JP2002079947A - Electric power steering system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering system capable of obtaining sufficient assist force, hardly causing vibration and noise, and securing some steering properties even when a motor is stopped. SOLUTION: A vernier motor 1 is constructed at one end of a rack bar 93 and a housing 95 to obtain the assist force for the rack bar 93.

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 In a steering apparatus, as shown in FIGS. 5 and 6, a pinion 92 is provided at a tip of a steering shaft 91 connected to a steering wheel 90, and the pinion 92 rotates with the steering shaft 91. Has become. A rack bar 93 is meshed with the pinion 92. The rack bar 93 converts the rotational movement of the steering shaft 91 into a linear movement in the longitudinal direction to change the steering angle of the tire 94. The pinion 92 and the rack bar 93 are housed in a housing 95. In particular, in the electric power steering apparatus, a motor is also housed in a housing 95, and a pinion 92 and a rack bar 93 are detected by detecting torque or the like acting on the steering shaft 91.
Can be assisted.

Here, as an electric power steering apparatus in which a motor assists a rack bar 93, a motor adopting a linear motor 96 is known as shown in FIG. 5 (Japanese Patent Publication No. 61-14032). Gazette). In this electric power steering device, a linear motor 96 is provided at one end of the rack bar 93.
The linear motor 96 includes a slider 96a and a stator 96b. The slider 96a is connected to a rack bar 93, and the stator 96b is fixed to a housing 95.

In this electric power steering apparatus, when assisted by the linear motor 96, a current calculated based on torque detected by a torque sensor or the like (not shown) or the like is supplied to the slider 96a. On the other hand, the stator 9
A predetermined current is supplied to 6b in advance to form a magnetic field. Therefore, the slider 96a receives a force in a direction perpendicular to the magnetic field according to the direction and magnitude of the supplied current. Then, the force received by the slider 96a is transmitted to the rack bar 93, and the assist force is applied to the rack bar 93.

On the other hand, as shown in FIG. 6, an electric power steering apparatus using a ball screw other than the above is known (Japanese Patent Laid-Open No. 2000-72008). In this electric power steering device, a rotation motor 97 and a ball screw 98 are provided at one end of a rack bar 93.

In this electric power steering apparatus, when assisted by the rotary motor 97, the rotational motion of the rotary motor 97 is converted into linear motion by the ball screw 98, and the rack bar 93 is slid.

[0007]

However, in the electric power steering apparatus employing the above-mentioned conventional linear motor, a linear motor generally has a smaller thrust than a rotary motor, and thus cannot provide a sufficient assisting force.

Here, since the linear motor does not require a ball screw or the like, and can increase the axial length, the surface area of the mover of the linear motor can be assumed to be 1.5 times the surface area of the mover of the rotary motor. . Here, since the force generated from the motor is considered to be proportional to the surface area of the mover,
Assuming that the force generated from the rotary motor is f [N], the force generated from the linear motor can be considered to be 1.5f [N].

In the linear motor, the generated force becomes the thrust as it is, so the thrust F1 [N] of the linear motor
Is represented by the following equation.

[0010]

## EQU1 ## F1 = 1.5f

On the other hand, if the diameter of the mover of the rotary motor is 50 mm, the axial length is 100 mm, the lead of the ball screw is 5 mm, and the deceleration efficiency is 0.8, the torque τ [N · m] and thrust F2 [N] are expressed by the following equations.

[0012]

Τ = 0.025f

[0013]

F2 = 2π × τ × 0.8 / 0.005 ≒ 25.1f

From the above, F1 / F2 ≒ 1 / 16.8.

Therefore, the thrust F1 of the linear motor
It can be seen that [N] is only about 1 / 16.8 of the thrust F2 [N] of the rotary motor and the ball screw.

On the other hand, in an electric power steering apparatus using a ball screw, vibration and noise are generated because a mechanical speed reducer and a converter such as a gear and a ball screw 98 are used. Further, when the rotation motor 97 is stopped by fail-safe against short-circuit of the electric system, the rotation motor 97 becomes a load.
0 becomes heavy, and comfortable steering performance cannot be secured.

The present invention has been made in view of the above-mentioned conventional circumstances, and can provide a sufficient assist force, hardly generate vibration and noise, and provide a certain degree of steering even when the motor is stopped. It is an object of the present invention to provide an electric power steering device capable of ensuring performance.

[0018]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have intensively studied electric power steering devices. When a linear vernier motor is established between the housing and the rack bar, the present inventors have found that the rack bar can be assisted with a sufficient assisting force, thereby completing the present invention.

That is, an electric power steering apparatus according to the present invention is provided at a tip of a steering shaft and rotates with the steering shaft. The pinion meshes with the pinion to convert the rotational movement of the steering shaft into a linear movement in the longitudinal direction. An electric power steering apparatus comprising: a rack bar that converts and changes a steering angle; a housing that houses the pinion and the rack bar; and an electric motor that applies auxiliary power to the rack bar.

In the electric motor, the housing is provided with a first number of fixed slots in the longitudinal direction at a first gap, respectively, and all the fixed slots and the same number of the fixed slots in the longitudinal direction of the rack bar are provided. Within the added length of the first gap, a third number of movable slots, which is a second number less or more than the first number, is respectively provided at a second gap, each fixed slot and each movable slot. Is a linear vernier motor in which a permanent magnet is housed, and a three-phase AC winding having the second few pole pairs is housed in one group of each of the fixed slots and each of the movable slots. There is a feature.

[0021]

In the electric power steering apparatus of the present invention, a linear vernier motor is established between the housing and the rack bar by such means, and the rack bar can be assisted with a sufficient assist force. In addition, since no mechanical speed reducer or converter such as a gear or a ball screw is used, vibration and noise hardly occur. Further, even when the motor is stopped by fail-safe against a short circuit of the electric system or the like, the load by the motor is small and the steering wheel does not become extremely heavy.

Therefore, according to the electric power steering apparatus of the present invention, a sufficient assist force can be obtained, vibration and noise hardly occur, and a certain degree of steering performance can be secured even when the motor is stopped. Can be.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings. The main mechanical configuration of the electric power steering apparatus according to the embodiment is the same as that shown in FIGS. 5 and 6 as shown in FIG. 1, and is different from the conventional mechanical configuration shown in FIGS. The same reference numerals are used for the same components, and the description thereof will be omitted.

In this electric power steering apparatus, as shown in FIG. 1, a linear vernier motor 1 is provided at one end of a rack bar 93 and a housing 95. In this vernier motor 1, as shown in FIGS. 2 and 3, the housing 95 has a housing body 95a and a stator 95b. Outer peripheral surface is housing body 95a
Is made of electromagnetic soft iron and has an annular shape surrounding the rack bar 93 and extending in the circumferential direction. On the inner peripheral surface of the stator 95b, fixed slots 95c which are annularly recessed are provided at first gaps 11 in the longitudinal direction. This fixed slot 95c has a first few S
(36 in the embodiment).

In each of the fixed slots 95c, the number of pole pairs is a second number p (3 in the embodiment) from the housing body 95a side.
The coils 5 (n) and 4 (n), which are three-phase AC windings, and the permanent magnet 3 are embedded. The coils 5 (n) are 5 (1), 5 (2),..., 5 (36) from one end in the longitudinal direction, and the coils 4 (n) are 4 (1), 4 (2),.
... 4 (36). Further, the permanent magnets 3 all have a ring shape magnetized to have the same polarity.

On the outer peripheral surface of the rack bar 93, a movable slot 93a which is annularly recessed and faces the fixed slot 95c is provided at a second gap 12 in the longitudinal direction. Ring-shaped permanent magnets 6 all having the same polarity are embedded in the movable slots 93a. The polarity of the permanent magnet 6 is opposite to that of the permanent magnet 3. Then, all the fixed slots 95c and the same number of the first gaps l1 are provided.
Are provided with a third number R (33 in the embodiment) of movable slots 93a within the added length 13 of.

That is, the fixed slot 95c is the first several S, the movable slot 93a is the third R, and the second slot is p, and the relationship of R = S ± p is established. In the embodiment, a relationship of 33 = 36-3 is established. Then, a three-phase alternating current having the second several p pole pairs is supplied to the coils 5 (n) and 4 (n). In this case, the housing 9
5 is a linear vernier motor 1 that applies auxiliary power to the rack bar 93 between the stator 95b and the rack bar 93.
Holds.

In the case of n = 1 to 12 which is one pole pair of the coils 5 (n) and 4 (n) of this electric power steering apparatus, as shown in FIG. Is supplied with three-phase alternating current. When n = 13 to 24 and n
Similarly, the three-phase alternating current shown in FIG. That is, when n = 13 to 24,
The three-phase alternating current shown in FIG. 4 is supplied with the value obtained by subtracting 12 from n as the value of n. When n = 25 to 36, n
The three-phase alternating current shown in FIG.

By changing the energization pattern applied to each phase, the position of the pole generated in the fixed slot moves.

The vernier motor 1 has a movable slot 9
3a and the permanent magnet 6 housed in the fixed slot 95c,
3, and a thrust is generated by the fundamental magnetic flux density generated by the action of the permeance pulsation at the openings of the fixed slot 95c and the movable slot 93a opposed thereto (refer to the Transactions of the Institute of Electrical Engineers of Japan (vol. 113-D, no. 10, 1993)). ).

According to the same magazine, the rotary vernier motor has a torque of R / p compared to a normal rotary motor.
And the speed in the rotation direction is p / R times. Therefore, in a rotary type vernier motor, p /
The same effect as when a speed reducer with a reduction ratio of R is provided can be realized electrically. In the embodiment, a linear vernier motor 1 is realized. In this vernier motor 1, a torque R / p times as large as that of a rotary motor is converted into a thrust and 1
The speed in the rotation direction of 1 time and p / R times is converted to the speed in the linear direction and becomes 1/11 times. As a result, according to the vernier motor 1 of the embodiment, it is understood that a large thrust can be obtained at a low speed without using a speed reducer.

Therefore, in this electric power steering apparatus, the rack bar 93 can be assisted with a sufficient assisting force. Also, mechanical reducers such as gears and ball screws,
Since a converter is not used, vibration and noise hardly occur. Furthermore, even when the vernier motor 1 is stopped by fail-safe for short-circuit of the electric system, the load by the vernier motor 1 is small, and the steering wheel 90 does not become extremely heavy.

Therefore, according to this electric power steering apparatus, a sufficient assist force can be obtained, vibration and noise hardly occur, and a certain degree of steering performance can be secured even when the vernier motor 1 is stopped. Can be.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an electric power steering device according to an embodiment.

FIG. 2 is a longitudinal sectional view of a vernier motor according to the electric power steering device of the embodiment.

FIG. 3 is an enlarged vertical sectional view of a vernier motor according to the electric power steering device of the embodiment.

FIG. 4 is a diagram showing a three-phase alternating current that energizes a coil of a vernier motor according to the electric power steering device of the embodiment.

FIG. 5 is a schematic view of an electric power steering device using a conventional linear motor.

FIG. 6 is a schematic view of a conventional electric power steering device using a rotary motor.

[Explanation of symbols]

 91: Steering shaft 92: Pinion 93: Rack bar 95: Housing 93a: Movable slot 95c: Fixed slot 3, 6: Permanent magnet 4 (n), 5 (n): Coil (three-phase AC winding)

Continued on the front page F term (reference) 3D033 CA03 5H641 BB06 BB19 GG02 GG04 GG20 HH03 HH14 HH15 HH16 JA09 JA19

Claims (2)

[Claims] 1. A steering shaft provided at a tip of a steering shaft,
A pinion that rotates with the steering shaft;
A rack bar that meshes with the pinion, converts the rotational movement of the steering shaft into a linear movement in the longitudinal direction to change the steering angle, a housing that houses the pinion and the rack bar, and an auxiliary power for the rack bar. An electric power steering apparatus comprising: an electric motor to be provided; wherein the electric motor is provided with a first plurality of fixed slots in the housing at a first gap in the longitudinal direction.
Within the added length of all the fixed slots and the same number of the first gaps in the longitudinal direction of the rack bar, there are a third number of movable slots, which is a second number less or more than the first number, respectively. A permanent magnet is accommodated in each of the fixed slots and each of the movable slots, and the second number is defined as the number of pole pairs in one group of each of the fixed slots and each of the movable slots. An electric power steering device, which is a linear vernier motor containing three-phase AC windings. 2. The electric power steering apparatus according to claim 1, wherein a three-phase AC winding is accommodated in each fixed slot.