JP7414754B2 - Electric power steering device, nut and pulley fixing structure, and manufacturing method of electric power steering device - Google Patents

Description

The present invention relates to an electric power steering device, a nut and pulley fixing structure, and a method for manufacturing the electric power steering device.

Patent Document 1 discloses a power steering device that transmits the driving force of an electric motor to a ball screw mechanism via an input pulley, a belt, and an output pulley made of resin, and converts it into an axial thrust of a rack shaft. . The output pulley is fastened to a nut of a ball screw mechanism by a screw. The output pulley has a hub portion located at one end in the axial direction of the output pulley, and a winding portion around which the belt is wound. Four screw insertion holes pass through the hub portion in the axial direction of the output pulley.

Japanese Patent Application Publication No. 2018-111406

In the above conventional technology, since the screw insertion hole extends in the axial direction and the opening on the nut side is formed at a right angle, when the output pulley is injection molded, the nut A burr is formed that protrudes to the side. For this reason, when the screw is temporarily tightened to align the nut and the output pulley, there is a risk that the burr will interfere and make adjustment difficult. Furthermore, if alignment adjustment is completed with a burr caught between the output pulley and the nut, the burr may be crushed when the screw is fully tightened, and the amount of eccentricity of the output pulley with respect to the nut may increase.
One of the objects of the present invention is to provide an electric power steering device, a nut and pulley fixing structure, and a method for manufacturing the electric power steering device, which can suppress the influence of burrs on alignment.

In the electric power steering device according to an embodiment of the present invention, the output pulley is arranged in an annular recess provided in the nut-side opening of the screw insertion hole in the direction of the rotation axis of the nut, and in a radially inner side of the annular recess with respect to the rotation axis. and an annular protrusion provided therein.

Therefore, the influence of burrs on alignment can be suppressed.

1 is a front partial cross-sectional view of an electric power steering device 1 according to a first embodiment. FIG. FIG. 3 is a cross-sectional view of the ball screw mechanism 4 of the first embodiment. 3 is an enlarged view of the main part of FIG. 2. FIG. 4 is an enlarged view of the main part of FIG. 3. FIG. (a) is a schematic diagram showing the injection molding process of Embodiment 1, and (b) is an enlarged view of the main part of (a). (a) is a schematic diagram showing a conventional injection molding process, and (b) is an enlarged view of the main part of (a). FIG. 2 is an enlarged cross-sectional view of a main part of a ball screw mechanism 4 according to a second embodiment. FIG. 3 is an enlarged view of a main part of a schematic diagram showing an injection molding process of Embodiment 2. FIG.

[Embodiment 1]
FIG. 1 is a partial front sectional view of the electric power steering device 1 of the first embodiment, and is a sectional view of the electric power steering device 1 taken along the axis of the steered shaft 2. As shown in FIG.
The electric power steering device 1 of the first embodiment transmits the driving force of the electric motor 3 to the steered shaft 2 via the ball screw mechanism 4, thereby imparting an assist force to the steering force of the driver.

The electric power steering device 1 includes a steering mechanism 5 that transmits the rotation of a steering wheel steered by a driver to a steering shaft 2 that steers steered wheels, and an assist mechanism 6 that applies an assist force to the steering shaft 2. has.
Each component of the electric power steering device 1 is housed in a housing 7 consisting of a first housing 8, a second housing 9, and a motor housing 10.
The steering mechanism 5 has a steering input shaft 12 connected to a steering wheel, and a pinion (not shown) that rotates together with the steering input shaft 12. The pinion meshes with a rack formed on the outer periphery of the steered shaft 2.

The assist mechanism 6 includes an electric motor 3 and a ball screw mechanism 4 that transmits the output of the electric motor 3 to the steered shaft 2. The output of the electric motor 3 is controlled by a motor controller according to the steering torque and steering amount input to the steering wheel by the driver.
The ball screw mechanism 4 includes a nut 11 and an output pulley 13. The output pulley 13 is a cylindrical member, and is fixed to the nut 11 so as to be rotatable therewith. A cylindrical input pulley 14 is fixed to the drive shaft 3a of the electric motor 3 so as to rotate therewith. The axis of rotation of the nut 11 is defined as a first reference axis L1, and the axis of rotation of the input pulley 14 is defined as a second reference axis L2. The second reference axis L2 is arranged to be offset in the radial direction with respect to the first reference axis L1. Note that the output pulley 13, which is integrally fixed to the nut 11, also has the first reference axis L1 as its rotation axis.

A belt 15, which is a transmission member, is wound between the input pulley 14 and the output pulley 13. Belt 15 is made of resin material. Note that the transmission member is not limited to a belt, and a chain or the like may be used. The driving force of the electric motor 3 is transmitted to the nut 11 via the input pulley 14, belt 15, and output pulley 13. The outer diameter of the input pulley 14 is smaller than the outer diameter of the output pulley 13. The input pulley 14, the output pulley 13, and the belt 15 constitute a reduction gear.

The nut 11 is formed into a cylindrical shape so as to surround the steered shaft 2, and is rotatably provided with respect to the steered shaft 2. A spiral groove is formed on the inner circumference of the nut 11, and this groove constitutes a nut-side ball screw groove 16. A spiral groove is formed on the outer periphery of the steering shaft 2 at a position axially away from the part where the rack is formed, and this groove constitutes a ball screw groove 17 on the steering shaft side. .
With the nut 11 inserted into the steered shaft 2, a ball circulation groove 18 is formed by the ball screw groove 16 on the nut side and the ball screw groove 17 on the steered shaft side. A plurality of metal balls 19 are filled in the ball circulation groove 18. When the nut 11 rotates, the ball 19 moves within the ball circulation groove 18, and the steered shaft 2 moves in the longitudinal direction with respect to the nut 11. The balls 19 that have reached one end or the other end of the ball circulation groove 18 are returned to the other end or one end of the ball circulation groove 18 via the tube (circulation mechanism) 4a.

Next, the nut 11 and output pulley 13 of the first embodiment will be explained in detail using FIGS. 2 and 3. FIG. 2 is a sectional view of the ball screw mechanism 4 of the first embodiment, and FIG. 3 is an enlarged view of the main part of FIG. 2.
In FIG. 1, the X-axis is set in the axial direction of the steering shaft 2, the direction from the steering mechanism 5 side to the ball screw mechanism 4 side is the positive X-axis direction, the direction orthogonal to the X-axis is the radial direction, and the The direction around the axis is defined as the circumferential direction.
The center portion of the nut 11 in the X-axis direction is formed to have a smaller diameter than both end portions in the X-axis direction, and the nut-side ball screw groove 16 is formed on the inner periphery of the center portion in the X-axis direction.
An inner race 20a of a ball bearing 20 is integrally formed at the end of the nut 11 in the negative direction of the X-axis. The ball bearing 20 supports the nut 11 with respect to the first housing 8 so as to be rotatable in the circumferential direction. The ball bearing 20 has an inner race 20a, an outer race 20b, and balls 20c. The outer race 20b is fixed to the first housing 8. Ball 20c is interposed between inner race 20a and outer race 20b. Four female threaded portions 21 are formed at the end of the nut 11 in the positive direction of the X-axis. The female threaded portion 21 extends along the X-axis direction. Each female threaded portion 21 is arranged at 90° intervals in the circumferential direction.

The output pulley 13 is formed into a bottomed cup shape by injection molding using a resin material containing glass fiber. In the first embodiment, a disk gate (diaphragm gate) type is used as a gate during injection molding. The output pulley 13 has a hub portion 22 and a wrapping portion 23. The inner surface (side surface in the negative X-axis direction) 22b of the hub portion 22 contacts the outer surface (side surface in the positive X-axis direction) 11a of the nut 11. The hub portion 22 is formed into a substantially annular disk shape. Four screw insertion holes 22c pass through the hub portion 22 in the X-axis direction. Each screw insertion hole 22c is arranged at 90° intervals in the circumferential direction. A screw 24 is inserted into each screw insertion hole 22c from the X-axis positive direction side.

The screw 24 fastens the output pulley 13 and the nut 11. The screw 24 has a head 25 and a shaft 26. The outer shape of the head 25 is approximately circular when viewed from the X-axis direction. The shaft portion 26 is formed with a male threaded portion (a male threaded thread groove) 26a. The male threaded portion 26a is fitted into the female threaded portion 21 of the nut 11 by screw action. A washer 27 is interposed between the screw 24 and the outer surface (X-axis positive side surface) 22a of the hub portion 22. The washer 27 is formed into an annular disk shape. The outer diameter of the washer 27 is larger than the outer diameter of the head 25. The hub portion 22 has a steered shaft insertion hole 28 at its radial center. The steered shaft 2 passes through the steered shaft insertion hole 28.

The wrapping portion 23 is formed in a cylindrical shape extending from the outer periphery of the hub portion 22 in the negative direction of the X-axis. The wrapping part 23 has an outer cylinder part 29, an inner cylinder part 30, and 16 bridge parts 31. The outer cylinder portion 29 is formed into a cylindrical shape. A belt 15 is wound around the outer cylinder portion 29. The inner cylinder part 30 is located radially inside the outer cylinder part 29. The inner cylinder part 30 is formed into a cylindrical shape having a smaller diameter than the outer cylinder part 29. An end of the outer cylinder part 29 in the positive direction of the X-axis is connected to the inner cylinder part 30. The bridge portion 31 extends in the radial direction between the outer tube portion 29 and the inner tube portion 30, and connects the outer tube portion 29 and the inner tube portion 30. Each bridge portion 31 is arranged at intervals of 22.5° in the circumferential direction. The wrapping portion 23 and the hub portion 22 are smoothly connected by a connecting portion 32. In the axial cross section of the output pulley 13 passing through the rotational axis of the nut 11, the connecting portion 32 is formed in an arc shape.

FIG. 4 is an enlarged view of the main part of FIG. 3.
On the inner surface 22b of the hub portion 22, an annular recess 33 is provided at the opening of each screw insertion hole 22c. The annular recess 33 is formed in the shape of a truncated cone in the X-axis direction, with an upper base disposed on the X-axis positive direction side and a lower base disposed on the X-axis negative direction side.
The annular protrusion 34 is provided on the radially inner side of the bottom 33a of the annular recess 33, that is, at the opening of the screw insertion hole 22c, and protrudes toward the negative side of the X-axis. The annular protrusion 34 is a burr formed during injection molding of the output pulley 13, and is provided over the entire circumference in the circumferential direction with respect to the X-axis. A gap is formed between the tip 34a of the annular projection 34 and the outer surface 11a of the nut 11.

Next, in the method for manufacturing the electric power steering device 1 of Embodiment 1, an injection molding process of injection molding the output pulley 13, an alignment process of aligning the output pulley 13 with respect to the nut 11, and a process of aligning the output pulley 13 with the nut The fixing process of fixing to 11 will be explained.
FIG. 5(a) is a schematic diagram showing the injection molding process of Embodiment 1. In the injection molding process, the output pulley 13 is injection molded using a mold consisting of a core 35 and a cavity 36. The core 35 has two annular protrusions 37 for forming an annular recess 33 in the output pulley 13. The annular protrusion 37 projects toward the cavity 36. Further, two core pins 38 penetrate through the core 35. The core pin 38 is for forming the screw insertion hole 22c in the output pulley 13, and protrudes from the center of the annular convex portion 37 toward the cavity 36.

In the injection molding process, the output pulley 13 having the annular recess 33 and the screw insertion hole 22c is molded by injecting resin containing glass fiber into the internal space of the mold through a gate (not shown). At this time, since a large pressure is applied inside the mold during injection molding, a slight gap is created between the core 35 and the core pin 38, as shown in FIG. 5(b). As the resin protrudes into this gap, a burr (film burr) is generated at the bottom 33a of the annular recess 33 and at the opening of the screw insertion hole 22c, and this burr becomes an annular protrusion 34.

Next, in the alignment step, the screw 24 is inserted into the screw insertion hole 22c from the positive X-axis side with the inner surface 22b of the hub portion 22 of the output pulley 13 in contact with the outer surface 11a of the nut 11. , the nut 11 and the output pulley 13 are temporarily tightened. The fastening torque at this time is relatively weak enough to push the side surface (wrapping portion 23) of the output pulley 13 in a direction perpendicular to the X-axis. In the alignment process, in this temporarily tightened state, the eccentricity (runout) of the output pulley 13 with respect to the nut 11 is adjusted to be within an allowable range.
In the fixing process, the output pulley 13 is fixed to the nut 11 by fully tightening the screw 24 to a specified torque.

Next, the effects of the first embodiment will be explained.
FIG. 6(a) is a schematic diagram showing a conventional injection molding process. In the conventional injection molding process, an annular concave portion is formed by providing a tapered portion as an annular convex portion on a core pin. Therefore, during injection molding, burrs are formed on the inner surface of the output pulley that comes into contact with the outer surface of the nut during assembly, as shown in FIG. 6(b). Furthermore, when the mold expands due to the residual austenite in the mold transforming into martensite over time, the fitting portion with the core pin becomes misaligned, and a burr-like protrusion occurs due to the step. If these cannot be removed in the deburring process, the burrs will interfere with the nut during the alignment process, making adjustment difficult. Furthermore, if the alignment adjustment is completed with the burr still in place, the burr will be crushed during the fixing process and the eccentricity of the output pulley with respect to the nut will change.

On the other hand, in the injection molding process of Embodiment 1, the annular convex portion 37 is provided on the core 35 instead of the core pin 38, so the burr caused by the gap between the core 35 and the core pin 38 is removed from the annular concave portion 33. It is formed at the opening of the screw insertion hole 22c in the bottom portion 33a. That is, the burrs generated during injection molding remain within the annular recess 33 and do not reach the inner surface 22b that contacts the outer surface 11a of the nut 11. Furthermore, even if the core 35 expands and the fitting portion with the core pin 38 is displaced, the burr-like protrusion is formed within the annular recess 33 and therefore does not reach the inner surface 22b. Therefore, the influence of burrs on alignment can be suppressed during the alignment process and the fixing process. In addition, burrs do not get in the way during the alignment process, and a preliminary burr removal process is not required, which facilitates manufacturing.

Here, if there is any contamination on the surface of the output pulley or nut, it will affect alignment in the same way as burrs. Generally, the output pulley itself has a camera process to detect contamination when it is assembled, so the risk of bringing it in is small. On the other hand, screws are not cleaned after delivery and are put into the production line in their delivered state, so contaminants and anti-rust oil on the screw surface get into the gap between the output pulley and the nut while the screw is being tightened. there is a possibility.

The output pulley 13 of the first embodiment has an annular recess 33 provided in the nut-side opening of the screw insertion hole 22c in the X-axis direction, which is the rotation axis direction of the nut 11, and an annular recess 33 provided on the radially inner side with respect to the X-axis. An annular projection 34. Thereby, as shown in FIG. 4, the annular protrusion 34 can prevent contaminants and antirust oil adhering to the screw surface from entering between the output pulley 13 and the nut 11. Further, since the annular protrusion 34 is provided on the entire circumference in the circumferential direction with respect to the X-axis, the intrusion of contamination and antirust oil can be further suppressed compared to a case where the annular protrusion is provided on a part of the circumferential direction. Furthermore, since the annular protrusion 34 is formed integrally with the output pulley 13, manufacturing is easy.

When the electric motor 3 generates a large torque, the output pulley 13 is pulled by the belt 15, and a force acts in the radial direction, that is, in the direction in which the amount of eccentricity of the output pulley 13 with respect to the nut 11 changes. To prevent this, the axial force of the screw 24 can be increased to increase the friction, but since the output pulley 13 is made of resin, there is a risk of cracking. Since the output pulley 13 of the first embodiment has a larger annular recess 33 than the conventional product, the wall thickness of the output pulley 13 on which the axial force acts is smaller than that of the conventional product. This increases the deflection when subjected to the same axial force, and this deflection functions as a spring washer, thereby suppressing loosening of the screw 24 and suppressing radial movement of the output pulley 13 with respect to the nut 11. can be achieved.

Since the annular protrusion 34 of the first embodiment is a burr formed during injection molding of the output pulley 13, the burr can be used to prevent contamination from entering between the output pulley 13 and the nut 11. Since the output pulley 13 is made of a resin containing glass fibers, the burr during injection molding, that is, the annular protrusion 34, can be made harder than resin that does not contain glass fibers. That is, by molding the output pulley 13 with a resin containing glass fiber, the strength of the annular protrusion 34 can be improved. Further, the annular protrusion 34 is located radially inside the bottom portion 33a in the X-axis direction. Since the bottom portion 33a is planar, the support strength of the annular projection 34 can be improved compared to a case where an annular projection is provided on the taper.

The annular recess 33 of the first embodiment is formed in a truncated conical shape with an upper court (bottom 33a) on one side and a lower base on the other side in the X-axis direction. Thereby, when the output pulley 13 is injection molded, the annular recess 33 can be formed at the same time. Here, if the concave portion were only tapered, the core of the mold would need to have an acute convex portion, which would cause severe wear of the core. Therefore, by forming the core into a trapezoidal shape as in Embodiment 1, the tip of the convex portion of the core becomes flat, so that wear of the core can be suppressed and durability can be improved.

[Embodiment 2]
Since the basic configuration of the second embodiment is the same as that of the first embodiment, only the parts that are different from the first embodiment will be explained.
FIG. 7 is an enlarged cross-sectional view of a main part of the ball screw mechanism 4 of the second embodiment, and the annular protrusion 34 of the second embodiment has an inclined portion 34b on the outside in the radial direction with respect to the X-axis. The annular convex portion 37 of the core 35 used in the injection molding process has an inclined surface 37a on the inside in the radial direction. According to this method, the annular protrusion 34 can be reliably formed without depending on burrs formed during injection molding. In addition, since the annular projection 34 having the inclined portion 34b on the radially outer side can further expand the area of the connecting portion with the bottom portion 33a compared to the case of the first embodiment, the support strength of the annular projection 34 can be improved.

[Other embodiments]
Although the embodiments for carrying out the present invention have been described above, the specific configuration of the present invention is not limited to the configuration of the embodiments, and design changes may be made within the scope of the gist of the invention. are also included in the present invention.
For example, the annular protrusion may be provided not on the entire circumference but on a part of the circumference.
The annular recess may have an R shape instead of being tapered.
The nut and pulley fixing structure of the present invention is applicable not only to an electric power steering device but also to a mechanism that transmits rotational force from an electric motor to a nut of a ball screw mechanism via a pulley, and is similar to the embodiment. The effects of this can be obtained.

1 Electric power steering device
2 Steering shaft
3 electric motor
4 Ball screw mechanism
4a tube (circulation mechanism)
11 Nut
13 Output pulley
16 Nut side ball screw groove
17 Ball screw groove on steering shaft side
18 Ball circulation groove
19 balls
22 Hub section
22c screw insertion hole
23 Wrapping section
24 screw
33 Annular recess
34 Annular process
35 cores
36 cavity
37 Annular convex part
38 core pin

Claims (12)

An electric power steering device,
a steering shaft that steers the steered wheels by moving in an axial direction as the steering wheel rotates;
A ball screw mechanism having a nut, a ball circulation groove, a plurality of balls and a circulation mechanism,
The nut is formed in an annular shape surrounding the steered shaft,
The ball circulation groove includes a steered shaft-side ball screw groove spirally provided on the outer periphery of the steered shaft, and a nut-side ball screw groove spirally provided on the inner periphery of the nut,
the plurality of balls are arranged in the ball circulation groove,
The circulation mechanism circulates the plurality of balls from one end of the ball circulation groove to the other end.
the ball screw mechanism;
An output pulley, which is molded from resin and has a hub part, a winding part, a screw insertion hole, an annular recess, and an annular protrusion,
The hub portion contacts one end surface of the nut in the direction of the rotational axis of the nut,
The wrapping portion is provided integrally with the hub portion and is formed in a cylindrical shape,
The screw insertion hole is provided in the hub portion and penetrates in the direction of the rotation axis,
The annular recess is provided at an opening on the nut side of the screw insertion hole in the direction of the rotation axis,
The annular protrusion is provided on the inner side of the annular recess in the radial direction with respect to the rotation axis,
the output pulley;
a screw inserted into the screw insertion hole and fastening the nut and the output pulley;
an electric motor that rotates the output pulley;
An electric power steering device equipped with The electric power steering device according to claim 1,
The annular protrusion is integrally formed with the output pulley.
Electric power steering device. The electric power steering device according to claim 2,
The annular protrusion has an inclined portion on the outside in the radial direction with respect to the rotation axis.
Electric power steering device. The electric power steering device according to claim 3,
The output pulley is molded from resin containing glass fiber.
Electric power steering device. The electric power steering device according to claim 2,
The annular protrusion is a burr formed during molding of the output pulley.
Electric power steering device. The electric power steering device according to claim 1,
The annular recess is formed in a truncated conical shape with an upper base on one side and a lower base on the other side in the direction of the rotation axis.
Electric power steering device. The electric power steering device according to claim 6,
The annular protrusion is located on the inner side of the upper base in the radial direction with respect to the rotational axis.
Electric power steering device. The electric power steering device according to claim 1,
The annular protrusion is provided on the entire circumference in the circumferential direction with respect to the rotation axis,
Electric power steering device. A nut and pulley fixing structure for fixing a pulley that transmits rotational force from an electric motor to a nut of a ball screw mechanism that moves a screw shaft in the axial direction,
The ball screw mechanism includes the nut, a ball circulation groove, a plurality of balls, and a circulation mechanism,
The nut is formed in an annular shape surrounding the screw shaft,
The ball circulation groove includes a screw shaft side ball screw groove spirally provided on the outer periphery of the screw shaft, and a nut side ball screw groove spirally provided on the inner periphery of the nut,
the plurality of balls are arranged in the ball circulation groove,
The circulation mechanism circulates the plurality of balls from one end of the ball circulation groove to the other end,
The pulley is molded from resin and has a hub portion, a winding portion, a screw insertion hole, an annular recess, and an annular protrusion,
The hub portion contacts one end surface of the nut in the direction of the rotational axis of the nut,
The wrapping portion is provided integrally with the hub portion and is formed in a cylindrical shape,
The screw insertion hole is provided in the hub portion and penetrates in the direction of the rotation axis,
The annular recess is provided at an opening on the nut side of the screw insertion hole in the direction of the rotation axis,
The annular protrusion is provided on the inner side of the annular recess in the radial direction with respect to the rotation axis,
a screw inserted into the screw insertion hole and fastening the nut and the pulley;
Fixed structure of nut and pulley. The nut and pulley fixing structure according to claim 9,
The annular protrusion is a burr formed during molding of the pulley.
Fixed structure of nut and pulley. a steering shaft that steers the steered wheels by moving in an axial direction as the steering wheel rotates;
A ball screw mechanism having a nut, a ball circulation groove, a plurality of balls and a circulation mechanism,
The nut is formed in an annular shape surrounding the steered shaft,
The ball circulation groove includes a steered shaft-side ball screw groove spirally provided on the outer periphery of the steered shaft, and a nut-side ball screw groove spirally provided on the inner periphery of the nut,
the plurality of balls are arranged in the ball circulation groove,
The circulation mechanism circulates the plurality of balls from one end of the ball circulation groove to the other end.
the ball screw mechanism;
An output pulley, which is molded from resin and has a hub part, a winding part, a screw insertion hole, an annular recess, and an annular protrusion,
The hub portion contacts one end surface of the nut in the direction of the rotational axis of the nut,
The wrapping portion is provided integrally with the hub portion and is formed in a cylindrical shape,
The screw insertion hole is provided in the hub portion and penetrates in the direction of the rotation axis,
The annular recess is provided at an opening on the nut side of the screw insertion hole in the direction of the rotation axis,
The annular protrusion is provided on the inner side of the annular recess in the radial direction with respect to the rotation axis,
the output pulley;
a screw inserted into the screw insertion hole and fastening the nut and the output pulley;
an electric motor that rotates the output pulley;
A method of manufacturing an electric power steering device comprising:
an injection molding step of injection molding the output pulley using a mold consisting of a core and a cavity;
The core includes an annular protrusion that protrudes toward the cavity and corresponds to the annular recess, and a cylindrical core pin that protrudes from the center of the annular protrusion toward the cavity and corresponds to the screw insertion hole. have,
A method for manufacturing an electric power steering device. A method for manufacturing an electric power steering device according to claim 11, comprising:
an alignment step of aligning the output pulley with respect to the nut while the screw is inserted from the opposite side of the screw insertion hole to the nut and temporarily tightened;
After the alignment step, a fixing step of fully tightening the screw to fix the output pulley to the nut;
A method for manufacturing an electric power steering device comprising:

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