Coaster for electric power steering device

Abstract

The embodiments disclosed herein relate to a base for an electric power steering device. These embodiments provide a base for an electric power steering device comprising: a worm shaft with a first end connected to a motor shaft and a second end opposite the first end, wherein a first worm shaft bearing and a second worm shaft bearing are coupled to the first end and the second end, respectively; a gearbox housing in which the first worm shaft bearing, the second worm shaft bearing, and the worm shaft are accommodated; and a moisture absorption compensation element supported on and coupled to an inner circumferential surface of the gearbox housing in the direction in which the worm shaft meshes with the worm wheel, and supporting the worm shaft in the direction opposite to the direction in which the worm shaft meshes with the worm wheel.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to Korean Patent Application No. 10-2016-0130912, filed on October 10, 2016 and published as KR 2018 0039519 A, which is hereby incorporated by reference for all purposes as if fully disclosed herein. BACKGROUND OF THE INVENTION 1. Field of the Invention

[0002] Embodiments disclosed herein relate to a reducer of an electric power steering apparatus. More specifically, the present disclosure relates to a reducer of an electric power-assisted steering apparatus provided with a moisture absorption compensation part to be able to solve the problem of moisture absorption of a worm shaft and the problems caused thereby. 2. Description of the state of the art

[0003] The conventional electric power steering reducer has a problem in that, as the worm and worm gear, which are rotated by the motor drive, age, rattling noises are generated due to looseness and backlash caused by wear and tear of the worm and worm gear. In addition, the rattling noise is further amplified by the reverse load applied to a wheel when driving on bumpy roads.

[0004] Furthermore, the worm gear is made of a metal such as steel, while the worm wheel is made entirely or partially (outer peripheral area) of a plastic material to overcome frictional resistance with the worm gear. When the vehicle is operated in a high-temperature and high-humidity environment, the plastic worm gear absorbs moisture and expands, changing the dimensions of the worm gear to increase torque, resulting in a stronger steering feel for the driver and a deterioration in performance.

[0005] Publication CN 102 030 032 A discloses a reduction gear of an electric power steering device. The reduction gear includes a worm shaft bearing supporting an opposite side end of the motor shaft coupling portion of a worm shaft. The worm shaft is formed with a worm gear that meshes with a worm wheel. A bearing holder of the reduction gear is coupled to the worm shaft bearing and encloses an outer gear of the worm shaft bearing. An elastic ring is interposed between the worm shaft bearing and the bearing holder. An elastic support is provided in an inner peripheral surface of a gear housing in a direction opposite to the worm wheel to support an end portion of the worm shaft in a direction of the worm wheel.In order to support the end portion of the worm shaft and prevent the occurrence of gapping and rattling noises that may be caused by backlash and backward loading, a support member is positioned between an outer peripheral surface of the bearing holder and the inner peripheral surface of the gear housing. SUMMARY OF THE INVENTION

[0006] Against the background described above, the invention disclosed herein and its embodiments were devised, and it is an object of the invention and its embodiments to provide a reducer of an electric power steering apparatus in which, by minimizing an increase in torque due to moisture absorption of the worm wheel and the resulting deformation of the worm wheel, the deterioration of the driver's steering feel and the performance of the reducer can be prevented, the occurrence of backlash due to wear and tear of the worm and the worm wheel can be prevented, and the generation of rattling noise due to looseness and a reverse input load can be prevented.

[0007] In addition, the objects of the embodiments disclosed herein are not limited thereto, and other objects not described above can be clearly understood by a person skilled in the art from the following description.

[0008] To achieve the above-mentioned objects according to the invention, a reducer of an electric power steering device is proposed according to the main claim. Some embodiments and further developments of the invention are specified in the dependent claims. A reducer of an electric power steering device according to the invention comprises: a worm shaft having a first end connected to a motor shaft and a second end opposite to the first end, wherein a first worm shaft bearing and a second worm shaft bearing are connected to the first end and the second worm shaft bearing, respectively.the second end; a gear housing in which the first worm shaft bearing, the second worm shaft bearing, and the worm shaft are housed; and a moisture absorption compensation member supported on and coupled to an inner peripheral surface of the gear housing in a direction in which the worm shaft meshes with the worm wheel, and supporting the worm shaft in a direction opposite to the direction in which the worm shaft meshes with the worm wheel. According to the invention, the moisture absorption compensation member includes a first compensation member and a second compensation member which have wedge shapes and are engaged with each other.

[0009] According to the above-described embodiments, by minimizing an increase in torque due to moisture absorption of the worm wheel and the resulting deformation of the worm wheel, it is possible to prevent deterioration of the driver's steering feel and the performance of the reducer.

[0010] In addition, in the reducer of an electric power steering device, it is possible to prevent the generation of backlash due to wear and tear of the worm and the worm wheel, and to prevent the generation of rattling noise due to looseness and a reverse input load. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings in which: Fig. 1 is a view illustrating the configuration of an electric power steering apparatus; Fig. 2 is a cross-sectional view illustrating a reducer of an electric power steering apparatus; Fig. 3 is an exploded perspective view illustrating a reducer of an electric power steering apparatus according to the embodiments disclosed herein; Fig. 4 is a perspective view illustrating a part of the reducer of the electric power steering apparatus according to the embodiments; Fig. 5 is a cross-sectional view illustrating a part of the reducer of the electric power steering apparatus according to the embodiments; Fig. 6 is a perspective view illustrating a part of the reducer of the electric power steering apparatus according to the embodiments; Fig. 7 is a cross-sectional view illustrating a part of the reducer of the electric power steering apparatus according to the embodiments; Fig. Fig. 8 is a cross-sectional view illustrating the reducer of the electric power steering apparatus according to the embodiments; and Fig. 9 is a cross-sectional view illustrating the reducer of the electric power steering apparatus according to the embodiments. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0012] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. When adding reference numerals to elements in each drawing, the same elements are designated by the same reference numerals wherever possible, even though they are shown in different drawings. Furthermore, in the following description of the present disclosure, a detailed description of their included known functions and configurations is omitted when doing so might obscure the clarity of the subject matter of the present disclosure.

[0013] Additionally, terms such as first, second, A, B, (a), (b), or the like may be used herein when describing components of the present disclosure. These terms are used merely to distinguish one structural element from other structural elements, and a property, order, sequence, and the like of a corresponding structural element are not limited by the term. It should be noted that where the description describes a component as being "connected," "coupled," or "joined" to another component, a third component may be "connected," "coupled," or "joined" between the first and second components, although the first component may be directly connected, coupled, or joined to the second component.

[0014] Fig. 1 is a view illustrating the configuration of an electric power steering device. As shown in Fig. 1, a conventional electric power steering apparatus 100 includes a steering system 130 extending from a steering wheel 102 to opposite vehicle wheels 126, and a power assist mechanism 140 configured to provide steering assist force to the steering system 130.

[0015] The steering system 130 includes a steering shaft 106 connected on one side to the steering wheel 102 for rotation with the steering wheel 102, and on the other side to a pinion shaft 108 via a pair of universal joints 104. Additionally, the pinion shaft 108 is connected to a rack 112 through a rack-and-pinion mechanism 110, and the opposite ends of the rack 112 are respectively connected to the vehicle wheels 126 through tie rods 122 and link arms 124.

[0016] The power assist mechanism 140 includes: a torque sensor 142 configured to detect a torque applied by the driver to the steering wheel 102 and output an electrical signal proportional to the detected torque; an electronic control unit 144 configured to generate a control signal based on the electrical signal transmitted from the torque sensor 142; a motor 146 configured to generate an assist force based on the control signal transmitted from the electronic control unit 144; and a reducer 150 including a worm 152 and a worm wheel 156 for transmitting the assist force generated by the motor 146 to the steering shaft 106.

[0017] Accordingly, the electric power steering apparatus is configured such that a torque generated by the rotation of the steering wheel 102 is transmitted to the rack 112 via the rack and pinion mechanism 110, and the assist force generated by the motor 146 according to the generated torque is transmitted to the rack 112.

[0018] That is, the torque generated by the rotation of the steering wheel 102 and the assist force generated by the motor 146 are combined to cause the rack 112 to move in an axial direction.

[0019] Fig. 2 is a cross-sectional view illustrating a reducer of an electric power steering device. As shown in Fig. As illustrated in Figure 2, the reducer 150 is provided with a worm shaft 254 formed with a worm 152, and worm shaft bearings 257 are respectively disposed at the opposite ends of the worm shaft 254 to support the worm shaft 254. To prevent the worm shaft bearings 257 from loosening in the axial direction of the worm shaft 254, a locking pin 210 is fitted between a damping coupler 240 and the worm shaft bearings 257, and the locking pin 210 is fixed by a locking nut 220.

[0020] The worm shaft 254 has a structure in which the worm shaft 254 is connected to the motor 146 via a damping coupler 240 such that the worm shaft 254 is rotated by the drive of the motor 146.

[0021] Additionally, a worm gear 156 is disposed on one side of the outer diameter of the worm 152 to mesh with the worm 152 formed on the worm shaft 254. The worm gear 156 is configured to transmit the torque of the worm shaft 254, exerted by the drive of the motor 146, to the steering shaft 106 by being mounted on the steering shaft 106, which is configured to transmit the torque of the driver-operated steering wheel 102.

[0022] The worm 152, the worm wheel 156, and the like are arranged within a gear case 260, and the motor 146 is arranged on one side of the gear case 260 to provide driving force to the worm shaft 254. The gear case 260 and the motor 146 are coupled together by a motor cover 230 with a bolt 250.

[0023] In each of the worm shaft bearings 257, balls 258 are arranged between an inner raceway 280 and an outer raceway 270, thereby supporting the rotation of the worm shaft 254, which is connected to the motor 146 at the end of the gear housing 260.

[0024] The reducer of the electric power steering device according to the embodiments includes a moisture absorption compensation part supported on the inner peripheral surface of the gear housing and coupled thereto in the direction in which the worm shaft meshes with the worm wheel, and an elastic part supported on the inner peripheral surface of the gear housing and coupled thereto in a direction opposite to the direction in which the worm shaft meshes with the worm wheel, thereby minimizing the moisture absorption of the worm wheel and the increase in torque due to the moisture absorption of the worm wheel 156 and the resulting dimensional deformation of the worm wheel, and can prevent backlash from occurring due to wear and tear of the worm and the worm wheel, thereby preventingthat a rattling noise is generated by loosening and a reversed input load.

[0025] Fig. 3 is an exploded perspective view illustrating a reducer of an electric power steering apparatus according to the embodiments disclosed herein. Fig. 4 is a perspective view illustrating a part of the reducer of the electric power steering apparatus according to the embodiments, Fig. 5 is a cross-sectional view illustrating a part of the reducer of the electric power steering apparatus according to the embodiments, and Fig. 6 is a perspective view illustrating a part of the reducer of the electric power steering apparatus according to the embodiments. Fig. 7 is a cross-sectional view illustrating a part of the reducer of the electric power steering apparatus according to the embodiments, Fig. Fig. 8 is a cross-sectional view illustrating the reducer of the electric power steering apparatus according to the embodiments, and Fig. 9 is a cross-sectional view illustrating the reducer of the electric power steering apparatus according to the embodiments.

[0026] As illustrated in the drawings, a reducer of an electric power steering device according to embodiments includes: a worm shaft 254 having a first end connected to a motor shaft and a second end opposite to the first end, a first worm shaft bearing 256 and a second worm shaft bearing 257 coupled to the first end and the second end, respectively; a gear case 260 in which the first worm shaft bearing 256, the second worm shaft bearing 257, and the worm shaft 254 are housed; and a moisture absorption compensation part 310 supported on and coupled to an inner peripheral surface of the gear case 260 in a direction in which the worm shaft 254 meshes with the worm wheel 156, and that supports the worm shaft in a direction opposite to the direction in which the worm shaft meshes with the worm wheel.

[0027] The reducer is configured such that the worm shaft 254 and the worm gear 156 are locked together by the driving force of the motor 146 to rotate the steering shaft 201, thereby assisting the driver's steering effort. The first worm shaft bearing 156 and the second worm shaft bearing 257 are respectively fixed to the first end and the second end of the worm shaft 254, which are opposite to each other, thereby supporting the rotation of the worm shaft 254, which is locked to the shaft of the motor 146, when the motor 146 is driven.

[0028] The worm gear 156 and the worm shaft 254, which are locked to the steering shaft 201, are accommodated in the gear housing 260 together with the first worm shaft bearing 256 and the second worm shaft bearing 257.

[0029] In addition, the second worm shaft bearing 257 is composed of an inner raceway 157a coupled to an end portion 254a of the worm shaft 254, balls 257c, and an outer raceway 257b. The moisture absorption compensation member 310 is supported and coupled between the inner peripheral surface of the gear housing 260 and the outer raceway 257b of the second worm shaft bearing 257 in the direction in which the worm shaft 254 meshes with the worm gear 156, so that the moisture absorption compensation member 310 is capable of compensating the degree of expansion of the worm gear 156 caused by moisture absorption.

[0030] In addition, an elastic member 320 is supported and coupled between the inner peripheral surface of the gear housing 260 and the outer raceway 257b of the second worm shaft bearing 257 in a direction opposite to the direction in which the worm shaft 254 meshes with the worm gear 156, that is, the position at which the moisture absorption compensating member 310 is coupled, so that the elastic member 320 is capable of absorbing shock and rattling noise while compensating for the backlash between the worm shaft 254 and the worm gear 156.

[0031] The cap part 330 may be coupled to the gear housing 260 to prevent the elastic part 320 from being separated from the gear housing 260. The cap part 330 may be formed to be screw-coupled to the gear housing 260, so that the elastic support force of the elastic part 320 can be adjusted depending on a screw fastening degree, and the assemblability of the elastic part 320 can be improved.

[0032] Here, the moisture absorption compensation part 310 is made of a plastic material that is the same as the plastic material of the worm wheel 156 in terms of the amount of moisture absorption expansion, so that the moisture absorption compensation part 310 is also expanded to an extent corresponding to the amount of expansion of the worm wheel 156.

[0033] That is, in the case where the vehicle is operated in a high-temperature and high-humidity environment, when the worm wheel 156 formed of a plastic material absorbs moisture from the surrounding air and expands to change the size of the worm wheel 156, the moisture absorption compensation member 310 can also absorb moisture to expand to the same extent, thereby displacing the second worm shaft bearing 257 and the worm shaft 254 to a side opposite to the worm wheel 156, so that the elastic member 320 is compressed, and as a result, an excessive coupling force is not generated between the worm shaft 254 and the worm wheel 156.

[0034] Therefore, the moisture absorption compensation part 310 absorbs the expansion amount that is the same as the expansion amount of the worm gear 156, so that the supporting force of the worm shaft 254 and the worm gear 156 is maintained at the same supporting force as that exerted before the moisture absorption. Therefore, the excessive torque increase between the worm shaft 254 and the worm gear 156 can be minimized, and as a result, the steering feel is prevented from deteriorating.

[0035] The moisture absorption compensation part 310 may be formed of one or more materials selected from a group consisting of polyamide 6, polyamide 66, polyamide 46 and polyamide 12.

[0036] In addition, the moisture absorption compensating member 310 is assembled with the gear case 260 in the state in which a respective wedge-shaped first and second compensating members 310a and 310b form a pair and are engaged with each other.

[0037] First, as in Fig. 4, the first compensation part 310a includes a plurality of projections 311 formed in a wedge shape and grooves 312 each formed between the projections 311 in a shape arranged to be connected to the second worm shaft bearing 257 in the direction of the gear case 260.

[0038] In addition, the second compensation part 310b is formed as a pair with the first compensation part 310a such that the projections 311 and the grooves 312 of the second compensation part 310b are engaged with the grooves 312 and the projections 311 of the first compensation part 310a, respectively.

[0039] In addition, as in Fig. 5, in the state where the first compensation part 310a and the second compensation part 310b are engaged with each other, a space S is formed between the tip ends of the projections 311 and the inner ends of the grooves 312, so that the contact area between the first and second compensation parts 310a and 310b and the ambient air is increased, and as a result, the moisture absorption and expansion of the moisture absorption compensation part 310 can be excellently performed.

[0040] In addition, as described in the Fig. 6 and Fig. As illustrated in Figure 7, the first compensation part 310a and the second compensation part 310b include one or more track grooves 313 and 315 formed in one or both of the first and second sides of each of the projections 311, which are opposite to each other. Because the track grooves 313 and 315 are arranged in this manner, the contact area between the moisture absorption compensation part 310 and the ambient air is increased, so that the moisture absorption and expansion of the moisture absorption compensation part 310 can be excellently performed.

[0041] In addition, as in Fig. As illustrated in FIG. 7, the first compensation part 310a and the second compensation part 310b are arranged such that the track grooves 315 of the first compensation part 310a and the track grooves 313 of the second compensation part 310b are stacked at a position where the track grooves 315 of the first compensation part 310a and the track grooves 313 of the second compensation part 310b correspond to each other in the state where the first compensation part 310a and the second compensation part 310b are engaged with each other. As a result, the space S between the track grooves 315 and 313 is formed so that the contact area with the ambient air is increased, and as a result, moisture absorption and expansion can be excellently performed.

[0042] Since the volume of the moisture absorption compensation part 310 is much smaller than that of the worm wheel 156 and the moisture absorption compensation part 310 is also mounted in a narrower space than the worm wheel 156, it is possible to prevent the expansion amount of the moisture absorption compensation part 310 from being reduced compared to the expansion amount of the worm wheel 156.

[0043] An adjustment part 340 may be coupled to a mounting hole 341 formed in the gear housing 260 to adjust the upper and lower supporting forces of the moisture absorption compensation part 310 and the elastic part 320 so that the first compensation part 310a and the second compensation part 310b can be supported in the direction in which the first compensation part 310a and the second compensation part 310b are engaged with each other.

[0044] This means that in Fig. 3 illustrate coordinate axes, the direction of the worm shaft 254 is set in the X-axis, the direction perpendicular to the worm shaft 254 and connecting the centers of the worm shaft 254 and the worm wheel 156 is set in the Z-axis direction, the direction perpendicular to the X-axis and the Z-axis is set in the Y-axis direction, it is possible to adjust the insertion depth of the first compensation part 310a and the second compensation part 310b depending on the fastening depth of the adjustment part 340 in the fastening hole as in Fig. 6, which illustrates a plane perpendicular to the X-axis.

[0045] In addition, the mounting surface of the gear housing 260 to which the second worm shaft bearing 257 is coupled is formed such that the clearance of the mounting surface 260b in the vertical direction in which the worm shaft 254 and the worm wheel 156 mesh with each other is larger than that of the mounting surface 260a in the left and right directions, so that the second worm shaft bearing is movable in the vertical direction.

[0046] Accordingly, when the operator adjusts the fastening size of the adjusting member 340, the vertical position of the first worm shaft bearing 256 is set, and at the same time, the elastic support force of the elastic member 320 is also adjusted.

[0047] According to the embodiments having the above-described shape and configuration, in the reducer of the electric power steering apparatus, it is possible to prevent the driver's steering feel and the reducer performance from being deteriorated by minimizing a torque increase due to moisture absorption of the worm wheel 156 and the resulting dimensional deformation of the worm wheel.

[0048] In addition, it is possible to prevent backlash from being generated due to wear and tear of the worm and worm wheel, and to prevent rattling noise from being generated by loosening and reverse input load.

[0049] Although all elements constituting embodiments of the present disclosure are described above as being combined into a single unit or combined to operate as a single unit, the present disclosure is not necessarily limited to such embodiments. That is, at least two elements of all structural elements can be selectively combined and operated without departing from the scope of the present disclosure.

[0050] Additionally, since terms such as "including," "comprising," and "having" imply that one or more corresponding components may exist, unless expressly stated otherwise, this should be interpreted to mean that one or more other components may be included. All terms used in a technical, scientific, or other sense correspond to the meanings understood by one of ordinary skill in the art, unless expressly stated otherwise. General terms found in dictionaries should not be interpreted too ideally or impractically in the context of the relevant technical literature, unless the present disclosure expressly states otherwise.

[0051] The above embodiments have been described merely for the purpose of illustrating the technical idea of ​​the present disclosure, and those skilled in the art will recognize that various modifications and changes are possible without departing from the scope and spirit of the present disclosure. Therefore, the embodiments presented in the present disclosure are intended to illustrate the scope of the technical idea of ​​the present disclosure, and the scope of the present disclosure is not limited by the embodiment. The scope of the present disclosure is to be interpreted based on the accompanying claims in such a manner that all technical ideas included in the range equivalent to the claims belong to the present disclosure.

Claims

[1] A coaster (150) of an electric power steering device, comprising: a worm shaft (254) having a first end connected to a motor shaft and a second end opposite the first end, a first worm shaft bearing (256) coupled to the first end, and a second worm shaft bearing (257) coupled to the second end; a gear housing (260) in which the first worm shaft bearing (256), the second worm shaft bearing (257) and the worm shaft (254) are accommodated; and a moisture absorption compensation part (310) supported on and coupled to an inner peripheral surface of the gear housing (260) in a direction in which the worm shaft (254) meshes with the worm wheel (156), and supporting the worm shaft (254) in a direction opposite to the direction in which the worm shaft (254) meshes with the worm wheel (156), characterized by , that the moisture absorption compensation part (310) includes a first compensation part (310a) and a second compensation part (310b) which have wedge shapes and are in engagement with each other. [2] The reducer (150) according to claim 1, further comprising: an elastic member (320) supported on and coupled to an inner peripheral surface of the gear housing (260) in a direction opposite to the direction in which the worm shaft (254) meshes with the worm wheel (156), and supporting the worm shaft toward the moisture absorption compensating member (310). [3] Coaster (150) according to claim 2, further comprising: a cap member (330) coupled to the gear housing (260) to prevent the elastic member (320) from being separated. [4] The coaster (150) according to any one of claims 1 to 3, wherein the moisture absorption compensating member (310) is made of a plastic material having a hygroscopic expansion amount equal to a hygroscopic expansion amount of a plastic material constituting the worm wheel (156). [5] Coaster (150) according to one of claims 1 to 4, wherein the moisture absorption compensating part (310) is formed from one or more materials selected from a group consisting of polyamide 6, polyamide 66, polyamide 46 and polyamide 12. [6] The reducer (150) according to any one of claims 1 to 5, wherein the first compensation part (310a) has a plurality of projections (311) each formed in a wedge shape, and a plurality of grooves (312) each formed between the projections and connected to the second worm shaft bearing (257) in a direction of the gear housing (260); and wherein the second compensation part (310b) is formed in a pair with the first compensation part (310a) such that the projections (311) and the grooves (312) of the second compensation part (310b) are engaged with the grooves and projections of the first compensation part (310a), respectively. [7] The coaster (150) according to claim 6, wherein in a state in which the first compensation part (310a) and the second compensation part (310b) are engaged with each other, a space (S) is formed between tip ends of the projections (311) and inner ends of the grooves (312). [8] A coaster (150) according to claim 6 or 7, wherein each of the first compensation part (310a) and the second compensation part (310b) includes one or more track grooves (313, 315) formed on one or both of a first and a second side of each of the projections (311) which are opposite to each other. [9] A coaster according to claim 8, wherein the first compensation part (310a) and the second compensation part (310b) are arranged such that the track grooves (315) of the first compensation part (310a) and the track grooves (313) of the second compensation part (310b) are stacked on top of each other at a position where the track grooves (315) of the first compensation part (310a) and the track grooves (313) of the second compensation part (310b) correspond to each other in a state in which the first compensation part (310a) and the second compensation part (310b) are engaged with each other. [10] Coaster (150) according to one of claims 6 to 9, further comprising: an adjustment part (340) coupled to a mounting hole (341) formed in the gear housing (260) and configured to support the first compensation part (310a) or the second compensation part (310b) in a direction in which the first compensation part and the second compensation part are fitted into each other.

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