JP2013193713A - Reduction gear of electric power steering apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering apparatus which includes a reduction gear using a toothed belt, and which eliminates the risk of disabling steering, because rotation of at least a driven-side toothed pulley is not locked by meshing with broken toothed belt, even when the toothed belt is broken.SOLUTION: In a reduction gear of an electric power steering apparatus 10, a gap G between an inner peripheral surface A, facing at least a driven-side toothed pulley 40, of a housing 11 and an outer peripheral surface B of the driven-side toothed pulley 40 is set larger than twice the thickness t of a toothed belt 50.

Description

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

  As a reduction device for an electric power steering device, as described in Patent Document 1, a rack shaft is supported on a housing so as to be linearly movable, an electric motor is attached to the housing, and a drive-side toothed pulley coupled to the rotating shaft of the electric motor Is transmitted to the rack shaft via a power transmission mechanism including a driven side toothed pulley connected to the driving side toothed pulley via a toothed belt. FIG. 5 shows this reduction gear, wherein 1 is a housing, 2 is a driving side toothed pulley, 3 is a driven side toothed pulley, and 4 is a toothed belt.

  In the reduction gear described in Patent Document 1, at least the inner peripheral surface of the housing facing the toothed belt wound around the driven-side toothed pulley and the back side of the toothed belt wound around the driven-side toothed pulley Is set to be greater than the tooth height of the toothed belt.

  As a result, even if the toothed belt breaks, the toothed belt is caught between the inner peripheral surface of the housing and the outer peripheral surface of the driven side toothed pulley, and the driven side toothed pulley is rotationally locked. There is no. Therefore, even when the driven-side toothed pulley is interlocked with the rack shaft via a power transmission mechanism such as a ball screw, there is no possibility that manual steering cannot be disabled by the rotation lock of the driven-side toothed pulley.

Patent 4166242

  In the reduction device of the electric power steering device described in Patent Document 1, at least an inner peripheral surface of the housing facing the toothed belt wound around the driven-side toothed pulley and a tooth wound around the driven-side toothed pulley The clearance with the back side of the attached belt is merely set to be greater than the tooth height of the toothed belt. Therefore, the tip of the broken toothed belt hangs down on the inside of the housing and is wound around the tooth surface of the driven toothed pulley facing the inside of the housing. There is a risk of overlapping with the other end. As a result, the two-layered toothed belt enters into a narrow gap between the inner peripheral surface of the housing and the outer peripheral surface of the driven side toothed pulley, and is engaged with the gap, whereby the driven side toothed pulley is rotationally locked. Manual steering may become unsteerable.

  An object of the present invention is to provide an electric power steering apparatus having a reduction gear using a toothed belt, and even if the toothed belt breaks, at least the driven toothed pulley is rotationally locked by the biting of the broken toothed belt. An object of the present invention is to provide an electric power steering device that does not cause the possibility of steering failure.

  According to the first aspect of the present invention, the rack shaft is supported on the housing so as to be linearly movable, the electric motor is attached to the housing, and the rotational force of the driving side toothed pulley coupled to the rotating shaft of the electric motor is applied to the driving side teeth. In a reduction device for an electric power steering device that transmits to a rack shaft via a power transmission mechanism including a driven side toothed pulley connected to a toothed pulley via a toothed belt, the inner side of the housing facing at least the driven side toothed pulley The clearance between the peripheral surface and the outer peripheral surface of the driven-side toothed pulley is set to be larger than twice the thickness of the toothed belt.

  The invention according to claim 2 is an electric power steering apparatus including the speed reduction device according to claim 1.

(Claims 1 and 2)
(a) In the electric power steering apparatus having a reduction gear using a toothed belt, a gap between at least an inner peripheral surface of the housing facing the driven-side toothed pulley and an outer peripheral surface of the driven-side toothed pulley is a tooth It was set to be larger than twice the thickness of the attached belt.

  Therefore, both ends of the broken toothed belt overlap around the driven toothed pulley inside the housing, and the two-layered toothed belt has a gap between the inner peripheral surface of the housing and the outer peripheral surface of the driven toothed pulley. The gap is greater than twice the thickness of the toothed belt. As a result, the toothed belt does not bite into the gap and the driven-side toothed pulley is not rotationally locked. The driven toothed pulley is free to rotate and does not lock, and there is no possibility that the manual steering of the electric power steering apparatus cannot be steered.

FIG. 1 is a front view showing the entire electric power steering apparatus. FIG. 2 is a cross-sectional view showing the speed reducer. FIG. 3 is an enlarged cross-sectional view showing a main part of the reduction gear. FIG. 4 is a schematic view showing a state where the toothed belt is broken in the housing of the reduction gear. FIG. 5 is a schematic diagram showing a conventional example.

  As shown in FIG. 1, the electric power steering apparatus 10 includes a first gear housing 11A and a second gear housing 11B in which the gear housing 11 is divided, and a steering input is input to the gear housing 11 (first gear housing 11A). The shaft 12 is supported, an output shaft (not shown) is connected to the input shaft 12 via a torsion bar 13, a pinion (not shown) is provided on the output shaft, and the rack shaft 14 meshing with the pinion is connected to the gear housing 11. It is supported so that it can move linearly in the left-right direction. A steering torque sensor (not shown) is provided between the input shaft 12 and the output shaft. The steering torque sensor detects the steering torque based on the relative rotational displacement generated between the input shaft 12 and the output shaft due to the elastic torsional deformation of the torsion bar caused by the steering torque applied to the steering wheel.

  The electric power steering apparatus 10 has both end portions of the rack shaft 14 projecting from both sides of the gear housing 11 (first gear housing 11A, second gear housing 11B), and tie rods 15A, 15B are connected to the end portions of the rack shaft 14, The left and right wheels can be steered via tie rods 15A and 15B that are linked to the 14 linear movements.

  The electric power steering device 10 includes an electric motor 20. The electric motor 20 is attached to a bearing housing 21 fixed to the first gear housing 11A, and the serration of the drive shaft 32 of the drive side toothed pulley 30 is coaxially coupled to the serration hole of the rotary shaft 20A of the electric motor 20. ing.

  The electric power steering device 10 has a large-diameter driven-side toothed pulley 40 connected to the small-diameter driving-side toothed pulley 30 via a toothed belt 50 by the rotational force of the driving-side toothed pulley 30 provided by the electric motor 20. Is transmitted to the rack shaft 14 through a power transmission mechanism including a speed reducer.

  As shown in FIGS. 2 and 3, the drive-side toothed pulley 30 has flange members 33 and 34 having a larger outer diameter than the tooth portion 31A on both sides of the tooth portion 31A provided on the drive shaft 32 of the pulley body 31. Prepare. The flange members 33 and 34 on both sides regulate the winding position of the toothed belt 50 wound around the tooth portion 31A and prevent the falling off.

  In the drive side toothed pulley 30, two rolling bearings 35 and 36 are loaded on a drive shaft 32 extending to one side of the tooth portion 31 </ b> A of the pulley body 31, and these bearings 35 and 36 are supported by the above-described bearing housing 21. doing. Here, the bearing 35 is sandwiched between both end surfaces of the outer ring 35 </ b> A by a stepped portion 21 </ b> J near the motor of the small-diameter bearing holding hole of the bearing housing 21 and a retaining ring 35 </ b> C engaged with the bearing holding hole of the bearing housing 21. The position of the inner ring 35B is fixed and the position of the inner ring 35B is fixed and restricted by a retaining ring 35D engaged with the drive shaft 32 at one end surface near the motor. The bearing 36 is positioned between both end surfaces of the outer ring 36 </ b> A between the stepped portion 21 </ b> K near the motor of the large-diameter bearing holding hole of the bearing housing 21 and the retaining ring 36 </ b> C engaged with the bearing holding hole of the bearing housing 21. Has been fixed. The inner ring 36 </ b> B of the bearing 36 sandwiches the flange member 33 between the end surface of the tooth portion 31 </ b> A of the pulley main body 31 near the motor.

  As shown in FIGS. 2 and 3, the driven-side toothed pulley 40 includes a tooth portion 41 </ b> A on the outer periphery of a cup-shaped pulley body 41, and a hollow cylindrical boss 42 at the center of the pulley body 41.

  The electric power steering apparatus 10 is provided with a ball screw 60 on the rack shaft 14, a ball nut 62 that meshes with the ball screw 60 via a ball 61, and a rolling bearing supported on the gear housing 11 (first gear housing 11 </ b> A). A ball nut 62 is rotatably supported by 63. The boss 42 of the driven-side toothed pulley 40 is fixed to the outer periphery of the ball nut 62. Here, the bearing 63 is positioned between both end surfaces of the outer ring 63A by a stepped portion 11J of the bearing holding hole of the first gear housing 11A and a bearing nut 64 screwed into the bearing holding hole of the first gear housing 11A. Regulated and fixed. The boss 42 of the driven-side toothed pulley 40 and the inner ring 63B of the bearing 63 are screwed to the outer periphery of the ball nut 62 at one end step 62J on the outer periphery of the ball nut 62 and the other end on the outer periphery of the ball nut 62. It is clamped and fixed between the locking nuts 65.

  The electric power steering device 10 includes a tooth portion 31A of the pulley body 31 of the driving-side toothed pulley 30 on the electric motor 20 side and a tooth portion 41A of the pulley body 41 of the driven-side toothed pulley 40 on the ball nut 62 side. The toothed belt 50 is wound around, and the rotational force of the driving side toothed pulley 30 is transmitted from the toothed belt 50 to the ball nut 62 via the driven side toothed pulley 40 and then to the rack shaft 14, and the rack shaft 14 is straightened. Move.

Hereinafter, the operation of the electric power steering apparatus 10 will be described.
(1) When the steering torque detected by the steering torque sensor is lower than a predetermined value, the steering assist force is unnecessary and the electric motor 20 is not driven.

  (2) Since the steering assist force is required when the steering torque detected by the steering torque sensor exceeds a predetermined value, the electric motor 20 is driven. The rotational force of the driving-side toothed pulley 30 based on the torque generated by the electric motor 20 is transmitted from the toothed belt 50 to the ball nut 62 via the driven-side toothed pulley 40, and the rack shaft 14 is straightened through the ball screw 60. The steering assist force is moved.

  However, in the electric power steering apparatus 10, even if the toothed belt 50 is broken, at least the driven-side toothed pulley 40 is not rotationally locked due to the biting of the broken toothed belt 50, so that steering may be impossible. In order to provide an electric power steering apparatus without the following, the following configuration is provided.

  As shown in FIG. 4, the electric power steering apparatus 10 includes an inner peripheral surface A that faces at least a tooth surface of the tooth portion 41 </ b> A of the driven-side toothed pulley 40 of the gear housing 11 (second gear housing 11 </ b> B), and the driven side. The gap G with the outer peripheral surface B of the toothed pulley 40 (the tooth surface of the tooth portion 41A) is set to be larger than twice the thickness t of the toothed belt 50 (G> 2t). In order to make the gear housing 11 compact, 3t> G> 2t, and more preferably 2.5t> G> 2t.

According to the present embodiment, the following operational effects can be obtained.
(a) In the electric power steering apparatus 10 having a reduction gear using the toothed belt 50, an inner peripheral surface A of the housing 11 facing at least the driven side toothed pulley 40 and an outer peripheral surface of the driven side toothed pulley 40 The gap G with B was set to be larger than twice the thickness t of the toothed belt 50.

  Therefore, both ends of the broken toothed belt 50 overlap around the driven toothed pulley 40 inside the housing 11, and the double toothed belt 50 overlaps the inner peripheral surface A of the housing 11 and the driven toothed pulley 40. The gap G is larger than twice the thickness t of the toothed belt 50 even if it enters the gap G between the outer peripheral surfaces B. Thereby, the toothed belt 50 does not bite into the gap G, and the driven side toothed pulley 40 is not rotationally locked. The driven-side toothed pulley 40 is free to rotate and does not lock, and there is no possibility that the manual steering of the electric power steering device 10 cannot be steered.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, and even if there is a design change or the like without departing from the gist of the present invention. It is included in the present invention. For example, in the present invention, the gap between the inner peripheral surface of the housing facing the drive-side toothed pulley and the outer peripheral surface of the drive-side toothed pulley may be set larger than twice the thickness of the toothed belt. .

  In the present invention, the rack shaft is supported on the housing so as to be linearly movable, and an electric motor is attached to the housing, and the rotational force of the driving-side toothed pulley coupled to the rotating shaft of the electric motor is applied to the driving-side toothed pulley. In a reduction device for an electric power steering device that transmits to a rack shaft via a power transmission mechanism that includes a driven side toothed pulley connected via a belt, an inner peripheral surface of the housing that faces at least the driven side toothed pulley; The clearance with the outer peripheral surface of the driven side toothed pulley is set to be larger than twice the thickness of the toothed belt. As a result, in the electric power steering apparatus having a reduction gear using a toothed belt, even if the toothed belt breaks, at least the driven toothed pulley is not rotationally locked by the biting of the broken toothed belt. Thus, an electric power steering device that is not likely to be unsteerable can be provided.

DESCRIPTION OF SYMBOLS 10 Electric power steering apparatus 11 Housing 14 Rack shaft 20 Electric motor 20A Rotating shaft 30 Drive side toothed pulley 40 Drive side toothed pulley 50 Toothed belt 60 Ball screw A Inner surface B Outer surface G Gap t Thickness

Claims (2)

The rack shaft is supported on the housing so that it can move linearly, and an electric motor is attached to the housing, and the rotational force of the driving-side toothed pulley coupled to the rotating shaft of the electric motor is applied to the driving-side toothed pulley via a toothed belt. In the reduction device of the electric power steering device that transmits to the rack shaft through the power transmission mechanism including the driven side toothed pulley connected to
An electric motor characterized in that a gap between at least an inner peripheral surface of the housing facing the driven-side toothed pulley and an outer peripheral surface of the driven-side toothed pulley is set to be larger than twice the thickness of the toothed belt. Reducer for power steering device.   An electric power steering apparatus comprising the speed reducer according to claim 1.

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