JP6390314B2 - Electric power steering device - Google Patents

Description

  The present invention is used as a steering device for an automobile. By using an electric motor as auxiliary power, the improvement of an electric power steering device for reducing the force required for the driver to operate the steering wheel is improved. About.

  Power steering devices are widely used as devices for reducing the force required for the driver to operate the steering wheel when giving a steering angle to the steered wheels (usually the front wheels except for special vehicles such as forklifts). It is used. In addition, an electric power steering apparatus that uses an electric motor as an auxiliary power source in such a power steering apparatus has begun to spread in recent years. Compared with a hydraulic power steering device, the electric power steering device is advantageous in that it can be made smaller and lighter, can easily control the magnitude (torque) of auxiliary power, and has less engine power loss.

  Various structures of the electric power steering apparatus are known. In any structure, the electric motor is mounted on the rotating shaft that is rotated by the operation of the steering wheel and gives a steering angle to the steered wheels in accordance with the rotation. The auxiliary power is applied through a reduction gear. In general, a worm reducer is used as the reducer. In the case of an electric power steering device using a worm speed reducer, a worm that is rotationally driven by the electric motor and a worm wheel that rotates together with the rotating shaft are engaged with each other, and auxiliary power of the electric motor is applied to the rotating shaft. Communicate freely.

  For example, Patent Document 1 discloses an electric power steering device as shown in FIGS. A front end portion of a steering shaft 2 that is a rotating shaft that is rotated in a predetermined direction by the steering wheel 1 is rotatably supported inside the housing 3, and the worm wheel 4 is fixed to this portion. Worm teeth 5 meshing with the worm wheel 4 are provided in the axial direction intermediate portion of the worm shaft 6, and both ends of the worm 8 driven to rotate by the electric motor 7 are paired with a pair of rolling bearings 9 a such as a deep groove ball bearing, 9b is rotatably supported in the housing 3. In this state, the worm wheel 4 and the worm teeth 5 are engaged with each other so that the auxiliary power of the electric motor 7 can be transmitted to the worm wheel 4.

  FIG. 9 shows a more specific structure of the electric power steering apparatus. The worm wheel 4a is externally fixed by an interference fit or the like between the pair of rolling bearings 11a and 11b in the rotating shaft 10 serving as an output portion of the electric power steering apparatus, and rotates together with the rotating shaft 10. I try to do it. The rotary shaft 10 is coupled to the front end portion of the steering shaft 2a by a torsion bar 12 in a state in which only the rotation is supported by the rolling bearings 11a and 11b in the housing 3a. The electric motor 7 (see FIGS. 7 to 8) rotates the worm 8a according to the direction and magnitude of the torque applied to the steering shaft 2a detected by the torque sensor 13, and supplies auxiliary torque to the rotary shaft 10. Give. The rotation of the rotating shaft 10 is transmitted to the input shaft of the steering gear unit 16 via the pair of universal joints 14a and 14b and the intermediate shaft 15, and gives a desired steering angle to the steered wheels.

  In the case of the conventional electric power steering apparatus as described above, grease (lubricating oil) is applied to the housing 3 (3a) in order to ensure lubricity of the meshing portion between the worm wheel 4 (4a) and the worm teeth 5. Filled. However, as will be described later, in the case of the conventional structure, there is room for improvement from the aspect of continuously supplying grease to the meshing portion of the worm wheel 4 (4a) and the worm tooth 5 over a long period of time. is there. That is, in the housing 3 (3a), the fitting cylinder part 20 of the cover 19 is fitted into the opening 18 of the main body part 17 by gap fitting, and the main body part 17 and the cover 19 are coupled and fixed by the bolts 21 and 21. It is composed by doing. A small gap is provided between the opening 18 of the main body portion 17 and the outer peripheral surface of the fitting cylinder portion 20 of the cover 19 in order to ensure ease of assembly of the housing 3 (3a). It has been. Therefore, when the base oil in the grease adhering to the vicinity of the fitting part (joining part) between the opening 18 and the fitting cylinder part 20 is separated (separated) from the thickener, the separated base oil is converted into a capillary tube. Due to a phenomenon, there is a possibility that leakage occurs between the opening 18 and the outer peripheral surface of the fitting cylinder portion 20 to the outside of the housing 3 (3a), adheres to the vehicle interior, and causes stain. . In view of such circumstances, in the case of the illustrated example, an O-ring 26 is provided between the base portion of the fitting tube portion 20 and the opening portion 18 to prevent leakage of the base oil. .

  Further, as the worm wheel 4 (4a) and the worm teeth 5 are engaged with each other, a part of the grease applied to the engagement portions of the worm wheel 4 (4a) and the worm teeth 5 is released from the engagement portions. It is pushed out and adheres to the inner surface of the housing 3 (3a) (sticks and stops in place). If the grease adheres to the inner surface of the housing 3 (3a), it is difficult to supply the grease to the meshing portion again, and there is a possibility that the grease is insufficient at the meshing portion. On the other hand, it is conceivable to apply a large amount of grease to the meshing portion between the worm wheel and the worm tooth of the worm shaft to ensure lubrication of this meshing portion over a long period of time. However, if a large amount of grease is applied to the meshing portion, the stirring resistance of the grease increases at a low temperature, and it becomes impossible to apply a desired amount of auxiliary power to the worm wheel (steering shaft). It may increase.

JP 2011-094763 A

  In view of the circumstances as described above, the present invention has been invented to realize a structure capable of supplying high-quality grease over a long period of time to the meshing portion between the worm wheel and the worm tooth of the worm shaft. is there.

The electric power steering apparatus of the present invention includes a housing, a rotating shaft, a worm wheel, and an electric motor.
Of these, the housing is supported by a fixed portion and does not rotate. Specifically, such a housing is formed by closing the opening of the main body with a cover.
The rotating shaft is rotatably provided with respect to the housing, and is rotated by an operation of a steering wheel, and gives a steering angle to the steered wheels in accordance with the rotation.
The worm wheel is supported on a part of the rotating shaft inside the housing, concentrically with the rotating shaft, and rotates together with the rotating shaft.
The worm is formed by providing worm teeth at an axially intermediate portion of the worm shaft, and is supported rotatably with respect to the housing in a state where the worm teeth are engaged with the worm wheel.
The electric motor rotationally drives the worm.

In particular, in the electric power steering apparatus of the present invention, the housing is configured by closing the opening of the hollow cylindrical main body with a cover. And at least the inner surface of the housing housing the worm wheel, the portion of the main body portion and the cover that are in contact with each other, the side surface of the worm wheel, and the tip surface of the worm wheel are oil-repellent. The coating layer is formed.

Preferably when implementing an electric power steering apparatus of such the present invention described above, the pre-Symbol coating layer, also formed in the tooth crest of the worm surfaces.
Moreover, when implementing the electric power steering apparatus of this invention, you may form the said coating layer in the part which remove | deviated from the said worm tooth among the said worm shafts.
The coating layer may also be formed on the inner surface of a portion of the housing that houses the worm.

Further, when practicing the present invention, such as described above, specifically, the pre-Symbol coating layer, a fluorine resin and a fluorine resin paint film formed by being applied by spray or brush.

The electric power steering apparatus of the present invention configured as described above can supply high-quality grease over a long period of time to the meshing portion between the worm wheel and the worm teeth of the worm shaft.
That is, since an oil-repellent coating layer is formed on the inner surface of the housing that accommodates the worm wheel, the base oil in the grease sealed inside the housing adheres to the inner surface of the housing. The contact angle can be increased. For this reason, it can prevent that this base oil leaks outside from the junction part of the main-body part which comprises this housing, and a cover by capillary action. As a result, it is possible to suppress the occurrence of stains due to the grease adhering to the vehicle interior. Further, it is possible to suppress the grease from adhering to the inner surface of the housing. Accordingly, good quality grease can be supplied over a long period of time to the meshing portion of the worm wheel and the worm shaft worm, and the durability of the electric power steering apparatus can be improved.

Sectional drawing which shows one example of embodiment of this invention. XX sectional drawing of FIG. Sectional drawing (A) which takes out and shows the main-body part which comprises a housing, and the partial cut end view (B) which shows the state seen from the left of (A). Sectional drawing (A) which takes out and shows the cover which comprises a housing, and end view (B) which shows the state seen from the right side of (A). The side view (A) which takes out and shows a worm wheel, and the side view (B) shown in the state before giving gear cutting to this worm wheel. The side view which takes out and shows a worm shaft. The partial cutaway side view which shows an example of the steering device of conventional structure. FIG. 8 is an enlarged YY sectional view of FIG. 7. The figure which shows a more specific structure and is equivalent to the ZZ cross section of FIG.

  1 to 6 show an example of an embodiment of the present invention. A feature of the present invention, including this example, is that high-quality grease is supplied over a long period of time to the meshing portion of the worm wheel and the worm shaft worm. The electric power steering apparatus of the present example has basically the same configuration as the electric power steering apparatus shown in FIGS. 7 to 9 described above, and includes a steering shaft 2a that is rotated in a predetermined direction by the steering wheel 1. The front end is rotatably supported inside the housing 3b, and the worm wheel 4b is fixed to the rotary shaft 10 coupled to the front end of the steering shaft 2a via the torsion bar 12. In the case of this example, the housing 3b is configured such that the fitting cylinder portion 20 of the cover 19a is fitted in the opening 18 of the main body portion 17a, and the main body portion 17a and the cover 19a are coupled and fixed by bolts 21 and 21. It is configured. Of these, the main body portion 17a has a hollow cylindrical shape as a whole, and has a small-diameter portion 22 that houses the base half portion (the right half portion in FIG. 2) of the rotary shaft 10 that is rotationally driven by the electric motor 7. The large diameter portion 23 surrounding the outer periphery of the worm wheel 4b, the annular portion 24 connecting the small diameter portion 22 and the large diameter portion 23, and the worm provided in a state where a part of the large diameter portion 23 is opened. And an accommodating portion 25. The central axis of the large-diameter portion 23 and the central axis of the worm accommodating portion 25 are in a twisted positional relationship with each other. The cover 19a closes the opening 18 by fitting the fitting cylinder 20 into an opening 18 provided at the tip of the large diameter portion 23 constituting the main body 17a. Both the main body 17a and the cover 19a are made by die-casting an aluminum light alloy. However, the main body 17a and the cover 19a may be made of synthetic resin. In the case of this example, a sealing material such as an O-ring 26 (see FIG. 9) is not provided between the base of the fitting cylinder 20 and the opening 18.

  The worm wheel 4b is externally fixed by an interference fit or the like between the pair of rolling bearings 11c and 11d in the rotary shaft 10 serving as an output portion of the electric power steering device. It is trying to rotate with. The worm wheel 4b is manufactured by connecting and fixing a synthetic resin tooth portion 29 around a metal wheel portion 28 for the purpose of reducing the manufacturing cost and reducing the weight. The rotating shaft 10 is supported in the housing 3b by the both rolling bearings 11c and 11d so as to be rotatable only. That is, the bearing holding part provided in the axial direction intermediate part of the rotating shaft 10 on the inner diameter side of the annular part 24 constituting the main body part 17a by one of the rolling bearings 11c and 11d. 27a is rotatably supported, and the portion near the tip of the rotating shaft 10 (the portion near the left end in FIG. 2) can be rotated by the other rolling bearing 11d to a bearing holding portion 27b provided on the inner diameter side of the cover 19a. I support it. In the case of this example, one of the rolling bearings 11c and 11d is not provided with seals at both ends of the cylindrical space between the inner peripheral surface of the outer ring and the outer peripheral surface of the inner ring. Open type.

  Both ends of the worm 8b are rotatably supported in the worm accommodating portion 25 of the housing 3b by a pair of rolling bearings 9a and 9b which are deep groove type ball bearings. A worm tooth 5a is provided at an axially intermediate portion of the worm shaft 6a of the worm 8b, and the worm tooth 5a is engaged with the worm wheel 4b so that auxiliary power of the electric motor 7 can be transmitted to the worm wheel 4b. Yes. The electric motor 7 rotationally drives the worm 8b according to the direction and magnitude of the torque applied to the steering shaft 2a detected by the torque sensor 13, and applies auxiliary torque to the rotating shaft 10. The rotation of the rotating shaft 10 is transmitted to the input shaft of the steering gear unit 16 via the pair of universal joints 14a and 14b and the intermediate shaft 15, and gives a desired steering angle to the steered wheels.

  In the electric power steering apparatus of this example, the housing 3b is filled with grease in order to ensure the lubricity of the meshing portion between the worm wheel 4b and the worm teeth 5a. In the case of this example, of the inner surface of the housing 3b, the inner peripheral surface of the large-diameter portion 23 of the main body portion 17a and the one side surface of the annular ring portion 24 (the oblique lattice in FIG. And an oil-repellent coating layer is formed on the other side surface of the cover 19a (portion shown with a diagonal lattice in FIG. 4). This coating layer is provided by applying a fluorine resin such as polytetrafluoroethylene resin (PTFE) by spraying or brushing. Further, in the case of this example, the oil repellency is also applied to the side surface and the tooth tip surface of the worm wheel 4b and the tooth tip surface (portion shown with a diagonal grid in FIG. 5) and the tooth tip surface of the worm tooth 5a. The coating layer is formed. Further, a synthetic resin mixed with a highly lipophilic material may be exposed on the tooth surface of the tooth portion 29 of the worm wheel 4b. That is, in the worm wheel 4b, a synthetic resin tooth portion 29 such as nylon resin or polyamide 6 (PA6) is coupled and fixed around the metal wheel portion 28 in order to reduce manufacturing cost and weight. Although it is comprised by the thing, the material more lipophilic than this synthetic resin can also be mixed in the synthetic resin which comprises this tooth | gear part 29. FIG. In this case, specifically, a synthetic resin mixed with a highly lipophilic material is bonded and fixed around the wheel portion 28 of the wheel material 30 as shown in FIG. And the oil-repellent coating layer is formed by apply | coating a fluororesin to the surface (both sides and outer peripheral surface) of this synthetic resin. Thereafter, the outer peripheral surface of the wheel material 30 is cut by a hobbing machine to provide an oil-repellent coating layer on the side surface and the tooth tip surface of the tooth portion 29 of the worm wheel 4b, and the worm teeth 5a. A synthetic resin material in which a highly lipophilic material is mixed is exposed on the tooth surface meshed with. Further, in order to form a coating layer on the tooth tip surface of the worm tooth 5a, a fluororesin is applied to the outer peripheral surface of the synthetic resin material before the worm tooth 5a is formed on the material of the worm shaft 6a. By doing so, an oil-repellent coating layer is formed in advance. Then, by forming (cutting out) the worm teeth 5a, an oil-repellent coating layer is provided on the tooth tip surface of the surface of the worm teeth 5a. In addition to this tooth tip surface, an oil-repellent coating layer is also provided on a portion of the worm shaft 6a that is axially deviated from the worm tooth 5a (portion shown with a diagonal lattice in FIG. 6). May be.

According to the electric power steering apparatus of this example as described above, good quality grease can be supplied over a long period of time to the meshing portion of the worm wheel 4b and the worm tooth 5a.
That is, of the inner surface of the housing 3b, the inner peripheral surface of the large-diameter portion 23 of the main body portion 17a and one side surface of the circular ring portion 24, the other side surface of the cover 19a, the side surface of the tooth portion 29 of the worm wheel 4b, and An oil-repellent coating layer is formed on the tooth tip surface and the tooth tip surface of the worm tooth 5a. For this reason, the contact angle with respect to the base oil in the grease sealed inside the housing 3b can be increased (specifically, it is larger than 60 °, preferably 90 ° or more). The base oil can be prevented from leaking to the outside by a capillary phenomenon from a joint portion (a portion between the opening portion 18a and the outer peripheral surface of the fitting tube portion 20) between the main body portion 17a and the cover 19a. Occurrence of stains due to adhering to the passenger compartment can be suppressed. At the same time, it is possible to prevent the grease from adhering to the inner surface of the housing 3b (sticking and stopping in place). Therefore, good quality grease can be supplied over a long period of time to the meshing portion between the worm wheel 4b and the worm tooth 5a.

  Particularly in the case of this example, since the main body 17a and the cover 19a constituting the housing 3b are made by light alloy die casting, a large number of minute irregularities are formed on the surfaces of the main body 17a and the cover 19a. Has been. For this reason, compared with the case where the main body portion 17a and the cover 19a are made by a machining method with few minute uneven portions formed on the surface after machining, such as machining such as cutting and grinding, The oil repellency of the coating layer can be improved. Furthermore, the manufacturing cost of the housing 3b can be reduced by reducing the processing cost. Further, in the case of this example, a seal such as an O-ring 26 (see FIG. 9) or the like as provided in the case of the conventional structure described above is provided between the base portion of the fitting tube portion 20 and the opening portion 18. Since there is no need to provide a material, the cost can be reduced also from this aspect.

  Further, in the case of this example, since the synthetic resin material mixed with a highly lipophilic material is exposed on the tooth surface of the tooth portion 29 of the worm wheel 4b, the grease can be easily attached to the tooth surface. Therefore, the meshing portion can be lubricated for a long period of time, and the durability of the electric power steering apparatus can be further improved.

In the case of this example, one of the pair of rolling bearings 11c and 11d that rotatably supports the rotary shaft 10 is connected between the inner peripheral surface of the outer ring and the outer peripheral surface of the inner ring. It is an open type in which no seal is provided at both ends of the cylindrical space. For this reason, it is possible to prevent the pressure in the housing 3b from increasing as the temperature in the housing 3b rises during the operation of the electric power steering apparatus, and the grease filled in the housing 3b can be prevented. Leakage to the outside can be prevented.
In carrying out the present invention, in addition to the inner peripheral surface of the large-diameter portion 23 of the main body portion 17a, one side surface of the annular ring portion 24, and the other side surface of the cover 19a among the inner surface of the housing 3b, An oil-repellent coating layer may be provided on other portions such as the inner peripheral surface of 25 and the front end surface of the fitting tube portion 20.

DESCRIPTION OF SYMBOLS 1 Steering wheel 2, 2a Steering shaft 3, 3a, 3b Housing 4, 4a, 4b Worm wheel 5, 5a Worm tooth | gear 6, 6a Worm shaft 7 Electric motor 8, 8a, 8b Worm 9a, 9b Rolling bearing 10 Rotating shaft 11a- 11d Rolling bearing 12 Torsion bar 13 Torque sensor 14a, 14b Universal joint 15 Intermediate shaft 16 Steering gear unit 17, 17a Main body part 18 Opening part 19, 19a Cover 20 Fitting cylinder part 21 Bolt 22 Small diameter part 23 Large diameter part 24 Circle Part 25 Worm housing part 26 O-ring 27a, 27b Bearing holding part 28 Wheel part 29 Tooth part 30 Wheel material

Claims (4)

A non-rotating housing supported by a fixed part;
A rotating shaft provided rotatably with respect to the housing, rotated by an operation of a steering wheel, and giving a steering angle to a steered wheel in accordance with the rotation;
A worm wheel that is supported concentrically with the rotating shaft and rotates together with the rotating shaft in a part of the rotating shaft inside the housing;
A worm that is formed by providing a worm tooth at an axially intermediate portion of the worm shaft, and is rotatably supported inside the housing in a state where the worm tooth is engaged with the worm wheel;
In an electric power steering apparatus provided with an electric motor for rotationally driving the worm,
The housing is configured by closing the opening of the hollow cylindrical main body with a cover,
Oil repellent coating on at least the inner surface of the housing housing the worm wheel, the portion of the main body portion and the cover that are in contact with each other, and the side surface and the tooth tip surface of the worm wheel. An electric power steering device characterized by forming a layer.   The electric power steering apparatus according to claim 1, wherein the coating layer is also formed on a tooth tip surface of the surface of the worm. 3. The electric power steering apparatus according to claim 1, wherein the coating layer is also formed on a portion of the worm shaft that is axially detached from the worm teeth.   The electric power steering apparatus according to any one of claims 1 to 3, wherein the coating layer is a fluororesin coating film.

Images