Automotive actuator and method of manufacturing the same

Abstract

To provide a connection between an inner ring of a bearing and a shaft or a pipe.SOLUTION: An actuator (4) comprising: an inner ring (24) made of metal; an outer ring (28) made of metal and coaxial to the inner ring (24) about a rotation axis (X-X); and means for allowing a relative rotation of the inner ring (24) with respect to the outer ring (28) about the rotation axis. Rolling elements (32) interposed between the inner ring (24) and the outer ring (28), the axial shoulders (36) being axially spaced apart along an axial direction parallel to the axis of rotation so as to axially constrain the inner ring (24) relative to the shaft or tube (8), the shaft or tube (8) being co-molded onto the inner ring (24) so as to axially constrain the inner ring (24) between the axial shoulders (36); At least one injection point of the plastic material of the shaft or tube (8) is arranged close to said axial shoulder (36).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to an actuator for an automobile and a method for manufacturing the same. [Background technology]

[0002] In general, in the automotive sector, it is known to manufacture actuators for transmission devices, for example, which comprise a shaft or a tube associated with a bearing having rolling elements.

[0003] Typically, the shaft may be solid or hollow, and the tube may then comprise a nut thread, which may be joined using a thread. The screw or shaft may be connected to at least one gear, cogwheel, or the like.

[0004] The bearing includes an inner ring and an outer ring, and the rolling elements are disposed between the inner ring and the outer ring, allowing relative rotation between the inner ring and the outer ring.

[0005] The connection between the inner ring of the bearing and the shaft or tube is a critical and delicate element.

[0006] In practice, such connections are usually made by means of an interference fit. However, interference techniques are not always applicable, particularly between metallic parts, and thus between the inner ring of a bearing (which is metallic) and a shaft or a tube, which must also be made of metallic material.

[0007] Therefore, except for low torque transmission applications with a relatively low degree of interference, it is not possible to apply interference couplings between bearings and shafts or tubes, which are generally made from resins (e.g. reinforced resins) or polymeric materials.

[0008] Furthermore, in the automotive field, shafts or tubes often have to withstand large axial loads directed along the general axis of elongation (as well as the axis of rotation) of the shaft or tube. Such large loads are also cyclic fatigue loads, and therefore expose the parts to considerable mechanical stresses that must be adequately absorbed by the connection between the bearing and the shaft or tube. Summary of the Invention

[0009] Therefore, a need is felt to overcome the deficiencies and limitations noted with respect to the prior art.

[0010] Such a need is met by an actuator according to claim 1 and a method according to claim 12. [Brief explanation of the drawings]

[0011] Further features and advantages of the present invention will become more apparent from the following detailed description of the preferred, non-limiting embodiments. [Figure 1] 1A-1C are perspective views of an actuator for an automotive application in an assembled configuration in different orientations according to an embodiment of the present invention; [Figure 2] 1A-1C are perspective views of an actuator for an automotive application in an assembled configuration in different orientations according to an embodiment of the present invention; [Figure 3] 3A and 3B are cross-sectional perspective views of the actuators of FIGS. 1 and 2, respectively. [Figure 4] 3A and 3B are cross-sectional perspective views of the actuators of FIGS. 1 and 2, respectively. [Figure 5] 10 is a cross-sectional view of an actuator according to a further embodiment of the present invention in an assembled configuration; [Figure 6] 10 is a cross-sectional view of an actuator according to a further embodiment of the present invention in an assembled configuration; [Figure 7] 7A and 7B are perspective views of the separate parts of the actuator of FIGS. 5-6. [Figure 8]1 is an assembled perspective view of an actuator according to the present invention; FIG.

[0012] Elements or parts of elements that are common to the embodiments described below are indicated using the same reference numerals. DETAILED DESCRIPTION OF THE INVENTION

[0013] Referring to the aforementioned figures, an overall view of an actuator for automotive applications according to the present invention is collectively indicated using the numeral 4.

[0014] The automotive application of the present invention is subject to change and does not constitute a limitation. By way of example only, the present invention may be applied to parking brakes, valves, gearbox actuators, gearbox actuators, etc.

[0015] The actuator 4 comprises a shaft or tube 8 which comprises a coupling seat 12 arranged on its outer wall 16 .

[0016] The shaft or tube 8 is axisymmetric about an axis of symmetry SS and has a circular cross section, and furthermore the shaft or tube is made by moulding of a plastic material, as will be explained better below.

[0017] The actuator 4 further comprises a rolling bearing 20 comprising a metal inner ring 24 and a metal outer ring 28 coaxial with the inner ring 24 about an axis of rotation XX parallel to the axis of symmetry SS of the shaft or tube 8.

[0018] The actuator 4 further comprises rolling elements 32 interposed between the inner ring 24 and the outer ring 28, which enable relative rotation of the inner ring 24 with respect to the outer ring 28 about the rotation axis XX.

[0019] The rolling elements 32 may comprise balls or rollers. Preferably, the rolling bearing 20 is of a mixed axial / radial type. In other words, the rolling bearing 20 is configured to support both an axial load parallel to the rotation axis XX and a radial load along a radial direction perpendicular to and incident on the rotation axis XX.

[0020] The coupling seat 12 of the shaft or tube 8 comprises a pair of axial shoulders 36 which project a radial height 40 relative to the outer wall 16 of the shaft or tube 8 along a radial direction RR perpendicular to and incident on the axis of rotation XX.

[0021] In particular, the axial shoulders 36 are axially spaced apart along an axial direction parallel to the axis of rotation XX so as to axially restrain the inner ring 24 of the rolling bearing 20 relative to the shaft or tube 8 .

[0022] In other words, the axial shoulders 36 are spaced exactly the axial width of the inner ring 24 of the rolling bearing 20 so as to create a bilateral axial restraint for the inner ring 24 .

[0023] As mentioned above, the shaft or tube 8 is made from a plastic material, and in particular, the shaft or tube 8 is co-molded onto the inner ring 24 so as to axially restrain the inner ring 24 between the axial shoulders 36.

[0024] The radial height 40 of the axial shoulder 36 is preferably less than the radial thickness 44 of the inner ring 24 along that radial direction RR.

[0025] It should be noted that for the strength of the molded part, it is optimal for the axial shoulder 36 in question to have exactly the same inner diameter as the inner ring 24 (fifth wheel) of the rolling bearing 20; in other words, 100% radial coverage is desired, or in other words, it is desired that each axial shoulder has exactly the inner diameter of the inner ring 24.

[0026] However, this condition of maximum radial coating poses a distinct risk that molten plastic may inadvertently flow into the rolling bearing 20 during molding, thereby impairing its operation.

[0027] It has therefore been found to be advantageous to reduce the contact and clamping area between the injection mould and the inner ring 24 in order to stop the flow of molten plastic during moulding and prevent it from contaminating the rolling bearing 20. In particular, it has been found that the best compromise between mechanical resistance / adhesion between the parts and shielding of the rolling bearing 20 from the molten plastic is achieved by requiring the maximum diameter 64 of the axial shoulder 36 to be 70% to 80% of the inside diameter 68 of the inner ring 24.

[0028] This dimensioning offers a particular advantage: during the co-molding process, the plastic material is actually prevented from flowing into the volume of the rolling bearing 20 that houses the rolling elements 32 .

[0029] As mentioned above, the axial shoulder 36 is a part that is subjected to extreme mechanical stresses, and for this reason it is important that the molding ensures an optimal bond between the same axial shoulder 36 and the inner ring 24.

[0030] Furthermore, after the molding process, the axial shoulder 36 must be particularly compact and strong. To this end, the injection molding should provide certain special arrangements aimed at ensuring accurate molding and adequate mechanical strength in the most stressed areas.

[0031] Advantageously (FIG. 8), it has been found that the positioning of at least one injection point 60 of the plastic material is envisaged in the vicinity of said axial shoulder 36, which constitutes the area of ​​the part that is most mechanically stressed, in this way allowing a greater compaction of the material after the molding process. Indeed, during the post-molding cooling process, the press continues to apply a load to the still hot and slightly fluid material, thereby helping to improve the properties of the material close to the injection point and therefore close to said axial shoulder 36, making it therefore particularly compact and strong.

[0032] According to one embodiment (FIG. 8), the possibility of using multiple injection points 60 in the vicinity of the axial shoulder 36 is provided, in this way the filling of the mold with the molten material is further improved and the distribution of the glass fibers embedded in the molten plastic material is homogenized, thereby increasing the toughness of the molded plastic part.

[0033] Preferably (FIG. 8), three injection points 60 are provided, equally spaced angularly relative to the axis of rotation XX.

[0034] According to one possible embodiment, the material of the shaft or tube 8 comprises molybdenum disulfide and / or Teflon. These are materials that have, in particular, lubricating properties, and their use is advantageous insofar as it makes it possible to avoid the use of lubricants such as oil or grease in the volume of the rolling bearing 20 that houses the rolling elements 32. In other words, self-lubricating additives such as molybdenum disulfide and / or Teflon act as lubricants for the rolling elements 20.

[0035] According to one possible embodiment, the material of the shaft or tube 8 comprises PA66-GF50.

[0036] As mentioned above, the actuator 4 can have a variety of uses.

[0037] For example, at least one gear 48 and / or torque take-off device may be connected to the shaft or tube 8 .

[0038] Preferably, but not necessarily, the tube 8 is hollow and defines a nut thread 52 that is engaged with a threaded shaft 56 that is operatively connected to a power take-off device.

[0039] Next, a method for manufacturing an actuator for an automobile according to the present invention will be described.

[0040] In particular, the method provides for providing a rolling bearing 20 comprising a metal inner ring 24, a metal outer ring 28 coaxial with the inner ring 24 about a rotation axis XX, and rolling elements 32 interposed between the inner ring 24 and the outer ring 28 to enable relative rotation between the inner ring 24 and the outer ring 28 about the rotation axis XX.

[0041] The method then proceeds to overmold, with a plastic material, the shaft or tube 8 provided with the coupling seat 12 on its outer wall 16 onto the inner ring 24 .

[0042] In particular, the coupling seat 12 comprises a pair of axial shoulders 36 which project relative to the outer wall 16 of the shaft or tube 8 by a radial height 40 along a radial direction RR perpendicular to and incident on the axis of rotation XX.

[0043] The axial shoulders 36 are axially spaced apart along an axial direction parallel to the axis of rotation XX so as to axially restrain the inner ring 24 relative to the shaft or tube 8 .

[0044] In particular, the axial distance between the axial shoulders 36 is exactly equal to the axial thickness of the inner ring 24 .

[0045] The radial height 40 of the axial shoulder 36 is preferably less than the radial thickness 44 of the inner ring 24 along that radial direction RR.

[0046] The material of the shaft or tube 8 preferably comprises molybdenum disulfide and / or Teflon.

[0047] For example, the material of the shaft or tube 8 includes PA66-GF50.

[0048] According to one possible embodiment, before overmolding, a step of preheating the rolling bearing 20 is envisaged, before entering the mold, at a temperature equal to approximately 50% of the molding temperature of the plastic material.

[0049] Such a preheating step makes it possible to obtain a good bond between the parts of the actuator 4, in particular between the inner ring 24 and the shaft or tube 8.

[0050] In particular, it is preferred to increase the temperature of the metal element being formed, i.e. the bearing ring, in order to promote optimal flow of the molten plastic and enable it to adhere optimally to the surface of the element.

[0051] Therefore, it is optimal to increase the temperature of the rolling bearing 20 (ball bearing, roller, etc.) until it reaches the operating temperature of the mold; in other words, theoretically, it is preferable to preheat the mold to 100% of the melting temperature of the plastic to be injected, but in practice it has been verified that preheating the mold to a temperature of 50% to 60% of the melting temperature of the plastic material to be injected makes it possible to ensure optimal adhesion of the plastic to the bearing without further damaging the gasket (typically made of rubber) and the lubricant pre-distributed inside the rolling bearing 20.

[0052] As can be seen from what has been described, the present invention overcomes the shortcomings present in the prior art.

[0053] In particular, the actuator comprises a connection between the shaft or tube and the rolling bearing obtained by overmolding, such a connection being capable of transmitting a considerable torque, which is greater than that of known solutions which instead provide an interference fit.

[0054] By providing an axial shoulder that is overmolded onto the inner ring, a strong bond between the inner ring and the shaft or tube can be obtained. Indeed, upon cooling after molding and the resulting shrinkage, the shoulder tends to close over the inner ring, thereby increasing the fastening of the inner ring.

[0055] Advantageously, at least one injection point of the plastic material is positioned near the axial shoulder, which constitutes the area of ​​the part that is most mechanically stressed; in this way, it has been found that a greater compression of the material after molding is possible. Indeed, during the post-molding cooling process, the press continues to apply a load to the still hot and slightly fluid material, thereby helping to improve the properties of the material close to the injection point and therefore the axial shoulder, making it particularly compact and strong. This arrangement makes it possible to obtain mechanical parts that are particularly resistant not only to high loads but also to cyclic fatigue loads in particular.

[0056] Additionally, adding a lubricating additive (molybdenum disulfide, Teflon, etc.) to the plastic material facilitates the molding process and adhesion to the inner ring.

[0057] Furthermore, the lubricant embedded in the plastic material makes it possible to prevent the chambers of the rolling elements from filling up with bearing grease.

[0058] In this way, the rolling elements are lubricated more economically. This solution is also less heavy and less costly than conventional solutions and is not subject to maintenance (e.g., changing or topping up grease, etc.).

[0059] In other words, molybdenum disulfide is used as a self-lubricating additive in plastic materials, avoiding the use of additional lubricants in the actuator.

[0060] Additionally, molybdenum disulfide (MoS2) is an additive with a lower environmental impact than typically used Teflon-based additives, and furthermore, molybdenum disulfide (unlike PTFE) is not subject to any restrictions on its use in the near future.

[0061] The height of the axial shoulder is appropriately selected to ensure, on the one hand, adhesion to the shaft or tube and, on the other hand, to prevent the molded plastic material from flowing into the chamber containing the rolling elements.

[0062] To ensure a successful plastic molding process and optimal adhesion between the components, it is advantageous to preheat the bearing before it enters the mold to a temperature equal to approximately 50% to 60% of the molding temperature of the plastic material. This ensures proper overmolding and therefore optimal fixation between the shaft or tube and the inner ring of the rolling bearing. At the same time, damage to the gasket (typically made of rubber) and the lubricant pre-distributed inside the rolling bearing is avoided.

[0063] Those skilled in the art can make numerous modifications and variations to the above solutions to meet their particular foreseeable needs.

[0064] The scope of protection of the present invention is defined by the following claims.

[0065] List of References 4: Actuator 8: Shaft or tube 12: Conjunction locus 16:Outer wall 20: Rolling bearing 24: Insider 28: Outer ring 32: Rolling element 36: Axial shoulder 40: Radial height 44: Radial thickness 48: Gears 52: Nut screw 56: Threaded shaft 60: Injection point 64: Maximum diameter 68: Inner diameter SS: Symmetry axis XX::rotation axis RR::Radial

Claims

1. An actuator (4), a shaft or tube (8) provided with a coupling seat (12) on its outer wall (16), said shaft or tube (8) being made by moulding a plastic material; a rolling bearing (20) comprising a metal inner ring (24), a metal outer ring (28) coaxial with the inner ring (24) about a rotation axis (X-X), and rolling elements (32) interposed between the inner ring (24) and the outer ring (28) and enabling relative rotation of the inner ring (24) with respect to the outer ring (28) about the rotation axis (X-X); the coupling seat (12) comprises a pair of axial shoulders (36) projecting with respect to the outer wall (16) of the shaft or tube (8) a radial height (40) along a radial direction (R-R) perpendicular to and incident on the axis of rotation (X-X), the axial shoulders (36) being axially spaced apart along an axial direction parallel to the axis of rotation (X-X) so as to axially restrain the inner ring (24) relative to the shaft or tube (8); an actuator (4) in which the shaft or tube (8) is co-molded onto the inner ring (24) so ​​as to axially restrain the inner ring (24) between the axial shoulders (36), and at least one injection point (60) of the plastic material of the shaft or tube (8) is located close to the axial shoulders (36).

2. The actuator (4) of claim 1, wherein a plurality of injection points (60) are provided adjacent the axial shoulder (36).

3. An actuator (4) according to claim 2, wherein three injection points (60) are provided on said axial shoulder (36) at equal angular intervals relative to said axis of rotation (XX).

4. 4. The actuator (4) of claim 1, 2 or 3, wherein the radial height (40) of the axial shoulder (36) is less than a radial thickness (44) of the inner ring (24) along the radial direction (R-R).

5. The actuator (4) according to claim 4, wherein the maximum diameter (64) of the axial shoulder (36) is 70% to 80% of the inner diameter (68) of the inner ring (24) of the rolling bearing (20).

6. An actuator (4) according to any one of claims 1 to 5, wherein the material of the shaft or tube (8) comprises molybdenum disulfide and / or Teflon.

7. An actuator (4) according to any one of claims 1 to 6, wherein the material of the shaft or tube (8) comprises PA66-GF50.

8. An actuator (4) according to any one of the preceding claims, wherein at least one gear (48) and / or torque take-off device is connected to said shaft or tube (8).

9. The actuator (4) according to any one of claims 1 to 8, wherein the rolling elements (32) comprise balls or rollers.

10. An actuator (4) according to any one of claims 1 to 9, wherein the tube (8) is hollow and defines a nut thread (52) for engagement with a threaded shaft (56) operably connected to a power take-off device.

11. The actuator (4) according to any one of claims 1 to 10, wherein the rolling bearing (20) is of a mixed axial and radial type.

12. 1. A method of manufacturing an actuator, comprising: - providing a rolling bearing (20) comprising a metal inner ring (24), a metal outer ring (28) coaxial with said inner ring (24) about the axis of rotation (X-X), and rolling elements (32) interposed between said inner ring (24) and said outer ring (28) and enabling relative rotation of said inner ring (24) with respect to said outer ring (28) about said axis of rotation (X-X); - overmolding, with a plastic material, a shaft or tube (8) provided with a coupling seat (12) on its outer wall (16) onto said inner ring (24), the coupling seat (12) comprises a pair of axial shoulders (36) projecting with respect to the outer wall (16) of the shaft or tube (8) a radial height (40) along a radial direction (R-R) perpendicular to and incident on the axis of rotation (X-X), the axial shoulders (36) being axially spaced apart along an axial direction parallel to the axis of rotation (X-X) so as to axially restrain the inner ring (24) relative to the shaft or tube (8); - at least one injection point (60) of said plastic material of said shaft or tube (8) is arranged in the vicinity of said axial shoulder (36).

13. The method of claim 12, including injecting the plastic material through a plurality of injection points (60) located near the axial shoulder (36).

14. 14. The method of claim 13, wherein three injection points (60) are provided on the axial shoulder (36) that are equally spaced angularly relative to the axis of rotation (X-X).

15. 15. The method of claim 12, 13 or 14, wherein the radial height (40) of the axial shoulder (36) is less than a radial thickness (44) of the inner ring (24) along the radial direction (R-R).

16. The method (4) of claim 15, wherein the maximum diameter (64) of the axial shoulder (36) is 70% to 80% of the inner diameter (68) of the inner ring (24) of the rolling bearing (20).

17. The method according to any one of claims 12 to 16, wherein the material of the shaft or tube (8) comprises molybdenum disulfide and / or Teflon.

18. The method according to any one of claims 12 to 17, wherein the material of the shaft or tube (8) comprises PA66-GF50.

19. 19. The method according to any one of claims 12 to 18, wherein a step of preheating the rolling bearing (20) before overmolding is envisaged at a temperature equal to about 50% to 60% of the molding temperature of the plastic material before entering the mold.

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