JPH0585373A - Motor-driven rear wheel steering gear - Google Patents

Abstract

(57) [Summary] [PROBLEMS] An object of the present invention is to provide an electric rear wheel steering system in which productivity is improved by not using a hypoid gear, and the reverse efficiency is 0 as in the hypoid gear. In a rear wheel steering system including a power unit for controlling an output according to a steering angle of front wheels by a controller, an electric motor m attached to a casing 1 and the electric motor m
And a ring 26 that rotates by this transmission mechanism, an acme screw part 28 formed inside the ring 26, and a rod 17 having a worm 30 that meshes with the acme screw part 28. Has been done.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric rear wheel steering system provided with an optimum transmission mechanism for transmitting the rotation of an electric motor to a rod.

[0002]

2. Description of the Related Art FIGS. 3 to 5 show a conventional electric rear wheel steering system. This device is configured as follows. First, the hypoid gear pinion 3 is attached to the motor shaft 2 of the electric motor m fixed to the casing 1. The hypoid gear pinion 3 meshes with the hypoid gear wheel 4. The hypoid gear pinion 3 and the hypoid gear wheel 4 constitute a gear group. Since the gear groups are combined so as to satisfy the condition that the reverse efficiency is 0, the gear groups receive the external force transmitted from the rear wheel (not shown) during traveling. Therefore, the electric motor m is not rotated by the external force from the rear wheels.

Further, the hypoid gear wheel 4 is
It is rotatably supported by the casing 1 by bearings 5 and 6. A support shaft 7 is fitted and fixed to the hypod gear wheel 4. A plate body 9 having a cutout portion 8 is attached to the upper portion of the support shaft 7. The plate body 9 is connected to a potentiometer 11 provided on the cover 10. The support shaft 7 and the potentiometer 11 are connected as follows. That is, the potentiometer 11 has the lever portion 12. The lever portion 12 is fitted in the cutout portion 8 of the plate body 9. As a result, the rotation of the support shaft 7 is transmitted to the potentiometer 11. Further, since the potentiometer 11 is connected to a controller (not shown), the potentiometer 11 can detect the rotation angle of the support shaft 7 and send the information to the controller.

A cylindrical recess 13 is formed in the vicinity of the lower central portion of the hypoid gear wheel 4. A spherical bearing 14 provided in the recess 13 rotatably supports one end of the stud shaft 15. The stud shaft 15 is eccentric with respect to the support shaft 7 of the hypoid gear wheel 4 by an eccentric amount e. (See Figure 5)

A taper portion 16 is formed on the other end of the stud shaft 15, that is, on the side opposite to the spherical bearing 14. The tapered portion 16 is adapted to coincide with the tapered hole portion 18 formed in the rod 17. The taper portion 16 is fitted and fixed in the taper hole portion 18. Further, another potentiometer 19 shown in FIG. 4 is attached to the rod 17. The potentiometer 19 detects the moving distance of the rod 17 and sends the information to the controller. The rod 17 is slidably supported by a bush 43 attached to the casing 1. Further, the rod 17 moves along the axial direction thereof. The movement is transmitted to the side rods (not shown) attached to both ends of the rod 17 and the rear wheels attached via the side rods to steer the rear wheels. In other words, since the moving distance of the rod 17 corresponds to the steering angle of the rear wheels,
By measuring the moving distance of the rod 17, the steering angle of the rear wheels can be known. Thereby, the moving distance of the rod 17 is read by the potentiometer 19 and the information is sent to the controller.

The operation of the electric rear wheel steering system configured as described above will be described below. First, when the electric motor m whose rotation is controlled by a signal from a controller (not shown) is rotated, the hypoid gear pinion 3 attached to the motor shaft 2 is also rotated. As a result, the hypoid gear wheel 4 meshing with the hypoid gear pinion 3 also rotates. When the hypoid gear wheel 4 rotates, the stud shaft 15 rotates around the axis of the hypoid gear wheel 4. (Stud shaft 15
Is eccentric with respect to the support shaft 7 of the hypoid gear wheel 4 by an eccentric amount e. ) Such movement of the stud shaft 15 is allowed only in the linear direction along the axis of the rod 17. And for other movements, spherical bearing 1
Absorbed by 4. Therefore, the rotation of the electric motor m is converted into the linear motion of the rod 17 as described above, and the rear wheels (not shown) at both ends of the rod 17 are steered. Further, even if the external force from the rear wheel is transmitted to the gear group, the reverse efficiency of the gear group is 0, so that the electric motor m is not rotated by the force from the rear wheel side.

[0007]

The conventional electric rear wheel steering system as described above has the following problems. That is, in order to reduce the reverse efficiency to zero, the conventional device uses a hypopod gear. A hypoid gear is a kind of staggered gear that uses a part of a hyperboloid of revolution as a pitch surface and provides rotation between two axes that are not parallel and do not intersect. For this reason,
The shape of the tooth itself is also complicated. Further, in order to make the reverse efficiency zero by using this hypoid gear, γ <ρ (1) ψ _P : spiral angle γ = 90 ° −ψ _P (2) μ: friction coefficient ρ = tan ⁻¹ (μ / cos θ ) (3) θ: pressure angle, γ: reverse efficiency, and in order to rotate the hypoid gear smoothly, the hypoid gear pinion 3
It is necessary to adjust the degree of contact between the hypoid gear wheel 4 and the hypoid gear wheel 4. Due to these various conditions being overlapped, there is a problem that the number of work steps for increasing the assembling accuracy increases. Further, for the same reason as described above, there is also a problem that the production cost is increased because a dedicated gear cutting machine is required to manufacture the hypoid gear.

An object of the present invention is to provide an electric rear wheel steering system which does not use a hypoid gear to improve productivity and which has a reverse efficiency of 0 as well as a hypoid gear.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, according to the present invention, in a rear wheel steering system including a power unit for controlling an output according to a steering angle of front wheels by a controller, rotation is controlled by the controller. The electric motor is attached to the casing, and in the casing, a transmission mechanism for transmitting the rotation of the electric motor, a ring rotated by the transmission mechanism, an acme screw portion formed inside the ring, and the acme. And a rod forming a worm that meshes with the threaded portion.

[0010]

When the electric motor rotates, the rotation causes the ring to rotate via the transmission mechanism. The rotation of the ring also rotates the acme screw portion in the ring, and the rotation is transmitted to the worm meshing with the acme screw portion. Further, since the worm is formed on the rod, the rotation of the electric motor is eventually transmitted to the rod as described above to steer the rear wheels attached to both ends of the rod. In addition, since the reverse efficiency of this combination of the acme screw part and the worm is 0,
The external motor from the rear wheels does not rotate the electric motor. This prevents the rear wheels from being unnecessarily steered even if an external force acts from the rear wheels.

[0011]

1 to 3 show an embodiment of the present invention. The same reference numerals are used for the same components as those of the conventional example described above,
Detailed description thereof will be omitted.

FIG. 1 shows a first embodiment, which has the following structure. That is, the electric motor m is fixed to the casing 1 with the bolt 20. This electric motor m is
The rotation is controlled by a signal from a controller (not shown). A motor gear 21 is attached to the tip of the motor shaft 2 of the electric motor m. The potentiometer 11 is connected to the tip of the motor gear 21, detects the rotation angle of the electric motor m, and sends the signal to the controller. The motor gear 21 meshes with an intermediate gear 22 inside the casing 1. The rotary shaft 23 of the intermediate gear 22 is supported by a bearing 24. The intermediate gear 22 meshes with the gear ring 25.

The gear ring 25 has a gear 27 formed on the outer peripheral portion of the ring 26. A gear 24 on the outer peripheral portion of the ring 23 meshes with the intermediate gear 22. The gear ring 25 has a rotating shaft 29 and a bearing 24.
It is rotatably supported by. Also, this gear ring 2
An acme screw portion 28 is formed inside the member 5. The rod 17 penetrates the inside of the rotary shaft portion 29 of the gear ring 25. The rod 17 is slidably supported by a bush 43 attached to the casing 1. A worm 30 is formed on the rod 17. The worm 30 meshes with the acme screw portion 28 in the gear ring 25. Also, the gear ring 25
A groove 31 is provided at one end of the rod 17 protruding from both ends of the. The potentiometer 19 is connected to the groove 31 to detect the movement of the rod 17, and the information is sent to the controller. Further, a flat surface 32 is formed on one end of the rod 17 at a portion protruding from the gear ring 25. A rod rotation stopper 33 is provided in the casing 1 at a position corresponding to the flat surface 32 to prevent the rod 17 from rotating.

The operation of the rear wheel steering system having the above structure is as follows. That is, the electric motor m rotates, and the motor gear 21 attached to the tip of the motor shaft 2 rotates. Then, the intermediate gear 22 meshing with the motor gear 21 meshes with the gear 27 formed on the outer peripheral portion of the gear ring 25 to rotate the gear ring 25. As the gear ring 25 rotates, the acme screw portion 28 formed in the gear ring 25 also rotates. At this time, the worm 30 formed on the rod 17 is
, The rotation of the acme screw portion 28 is converted into the linear movement of the rod 17. When the rod 17 moves in the axial direction, the rear wheels (not shown) are steered accordingly. In this way, the rotation of the electric motor m moves the rod 17 in the direction along the axis of the rod 17 via the motor gear 21, the intermediate gear 22, and the gear ring 25. The rod 17 moves in the direction along the axis to steer the rear wheels.

At this time, even if an external force acts in the direction of moving the rod 17 from the rear wheel, the external force is still applied to the acme screw portion 28.
It does not rotate the electric motor m. Because the worm 30 formed on the rod 17
This is because the acme screw portion 28 has exactly the same relationship as the bolt and nut. That is, the rod 17 on which the worm 30 is formed corresponds to a bolt, and the gear ring 25 on which the acme screw portion 28 is formed corresponds to a nut.
When the nut is engaged with the bolt, the nut cannot be rotated even if a force is applied in a linear direction along the axis of the bolt. The same applies to the worm 30 and the gear ring 25. That is, since the worm 30 formed on the rod 17 corresponding to the bolt has a small helix angle, the force along the axial direction of the rod 17 is applied to the acme screw portion formed inside the gear ring 25 corresponding to the nut. It is received by 28 and does not rotate the gear ring 25. As described above, by combining the worm 30 and the acme screw portion 28, the gear ring 25 is not rotated by the external force from the rear wheel, and the reverse efficiency can be zero as in the hypoid gear group.

FIG. 2 shows a second embodiment of the present invention. Unlike the first embodiment, the motor shaft 2 of the electric motor m and the rod 17 are arranged coaxially, and the rotational force of the electric motor m is transmitted to the rod 17 by the planetary gear device.
The structure is as follows.

The motor shaft 2 of the electric motor m is hollow. The motor shaft 2 is rotatably supported by the casing 1 by a pair of bearings 34. Also,
A rotation sensor 35 for detecting the rotation state of the electric motor m is provided at one end of the electric motor m. A sun gear 36 that constitutes a planetary gear device is formed on the outer peripheral portion of one end of the motor shaft 2. A planetary gear 37 meshes with the sun gear 36. Further, a ring gear 38 formed in the casing 1 meshes with the planetary gear 37. This ring gear 38 is the sun gear 3
6 and the axis are the same.

The shaft portion 40 of the ring 26 is fitted in the rotation center portion 39 of the planetary gear 37. In this way, the shaft portion 40 of the ring 26 is fitted into the planetary gear 37. At this time, the motor shaft 2 of the electric motor m and the rotating shaft portion 41 of the ring 26 have the same center. The left and right sides of the ring 26 are rotatably supported by the casing 1 on the casing 1 in FIG. An acme screw portion 28 is formed inside the ring 26 as in the first embodiment. This electric motor m penetrates the inner peripheral portion of the hollow motor shaft 2,
A worm 30 is formed on the rod 17 that meshes with the acme screw portion 28 formed inside the ring 26, similarly to the first embodiment. Further, a potentiometer 19 for detecting the stroke of the rod 17 and a rod rotation stopper 31
The arrangement position and function are the same as those in the first embodiment.

The second embodiment constructed as described above operates as follows. That is, when the electric motor m rotates under the control of a signal from a controller (not shown), the sun gear 3 formed on the motor shaft 2 of the electric motor m.
6 rotates. When the sun gear 36 rotates, the planetary gear 37 revolves around the sun gear 36 while rotating on its axis. As the planetary gear 37 revolves around the sun gear 36, the ring 26 also rotates. When the ring 26 rotates, the acme screw portion 28 inside the ring 26 also rotates. By the rotation of the acme screw portion 28, the worm 30 of the rod 17 that meshes with the acme screw portion 28 moves to the left and right in the figure as in the first embodiment. As a result, the rear wheels (not shown) attached to both ends of the rod 17 are steered. Also at this time, similarly to the first embodiment, even if the force for moving the rod 17 is exerted by the external force from the rear wheel, the acme screw portion 2
8 does not receive the force to rotate the electric motor m. As a result, unnecessary steering of the rear wheels can be suppressed.

[0020]

[Effect] The rotation of the electric motor is transmitted to the ring via the transmission mechanism, and the acme screw portion formed in the ring and the worm formed on the rod are meshed with each other to change the rotational force from the ring into the linear movement of the rod and the rear wheel. Since it is steered, it is necessary to use parts such as a hypopod gear that require an extra process such as working with a special machine and adjusting tooth contact. Therefore, the manufacturing price can be reduced. Further, as can be seen from the shapes, the acme screw portion and the worm do not require the above-mentioned extra steps. For this reason, the accuracy can be easily controlled, the manufacturing cost can be reduced, and the maintenance can be easily performed.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment.

FIG. 2 is a sectional view of a second embodiment.

FIG. 3 is a sectional view of a conventional example.

FIG. 4 is an enlarged cross-sectional view taken along the line IV of FIG.

5 is a sectional view taken along line VV of FIG.

[Explanation of symbols]

 1 Casing 17 Rod 23 Ring 28 Acme screw part 30 Worm m Electric motor

Claims (1)

[Claims] 1. A rear wheel steering system including a power unit for controlling an output according to a steering angle of front wheels by a controller, wherein an electric motor whose rotation is controlled by the controller is attached to the casing, and the electric motor is installed in the casing. A configuration in which a transmission mechanism that transmits the rotation of the motor, a ring that is rotated by the transmission mechanism, an acme screw portion formed inside the ring, and a rod that forms a worm that meshes with the acme screw portion are provided. Electric rear wheel steering system.