GB2411930A

GB2411930A - Driveshaft plunging units

Info

Publication number: GB2411930A
Application number: GB0405123A
Authority: GB
Inventors: John Edward Holland; John Richard Kenyon
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2004-03-08
Filing date: 2004-03-08
Publication date: 2005-09-14
Anticipated expiration: 2024-03-08
Also published as: GB2411930B; GB0405123D0

Abstract

A plunging unit for a driveshaft which includes a plunging shaft 1 and an outer tube 2 which are arranged so as to be centered on a longitudinal axis XX. The outer tube 2 is provided with circumferentially distributed outer running grooves 8 which extend parallel to the longitudinal axis XX. The outer face 3 of the plunging shaft 1 is provided with inner running grooves 4 which extend parallel to the longitudinal axis XX and are positioned opposite the outer running grooves 8. Identical groups of balls 6 are held in a sleeve-shaped cage 7 and are, in pairs of opposed outer running grooves 8 and inner running grooves 4, arranged coaxially around the plunging shaft 1. The cage 7 is displaceable relative to the outer tube 2 and the plunging shaft 1 between two endstops 10, 11. Opposite ends 7a, 7b of the cage 7 can abut compression springs 9,10 so that in use, during low or zero torque driving conditions, the compression springs can apply a biasing force to shift the ball cage 7 to a position away from the endstops 10 or 11.

Description

Driveshaft olunnina units The present invention relates to a driveshaft

plunging unit for transmitting torque within a motor vehicle driveling.

Typically, a motor vehicle driveling includes a driveshaft comprising two joints which permit articulation angles only and which are connected to one another by a connecting shaft and a plunging unit which serves to allow for any changes in the distance between the articulation centers of the joints, e.g. due to suspension travel.

US 6,585,602 describes such a driveshaft plunging unit which includes an outer tube which is arranged so as to be centered on a longitudinal axis and which is provided with circumferentially distributed outer running grooves which extend parallel to the longitudinal axis. The plunging unit also includes an inner shaft whose outer face is provided with inner running grooves which extend parallel to the longitudinal axis and which are positioned opposite the outer running grooves. The plunging unit also includes a ball cage arranged coaxially around the inner shaft, the ball cage serving to axially space groups of balls which are displaceable relative to the outer tube and inner shaft in the pairs of opposed outer running grooves and inner running grooves. The plunging unit includes endstops for limiting the axial movement of the ball cage relative to the inner shaft during the extension motion and compression motion.

Whilst this known driveshaft plunging unit might provide good characteristics, in certain circumstances when it is used in the driveshafts for driven front wheels of a vehicle it can have the disadvantage of acting as a path for engine frequency vibration which is transmitted axially along the driveshaft to the wheels and tyres, then back towards the occupants via the suspension and steering rack. This can occur after extended periods of driving when the cage can creep or migrate towards one end of the unit. If this happens and the cage abuts one of the endstops then plunging movement in one direction can only occur with skidding of the balls since the cage is unable to move.

In accordance with a first aspect, the present invention provides a plunging unit for a driveshaft which includes a plunging shaft and an outer tube which are arranged so as to be centered on a longitudinal axis, the tube being provided with circumferentially distributed outer running grooves which extend parallel to the longitudinal axis and the outer face of the plunging shaft being provided with inner running grooves which extend parallel to the longitudinal axis and which are positioned opposite the outer running grooves, and rolling contact members which are held in a sleeve-shaped cage and arranged coaxially around the plunging shaft in pairs of opposed outer running grooves and inner running grooves, the cage being displaceable relative to the outer tube and the plunging shaft between two endstops, wherein a resilient biasing means is arranged so that in use during low or zero torque driving conditions, the resilient biasing means can apply a biasing force to shift the ball cage to a position away from the endstops.

One advantage of the present invention is that by re-centering the ball cage during low or zero torque driving conditions, it avoids any undue increase in the plunging force required to compress or extend the shaft when the ball cage reaches its endstop and which can otherwise lead to excess vehicle vibration.

In accordance with a second aspect, the present invention provides a vehicle incorporating the plunging unit for driveshaft in accordance with the first aspect.

In a preferred embodiment, the resilient biasing means includes a compression spring having an end portion in contact with the endstops.

The endstops may be provided with a location feature for the corresponding compression spring.

In an other embodiment, the resilient biasing means may be connected to the ball cage. The ball cage may provided with a location feature for the corresponding compression spring.

The invention will now be described by way of example with reference to the accompanying drawings of which: Fig.1 is a longitudinal section through one embodiment of an plunging unit according to the present invention, shown in a normal operating condition; Fig.2 is a view similar to that of Fig. 1 showing the plunging unit in an extended condition; Fig. 3 is a view similar to that of Fig. 1 showing the plunging unit in a compressed condition; Fig.4 is a scrap view of Fig. 1 to a larger scale; Fig. 5 is a perspective view of a mechanical element of the plunging unit shown in Fig. 4; Fig.6 is a view similar to that of Fig.1, through another embodiment of a plunging unit in accordance with the present invention; Fig.7 is a view similar to that of Fig. 6 showing the plunging unit in a compressed condition; and Fig.8 is a view similar to that of Fig. 6 showing the plunging unit in an extended condition.

Referring to Figs.1 to 4, there is shown a plunging unit for a driveshaft, in this case one of a pair of shafts extending laterally to drive road wheels on each side of a vehicle.

Such a unit is typically used on four wheel drive vehicles with independent front suspension. - 4

The plunging unit is arranged so as to be centred on a longitudinal axis XX and comprises a plunging shaft 1 and a tube 2. The outer face 3 of the plunging shaft 1 is provided with inner running grooves 4 for rolling contact members 5, the grooves extending parallel to the longitudinal axis XX and being circumferentially distributed around the axis XX.

The rolling contact members 5 are in the form of six identical groups of six balls 6 which are arranged at identical distances from one another. The balls 6 are held in a sleeve-shaped cage 7 which is made of plastic. The tube 2 is also provided in its bore 2a with circumferentially distributed outer running grooves 8 which are arranged opposite the inner running grooves 4 and also extend parallel to the longitudinal axis XX. For manufacturing convenience there are twelve outer running grooves 8 in the tube 2 so that alternate grooves are unused.

Thus, a respective pair of corresponding running grooves 4, 8 of the plunging shaft 1 and tube 2 are arranged face-to-face when they are assembled to one another.

Movement of the ball cage 7 in the axial direction along the longitudinal axis XX is controlled by resilient biasing means which in this example comprises a first set of compression springs 9 arranged on one side of the ball cage 7 and a second set of compression springs 10 arranged on the other side of the ball cage 7, the springs 9, 10 being fitted within corresponding pairs of the running grooves 4, 8 of the plunging shaft 1 and tube 2.

The tube 2 further includes in its bore 2a a first endstop 11 (Fig. 5) and a second endstop 12 which are arranged to limit the rolling displacement travel of the ball cage 7 in the inner 4 and outer 8 running grooves during movement of the plunging unit towards the compressed condition (Fig.2) or the extended condition (Fig. 3). - 5

The first endstop 11 is a cup-shaped and has an tapered end portion 14 and an outer face which is provided with twelve ribs 13 extending parallel to the longitudinal axis XX and being circumferentially distributed around the axis XX for cooperating with the outer running grooves 8 of the tube 2. The first endstop 11 is inserted into the bore 2a of the tube 2 until the tapered end portion abuts against the tapered bore portion of the bore 2a.

In this particular example, there are two springs in each set, arranged diametrically opposite each other.

The first endstop 11 is further provided with a number of location features 11a for co- operation with the first set of compression springs 9.These location features 11a are in the form of circumferentially distributed tongues 11a which extend parallel to the longitudinal axis XX towards the cage 7 at a step which defines an abutment face 11b for abutment against a first end 9a of the compression spring 9. Thus each springs 9 is mounted coaxially around a corresponding tongue 11 a. Each tongue 11 a is longer than the coilbound compressed length of the spring 9 and its free end defines an abutment face 11c for contacting the cage 7, thereby protecting the compression springs The second endstop 12 is annular and has an outer face which is provided with ribs corresponding to the ribs 13. The second endstop 12 is retained inside the tube 2 by a circlip or snap ring 30 which is accommodated in a groove near the aperture of the bore 2a.

The second endstop 12 is also provided with tongues 12a corresponding to the tongues 1 1 a, each tongue 1 2a extending towards the cage at a step defining an abutment face 12b for abutment against the first end 10a of a respective compression spring 10 and having a free end defining an abutment face 12c for the cage 7.

When the driveshaft is in operation, the tube 2 can move axially relative to the plunging shaft 1, the balls 6 rolling in the inner running grooves 4 and in the outer running grooves 8. - 6

In the extended condition of the plunging unit (Fig.2), the springs 9 of the first set have a free extended length L2 while in the compressed condition, the springs 10 of the second set have a free extended length L1. Hence, the cage 7 can normally move over a range L3 (Fig.4) less the length of the cage without contacting the springs 9, 10 and thus without any axial bias other than that caused by a small compressive preload on the balls 6 imparted during assembly.

The first set of compression springs 9 includes two compression springs, each having a length equal to 35mm and a spring-rate equal to 0.36N/mm, that is to say a total rate of 0.72N/mm. The second set of compression springs 10 includes two compression springs, each having a length equal to 11mm and a spring-rate equal to 1N/mm, that is to say a total rate of 2N/mm.

During a compression motion, and similarly a extension motion, e.g. as can occur in an extreme steering or articulation manoeuvre, the ball cage 7 may travel against the endstop 11 or 12 whilst the corresponding springs 9, 10 are compressed. The low rate of the springs 9, 10 ensures that only a low end load is imposed on the plunging unit so that there is a minimal feedback of vibration from the power train to the suspension. On the other hand, if the cage 7 moves towards one endstops 10 or the other as can occur during extended periods of normal driving, the compression springs 9, 10 can apply a small biasing force to shift the ball cage 7 away from the endstop 11 or 12 and back into the normal range of movement depicted by L3. This occurs during normal driving when there is a low or zero torque in the plunging shaft 1, e.g. when the driver lifts the accelerator pedal.

This avoids the cage 7 contacting either of the endstops 11, 12 and hence avoids the problem of vibration as explained in relation to the prior art due to the balls 6 having to slide rather than roll. Typically the force required to compress or extend the plunging unit in use on the vehicle is about ON whereas if contact between the cage and the endstop occurs this can rise to about 350N.

In a modification, the first and second set of compression springs 9, 10 is assembled such that they abut by their second ends 9b, 1 Ob with opposite ends 7a, 7b of the ball cage 7 and by their first ends 9a, 1 Oa with the endstops 1 1, 12.

It will be appreciated that in a such arrangement, the first and second set of compression springs 9, 10 can be assembled with a small preload so that continuous re- centering of the ball cage 7 between its endstops 10 and 11 occurs during low or zero torque in the driveshaft. In this case, the first set of compression springs 9 applies a force continuously against the ball cage which is opposite to the force applied continuously by the second set of compression springs 10. Hence, during the low or zero torque the ball cage 7 is moved to a balance position by the force applied by the first and second set of springs 9, 10. In a such a case L3 is equal to the length of the cage 7.

As shown in Figs. 6 to 8, an alternative arrangement of the resilient biasing means may be made in which the first set of compression springs 9 is replaced by a single compression spring 20 arranged coaxially around the plunging shaft 1 and the second set of compression springs 10 is replaced by a similar spring 21.

Each spring 20, 21 is arranged without contact and preload with the ball cage 7 as shown in Fig. 5. In this manner, in the extended condition of the plunging unit (Fig. 8), the spring 20 has a free extended length L4 while in the compressed condition, the spring 21 has a free extended length L5 (Fig. 7). Thus, the cage 7 can normally move over a range L6 (Fig. 6) without contacting the springs and thus without any axial bias.

In a modification (not shown), each endstop 22, 23 is provided with a circumferential tongue at a step which defines an abutment face for abutment against the first end portion of the spring 20, 21 in order to protect the springs 20, 21 from damage during extreme compression or extension of the shaft.

In the preferred embodiments described above the springs 9,10; 20,21 always react against an endstop secured on the tube 2 but it will be appreciated that the principles of the present invention can be applied if the springs react against stops secured on the plunging shaft 1, or one of each.

Similarly, the location features of the tongues could be arranged at the ends of the ball cage. In such a case, the first and second set of springs can be linked to the ball cage in order to follow the ball cage, the springs acting to shift the ball cage away from the endstops during the low or zero torques.

Although in each of the above examples a biasing spring or set of springs is arranged on each side of the cage, there may be only one spring or set of springs if the tendency for - the cage to creep during normal driving is in one direction only. Alternatively, one spring or set of springs may be used in conjunction with a spring cage which is linked to the ball cage so that the spring or set of springs are compressed irrespective of the direction of movement of the cage. - 9 -

Claims

1. A plunging unit for a driveshaft which includes a plunging shaft and an outer tube which are arranged so as to be centered on a longitudinal axis, the tube being provided with circumferentially distributed outer running grooves which extend parallel to the longitudinal axis and the outer face of the plunging shaft being provided with inner running grooves which extend parallel to the longitudinal axis and which are positioned opposite the outer running grooves, and rolling contact members which are held in a sleeve-shaped cage and arranged coaxially around the plunging shaft in pairs of opposed outer running grooves and inner running grooves, the cage being displaceable relative to the outer tube and the plunging shaft between two endstops, wherein a resilient biasing means is arranged so that in use during low or zero torque driving conditions, the resilient biasing means can apply a biasing force to shift the ball cage to a position away from the endstops.

2. A plunging unit according to claim 1 wherein the resilient biasing means is arranged at each end of the cage.

3. A plunging unit according to claim 1 or claim 2 wherein the resilient biasing means has a low rate which is less than 2N/mm.

4. A plunging unit according to any preceding claim wherein the resilient biasing means includes a compression spring having an end portion in contact with the endstops.

5. A plunging unit according to claim 4 wherein the endstops is provided with a location feature for the corresponding compression spring.

6. A plunging unit according to any of claims 1 to 3 wherein the resilient biasing means is connected to the ball cage. 1, - 1 0

7. A plunging unit according to claim 6 wherein the ball cage is provided with a location feature for the corresponding compression spring.

8. A plunging unit according to claim 5 or claim 7 wherein the location feature comprises a tongue which extends parallel to the longitudinal axis at a step which defines an abutment face for abutment against the end of the compression spring.

9. A plunging unit according to claim 8 wherein the length of the tongue is greater than the coil bound length of the corresponding spring.

10. A plunging unit according to any preceding claim wherein at least one of said pair of opposed outer running grooves and inner running grooves has a corresponding compression spring arranged between them, the compression spring having a first end for abutment with the end of the cage and a second end for abutment with the endstops.

11. A plunging unit according to any of claims 1 to 9 wherein the compression spring is arranged coaxially around the plunging shaft.

12. A plunging unit according to any foregoing claim wherein the or each compression spring is preloaded.

13. A vehicle incorporating a plunging unit according to any foregoing claim.

14. A plunging unit for a vehicle driveshaft substantially as described herein with reference to Figs. 1 to 5 or Figs.6 to 8 of the accompanying drawings.

1. A plunging unit for a driveshaft which includes a plunging shaft and an outer tube which are arranged so as to be centered on a longitudinal axis, the tube being provided with circumferentially distributed outer running grooves which extend parallel to the longitudinal axis and the outer face of the plunging shaft being provided with inner running grooves which extend parallel to the longitudinal axis and which are positioned opposite the outer running grooves, and rolling contact members which are held in a sleeve-shaped cage and arranged coaxially around the plunging shaft in pairs of opposed outer running grooves and inner running grooves, the cage being displaceable relative to the outer tube and the plunging shaft between two endstops, wherein a resilient biasing means is arranged so that in use during low or zero torque driving conditions, the resilient biasing means can apply a biasing force to shift the ball cage to a position away from the endstops and in which one of the endstops is secured on the tube and the other of the endstops is secured on the plunging shaft.

6. A plunging unit according to any of claims 1 to 3 wherein the resilient biasing means is connected to the ball cage. -l2

13. A vehicle incorporating a plunging unit according to any foregoing claim.