JP2006069517A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of ensuring smooth operation while being miniaturized. <P>SOLUTION: A nut 45 is inserted in and fixed to a sleeve 50. Irrespective of the shape of an outer circumferential surface of the nut 45, a driven gear part 50a to receive the power transmitted from an electric motor 35 can be provided on outer circumferential surfaces outwardly in the radial direction of rolling raceways (23b, 45f) in the sleeve 50, and when the power is transmitted from the electric motor 35 to the driven gear part 50a, a smooth operation can be performed by suppressing the entanglement of the nut 45. Further, by providing the driven gear part 50a to receive the transmission transmitted from the electric motor 35 on outer circumferential surfaces outwardly in the radial direction of the rolling raceways (23b, 45f), the length in the axial direction of the sleeve 50 and the nut 45 can be suppressed. In addition, the nut 45 having a female screw 45f formed therein is inserted in and fixed to the sleeve 50 having the driven gear part 50a formed thereon, both components can be separately worked, and the manufacturing cost can be reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus provided with a ball screw mechanism.

  2. Description of the Related Art There is known an electric power steering device that drives an electric motor in accordance with steering torque and transmits the rotational force of the electric motor to a rack shaft to assist steering. Here, in order to convert the rotational force of the electric motor into the thrust of the rack shaft, a ball screw mechanism may be used (see Patent Document 1).

Japanese Patent Publication No. 6-504

  By the way, in the electric power steering apparatus described in Patent Document 1, a gear is integrally formed on the outer periphery of the nut of the ball screw mechanism, and the power of the electric motor is transmitted to the nut via the gear. It has become. However, when the nut and the screw shaft rotate relative to each other, a circulation path for returning the ball from one end of the rolling path to the other end is necessary. However, Patent Document 1 does not disclose anything about the circulation path. Therefore, it is considered that a tube or a top, which is a general circulation path, is used for such a nut. However, if a gear is formed on the outer periphery of the nut, it is difficult to dispose the tube or the piece across the gear. Therefore, regardless of the drawings of Patent Document 1, the electric power steering device disclosed in Patent Document 1 should be considered that the nut gear is displaced from the rolling path in the axial direction.

  However, assuming that the nut gears are arranged so as to be displaced outward in the axial direction from the rolling path, the torque transmitted from the electric motor is input to one end of the nut, so the nut is easily twisted and smooth. Power transmission cannot be performed. Also, when transmitting a large torque, the tooth width of the gear must be increased in order to reduce the surface pressure of the tooth surface, which increases the axial length of the nut, and the electric power steering device There is also a problem that compactness cannot be achieved.

  The present invention has been made in view of the problems of the prior art, and an object thereof is to provide an electric power steering apparatus that can ensure a smooth operation while achieving compactness.

The electric power steering apparatus of the present invention is
An electric motor;
A rack shaft coupled to a steering mechanism, and a power transmission mechanism for transmitting power from the electric motor to the rack shaft,
The power transmission mechanism is connected to or integrated with the rack shaft and includes a male screw groove, a nut disposed around the screw shaft and provided with a female screw groove, the male screw groove, and the screw shaft. A plurality of rolling elements capable of rolling in a rolling path formed between the female screw groove and a sleeve having a receiving portion for receiving power transmitted from the electric motor;
The nut is inserted and fixed with respect to the sleeve so that the receiving portion is located radially outward of the rolling path, and rotates integrally with the nut.

  According to the electric power steering apparatus of the present invention, the nut is inserted and fixed with respect to the sleeve so as to rotate integrally. Therefore, the electric power steering device is independent of the shape of the outer peripheral surface of the nut. A receiving portion for receiving power transmitted from the motor can be provided on the outer circumferential surface of the rolling path in the radial direction of the sleeve, etc., so that when power is transmitted from the electric motor to the receiving portion, The nut can be prevented from being twisted to enable smooth operation. Moreover, the axial direction length of the said sleeve and nut can also be suppressed by providing the receiving part which receives the motive power transmitted from the said electric motor in the outer peripheral surface of the radial direction outer side of the said rolling path. Further, since the nut having the female screw groove is inserted and fixed to the sleeve having the receiving portion, both can be processed separately, and thus the manufacturing cost can be reduced.

  The nut includes a main body provided with a circulation path for the rolling elements extending in an axial direction, a rolling element provided at both ends of the main body and rolling on the rolling paths, in a tangential direction and a lead angle of the rolling path. A deflector that scoops up in the direction and returns to the circuit is preferred.

  For example, according to the prior art described in Japanese Patent Application Laid-Open No. 2004-176826, instead of using a circulating member, an axial groove is provided on the outer periphery of the nut, and a groove connecting this to the spiral groove inside the nut is provided on both end faces. Have. However, with this connection configuration, the rolling direction of the ball changes greatly when moving from the spiral groove to the axial groove, so that the ball may not move smoothly and the operation may deteriorate. In addition, since the groove shape is complicated, the time required for processing increases and the cost increases.

  On the other hand, according to the present invention, the deflector scoops the rolling elements provided on both ends of the main body and rolling on the rolling path in the tangential direction and the lead angle direction of the rolling path, and returns to the circulation path. The ball can be circulated while maintaining the optimum clearance between the ball and the circulation path, and the change of the rolling direction of the rolling element can be suppressed, so that the ball can be smoothly moved and operated. Becomes better. Further, since the deflector can be provided separately from the nut, the nut can be easily processed.

  By providing the deflector instead of a tube or a piece, serrations and teeth can be formed on the outer peripheral surface of the nut, which facilitates fitting and fixing with the sleeve, but a nut having an end cap It may be. Further, a nut provided with a top and a tube can be used as long as it can be fitted and fixed to the sleeve.

  The nut is preferably fitted and fixed to the sleeve.

  The nut is preferably serrated to the sleeve.

  It is preferable that an elastic body is interposed between the nut and the sleeve. In this case, power transmission between the nut and the sleeve may be performed using the shearing force of the elastic body, or may be performed using the compression force.

  A convex portion is provided on the outer peripheral surface of the nut, a concave portion is provided on the inner peripheral surface of the sleeve, and the nut is engaged with the sleeve so that the convex portion is engaged with the concave portion. It is preferable.

  The shape of the nut can be optimized when at least a part of the convex portion is provided radially outward of the circulation path of the main body.

  If a buffer member is disposed between the convex portion and the concave portion in the circumferential direction, it can be mitigated even if an impact force from the electric motor or the rack shaft is transmitted.

  The nut and the sleeve each have a protrusion extending in the axial direction, and when the first buffer is disposed between the nut and the protrusion of the sleeve, the torque is transmitted by the first buffer. Vibration and noise can be suppressed, axial backlash between the nut and the sleeve can be eliminated, and a misalignment suppressing effect can be expected.

  If one of the nut and the sleeve has a protrusion extending in the axial direction and the other has a recess that engages with the protrusion, power can be transmitted between the nut and the sleeve. .

  When the first buffer is disposed between the protrusion and the recess, the first buffer suppresses vibration and noise during torque transmission, and eliminates axial play between the nut and the sleeve. Furthermore, the effect of suppressing misalignment can be expected.

  It is preferable that the gap that is reduced by relative movement in the compressing direction of the first buffer body is provided between the nut and the sleeve because the effect of the first buffer body can be effectively exhibited.

  When a second shock absorber is disposed between the screw member and the nut, the vibration and noise during torque transmission are generated by the second shock absorber. In addition, the axial play between the nut and the sleeve can be eliminated, and a misalignment suppressing effect can be expected.

  It is preferable that a gap that is reduced by relative movement in the direction in which the second buffer body is compressed is provided between the nut and the screw member because the effect of the second buffer body can be effectively exhibited. .

  It is preferable that the nut and the sleeve are connected by a key and rotate integrally with each other because torque transmission can be reliably performed with a simple configuration.

  The receiving portion is a gear portion formed on the outer peripheral surface of the sleeve, and it is preferable that the power from the electric motor is transmitted through another gear meshing with the receiving portion. It may be transmitted via an attached belt or chain.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a main part of the electric power steering apparatus according to the first embodiment. In FIG. 1, the electric power steering apparatus 11 has a housing 21 fixed to a vehicle body (not shown). A rack shaft 23 is supported so as to be movable in the axial direction so as to penetrate the housing 21 horizontally. Although not shown, a pinion is formed at the lower end of the input shaft connected to the steering wheel and meshes with the rack teeth of the rack shaft 23. The rack shaft 23 moves to the left and right in the figure by the rotation of the input shaft. It is supposed to be. Both ends of the rack shaft 23 are connected to tie rods (not shown) of the steering mechanism.

  An electric motor 35 is attached to the housing 21 so that the rack shaft 23 and the axis are parallel to each other. The output shaft 35a of the electric motor 35 is fixed to the drive shaft 37 so as to be relatively displaceable in the axial direction by serration coupling and integrally in the rotational direction. The drive shaft 37 is rotatably supported with respect to the housing 21 by bearings 20 and 22, and has a drive gear portion 37 a at a portion sandwiched between the bearings 20 and 22.

  An intermediate shaft 38 is disposed between the drive shaft 37 and the rack shaft 23. The intermediate shaft 38 is rotatably supported with respect to the housing 21 by bearings 24 and 25, and has an intermediate gear portion 38 a that meshes with the drive gear portion 37 a at a portion sandwiched between the bearings 24 and 25. .

  A cylindrical sleeve 50 is disposed around the rack shaft 23, and is rotatably supported with respect to the housing 21 by ball bearings 26 and angular ball bearings 27 and 27. A nut 45 through which the rack shaft 23 passes is fitted in the sleeve 50 and is fixed by a screw member 51 screwed into the inner periphery thereof. Therefore, the sleeve 50 and the nut 45 rotate integrally.

  The inner rings of the angular ball bearings 27, 27 are fixed while being preloaded by an inner ring retainer 52 that is screwed into the inner circumference of the sleeve 50, and the outer rings of the angular ball bearings 27, 27 are screwed into the inner circumference of the housing 21. It is fixed by an outer ring retainer 53. Therefore, the sleeve 50 is attached in a state in which the backlash is suppressed in the axial direction.

  The nut 45 includes a central hollow cylindrical main body 45a and deflectors 45b and 45b at both ends. The main body 45a forms a circulation path 45c penetrating in the axial direction, and each deflector 45b scoops up the transferred rolling element 65 in the tangential direction of the rolling path and in the lead angle direction and returns it to the circulation path 45c. A scooping piece 45d is formed. Further, a driven gear portion (receiving portion) 50 a that meshes with the intermediate gear portion 38 a is provided in a portion sandwiched between the bearings 26 and 27 of the sleeve 50. The drive gear portion 37a, the intermediate gear portion 38a, and the driven gear portion 50a constitute a gear pair.

  A male screw groove 23b is formed in a part of the outer peripheral surface of the rack shaft 23 which is integral with the screw shaft (may be connected with another part). A nut 45 is disposed around the male screw groove 23b, and a female screw groove 45f is formed on the inner peripheral surface of the main body 45a facing the male screw groove 23b. A large number of balls 65 are rollably arranged in a spiral space (rolling path) formed by the male screw groove 23b and the female screw groove 45f.

  The operation of this embodiment will be described. Although not shown, when the driver rotates the steering wheel, the rotational force is transmitted to the input shaft. When the input shaft rotates, the rack teeth meshed with the pinion are pushed, the rack shaft 23 moves in the axial direction, and the steering mechanism (not shown) is driven via the tie rod, so that the wheels are steered. ing.

  At this time, a torque sensor (not shown) detects the steering torque, and a CPU (not shown) supplies electric power to the electric motor 35 according to the amount, so that the drive gear portion 37a rotates with the output shaft, and the intermediate gear. The driven gear 50a meshed via the portion 38a is rotated at a predetermined reduction ratio. As a result, the nut 45 is rotated together with the sleeve 50, and the rotational motion is converted into the axial motion of the rack shaft 23 via the ball 65. The ball 65 rolled to one end of the rolling path is picked up by the deflector 45b and returned to the other end via the circulation path 45c. An auxiliary steering force can be output using the axial force of the rack shaft 23.

  In the electric power steering apparatus 11 according to the present embodiment, the nut 45 is inserted and fixed with respect to the sleeve 50 so as to rotate integrally. Therefore, regardless of the shape of the outer peripheral surface of the nut 45. The driven gear portion 50a that receives the power transmitted from the electric motor 35 can be provided on the outer circumferential surface of the sleeve 50 in the radial direction of the rolling path (23b, 45f), whereby the power is driven by the electric motor 35. When transmitted to the gear portion 50a, the nut 45 can be prevented from being twisted to enable smooth operation. Further, by providing a driven gear portion 50a that receives power transmitted from the electric motor 35 on the outer circumferential surface of the rolling path (23b, 45f) in the radial direction, the axial length of the sleeve 50 and the nut 45 is suppressed. You can also. Further, since the nut 45 having the female screw groove 45f is inserted and fixed to the sleeve 50 having the driven gear portion 50a, both can be processed separately, so that the manufacturing cost can be reduced.

  FIG. 2A is an axial sectional view of the ball screw mechanism according to the second embodiment, and FIG. 2B is an arrow formed by cutting the nut of FIG. 2A along the line IIB-IIB. Although it is the figure seen in the direction, the ball is omitted. In FIG. 2, the sleeve 150 and the nut 145 are serrated. More specifically, the nut 145 is inserted into the sleeve 150 by engaging the female serration 150b formed on the inner periphery of the sleeve 150 with the same number of male serrations 145g formed on the outer periphery of the nut 145. It is inserted and fixed, so that it can rotate integrally. As a result, even when a high torque is transmitted between the sleeve 150 and the nut 145, relative slippage between the two can be suppressed. Other configurations are the same as those in the embodiment shown in FIG.

  FIG. 3A is an axial sectional view of the ball screw mechanism according to the third embodiment, and FIG. 3B is an arrow formed by cutting the nut of FIG. 3A along the line IIIB-IIIB. Although it is the figure seen in the direction, the ball is omitted. In FIG. 3, on the outer periphery of the nut 245, the protruding portion 245g extends in the axial direction so as to cover the circulation path 245c (that is, at least a part is located radially outward). It is provided as it exists. On the other hand, a groove 250b, which is a recess corresponding to the raised portion 245g, is formed on the inner periphery of the sleeve 250. The nut 245 is inserted and fixed in the sleeve 250 so that the raised portion 245g is engaged with the groove 250b, and thus can rotate integrally. As a result, even when a high torque is transmitted between the sleeve 250 and the nut 245, the relative slip of both can be suppressed, and the thickness of the nut 245 can be reduced. Other configurations are the same as those in the embodiment shown in FIG.

  Note that the number of raised portions is not necessarily limited to one. For example, as shown in FIG. 4A, two raised portions 245g ′ opposed to the groove 250b ′ are provided at a 180 degree phase, or as shown in FIG. 4B, the groove Four raised portions 245g "facing 250b" can be provided in a 90-degree phase, but the number and phase are not limited to these.

  Depending on the nut, there may be two circulation paths. Therefore, for example, as in the modification shown in FIG. 5A, two raised portions 245g ′ opposed to the groove 250b ′ are formed so as to cover the circulation path 245c ′ provided in a 180-degree phase. As shown in FIG. 5 (b), there are four raised portions 245g ″ facing the groove 250b ″ (two of them are so as to cover the circulation path 245c ″ provided in a 180-degree phase). ), 90 degree phase.

  FIG. 6 is a cross-sectional view in the direction perpendicular to the axis of the ball screw mechanism according to the fourth embodiment, but the balls are omitted. In FIG. 6, external teeth 345 g are formed on the entire outer periphery of the nut 345, while internal teeth 350 b are formed on the entire periphery of the sleeve 350. The outer diameter of the nut 345 is smaller than the inner diameter of the sleeve 350. Therefore, the outer teeth 345g and the inner teeth 350b are not directly engaged with each other, and a cylindrical toothed belt 353 is inserted therebetween. The toothed belt 353 has teeth on the inner and outer circumferences, the inner teeth mesh with the outer teeth 345g, and the outer teeth mesh with the inner teeth 350b. Thereby, the sleeve 350 and the nut 345 can rotate integrally. According to the present embodiment, since the toothed belt 353 functions as an elastic body, the impact force transmitted between the sleeve 350 and the nut 345 can be reduced. Instead of the toothed belt 353, rubber or resin may be welded between the sleeve 350 and the nut 345 so as to function as an elastic body.

  FIG. 7 is a cross-sectional view in the direction perpendicular to the axis of the ball screw mechanism according to the fifth embodiment, but the balls are omitted. In FIG. 7, the protruding portion 445 g extends in the axial direction on the outer periphery of the nut 445 so as to cover the circulation path 445 c (that is, at least a part is located radially outward). It is provided as it exists. On the other hand, a groove 450b which is a recess corresponding to the raised portion 445g is formed on the inner periphery of the sleeve 450. The width of the groove 450b is larger than the width of the raised portion 445g, and when the raised portion 445g is engaged with the groove 450b, a buffer member 453 (preferably made of rubber or resin material) is formed in both circumferential spaces generated. ). When torque transmission occurs between the sleeve 450 and the nut 445, the raised portion 445g which is a convex portion moves relatively in the groove 450b, but even when an impact force is generated at this time, the buffer member 453 is applied. It is designed to reduce the impact force.

  Note that the number of raised portions is not necessarily limited to one. For example, as in the modification shown in FIG. 8, two raised portions 445g ′ facing the groove 450b ′ are provided in a 180-degree phase, or the bumps facing the groove 450b ″ as in the modification shown in FIG. Four portions 445g ″ may be provided with a 90-degree phase, but the number and phase are not limited thereto.

  FIG. 10 is a cross-sectional view of a main part of an electric power steering apparatus 511 according to the sixth embodiment. In the present embodiment, only differences from the embodiment shown in FIG. 1 will be described, and the description of the common configuration will be omitted by attaching the same reference numerals.

  In the present embodiment, instead of omitting the intermediate shaft, a toothed belt 55 that engages with the gear portion 37a of the drive shaft 37 and the driven gear portion 50a of the sleeve 50 is provided. Therefore, if the drive gear portion 37a rotates together with the output shaft 35a of the electric motor 35, the driven gear portion 50a is rotated at a predetermined reduction ratio via the toothed belt 55. As a result, the sleeve 50 and the nut 45 also rotate, so that the power of the electric motor 35 can be transmitted to the screw shaft 23. A chain may be used instead of the toothed belt. Needless to say, the ball screw mechanism according to the modified examples of FIGS.

  FIG. 11 is a cross-sectional view of a main part of an electric power steering apparatus 611 according to the seventh embodiment. FIG. 12 is an exploded perspective view of the nut and sleeve according to the present embodiment, but the bearing is omitted. Fig.13 (a) is a figure which shows the end surface of the nut concerning this Embodiment, FIG.13 (b) cut | disconnected the structure of Fig.13 (a) by the XIIIC-XIIIC line | wire and looked at the arrow direction. FIG. 13C is a diagram showing a deflector. In the present embodiment, only differences from the embodiment shown in FIG. 1 will be described, and the description of the common configuration will be omitted by attaching the same reference numerals.

  In the present embodiment, the configurations of the nut and the sleeve are different. More specifically, as shown in FIG. 12, on the bottom wall 650b of the sleeve 650, four prismatic projections 650c protrude in the axial direction at intervals of 90 degrees in the circumferential direction (extend from the bottom surface in the axial direction). Formed).

  Further, four prismatic projections 645g are formed in the end surface of the main body 645a of the nut 645 facing the sleeve 650 so as to protrude in the axial direction at intervals of 90 degrees in the circumferential direction. Between the nut 645 and the sleeve 650, a ring-shaped first buffer (made of rubber or resin) 635 is disposed. The first buffer body 635 forms eight groove portions 635a at intervals of 45 degrees in the circumferential direction. The shape of the groove 635a corresponds to the protrusions 645g and 650c.

  At the time of assembly, the protrusion 645g of the nut 645 is disposed so as to pass through the groove 635a of the first buffer 635, and the protrusion 650c of the sleeve 650 passes through the remaining groove 635a of the first buffer 635. That is, the first buffer 635 is positioned between the protrusions 645g and 650c alternately arranged in the circumferential direction. In this state, the nut 645 and the sleeve 650 are assembled so as to rotate integrally by screwing the male screw portion 51a of the screw member 51 into the female screw portion 650d formed on the inner periphery of the end portion of the sleeve 650. The bearings 27 and 27 can be assembled by fitting the bearings 27 and 27 (see FIG. 11) on the outer periphery of the sleeve 650 and screwing the male screw portion 52a of the inner ring retainer 52 into the female screw portion 650d.

  According to the present embodiment, since the first buffer 635 is disposed between the projection 645g of the nut 645 and the projection 650c of the sleeve 650, the first buffer 635 is deformed when torque is transmitted. As a buffering effect, vibration and noise during torque transmission can be suppressed, axial backlash between the nut 645 and the sleeve 650 can be eliminated, and a misalignment suppressing effect can also be expected.

  For example, the same function can be exhibited even if a recess corresponding to the protrusion 650c of the sleeve 650 (or the protrusion 645g of the nut 645) is provided in the nut 645 (or the sleeve 650) and engaged therewith.

  Furthermore, as shown in FIG. 12, the main body 645a of the nut 645 has an axial groove 645c formed on the outer periphery. The axial groove 645c is configured so that the outer periphery is covered with an inner peripheral surface 650e when a nut 645 is fitted to a sleeve 650 indicated by a one-dot chain line in FIG. 13B, thereby forming a circulation path. . In the above-described embodiment, all the circulation paths penetrate the nut body, but a long drill is required to form this, and machining is relatively difficult. On the other hand, according to the present embodiment, the axial groove 645c can be easily machined by milling or the like. Further, in the circulation path of the through hole type, the thickness of the nut main body becomes thick as shown by the dotted line in FIG. 13A, but in this embodiment, the thickness of the main body 645a can be made thin as shown by the solid line, It is possible to provide a ball screw mechanism that can easily accelerate and decelerate while keeping the inertial mass low.

  Similarly to the above-described embodiment, also in this embodiment, the deflector 645b shown in FIG. 13 (c) is configured so that the ball 65 that has rolled on the rolling path in the nut 645 is shown in FIG. 13 (a). In FIG. 13 (b), it is scooped up in the tangential direction of the transfer path and scooped up in the lead angle θ direction and sent out to the axial groove 645c.

  FIG. 14 is a cross-sectional view of a main part of an electric power steering apparatus 711 according to the eighth embodiment. In the present embodiment, only differences from the embodiment shown in FIG. 11 will be described, and the description of the common configuration will be omitted by attaching the same reference numerals.

  In the present embodiment, instead of omitting the intermediate shaft, a toothed belt 55 that engages with the gear portion 37a of the drive shaft 37 and the driven gear portion 650a of the sleeve 650 is provided. Accordingly, when the drive gear portion 37a rotates together with the output shaft 35a of the electric motor 35, the driven gear portion 650a is rotated at a predetermined reduction ratio via the toothed belt 55. As a result, the sleeve 650 and the nut 645 also rotate, so that the power of the electric motor 35 can be transmitted to the screw shaft 23. A chain may be used instead of the toothed belt.

  FIG. 15: is principal part sectional drawing of the electrically driven power steering apparatus 811 concerning 9th Embodiment. FIG. 16 is an exploded perspective view showing the nut and inner ring restraint according to the present embodiment. In the present embodiment, only differences from the embodiment shown in FIG. 11 will be described, and the description of the common configuration will be omitted by attaching the same reference numerals.

  In the present embodiment, as shown in FIG. 16, four prismatic protrusions 845 h are formed on the end surface of the nut 845 on the inner ring retainer 852 side so as to protrude in the axial direction at intervals of 90 degrees in the circumferential direction. .

  As in the above-described embodiment, four prismatic projections 845g are formed on the end surface of the nut 845 on the sleeve bottom wall side so as to protrude in the axial direction at intervals of 90 degrees in the circumferential direction.

  A ring-shaped second buffer (made of rubber or resin) 835 is disposed between the nut 845 and the inner ring retainer 852. The second buffer body 835 forms four groove portions 835a at intervals of 90 degrees in the circumferential direction. The shape of the groove 835a corresponds to the protrusion 845h.

  At the time of assembly, the protrusion 845h of the nut 845 is disposed so as to fit into the groove 835a of the second buffer body 835 as shown in FIG. 15, but the protrusion 845h does not penetrate the second buffer body 835 and suppresses the inner ring. A clearance Δ2 is defined between the end face 852 and the end face 852. On the other hand, the protrusion 845g of the nut 845 is disposed so as to fit into the groove portion of the first buffer body 635 shown in FIG. 15. However, the protrusion 845g does not penetrate through the first buffer body 635 and does not penetrate the bottom surface of the sleeve 650. Define the clearance Δ1. In such a state, the bearings 27 and 27 (see FIG. 15) are fitted to the outer periphery of the sleeve 650, and the male threads 852a of the inner ring restraint 852 are screwed into the sleeve 650, whereby the bearings 27 and 27 can be assembled. .

  According to the present embodiment, the clearance Δ2 is defined between the nut 845 and the inner ring retainer 852, and the clearance Δ1 is defined between the nut 845 and the sleeve 650. Therefore, the first buffer 635 or the second buffer By giving elastic deformation to the body 835, the nut 845 can move in the axial direction, and thereby the above-described buffering effect can be enhanced. Further, since the deflectors 845b provided at both ends of the main body 845a of the nut 845 are suppressed by the first buffer body 635 and the second buffer body 835, when the ball 65 comes into contact with the deflector 845b during operation, the noise is generated. It can also suppress and absorb vibrations.

  FIG. 17 is a cross-sectional view of a main part of an electric power steering apparatus 911 according to the tenth embodiment. In the present embodiment, only differences from the embodiment shown in FIG. 15 will be described, and the description of the common configuration will be omitted by attaching the same reference numerals.

  In the present embodiment, instead of omitting the intermediate shaft, a toothed belt 55 that engages with the gear portion 37a of the drive shaft 37 and the driven gear portion 650a of the sleeve 650 is provided. Accordingly, when the drive gear portion 37a rotates together with the output shaft 35a of the electric motor 35, the driven gear portion 650a is rotated at a predetermined reduction ratio via the toothed belt 55. As a result, the sleeve 650 and the nut 845 also rotate, so that the power of the electric motor 35 can be transmitted to the screw shaft 23. A chain may be used instead of the toothed belt.

  In the embodiment described above, torque transmission may be performed by directly engaging the protrusions of the nut and the sleeve or the protrusions and the recesses without interposing the first buffer.

  FIG. 18 is a cross-sectional view of main parts of an electric power steering apparatus 1011 according to the eleventh embodiment. FIG. 19 is a view of the configuration of FIG. 18 taken along the line IXX-IXX and viewed in the direction of the arrow, but the screw shaft and the ball are omitted. In the present embodiment, only differences from the embodiment shown in FIG. 1 will be described, and the description of the common configuration will be omitted by attaching the same reference numerals.

  In the present embodiment, the nut and the sleeve are connected by a key. More specifically, in FIG. 19, a key groove 1045j extending in the axial direction is formed on the outer peripheral surface of the nut 1045, and a key extending in the axial direction is formed on the inner peripheral surface of the sleeve 1050 opposite thereto. A groove 1050f is formed. Since the prismatic key 1035 is arranged in the space formed by the key grooves 1045j and 1050f, torque can be transmitted from the sleeve 1050 to the nut 1045 by using the shearing force of the key 1035.

  FIG. 20 is a cross-sectional view of a main part of an electric power steering apparatus 1111 according to the twelfth embodiment. In the present embodiment, only differences from the embodiment shown in FIG. 18 will be described, and the description of the common components will be omitted by attaching the same reference numerals.

  In this embodiment, instead of omitting the intermediate shaft, a toothed belt 55 that engages with the gear portion 37a of the drive shaft 37 and the driven gear portion 1050a of the sleeve 1050 is provided. Accordingly, when the drive gear portion 37a rotates together with the output shaft 35a of the electric motor 35, the driven gear portion 1050a is rotated at a predetermined reduction ratio via the toothed belt 55. As a result, the sleeve 1050 and the nut 1045 also rotate, so that the power of the electric motor 35 can be transmitted to the screw shaft 23. A chain may be used instead of the toothed belt.

  As described above, the present invention has been described in detail with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be appropriately changed and improved without departing from the spirit thereof. Of course there is. The present invention is also applicable to a so-called steer-by-wire (SBW) type steering mechanism in which a steering wheel and a rack shaft are not mechanically connected, a rear wheel steering mechanism used in a four-wheel steering (4WS) vehicle, and the like. .

It is principal part sectional drawing of the electric power steering device concerning 1st Embodiment. FIG. 2A is an axial sectional view of the ball screw mechanism according to the second embodiment, and FIG. 2B is an arrow formed by cutting the nut of FIG. 2A along the line IIB-IIB. It is the figure seen in the direction. FIG. 3A is an axial sectional view of the ball screw mechanism according to the third embodiment, and FIG. 3B is an arrow formed by cutting the nut of FIG. 3A along the line IIIB-IIIB. It is the figure seen in the direction. It is an axis orthogonal cross section of the ball screw mechanism concerning a modification. It is an axis orthogonal cross section of the ball screw mechanism concerning a modification. It is an axial cross-sectional view of the ball screw mechanism according to the fourth embodiment. FIG. 10 is a cross-sectional view in the direction perpendicular to the axis of a ball screw mechanism according to a fifth embodiment. It is an axis orthogonal cross section of the ball screw mechanism concerning a modification. It is an axis orthogonal cross section of the ball screw mechanism concerning a modification. It is principal part sectional drawing of the electrically driven power steering apparatus concerning 6th Embodiment. It is principal part sectional drawing of the electrically driven power steering apparatus 611 concerning 7th Embodiment. It is a disassembled perspective view of the nut and sleeve concerning 7th Embodiment. Fig.13 (a) is a figure which shows the end surface of the nut concerning this Embodiment, FIG.13 (b) cut | disconnected the structure of Fig.13 (a) by the XIIIC-XIIIC line | wire and looked at the arrow direction. FIG. 13C is a diagram showing a deflector. It is principal part sectional drawing of the electrically driven power steering apparatus 711 concerning 8th Embodiment. It is principal part sectional drawing of the electrically driven power steering apparatus 811 concerning 9th Embodiment. It is a disassembled perspective view which shows the nut and inner ring restraint concerning 9th Embodiment. It is principal part sectional drawing of the electrically driven power steering apparatus 911 concerning 10th Embodiment. It is principal part sectional drawing of the electric power steering apparatus 1011 concerning 11th Embodiment. It is the figure which cut | disconnected the structure of FIG. 18 by the IXX-IXX line | wire, and looked at the arrow direction. It is principal part sectional drawing of the electrically driven power steering apparatus 1111 concerning 12th Embodiment.

Explanation of symbols

11, 511-1111 Electric power steering device 23 Screw shaft 45-1045 Nut 50-1050 Sleeve 55 Toothed belt 65 Ball

Claims (18)

An electric motor;
A rack shaft coupled to a steering mechanism, and a power transmission mechanism for transmitting power from the electric motor to the rack shaft,
The power transmission mechanism is connected to or integrated with the rack shaft and includes a male screw groove, a nut disposed around the screw shaft and provided with a female screw groove, the male screw groove, and the screw shaft. A plurality of rolling elements capable of rolling in a rolling path formed between the female screw groove and a sleeve having a receiving portion for receiving power transmitted from the electric motor;
The electric power steering characterized in that the nut is inserted and fixed with respect to the sleeve so that the receiving portion is located radially outward of the rolling path and is rotated integrally. apparatus.   The nut includes a main body provided with a circulation path for the rolling elements extending in an axial direction, a rolling element provided at both ends of the main body and rolling on the rolling paths, in a tangential direction and a lead angle of the rolling path. The electric power steering apparatus according to claim 1, comprising a deflector that scoops up in a direction and returns to the circulation path.   The electric power steering apparatus according to claim 1, wherein the nut is fitted and fixed to the sleeve.   The electric power steering apparatus according to claim 1, wherein the nut is serrated to the sleeve.   The electric power steering apparatus according to claim 1, wherein an elastic body is interposed between the nut and the sleeve.   A convex portion is provided on the outer peripheral surface of the nut, a concave portion is provided on the inner peripheral surface of the sleeve, and the nut is engaged with the sleeve so that the convex portion is engaged with the concave portion. The electric power steering device according to claim 1, wherein the electric power steering device is provided.   The electric power steering apparatus according to claim 6, wherein at least a part of the convex portion is provided radially outward of the circulation path of the main body.   The electric power steering apparatus according to claim 6 or 7, wherein a buffer member is disposed between the convex portion and the concave portion in the circumferential direction.   The said nut and the said sleeve each have the processus | protrusion extended in an axial direction, Furthermore, the 1st buffer is arrange | positioned between the processus | protrusion of the said nut and the said sleeve, The Claim 1 or 2 characterized by the above-mentioned. The electric power steering apparatus as described.   3. The electric type according to claim 1, wherein one of the nut and the sleeve has a protrusion extending in an axial direction, and the other has a recess that engages with the protrusion. 4. Power steering device.   The electric power steering apparatus according to claim 10, wherein the first buffer is disposed between the protrusion and the recess.   12. The electric motor according to claim 9, wherein a gap that is reduced by relative movement in a direction in which the first buffer is compressed is provided between the nut and the sleeve. Power steering device.   13. The screw according to claim 1, further comprising: a screw member that is screwed onto an inner periphery of the sleeve, wherein a second buffer body is disposed between the screw member and the nut. Electric power steering device.   14. The electric power steering apparatus according to claim 13, wherein a gap that is reduced by relative movement in a direction in which the second buffer body is compressed is provided between the nut and the screw member. .   3. The electric power steering apparatus according to claim 1, wherein the nut and the sleeve are connected by a key and rotate integrally. 4.   The electric power steering apparatus according to any one of claims 1 to 15, wherein the receiving portion is a gear portion formed on an outer peripheral surface of the sleeve.   The electric power steering apparatus according to claim 16, wherein the gear portion meshes with another gear. The electric power steering device according to claim 16, wherein the gear portion is engaged with a toothed belt.

Images