POLYMER DRIVE BELT PULLEY FOR ELECTRIC POWER STEERING

Abstract

Drive belt pulley assembly for an electric power steering system, comprising: a motor shaft (14) extending axially from an electric motor; and a drive pulley (16) coupled to the motor shaft (14) and arranged between the motor shaft (14) and a belt (20) to transmit the rotation of the motor shaft (14) to the belt (20), the drive pulley (16) comprising: a radial retaining section (30) with an inner diameter (36) defining a first section of a central opening (18) in which the motor shaft (14) is arranged, wherein the radial retaining section (30) transmits a radial load of the belt (20) to the motor shaft (14); and an axial retaining section (50) extending axially from the radial retaining section (30), wherein the axial retaining section (50) defines a second section of the central opening (18) in which the motor shaft (14) is arranged, wherein the inner diameter of the axial retaining section (50) engages in a splined mesh with the motor shaft (14) to rotatably couple the drive pulley (16) to the motor shaft (14), wherein the axial retaining section (50) includes a flange (70) which projects radially inwards from the inner diameter of the axial retaining section (50) to be arranged in a groove (72) of the motor shaft (14) in order to axially hold the drive pulley (16) relative to the motor shaft (14), wherein the axial retaining section (50) of the drive pulley (16) comprises a first arcuate section (58) and a second arcuate section (60), each having a semicircular cross-section and separated from each other by an axially extending slot (62), wherein the flange (70) of the axial retaining section (50) of the drive pulley (16) is located at a distal end (52) of the drive pulley (16) relative to the position of the electric motor.

Description

AREA OF INVENTION

[0001] This disclosure relates generally to steering systems and in particular to a polymer drive pulley for an electric power steering system. BACKGROUND

[0002] Vehicle steering systems typically include a driver interface, such as a steering wheel, connected to one end of a steering column. When the driver turns the steering wheel, the angular movement is transferred to the steering column, which then rotates. The other end of the steering column is connected to the vehicle's steered wheels, for example, via a rack and pinion drive. As the steering column rotates, the rack and pinion cause the wheels to turn, steering the vehicle in a desired direction.

[0003] Many steering systems incorporate a power steering mechanism that reduces the amount of force a driver needs to apply to turn the steering wheel the desired amount. A typical mechanism includes a motor shaft from an electric motor that drives the power steering mechanism. Some power steering mechanisms include a pulley assembly that is actuated by transferring rotation from the motor shaft to a drive pulley, which in turn drives the rotation of one or more pulleys via one or more belts.

[0004] A typical drive pulley is made of sintered iron, which requires post-processing to achieve the correct bore diameter. Such designs rely on friction due to an interference fit to transmit the motor torque to the synchronous belt. Assembling the design described above requires a press to mount the pulley to the motor shaft. An arrangement that reduces the costs associated with material and assembly processes would be well received in the field.

[0005] EP 3 385 572 A1 discloses an output pulley arrangement for an electric power steering system, comprising: a motor shaft extending axially from an electric motor, and a drive pulley coupled to the motor shaft and arranged between the motor shaft and a belt to transmit the rotation of the motor shaft to the belt and, via the belt, to an output pulley. The output pulley is coupled to a ball nut and comprises: a radial retaining section with an inner diameter defining a first section of a central opening in which the ball nut is arranged, the radial retaining section transmitting a radial load of the belt to the ball nut;and an axial retaining section extending in the axial direction from the radial retaining section in the form of hooks, wherein the axial retaining section defines a second section of the central opening in which the ball screw nut is arranged, wherein the output pulley is in splined connection with the ball screw nut to rotatably couple the output pulley to the ball screw nut, wherein the hooks of the axial retaining section each include a projection extending radially inward from the inner diameter of the axial retaining section to be arranged in a groove of the ball screw nut to axially hold the output pulley relative to the ball screw nut.

[0006] US Patent 5,275,577 A discloses a drive pulley arrangement comprising: a motor shaft extending axially from an electric motor; and a drive pulley coupled to the motor shaft and positioned between the motor shaft and a belt to transmit the rotation of the motor shaft to the belt.The drive pulley comprises: a radial retaining section with an inner diameter defining a central opening in which the motor shaft is arranged, wherein the radial retaining section transmits a radial load of the belt to the motor shaft via a splined connection; and an axial retaining section extending axially from the radial retaining section, wherein the axial retaining section defines hooks between which the motor shaft is arranged, each hook having a projection extending radially inward from the inner diameter of the axial retaining section to be arranged in a groove of the motor shaft in order to hold the drive pulley axially relative to the motor shaft.

[0007] US Patent 7,198,425 B2 discloses a connection between two nested shafts that, when assembled, transmit torque via a splined connection. The inner shaft has an axial extension with a groove that can be inserted through a bore in the outer shaft, so that the groove protrudes from the outer shaft or, alternatively, is located within the bore. To axially secure the two shafts, a clamping device, e.g., a snap ring, is inserted into the groove.

[0008] A pulley made of a polymer is known from EP 2 713 078 B1.

[0009] Expansion joints are known from HILDEBRAND, Siegfried: Indirect expansion joints. In: Precision Mechanical Components, 2nd, revised edition. Munich: Hanser, 1972. Title page + imprint + table of contents pp. 280-283. ISBN 3-446-10061-x.

[0010] DE 23 14 000 A teaches how to connect a toothed section of an outer diameter of a pulley with a radial retaining section over an annular web.

[0011] The object of the present invention is to provide an improved drive pulley arrangement.

[0012] This problem is solved by a drive pulley arrangement with the features of claim 1, a drive pulley arrangement with the features of claim 7 and a drive pulley with the features of claim 13.

[0013] Advantageous embodiments are specified in the dependent claims. SUMMARY

[0014] According to one aspect of the disclosure, a drive pulley assembly for an electric power steering system comprises a motor shaft extending axially from an electric motor. The pulley assembly also includes a drive pulley coupled to the motor shaft and positioned between the motor shaft and a belt to transmit the rotation of the motor shaft to the belt. The drive pulley includes a radial retaining section with an inner diameter that defines a first section of a central opening in which the motor shaft is located, the radial retaining section transmitting a radial load of the belt to the motor shaft.The drive pulley also includes an axial retaining section extending axially from the radial retaining section, the axial retaining section defining a second section of the central opening in which the motor shaft is arranged, the inner diameter of the axial retaining section engaging in a serrated mesh with the motor shaft to rotatably couple the drive pulley to the motor shaft, the axial retaining section including a flange projecting radially inward from the inner diameter of the axial retaining section to be arranged in a groove of the motor shaft to axially hold the drive pulley relative to the motor shaft.

[0015] According to another aspect of the disclosure, a drive pulley assembly for an electric power steering system comprises a motor shaft extending axially from an electric motor. The pulley assembly also includes a drive pulley coupled to the motor shaft and positioned between the motor shaft and a belt to transmit the rotation of the motor shaft to the belt. The drive pulley is made of a polymer material. The drive pulley includes a radial retaining section with an inner diameter that defines a first section of a central opening in which the motor shaft is located, the radial retaining section transmitting a radial load of the belt to the motor shaft.The drive pulley also has an axial retaining section extending axially from the radial retaining section, the axial retaining section defining a second section of the central opening in which the motor shaft is arranged, the inner diameter of the axial retaining section engaging in serration with the motor shaft to couple the drive pulley to the motor shaft in a rotational manner, the axial retaining section comprising a first arcuate section and a second arcuate section separated from each other by an axially extending slot to provide flexibility for the axial retaining section.

[0016] According to another aspect of the disclosure, a drive pulley is provided for coupling to a motor shaft of an electric motor that drives an electric power steering system of a vehicle. The drive pulley comprises a radial retaining section with an inner diameter that defines a first section of a central opening in which the motor shaft is arranged.The drive pulley also has an axial retaining section extending axially from the radial retaining section, the axial retaining section defining a second section of the central opening in which the motor shaft is arranged, the axial retaining section including a flange projecting radially inward from the inner diameter of the axial retaining section to be positioned in a groove of the motor shaft to axially retain the drive pulley relative to the motor shaft, the axial retaining section including a first arcuate section and a second arcuate section separated from each other by an axially extending slot to provide flexibility for the axial retaining section, the drive pulley being formed from a polymer material.

[0017] These and other advantages and features will become clearer from the following description in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The subject matter, which is considered the invention, is specifically highlighted and claimed in detail in the claims at the end of the description. The foregoing and further features and advantages of the invention will become clear from the following detailed description in conjunction with the accompanying drawings, in which: Fig. 1 is a schematic sectional view of a drive pulley arrangement; Fig. 2 a perspective view of the first end of a drive pulley of the drive pulley assembly; Fig. 3 is a perspective view of the second end of the drive pulley; Fig. 4 is a side view of the drive pulley; Fig. 5 is a sectional view of the drive pulley; Fig. 6 is a view of a first end of the drive pulley; and Fig. Figure 7 shows a view of the second end of the drive pulley. DETAILED DESCRIPTION

[0019] With reference to the figures, which describe the present disclosure with reference to specific embodiments, it is understood that the disclosed embodiments merely illustrate the present disclosure, which may be implemented in various and alternative forms. Various elements of the disclosed embodiments may be combined or omitted to form further embodiments of the present disclosure. The figures are not necessarily drawn to scale; some features may be exaggerated or minimized to show details of certain components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for instructing the person skilled in the art in applying the present disclosure.

[0020] Fig. Figure 1 shows part of an electric power steering (EPS) system 10. The EPS system can be used in conjunction with a motor vehicle. The EPS system 10 comprises a power package with a power device, such as an electric motor (not shown). The power package is an assembly containing various components, such as a motor in a motor housing 12 and a control unit. A motor shaft 14 extends axially A from the power package to a distal shaft end 15 relative to the electric motor.

[0021] A drive pulley 16 is coupled to the motor shaft 14. The drive pulley 16 is at least partially formed from a polymer material. In some embodiments, the drive pulley 16 is an injection-molded polymer drive pulley. The drive pulley 16 defines a substantially cylindrical opening 18 extending in axial direction A. The opening 18 is dimensioned to surround a portion of the motor shaft 14. A portion of the drive pulley 16 is positioned between the motor shaft 14 and a belt 20. The belt 20 surrounds the drive pulley 16 and a driven pulley (not shown) to transmit the rotation of the drive pulley 16 to the driven pulley, ultimately resulting in the transmission of an assisting force for steering maneuvers.For example, the assisting force can be provided to a rack and pinion element (not shown) of a steering system to impart a rotation to road wheels.

[0022] Although the drive pulley arrangement described here refers to an electric rack and pinion power steering system, it is understood that the scope of protection of the disclosed invention includes other applications that would benefit from the drive pulley arrangement.

[0023] The Fig. Figures 2-7 illustrate the drive pulley 16 in more detail. Referring to the Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6 to Fig. 7 and with continued reference to Fig. The drive pulley 16 comprises a radial retaining section 30 extending from a first end 32 to a second end 34. The radial retaining section 30 extends radially from an inner diameter 36 to an outer diameter 38. The inner diameter 36 surrounds a portion of the motor shaft 14. In some embodiments, the inner diameter 36 and the motor shaft 14 are in an interference fit. In other embodiments, the inner diameter 36 and the motor shaft have a sliding fit.

[0024] An annular web 40 extends radially outward from the radial retaining section 30 to connect the radial retaining section 30 to a toothed section 42 of the drive pulley 16. The annular web 40 is used for certain applications, such as in Fig. 1 shown; however, other embodiments with different design requirements (e.g., degree of interference between shaft and pulley, tolerance sensitivity with respect to the final outer diameter, formability, etc.) do not require a web 40 as shown in the Fig. Figures 2-7 show the toothed section 42 having an outer diameter surface comprising several teeth 44 for engaging the belt 20. The radial retaining section 30 transmits the radial load of the belt 20 to the motor shaft 14. Embodiments incorporating the annular web 40 provide dimensional separation between the tooth interface and the radial retaining section, thus reducing expansion due to the interference fit. The annular web 40 also aids in the manufacture of the pulley by minimizing thick sections that are problematic in injection molding. Furthermore, the annular web 40 reduces the mass required for large pulleys.

[0025] An axial retaining section 50 of the drive pulley 16 extends axially from the second end 34 of the radial retaining section 30 to a distal end 52 of the drive pulley. Like the radial retaining section 30, the axial retaining section 50 extends radially outward from an inner diameter to an outer diameter. The inner diameter of the axial retaining section 50 defines a remainder of the central opening 18 in combination with the inner diameter of the radial retaining section 30. In some embodiments, the cross-sectional area of ​​the central opening 18 remains substantially constant over its entire axial distance. However, in some embodiments, the opening 18 tapers to reduce the cross-sectional area as it transitions from the section defined by the radial retaining section 30 to the section defined by the axial retaining section 50.The inner diameter of the axial holding section 50 has serrated teeth 54 which are rotationally coupled to a serrated area 56 of the motor shaft 14.

[0026] The axial retaining section 50 comprises a first arcuate section 58 and a second arcuate section 60, separated from each other by an axially extending slot 62. In other words, the axial retaining section 50 does not extend continuously in the circumferential direction. In some embodiments, the arcuate sections 58 and 60 have a semicircular cross-section. The slot 62 provides a material break between the first arcuate section and the second arcuate section 60. This material break provides flexibility for the axial retaining section 50 because the drive pulley 16 is made of a material such as a polymer, which is not as rigid as metal. This is advantageous during the installation of the drive pulley 16 onto the motor shaft 14.In particular, the motor shaft 14 can be inserted into the central opening 18 of the drive pulley 16 (or the drive pulley 16 installed above the motor shaft 14), while a radially inwardly projecting axial retaining feature 70 of the axial retaining section 50 is accommodated.

[0027] While the axial retaining section 50 is described above as having two arcuate sections 58, 60, it is understood that the axial retaining section 50 can contain more arcuate sections, each separated by a respective slot 62. In such embodiments, the arcuate sections are axially extending fingers.

[0028] The axial retaining feature 70 is a radially inwardly projecting structure, such as a flange, and provides axial retention of the drive pulley 16 relative to the motor shaft 14. During assembly, the drive pulley 16 is slid axially over the motor shaft 14 until the axial retaining feature 70 is positioned in a recessed groove 72 of the motor shaft 14. In some embodiments, the recessed groove 72 is located near the distal end 15 of the motor shaft 14, and in other embodiments, the axial retaining feature 70 is located at the distal end 52 of the drive pulley. The flexible capability of the axial retaining section 50 allows the arc-shaped sections 58, 60 to deflect outwards during assembly, so that the axial retaining feature 70 can move over the outer diameter of the motor shaft 14 until the axial retaining feature 70 is positioned in the recessed groove 72 of the motor shaft 14 (e.g.B. locked or snapped into place).

[0029] Once the drive pulley 16 and the motor shaft 14 are in an assembled state (i.e., the axial retaining feature 70 is within the groove 72), the deflection of the axial retaining section 50 is eliminated by a compression ring 74 surrounding the axial retaining section 50. In some assembly processes, the compression ring 74 is fitted to the drive pulley 16 before the drive pulley 16 is fitted to the motor shaft 14. In other embodiments, a compression ring is not required at all. In some embodiments, the compression ring 74 is a split metal ring, such as a split steel ring.

[0030] The embodiments disclosed here reduce the cost of the drive pulley.

Claims

[1] Drive belt pulley assembly for an electric power steering system, comprising: a motor shaft (14) extending axially from an electric motor; and a drive pulley (16) coupled to the motor shaft (14) and arranged between the motor shaft (14) and a belt (20) to transmit the rotation of the motor shaft (14) to the belt (20), the drive pulley (16) comprising: a radial retaining section (30) with an inner diameter (36) defining a first section of a central opening (18) in which the motor shaft (14) is arranged, wherein the radial retaining section (30) transmits a radial load of the belt (20) to the motor shaft (14); and an axial retaining section (50) extending axially from the radial retaining section (30), wherein the axial retaining section (50) defines a second section of the central opening (18) in which the motor shaft (14) is arranged, wherein the inner diameter of the axial retaining section (50) engages in a splined mesh with the motor shaft (14) to rotatably couple the drive pulley (16) to the motor shaft (14), wherein the axial retaining section (50) includes a flange (70) which projects radially inwards from the inner diameter of the axial retaining section (50) to be arranged in a groove (72) of the motor shaft (14) in order to axially hold the drive pulley (16) relative to the motor shaft (14), wherein the axial retaining section (50) of the drive pulley (16) comprises a first arcuate section (58) and a second arcuate section (60), each having a semicircular cross-section and separated from each other by an axially extending slot (62), wherein the flange (70) of the axial retaining section (50) of the drive pulley (16) is located at a distal end (52) of the drive pulley (16) relative to the position of the electric motor. [2] Drive pulley arrangement for an electric power steering system according to claim 1, wherein the drive pulley (16) is made of a polymer material. [3] Drive pulley arrangement for an electric power steering system according to claim 1, further comprising a compression ring (74) surrounding the axial retaining section (50). [4] Drive pulley arrangement for an electric power steering system according to claim 3, wherein the compression ring (74) is a split metal ring. [5] Drive pulley arrangement for an electric power steering system according to claim 1, further comprising a toothed section (42) on an outer diameter (38) of the drive pulley (16) to engage with the belt (20). [6] Drive pulley arrangement for an electric power steering system according to claim 5, wherein the toothed section (42) of the outer diameter (38) of the drive pulley (16) is connected to the radial retaining section (30) with an annular web (40). [7] Drive belt pulley assembly for an electric power steering system, comprising: a motor shaft (14) extending axially from an electric motor; and a drive pulley (16) coupled to the motor shaft (14) and arranged between the motor shaft (14) and a belt (20) to transmit the rotation of the motor shaft (14) to the belt (20), wherein the drive pulley (16) is made of a polymer material and includes: a radial retaining section (30) with an inner diameter (36) defining a first section of a central opening (18) in which the motor shaft (14) is arranged, wherein the radial retaining section (30) transmits a radial load of the belt (20) to the motor shaft (14); and an axial retaining section (50) extending axially from the radial retaining section (30), wherein the axial retaining section (50) defines a second section of the central opening (18) in which the motor shaft (14) is arranged, wherein the inner diameter of the axial retaining section engages in a serrated mesh with the motor shaft (14) to rotatably couple the drive pulley (16) to the motor shaft (14), wherein the axial retaining section (50) comprises a first arcuate section (58) and a second arcuate section (60), each having a semicircular cross-section and separated from each other by an axially extending slot (62) to provide flexibility for the axial retaining section (50), wherein the axial retaining section (30) comprises a flange (70) projecting radially inward from the inner diameter of the axial retaining section (50) to be arranged in a groove (72) of the motor shaft (14) to axially retain the drive pulley (16) relative to the motor shaft (14), wherein the flange (70) of the axial retaining section (50) of the drive pulley (16) is located at a distal end (52) of the drive pulley (16) relative to the position of the electric motor. [8] Drive pulley arrangement for an electric power steering system according to claim 7, wherein the first arc-shaped section (58) and the second arc-shaped section (60) each have a semicircular cross-section. [9] Drive pulley arrangement for an electric power steering system according to claim 8, further comprising a compression ring (74) surrounding the axial retaining section (50). [10] Drive pulley arrangement for an electric power steering system according to claim 9, wherein the compression ring (74) is a split metal ring. [11] Drive pulley arrangement for an electric power steering system according to claim 7, further comprising a toothed section (42) on an outer diameter (38) of the drive pulley (16) to engage with the belt (20). [12] Drive pulley arrangement for an electric power steering system according to claim 11, wherein the toothed section (42) of the outer diameter (38) of the drive pulley (16) is connected to the radial retaining section (30) with an annular web (40). [13] Drive pulley (16) for coupling to a motor shaft (14) of an electric motor which drives an electric power steering system of a vehicle, wherein the drive pulley (16) comprises: a radial retaining section (30) with an inner diameter (36) that defines a first section of a central opening (18) in which the motor shaft (14) is arranged; and an axial retaining section (50) extending axially from the radial retaining section (30), wherein the axial retaining section (50) defines a second section of the central opening (18) in which the motor shaft (14) is arranged, wherein the axial retaining section (50) includes a flange (70) projecting radially inward from the inner diameter of the axial retaining section (50) to be arranged in a groove (72) of the motor shaft (14) to axially retain the drive pulley (16) relative to the motor shaft (14), wherein the axial retaining section (50) includes a first arcuate section (58) and a second arcuate section (60), each having a semicircular cross-section and separated from each other by an axially extending slot (62) to provide flexibility for the axial retaining section (50), wherein the drive pulley (16) is formed from a polymer material. wherein the inner diameter of the axial retaining section is in serrated engagement with the motor shaft (14), wherein the flange (70) of the axial retaining section (50) of the drive pulley (16) is located at a distal end (52) of the drive pulley (16) relative to the position of the electric motor and the groove (72) is located near the distal end (15) of the motor shaft (14).

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