JP2002156025A - Electric power steering unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric steering unit in which the strength of a synthetic resin-made worm wheel for transmitting the rotation of an electric actuator for generating steering assisting force is improved to enable high output of the electric actuator, and the worm wheel is reduced in diameter to achieve space-saving. SOLUTION: The rotation of the electric actuator 8 for generating steering assisting force is transmitted to an axle 6 through a worm 9 and a worm wheel 10. The worm wheel 10 is made of synthetic resin. The relative viscosity of the worm wheel 10 by the formic acid method ranges from 100 to 300.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of controlling rotation of an electric actuator for generating a steering assist force by using a worm, a bevel gear,
Or, a drive gear constituted by a hypoid gear, a worm wheel, a bevel gear meshing with the drive gear,
Alternatively, the present invention relates to an electric power steering device that transmits power to wheels via a driven gear constituted by a hypoid gear.

[0002]

2. Description of the Related Art An electric power steering device for transmitting the rotation of an electric actuator for generating a steering assist force to wheels via a driving gear and a driven gear is used in a mini car or a small car, and the driven gear is made of a synthetic resin material. The weight and the noise are reduced by using the product.

[0003]

In recent years, there has been a demand for lower fuel consumption of vehicles in order to deal with environmental problems.
Also in electric power steering devices used for large vehicles, it is required that the driven gear be made of a synthetic resin material. For that purpose, it is necessary to increase the output of the electric actuator as compared with a mini vehicle, so it is necessary to improve the tooth root strength of a driven gear that reduces the rotation of the electric actuator. Further, it is desired to improve the fatigue strength and the backlash increasing characteristic of the driven gear. The backlash increase characteristic is the amount of backlash after rotating the drive gear and driven gear with a specified load while engaging the specified gear, and after the specified number of revolutions.If the backlash becomes excessive, the rattling noise will occur. There is a problem that it becomes larger.

However, the conventional synthetic resin driven gear is
There was not enough root strength to withstand the increase in the output of the electric actuator, and the fatigue strength and the backlash increasing characteristics were not sufficient.

[0005]

According to a first aspect of the present invention, a rotation of an electric actuator for generating a steering assist force is controlled by a worm,
In an electric power steering device that transmits power to wheels through a worm wheel that meshes with the worm, the worm wheel is formed of a synthetic resin material, and the formed worm wheel has a relative viscosity of 100 or more and 300 or less by a formic acid method. It is characterized by having been done. According to the configuration of the first aspect of the present invention, the worm wheel that transmits the rotation of the electric actuator is made of a synthetic resin material, so that the weight and noise can be reduced, and the worm wheel is formed of the synthetic resin material. By setting the relative viscosity of the worm wheel by the formic acid method to 100 or more, the tooth root strength of the worm wheel can be improved, and the relative viscosity is 3
By setting the ratio to 00 or less, moldability can be ensured. The first invention of this case is based on the following findings. According to a general theoretical formula applied to a metal gear, the tooth root strength of the gear is correlated with the tensile strength and bending strength of the gear material. However, in the case of a synthetic resin worm wheel, the root strength does not correlate with the tensile strength or bending strength of the material. In fact, when synthetic fibers were filled with reinforcing fibers in order to improve the tensile strength and the bending strength, when the amount of filling was too large, the tooth root strength was lower than when not filled. this is,
The root strength of the synthetic resin worm wheel is determined by the balance between the reduction of the surface pressure acting on the teeth based on the elasticity of the synthetic resin material and the strength of the synthetic resin material. The inventors have newly found that the root strength can be improved by increasing the viscosity of the synthetic resin material, and have reached the first invention of the present application. In other words, the relative viscosity of the worm wheel made of a synthetic resin material is set to 10
By setting the value to 0 or more, the root strength of the worm wheel is increased, thereby improving the fatigue strength and the backlash increasing characteristic. In the first aspect of the present invention, the moldability can be ensured by setting the relative viscosity of the synthetic resin worm wheel to 300 or less.

[0006] The synthetic resin material in the first invention of the present invention is preferably a solid material. Thus, wear of the worm meshing with the worm wheel can be prevented without heat-treating the worm.

In the first aspect of the present invention, it is preferable that the synthetic resin material is filled with a reinforcing fiber, and a filling ratio of the reinforcing fiber to the synthetic resin material is 5% by weight or more and less than 10% by weight. By filling the reinforcing fibers, dimensional changes due to water absorption and heat of the synthetic resin material can be prevented, and dimensional stability of the worm wheel can be improved. At this time, it is preferable that the worm is heat-treated and cured to prevent abrasion. By setting the filling ratio of the reinforcing fibers to the synthetic resin material to be less than 10% by weight, it is possible to secure the relief of the surface pressure acting on the teeth based on the elasticity of the synthetic resin material and prevent the reduction of the root strength of the worm wheel. When the content is 5% by weight or more, the reinforcing fibers can be uniformly dispersed in the synthetic resin material.

The worm wheel is integrated with a metal sleeve, and the worm wheel is formed by injecting a synthetic resin material into a mold in which the metal sleeve is inserted. The teeth formed along the circle concentric with the circle along which the teeth of the worm wheel are formed at the joint with the worm wheel, and the synthetic resin material forming the worm wheel is formed on the metal sleeve. Between the worm wheel and the metal sleeve prevents relative rotational displacement of the worm wheel and the metal sleeve about the axial center, so that the tooth module in the sleeve is smaller than the worm wheel tooth module. Is preferred. By making the tooth module on the outer circumference of the sleeve smaller than the tooth module of the driven gear, the rotational force of the electric actuator can be received by the teeth of the sleeve simultaneously with the teeth of the worm wheel. In this case, the synthetic resin material constituting the worm wheel is filled in the recess formed in the metal sleeve, so that the relative rotational displacement between the worm wheel and the metal sleeve is prevented, and The minimum width of the opening of the concave portion in the sleeve is 1 mm or more,
Preferably, the depth of the concave portion in the metal sleeve is 4 mm or less. As a result, the worm wheel made of a synthetic resin material and the metal sleeve are integrated, and the worm wheel can be pressed into the outer periphery of the rotating body via the metal sleeve or firmly fixed via a key or the like. . When the minimum width of the opening of the concave portion is 1 mm or more, the fluidity of the synthetic resin material at the time of molding can be ensured, and the synthetic resin material can be reliably filled in the concave portion. The minimum width of the opening size of the concave portion By setting the depth dimension to 4 mm or less, it is possible to prevent voids from occurring and prevent a decrease in strength.

According to the second aspect of the present invention, the rotation of the electric actuator for generating a steering assist force is controlled by a drive gear constituted by a bevel gear or a hypoid gear, and a bevel gear engaged with the bevel gear or a driven gear constituted by a hypoid gear engaged with the hypoid gear. In an electric power steering apparatus that transmits power to wheels through a driven gear, the driven gear is formed of a synthetic resin material, and the formed driven gear has a relative viscosity of 100 or more and 300 or more by a formic acid method.
It is characterized as follows. According to the configuration of the second aspect of the present invention, the driven gear for transmitting the rotation of the electric actuator is made of a synthetic resin material, so that the weight and noise can be reduced, and the driven gear is formed of the synthetic resin material. By setting the relative viscosity of the driven gear by the formic acid method to 100 or more, the tooth root strength of the driven gear can be improved, and by setting the relative viscosity to 300 or less, formability can be ensured. In the second invention of the present invention, the root viscosity of the driven gear is increased by setting the relative viscosity of the driven gear made of a synthetic resin material to a value larger than the conventional value of 100 or more, thereby improving the fatigue strength and the backlash increasing characteristics. Was. In the second aspect of the present invention, the formability can be ensured by setting the relative viscosity of the synthetic resin driven gear to 300 or less.

In the second aspect of the present invention, it is preferable that the synthetic resin material is filled with a reinforcing fiber, and a filling ratio of the reinforcing fiber to the synthetic resin material is 5% by weight or more and 60% by weight or less. In the second invention, the filling of the reinforcing fibers can prevent dimensional changes due to water absorption or heat of the synthetic resin material, thereby improving the dimensional stability of the driven gear, and can further prevent a decrease in the strength of the driven gear. By setting the filling ratio of the reinforcing fibers to the synthetic resin material to 5% by weight or more, the reinforcing fibers can be uniformly dispersed in the synthetic resin material. The filling ratio of the reinforcing fibers to the synthetic resin material is 60
By setting the content to not more than% by weight, moldability can be ensured. In addition,
In this case, it is preferable that the drive gear is heat-treated and cured to prevent wear.

The synthetic resin material for forming the driven gear according to the second aspect of the present invention may be a solid material. Thus, wear of the drive gear meshing with the driven gear can be prevented without heat-treating the drive gear.

The driven gear according to the second aspect of the present invention is integrated with a metal sleeve, and the driven gear is formed by injecting a synthetic resin material into a mold in which the metal sleeve is inserted, and At the joint portion of the metal sleeve with the driven gear, a tooth line is formed along a circle concentric with the circle along which the tooth line of the driven gear is formed, and the synthetic resin material constituting the driven gear is formed on the metal sleeve. By filling in the recesses between the formed teeth, the relative rotational displacement of the driven gear and the metallic sleeve about the axial center is prevented, and the tooth module in the sleeve is smaller than the tooth module in the driven gear. Preferably, it is reduced. By making the tooth module on the outer periphery of the sleeve smaller than the tooth module of the driven gear, the rotational force of the electric actuator can be received by the tooth of the driven gear and also by the tooth of the sleeve. In this case, the synthetic resin material forming the driven gear is filled in the recess formed in the metal sleeve, so that the relative rotational displacement between the driven gear and the metal sleeve is prevented, and The minimum width of the opening of the recess in the sleeve is 1 mm or more and 4 mm or less, and the depth of the recess in the metal sleeve is 4 m.
m or less. As a result, the driven gear made of a synthetic resin material and the metal sleeve are integrated, and the driven gear can be pressed into the outer periphery of the rotating body via the metal sleeve or firmly fixed via a key or the like. .
When the minimum width of the opening of the concave portion is 1 mm or more, the fluidity of the synthetic resin material at the time of molding can be secured, and the synthetic resin material can be reliably filled in the concave portion. The minimum width of the opening size of the concave portion By setting the depth dimension to 4 mm or less, it is possible to prevent voids from occurring and prevent a decrease in strength. Further, the distance between the tooth bottom of the driven gear and the tooth top of the metal sleeve is 2 m.
It is preferable that the length is not less than m and not more than 4 mm. The distance between the tooth bottom of the driven gear and the tooth top of the metal sleeve is 2 mm
With the above, the strength and the durable life of the driven gear can be ensured, and when the distance is set to 4 mm or less, the generation of voids can be prevented and the reduction in strength can be prevented.

It is preferable that the worm wheel and the driven gear in the present invention are injection-molded from a synthetic resin material. Injection molding can reduce molding costs. The gate of the mold for the injection molding is preferably a film gate. Thereby, even if the relative viscosity of the synthetic resin material injected into the cavity of the mold is large,
The cavity can be uniformly filled with a synthetic resin material to prevent a reduction in moldability.

In the present invention, the synthetic resin material for shaping the worm wheel and the driven gear is preferably a nylon-based synthetic resin material. In the case of high-viscosity nylon, the initial strength such as the tensile strength and bending strength of the material itself does not change from that of a synthetic resin material with normal viscosity.However, the worm wheel and driven gear made of high-viscosity nylon have higher root strength, and the viscosity is lower. Even if it becomes higher, the performance related to water absorption and thermal deterioration does not decrease. Further, even if the relative viscosity of the nylon-based synthetic resin material is high, it is excellent in moldability and can extend the life.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An electric power steering apparatus 1 for a vehicle according to a first embodiment shown in FIG. 1 transmits a steering torque generated by steering of a steering wheel 2 to a pinion 4 by a steering shaft 3 so that the steering torque is transmitted. The rack 5 meshing with the pinion 4 is moved. The movement of the rack 5 is tie rod, knuckle arm, etc. (not shown)
The steering angle changes by being transmitted to the wheels 6 via the steering wheel.

In order to apply a steering assist force corresponding to the steering torque transmitted by the steering shaft 3, a torque sensor 7 for detecting the steering torque and a motor (electric actuator) driven in accordance with the detected steering torque ) 8, a metal worm 9 provided on the outer periphery of a drive shaft 50 driven by the motor 8, and a worm wheel 10 meshing with the worm 9 and attached to the steering shaft 3. The rotation of the motor 8 is transmitted from the steering shaft 3 through the worm 9 and the worm wheel 10 to the wheels 6.
, A steering assist force can be applied. As shown in FIG. 2, the drive shaft 50 driven by the motor 8 attached to the housing 21
Are supported via bearings 62 and 63.

The steering shaft 3 includes a first shaft 3a connected to the steering wheel 2, a cylindrical second shaft 3b connected to the first shaft 3a by a pin 22, and an outer periphery of the second shaft 3b. And a third cylindrical shaft 3c that is rotatably fitted through a bush 25. Each shaft 3
A torsion bar 23 is inserted as an elastic member along the centers of a, 3b, and 3c. The torsion bar 23
Is connected to the first shaft 3a and the second shaft 3b by the pin 22, and the other end is connected to the third shaft 3c by the pin 24. Thereby, the second shaft 3b and the third shaft 3c can be elastically rotated relative to each other in accordance with the steering torque.

The second shaft 3b is supported via a bush 31 by a steering column 30 pressed into the housing 21. The third shaft 3c is
The housing 21 is supported via bearings 26 and 27. The worm wheel 10 is integrated with the outer periphery of the metal sleeve 11 fitted on the outer periphery of the third shaft 3c. The sleeve 11 is the third shaft 3
c, and is firmly fixed through a key or the like. Note that a torque limiter mechanism may be provided between the sleeve 11 and the third shaft 3c so that the worm wheel 10 and the steering shaft 3 rotate relatively when an excessive torque is applied.

The torque sensor 7 includes a second shaft 3b
And a second detection ring 37 made of a magnetic material fixed to the third shaft 3c.
And a detection coil 33 that covers a space between the two detection rings 36 and 37. A plurality of teeth 36a provided on the end face of the first detection ring 36 along the circumferential direction;
7, an area facing the plurality of teeth 37a provided along the circumferential direction on the end surface of the second shaft 7 changes according to an elastic relative rotation corresponding to the steering torque of the second shaft 3b and the third shaft 3c.
Since the magnetic resistance to the magnetic flux generated by the detection coil 33 changes in accordance with the change, the steering torque can be detected based on the output of the detection coil 33. The torque sensor 7 may have a known configuration. According to the signal corresponding to the detected steering torque, the motor 8
The rotation of the motor 8 is transmitted to the steering shaft 3 via the worm 9 and the worm wheel 10.

The worm wheel 10, which is a reduction gear for rotating the motor 8, is made of a synthetic resin material and is formed through an injection molding process. The value of the relative viscosity (VR) of the formed worm wheel 10 measured by the formic acid method is 100 or more and 300 or less. In this embodiment, the synthetic resin material is, for example, PA (polyamide) 6, PA
66, PA46, PA12, PA11, PPA (polyparabanic acid), PA6T, PA6.6T and high-viscosity nylon-based synthetic resin materials, and other materials are solid materials filled with nothing.

As the relative viscosity of the worm wheel 10 increases, the viscosity of the synthetic resin pellets used as a raw material also increases. Then, since the viscosity of the solution in which the pellets are melted increases, the formability when the worm wheel 10 is formed by injecting the solution into the cavity of the mold decreases. Therefore, in this embodiment, as shown in FIG. 3, the gate 90 of the mold 90 of the worm wheel 10 is used.
a is a film gate. Thereby, even if the relative viscosity is large, the material can be uniformly filled in the cavity 90b. In order to uniformly fill the cavity 90b with the material, the thickness t of the gate 90a is set.
Is preferably 2.5 mm or more.
The length L is preferably as short as possible, but is preferably 40 mm or more and 50 mm or less because it is necessary to secure mold rigidity. The inlet diameter D1 of the runner 90c is 4 mm or more to reduce the flow resistance of the material. In addition, the diameter of the runner 90c is preferably set to 6 mm or less to reduce the resistance due to a step difference from the diameter of the material injection nozzle (usually 3 mm). It may be equal to the diameter of the gate 90a.

At the time of the injection molding, the sleeve 11
The worm wheel 10 is molded by injecting a synthetic resin material into the molding die 90 in which the worm wheel 10 is inserted, and after the molding, the material filled in the gate 90a and the runner 90c is removed and the teeth of the worm wheel 10 are finished. Etc. are performed by machining. A tooth row along a circle concentric with a circle along the tooth row of the worm wheel 10 is formed on the outer periphery of the sleeve 11 at the joint portion with the worm wheel 10. By filling the synthetic resin material forming the worm wheel 10 into the concave portion 11a between the teeth of the sleeve 11, the relative rotational displacement and the radial relative displacement of the worm wheel 10 and the sleeve 11 around the axis are reduced. Is blocked. Also, by forming the worm wheel 10 so as to embrace both end surfaces of the sleeve 11,
Axial relative displacement between the worm wheel 10 and the sleeve 11 is prevented. The minimum width at the opening of the concave portion 11a of the sleeve 11, that is, the circumferential relative distance at the apex of each tooth on the outer periphery of the sleeve 11 from the adjacent tooth is 1 m
m and 4 mm or less, and the depth of the recess 11a is 4 mm or less. By setting the minimum width of the opening of the concave portion 11a to 1 mm or more, the fluidity of the synthetic resin material at the time of molding can be ensured and the synthetic resin material can be reliably filled in the concave portion 11a. By setting the small width and the depth dimension to 4 mm or less, it is possible to prevent voids and prevent a decrease in strength. The recess 11a
Is not particularly limited, for example, a radius of 0.5 in the axial direction.
mm or more, a spur gear having teeth on the outer periphery of the sleeve 11 having an involute tooth shape, or a knurled shape having a pitch of 1 mm or more. Furthermore, the tooth module at the outer periphery of the sleeve 11 is preferably smaller than the tooth module of the worm wheel 10, so that the torque of the motor 8 is received by the teeth of the worm wheel 10 and at the same time the teeth of the sleeve 11 But you can.

According to the configuration of the first embodiment, the worm wheel 10 for transmitting the rotation of the motor 8 is made of a synthetic resin material, so that the weight and noise can be reduced, and the worm wheel can be reduced. By setting the relative viscosity of the worm wheel to 100 or more, the root strength, fatigue strength and backlash increasing characteristics of the worm wheel can be improved, and by setting the relative viscosity to 300 or less, formability can be ensured. In addition, the worm wheel made of high viscosity nylon has high tooth root strength,
Even if the viscosity increases, the performance regarding water absorption and thermal deterioration does not decrease. The molding cost can be reduced by injection molding the worm wheel 10 from a synthetic resin material. Since the synthetic resin material is a solid material, wear of the worm 9 can be prevented without heat-treating the worm 9.

A vehicle electric power steering apparatus 101 according to a second embodiment shown in FIG.
By transmitting the steering torque generated by the steering in 02 to the pinion 104 by the steering shaft 103, the rack 105 meshing with the pinion 104 is moved. The movement of the rack 105 is transmitted to wheels (not shown) via tie rods, knuckle arms, etc. (not shown), and the steering angle changes.

In order to apply a steering assist force corresponding to the steering torque transmitted by the steering shaft 103, a torque sensor for detecting the steering torque is provided with a sensor housing 122 integrated with a rack housing 121 covering the rack 105. It is built in. The known torque sensor having the same structure as that of the first embodiment can be used. A motor (electric actuator) 108 driven according to a signal corresponding to the detected steering torque is mounted on a motor holder 123 mounted on the rack housing 121.

A rotation transmission mechanism 150 for transmitting the rotation of the motor 108 to the rack 105 is provided. The rotation transmission mechanism 150 is driven by the motor 108 and supported by a motor holder 123 via a bearing 124, and a metal drive-side bevel gear (drive gear) integrated with the drive shaft 151. 152, a driven bevel gear (driven gear) 153 meshing with the driving bevel gear 152, and a rack housing 121 which is inserted into the driven bevel gear 153 via a metal sleeve 154 so as to be able to rotate together therewith.
And a ball screw 157 integrally provided on the outer periphery of the rack 105 so as to mesh with the ball nut 156. Thus, the rotation of the motor 108 is transmitted to the ball nut 156 via the drive-side bevel gear 152 and the driven-side bevel gear 153, and the rotation of the ball nut 156 is converted into the axial displacement of the rack 105 by the ball screw 157. , A steering assist force can be applied. The sleeve 154 is press-fitted into the ball nut 156 or firmly fixed via a key or the like.

The driven bevel gear 153, which is a reduction gear for rotating the motor 108, is made of a synthetic resin material and is formed through an injection molding process. The relative viscosity (VR) of the formed driven bevel gear 153 by the formic acid method is 1
It is set to be 00 or more and 300 or less. In this embodiment, the synthetic resin material is, for example, PA (polyamide) 6, PA
66, PA46, PA12, PA11, PPA (polyparabanic acid), PA6T, PA6.6T.

The synthetic resin constituting the driven bevel gear 153 is filled with reinforcing fibers. The filling ratio of the reinforcing fibers to the synthetic resin material is 5% by weight or more and 60% by weight or less. In this embodiment, glass fibers are filled as the reinforcing fibers. The reinforcing fibers are not limited to glass fibers, but may be filled with, for example, carbon fibers, potassium titanate whiskers, aramid fibers, or the like.

At the time of the injection molding, as shown in FIG. 5, the molding die 19 with the sleeve 154 inserted thereinto.
The driven bevel gear 153 is molded and integrated with the sleeve 154 by injecting the synthetic resin material into the inside. After the molding, the gate 190a and the runner 190c
The removal of the material filled in the gears and the finishing of the teeth of the driven bevel gear 153 are performed by machining.

As shown in FIGS. 6A and 6B, the sleeve 154 has a cylindrical peripheral wall 154a, and one end of the peripheral wall 154a is inserted into the center hole of the driven bevel gear 153. . A projecting portion 154b projecting radially outward from the other end of the peripheral wall 154a;
b has an annular projecting portion 154c projecting from the outer peripheral side toward one end of the peripheral wall 154a. Its annular projection 154
c is a joint portion with the driven side bevel gear 153, where the teeth formed by the plurality of teeth 154d are along a circle concentric with the circle formed by the teeth formed by the teeth 153a of the driven bevel gear 153. Is formed. The synthetic resin material forming the driven bevel gear 153 is filled in the recess 154e between the teeth 154d of the sleeve 154, so that the driven bevel gear 153 and the sleeve 1 are filled.
The relative rotational displacement of the shaft center with respect to 54 is prevented. An annular recess 154f is formed between the outer periphery of the peripheral wall 154a and the inner periphery of the annular protrusion 154c, and the annular recess 154f is formed.
f, the driven bevel gear 153 and the sleeve 1 are filled with the synthetic resin material forming the driven bevel gear 153.
The relative displacement with respect to the radial direction is prevented. The outer end 154c 'of the annular projection 154c projects radially outward from the overhang 154b. Its outer end 15
The driven bevel gear 153 is formed to embrace the driven bevel gear 153 and the sleeve 15c.
4, relative axial displacement is prevented.

The minimum width W1 of the opening of the concave portion 154e between the teeth 154d of the sleeve 154, that is, the circumferential distance at the crest of each tooth 154d on the outer periphery of the sleeve 154 from the adjacent tooth is 1 mm or more and 4 mm. The depth W2 of the recess 154e is set to 4 mm or less. The shape of the concave portion 154e is not particularly limited. For example, the concave portion 154e has a semicircular inner surface having a radius of 0.5 mm or more in the axial direction, or the tooth 154d is
3 and a knurled shape having a pitch of 1 mm or more. Furthermore, the module of the teeth 154d on the outer periphery of the sleeve 154 is made smaller than the module of the teeth of the driven bevel gear 153,
Thereby, the rotational force of the motor 108 is received by the teeth of the driven bevel gear 153 and at the same time, the teeth 154 of the sleeve 154 are received.
d can also be received. The minimum width W3 of the opening of the annular concave portion 154f of the sleeve 154, that is, the peripheral wall 15
4a and the inner circumference of the annular projection 154c are 1
mm or more and 4 mm or less. The annular recess 154
The depth dimension W4 of f is 1 mm or more and 4 mm or less.
The distance W5 between the outer circumference of the overhang 154b and the outer circumference of the outer end 154c 'of the annular projection 154c is 1 mm or more and 4 mm.
It is as follows. The axial distance W6 of the outer periphery of the overhang portion 154b is 1 mm or more and 4 mm or less. The outer periphery of the cross section including the axis at the outer end 154c 'of the annular projection 154c is formed along a semicircle, and the diameter W7 of the semicircle is 1
mm or more and 4 mm or less. The above dimensions W1, W3 ~
When W7 is 1 mm or more, the flowability of the synthetic resin material during molding can be ensured and the synthetic resin material can be reliably filled. Further, by setting the dimensions W1 to W7 to 4 mm or less, it is possible to prevent the occurrence of voids and prevent a decrease in strength. The distance W8 between the tooth bottom of the driven side bevel gear 153 and the tooth top of the sleeve 154 is 2 mm or more and 4 mm or less. By setting the distance W8 to 2 mm or more, the strength and the durability life of the driven-side bevel gear 153 can be secured, and 4 mm
By setting as follows, it is possible to prevent voids from occurring and to prevent a decrease in strength.

According to the configuration of the second embodiment, the driven bevel gear 153 for transmitting the rotation of the motor 108 is made of a synthetic resin material, so that the weight and noise can be reduced. By setting the relative viscosity of the synthetic resin driven bevel gear 153 to a value of 100 or more, which is larger than the conventional value, the tooth root strength can be increased, thereby improving the fatigue strength and the backlash increasing characteristics. Further, by setting the relative viscosity of the driven bevel gear 153 made of a synthetic resin material to 300 or less, formability can be ensured. By filling the synthetic resin material with the reinforcing fibers, a decrease in the strength of the driven-side bevel gear 153 can be prevented, and dimensional change due to water absorption or heat of the synthetic resin material can be prevented, thereby improving dimensional stability. By setting the filling ratio of the reinforcing fibers to the synthetic resin material to 5% by weight or more, the reinforcing fibers can be uniformly dispersed in the synthetic resin material. By setting the filling ratio of the reinforcing fibers to the synthetic resin material at 60% by weight or less, there is no problem due to excessive addition, and the moldability can be ensured. The filling ratio of the reinforcing fibers to the synthetic resin material is more preferably not less than 10% by weight and not more than 30% by weight. In addition, a worm wheel made of high-viscosity nylon has a high root strength, and performance with respect to water absorption and thermal deterioration does not decrease even if the viscosity increases. By molding the driven bevel gear 153 from a synthetic resin material, the molding cost can be reduced. The teeth of the drive-side bevel gear 152 are preferably cured by heat treatment to prevent wear.

The present invention is not limited to the above embodiments.
For example, the synthetic resin material that is the material of the worm wheel in the first embodiment may be filled with 5% by weight or more and less than 10% by weight of the reinforcing fiber, and the filling of the reinforcing fiber causes the synthetic resin material to absorb water or heat. Dimensional change can be prevented to improve dimensional stability. The reinforcing fibers are preferably made of potassium titanate whiskers, aramid fibers or the like in order to prevent wear of the worm meshing with the worm wheel. Further, the synthetic resin material constituting the driven gear in the second embodiment may be a solid material. In the second embodiment, a hypoid gear may be used as the drive gear and the driven gear instead of the bevel gear. In addition, as the material of the worm wheel in the first invention and the driven gear in the second invention, thermoplastic synthetic resin materials such as PPS (polyphenylene sulfide), PES (polyether sulfone), POM (polyacetal) other than nylon are used. You may.

[0034]

Example 1 A root strength test, a fatigue strength test, and a durability test of the worm wheel of the first embodiment were performed. The worm wheel is injection molded from solid PA66 material,
Those having relative viscosities of 50 and 90 by the formic acid method were Comparative Examples a and b, and those having 140, 180 and 200 were Examples c, d and e. The root strength test adds torque to the worm with the worm wheel locked,
The torque applied to the worm when the teeth of the worm wheel were broken was measured as the root strength of the worm wheel. In the fatigue strength test, the steering wheel was reciprocated at a constant rotation angle while a constant load was applied from the wheel side, and the number of reciprocating rotations when teeth of the worm wheel were broken was measured. In the durability test, the steering wheel was reciprocated a fixed number of times at a fixed rotation angle with a constant load applied from the wheel side, and the value of the worm wheel teeth and worm The amount of backlash between the teeth was measured. Table 1 below shows the results of each test. In addition, each measured value is represented by a ratio to the value of Comparative Example a, with the value of Comparative Example a being 1.

[0035]

[Table 1]

From the first embodiment, it can be confirmed that according to the first aspect of the present invention, it is possible to improve the strength, the life, and the backlash increasing characteristic of the synthetic resin worm wheel.

[0037]

Example 2 A tooth root strength test of the driven bevel gear of the second embodiment was performed. An example in which the driven bevel gear was injection molded from a solid material of PA66 having a relative viscosity of 180 by the formic acid method, and a PA having a relative viscosity of 60 by the formic acid method.
What was injection-molded from 66 solid materials was used as a comparative example. In the tooth root strength test, torque is applied to the drive bevel gear while the driven bevel gear is locked, and the torque applied to the drive bevel gear when the tooth of the driven bevel gear is damaged is applied to the tooth strength of the driven bevel gear. Was measured.
As a result, the torque of the comparative example was 35 Nm, and the torque of the example was 51 Nm. According to the second embodiment of the present invention, it can be confirmed that the strength of the synthetic resin drive-side bevel gear can be improved.

[0038]

According to the present invention, the strength of the synthetic resin worm wheel, bevel gear, and hypoid gear for transmitting the rotation of the electric actuator for generating steering assist force is improved, and the electric actuator can be increased in output. It is possible to provide an electric power steering device capable of saving space by reducing the diameter of the driven gear, and preventing a decrease in performance relating to water absorption and thermal deterioration and extending the life.

[Brief description of the drawings]

FIG. 1 is a sectional view of an electric power steering device according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is an explanatory diagram of a configuration of a worm wheel forming die according to the first embodiment of the present invention.

FIG. 4 is a sectional view of an electric power steering apparatus according to a second embodiment of the present invention.

FIG. 5 is a configuration explanatory view of a molding die of a driven-side bevel gear according to a second embodiment of the present invention.

FIG. 6 is a sectional view of a driven bevel gear and a sleeve in an electric power steering apparatus according to a second embodiment of the present invention, and FIG. 6 is a partial plan view of the sleeve.

[Explanation of symbols]

 6 wheel 8, 108 motor 9 worm 10 worm wheel 11 sleeve 152 drive-side bevel gear 153 driven-side bevel gear 154 sleeve

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F16H 55/17 F16H 55/17 Z // C08L 77:00 C08L 77:00 F term (reference) 3D033 CA04 3J009 DA16 DA17 EA16 EA19 EA23 EA32 EB06 FA08 3J030 BA02 BA03 BB16 BC08 CA10 4F072 AA02 AB09 AD44 AG04 AH05 AK04 AK15 AL16

Claims (13)

[Claims] An electric power steering device for transmitting the rotation of an electric actuator for generating a steering assist force to wheels via a worm and a worm wheel meshing with the worm, wherein the worm wheel is formed of a synthetic resin material, An electric power steering device, wherein a relative viscosity of the formed worm wheel by a formic acid method is 100 or more and 300 or less. 2. The electric power steering apparatus according to claim 1, wherein said synthetic resin material is a solid material. 3. The electric power steering apparatus according to claim 1, wherein the synthetic resin material is filled with reinforcing fibers, and a filling ratio of the reinforcing fibers to the synthetic resin material is 5% by weight or more and less than 10% by weight. . 4. The electric power steering apparatus according to claim 1, wherein said worm wheel is injection-molded from said synthetic resin material. 5. The worm wheel is integrated with a metal sleeve, and the worm wheel is formed by injecting a synthetic resin material into a mold in which the metal sleeve is inserted. At the joint between the worm wheel and the worm wheel, a dentition is formed along a circle concentric with a circle along which the worm wheel is formed, and a synthetic resin material constituting the worm wheel is formed on the metal sleeve. By filling the recesses between the teeth, the relative rotational displacement of the worm wheel and the metal sleeve about the axis is prevented, and the tooth module in the sleeve is smaller than the worm wheel tooth module. The electric power steering device according to claim 4. 6. A synthetic resin material constituting the worm wheel is filled in a concave portion formed in the metal sleeve, so that relative rotation displacement between the worm wheel and the metal sleeve is prevented. The minimum width of the opening of the recess in the metal sleeve is 1 mm or more and 4 mm or less, and the depth of the recess in the metal sleeve is 4 m.
The electric power steering device according to claim 5, wherein m is equal to or less than m. 7. The rotation of an electric actuator for generating a steering assist force is transmitted to wheels via a drive gear constituted by a bevel gear or a hypoid gear and a bevel gear engaged with the bevel gear or a driven gear constituted by a hypoid gear engaged with the hypoid gear. In the electric power steering apparatus for transmitting power, the driven gear is formed of a synthetic resin material, and the formed driven gear has a relative viscosity of 100 or more and 300 or less by a formic acid method. . 8. The synthetic resin material is filled with reinforcing fibers, and the filling ratio of the reinforcing fibers to the synthetic resin material is set to 5% by weight or more and 60% by weight or less. Electric power steering device. 9. An electric power steering apparatus according to claim 7, wherein said synthetic resin material is a solid material. 10. The electric power steering apparatus according to claim 7, wherein said driven gear is injection-molded from said synthetic resin material. 11. The driven gear is integrated with a metal sleeve, and the driven gear is formed by injecting a synthetic resin material into a molding die in which the metal sleeve is inserted. At the joint with the driven gear in the sleeve made of the driven gear, a tooth row is formed along a circle concentric with the circle along which the tooth row of the driven gear is formed, and a synthetic resin material constituting the driven gear is formed on the metal sleeve. By filling the recesses between the teeth, the relative rotational displacement of the driven gear and the metallic sleeve about the axis is prevented, and the tooth module in the sleeve is made smaller than the tooth module of the driven gear. The electric power steering device according to claim 10. 12. A synthetic resin material constituting said driven gear,
By filling the recess formed in the metal sleeve, the relative rotational displacement between the driven gear and the metal sleeve is prevented, and the minimum width of the opening of the recess in the metal sleeve is 1 mm or more and 4 mm or less. 12. The electric power steering apparatus according to claim 11, wherein a depth dimension of the concave portion in the metal sleeve is 4 mm or less. 13. An electric power steering apparatus according to claim 1, wherein said synthetic resin material is a nylon-based synthetic resin material.