JP2006069518A - 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 scoops up balls 65 from rolling raceways (23b, 45f) to a tangential direction of the rolling raceways or in the direction of a lead angle. As a result, the balls 65 are scooped up to a circulation path 45c with their rolling direction unchanged, so that smooth rolling can be achieved, and operation noise and vibration can be suppressed to low levels. <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).

  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, in order to increase the rotation of the nut, it is desired to suppress the inertia. Moreover, it is desired to keep the outer shape of the electric power steering device small, and for this purpose, it is preferable to make the outer diameter of the nut smaller.

  On the other hand, in the electric power steering apparatus described in Patent Document 2, end caps are attached to both ends of the nut of the ball screw mechanism for circulating the ball.

Japanese Patent Publication No. 6-504 Japanese Unexamined Patent Publication No. 2000-225956

  A schematic cross-sectional view of such a conventional ball screw mechanism is shown in FIG. As shown in the figure, in the case of the end cap type, the end face of the nut N is completely covered with the end cap ED. Therefore, when power is transmitted from the axial direction to the nut N for power transmission, the end cap ED If power is transmitted through the internal circuit, the internal circulation path may be distorted by the stress due to power transmission, and appropriate ball circulation may not be achieved, or the end cap ED may be damaged. However, if the end cap ED is thickened to increase the rigidity, the nut N becomes larger and heavier, and the inertial force that adversely affects assist control also increases.

  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
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. It consists of a deflector scooped up in the direction and returned to the circulation path.

  According to the electric power steering apparatus of the present invention, the nut is provided at both ends of the main body and scoops the rolling elements rolling the rolling path in the tangential direction and the lead angle direction of the rolling path. Since the deflector that returns to the right side is provided, scooping can be performed without changing the rolling direction of the rolling elements, so that smooth rolling can be ensured, and operating noise and vibration can be kept low. In particular, by providing the deflector, there is no need to provide a conventional frame or tube on the outer peripheral surface of the nut, and therefore the outer diameter of the nut can be kept small. Also, the axial length of the nut can be kept short compared to the end cap type.

  It is preferable that the nut is provided with a receiving portion that receives power transmitted from the electric motor on the outer side in the radial direction of the rolling path.

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

  The deflector is fixed to the nut using an annular fixing member that is press-fitted into the nut, and the fixing member has a female serration portion that engages with a male serration portion of an external member, It is preferable that power transmission is performed through the engaged male serration portion and female serration portion because power transmission can be performed without increasing the outer diameter of the nut.

  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. FIG. 2 is a view of the nut of FIG. 1 cut along the line II-II and viewed in the direction of the arrow, but the screw shaft and the ball are omitted. 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 nut 45 is disposed around the rack shaft 23, and is rotatably supported with respect to the housing 21 by a ball bearing 26 and a double-row angular ball bearing 27. The inner ring of the double row angular ball bearing 27 is fixed while being preloaded by the inner ring restraint 51 that is screwed onto the inner circumference of the nut 45, and the outer ring of the double row angular ball bearing 27 is screwed into the inner circumference of the housing 21. It is fixed by an outer ring retainer 52. Therefore, the nut 45 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 at both ends (only one side is shown). As shown in FIG. 2, the main body 45a forms a circulation path 45c penetrating in the axial direction.

  4 is an enlarged view of a portion indicated by an arrow IV in the configuration of FIG. 1, and FIG. 5 is a view of the configuration of FIG. 4 taken along the line VV and viewed in the direction of the arrow. Each deflector 45b (only one shown in FIGS. 4 and 5) attached by a fixing plate 45h screwed to the main body 45a causes the ball 65 transferred to the lead angle (θ of the screw shaft as shown in FIG. ) And as shown in FIG. 5, scooping pieces 45 d are formed to be returned to the circulation path 45 c by scooping up in the tangential direction of the rolling path (screw groove).

  In FIG. 1, a fixing plate 45 g is screwed to the left end of the main body 45. Further, a driven gear portion (receiving portion) 45e that meshes with the intermediate gear portion 38a is provided at a portion sandwiched between the bearings 26 and 27 of the main body 45a. The drive gear portion 37a, the intermediate gear portion 38a, and the driven gear portion 45e 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 screw shaft 23, the nut 45, and the ball 65 constitute a ball screw mechanism (power transmission mechanism).

  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 gear part 45e engaged through the part 38a is rotated at a predetermined reduction ratio. As a result, the nut 45 also rotates, and this rotational motion is converted into the axial motion of the rack shaft 23 via the balls 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 scoops up the ball 65 from the rolling path (23b, 45f) in the tangential direction and the lead angle direction of the rolling path, so that the rolling direction of the ball 65 is changed. Since it can scoop up to circulation way 45c, without changing, smooth rolling can be secured and operation sound, vibration, etc. can be suppressed low. Further, since the deflectors 45b are provided at both ends of the main body 45a, it is not necessary to provide a frame or a tube on the outer peripheral surface of the main body 45a, and the receiving portion that receives the power transmitted from the electric motor 35, that is, the driven gear portion 45e is used as a rolling path. Therefore, when the power is transmitted from the electric motor 35 to the driven gear portion 45e, the nut 45 is prevented from being twisted to enable smooth operation. it can. Further, the axial length of the nut 45 can also be suppressed by providing the driven gear portion 45e that receives the power transmitted from the electric motor 35 on the outer circumferential surface of the rolling path radially outward.

  FIG. 3 is a cross-sectional view of a main part of the electric power steering apparatus 111 according to the second embodiment. In the present embodiment, only different points from the embodiment shown in FIGS. 1 and 2 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 45e of the main body 45 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 45e is rotated at a predetermined reduction ratio via the toothed belt 55. As a result, the nut 45 also rotates, 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. 6 is a cross-sectional view of a main part of an electric power steering apparatus 211 according to the third embodiment. FIG. 7 is an exploded view of the nut and the driven gear, and FIG. 8 is a view seen in the axial direction with the deflector removed from the nut.

  In FIG. 6, the electric power steering apparatus 211 has a housing 121 fixed to a vehicle body (not shown). The housing 121 is divided into three parts in FIG. 6, and is integrated by bolting from the members 121A, 121B, and 121C. A rack shaft 123 is supported so as to be movable in the axial direction so as to penetrate the housing 121 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 123. The rack shaft 123 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 123 are connected to tie rods (not shown) of the steering mechanism.

  An electric motor (not shown) is attached to the housing 121 so that the rack shaft 123 and the axis are parallel to each other. The power of the electric motor is transmitted to an intermediate shaft 138 that is only partially shown in FIG. The intermediate shaft 138 is rotatably supported with respect to the housing 121 by bearings 124 and 125, and has an intermediate gear portion 138 a at a portion sandwiched between the bearings 124 and 125.

  A nut 145 is disposed around the rack shaft 123 and is rotatably supported with respect to the housing 121 by a double-row angular ball bearing 127. This will be described more specifically. A thin cylindrical sleeve 139 is disposed so as to fit in the inner hole 121a in the member 121A of the housing 121. In addition, the ring-shaped member 130, the first buffer member 131, the outer ring 127a of the double row angular ball bearing 127, and the second buffer member 132 are arranged in this order from the bottom surface (left side in FIG. 6) of the inner hole 121a. It is fixed by a lock member 133 to be joined. The first buffer member 131 has an elastic body 131 a that contacts the ring-shaped member 130. In addition, the second buffer member 132 has an elastic body 132 a that abuts against the lock member 133. Due to the elastic deformation of the elastic bodies 131a and 132a, the double-row angular ball bearing 127 can move in the axial direction together with the nut 145 within a limited range. The outer ring 127 a is fitted to the inner peripheral surface of the sleeve 139.

  The inner rings 127b and 127b of the double row angular ball bearing 127 that are divided into two and arranged in the axial direction are fitted to the outer peripheral surface of the nut 145, and the right end in the drawing is the outer periphery formed near the right end of the nut 145. It contacts the step 145h. Further, the left end of the inner rings 127b and 127b is in contact with the right end of the screw member 134, and preload is applied thereto. The screw member 134 is screwed into a screw portion 145k formed on the outer peripheral surface of the nut 145. The preload can be adjusted by the screwing amount of the screw member 134.

  In FIG. 7, the nut 145 includes a hollow cylindrical main body 145a and deflectors 145b provided at both ends thereof. The main body 145a forms a circulation path 145c (see FIG. 6) penetrating in the axial direction, and each deflector 145b scoops up the transferred ball 165 in the tangential direction of the rolling path and in the lead angle direction. A scooping piece 145d to be returned to is formed. The deflector 145b has the same shape as the deflector 45b shown in FIGS.

  In FIG. 7, a deflector 145 b is disposed at the left end of the main body 145 a of the nut 145, and is fixed by a donut disk-shaped holding plate 135 screwed to the main body 145 a by a screw 136. On the other hand, a deflector 145b is disposed at the right end of the main body 145a of the nut 145, and is fixed by an annular member 147 that is press-fitted into a large-diameter portion 145j formed on the inner periphery of the right end of the nut 145. A female serration portion 147 a is formed on the inner periphery of the annular member 147.

  In FIG. 6, a hollow driven gear 137 that is a driven member (external member) is rotatably supported at both ends by bearings 126 and 129 with respect to the housing 121, and is a driven gear that meshes with the intermediate gear portion 138a. In addition to having a portion 137a, a male serration portion 137b is formed on the outer periphery of the left end. The intermediate gear portion 138a and the driven gear portion 137a constitute a gear pair. The nut 145 and the like can be assembled from the right side of the drawing with the members 121A and 121B of the housing 121 removed.

  By engaging the male serration portion 137b of the driven gear 137 and the female serration portion 147a of the annular member 147, the driven gear 137 and the fixed member 147 can move relative to each other in the axial direction, but cannot rotate relative to each other in the rotational direction. Connected. The reason why the driven gear 137 and the fixed member 147 can be moved relative to each other in the axial direction is to exhibit the buffering effect of the elastic bodies 131a and 132a. Even when a large load is transmitted between the male serration portion 137 b of the driven gear 137 and the female serration portion 147 a of the annular member 147, since the stress is not directly applied to the deflector 145 b, the deformation of the ball 165 is suppressed. Rolling defects are not incurred.

  Thus, according to the present embodiment, the nut 145 can be easily manufactured by press-fitting the annular member 147 formed with the female serration portion 147a without forming the female serration portion in the nut 145. There is an advantage and the point that the outer diameter of the nut 145 and the inner diameter of the female serration portion 147a are irrelevant and can be arbitrarily replaced with an annular member in which the outer diameter of the serration, the number of teeth, etc. are changed according to the specification.

  In FIG. 6, a male screw groove 123b is formed in a part of the outer peripheral surface of the rack shaft 123 that is integral with the screw shaft (may be connected as a separate part). A nut 145 is disposed around the male screw groove 123b, and a female screw groove 145f is formed on the inner peripheral surface of the main body 145a facing the male screw groove 123b. In a spiral space (rolling path) formed by the male screw groove 123b and the female screw groove 145f, a large number of balls (rolling elements) 165 are arranged to roll freely. The screw shaft 123, the nut 145, and the ball 165 constitute a ball screw mechanism (power transmission mechanism).

  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 123 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 according to the amount, so that the driven gear portion 137a meshed via the intermediate gear portion 138a, It is rotated at a predetermined reduction ratio. Accordingly, the rotational power is transmitted from the driven gear 137 to the nut 145 via the fixing member 147, and the rotational motion of the nut 145 is converted to the axial motion of the rack shaft 123 via the ball 165. The ball 165 rolled to one end of the rolling path is picked up by the deflector 145b and returned to the other end via the circulation path 145c. An auxiliary steering force can be output using the axial force of the rack shaft 123.

  FIG. 10 is a cross-sectional view of a main part of an electric power steering apparatus 311 according to the fourth embodiment. In the present embodiment, only differences from the embodiment shown in FIG. 6 will be described, and the description of the common components will be omitted by attaching the same reference numerals.

  In the present embodiment, instead of omitting the intermediate shaft, a toothed belt 155 that transmits power to the gear portion 137a of the driven shaft 137 is provided. Therefore, the power from the electric motor (not shown) is transmitted to the driven shaft 137 via the toothed belt 155, and the nut 145 connected thereto is also rotated, so that the power of the electric motor is transmitted to the screw shaft 123. Can do. 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 apparatus 11 concerning 1st Embodiment. It is the figure which cut | disconnected the nut of FIG. 1 by the II-II line | wire, and looked at the arrow direction. It is principal part sectional drawing of the electrically driven power steering apparatus 111 concerning 2nd Embodiment. It is a figure which expands and shows the site | part shown by arrow IV of the structure of FIG. FIG. 5 is a view of the configuration of FIG. 4 taken along the line VV and viewed in the direction of the arrow. It is principal part sectional drawing of the electrically driven power steering apparatus 211 concerning 3rd Embodiment. FIG. 7 is an exploded view of the nut and the driven gear. FIG. 8 is a view seen in the axial direction with the deflector removed from the nut. It is a schematic sectional drawing of an end cap type ball screw mechanism. It is principal part sectional drawing of the electrically driven power steering apparatus 311 concerning 4th Embodiment.

Explanation of symbols

11, 111, 211, 311 Electric power steering device 23, 123 Screw shaft 45, 145 Nut 55 Toothed belt 65, 165 Ball

Claims (6)

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
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. An electric power steering apparatus comprising a deflector that scoops up in a direction and returns to the circulation path.   2. The electric power steering apparatus according to claim 1, wherein the nut is provided with a receiving portion that receives power transmitted from the electric motor, radially outward of the rolling path.   The electric power steering apparatus according to claim 2, wherein the receiving portion is a gear portion formed on an outer peripheral surface of the nut.   The electric power steering apparatus according to claim 3, wherein the gear portion meshes with another gear.   The electric power steering apparatus according to claim 3, wherein the gear portion is engaged with a toothed belt. The deflector is fixed to the nut using an annular fixing member that is press-fitted into the nut, and the fixing member has a female serration portion that engages with a male serration portion of an external member, 6. The electric power steering apparatus according to claim 1, wherein power transmission is performed via the engaged male serration portion and the female serration portion.

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