EP1631472A1

EP1631472A1 - Drive system for a wheel, particularly a front wheel, coupled to a chassis

Info

Publication number: EP1631472A1
Application number: EP03817131A
Authority: EP
Inventors: Roald H. Pedersen
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-06-06
Filing date: 2003-06-06
Publication date: 2006-03-08
Also published as: AU2003232395A1; WO2004108462A1

Abstract

The invention refers to a drive system for a wheel coupled to a chassis, comprising a rotary driving means, a rotary driven means and coupling means surrounding said rotary driving and driven means for transferring a driving force from said rotary driving means to said rotary driven means. What is provided according to the invention is that said wheel is movable laterally relative to said chassis from a first position to a second position, and said rotary driving and driven means are coupled to said wheel so that their angular orientations relative to the chassis change by the same amount when said wheel is moved from said first position to that second position.

Description

DRIVE SYSTEM FOR A WHEEL, PARTICULARLY A FRONT WHEEL, COUPLED TO A CHASSIS

The invention refers to a drive system for a wheel, particularly a front wheel, coupled to a chassis, said system comprising a rotary driving means, a rotary driven means and coupling means surrounding said rotary driving and driven means for transferring a driving force from said rotary driving means to said rotary driven means.

Drive systems as described above are known from the prior art.

The subject matter of international patent application PCT/IB 02/05833 filed on December 20, 2002 is a wheel suspension mechanism for both front and rear wheels for a tiltable vehicle, with the option of having a variable track. Said international patent application is, however, silent about any drive system.

US-A-4,003,443 describes a drive system for a rear wheel, said rear wheel being movable vertically relative to a chassis from a first position to a second position. It is an object of the present invention to provide a drive syste of the kind mentioned above and suitable for being used in vehicles with variable track and/or with a front wheel suspension allowing a tilting movement of the vehicle.

According to the invention, what is provided is the following:

Said wheel is movable laterally relative to said chassis from a first position to a second position, and

said rotary driving and driven means are coupled to said wheel so that their angular orientations relative to the chassis change by the same amount when said wheel is moved from said first position to said second position.

Alternatively or additionally, what is provided is the following:

said rotary driving and driven means are coupled to said chassis and said wheel, respectively, so that said rotary driven means is moved laterally relative to said rotary driving means when said wheel is moved from said first position to said second position.

Furthermore, additionally or alternatively, what is provided in case that said wheel is a front wheel is the following:

Said front wheel is movable vertically relative to said chassis from a first position to a second position, and

said rotary driving and driven means are coupled to said chassis and said front wheel, respectively, so that said rotary driven means is moved vertically relative to the chassis when said front wheel is moved from said first position to said second position. In other words, according to the invention, in case of a lateral and/or vertical movement of the (front) wheel, the rotary driving means, the rotary driven means and/or the coupling means are moved so as to coincide with or to compensate for said lateral and/or vertical movement of the (front) wheel.

With view to said lateral and/or vertical movements of said wheel, what is to be noted is that said movements might also include movements in other directions. For example, an orbiting movement of the wheel around a more or less vertical axis is looked at as being a lateral movement in the meaning of the terminology above, because it includes a lateral component of movement, although said lateral component is combined with a forward or backward component. The same applies, mutatis mutandis, to an orbiting movement around a more or less horizontal axis, which movement is looked at as being a vertical movement, although it includes a forward or backward moving component.

According to a preferred embodiment, particularly in case that said rotary driving and driven means are coupled to the wheel so that their angular orientations relative to the chassis change by the same amount when the wheel is moved from a first position to a second position, the rotary driving means is a drum, a pulley or a sprocket.

Particularly in case that said rotary driving and driven means are coupled to the chassis and the wheel, respectively, so that said rotary driven means is moved laterally relative to said rotary driving means when said wheel is moved from said first position to said second position, the rotary driving means is a shaft, a drum, a pulley or a sprocket being mounted thereon, coupled with view to rotation, but axially shiftable.

Likewise, as preferred according to the invention, the rotary driven means is a drum, a pulley or a sprocket in the first case, whereas the rotary driven means is a shaft, a drum, a pulley or a sprocket being mounted to the shaft coupled with view to rotation, but axially shiftable, in the second case.

The coupling means is preferably a belt, particularly a toothed belt or a vee-belt, or a chain. According to a further preferred embodiment of the invention, the coupling means is a belt, particularly a toothed belt, and the driving and/or driven means is/are a drum or a pulley, the axial length thereof being greater than the width of the belt.

Advantageously, the drum or pulley has at least one flange. Namely, thereby, excessive lateral shifting of the belt with view to the drum or pulley can be prevented.

According to a preferred embodiment of the invention, what is provided is a pendulum arm coupling said wheel to said chassis.

Preferably, what is provided is a cardan joint for coupling said wheel to said pendulum arm.

In order to keep said coupling means, e.g. a belt, under more or less constant tension, it is furthermore preferred that said pendulum arm is pivotable around a rotational axis of said rotary driving means.

To this end, the pivoting axis and the rotational axis need only to coincide "more or less", particularly within usual tolerances.

In order to hold the respective wheel movable relative to the chassis both vertically and laterally, what is more preferred is a ball joint or a cardan joint for coupling said pendulum arm to said chassis.

It is true that to a certain extent the driving means, the driven means and the coupling means might adjust each other with view to their positions. However, preferably, what is provided is a guiding means for adjusting the driving means, the driven means and/or the coupling means.

Such a guiding means is preferably mechanically coupled to the wheel.

Additionally or alternatively, the guiding means is driven by a motor. According to a preferred embodiment of the invention, the guiding means includes a guiding fork.

Particularly in case that the wheel is a front wheel, according to the invention, what is provided is a constant velocity joint for coupling said wheel to said driven means.

According to a further preferred embodiment, the wheel is movable laterally (vertically) relative to the chassis by orbiting around an axis and said driving (driven) means is rotatable or orbitable around the same axis. Once more, what is meant by "the same" axis is that the respective orbiting axes "more or less" coincide.

Thereby, disadvantageous momentums are prevented, and the tensioning of the coupling means is kept undisturbed by lateral and vertical wheel movements.

Finally, a preferred embodiment of the invention provides tensioning means for tensioning said coupling means. Said tensioning means might include biasing means which might be adjustable to be blocked against being compressed exceeding a predetermined amount.

In the following, the invention is described referring to preferred embodiments thereof shown in the figures. In detail,

figure 1 shows a diagrammatic perspective view of a first preferred embodiment of the drive system according to the invention,

figure 2 shows a top view of the system according to figure 1 ,

figure 3 shows a diagrammatic perspective view of a guiding means used in the embodiments of figures 1 and 2,

figure 4 shows a diagrammatic perspective view of a second embodiment of the drive system according to the invention,

figure 5 shows a top view of the embodiment according to figure 5, but with some amendments, and figure 6 shows a diagrammatic perspective view of further drive system details.

Figures 1 and 2 show diagrammatic views of the right hand side rear wheel suspension and drive system. The assembly comprises pendulum arms 1 connected to the vehicle chassis (not shown) through cardan joints 13 or through ball joints (not shown). The rear wheels 24 (not shown in figure 1) revolve around axles 3 which are integral with or fixed to the carriers 5. The carriers 5 revolve around the king pins 4, and the "parallel arm" extensions directed inwards towards the middle of the vehicle of the carriers are connected to the parallel rods 6 through the joints 7. The parallel rods 6 are attached to joints 41 through joints 22. Said joints revolve around the tubular supports 44 which are fixed to the transmission housing 34.

The extendable elements 19 are connected to joints 41 through pin joints 21 and support pendulum arms 1 through the pin joints 20.

The drive transmission casing 34 provides the drive output shaft(s) 17. It is understood that the left and right hand side shafts may be integral, or they may be separate shafts driven by a regular differential (as in cars), as indicated by the bevel gears 18 in figure 1. The road wheels 24 are fixed to the drums 10 which extend inwards towards the center of the vehicle and out of the area of the wheels. This portion of the drums is executed as toothed wheels which are engaged by toothed belts 12 or chains (not shown). It should be mentioned here that alternatively having vee-grooves for vee-belts instead of toothed means is within the scope of the invention.

The execution for toothed belts as shown has shoulder flanges 11 guiding the sides of the toothed belts, thus the sideways positions of the belts in some situations.

The toothed belts engage with a toothed drum 16 which are fixed to the output shaft(s) 17.

The line 42 in figure 2 shows how the positions of the wheels are following an arc around joints 13 when the track width is being varied. The wheels are kept parallel by the means of the parallel rods 6. It is seen that the belts or the chains are slightly tightened briefly when the mechanism is moving the wheels outwards. It is also seen that in the wide track position of the mechanism slight slackening of the belts or chains may occur. It has to be borne in mind here that the wide track configuration is mainly to be used briefly for slow- speed and parking manoeuvres when the transmission is not so strained.

However, should excessive slack of the belts or chains occur in the wide track position, it is possible to take up this slack through the tensioning rollers 29 (not shown in figure 1) which are rotationally fixed to the lever arms 35 which are again pivotally fixed to the pendulum arms 1. The actuators 43 are fixed to said pendulum arms and actuate said lever arms. These actuators may be spring loaded in all situations and axially non-reversible in some situations. Thus the slack of the belts or the chains in the wide track position of the mechanism may be taken up by the forces of the actuators. When the actuators at the same time are being temporarily blocked against being compressed - for example by hydraulic means - it is clear that reversing of drive moments such as can happen due to vibrations or the vehicle itself being reversed, will not cause the actuators to decompress. In this way the tensioning is upheld when needed. When moving the mechanism back to the narrow track position, the blockings of the actuators are ended.

The pendulum arms 1 are - in all track width positions - pivoting "vertically" around an axis through joints 13 and 41. It is clear that when this axis is more or less concentric with the revolving axis of the drums 16, the large wheel movements occuring when the vehicle is being tilted in a curve do not affect the tensions of the belts or the chains.

From PCT/IB 02/05833 dealing with the wheel suspension parts less the drive systems referred to here, it is clear that the extension and narrowing of the track takes place in transient driving speed situations, particularly when the vehicle moves forward. Thus the toothed belts, which due to the guiding flanges 11 are following the sideways position of the wheels when the wheel track is being varied, during a few revolutions of the drums 16 will climb sideways on said drum until the belts again engage the drums 16 at a right angle. Recent experiments in a test rig involving such transmission elements have confirmed that this effect takes place in all the load situations which a given toothed belt can transmit. Using chains instead of toothed belts calls for chain wheels which can shift their position sideways according to the needs of the chain line.

When the output shafts are executed as splined shafts 17a such as with the alternative solution shown in figure 3 (splines not shown), the toothed wheel 16a being internally splined and in mesh with said shaft, but free to move axially, will tend to adjust its position axially to that dictated by the belts or chains. It is clear that this solution is also relevant to belt transmissions of the vee-belt type. The axial movements of the wheels 16a to ensure the correct position for engaging chains or belts for all wheel track variations may be induced upon the wheels 16a by alternative means, such as through the guiding forks

25. Said forks are being engaged and actuated by the threaded shaft 27 through the integral threaded portions 26. It is understood that when the threaded shaft 27, which is arrested axially and which has a left hand thread on one side and a right hand thread on the other side, is rotated, the wheels 16a are actuated axially. The connections between the wheels 16a and forks 25 advantageously consist of low-friction axial bearings (not shown) capable of transmitting axial thrust in both directions. The rotation of the threaded shaft may be through an electric stepper motor (not shown) and may be fully synchronized with the wheel track through an electronic guiding system.

As an alternative, mechanical connections between the pendulum arms 1 or extendable elements 19 and the forks 25 can be employed for positioning the forks, with the advantage of achieving autonomous alignment of said forks, thus wheels 16a, to the sideways position of the road wheels 24 on each side of the vehicle.

Figures 3 and 4 show diagrammatic views of the right hand side of the front wheel suspension and drive system.

The pendulum arms 1 are attached to the transmission housing 34 (not shown in figure 4) through the cardan joints 13. Said joints are arranged to have one revolving axis around the tubes 41 which are fixed to the transmission housing 34. The cardan joints each extend outwards into two yokes 47 which house the pin joints defining the second cardan joint axis defining said cardan joints and said connection to the pendulum arms. The pendulum arms 1 have integral cylindrical housings 45 which house ring elements 46 which are free to rotate but are arrested axially. Said ring elements are each rotationally connected to two yokes which are integral with the carriers 5, making in effect cardan joint connections between the pendulum arms and the carriers.

The carriers 5 house the bearings which support the hubs (not shown) which the wheels 24 (not shown in figure 4) are attached to, which are again connected to the outer portion of the constant velocity joints 33.

It is thus understood that the outer parts of the constant velocity joints are in effect fixed to the wheels.

The carriers 5 have steering arm extensions towards the middle of the vehicle, which are connected to steering rods 6 through ball joints 7. The steering rods are attached to the steering arms 8 through the ball joints 22, and the steering arms 8 revolve around the axis defined by the steering shaft 9. Cardan joints may advantageously be employed instead of ball joints 22, giving greater compound angular freedom in addition to preventing steering rod 49 from swivelling due to gravity- and inertia effects, particularly in case that said steering rod is kinked.

Said carriers 5 are further extending to the upper ball joints 48 (not shown in figure 5) linking the carriers to the upper arms 49. Said arms are attached to the chassis (not shown) through the ball joints 50.

The pendulum arms 1 are supported sideways by the extendable elements 19 through the pin joints 20, the element 19 itself being supported by the elements 41 through the pin joints 21.

The driven shafts 30 are connected to the constant velocity joint 33 and are supported by bearings (not shown) in the bearing housings 31, which are integral with the pendulum arms 1. Said pendulum arms are vertically supported by the spring and damper elements 14 by the spherical joints 15. It is understood from PCT/IB 02/05833 that the spring and damper units on each lateral side of the vehicle may be connected to ensure the tiltability of the vehicle, especially in the narrow track configuration. It is understood from the same application that the tiltability may be manipulated, and in particular restricted when the elements 19 are extended to move the wheels into a wide track configuration.

Toothed wheels 32 are fixed to the inner part 31 of the driven shafts 30 and engage the toothed belt 12. It is, however, again understood that the system may equally well comprise chains and chain wheels as well as vee-belts and vee-grooved belt wheels.

The toothed belts 12 are driven by the toothed wheels 23, which are integral with the constant velocity joints 28 which are connected to the output shaft(s) 17 in the final drive housing 34. It is again understood that the shaft(s) 17 may comprise one integral shaft or two separate shafts being driven by a differential mechanism, as indicated by the bevel gears 18 in figure 6.

Figure 4 and especially the top view perspective of figure 5 show how the joints 13 revolve around a horizontal axis (when the vehicle is upright) transverse to the forward direction of the vehicle. Furthermore, figure 5 shows how the belt or chain lines may be at an angle towards the mid plane in the longitudinal direction of the vehicle.

It is understood that this angle impaired upon the constant velocity joints 33 and 28 - which may typically be between 5 and 12 degrees - is within the normal working angles for continuous heavy load use of constant velocity joints for passenger cars.

The angular orientations of the constant velocity joints 28 are defined by the support bearings 51 which are integral with the pendulum arms 1. It is clear that when the "vertical" axes 37 of the cardan joints 13 are more or less concentric with the kinematic center of the constant velocity joints 28, the constant velocity joints will follow the angular position of the pendulum arms 1 around the "vertical" axes of said cardan joints.

Although practical tests have shown that the constant velocity joints shall align their working angles with the direction imposed onto them by belts or chains, the joints need to be supported against falling over into an angle traverse to the plane defined by said belts or chains. The support bearings ensure that this does not happen by keeping the joints "upright". It is also clear that the support bearings enable the use of a belt or chain line which are off-center compared to the kinematic center of the constant velocity joint, should this be needed.

It is understood that the fact that the constant velocity joints are transferring drive moments and moments does not impair that their angular directions are guided as described.

It is the very nature of constant velocity joints to transfer the axis of rotation for the connected elements without varying the angular transfer (speed) such as for example joints of the cardan type do. This has the effect of the joints allowing themselves to be induced a transfer angle without resisting this to any significant degree when transferring moments and when rotating objects with significant mass inertias.

The above-mentioned solutions and characteristics in their combination allow constant velocity joints 28 to be aligned to the direction imposed upon them by the driven belts or chains, again enabling a sound link between said elements and the wheel 24, ensuring reliability and a long life of the drive system.

It is seen from figure 5 that the angle of the belt or chain drive towards the mid plane of the vehicle in the forward direction enables a tight packaging of the suspension and drive elements within the very restricted area which is available in such a vehicle suspension and drive system.

It is furthermore understood that when the pendulum arms 1 are pivoted outwards by extending the links 19, the driven shafts 30, thus the wheels 24, follow this movement and change their angle as seen in the perspective of figure 5, correspondingly.

It follows that the working angles of the constant velocity joints 33 and 28 change correspondingly. It then follows that the mechanism also provides a drive for the road wheels in the extended track position of the mechanism, as well as for all transient tracks in between. Said imposed angle of the constant velocity joints may be approximately 15 to 20 degrees when the pendulum arms are being extended 25 to 30 degrees due to the driveline angle in the narrow track position of the mechanism being in the other angular direction.

It has to be noted that in the wide track configuration the vehicle will be driven slowly with small drive moments, such as when coming to a standstill or in parking manoeuvres. The resulting angular freedom of the constant velocity joints 33 is lessened due to the already imposed angle in the wide track configuration for wheel steering angles which are seen anti-clockwise in the perspective of figure 5.

This reduces the achievable steered angle of the outer wheel in a curve in parking manoeuvres.

Today there are constant velocity joints on the market which have an angular freedom of up to 50 degrees. This then leaves approximately 30 to 35 degrees of steering angle for the outer road wheel in a curve. It is known from the "Ackermann" theory that the inner wheel in a tight bend demands more steering lock (angle) than the outer wheel, typically around 40 degrees for a vehicle with a relatively short wheelbase.

Thus, one can conclude that the remaining steering lock for the outer wheel suffices in this configuration.

It has been shown that the mid plane of the belt or chain drive can be placed to coincide with the axis 37 of constant velocity joints 28 both in the extended and non- extended wheel track positions. This ensures that there shall be no change of the tension of the belts or chains due to vertical (when tilting and when encountering road irregularities) or horizontal wheel movements (when extending the track). This is most beneficial for the transmission - particularly for toothed belts, which do not tolerate much slack before starting to climb over the teeth of the toothed wheels.

If said concentricity, for some reasons, is not practical, one can provide a configuration where the belt midplanes are slightly off center and shifting somewhat during the variation of the track width, and that this is compensated for in the case of using a toothed belt drive, by having the toothed wheels 32 wider than the belts, allowing the belts to shift sideways somewhat. The toothed wheels 28 are ideally executed with guiding flanges 11 which do not allow significant sideways movements of the toothed belt.

In effect we are - when it comes to sideways shifting of the belt on wheels 32 - dealing with the same effects as described for the rear suspension and drive mechanism in figures 1 and 2.

Figure 6 shows how the angular directions of the constant velocity joints may be induced upon the joints by an alternative guiding system. Again 17 indicates the transmission drive output shaft(s), 28 the constant velocity joints, 12 the belts or chains, and 23 the wheels connected to - and driving - the belts or chains. 25 are angular guiding forks, connected to the constant velocity joints through bearings (not shown), 39 is a forked rod pivotally connecting the guiding forks 25 to ensure that they rotate the same angle, but in opposite directions. 40 denotes an actuator which in one end is pivotally connected to the chassis or transmission casing (neither shown), and has the other end actuating an extension of one of the guiding forks 25. It is noted that the constant velocity joint centers 37 are on line with vertical axes (referring to the vehicle being in an upright position) through the pivot points 38 connecting the forks 25 to the chassis or transmission housing.

The relationship between the axial movement of the actuator and the angular movements of the guiding forks, thus the constant velocity joints, can be established for all angles. Thus an electronic guiding system can control the movements in coordination with the wheel track extension movements of the pendulum arms in figures 4 and 5, thus the instantaneous angle of the belts or chains.

An alternative to the guiding system in figures 4, 5 and 6 is to make articulated mechanical connections between the pendulum arms 1 or extendable elements 19 and the forks 25, again ensuring direct and autonomous relations between the track extension - thus drive belt or chain angle - and the imposed angle of the constant velocity joints 28 on each side of the vehicle. The features mentioned and shown in the above description, in the claims and in the drawings may both separately and in combination with one another be essential for the invention.

Claims

1. Drive system for a wheel (24) coupled to a chassis, comprising

a rotary driving means (23),

a rotary driven means (32) and

coupling means (12) surrounding said rotary driving and driven means (23, 32) for transferring a driving force from said rotary driving means (23) to said rotary driven means (32),

characterized in that

said wheel (24) is movable laterally relative to said chassis from a first position to a second position, and

said rotary driving and driven means (23, 32) are coupled to said wheel (24) so that their angular orientations relative to the chassis change by the same amount when said wheel (24) is moved from said first position to said second position.

2. Drive system for a wheel (24) coupled to a chassis, comprising

a rotary driving means (17),

a rotary driven means (10) and

coupling means (12) surrounding said rotary driving and driven means (17, 10) for transferring a driving force from said rotary driving means (17) to said rotary driven means (10),

characterized in that said wheel (24) is movable laterally relative to said chassis from a first position to a second position, and

said rotary driving and driven means (17, 10) are coupled to said chassis and said wheel (24), respectively, so that said rotary driven means (10) is moved laterally relative to said rotary driving means (17) when said wheel (24) is moved from said first position to said second position.

3. The drive system according to claims 1 and 2.

4. Drive system for a front wheel (24) coupled to a chassis, particularly according to one of the preceding claims, comprising

a rotary driving means (17, 23),

a rotary driven means (10, 32) and

coupling means (12) surrounding said rotary driving and driven means (17, 23; 10, 32) for transferring a driving force from said rotary driving means (17, 23) to said rotary driven means (10, 32),

characterized in that

said front wheel (24) is movable vertically relative to said chassis from a first position to a second position, and

said rotary driving and driven means (17, 23; 10, 32) are coupled to said chassis and said front wheel (24), respectively, so that said rotary driven means (10, 32) is moved vertically relative to the chassis when said front wheel (24) is moved from said first position to said second position.

5. The drive system according to any preceding claim, characterized in that the rotary driving means is a drum (23), a pulley or a sprocket.

6. The drive system according to any of claims 1 to 4, characterized in that the rotary driving means is a shaft (17a), a drum, a pulley (16a) or a sprocket being mounted thereon, coupled with view to rotation, but axially shiftable.

7. The drive system according to any preceding claim, characterized in that the rotary driven means is a drum (32), a pulley or a sprocket.

8. The drive system according to any of claims 1 to 6, characterized in that the rotary driven means is a shaft, a drum, a pulley or a sprocket being mounted to the shaft coupled with view to rotation, but axially shiftable.

9. The drive system according to any preceding claim, characterized in that said coupling means is a belt, particularly a toothed belt (12) or a vee-belt or a chain.

10. The drive system according to any preceding claim, characterized in that the coupling means is a belt, particularly a toothed belt (12), and the driving and/or driven means is/are a drum (10, 16, 23, 32) or a pulley, the axial length thereof being greater than the width of the belt (12).

11. The drive system according to claim 10, characterized in that the drum (10, 16, 23,

32) or pulley has at least one flange (11).

12. The drive system according to any preceding claim, characterized by a pendulum arm (1) coupling said wheel (24) to said chassis.

13. The drive system according to claim 12, characterized by a cardan joint (13) or a ball joint for coupling said pendulum arm (1) to said chassis.

14. The drive system according to claim 12 or 13, characterized by a cardan joint (45, 46) for coupling said wheel (24) to said pendulum arm (1).

15. The drive system according to claim 13 or 14, characterized in that said pendulum arm (1) is pivotable around a rotational axis of said rotary driving means (17, 23).

16. The drive system according to any preceding claim, characterized by ^" a guiding means (25, 26, 27) for adjusting the driving means (23), the driven means (32) and/or the coupling means (12).

17. The drive system according to claim 16, characterized in that the guiding means (25, 26, 27) is mechanically coupled to the wheel (24).

18. The drive system according to claim 16 or 17, characterized in that the guiding means (25, 26, 27) is driven by a motor.

19. The drive system according to any of claims 16 to 18, characterized in that the guiding means (25, 26, 27) includes a guiding fork (25).

20. The drive system according to any preceding claim, characterized by a constant velocity joint (33) for coupling said wheel (24) to said driven means (32).

21. The drive system according to any preceding claim, characterized in that said wheel (24) is movable laterally relative to said chassis by orbiting around an axis (37) and said rotary driving means (23) is rotatable or orbitable around the same axis.

22. The drive system according to any preceding claim, characterized in that said wheel (24) is movable vertically relative to said chassis by orbiting around an axis and said rotary driven means (32) is orbitable around the same axis.

23. The drive system according to any preceding claim, characterized by tensioning means (29, 43) for tensioning said coupling means (12).

24. The drive system according to claim 23, characterized in that said tensioning means (29, 43) includes a biasing means (43).

25. The drive system according to claim 24, characterized in that said biasing means (43) is adjustable to be blocked against being compressed exceeding a predetermined amount.