Screw And Nut Linear Drive Assembly

Abstract

A screw and nut linear drive assembly includes a housing, a screw within the housing, an electric motor for rotating the screw, a nut which is driven, when the screw is rotated, to move linearly in a longitudinal direction coinciding with the screw axis, and an axial force transfer arrangement to transfer force from the nut to a push rod to be connected to a member to be actuated by the assembly. The transfer arrangement includes a sequential arrangement of a first and a second axial force transferring component in force transmitting contact that are configured such that first contact points between the first and second axial force transferring components define a first axis (in a plane perpendicular to the longitudinal direction, about which the second axial force transferring component is capable of tilting with respect to the first axial force transferring component to reduce torque transfer to the nut).

Claims

1. A screw and nut linear drive assembly comprising: a housing (2), a screw (6) within the housing, an electric motor for rotating the screw (6), a nut (4) which is driven, when the screw (6) is rotated, to move linearly in a longitudinal direction coinciding with the screw axis, and an axial force transfer arrangement to transfer force from the nut (4) to a push rod (8) to be connected to a member to be actuated by the screw and nut linear drive assembly, characterized in that the axial force transfer arrangement comprises a sequential arrangement of axial force transferring components which comprises, in the direction from the push rod (8) to the nut (4), a first axial force transferring component (10) and a second axial force transferring component (20) in force transmitting contact with each other, and in that the first and second axial force transferring components (10, 20) are configured such that first contact points (42) between the first axial force transferring component (10) and the second axial force transferring component (20) define a first axis (40) in a plane perpendicular to the longitudinal direction, about which first axis (40) the second axial force transferring component (20) is capable of tilting with respect to the first axial force transferring component (10) in order to reduce transfer of any torque to the nut (4).

2. The screw and nut linear drive assembly according to claim 1, characterized in that the first axis (40) is oriented perpendicular to a transverse line connecting the central screw axis with the point of the axial force transfer arrangement where the push rod (8) is coupled to the axial force transfer arrangement.

3. The screw and nut linear drive assembly according to claim 1, characterized in that the sequential arrangement of axial force transferring components comprises a third axial force transferring component (30) which is disposed between the nut (4) and the second force transmitting component (20) and which is in force transmitting contact with the second force transmitting component (20), and in that the second and third axial force transferring components (20, 30) are configured such that second contact points (52) between them define a second axis (50) in the plane perpendicular to the longitudinal direction about which second axis (50) the second axial force transferring component (20) is capable of tilting with respect to the third axial force transferring component (30), wherein the second axis (50) is oriented perpendicular to the first axis (40).

4. The screw and nut linear drive assembly according to claim 1, characterized in that the first axial force transferring component (10) is a preload plunger guided for linear movement in the housing along the longitudinal direction, said preload plunger having a recess disposed in a front face thereof and configured to receive and to be coupled to the push rod (8), wherein the preload plunger comprises a central bore forming an opening in a back face opposite to the front face and having, opposite to the opening, an abutment surface (14) formed by a circumferential shoulder in the central bore, which abutment surface (14) provides the first contact points (42), and the second axial force transferring component (20) is a bushing tube at least partially received in the central bore, the bushing tube and the abutment surface (14) of the preload plunger being configured to come into abutment with each other in two diametrically opposite first contact points (42) only, an outer wall of the bushing tube being provided with resilient surface features (22) which permit tilting movements of the bushing tube with respect to the central bore of the preload plunger about the first axis (40) connecting the two diametrically opposite first contact points (42).

5. The screw and nut linear drive assembly according to claim 3, characterized in that the third axial force transferring component (30) is an axial load carrier ring being guided for linear movement with the nut and being in driving contact coupled to the nut, wherein rotation stop arms (32) extend from the axial load carrier ring and are received in recesses of the preload plunger configured to prevent rotational movement of the axial load carrier ring relative to the preload plunger, wherein end faces of the axial load carrier ring and the bushing tube facing each other are configured such that they come into abutment against each other in two diametrically opposite second contact points (52) only, the two diametrically opposite second contact points (52) defining the second axis (40) perpendicular to the first axis (40).

6. The screw and nut linear drive assembly according to claim 3, characterized in that the resilient surface features (22) of the bushing tube comprise two bulges projecting from and circumferentially extending around the outer wall of bushing tube and being spaced apart in axial direction of the bushing tube, wherein the bulges are made of elastic material and are dimensioned to be in contact with the inner wall of the central bore of the preload plunger when the bushing tube is received in the central bore of the preload plunger.

7. The screw and nut linear drive assembly according to claim 1, characterized in that the screw and nut linear drive assembly is configured as a ball screw and nut assembly or as a leadscrew and nut assembly.

8. The screw and nut linear drive assembly according to claim 2, characterized in that the sequential arrangement of axial force transferring components comprises a third axial force transferring component (30) which is disposed between the nut (4) and the second force transmitting component (20) and which is in force transmitting contact with the second force transmitting component (20), and in that the second and third axial force transferring components (20, 30) are configured such that second contact points (52) between them define a second axis (50) in the plane perpendicular to the longitudinal direction about which second axis (50) the second axial force transferring component (20) is capable of tilting with respect to the third axial force transferring component (30), wherein the second axis (50) is oriented perpendicular to the first axis (40).

9. The screw and nut linear drive assembly according to claim 2, characterized in that the first axial force transferring component (10) is a preload plunger guided for linear movement in the housing along the longitudinal direction, said preload plunger having a recess disposed in a front face thereof and configured to receive and to be coupled to the push rod (8), wherein the preload plunger comprises a central bore forming an opening in a back face opposite to the front face and having, opposite to the opening, an abutment surface (14) formed by a circumferential shoulder in the central bore, which abutment surface (14) provides the first contact points (42), and the second axial force transferring component (20) is a bushing tube at least partially received in the central bore, the bushing tube and the abutment surface (14) of the preload plunger being configured to come into abutment with each other in two diametrically opposite first contact points (42) only, an outer wall of the bushing tube being provided with resilient surface features (22) which permit tilting movements of the bushing tube with respect to the central bore of the preload plunger about the first axis (40) connecting the two diametrically opposite first contact points (42).

10. The screw and nut linear drive assembly according to claim 3, characterized in that the first axial force transferring component (10) is a preload plunger guided for linear movement in the housing along the longitudinal direction, said preload plunger having a recess disposed in a front face thereof and configured to receive and to be coupled to the push rod (8), wherein the preload plunger comprises a central bore forming an opening in a back face opposite to the front face and having, opposite to the opening, an abutment surface (14) formed by a circumferential shoulder in the central bore, which abutment surface (14) provides the first contact points (42), and the second axial force transferring component (20) is a bushing tube at least partially received in the central bore, the bushing tube and the abutment surface (14) of the preload plunger being configured to come into abutment with each other in two diametrically opposite first contact points (42) only, an outer wall of the bushing tube being provided with resilient surface features (22) which permit tilting movements of the bushing tube with respect to the central bore of the preload plunger about the first axis (40) connecting the two diametrically opposite first contact points (42).

11. The screw and nut linear drive assembly according to claim 4, characterized in that the third axial force transferring component (30) is an axial load carrier ring being guided for linear movement with the nut and being in driving contact coupled to the nut, wherein rotation stop arms (32) extend from the axial load carrier ring and are received in recesses of the preload plunger configured to prevent rotational movement of the axial load carrier ring relative to the preload plunger, wherein end faces of the axial load carrier ring and the bushing tube facing each other are configured such that they come into abutment against each other in two diametrically opposite second contact points (52) only, the two diametrically opposite second contact points (52) defining the second axis (40) perpendicular to the first axis (40).

12. The screw and nut linear drive assembly according to claim 4, characterized in that the resilient surface features (22) of the bushing tube comprise two bulges projecting from and circumferentially extending around the outer wall of bushing tube and being spaced apart in axial direction of the bushing tube, wherein the bulges are made of elastic material and are dimensioned to be in contact with the inner wall of the central bore of the preload plunger when the bushing tube is received in the central bore of the preload plunger.

13. The screw and nut linear drive assembly according to claim 4, characterized in that the resilient surface features (22) of the bushing tube comprise two bulges projecting from and circumferentially extending around the outer wall of bushing tube and being spaced apart in axial direction of the bushing tube, wherein the bulges are made of elastic material and are dimensioned to be in contact with the inner wall of the central bore of the preload plunger when the bushing tube is received in the central bore of the preload plunger.

14. The screw and nut linear drive assembly according to claim 2, characterized in that the screw and nut linear drive assembly is configured as a ball screw and nut assembly or as a leadscrew and nut assembly.

15. The screw and nut linear drive assembly according to claim 3, characterized in that the screw and nut linear drive assembly is configured as a ball screw and nut assembly or as a leadscrew and nut assembly.

16. The screw and nut linear drive assembly according to claim 4, characterized in that the screw and nut linear drive assembly is configured as a ball screw and nut assembly or as a leadscrew and nut assembly.

17. The screw and nut linear drive assembly according to claim 5, characterized in that the screw and nut linear drive assembly is configured as a ball screw and nut assembly or as a leadscrew and nut assembly.

18. The screw and nut linear drive assembly according to claim 6, characterized in that the screw and nut linear drive assembly is configured as a ball screw and nut assembly or as a leadscrew and nut assembly.

Description

[0013] In the following a preferred embodiment of the invention will be described with reference to the drawings in which:

[0014] FIG. 1 shows a perspective view of a screw and nut linear drive assembly in the form of an electric clutch actuator;

[0015] FIG. 2 shows a top view of the electric clutch actuator of FIG. 1, with a central portion of a housing cut out and internal components being shown in cross-section;

[0016] FIG. 3 shows a side view of the electric clutch actuator of FIG. 1, with a central portion of a housing cut out and internal components being shown in cross-section;

[0017] FIG. 4 is an enlarged partial view of the cross-section portion of FIG. 2;

[0018] FIG. 5 is an enlarged partial view of the cross-section portion of FIG. 3;

[0019] FIG. 6 is a perspective view of a part of the axial force transfer arrangement of FIGS. 2 to 5;

[0020] FIG. 7 is a schematic plan view of the axial force transfer arrangement along a first axis which is disposed in a transverse plane perpendicular to an axial direction; and

[0021] FIG. 8 is a schematic plan view of the axial force transfer arrangement of FIG. 7 along a second transverse axis, which second axis is disposed perpendicular to the first axis.

[0022] FIG. 1 shows a perspective view of a linear screw and nut drive assembly, here embodied by an electric clutch actuator 1. The electric clutch actuator 1 comprises a housing 2 from which a moveable push rod 8 extends which is driven by the electric clutch actuator for linear movement. The push rod 8 is configured to be connected to a member to be actuated by the linear drive assembly, in this case to one end of a clutch lever (not shown) which is pivotably mounted to be pivoted by the push rod 8 between an engaged and a disengaged position.

[0023] The electric clutch actuator 1 includes an electric motor and a transmission (both not shown) within the housing 2. The electric motor drives, via the transmission, a screw (spindle) to rotate around the longitudinal direction defined by the central axis of rotation of screw. In this case the screw and the nut form a ball screw assembly. In such ball screw assembly the helical grooves of the screw are in indirect engagement with internal helical grooves of a nut via balls which roll within these grooves and which are returned by a ball return system after they reached an end of engagement end of the nut. The nut is axially moveable within the housing but held in a manner such that it is prevented from rotation about the central screw axis.

[0024] Alternatively there may be a direct driving engagement between the screw and the nut (lead screw and nut drive assembly). However, as mentioned before in the embodiment shown in the Figures, the present invention is embodied by a linear drive utilizing a ball screw assembly consisting of a screw and a nut, each with matching helical grooves, and balls which roll between these grooves and which provide the only contact between the nut and the screw. When screw and nut rotate with respect to each other, the balls are returned by a ball return system back into the ball screw and nut thread raceways formed by the helical grooves.

[0025] With reference to FIGS. 2 and 3 a first overview of the internal structure of the electric clutch actuator 1 will be given, wherein FIG. 2 shows a top view of the electric clutch actuator with a central portion of its housing cut out and the interior shown in cross-section, wherein FIG. 3 shows a similar view as a side view, i.e. the view axis is rotated by 90? around the longitudinal axis compared to FIG. 2. In FIG. 2 the push rod 8 is visible in the interior of the housing 2 in cross-section, and in a side view projecting from the housing. As can be seen in FIG. 2 the push rod 8 is transversely (in a plane perpendicular to the longitudinal axis (=rotational axis of the screw 6) offset with respect to the longitudinal axis of the screw 6. For this reason, if a force is transmitted to the push rod 8, as a reaction a torque is created which is acting between the push rod 8 and the nut 4 which is driven to provide the force for the push rod.

[0026] In FIG. 3 the push rod 8 is only visible with its projecting portion outside of the housing, whereas it is out of the plane of the cross-section in the cut out portion of the interior of the housing.

[0027] When the screw 6 is driven to rotate, the nut 4 linearly moves along the screw. The nut 4 is guided in the housing for linear movement along the longitudinal axis of the screw, but rotation around the longitudinal axis is prevented.

[0028] The axial force transfer arrangement transferring force from the nut 4 to the push rod 8 will now be described in more detail first with reference to FIGS. 2 and 3, and then in more detail with reference to the enlarged cross-sectional views of FIGS. 4 and 5, and the schematic views in FIGS. 7 and 8.

[0029] With reference to FIGS. 2 and 3 the axial force transfer arrangement comprises, in the direction from the push rod 8 to the nut 4 a first force transferring component 10, a second force transferring component 20, and a third force transferring component 30, the components of each pair of subsequent force transferring components being in force transferring contact with each other. In this manner the nut 4 is in force transferring contact with the push rod 8 through the axial force transfer arrangement comprising a train of force transferring components 10, 20, 30.

[0030] With reference to FIGS. 4 and 5 the first force transferring component 10 is a preload plunger guided for linear movement within the housing 2. The preload plunger has in a front face thereof a recess in which the end portion of push rod 8 is received and connected thereto. The preload plunger has a central bore which partially extends into the preload plunger from a back face opposite to the front face into and partially through the preload plunger. The central bore is continued through the remaining portion of the preload plunger by a smaller diameter hole so that the screw 6 extends through the central bore and further through the central hole, and so extends completely through the preload plunger 10. The central bore of the preload plunger is provided with an abutment ring 12 resting on a shoulder end face of the central bore. A side surface of the abutment ring 12 provides an abutment surface 14 of the central bore which will be discussed in more detail below.

[0031] The second force transferring component 20 is a bushing tube received in the central bore. The outer wall of the bushing tube 20 is provided with resilient features 22, in the embodiment shown by two circumferentially extending ridges of elastic material.

[0032] As can be seen in the view of FIG. 5 the outer wall of the bushing tube 20 with its ridges 22 has contact with the inner wall of the central bore, whereas in the view of FIG. 4 the outer wall of the bushing tube has no contact with the inner wall of central bore of the preload plunger. This configuration is such that the preload plunger 10 is in principle capable of being tilted about an axis perpendicular to the Figure plane of FIG. 4, without transferring such tilting movement to the second force transferring component 20 in the form of the bushing tube. This ability of relative tilting movement between the second force transferring components 10 and 20 is also a result of the configuration of the first and second force transferring components 10, 20 in such a manner that their contact surfaces define a first axis about which the first force transferring component 10 may pivot with respect to the second force transferring component 20. In the embodiment shown the first contact points between the first and second force transferring components 10, 20 are disposed diametrically opposite with respect to the longitudinal axis. Thus, there are two diametrically opposite contact points, as seen in the view of FIG. 5, where the first and second force transferring components 10 and 20 are in direct contact with each other, whereas in the remaining portion of the circumference between the diametrically opposite contact points there is a gap between the abutment surface 14 of abutment ring 12 of the preload plunger and the bushing tube, see FIG. 4.

[0033] This configuration of the first contact points between the first and second force transferring components 10, 20 is illustrated in a schematic way in FIGS. 7 and 8. As can be seen in FIG. 7 there is contact between the first and second force transferring components 10, 20 at first contact points 42 located in close proximity to the intersection point of the first axis 40 which is the viewing axis of FIG. 7. FIG. 8 shows a corresponding view with the view axis rotated by 90?. Now the first contact points 42 are visible as two diametrically opposite first contact points 42 between the first and second force transferring components 10, 20. With reference to FIG. 7 again, this configuration of first contact points 42 defining a first axis 40 (perpendicular to the Figure plane of FIG. 7) permits a certain pivotal movement of the first force transferring component 10 with respect to the second force transferring component 20. This tilting movement is indicated in FIG. 7 by the semi-circular arrow around the first axis 40.

[0034] Referring to FIGS. 4 and 5 again the description of the axial force transfer arrangement will now be continued. The second force transferring component 20 cooperates with a third force transferring component 30 which in the embodiment shown is a load carrier ring 30 which is disposed between the bushing tube 20 and an outwardly projecting portion of the nut 4. The load carrier ring 30 is further provided with two opposite, longitudinally extending rotation stop arms 32 which extend into recesses formed in the preload plunger 10 to prevent rotational movement of the load carrier ring 30 about the longitudinal axis; as a consequence, rotational movements are also prevented for the nut 4 which is coupled to the load carrier ring 30.

[0035] As can be seen in FIG. 4, the second force transferring component 20 is, in the plane of the cross-section of FIG. 4, in direct contact with the adjacent load carrier ring as the third force transferring component 30. Again two diametrically opposite second contact points between the second and third force transferring components 20, 30 are formed in the plane of the cross-section of FIG. 4, whereas the contact surfaces are configured that there is no direct contact between the first and second force transferring components 20, 30 in the remaining portion of the circumference. As can be seen in view of FIG. 5 in which the plane of the cross-section is rotated by 90? with respect to FIG. 4, in FIG. 5 there is a gap between the load carrier ring as the third force transferring component 30 and the bushing tube as the second force transferring component 20. This arrangement of the second contact points between the second and third force transferring components 20, 30 can be better understood with reference to the schematic views of FIGS. 6-8. As can be seen in the view of FIG. 7 there are two diametrically opposite contact points 52 formed by two small projections. These second contact points 52 are also visible in FIG. 6 which is a perspective view of the couple of load carrier ring 30 and bushing tube 20: In the circumferential area of the rotation stop arms 32 there are small projecting knobs on the inner side of the load carrier ring 30 which form the second contact points and which contact the end surface of the tube bushing 20.

[0036] Whereas in the view of FIG. 7 the two second, diametrically opposite contact points 52 are spaced apart, in the view rotated by 90? around the longitudinal direction as shown in FIG. 8 the two diametrically opposite second contact points 52 are now in line in the view axis of FIG. 8 (the view axis coinciding with the second axis 50) and are visible in the middle around the second axis 50 which is oriented perpendicular to the Figure plane of FIG. 8. This arrangement of two diametrically opposite contact points 52 between the second and third force transferring components 20, 30 defines this second axis 50 and allows a certain tilting movement between the first and second force transferring components 20 and 30 about the second axis 50.

[0037] As can also be seen in FIGS. 7 and 8 the first axis 40 and the second axis 50 are oriented perpendicularly to each other in a plane transverse to the longitudinal axis. In this manner the axial force transfer arrangement formed by the first, second, and third axial force transferring components 10, 20, 30 forms a double joint with two perpendicular joint axes, which cooperate to absorb any torque created by a force input to the push rod (counter force generated by the member being actuated via the push rod) which is offset with respect to the longitudinal screw axis or by any tolerances of the components of the axial force transferring components or bearings or guiding components.