JPS6365549B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a device for steering both the front wheels and the rear wheels of a four-wheeled vehicle such as an automobile, that is, a four-wheel steering device that steers both the front wheels and the rear wheels by steering the front wheels, which are steered wheels. . Conventionally, steering devices in four-wheeled vehicles steer only the front wheels, and the rear wheels tend to steer actively, although they do some toe-in or toe-out depending on the driving situation, regardless of the steering of the front wheels. I haven't gotten used to it. However, recently, a four-wheel steering device has been proposed in which both the front wheels and the rear wheels are steered (for example, Japanese Patent Laid-Open No. 55-91458), and research on this type of device is being carried out. According to the four-wheel steering system, convenient maneuvering that was previously impossible and driving with improved steering performance are possible depending on various driving conditions of the vehicle. for example,
When maneuvering a vehicle at extremely low speeds, such as parallel parking or parking in a garage, by steering the rear wheels in the opposite direction to the front wheels (this is called anti-phase), it is possible to significantly change the direction of the vehicle. This makes it possible or easy to park in narrow spaces, which was previously impossible or extremely difficult. Also, U
This is also advantageous when turning, since the minimum turning radius can be made small. Furthermore, by steering the rear wheels in a phase opposite to that of the front wheels, the difference between the inner wheels can be minimized or eliminated, which is advantageous when turning a narrow corner. Also,
When steering a vehicle at such extremely low speeds, if the rear wheels are steered in the same direction as the front wheels (this is called in-phase), it is possible to move the entire vehicle in parallel, making it easier to park or park the vehicle. It is often useful when On the other hand, when changing lanes while driving at medium to high speeds, if four-wheel steering is performed in the same phase, lateral force is applied to the front and rear wheels at the same time, making it possible to change lanes smoothly without phase lag, thereby suppressing yawing. This allows you to change lanes at high speed without fear. Furthermore, when cornering, the direction of the vehicle can be effectively changed by steering the rear wheels in opposite phases. Furthermore, when driving straight ahead, if the rear wheels are steered in a direction that counteracts the effect of external disturbances such as crosswinds, stable driving can be maintained against external disturbances, and stable high speeds can be achieved. It is also possible to obtain straightness. Additionally, even if you accelerate or decelerate while keeping the steering angle of the front wheels constant during a turn, the steering angle of the rear wheels will change in accordance with the acceleration or deceleration, so that you will not deviate from your course and make a stable turn. It can also be done. In other words, in conventional vehicles, the steering characteristics are adjusted to slightly understeer in order to maintain straight-line stability, and when accelerating during a turn, there is a tendency for the vehicle to deviate outward from the course. By doing so, the deviation can be corrected and stable turning can be achieved. In terms of comfort, it is possible to obtain a smaller minimum turning radius with the same wheelbase, so the wheelbase can be increased, and in addition to this, the actual steering angle of the front wheels can be reduced. It has many advantages, including the ability to experiment with new designs. As described above, four-wheel steering has many practical advantages and is extremely useful. Regarding this four-wheel steering, various specific configurations have been proposed so far to effectively steer the rear wheels. For example, a system in which four-wheel steering is performed in opposite phases at low speeds and in the same phase at high speeds (Japanese Patent Application Laid-open No. 1983-1999)
91457), the same phase when the steering angle of the front wheels is small, and the opposite phase when it is large (Japanese Patent Application Laid-open No. 1983-
No. 5270) The rear wheels are steered in proportion to the steering angle of the front wheels only when the steering angle of the front wheels is below a predetermined range, and when the steering angle of the front wheels is above a predetermined range, the rear wheels are steered regardless of the steering angle of the front wheels. Fixed angle (Unexamined Japanese Patent Publication No. 1983-
163969) etc. are known. These four-wheel steering devices, when the vehicle speed is low,
Or, based on the empirical rule that when the front wheel steering angle is large, it is often necessary to change the direction of the vehicle significantly, and when the vehicle speed is high or the front wheel steering angle is small, it is often desired to make a slight lateral movement. The rear wheels are always steered in the desired direction. However, when the vehicle is actually running, there are cases where it is desired to steer the rear wheels at an angle that is different from the angle that is automatically determined based on the vehicle speed and the front wheel steering angle. For example, when parking in a garage or parallel parking, if the rear wheels are turned significantly in the same phase as the front wheels (by an angle equal to the steering angle of the front wheels), the vehicle will move diagonally in parallel, and This is extremely convenient when parking or when you want to move the vehicle laterally in a narrow garage. Also, when parking in a narrow alley near a wall, etc., if the rear wheels are steered in the same phase as the front wheels, it is extremely easy to do so without having to repeatedly turn the steering wheel. It is possible and convenient. In this case, there is no need to worry about the vehicle body coming into contact with a wall or the like, and the vehicle can be parked very easily and moved away from the wall. This is a common occurrence in actual driving, and it would be convenient if the entire vehicle body could be moved laterally, especially when parking in a busy area in a city. Conversely, there are times when it is desired to steer the rear wheels in the opposite phase. That is, if the rear wheels can be steered in opposite phases, the minimum turning radius can be reduced, making it easier to park the vehicle, etc., and the difference between the inner wheels when turning can be reduced, making it easier to turn around narrow corners, which is convenient. Furthermore, in the past, with the exception of special vehicles, vehicles were usually steered by steering only the front wheels, and it was difficult for drivers to suddenly drive a four-wheel steering vehicle after steering. Because the trajectory of the wheels is different to some extent and the behavior of the car is also different, the driving sensation may be unfamiliar and may feel strange at first, and some people may prefer conventional steering using only the front wheels. Therefore, if the driver can freely select either the 4-wheel steering mode or the 2-wheel (front wheel) steering mode, that is, the zero-phase mode, it would be convenient for the driver and avoid unfamiliar modes. This also reduces the psychological burden and is favorable from a safety standpoint. Taking the above points into consideration, the driver can arbitrarily set automatic control mode, same-phase fixed mode, opposite-phase fixed mode, and zero-phase fixed mode (two-wheel steering mode).
A four-wheel steering system is conceivable, but if the driver were to be able to select one at his/her discretion, it would be possible to use a four-wheel steering system while driving, especially while driving at medium to high speeds, for example, when changing from automatic control mode to fixed If the fixed mode is in opposite phase, the car body will be steered greatly for a small front wheel steering angle, and if the fixed mode is in the same phase, the car will move laterally when cornering, and if the fixed mode is in zero phase. Even in this case, there is a problem in that the vehicle body posture changes, which is an undesirable characteristic for driving the vehicle. In view of the above-mentioned problems, the present invention enables selection of an automatic control mode in which the rear wheel steering angle characteristic relative to the front wheel steering angle changes depending on the vehicle speed, and a fixed mode in which it does not change. An object of the present invention is to provide a four-wheel steering system that solves the above-mentioned problems caused by the conversion from the control mode to the fixed mode. The four-wheel steering device according to the present invention includes a steering device that steers the front wheels, a rear wheel steering device that steers the rear wheels, a vehicle speed sensor, and a rear wheel steering angle characteristic that changes with respect to the front wheel steering angle depending on the vehicle speed. There are multiple settings, and at least in the high speed range, the characteristics of the rear wheel steering angle with respect to the front wheel steering angle are controlled to be in the same phase,
and an automatic control mode in which the characteristic is set such that the increase rate of the rear wheel steering angle relative to the front wheel steering angle in a region where the front wheel steering angle is large is smaller than the increase rate in a region where the front wheel steering angle is small; a controller that has a fixed mode that sets this characteristic regardless of the vehicle speed, and selects these two modes to control the rear wheel steering device according to the front wheel steering angle;
mode selection means for instructing the controller which mode to select; and prohibition means connected to the output of the vehicle speed sensor for prohibiting the mode selection means from switching from the automatic control mode to the fixed mode when the vehicle speed exceeds a set vehicle speed. It is characterized by consisting of. According to the four-wheel steering system configured as described above, even if the driver accidentally or intentionally operates the mode selection means while driving at medium to high speeds (vehicle speed higher than a predetermined value), the automatic control mode can be switched from the fixed mode to the fixed mode. 4-wheel steering control, which is preferable for safety, can be performed without switching to the four-wheel steering control. In the automatic control mode described above, the rear wheels are controlled in the same phase as the front wheels at least in the high speed range, so at high vehicle speeds, lateral acceleration can be obtained with good responsiveness and lane changes can be made quickly. In addition, in controlling the rear wheels in the same phase as the front wheels in the high speed range, the ratio of increase in the rear wheel steering angle to the front wheel steering angle is small in the large front wheel steering angle region, so the direction of the vehicle is controlled. If the front wheels are steered significantly to change the front wheels, the front wheels will be steered significantly inward relative to the rear wheels.
Good turning performance can be obtained. Furthermore, as the fixed mode, for example, the rear wheels are largely steered in the same phase with a constant steering ratio (for example, 1) regardless of the vehicle speed, and the vehicle body is moved diagonally (the same phase is fixed). mode), a mode that allows the vehicle to turn in a small direction by steering the rear wheels largely in the opposite phase with a constant steering ratio (e.g. -1) regardless of vehicle speed (reverse phase fixed mode), or It is possible to adopt a system that maintains the steering ratio at zero regardless of the 2WS state (zero phase fixed mode). Note that if the same phase locking mode is selected at low speeds, diagonal movement facilitates side-to-side parking or parallel parking, and if the opposite phase locking mode is selected at low speeds, the turning radius becomes smaller, making it easier to park the vehicle in a garage. Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a graph showing the characteristics of the rear wheel steering angle θ _R with respect to the front wheel steering angle θ _F in an embodiment of the four-wheel steering system of the present invention. In the example of FIG. 1, an example of the fixed mode is shown by a solid line, and an example of the automatic control mode is shown by a dashed line. In addition,
The characteristic of the rear wheel turning angle θ _R with respect to the front wheel turning angle θ F is the same whether θ _F is the right steering angle or the left steering angle, so _only one is shown in the figure. In the case of the above automatic control mode, the ratio of the rear wheel steering angle θ _R to the front wheel steering angle θ _F (steering ratio θ _R /θ _F ) generally increases as the vehicle speed increases, and increases as the vehicle speed decreases. It becomes smaller as the speed increases, and becomes negative (opposite phase) at extremely low speeds. Furthermore, in this embodiment, in the medium to high speed range, when the front wheel steering angle θ _F becomes larger than a predetermined value, the rear wheel steering angle θ _R does not increase even if the front wheel steering angle θ _F increases, and remains constant at each vehicle speed. It's starting to happen. In other words, the steering angle θ _R of the rear wheels
After the front wheels are steered to a certain extent, they become constant and are not steered any further. This is based on the empirical rule that the front wheel steering angle θ _F is large when the vehicle wants to change its direction. This is to make it easier to change the direction of the vehicle by steering. Examples of fixed modes include in-phase fixed mode,
Examples of zero-phase fixed mode and anti-phase fixed mode are shown, and in the same phase fixed mode example, the rear wheel steered angle θ _R increases at a constant rate as the front wheel steered angle θ _F increases.
increases, and in the case of the zero-phase fixed mode example, the rear wheel turning angle θ _R is always zero regardless of the size of the front wheel turning angle θ _F , and in the case of the anti-phase fixed mode example, the front wheel turning angle θ _F As the rear wheel turning angle θ R increases, the rear wheel turning angle θ _R decreases. For example, the change between the automatic control mode and the fixed mode can be made freely by operating a switch when the vehicle speed is lower than a predetermined set vehicle speed, and automatically when the vehicle speed is higher than the predetermined set vehicle speed. is configured to go into automatic control mode. Next, with reference to FIGS. 2 and 3, a specific configuration of the four-wheel steering system having two modes as in the above embodiment will be explained. FIG. 2 shows an example using a hydraulic system, and FIG. 3 shows an example using a link mechanism. In the configuration shown in FIG. 2, front wheels 1, 1, rear wheels 2,
An output 4a of a front wheel steering angle sensor 4 which is mechanically separated from 2 and detects the steering angle θ _H of the steering wheel 3.
is input into the controller 10 of the rear wheel steering device,
The rear wheels 2, 2 are steered by this input signal. As is well known, the front wheel steering device moves a rack 6 in the width direction of the vehicle (indicated by arrow A) using a pinion 5 fixed to a steering shaft 3A to which a steering wheel 3 is fixed. The knuckle arms 8, 8 of the left and right front wheels 1, 1 are connected to the left and right front wheels 1, 1 through tie rods 7, 7 that are continuous at both ends.
are rotated around their shafts 8a, 8a to rotate the front wheels 1,
1 to the left and right. That is, when the steering wheel 3 in the figure is rotated in the direction of arrow L, the steering shaft 3A is rotated in the direction of arrow L, the pinion 5 is also rotated in the L direction, and the rack 6 is moved in the L direction. As a result, the knuckle arms 8, 8 of the left and right front wheels 1, 1 rotate in the L direction via the links 7, 7, and the front wheels 1, 1 rotate in the L direction via the links 7, 7.
1 in the L direction around the shafts 8a, 8a of the knuckle arms 8, 8, and steer it to the left. At this time,
The steering angle sensor 4 outputs as an output signal 4a that the steering wheel 3 has rotated by an angle θ _H in the L direction, and this is sent to the controller 1 of the rear wheel steering device.
input to the front wheel turning angle input 10A of 0. The controller 10 is supplied with power by a power source 11, and in addition to the front wheel steering angle input 10A, a control mode signal input 10B and a rear wheel steering angle sensor 13 are provided.
The hydraulic main pump 21 is equipped with a feedback input 10C connected to a steering direction output 10D connected to a solenoid 20 that controls the steering direction of the rear wheels, and a hydraulic main pump 21 that controls the steering angle θ _R of the rear wheels. Hydraulic pump motor output 10 connected to motor 21A
It is equipped with E. Output from the vehicle speed sensor 12,
The comparator 50A compares the output adjusted to the set vehicle speed level by the variable resistor 50B, and when the output from the vehicle speed sensor 12 is smaller than the set speed level, that is, when the vehicle speed is less than the set speed.
A HIGH level signal is output from the comparator 50A when the output from the vehicle speed sensor 12 is higher than the set speed level, that is, when the vehicle speed is higher than the set speed, and this signal and the signal from the mode selection switch 14 are ANDed. A control mode signal 10B as shown in Table 1 is sent to the controller 10 from the AND gate 50C.

[Table] The hydraulic main pump 21 includes a pump 21B that discharges oil (hydraulic oil), and this pump 21B is connected to a hydraulic actuator 23 via a steering direction switching valve 22, and this valve 22 and the pump Between 21B and 21B, the oil outgoing path 24A and the oil return path 24C are short-circuited, and an orifice 2 is installed on the way.
4b is provided, and an oil reservoir 25 is provided in the middle of the oil return path 24C.
are arranged. The steering direction switching valve 22 is connected to the oil outgoing path 24A.
and a valve part consisting of two inlets connected to the oil return path 24C and two outlets communicating with the inlets,
There are three valve parts 22A, reverse 22B, and stop 22C that can be switched in parallel, and by operating the solenoid 20, these three valve parts 22A, 22
Either one of B and 22C is the oil outgoing path 24.
A, it is designed to be connected to the return route 24C.
The two outlets of this valve 22 are connected to a right oil passage 23R and a left oil passage 23L of a hydraulic actuator 23, respectively, and these right oil passage 23R and left oil passage 23L are connected to the outgoing path 24A through this valve 22. It is connected to the return route 24C. Due to the pressure difference applied to the hydraulic actuator 23 and the right and left oil passages 23R, 23L, the rod 26, which is its output shaft, is moved in the width direction of the vehicle (indicated by arrow B), and the output shaft is moved to the rear via the tie rods 27, 27. The knuckle arms 28, 28 of the wheels 2, 2 are rotated around their shafts 28a, 28a, thereby steering the rear wheels 2, 2 left and right. In the illustrated example, when the front wheels 1, 1 are steered in the left direction L and the rear wheels 2, 2 are steered in the same phase as the front wheels 1, 1, the steering direction switching valve 22 is set to the positive 22A position. The oil flows from the outgoing path 24A through the orifice path 24B to the return path 24C, and returns to the pump 21B via the reservoir 25. This results in
The pressure in front of the orifice 24b, that is, on the outward path 24A side, becomes high, and the pressure behind the orifice 24b, that is, on the return path 24C side, becomes low, and the valve 22
The pressure in the right oil passage 23R becomes higher than the pressure in the left oil passage 23L through the positive 22A portion of the hydraulic actuator 23.
is driven in the L direction. The amount of drive at this time is determined by the amount of current input to the main pump motor 21A. As a result, the rear wheels 2, 2 are steered in the left direction L via the tie rods 27, 27, and the rear wheels 2, 2 are steered in the same phase as the front wheels 1, 1. When the front wheels 1, 1 are steered to the right and the rear wheels 2, 2 are steered in the same phase as the front wheels 1, 1, the steering direction switching valve 22 is set to the reverse 22B position, and the right oil The pressure relationship between the passage 23R and the left oil passage 23L is reversed to that described above, and the actuating rod 26 is driven rightward. In addition, when steering the rear wheels 2, 2 in the opposite phase to the front wheels 1, 1, the correspondence between the steering direction and the forward direction 22A and reverse direction 22B of the steering direction switching valve 22 is reversed from the above-mentioned case of the same phase. That is, when steering the front wheels 1, 1 to the left, it is set to reverse 22B, and when steering the front wheels 1, 1 to the right, it is set to forward 22A. When the steering angle θ _R of the rear wheels 2, 2 is set to zero, the stop 22C portion of the valve 22 is connected to the oil passage to cut off the communication between the pump 21B and the hydraulic actuator 23, and the hydraulic actuator 23 The pressure difference between the left and right oil passages 23L and 23R is eliminated, and the actuating rod 26 is set in a neutral position. At this time, in order to ensure that the actuating rod 26 is set in the neutral position, the actuating rod 26 is
It is desirable to apply a set load to the holder so that it is mechanically biased to the neutral position. The steering direction and the magnitude of the steering angle of the front wheels 1, 1 are input to the controller 10 by the output 4a of the front wheel steering angle sensor 4, and the rear wheels 2, 2 are inputted to the controller 10 by the output 4a of the front wheel steering angle sensor 4. The controller 10 determines whether to set the phase or the opposite phase according to the vehicle speed detected by the vehicle speed sensor 12 and according to a preset vehicle speed correspondence pattern. 4 using a hydraulic actuator like the one above
According to the wheel steering device, the rear wheels can be smoothly steered without applying a special load to the steering wheel for four-wheel steering, which is advantageous in practice. However, hydraulic equipment includes motors, pumps,
In addition, heavy and costly parts such as hydraulic actuators and control valves are required, which increases the weight of the vehicle and complicates manufacturing assembly, leading to high costs. Not suitable. Therefore, a four-wheel steering system using a simple link mechanism may be advantageous in practice. An example of this type of link type mechanism will be explained below with reference to FIG. In the configuration of FIG. 3, the same members as those in the configuration of FIG. 2 are given the same reference numerals, and their explanations will be omitted. In the link type configuration shown in FIG. 3, a slot 6A for sliding engagement is provided in a part of the rack 6 that is moved in the width direction of the vehicle by the steering wheel 3, and the rear wheels 2, 2 are steered from this slot 6A. Slot 41A provided in rod 41 for sliding engagement
The front wheels 1 and 1 are connected by a link mechanism between the front wheels 1 and 1.
The rear wheels 2, 2 corresponding to the steering angle θ _F are steered in a desired direction by a desired steering angle θ _R . This link mechanism has a first L-shaped lever 3 that is pivotally supported on a fixed shaft 31a and has one end 31A that is slidably engaged with a sliding engagement slot 6A on the front wheel side.
1. A connecting lever 3 whose one end 32A is rotatably connected to the other end 31B of the first L-shaped lever 31.
2. One end 33 is attached to the other end 32B of this connecting lever 32.
A swinging lever 33 with the other end 33B pivotally supported on a fixed shaft 33a, and one end 34A of the swinging lever 33 rotatable on a connecting shaft between the one end 33A of the swinging lever 33 and the other end 32B of the intermediate lever 32. A control lever 34 connected to the control lever 34 is slidably engaged in the vicinity of the free end of the control lever 34, and is pivotally supported with a rotation shaft 35A on a feed sleeve 36 screwed into a screw rod 37. A motor 3 for rotating the receiving sleeve 35 and the screw rod 37.
8. A connecting lever 39 whose one end 39A is pivotally supported by a shaft support provided at an intermediate position of the control lever 34, and one end 40A is connected to the other end 39B of this connecting lever 39, and the other end 40B is connected to the rear wheel side. The second slot 41A is slidably engaged with the slot 41A for sliding engagement.
It consists of an L-shaped lever 40. The motor 38 is connected to a controller 50 and driven by the output of the controller 50.
This controller 50 is supplied with power from a power source 51 and receives the output of an AND gate 50C.
This AND gate 50C has a variable resistor 50B that adjusts the output of the vehicle speed sensor 52 and the set speed level.
A signal obtained by comparing the output of the mode selection switch 54 with the output of the mode selection switch 54 is input, and the control signal shown in Table 1 is sent to the controller 50 from the AND gate 50C. Further, a potentiometer 53 is disposed near the screw rod 37 to feed back the position of the feed sleeve 36 screwed onto the screw rod 37 to the input of the motor 38, and controls the position of the feed sleeve 36. It's becoming like that. Furthermore, the output of a steering angle sensor 56 that detects the steering angle θ _H of the steering wheel is input to the controller 50 . According to the four-wheel steering device equipped with the link mechanism described above, when the steering wheel 3 is rotated to the left (in the direction of arrow L), the pinion 5, rack 6, tie rods 7, 7, knuckle arms 8, 8, front wheels 1, 1 all rotate or move in the direction of arrow L, and at the same time steer the front wheels 1, 1 to the left, the first
The L-shaped lever 31 is rotated around the fixed shaft 31a.
The swing lever 33 is rotated in the L direction around the fixed shaft 33a via the intermediate lever 32, and the control lever 34 receives the sleeve 35.
The connecting lever 39 is moved in the L direction, and at the same time, the second L-shaped lever 40 is rotated in the L direction to move the steering rod 41 of the rear wheels 2, 2 in the L direction. This causes the rear wheels 2, 2 to be steered to the left in the same phase. When the controller 50 selects the control mode shown in Table 1, the motor 38 is driven to move the feed sleeve 36 downward (to the left of the vehicle) in the figure.
The feed sleeve 36 is connected to one end 39A of the connecting lever 39.
When the control lever 34 swings around the rotation axis 35A of the receiving sleeve 35, the connecting lever 39 does not move forward or backward (in the left-right direction in the figure) when it reaches the position shown in FIG. Not done. When the receiving sleeve 35 is further moved downward by the drive of the motor 38 and exceeds the position of the one end 39A of the connecting lever 39, the swinging of the control lever 34 in the same direction as above (L direction) causes the connecting lever 39 to move as described above. On the contrary, move it forward. This is because the control lever 34 swings around the pivot shaft 35A of the receiving sleeve 35. Therefore in this case the third L-shaped lever 40
rotates in the direction of arrow R, the steering rod 41 of the rear wheels 2, 2 moves in the direction of arrow R, the rear wheels 2, 2 are steered to the right, and four-wheel steering with opposite phases is performed. It turns out. In this way, by driving and controlling the motor 38 with the output of the controller 50, the receiving sleeve 35 is moved via the sending sleeve 36, thereby changing the position of the pivot axis of the control lever 34. As a result, the direction of steering of the rear wheels 2, 2 can be changed by changing the moving direction of the connecting lever 39. Furthermore, by controlling the distance of movement of the receiving sleeve 35, the magnitude of the steering angle θ _R of the rear wheels 2, 2 in the same phase and in the opposite phase can also be changed. By the output of the controller 50, the front wheels 1,
It becomes possible to arbitrarily control the direction and magnitude of the steering of the rear wheels 2, 2 in accordance with the steering of the rear wheels 1. For example, the controller 50 includes a vehicle speed sensor 5.
2. Since the output from the steering angle sensor 56 is input, when the automatic control mode is selected, steering is performed according to the magnitude of the steering angle θ _F of the front wheels 1, 1 via the above link. It is possible to control the magnitude (including the direction) of the steering angle θ _R of the rear wheels 2, 2, which can be controlled according to the characteristics of the steering ratio in the automatic control mode described in the above embodiment. In addition, when the fixed mode is selected, if the fixed mode is the same phase fixed mode, only at _low speeds, for example, the wheels ₂ 2, it becomes possible to move the vehicle laterally regardless of the vehicle speed. Of course, in the case of the reverse phase fixed mode, only at low speeds, for example, the rear wheels 2, 2 are steered by a steering angle - θ _R , which is equal in magnitude to the steering angle θ _F of the front wheels 1, 1 and opposite in direction. However, in the case of the zero phase fixed mode, the steered angle θ _R of the rear wheels 2, 2 can be made zero regardless of the steered angle θ _F of the front wheels 1, 1 only at low speeds. Note that the control characteristics in the in-phase and anti-phase fixed modes are not necessarily limited to linear ones as shown in FIG. 1, but may be in a specific curved pattern. In addition, the control characteristic pattern in the automatic control mode is also
This is not limited to the example shown in the figure, but is a vehicle speed sensitive type in which multiple settings are made such that the rear wheel steering angle characteristics relative to the front wheel steering angle change depending on the vehicle speed, and the above characteristics are the same at least in the high speed range. If the high-speed range in-phase characteristic is set such that the increase rate of the rear wheel steering angle with respect to the front wheel steering angle is smaller in the region where the front wheel steering angle is large than in the region where the front wheel steering angle is small. Any kind of thing is fine. In this way, even with the link type configuration shown in FIG. 3, it is possible to realize the rear wheel turning angle characteristics with respect to the front wheel turning angle as in the above-described embodiment. In particular, this link type mechanism is lighter in weight than a hydraulic type, has a simpler structure, is easier to assemble, and can be manufactured at a lower cost, making it suitable for small vehicles. As explained in detail above, the four-wheel steering system of the present invention has the above-mentioned automatic control mode and fixed mode, and is configured to prohibit switching from the automatic control mode to the fixed mode above a certain set vehicle speed. Therefore, when driving at medium to high speeds, even if the mode selection switch is operated by mistake, the fixed mode will not be set. In other words, sudden changes in rear wheel steering due to mode switching are prevented, and four-wheel steering is preferred for safety. can be controlled.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of automatic control mode and fixed mode in the four-wheel steering system of the present invention, FIG. 2 is a schematic diagram showing an example of the four-wheel steering system of the present invention using hydraulic pressure, and FIG. 1 is a schematic diagram showing an example of a four-wheel steering device of the present invention using a link mechanism. 1... Front wheel, 2... Rear wheel, 3... Steering wheel, 4, 56... Steering angle sensor, 5... Pinion, 6... Rack, 7, 27... Tie rod, 8, 28... Knuckle arm, 10,50...
... Controller, 12, 52 ... Vehicle speed sensor, 1
4... Second mode selection switch, 20... Solenoid, 21... Main pump, 22... Rear wheel steering direction switching valve, 23... Hydraulic actuator,
25... Reservoir, 26... Rear wheel steering rod,
31... First L-shaped arm, 32... Intermediate lever, 33... Rocking lever, 34... Control lever, 34A... Pivotal support, 35... Receiving sleeve, 35A... Rotating shaft, 36... ...feeding sleeve,
37... Screw rod rod, 38... Drive motor, 39... Connection lever, 40... Second L-shaped lever, 41... Rear wheel steering rod, 50A... Comparator, 50B... Variable resistance, 50C... …
AND gate.

Claims (1)

[Claims] 1 A steering device that steers the front wheels, a rear wheel steering device that steers the rear wheels, a vehicle speed sensor, and a plurality of settings such that the rear wheel steering angle characteristics relative to the front wheel steering angle change depending on the vehicle speed, and at least a high speed The characteristics of the rear wheel steering angle relative to the front wheel steering angle are controlled to be in the same phase in the region where the front wheel steering angle is large. There is an automatic control mode that sets the increase rate to be smaller than the rate of increase in a small area, and a fixed mode that sets this characteristic regardless of the vehicle speed. A controller that controls the steering angle according to the front wheel turning angle, a mode selection means that instructs the controller which mode to select, and a vehicle speed sensor output.
A four-wheel steering system for a vehicle, comprising prohibition means for prohibiting the mode selection means from switching from the automatic control mode to the fixed mode.