V・ψTGθR: Rear wheel target steering angle θF: Front wheel steering angle V: Vehicle speed φ: Yaw rate KF, KR: Based on a constant determined by the characteristics of the vehicle. It has been proposed to steer the rear wheels.Here, the constant KPSKl? is determined by the following equation.

KP-C, /C2 KR=WV/g-(C212-C+ I ri/VζW
/ C2g c,,c2: Cornering power W: Weight 11: Distance between the center of gravity of the vehicle and the front wheel axle 12: Distance between the center of gravity of the vehicle and the rear wheel axle, that is, at low speeds, V is small and the influence of the second term is small; However, as the speed increases, both the vehicle speed V1 and the yaw rate increase, and the influence of the second term increases, resulting in the same phase. 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 phase is 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) In such a device, the front wheel steering angle is in reverse phase, and the yaw rate is in the same phase as a component for steering the rear wheels, so the front wheel steering angle and yaw rate are used for control. In this case, it is common practice to provide a dead zone, including hysteresis, to remove noise components and unnecessary micro-vibration components from the sensor system. Making it smaller than the dead zone of the in-phase component makes it stable, and making the dead zone of the in-phase component larger makes it sporty (quick), so the problem is how to set it up.

The present invention has been made in view of the above points, and by changing the dead zone of the front wheel steering angle and yaw rate according to the driving condition of the vehicle, it is possible to selectively use the stable/sporty mode as needed. The purpose is to provide a wheel steering device.

(Means for Solving the Problems) The present invention is based on the mathematical formula % TGθR: Target steering angle of the rear wheels θF: Steering angle of the front wheels V2 Vehicle speed m: Yaw rate KP, KR: Based on coefficients determined by vehicle characteristics In order to achieve the above object, the invention of claim (1) is characterized by a rear wheel steering device for a vehicle having a steering control means for steering the rear wheels. The invention of claim (2) is characterized in that the invention includes a dead zone changing means that receives the output of the detecting means and reduces a dead zone of the yaw rate as the vehicle speed increases, and a vehicle speed detecting means for detecting the vehicle speed; The invention of claim (3) is characterized in that the output of the vehicle has a dead zone changing means that reduces the dead zone as the vehicle speed increases so that the yaw rate is smaller than the steering angle of the front wheels. The invention as claimed in claim (4) is characterized in that it has a dead zone changing means that can manually change the dead zone, and includes: a vehicle speed detecting means for detecting vehicle speed; a reversing detecting means for detecting backward movement of the vehicle; The invention of claim (5) is characterized in that the means receiving the output of the backward detecting means has dead zone changing means for reducing the dead zone of the steering angle of the front wheels as the vehicle speed increases when the vehicle is moving backwards. The present invention is characterized in that it has a friction coefficient detection means for detecting a friction coefficient, and a dead zone changing means that receives the output of the friction coefficient detection means and reduces the dead zone of the yaw rate when the friction coefficient of the road surface is low.

(Function) According to the invention of claim (1), since the dead zone of the yaw rate is reduced in the high speed range, it is possible to appropriately respond to changes in the yaw rate due to disturbances, etc. in the high speed range.

According to the invention of claim (2), it is desired to reduce the dead zone of the front wheel steering angle and yaw rate in order to improve stability in a high-speed range, but by increasing the ratio of the small dead zone of the yaw rate, the yaw rate becomes faster. , the response in the in-phase direction increases, and stability increases.

According to the invention of claim (3), depending on the driver's preference,
The size of the dead zone for the front wheel steering angle can be changed by switching.

According to the invention of claim (4), the dead zone of the front wheel steering angle becomes extremely large as the vehicle speed increases, so that the stability when reversing is improved.

According to the invention of claim (5), when the coefficient of friction is small, the dead zone of the yaw rate is made small to improve stability.

(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,
IL and IR are the left and right front wheels, respectively, and 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 device IMA, and the left and right rear wheels 2L and 2
R is 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 4L, respectively.

4R, a pair of left and right Tyrozods, and a relay rod 5 that connects 4L and 4R. A steering mechanism C is linked to the front wheel steering mechanism A, and the steering mechanism C is of a rack-and-binion 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 and IOR, and a tie rod 1.
．． IL, IIR, and the pair of left and right tie rods 11. L
, and a relay rod 12 that connects the IIRs, and a neutral holding means 13 is attached to the relay rod 12.

As shown in detail in FIG. 2, the neutral holding means 13 has a casing fixed to the vehicle body 14, and a pair of spring receivers 16a, i6b are loosely fitted into the casing 15. A compression spring 17 is arranged between the springs 16b and 16b. The relay rod 12 extends through the casing 15, and a pair of flanges N12a, 12b are formed on the relay rod 12 at an interval.
The relay rod 12 is always urged 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 mechanism B is linked to a servo motor 20 that serves as a drive source for steering the rear wheels 2L and 2R. In the linkage mechanism between the relay rod 12 and the servo motor 20,
A clutch 22 is interposed. Thereby, the clutch 22 is configured to mechanically disconnect the servo motor 20 and the rear wheel steering mechanism B as appropriate.

With the above configuration, when the clutch 22 is in the connected state, the relay rod 12 is displaced to the left or right in FIG. 1 due to forward or reverse rotation of the servo motor 20, 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 formula.

Formula % Formula % TGθR: Rear wheel target steering angle θF2 Front wheel steering angle ■: Vehicle speed φ: Yaw rate Coefficients KF and KR are constants determined by vehicle characteristics, but are variables that change based on vehicle speed, etc. You can also use it as

In order to perform the above control, the control unit U has a steering control means 101 that steers the rear wheels based on the above formula, and further receives the output of the vehicle speed detection means and receives the front wheel steering angle θF.
(see FIG. 4, broken line) and the dead zone of yaw rate g (see FIG. 4, solid line) as the vehicle speed V increases (see FIG. 8).

Further, the dead zone changing means 102, as shown in FIG.
The ratio of reducing the dead zone is such that the yaw rate φ is larger than the front wheel steering angle θF.

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 G sensor 33, and a rear G sensor 34 are input. 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 TGθR using the above formula, taking into account the yaw rate φ, and calculates the required rear wheel steering amount. A corresponding control signal 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.
A vehicle speed sensor 36 is added to the encoder 32, and a rear wheel steering angle sensor 37 is added to the encoder 32 to detect the mechanical displacement of a member closer to the relay rod 12 than the clutch 22. , 35, 36, and 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 is assumed that a failure has occurred, and the rear wheels 2L, 2R are controlled in the fail mode. is designed to hold it in a neutral position.

Both lateral G sensors 33 and 34 are respectively disposed on the central axis of the vehicle body in front and behind the center of gravity, and the lateral G detected by these sensors is used to detect yaw rate.

The current yaw rate φn is calculated from the outputs of both lateral G sensors 33 and 34 using the following equation.

c? n-tjIn-+ + (GF-GR) t/
D required n-1: Previous yaw rate GF: Output GR of front lateral G sensor 33; Output t of rear lateral G sensor 34: Δ-1 Fixed interval 1: Distance between both lateral G sensors Note that instead of the lateral G sensor It is also possible to add a yaw rate sensor that directly detects the yaw rate.

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.
Although not shown, a signal representing no power generation is input from the alternator's terminal.

The vehicle height sensor 39 detects the height of the vehicle, thereby directly detecting the vehicle's weight loss. 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 value exceeds a predetermined value.

Control is performed by two interconnected main controllers 50A and sub-controllers 50B, and each controller 50A, 5Q13 has a heel sensor 30, 3.
7, 39.40 and the L terminal of the alternator are inputted to the sensors 31, 36.3 respectively via the analog buffer 51 and the A/D converter 52.
7 and switches 41, 42, and 43 are input to each via a digital buffer 53, and signals from both G sensors 33 and 34 are input to the main via another analog buffer 54 and an A/D converter 55. It is input to 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. Also, in the OR circuit 75, a warning lamp 76 is turned on when the two signals do not match.

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

In the figure, 77 is a voltage control circuit that has a 5V regulator and resets the main controller 50A in the event of an abnormality, 78 is a battery, 79 is an ignition switch, and 80 is a fuse. Therefore, according to the above configuration, As shown by the solid line in Figure 4, the dead zone of the yaw rate becomes smaller as the vehicle speed increases, so that the rear wheels are steered in the same phase direction in response to changes in the yaw rate φ caused by external disturbances etc. at high speeds. be done.

In addition, in order to improve stability at high speeds, both the front wheel steering angle dead zone and the yaw rate dead zone are made smaller.
By making the ratio that reduces the dead band of the yaw rate larger than the ratio that reduces the dead band of the front wheel steering angle, the yaw rate becomes effective before the front wheel steering angle θF, and the response in the in-phase direction is greater than the reaction in the opposite phase direction. It is now more sensitive and more stable at high speeds.

In the above embodiment, the dead zone of the front wheel steering angle and yaw rate is automatically changed by the dead zone changing means, but a manual switch 38 may be provided so that the dead zone can be changed manually by the driver. In other words, as shown in Fig. 5, in order to obtain a feeling of sport, the dead zone of the front wheel steering angle θF should be made smaller overall compared to normal conditions (see the broken line in Fig. 5), and in order to obtain a sense of stability, the dead zone of the front wheel steering angle θF should be made smaller overall. It is only necessary to increase the overall dead zone compared to normal times (5th m: see the dotted chain line).

In addition, as shown in factor 6, as the vehicle speed increases, the dead zone of the front wheel steering angle θF is made extremely large (see the 6th m: dotted chain line) to increase stability when reversing. As shown in Figure 7, when the friction coefficient is small, the yaw rate φ
It is also possible to increase the stability by reducing the dead zone (7th m: see the dotted chain line).

(Effects of the Invention) As described above, the invention of claim (1) reduces the dead zone of the yaw rate in the high-speed range, so it responds appropriately to changes in the yaw rate due to disturbances, etc. in the high-speed range, and improves stability. .

In the invention of claim 2, by making the reduction ratio of the dead zone of the yaw rate larger than the dead zone of the front wheel steering angle, the yaw rate becomes effective first, the response in the same phase direction becomes larger, and stability increases.

According to the invention of claim (3), the dead zone of the front wheel steering angle can be switched and changed according to the driver's preference.

According to the invention of claim (4), the dead zone of the front wheel steering angle becomes extremely large as the vehicle speed increases, so that the stability when reversing is improved.

According to the invention of claim (5), when the coefficient of friction is small, the dead zone of the yaw rate is made small to improve stability.

[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 Figs. 4 to 7. is an explanatory diagram of the dead zone, and FIG. 8 is a block diagram of the control unit. U...Control unit 30...Handle steering angle sensor 31.36...Vehicle speed sensor 33°34...Lateral G sensor 35... Front wheel steering angle sensor 38...Manual switch 40...Raindrop sensor 42...Reverse switch 01...Steering angle control means 02... Dead band changing means 31°33°U...Control unit 30...Handle steering angle sensor 36...Vehicle speed sensor 34...Lateral G sensor 35... ...Front wheel steering angle sensor 38...Manual switch 40...Raindrop sensor 42...River, switch 01...Steering angle control means 02.・・・・・・Dead band changing means Tonneau L Fig. 2 61 Vehicle direction Fig. 4 Single speed Fig. 5 High → Fig. 6 Otori speed Fig. 7 High →

Claims (5)

[Claims] (1) Formula TGθR=-KF・θF+KR・V・ψ TGθR: 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. The vehicle having steering control means for steering is characterized by having vehicle speed detection means for detecting vehicle speed, and dead zone changing means for receiving the output of the vehicle speed detection means and reducing the dead zone of the yaw rate as the vehicle speed increases. Vehicle rear wheel steering device. (2) Formula TGθR=-KF・θF+KR・V・ψ TGθR: 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 a vehicle having steering control means for steering, a vehicle speed detection means for detecting vehicle speed, and a dead zone that receives the output of the vehicle speed detection means and reduces the ratio of the dead zone as the vehicle speed increases so that the yaw rate is smaller than the steering angle of the front wheels. 1. A rear wheel steering device for a vehicle, comprising: changing means. (3) Formula TGθR=-KF・θF+KR・V・ψ TGθR: 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. What is claimed is: 1. A rear wheel steering device for a vehicle, comprising a steering control means for steering, characterized in that the device includes a dead zone changing means capable of manually switching the dead zone of the steering angle of the front wheels. (4) Formula TGθR=-KF・θF+KR・V・ψ TGθR: 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 a vehicle having a steering control means for steering, the vehicle speed detecting means detects the vehicle speed, the reversing detecting means detects the reversing of the vehicle, and the vehicle speed increases when reversing in response to the outputs of the vehicle speed detecting means and the reversing detecting means. 1. A rear wheel steering device for a vehicle, comprising dead zone changing means for reducing a dead zone of a steering angle of a front wheel as the steering angle increases. (5) Formula TGθR=-KF・θF+KR・V・ψ TGθR: Target steering angle of rear wheels θF: Steering angle of front wheels V: Vehicle speed ψ: Yaw rate KF, KR: Adjustment of rear wheels based on coefficients determined by vehicle characteristics. In a device having a steering control means for steering, a friction coefficient detection means detects a friction coefficient of a road surface, and a dead zone change that reduces a dead zone of a yaw rate when the friction coefficient of the road surface is low based on the output of the friction coefficient detection means. A rear wheel steering device for a vehicle, characterized in that it has a means.