JP2001071917A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a determined specified limit torque in a torque limiter provided in an electric power steering device to improve the durable reliability. SOLUTION: With the electric power steering device 10, a torque limiter 30 which slips by a specified torque is interposed between a nut side member (nut 22) of a ball screw device 14 and a rotor side member (sleeve 18) of an electric motor 13. In this case, the torque limiter 30 is made up of a fitting-ring 31 and an elastic ring 32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an electric power steering apparatus.

[0002]

2. Description of the Related Art An electric power steering apparatus includes a housing, a rack shaft meshed with a pinion connected to an input shaft and movably supported by the housing, and an electric motor disposed around the rack shaft in the housing. And a ball screw device for transmitting the torque of the electric motor to the rack shaft. In such an electric power steering device,
If the stroke of the rack shaft is suddenly stopped, for example, when the tire rides on a curb during steering, the inertia force of the motor that was rotating at a high speed at the ratio of the lead of the ball screw exerts a large impact force on the screw groove of the ball screw. As a result, the function of the ball screw is reduced, such as damage to the screw groove, and the steering feeling is deteriorated.

Therefore, in the prior art, in order to reduce the impact acting on the ball screw device, a torque limiter is provided in the torque transmission path of the motor as described in Japanese Patent Application Laid-Open No. Hei 9-56515. That is, as shown in FIG. 4, a sleeve 2 integral with a rotor 1 of a motor is closely fitted to a nut 3 of a ball screw device, and an elastic ring 4 is interposed in a close fitting portion 5 between the sleeve 2 and the nut 3. Things.

[0004]

However, in the prior art, the elastic ring 4 has a corrugated cross section to ensure resilience, and only a part of the inner peripheral surface is formed on the sleeve 2 and a part of the outer peripheral surface is formed. Only the nut is brought into contact with the nut 3. For this reason, the inner and outer peripheral surfaces of the elastic ring 4 partially contact each of the sleeve 2 and the nut 3 to locally increase the surface pressure generated therebetween, and the slip surface of the elastic ring 4 and the sleeve 2 and the elastic ring 4 The wear of the slip surface of the nut 3 is promoted, and the friction state of the elastic ring 4 fluctuates with time. The fluctuation of the frictional state of the elastic ring 4 makes it impossible to maintain a predetermined limit torque, and impairs the durability reliability of the torque limiter.

An object of the present invention is to maintain a predetermined limit torque set for a torque limiter provided in an electric power steering device, and to improve durability reliability.

[0006]

According to a first aspect of the present invention, a housing, a rack shaft meshed with a pinion connected to an input shaft and movably supported by the housing, and a rack shaft in the housing. In an electric power steering device having a motor disposed around the ball screw device for transmitting the torque of the motor to the rack shaft, between a nut-side member of the ball screw device and a rotor-side member of the motor,
A torque limiter that slips at a predetermined torque is interposed, and the torque limiter includes a fitting ring having a fitting surface entirely contacting one of the nut-side member and the rotor-side member, and a fitting surface of the fitting ring. It comprises an elastic ring pressed against one of the nut-side member and one of the rotor-side members, and slips on the fitting surface of the fitting ring.

According to a second aspect of the present invention, in the first aspect of the present invention, the fitting ring is further inscribed in an elastic ring, and an inner peripheral surface of the fitting ring is entirely in contact with the rotor side member. The fitting surface is used, and the outer peripheral surface of the elastic ring is supported by the nut-side member.

[0008]

According to the first aspect of the present invention, the following operations are provided. The torque limiter consists of a fitting ring and an elastic ring,
The fitting surface of the fitting ring slipping with the limit torque was brought into full contact with one of the nut-side member and the rotor-side member.
As a result, the surface pressure acting on the mating surface of the mating ring is reduced (compared to that in which the mating surface makes partial contact), and the frictional state of the mating surface (slip surface) of the mating ring over time is reduced. Can be suppressed, and as a result, the predetermined limit torque of the torque limiter can be maintained, and the durability reliability can be improved.

According to the second aspect of the present invention, the following operations are provided. The fitting ring was inscribed in the elastic ring, and the inner peripheral surface of the fitting ring was brought into full contact with the rotor side member. The rotational force based on the impact torque due to the inertial force of the electric motor is maximized on the inner peripheral surface of the fitting ring, which is the minimum radius of rotation among the components (fitting ring and elastic ring) of the torque limiter.
Therefore, the torque limiter can provide the inner peripheral surface (fitting surface) of the fitting ring even under a simple mounting structure in which the fitting ring and the elastic ring are simply inserted between the nut-side member and the rotor-side member.
As a matter of course, it becomes possible to slip.

[0010]

FIG. 1 is a sectional view showing an electric power steering apparatus, FIG. 2 is an enlarged sectional view of a main part of FIG. 1, FIG. 3 is a sectional view taken along line III-III of FIG. 2, and FIG. It is a schematic diagram which shows a technique.

The electric power steering apparatus 10 is shown in FIG.
As shown in FIG. 2, the housing 11 includes a housing 11, a rack shaft 12, an electric motor 13, and a ball screw device 14.

The housing 11 includes a first housing 11A.
(Pinion-side housing), second housing 11B (motor-side housing), and third housing 11C (nut-side housing) are press-fitted coaxially with each other, and then caulked and fixed.

The rack shaft 12 is engaged with a pinion (not shown) connected to an input shaft 15 to which a steering wheel is connected via a torsion bar (not shown), and is supported by the housing 11 so as to be movable in the left-right direction. I have. Both ends of the rack shaft 12 protrude to the left and right of the housing 11, and tie rods 16A and 16B are connected to their ends, so that the left and right wheels can be steered via the tie rods 16A and 16B by the left and right movement of the rack shaft 12. I have.

The electric motor 13 is arranged around the rack shaft 12 in the housing 11 and is fixed to the inner periphery of the second housing 11B (not shown), and is arranged around the rack shaft 12 with a gap therebetween. And a rotor 17. The electric motor 13 is fixed to the inner periphery of the rotor 17 and
2 is provided with a sleeve 18 coaxial with the sleeve 2.

The ball screw device 14 has a nut 22 held by a third housing 11C of the housing 11 via a bearing 21. A screw groove 23A of the nut 22 and a screw groove 23B provided on the rack shaft 12 are formed. Steel ball 2 between
3 is held. When the torque of the rotor 17 due to the operation of the electric motor 13 is transmitted to the nut 22 via the torque limiter 30 described below, the ball screw device 14
This rotation is converted into the axial movement of the rack shaft 12. still,
In FIG. 2, reference numeral 24 denotes an inner lock nut for locking the inner race of the bearing 21 to the nut 22, and reference numeral 25 denotes an outer lock nut for locking the outer race of the bearing 21 to the third housing 11C.

However, the electric power steering device 1
2, a predetermined distance is provided between a nut 22 (nut-side member) of the ball screw device 14 and a sleeve 18 (rotor-side member) fixed to the rotor 17 of the electric motor 13, as shown in FIGS. A torque limiter 30 that slips at the limit torque is provided.

The torque limiter 30 fits the outer peripheral surfaces 18A and 18B of the distal end of the sleeve 18 into the insertion holes 22A provided in the inner peripheral of the nut 22.
A, a fitting ring 3 fits in a ring groove 18C provided between
1 and an elastic ring 32. The outer peripheral surfaces 18A and 18B of the sleeve 18 are fitted into the insertion holes 22A of the nut 22 with a gap.

The fitting ring 31 has a flat bearing shape and is inscribed in the elastic ring 32. The inner surface of the fitting ring 31 is a fitting surface 31A that is entirely in contact with the outer surface of the ring groove 18C of the sleeve 18. The elastic ring 32 has a wavy shape in both the width direction and the circumferential direction, and the fitting surface 31A of the fitting ring 31 is fixed to the sleeve 18 while the outer peripheral surface is backed up by the inner peripheral surface of the insertion hole 22A of the nut 22. Press against Then, the torque limiter 30 slips on the fitting surface 31A of the fitting ring 31.

The torque limiter 30 applies the fitting surface 31 A of the fitting ring 31 to the sleeve 18 by the elastic force of the elastic ring 32 at the torque normally used for the electric power steering device 10 (torque smaller than the limit torque). It keeps pressing without slipping and transmits the torque of the torque limiter 30. On the other hand, the stroke of the rack shaft 12 is suddenly stopped, for example, when the tire rides on a curb during steering, and the inertia force of the electric motor 13 that has been rotating at a high speed at the ratio of the lead of the ball screw device 14 is reduced by the screw of the ball screw device 14. The elastic ring 32 caused by applying a large impact force to the groove
For the impact torque (limit torque) exceeding the elastic force of the ball screw device 14, the fitting surface 31 A of the fitting ring 31 slides against the sleeve 18 so as not to transmit the torque of the electric motor 13. To prevent damage to the thread groove.

The fitting ring 31 can be a plastic bearing, a metal (copper, iron, sintered, etc.) bearing, or a ceramic bearing. The fitting ring 31 is, for example, a dry bearing Dyedine D manufactured by Daido Metal Industry Co., Ltd.
D (trade name) (ethylene tetrafluoride resin inner layer, porous intermediate layer, copper outer layer) and the like having excellent wear resistance and low friction characteristics can be suitably used.

Therefore, according to the present embodiment, the following operations are provided. The torque limiter 30 includes the fitting ring 31 and the elastic ring 3.
2, the fitting surface 31A of the fitting ring 31 slipping by the limit torque was brought into full contact with one of the nut 22 and the sleeve 18. As a result, the surface pressure acting on the fitting surface 31A of the fitting ring 31 is reduced (compared to that in which the fitting surface 31A partially contacts), and the fitting surface 3 of the fitting ring 31 is reduced.
Variations in the frictional state over time of 1A (slip surface) can be suppressed, and as a result, a predetermined limit torque of the torque limiter 30 can be maintained, and durability reliability can be improved.

The fitting ring 31 was inscribed in the elastic ring 32, and the inner peripheral surface of the fitting ring 31 was brought into full contact with the sleeve 18. The rotational force based on the impact torque caused by the inertial force of the electric motor 13 is generated on the inner peripheral surface of the fitting ring 31 which is the minimum turning radius portion among the components (the fitting ring 31 and the elastic ring 32) of the torque limiter 30. Will be the largest. Therefore, the torque limiter 30 can be mounted on the inner peripheral surface (the fitting surface 31A) of the fitting ring 31 even under a simple assembly structure in which the fitting ring 31 and the elastic ring 32 are simply inserted between the nut 22 and the sleeve 18. ) Naturally allows slipping.

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, and the design may be changed without departing from the gist of the present invention. The present invention is also included in the present invention. For example, the present invention can employ the following modifications.

(1) The fitting ring is circumscribed to the elastic ring, and the outer peripheral surface of the fitting ring is a fitting surface which is in full contact with one of the nut side member and the rotor side member and slips with a limit torque. The inner peripheral surface of which is supported by the other of the nut-side member and the rotor-side member. At this time, the elastic ring is connected to the other side member by serration etc.,
Slip is prevented.

(2) A case where the fitting ring is inscribed in the elastic ring, and the inner peripheral surface of the fitting ring is a fitting surface which makes full contact with one of the nut side member and the rotor side member and slips with the limit torque. In addition, in order to reliably prevent the elastic ring from slipping, the elastic ring can be coupled to the other of the nut-side member and the rotor-side member by serration or the like.

(3) In order to prevent slippage between the fitting ring and the elastic ring both when the fitting ring is inscribed in the elastic ring and when the fitting ring is circumscribed, both may be connected by serration or the like. good.

[0027]

As described above, according to the present invention, the predetermined limit torque set for the torque limiter provided in the electric power steering apparatus can be maintained, and the durability reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an electric power steering apparatus.

FIG. 2 is an enlarged sectional view of a main part of FIG.

FIG. 3 is a sectional view taken along the line III-III in FIG. 2;

FIG. 4 is a schematic view showing a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Electric power steering device 11 Housing 12 Rack shaft 13 Electric motor 14 Ball screw device 15 Input shaft 17 Rotor 18 Sleeve (Rotor side member) 22 Nut (Nut side member) 30 Torque limiter 31 Fitting ring 31A Fitting surface 32 Elastic ring

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Akira Fujisaki 112-1 Hagadai, Haga-cho, Haga-gun, Tochigi F-term in Showa Tochigi Development Center Co., Ltd. 3D033 CA02 CA05

Claims (2)

[Claims] 1. A housing, a pinion connected to an input shaft meshed with the input shaft, a rack shaft movably supported by the housing, an electric motor disposed around the rack shaft in the housing, and a rack for torque of the electric motor. An electric power steering device having a ball screw device for transmitting to a shaft, wherein a torque limiter that slips at a predetermined torque is interposed between a nut-side member of the ball screw device and a rotor-side member of the electric motor, A fitting ring having a fitting surface in which the torque limiter is in full contact with one of the nut member and the rotor member; and an elastic ring for pressing the fitting surface of the fitting ring against one of the nut member and the rotor member. An electric power steering device, comprising: a slip ring on a fitting surface of a fitting ring. 2. The fitting ring is inscribed in an elastic ring,
2. The electric power steering apparatus according to claim 1, wherein an inner peripheral surface of the fitting ring is a fitting surface that is in full contact with the rotor member, and an outer peripheral surface of the elastic ring is supported by the nut member.