JP2011088462A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device achieving space saving. <P>SOLUTION: The electric power steering device includes a rack shaft 1 for steering a wheel, a casing 2 for supporting the rack shaft 1, a casing cover 3 fixed to the casing 2 and closing an opening of the casing 2, and a ball screw mechanism 30 housed in the casing 2 and converting a rotational force of an electric motor 21 into an axial movement of the rack shaft 1. The ball screw mechanism 30 includes a cylindrical ball nut 31 screwed with a spiral groove 1a of the rack shaft 1, a nut holder 34 rotating while supporting the ball nut 31, a bearing 35 rotatably supporting the nut holder 34 in the casing 2, and a plate 36 fixed by being sandwiched between the casing 2 and the casing cover 3 and regulating the axial movement of the bearing 35. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electric power steering device for a vehicle.

  2. Description of the Related Art As a power steering device that assists a steering wheel operation performed by a driver, an electric power steering device that assists the steering wheel operation using the rotational force of an electric motor is known.

  Patent Document 1 discloses an electric power steering device in which a rack bar having both ends connected to left and right tie rods moves in the axial direction by the rotational force of an electric motor transmitted via a ball screw mechanism to assist steering operation. Is disclosed.

JP 2008-254494 A

  However, in Patent Document 1, the bearing that supports the rack bar is fixed to the housing by fastening a ring-shaped fastening member, and movement in the axial direction is restricted. Therefore, it is necessary to secure a fixing space for the fastening member and a work space for fastening the fastening member.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide an electric power steering device capable of saving space.

  The present invention relates to a rack shaft for steering a wheel, a casing that supports the rack shaft, a casing cover that is fixed to the casing and closes an opening of the casing, and is accommodated in the casing. A ball screw mechanism that converts a rotational force into an axial movement of the rack shaft, and the axial movement of the rack shaft by the rotational force of the electric motor transmitted through the ball screw mechanism. In the electric power steering apparatus that assists the rotation of the electric motor, the ball screw mechanism includes a cylindrical ball nut that is screwed into a spiral groove formed on the rack shaft, and the rotation of the electric motor that supports the ball nut. A nut holder that rotates, provided facing the opening of the casing, the nut holder A bearing for rotatably supporting said casing is fixed by being sandwiched between the casing cover and the casing, characterized in that it and a plate for restricting the movement in the axial direction of the bearing.

  According to the present invention, the axial movement of the bearing supporting the nut holder is restricted by the plate that is sandwiched and fixed between the casing and the casing cover. Since the fastening means for fastening to the casing is not formed on the plate, the plate can be reduced in size compared to the case where the fastening means is formed. Moreover, since the plate for fixing a bearing can be assembled if there is a space corresponding to the size of the plate, no special work space is required.

  Therefore, space saving of the electric power steering device is possible.

It is sectional drawing which shows the electric power steering apparatus which concerns on embodiment of this invention. It is principal part sectional drawing of the electric power steering apparatus which concerns on embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, the overall configuration of the electric power steering apparatus 100 according to the present embodiment will be described with reference to FIG. The electric power steering apparatus 100 is mounted on a vehicle and assists a steering wheel operation performed by a driver.

  The electric power steering apparatus 100 includes a rack shaft 1 having left and right wheels connected to both ends via tie rods (not shown), a steering apparatus 10 for transmitting a handle operation to the rack shaft 1, and rotation of an electric motor 21. And a ball screw mechanism 30 that converts force into movement of the rack shaft 1 in the axial direction.

  The rack shaft 1 is incorporated in a substantially cylindrical casing 2 that is fastened to the vehicle body and is formed by opening an axial end of the rack shaft 1, and a casing cover 3 that closes the opening of the casing 2. Both ends of the casing are inserted through the casing 2 and the casing cover 3. A rack (not shown) is formed on the rack shaft 1.

  The steering device 10 coaxially connects an input shaft 12 that rotates in conjunction with a steering wheel, a pinion shaft (not shown) having a pinion (not shown) formed on the outer periphery thereof, and the input shaft 12 and the pinion shaft. A torsion bar (not shown) and a torque sensor (not shown) for detecting torque acting on the torsion bar are provided.

  The pinion of the steering device 10 meshes with the rack of the rack shaft 1. One end of the rack shaft 1 is supported by the casing 2 at a meshing portion with the pinion, and the other end is supported by the casing cover 3 by a bush (not shown) provided in the casing cover 3. As described above, the rack shaft 1 is supported by the casing 2 and the casing cover 3 and is restricted from moving in the radial direction, and is provided to be movable only in the axial direction. The casing cover 3 is fixed by bolts fastened to the casing 2.

  Since the rack shaft 1 and the steering device 10 are connected via a rack and a pinion, the rack shaft 1 moves in the axial direction and the wheels are steered when the driver operates the steering wheel.

  The electric motor 21 is driven based on the torque detected by the torque sensor of the steering device 10, and an assist force that assists the steering force applied by the driver to the steering wheel is applied to the rack shaft 1. This assist force is transmitted by the assist mechanism 20 that transmits the rotational force of the electric motor 21 to the ball screw mechanism 30.

  Next, the assist mechanism 20 and the ball screw mechanism 30 will be described with reference to FIG.

  The assist mechanism 20 includes a drive pulley 22 that is fixed to the rotating shaft of the electric motor 21 and rotates as a unit, a driven pulley 24 that is transmitted to the rotation of the drive pulley 22 and is fixed to the nut holder 34 and rotates as a unit, and a drive pulley. And a belt 23 that is wound between the pulley 22 and the driven pulley 24 and transmits the rotation of the driving pulley 22 to the driven pulley 24. The assist mechanism 20 is accommodated in the casing cover 3.

  The diameter of the driven pulley 24 is set to be larger than that of the driving pulley 22, and the rotation of the electric motor 21 is decelerated to transmit the amplified torque to the driven pulley 24. The rotational force of the driven pulley 24 is transmitted to the nut holder 34 and converted into the movement of the rack shaft 1 in the axial direction via the ball screw mechanism 30.

  The ball screw mechanism 30 is disposed between two support portions including a meshing portion with the pinion of the steering device 10 and a bush (not shown) provided on the inner periphery of the casing cover 3. The ball screw mechanism 30 is housed in the casing 2.

  The ball screw mechanism 30 includes a spiral groove 1a formed on the outer periphery of the rack shaft 1, a ball nut 31 formed in a cylindrical shape covering the outer periphery of the rack shaft 1, and a spiral groove 31a formed on the inner periphery, and the rack shaft. A plurality of balls 32 interposed between one spiral groove 1 a and the spiral groove 31 a of the ball nut 31, and the rotational force of the electric motor 21 is applied to the axis of the rack shaft 1 via the ball nut 31 and the ball 32. It is converted to movement in the direction. The rack shaft 1 and the ball nut 31 are configured such that the spiral grooves 1 a and 31 a are screwed through the balls 32, but may be configured to be screwed directly without using the balls 32.

  The ball nut 31 is supported on the inner periphery of a cylindrical nut holder 34 that covers the outer periphery of the rack shaft 1. The nut holder 34 is formed to extend in the axial direction of the rack shaft 1, and the outer periphery of one end thereof is press-fitted into the inner periphery of the driven pulley 24 and connected to the driven pulley 24.

  The nut holder 34 is provided with a driven pulley 24 at one end portion, the outer periphery of the intermediate portion is supported by a bearing 35, and the ball nut 31 is supported on the inner periphery of the free end portion. A bearing 39 is provided on the outer periphery of the ball nut 31 near the other end of the nut holder 34. Thereby, the ball nut 31 to which the force due to the movement of the rack shaft 1 in the axial direction is transmitted via the ball 32 is rotatably supported by the casing 2.

  A bearing 35 is interposed between the outer periphery of the nut holder 34 and the inner periphery of the casing 2. As described above, the nut holder 34 is rotatably supported by the casing 2 via the bearing 35 and rotates with the rotation of the driven pulley 24.

  The bearings 35 are angular bearings and are arranged in a state where they are opposed to each other. The bearing 35 is provided facing the opening of the casing 2. One end of the bearing 35 is locked by a stepped portion 2 a formed on the inner periphery of the casing 2 and a stepped portion 34 a formed on the outer periphery of the nut holder 34, and the other end is formed on the inner periphery of the casing 2. It is locked by an annular plate 36 fitted in the stepped portion 2 b and a nut 37 that is screwed onto the outer periphery of the nut holder 34 and fastened. Thus, the bearing 35 is configured to rotatably support the nut holder 34 on the casing 2 and to restrict movement of the nut holder 34 in the axial direction.

  The plate 36 is sandwiched and fixed between the casing 2 and the casing cover 3 and is provided to restrict the movement of the bearing 35 in the axial direction. The plate 36 is formed in an annular shape so as to be in contact with the annular bearing 35 over the entire circumference. However, the plate 36 is not limited to the annular shape as long as the bearing 35 can be fixed to the casing 2.

  A step 2b into which the plate 36 is fitted is formed in the casing 2 that sandwiches the plate 36. The casing cover 3 is formed with a flange portion 3 a for fastening the casing 2 with bolts and a protruding portion 3 b that protrudes from the inside toward the casing 2.

  The step portion 2 b is formed in a concave shape corresponding to the shape of the plate 36 in the opening of the casing 2. When the plate 36 is inserted into the stepped portion 2b, the opening of the casing 2 is substantially flush. Actually, the stepped portion 2b is formed shallower than the thickness of the plate 36, and the plate 36 is sandwiched between the casing 2 and the casing cover 3 to prevent the plate 36 from rattling.

  The flange portion 3 a abuts against a part of the plate 36 in an annular shape, and fixes the plate 36 to the casing 2. The casing cover 3 is formed so as to continuously surround a part of the outer periphery of the drive pulley 22 and a part of the outer periphery of the driven pulley 24. In order to fix the plate 36 in a region where the flange portion 3a does not come into contact, the casing cover 3 is provided with a protruding portion 3b.

  The protrusion 3 b is a protrusion formed inside the casing cover 3. The protrusion 3b abuts against a part of the plate 36 so as to complement the region where the flange 3a cannot abut, and fixes the plate 36 to the casing 2. The protruding portion 3b is between the driving pulley 22 and the driven pulley 24, passes through the annular belt 23 that hangs on the driving pulley 22 and the driven pulley 24, and straddles the casing 2 and the plate 36 at the tip thereof. Abut.

  From the above, the plate 36 is pressed toward the casing 2 evenly over substantially the entire circumference by the flange portion 3 a and the projection portion 3 b of the casing cover 3.

  Note that the contact surface of the flange portion 3a of the casing cover 3 with the casing 2 and the tip surface of the projection 3b are formed flush with each other. Therefore, since the processing is easy, the cost can be reduced and the processing accuracy can be improved.

  Since the plate 36 does not include a fastening means for fastening to the casing 2, a space for fastening means or a special work space for fastening is not required. Therefore, space saving is possible. Moreover, since it is not necessary to form a fastening means, a man-hour and cost can be reduced.

  The plate 36 is temporarily fixed to the casing 2 with bolts 41. Therefore, the plate 36 is fixed to the casing 2 even when the casing cover 3 is not attached. That is, since the movement of the bearing 35 in the axial direction is restricted by the plate 36, the ball screw mechanism 30 is fixed to the inner periphery of the casing 2. This bolt 41 corresponds to temporary fixing means.

  By the way, when the tension adjustment operation of the belt 23 is performed after the plate 36 is sandwiched and fixed between the casing 2 and the casing cover 3, a hole for confirming the tension of the belt 23 needs to be formed in the casing cover 3. is there. When the hole is formed, a plug for closing the hole is required, the number of parts may be increased, and workability may be deteriorated, and there is a possibility that the sealing performance may be disadvantageous.

  On the other hand, in the electric power steering apparatus 100, the plate 36 can be temporarily fixed to the casing 2 by the bolt 41, so that the nut holder 34 is fixed even when the casing cover 3 is removed. Therefore, since the positions of the drive pulley 22 and the driven pulley 24 are determined, it is possible to perform a tension adjustment operation for adjusting the tension of the belt 23 with the casing cover 3 removed.

  Even if the bolt 41 is not provided, the plate 36 is fixed by being sandwiched between the casing 2 and the casing cover 3, and the tension of the belt 23 can be adjusted by forming a hole in the casing cover 3. Therefore, the bolt 41 may not be provided. In the case where the bolt 41 is not provided, the plate 36 can be further reduced, so that further space saving of the electric power steering apparatus 100 is possible.

  The ball nut 31 is supported on the other end of the nut holder 34. The ball nut 31 is sandwiched between a stepped portion 34b formed on the inner periphery of the nut holder 34 and a nut 38 screwed into the inner periphery from the opening of the nut holder 34 and moved in the axial direction. And relative rotation is restricted. Further, in order to restrict relative rotation of the ball nut 31 with respect to the nut holder 34 when the nut 38 is loosened, a bolt 40 that is inserted through the nut holder 34 and screwed to the outer periphery of the ball nut 31 is provided. It is done. Thus, the ball nut 31 is fixed to the nut holder 34 and rotates integrally with the nut holder 34.

  The rotation of the ball nut 31 is converted into movement of the rack shaft 1 in the axial direction via the balls 32 and the spiral groove 1 a of the rack shaft 1. When the electric motor 21 is driven and the ball nut 31 rotates, an assist force that assists the steering force applied to the steering wheel by the driver is applied to the rack shaft 1.

  According to the above embodiment, there exist the effects shown below.

  In the electric power steering apparatus 100, the bearing 35 that supports the rack shaft 1 is restricted from moving in the axial direction by an annular plate 36 that is sandwiched and fixed between the casing 2 and the casing cover 3. Since the fastening means for fastening to the casing 2 is not formed on the plate 36, the plate 36 can be reduced in size compared to the case where the fastening means is formed. Further, the plate 36 can be assembled and fixed if there is a space corresponding to the size thereof, so that no special work space is required. Therefore, space saving of the electric power steering apparatus 100 is possible.

  Further, since the plate 36 is temporarily fixed to the casing 2 with bolts 41, the plate 36 is fixed to the casing 2 even when the casing cover 3 is not attached. Therefore, it is possible to adjust the tension of the belt 23 with the casing cover 3 removed.

  The present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

  The present invention can be applied to an electric power steering device mounted on a vehicle.

DESCRIPTION OF SYMBOLS 100 Electric power steering apparatus 1 Rack shaft 2 Casing 3 Casing cover 10 Steering apparatus 20 Assist mechanism 21 Electric motor 22 Drive pulley 23 Belt 24 Driven pulley 30 Ball screw mechanism 31 Ball nut 34 Nut holder 35 Bearing 36 Plate 41 Bolt

Claims (4)

A rack shaft for steering the wheels;
A casing for supporting the rack shaft;
A casing cover fixed to the casing and closing an opening of the casing;
A ball screw mechanism that is housed in the casing and converts the rotational force of the electric motor into movement in the axial direction of the rack shaft,
In the electric power steering device that assists the movement of the rack shaft in the axial direction by the rotational force of the electric motor transmitted through the ball screw mechanism,
The ball screw mechanism is
A cylindrical ball nut screwed into a spiral groove formed in the rack shaft;
A nut holder that supports the ball nut and rotates as the electric motor rotates,
A bearing that faces the opening of the casing and rotatably supports the nut holder on the casing;
An electric power steering apparatus comprising: a plate fixed by being sandwiched between the casing and the casing cover and restricting movement of the bearing in the axial direction.   The electric power steering apparatus according to claim 1, further comprising temporary fixing means for temporarily fixing the plate to the casing. An assist mechanism that is housed in the casing cover and transmits rotation of the electric motor to the nut holder;
The assist mechanism is
A driving pulley fixed to the rotating shaft of the electric motor and rotating as a unit;
A driven pulley fixed to the nut holder and rotating as a unit;
The electric power steering apparatus according to claim 2, further comprising: a belt that is wound around the drive pulley and the driven pulley. The casing cover is
A flange portion that contacts and fixes a part of the plate;
The electric power steering apparatus according to claim 3, further comprising: a protrusion that passes through an inner periphery of the belt and is in contact with and fixed to a part of the plate.

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