JP3816691B2 - Rack and pinion type electric power steering system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rack and pinion type electric power steering apparatus that applies a steering assist force by rotating a ball nut screwed to a ball screw shaft integrated with a rack by a motor.
[0002]
[Prior art]
As a rack and pinion type electric power steering device, a ball nut that is screwed via a circulating ball to a ball screw shaft that is integrated with a rack that meshes with a pinion that rotates by steering is given a steering assist force along the axial direction of the rack. A device that is driven to rotate by a motor has been conventionally used. The motor includes a stator that is fixed to a housing side that covers the rack, and a rotor that is rotatably supported by the housing side via a rolling bearing and into which the rack is inserted.
[0003]
In order to facilitate relative rotation between the ball screw shaft and the ball nut, lubricating grease is applied to the raceway surface of the circulating ball. Further, in order to facilitate the rotation of the rolling bearing for supporting the rotor, lubricating grease is sealed in the bearing inner space between the outer ring and the inner ring, and the rolling bearing has a bearing inner space and an outer space. By being a sealed type having a seal that shields the grease, the outflow of grease and the intrusion of dust are restricted, and the life is not shortened due to dust biting and poor lubrication.
[0004]
[Problems to be solved by the invention]
Conventionally, since the grease on the raceway surface of the circulating ball has only been applied at the beginning of assembly, there is a risk that the grease will break due to long-term use and the wear will locally increase on the raceway surface. Further, the sealed rolling bearing used for supporting the rotor is expensive and causes an increase in cost.
[0005]
An object of the present invention is to provide an electric power steering apparatus that can solve the above-described problems.
[0006]
[Means for Solving the Problems]
The present invention includes a pinion that rotates by steering, a rack that meshes with the pinion, a ball screw shaft that is integrated with the rack, a ball nut that is screwed to the ball screw shaft via a circulating ball, and a A motor that rotationally drives the ball nut and a housing that covers the rack are provided so that a steering assist force along the axial direction can be applied. The motor includes a stator that is fixed to the housing side, and a housing that is fixed to the housing side. In a rack and pinion type electric power steering apparatus having a rotor that is rotatably supported and into which the rack is inserted, the housing includes a cylindrical first housing and a cylindrical shape that are arranged in parallel along the axial direction of the rack. and a second housing, in its second Haujin grayed, the ball subscriptions Formed grease retaining space having an opening facing the outer periphery of the over the shaft, the said rotor supporting rolling bearing in the first housing is inserted, the outer ring of the rolling bearing is formed on the inner peripheral side of the first housing And one end surface of the second housing inserted into the first housing, the one end surface of the second housing is disposed opposite to the bearing inner space between the outer ring and the inner ring of the rolling bearing. The rolling bearing is arranged between the stator and the grease holding space in the axial direction of the rack .
According to the configuration of the present invention, the grease flowing out from the opening of the grease holding space is supplied to the outer periphery of the ball screw shaft, so that there is no shortage of grease on the raceway surface of the circulating ball in the ball screw shaft and the ball nut. Lubrication of the raceway surface can be stably performed for a long time without adding special parts. In addition, without using an expensive sealed type as a rolling bearing for supporting the rotor, it is possible to prevent the grease sealed in the bearing inner space from flowing out to the outside and to infiltrate dust from the second housing side into the bearing inner space. , And can be regulated by the end surface of the second housing.
[0007]
In the present invention, the inner diameter of the second housing is made smaller than the outer diameter of the inner ring of the rolling bearing, and the second housing is arranged such that the inner ring and one end surface of the second housing face each other with a minute distance therebetween. It is preferable that a chamfered portion is formed on one end side of the inner circumference .
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A rack and pinion type electric power steering apparatus 1 shown in FIG. 1 includes a pinion 3 that rotates by steering a steering wheel (not shown) coupled to an input shaft 2, and a rack 4 that meshes with the pinion 3. Wheels (not shown) are connected to both ends of the rack 4 via ball joints 5, tie rods 6, and knuckle arms. When the rack 4 is moved in the axial direction by the rotation of the pinion 3 by steering, the steering angle of the vehicle is changed.
[0009]
A torque sensor 7 is provided in a pinion housing 30 that covers the pinion 3 and the rack 4. As the torque sensor 7, a known sensor that detects a steering torque transmitted to the pinion 3 by steering of the steering wheel can be used.
[0010]
As shown in FIG. 2, a ball nut 63 is screwed onto a ball screw shaft 61 formed with a screw groove 61 a integrated with the rack 4 via a circulation ball 62.
[0011]
A brushless motor 8 that rotationally drives the ball nut 63 is provided so that a steering assist force along the axial direction of the rack 4 can be applied. The brushless motor 8 is fixed to the inner peripheral side of a cylindrical rack housing 31 that covers the rack 4, and is inserted into the stator 8 a and is rotatably supported by the inner peripheral side of the rack housing 31. It has a cylindrical rotor 8b, a rotational phase detection sensor 8c for the rotor 8b, and a magnet 8d integrated on the outer peripheral side of the rotor 8b. The rack 4 is inserted into the rotor 8b through the gap so as to be movable in the axial direction.
[0012]
The rack housing 31 includes a cylindrical first housing 31 a and a cylindrical second housing 31 b that are arranged in parallel along the axial direction of the rack 4. One end side of the second housing 31b has a larger diameter than the other end side. A male screw portion 72 formed on the outer periphery on one end side of the second housing 31b is screwed to the female screw portion 71 formed on the inner periphery of the first housing 31a. Thereby, the one end side of the 2nd housing 31b is inserted in the other end side of the 1st housing 31a via the seal member 85 so that removal is possible.
[0013]
As shown in FIG. 3, one end of the first housing 31 a is connected to the pinion housing 30 via an annular spacer 33. One end side of the rotor 8b is supported by the rack housing 31 side via a first rolling bearing 32 fitted to the inner periphery of the spacer 33. The first rolling bearing 32 for supporting the rotor 8b is a four-point contact ball bearing, and has an inner ring 32a, an outer ring 32b, and a bearing ball 32c. The inner ring 32a is sandwiched between a step on the outer periphery of the rotor 8b and a nut 34 screwed onto the outer periphery of the rotor 8b. The outer ring 32b is composed of a pair of annular members 32b ′ and 32b ″ arranged in parallel in the rack axial direction so as to sandwich the bearing ball 32c, and an annular screw 35 screwed to the inner circumferential step of the spacer 33 and the inner circumference of the spacer 33. It is sandwiched between.
[0014]
As shown in FIG. 4, the ball screw shaft 61 is supported by the rack housing 31 side via a bush 88 fitted to the inner periphery of the other end side of the second housing 31b. The rack 4 projects out of the rack housing 31 from the opening on one end side of the pinion housing 30 and the opening on the other end surface side of the second housing 31b. Each end of the rack 4 protruding from the pinion housing 30 and the second housing 31 b is covered with an extendable cover 89.
[0015]
As shown in FIG. 2, the rotor 8b and the ball nut 63 are arranged coaxially. A receiving portion 81 facing one end of the ball nut 63 and a cylindrical covering portion 82 covering the outer periphery of the ball nut 63 are integrated with the other end of the rotor 8b. The receiving portion 81 has an annular shape integrated with the other end of the rotor 8b. The covering portion 82 is coaxial with the rotor 8b, one end side is integrated with the outer end of the receiving portion 81, and the other end side is open.
[0016]
The receiving part 81 is provided with means for pressing one end of the ball nut 63 along the axial direction of the rack 4. That is, the ring-shaped pressing member 83 having the external thread portion 83a on the outer periphery is screwed to the rotor 8b side via the internal thread portion 82a formed on the inner periphery on the other end side of the covering portion 82, so that the ball nut 63 Opposite the other end. Thus, the end surface 63 a on one end side of the ball nut 63 can be pressed against the end surface 81 a of the receiving portion 81 by screwing the pressing member 83 toward the rotor 8 b and pressing the ball nut 63. Therefore, based on the frictional resistance between the end surface 81 a of the receiving portion 81 and the end surface 63 a of one end of the ball nut 63, rotational torque can be transmitted between the rotor 8 b and the ball nut 63. Note that a recess 83b for insertion of a rotary operation tool is formed on the inner periphery of the pressing member 83.
[0017]
As shown in FIG. 2, the other end side of the rotor 8 b is supported by the inner peripheral side of the rack housing 31 via the second rolling bearing 36. That is, the second rolling bearing 36 for supporting the rotor 8b is an unsealed ball bearing, and is inserted between the outer periphery of the covering portion 82 integrated with the rotor 8b and the inner periphery of the first housing 31a. And is disposed between the first rolling bearing 32 and the second housing 31b. The outer ring 36a of the second rolling bearing 36 is sandwiched between a step 31a 'formed on the inner periphery of the first housing 31a and one end surface 31b' of the second housing 31b.
[0018]
Grease is sealed in the bearing inner space 36 ′ between the outer ring 36 a and the inner ring 36 b of the second rolling bearing 36. One end face 31 b ′ of the second housing 31 b is disposed opposite to the bearing inner space 36 ′ of the second rolling bearing 36. In the present embodiment, as shown in FIG. 5, the inner diameter d of the second housing 31b is made smaller than the outer diameter D of the inner ring 36b of the second rolling bearing 36, and the inner ring 36b and one end surface 31b ′ of the second housing 31b. Is chamfered on the one end side of the inner periphery of the second housing 31b. The minute distance δ is in contact with the bearing inner space 36 ′, particularly the outer ring 36a. The outflow of the grease enclosed in the space surrounded by the inner ring 36b, the rolling element 36c and the retainer 36d to the outside of the bearing 36 and the intrusion of dust into the bearing inner space 36 'from the second housing 31b side is performed in the second housing. It is preferable that the inner diameter of the second housing 31b is slightly larger than the outer diameter of the inner ring 36b of the second rolling bearing 36. Thus, the inner ring 36b and the one end surface 31b 'of the second housing 31b may be opposed to each other with a small distance.
[0019]
A grease holding space 90 for holding grease is formed on the inner periphery of the rack housing 31. In this embodiment, the grease holding space 90 is an annular shape surrounding the outer periphery of the ball screw shaft 61, and has an opening 90 a that faces the outer periphery of the ball screw shaft 61 and the pressing member 83. A grease nipple 91 for replenishing grease to the grease holding space 90 from the outside of the rack housing 31 is attached to the second housing 31b. Thereby, grease is periodically replenished to the grease holding space 90, and it is possible to permanently prevent the grease from running out on the ball raceway surfaces of the ball screw shaft 61 and the ball nut 63.
[0020]
The torque sensor 7 and the sensor 8c are connected to a control device (not shown), and the control device rotates according to the steering torque detected by the torque sensor 7 and the rotational phase of the rotor 8b detected by the sensor 8c. Driving AC current is input to the brushless motor 8. Accordingly, the ball nut 63 is rotationally driven by the brushless motor 8, and the steering assist force along the longitudinal direction of the rack 4 is applied according to the steering torque by the rotational drive of the ball nut 63. A known control device can be used.
[0021]
According to the above configuration, since the grease flowing out from the opening 90 a of the grease holding space 90 is supplied to the outer periphery of the ball screw shaft 61, the grease is insufficient on the raceway surface of the circulating ball 62 in the ball screw shaft 61 and the ball nut 63. In other words, the raceway surface can be stably lubricated for a long time without adding special parts. Further, due to the one end surface 31b 'of the second housing 31b, the grease sealed in the bearing inner space 36' of the second rolling bearing 36 flows out to the outside, and the second housing 31b side into the bearing inner space 36 ' Can control the intrusion of dust.
[0022]
The present invention is not limited to the above embodiment. For example, a grease holding space having an opening facing the outer periphery of the ball screw shaft 61 may be formed in the inner periphery of the rotor 8b or the pressing member 83 together with the grease holding space in the inner periphery of the second housing . Also, grease retaining space is not limited to circular, recesses having an opening opposing, for example, in part of the peripheral direction of the ball screw shaft may be formed by forming the second Haujin grayed. Moreover, a motor is not limited to a brushless motor, Various motors can be employ | adopted.
[0023]
【The invention's effect】
According to the present invention, it is possible to prevent local wear on the ball raceway surface of the ball screw shaft and the ball nut, and to further reduce the cost and extend the life of the rotor support bearing of the steering assist force generation motor. It is possible to provide an electric power steering device that can be used.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a rack and pinion type electric power steering apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a main part of the rack and pinion type electric power steering apparatus according to an embodiment of the present invention. FIG. 4 is a partial sectional view of one end of a motor in a rack and pinion type electric power steering apparatus according to an embodiment. FIG. 4 is a partial sectional view of a rack and pinion type electric power steering apparatus according to an embodiment of the present invention. Partial enlarged sectional view of the pinion type electric power steering device [Explanation of symbols]
3 Pinion 4 Rack 8 Motor 8a Stator 8b Rotor 31 Rack housing 31a First housing 31a 'Step 31b Second housing 31b' One end surface 36 Second rolling bearing 61 Ball screw shaft 62 Circulating ball 63 Ball nut 90 Grease holding space

Claims (2)

A pinion rotating by steering,
A rack meshing with the pinion,
A ball screw shaft integrated into the rack;
A ball nut screwed to the ball screw shaft via a circulating ball;
A motor that rotationally drives the ball nut so that a steering assist force along the axial direction of the rack can be applied;
A housing covering the rack,
In the rack and pinion type electric power steering apparatus, the motor includes a stator fixed to the housing side, and a rotor that is rotatably supported by the housing side and into which the rack is inserted.
The housing has a cylindrical first housing and a cylindrical second housing arranged in parallel along the axial direction of the rack,
In its second Haujin grayed, grease retaining space having an opening facing the outer periphery of the ball screw shaft is formed,
A rolling bearing for supporting the rotor is inserted into the first housing,
The outer ring of the rolling bearing is sandwiched between a step formed on the inner peripheral side of the first housing and one end face of the second housing inserted into the first housing,
One end surface of the second housing is disposed opposite to the bearing inner space between the outer ring and the inner ring of the rolling bearing,
The rolling pinion type electric power steering apparatus , wherein the rolling bearing is disposed between the stator and the grease holding space in the axial direction of the rack. The inner diameter of the second housing is made smaller than the outer diameter of the inner ring of the rolling bearing, and the inner ring and the one end surface of the second housing are opposed to each other with a small distance. The rack and pinion type electric power steering apparatus according to claim 1 , wherein a chamfered portion is formed on one end side .

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