JPH07137644A - Motor-operated power steering device - Google Patents

Abstract

PURPOSE:To simplify constitution by integrally constituting an output shaft of a motor and an worm shaft constituting a speed reducer. CONSTITUTION:An output shaft 16 of a motor M and a shaft of a worm gear 12 are integrally formed, and they are integrated by shaft supporting the output shaft 16 on three points by bearings 18a, 18b, 19a in a gear case 18 and a motor case 19, and by engaging a projection part 11d of a gear part 11b with a hole 11e, a worm wheel 11 is integrated with a metal ring 11a key-stopped on a lower side column shaft 2B. Additionally, it is devised so that an alternate function of a clutch is performed by cutting the projection part 11d in the case when torque of more than a specified value works on the gear part 11b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device which is mounted on an automobile and assists a force required to operate a steering wheel by a rotational force of an electric motor.

[0002]

2. Description of the Related Art An electric power steering system in which a steering assisting motor is driven on the basis of a detection result of a steering torque applied to a steering wheel so that a force required for steering an automobile is assisted by a rotational force of the motor. The device is being developed.

FIG. 4 is a schematic sectional view of a conventional column type power steering apparatus for steering an automobile, and FIG. 5 is a partial sectional view taken along line VV in FIG. In FIGS. 4 and 5, 2A indicates an upper column shaft and 2B indicates a lower column shaft. The upper column shaft 2A is rotatably supported by the column housing 3, a steering wheel (not shown) is attached to the upper end of the upper column shaft 2A, and the lower end of the upper column shaft 2A is connected to the upper end of the lower column shaft 2B and the torsion bar 4. It is connected. The lower end of the lower column shaft 2B is connected to a pinion shaft and a rack shaft of a steering mechanism (not shown). At the top of the torsion bar 4, the upper column shaft
A torque sensor 5 for detecting the torque acting on 2A is provided, and its output signal is given to an energization control unit (not shown).

A worm wheel 31 is fitted over the lower column shaft 2B and is fixed to a flange 38 provided on the lower column shaft 2B. The worm wheel 31 is an intermediate portion of a worm shaft 32 connected to the motor M. It meshes with the worm gear 33, which has a toothed portion. The worm shaft 32 meshing with the worm wheel 31 is supported by the gear case 37 on both sides by bearings 39a and 39b, and a serration 32a is formed at a portion protruding from the bearing 39a to the motor M side. The case 35 of the motor M is a gear case that houses the worm wheel 31, the worm shaft 32 and the electromagnetic clutch 36.
It is attached to 37.

A main driving portion 36a of an electromagnetic clutch 36 for engaging and disengaging the output of the motor M is externally fitted to the output shaft 34 of the motor M, and a driven portion 36b faces the worm shaft 32 side. The driven portion 36b is internally fitted and coupled to the worm shaft 32 with serrations 32a. The driven portion 36b is supported by a serration 32a and a bearing 34a fitted onto the output shaft 34 of the motor M.

In such a power steering device, when the steered wheels are rotated, a torque acts on the torsion bar 4 via the upper column shaft 2A by the operation, and the torque sensor 5 detects the torque. A signal of the detected torque is given to an energization control unit (not shown), the energization control unit operates to drive the motor M, and is also transmitted to the electromagnetic clutch 36 so that the worm shaft 32 rotates and the worm wheel 31 rotates. The rotation of the worm wheel 31 rotates the lower column shaft 2B to assist the steering force.

[0007]

In the column type electric power steering apparatus as described above, the motor M and the worm gear 33 constituting the speed reducer have a separated structure with an electromagnetic clutch 36 interposed. The output shaft 34 of the motor M has bearings 39a and 39 at both ends thereof and the electromagnetic clutch 36 at a total of three places, and the worm shaft 32 has bearings at both ends thereof.
The motor case 35 and the gear case 37 are rotatably supported by using b and are fastened with bolts. Therefore, after assembly, the worm shaft 32 and the output shaft 34 of the motor M are supported by five bearings, and it is difficult for each bearing to absorb the misalignment, and it takes time to assemble and torque unevenness occurs. It was the cause of the outbreak.

The present invention has been made in view of such circumstances, and an object of the present invention is to make the output shaft of the motor and the worm shaft integral with each other, thereby greatly simplifying the configuration and facilitating the assembly. The purpose of the present invention is to provide an electric power steering device.

[0009]

In an electric power steering apparatus according to the present invention, an output shaft of a motor is connected to a steering mechanism via a speed reducer including a worm shaft and a worm wheel, and a steering force is generated by a rotational force of the motor. In the electric power steering device, the worm shaft is integrally formed with the output shaft of the motor, and the motor and the steering mechanism are disconnected when a torque larger than a predetermined value is applied to the reduction gear. A torque limiter is provided.

[0010]

According to the present invention, the output of the motor is transmitted to the column through the worm shaft and the worm wheel that constitute the speed reducer without passing through the electromagnetic clutch, and the configuration is greatly simplified. Moreover, even if a trouble occurs in which the motor or the worm gear is locked, when the steering force exceeds a certain level, the transmission of force is interrupted between the output shaft of the motor and the steered wheels, and the steerability is not impaired.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 1 is a partial cross-sectional view of an electric power steering apparatus according to the present invention, in which M is a motor and 1
Reference numerals 1 and 12 represent worm wheels and worm gears that constitute the speed reducer. The output shaft 16 of the motor M is a worm gear
The worm gear 12 is directly formed on the outer circumference of one end of the output shaft 16 protruding from the motor case 19, and the bearings 18a and 18b are provided at both ends of the worm gear 12, respectively. Is rotatably supported by the gear case 18, and the other end is rotatably supported by the motor case 19 by the bearing 19a.

The output shaft 16 located in the motor case 19 is knurled at the center, and the core 20 is provided on the outer periphery of the output shaft 16.
A coil 22 is arranged around the coil 22 with an insulating sinter coating 21 interposed therebetween, and a core 24 is further wrapped around the coil 22 with an insulating coating 23.

A contact portion 26 connected to the coil 22 is provided on the outer periphery of the output shaft 16 adjacent to the position where the coil 22 is arranged, with a commutator 25 interposed. Motor case
Reference numeral 19 is composed of a cylindrical main case 19b and a side case 19c that closes one end of the main case 19b. Inside the main case 19b, there is a magnet 27 facing the periphery of the coil 22, and a contact portion.
A brush 28 is arranged at a position facing 26. Magnet 27
Is a cover 27 made of stainless steel on the inner surface facing the coil 22.
covered with a. The brush 28 is biased and held so that the brush 28 is slidably contacted to the contact portion 26 with a spring 28b interposed in the brush holder 28a. 29 is a side case 19 of the motor case 19.
It is a plug fitted in the cylindrical part of c.

The motor case 19 and the gear case 18 are integrally fastened by a bolt 30 that fastens the main case 19b and the side case 19c of the motor case 19 together. FIG. 2 is a partially enlarged side view of the worm wheel. The worm wheel 11 is constructed by fixing a gear portion 11b to a metal ring 11a keyed to the lower column shaft 2B. The gear part 11b of the worm wheel 11 is made of synthetic resin in an annular shape, and has a toothed part 11c on the outer peripheral surface and an annular part with a protruding part 11d formed on part of the inner peripheral surface. The protrusion 11d is externally fitted and fixed to the metal ring 11a in a state of being engaged with a hole 11e formed in a part of the outer circumference of the metal ring 11a in the circumferential direction.

The number of protrusions, the cross-sectional area, and the number of holes into which they are inserted are not particularly limited, and may be set as necessary. That is, the force F F given by the following formula = shear strength of resin × cross-sectional area × number is determined so as to have the following relationship. Maximum input from motor M <F <force greater than human steering force

FIG. 3 is a schematic view showing another embodiment of the worm wheel according to the present invention. A ridge 11f extending in a direction parallel to the axis is provided at one location on the inner peripheral surface of the gear 11b. A concave groove formed by forming this ridge 11f on the outer peripheral surface of the metal ring 11a.
It is fitted onto the metal ring 11a while being engaged with the inside of 11g. The number, thickness, height, etc. of the protrusions 11f are not particularly limited and may be set as necessary.

In such a device of the present invention, the torque applied to the torsion bar through the steering wheel is detected by the torque sensor, and a drive signal corresponding to the torque is given to the motor M via an energization control unit (not shown). The motor M
Rotates. The rotation of the motor M is transmitted to the worm wheel 11 via the worm gear 12 provided on the output shaft 16, and the lower column shaft 2B is rotationally driven to assist the steering force.

On the other hand, when the motor M is locked due to a trouble, the worm gear 12 and the worm wheel 11 are also locked, and when the driver applies a steering force to the steering wheel, a large torque exceeding the normal steering force is applied to the worm wheel 11. It will be. As a result, a large shearing force acts on the protrusion 11d (or the protrusion 11f) of the gear 11b through the metal ring 11a of the worm wheel 11, and when this shearing force exceeds a predetermined force F, the protrusion 11d (or the protrusion 11f). 11f) is cut off,
The restraint force between the metal ring 11a and the gear portion 11b is released and the free rotation state is established, the restraint force between the lower column shaft 2B and the output shaft 16 of the motor M is released, and the force transmission is interrupted. It has the same effect as disengaging the clutch.

[0019]

As described above, in the electric power steering apparatus according to the present invention, the clutch can be eliminated and the motor output shaft and the worm shaft can be integrally structured, so that the structure can be greatly simplified and the misalignment of the bearing can be considered. Since the worm wheel is provided with a connecting portion between the gear portion and the shaft portion, which allows the worm wheel to freely rotate when a force greater than a predetermined value is applied, the motor is locked. Even if it happens, you can easily eliminate this,
The present invention has excellent effects such as ensuring safe steering.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of an electric power steering device according to the present invention.

FIG. 2 is a side view showing a connecting structure of a worm and a worm wheel.

FIG. 3 is an explanatory view showing another embodiment of the worm wheel.

FIG. 4 is an explanatory diagram showing a configuration of a conventional electric power steering device.

5 is an enlarged cross-sectional view taken along the line VV of FIG.

[Explanation of symbols]

 11 Worm wheel 11a Metal ring 11b Gear part 11c Tooth part 11d Projection part 11e hole 12 Worm gear 16 Output shaft 18 Gear case 18a, 18b Bearing 19 Motor case 19a Bearing 19b Main case 19c Side case 20 Core 22 Coil 28 Brush M motor

Claims (1)

[Claims] 1. An output shaft of a motor is connected to a steering mechanism through a speed reducer including a worm shaft and a worm wheel,
In an electric power steering device in which a steering force is assisted by a rotational force of a motor, the worm shaft is integrally formed with an output shaft of the motor, and the motor is operated when a torque larger than a predetermined value acts on the speed reducer. An electric power steering apparatus comprising a torque limiter for releasing the connection between the steering mechanism and the steering mechanism.