VL joint for a propeller shaft with an optimized crash behavior

A VL constant velocity universal joint for accommodating axial displacements in a propeller shaft of a motor vehicle and for connecting a drive unit to a rear axle gearbox has at least two articulatably connected shaft portions, with a standard plunge which is usable in a damage-free way. An outer joint part has outer ball tracks and an inner joint part has inner ball tracks. A plurality of torque transmitting balls are guided in the outer and inner ball tracks associated with one another. Associated outer ball tracks and inner ball tracks form angles of intersection with respect to a central axis A of the joint. The angles are of identical size but set in opposite directions. A ball cage is provided with a plurality of cage windows each accommodating one of the balls and which hold the balls in one plane when the joint is axially displaced or articulated. The outer joint part is connected to an annular flange and the inner joint part to a connecting shaft, wherein when the outer joint part is displaced relative to the inner joint part, the effective guiding length of the ball tracks in one of the two joint parts is shorter than that of the ball tracks in the other one of the two joint parts. Stop means are provided which become effective at the end of the standard plunge to prevent the balls from leaving the ball tracks with the shorter length. The stop means comprise nominal deformation means which are deformable when the standard plunge is exceeded.

BACKGROUND OF THE INVENTION
 The invention relates to a VL constant velocity universal joint for
 accommodating axial displacements in a propeller shaft of a motor vehicle
 and for connecting a drive unit to a rear axle gearbox, having at least
 two articulatably connected shaft portions, a standard plunge usable in a
 damage-free way, an outer joint part with outer ball tracks, an inner
 joint part with inner ball tracks, a plurality of torque transmitting
 balls each guided in outer and inner ball tracks associated with one
 another, with associated outer ball tracks on the one hand and inner ball
 tracks on the other hand, forming angles of intersection in respect of the
 central axis A of the joint, which are of identical size but are set in
 opposite directions, and having a ball cage which is provided with a
 plurality of cage windows each accommodating one of the balls and which
 hold the balls in one plane when the joint is axially displaced or
 articulated, with the outer joint part having to be connected to an
 annular flange and the inner joint part to a connecting shaft.
 Propeller shafts of this type are used in motor vehicles to transmit torque
 from a front drive unit to the rear axle. Apart from having to ensure
 functional safety under normal operating conditions, these structures also
 have to fulfil certain requirements in the case of a vehicle crash wherein
 the front part of the vehicle and thus the first part of the propeller
 shaft is displaced towards the rear axle. To prevent the shaft from
 kinking towards the vehicle cell and in order not to prevent a greatest
 possible absorption of energy in the front part of the vehicle through
 deformation work, by supporting the drive unit at the rear axle, and to
 avoid any damage to the rear axle, it must be possible to shorten the
 shafts further beyond the range predetermined by the standard plunge of
 the VL joint with a minimum of energy being absorbed. The component
 particularly suitable for accommodating such shortening is the respective
 axially plungeable constant velocity universal joint in the propeller
 shaft.
 Propeller shafts of this type for motor vehicles are known from DE 42 24
 201 C2 wherein it is proposed that at the end of the predetermined
 standard plunging distance between the outer joint part and the inner
 joint part, the balls of the cage stop against the annular flange and that
 the connection between the plug-in shaft and the inner joint part is to be
 destroyed. Hereafter, the plug-in shaft slides into the annular flange and
 into the hollow shaft adjoining same. This embodiment presupposes plug-in
 shafts which, with a reduced diameter, follow the toothed region engaging
 a correspondingly toothed region in the inner joint part.
 DE 43 44 177 C1 describes a similar type of propeller shaft for motor
 vehicles, which comprises a cage-less joint with axis-parallel ball
 tracks, which cage-less joint, in operation, is suitable for very small
 articulation angles only. With this embodiment, the plug-in shaft cannot
 be slid in beyond the predetermined standard plunging region unless the
 outer joint part and the adjoining tubular shaft are deformed, thus
 absorbing a large amount of energy.
 SUMMARY OF THE INVENTION
 It is the object of the present invention to provide a VL constant velocity
 universal joint for a propeller shaft of a motor vehicle, which joint,
 after the predetermined standard plunging distance has been exceeded, is
 destructible with only a small amount of energy being absorbed and which,
 in an non-obstructive way, permits the plug-in shaft to be inserted
 further along a considerable length towards the annular flange.
 The objective is achieved in that, when the outer joint part is displaced
 relative to the inner joint part, the effective guiding length of the ball
 tracks in one of the two joint parts, in the sense of shortening the
 propeller shaft, is shorter than the effective guiding length of the ball
 tracks in the other one of the two joint parts; that there are provided
 stop means which become effective at the end of the standard plunging path
 to prevent the balls from leaving the ball tracks with the shorter guiding
 length; and that the stop means comprise nominal deformation means which
 are deformable when the standard plunging path is exceeded.
 The effect of these measures consists in that, after a predetermined
 standard plunging length has been exceeded, there first become effective
 stop means which prevent unintended dismantling during transport and
 assembly and which, without suffering any damage, limit any drive unit
 displacement relative to the rear axle drive, such displacement occurring
 in service under extreme service loads. In the case of loads exceeding the
 aforementioned loads, which only occur as a result of deformation suffered
 by the front part of the vehicle in an accident, the nominal deformation
 means are destroyed. Thereafter, with only slight resistance forces having
 to be overcome, the balls are caused to leave the ball tracks of one of
 the two joint parts so that axial forces can non longer be supported by
 the propeller shaft and the transmission of torque ceases immediately.
 This means that the propeller shaft can be shortened further while
 absorbing only small amounts of energy.
 According to first preferred embodiments it is proposed that, starting from
 a central plane of the joint, the inner ball tracks at the shaft
 connection end are shorter than the outer ball tracks at the annular
 flange end or the outer ball tracks at the annular flange end are shorter
 than the inner ball tracks at the shaft connection end.
 In these embodiments, there are provided stop means which, as nominal
 deformation means, have to be deformed or destroyed before the balls are
 able to leave the ball tracks. The stop means can be provided directly at
 the ends of the respective shorter ball tracks, for example in the form of
 annular members arranged between the connecting shaft and the inner joint
 part or the outer joint part and the annular flange or they can be
 provided locally independently of the shorter ball tracks in the form of a
 cover which is inserted into the annular flange or the adjoining tubular
 shaft and against which there stops the inner joint part and,
 respectively, a front end of the connecting shaft inserted into same.
 According to a second embodiment it is proposed that the inner ball tracks
 in the inner joint part comprise track end portions consisting of an
 elastically resilient or easily plastically deformable material and that
 in the circumferential direction, the cage windows form fixed end stops
 for the balls when these reach the track end portions. When, by reaching
 the fixed end stops in the cage windows, the balls are prevented from
 moving further in the circumferential direction and thus from being
 displaced further along the ball tracks extending at an angle of
 intersection, axially moving the balls out of said ball tracks while
 deforming the track end portions is achieved. In this embodiment, said
 track end portions form the destructible nominal deformation means of the
 stop means, i.e. in this case, too, the effective guiding length of one of
 the joint parts is reduced. The plasticity of the track end portions can
 be achieved by doing without hardening the respective joint parts in this
 region.
 The annular members which serve as nominal deformation means may consist of
 plate metal rings or plastic rings. The annular elements may optionally
 cooperate with the balls or with the cage. By providing the annular
 elements or cover parts in the annular flange with a suitable design, it
 is possible to set the absorption of a defined amount of energy after the
 dismantling of the joint, while shortening the propeller shaft further,
 provided this is desirable as an additional measure towards the absorption
 of energy in the front part of the vehicle in the case of a vehicle
 accident. The cover parts can also be used as means additional to the
 second embodiment.
 Fixed stops can be provided at the ends of the respective longer ball
 tracks. Alternatively, it is possible to provide axial stops between the
 inner joint part and the ball cage. As a result, even if the connecting
 shaft is pushed further into the annular flange, the balls, after having
 left the shorter ball tracks, are held at the ends of the longer ball
 tracks, while being radially supported on an adjoining shaft shank or in
 an adjoining hollow shaft.
 Modifications of the above within the limits of the respective technical
 know-how are possible. Special embodiments are defined in the subclaims,
 with reference being made here to the contents of the subclaims.

BRIEF DESCRIPTION OF A PREFERRED EMBODIMENT
 To the extent that the designs of the inventive assemblies correspond to
 one another, FIGS. 1 to 5 will be described jointly below. A constant
 velocity universal joint 11 comprises an outer joint part 12, an inner
 joint part 13, a ball cage 14 and torque transmitting balls 15 each held
 in a cage window 19. The joint 11 is an axially plungeable VL constant
 velocity universal joint whose details are provided with the respective
 reference numbers in the individual Figures. The outer and inner tracks
 16, 17 which are associated with one another, with one of each, jointly,
 carrying a ball 15, extend, as is known in itself, at angles of
 intersection relative to the joint axis A, which angles are of equal size,
 but face opposite directions. As a result, in the case of relative
 displacement movements between the outer joint part 12 and the inner joint
 part 13, the cage 14 with the balls 15 is guided on to half the
 displacement path relative to each of the two joint components 12, 13. The
 outer joint part 12 is connected to an annular flange 31 which is flanged
 to the outer joint part by means of bolts 32. The annular flange is
 followed by a hollow shaft 33, with the hollow shaft 33 according to FIGS.
 1 to 4 being connected to the annular flange 31 by means of a friction
 weld 34. Into the inner joint part 13 there is inserted a connected shaft
 36 which, at a certain distance from the joint, is supported by an elastic
 shaft bearing 37. A plate metal cap 38 is secured to the outer joint part
 by means of bolts 32. A rolling boot 39 seals the plate metal cap 38
 relative to the connecting shaft 36.
 In FIG. 1, the inner ball tracks 17.sub.1, with reference to a central
 joint platen E, are so short at the plug-in shaft end that, when the
 plug-in shaft 36.sub.1 is slid in towards the annular flange 31.sub.1, the
 balls lose their guidance in the inner ball tracks 17.sub.1 at the shaft
 connection end before the same situation can arise in the outer ball
 tracks 16.sub.1 at the annular flange end. This, in any case, is prevented
 in that in the annular flange 31.sub.1, an end stop 40.sub.1 for the balls
 15.sub.1 limits a further insertion of the balls 15.sub.1 and the cage
 14.sub.1 towards the annular flange 31.sub.1. As a result of this measure,
 the balls at the ends of the inner ball tracks 17.sub.1 are caused to stop
 against a plate metal ring 18.sub.1 which is secured between the inner
 joint part 13.sub.1 and an annular collar 41.sub.1 on the shaft shank
 36.sub.1. On the one hand, the ring 18.sub.1 forms the stop means, with
 its purpose being to prevent the joint from being lost prior to assembly,
 and on the other hand, in the mounted condition of the joint as
 illustrated, the ring 18.sub.1 serves as an easily destroyable nominal
 deformation element which, when the plug-in shaft 36.sub.1 is inserted
 further into the annular flange 31.sub.1, permits the joint to be
 dismantled so that it can no longer accommodate any axial forces and can
 no longer transmit any torque. Any further insertion of the plug-in shaft
 .sup.36.sub.1 into the annular flange 31.sub.1 is prevented by a plate
 metal cover 42.sub.1 which cannot be displaced by the plug-in shaft
 36.sub.1 towards the hollow shaft 33.sub.1 unless slightly increased
 friction forces are overcome. However, the primary function of the cover
 42.sub.1 is to seal the joint towards the outside, i.e. towards the hollow
 shaft 33.sub.1.
 FIG. 2 shows a joint which largely corresponds to the joint illustrated in
 FIG. 1. However, it deviates from FIG. 1 in that it does not comprise a
 part which corresponds to the plate metal ring 18 shown in FIG. 1. The
 function of the stop means and of the nominal deformation means is
 fulfilled entirely by the cover 42.sub.2 which cooperates with the
 spherical end 43.sub.2 of the connecting shaft 36.sub.2 in such a way that
 articulation movements can take place in the point of contact without the
 position of the joint center M being adversely affected. Otherwise, all
 details in FIG. 2 correspond to those in FIG. 1.
 The joint illustrated in FIGS. 3A and B largely corresponds to that shown
 in FIGS. 1 and 2. However, it deviates from FIGS. 1 and 2 in that, with
 reference to the central joint plane E, the length of the inner ball
 tracks 17.sub.3 at the plug-in shaft end is identical to that of the outer
 ball tracks 16.sub.3 at the annular flange end. The cross-hatched areas
 which include the cross-sectional area and the surface area, indicates
 that the material of the ball tracks has been hardened. It can be seen
 that the inner ball tracks 17.sub.3 comprise unhardened track end regions
 20.sub.3 which limit the effective guiding length of the inner ball tracks
 17.sub.3 to the hardened parts. For this purpose, there has to be provided
 a ball cage 14.sub.3 whose cage windows are so short in the
 circumferential direction that the balls 15.sub.3 are prevented from
 entering the unhardened end regions 20.sub.3 in the direction of the
 angles of intersection of the ball tracks. In this way, the end regions
 become destroyable stop elements in that the balls 15.sub.3 are axially
 pulled out of the inner joint part 13.sub.3 in the position as held in the
 circumferential direction. The illustrated cover 42.sub.3 in the annular
 flange 31.sub.3 primarily serves to seal the joint towards the outside in
 the direction of the tubular shaft 33.sub.3.
 FIG. 4 shows a joint which, while being modified in respect of its
 individual parts and its function, fully corresponds to the joint shown in
 FIG. 1. Only the shape of the plate metal ring 18.sub.4 is different,
 which is clamped on to the inner joint part 13.sub.4 so as to be
 self-holding and which, even prior to the assembly of the joint, serves to
 prevent the joint from being lost. The shape of the annular flange
 31.sub.4 also differs, both in respect of the flange as a whole and
 especially in respect of the end stop 40.sub.4 for the balls 15.sub.4. In
 this embodiment, the bolts 32.sub.4 are secured by nuts 43.sub.4. The
 functions correspond to those described with reference to FIG. 1.
 FIG. 5 shows a joint whose design is similar to that shown in FIG. 4.
 However, with reference to the central joint plane E, the ball tracks
 16.sub.5 in the outer joint part 12.sub.5 at the annular flange end are
 shorter than the ball tracks 17.sub.5 in the inner joint part 13.sub.5 at
 the connecting shaft end. Between the outer joint part 12.sub.5 and the
 annular flange 31.sub.5 there is clamped in a plastic ring 18.sub.5 which
 constitutes the stop means, which prevents the joint from being lost prior
 to assembly and which serves as a nominal deformation element in the
 mounted condition. While the plug-in shaft 36.sub.5 is inserted into the
 annular flange 31.sub.5, the ring 18.sub.5 can easily be deformed or
 destroyed, so that the balls 15.sub.5 leave the tracks 16.sub.5 in the
 outer joint part before they leave the tracks 17.sub.5 in the inner joint
 part 13.sub.5. This, incidentally, is prevented by the stop of the inner
 joint part 13.sub.5 and an inner stop face 43.sub.5 of the ball cage
 14.sub.5. A plate metal cover 42.sub.5 inserted into the annular flange
 31.sub.5 again serves to seal the joint towards the outside in the
 direction of the tubular shaft 33.sub.5. When inserted into the plug-in
 shaft 36.sub.5 it is also able to accommodate additional deformation or
 friction forces. The gap between the outer joint part 12.sub.5 and the
 annular flange 31.sub.5 is sealed by the plastic ring 18.sub.5.
 A worker in this art would recognize these embodiments are only examples,
 and that other modifications come within this invention. Thus, the claims
 should be studied to determine the true scope and content of this
 invention.