JP2605730B2 - Rear wheel steering system for front and rear wheel steering vehicles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a front and rear wheel for steering a rear wheel by converting a rotary motion from an actuator into a reciprocating motion of a relay rod that connects the left and right rear wheels so as to be steerable. The present invention relates to a rear wheel steering device for a steered vehicle.

(Prior Art) Conventionally, this type of device includes an electric motor as an actuator for generating a rotational force, a worm gear fixed to an output shaft of the motor, as disclosed in Japanese Patent Application Laid-Open No. 61-196870. A worm wheel that meshes with the gear, and a conversion mechanism that converts the rotational motion of the wheel into a reciprocating motion of a relay rod that connects the left and right rear wheels so as to be steerable, and the worm gear and the worm wheel according to the rotation of the electric motor. By displacing the relay rod via the conversion mechanism and steering the left and right rear wheels, and setting the advance angle of the worm gear to be smaller than the friction angle, the reverse input from the worm wheel to the worm gear, that is, the relay rod from the left and right rear wheels, Reverse input to the electric motor via the conversion mechanism, worm wheel and worm gear is prohibited, and the left and right rear wheels are electrically driven. So that were not unsteady independently by disturbance of the rotation of the over data.

(Problems to be Solved by the Invention) However, in the above-described conventional device, the gear mechanism including the worm gear and the worm wheel is used, so that the transmission efficiency of the steering force from the electric motor to the left and right rear wheels is improved. Gets worse. As a result, a large output motor must be used as the electric motor, which raises the manufacturing cost of the motor and increases the size of the motor.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to reduce the manufacturing cost of an actuator that generates a rotating force and to reduce the size of the actuator without impairing the effect of the conventional device due to the prohibition of the reverse input. It is an object of the present invention to provide a rear-wheel steering device for front-rear-wheel steering vehicles capable of realization.

(Means for Solving the Problems) In order to solve the above problems and achieve the object of the present invention,
A structural feature of the present invention is a front and rear wheel steering system including an actuator that generates a rotational force, and a conversion mechanism that converts a rotational motion from the actuator into a reciprocating motion of a relay rod that connects the left and right rear wheels so as to be steerable. In a rear wheel steering device for a vehicle, a screw gear mechanism including a drive gear and a driven gear is interposed between the actuator and the conversion mechanism, and the torsion angle of the drive gear is equal to or greater than an angle obtained by subtracting frictional force from 90 degrees. And the rotation axis of the driven gear is set within an acute angle between the rotation axis of the drive gear and the tooth trace direction of the drive gear and the driven gear.

(Effects of the Invention) In the present invention configured as described above, the actuator and the conversion mechanism are connected using the screw gear mechanism, and the torsion angle of the drive gear constituting the gear mechanism is reduced.
Since the angle was set to be greater than the angle obtained by subtracting the friction angle from 90 degrees, in other words, the corner angle (the angle obtained by subtracting the twist angle from 90 degrees) was set to be smaller than the friction angle. , That is, reverse input from the left and right rear wheels to the actuator via the relay rod, conversion mechanism, driven gear, and drive gear is prohibited. In addition, as shown in FIG.
Since the L2 to set into an acute angle sandwiched by the rotating axis L1 and the drive gear and the tooth trace direction L3 of the driven gear of the drive gear, the axial angle beta ₃ of the screw gear mechanism of the worm gear mechanism in the prior art device axis The angle becomes smaller than the angle (90 degrees), and the transmission efficiency η from the drive gear to the driven gear increases as shown in FIG. As a result, the transmission efficiency of the steering force from the actuator to the left and right rear wheels is also increased, and a relatively low-power actuator can be used. Thus, the manufacturing cost of the actuator can be reduced and the actuator can be reduced in size without impairing the effect of preventing the left and right rear wheels from wobbling in the conventional device due to the prohibition of the reverse input.

Further, since the rotation axis L2 of the driven gear is set within the acute angle and the coaxial L2 is not set in the hatching as shown in FIG. 12, slippage between the tooth surfaces of the drive gear and the driven gear is prevented. The speed _Vf decreases. Because the slip velocity V _f of the case according to the present invention is defined as _{V f = V 1 · sinβ 1} -V 2 · sinβ 2, and 12 in the hatching the rotation axis L2 of the driven gear in FIG. As shown in FIG. Slip speed when set to
The V _f is to be defined as _{V f = V 1 · sinβ 1} + V 2 · sinβ 2. Here, β ₁ is the torsion angle of the drive gear, and β ₂ is the torsion angle of the driven gear. As described above, according to the present invention, the sliding speed _Vf can be set small, so that the wear on the tooth surfaces of the drive gear and the driven gear can be reduced, and the durability of each gear improves.

Further, the rotation axis L2 of the driven gear so as to set said acute angle, a coaxial L2 as shown in FIG. 13 Not having to be set in the hatching in the figure, the direction of rotation V ₂ and the teeth of the driven gear Biting of the teeth of each gear ascending with the streak direction L3 can be reduced to some extent. As a result, it is possible to better prevent the drive gear and the driven gear from being deactivated and the tooth surfaces of the gears from being damaged.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 2 schematically shows the entire front and rear wheel steering vehicle according to the present invention. The front and rear wheel steering vehicle includes a front wheel steering device A for steering left and right front wheels FW1 and FW2, a rear wheel steering device B for steering left and right rear wheels RW1 and RW2, and a control device C for controlling the rear wheel steering device B.
And

The front wheel steering device A has a steering shaft 11. The upper end of the steering shaft 11 is connected to the steering handle 12, and the lower end of the coaxial 11 is connected to a relay rod 15 that penetrates into the gear box 13 and penetrates the housing 14 in the box 13 in the left-right direction. Relay rod 15 according to rotation of steering handle 12
Are displaced in the left-right direction. Relay rod
The left and right ends of 15 are connected to the left and right front wheels FW1 and FW2 via left and right tie rods 16a and 16b and left and right knuckle arms 17a and 17b, and the left and right front wheels FW1 and FW2 are steered according to the displacement of the relay rod 15 in the left and right direction. It has become so.

The rear wheel steering device B connects the left and right rear wheels RW1 and RW2 to the right and left tie rods 2.
It has a relay rod 23 that is steerably connected via 1a, 21b and left and right knuckle arms 22a, 22b. Relay rod 23
As shown in FIG. 1 to FIG. 3, the shafts penetrate axially through cylindrical housings 24 and 25 connected at a central portion. A spline connection between an annular inner spline member 27 fixed non-rotatably by a screw 26 and an outer spline portion 23a formed on the outer periphery of the right end of the relay rod 23 makes the relay rod 23
Are supported so that they cannot rotate and can be displaced in the axial direction.

An electric motor 28 is mounted on the housing 25,
The motor 28 is assembled to the housings 24 and 25 by screws 32 together with the gear housing 31. The output shaft 28a of the electric motor 28 is rotatably supported by the gear housing 31 via bearings 32a and 32b. An eccentric cam portion 33a of an eccentric cam member 33 is fitted in the distal end cylindrical portion of the gear housing 31, and the eccentric cam member 33 is fixed to the housing 24 by a connecting member 34 serrated and connected to the member 33. As shown in FIG. 1 and FIG.
The pair of bolts 35a, 35b are fixed to the housing 24 by screwing into screw holes 34a, 34b provided in the member 34 and screw holes 24a, 24b provided in the housing 24. Further, each of the coupling member 34 and the housing 24 has another set of screw holes 34c and 34c.
d, 24c, 24d are provided, and the fixing position of the coupling member 34 to the housing 24 is slightly rotated from the fixing position by screwing the bolts 35a, 35b into the screw holes 34c, 34d, 24c, 24d. Is available. By changing the fixing position of the coupling member 34 with respect to the housing 24 and the serration coupling position between the coupling member 34 and the eccentric cam member 33, the eccentric cam member 33 is rotated by a small angle with respect to the housing 24 while the housing is rotated. 24, the position of the gear housing 31, that is, the output shaft 28 a of the electric motor 28 can be adjusted by the action of the eccentric cam 33 a when assembling the present device.

As shown in FIGS. 1 and 5, a drive gear 36 is screwed onto the outer periphery of the output shaft 28a of the electric motor 28, and the drive gear 36 is engaged with a key 37 press-fitted into the output shaft 28a. In some cases, it rotates in conjunction with the coaxial 28a.
However, the groove formed in the drive gear 36 and the key 37 enters
The width of 36a is slightly wider than that of key 37. Accordingly, when the drive gear 36 bites into a driven gear 46 described later, the output shaft is driven by the electric motor 28.
The relative rotation of the drive gear 36 of 28a to the groove 36a and the key 37
And the relative rotation allows the drive gear
36 is slightly displaced in the axial direction of the output shaft 28a, and the biting is released.

A ball nut 41 is screwed onto the outer periphery of the relay rod 23 via a plurality of balls as shown in FIGS. The ball nut 41 is supported by the housing 24 via the bearings 42a and 42b so as to be rotatable and non-displaceable in the axial direction.
23 are displaced in the axial direction. Ball nut
A driven gear 46 is fixed on the outer periphery of 41 by a key 43, a nut member 44 and a screw 45. The gear 46 and the drive gear 36 constitute a screw gear mechanism. In such a case, as shown in FIG. 1 and FIG.
The helix angle beta ₁ sandwiched by the rotational axis L1 and the tooth trace direction L3 of the gears 36 and 46 are set above the angle obtained by subtracting the friction angle of the gear mechanism 90 degrees, for example, about 80 to 85 degrees .
In other words, the advance angle (90 ° −β ₁ ) is set to be equal to or less than the friction angle of the gear mechanism, for example, about 5 to 10 degrees. Further, the rotating shaft L2 of the driven gear 46 is the two shafts L1, L3
Is set sandwiched by the acute angle by, for example, the helix angle beta ₂ of the gear 46 which is sandwiched between the rotation axis L2 of the driven gear 46 and the tooth trace direction L3 together with is set to about 0 to 75 degrees, both shaft angle beta ₃ sandwiched by the rotary shaft L1, L2 of the gear 36 and 46 is set to about 10 degrees, for example.

Further, the rear wheel steering device B includes a rear wheel steering restriction mechanism for restricting the steering of the left and right rear wheels RW1 and RW2. The mechanism includes a sleeve 51 for restricting the rotation of the ball nut 41 for the restriction.
Having. As shown in FIGS. 1, 3, 6, and 7, the sleeve 51 is non-rotatably fixed to the outer spline portion 51a formed on the outer periphery thereof and the inner periphery of the housing 24 by a screw 52. By the spline connection with the annular inner spline member 53, it is supported by the housing 24 so as to be non-rotatable and axially displaceable. As shown in FIGS. 1, 3, and 6, an inner spline portion 51b is formed at an intermediate portion on the inner periphery of the sleeve 51, and the sleeve 51 is moved to a first position (FIGS. 1 and 3). When the sleeve 51 is in the
Inhibits rotation of the nut 41 by spline connection between the spline portion 51b and an outer spline portion 41a formed on the outer periphery of the ball nut 41. As shown in FIGS. 1, 3, and 7, a pair of front and rear projections 51c, 51c are integrally formed at the upper right end of the inner periphery of the sleeve 51. When the sleeve 51 is displaced leftward from the first position and is at the second position, the sleeve 51 is formed by engagement of the protrusions 51c, 51c with a pair of protrusions 41b, 41b formed on the outer periphery of the ball nut 41. Rotate the nut 41 90 degrees from the reference rotation position
Limit within degrees. Further, when the sleeve 51 is displaced leftward from the second position and is at the third position, the above-described prohibition and restriction are released, and the ball nut 41 rotates freely.

The sleeve 51 is constantly pressed rightward by a spring 54, and is moved to a first position (FIG. 1 and FIG. 3) by a fork 55 engaged with a groove 51d formed in a circumferential direction on the outer periphery of the sleeve 51. Position) to the left in two steps (second or third position). The fork 55 is driven by two first and second diaphragm type cylinders 56 and 57.
Is, as shown in FIGS. 1, 3, 8, and 9,
It is mounted on a case 58 fixed to the side of the housing 24. The first diaphragm type cylinder 56 is a diaphragm 56
The upper and lower chambers 56b, 56c are divided by a.
The first drive rod 6 fixed to the center of the diaphragm 56a in accordance with the pressure difference caused by the atmospheric pressure supplied to the
Move 1 up and down. The second diaphragm type cylinder 57 is divided into upper and lower chambers 57b and 57c by a diaphragm 57a having an effective pressure receiving area larger than that of the diaphragm 56a.
The second drive rod 62 fixed to the center of the diaphragm 57a is moved up and down according to the pressure difference due to the atmospheric pressure or the suction pipe negative pressure supplied to b and 57c. In this case, the second drive rod 62
When the rod 62 is displaced downward, the upward displacement of the first drive rod 61 is regulated to move the rod 61 to the lowermost position (first position) and the uppermost position (third position). ) Is set so as to be maintained at an intermediate position (second position). In addition,
The upper chamber 56b of the first diaphragm cylinder 56 and the lower chamber 57c of the second diaphragm cylinder 57 communicate with each other via a hole 63a provided in a partition 63 between the cylinders 56,57.

A guide groove 61 is provided at a lower part of the first drive rod 61 at right angles to the axial direction.
a pin 64a provided at one end of an L-shaped lever 64 is slidably fitted in the groove 61a. The lever 64 is rotatably supported on the case 58 by a pin 65 penetrating the lever 64 at the center thereof, and is rotated about the pin 65 by the vertical movement of the first drive rod 61. . A pin 64b is also provided at the other end of the lever 64, and the pin 64b is slidably fitted in a groove 66a formed in a connecting rod 66 to which the fork 55 is fixed at its base. The connecting rod 66 is supported by the case 58 so as to be slidable in the axial direction, and is displaced in the left-right direction in response to the rotation of the lever 64, thereby displacing the fork 56 in the same direction.

As shown in FIG. 2, the control device C includes a front wheel steering angle sensor 71, a vehicle speed sensor 72, a rotation angle sensor 73, and a rear wheel steering angle sensor.
74, a steering limit detection switch 75, and a steering inhibition detection switch 76.

The front wheel steering angle sensor 71 detects the steering angle θf of the left and right front wheels RW1 and RW2 based on the rotation angle of the steering shaft 11, and outputs a detection signal representing the steering angle θf. The vehicle speed sensor 72 detects the vehicle speed V based on the rotational speed of a converter (not shown) or the left and right front wheels FW1 and FW2 and the left and right rear wheels RW1 and RW2, and outputs a detection signal representing the vehicle speed V. As shown in FIGS. 1 to 3, the rotation angle sensor 73 is mounted on the rear end of the electric motor 28, detects the rotation angle of the motor 28, and outputs a detection signal indicating the rotation angle. As shown in FIGS. 1 and 3, the rear wheel steering angle sensor 74 includes a gear 74a that meshes with a male screw 23b formed on an outer peripheral portion of the relay rod 23, and rotates the gear 74a with the displacement of the relay rod 23. The displacement of the rod 23 depending on the angle, that is, the left and right rear wheels RW1, RW
The second steering angle θr is detected, and a detection signal representing the steering angle θr is output. As shown in FIGS. 1 and 2, the steering limit detection switch 75 is mounted on the case 58 and connected to the connecting rod 66.
The rod 6 is engaged with the notch 66b formed on the outer peripheral surface of the rod.
6 and the fork 55 from the first position (the position in FIG. 1) to the second position.
It detects the displacement to the position and outputs the same detection signal. The steering inhibition detection switch 76 is, as shown in FIGS.
The engagement between the connecting rod 66 and the fork 5 by engagement with a notch 55a formed on the outer periphery of the base of the fork 55 attached to the case 58
5 to detect the displacement from the first position (the position in FIG. 1) or the second position to the third position and output the detection signal. The first to third positions correspond to the first to third positions of the sleeve 51.

Front wheel steering angle sensor 71, vehicle speed sensor 72, rotation angle sensor 73
And each detection signal from the rear wheel steering angle sensor 74 is supplied to a rear wheel steering angle control circuit 77.
77 determines a target rear wheel steering angle based on the detected front wheel steering angle θf and the detected vehicle speed V, and calculates a target rotation angle of the electric motor 28 based on the target rear wheel steering angle and the detected rear wheel steering angle θr. Based on the target rotation angle and the detected rotation angle, the motor 28
And outputs a control signal for rotating. A drive circuit 78 is connected to the rear wheel steering control circuit 77, and the drive circuit 78 drives the electric motor 28 according to the braking signal.

The detection signal from the vehicle speed sensor 72 is also supplied to a vehicle speed determination circuit 81.
And determines whether or not the vehicle is traveling at a low speed, and outputs a vehicle speed determination signal. In addition, each sensor 71, 72, 7
3, 74 and the respective detection signals from the respective detection switches 75, 76 are supplied to a failure judgment circuit 82.
Reference numeral 82 determines a failure in the rear wheel steering system based on an intersystem of various detection signals, and outputs a failure determination signal. An excitation control circuit 83 is connected to the vehicle speed determination circuit 81 and the failure determination circuit 82,
The control circuit 83 controls the electromagnetic switching valves 84, 85, 86 based on the vehicle speed determination signal and the failure determination signal as described below.

(1) When the vehicle is traveling at a low speed and no failure occurs in the rear wheel steering system, the electromagnetic switching valves 84, 85, 86 are set to the excited state.

(2) When the vehicle is traveling at a medium to high speed and no failure occurs in the rear wheel steering system, the electromagnetic switching valve 84 is set to the non-excited state and the electromagnetic switching valves 85 and 86 are set to the excited state. .

(3) When a failure occurs in the rear wheel steering system, an electromagnetic switching valve
Set 84,85,86 to de-energized state.

As shown in FIGS. 2 and 8, the electromagnetic switching valve 84
A conduit P1 communicating with the upper chamber 57b of the diaphragm cylinder 57
And a conduit P4 which communicates with an intake manifold (not shown) of the engine and supplies the negative pressure of the intake pipe, and connects the upper chamber 57b to the conduit P1 in a non-excited state (the state shown in FIG. 2).
And the upper chamber 57b is set to a negative pressure via conduits P4 and P1 in the excited state (switching state). The electromagnetic switching valve 85 is a conduit P communicating with the upper chamber 56b of the diaphragm cylinder 56 (and the lower chamber 57C of the diaphragm cylinder 57).
The upper chamber 56b (and the lower chamber 57C) is set to the atmospheric pressure via the conduit P2 in the non-excited state (the state shown in FIG. 2) and is excited (the switching state). ) At upper room 56b
(And lower chamber 57C) is set to negative pressure via conduits P4 and P2.
The electromagnetic switching valve 86 is a lower chamber 56C of the diaphragm type cylinder 56.
The lower chamber 56C is set to a negative pressure via conduits P4 and P3 in a non-excited state (the state shown in FIG. 2) and is excited (switched). 56C
Is set to atmospheric pressure via conduit P3.

Next, the operation of the embodiment configured as described above will be described.

First, the case where the rear wheel steering system is operating normally and the vehicle is running at low speed will be described. In such a case, the excitation control circuit 83 includes a vehicle speed determination circuit 81 and a failure determination circuit.
Since the electromagnetic switching valves 84, 85, and 86 are excited in cooperation with 82, the switching valves 84, 85, and 86 are switched from the state shown in FIG. 2 to the upper and lower chambers 57b and 57c of the diaphragm cylinder 57 and the diaphragm type. The upper chamber 56b of the cylinder 56 is set at a negative pressure, and the lower chamber 56c of the diaphragm cylinder 56 is set at the atmospheric pressure. Thus, the diaphragm 56a pushes the first drive rod 61 up to the uppermost position (third position). At this time, the second drive rod 62 is also pushed up by the pushing up of the first drive rod 61. Due to the upward displacement of the first drive rod 61, the lever 64 rotates clockwise in FIG. 8 and presses the connecting rod 66 and the fork 55 leftward to move the rod 66 and the fork 55 to the third position. Displace. Due to this displacement, the sleeve 51 is also displaced to the third position, the spline connection between the inner spline portion 51b and the outer spline portion 41a is released, and the engagement by the protrusions 41b, 51c is released.
The ball nut 41 becomes freely rotatable.

In such a state, the left and right front wheels are
When RW1 and RW2 are steered, the drive circuit 78 outputs various sensors 71 to 7
4 and the electric motor 2 in cooperation with the rear wheel steering angle control circuit 77.
8, and the motor 28 rotates the output shaft 28a.
This rotational power is transmitted to the ball nut 41 via the drive gear 36 and the driven gear 46, and the nut 41 is connected to a relay rod.
Rotate on the outer circumference of 23. The rotation of the ball nut 41 is converted into an axial displacement of the relay rod 23, which is connected to the left and right tie rods 21a, 21b and the left and right knuckle arms 22a, 22b.
The left and right rear wheels RW1 and RW2 are steered through. Left and right rear wheel R
In the steering of W1 and RW2, as described above, the ball nut 41
The rotation of the rear wheels RW1 and RW2 is steered sufficiently large.

Next, a case will be described in which the rear wheel steering system is operating normally and the vehicle is traveling at medium to high speed. In such a case, the excitation control circuit 83 includes a vehicle speed determination circuit 81 and a failure determination circuit.
Since the electromagnetic switching valve 84 is de-energized and the electromagnetic switching valves 85 and 86 are energized in cooperation with the electromagnetic switching valve 82, the electromagnetic switching valves 85 and 86 are switched from the state shown in FIG.
The upper chamber 57b and the lower chamber 56c of the diaphragm cylinder 56 are set to the atmospheric pressure and the lower chamber 57 of the diaphragm cylinder 57 is set.
And the upper chamber 56b of the diaphragm type cylinder 56 is set to a negative pressure. As a result, the diaphragm 56a pushes up the first drive rod 61, but the diaphragm 57a has a larger effective pressure receiving area than that of the diaphragm 56a, so the second drive rod 61 is pushed with a larger force than the force pushing up the first drive rod 61. When the rod 62 is pushed down, the first drive rod 61 is set to the second position (intermediate position). Due to the displacement of the first drive rod 61, the lever 64 rotates clockwise in FIG. 8 to move the sleeve 51 through the connecting rod 66 and the fork 55 to the second position as described above.
Displace to position. Due to the displacement of the sleeve 51, the spline connection between the inner spline portion 51b and the outer spline portion 41a is released, but the engagement by the projections 41b, 51c is not released, and the ball nut 41 is moved left and right from the reference rotation position. 90
It is possible to rotate within the range of degrees.

In this state, when the left and right front wheels FW1, FW2 are steered, the left and right rear wheels RW1, RW2 are also steered as described above,
The steering angle is controlled within a steering angle range corresponding to the rotation range of the ball nut. As a result, when the vehicle is traveling at a medium to high speed, the steering angles of the left and right rear wheels RW1 and RW2 are limited to within a predetermined range, thereby ensuring the safety of traveling of the vehicle.

Drive gear 3 for steering such left and right rear wheels RW1, RW2
In the rotation of the driven gear 46 and the driven gear 46, as shown in FIG. 10, the rotation axis L2 of the driven gear 46 is set at an acute angle between the rotation axis L1 of the drive gear and the tooth lead direction L3. shaft angle β ₃ of 46 90
The drive gear 36 as shown in FIG.
The transmission efficiency from the gear to the driven gear 46 increases. As a result, the transmission efficiency of the steering force from the electric motor 28 to the left and right rear wheels RW1, RW2 is also increased, and a small and light motor having a relatively small output can be used as the motor 28.

Further, since the rotation axis L2 of the driven gear 46 is set within the acute angle and the coaxial L2 is not set in the hatching as shown in FIG. 12, slippage between the tooth surfaces of the drive gear 36 and the driven gear 46 is prevented. The vehicle speed _Vf decreases. Because the slip velocity V _f in the above embodiment V _f = V ₁ · sinβ ₁
-V ₂ · sinβ ₂ and is defined, and the slipping velocity V _f of the case of Figure 12 is to be defined as _{V f = V 1 · sinβ 1} + V 2 · sinβ 2. As a result, the drive gear 36 and the driven gear
Wear of each tooth surface of 46 can be reduced, and both gears 36, 4
6, the durability is improved.

Further, since the rotation axis L2 of the driven gear 46 is set within the acute angle and the coaxial L2 is not set in the hatching as shown in FIG. 13, the rotation direction V _{2 of the} driven gear 46
The biting of the teeth between the gears 36 and 46 due to the asymptotic relationship between the gear and the tooth trace direction L3 can be reduced to some extent. As a result, non-operation of the drive gear 36 and the driven gear 46 and damage to the tooth surface can be better prevented. Even if the biting occurs, the width of the groove 36a is set slightly larger than the width of the key 37 as shown in FIG.
The relative rotation of the drive gear 36 with respect to the drive gear 36 is slightly permitted, and the bite is released because the drive gear 36 is slightly displaced in the axial direction of the output shaft 28a by this relative rotation.

On the other hand, during steering of the left and right rear wheels RW1, RW2, the rear wheels RW1, RW2
External force is applied to the left and right nut arms 22a,
22b, left and right tie rods 21a, 21b, the relay rod 23, even if the reverse input drive gear 36 through a ball nut 41 and the driven gear 46, the helix angle beta ₁ of the drive gear 36 and the angle or minus the angle of friction of 90 degrees In other words, since the leading angle (90 ° −β ₁ ) is set to be equal to or smaller than the friction angle, the gear 36 is not rotated by the reverse input. As a result, the left and right rear wheels RW1, RW2 do not fluctuate due to the external force.

Finally, a case where a failure occurs in the rear wheel steering system will be described. In such a case, the excitation control circuit 83
The solenoid-operated switching valves 84, 85, 86 are de-energized in cooperation with the above, so that the switching valves 84, 85, 86 are in the state of FIG. 2 and the upper and lower chambers 57b, 57c of the diaphragm cylinder 57 and the diaphragm type The upper chamber 56b of the cylinder 56 is set to atmospheric pressure, and the lower chamber 56c of the diaphragm cylinder 56 is set to negative pressure. As a result, the diaphragm 56a pushes down the first drive rod 61 to the lowest position, and the rod 61 is set to the first position (the position in FIG. 8). This allows the lever 64, connecting rod
The fork 55 and the sleeve 51 are in the state shown in FIGS. 1, 3 and 8, and the inner spline portion 51b and the outer spline portion 41a are connected, so that the rotation of the ball nut 41 is prohibited.

In this state, even if the left and right front wheels FW1 and FW2 are steered and the electric motor 28 is driven by the drive circuit 78,
RW1 and RW2 are not steered, and the traveling safety of the vehicle is ensured.

[Brief description of the drawings]

FIG. 1 is a cross-sectional plan view of a rear wheel steering device showing one embodiment of the present invention, FIG. 2 is an overall schematic diagram of a front and rear wheel steering vehicle incorporating a rear wheel steering device according to the present invention, and FIG. FIG. 1 is a longitudinal sectional front view of the rear wheel steering device, FIG. 4 is an external view taken along line IV-IV of FIG. 1, and FIG. 5 is a view taken along line VV of FIG. FIG. 6 is a sectional view showing an assembled state of the drive gear, and FIG.
FIG. 7 is a cross-sectional view showing an assembled state of the sleeve as viewed along the line VI-VI, FIG. 7 is a cross-sectional view showing an assembled state of the sleeve as viewed along the line VII-VII in FIG. 3, and FIG. VIII-VI in FIG.
FIG. 9 is a cross-sectional view taken along II, FIG. 9 is a cutaway view showing the assembled state of the fork and lever taken along IX-IX in FIG. 1,
FIG. 10 is a state diagram showing the mounting angles of the drive gear and the driven gear, FIG. 11 is a graph showing the transmission efficiency of the drive gear and the driven gear, and FIGS. 12 and 13 show different mounting angles of the drive gear and the driven gear. FIG. Description of symbols A: front wheel steering device, B: rear wheel steering device, C: control device, FW1, FW2 ... front wheel, RW1, RW2 ... rear wheel, 23 ... relay rod, 24, 25 ... Housing, 28 …… Electric motor, 3
1 ... Gear housing, 33 ... Eccentric cam member, 36 ... Drive gear, 36a ... Groove, 37 ... Key, 41 ... Ball nut, 41a ... Outer spline part, 41b ... Protrusion, 46 ... …
Driven gear, 51 ... Sleeve, 51a ... Outer spline, 51b ... Inner spline, 51c ... Protrusion, 53 ... Inner spline member, 54 ... Spring, 55 ... Fork,
56,57 …… Diaphragm cylinder, 58 …… Case, 61,
62: Drive rod, 64: Lever.

Claims (1)

(57) [Claims] A rear wheel for a front and rear wheel steering vehicle, comprising: an actuator for generating a rotational force; and a conversion mechanism for converting a rotational motion from the actuator into a reciprocating motion of a relay rod that connects the left and right rear wheels so as to be steerable. In the steering device, a screw gear mechanism including a drive gear and a driven gear is interposed between the actuator and the conversion mechanism, and the torsion angle of the drive gear is set to be equal to or greater than an angle obtained by subtracting a friction angle from 90 degrees, A rear wheel steering device for a front and rear wheel steering vehicle, wherein the rotation axis of the driven gear is set within an acute angle between the rotation axis of the drive gear and the tooth trace direction of the drive gear and the driven gear.