JP4658341B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in an electric power steering apparatus.
[0002]
[Prior art]
In recent years, electric power steering devices have been frequently used in order to reduce the steering force of the steering wheel to give a comfortable steering feeling. This type of electric power steering device generates an auxiliary torque corresponding to the steering torque with an electric motor, and transmits this auxiliary torque to the rack shaft of the steering system. For example, Japanese Patent Laid-Open No. 7-165089 “Steering Device” (Hereinafter referred to as “conventional technology”) is known.
[0003]
As shown in FIGS. 1, 2, and 4 of the above publication, the conventional technology described above applies steering torque applied to the steering wheel 3 (the numbers are those cited in the publication; the same applies hereinafter) to the steering shaft 4. The torsion bar, the output shaft 5, and the rack and pinion mechanism are transmitted to the rack shaft 2, and the auxiliary torque generated by the motor 20 according to the steering torque is transmitted to the rack shaft 2 via the ball nut mechanism 33. A steering wheel (not shown) is steered by the rack shaft 2. The rotor 22 of the electric motor 20 is rotatably supported and accommodated in the housing 1 via ball bearings 31 and 32. The ball nut mechanism 33 is a torque transmission member that transmits auxiliary torque generated by the electric motor 20 to the rack shaft 2.
[0004]
Further, another embodiment of the above prior art is that one end of the rotor 22 is integrally attached to the nut of the ball nut mechanism 33 as shown in FIG. In this case, the housing 1 rotatably supports and accommodates the rotor 22 via the ball bearing 51 and rotatably supports and accommodates the nut of the ball nut mechanism 33 via the needle bearing 52. .
[0005]
[Problems to be solved by the invention]
In recent years, there has been an increasing demand for promoting weight reduction of vehicles to improve fuel efficiency. In order to achieve this requirement, the weight of the steering device has also been reviewed. The material of the housing 1 of the steering device, the bearings 31, 32, 51, 52, and the shafts is generally steel and is relatively heavy. In particular, since the housing 1 has a large weight ratio in the total weight of the steering device, the housing 1 is an object of weight reduction. In order to make the housing 1 lightweight, it is conceivable to change the material to a lightweight alloy material such as aluminum or magnesium.
[0006]
However, the linear expansion coefficients of steel and lightweight alloy materials are greatly different. Further, the steering device is arranged in a place that is easily affected by the heat of the engine and the outside air temperature. And it is easy to receive the influence of the heat_generation | fever from the electric motor 20 used on comparatively severe conditions. As described above, since the steering device is used under a condition in which the temperature change is severe, sufficient consideration must be given to the difference in thermal expansion between the housing 1 and other members.
For example, when the linear expansion coefficient of the housing 1 is larger than the linear expansion coefficients of the bearings 31, 32, 51, 52, the fitting hole of the housing 1 and the bearing increase as the temperature increases if the temperature conditions are the same. The radial gaps between 31, 32, 51, and 52 are increased. If this gap is not appropriate, vibration is generated, which causes noise.
[0007]
Accordingly, an object of the present invention is to absorb a radial thermal expansion difference between a motor case and a bearing in a motor and a radial thermal expansion difference between a housing and a bearing in an electric power steering apparatus. To provide technology.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, according to a first aspect of the present invention, there is provided an electric power steering system in which a supplementary torque generated by an electric motor according to a steering torque is added to a steering system from a steering wheel to a steering wheel via a torque transmission member. A torque transmitting member that can be rotated by an electric motor is rotatably supported and accommodated in a housing via a first bearing, the first bearing is attached to the housing by a lock screw, and the electric motor is the motor case is made of aluminum material or aluminum alloy material, in the electric power steering apparatus for rotatably supported by and housed rotor via a second bearing made of a steel material, the housing and the first bearing and during, among between the motor case and the second bearing, the motor case and the second bearing Characterized in that interposed thermal expansion absorbing material only.
[0009]
Even if the linear expansion coefficients of the motor case and the second bearing are different, the difference in thermal expansion between the radial direction between the motor case and the second bearing can be absorbed by the thermal expansion absorbing material. The gap of the fitting portion of the second bearing with respect to the motor case can always be kept appropriate.
[0010]
Further, according to the first aspect , the electric motor case is made of an aluminum material or an aluminum alloy material, and the second bearing is made of a steel material .
The electric motor case can be reduced in weight, and as a result, the entire electric power steering apparatus can be reduced in weight. Furthermore, a cheap thing, such as a general rolling bearing, is employable as a 2nd bearing.
[0014]
According to a second aspect of the present invention, the thermal expansion absorber is made of a resin material.
A thermal expansion absorbent material having good thermal expansion absorption performance can be made with good workability and low cost.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. The drawings are viewed in the direction of the reference numerals.
FIG. 1 is a schematic diagram of an electric power steering apparatus according to the present invention.
The electric power steering apparatus 10 includes a steering system 20 from a vehicle steering wheel 21 to steering wheels 29, 29, and an auxiliary torque mechanism 40 that applies auxiliary torque to the steering system 20. The electric power steering device 10 is an end take-off type steering device in which steering torque is extracted from both ends of the rack shaft 26.
[0016]
The steering system 20 is connected to a steering wheel 21 via a steering shaft 22 and universal shaft joints 23, 23, and a pinion shaft 24 is connected to the pinion shaft 24 via a rack and pinion mechanism 25. The left and right steering wheels 29, 29 are connected to both ends of 26 through left and right tie rods 27, 27 and knuckle 28, 28.
The rack and pinion mechanism 25 is obtained by meshing a rack 32 formed on the rack shaft 26 with a pinion 31 formed on the pinion shaft 24.
When the driver steers the steering wheel 21, the left and right steering wheels 29, 29 can be steered by the steering torque via the rack and pinion mechanism 25 and the left and right tie rods 27, 27.
[0017]
The auxiliary torque mechanism 40 detects the steering torque of the steering system 20 applied to the steering wheel 21 by the steering torque sensor 41, generates a control signal by the control means 47 based on this detection signal, and converts the steering torque to the steering torque based on this control signal. A corresponding auxiliary torque is generated by the electric motor 50, and the auxiliary torque is transmitted to the rack shaft 26 via a ball screw 70 as a torque transmission member.
[0018]
In summary, the electric power steering apparatus 10 transmits the steering torque applied to the steering wheel 21 of the vehicle to the rack shaft 26 via the rack and pinion mechanism 25, and the electric motor 50 is generated according to the steering torque. Auxiliary torque is applied to the rack shaft 26 from the output shaft of the electric motor 50 via the ball screw 70, and the steering wheels 29 and 29 are steered by the rack shaft 26. Therefore, the steering wheels 29 and 29 can be steered by the combined torque obtained by adding the auxiliary torque of the electric motor 50 to the steering torque of the steering system 20.
[0019]
FIG. 2 is an overall configuration diagram of the electric power steering apparatus according to the present invention, and shows a cross-section of the main part.
The electric power steering apparatus 10 includes a rack and pinion mechanism 25 (see FIG. 1), an electric motor 50, and a ball screw 70 that are housed in a housing 101 that extends in the vehicle width direction (the left-right direction in the figure).
The housing 101 is assembled into one elongated gear box by bolting one end surfaces of the generally tubular first housing 102 and second housing 103 together. The first housing 102 includes a bracket 104 for attaching to a vehicle body (not shown). The second housing 103 also serves as an electric motor case in the electric motor 50.
[0020]
The rack shaft 26 extending in the vehicle width direction is a shaft that penetrates the housing 101 so as to slide in the vehicle width direction. Such a rack shaft 26 is connected to the rack and pinion mechanism 25 at one end on the right side of the figure, and is connected to the ball screw 70 at the substantially longitudinal center position, and is located at the other end side (position closer to the end than the ball screw 70) ) In which the electric motor 50 is arranged.
In the figure, 105 and 105 are ball joints, and 106 and 106 are dust seal boots.
[0021]
FIG. 3 is a cross-sectional view of a main part around the rack shaft, the electric motor, and the ball screw according to the present invention.
The electric motor 50 includes a cylindrical ferromagnetic yoke 51 fitted in the second housing 103, and a plurality of permanent magnet stators 52 (...) arranged in the yoke 51. The same shall apply hereinafter), and the stators 52... Aligned in the second housing 103 in an aligned state, the internal stator holder 54, and the interior of the stators 52 (ie, the internal stator holder 54. And a rotor 55 disposed inside.
[0022]
The rotor 55 includes a tubular output shaft 56 that is rotatably fitted to the rack shaft 26, a core 57 that is fitted to the outer peripheral surface of the output shaft 56, and a coil that is wound around the outer peripheral surface of the core 57. 58 and a commutator 59 connected to the coil 58. The commutator 59 is attached to the outer peripheral portion of the output shaft 56 at the side of the coil 58, and a flat surface facing the left end side (the left side in the figure) of the rack shaft 26 is a brush contact surface.
The brush 61 that contacts the brush contact surface of the commutator 59 is accommodated in the second housing 103 via the brush holder 62. Reference numeral 63 denotes a compression spring for generating a brush bullet, and reference numeral 64 denotes a brush cord.
[0023]
The ball screw 70 includes a screw portion (thread groove) 71 formed on the rack shaft 26, a large number of balls 72 (... indicates a plurality, the same applies hereinafter), and a ball 72. A ball nut mechanism comprising a nut 73 of the outer cylinder part attached via The ball screw 70 transmits the auxiliary torque of the electric motor 50 from the nut 73 to the screw portion 71 via the balls 72..., And the ball 72 that has reached the end of the thread groove of the nut 73. Is a general configuration of a so-called internal circulation type or external circulation type in which circulation is performed through a tube (not shown).
[0024]
By the way, the output shaft 56 of the electric motor 50 is connected to the nut 73 of the ball screw 70 via the torque limiter 90 so that a torque exceeding a certain level is not transmitted. More specifically, a groove having a constant width is formed on the outer peripheral surface of the output end 56a of the output shaft 56 over the entire circumference, and a ring-shaped torque limiter 90 is fitted into the groove, thereby the output shaft 56 of the electric motor 50 and A torque limiter 90 is interposed between the inner peripheral surface of the nut 73. The torque limiter 90 is a member that connects the output shaft 56 and the inner peripheral surface of the nut 73 by a frictional force, and that slips and interrupts torque transmission when a torque exceeding a certain level is applied, and is generally a tolerance ring ( It is also called tolerance ring). Excessive torque does not act on the electric motor 50.
The output shaft 56 may be directly connected to the nut 73 without using the torque limiter 90. Further, the output shaft 56 may be formed integrally with the nut 73.
[0025]
The auxiliary torque generated by the electric motor 50 is transmitted to the rack shaft 26 through the path of the output shaft 56 → the torque limiter 90 → the nut 73 of the ball screw 70 → the ball 72. As a result, the auxiliary torque can be converted into thrust (axial force on the rack shaft 26) and applied to the rack shaft 26.
[0026]
This figure shows that the flange 103a at one end of the second housing 103 is coupled to the flange 102a at one end of the first housing 102 by a bolt 136.
In the electric power steering apparatus 10, a ball screw 70 as a torque transmitting member that can be rotated by the electric motor 50 is rotatably supported and stored in the first housing 102 (housing 101) via the first bearing 131. Is.
[0027]
Specifically, the first housing 102 is integrally formed with a ball screw storage portion 102b for fitting into the second housing 103, and a nut 73 is interposed in the ball screw storage portion 102b via a first bearing 131. It is what supported. The first bearing 131 is a rolling bearing in which axial movement with respect to the first housing 102 is restricted by the lock screw 134 and the center of the nut 73 or a position near the nut 73 is rotatably supported.
[0028]
The nut 73 includes a support portion 74 fitted to the first bearing 131 and a large-diameter portion 75 that is connected to one end of the support portion 74 and has a larger diameter than the support portion 74. The axial movement of the nut 73 relative to the first housing 102 can be restricted by sandwiching the first bearing 131 fitted to the support portion 74 between the large diameter portion 75 and the lock screw 135. As a result, the nut 73 can rotate and cannot move in the axial direction.
[0029]
As described above, since the output end 56 a of the output shaft 56 is fitted and connected to the inner peripheral surface of the nut 73, the first housing 102 is connected to the output end of the output shaft 56 via the nut 73 and the first bearing 131. The 56a side can be rotatably supported.
In the figure, 137 and 138 are spacers, and 139 is an O-ring.
[0030]
Further, the electric power steering apparatus 10 is configured such that the rotor 55 is rotatably supported and accommodated in a second housing 103 as an electric motor case via a second bearing 132 and a bush 133. Specifically, the second output shaft 132 made of a rolling bearing is rotatably supported on the non-output end side of the output shaft 56.
[0031]
The bush 133 is a thermal expansion absorbing material interposed between the inner peripheral surface (bearing fitting hole) of the second housing 103 and the outer peripheral surface of the outer ring of the second bearing 132. The reason why the bush 133 is interposed will be described below.
[0032]
In the present invention, the second housing 103 as an electric motor case is made of an aluminum material or an aluminum alloy material (for example, an aluminum alloy casting), and the second bearing 132 is made of a material different from the second housing 103, that is, a steel material. It is characterized by that. Since the second housing 103 is made of an aluminum material or an aluminum alloy material, the entire electric power steering device 10 can be reduced in weight. Furthermore, by configuring the second bearing 132 with a material different from that of the second housing 103, an inexpensive one such as a general rolling bearing can be employed.
[0033]
On the other hand, the linear expansion coefficients of the second housing 103 and the second bearing 132, which are different from each other, are different from each other. In contrast, in the present invention, the bush 133 is interposed between the second housing 103 and the second bearing 132.
The bush 133 plays a role of a thermal expansion absorbent that absorbs a radial thermal expansion difference between the second housing 103 and the second bearing 132, and is a cylindrical member having a constant width. The material of the bush 133 is a resin material such as PBT (polybutylene terephthalate) containing 30% of glass.
[0034]
FIG. 4 is a characteristic diagram of a bush (thermal expansion absorber) according to the present invention, and shows measured values of thermal expansion absorption characteristics of an example using a bush 133 made of PBT containing 30% glass. D, d, t are defined as follows.
D: Inner diameter (mm) of the bearing fitting hole of the second housing 103
d: outer diameter of the second bearing 132 (mm)
t: thickness of the bush 133 (mm)
However, each numerical value is an actual measurement value measured under each temperature condition, and a dimension at a temperature of 20 ° C. is used as a reference value.
[0035]
According to this figure, it can be seen that the value of “Δ1−Δ2” at the temperature of −40 to 100 ° C. falls within the range of −0.0002 to 0.0002. Therefore, it can be seen that the bush 133 can sufficiently absorb the radial thermal expansion difference between the second housing 103 and the second bearing 132.
[0036]
FIG. 5 is a modification of the electric power steering apparatus according to the present invention, and is a cross-sectional view of the main part corresponding to FIG.
The electric power steering apparatus 10 according to the modified example includes (1) a bush 133 as a thermal expansion absorber interposed between the second housing 103 and the second bearing 132, and (2) the first housing 102 and the first bearing. A bush 141 serving as a thermal expansion absorbing material is also interposed between the first and second members 131. The material of the bush 141 is the same as that of the bush 133. A difference in radial thermal expansion between the first housing 102 and the first bearing 131 can be absorbed.
[0037]
In this modification, the first and second housings 102 and 103 are made of an aluminum material or an aluminum alloy material, and the first and second bearings 131 and 132 are made of a material different from that of the first and second housings 102 and 103. That is, it is characterized by comprising steel. Since the first and second housings 102 and 103 are made of aluminum or aluminum alloy, the entire electric power steering apparatus 10 can be further reduced in weight. Further, by configuring the first and second bearings 131 and 132 with a material different from that of the first and second housings 102 and 103, an inexpensive one such as a general rolling bearing can be employed.
Since other configurations and operations are the same as those shown in FIGS. 1 to 4, the same reference numerals are given and description thereof is omitted.
[0038]
In the above-described embodiment of the present invention, the torque transmission member may be any member as long as the auxiliary torque generated by the electric motor 20 is added to the steering system 20 by being rotated by the electric motor 50, and is limited to the ball screw 70. It is not a thing. The torque transmission member can be various gears such as a worm or a wheel in a worm gear mechanism.
In addition, only the first housing 102 is made of an aluminum material or an aluminum alloy material, and only the first bearing 131 is made of a material different from that of the first housing 102, and the first housing 102 and the first bearing 131 are interposed between them. By interposing a bush 141 as a thermal expansion absorber, a radial thermal expansion difference between the first housing 102 and the first bearing 131 may be absorbed.
Furthermore, the electric motor case of claim 1 and the housing of claim 3 are not limited to aluminum-based materials, but may be other lightweight alloy materials such as magnesium-based materials.
[0039]
【The invention's effect】
The present invention exhibits the following effects by the above configuration.
Since the thermal expansion absorbing material is interposed between the electric motor case housing the rotor and the second bearing supporting the rotor, the linear expansion coefficient of the electric motor case and the second bearing is different. Also, it is possible to absorb the radial thermal expansion difference between the motor case and the second bearing. Therefore, the gap of the fitting portion of the second bearing with respect to the electric motor case can always be kept appropriate.
[0040]
Further, according to the first aspect of the present invention, it is possible to reduce the weight by configuring the motor case with an aluminum material or an aluminum alloy material. As a result, the entire electric power steering device can be reduced in weight. Further, by configuring the second bearing with a steel material , an inexpensive one such as a general rolling bearing can be employed.
[0043]
According to the second aspect of the present invention, since the thermal expansion absorber is made of a resin material, the thermal expansion absorber having good thermal expansion absorption performance can be made with good workability and low cost.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an electric power steering apparatus according to the present invention. FIG. 2 is an overall configuration diagram of an electric power steering apparatus according to the present invention. Sectional view [Fig. 4] Characteristic diagram of bush (thermal expansion absorbing material) according to the present invention [Fig. 5] Variation diagram of electric power steering apparatus according to the present invention [Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Electric power steering apparatus, 20 ... Steering system, 21 ... Steering wheel, 29 ... Steering wheel, 50 ... Electric motor, 55 ... Rotor, 70 ... Torque transmission member (ball screw), 101 ... Housing, 102 ... First housing, 103 ... Electric motor case (second housing), 131, 132 ... Bearings (first and second bearings), 133, 141 ... Thermal expansion absorbing material (bush).

Claims (2)

An electric power steering device that adds a compensation torque generated by an electric motor according to a steering torque to a steering system from a steering wheel to a steering wheel via a torque transmission member ,
The torque transmitting member that can be rotated by the electric motor is rotatably supported and housed in a housing via a first bearing,
The first bearing is attached to the housing by a lock screw;
In the electric power steering apparatus in which the electric motor is configured to rotatably support and house the rotor via the second bearing made of steel in the electric motor case made of aluminum material or aluminum alloy material ,
And between said housing first bearing, of between said motor casing second bearing, characterized in that only the interposed thermal expansion absorbing member between said motor case second bearing Electric power steering device. Electric power steering apparatus according to claim 1 Symbol mounting, characterized in that the thermal expansion absorbing material formed of a resin material.

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