JPH058740A - Electric four-wheel steering apparatus - Google Patents

Abstract

(57) [Summary] [Purpose] To restore the neutral position in the event of a failure without providing a centering spring on the rear wheel output shaft 11. As a result, the drive electric motors 37a and 37b are downsized. [Structure] With the axial displacement of the rear wheel output shaft 11,
The steering angle is applied to the rear wheels. First and second electric motor 37
First and second speed reducers 46a and 46b are provided between the a and 37b and the rear wheel output shaft 11. Each speed reducer 46a,
46b efficiently transmits power from the electric motors 37a, 37b to the rear wheel output shaft 11. However, the efficiency of power transmission from the rear wheel output shaft 11 to the electric motors 37a and 37b is low. With the above configuration, even if one electric motor fails, the rear wheel output shaft 11 can be returned to the neutral position.
Further, even if one of the electric motors runs out of control, an excessive steering angle is not given to the rear wheels.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The electric four-wheel steering system according to the present invention is used as a steering system for an automobile. When the course of the automobile is changed, not only the front wheels but also the rear wheels are turned to rotate. The radius is reduced or the running stability of the vehicle can be maintained.

[0002]

2. Description of the Related Art In order to easily change the course on a narrow road, the turning radius of the vehicle is made small, or the traveling stability of the vehicle is maintained even when the course is changed at high speed. Therefore, in recent years, a four-wheel steering system has been used in which not only the front wheels but also the rear wheels are operated when the steering wheel is operated.

In addition to steering the rear wheels simply in connection with the steering of the front wheels, in order to give a proper steering angle to the rear wheels in accordance with various conditions that affect turning performance such as vehicle speed, An electric four-wheel steering system in which a steering angle is applied to the rear wheels by an electric motor has also been studied.

For example, the inventor of the present invention previously invented an electric four-wheel steering device as shown in FIGS. 5 and 6 (Japanese Patent Application No. 235553, 1990). The electric four-wheel steering system according to this prior invention uses the electric motor to apply the steering angle to the rear wheels only when the traveling speed of the vehicle is relatively low. The steering angle is applied to the rear wheels by a so-called compliance steer mechanism that applies the steering angle to the rear wheels based on the force.

In the electric four-wheel steering system according to the present invention, the movement of the steering wheel 1 provided at the driver's seat is transmitted to the steering gear 3 by the steering shaft 2 and the output shaft 4 for the front wheel is used as the shaft. Direction (left and right direction in FIG. 5), and a pair of left and right knuckle arms 5 connected to both ends of the front wheel output shaft 4, respectively.
A desired steering angle is imparted to the front wheels 6, 6 via 5.

Steering angle sensors 8 and 8 are supported on a steering column 7 through which the steering shaft 2 is inserted, and the front wheels 6 and 6 are detected from the rotation angles of the steering shaft 2 detected by the steering angle sensors 8 and 8. The rudder angle given to the can be detected. The two rudder angle sensors 8 and 8 are provided for fail-safe so that desired control can be performed even if one of the rudder angle sensors 8 fails.

Further, a housing 10 for accommodating a steering angle imparting mechanism for the rear wheels 9 and 9 on the rear floor surface of the vehicle cannot be displaced in the width direction of the vehicle (left and right direction in FIGS. 5 and 6). As
It is supported. The rear wheel output shaft 11 is inserted inside the housing 10 in the left-right direction (width direction of the vehicle). The rear wheel output shaft 11 is configured to give a steering angle to the rear wheels 9 and 9 by displacing in the axial direction (left and right directions in FIGS. 5 and 6). The knuckle arm 13 and the rear wheel 9 and the rear wheel 9 and 9, respectively.
Bound by 3.

As the rear wheel output shaft 11 is axially displaced, the rear wheels 9, 9 are moved to the steering center 14,
The rear wheel 9 is swung about 14, and a steering angle commensurate with the amount of displacement of the rear wheel output shaft 11 is given to the rear wheels 9, 9. Also, the steering centers 14, 14 of the rear wheels 9, 9 are
The rear wheels 9, 9 are located at the rear (downward in FIG. 5) in the forward direction of the vehicle (upward in FIG. 5) by a distance l from the force application points 12, 12 (center of the contact surface between the lower surface of the tire and the ground). ing.

On the other hand, at the intermediate portion of the rear wheel output shaft 11,
Rack teeth 15 are fixedly provided on the inside of the housing 10. A pinion tooth 17 is provided at one end (upper end in FIGS. 5 and 6) of the transmission shaft 16 rotatably supported inside the intermediate portion of the housing 10 in a twisted positional relationship with the rear wheel output shaft 11. Fix the pinion teeth 1
7 is meshed with the rack teeth 15. A worm wheel 18 is fixed to the other end of the transmission shaft 16 (lower end in FIGS. 5 and 6).

Further, a worm 21 is fixedly mounted on an output shaft 20 which is rotationally driven through an electromagnetic clutch 31 by a rotational drive shaft (not shown) of an electric motor 19 fixed to the outer surface of the housing 10. By engaging the worm 21 with the worm wheel 18, rotation of the output shaft 20 constitutes a deceleration mechanism for axially displacing the rear wheel output shaft 11.

This reduction mechanism has reversibility in the direction of power transmission, and in addition to displacing the rear wheel output shaft 11 in the axial direction as the output shaft 20 rotates, the rear wheel output shaft 11 is also displaced. The output shaft 20 is rotated along with the axial displacement of the output shaft. However, by suppressing the reverse efficiency of the reduction mechanism to be low, the load due to the compression of the centering spring 25, which will be described later, is maintained as it is when the meander angle given to each of the rear wheels 9, 9 is maintained as it is.
I try not to join 9. An encoder 32 is attached to the electric motor 19 so that the amount of rotation of the electric motor 19 can be detected, and the detected value is input to the controller 24 described below.

At one end of the transmission shaft 16, an encoder,
Two displacement sensors 22 and 22 such as potentiometers are provided so that the displacement amount of the rear wheel output shaft 11 can be detected via the transmission shaft 16. These two displacement sensors 22, 22
The detection signal sent from the control unit 24 controls the energization of the electric motor 19 together with the detection signals from the steering angle sensors 8 and 8 and the detection signal from the vehicle speed sensor 23 that detects the vehicle speed. .. The displacement sensor 22,
The reason why two 22 are provided is also for fail-safe purpose.

Then, the controller 24 controls the electromagnetic clutch 31 only when the traveling speed of the vehicle detected by the vehicle speed sensor 23 is a constant value (for example, 40 km / h) or less.
And the rear wheels 9 by the electric motor 19 based on signals from the steering angle sensors 8 and 8 and the vehicle speed sensor 23.
The steering angle is given to 9. At this time, the energization of the electric motor 19 is controlled based on the signal from the encoder 32. Also, the displacement sensor 2 provided at the end of the transmission shaft 16
Reference numerals 2 and 22 detect the steering angle actually given to the rear wheels 9 and 9 and input the detected value to the controller 24.

The rear wheel output shaft 11 is elastically supported by the housing 10 fixed to the vehicle body so as to be slightly displaceable in the axial direction (left and right directions in FIGS. 5 and 6). .. That is, a pair of seat plates 26, 26 are provided in the intermediate portion of the rear wheel output shaft 11 with a space therebetween.
It is possible to freely displace in the axial direction of
A centering spring 25 is provided between the inner side surfaces of the two seat plates 26, 26 so as to return the rear wheel output shaft 11 to the neutral position even when the electric motor 19 fails.
Is provided.

Further, a pair of step portions 27, 27 are formed on the inner peripheral surface of the housing 10 so as to be spaced apart from each other, and the outer surface outer peripheral portions of the pair of seat plates 26, 26 are formed. , Facing the stepped portions 27, 27, respectively. In addition, a pair of stop rings 2 are provided on the outer peripheral surface of the intermediate portion of the rear wheel output shaft 11 at a position sandwiching the pair of seat plates 26, 26.
8 and 28 are fastened to limit the movement of the seat plates 26 and 26 with respect to the rear wheel output shaft 11. Further, disc springs 29, 29 are provided between the outer surfaces of the pair of seat plates 26, 26 and the step portions 27, 27 and the stop rings 28, 28.
Is provided.

The elastic force required to completely crush the disc springs 29, 29 is made smaller than the elastic force when the centering spring 25 starts to be compressed, so that the housing 1
When the rear wheel output shaft 11 is displaced with respect to 0, the disc leaf springs 29, 29 are first displaced (crushed) as indicated by the straight line a in FIG. After the disc leaf spring 29 of FIG. 2 is completely crushed, the centering spring 25 is moved to the pair of seat plates 2 as shown by the straight line b in FIG.
The compression is started between 6 and 26. However, when the disc leaf springs 29, 29 are completely compressed, the spring load is expected to be applied to the rear wheel output shaft 11 based on the centrifugal force generated in the expected operating state. It is slightly larger than the maximum lateral load F _MAX .

In the electric four-wheel steering system of the prior invention constructed as described above, the vehicle has a constant speed (for example, 40 km / km).
h) When traveling below, the controller 24 controls the energization of the electric motor 19 based on the signals from the steering angle sensors 8, 8 and the vehicle speed sensor 23, and if necessary, the rear wheels 9, 9
To give the desired steering angle. At this time, the electromagnetic clutch 31 is energized to keep the electromagnetic clutch 31 engaged.

That is, when the vehicle runs at low and medium speeds,
In order to improve the turning performance of the vehicle, the steering angles of the rear wheels 9 and 9 in the opposite phase to the front wheels 6 and 6 are applied, but the steering angle applied to the rear wheels 9 and 9 is shown by the solid line c in FIG. As shown in, decrease as vehicle speed increases. In this case, the steering angle given to the rear wheels 9 is the displacement sensor 2 provided at one end of the transmission shaft 16.
2 and 22, and the detected value is input to the controller 24 for fail-safe.

Incidentally, the steering angle ratio represented on the vertical axis in FIG.
Steering angle θ _R given to rear wheels and steering angle θ _F given to front wheels
The larger the absolute value of the ratio (θ _R / θ _F ) is, the larger the steering angle applied to the rear wheels is. Further, the steering angles of the front and rear wheels have the same phase in the region above the horizontal axis, and have opposite phases in the region below.

On the other hand, when the vehicle travels over the constant speed (40 km / h), the electromagnetic clutch 31 is de-energized and the electromagnetic clutch 31 is disconnected. Along with this, the steering angle sensors 8 and 8 and the vehicle speed sensor 2
The controller 24 does not control the steering angle of the rear wheels 9, 9 regardless of the signals from the vehicle. Further, if necessary, the power supply to the electric motor 19 is also stopped.

As described above, when the course is changed when the vehicle travels at a certain speed, the rear wheels 9 and 9 are steered in the same phase as the front wheels 6 and 6 based on the centrifugal force. This is given to maintain the stability of the vehicle when changing course.

For example, when the front wheels 6, 6 are displaced in the direction of the arrow α in FIG. 5 based on the operation of the steering wheel 1, the rear wheels 9, 6 are caused by the centrifugal force accompanying the course change of the vehicle.
9 is swung to the right in FIG. 5, and a lateral force F is applied to each of the rear wheels 9, 9 due to the friction between each of the rear wheels 9, 9 and the road surface, as indicated by an arrow β in the figure. This force F is applied to the contact surface between the rear wheels 9 and 9 and the road surface, that is, the vertical plane including the force application points 12 and 12 of each rear wheel 9 and 9. On the other hand, the steering center 1 of each rear wheel 9, 9
Since the wheels 4 and 14 are located rearward of the force application points 12 and 12 by the distance 1 in the forward direction of the vehicle, the rear wheels 9 and 9 are
The steering wheel is steered in the direction of arrow γ in FIG. 5 with the moment F · l.

In this way, as the rear wheels 9, 9 are steered in the direction of the arrow γ, the rear wheel output shaft 11 is displaced in the axial direction, and one side (left side of FIGS. 5 and 6). The disc leaf spring 29 is compressed. Therefore, the steering angle applied to each of the rear wheels 9, 9 is the force applied in the axial direction of the rear wheel output shaft 11 based on the lateral force F, and the rear wheel based on the compression of the disc leaf spring 29. It is held in a state in which the force applied to the output shaft 11 for use is balanced.

Therefore, when the vehicle speed exceeds a certain value,
The steering angles applied to the rear wheels 9 and 9 are always in the same phase as the front wheels 6 and 6, as indicated by a broken line d in FIG. Further, in this case, the magnitude of the steering angle applied to the rear wheels 9 and 9 depends on the magnitude of the lateral force F applied to the rear wheels 9 and 9 due to the centrifugal force accompanying the course change of the vehicle. Only fixed, vehicle speed and front wheels 6,
It is not directly related (though indirectly indirectly related) to the size of the steering angle given to No. 6.

Moreover, since the compression allowances of the disc leaf springs 29, 29 are limited, an excessive steering angle is not given to the rear wheels 9, 9. As described above, when the vehicle is traveling at high speed, the steering angle is not applied to the rear wheels 9 by the electric motor 19,
Although the steering angle is given to the rear wheels 9 and 9 only by a physical force, a mechanism for stopping the energization of the electromagnetic clutch 31 and the electric motor 19 when the traveling speed of the vehicle exceeds a certain value. Since it is simple, the reliability of the mechanism can be sufficiently ensured, and the fail-safe mechanism added to this mechanism can also be simple and highly reliable.

[0026]

By the way, for example, an electric four-wheel steering system for imparting a steering angle to a rear wheel by an electric motor, including the electric four-wheel steering system according to the previous invention constructed and operated as described above. When the above is actually incorporated in an automobile, it is desired to improve the following points.

First, as a first improvement, it is desired to omit the centering spring 25. That is, the centering spring 25 incorporated for fail-safe has a large elasticity so that the rear wheel output shaft 11 can be returned to the neutral position even when the electric motor 19 fails and does not move. For this reason, the force required to displace the rear wheel output shaft 11 by the electric motor 19 at a normal time becomes large, which causes an increase in the size of the electric motor 19 and an increase in current consumption.

In order to solve such a problem, it is desired to realize a fail-safe structure that returns the rear wheel output shaft 11 to the neutral position when the electric motor fails even if the centering spring 25 is omitted.

Next, as a second improvement, the electric motor 1
9 It is desired to prevent the output shaft 11 for the rear wheels from being accidentally displaced at the time of failure. That is, when the electric motor 19 runs away (inadvertently rotates) due to some cause such as a short circuit of the wiring, the rear wheel output shaft 11 is displaced while compressing the centering spring 25, and the rear wheel 9, 9 is moved to the rear wheels 9, 9. The steering angle is given. In an actual case, since the displacement sensors 22 and 22 detect an abnormal displacement and the controller 24 cuts off the power supply to the electric motor 19 from the base, the rear wheels 9 and 9 are dangerously steered. Although it is considered that the angle is not applied, an unfavorable steering angle may be applied to the rear wheels 9 in the short time until the electric motor 19 stops. ..

In order to solve such a problem, it is desired to realize a structure in which the rear wheel output shaft 11 is not displaced even when the electric motor runs out of control.

The electric four-wheel steering system of the present invention was invented in view of the above-mentioned circumstances.

[0032]

An electric four-wheel steering system according to the present invention includes a rear wheel output shaft for imparting a steering angle corresponding to a displacement amount to a rear wheel by axial displacement. An electric motor, which is provided between the first electric motor and the rear wheel output shaft, displaces the rear wheel output shaft in the axial direction when the first electric motor is energized. The first reduction gear, the second electric motor, and the second electric motor, which are provided between the second electric motor and the rear wheel output shaft, and are energized to the second electric motor. Control for displacing the rear wheel output shaft in the same direction by controlling a second speed reducer for displacing the rear output shaft in the axial direction and the first and second electric motors And a container. Then, the first and second speed reducers reduce the movement of the rear wheel output shaft to the first direction in comparison with the efficiency in the forward direction of transmitting the movements of the first and second electric motors to the rear wheel output shaft. , The efficiency of the reverse direction transmitted to the second electric motor is reduced.

[0033]

When the steering angle is applied to the rear wheels by the electric four-wheel steering system of the present invention configured as described above, the controller energizes the first and second electric motors, The second electric motor displaces the rear wheel output shaft through the first and second speed reducers in the axial direction to impart a steering angle to the rear wheels.

Even if one of the electric motors fails in the state where the steering angle is applied to the rear wheels, the other electric motor returns the output shaft for the rear wheels to the neutral position and applies it to the rear wheels. The steering angle can be eliminated. Therefore, it is not necessary to provide a centering spring on the rear wheel output shaft, or even if a centering spring is provided, the output force of the first and second electric motors need not be so large. Absent.

Further, even if any of the electric motors runs out of control, the rear wheel output shaft will not be accidentally displaced. That is, even if one of the electric motors runs out of control, as long as the other electric motor is operating normally, the output shaft for the rear wheels does not move due to the existence of the speed reducer having low reverse efficiency. The output shaft prevents the steering angle from being inadvertently applied to the rear wheels.

[0036]

FIG. 1 shows a first embodiment of the present invention. The rear wheel output shaft 11 is inserted into a cylindrical case 33 supported under the floor of the automobile through a slide bearing 34 so as to be displaceable in the axial direction (the left-right direction in FIG. 1). At both ends of the rear wheel output shaft 11, universal joints 35, 3 are respectively provided.
One end of each of the connecting rods 36, 36 is connected to each other via 5. By connecting the other ends of the connecting rods 36, 36 to the tips of the knuckles for steering the rear wheels, the left and right rear wheels are adjusted according to the displacement amount in accordance with the displacement of the rear wheel output shaft 11. The steering angle is given.

A first electric motor 37a and a second electric motor 37b are provided on both sides of the case 33 so that the output shafts 38a and 38b of the electric motors 37a and 37b are parallel to the central axis of the case 33. It is supported and fixed. Transmission shafts 39a and 39b are respectively coupled to the tip ends of the output shafts 38a and 38b via electromagnetic clutches 40a and 40b, and when the electromagnetic clutches 40a and 40b are connected, the transmission shafts 39a and 39b are Each output shaft 38a, 3
It is designed to rotate with 8b.

The transmission shafts 39a and 39b are rotatably supported by a pair of bearings 41 and 41, respectively. Then, one end of each transmission shaft 39a, 39b is connected to each output shaft 38a, 38b via each electromagnetic clutch 40a, 40b as described above, and the other end is provided with an encoder 42a, 42b. The transmission shafts 39a, 39
The rotation angle of b can be detected freely.

In addition, brakes 43a and 43b and worms 44a and 44b are provided in the middle of the transmission shafts 39a and 39b in this order from the electromagnetic clutches 40a and 40b.
And are provided in series with each other. Worm 44 in this
a and 44b are worm wheels 45 described later, respectively.
By engaging with a and 45b, the first and second speed reducers 46
a and 46b.

On the other hand, rack teeth 15 are integrally formed on the outer peripheral surface of the intermediate portion of the rear wheel output shaft 11. In the vicinity of the rear wheel output shaft 11, first and second rotary shafts 47a,
47b is rotatably supported by bearings 48 and 49 in a torsional positional relationship with the rear wheel output shaft 11. Then, the first and second rotary shafts 47a, 47b
50a, 50b formed on the outer peripheral surface of the tip of the
Are engaged with the rack teeth 15, respectively.

The worm wheels 45a and 45b fixed to the base ends of the first and second rotary shafts 47a and 47b are
By engaging the worms 44a and 44b,
The second reduction gears 46a and 46b are configured. Further, encoders 52a and 52b are provided at the base ends of the first and second rotary shafts 47a and 47b, and an encoder 62 is provided at the distal end of the second rotary shaft 47b. The displacement amount of the rear wheel output shaft 11 can be detected through the rotation angle of the shafts 47a and 47b. The three encoders 52a, 52b and 62 are provided so that even if any one of the encoders fails, the rear wheel output shaft 11 is set to the neutral position based on the signals from the remaining two encoders. This is to make it return to.

As mentioned above, each is a worm 44a,
44b and worm wheels 45a and 45b are incorporated into these first and second speed reducers 46a and 46b.
Compared with the efficiency in the forward direction of transmitting the movements of the first and second electric motors 37a, 37b to the rear wheel output shaft 11,
The movement of the rear wheel output shaft 11 is controlled by the first and second electric motors 37.
The efficiency in the reverse direction transmitted to a and 37b is low.

Further, a controller (not shown) includes the first and second electric motors 37a and 37b and the electromagnetic clutch 40a.
40b and the brakes 43a and 43b are controlled,
The output shaft 1 for the rear wheel is driven by both electric motors 37a and 37b.
1 is displaced in the same direction.

When the steering angle is applied to the rear wheels by the electric four-wheel steering system of the present invention configured as described above, the controller connects the electromagnetic clutches 40a and 40b and the brakes 43a and 43b. Is released (as a non-braking state), and the first and second electric motors 37a, 37b are energized.

As a result of energizing the first and second electric motors 37a, 37b, the output shafts 38a, 38b, the transmission shaft 39
a, 39b, worms 44a, 44b, first and second rotary shafts 47a, 47b, pinion teeth 50a, 50b, and rack teeth 15, the rear wheel output shaft 11 is displaced in the axial direction. .. Then, with the displacement of the rear wheel output shaft 11, the connecting rods 36, 36 are pushed and pulled,
A steering angle is given to the rear wheels.

When one of the electric motors 37a (or 37b) fails while the steering angle is applied to the rear wheels, the controller controls the other electric motor 37b (or 37a) for the rear wheels. The output shaft 11 is returned to the neutral position and the steering angle applied to the rear wheels is eliminated. At this time, if necessary, the connection of the electromagnetic clutch 40a (or 40b) on the side of the electric motor 37a (or 37b) is disconnected, and the rotation of the other electric motor 37b (or 37a) is smoothly performed. Like (Failed electric motor 37a (or 37b)
However, so that it does not hinder the rotation).

Since the reverse efficiencies of the first and second speed reducers 46a and 46b are low, one of the rotating shafts 47a is not driven to rotate due to the failure of any one of the electric motors 37a (or 37b). (Or 47b), it takes some force to return the rear wheel output shaft 11 to the neutral position by the other electric motor 37b (or 37a), but the electric motor 37a (or 37b) The electromagnetic clutch 40a unless
Even if (or 40b) is still connected, the rear wheel output shaft 11 can be sufficiently returned to the neutral position. Even if the electric motor 37a (or 37b) cannot rotate due to seizure or the like, the electromagnetic clutch 40a (or 40)
By disconnecting the connection of b), the rear wheel output shaft 11 can be returned to the neutral position.

Therefore, it is necessary to provide the rear wheel output shaft 11 which constitutes the electric four-wheel steering system of the present invention with the centering spring 25 (FIGS. 5 to 6) as in the case of the above-mentioned prior invention. It will either disappear, or even if it is provided, it will be less elastic. Therefore, in order to give the steering angle to the rear wheels in the normal state, in order to displace the rear wheel output shaft 11, a large force that overcomes the large elasticity of the centering spring 25 is not required. Therefore, the outputs of the first and second electric motors 37a, 37b for steering the rear wheels need not be so large. When going straight, the rear wheel output shaft 11 is
When it is necessary to maintain the neutral position, the brakes 43a and 43b prevent the transmission shafts 39a and 39b from rotating.

Further, as described above, the first and second speed reducers 46
Since the reverse efficiency of a and 46b is suppressed low, the first and second electric motors 37a and 37b make the same movement (rotational movement that displaces the rear wheel output shaft 11 in the same direction by the same amount). Only in this case, the rear wheel output shaft 11 is displaced in the axial direction. Therefore, one of the electric motors 37a
Even if (or 37b) runs out of control, the rear wheel output shaft 11 will not be accidentally displaced.

That is, even if one of the electric motors 37a (or 37b) runs out of control, the other electric motor 37a
As long as b (or 37a) is operating normally, the worm 44 on the side of the other electric motor 37b (or 37a) due to the presence of the speed reducer 46b (or 46a) having low reverse efficiency.
b (or 44a) does not rotate. Therefore, the rear wheel output shaft 11 does not move, and the rear wheel output shaft 11 does not move.
As a result, the steering angle will not be inadvertently applied to the rear wheels.

It should be noted that the controller is the encoder 42
Output signals from a, 42b, 52a, 52b and 62 are constantly monitored, and if an abnormal steering angle is given to the rear wheels, the rear wheel output shaft 11 is immediately returned to the neutral position. After that, the electromagnetic clutches 40a and 40b are disconnected, and the brakes 43a and 43b are operated (brought into a braking state). In this state, no steering angle is applied to the rear wheels, and the vehicle can be handled in the same manner as when a normal two-wheel steering device is incorporated. The encoder 5
2a, 52b, 62 have a smaller amount of rotation to be detected than the encoders 42a, 42b, so potentiometers, etc.
Other displacement sensors can be substituted.

Next, FIG. 2 shows a second embodiment of the present invention. The first embodiment described above corresponds to the first and second speed reducers 46.
In order to configure a and 46b, the two rotary shafts of the first rotary shaft 47a and the second rotary shaft 47b are used, whereas in the case of the present embodiment, the bearings 48 and 48 are used. Worm wheels 45a and 45b are fixed to both ends of a single rotary shaft 51 that is rotatably supported. or,
Pinion teeth 5 formed in the intermediate portion of the one rotary shaft 51
0 is meshed with rack teeth 15 formed on the rear wheel output shaft 11, and the rear wheel output shaft 11 is displaced in the axial direction as the rotary shaft 51 rotates. is doing. The encoders 52a, 52b and 62 for detecting the displacement amount of the rear wheel output shaft 11 are provided with the single rotary shaft 51.
It is attached to both ends of. Other configurations and operations are similar to those of the above-described first embodiment.

Next, FIG. 3 shows a third embodiment of the present invention. In each of the first and second embodiments described above, the first and second speed reducers 46a and 46b having low reverse efficiency are installed in the worm 44.
In the case of the present embodiment, the square screw portion 53 formed on the outer peripheral surface of the intermediate portion of the rear wheel output shaft 11 and the square screw portion 53 and the worm wheels 45a and 45b are provided. A pair of nut pieces 54a, 54 screwed into the screw portion 53
b and the first and second speed reducers 46 having low reverse efficiency.
a and 46b.

The nut pieces 54a, 54b are supported by a support device (not shown) at the positions shown in FIG. 3 so as to be rotatable (displaceable in the axial direction). The driven gears 55a and 55b formed on the outer peripheral surfaces of the end portions of the nut pieces 54a and 54b are meshed with the drive gears 56a and 56b fixed to the transmission shafts 39a and 39b. Further, by mounting the encoders 52a, 52b and 62 on both ends of the pinion shaft 58 meshed with the rack teeth 57 formed on the outer peripheral surface of the intermediate portion of the rear wheel output shaft 11,
The amount of displacement of the rear wheel output shaft 11 in the axial direction can be detected. Other configurations and operations are similar to those of the above-described first and second embodiments.

Next, FIG. 4 shows an auxiliary device in the case of constituting the electric four-wheel steering system of the present invention. In the case of the electric four-wheel steering system of the present invention, the
Since the second electric motors 37a and 37b are synchronously rotated, if the two motors 37a and 37b are not reliably synchronized, the worms 44a and 44b forming the first and second speed reducers 46a and 46b are formed. And worm wheel 45a,
45b, or square screw portion 53 and nut pieces 54a, 54
There is a risk that the rear wheel output shaft 11 will not be displaced smoothly due to strong friction with each other or meshing with each other in a significant case. Of course, it is possible to eliminate such a problem by ensuring that the first and second motors 37a and 37b are synchronized with each other.
Since a, 37b and a control circuit with high precision are required, the manufacturing cost of the electric four-wheel steering device increases.

Therefore, as shown in FIG. 4, the worm 44a
One of the transmission shafts 39a (3
If 9b) is elastically displaceable in the axial direction,
When there is a slight difference in rotation between the first and second electric motors 37a and 37b, either one of the transmission shafts 39a
This difference can be absorbed by displacing (39b) in the axial direction.

That is, the transmission shaft 39a (39b) supported by a pair of bearings 59, 59 arranged at a distance from each other.
Of the worm 44a (44b) and the bearings 59, 59 on the outer peripheral surface of the worm 44a (44b).
0 and 60 are formed. And each collar part 60, 60
And the bearings 59, 59 between the elastic material 6 such as a disc spring.
The elastic members 61 and 61 are sandwiched between the elastic members 61 and 61 while being elastically slightly pressed. Therefore, the transmission shaft 39a (39
In b), a slight elastic displacement is freely possible in the axial direction, and when there is a difference in rotation of the first and second electric motors 37a, 37b, the transmission shaft 39a (39b) is By displacing in the direction, this difference is absorbed, and a smooth displacement in the axial direction of the rear wheel output shaft 11 is secured.

The electric four-wheel steering system of the present invention has a structure in which the rear wheel output shaft is axially displaced based on the energization of the electric motor to impart a steering angle to the rear wheels. If so, it can be applied. That is, the electric four-wheel steering device to which the present invention is applied does not need to have the compliance steer mechanism incorporated therein, unlike the electric four-wheel steering device according to the previous invention.

[0059]

Since the electric four-wheel steering system of the present invention is constructed and operates as described above, a small-sized and low-power electric motor can be used as the electric motor constituting the electric four-wheel steering system. As a result, not only the manufacturing cost can be reduced, but also the degree of freedom of the installation position of the electric motor is increased, and the design of the electric four-wheel steering device can be facilitated.

Further, even if the electric motor runs out of control, it is possible to reliably prevent the steering angle from being inadvertently applied to the rear wheels.
A high degree of safety can be secured.

[Brief description of drawings]

FIG. 1 is a plan view of an essential part showing a first embodiment of the present invention.

FIG. 2 is a plan view of an essential part showing the second embodiment.

FIG. 3 is a plan view of an essential part showing the third embodiment.

FIG. 4 is a main part plan view showing an accessory device in the case of configuring the electric four-wheel steering system of the present invention.

FIG. 5 is a partial cross-sectional plan view showing the electric four-wheel steering system of the previous invention.

FIG. 6 is an enlarged view of part A of FIG.

FIG. 7 is a diagram showing a relationship between a displacement amount of the rear wheel output shaft in the axial direction and a spring load applied in the axial direction of the rear wheel output shaft.

FIG. 8 is a diagram showing the relationship between vehicle speed and steering angle ratio.

[Explanation of sign]

 1 Steering Wheel 2 Steering Shaft 3 Steering Gear 4 Front Wheel Output Shaft 5 Knuckle Earl 6 Front Wheel 7 Steering Column 8 Snake Angle Sensor 9 Rear Wheel 10 Housing 11 Rear Wheel Output Shaft 12 Force Point 13 Knuckle Ear 14 Snake Center 15 Rack Teeth 16 Transmission shaft 17 Pinion teeth 18 Worm wheel 19 Electric motor 20 Output shaft 21 Worm 22 Displacement sensor 23 Vehicle speed sensor 24 Controller 25 Centering spring 26 Seat plate 27 Step part 28 Stop ring 29 Disc leaf spring 31 Electromagnetic clutch 32 Encoder 33 Case 34 Sliding bearing 35 Universal joint 36 Connecting rod 37a First electric motor 37b Second electric motor 38a Output shaft 38b Output shaft 39a Transmission shaft 39b Transmission shaft 40a Electromagnetic clutch 40b Electromagnetic clutch Switch 41 bearing 42a encoder 42b encoder 43a brake 43b brake 44a worm 44b worm 45a worm wheel 45b worm wheel 46a first reducer 46b second reducer 47a first rotary shaft 47b second rotary shaft 48 bearing 49 bearing 50 pinion tooth 50a pinion tooth 50b pinion tooth 51 rotating shaft 52a encoder 52b encoder 53 square screw part 54a nut piece 54b nut piece 55a driven gear 55b driven gear 56a drive gear 56b driving gear 57 rack tooth 58 pinion shaft 60 bearing 59 bearing Elastic material 62 Encoder

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kaoru Seino 12 1390, Yawatacho, Takasaki City, Gunma Prefecture

Claims (1)

Claim: What is claimed is: 1. A rear wheel output shaft for imparting a steering angle according to a displacement amount to a rear wheel by axial displacement, a first electric motor, and the first electric motor. A first speed reducer provided between the motor and the rear wheel output shaft for displacing the rear wheel output shaft in the axial direction when the first electric motor is energized; A second electric motor, which is provided between the second electric motor and the rear wheel output shaft, and which covers the rear wheel output shaft in the axial direction when the second electric motor is energized. A second speed reducer for displacing the second wheel, and a controller for controlling the first and second electric motors to displace the rear wheel output shaft in the same direction by the both electric motors,
The second reducer compares the movement of the first and second electric motors to the efficiency of the forward direction for transmitting the movements of the first and second electric motors to the rear wheel output shaft. An electric four-wheel steering system in which the reverse efficiency transmitted to the vehicle is low.