JP2012086739A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device which reduces a feeling of obstruction generated upon start of steering thereby attaining satisfactory steering feeling.SOLUTION: A shaft coupling 41 connecting one end part 26a of a worm shaft 26 to an output shaft 36 of a motor in a tiltable fashion includes a first yoke 51 fixed to the worm shaft 26, a second yoke 52 fixed to the output shaft 36 and a cross shaft 53 connecting the first and second yokes 51 and 52 so that a torque can be transmitted. The first and second yokes 51 and 52 have a pair of tabs 55 and a pair of tabs 58, respectively. In the tabs 55, shaft holes 56 into which shaft parts 61 of the cross shaft 53 are rotatably inserted are formed, while in the tabs 58, shaft holes 59 into which shaft parts 62 of the cross shaft 53 are rotatably inserted are formed. The other end part of the worm shaft 26 is provided axially movably relative to a housing 31, and the shaft holes 56 of the first yoke 51 and the shaft holes 59 of the second yoke 52 are formed in such a manner that the shaft parts 61 and 62 are relatively moved in the axial direction of the worm shaft 26.

Description

  The present invention relates to an electric power steering apparatus.

  2. Description of the Related Art Conventionally, some electric power steering apparatuses (EPS) give an assist force for assisting a steering operation to a steering system by rotationally driving a steering shaft using a motor as a drive source. As such an EPS, there is known an EPS provided with a speed reduction mechanism formed by meshing a worm shaft rotated by a motor and a worm wheel connected to a steering shaft.

  By the way, in the case of EPS using the deceleration mechanism as described above, rattling noise may occur due to the backlash when switching the steering direction or applying reverse input. Therefore, in such an EPS, in many cases, one end of the worm shaft is tiltably connected to the output shaft of the motor, and the other end of the worm shaft is pressed against the worm wheel by using an urging means. A so-called anti-backlash system that removes backlash by adjusting the distance between the axes is incorporated (for example, see Patent Document 1).

  As a shaft coupling for connecting such a worm shaft so as to be tiltable with respect to the output shaft of the motor, the above-mentioned Patent Document 1 includes a pair of joints (yokes) and an elastic body interposed therebetween. Have been disclosed (see Patent Document 1, FIG. 3). Patent Document 2 discloses a pair of yokes having a pair of tabs parallel to each other, an intermediate member in which a shaft portion rotatably inserted into a shaft hole formed in each tab extends in a cross shape, and (See Patent Document 2, FIG. 5).

  In the shaft coupling used in the EPS of Patent Document 2, the worm shaft tilts with respect to the motor shaft as one yoke rotates about the shaft portion with respect to the other yoke. Therefore, unlike the case where the worm shaft is tilted by compressing the elastic body like the shaft coupling used in the EPS of Patent Document 1, no repulsive force is generated even if the worm shaft is tilted, and the worm shaft is stable. There is an advantage that the shaft can be tilted.

Japanese Patent Laid-Open No. 2004-203154 JP 2006-118539 A

  By the way, in EPS provided with the deceleration mechanism as mentioned above, when rotating a steering shaft by steering operation, it is necessary to rotate a worm axis | shaft with the worm wheel connected with the steering shaft. Further, when the worm shaft and the worm wheel rotate, their respective tooth portions slide with each other. Therefore, at the start of steering, a steering force that exceeds the frictional force (static frictional force) acting between the teeth of the worm shaft and the worm wheel is required.

  Here, in the EPS incorporating the anti-backlash system as described above, the worm shaft is pressed against the worm wheel, so that the frictional force acting between these teeth is increased. This may lead to a decrease in steering feeling. As a result, delicate steering with a small amount of steering becomes difficult, and when the traveling direction of the vehicle is slightly changed, it may be necessary to repeatedly turn the steering wheel until the desired traveling direction is reached. There was a problem of increasing the burden.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an electric power steering device that can realize a good steering feeling by reducing the feeling of catching that occurs at the start of steering. There is to do.

  In order to achieve the above object, a first aspect of the present invention is directed to a speed reduction mechanism formed by meshing a worm shaft and a worm wheel, a motor connected to a steering shaft via the speed reduction mechanism, and an output of the motor. In the electric power steering apparatus comprising: a shaft coupling that connects the one end portion of the worm shaft with respect to the shaft so as to be tiltable; and an urging means that urges the other end portion of the worm shaft toward the worm wheel. The shaft coupling includes a first yoke coupled to the worm shaft, a second yoke coupled to the output shaft, and a transmission member that couples the first yoke and the second yoke so that torque can be transmitted. The first yoke and the second yoke each have a pair of tabs in which shaft holes are formed, and the transmission member is rotatably inserted into each shaft hole. The other end of the worm shaft is provided so as to be movable in the axial direction with respect to the housing that houses the speed reduction mechanism, and the shaft hole of the first yoke and the shaft of the second yoke At least one of the holes is characterized in that the shaft portion is formed to be relatively movable in the axial direction of the worm shaft.

  In the above configuration, since the shaft portion of the transmission member can move in at least one of the shaft hole of the first yoke and the shaft hole of the second yoke in the axial direction of the worm shaft, the first yoke is relative to the second yoke. It becomes possible to move relative to the axial direction of the worm shaft. Since the other end of the worm shaft is provided so as to be movable in the axial direction with respect to the housing, the worm shaft moves relative to the second yoke in the axial direction of the worm shaft, It becomes possible to move in the axial direction integrally with the first yoke. Thus, at the start of steering, the worm wheel can rotate in the axial direction integrally with the first yoke without sliding between the tooth portion of the worm wheel and the tooth portion of the worm shaft. Therefore, it is possible to reduce the feeling of catching and realize a good steering feeling. In the above configuration, since the first yoke moves relative to the second yoke in the axial direction, for example, when the serration is formed on the worm shaft and the first yoke and these are connected so as to be relatively movable in the axial direction. In comparison, the sliding resistance during movement of the worm shaft can be reduced, and the worm shaft can be smoothly moved in the axial direction.

  According to a second aspect of the present invention, in the electric power steering apparatus according to the first aspect, a first axial elasticity interposed in the axial direction between the shaft hole and the shaft portion of the first yoke. And a second axial elastic body interposed in the axial direction between the shaft hole and the shaft portion of the second yoke.

According to the above configuration, when the first yoke moves relative to the second yoke in the axial direction, the shaft portion can be prevented from colliding with the inner surface of the shaft hole, and the generation of abnormal noise can be suppressed.
According to a third aspect of the present invention, in the electric power steering device according to the first or second aspect, the first yoke is interposed between the shaft hole and the shaft portion in the rotation direction of the first yoke. And a second rotational elastic body interposed in the rotational direction of the second yoke between the shaft hole and the shaft portion of the second yoke. And

  According to the above configuration, the transmission member can move in the direction orthogonal to the worm shaft by elastically deforming the first rotational direction elastic body and the second rotational direction elastic body, and therefore the shaft center and output of the worm shaft. These shafts can be connected in a state where the shaft center is eccentric. That is, it is possible to allow a deviation of the axial center between the worm shaft and the output shaft. As a result, it is possible to prevent an excessive load from acting on a bearing or the like that supports the output shaft due to the deviation of the shaft center between the worm shaft and the output shaft, and to reduce the transmission loss of the motor torque.

  According to a fourth aspect of the present invention, in the electric power steering apparatus according to any one of the first to third aspects, the one end side of the worm shaft is a base portion to which the output shaft of the second yoke is fixed. The gist of the invention is that it is rotatably supported by a rolling bearing provided on the surface.

  According to the above configuration, the rolling bearing that supports the one end portion side of the worm shaft is disposed closer to the motor side than the tilt center of the worm shaft (the shaft portion of the transmission member that constitutes the shaft coupling). Therefore, when the rolling bearing is provided closer to the worm shaft than the center of tilting, that is, when the rolling bearing supports a portion that is displaced by tilting of the worm shaft, the worm shaft is maintained even if the internal clearance of the rolling bearing is reduced. It is possible to tilt, and the generation of abnormal noise can be suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the electric power steering apparatus which can reduce the feeling of catch produced at the time of steering start, and can implement | achieve favorable steering feeling can be provided.

The schematic block diagram of an electric power steering device (EPS). Sectional drawing which shows schematic structure of the EPS actuator of this embodiment. AA sectional drawing of FIG. (A) The exploded perspective view of a shaft coupling, (b) The perspective view of a shaft coupling. The expanded sectional view which shows the shaft coupling vicinity of this embodiment. BB sectional drawing of FIG. The expanded sectional view which shows another shaft coupling vicinity. The expanded sectional view which shows another shaft coupling vicinity.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
As shown in FIG. 1, in an electric power steering apparatus (EPS) 1, a steering shaft 3 to which a steering 2 is fixed is connected to a rack shaft 5 via a rack and pinion mechanism 4. Thereby, the rotation of the steering shaft 3 accompanying the steering operation is converted into a reciprocating linear motion of the rack shaft 5 by the rack and pinion mechanism 4. The steering shaft 3 is formed by connecting a column shaft 8, an intermediate shaft 9, and a pinion shaft 10. The reciprocating linear motion of the rack shaft 5 accompanying the rotation of the steering shaft 3 is transmitted to a knuckle (not shown) via tie rods 11 connected to both ends of the rack shaft 5, whereby the steered angle of the steered wheels 12. That is, the traveling direction of the vehicle is changed.

  The EPS 1 also includes an EPS actuator 22 that applies an assist force for assisting the steering operation to the steering system using the motor 21 as a drive source. The EPS actuator 22 of the present embodiment is configured as a so-called column-type EPS actuator, and the motor 21 is drivingly connected to the column shaft 8 via a speed reduction mechanism 24. The speed reduction mechanism 24 is configured by meshing a worm wheel 25 connected to the column shaft 8 and a worm shaft 26 connected to the motor 21. The rotation of the motor 21 is decelerated by the deceleration mechanism 24 and transmitted to the column shaft 8 so that the motor torque is applied to the steering system as an assist force.

Next, the configuration of the EPS actuator in the present embodiment will be described.
As shown in FIG. 2, the EPS actuator 22 includes a housing 31 that houses the speed reduction mechanism 24. The housing 31 includes a worm shaft housing portion 32 in which the worm shaft 26 is housed, and a worm wheel housing portion 33 that is formed continuously with the worm shaft housing portion 32 and in which the worm wheel 25 is housed. . The worm shaft housing portion 32 is a cylindrical space extending in the axial direction (left and right direction in FIG. 2) of the worm shaft 26, and one end side (right side in FIG. 2) is a motor fixing hole 34 to which the motor 21 is fixed. Communicating with Further, the other end side (left side in FIG. 2) of the worm shaft accommodating portion 32 is opened to the outside, and the opening end is closed by the end cover 35.

  The motor 21 is fixed to the housing 31 so that the axial direction of the output shaft 36 is orthogonal to the axial direction of the steering shaft 3 (column shaft 8) penetrating the housing 31. The worm shaft 26 connected to the output shaft 36 is rotatably supported at both ends by first and second rolling bearings 37 and 38 provided in the housing 31 and connected to the steering shaft 3. Is engaged with the worm wheel 25. In the present embodiment, ball bearings are employed as the first and second rolling bearings 37 and 38.

  Here, the EPS actuator 22 of the present embodiment has a so-called anti-backlash for removing the backlash by adjusting the inter-axis distance between the worm wheel 25 and the worm shaft 26 constituting the speed reduction mechanism 24.・ The system is installed.

  More specifically, one end portion (right end portion in FIG. 2) 26 a of the worm shaft 26 is connected to the output shaft 36 of the motor 21 via a shaft coupling 41 so as to be tiltable. On the other hand, the other end portion (left end portion in FIG. 2) 26 b of the worm shaft 26 is rotatably supported by a second rolling bearing 38. The second rolling bearing 38 is provided so as to be movable in a direction in which the second rolling bearing 38 comes in contact with and separates from the worm wheel 25 (vertical direction in FIG. 2), and is a curved plate as a biasing means curved so as to surround the outer periphery thereof. The spring 42 is biased toward the worm wheel 25 side. The other end 26 b is press-fitted into the inner ring of the second rolling bearing 38.

  Specifically, a support portion 43 for accommodating and supporting the second rolling bearing 38 and the curved leaf spring 42 is formed on the other end side of the worm shaft accommodating portion 32. The inner diameter of the support portion 43 is formed larger than the outer diameter of the second rolling bearing 38. Accordingly, the second rolling bearing 38 is provided in the support portion 43 so as to be movable in a direction in which the second rolling bearing 38 is in contact with or separated from the worm wheel 25. The second rolling bearing 38 is provided with a space in the axial direction of the worm shaft 26 between the end cover 35 and the other end portion 26 b of the worm shaft 26 is connected to the second rolling bearing 38. It is integrally provided to be movable in the axial direction. Note that an arc-shaped elastic ring 44 made of an elastic material is provided in the support portion 43, and between the curved leaf spring 42 and the support portion 43, and between the end cover 35 and the second rolling bearing 38. It is possible to prevent abnormal noise from being generated.

  As shown in FIG. 3, the curved leaf spring 42 includes an arcuate arc portion 45 that is in contact with the outer ring 38 a of the second rolling bearing 38, and a spring portion 46 that is disposed radially outward from the arc portion 45. These spring portions 46 and connection portions 47 that connect both ends of the arc portion 45 are respectively formed. On the peripheral wall of the support portion 43, an accommodation recess 48 for accommodating the spring portion 46 of the curved leaf spring 42 is formed on the side opposite to the worm wheel 25 (upper side in FIG. 3). The second rolling bearing 38 is biased toward the worm wheel 25 side (the lower side in FIG. 3) by the spring portion 46 abutting against the bottom surface 48a of the housing recess 48 and pressing the bottom surface 48a. Has been. As a result, as shown in FIG. 2, the worm shaft 26 tilts about the base end side thereof, the distance between the worm shaft 26 and the worm wheel 25 is adjusted, and the backlash is removed. Yes.

(Connection structure between worm shaft and output shaft)
Next, a connection structure between the worm shaft and the motor output shaft in the EPS of the present embodiment will be described.

  As shown in FIGS. 4A and 4B, the shaft coupling 41 includes a first yoke 51 connected to the worm shaft 26, a second yoke 52 connected to the output shaft 36, and the first yoke 51. A cross shaft 53 is provided as a transmission member that couples the second yoke 52 so that torque can be transmitted.

  The first yoke 51 includes a base portion 54 formed in a columnar shape and a pair of tabs 55 extending from the base portion 54 in the axial direction thereof, and is formed in a substantially U shape. Each tab 55 is formed in a substantially flat plate shape facing each other, and a shaft hole 56 penetrating in the thickness direction is formed at a position facing each tab 55.

  The second yoke 52 is formed in substantially the same shape as the first yoke 51, and has a base 57 formed in a columnar shape and a pair of tabs 58 extending in the axial direction from the base 57, and is substantially U-shaped. Is formed. Each tab 58 is formed in a substantially flat plate shape facing each other, and a shaft hole 59 penetrating in the thickness direction is formed at a position facing each tab 58.

  The cross shaft 53 protrudes in a direction orthogonal to each shaft portion 61 and a pair of shaft portions 61 that are rotatably inserted into the respective shaft holes 56 of the first yoke 51, and each shaft hole of the second yoke 52. 59 has a pair of shaft portions 62 that are rotatably inserted. As shown in FIG. 4B, the shaft coupling 41 has the tabs 55 of the first yoke 51 and the tabs 58 of the second yoke 52 arranged alternately and protrudes in a cross shape of the cross shaft 53. The shaft portions 61 and 62 are assembled so as to be rotatably inserted into the corresponding shaft holes 56 and 59.

  As shown in FIGS. 5 and 6, the base 54 of the first yoke 51 is formed with a round hole-like fitting hole 54 a that opens on the opposite side of each tab 55. The first yoke 51 is coupled to the worm shaft 26 so as to be axially movable and rotatable by press-fitting one end portion 26a of the worm shaft 26 into the fitting hole 54a. On the other hand, the base portion 57 of the second yoke 52 is formed with a round hole-like fitting hole 57 a that opens to the opposite side of each tab 58. The second yoke 52 is coupled to the output shaft 36 so as to be axially movable and rotatable by the other end 36a of the output shaft 36 being press-fitted into the fitting hole 57a. Accordingly, the motor torque is transmitted from the output shaft 36 and the second yoke 52 to the first yoke 51 and the worm shaft 26 via the shaft portions 61 and 62 of the cross shaft 53. The worm shaft 26 is configured to tilt with respect to the output shaft 36 of the motor 21 as the first yoke 51 rotates about the shaft portions 61 and 62 with respect to the second yoke 52. Yes.

  Here, in the present embodiment, the shaft hole 56 of the first yoke 51 and the shaft hole 59 of the second yoke 52 are configured such that the inserted shaft portions 61 and 62 are relatively movable in the axial direction of the worm shaft 26. ing.

  More specifically, the shaft hole 56 of the first yoke 51 extends from the vicinity of the center of each tab 55 in the axial direction of the worm shaft 26 (left-right direction in FIGS. 5 and 6) and at the tip side of the tab 55 (right side in FIG. 5). ) In the shape of a long hole opened. On the other hand, the shaft hole 59 of the second yoke 52 extends from the vicinity of the center of each tab 58 in the axial direction of the output shaft 36 (left-right direction in FIGS. 5 and 6) and on the tip side of the tab 58 (left side in FIG. 6). It is formed in the shape of an open long hole. The inner surface of each shaft hole 56 of the first yoke 51 is provided with a substantially U-shaped first elastic body 63 that contacts the entire surface, and the inner surface of each shaft hole 59 of the second yoke 52 includes Second elastic bodies 64 are provided respectively.

  As shown in FIG. 5, the first elastic body 63 has an end wall portion 63 a in contact with an end surface in the longitudinal direction of the shaft hole 56 (axial direction of the worm shaft 26), and a side surface along the longitudinal direction of the shaft hole 56. It consists of a pair of side wall parts 63b which contact | abut. The end wall portion 63 a is interposed between each shaft hole 56 and the shaft portion 61 in the axial direction of the worm shaft 26, and the side wall portion 63 b is interposed between each shaft hole 56 and the shaft portion 61. It is interposed in the direction of rotation. That is, in the present embodiment, the end wall 63a corresponds to the first axial elastic body, and the side wall 63b corresponds to the first rotational elastic body.

  As shown in FIG. 6, the second elastic body 64 has an end wall portion 64 a that contacts the end surface of the shaft hole 59 in the longitudinal direction (the axial direction of the output shaft 36), and a side surface along the longitudinal direction of the shaft hole 59. It consists of a pair of side wall parts 64b which contact | abut. The end wall portion 64 a is interposed between each shaft hole 59 and the shaft portion 62 in the axial direction of the worm shaft 26, and the side wall portion 64 b is interposed between each shaft hole 59 and the shaft portion 62. It is interposed in the direction of rotation. That is, in the present embodiment, the end wall portion 64a corresponds to the second axial elastic body, and the side wall portion 64b corresponds to the second rotational elastic body. A gap having a width substantially equal to the diameter of the shaft portion 61 is formed between the side wall portions 63b, and a gap having a width substantially equal to the diameter of the shaft portion 62 is formed between the side wall portions 64b. Yes.

  As shown in FIGS. 5 and 6, the base portion 57 of the second yoke 52 is rotatably supported in the worm shaft housing portion 32 by the first rolling bearing 37, and the one end portion 26 a side of the worm shaft 26 is The first rolling bearing 37 is rotatably supported. The first rolling bearing 37 is provided on a fixed portion 65 having a larger diameter than the worm shaft housing portion 32 formed on one end side of the worm shaft housing portion 32. The first rolling bearing 37 is provided in a state in which movement in the axial direction is restricted with respect to the housing 31 by a fixing member 66 whose outer ring is fixed to one end of the worm shaft housing portion 32.

  In the shaft coupling 41 configured in this way, when the first yoke 51 moves relative to the second yoke 52 along the axial direction of the worm shaft 26, the first and second elastic bodies 63, As the end wall portions 63a and 64a of the 64 are compressed, the shaft portions 61 and 62 of the cross shaft 53 relatively move in the axial direction within the corresponding shaft holes 56 and 59. On the other hand, when the first yoke 51 moves relative to the direction away from the second yoke 52 along the axial direction of the worm shaft 26, the first and second elastic bodies 63 and 64 are not deformed, and the cross The shaft portions 61 and 62 of the shaft 53 relatively move in the axial direction within the corresponding shaft holes 56 and 59. The worm shaft 26 moves relative to the second yoke 52 in the axial direction of the worm shaft 26, so that the worm shaft 26 moves integrally with the first yoke 51 in the axial direction. It is configured as follows.

As described above, according to the present embodiment, the following operational effects can be achieved.
(1) A shaft coupling 41 that connects the end portion 26 a of the worm shaft 26 to the output shaft 36 of the motor 21 so as to be tiltable is fixed to the first yoke 51 fixed to the worm shaft 26 and the output shaft 36. The second yoke 52 and a cross shaft 53 that connects the first yoke 51 and the second yoke 52 so as to transmit torque are provided. The first yoke 51 and the second yoke 52 each have a pair of tabs 55 and 58 formed with shaft holes 56 and 59 into which the shaft portions 61 and 62 of the cross shaft 53 are rotatably inserted. The other end portion 26b of the worm shaft 26 is provided so as to be movable in the axial direction with respect to the housing 31, and the shaft hole 56 of the first yoke 51 and the shaft hole 59 of the second yoke 52 are connected to the shaft portions 61 and 62. The shaft 26 is formed so as to be relatively movable in the axial direction.

  In the above configuration, since the other end portion 26 b of the worm shaft 26 is provided so as to be movable in the axial direction with respect to the housing 31, the worm shaft 26 includes the first yoke 51 with respect to the second yoke 52. By relative movement in the axial direction, the first yoke 51 and the first yoke 51 can be moved in the axial direction. Thus, at the start of steering, the tooth portion of the worm wheel 25 and the tooth portion of the worm shaft 26 do not slide, and the worm shaft 26 moves in the axial direction integrally with the first yoke 51, so that the worm wheel 25. Since it becomes possible to rotate, a feeling of catching can be reduced and a good steering feeling can be realized. In the above configuration, since the first yoke 51 moves relative to the second yoke 52 in the axial direction, for example, serrations are formed on the worm shaft 26 and the first yoke 51 so that they can be moved relative to each other in the axial direction. Compared to the connection, the sliding resistance during movement of the worm shaft 26 is reduced, and the worm shaft 26 can be smoothly moved in the axial direction.

  (2) Each of the first elastic body 63 having an end wall portion 63 a interposed in the axial direction of the worm shaft 26 between each shaft hole 56 and the shaft portion 61 of the first yoke 51 and each of the second yoke 52. A second elastic body 64 having an end wall portion 64 a interposed between the shaft hole 59 and the shaft portion 62 in the axial direction of the worm shaft 26 is provided.

  According to the above configuration, when the first yoke 51 moves relative to the second yoke 52 in the direction of approaching along the axial direction of the worm shaft 26, the shaft portions 61 and 62 have the shaft holes 56 and 59. Can be prevented from colliding with the inner surface, and the generation of abnormal noise can be suppressed. Further, when the motor torque is transmitted, it is possible to suppress the generation of abnormal noise between the shaft portions 61 and 62 and the shaft holes 56 and 59.

  (3) The first elastic body 63 having the side wall portion 63b interposed in the rotational direction of the first yoke 51 between each shaft hole 56 and the shaft portion 61 of the first yoke 51, and the second yoke 52 A second elastic body 64 having a side wall portion 64b interposed in the rotational direction of the second yoke 52 is provided between each shaft hole 59 and the shaft portion 62.

  According to the above configuration, the cross shaft 53 can move in a direction perpendicular to the worm shaft 26 by elastically deforming the side wall portions 63b and 64b, so that the shaft center of the worm shaft 26 and the shaft of the output shaft 36 can be obtained. These shafts can be connected in a state where the center is eccentric. In other words, it is possible to allow a shift of the axial center between the worm shaft 26 and the output shaft 36. As a result, it is possible to prevent an excessive load from acting on a bearing or the like that supports the output shaft 36 due to a shift in the axial center between the worm shaft 26 and the output shaft 36, and to reduce transmission loss of motor torque. it can. Further, when the motor torque is transmitted, it is possible to suppress the generation of abnormal noise between the shaft portions 61 and 62 and the shaft holes 56 and 59.

  (4) The one end portion 26a side of the worm shaft 26 is rotatably supported by a first rolling bearing 37 provided on the base portion 57 of the second yoke 52, and the other end portion 26b side is supported by the other end portion 26b. The second rolling bearing 38 provided in the upper part of the bearing is rotatably supported.

  According to the above configuration, the first rolling bearing 37 that supports one end of the worm shaft 26 is disposed closer to the motor 21 than the tilt center O of the worm shaft 26. Therefore, the first rolling bearing 37 is provided closer to the worm shaft 26 than the tilting center O, that is, the first rolling bearing 37 supports the portion displaced by the tilting of the worm shaft 26. Even if the internal clearance of the rolling bearing 37 is reduced, the worm shaft 26 can be tilted, and the generation of abnormal noise can be suppressed.

In addition, the said embodiment can also be implemented in the following aspects which changed this suitably.
In the above embodiment, the first elastic body 63 having the end wall portion 63a and the side wall portion 63b is provided in each shaft hole 56 of the first yoke 51. However, the present invention is not limited thereto, and each shaft hole 56 may be provided with an elastic body having only an end wall portion so that the shaft portion 61 of the cross shaft 53 is in sliding contact with the side surface along the longitudinal direction of the shaft hole 56. . Alternatively, each shaft hole 59 may be provided with an elastic body having only a side wall portion so that the shaft portion 61 of the cross shaft 53 is in sliding contact with the end surface of the shaft hole 56. Further, the first elastic body 63 may not be provided in each shaft hole 56. Similarly, each shaft hole 59 of the second yoke 52 may be provided with an elastic body having only an end wall portion or an elastic body having only a side wall portion, and the second elastic body 64 may not be provided.

  In the above embodiment, the first rolling bearing 37 supports the base portion 57 of the second yoke 52, but is not limited thereto, and supports the base portion 54 of the first yoke 51 and the one end portion 26 a of the worm shaft 26. You may make it do.

  In the above embodiment, the biasing means is configured by the curved leaf spring 42 that is curved in an arc shape so as to surround the outer periphery of the second rolling bearing 38. The biasing means may be configured by another member such as a coil spring as long as it can be biased so as to be close to the wheel 25.

  In the above embodiment, the transmission member that connects the first yoke 51 and the second yoke 52 so as to be able to transmit torque is configured by the cross shaft 53 having two axes orthogonal to each other. However, the present invention is not limited to this, for example, a rectangular parallelepiped main body having a power transmission surface that slides against the inner surfaces of the tabs 55 and 58 of the first yoke 51 and the second yoke 52, and protrudes in a cross shape from the main body. The transmission member may be configured by an intermediate member (see Patent Document 2) having four shaft portions (convex portions).

  In the above embodiment, the other end portion 26 b of the worm shaft 26 and the second rolling bearing 38 are integrated with each other so as to be movable in the axial direction with respect to the housing 31. However, the present invention is not limited to this. For example, the other end 26b is fitted into the inner ring of the second rolling bearing 38 with a gap, and an elastic body is provided that is clamped in the axial direction between the inner ring and the worm shaft 26. Thus, the other end 26 b may be movable in the axial direction with respect to the housing 31.

  In the above embodiment, the shaft holes 56 and 59 of the first yoke 51 and the second yoke 52 are formed so that the shaft portions 61 and 62 of the cross shaft 53 can be relatively moved in the axial direction of the worm shaft 26. However, the present invention is not limited thereto, and only one of the shaft holes 56 and 59 may be formed such that the corresponding shaft portions 61 and 62 can be relatively moved in the axial direction of the worm shaft 26. Specifically, as shown in FIG. 7, for example, the shaft hole 56 of the first yoke 51 is formed in a long hole shape extending in the axial direction of the worm shaft 26, and the shaft hole 59 of the second yoke 52 is formed of the cross shaft 53. You may form in the shape of a round hole which has the same internal diameter as each axial part 62.

  In the above embodiment, as shown in FIG. 8, the shaft holes 56 and 59 of the first yoke 51 and the second yoke 52 are formed into round holes having the same diameter as the shaft portions 61 and 62 of the cross shaft 53. In addition, the one end portion 26 a side of the worm shaft 26 may be rotatably supported by the first rolling bearing 37 provided on the base portion 57 of the second yoke 52. In the case of such a configuration, the shaft portions 61 and 62 are restricted from moving relative to each other in the axial direction of the worm shaft 26 in the shaft holes 56 and 59, but the one end portion 26a of the worm shaft 26 is Since it is supported by the first rolling bearing 37 provided on the base portion 57 of the second yoke 52, the same operation and effect as (4) of the above embodiment can be obtained.

  In the above-described embodiment, the present invention is embodied in a so-called column type EPS 1, but is not limited thereto, and may be applied to a so-called pinion type EPS that applies an assist force to the pinion shaft 10, for example.

Next, technical ideas that can be understood from the above embodiments and other examples will be described below together with their effects.
(A) A speed reduction mechanism formed by meshing a worm shaft and a worm wheel, a motor drivingly connected to the steering shaft via the speed reduction mechanism, and one end of the worm shaft can be tilted with respect to the output shaft of the motor And an urging means for urging the other end portion of the worm shaft toward the worm wheel side, wherein the shaft coupling is coupled to the worm shaft. A yoke, a second yoke coupled to the output shaft, and a transmission member that couples the first yoke and the second yoke so as to be able to transmit torque, the transmission member projecting in a cross shape And the first yoke and the second yoke each have a pair of tabs formed with shaft holes into which the shaft portions are rotatably inserted. One end side of the arm shaft, the electric power steering apparatus characterized by being rotatably supported by a rolling bearing provided on the base portion in which the output shaft of the second yoke is fixed. According to the said structure, there can exist an effect similar to the effect of Claim 4.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device (EPS), 3 ... Steering shaft, 21 ... Motor, 24 ... Deceleration mechanism, 25 ... Worm wheel, 26 ... Worm shaft, 26a ... One end, 26b ... Other end, 31 ... Housing, 36 ... output shaft, 37 ... first rolling bearing, 41 ... shaft coupling, 42 ... curved leaf spring, 51 ... first yoke, 52 ... second yoke, 53 ... cross shaft, 54,57 ... base, 55,58 ... Tab, 56, 59 ... shaft hole, 61, 62 ... shaft portion.

Claims (4)

A speed reduction mechanism that engages a worm shaft and a worm wheel, a motor that is drivingly connected to the steering shaft via the speed reduction mechanism, and one end portion of the worm shaft that is tiltably connected to the output shaft of the motor In the electric power steering apparatus comprising a shaft coupling and an urging means for urging the other end portion of the worm shaft toward the worm wheel,
The shaft coupling includes a first yoke coupled to the worm shaft, a second yoke coupled to the output shaft, and a transmission member that couples the first yoke and the second yoke so as to transmit torque. The transmission member has a shaft portion protruding in a cross shape, and the first yoke and the second yoke have a pair of tabs in which shaft holes into which the shaft portion is rotatably inserted are formed. Each of which has
The other end of the worm shaft is provided so as to be axially movable with respect to a housing that houses the speed reduction mechanism,
At least one of the shaft hole of the first yoke and the shaft hole of the second yoke is formed such that the shaft portion is relatively movable in the axial direction of the worm shaft. The electric power steering apparatus according to claim 1, wherein
A first axial elastic body interposed in the axial direction between the shaft hole of the first yoke and the shaft portion;
An electric power steering apparatus comprising: a second axial elastic body interposed in the axial direction between the shaft hole of the second yoke and the shaft portion. In the electric power steering apparatus according to claim 1 or 2,
A first rotational-direction elastic body interposed in the rotational direction of the first yoke between the shaft hole of the first yoke and the shaft portion;
An electric power steering apparatus comprising: a second rotational direction elastic body interposed in the rotational direction of the second yoke between the shaft hole of the second yoke and the shaft portion. In the electric power steering device according to any one of claims 1 to 3,
An electric power steering apparatus, wherein one end portion side of the worm shaft is rotatably supported by a rolling bearing provided at a base portion to which the output shaft of the second yoke is fixed.

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