Electromechanical assisted steering system
By using spring elements in an electromechanical auxiliary steering system for axial pretension of the worm shaft, the problems of high tolerance compensation cost and complex assembly in the prior art are solved, and cost reduction and effective maintenance of tolerance range are achieved.
Patent Information
- Application Number
- CN202010495121.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Priority Date
- 2019-06-05
- Filing Date
- 2020-06-03
- Publication Date
- 2024-12-13
- Estimated Expiration
- 2040-06-03
AI Technical Summary
Production tolerance compensation for worm drives in existing electromechanical assisted steering systems requires additional additional components, resulting in increased cost and assembly complexity, and inability to effectively deal with dimensional changes caused by temperature, humidity and wear.
The axial pretension of the worm shaft is used to compensate for the dimensional tolerance by selecting the appropriate spring stiffness, and axial openings are provided on the worm shaft to receive the spring element, reducing the impact on the drive shaft and avoiding other components. Use of
Reduces the production cost of worm drives, simplifies the assembly process, and effectively maintains the predefined pretension tolerance range, reduces sensitivity to axial dimensional deviations, and avoids the use of additional components.
Smart Images
Figure CN112046600B_ABST
Abstract
Description
Technical Field
[0001] The invention relates to an electromechanically assisted steering system having a worm drive. Background Art
[0002] Certain types of electromechanically assisted steering systems known in the prior art have a worm drive, whereby an auxiliary motor of the steering system is connected in a force-transmitting manner to the steering column (steering system with steering column assistance, usually expressed in English as "EPS column drive") or to a pinion engaged with the rack of the steering system (steering system with a single pinion drive or steering system with a dual pinion, usually expressed in English as "pinion drive EPS" and / or "dual pinion EPS").
[0003] The worm shaft of the worm drive is usually rotatably mounted on the end assigned to the electric motor by means of a fixed bearing. A clutch device and a pretensioning device are provided between the worm shaft and the drive shaft of the electric motor in order to apply a pretensioning force to the worm shaft in the axial direction and to keep the pretensioning force within a specific tolerance range, wherein the clutch device connects the worm shaft to the drive shaft in a torque-transmitting manner.
[0004] The worm shaft is movable with a predefined axial play, so that even in the presence of vibrations in the worm drive, it can follow the assigned worm gear without play due to the pretensioning force.
[0005] The pretensioning force is always designed to be within a predefined tolerance range. In this case, the specific requirement is to compensate for the production tolerances that exist in the worm drive. In addition, the dimensions of the worm gear mechanism may change due to temperature, humidity and / or wear, which also has to be compensated.
[0006] In the electromechanical assisted steering systems known in the prior art, additional components are often used to compensate for these tolerances. However, these additional components lead to further costs and increase the complexity of the assembly of the steering system, in particular the worm drive. Summary of the invention
[0007] It is therefore an object of the present invention to provide an electric power steering system in which the disadvantages of the prior art are remedied.
[0008] According to the invention, this object is achieved by an electromechanical assisted steering system, which has a worm drive, an electric motor, and a spring element, the worm drive comprising a worm shaft and a worm gear mechanism, and the electric motor having a drive shaft. The worm shaft has a first bearing portion at the end assigned to the electric motor, which is connected to the drive shaft in a torque-transmitting manner. The worm shaft has a second bearing portion, which is arranged at an end of the worm shaft facing away from the first bearing portion. The spring element is connected to the first bearing portion so as to transmit an axial force in the axial direction, so that the spring element axially pretensions the worm shaft relative to the worm gear mechanism. The tolerance compensation of the worm drive in the axial direction of the worm shaft is carried out only via the spring element. The worm shaft has an axial opening at its end assigned to the electric motor, and the spring element is at least partially received in the axial opening. The drive shaft at its end assigned to the worm shaft projects into the axial opening by no more than one eighth of the axial extent of the axial opening, or the drive shaft at its end assigned to the worm shaft terminates outside the axial opening.
[0009] Therefore, in the electromechanical assisted steering system according to the invention, no further components are required in addition to the spring element to compensate for dimensional tolerances of the worm drive, thereby reducing the production costs of the worm drive and simplifying assembly.
[0010] Specifically, in the electromechanical assisted steering system according to the present invention, compensation for axial dimension tolerances is achieved by selecting an appropriate spring stiffness of the spring element, wherein the spring stiffness is lower than the usual level in the prior art. When the spring stiffness is low, deviations in the axial dimension result in smaller changes in the axial pretensioning force.
[0011] The spring rate is selected such that, even in the case of expected maximum deviations of the axial dimension, the axial pretensioning force is still within a predefined tolerance range for the axial pretensioning force.
[0012] In this case, the predefined tolerance range is, for example, 200 N to 300 N, in particular 225 N to 275 N.
[0013] The spring element can be a helical spring or a wave spring, in particular a wave spring unit. Helical springs have the advantage that they are very advantageous in terms of production, thereby reducing the costs of the worm drive. Wave springs and / or wave spring units have the advantage that they require less axial construction space than a comparable helical spring when the same prestressing force must be applied.
[0014] According to one feature of the invention, the spring element is axially supported at one end thereof directly on the worm shaft, in particular wherein the spring element is axially supported at its other end on the drive shaft. The drive shaft thus absorbs the pretensioning force exerted by the spring element, which is why in this embodiment of the invention the electric motor is preferably configured as a double-bearing motor, wherein the drive shaft is mounted by means of two bearings.
[0015] A further feature of the invention provides that the worm shaft has an axial opening at its end assigned to the electric motor, in which the spring element is at least partially received. As a result, more construction space is available for the spring element and the spring stiffness of the spring element can be specified to be lower. As a result, the electromechanical assisted steering system is less sensitive to axial dimensional tolerances.
[0016] In another embodiment of the present invention, the spring element is supported directly on the axial limiting wall of the axial opening at one end. Therefore, no other components are arranged between the axial limiting wall and the spring element. Therefore, the entire length of the axial opening can be used as a construction space for the spring element.
[0017] Preferably, the drive shaft projects into the axial opening at its end assigned to the worm shaft, not exceeding one eighth of the axial extent of the axial opening, or ends outside the axial opening. As a result, more construction space is available for the spring element, and the spring stiffness of the spring element can be set to a lower specification. As a result, the electromechanical assisted steering system is less sensitive to axial dimensional tolerances.
[0018] Preferably, the drive shaft and the worm shaft do not contact each other. Therefore, there is no friction between the drive shaft and the worm shaft.
[0019] Optionally, a static radial offset and / or a dynamic radial offset between the drive shaft and the worm shaft during operation of the worm drive can be compensated by the spring element. Therefore, the spring element is designed so that the maximum radial offset between the drive shaft and the worm shaft is within the radial mobility of the spring element defined by the flexibility of the spring element.
[0020] According to one feature of the invention, the spring element is guided by the radial limiting wall of the axial opening and / or by a pin, which is arranged at the front of the drive shaft facing the worm shaft. In other words, the axial limiting wall of the axial opening represents a bushing for the spring element. The axial limiting wall prevents the spring element from buckling under loads on its end assigned to the worm shaft. Similarly, the pin prevents the spring element from buckling under loads on its end assigned to the drive shaft.
[0021] A further embodiment of the invention provides that the worm shaft is rotatably mounted on its second bearing part by means of a bearing, in particular a floating bearing, wherein the spring element is axially supported on the bearing at one end thereof, and wherein the bearing transmits the axial pretensioning force of the spring element to the worm shaft. Since the spring element in this embodiment is not supported on the drive shaft of the electric motor, the axial dimensional tolerances of the drive shaft are irrelevant for setting the pretensioning force. In this respect, the worm drive therefore represents a closed functional unit that can be tested.
[0022] In particular, the drive shaft has no axial pretensioning.Thus, in this embodiment, the electric motor can be configured as a single-bearing motor, wherein the drive shaft is mounted by means of a single bearing.
[0023] The bearing may be configured as a four-point bearing. This type of bearing is particularly suitable for transmitting axial forces, in particular between an outer race of the bearing and an inner race of the bearing. However, any other suitable type of bearing may also be used.
[0024] Another feature of the invention provides that the spring element is axially supported on the outer race of the support, wherein the worm shaft is mounted in the inner race of the support. The axial pretensioning force of the spring element is thus transmitted from the outer race of the support to the inner race and from the inner race to the worm shaft.
[0025] Preferably, the spring element has a spring constant of at most 100 N / mm, in particular a spring constant between 5 N / mm and 70 N / mm, preferably a spring constant between 10 N / mm and 30 N / mm. It has been shown that by setting the specification of the spring constant within this range, both the axial preload force can be reliably kept within the tolerance range and axial dimensional tolerances can be reliably compensated. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Other advantages and features of the present invention will be apparent from the following description and from the accompanying drawings, to which reference is made.
[0027] - Figure 1 The electromechanically assisted steering system according to the invention is shown in a cross-sectional view according to a first embodiment;
[0028] - Figure 2a and Figure 2b The cross-sectional view shows Figure 1 Details of the electromechanical assisted steering system according to the present invention; and
[0029] - Figure 3 An electromechanically assisted steering system according to the invention is shown in a sectional view according to a second embodiment. DETAILED DESCRIPTION
[0030] Figures 1 to 3 An electromechanically assisted steering system 10 for a motor vehicle is schematically shown, in each case in a sectional view, and comprises a worm drive 12 with a worm shaft 14 and a worm gear 16 .
[0031] The worm shaft 14 has, at one end thereof, a first bearing portion 18 on which the worm shaft 14 is rotatably mounted about its axial direction A by means of a fixed bearing 20 .
[0032] The worm shaft 14 has at its other end a second bearing portion 22 on which the worm shaft 14 is rotatably mounted about its axial direction A by means of a floating bearing 24 .
[0033] Furthermore, the floating bearing 24 together with the worm shaft 14 is pivotable in a predefined manner relative to the worm gear 16, wherein the center of the pivoting movement is in the region of the fixed bearing 20 and wherein the plane of the pivoting movement is parallel to the worm gear 16. Figure 1 The cutting planes coincide with each other.
[0034] In order to damp such a pivoting movement, a damping device 26 which is configured to damp a pivoting movement of the worm shaft 14 can be provided in the region of the floating bearing 24 .
[0035] exist Figure 1 and Figure 3 In the example actually shown in FIG. 2 , the damping device 26 is a spring.
[0036] The steering system 10 furthermore has an electric motor 28 which is assigned to the first bearing part 18 of the worm shaft 14 .
[0037] The electric motor 28 has a drive shaft 30 which is connected via a clutch device 32 in a torque-transmitting manner to the worm shaft 14 and therefore also to the worm gear 16 .
[0038] The worm gear mechanism 16 is in turn coupled in a force-transmitting manner to a steering column or a rack of the steering system 10. In this case, therefore, it is an electrically assisted steering system 10 with a steering column drive and / or a rack and pinion drive.
[0039] The electric motor 28 therefore assists the driver when steering the motor vehicle by applying an assisting force and / or an assisting torque to the steering column and / or the rack via the drive shaft 30 , the worm shaft 14 and the worm gear 16 .
[0040] In such an electromechanically assisted steering system, the worm shaft 14 must be axially prestressed relative to the worm gear 16 , so that the worm shaft 14 can follow the worm gear 16 even in the presence of vibrations in the worm drive 12 .
[0041] In this case, the pretensioning force is always designed to be within a predefined tolerance range, for example 200 N to 300 N, in particular 225 N to 275 N. In this case, the production tolerances present in the worm drive 12 must be compensated in order to keep the pretensioning force within the predefined tolerance range. In addition, the dimensions of the worm gear 16 may change due to temperature, humidity and / or wear, which also must be compensated.
[0042] exist Figure 1 The embodiments shown and Figure 3 In the illustrated embodiment, the pretensioning of the worm shaft 14 relative to the worm gear 16 is performed by means of a spring element 34 , the arrangement and operation of which will be described in more detail below.
[0043] The spring element 34 is, for example, a helical spring or a wave spring, in particular a wave spring unit.
[0044] according to Figure 1 , Figure 2a and Figure 2b In the illustrated first exemplary embodiment of the steering system 10 , the spring element 34 is supported at one end on the drive shaft 30 and at the other end directly on the worm shaft 14 .
[0045] Since in this embodiment an axial force is applied to the drive shaft 30 via the spring element 34 , the electric motor 28 is preferably a double-bearing motor, in which the drive shaft 30 is mounted by means of two bearings.
[0046] The worm shaft 14 has an axial opening 36 in the region of the first bearing portion 18 , in which the spring element 34 is at least partially received. The spring element 34 is supported at its end facing away from the drive shaft 30 on an axially delimiting wall of the axial opening 36 .
[0047] In this case, the radially limiting wall of the axial opening 36 serves as a guide for the spring element 34. In other words, the radially limiting wall of the axial opening 36 thus represents a bushing for the spring element 34 which prevents the spring element 34 from buckling under load.
[0048] Furthermore, a pin 38 is arranged on the drive shaft 30 at its end assigned to the worm shaft 14, wherein the spring element 34 is guided via the pin 38. The pin 38 prevents the spring element 34 from buckling under load at its end assigned to the drive shaft 30.
[0049] The spring element 34 is therefore guided at least at its two ends by radially limiting walls of the axial opening 36 and / or by the pin 38 , in order to prevent the spring element 34 from buckling under load.
[0050] Preferably, the drive shaft 30 and the worm shaft 14 do not contact each other, so that there is no direct contact between the drive shaft 30 and the worm shaft 14 .
[0051] Static radial offsets that may exist for this reason and / or dynamic radial offsets that occur between the drive shaft 30 and the worm shaft 14 during operation of the worm drive 12 are compensated by the spring element 34 .
[0052] The spring element 34 is therefore designed such that the maximum radial offset existing between the drive shaft 30 and the worm shaft 14 lies within the radial mobility of the spring element 34 defined by the flexibility of the spring element 34 .
[0053] like Figure 1 , Figure 2a and Figure 2b As indicated in FIG. 1 , the drive shaft 30 terminates outside the axial opening 36 and / or extends into the axial opening, and does not exceed the axial range of the axial opening 36 at most. One eighth of .
[0054] As a result, there is more construction space available for the spring element 34 , as a result of which the spring element can be dimensioned with a lower spring rate than is customary in the prior art.
[0055] More specifically, the spring element 34 has a spring constant K of at most 100 N / mm, preferably a spring constant K between 5 N / mm and 70 N / mm, further preferably a spring constant K between 10 N / mm and 30 N / mm.
[0056] This selection of the spring constant K ensures that the spring element 34 applies a prestressing force to the worm shaft 14 within a predefined tolerance range.
[0057] At the same time, due to the low spring constant, the spring element 34 can compensate for axial dimensional tolerances of the worm drive 12 and / or the electric motor 28, in particular also of the drive shaft 30. No further components are required to compensate for axial dimensional tolerances.
[0058] according to Figure 3 In the second exemplary embodiment of the steering system 10 shown, the spring element 34 is arranged at the end of the worm shaft 14 facing away from the electric motor 28 .
[0059] The spring element 34 is supported at its one end on the floating bearing 24 , more specifically on an outer race 42 of the floating bearing 24 , and at its other end on a housing part 40 of the worm drive 12 .
[0060] In the exemplary embodiment shown, housing portion 40 is a removable protective cover.
[0061] The floating bearing 24 transfers the axial pretensioning force of the spring element 34 from an outer race 42 of the floating bearing 24 to an inner race 44 of the floating bearing 24 and thereby to the worm shaft 14 which is mounted in the inner race 44 of the floating bearing 24 .
[0062] Therefore, the floating bearing 24 is preferably a bearing suitable for transmitting axial forces. For example, the floating bearing 24 is a four-point bearing, but any other suitable type of bearing may also be used.
[0063] Since in this embodiment the spring element 34 is not supported on the drive shaft 30, there is no axial pretensioning of the drive shaft 30. Thus, in this embodiment, the electric motor 28 can be configured as a single-bearing motor, wherein the drive shaft 30 is mounted by means of a single bearing.
[0064] The spring element 34 can be fixedly connected to the outer race of the floating bearing 24, so that with the pivoting movement of the worm shaft 14, the spring element 34 is bent and thus counteracts the pivoting movement. In particular, the damping device 26 can be omitted.
Claims
1. An electromechanical assisted steering system (10), comprising a worm drive (12), an electric motor (28), and a spring element (34), wherein the worm drive comprises a worm shaft (14) and a worm gear mechanism (16), and the electric motor has a drive shaft (30). in, The worm shaft (14) has a first bearing section (18) at the end assigned to the electric motor (28), which is connected to the drive shaft (30) in a torque-transmitting manner. The worm shaft (14) has a second supporting portion (22), and the second supporting portion is arranged at an end of the worm shaft (14) facing away from the first supporting portion (18). wherein the spring element (34) is connected to the first bearing portion (18) in order to transmit an axial force in an axial direction (A) so that the spring element (34) axially pretensions the worm shaft (14) relative to the worm gear (16), wherein tolerance compensation of the worm drive (12) in the axial direction (A) of the worm shaft (14) is performed exclusively via the spring element (34), wherein the worm shaft (14) has an axial opening (36) at its end assigned to the electric motor (28), in which the spring element (34) is at least partially received, and The drive shaft (30) extends into the axial opening at its end assigned to the worm shaft (14), and does not exceed one eighth of the axial range (1) of the axial opening (36), or the drive shaft terminates outside the axial opening (36) at its end assigned to the worm shaft.
2. The electromechanical assisted steering system (10) according to claim 1, wherein: The spring element (34) is axially supported at one end thereof directly on the worm shaft (14).
3. The electromechanical assisted steering system (10) according to claim 2, wherein: The spring element (34) is axially supported at its other end on the drive shaft (30).
4. The electromechanical assisted steering system (10) according to claim 2 or 3, wherein: The spring element (34) is supported at the one end directly on an axially limiting wall of the axial opening (36).
5. The electromechanical assisted steering system (10) according to any one of claims 1 to 3, wherein: The spring element (34) is guided by radially delimiting walls of the axial opening (36) and / or by a pin (38) which is arranged at the front side of the drive shaft (30) facing the worm shaft (14).
6. The electromechanical assisted steering system (10) according to claim 4, wherein: The spring element (34) is guided by radially delimiting walls of the axial opening (36) and / or by a pin (38) which is arranged at the front side of the drive shaft (30) facing the worm shaft (14).
7. The electromechanical assisted steering system according to claim 1, wherein: The worm shaft (14) is rotatably mounted on its second bearing portion (22) by means of a bearing, wherein the spring element (34) is axially supported on the bearing at one end thereof and the bearing transmits the axial pretensioning force of the spring element (34) to the worm shaft (14).
8. The electromechanical assisted steering system (10) according to claim 7, wherein: The bearing is a floating bearing (24).
9. The electromechanical assisted steering system (10) according to claim 7, wherein: The support is configured as a four-point support.
10. The electromechanical assisted steering system (10) according to any one of claims 7 to 9, wherein: The spring element (34) is axially supported on an outer race (42) of the support, wherein the worm shaft (14) is mounted in an inner race (44) of the support.
11. The electromechanical assisted steering system (10) according to any one of claims 1 to 3, wherein: The spring element (34) has a spring constant (K) of at most 100 N / mm.
12. The electromechanical assisted steering system (10) according to claim 11, wherein: The spring element (34) has a spring constant (K) between 5 N / mm and 70 N / mm.
13. The electromechanical assisted steering system (10) according to claim 12, wherein: The spring element (34) has a spring constant (K) between 10 N / mm and 30 N / mm.