Field of the invention

A first aspect of the present invention relates to a shaft device comprising a rotatable shaft which has a hole running through it in its longitudinal direction.

The invention relates also to a bearing arrangement provided with such a shaft device, a gearbox provided with such a bearing arrangement, and a motor vehicle provided with such a gearbox.

A second aspect of the invention relates to a method for supporting a shaft.

Background to the invention

In many contexts, a shaft which needs support is made of different material from the supporting structure, e.g. a gearbox housing in which the shaft is supported. The shaft is usually made of steel and the surrounding supporting structure may be made of some other material, e.g. aluminium. The fact that the shaft and the supporting structure are made of different materials with different thermal expansion coefficients causes a problem, particularly where the materials are steel and aluminium. This applies more particularly to axial bearing arrangements. In the case for example of a gearbox in a large vehicle, the difference in thermal expansion between room temperature and operating temperature will be up to about 0.5 mm between the ends of the shaft. This entails the problem of maintaining the play or pre-stress which has been set at room temperature. The problem of bearing play changing as a result of differing thermal expansions of the shaft and the supporting structure is addressed inter alia in WO 2008/005788, US 5 325 599 and US 5 386 630, but those specifications are mainly concerned with measures relating to an individual bearing and how it is set. None of those specifications indicates a comprehensive solution. The object of the present invention is to make supporting a shaft possible in such a way that the problems arising from differing thermal expansion coefficients of shaft and supporting structure respectively are eliminated or at least reduced. Summary of the invention

The first aspect of the invention is that the object stated is achieved by a shaft device of the kind indicated in the introduction having the special features that the device further comprises a rod which runs in the longitudinal direction of the shaft, through the hole from a first end of the shaft to a second end of the shaft, and is provided at said first end with a radially directed support element which is situated axially beyond said first end, extends radially beyond the outside diameter of the shaft at said first end and has an axial inner surface with a radially outer portion and a radially inner portion, the radially outer portion being displaced axially in towards the shaft relative to the radially inner portion.

This makes it easy for the support element to be axially free from axial contact with the shaft end and the rotating parts of the bearing, while at the same time the outer ring of the bearing may be given support at an axial position which coincides with the end of the shaft or at an axial position a short distance in on the shaft.

A shaft device thus configured makes it possible for the shaft to be supported without the precision of the bearing being affected by temperature changes. The rod may be fixed axially relative to the shaft at the second end of the shaft, thereby substantially maintaining the axial position of the support element relative to the shaft irrespective of temperature changes. This does of course presuppose that the rod is made of material with approximately the same thermal expansion coefficient as the material of the shaft. With advantage, the rod and the shaft will be made of the same material, e.g. steel. The rod and shaft being made of the same material will maximise the precision with regard to maintaining the relative axial position of the support element and the first shaft end.

Where the shaft is to be supported in a bearing arrangement which comprises inter alia an axial force absorbing rolling bearing at or near to the first end of the shaft, the support element may serve as axial support for the stationary ring of the bearing. As the relative axial position of the support element and the shaft end is not affected by temperature changes, the bearing precision, i.e. the play or pre-stress which has been set, will not change. If instead the outer ring is fitted in, and receives its axial support from, the surrounding supporting structure, its axial position relative to the shaft end will change with changing temperature and will therefore require compensatory measures and adjustments.

The invented shaft device thus eliminates problems associated with such compensatory measures, since the support element provides an axial support surface which is not affected by temperature changes. The invented device therefore makes it easy to support the shaft in a simple way with optimum setting within a large temperature range. It also eliminates the need to adopt other measures for setting a fixed bearing play.

It is advantageous, albeit not necessary, that the hole through the shaft be circular and advantageous that it be coaxial with the shaft. The rod is also with advantage circular and should be coaxial with the hole.

According to a preferred embodiment of the invented shaft device, the support element extends radially beyond the outside diameter of the shaft at a number of points distributed in the circumferential direction. A support element thus configured makes axial support possible at a number of points, distributed in the circumferential direction, on the outer ring of the rolling bearing, so that the force absorption is distributed.

According to a further preferred embodiment, these points are distributed at equal mutual spacing in the circumferential direction. The support for the absorption of axial forces will thus be symmetrically evenly distributed so that the force on the outer ring will be evenly distributed and the risk of obliquity of the outer ring is eliminated.

According to a further preferred embodiment, the support element extends beyond the outside diameter round the whole circumference of the shaft. The force absorption will thus be as evenly distributed as possible, resulting in optimum operating safety. To this end, the support element may for example have a circular outer contour and take the form of a disc.

According to a further preferred embodiment, the support element is fixed to the rod by fastening means so arranged as to make it possible to set the axial position of the support element on the rod.

The axial position of the support element relative to the shaft may therefore be adapted so as to achieve optimum precision for the axial support of the outer ring at the operating temperatures which are to be expected. The arrangement also caters for a certain amount of post-adjustment. According to a further preferred embodiment, the fastening means comprises a threaded portion of the rod and a nut.

Said axial positioning of the support element can thus be effected in a simple and reliable way. According to a further preferred embodiment, the rod is provided with radial play in the hole.

Risk of contact between the rod and the shaft, which would lead to friction losses and risk of operational malfunctions, is thus prevented.

According to a further preferred embodiment, the rod is provided at the second end of the shaft with a second radially directed support element situated axially beyond said second end and extending radially beyond the outside diameter of the shaft at said second end.

This embodiment also makes it possible for an axial force absorbing rolling bearing at the second end of the shaft to be given the same kind of axial support. As the support element is pressed against the respective outer ring of a rolling bearing at each shaft end, the axial distance between the outer rings will change in unison with changes in the length of the shaft which arise from temperature changes, i.e. the axial distance is relatively fixed. The result is an easy-to-handle shaft package which can, with assured bearing precision, be fitted in a supporting structure. With advantage, the supporting structure will have axial support surfaces which limit the possibility of outward axial movement of the respective support element.

According to a further preferred embodiment, the second support element is configured as indicated above for the first support element, in particular according to any of the preferred embodiments described above. The second support element will thus also afford similar advantages. The support elements are with advantage configured identically but may alternatively be configured according to mutually different embodiments.

According to a further preferred embodiment, the rod is provided with axial fixing means at the second end of the shaft to fix the axial position of the corresponding end of the rod relative to a supporting structure.

This embodiment constitutes an alternative to the embodiment last described above and makes it easy to fit the shaft device at the first shaft end, since the first support ring will thus need no special stop to prevent outward axial movement.

A bearing arrangement according to the invention comprises both the invented shaft device, in particular in accordance with any of the latter's preferred embodiments, and at least a first axial force absorbing rolling bearing with a ring which rotates with the shaft, a stationary ring and, disposed between them, rolling elements, said first support element being adapted to pressing against the stationary ring, the axial mobility of which is therefore only limited on one side by the rolling elements of the bearing and on the other side by said first support element.

In this patent application, axial force absorbing rolling bearing means not only a bearing which absorbs only axial forces but also a bearing which absorbs both axial and radial forces, e.g. a taper rolling bearing.

According to a preferred embodiment of the invented bearing arrangement, the latter further comprises a second axial force absorbing rolling bearing for axial force acting in the opposite direction to the axial force which the first axial bearing is adapted to absorbing, which second rolling bearing has a ring which rotates with the shaft, a stationary ring and, situated between them, rolling elements, said second support element being adapted to pressing against the stationary ring, the axial mobility of which is therefore only limited on one side by the rolling elements of the bearing and on the other side by said second support element.

A gearbox according to the invention comprises a bearing arrangement in accordance with the invention. A vehicle according to the invention comprises a gearbox in accordance with the invention.

The invented bearing arrangement, the invented gearbox and the invented vehicle afford advantages of the same kind as the advantages described above of the invented shaft device and its preferred embodiments. The second aspect of the invention is a method for supporting a shaft, which comprises the special measures that

- a hollow shaft is provided,

- a rod protrudes in through the hole in the shaft, - the shaft is supported by bearings which each comprise a first axial force absorbing rolling bearing, with a ring which is rotatable with the shaft, a stationary ring and, between them, rolling elements,

- a first support element comprising an axial inner surface with a radially outer portion and a radially inner portion, the radially outer portion being axially displaced in towards the shaft relative to the radially inner portion, is fitted on the rod at a first end of the shaft,

- the radially outer portion of said first support element is caused to press the stationary ring against the rolling elements of the rolling bearing so that the axial mobility of the stationary ring is only limited on one side by the rolling elements of the bearing and on the other side by said first support element,

- the bearing of the shaft is fitted in a supporting structure in such a way that the supporting structure limits the axial mobility of said first support element.

According to preferred embodiments of it, the invented method is applied when using a shaft device in accordance with the invention, in particular in accordance with any of the preferred embodiments of the shaft device.

The invented method also affords advantages of the same kind as indicated above for the invented shaft device and its preferred embodiments.

The invention is further explained by the detailed description of embodiment examples of it set out below with reference to the accompanying drawings.

Brief description of the drawings

Fig. 1 is a longitudinal section through part of a gearbox according to a first embodiment of the invention.

Fig. 2 is a corresponding section according to a second embodiment example.

Description of embodiment examples

Figure 1 is a longitudinal section through part of a gearbox according to the invention. The gearbox has a housing 1 constituting a supporting structure for the shafts of the gearbox. The gearbox in the example has a mainshaft 2 and a countershaft 4. The invention is described with reference to the countershaft 4, which is provided with a shaft device and a bearing arrangement in accordance with the invention. Other parts of the gearbox are in principle of conventional kinds and are not described in more detail here. The countershaft 4, hereinafter called the shaft 4, is provided with a number of gearwheels 5 in cooperation with the mainshaft 2.

The shaft 4 is supported in a first taper rolling bearing 7 at one end of the shaft 4, and a second taper rolling bearing 8 at the opposite end of the shaft 4. A concentric circular hole 9 is accommodated in the shaft 4 and runs through the whole length of the shaft 4. A rod 10 extends through the hole 9 with a small amount of play therein so that contact with the shaft is prevented. The rod is fastened by its left end in the diagram to a portion 1 1 of the end wall of the housing. The fastening is effected by the end 13 of the rod 10 being threaded and screwed into a threaded hole in the portion 1 1 of the end wall. A support element 14 in the form of a circular disc 14 is fastened to the right end of the rod 10. The disc 14 has a central hole by means of which it is drawn onto the rod 10 and screwed firmly by means of a nut 17 and a threaded end portion of the rod 10.

The inner side of the radially outer portion 142 of the disc 14 is pressed towards the stationary outer ring 71 of the bearing 7 by suitable screwing of the left end of the rod 10 into the hole 12 in the end wall portion 1 1 and/or tightening of the nut 17. The disc 14 thus provides the bearing 7 with support to absorb axial forces which act towards the right.

The support of the left end of the shaft 4 in this example is of conventional configuration whereby the outer ring of the second bearing 8 abuts against an axial support surface of the end wall portion 1 1 in order to absorb axial forces which act towards the left.

The housing 1 is made of aluminium and the shaft 4 and the rod 10 running through it are made of steel. If the gearbox warms to a higher temperature than that which applies in the state depicted in Fig. 1 , both the housing 1 and the shaft 4 and rod 10 will expand both radially and axially. As the housing 1 is made of aluminium, it will expand to a greater degree than the shaft 4 and rod 10. In the radial direction the values concerned are so small that they do not cause any problems, whereas the difference in expansion in the axial direction may amount to several tenths of a millimetre.

When the housing 1 expands axially relative to the shaft, the result is that the portion 21 of the housing in which the right bearing 7 is fitted moves to the right relative to the end of the shaft 4 and relative to the disc 14 fastened to the rod 10. As said portion 21 of the housing has no axial stop surface for the outer ring 71 , the axial support of the bearing 7 is not affected. It takes the form of the disc 14 and its position is unchanged relative to the shaft. Thus the play or pre-stress settings of the two bearings 7, 8 are not affected by the temperature difference. As illustrated, the disc 14 has a radially outer portion with a surface 142 facing towards the outer ring 71 of the bearing and displaced inwards relative to the remainder of the disc. The purpose of this is to create a clearance space between the disc 14 and the shaft and the rolling elements respectively. An alternative possibility is to provide an intermediate ring between the outer ring 71 and the disc 14. A more accentuated displacement of the surface 142 or an intermediate ring of significant axial extent will make it possible for the axial bearing 7 to be situated slightly in on the shaft.

The second embodiment example illustrated in Fig. 2 differs from that in Fig. 1 as regards the fastening of the rod and as regards a detail of the disc at the right end of the shaft, but is otherwise configured in the same way.

In this example, the rod 10 is not fixed to the housing end wall but is also provided at its left end with a device of a similar kind to that at its right end. Thus the rod is not anchored in the housing at the left end. Instead, a stop element 14b in the form of a disc 14b is fastened to the rod 10 by a threaded nut 17b. Thus the shaft 4, the rod 10, the two discs 14, 14b and the bearings 7, 8 will constitute a composite package with fixed spacing, irrespective of temperature, between the bearings 7, 8 so that the latter maintain unchanged settings.

At the left end of the shaft, the disc 14b is clamped between the outer ring 81 of the bearing and an axial support surface 1 10b of an end wall portion 1 1 b of the housing. At the right end of the shaft a stop ring 18 is fastened in a housing portion 21 b to limit axial movement of the disc 14 outwards from the shaft.

When the housing 1 expands axially relative to the shaft 4, the distance between the axial support surface 1 10b in the end wall portion 1 1 b and the stop ring 18 will increase several tenths of a millimetre more than the distance between the discs 14, 14b. Corresponding axial play will thus occur but will not affect the pre-settings of the bearings, which are maintained by the holding-together forces between the discs 14, 14b. The shaft is thus provided with a certain axial mobility, but this is acceptable from other points of view than the bearing arrangement, which of course is itself not affected. The axial force from the package is absorbed by the axial support surface 1 10b in the end wall portion 1 1 b or by the support ring 18 in the housing portion 21 b, depending on the direction in which the axial force acts.