JP2877346B2 - Vehicle rear wheel steering system - Google Patents

Description

Description: TECHNICAL 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, a device for steering rear wheels according to a vehicle speed and a front wheel steering angle is known. At low speeds, the rear wheels are controlled in opposite phases according to the front wheel steering angle, and at high speeds, they are controlled in phase according to the front wheel steering angle.

However, in the case of such control, in the initial stage of turning, when turning around a corner while slowly steering the steering wheel, the steering angle amounts of the front wheels and the rear wheels are different, so a necessary yaw rate is generated and no problem occurs. However, if the steering wheel is turned sharply, the rear wheels are in phase at high speed, so the vehicle advances diagonally, the yaw rate is suppressed, and the slip angle β between the direction of the vehicle and the traveling direction is 0. In addition, the demand to change the direction of the driver is not satisfied.

That is, at the time of initial steering, first change the direction,
It is then desirable to be in phase and stable, so that a slip angle β = 0 is always achieved.

In order to satisfy the above requirements, TGθR = −KF · θF + KR · V · TGθR: target steering angle of the rear wheel θF: steering angle of the front wheel V: vehicle speed: yaw rate KF, KR: for example, wheel base, vehicle weight, center of gravity It has been proposed to steer the rear wheels based on a constant determined by vehicle characteristics such as balance. Here, KF and KR are determined by, for example, the following equations.

_{KF = C 1 / C 2 KR} = WV / g- (C 2 1 2 -C 1 1 1) / V ≒ W / C 2 g C 1, C 2: cornering power W: Weight 1 _1: and the center of gravity of the vehicle Distance from front wheel axle 1 ₂ : Distance between center of gravity of vehicle and rear wheel axle That is, the steering angle of the front wheels is in the opposite phase, and the vehicle speed V and the yaw rate are in phase and serve as components for steering the rear wheels. Therefore, when the rear wheel is at a low speed, V is small and the influence of the second term is small, so the phases are reversed. However, at a high speed, both the vehicle speed V and the yaw rate increase, and the influence of the second term increases. Be in phase. However, since the yaw rate is still small at the beginning of the turn, the effect of the second term is not so large, and the phase is reversed.

By the way, as disclosed in, for example, Japanese Patent Application Laid-Open No. 57-44568, there is known a device that turns the rear wheels according to the output of a yaw rate sensor in order to correct the influence of disturbance such as crosswind.

(Problems to be Solved by the Invention) However, according to the above equation, KF and KR are constants, but they are constants, and it is difficult to actually apply them to vehicles. For example, at low speeds, the steering angle of the front wheels is about 35 degrees, so if the rear wheels are steered to the same extent, a very small turn will be effective, causing the vehicle to swing back, and two-wheel steering (where the rear wheels are not steered). I feel uncomfortable from getting used to 2WS)
Difficult to ride.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rear wheel steering device of a vehicle that can achieve both turning performance at low speed and stability at high speed.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides the following formula: TGθR = −KF · θF + KR · V · TGθR: target steering angle of rear wheels θF: steering angle of front wheels V: vehicle speed: yaw rate KF, KR: a vehicle speed detecting means for detecting a vehicle speed of a vehicle having a rear wheel steering device having a turning control means for turning the rear wheels based on a coefficient determined by a characteristic of the vehicle; And outputs the coefficient KF
Is changed to a predetermined value smaller than 1 in the low speed range, is set to approximately 1 in the medium speed range, and is decreased to a value smaller than 1 in the high speed range, and the coefficient KR is substantially reduced in the medium speed range. Changing means for setting the value to 0.

(Operation) According to the present invention, the coefficient KF is changed so as to increase with an increase in the vehicle speed V. Therefore, in a low-speed range where the vehicle speed V is low, the rear wheel steering angle becomes small, and the steering becomes close to two-wheel steering. The feeling of incompatibility that comes from getting used to two-wheel steering disappears,
The butt swing phenomenon is suppressed. In the medium speed range, which is the normal range, K
F is set to approximately 1, steering is performed in a highly responsive manner with respect to a change in the front wheel steering angle, the slip angle β = 0 is substantially achieved, and the steering is improved. The effect of the change in is reduced, and the stability is increased.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In FIG. 1 showing the overall configuration of a rear wheel steering device of a vehicle, 1L and 1R are left and right front wheels, 2L and 2R are left and right rear wheels, and left and right front wheels 1L and 1R are linked by a front wheel steering mechanism A. The left and right rear wheels 2L, 2R are linked by a rear wheel steering mechanism B.

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

Thus, when the steering wheel 8 is turned to the right, the relay rod 5 is displaced leftward in FIG.
The knuckle arms 3L and 3R are steered rightward in the clockwise direction in the figure by an amount corresponding to the operation displacement amount of the steering wheel 8, that is, the steering angle of the steering wheel. Similarly, when the operation of turning the steering wheel 8 to the left is performed, the left and right front wheels 1L and 1R are steered to the left according to the amount of operation displacement.

Similarly to the front wheel steering mechanism B, the rear wheel steering mechanism A also includes a pair of left and right knuckle arms 10L, 10R and tie rods 11L, 11R.
And a relay rod 12 for connecting the pair of left and right tie rods 11L and 11R to each other. The relay rod 12 is provided with a neutral holding means 13.

The neutral holding means 13 is, as shown in detail in FIG.
The casing 15 has a casing 15 fixed thereto. A pair of spring receivers 16a and 16b are loosely fitted in the casing 15, and a compression spring 17 is disposed between the spring receivers 16a and 16b. The relay rod 12 extends through the casing 15, and the relay rod 12 is formed with a pair of flange portions 12a and 12b at intervals, and the flange portions 12a and 12b
The relay rods 12 are always urged to a neutral position by a compression spring 17. The compression spring 17 has a spring force enough to overcome the side force during cornering.

The rear wheel turning mechanism B is linked to a servomotor 20 as a drive source for turning the rear wheels 2L and 2R. The clutch 22 is provided in the linking mechanism between the relay rod 12 and the servomotor 20.
Is interposed. With this clutch 22, the linkage between the servo motor 20 and the rear wheel steering mechanism B can be mechanically disconnected as appropriate.

With the above configuration, when the clutch 22 is in the connected state, the forward or reverse rotation of the servomotor 20 causes the relay rod 12 to be displaced leftward or rightward in FIG. The steering is turned clockwise or counterclockwise in the figure by an amount corresponding to the rotation amount of the servo motor 20 about the center of movement.

On the other hand, when the clutch 22 is in the disengaged state, the rear wheels 2L, 2R are forcibly returned to the neutral position by the neutral holding means 13, and are held at the neutral position. That is, when the clutch 22 is disengaged,
It is a so-called 2WS vehicle in which only L and 1R are steered.

The control of the rear wheel steering is performed based on the following equation.

Formula TGθR = −KF · θF + KR · V · TGθR: Target steering angle of rear wheel θF: Steering angle of front wheel V: Vehicle speed: Yaw rate Note that coefficients KF and KR are variables that are changed based on vehicle speed and depend on vehicle characteristics. As a specific example, as shown in FIG. 3, for example, as shown in FIG. 3, the KF is about 0.35 up to around 10 km / h for practical use on the low speed side, but the vehicle speed exceeds 10 km / h. 40km / h gradually increasing with increasing V
It becomes substantially 1 in the vicinity, and almost achieves the slip angle β = 0 to secure the maneuverability. Then, when the vehicle speed exceeds 80 km / h, in order to secure the linear stability on the high speed side, it gradually decreases with increasing vehicle speed, and the response to changes in the front wheel steering angle is reduced. At the time of reverse driving, it is about 0.35 at 5 km / h or less where small turning is required,
Above / h, it decreases with increasing vehicle speed to ensure stability.

On the other hand, as shown in FIG. 4, KR gradually increases when the speed exceeds 10 km / h, and is changed to increase to 0.005 near 30 km / h.

In order to perform the above control, the control unit U includes a turning control unit 101 that turns the rear wheels based on the above formula,
Receiving the output of the vehicle speed sensor 31 (36), the coefficient KF is changed to a predetermined value smaller than 1 in the low speed range, to approximately 1 in the middle speed range, and to a value smaller than 1 in the high speed range, And changing means 102 for setting the coefficient KR such that the vehicle slip angle becomes substantially zero (see FIG. 6). That is, the coefficients KF and KR in the above equation are changed by the changing means 10
According to 2, the vehicle speed is changed based on the vehicle speed, for example, as shown in FIGS. 3 and 4 described above.

Specifically, as shown in FIG. 1, a steering angle sensor 30, a vehicle speed sensor 31, an encoder 32 for detecting the rotational position of the servomotor 20, a front side G sensor 33, and a rear side G
The signal from the sensor 34 is input. In the control unit U, the coefficients KF and KR are changed according to the vehicle speed, and the target value is calculated based on the steering angle θF (the steering angle of the front wheels), the vehicle speed V and the yaw rate using the above formula. The wheel steering angle TGθR is calculated, and a control signal corresponding to the required rear wheel steering amount is output to the servomotor 20. Thus, the encoder 32 constantly monitors whether the operation of the servomotor 20 is properly performed, that is, the rear wheels are controlled under feedback control.
Steering of 2L and 2R is performed.

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

That is, as shown in FIG.
, A front wheel steering angle sensor 35 is added to the vehicle speed sensor 31, a vehicle speed sensor 36 is added to the vehicle speed sensor 31, and a rear wheel steering angle for detecting a mechanical displacement of a member on the relay rod 12 side of the clutch 22 with respect to the encoder 32. Sensor 37 is added
In 30, 31, 32, 35, 36, and 37, the rear wheel steering is performed only when both of the corresponding sensors detect the same value. That is, when the vehicle speed detected by the vehicle speed sensor 31 is different from the vehicle speed detected by another vehicle speed sensor 36 in the sensors 30 to 32 and 35 to 37, for example, the rear wheel 2L is controlled by the control in the fail mode because a failure has occurred. , 2R are held in a neutral position.

The two lateral G sensors 33 and 34 are disposed before and after the center of gravity of the vehicle body with the center of gravity interposed therebetween, and detect the magnitude of the lateral G and are used for detecting the yaw rate.
The current yaw rate n is calculated from the outputs of 33 and 34 by the following equation.

_{n = n- 1 + (G F} -G R) t / l n- 1: previous yaw rate G _F: Output G _R of the front lateral G sensor 33: output t of the rear lateral G sensor 34: measurement interval l: both Note that a yaw rate sensor for directly detecting a yaw rate may be added instead of the lateral G sensor.

For various controls, the control unit U includes a vehicle height sensor 39, a raindrop sensor 40, and a brake switch 4.
1. Signals from the reverse switch 42 and the accelerator switch 43 are input, and although not shown, a signal indicating the presence or absence of power generation is input from the L terminal of the alternator.

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

The control is performed by a main controller 50A and a sub-controller 50B which are linked to each other. Each controller 50A, 50B receives signals from various sensors 30, 37, 39, 40 and the L terminal of the alternator by the analog buffer 51 and Signals are input to each through an A / D converter 52, and signals from the sensors 31, 35, 36 and switches 41, 42, 43 are input to each via a digital buffer 53. The signal from 34 is input to the main controller 50A via another analog buffer 54 and A / D converter 55.

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 a target rear wheel steering angle. The rotation amount of the servo motor 20 is detected 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 and matched in the AND circuits 71 and 72, the clutch 7
3,74 are connected so that the rear wheels can be steered. The comparison is also made in the OR circuit 75, and when the two signals do not match, the warning lamp 76 is turned on.

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

In the figure, 77 is a voltage control circuit having a 5V regulator and resetting the main controller 50A in the event of an abnormality, 78 is a battery, 79 is an ignition switch,
Therefore, 80 is a fuse. Therefore, according to the above configuration, in the low-speed range, in order to limit the steering angle from a practical point of view, the KF is set below 10 km / h.
Is set to 0.35, which is much smaller than 1, and the steering angle θ _F
The change in the rear wheel steering angle θ _R with respect to the change in the steering angle is reduced, and the sense of incongruity from the familiarity with the two-wheel steering is eliminated.

When the speed exceeds 10 km / h, it gradually approaches 1, and in the medium speed range (40 km / h to 80 km / h), which is a normal service range, KF
Is set to approximately 1, so that the slip angle β = 0 is substantially achieved, and the maneuverability is ensured.

Furthermore, in the high speed range exceeding 80 km / h, in order to emphasize the high-speed straight running stability, the rear wheel steering angle by KF is controlled so as to decrease gradually, the change of the steering wheel angle theta _F as the vehicle speed increases theta reversed phase change of the direction of the _R becomes small, the influence due to the change in steering wheel angle theta _F is designed to be smaller.

Further, when the vehicle is traveling backwards, the KF is about 0.35 below 5 km / h, where a small turn is particularly required.
Beyond h, it gradually decreases to ensure running stability.

(Effect of the Invention) As described above, according to the present invention, the coefficient KF is changed to a predetermined value smaller than 1 in the low speed range, to approximately 1 in the medium speed range, and to a value smaller than 1 in the high speed range. Since the coefficient KR is set so that the slip angle of the vehicle is substantially zero in the medium speed range, it is possible to achieve both turning performance in the low speed range and running stability in the high speed range, and furthermore, in the normal range. Maneuverability in a certain medium speed range is also ensured.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention, FIG. 1 is an overall configuration diagram of a rear wheel steering device of a vehicle, FIG. 2 is an enlarged sectional view of a neutral holding means, and FIGS. 3 and 4 show changes in KF and KR. FIG. 5 is a block diagram of a control system, and FIG. 6 is a block diagram of a control unit. U Control unit 30 Steering angle sensor 31, 36 Vehicle speed sensor 33, 34 Side G sensor 35 Front wheel steering angle sensor 101 Steering angle control means 102 Changing means

──────────────────────────────────────────────────続 き Continuing on the front page (56) References Hisao Sato, 3 others, "Kinematic characteristics of front and rear wheel steering vehicles for rear wheel steering by yaw rate feedback", Outline of the presentation at the Traffic Safety and Pollution Research Institute in 1979 , Ministry of Transportation, Traffic Safety and Pollution Research Institute, December 18, 1979, p16-p32 (58) Fields investigated (Int. Cl. ⁶ , DB name) B62D 6/00 B62D 7/14

Claims (1)

(57) [Claims] 1. The formula TGθR = −KF · θF + KR · V · TGθR: target steering angle of the rear wheel θF: steering angle of the front wheel V: vehicle speed: yaw rate KF, KR: the rear wheel is determined based on a coefficient determined by the characteristics of the vehicle. A vehicle rear wheel steering device having a turning control means for turning, comprising: vehicle speed detecting means for detecting a vehicle speed of the vehicle; receiving the output of the vehicle speed detecting means; Value in the medium speed range, it is almost 1.
The coefficient KR is changed to a value smaller than 1 in the high-speed range, and the coefficient KR is set to substantially zero in the medium-speed range.
A rear wheel steering device for a vehicle, comprising: a change unit configured to set the rear wheel steering wheel.