Power transmission device of power steering device

Abstract

Power transmission device of an electric power steering device, comprising: a drive shaft (312) of a motor (310) with a receiving part (314) formed in a center of rotation of the motor and having the form of a hollow hole; a coupling element (330) inserted into an inner circumferential surface of the receiving part (314) and having an axial through-hole (332); and a transmission shaft (320) comprising a coupling part (322) formed on one side of the shaft for insertion into and coupling with the axial through-hole (332), and a gear part (324) formed on the other side of the shaft, wherein the receiving part (314) comprises one or more axial recesses (316a) and axial ribs (316b) formed on the inner circumferential surface of the receiving part, and the coupling member (330) comprises one or more recesses (334b) and ribs (334a).which are formed on the outer circumferential surface of this to correspond to the recesses (316a) and the ribs (316b) of the receiving part (314), wherein at least one of the ribs (334a) formed on the outer circumferential surface of the coupling member (330) is elastically deformed by compression and coupled to the rib (316b) formed on the inner circumferential surface of the receiving part (314), and wherein three ribs (334a) of the ribs (334) of the coupling member (330) are elastically deformed by compression and coupled to the ribs (316b) of the receiving part (314), each of the three ribs (334a) being designed such that it has a width narrower than a width of the recesses (316a) so that a space is formed, and each of the three ribs (334a) of the coupling member (330) is formed in such a way that it overlaps with a rib (316b) in the receiving part (314) adjacent to it, such that the rib (334a) is elastically deformed and coupled by pressure,wherein the three ribs (334a) are formed by the ribs (334) of the coupling member (330) at regular intervals in the circumferential direction on the coupling member (330).

Description

BACKGROUND OF THE INVENTION 1. Field of the invention The present invention relates to a power transmission device of a power steering system. In particular, the present invention relates to a power transmission device of a power steering system that is capable of reducing rattling noises generated when backlash increases due to wear of a gear or is generated due to a shock transmitted from a road surface via a vehicle wheel and a steering shaft, while improving the steering feel of a driver by reducing a locking sensation and rotational resistance between a drive shaft of an engine and a transmission shaft. 2. Description of the state of the art Fig. 1 is a partial sectional view illustrating a conventional power transmission device of a power steering system. As illustrated in Fig. 1, the power transmission device of a power steering device includes a motor 130, a drive shaft 205, an inner rotor 220, an outer rotor 215, an elastic body 210, a first bearing 250, a worm shaft 235, a worm wheel 245, a second bearing 270, a compression screw 255, a compression spring 265 and a gearbox housing 260. The motor 130 has a drive shaft 205 extending outside a motor housing, and a hollow outer rotor 215 is connected to the drive shaft 205 in such a way that they are locked together. The first bearing 250 and the second bearing 270 fix the worm gear 245 against a worm gear 240, which is installed on a steering shaft 102. The compression spring 265 supports the second bearing 270, which is configured to support the worm gear 245 against the worm gear 240 by means of the compression screw 255 and which is installed on the worm gear 245. Accordingly, when the compression screw 255 is tightened, it moves to compress the compression spring 265, and consequently the worm gear 245 can be brought into rigid engagement with the worm gear 240 by the compression force of the compression spring 265. An inner rotor 220 is connected to the worm shaft 235, wherein the inner rotor 220 is configured to be inserted into the outer rotor 215 connected to the drive shaft 205. The power transmission device of a power steering system as described above controls the drive of a motor by means of an electronic control unit provided in a vehicle, according to a driving condition of the vehicle, and the rotational force of the worm shaft generated by the drive of the motor is added to the rotational force of a steering wheel operated by a driver in order to be transmitted to a steering shaft in such a way as to smooth and stabilize the steering condition of the driver. However, the conventional power transmission device of a power steering system has a problem in that manufacturing and assembly errors in the worm shaft and a coupling part of the motor shaft accumulate to such an extent that the motor's drive shaft and the worm shaft are not positioned coaxially, the bearings feel jammed, and the rotational resistance of the worm shaft increases. Furthermore, as the worm and worm gear age, play develops due to wear, a rattling noise occurs due to flank backlash, and the rattling noise, caused by shocks transmitted from a road surface via a vehicle wheel and the steering shaft, creates an unpleasant feeling for the driver when operating the steering wheel. JP 2007 161165A discloses a power transmission mechanism arranged between a drive shaft and an output shaft to transmit power between the two shafts. SUMMARY OF THE INVENTION The present invention was made in view of the problems described above, and it is an object of the present invention to provide a power transmission device for an electric power steering device which is capable of reducing rattling noises which are generated when the backlash is increased due to wear of a gear, or which are generated due to shocks transmitted from a road surface via a vehicle wheel and a steering shaft, while improving the steering feel of a driver by reducing a locking sensation and rotational resistance between a drive shaft of an engine and a transmission shaft. To solve the problem, the present invention provides a power transmission device for an electric power steering device, comprising: a drive shaft of a motor with a receiving part formed at a center of rotation of the same; a coupling element inserted into the receiving part and having an axial through-hole; and a transmission shaft comprising a coupling element formed on one side of the same in order to be coupled to the axial through-hole, and a gear element formed on the other side of the same. According to the present invention described above, it is possible to reduce rattling noises generated by a power transmission device of an electric power steering device when the backlash increases due to wear of a gear, or generated due to shocks transmitted from a road surface via a vehicle wheel and a steering shaft, while improving the steering feel of a driver by reducing a locking sensation and rotational resistance between a drive shaft of an engine and a transmission shaft. BRIEF DESCRIPTION OF THE DRAWINGS The aforementioned and other problems, features, and advantages of the present invention will be better understood with reference to the following detailed description, which is given in conjunction with the accompanying drawings, in which: Fig. 1 is a partial sectional view illustrating a conventional power transmission device of an electric power steering device; Fig. 2 is a perspective view illustrating a power transmission device of an electric power steering device according to the present invention in a partially disassembled state; Fig. 3 is a sectional view illustrating a part of the power transmission device of an electric power steering device according to an embodiment of the present invention; Fig. 4a and Fig.Figure 4b shows sectional views illustrating part of the power transmission device of an electric power steering device according to the present invention in a state in which a rib is deformed; Figures 5a and 5b show sectional views illustrating part of a power transmission device of an electric power steering device according to different embodiments of the present invention; Figure 6 is a perspective view illustrating a power transmission device of an electric power steering device according to another embodiment of the present invention in a partially disassembled state; Figure 7 is a sectional view illustrating part of the power transmission device of an electric power steering device according to yet another embodiment of the present invention; and Figure 8 shows...Figure 8 is a perspective view illustrating a power transmission device of an electric power steering device according to yet another embodiment of the present invention in a partially disassembled state. DETAILED DESCRIPTION OF THE EXECUTION EXAMPLES Some exemplary embodiments of the present invention are described in detail below with reference to illustrative drawings. In describing the elements of the present invention, terms such as "first," "second," "A," "B," "(a)," "(b)," and the like may be used. These terms are used only to distinguish one structural element from other structural elements, and a property, sequence, sequence, and the like of a corresponding structural element are not limited by the term. It should be noted that if the description states that one component is "connected," "coupled," or "united" with another component, a third component may be "connected," "coupled," or "united" between the first and second components, even though the first component may be directly connected, coupled, or united with the second component. Fig. 2 is a perspective view showing a power transmission device of an electric power steering system according to the present invention in a partially disassembled state, and Fig. 3 is a sectional view illustrating a part of the power transmission device of an electric power steering system according to an embodiment of the present invention. Figs. 4a and 4b are sectional views illustrating a part of the power transmission device of an electric power steering system according to the present invention in a state in which a rib is deformed, and Figs. 5a and 5b are sectional views illustrating a part of a power transmission device of an electric power steering system according to different embodiments of the present invention. A characteristic structure is described in detail with reference to Figures 2 and 3. As illustrated in these drawings, the power transmission device of an electric power steering device according to the present invention comprises: a drive shaft 312 of a motor 310, which has a receiving part 314 formed at a pivot point; a coupling element 330 inserted into the receiving part 314 and having an axial through-hole 332; and a transmission shaft 320, which includes a coupling element 322 formed on one side of the shaft to be coupled to the axial through-hole 332, and a gear element 324 formed on the other side of the shaft. The motor 310 has a drive shaft 312 which extends towards the outside of the motor housing 318, with a receiving part 314 being formed in the center of rotation of the drive shaft 312. The receiving part 314 can be a groove with an axial depth at the center of rotation or a hollow hole. On the inner circumferential surface of the receiving part 314, one or more axial recesses 316a and ribs 316 are formed. The coupling element 330 includes an axial through-hole 332 and one or more ribs 334a and recesses 334b ​​formed on its outer circumferential surface to correspond to the recesses 316a and ribs 316b of the receiving part 314. The coupling element 330 is inserted into the receiving part 314 and coupled to it in such a way that at least one of the ribs 334a formed on the outer circumferential surface of the coupling element 330 is elastically deformed by compression and coupled to the ribs 316b formed on the inner circumferential surface of the receiving part 314. This means that at least one of the ribs 334a formed on the outer circumferential surface of the coupling member 330 is elastically deformed by pressure and coupled to the ribs 316b formed on the inner circumferential surface of the receiving part 314. In the present invention, for example, three ribs 334a, which are elastically deformed and coupled by pressure, are formed at regular intervals in the circumferential direction on the coupling member 330, as illustrated in Fig. 3. That is, three ribs 334a, elastically deformed and coupled by pressure, are formed on the coupling member 330 at intervals of 120°. Instead, two or more of the multiple ribs 334a formed on the outer circumferential surface of the coupling member 330 can be designed such that they are elastically deformed by pressure and coupled to the ribs 316b formed on the inner circumferential surface of the receiving part 314. In addition, the ribs 334a of the coupling member 330, which are partially elastically deformed by pressure and coupled to the ribs 316b formed on the inner circumferential surface of the receiving part 314, are formed such that they are smaller than the recesses 316a formed in the inner circumferential surface of the receiving part 314. Accordingly, at the time when the coupling member 330 and the receiving part 314 are coupled together, the ribs 334a formed on the outer circumferential surface of the coupling member 330 are formed in such a way that they are elastically deformed by pressure and coupled with the ribs 316b formed on the inner circumferential surface of the receiving part 314, such that they are smaller than the recesses 316a of the receiving part 314, so that the ribs 334a are deformed and coupled in empty spaces. That is, the width of each rib 334a is formed such that it is narrower than the width of each depression 316a in order to form a space and to overlap with an adjacent rib 316b in such a way that the rib 334a is elastically deformed and coupled by pressure. In other words, as illustrated in Fig. 4a, when a rib 334a, which is designed to be elastically deformed by pressure and is coupled to a rib 316b of the receiving part 314, is deformed and coupled as illustrated in Fig. 4b, an elastic recovery is continuously generated under the ribs 334a of the coupling member 330 to eliminate any play between the drive shaft 312 and the coupling member 330. Accordingly, with the aid of the elastic restoration of the ribs 334a, even if the drive shaft 312 of the motor 310, which is coupled to the coupling element 330, and the coupling part 322 of the transmission shaft 320, which will be described later, are not positioned coaxially or if the transmission shaft 320 is moved due to a shock exerted from the road surface, the center of rotation of the transmission shaft 320 moves at the time of driving the motor 310 to the drive shaft 312 of the motor 310, so that the driving force of the motor 310 can be transmitted stably to the transmission shaft 320. Here, the coupling element 330 is formed from a synthetic resin, such as rubber or plastic, to provide damping in such a way as to prevent the generation of rattling noises, even when shocks are exerted from a road surface while the vehicle is in motion. As described above, because at least one of the ribs 334a, which are formed on the outer circumferential surface of the coupling member 330, is elastically deformed by pressure and coupled to a rib 316b, which is formed on the inner circumferential surface of the receiving part 314, it can be prevented that the coupling member 330 is moved by the frictional force between the ribs 316b and 334a or slips in the axial direction. Additionally, as illustrated in Fig. 5, to prevent the coupling member 330 from moving or slipping in the axial direction, at least one rib 334a is formed below the ribs 334a formed on the outer circumferential surface of the coupling member 330 such that it is larger than a recess 316a. In particular, as illustrated in Fig. 5a, the width of the rib 334a can be such that it is wider than the width of the recess 316a, or, as illustrated in Fig. 5b, the projecting height of the rib 334a can be such that it is greater than the depth of the recess 316a. That is, in Fig. 5a, the projecting height of the rib 334a is less than the depth of the recess 316a in order to form a space, and the width of the rib 334a is such that it is wider than the width of the recess 316a, so that the recess 316a and the rib 334a, which overlap each other, are elastically deformed by pressure and coupled together. Additionally, in Fig. 5b the width of the rib 334a is narrower than the width of the recess 316a in order to form a space, and the projecting height of the rib 334a is formed such that it is greater than the depth of the recess 316a, so that the recess 316a and the rib 334a, which overlap each other, are elastically deformed by pressure and coupled together. Fig. 6 is a perspective view illustrating a power transmission device of an electric power steering device according to another embodiment of the present invention in a partially disassembled state, and Fig. 7 is a sectional view of a part of the power transmission device of an electric power steering device according to another embodiment of the present invention. A characteristic structure is described in detail below with reference to Figures 6 and 7. As illustrated in these drawings, one or more recesses 336b and one or more ribs 336a are formed on the inner circumferential surface of the coupling member 330, and a coupling part 322 of a transmission shaft 320, which will be described later, is inserted into the coupling member 330 and coupled to it. The transmission shaft 320 includes a coupling part 322, which is formed on one side of it and is coupled to an axial through-hole 332 of the coupling member 330, and a gear part 234, which is formed on the other side. Additionally, the coupling part 322, which is inserted into and coupled to the inner circumferential surface of the coupling element 330, includes one or more ribs 326b and recesses 326a formed on the outer circumferential surface of the same to correspond to the recesses 336b and ribs 336a formed on the inner circumferential surface of the coupling part 330, wherein at least one of the ribs 336a formed on the inner circumferential surface of the coupling element 330 is designed such that it is elastically deformed by pressure and is coupled to the ribs 326b formed on the outer circumferential surface of the coupling part 322. This means that at least one of the ribs 336a, which are formed on the inner circumferential surface of the coupling member 330, is elastically deformed by pressure and coupled to the ribs 326b, which are formed on the outer circumferential surface of the coupling part 322. In the present invention, for example, three ribs 336a, which are elastically deformed and coupled by pressure, are formed at regular intervals in the circumferential direction on the coupling member 330, as illustrated in Fig. 7. That is, three ribs 336b, elastically deformed and coupled by pressure, are formed on the coupling member 330 at intervals of 120° each. Instead, two or more of the multiple ribs 336a formed on the inner circumferential surface of the coupling member 330 can be designed such that they are elastically deformed by pressure and coupled to the ribs 326b formed on the coupling part 322. In addition, the ribs 336a of the coupling member 330, which are partially elastically deformed by pressure and coupled to the ribs 326b formed on the outer circumferential surface of the coupling part 322, are formed in such a way that they are smaller than the recesses 326a formed in the outer circumferential surface of the coupling part 322. Accordingly, at the time when the coupling member 330 and the coupling part 322 are coupled together, the ribs 336a formed on the inner circumferential surface of the coupling member 330 are formed in such a way that they are elastically deformed by pressure and coupled with the ribs 326b formed on the outer circumferential surface of the coupling part 322, such that they are smaller than the recesses 326a of the coupling part 322, so that the ribs 336a are deformed and coupled in empty spaces. That is, the width of each rib 336b is designed to be narrower than the width of each depression 326a in order to form a space and to overlap with an adjacent rib 326b in such a way that the rib 336a is elastically deformed and coupled by pressure. In other words, when a rib 336a, which is formed to be elastically deformed by pressure and coupled to a rib 326b of the coupling part 322, is deformed and coupled under the ribs 336a of the coupling member 330, an elastic restoration is continuously generated to eliminate any play between the transmission shaft 320 and the coupling member 330. Accordingly, with the aid of the elastic restoration of the ribs 336a, even if the drive shaft 312 of the motor 310, which is coupled to the coupling element 330, and the coupling part 322 of the transmission shaft 320, which will be described later, are not positioned coaxially or if the transmission shaft 320 is moved due to a shock exerted by a road surface, the center of rotation of the transmission shaft 320 moves at the time of driving the motor 310 to the drive shaft 312 of the motor 310 in such a way that the driving force of the motor 310 can be transmitted stably to the transmission shaft 320. As described above, the frictional force between the ribs 336a and 326b prevents the coupling member 330 from moving or slipping in the axial direction, since at least one of the ribs 336a, which are formed on the inner circumferential surface of the coupling member 330, is elastically deformed by pressure and coupled with a rib 326b, which is formed on the outer circumferential surface of the coupling part 322. Fig. 8 is a perspective view illustrating a power transmission device of an electric power steering device according to yet another embodiment of the present invention in a partially disassembled state. In the preceding embodiments, it was explained that the receiving part 314 of the motor shaft 312 is formed as a hole, and the gear part 324 of the transmission shaft 320 is formed as a sun gear of a planetary gear, and the coupling element 330 is coupled to the receiving part 314, and the coupling part 322 of the transmission shaft is coupled to the axial through-hole 332 of the coupling element 330; but the present invention is not limited thereto. That is, the receiving part 314 can be formed as a recess in the motor shaft 312, as illustrated in Fig. 8, and the gear part 324 of the transmission shaft 320 can be formed as a worm gear such that the coupling member 330 can be coupled to the receiving part 314 and the coupling part 322 of the transmission shaft 320 can be coupled to the axial through hole 332 of the coupling member 330. As described above, according to the present invention it is possible to reduce rattling noises that are generated when the clearance increases due to wear of a gear, or that are generated due to shocks transmitted from a road surface via a vehicle wheel and a steering shaft, while improving the steering feel of a driver by reducing a locking sensation and rotational resistance between a drive shaft of an engine and a transmission shaft.

Claims

Power transmission device of an electric power steering device, comprising: a drive shaft (312) of a motor (310) with a receiving part (314) formed in a center of rotation of the motor and having the form of a hollow hole; a coupling element (330) inserted into an inner circumferential surface of the receiving part (314) and having an axial through-hole (332); and a transmission shaft (320) comprising a coupling part (322) formed on one side of the shaft for insertion into and coupling with the axial through-hole (332), and a gear part (324) formed on the other side of the shaft, wherein the receiving part (314) comprises one or more axial recesses (316a) and axial ribs (316b) formed on the inner circumferential surface of the receiving part, and the coupling member (330) comprises one or more recesses (334b) and ribs (334a).which are formed on the outer circumferential surface of this to correspond to the recesses (316a) and the ribs (316b) of the receiving part (314), wherein at least one of the ribs (334a) formed on the outer circumferential surface of the coupling member (330) is elastically deformed by compression and coupled to the rib (316b) formed on the inner circumferential surface of the receiving part (314), and wherein three ribs (334a) of the ribs (334) of the coupling member (330) are elastically deformed by compression and coupled to the ribs (316b) of the receiving part (314), each of the three ribs (334a) being designed such that it has a width narrower than a width of the recesses (316a) so that a space is formed, and each of the three ribs (334a) of the coupling member (330) is formed in such a way that it overlaps with a rib (316b) in the receiving part (314) adjacent to it, such that the rib (334a) is elastically deformed and coupled by pressure,wherein the three ribs (334a) are formed by the ribs (334) of the coupling member (330) at regular intervals in the circumferential direction on the coupling member (330). Power transmission device according to claim 1, in which at least one of the ribs (334a) formed on the outer circumferential surface of the coupling member (330) is formed such that it has a width wider than the width of the recesses (316a) formed on the inner circumferential surface of the receiving part (314), such that the rib is elastically deformed and coupled by pressure. Power transmission device according to claim 1, in which at least one of the ribs (334a) formed on the outer circumferential surface of the coupling member (330) is formed such that it has a height greater than the depth of the recesses (316a) formed on the inner circumferential surface of the receiving part (314) such that the rib (334a) is elastically deformed and coupled by pressure. Power transmission device according to claim 1, wherein the coupling part (322) includes an axial recess (326a) and an axial rib (326b) formed on an outer circumferential surface, and the coupling member (330) includes one or more ribs (336a) and one or more recesses (336b) formed on an inner circumferential surface of the coupling member to correspond to the recess (326a) and the rib (326b) of the coupling part (322). Power transmission device according to claim 4, in which at least one of the ribs (336a) formed on the inner circumferential surface of the coupling member (330) is elastically deformed by pressure and coupled to the rib (326a) formed on the outer circumferential surface of the coupling part (322). Power transmission device according to claim 5, in which a rib is formed under the ribs (336a) of the coupling member (330), which is elastically deformed by pressure and coupled to the rib (326b) of the coupling part (322), such that it has a width which is narrower than the recess (326a) of the coupling part (322) in such a way that a space is formed, and is formed to overlap with the rib (326b) of the coupling part (322) adjacent to it in such a way that the rib is elastically deformed by pressure and coupled.

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