POWER STEERING SYSTEM AND POWER STEERING SYSTEM AUXILIARY ASSEMBLY

Abstract

Power steering system (10), comprising: a rack housing (12) which is arranged to receive a rack element (16) which is displaceable in the longitudinal direction; an auxiliary cover (18) connected to the rack housing (12), wherein the rack housing (12) and the auxiliary cover (18) define a cavity; and an auxiliary arrangement which is at least partially arranged within the cavity, the auxiliary arrangement comprising: a drive assembly (20) which is connected to the rack housing (12), wherein the drive assembly (20) has a drive assembly shaft extending therefrom; a driving pulley (30) which is coupled to the drive unit shaft; a single bearing (82) arranged in a bore defined by the driving pulley (30); a mechanical fastening element that couples the driving pulley (30) to the auxiliary cover (18); and a driven pulley (32) arranged around the rack element (16).

Description

AREA OF INVENTION

[0001] The embodiments disclosed here relate to power steering systems and in particular to an electric power steering system with a driving cam pulley. BACKGROUND

[0002] A power steering system may include a power steering mechanism that is movably mounted relative to a housing during assembly. The power steering mechanism is mounted movably to allow other assembly operations to take place before final assembly. Once these other operations are complete, the power steering mechanism is then positioned on the housing. Maintenance of the power steering mechanism can alter the tension or engagement between other components of the power steering system, which can affect the system's performance.

[0003] Existing systems comprise two toothed pulleys and a smooth tensioner pulley in combination with a synchronous belt. The distance between the driving and driven pulleys is fixed within the rack housing such that the tensioner pulley incorporates a cam for adjusting the belt tension. Once the desired belt tension is achieved, the tensioner pulley's cam is locked in place with a threaded fastener. The driving pulley has internal teeth that mesh with external teeth on the drive unit's motor shaft. However, the reverse configuration is also being considered. The driving pulley is radially supported at both ends within the rack housing by ball bearings.The ball bearings are press-fitted to the driving pulley, and the bearing closest to the pinion is held axially to the housing between a bearing bore and a chamfered retaining ring. The system described above allows the factory-set belt tension to remain unchanged if the drive unit is replaced during maintenance.

[0004] The existing systems require an additional component, specifically the tensioning cam / pulley, to allow for belt tension adjustment. While these systems eliminate the possibility of belt drive misalignment caused by motor shaft tilt, they are susceptible to misalignment due to bearing bore offset. The drive pulley design requires two bearings, meaning each bearing has excess load-carrying capacity.

[0005] US 2019 / 0375448 A1 discloses a power steering system comprising a rack housing suitable for receiving a longitudinally displaceable rack element. The power steering system also includes an auxiliary cover connected to the rack housing, wherein the rack housing and the auxiliary cover define a cavity. The power steering system further comprises an auxiliary assembly located at least partially within the cavity. The auxiliary assembly includes a drive unit connected to the rack housing and the auxiliary cover, wherein the drive unit has a drive unit shaft extending therefrom.The auxiliary assembly also includes a drive pulley with a drive pulley shaft extending between the rack housing and the auxiliary cover, wherein the drive pulley shaft and the drive unit shaft are separate shafts and are functionally coupled. The auxiliary assembly also includes a driven pulley arranged around the rack element. Further prior art is known from US 2018 / 0 118 252 A1, US 2017 / 0 029 017 A1, US 2007 / 0 102 230 A1, US 2006 / 0 183 583 A1, US 10 995 799 B2, DE 601 16 472 T2 and DE 11 79 770 A. SUMMARY

[0006] The object of the invention is to provide an improved power steering system and an improved power steering system auxiliary assembly.

[0007] To solve the problem, a power steering system with the features of claim 1 and a power steering system auxiliary assembly with the features of claim 9 are provided. Advantageous embodiments of the invention can be found in the dependent claims, the description, and the drawings.

[0008] According to one aspect of the disclosure, a power steering system comprises a rack housing arranged to accommodate a longitudinally displaceable rack element. The system also comprises an auxiliary cover connected to the rack housing, the rack housing and auxiliary cover defining a cavity. The system further comprises an auxiliary assembly located at least partially within the cavity. The auxiliary assembly includes a drive unit connected to the rack housing, the drive unit having a drive unit shaft extending from it. The auxiliary assembly also includes a driving pulley connected to the drive unit shaft. The auxiliary assembly further comprises a single bearing located in a bore defined by the driving pulley.The auxiliary assembly also includes a mechanical fastener that couples the driving pulley to the auxiliary cover. The auxiliary assembly also comprises a driven pulley arranged around the rack element.

[0009] According to another aspect of the disclosure, an auxiliary assembly of a power steering system is provided, which is arranged in a cavity defined by a rack housing and an auxiliary cover. The auxiliary assembly includes a drive unit connected to the rack housing, the drive unit having a drive unit shaft extending from it. The auxiliary assembly also includes a driving pulley connected to the drive unit shaft. The auxiliary assembly further includes a bearing arranged in a bore defined by the driving pulley.The auxiliary assembly further includes a mechanical fastening element that couples the driving pulley to the auxiliary cover, wherein the bore of the driving pulley has a central axis and the mechanical fastening element has a fastening element axis, the central axis being offset from the fastening element axis.

[0010] These and other advantages and features will be better understood in the following description in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The subject matter, which is considered to be the present disclosure, is specifically disclosed and separately claimed in the claims at the end of the description. The foregoing and other features and advantages of the present disclosure will become apparent from the following detailed description in conjunction with the accompanying drawings, in which: Fig. 1. A cross-sectional view of a part of a power steering system according to one aspect of disclosure; and Fig. 2 is a schematic top view of a driving pulley of the power steering system. DETAILED DESCRIPTION

[0012] With reference to the figures, the present disclosure is now described in relation to certain embodiments, without limiting them. It should be understood that the disclosed embodiments are merely examples of the present disclosure, which is implemented in various and alternative forms. The figures are not necessarily to scale, as some features may be emphasized or minimized to show details of certain components. Therefore, certain structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for instructing a person skilled in the art on how to apply the present disclosure.

[0013] With reference to Fig. Figure 1 shows a power steering system 10, for example, an electric power steering system that can be used in conjunction with a motor vehicle. The power steering system 10 comprises a rack housing 12 and a power steering assist system 14. A longitudinally displaceable rack element 16 extends at least partially through the rack housing 12. The rack element 16 is effectively connected to a driven pulley 32 to allow translation or displacement along a longitudinal axis A relative to the rack housing 12, in order to enable the pivoting or turning of at least one vehicle wheel (not shown).

[0014] The power steering assist system 14 can comprise an auxiliary cover 18, a drive unit 20, and an auxiliary assembly 22. The auxiliary cover 18 can be effectively connected to an end 23 of the rack housing 12. At least a portion of the rack housing 12 can extend into and / or through the auxiliary cover 18. The auxiliary assembly 22 can be arranged in a cavity defined between portions of the auxiliary cover 18 and the rack housing 12. The auxiliary cover 18 can have a variety of features for rotatably mounting components of the auxiliary assembly 22 and / or the rack element 16.

[0015] The drive unit 20 can, as in Fig. The drive unit 20, as shown in Figure 1, may be effectively connected to a part of the rack housing 12, or, in other embodiments, effectively connected to a part of the auxiliary cover 18. The drive unit 20 may include an electric motor or similar device housed in a motor casing. The drive unit 20 may also include a drive unit motor shaft 24 extending from the drive unit 20 along an axis B that is parallel, but not coaxial, to the longitudinal axis A along which the rack element 16 extends.

[0016] The drive unit motor shaft 24 is toothed with a driving pulley 30 to enable the transmission of motor shaft torque from the drive unit motor shaft 24 to the driving pulley 30. The drive unit motor shaft 24 is inserted into a hollow end of the driving pulley 30 and toothed with it or coupled by a mechanical fastening.

[0017] The auxiliary assembly 22 can be arranged to exert an auxiliary force from the drive unit 20 onto the rack element 16 to enable the pivoting movement of at least one vehicle wheel. The auxiliary assembly 22 comprises the driving pulley 30 and the driven pulley 32, thus constituting a belt drive system. In particular, however, a tensioning pulley (or idler pulley) is not present in the embodiments of the entire assembly presented here. The driven pulley 32 is arranged around the rack element 16. The steering assistance force can be transmitted from the driving pulley 30 to the driven pulley 32 via a belt 90 that extends around the driving pulley 30 and the driven pulley 32.

[0018] Now, with reference to Fig. 1 and Fig. 2 is the driving pulley 30 in Fig. 2 is shown in more detail. The driving pulley 30 is referred to here as a cam-driven pulley. The driving pulley 30 is made of plastic in some embodiments, but alternative materials such as metal can be used to form the driving pulley 30 in other embodiments. A first end 70 of the driving pulley 30 contains a split internal toothing, which is radially pressed together with a steel band 72, and is configured to engage an external toothing portion of the drive unit motor shaft 24 to form the toothed coupling described above for transmitting torque from the motor shaft 24 to the driving pulley 30 ( Fig. 1) A second end 74 of the driving pulley 30 includes a shaped flange 75 extending radially from an outer diameter 76 and defining a bearing bore 78 with an inner diameter 80. A bearing 82 is pressed into the bearing bore 78 of the driving pulley 30 and includes a cam disc integrated on an inner surface 84 thereof to allow tensioning of a belt 90 that extends around the driving pulley 30 and the driven pulley 32. The bearing cam disc is fastened to the auxiliary cover 18 by a threaded fastener 92.

[0019] As in Fig.As shown more clearly in Figure 2, the central axis B of the bearing bore 78 of the driving pulley 30 is offset relative to the axis C of a bearing opening 95 in which the threaded fastening element 92 is located. In other words, the opening 95 of the bearing is not centered. The offset between the axis C of the bearing opening and the axis B of the bearing bore maintains the desired belt tension. The degree to which axes B and C are offset can vary depending on the specific application. In some embodiments, the offset is at least 0.25 millimeters. In such an embodiment, a total radial movement of 0.5 millimeters is permissible. Regardless of the degree of offset, it should be understood that the offset is intentional and calculated and is not due to manufacturing processes or tolerances.

[0020] The embodiments presented here eliminate the tensioning pulley, which adds cost and friction to the belt drive. Since only a single ball bearing is used with the driving pulley 30, the driving pulley is also able to rotate around this bearing and align itself with the driven pulley 32.

[0021] In other drive unit systems, the belt tension may be reset after a drive unit maintenance procedure in which the drive unit is removed. Resetting the belt tension can lead to improperly set belt tension, which may reduce auxiliary loads or increase system friction.

[0022] The embodiments disclosed here enable the belt tension to retain or maintain its original factory setting and minimize fluctuations in belt tension even during maintenance work in which the drive unit 20 is removed.

[0023] The embodiments disclosed here also separate the drive unit 20 from the belt tensioning process, in contrast to other unit systems. This separation of the drive unit 20 from the belt tensioning process allows a service technician to remove only the old drive unit, clean the sealing surface, and install the new drive unit on the rack housing 12 and / or the auxiliary cover 18. This prevents a service technician from altering the factory belt tension setting, thus protecting the friction and durability functions of the system.

[0024] The assembly of the power steering system 10 is further improved by the fact that the belt tensioning can be carried out before the installation of the drive unit 20 and / or the auxiliary cover 18. Pre-tensioning simplifies the assembly process of the power steering system 10 and simultaneously prevents changes in belt tension after the installation of the drive unit 20.

[0025] Although the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to these disclosed embodiments. Rather, the present disclosure can be modified to include any number of variations, changes, substitutions, or equivalent arrangements not previously described, but which are consistent with the spirit and scope of the present disclosure. Furthermore, although various embodiments of the present disclosure have been described, it is understood that aspects of the present disclosure may only encompass some of the described embodiments. Accordingly, the present disclosure is not to be considered as limited by the foregoing description.

Claims

[1] Power steering system (10), comprising: a rack housing (12) which is arranged to receive a rack element (16) which is displaceable in the longitudinal direction; an auxiliary cover (18) connected to the rack housing (12), wherein the rack housing (12) and the auxiliary cover (18) define a cavity; and an auxiliary arrangement that is at least partially located within the cavity, the auxiliary arrangement comprising: a drive assembly (20) which is connected to the rack housing (12), wherein the drive assembly (20) has a drive assembly shaft extending therefrom; a driving pulley (30) which is coupled to the drive unit shaft; a single bearing (82) arranged in a bore defined by the driving pulley (30); a mechanical fastening element that couples the driving pulley (30) to the auxiliary cover (18); and a driven pulley (32) arranged around the rack element (16). [2] Power steering system (10) according to claim 1, wherein the bore of the driving pulley (30) has a central axis and the mechanical fastening element has a fastening element axis, wherein the central axis is offset to the fastening element axis. [3] Power steering system (10) according to claim 2, wherein the central axis is offset by at least 0.25 millimeters from the fastening element axis. [4] Power steering system (10) according to claim 1, wherein the driving pulley (30) is coupled to the drive unit shaft by means of a toothed coupling. [5] Power steering system (10) according to claim 4, wherein the driving pulley (30) has an opening (95) at one end of the driving pulley (30) with internal teeth and the drive unit shaft has external teeth that engage with the internal teeth of the driving pulley (30). [6] Power steering system (10) according to claim 4, wherein the driving pulley (30) has external teeth and the drive unit shaft has internal teeth. [7] Power steering system (10) according to claim 1, wherein the driving pulley (30) is made of plastic. [8] Power steering system (10) according to claim 1, wherein the driving pulley (30) is made of metal. [9] Power steering system auxiliary assembly arranged in a cavity defined by a rack housing (12) and an auxiliary cover (18), the power steering system auxiliary assembly comprising: a drive unit (20) which is connected to the rack housing (12), wherein the drive unit (20) has a drive unit shaft extending therefrom, a driving pulley (30) which is coupled to the drive unit shaft; a bearing (82) arranged in a bore defined by the driving pulley (30); and a mechanical fastening element that couples the driving pulley (30) to the auxiliary cover (18), wherein the bore of the driving pulley (30) has a central axis and the mechanical fastening element has a fastening element axis, wherein the central axis is offset from the fastening element axis. [10] Power steering system auxiliary assembly according to claim 9, wherein the power steering system auxiliary assembly consists of a single bearing (82) in contact with the driving pulley (30). [11] Power steering system auxiliary assembly according to claim 9, wherein the central axis is offset by at least 0.25 millimeters to the fastening element axis. [12] Power steering system auxiliary assembly according to claim 9, wherein the driving pulley (30) is coupled to the drive unit shaft by means of a toothed coupling. [13] Power steering system auxiliary assembly according to claim 12, wherein the driving pulley (30) has an opening (95) at one end of the driving pulley (30) with internal teeth and the drive unit shaft has external teeth which engage in the internal teeth of the driving pulley (30). [14] Power steering system auxiliary assembly of claim 12, wherein the driving pulley (30) has external teeth and the drive unit shaft has internal teeth. [15] Power steering system auxiliary assembly according to claim 9, wherein the driving pulley (30) is made of plastic. [16] Power steering system auxiliary assembly according to claim 9, wherein the driving pulley (30) is made of metal.

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