JP2022170823A - electric power steering device - Google Patents

Abstract

To provide an electric power steering device that can decrease the number of components and facilitate assembly operation.SOLUTION: An electric power steering device includes: an input shaft (inner shaft) 46; an output shaft 12 disposed coaxially with the input shaft on the front side in an axial direction of the input shaft; a torque sensor 14 disposed on the outer side in a radial direction of the input shaft; a worm wheel 16 externally fixed on an outer circumferential surface of the output shaft 12; a worm 17 rotatably driven by an electric motor; and a housing case 10 including a sensor housing 28 and a gear housing 29 that are connected to each other. The sensor housing 28 houses the torque sensor 14. The gear housing 29 houses the worn wheel 16 and the worm 17. The output shaft 12 is rotatably supported by the housing case 10 with only one rolling bearing 18 supported by the gear housing 29.SELECTED DRAWING: Figure 2

Description

The present invention relates to an electric power steering system.

In the steering system of an automobile, when the steering wheel is rotated by the driver's operation, the rotation of the steering wheel is transmitted to the pinion shaft of the steering gear unit via the steering shaft and the intermediate shaft, and the rack shaft of the steering gear unit is rotated. Converted to linear motion. As a result, the pair of tie rods is pushed and pulled, and a steering angle corresponding to the amount of operation of the steering wheel is imparted to the pair of steered wheels.

Also, in recent years, an electric power steering apparatus has become widespread, which uses an electric motor as an auxiliary power source to reduce the force required for the driver to operate the steering wheel. An electric power steering device includes an electric assist device that generates auxiliary power. The electric assist device includes a worm speed reducer capable of obtaining a large reduction ratio as a speed reducer for increasing the torque of the electric motor. The worm speed reducer includes a worm having worm teeth on its outer peripheral surface and a worm wheel having wheel teeth that mesh with the worm teeth on its outer peripheral surface.

FIG. 10 shows the structure described in International Publication No. 2019/139060 as an example of an electric assist device that constitutes a conventional electric power steering device. The electric assist device 100 includes an input shaft 101, an output shaft 102, a torque sensor 103, a worm wheel 104, a worm 105, a housing case 106, a pair of rolling bearings 107a and 107b, and an electric motor 111 (not shown). and

The input shaft 101 is a steering force transmission member that is rotationally driven based on the operation of the steering wheel. The output shaft 102 is a steering force transmission member arranged axially forward of the input shaft 101 and coaxial with the input shaft 101 . The torque sensor 103 is arranged radially outside the input shaft 101 . The worm wheel 104 is fitted and fixed to the outer peripheral surface of the output shaft 102 . A worm 105 is meshed with the worm wheel 104 . Housing case 106 has a sensor housing 108 and a gear housing 109 coupled together. A sensor housing 108 houses the torque sensor 103 . Gear housing 109 accommodates worm wheel 104 and worm 105 . A pair of rolling bearings 107 a and 107 b rotatably supports the output shaft 102 with respect to the housing case 106 at two front and rear positions with the worm wheel 104 interposed therebetween. The electric motor 111 is supported by the housing case 106 . Regarding the electric power steering device, the front-rear direction refers to the front-rear direction of the vehicle.

The front rolling bearing 107a of the pair of rolling bearings 107a and 107b is supported by the gear housing 109, and the rear rolling bearing 107b of the pair of rolling bearings 107a and 107b is supported by the gear housing. It is supported by an intermediate plate 110 located between the sensor housing 108 and the gear housing 109, which is a different part from 109.

An electric power steering device having such an electric assist device 100 measures the steering torque input from the steering wheel with the torque sensor 103, and controls energization of the electric motor 111 based on this measurement signal. The torque of the electric motor 111 is increased by being transmitted to the worm wheel 104 via the worm 105 and then applied to the output shaft 102 as auxiliary power. This reduces the force required by the driver to operate the steering wheel.

WO2019/139060

The conventional electric power steering system as described above still has room for improvement. That is, in the conventional electric power steering device, a pair of rolling bearings 107a and 107b are used to rotatably support the output shaft 102 with respect to the housing case 106. The front rolling bearing 107a of 107b is supported by the gear housing 109, and the rear rolling bearing 107b of the pair of rolling bearings 107a and 107b is an intermediate plate 110 which is a component different from the gear housing 109. supported by As a result, not only does the number of parts including the number of rolling bearings increase, but assembly work tends to be complicated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electric power steering apparatus that reduces the number of parts and facilitates assembly work.

An electric power steering device according to one aspect of the present invention includes an input shaft, an output shaft, a torque sensor, a worm wheel, a worm, a housing case, and one rolling bearing.
The input shaft is rotationally driven based on the operation of the steering wheel.
The output shaft is arranged axially forward of the input shaft and coaxial with the input shaft.
The torque sensor is arranged radially outwardly of the input shaft.
The worm wheel has wheel teeth on its outer peripheral surface and is fitted and fixed to the outer peripheral surface of the output shaft.
The worm has worm teeth meshing with the wheel teeth on its outer peripheral surface, and is rotationally driven by an electric motor.
The housing case has a sensor housing and a gear housing coupled together.
The sensor housing accommodates the torque sensor.
The gear housing accommodates the worm wheel and the worm.
The output shaft is rotatably supported by the housing case using only the one rolling bearing supported by the gear housing.

In the electric power steering device of one aspect of the present invention, the rolling bearing includes an outer ring, an inner ring, and a plurality of rolling elements arranged between the outer ring and the inner ring, and the plurality of rolling elements is 50% or more of the outer diameter of the wheel tooth.

In one aspect of the electric power steering device of the present invention, the rolling bearing is arranged axially forward of the wheel teeth.

In this case, in the electric power steering apparatus according to one aspect of the present invention, the base of the yoke of the universal joint is externally fitted and fixed to the outer peripheral surface of the axially front side portion of the output shaft, and the axially rearward side of the base is fixed. is disposed radially inward of the rolling bearing.

In one aspect of the electric power steering device of the present invention, the rolling bearing is arranged axially rearward of the wheel teeth.

In one aspect of the electric power steering device of the present invention, the rolling bearing includes an outer ring, an inner ring, and a plurality of rolling elements arranged between the outer ring and the inner ring, and the outer ring is the gear housing. and the inner ring is supported by the worm wheel.

The electric power steering device according to one aspect of the present invention further includes a sealing member that seals between the worm wheel and the housing case.

In one aspect of the electric power steering device of the present invention, the sealing member seals between the worm wheel and the gear housing.

According to the electric power steering device of one aspect of the present invention, the number of parts can be reduced and the assembly work can be easily performed.

FIG. 1 is a partially cutaway side view showing an electric power steering apparatus according to a first embodiment of the invention. FIG. 2 is a diagram schematically showing the AA section of FIG. FIG. 3 is a schematic view of the worm, the outer wheel member of the worm wheel, and only one rolling bearing taken out and viewed from the axial direction. FIG. 4 is a diagram corresponding to FIG. 2 showing the structure of a comparative example with respect to the first example of the embodiment of the invention. FIG. 5 is a diagram corresponding to FIG. 2, showing a second example of the embodiment of the present invention. FIG. 6 is a diagram corresponding to FIG. 2 showing a third embodiment of the present invention. FIG. 7 is a diagram corresponding to FIG. 2, showing a fourth example of the embodiment of the present invention. FIG. 8 is a diagram corresponding to FIG. 2, showing a fifth example of the embodiment of the present invention. FIG. 9 is a diagram corresponding to FIG. 2, showing a sixth example of the embodiment of the present invention. FIG. 10 is a cross-sectional view of an electric assist device that constitutes a conventional electric power steering device.

[First example of embodiment]
A first example of an embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG.

In the following description of the electric power steering device 1, the front-rear direction refers to the front-rear direction of the vehicle. Specifically, the left side of FIGS. 1 and 2 is the front side, and the right side of FIGS. 1 and 2 is the rear side.

The electric power steering device 1 of this example is a column assist type electric power steering device, and includes a steering wheel 2, a steering shaft 3, a steering column 4, a pair of universal joints 5a and 5b, and an intermediate shaft 6. , a steering gear unit 7 , a pair of tie rods 8 , and an electric assist device 9 .

The steering wheel 2 is fixed to the rear end of the steering shaft 3 rotatably supported inside the steering column 4 . A front end of the steering shaft 3 is inserted inside a housing case 10 fixed to a front end of the steering column 4 and connected to an output shaft 12 via a torsion bar 11 .

Rotation of the output shaft 12 is transmitted to the pinion shaft 13 of the steering gear unit 7 via the pair of universal joints 5 a and 5 b and the intermediate shaft 6 . By converting the rotation of the pinion shaft 13 into the linear motion of a rack shaft (not shown), the pair of tie rods 8 are pushed and pulled to impart a steering angle to the steered wheels.

The structure of this example also has a telescopic mechanism for adjusting the front-rear position of the steering wheel 2 . For this reason, the steering column 4 is configured such that the front end of a tubular outer column 45 is fitted onto the rear end of the tubular inner column 44 so as to be relatively displaceable in the axial direction. is configured to be extendable. Further, the steering shaft 3 is configured by spline-engaging the inner peripheral surface of the front end portion of the tubular outer shaft 47 with the outer peripheral surface of the rear end portion of the inner shaft 46 so that the inner shaft 46 and the outer shaft 47 are connected. 47, and the entire length can be expanded and contracted. The outer shaft 47 is rotatably supported inside the outer column 45 by a ball bearing (not shown) with its rear end protruding rearward from the outer column 45 . Therefore, when adjusting the longitudinal position of the steering wheel 2 fixed to the rear end of the outer shaft 47 , the outer column 45 along with the outer shaft 47 moves in the longitudinal direction with respect to the inner column 44 and the inner shaft 46 . The displacement causes the steering shaft 3 and the steering column 4 to expand and contract.

The electric assist device 9 is a device that generates an assist torque for reducing the force required for the driver to operate the steering wheel 2 . The electric assist device 9 of this example includes an output shaft 12 , a torque sensor 14 , a worm reduction gear 15 having a worm wheel 16 and a worm 17 , a housing case 10 and one rolling bearing 18 . Further, the electric assist device 9 of this example further includes a torsion bar 11, an electric motor 19, a seal member 20, and an ECU (not shown).

The output shaft 12 is arranged coaxially with the inner shaft 46 on the front side of the inner shaft 46 corresponding to the input shaft. The inner shaft 46 and the output shaft 12 are connected via the torsion bar 11 . In the case of carrying out the present invention, the input shaft can also be configured by a shaft separate from the steering shaft, which is coupled to the front end of the steering shaft so as to be capable of transmitting torque.

The torque sensor 14 is arranged radially outside the front end of the steering shaft 3 and is capable of detecting the twist direction and amount of the torsion bar 11 .

The worm wheel 16 has wheel teeth 21 on its outer peripheral surface and is fitted and fixed to the outer peripheral surface of the output shaft 12 . Specifically, the worm wheel 16 is fitted onto the outer peripheral surface of the output shaft 12 at the intermediate portion in the axial direction so as not to rotate relative to the output shaft 12 .

In this example, the worm wheel 16 comprises an inner wheel member 22 made of metal and an outer wheel member 23 made of synthetic resin.

The inner wheel member 22 includes a hollow disc-shaped side plate portion 24, a cylindrical fitting base portion 25 connected to the radially inner end portion of the side plate portion 24, and a radially intermediate portion of the side plate portion 24 to the entire circumference. It has a cylindrical support tube portion 26 that protrudes axially forward across. The fitting base 25 has an axial dimension larger than that of the side plate portion 24 . In the illustrated example, the radial inner end portion of the side plate portion 24 is connected to the axial intermediate portion of the fitting base portion 25 . The fitting base 25 is fitted onto the outer peripheral surface of the axially intermediate portion of the output shaft 12 so as not to rotate relative to the output shaft 12 . The axially forward end of the support cylinder portion 26 protrudes further axially forward than the fitting base portion 25 .

The outer wheel member 23 is coupled and fixed to the inner wheel member 22 so as to cover the radially outer end portion of the side plate portion 24 of the inner wheel member 22 over the entire circumference. The wheel teeth 21 are provided on the outer peripheral surface of the outer wheel member 23 .

The worm 17 has worm teeth 27 meshing with the wheel teeth 21 on its outer peripheral surface, and is rotationally driven by an electric motor 19 fixed to the housing case 10 . The central axis of the worm 17 is twisted with respect to the central axis of the worm wheel 16 , that is, the central axis of the output shaft 12 . Also, the base end of the worm 17 is coupled to the output shaft of the electric motor 19 so that torque can be transmitted.

The housing case 10 has a sensor housing 28 and a gear housing 29 coupled together.

A sensor housing 28 houses the torque sensor 14 . In this example, the sensor housing 28 is made of metal or synthetic resin and has an annular shape as a whole. Such a sensor housing 28 includes a cylindrical tubular portion 30 arranged radially outward of the torque sensor 14 and a hollow body extending radially inward from the axial rear end of the tubular portion 30 . A disk-shaped side plate portion 31, a cylindrical fitting tube portion 32 extending axially rearward from the radially inner end portion of the side plate portion 31, and an axially front end portion of the tubular portion 30. and a flange portion 33 extending radially outwardly from the . A front end portion of the steering column 4 , that is, a front end portion of the inner column 44 is externally fitted and fixed to the outer peripheral surface of the fitting cylinder portion 32 .

A gear housing 29 is arranged on the front side of the sensor housing 28 and accommodates the worm wheel 16 and the worm 17 . In this example, the gear housing 29 is made of metal or synthetic resin and has an annular shape as a whole, and is arranged radially outside the output shaft 12 , the worm 17 , and the worm wheel 16 . Such a gear housing 29 includes a worm wheel accommodation portion 34 that accommodates the worm wheel 16 and a worm accommodation portion 35 that accommodates the worm 17 .

The worm wheel housing portion 34 includes a cylindrical tubular portion 36 disposed radially outwardly of the worm wheel 16 and a hollow disc-shaped portion extending radially inward from the front end of the tubular portion 36 . It has a side plate portion 37 and a flange portion 38 extending radially outward from the rear end portion of the cylindrical portion 36 . The side plate portion 37 is arranged radially outside the support cylinder portion 26 of the inner wheel member 22 .

The worm housing portion 35 is configured in a cylindrical shape as a whole, and an axially intermediate portion thereof is connected to a portion of the outer peripheral edge portion of the worm wheel housing portion 34 in the circumferential direction. The inner space of the worm housing portion 35 communicates with the inner space of the worm wheel housing portion 34 . The central axis of the worm housing portion 35 is twisted with respect to the central axis of the worm wheel housing portion 34 . The worm 17 is rotatably supported inside the worm housing portion 35 by a rolling bearing (not shown).

The sensor housing 28 and the gear housing 29 are opposed to each other at their axial ends, and their flange portions 33, 33 are connected by a connecting member such as a bolt (not shown).

In this example, the output shaft 12 is rotatably supported by the housing case 10 using only one rolling bearing 18 supported by the gear housing 29 . In this example, the rolling bearing 18 is arranged axially forward of the wheel tooth 21 .

The rolling bearing 18 includes an outer ring 39 , an inner ring 40 , and a plurality of rolling elements 41 arranged between the outer ring 39 and the inner ring 40 . The outer ring 39 is supported by the gear housing 29 , and more specifically, is internally fitted and supported by the inner peripheral surface of the side plate portion 37 of the gear housing 29 . The inner ring 40 is supported by the worm wheel 16 . Specifically, the inner ring 40 is fitted and supported on the outer peripheral surface of the axially front end of the support cylinder portion 26 of the inner wheel member 22 . That is, in this example, the output shaft 12 is rotatably supported by one rolling bearing 18 via the worm wheel 16 with respect to the gear housing 29 .

In the illustrated example, the rolling bearing 18 is a deep groove ball bearing using balls as the rolling elements 41 . However, when carrying out the present invention, various types of rolling bearings such as three-point contact type or four-point contact type ball bearings and roller bearings are used as rolling bearings for rotatably supporting the output shaft with respect to the housing. be able to.

In this example, the pitch circle diameter PCD of the plurality of rolling elements 41 forming the rolling bearing 18 is 50% or more of the outer diameter D21 of the wheel teeth 21 of the worm wheel 16 . More preferably, the pitch diameter PCD is 70% or more of the outer diameter D21.

In this example, the rolling bearing 18 has openings on both sides in the axial direction of the internal space in which the plurality of rolling elements 41 are arranged between the inner peripheral surface of the outer ring 39 and the outer peripheral surface of the inner ring 40. It has a seal ring (not shown) that closes at least the opening on the front side in the axial direction. In this example, the seal ring prevents the grease that lubricates the meshing portion between the wheel tooth 21 and the worm tooth 27 from leaking into the outer space of the housing case 10 through the inner space of the rolling bearing 18 .

The seal member 20 seals between the worm wheel 16 and the housing case 10 . Specifically, the sealing member 20 has an annular shape as a whole, and is fixed to the axially front end of the cylindrical portion 30 of the sensor housing 28 over the entire circumference. The axially front end of the sealing member 20, which is the tip, is in sliding contact with the axially rearward side surface of the outer wheel member 23 constituting the worm wheel 16 over the entire circumference. In this example, the seal member 20 allows the grease that lubricates the meshing portion between the wheel tooth 21 and the worm tooth 27 to pass between the cylindrical portion 30 and the outer wheel member 23 and into the inner space of the sensor housing 28. Prevents intrusion.

In addition, in the structure of this example, the base portion 43 of the yoke 42 constituting the rear universal joint 5a is fitted and fixed to the outer peripheral surface of the output shaft 12 on the front side in the axial direction. In this state, the axial rear end of the base portion 43 is arranged radially inward of the rolling bearing 18 .

In the electric power steering apparatus 1 as described above, when the driver operates the steering wheel 2 , the torque sensor 14 detects the twist direction and amount of the torsion bar 11 . In addition, the ECU calculates the assist torque based on the steering torque information calculated based on the twist direction and twist amount of the torsion bar 11 detected by the torque sensor 14, the vehicle speed information measured by a vehicle speed sensor (not shown), and the like. to decide. Further, the direction and amount of energization of the electric motor 19 are controlled by the ECU. Also, the worm speed reducer 15 increases the torque of the electric motor 19 and transmits it to the output shaft 12 . As a result, an auxiliary torque is applied to the output shaft 12, so that the pair of tie rods 8 can be pushed and pulled with a force greater than the force applied to the steering wheel 2 by the driver.

According to the electric power steering apparatus 1 of this example as described above, the number of parts can be reduced and the assembly work can be easily performed.

This point will be specifically described using the structure of the comparative example shown in FIG. In the structure of the comparative example, as in the conventional structure, the output shaft 12 is rotatably supported on the housing case 10z by a pair of rolling bearings 18za and 18zb at two front and rear positions with the worm wheel 16z interposed therebetween. . This prevents the output shaft 12 from tilting with respect to the housing case 10z due to the load component directed in the axial direction of the output shaft 12 in the meshing load acting on the meshing portion between the wheel tooth 21 and the worm tooth 27. ing.

Of the pair of rolling bearings 18za and 18zb, the front rolling bearing 18za is supported by the gear housing 29z. Specifically, the outer ring 39za that constitutes the front rolling bearing 18za is internally fitted and supported by the inner peripheral surface of the side plate portion 37z of the gear housing 29z. An inner ring 40za forming the front rolling bearing 18za is externally supported by a portion of the outer peripheral surface of the output shaft 12 adjacent to the front side of the worm wheel 16z.

Of the pair of rolling bearings 18za and 18zb, the rear rolling bearing 18zb is supported by an intermediate plate 48 which is a component different from the gear housing. That is, in the structure of the comparative example, the housing case 10z includes a hollow disk-shaped intermediate plate 48 arranged between the sensor housing 28 and the gear housing 29z in the front-rear direction. An outer ring 39zb forming the rear rolling bearing 18zb is internally fitted and supported by the inner peripheral surface of the intermediate plate 48 . An inner ring 40zb forming the rear rolling bearing 18za is externally supported by a portion of the outer peripheral surface of the output shaft 12 adjacent to the rear side of the worm wheel 16z.

Note that, as in the structure of the comparative example, when the inner ring 40zb constituting the rear rolling bearing 18za is externally supported by a portion of the outer peripheral surface of the output shaft 12 adjacent to the rear side of the worm wheel 16z, the sensor If the inner diameter of the tubular portion 30 of the housing 28 can be made sufficiently small, the inner peripheral surface of the tubular portion 30 can internally fit and support the outer ring 39zb that constitutes the rear rolling bearing 18zb. However, similar to the structure of this example, in the structure of the comparative example, the outer diameter of the torque sensor 14 arranged radially inside the cylindrical portion 30 is large. Since the size is 60% or more of the outer diameter D21 of the 16 wheel teeth 21, the inner diameter of the cylindrical portion 30 cannot be sufficiently reduced. For this reason, in the structure of the comparative example, a hollow disk-shaped intermediate plate 48 is arranged between the sensor housing 28 and the gear housing 29z in the front-to-rear direction. It internally fits and supports an outer ring 39zb that constitutes the bearing 18zb.

In contrast to the structure of the comparative example as described above, in the structure of this example, the output shaft 12 is rotatably supported by the housing case 10 using only one rolling bearing 18 . That is, in the structure of this example, the number of rolling bearings for rotatably supporting the output shaft 12 with respect to the housing case 10 can be reduced to one when compared with the conventional structure and the structure of the comparative example. Therefore, the number of parts can be reduced accordingly, and the assembly work can be easily performed.

Moreover, in the structure of this example, the intermediate plate 48 can be omitted when compared with the structure of the comparative example. Therefore, also from this point of view, the number of parts can be reduced and the assembly work can be easily performed.

In addition, in the structure of this example, the output shaft 12 is rotatably supported by the housing case 10 using only one rolling bearing 18 . The inner wheel member 22 is externally fitted and supported on the outer peripheral surface of the support cylinder portion 26 of the inner wheel member 22, which is a portion having a larger diameter than the inner wheel member 22. Therefore, in the structure of this example, when compared with the structure of the comparative example, it is possible to ensure a large pitch circle diameter PCD of the rolling elements 41 of the rolling bearing 18 and to ensure a large moment rigidity of the rolling bearing 18. . For this reason, the tilting of the output shaft 12 with respect to the housing case 10 due to the load component directed in the axial direction of the output shaft 12 in the meshing load acting on the meshing portion between the wheel teeth 21 and the worm teeth 27 is 1 The individual rolling bearings 18 can effectively prevent this. In addition, in the structure of this example, the distance from the meshing portion between the wheel tooth 21 and the worm tooth 27 to the rolling bearing 18 is shorter than in the structure of the comparative example. Therefore, of the meshing load acting on the meshing portion, the load component directed in the radial direction of the output shaft 12 can be efficiently supported by the rolling bearing 18 . Therefore, the one rolling bearing 18 can effectively prevent the output shaft 12 from tilting with respect to the housing case 10 due to such a load component directed in the radial direction of the output shaft 12 .

Further, in the structure of this example, the meshing load acting on the meshing portion between the wheel tooth 21 and the worm tooth 27 can It is distributed and supported by the rolling elements 41 present in the region opposite to the meshing portion (lower side in FIGS. 2 and 3). In particular, in the structure of this example, a large pitch diameter PCD of the rolling elements 41 can be ensured, so that the number of the rolling elements 41 that disperse and support the meshing load can be increased. Therefore, the durability of the rolling bearing 18 can be sufficiently ensured.

Further, in the structure of this example, the intermediate plate 48 can be omitted when compared with the structure of the comparative example, so the axial dimension of the electric assist device 9 can be reduced. Therefore, the axial dimension of the steering column 4 can be increased accordingly. As a result, it is possible to increase the amount of stroke by which the outer column 45 is displaced forward with respect to the inner column 44 in the event of a secondary collision, thereby enhancing the protection of the driver. In addition, since the axial dimension of the electric assist device 9 can be reduced, the electric assist device 9 can be made lighter.

In the structure of this example, the base portion 43 of the yoke 42 constituting the rear universal joint 5a is fitted and fixed to the outer peripheral surface of the axially front side portion of the output shaft 12, and the base portion 43 is axially fixed. The rear end is arranged radially inside the rolling bearing 18 . Therefore, compared to a structure in which the entire base portion 43 is arranged on the front side of the rolling bearing 18 in the axial direction, the amount of protrusion of the output shaft 12 from the side surface of the gear housing 29 on the front side in the axial direction can be suppressed. Therefore, also from this aspect, the axial dimension of the electric assist device 9 can be reduced.

Further, in the structure of this example, the worm wheel 16 is rotatably supported inside the worm wheel accommodating portion 34 of the gear housing 29 by the rolling bearing 18, and inside the worm accommodating portion 35 of the gear housing 29. , a worm 17 is rotatably supported by a rolling bearing (not shown). That is, each of the worm wheel 16 and the worm 17 is rotatably supported with respect to the gear housing 29 . Therefore, compared to a structure in which the worm wheel 16 and the worm 17 are supported by different housings, it is easier to precisely regulate the positional relationship between the worm wheel 16 and the worm 17 .

[Second example of embodiment]
A second example of the embodiment of the invention will be described with reference to FIG.

In the structure of this example, the inner wheel member 22a that constitutes the worm wheel 16a does not have the support cylinder portion 26 (see FIG. 2), and the radial thickness of the fitting base portion 25a is the same as that of the embodiment. It is made larger than in the case of one example. In the structure of this example, the inner ring 40 of the rolling bearing 18 is externally supported by the outer peripheral surface of the portion of the fitting base portion 25a located axially forward of the side plate portion 24 . In the structure of this example, since the space between the outer peripheral surface of the output shaft 12 and the inner peripheral surface of the inner ring 40 is filled with the axial front side portion of the fitting base portion 25a, the rolling bearing 18 with respect to the output shaft 12 does not move. Support strength can be increased. It should be noted that the radial thickness of the portion of the fitting base 25a located on the rear side in the axial direction of the side plate portion 24 is the same as the thickness of the portion of the fitting base 25a located on the front side of the side plate portion 24 in the axial direction. It can also be smaller than the radial thickness.
Other configurations and effects are the same as those of the first embodiment.

[Third example of embodiment]
A third example of the embodiment of the invention will be described with reference to FIG.

In the structure of this example, the gear housing 29a has a stepped portion facing axially rearward on the inner peripheral surface of the side plate portion 37a, adjacent to the axially front side of the portion where the outer ring 39 of the rolling bearing 18 is fitted. It has a face 49 . The outer ring 39 is positioned in the axial direction by bringing its axially forward side surface into contact with the stepped surface 49 .

In the structure of this example, the inner wheel member 22b that constitutes the worm wheel 16b is a portion of the outer peripheral surface of the fitting base portion 25b that is adjacent to the axial rear side of the portion where the inner ring 40 of the rolling bearing 18 is fitted. , has a stepped surface 50 facing forward in the axial direction. In addition, the inner wheel member 22b has a locking groove 51 along the entire circumference in a portion of the outer peripheral surface of the fitting base 25b adjacent to the axially front side of the portion where the inner ring 40 is fitted. A radial inner portion of a retaining ring 52 is engaged with the engaging groove 51 . The inner ring 40 is axially positioned by being axially sandwiched between the step surface 50 and the radially outer portion of the retaining ring 52 .
Other configurations and effects are the same as those of the second embodiment.

[Fourth example of embodiment]
A fourth example of the embodiment of the invention will be described with reference to FIG.

In the structure of this example, the gear housing 29b has a step facing forward in the axial direction in a portion of the inner peripheral surface of the side plate portion 37b that is adjacent to the axial rear side of the portion where the outer ring 39 of the rolling bearing 18 is fitted. It has a face 53 . In addition, the gear housing 29b has a locking groove 54 along the entire circumference in a portion of the inner peripheral surface of the side plate portion 37b adjacent to the axially front side of the portion where the outer ring 39 of the rolling bearing 18 is fitted. A radially outer portion of a retaining ring 55 is engaged with the engaging groove 54 . The outer ring 39 is axially positioned by being axially sandwiched between the step surface 53 and the radially inner portion of the retaining ring 55 .
Other configurations and effects are the same as those of the third embodiment.

[Fifth example of embodiment]
A fifth example of the embodiment of the present invention will be described with reference to FIG.

In the structure of this example, the output shaft 12a has a large-diameter portion 56 in the axially intermediate portion, the outer diameter of which is larger than that of the adjacent portions on both sides in the axial direction. In the structure of this example, the fitting base portion 25c of the inner wheel member 22c constituting the worm wheel 16c is fitted on the rear side portion of the outer peripheral surface of the large diameter portion 56 so as to prevent relative rotation with respect to the output shaft 12a. . The inner ring 40 of the rolling bearing 18 is fitted and supported on the front portion of the outer peripheral surface of the large diameter portion 56 .
Other configurations and effects are the same as those of the first embodiment.

[Sixth example of embodiment]
A sixth example of the embodiment of the present invention will be described with reference to FIG.

In the structure of this example, the rolling bearing 18a is arranged axially behind the wheel tooth 21 . For this reason, in the structure of this example, the inner wheel member 22d that constitutes the worm wheel 16d has a cylindrical support tube portion 26a that extends axially rearward from the radially outer end portion of the side plate portion 24. have. The axially rear side portion of the support cylinder portion 26 a protrudes axially rearward from the axially rearward side surface of the outer wheel member 23 . In addition, the axially rearward end of the support cylinder portion 26 a is disposed radially outward of the torque sensor 14 . In this example, the outer ring 39a of the rolling bearing 18a is internally fitted and supported by the inner peripheral surface of the rear end in the axial direction of the gear housing 29c. Further, the inner ring 40a of the rolling bearing 18a is externally fitted and supported on the outer peripheral surface of the axially rearward end portion of the support cylinder portion 26a.

In this example, the rolling bearing 18a has openings on both sides in the axial direction of the internal space in which the plurality of rolling elements 41 are arranged between the inner peripheral surface of the outer ring 39a and the outer peripheral surface of the inner ring 40a. It has a seal ring (not shown) that closes at least the opening on the rear side in the axial direction. In this example, the seal ring prevents the grease that lubricates the meshing portion between the wheel tooth 21 and the worm tooth 27 from entering the inner space of the sensor housing 28 through the inner space of the rolling bearing 18a.

In this example, the seal member 20a is fixed along the entire circumference to the axial rear side surface of the radially inner end of the side plate portion 37 of the gear housing 29c. The axially rearward end portion of the seal member 20a, which is the tip portion, is in sliding contact with the axially forward side surface of the side plate portion 24 of the inner wheel member 22d over the entire circumference. In this example, the grease that lubricates the meshing portion between the wheel tooth 21 and the worm tooth 27 leaks to the outer space of the housing case 10 through the gap between the side plate portion 37 and the side plate portion 24 due to the sealing member 20a. prevent this from happening.
Other configurations and effects are the same as those of the first embodiment.

It should be noted that the present invention can be carried out by appropriately combining the configurations of the above-described embodiments within a range that does not cause contradiction.
When carrying out the present invention, the method of fixing the rolling bearing to the mating member for rotatably supporting the output shaft with respect to the gear housing, and the procedure for assembling a plurality of parts including the rolling bearing are particularly limited. not.

Reference Signs List 1 electric power steering device 2 steering wheel 3 steering shaft 4 steering column 5a, 5b universal joint 6 intermediate shaft 7 steering gear unit 8 tie rod 9 electric assist device 10, 10z housing case 11 torsion bar 12 output shaft 13 pinion shaft 14 torque sensor 15 Worm reducer 16, 16a, 16b, 16c, 16d, 16z Worm wheel 17 Worm 18, 18a, 18za, 18zb Rolling bearing 19 Electric motor 20, 20a Seal member 21 Wheel tooth 22, 22a, 22b, 22c, 22d Inner wheel member 23 outer wheel member 24 side plate portion 25, 25a, 25b, 25c fitting base portion 26, 26a support tubular portion 27 worm tooth 28 sensor housing 29, 29a, 29b, 29c, 29z gear housing 30 tubular portion 31 side plate portion 32 fitting Cylindrical portion 33 Flange portion 34 Worm wheel accommodating portion 35 Worm accommodating portion 36 Cylindrical portion 37, 37a, 37b, 37z Side plate portion 38 Flange portion 39, 39a, 39za, 39zb Outer ring 40, 40a, 40za, 40zb Inner ring 41 Rolling element 42 Yoke 43 Base 44 Inner column 45 Outer column 46 Inner shaft 47 Outer shaft 48 Intermediate plate 49 Stepped surface 50 Stepped surface 51 Locking groove 52 Retaining ring 53 Stepped surface 54 Locking groove 55 Retaining ring 56 Large diameter portion 100 Electric assist device 101 Input shaft 102 Output shaft 103 Torque sensor 104 Worm wheel 105 Worm 106 Housing case 107a, 107b Rolling bearing 108 Sensor housing 109 Gear housing 110 Intermediate plate 111 Electric motor

Claims (8)

an input shaft driven to rotate based on the operation of the steering wheel;
an output shaft arranged axially forward of the input shaft and coaxial with the input shaft;
a torque sensor arranged radially outward of the input shaft;
a worm wheel having wheel teeth on its outer peripheral surface and fitted and fixed to the outer peripheral surface of the output shaft;
a worm having worm teeth meshing with the wheel teeth on its outer peripheral surface and driven to rotate by an electric motor;
a housing case having a sensor housing and a gear housing coupled together;
The sensor housing accommodates the torque sensor,
The gear housing accommodates the worm wheel and the worm,
The output shaft is rotatably supported by the housing case using only one rolling bearing supported by the gear housing,
Electric power steering device. The rolling bearing comprises an outer ring, an inner ring, and a plurality of rolling elements arranged between the outer ring and the inner ring,
The pitch circle diameter of the plurality of rolling elements is 50% or more of the outer diameter of the wheel tooth,
The electric power steering device according to claim 1. The rolling bearing is arranged axially forward of the wheel tooth,
The electric power steering device according to claim 1 or 2. a base portion of a yoke of a universal joint is externally fitted and fixed to the outer peripheral surface of the axially front side portion of the output shaft;
an axial rear end of the base is disposed radially inward of the rolling bearing;
The electric power steering device according to claim 3. The rolling bearing is arranged axially rearward of the wheel tooth,
The electric power steering device according to claim 1. The rolling bearing comprises an outer ring, an inner ring, and a plurality of rolling elements arranged between the outer ring and the inner ring,
wherein the outer ring is supported by the gear housing and the inner ring is supported by the worm wheel;
The electric power steering device according to any one of claims 1 to 5. further comprising a seal member for sealing between the worm wheel and the housing case;
The electric power steering device according to any one of claims 1 to 6. the seal member seals between the worm wheel and the gear housing;
The electric power steering device according to claim 7.

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