JPH02162164A - Four-wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To obtain optional steering property by selecting the first control mode which steers rear wheels in the same phase as front wheels with the increasing ratio of the rear wheels steering angle in inverse proportion to the magnitude of the front wheel steering angle and the second control mode with a different characteristic. CONSTITUTION:A controller 10 controls the steering angle of rear wheels 2 via a solenoid 20, a selector valve 22, and a hydraulic actuator 23 according to the first or second control mode selected in response to the steering angle of front wheels 1 by a steering angle sensor 4. When the first control mode of automatic control is selected by selector switches 14A-14D, rear wheels 2 are steered according to the first control characteristic which steers rear wheels 2 in the same phase as front wheels 1 with the increasing ratio of the rear wheels steering angle in inverse proportion to the magnitude of the front wheel steering angle in the high-speed area by a car speed sensor 12. On the other hand, in the second control mode, one of control characteristics including the fixed same phase, fixed opposite phase, and two-wheel steering can be selected. The running stability and turning property at a high speed and the high- dimension steering property in the second control mode can be secured.

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-wheel vehicle such as an automobile, that is, a four-wheel steering system that steers the rear wheels as well as the front wheels by steering the front wheels, which are steering wheels. It is related to the device.

Conventionally, steering devices in four-wheeled vehicles steer only the front wheels, and although the rear wheels may toe in or out to some extent depending on the driving situation, regardless of the steering of the front wheels, they do not actively steer the rear wheels. is not. However, recently, a four-wheel steering device has been proposed in which both the front wheels and the rear wheels are steered, and research on this type of device is being carried out (for example, in Japanese Patent Application Laid-Open No. 55-91458).

The four-wheel steering system enables convenient maneuvering that was previously impossible, as well as driving with improved steering performance, depending on the 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, it is possible to significantly change the direction of the vehicle by steering the rear wheels in the opposite direction to the front wheels (this is called anti-phase). This makes it possible or convenient to park in tight spaces, which was previously impossible or extremely difficult. Further, in a U-turn, the minimum turning radius can be made small, which is advantageous. 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. In addition, when steering a vehicle at 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 and park. It is often convenient when parking in the garage.

On the other hand, when changing lanes while driving at medium to high speeds,
By performing four-wheel steering 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. At this time, yawing is suppressed, so you can change lanes at high speed without fear. can be done. 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, one that steers the four wheels in opposite phases at low speeds and the same phase at high speeds (Japanese Patent Laid-Open No. 55-91457), and one that steers the four wheels in the same phase when the front wheel steering angle is small and in opposite phases when it is large ( (Japanese Patent Application Laid-Open No. 56-5270) 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 regardless of the steering angle of the front wheels when the steering angle is above the predetermined range. The steering angle of the rear wheels is constant (Japanese Patent Laid-Open No. 58-16
No. 3989), etc. are known.

These four-wheel steering devices often require a large change in the direction of the vehicle when the vehicle speed is low or the front wheel steering angle is large, and a slight lateral change when the vehicle speed is high or the front wheel steering angle is small. The system always steers the rear wheels in the desired direction based on the empirical rule that there are many cases where a vehicle wants to move.

However, when the vehicle is actually running, there may be 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 or the front wheel steering angle. For example, when parking in a garage or parallel parking, the four-wheel steering system described above may cause the vehicle speed to be extremely low, or the front wheels to be steered at an extremely large angle, resulting in the rear wheels being steered very little or only in the opposite phase. This means that they will not be steered, but depending on the situation, you may want to steer them largely to the same phase. In other words, in such a case, if the rear wheels are steered largely 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, making it difficult to parallel park or narrow garages. This is extremely convenient when you want to move the vehicle laterally inside the vehicle. Also, when parking close to a wall in a narrow alley, you can
If the rear wheels are steered in the same phase as the front wheels, it is very easy to move the vehicle closer to the other side without having to repeatedly turn the steering wheel, which is very 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 and outer wheels when turning can be reduced, making it easier to turn around narrow corners, which is convenient.

In view of such practical demands, the present invention provides a four-way control system that allows for the selection of a second control mode that is arbitrarily different depending on the driver's request, in addition to the automatic first control mode that corresponds to the driving state. The object of the present invention is to provide a wheel steering device.

A four-wheel steering device according to the present invention includes: a steering device that steers front wheels; a rear wheel steering device that steers 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. At least in the high speed range, the characteristics of the rear wheel steering angle relative to the front wheel steering angle are controlled to be in the same phase, and the characteristics are set to vary with respect to the front wheel turning angle in a region where the front wheel turning angle is large. a first control mode in which rear wheel steering is controlled according to a first control characteristic set such that the increase rate of the steering angle is smaller than the increase rate in a region where the front wheel steering angle is small; control means for controlling the rear wheel steering device by selecting one of the second control modes for controlling rear wheel steering according to different second control characteristics; It is characterized by comprising a selection means for selecting either one.

The second control mode includes, for example, control in which 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 in the lateral direction. A fixed mode in which the wheels are steered in opposite phases to perform control to improve the turning performance of the vehicle body, a two-wheel steering mode in which the rear wheels are always in zero phase, etc. can be adopted.

According to the four-wheel steering system for a vehicle according to the present invention configured as described above, the first control mode is controlled according to the first control characteristic as described above, and the second control mode is controlled according to the first control characteristic as described above, and The driver can appropriately select the second control mode in which control is performed according to the control characteristics using the selection means as necessary, and therefore can perform various maneuvers according to the control mode corresponding to various driving demands.

Furthermore, when the first control mode is selected, 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 sensitively and with good responsiveness. It is possible to change lanes and obtain good driving stability, and when controlling the rear wheels in the same phase as the front wheels in the high speed range, the increase ratio of the rear wheel steering angle to the front wheel steering angle is the large front wheel steering angle. Since the steering wheel is designed to be small in the area, if the front wheels are steered significantly to change the direction of the vehicle, the front wheels will be steered largely relative to the rear wheels, resulting in good turning performance. be able to.

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

In the embodiment described below, two control modes are used as the second control mode.
Although it is equipped with three modes: a wheel steering mode, a same-phase locking mode, and a reverse-phase locking mode, this second control mode does not necessarily have to be a mode that includes a plurality of modes as in the embodiment. For example, it may be only the two-wheel steering mode, only the in-phase or anti-phase fixed mode, or even only a mode having any other control content.

FIGS. 1, 2, and 3 are graphs showing the characteristics of the front wheel turning angle (θF) and the rear wheel turning angle (θR) in an embodiment of the four-wheel steering system of the present invention.

FIG. 1 shows an example of the two-wheel steering mode, which is one of the second control modes, and the rear wheel steering angle θ includes the front wheel steering angle θ.
It is always zero regardless of the magnitude of F, and shows the case where steering is performed only by the front wheels, as in a conventional car.

FIG. 2 shows an example of the automatic control mode, which is the first control mode. In this mode, as shown in the figure, there are multiple control modes in which the rear wheel steering angle characteristics relative to the front wheel steering angle change depending on the vehicle speed. At the same time, the characteristics of the rear wheel steering angle are controlled to be in the same phase as the front wheel steering angle at least in a high speed range, and the characteristic is an increase rate of the rear wheel steering angle with respect to the front wheel steering angle in a region where the front wheel steering angle is large. is set to be smaller than the rate of increase in the region where the front wheel steering angle is small. More specifically, the front wheel steering angle θF
The ratio of the rear wheel steering angle θR to the steering angle θR (steering ratio θR/θF) is
Overall, the higher the vehicle speed (Ve) is, the larger it becomes, and the lower the vehicle speed is, the smaller it becomes, and at extremely low speeds, it becomes negative (opposite phase). In addition, in this embodiment, in medium and high speed ranges, when the front wheel steering angle θF becomes larger than the set value, even if the front wheel steering angle θF increases, the rear wheel steering angle θ does not increase, and remains constant at each vehicle speed. It has become. That is, the steering angle θ of the rear wheels becomes constant after the front wheels are turned to a certain extent, and is not turned any further. This is based on the empirical rule that the front wheel steering angle θF is large when the vehicle wants to change its direction, so it suppresses the steering of the rear wheels in the same phase and allows the front wheels to move significantly relative to the rear wheels. This is to make it easier to change the direction of the vehicle when it is steered.

FIG. 3 shows an example of the same-phase and anti-phase fixed modes, which are one of the second control modes. In the case of the same-phase fixed mode, when the front wheel turning angle θF increases regardless of the driving condition, the rear The wheel steering angle θR also increases at a constant rate to be in the same phase as the front wheels, and in the case of anti-phase fixed mode, when the front wheel steering angle θF increases regardless of the driving condition, the rear wheel steering angle θR increases in phase with the front wheels, that is, θF. increases at a constant rate on the negative side of . As a result, in same-phase fixed mode, when steering, the front wheels and rear wheels are steered in the same phase, making it possible to move the vehicle diagonally, and in anti-phase fixed mode, when steering, the front and rear wheels are steered in opposite phases. Therefore, the turning radius of the vehicle can be reduced.

Next, according to FIGS. 4 and 5, the first control mode (automatic control mode) and the second control mode (
A specific configuration of a four-wheel steering device that allows selection of a two-wheel steering mode, a same-phase fixed mode, and an opposite-phase fixed mode will be described. Figure 4 shows an example using a hydraulic system, Figure 5
The figure shows an example using a link mechanism.

In the configuration shown in FIG. 4, the front wheels 1.1 and the rear wheels 2, 2 are mechanically separated, and the steering wheel 3 has a steering angle θ□
The output 4a of the front wheel steering angle sensor 4 that detects the front wheel steering angle is inputted to a controller 10 which is a control means of the rear wheel steering device, and the rear wheels 2.2 are steered by this input signal. As is well known, the front wheel steering device, which is a steering device, moves a rack 6 in the width direction of the vehicle (indicated by arrow A) by means of a pinion 5 fixed to a steering shirt 3A to which a steering wheel 3 is fixed. , the left and right front wheels 1 are connected to both ends of this rack 6 via continuous tie rods 7.7.
．． 1's knuckle arm 8.8 with its axis 8a.

8a to steer the front wheels 1.1 left and right. That is, when the steering wheel 3 in the figure is rotated in the direction of the arrow, the steering shaft 3A is rotated in the direction of the arrow, and the pinion 5 is also rotated in the direction of the arrow.
direction, and move the rack 6 to the left. As a result, the knuckle arms 8, 8 of the left and right front wheels 1.1 are rotated to the left via the links 7.7, and the front wheels 1.1 are rotated to the left about the shafts 8a, 8a of the knuckle arms 888. and steer to the left.

At this time, the front wheel steering angle sensor 4 outputs a signal 4a indicating that the steering wheel 3 has rotated to the left by an angle θH.
and outputs this as the controller 10 of the rear wheel steering device.
input to the front wheel steering angle input 10A.

The controller 10 is powered by a power source 11,
In addition to the front wheel steering angle input 10A, a vehicle speed input 10B connected to the vehicle speed sensor 12 and a feedback input 10C connected to the rear wheel steering angle sensor 13 are provided to further control the steering direction of the rear wheels. A steering direction output 10D connected to the solenoid 20, a hydraulic pump motor output 10E connected to the motor 21A of the hydraulic main pump 21 that controls the steering angle θR of the rear wheels, automatic control mode, same phase fixed mode, reverse Connected to changeover switches 14A, 14B, 14C, and 14D as selection means for selecting and switching between phase locking mode and two-wheel steering mode via display devices 14a, 14b, 14c, and 14d connected in series, respectively. It is equipped with a switching input 10F.

The hydraulic main pump 21 includes a pump 21B that discharges oil (hydraulic operation theory), and this pump 21B is connected to a hydraulic actuator 23 via a steering direction switching valve 22, and between this valve 22 and the pump 21B. An orifice path 24B is provided which short-circuits the oil outgoing path 24A and the oil outgoing path 24C, and includes an orifice 24b in the middle, and an oil reservoir 25 is arranged in the middle of the oil outgoing path 24C.

The steering direction switching valve 22 has two inlets connected to an oil outgoing path 24A and an oil return path 24C, and two inlets communicating therewith.
The valve part consisting of two outlets is
Three stop valves 22C are switchably provided in parallel, and these three valve parts 2 are operated by operating the solenoid 2o.
2A, 22B.

Any one of 22C is the oil outgoing path 24A1 and the outgoing path 2.
It is designed to be connected to 4C. The two outlets of this valve 22 are connected to the right oil passage 23R and the left oil passage 23L of the hydraulic actuator 23, respectively.
These right oil passage 23R and left oil passage 23L
The outgoing path 24A and the outgoing path 24 are connected via this valve 22.
It is connected to C.

The hydraulic actuator 23 has right and left oil passages 23R.
, 23L causes the rod 26, which is the output shaft thereof, to move in the width direction of the vehicle (indicated by arrow B), and the knuckle arms 2B, 28 of the rear wheels 2.2 are moved through the tie rods 27.27. It rotates around the shafts 28a, 28a, thereby steering the rear wheels 2.2 from side to side.

In the illustrated example, the front wheels 1.1 are steered to the left,
When steering the rear wheels 2.2 in the same phase as the front wheels 1.1, the steering direction switching valve 22 is set to the positive 22A position, and the oil is routed from the forward path 24A to the long path 2 through the orifice path 24B.
4C and returns to pump 21B via reservoir 25.

As a result, the front of the orifice 24b, that is, the outward path 24
The pressure on the A side increases, and the pressure on the rear side of the orifice 24b, that is, on the far path 24C side, decreases, causing the positive 2 side of the valve 22 to decrease.
Through the portion 2A, the pressure in the right oil passage 23R becomes higher than the pressure in the left oil passage 23L, and the operating rod 26 of the hydraulic actuator 23 is driven leftward. The amount of drive at this time is determined by the amount of current manually applied to the main pump motor 21A. As a result, the rear wheels 2, 2
is steered to the left via the tie rod 27°27,
The rear wheels 2,2 are steered in the same phase as the front wheels 1.1.

Steer front wheels 1 and 1 to the right, and turn rear wheels 2 and 2 to front wheels 1 and 1.
When steering in the same phase as the steering direction switching valve 22
is set to the reverse position 22B, the pressure relationship between the right oil 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 steering direction and the steering direction switching valve 22 are
The correspondence of 2A1 inverse 22B is opposite to the case of same phase as above,
In other words, when steering the front wheels 1.1 to the left, reverse 22
B, when steering the front wheel 1.1 to the right, use the positive 22A.
Set to .

Further, when the steering angle θk of the rear wheel 2.2 is set to zero, the stop 22C portion of the valve 22 is connected to the aisle passage to cut off the communication between the pump 21C and the hydraulic actuator 23,
Left and right oil passages 23L, 2 of the hydraulic actuator 23
Eliminate the pressure difference between 3B and set the actuating rod 26 to the neutral position. At this time, in order to ensure that the actuating rod 26 is set at the neutral position, it is desirable to apply a set load to the actuating rod 26 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. Which of the opposite phases to set is determined by the controller 10 in accordance with the vehicle speed detected by the vehicle speed sensor 12 in the automatic control mode and according to a preset vehicle speed correspondence pattern.

As described above, this controller 10 includes changeover switches 14A, 14B, 14C, and 14D, and display devices 14a, 14b, and 14c connected in series, respectively.
and 14d, and this changeover switch 14
A.

14B, 14C, and 14D are operated by the driver to select the first control mode or the second control mode, that is, the automatic control mode, or one of the same phase fixed mode, opposite phase fixed mode, and two-wheel steering mode. A selection can be made and at the same time this selected mode is indicated on the display. In other words, the driver can freely switch to any steering mode depending on the surrounding conditions, which is very convenient.

According to the four-wheel steering device using the hydraulic actuator as described above, 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 systems require heavy and costly components such as motors, pumps, hydraulic actuators, and control valves, which increase the weight of the vehicle and
It is not suitable for relatively small vehicles because it complicates manufacturing assembly and causes high costs. Therefore, a four-wheel steering system using a simple link mechanism may be advantageous in practice.

Hereinafter, an example of this type of link type mechanism will be explained with reference to FIG. In the configuration of FIG. 5, the same members as those in the configuration of FIG. 4 are designated by the same reference numerals, and their explanations will be omitted.

In the link type configuration shown in FIG. 5, 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. A link mechanism connects the rod 41 up to the sliding engagement slot 41A,
The rear wheels 2, 2 are steered in a desired direction and only to a desirable magnitude of the steered angle θ in accordance with the steered angle θF of the front wheels 1.1.

This link mechanism includes a first L-shaped lever 31 that has one end 31A that is slidably engaged with a sliding engagement thrower 6A on the front wheel side and is pivotally supported on a fixed shaft 31a; A connecting lever 32 having one end 32A movably connected to the other end 31B of the lever 31, and a swinging lever 33 having one end 33A connected to the other end 32B of the connecting lever 32 and the other end 33B being pivotally supported on a fixed shaft 33a. , the one end 3 of this swing lever 33
A control lever 34 whose one end 34A is rotatably connected to a connecting shaft between the intermediate lever 3A and the other end 32B of the intermediate lever 32.
The sleeve 35 and the screw rod 37 are slidably engaged in the vicinity of the free end of the control lever 34 and are pivotally supported with a rotation shaft 35A on a feed sleeve 36 screwed onto the screw rod 37. a motor 38 for rotating the control lever 34, and a connecting lever 39 whose one end 39A is pivotally supported by a shaft support 34A provided at an intermediate position of the control lever 34.
, and one end 4OA is attached to the other end 39B of this connection lever 39.
The second L-shaped lever 40 has its other end 40B slidingly engaged with the sliding engagement slot 41A on the rear wheel side.

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,
The output of the vehicle speed sensor 52 is input. 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, so as to control the position of the feed sleeve 36. There is. This controller 50 includes steering mode changeover switches 54A, 54B, 54C and 54 similar to the example shown in FIG.
Display devices 54a and 5 are each connected in series.
4b, 54c, and 54d, and the driver can operate the steering mode to select any desired steering mode.

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 the arrow), the pinion 5, the rack 6, the tie rod 7.7, the knuckle arm 8.8, and the front wheel 1 .1 all rotate or move in the direction of the arrow, steering the front wheels 1, 1 to the left, and at the same time turning the first L-shaped lever 31 around the fixed shaft 31a.
The swinging lever 33 rotates in the direction and rotates through the intermediate lever 32
The control lever 34 is rotated in the L direction around the fixed shaft 33a, the control lever 34 is swung in the L direction around the sleeve 35, and the connecting lever 39 is moved in the L direction. 40 in the L direction to move the steering rod 41 of the rear wheels 2.2 in the L direction, thereby steering the rear wheels 2.2 to the left in the same phase.

Changeover switches 54A, 54B, 54C and 54D
The motor 38 is driven by the controller 50 which has selected the steering mode, and the feed sleeve 36 moves downward (to the left of the vehicle) in the figure, and when the feed sleeve 36 reaches the position of the one end 39A of the connecting lever 39, Even if the control lever 34 swings around the rotation axis 35A of the sleeve 35, the connecting lever 39 does not move back and forth (in the left-right direction in the figure), so the rear wheel 2.2 is not steered.

When the sleeve 35 is moved further downward by the drive of the motor 38 and exceeds the position of one end 39A of the connection lever 39, the swing of the control lever 34 in the same direction as above (L direction) causes the connection lever 39 to move. Move it forward in the opposite way to the above. This is because the control lever 34 swings around the pivot shaft 35A of the sleeve 35. Therefore, in this case the L-shaped lever 40 of node 3
rotates in the direction of arrow R, the steering rod 41 of the rear wheel 2.2 moves in the direction of arrow R, the rear wheel 2.2 is steered to the right, and four-wheel steering with an opposite phase is performed. It turns out.

In this way, the output of the controller 50 causes the motor 38 to
The receiver moves the sleeve 35 through the feed sleeve 36, thereby changing the position of the axis of swing of the control lever 34 and, as a result, changing the direction of movement of the coupling lever 39. The steering direction of the wheels 2, 2 can be changed. Furthermore, the receiver is sleeve 3
By controlling the magnitude of the distance of movement of the front wheels 1. It becomes possible to arbitrarily control the direction and magnitude of the steering of the rear wheels 2.2 in response to the steering of the rear wheels 2.1.

Since the output from the vehicle speed sensor 52 is input to the controller 50, when the automatic control mode is selected, steering is performed via the above link according to the magnitude of the steering angle θF of the front wheels 1.1. It is possible to control the magnitude (including the direction) of the steering angle θR 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.

Also, when the same phase fixed mode is selected, for example, front wheel 1
．． The rear wheel 2 is rotated by a steering angle θR that is equal to the steering angle θF of 1.
．． 2, it becomes possible to move the vehicle laterally regardless of the vehicle speed.

Note that the control characteristics in the in-phase and anti-phase fixed modes are not necessarily limited to linear characteristics as shown in FIG. 1, but may be represented by curves. Furthermore, the control characteristic pattern in the automatic control mode is not limited to the example shown in Fig. 1, but a plurality of patterns may be set so that the rear wheel turning angle characteristic with respect to the front wheel turning angle changes depending on the vehicle speed. The vehicle speed sensitive type controls the above-mentioned characteristics to be in the same phase at least in the high-speed range, and the high-speed range in-phase characteristic is such that the ratio of increase in the rear wheel turning angle to the front wheel turning angle is small in the area where the front wheel turning angle is large. Any type of device may be used as long as it is set to be smaller than the area of .

In this way, even with the link type configuration shown in FIG.
It is possible to realize the rear wheel turning angle characteristics with respect to the front wheel turning angle as in the above-described embodiments. In particular, this link type mechanism is lighter in weight and has a simpler structure than the hydraulic type.
It is easy to assemble and can be manufactured at low cost, making it suitable for small vehicles.

As explained in detail above, the four-wheel steering system of the present invention includes:
A first control mode in which control is performed in accordance with the first control characteristic as described above, and a second control mode in which control is controlled in accordance with an appropriately set second control characteristic different from the first control characteristic, as required by the driver. It is possible to make an appropriate selection using the selection means, and therefore various maneuvers can be performed using control modes that correspond to various driving demands.

In addition, when the first control mode is selected, the rear wheels are controlled in the same phase as the front wheels at least in the high speed range, so lateral acceleration is sensitively and responsively obtained at high vehicle speeds. It is possible to change lanes and obtain good driving stability, and when controlling the rear wheels in the same phase as the front wheels in the high speed range, the increase ratio of the rear wheel steering angle to the front wheel steering angle is the large front wheel steering angle. Since the steering wheel is designed to be small in the area, if the front wheels are steered significantly to change the direction of the vehicle, the front wheels will be steered largely relative to the rear wheels, resulting in good turning performance. be able to.

That is, according to the four-wheel steering system for a vehicle according to the present invention, the first
The control mode ensures running stability and turning performance at high speeds, and by selecting different control modes, it is possible to drive appropriately in different situations, ensuring a high level of running stability. can.

[Brief explanation of the drawing]

1 to 3 are characteristic curves showing the relationship between the front wheel steering angle and the rear wheel steering angle in the four-wheel steering system of the present invention. Fig. 2 shows an example of the case of the steering mode, Fig. 2 shows an example of the case of the automatic control mode which is the first control mode, and Fig. 3 shows an example of the case of the in-phase and anti-phase fixed mode which is one of the second control modes. Each is shown below. FIG. 4 is a schematic diagram showing an example of the four-wheel steering system of the present invention that uses hydraulic pressure, and FIG.
It is a schematic diagram showing an example of a wheel steering device. 1... Front wheel 2... Rear wheel 3... Steering wheel 4... Steering angle sensor 5... Pinion 6... Rack 7
．． 27...Tie rod 8.28...Knuckle arm 10.50...Controller 12.52...
・Vehicle speed sensor 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 33 ... Rocking Moving lever 34... Control lever 34A... Shaft support 35A... Rotating shaft 37... Screw rod 39... Connection lever 40... Second L-shaped lever 32... Intermediate lever 35 ...The receiver is the sleeve 36...The feed sleeve 38...The drive motor 41...The rear wheel steering rod

Claims (1)

[Scope of Claims] A steering device that steers a front wheel, a rear wheel steering device that steers a rear wheel, a vehicle speed sensor, and a rear wheel steering angle characteristic that changes in accordance with vehicle speed with respect to a front wheel steering angle. A plurality of settings are made, and the characteristics of the rear wheel steering angle relative to the front wheel steering angle are controlled to be in the same phase at least in a high speed range, and the characteristic increases the rear wheel turning angle relative to the front wheel turning angle in a region where the front wheel turning angle is large. a first control mode in which rear wheel steering is controlled according to a first control characteristic whose ratio is set to be smaller than an increase rate in a region where the front wheel steering angle is small; and a second control mode which is different from the first control characteristic. a control means for controlling the rear wheel steering device by selecting one of a second control mode for controlling rear wheel steering according to control characteristics; and a control means for controlling the rear wheel steering device by selecting one of a second control mode for controlling rear wheel steering according to a control characteristic; and selecting one of a first and a second control mode in the control means. A four-wheel steering device for a vehicle, comprising a selection means.