JP2006213280A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device to support a motor shaft in a housing by using a bearing which is capable of generating abnormal noise even when vibrations are applied when a vehicle runs on a rough road. <P>SOLUTION: The electric power steering device comprises housings 12, 13, 14, a lack shaft 15 which is movably supported by the housings 12, 13, 14 and engaged with a pinion 22, an electric motor 30 to provide the assist torque to the lack shaft 15 via a motor shaft 32, a radial bearing 34 to support the motor shaft 32 in the radial direction, and a thrust bearing 33 to support the motor shaft 32 in the thrust direction, and further comprises a preloading rubber 20 to urge the motor shaft 32 in the thrust direction (X1 direction) with respect to the yoke housing 14. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering device, and more particularly to an electric power steering device configured to support a motor shaft in a housing using a bearing.

  Generally, an electric power steering device transmits rotation of a steering wheel to a rack shaft via an input shaft and a pinion shaft, and steers left and right front wheels via tie rods connected to both ends of the rack shaft. The steering torque applied to the steering wheel is detected by a torque sensor, an electric motor arranged on the rack shaft is driven based on the detected torque, and the output torque of the electric motor is transmitted to the rack shaft via a ball screw device. This assists the steering force.

  For example, in an electric power steering device having an arrangement in which an assisting electric motor is disposed around a rack shaft, as disclosed in Patent Document 1, a nut that constitutes a ball screw device is connected to a motor shaft of the electric motor. A thread groove formed on the rack shaft is engaged with a thread groove formed on the inner periphery of the nut via a ball.

  FIG. 4 is a main part configuration diagram of the electric power steering apparatus disclosed in Patent Document 1. As shown in FIG. FIG. 5 is an enlarged view of a portion indicated by an arrow B in FIG.

  As shown in the figure, the electric power steering apparatus 100 has a configuration in which a motor shaft 132 is disposed in a housing space formed by a first rack housing 112, a second rack housing 113, and a yoke housing 114. ing. The end of the motor shaft 132 in the direction of the arrow X1 in the drawing is supported by the first rack housing 112 by a thrust bearing 133. Further, the end of the motor shaft 132 in the direction of the arrow X2 in the drawing is supported by the yoke housing 114 by a radial bearing 134. Incidentally, reference numeral 131 in the figure denotes a drive stator that constitutes a part of the electric motor.

  The thrust bearing 133 supports a load applied to the motor shaft 132 in the thrust direction (in the direction of arrows X1 and X2 in the figure), and includes an outer ring 133A, an inner ring 133B, and a ball 133C. The radial bearing 134 supports a load applied to the motor shaft 132 in the radial direction (radial direction of the cylindrical motor shaft 132), and includes an outer ring 134A, an inner ring 134B, and a ball 134C. ing.

The outer ring 133A of the thrust bearing 133 is fixed to the first rack housing 112, and the inner ring 133B is fixed to the motor shaft 132. The outer ring 134A of the radial bearing 134 is in sliding contact with the inner surface of the yoke housing 114 via an O-ring 136, and the inner ring 134B is fixed to the motor shaft 132.
JP 2003-335249 A

  By the way, when a vehicle equipped with the electric power steering apparatus 100 configured as described above travels on a rough road, vibrations of the wheels are transmitted to the motor shaft 132 via the housings 112 to 114 and the bearings 133 and 134. . In the conventional electric power steering apparatus 100, the motor shaft 132 can move a little in the thrust direction (arrow X1, X2 direction in the figure).

  That is, the thrust bearing 133 generally has a slight movement margin in the thrust direction in order to receive a thrust load, and the radial bearing 134 has an outer ring 134A against the inner wall of the yoke housing 114 by an O-ring 136 for sealing. It can be moved slightly. For this reason, when vibration is applied to the electric power steering device 100 due to the rough road traveling as described above, the motor shaft 132 is displaced in the thrust direction (directions of arrows X1 and X2 in the drawing) in the housing space. There has been a problem that abnormal noise occurs in the thrust bearing 133 due to the above-described movement margin.

  The present invention has been made in view of the above points, and an object of the present invention is to provide an electric power steering device that can prevent the generation of abnormal noise even when vibration is applied during rough road driving.

  In order to solve the above-described problems, the present invention is characterized by the following measures.

The electric power steering apparatus according to the invention of claim 1
A housing;
A rack shaft that is movably supported by the housing and meshes with a pinion connected to a steering shaft;
An electric motor that is disposed around the rack shaft in the housing and applies assist torque to the rack shaft via a motor shaft;
A first bearing disposed between the housing and the motor shaft and supporting the motor shaft in a radial direction;
A second bearing disposed between the housing and the motor shaft and supporting the motor shaft in a thrust direction;
An urging member for urging the motor shaft with respect to the housing in the thrust direction is provided.

  According to the above invention, by providing the biasing member that biases the motor shaft in the thrust direction with respect to the housing, the biasing force of the biasing member biases the second bearing in the thrust direction via the motor shaft. It is applied as a pressurizing pressure. For this reason, it is possible to prevent the second bearing from rattling in the thrust direction and generating abnormal noise.

The invention according to claim 2
The electric power steering apparatus according to claim 1,
The first bearing is fixed to the motor shaft and is movable in the thrust direction with respect to the housing.
Fixing the biasing member to the housing;
The biasing member biases the first bearing to bias the motor shaft to the housing in the thrust direction via the first bearing. It is.

  According to the above invention, the biasing member fixed to the housing biases the first bearing, thereby biasing the motor shaft in the thrust direction with respect to the housing via the first bearing. The pressurization can be applied to the second bearing with a simple configuration.

The invention according to claim 3
The electric power steering apparatus according to claim 1 or 2,
The biasing member is rubber.

  According to the above invention, since the biasing member is made of rubber, it is possible to apply pressure to the second bearing at a low cost, and to prevent vibration from being transmitted between the motor shaft and the housing. Can do.

The invention according to claim 4
In the electric power steering device according to any one of claims 1 to 3,
The second bearing is a double row bearing.

  According to the above invention, by using the double row bearing as the second bearing, the double row bearing reliably supports the thrust load of the motor shaft because a plurality of balls (balls) are arranged in the axial direction. be able to. In addition, the double row bearing is more likely to be rattled than the single row bearing, but by providing an urging member, the occurrence of rattling can be reliably prevented.

  As described above, according to the present invention, since the urging force of the urging member is applied as a pressurizing force that urges the second bearing in the thrust direction, the occurrence of rattling in the second bearing is prevented. Therefore, it is possible to prevent abnormal noise from being generated in the electric power steering apparatus.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings.

  1 to 3 show an electric power steering apparatus 10. FIG. 1 is a cross-sectional view showing the overall configuration of the electric power steering device 10, FIG. 2 is a diagram showing the main configuration of the electric power steering device 10, and FIG. 3 is an enlarged view of the portion indicated by arrow A in FIG. It is a figure shown.

  In general, the electric power steering apparatus 10 includes a gear housing 11, a rack shaft 15, a pinion 22, an electric motor 30, a motor shaft 32, and the like. The gear housing 11 includes a hollow cylindrical first rack housing 12 and a second rack housing 13, and a yoke housing 14 provided between the rack housings 12 and 13. The housings 12, 13, and 14 are not shown. Coaxially connected by bolts.

  A rack shaft 15 is penetrated through the gear housing 11 so as to be movable in the axial direction, and both ends of the rack shaft 15 protruding from the first and second rack housings 12 and 13 are connected to the left and right front wheels via tie rods (not shown). Connected. The first rack housing 12 is provided with a pinion 22 connected to the steering shaft. The pinion 22 meshes with rack teeth 16 formed on the rack shaft 15.

  Therefore, when the driver operates the steering wheel, the pinion 22 is rotated via the steering shaft by this operating force, and the rotation of the pinion 22 is converted into the linear movement of the rack shaft 15 by the engagement of the pinion 22 and the rack teeth 16. As a result, the front wheels are steered through the tie rods.

  A cylinder hole 23 is formed in the first rack housing 12 at a position facing the pinion 22 across the rack shaft 15 in a direction perpendicular to the axis of the rack shaft 15. A rack guide 24 joined to the peripheral surface is slidably accommodated. The rack guide 24 presses the rack shaft 15 toward the pinion 22 by the spring force of the spring 25 provided on the back side thereof.

  The electric motor 30 is disposed around the rack shaft 15 in the yoke housing 14 constituting the gear housing 11 and has a function of applying assist torque to the rack shaft 15 via the motor shaft 32 as will be described later. . The electric motor 30 is a brushless DC motor and has a drive stator 31 as a stator and a motor shaft 32 as a rotor. The drive stator 31 is wound with a coil and is disposed on the inner wall of the yoke housing 14. The motor shaft 32 has a hollow cylindrical shape and is loosely fitted coaxially around the rack shaft 15.

  The end of the motor shaft 32 in the direction of the arrow X1 extends into the first rack housing 12 and is rotatably supported by the first rack housing 12 by a thrust bearing 33. Also, the end of the motor shaft 32 in the direction of the arrow X2 in the drawing extends into the second rack housing 13, and a position near this end is rotatably supported by the yoke housing 14 by a radial bearing 34.

  The thrust bearing 33 supports a load applied to the motor shaft 32 in the thrust direction (in the direction of arrows X1 and X2 in the figure), and includes an outer ring 33A, an inner ring 33B, and a ball 33C. In this embodiment, a double row bearing in which a plurality of balls 33C are arranged in the thrust direction is used as the thrust bearing 33. As described above, since the plurality of balls 33C are arranged in the axial direction in the double row bearing, the thrust direction load of the motor shaft 32 can be reliably supported.

  On the other hand, the radial bearing 34 supports a load applied to the motor shaft 32 in the radial direction (the radial direction of the cylindrical motor shaft 32). The radial bearing 34 includes an outer ring 34A, an inner ring 34B, and a ball 34C.

  The outer ring 33 </ b> A of the thrust bearing 33 is fixed to the first rack housing 12, and the inner ring 33 </ b> B is fixed to the motor shaft 32. The outer ring 34 </ b> A of the radial bearing 34 is in sliding contact with the inner surface of the yoke housing 14 via the O-ring 36, and the inner ring 34 </ b> B is fixed to the motor shaft 32.

  The thrust bearing 33 generally has a slight movement margin in the thrust direction in order to receive a thrust load. As shown in an enlarged view in FIG. 3, an O-ring 36 is disposed on the inner wall of the yoke housing 14, and the outer ring 34 </ b> A of the radial bearing 34 is in contact with the O-ring 36.

  The O-ring 36 is provided to provide a fluid-tight seal between the yoke housing 14 and the outer ring 34A. Thus, by arranging the O-ring 36 between the yoke housing 14 and the outer ring 34A, the radial bearing 34 supports the motor shaft 32 with respect to the yoke housing 14 in the radial direction, but in the thrust direction. With respect to (in the directions of the arrows X1 and X2), the yoke housing 14 is movable.

  The ball screw device 37 is provided at the end of the motor shaft 32 in the direction indicated by the arrow X2. The ball screw device 37 includes a screw groove 15B, a nut 38, a screw groove 38A, a ball 39, and the like. The nut 38 is attached to the inner peripheral position of the end of the motor shaft 32 in the direction of the arrow X2 in the drawing.

  A screw groove 38A is formed on the inner periphery of the nut 38, a screw groove 15B is formed on the outer periphery of the rack shaft 15 corresponding to the screw groove 38A, and a ball 39 is interposed between the screw grooves 38A and 15B. Thus, the rotational motion of the ball screw nut 38 that rotates together with the motor shaft 32 is converted into the axial motion of the rack shaft 15.

  With the configuration described above, power supplied to the electric motor 30 is controlled by the power steering control device (PSECU) to which signals from a torque sensor, a vehicle speed sensor, etc. (not shown) are input, and the electric motor 30 is driven. . When the motor shaft 32 is rotated by driving the electric motor 30, the nut 38 constituting the ball screw device 50 integrated with the motor shaft 32 is also rotated. Thereby, the rack shaft 15 in which the screw groove 15B is formed via the ball 39 is moved in the directions of the arrows X1 and X2, thereby assisting the steering force.

  Here, attention is focused on the radial bearing 34 and the end portion 13A of the second rack housing 13 in the direction of the arrow X1 in the drawing.

  As shown in each drawing, a preload rubber 20 is disposed between the outer ring 34 </ b> A of the radial bearing 34 and the end 13 </ b> A of the second rack housing 13. The preload rubber 20 may be configured to be fixed to either the end portion 13A or the outer ring 34A, but in this embodiment, an adhesive is used for the end portion 13A of the second rack housing 13 from the standpoint of assembly. The configuration is fixed.

  At this time, the preload rubber 20 is compressed while being disposed between the end portion 13A and the outer ring 34A. As described above, the inner ring 34 </ b> B of the radial bearing 34 is fixed to the motor shaft 32, and the outer ring 34 </ b> A is movable with respect to the yoke housing 14. For this reason, the preload rubber 20 urges the motor shaft 32 against the yoke housing 14 in the direction of the arrow X1 (thrust direction) through the radial bearing 34 by the accumulated elastic force.

  As a result, the biasing force of the preload rubber 20 is applied to the thrust bearing 33 via the radial bearing 34 and the motor shaft 32 as a pressure for biasing the inner ring 33B in the direction of the arrow X1 (thrust direction) in the figure. Therefore, even if there is a slight movement margin between the outer ring 33A and the inner ring 33B, the inner ring 33B is urged in the X1 direction by the preload applied by the preload rubber 20, and the movement margin is eliminated. ing.

  For this reason, even if the vehicle travels on a rough road and vibration is applied to the electric power steering apparatus 10, it is possible to reliably prevent the generation of noise in the thrust bearing 33. Further, since the preload rubber 20 is simply disposed between the end portion 13A of the second rack housing 13 and the outer ring 34A of the radial bearing 34, noise generation can be suppressed. Generation of abnormal noise can be prevented without complicating the configuration of the apparatus 10 and at low cost.

  Further, by using the preload rubber 20 as a means for urging the preload on the thrust bearing 33 as in this embodiment, the preload rubber 20 made of rubber is interposed between the second rack housing 13 and the motor shaft 32. Since it also has a function of preventing vibrations from being transmitted, it is possible to prevent abnormal noise from being generated in the electric power steering apparatus 10.

  Instead of the preload rubber 20, another elastic member can be used as a biasing member that biases the preload to the thrust bearing 33. For example, a configuration in which a disc spring is disposed between the end portion 13A and the outer ring 34A is also conceivable. In this configuration, a preload can be applied to the thrust bearing 33, but vibration is transmitted between the second rack housing 13 and the motor shaft 32, so that the biasing member is used as in the above-described embodiment. It is desirable to use rubber.

  In the above-described embodiment, since the outer ring 34A of the radial bearing 34 is movable with respect to the yoke housing 14 and the inner ring 34B is fixed to the motor shaft 32, the preload rubber 20 serving as an urging means is provided. Was disposed between the end 13A and the outer ring 34A. However, the position where the preload rubber 20 is disposed is not limited to this position, and the preload is applied in such a direction as to eliminate the movement margin (movement margin causing abnormal noise) of the thrust bearing 33. If possible, it may be arranged at another position.

FIG. 1 is a sectional view of an electric power steering apparatus according to an embodiment of the present invention. FIG. 2 is a configuration diagram of a main part of an electric power steering apparatus according to an embodiment of the present invention. FIG. 3 is an enlarged view of a portion indicated by an arrow A in FIG. FIG. 4 is a configuration diagram of a main part of an electric power steering apparatus as an example of the prior art. FIG. 5 is an enlarged view of a portion indicated by an arrow B in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electric power steering device 12 1st rack housing 13 2nd rack housing 14 Yoke housing 15 Rack shaft 20 Preload rubber 22 Pinion 30 Electric motor 31 Drive stator 32 Motor shaft 33 Thrust bearing 34 Radial bearing 36 O-ring 37 Ball screw device

Claims (4)

A housing;
A rack shaft that is movably supported by the housing and meshes with a pinion connected to a steering shaft;
An electric motor that is disposed around the rack shaft in the housing and applies assist torque to the rack shaft via a motor shaft;
A first bearing disposed between the housing and the motor shaft and supporting the motor shaft in a radial direction;
A second bearing disposed between the housing and the motor shaft and supporting the motor shaft in a thrust direction;
An electric power steering apparatus comprising an urging member for urging the motor shaft with respect to the housing in the thrust direction. The electric power steering apparatus according to claim 1,
The first bearing is fixed to the motor shaft and is movable in the thrust direction with respect to the housing.
Fixing the biasing member to the housing;
An electric motor characterized in that when the biasing member biases the first bearing, the motor shaft is biased in the thrust direction with respect to the housing via the first bearing. Power steering device. The electric power steering apparatus according to claim 1 or 2,
The electric power steering apparatus, wherein the urging member is rubber. In the electric power steering device according to any one of claims 1 to 3,
The electric power steering apparatus, wherein the second bearing is a double row bearing.

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