WO2010043253A1

WO2010043253A1 - Ball recirculating means and actuating device comprising such means.

Info

Publication number: WO2010043253A1
Application number: PCT/EP2008/063848
Authority: WO
Inventors: Eric Allegri; Christophe Durand; Torbjorn Hedman
Original assignee: Aktiebolaget Skf
Priority date: 2008-10-15
Filing date: 2008-10-15
Publication date: 2010-04-22
Also published as: DE112008004020T5

Abstract

Actuating device comprising an externally threaded screw (2), an internally threaded nut (4), and at least one series (6) of balls such that balls are engaged in the thread of the threaded screw and the thread of the nut, and provided with a ball recirculating means mounted on the nut and defining a recirculating channel to carry the balls from one end to the other end of their path inside the nut when the screw rotates relative to the nut. The recirculating means (8) can comprise two deflecting elements (14), engaged in radial holes (11) formed in the nut (4) and each having a ball deflecting channel (36), and can comprise an external beam (16) having a connecting channel (37), said ball recirculating channel (9) being defined in succession by the deflecting channel of one deflecting element, the connecting channel of the beam and the deflecting channel of the other deflecting element.

Description

Ball recirculating means and actuating device comprising such means

The present invention relates to actuating devices that comprise an externally threaded screw, an internally threaded nut, and circulating balls for coupling the screw and the nut, and which are provided with ball recirculating means to carry the balls from one end of their path to the other inside the nut when the screw rotates relative to the nut. Such actuating devices are often called ball screws. The known devices have numerous inconvenients and lead to unsatisfaction of users.

The present invention aims at eliminated some of those inconvenients and provides for an actuating device with improved security of the circulation of the balls and better confining and guiding of the recirculating balls.

Another objet of the invention is to reduce the operations for manufacturing the nut while at the same time avoid to cause the nut to become excessively fragile.

Another objet of the invention is to provide recirculating means with higher mechanical resistance while reducing the produced noise when the balls circulate.

Still another objet of the invention is to obtain ball recirculating means with an acceptable cost and easily dismountable.

Another objet of the invention is to provide such an actuating device which can be produced at a reduced cost.

In accordance with one embodiment of the invention, it is proposed a ball recirculating means able to be mounted on an internally threaded nut and defining a recirculating channel to carry balls from one end to the other end of a path inside the nut, along which the balls are engaged in the thread therof.

This ball recirculating means can comprise two deflecting elements able to be engaged in respective holes formed through the thickness of the nut and each having a ball deflecting channel (36) , in that it comprises a beam connectable to said deflecting elements and having a connecting channel, the deflecting channel of one of the deflecting elements, the connecting channel of the beam and the deflecting channel of the other deflecting element defining in succession said ball recirculating channel, and in that the deflecting elements and/or the beam comprise retaining means able to cooperate with the nut.

The recirculating means can comprise two deflecting elements engaged in radial holes formed in the nut and each having a ball deflecting channel, and can comprise an external beam having a connecting channel, said ball recirculating channel being defined in succession by the deflecting channel of one deflecting element, the connecting channel of the beam and the deflecting channel of the other deflecting element. With such deflecting channels in the deflecting elements and a connecting channel in the external beam, it is possible to shape and form a recirculating channel independently from the nut and well adapted to extract and release the balls and to confine and guide the recirculating balls. The separate deflecting elements and the separate beam can be provided with mutual locking means.

The deflecting elements can be engageable in said holes from the inside of the nut and can comprise projecting internal lateral parts able to bear against the inside of the wall of the nut. Said beam can comprise at least one part able to bear against the outside of the nut.

The deflecting elements can comprise positioning parts able to bear against the side walls of the thread of the nut. The deflecting elements can comprise centering parts able to bear against the end of the thread of the nut.

The deflecting elements each can have passages through which said beam can be passed.

The deflecting elements each can comprise two radial arms between which said beam is engaged, these arms and the beam being provided with mutual locking means.

The deflecting elements and the beam each can have planes o f mutual contact which extend parallel to the axis of the nut, and through which said deflecting channels and connecting channel communicate. The beam can comprise two connected parts between which the connecting channel can be formed internally.

The deflecting elements and the beam can comprise poka-yoke parts in order to ease their assembly or prevent errors during the mounting process. In accordance with another embodiment, it is proposed an actuating device comprising an externally threaded screw, an internally threaded nut, and at least one series of balls such that balls are engaged in the thread of the threaded screw and the thread of the nut along a path. The nut can be provided with a ball recirculating means in order to carry the balls from one end to the other end of their path inside the nut when the screw rotates relatively to the nut.

The beam can be at least partly engaged in an external groove formed in the wall of the nut. The nut can comprise a peripheral groove, and further can comprise a stationary ring with an annular groove, and rolling bodies inserted in the grooves so as to form a rolling bearing in order to rotatably mount the nut in a housing. Only for an example of application, it is proposed a power steering system for vehicle wheels.

This system can comprise a steering rack for steering the wheels, a motor for assisting the translation of the steering rack, and an actuating device as proposed, the nut being connected in rotation to the motor and the screw being connected in translation to the steering rack.

The nut can carry a pulley, this pulley having an internal groove in which the external part of the beam of the ball recirculating means extends at a distance from the faces of this groove.

The screw and the steering rack can be aligned and formed in a one-piece.

Actuating devices providing with ball recirculating means and applications will now be described by way of non-limiting examples illustrated in the drawing, in which :

- Figure 1 is a side view of an actuating or drive device made up of a threaded screw, a threaded nut, and balls, with ball recirculating means located in its upper part and having two deflecting elements ;

- Figure 2 is an enlarged radial section taken on H-II through the actuating device shown in Figure 1 , passing through a deflecting element, with the balls; - Figure 3 is a longitudinal section through the actuating device shown in Figure 1 , passing through a deflecting element, without the balls; - Figure 4 is an horizontal section taken on IV-IV through the actuating device shown in Figure 1 , passing through a beam, with the balls;

- Figure 5 is a longitudinal section through the nut, with the balls and the deflecting elements;

- Figure 6 is an external perspective view of the actuating device shown in Figure 1 , during assembly;

- Figure 7 is a perspective view of the ball recirculating means;

- Figure 8 shows a variant in a radial section corresponding to Figure 2; and

- Figure 9 shows this variant in an external view corresponding to a top view of Figure 1.

- Figure 10 shows a variant in a radial section corresponding to Figure 2, with possible poka-yoke features; - Figure 1 1 is an external perspective view of the actuating device shown in Figure 10, during assembly; and

- Figure 12 is a section of a steering gear using an actuating device.

An actuating or drive device 1 , illustrated in Figures 1 to 6, comprises : a threaded screw 2 having an external thread 3 ; a cylindrical nut 4 having an internal thread 5 whose internal diameter is bigger than the external diameter of the thread 3 of the screw 2; a series 6 of spherical balls 7 for connecting the screw 2 to the nut 4; and ball recirculating means 8 mounted on the nut 4 and defining a recirculating channel 9.

As shown particularly in figures 2 and 5 , the series 6 of spherical balls 7 is such that some balls are respectively engaged partly in the thread 3 of the threaded screw 2 and partly in the thread 5 of the nut 4, on a path 10 of the nut 4, while other balls are in the recirculating channel 9. The path 10 can be formed along several spires of the thread 5 of the nut 4.

A rotation of the threaded screw 2 and the nut 4 with respect to each other is transformed into a longitudinal translational movement of the one with respect to the other because the balls 7 of the series 6 o f balls roll along the threads 3 and 5 by following the path 10 in the nut 4 and run freely along the recirculating channel 9 from one end to the other of the path 10.

To accommodate the recirculating means 8, the nut 4 has, at either end of the path 10, two holes 1 1 and 12 passing through its thickness or wall. The nut 4 has also a longitudinal external groove 13 , not necessary, passing through the centers of the holes 1 1 and 12 and having an open end at one end of its wall, the width of this groove 13 being smaller than the diameter of the radial holes 1 1 and 12. In the example as shown on the figures, the holes 1 1 and 12 are parallel and comprised in a same longitudinal plane of the nut 4.

As shown particularly in figures 1 and 5 , the recirculating means 8 are separated or distinct from the nut 4 and comprise two deflecting elements or pegs 14 and 15 fitted into the radial holes 1 1 and 12 of the nut 4 and an external beam 16 connected or affixed to the deflecting elements 14 and 15 at two remote points along its length. For exemple, the external beam extends longitudinally in the groove 13 of the nut 4.

As seen particularly in figures 2 and 5 , the deflecting elements 14 and 15 each have a central cylindrical part 17 in their respective radial holes 1 1 and 12; internal parts 18 that extend across the gap between the thread 3 of the threaded screw 2 and the thread 5 of the nut 4, without however touching the thread 3 of the screw 2, and that can abut on the inside of the nut 4; and external parts 19 that are connectable to the beam 15. The deflecting elements 14 and 15 can therefore be placed in the radial holes 1 1 and 12 from the inside of the nut 4. The beam 16 can then be placed in the groove 13 and connected to the deflecting elements 14 and 15 from the outside of the nut 4, the beam 16 sitting on the bottom of the groove 13 so that the internal parts 18 of the deflecting elements 14 and 15 are kept in contact with the inside of the nut 4.

The mutual locking means connecting the beam 16 to the deflecting elements 14 and 15 are preferably reversible so that the recirculating means 8 are dismountable. One embodiment of the recirculating means 8 may be as described below.

As shown particularly in figure 2, the internal parts 18 of the deflecting elements 14 and 15 include portions 20 formed underneath the central parts 17 to project to one side in the form of angular positioning projections 20a designed to contact and follow the side walls of the thread 5 of the nut 4.

As shown particularly on figure 3 , the internal parts 18 of the deflecting elements 14 and 15 also comprise pairs of laterally projecting opposite flanges 21 and 22 designed to be in contact with the outer flats or edges of the two adjacent thread forms of the thread 5 of the nut 4.

The external parts 19 of the deflecting elements 14 and 15 comprise pairs of diametrically opposite arms 23 and 24 extending out from the central parts 17, partly inside the radial holes 1 1 and 12 and partly outside of them, leaving a gap between them and the walls o f these holes and forming passages longitudinally aligned with the external groove 13.

The ends of the above arms 23 and 24 are provided with hook- like teeth 25 and 26 projecting towards each other to define longitudinal passages in which the beam 16 is received longitudinally and held in position, in a reversible manner to be dismountable.

The beam 16, which is partly in and partly out of the longitudinal groove 13 of the nut 4, is rectangular in section and has an internal surface 27 in contact with radial surfaces 28 (figure 6) of the central parts 17 of the deflecting elements 14 and 15 , formed between the pairs of arms 23 and 24 of the deflecting elements 14 and 15 ; opposite lateral surfaces 29 and 30 in contact with the adjacent surfaces of these arms 23 and 24 ; and an external surface 31 with flanges 31 a and 31b along its longitudinal edges, these flanges or shoulders 31 a and 31b being parallel to the bottom surface 27 and engaged by the projecting teeth 25 and 26 of the arms 23 and 24 of the deflecting elements 14 and 15.

To hold the beam 16 longitudinally in position relative to the deflecting elements 14 and 15 , the opposing surfaces of the arms 23 and 24 of the deflecting elements 14 and 15 include projecting humps 32 and

33 situated at a distance from the radial surfaces 28 and engaged in depressions 34 and 35 formed in the opposite lateral surfaces 29 and 30 of the beam 16.

As shown particularly in figures 3 and 7, the internal surface 27 of the beam 16 also has projecting humps 27a and 27b situated between and at a distance from the deflecting elements 14 and 15 and in contact with the bottom of the longitudinal groove 13 of the nut 4, so that the beam 16 produces an outward tension in the deflecting elements 14 and 15 , thereby keeping the internal parts 18 of the deflecting elements 14 and 15 pressed against the nut 4.

The ends of the arms 23 and 24 of the deflecting elements 14 and 15 , where the projecting teeth 25 and 26 are located, have locating chamfers 23a and 24a which extend towards the passages between themselves. To define the recirculating channel 9, as shown more particularly in figures 2 and 3 , the deflecting elements 14 and 15 have internal continuous deflecting channels 36 and the beam 16 has a continuous connecting channel 37. As shown particularly in figures 2 and 3 , the internal deflecting channels 36 of the deflecting elements 14 and 15 are formed in their central parts 17 and internal parts 18 and are substantially curved. The deflecting channels 36 each have one open end placed at one end of their projection 20a and between the threads 3 and 5 of the threaded screw 2 and the nut 4 and oriented respectively towards the path 10 of the series

6 of balls 7 in the nut 4. The deflecting channels 36 each have another open end, formed radially relative to the nut 4, into the interfaces between the central parts 17 of the deflecting elements 14 and 15 and the beam 16. The internal parts 18 of the deflecting elements 14 and 15 are therefore mounted in opposite directions.

As shown particularly in figures 3 and 4, the internal connecting channel 37 of the beam 16 comprises a longitudinal part and curved end parts. The open end of the curved end parts are formed radially relative to the nut 4, at the interfaces between the central parts 17 of the deflecting elements 14 and 15 and the beam 16 for communication with the deflecting channels 36 of the deflecting elements 14 and 15 in the interface 27, 28.

In an illustrative embodiment, the deflecting elements 14 and 15 can be identical and made of a moulded material and the beam 16 may comprise two longitudinal parts 16a and 16b made of a moulded material, these two longitudinal parts 16a and 16b defining between themselves the connecting channel 37 and being joined together by complementarity of shapes. To mount the deflecting elements 14 and 15 and the beam 16 as defined above on the nut 4, the following method may be followed, as shown in figure 6 particularly.

The deflecting elements 14 and 15 may be installed in the holes 1 1 and 12 of the nut 4, from the inside the nut 4.

The beam 16 is then inserted between the arms 23 and 24 of the deflecting elements 14 and 15 , by displacement radially to the nut 4, until it is in the assembled position as described earlier, such that the hook-like teeth 25 and 26 of the the arms 23 and 24 of the deflecting elements 14 and 15 engage on the flanges 31 a and 31 b of the beam 16 and the projecting humps 32 and 33 on the arms 24 and 25 of the deflecting elements 14 and 15 engage in the depressions 34 and 35 o f the beam 16.

This operation is possible because of the elasticity of the material, which allows the arms 23 and 24 of the deflecting elements 14 and 15 to spread apart in the circumferential direction of the nut 4 when the beam 16 is pushed on and between the chamfers 23a and 24a of these arms, and to spring back to lock the teeth 25 and 26 of the arms 23 and

24 of the deflecting elements 14 and 15 over the flanges 31 a and 31b o f the beam 16, and which also allows the beam 16 to deform substantially in elastic flexion when its projecting humps 27a and 17b reach the bottom of the external groove 13 of the nut 4.

By this way, a tension is created in the deflecting elements and, further, the deflecting elements 14 and 15 and the beam 16 are held to each other and to the nut 4 by snaping or cliping engagements, without further action because the wall of the nut 4 is inserted between the internal parts 18 of the deflecting elements 14 and 15 and the beam 16, respectively beared on the inside and on the outside of the nut 4. Furthermore, the internal parts 18 of the deflecting elements 14 and 15 are positioned correctly to lift successively the balls at one end of the path 10 and to replace successively the balls at the other end of the path 10.

In a variant of the method of assembly, the beam 16 could be inserted into the groove 13 of the nut 4 by its open end longitudinally and could be slided longitudinally through the external parts 19 of the deflecting elements 14 and 15 , between their arms 23 and 24 and underneath the projecting teeth 25 and 26, until the beam 16 and the deflecting elements 14 and 15 reach the relative positions described above, with the advantages of the elasticity of the material as indicated earlier.

In a variant illustrated in figures 8 and 9, in which the similar pieces have the same references as above mentioned, the contact interfaces 38 and 39 of the projecting teeth 25 and 26 of the arms 23 and 24 of the deflecting elements 14 and 15 on the beam 16 could be sloped and the end surfaces of these arms could be approximately level with the external surface 31 of the beam 16, without the locating chamfers 23 a and 24a. In this variant, the assembly of the deflecting elements 14 and

15 and the beam 16 on the nut 4 can be performed by longitudinal movement of the beam 16 as described earlier.

In order to disassembly the ball recirculating means as above described, the inverse operations can be performed.

In a variant illustrated in figures 10 and 1 1 , in which the similar pieces have the same references as above mentioned, the identical deflecting elements 14 and 15 and the beam 16 are defined with poka- yoke parts as following.

The hook-like teeth 25 and 26 of the arms 23 and 24 of the deflecting elements 14 and 15 are positioned at different distances from the radial surface 28 thereof. The opposite shoulders 31 a and 31b of the beam 16, formed at each end of the beam, are located at different distances from its bottom surface 27 such as being able to cooperate with the hook-like teeth 25 and 26. The opposite shoulders 31 a and 3 1b cooperating with the deflecting elements 14 are inverted with respect to the opposite shoulders 31 a and 31b cooperating with the deflecting elements 15 , the faces 29 and 30 having respectively a shoulder 31 a and and a shoulder 31b at its ends.

So, there is only one possibility to couple a deflecting element at each end of the beam, such that the internal parts 18 of the deflecting elements 14 and 15 are necessarily placed in inverted directions.

Furthermore, in this variant, the projecting humps 32 are cancelled.

In all the examples as above described, it is possible to make the reflecting elements and the beam in an adapted plastic material or in a metal or in a bi-material of an insert and an over-moulded material.

The above-described examples are not the only ones and can be immediately modified as following.

The axis of the holes 1 1 and 12 receiving the deflecting elements

14 and 15 can be inclined with respect to each other, in radial planes o f the nut 4, without cutting the axis of the nut 4. The beam can be formed in order that the deflecting elements 14 and 15 are not aligned longitudinally but shifted peripherically to the nut 4. In this case, the beam can be arqued in order to follow the peripherical surface of the nut

4 and placed in a groove or not. The nut 4 can comprise several parallel threads 5 and can be adapted and can carry several corresponding ball recirculating means which can be shifted peripherically to the nut 4.

Referring to figure 12, it will be now described a specifical application of the operating device 1. This application is an insertion of the operating device 1 in a steering system 100 with power assistance means for vehicle wheels.

The nut 4 comprises an annular part 101 preferably adjacent to the part of the nut 4 having the thread 5. The part 101 has a peripherical groove 102 (also figure 3). This part 101 is enveloped by a stationary ring 103 mounted in a housing (not shown) of the steering system 100. The stationary ring 103 has an inner annular groove 104, and balls or rollers are inserted in the grooves 102 and 104 in order to form a rolling bearing for mounting rotatably the nut 4 in the housing. A notched pulley 105 is mounted on the nut 4, around its part having the thread 5. This pulley 105 has a longitudinal internal groove 106 in which the external part of the beam 16 of the ball recirculating means extends at a distance from the faces of this groove 106. The pulley 105 is affixed on the nut 4 by the means of longitudinal studs 107 inserted in corresponding longitudinal ioputer and inner grooves thereof.

The steering gear 100 comprises a motor 108 driving a notched pulley 109 wihich is coupled to the pulley 105 via a notched belt 1 10.

The steering gear 100 comprises also a rack bar 1 1 1 cooperating with a pinion 1 12 carried by a steering column 1 13 The rack bar 1 1 1 and the screw 2 are aligned longitudinally and are preferably formed in a one-piece 1 14 which is slidingly engaged in a housing.

When the motor is activated, the rotation of the pulley 109 is transmitted to the pulley 105 via the belt 1 10. This and the rotation o f the nut 4, with the pulley 107, is transmitted to the one-piece 1 14 via the series 6 of balls 7 in order to translate the rack bar 1 1 1 which then rotate the vehicle wheel or wheels in order, for example, to control the trajectory of the vehicle in a curve. Alternatively, the pulleys 105 and 109 can be gears which engage mutually, directly or indirectly via other gears.

Claims

1. Ball recirculating means able to be mounted on an internally threaded nut and defining a recirculating channel to carry balls from one end to the other end of a path inside the nut, along which the balls are engaged in the thread therof, characterized in that it comprises two deflecting elements (14, 15) able to be engaged in respective holes formed through the thickness of the nut and each having a ball deflecting channel (36), in that it comprises a beam ( 16) connectable to said deflecting elements and having a connecting channel (37), the deflecting channel of one of the deflecting elements, the connecting channel of the beam and the deflecting channel of the other deflecting element defining in succession said ball recirculating channel (9), and in that the deflecting elements ( 14, 15) and/or the beam ( 16) comprise retaining means able to cooperate with the nut.

2. Ball recirculating means according to claim 1 , in which said deflecting elements and said beam are provided with mutual locking means (25 , 26 ; 31 a, 31b).

3. Ball recirculating means according to Claim 2, in which the deflecting elements are engageable in said holes from the inside of the nut and comprise projected internal lateral parts (20a ; 21 , 22) able to bear against the inside of the wall of the nut and in which said beam comprises at least one part (27, 27a) able to bear on the outside of the nut (4).

4. Ball recirculating means according to any one of the preceding claims, in which the deflecting elements comprise positioning parts (20) able to bear against the side walls of the thread of the nut.

5. Ball recirculating means according to any one of the preceding claims, in which the deflecting elements comprise centering parts (21 ) able to bear against the end of the thread of the nut.

6. Ball recirculating means according to any one of the preceding claims, in which the deflecting elements each have passages through which said beam can be passed.

7. Ball recirculating means according to any one of the preceding claims, in which the deflecting elements each comprise two radial arms

(24, 25) between which said beam is engaged, these arms and the beam comprising mutual locking means (25 , 26 ; 31 a, 31b).

8. Ball recirculating means according to any one of the preceding claims, in which the deflecting elements and the beam each have surfaces (27, 28) of mutual contact through which said deflecting channels and connecting channel communicate.

9. Ball recirculating means according to any one of the preceding claims, in which the beam comprises two connected parts between which the connecting channel is formed internally.

10. Ball recirculating means according to any one of the preceding claims, in which the deflecting elements and the beam comprise poka-yoke parts.

1 1. An actuating device comprising an externally threaded screw (2), an internally threaded nut (4), and at least one series (6) of balls such that balls are engaged in the thread of the threaded screw and the thread of the nut along a path, the nut being provided with ball recirculating means according to any one of the preceding claims in order to carry the balls from one end to the other end of their path inside the nut when the screw (2) rotates relatively to the nut (4).

12. An actuating device according to claim 1 1 , in which the beam is at least partly engaged in an external groove ( 13) formed in the wall of the nut.

13. An actuating device according to claim 1 1 or 12, in which the nut (4) comprises a peripheral groove ( 102), and further comprising a stationary ring ( 103) with an annular groove (104), and rolling bodies inserted in the grooves ( 102, 103) so as to form a rolling bearing in order to rotatably mount the nut (4) in a housing.

14. A power steering system for vehicle wheels, comprising a steering rack for steering the wheels, a motor for assisting the translation of the steering rack, and an actuating device according to any one of claims 1 1 and 13 , the nut being connected in rotation to the motor and the screw being connected in translation to the steering rack.

15. Power steering system according to claim 15 , in which the nut carries a pulley, this pulley having an internal groove in which the external part of the beam of the ball recirculating means extends at a distance from the faces of this groove.

16. Power steering system according to claim 15 , in which the screw and the steering rack are aligned and formed in a one-piece.