Electric power steering device and method for assembling the same

Patent metadata

Field	Value
Publication number	US-2016304111-A1
Application number	US-201515102920-A
Country	US
Kind code	A1
Filing date	Jan 9, 2015
Priority date	Mar 5, 2014
Publication date	Oct 20, 2016
Grant date	—

Abstract

A cylindrical buckling prevention member is fitted on a spring shaft portion of a torsion bar, and an outer peripheral surface of the buckling prevention member is positioned close to or in contact with an inner peripheral surface of a hollow output shaft. Accordingly, when one of a pair of coupling shaft portions, which are axially end portions of the torsion bar, to be coupled to a coupling hole of a counter-shaft later is press-fitted into the coupling hole of the counter-shaft, the spring shaft portion of the torsion bar can be prevented from buckling.

First claim

What is claimed is:

1 . An electric power steering device of the present invention includes:
a hollow first shaft; a second shaft which is arranged coaxially with the first shaft; and a torsion bar which includes a pair of coupling shaft portions provided at both axial end portions thereof and a spring shaft portion provided between the pair of coupling shaft portions, and which is arranged at an inner diameter side of the first shaft, wherein one of the coupling shaft portions is coupled to the first shaft and the other of the coupling shaft portions is coupled to the second shaft, respectively, such that torque can be transmitted, wherein at least one of the coupling shaft portions is press-fitted into a coupling hole formed in a counter-shaft which is one of the first and second shafts, to which the one of the coupling shaft portions is to be coupled, wherein a steering force from a steering wheel is applied to either one of the first and second shafts, and wherein a buckling prevention member is fitted and supported or coupled and fixed on an outer peripheral surface of the spring shaft portion, and an outer peripheral surface of the buckling prevention member is positioned close to or in contact with an inner peripheral surface of the first shaft.

2 . The electric power steering device according to claim 1 ,
wherein the buckling prevention member is fitted and supported or coupled and fixed on a portion including an axially center portion of the outer peripheral surface of the spring shaft portion.

3 . The electric power steering device according to claim 1 ,
wherein the buckling prevention member includes a cylindrical member which has a cut-out extending in parallel or inclined with respect to a center axis thereof formed at one position in a circumferential direction.

4 . The electric power steering device according to claim 1 ,
wherein the buckling prevention member includes a cylindrical heat-shrinkable tube.

5 . The electric power steering device according to claim 1 ,
wherein the buckling prevention member includes a synthetic resin member which is injection-molded on an outer diameter side of the spring shaft portion.

6 . The electric power steering device according to claim 1 ,
wherein the buckling prevention member includes a rubber member which is vulcanization-bonded on the outer peripheral surface of the spring shaft portion.

7 . The electric power steering deice according to claim 1 ,
wherein a first stopper portion provided on one axial portion of the first shaft and a second stopper portion provided on one axial portion of the second shaft are engaged with each other with a circumferential gap therebetween such that relative rotations of the first and second shafts are restrained within a predetermined angle range, wherein the one of the coupling shaft portions is coupled to the first shaft such that torque can be transmitted and axial relative displacement is prevented, wherein the other of the coupling shaft portions is press-fitted into a coupling hole formed in the second shaft, and wherein there is a size relation that at assembling, after the buckling prevention member is arranged between the outer peripheral surface of the spring shaft portion of the torsion bar and the inner peripheral surface of the first shaft and the one of the coupling shaft portions is coupled to the first shaft such that torque can be transmitted and axial relative displacement is prevented and before press-fitting the other of the coupling shaft portions into the coupling hole formed in the second shaft, at least portions of the first and second stopper portions can be engaged with each other with a circumferential gap therebetween.

8 . The electric power steering deice according to claim 1 ,
wherein a first stopper portion provided on one axial portion of the first shaft and a second stopper portion provided on one axial portion of the second shaft are engaged with each other with a circumferential gap therebetween such that relative rotations of the first and second shafts are restrained within a predetermined angle range, wherein the one of the coupling shaft portions is press-fitted into a coupling hole formed in the first shaft, wherein the other of the coupling shaft portions is press-fitted into a coupling hole formed in the second shaft and abuts on a bottom end portion of the coupling hole, and wherein there is a size relation that at assembling, at a state where the other of the coupling shaft portions is press-fitted into the coupling hole formed in the second shaft and abuts on the bottom end portion of the coupling hole, after the buckling prevention member is arranged between the outer peripheral surface of the spring shaft portion of the torsion bar and the inner peripheral surface of the first shaft and before press-fitting the one of the coupling shaft portion into the coupling hole formed in the first shaft, at least portions of the first and second stopper portions can be engaged with each other with a circumferential gap therebetween.

9 . The electric power steering deice according to claim 1 ,
wherein a first stopper portion provided on one axial portion of the first shaft and a second stopper portion provided on one axial portion of the second shaft are engaged with each other with a circumferential gap therebetween such that relative rotations of the first and second shafts are restrained within a predetermined angle range, wherein the one of the coupling shaft portions is press-fitted into a coupling hole formed in the first shaft, wherein the other of the coupling shaft portions is press-fitted into a coupling hole formed in the second shaft and abuts on a bottom end portion of the coupling hole, and wherein there is a size relation that at assembling, before press-fitting of the coupling shaft portions such that while press-fitting the other of the coupling shaft portions into the coupling hole formed in the second shaft to abut on the bottom end portion of the coupling hole and the one of the coupling shaft portions is press-fitted into the coupling hole formed in the first shaft after the torsion bar arranged with the buckling prevention member is inserted into the inner diameter side of the first shaft, at least portions of the first and second stopper portions can be engaged with each other with a circumferential gap therebetween.

10 . The electric power steering device according to claim 1 ,
wherein the first shaft has a center hole, a tip portion of the center hole at a side of the second shaft is formed with a slide bush insertion hole, and a slide bush is inserted into the slide bush insertion hole.

11 . A method of assembling the electric power steering device according to claim 7 , the method comprising:
arranging the buckling prevention member between the outer peripheral surface of the spring shaft portion of the torsion bar and the inner peripheral surface of the first shaft and coupling the one of the coupling shaft portions to the first shaft such that torque can be transmitted and axial relative displacement is prevented; engaging at least portions of the first and second stopper portions each other with a circumferential gap therebetween; and press-fitting the other of the coupling shaft portions into the coupling hole formed in the second shaft at a state where a positional relation between the first and second shafts in a rotating direction is adjusted to a center position of the predetermined angle range.

12 . A method of assembling the electric power steering device according to claim 8 , the method comprising:
arranging the bucking prevention member of the torsion bar be

Assignees

• Nsk Ltd

Inventors

• Kurokawa Yoshifumi

Classifications

• B62D1/185

  adjustable by axial displacement, e.g. telescopically (B62D1/183, B62D1/187, B62D1/19 take precedence) · CPC title

• F16D1/06

  for attachment of a member on a shaft or on a shaft-end (attachment of marine propellers on shafts B63H23/34) · CPC title

• B62D1/16 Primary

  Steering columns · CPC title

• B62D5/0409 Primary

  Electric motor acting on the steering column · CPC title

• G01L3/105

  involving inductive means (G01L3/102, G01L3/104 take precedence) · CPC title