JPH0443831B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a four-wheel steering system for a vehicle that controls the steering of the rear wheels in accordance with the steering of the front wheels. This invention relates to a system that ensures stability and steering stability.

(Prior Art) Conventionally, this type of four-wheel steering system has been used, for example, as disclosed in Japanese Unexamined Patent Publication No. 55-91457, etc. By steering the rear wheels in the opposite direction (opposite phase), the minimum turning radius of the vehicle is reduced, making it easier to turn around in tight spots or park in the garage. By steering the rear wheels in the same direction (same phase) as the front wheels, the phase delay of the cornering force of the rear wheels with respect to the front wheels is shortened, allowing stable lane changes and gentle turns. What has been done is known.

(Problems to be Solved by the Invention) In this conventional vehicle, the steering of the rear wheels is controlled in immediate response to a change in the steering angle of the front wheels accompanying a steering operation. Therefore, when the vehicle is turning, where the front wheel steering angle becomes large, the original purpose described above can be fully achieved, but on the other hand, when driving straight, the rear wheel rotation is also affected by changes in the front wheel steering angle, which corresponds to play in the steering operation. The steering system reacts sensitively and the rear wheels are steered, resulting in
There was a problem that the straight-line stability of the vehicle was hindered.

Therefore, in view of these points, the present invention has been developed to adjust the rear wheel steering angle characteristics so that within the range of extremely small play in the steering angle, that is, the front wheel steering angle, the rear wheel steering angle is maintained in a straight-ahead state regardless of the steering of the front wheels. By setting a predetermined dead zone, the rear wheels are not steered at all even if the front wheels are steered within the range of play in the steering operation when driving straight, thereby improving the straight-line stability of four-wheel steering vehicles. The purpose of this is to ensure stable steering characteristics.

(Means for Solving the Problems) That is, the present invention provides a steering device for steering front wheels, a steering device connected to the steering device,
A rear wheel steering device includes a transmission means that mechanically extracts and transmits the amount of steering of the front wheels, and a rear wheel steering device that steers the rear wheels, and a rear wheel steering device that receives at least a vehicle speed signal and rotates the rear wheels in the same direction as the front wheel steering direction. A four-wheel steering system for a vehicle is equipped with a controller that controls the operation of the rear wheel steering system so that the rear wheels are steered in the same phase, and the rear wheels are steered substantially synchronously from the small steering angle range of the front wheels in a high vehicle speed range. The front wheels are steered in the same direction and in the same phase as the front wheels, while the front wheels are steered within a range corresponding to the amount of play of the steering device, which is set to an extremely small range of the front wheel steering angle corresponding to the straight-ahead state region. The present invention is characterized in that a dead zone setting means is mechanically provided in the rear wheel steering device to absorb the displacement of the transmission means accompanying the steering operation and maintain the rear wheel steering angle in a straight-ahead state.

(Function) With the above configuration, in the present invention, when the vehicle is traveling straight, even if the front wheels are steered within an extremely small range of the front wheel steering angle corresponding to the amount of play of the steering device, the The displacement of the transmission means is absorbed by the dead zone setting means, does not contribute to the steering of the rear wheels at all, and the rear wheel steering angle is maintained in a straight-ahead state. Therefore, it is possible to improve the straight-line stability of the four-wheel steering vehicle. In addition, at high vehicle speeds, the rear wheels are steered in the same direction and phase as the front wheels in substantially synchronization from the small steering angle range of the front wheels. The responsiveness of steering and stability of steering characteristics can be ensured by in-phase steering.

Furthermore, since the dead zone within the play range of the steering device is provided by a mechanical structure,
In addition to obtaining a reliable and reliable dead zone,
It is possible to easily solve problems such as assemblability and ensuring performance due to variations in parts in the mechanical transmission of front and rear wheel steering.

(Example) Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 1 shows the overall configuration of a four-wheel steering device according to an embodiment of the present invention. Reference numeral 1 denotes a steering device for steering left and right front wheels 2, 2, and the steering device 1 includes a steering wheel 3 (handle); A rack and pinion mechanism 4, left and right tie rods 5, 5,
It consists of left and right knuckle arms 6, 6.

On the other hand, 7 is a link-type rear wheel steering device for steering left and right rear wheels 8, 8, and the rear wheel steering device 7
is equipped with a left-right rear wheel steering rod 9 slidably supported on the vehicle body, and left and right knuckle arms 11, 11 are connected to both ends of the rear wheel steering rod 9 via left and right tie rods 10, 10, respectively. The rear wheels 8 are steered by moving the rear wheel steering rod 9 in the axial direction.

The rear wheel steering device 7 is equipped with a transmission mechanism 33 that mechanically extracts and transmits the amount of steering of the front wheels 2, 2, and the steering of the front and rear wheels 2, 8 is performed in conjunction with this transmission mechanism 33. It's becoming like that. That is, the rack and pinion mechanism 4 of the steering device 1
The rack 4a has an L-shaped link 34 supported on the vehicle body.
A first I-shaped link 35 extending in the longitudinal direction of the vehicle body is connected via the rack 4a.
is moved in the longitudinal direction of the vehicle body. One end of a variable lever ratio link 36 extending in the left-right direction of the vehicle body is connected to the rear end of the I-shaped link 35, and the variable link 36 is provided with a movable fulcrum 37 that is movable along the variable link 36. One end of the variable lever ratio link 36 is moved to follow the movement of the I-shaped link 35 using the position of the movable fulcrum 37 as a fulcrum. Further, the front end of a second I-shaped link 38 extending in the longitudinal direction of the vehicle body is connected to the central portion of the variable lever ratio link 36, and the rear end of the I-shaped link 38 is connected to an L-shaped link supported on the vehicle body. The rear wheel steering rod 9 is connected to the rear wheel steering rod 9 through a lever 39, and by rotating the L-shaped link 39 by moving the second I-shaped link 38 in the front-rear direction with the swinging of the variable lever ratio link 36, The left and right rear wheels 8, 8 are steered by moving a rear wheel steering rod 9.

The movable fulcrum 37 of the variable lever ratio link 36 is connected to a threaded member 42 that is threaded onto a threaded rod 41 in the left-right direction of the vehicle body that is rotationally driven by a motor 40.
The movable fulcrum 37 is moved along the variable lever ratio link 36 by moving the threaded member 42 in the lateral direction of the vehicle body by the rotation of the threaded rod 41 in conjunction with the operation of the motor 40. Movable fulcrum 3
7 is moved to the right by the central part of the variable link 36 (the connection part with the second I-shaped link 38) as shown in the figure, the central part of the variable link 36 moves to its one end (the connecting part with the first I-shaped link 38). 35), the second I-shaped link 38 is moved in the same direction as the first I-shaped link 35, and the rear wheels 8, 8 are moved in the same phase as the front wheels 2, 2. On the other hand, when the movable fulcrum 37 is moved between one end of the variable link 36 and the central part, the central part moves in the opposite direction to the one end, so that the second I The I-shaped link 38 is moved in the opposite direction to the first I-shaped link 35 to steer the rear wheels 8, 8 to a phase opposite to that of the front wheels 2, 2, and the movable fulcrum 37 is moved to the center of the variable link 36. When they are aligned, the second I-shaped link 38 stops moving regardless of the movement of one end of the variable link 36, so that the rear wheels 8, 8 are steered by the vehicle body regardless of the steering of the front wheels 2, 2. It is configured to maintain the steering angle θR in the longitudinal direction and make the steering angle θR zero. 43 is for urging and returning the rear wheels 8, 8 to a neutral position (straight traveling state) where the steering angle θR is zero by a pair of opposing springs 44, 44 that engage with the rear wheel steering rod 9. This is a neutral position return mechanism.

Furthermore, 26 is a front wheel steering angle sensor that detects the steering angle θF of the front wheels 2, 2, 27 is a vehicle speed sensor that detects the vehicle speed, and 45 is a rear wheel steering angle sensor that detects the position of the movable fulcrum 37 on the variable lever ratio link 36. Output signals from these sensors 26, 27, and 45 are input to a controller 28 that drives and controls the motor 40, that is, controls the rear wheel steering device 7. As shown in detail in FIG. 2, the controller 28 has a characteristic storage section 29 that stores the characteristics of the rear wheel steering device θR with respect to a preset front wheel steering angle θF. The above characteristics are, for example, the third
As shown in the figure, at low vehicle speeds, the front wheel steering angle θF
In response to an increase from zero, the rear wheel steering angle θR immediately changes from the same phase (the front and rear wheels 2 and 8 are in the same direction) to the opposite phase (the front and rear wheels 2 and 8 are in the opposite direction). On the other hand, at high vehicle speeds, as the front wheel steering angle θF increases, the rear wheel steering angle θR also increases in the same phase; It is set so that the ratio θR/θF of the steering angle θR changes, that is, the steering phase and steering ratio θR/θF of the front and rear wheels 2 and 8 change according to the vehicle speed, and the steering angle θR/θF changes according to the vehicle speed. The system generates a corresponding lateral G and yaw rate.

The controller 28 also stores the output signals from both the sensors 26 and 27 in the characteristic storage section 29.
a target steering angle calculation unit 30 that calculates a target rear wheel steering angle θR in that state by comparing it with a signal from the rear wheel steering angle θR;
The output signal from the target steering angle calculating section 30 is used as the rear wheel steering sensor 45 which indicates the actual position of the movable fulcrum 37.
A first comparator 46 outputs a deviation signal corresponding to the difference from the output signal from the first comparator 46, a triangular wave generating section 47 generates a predetermined triangular wave signal, and a triangular wave signal from the triangular wave generating section 47 is outputted from the third comparator 46. A second comparator 48 that discriminates the magnitude based on the deviation signal from the first comparator 46, and a transistor 49 that turns on in response to the output signal from the second comparator 48 to energize the motor 40. There is. Then, the target turning angle calculation section 30 calculates the target fulcrum position of the movable fulcrum 37 corresponding to the target rear wheel turning angle θR, and the second comparator 48 is set based on the output signal from the target turning angle calculation section 30. By changing the conductivity of the output signal and changing the collector current of the transistor 49, the motor 40 is operated to move the movable fulcrum 37 to the target position, and when the movable fulcrum 37 coincides with the target position, the first comparator 46 changes. When the deviation signal value becomes zero, the motor 40 is stopped and the movable fulcrum 37 is controlled to be held at the target position.

Furthermore, the second I-shaped link 38 is divided into a front side part 38a and a rear side part 38b at the middle part thereof, and a cylinder member 50 extending in the length direction of the link 38 is fixed to the rear end of the front side part 38a. A sliding member 51 attached to the front end of the rear side portion 38b is fitted into the cylinder member 50 so as to be slidable and non-removable so as to keep the front and rear side portions 38a and 38b concentric. When the steering angles θF and θR of the front and rear wheels 2 and 8 are both zero, that is, when the vehicle is running straight, the sliding member 51 is located at the center of the cylinder member 50, and at both the front and rear sides thereof. The stroke amount of each is set to correspond to the amount of play accompanying the steering operation, and therefore the front wheel steering angle θF is within an extremely small range (for example, −1°≦θF
≦1°), the front side 38 of the second I-rod 38
By moving only a and keeping the rear side part 38b in a stopped state, a dead zone is set in the characteristic of the rear wheel turning angle θR with respect to the front wheel turning angle θF so as to keep the rear wheel turning angle θR in a straight forward state. A dead zone setting means 52 is configured.

Therefore, in the above embodiment, when the vehicle is running, the current steering angle, that is, the front wheel turning angle θF, and the vehicle speed are detected by the front wheel turning angle sensor 26 and the vehicle speed sensor 27, respectively, and are input as signals to the controller 28. After receiving these signals, the controller 28 determines the target rear wheel turning angle θR in the driving state by comparing the rear wheel turning angle θR with respect to the front wheel turning angle θF stored in the characteristic storage unit 29.
When the front wheel steering angle θF is zero and the vehicle is traveling straight, the target rear wheel steering angle θR becomes zero, and the movable fulcrum 37 becomes the variable link. The motor 40 of the rear wheel steering device 7 is driven so as to coincide with the center portion of the rear wheel steering device 36. As a result, the movement of the second I-shaped link 38 is stopped regardless of the movement of one end of the variable link 36, and the rear wheels 8, 8 move forward and backward of the vehicle body regardless of the steering of the front wheels 2, 2. The steering angle θR becomes zero, and the vehicle is therefore kept running straight.

At that time, even if the front wheel steering angle θF slightly fluctuates within a predetermined angle range corresponding to play in steering operation, the fluctuation will be caused by the connecting portion (dead zone) between the front and rear side portions 38a and 38b of the second I-shaped link 38. Setting means 5
2), the transmission is cut off and is not transmitted to the rear wheels 8, 8, and the rear wheel steering device 7 does not operate in response to fluctuations in the front wheel steering angle θF within the range of play during steering operation. The rear wheel turning angle θR is kept at zero by the neutral position return mechanism 43, so that the straight-line stability of the vehicle can be improved even with a simple structure.

Further, when the front wheel turning angle θF increases to a predetermined angle or more due to the steering operation for turning, the front and rear side portions 38a of the second I-shaped link 38,
By integrating the rigidity of 38b, the rear wheel turning angle θR is controlled to change in accordance with the change in the front wheel turning angle θF. Therefore, even if there are variations due to manufacturing errors in the rear wheel steering device 7, the variations can be corrected by the dead zone setting means 5.
2, the rear wheels 8, 8 can be accurately steered in accordance with the steering of the front wheels 2, 2, and the steering characteristics of the vehicle can be stably ensured.

In addition, if such a dead zone is set, the front wheel steering angle θF and the rear wheel steering angle θR may not correspond to each other accurately due to variations in manufacturing errors of the various components that make up the rear wheel steering device 7. , even if the front wheel steering angle θF is zero and the rear wheel steering angle θR is assembled with a deviation to an angle other than zero, the deviation is absorbed by the dead zone and the steering angle of the front wheels 2, 2 is The rear wheels 8, 8 can be accurately steered in accordance with the intended steering direction and steering angle, and thus the steering characteristics of the vehicle can be stably ensured.

Further, since the dead zone is provided with a mechanical structure, it can be a reliable and highly reliable dead zone.

Note that the present invention is not limited to a four-wheel steering device including the link-type rear wheel steering device 7 as in the above embodiment.
The present invention can also be applied to four-wheel steering systems equipped with various other types of rear-wheel steering systems.

(Effects of the Invention) As explained above, according to the present invention, the steering device for front wheel steering is mechanically connected to the rear wheel steering device, and the rear wheels are mechanically steered in accordance with the steering of the front wheels. In a vehicle's four-wheel steering system, when the rear wheels are steered in the same phase as the front wheels in a high vehicle speed range, the rear wheels are steered within an extremely small range of the front wheel steering angle, which corresponds to the play of the steering system. By setting a dead zone that maintains the steering angle in a straight line, it is possible to absorb fluctuations in the front wheel steering angle due to play in the steering operation when the vehicle is traveling straight and prevent it from being transmitted to the rear wheel steering mechanism. As a result, the straight-line stability of the four-wheel steering vehicle can be improved. In addition, even if the rear wheel steering angle is shifted to a non-zero angle when the front wheel steering angle is zero due to variations in manufacturing errors in the components of the rear wheel steering device, the shift can be compensated for by the dead zone. It is possible to accurately obtain the steering direction and steering angle of the rear wheels relative to the front wheels.
Stable steering characteristics of the vehicle can be ensured. Furthermore, since the dead zone is provided mechanically, it is possible to provide a reliable and highly reliable dead zone.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention; FIG. 1 is a schematic diagram of the overall configuration, FIG. 2 is an explanatory diagram of the controller, and FIG. 3 is a diagram showing the rear wheel steering angle characteristics with respect to the front wheel steering angle stored in the controller. It is an explanatory diagram showing an example. 1...Steering device, 2...Front wheel, 7...
Rear wheel steering device, 8...Rear wheel, 9...Rear wheel steering rod, 26...Front wheel steering angle sensor, 27...Vehicle speed sensor, 28...Controller, 29...Characteristic storage unit, 33...Transmission Mechanism, 36... Lever ratio variable link, 37... Movable fulcrum, 38... Second I type link, 40... Motor, 50... Cylinder member, 5
1...Sliding member, 52...Dead band setting means.

Claims (1)

[Claims] 1. A steering device that steers the front wheels, a transmission means connected to the steering device that mechanically extracts and transmits the amount of steering of the front wheels, and a rear wheel steering device that steers the rear wheels, A four-wheel steering system for a vehicle, comprising: a controller that receives a signal and controls the operation of the rear wheel steering system so that the rear wheels are steered in the same phase as the front wheels in the same direction; In the vehicle speed range, the rear wheels are steered in the same direction and phase as the front wheels in substantially synchronization from the small steering angle range of the front wheels, while the front wheel steering angle corresponding to the straight-ahead state range is extremely small. A dead zone setting means is provided in the rear wheel steering device to maintain the steering angle of the wheels in a straight-line state by absorbing the displacement of the transmission means accompanying the steering operation of the front wheels within a range corresponding to the amount of play of the steering device set in the range. A four-wheel steering device for a vehicle, characterized in that it is mechanically provided in a vehicle.