FIELD OF THE INVENTION The invention relates to an axle lift device for a vehicle according to the preamble of claim 1.

BACKGROUND TO THE INVENTION AND PRIOR ART Vehicles which are inherently heavy, e.g. mobile cranes, and/or are intended to carry heavy loads, as in the case of heavy trucks, are often provided with double, often unsteered, rear axles to make it possible to minimise the load on the separate axles. This may for example be necessary in cases where the intended route cannot cope with heavy axle loading or where a single axle is insufficient to bear the weight of the vehicle.

However, a disadvantage of double axles is that they increase fuel consumption and tyre wear and also, in the case of unsteered axles, the turning radius on bends, so it is desirable to be able to raise one of the axles in a double-axle configuration, e.g. in a bogie, in situations where only one of the axles of the configuration is needed to bear the weight of the vehicle, as when a heavy truck travels unladen.

US 3 096 995 A refers to an axle lift for a vehicle, provided with air bellows adapted to raising and lowering one axle out of a double-axle configuration by means of a lever arm. The object is to reduce tyre wear and enhance the stability of the vehicle when travelling empty.

SUMMARY OF THE INVENTION The object of the present invention is propose for an axle of a vehicle an axle lift device which is protected from external influences while at the same time being of compact construction.

FECORD COPY - TRANSLATION

(Rule 12.4) The object indicated above is achieved according to the invention by an axle lift device according to the characterising part of claim 1. An axle lift device comprising at least one lift unit which is disposed between at least one frame-mounted bracket and one axle casing-mounted bracket according to the characterising part of claim 1 and which is positioned obliquely relative to the vehicle's vertical direction, whereby the axle lift device is adapted, with the lift unit substantially protected within the vehicle's frame, to raising and lowering the axle, affords for an axle of a vehicle the advantage of an axle lift device which is protected from external influences while at the same time being of compact construction.

According to an embodiment of the invention, the lift unit of the axle lift device takes the form of at least one air bellows.

According to another embodiment of the invention, the lift unit comprises at least two elements which may be air bellows.

According to a further embodiment of the invention, the axle lift device is associated with a powered axle and the lift unit comprises two elements each situated on their respective side of drive devices for a powered axle.

According to a further embodiment of the invention, the axle casing is fastened to a spring unit which supports the axle casing in a bracket disposed between a frame- mounted bracket, about which the spring unit is arranged for rotation, and an air spring unit which is fastened to the spring unit and which is itself attached to a frame-mounted bracket, whereby the axle is adapted to performing a pivoting movement about the fastening point of the spring unit in the frame-mounted bracket during raising and lowering of the axle.

BRIEF LIST OF THE DRAWINGS

The invention is explained in more detail below with reference to the attached drawings, in which: Fig. 1 depicts schematically two vehicles, each with its respective multi-axle

configuration

Fig. 2 depicts schematically part of a vehicle frame and an axle lift device for an axle according to an embodiment of the invention, with the axle lowered,

Fig. 3 depicts schematically part of a vehicle frame and an axle lift device for an axle according to Fig. 2, with the axle raised, Fig. 4 depicts schematically part of a vehicle frame and an axle lift device for an axle according to a further embodiment, and

Fig. 5 depicts schematically part of a vehicle frame and an axle lift device for an axle according to a further embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

As also indicated by the above brief description of the drawings, the term vehicle in this patent application comprises not only vehicles provided with an engine, as in the case of a tractor unit or a truck, but also vehicles with no engine, as in the case of a trailer.

The invention is exemplified below by a double-axle configuration but is also applicable to axle configurations with more than one axle, e.g. configurations with two, three or four axles, in which at least one axle of the multi-axle configuration is adapted to being raisable and lowerable as described in more detail below.

Fig. 1 depicts schematically two vehicles each with its respective multi-axle

configuration which more specifically constitute a vehicle train 1 comprising an engine- powered vehicle 2 with engine 4 (here a tractor unit) and a vehicle 6 with no engine (here a trailer), each of which vehicles 2, 6 has its respective multi-axle configuration 8, 10. The multi-axle configurations 8, 10 are here exemplified as a triple-axle

configuration 8 with three axles 12, 14, 16 and a double-axle configuration 10 with two axles 18, 20. The two multi-axle configurations depicted may alternatively be of some other kind, e.g. they may instead be two double-axle configurations with two axles each. A single vehicle, e.g. an engine-powered truck or an engine-powered tractor unit or a trailer with no engine, may have more than one multi-axle configuration, e.g. two double-axle configurations. The drawing further depicts a vehicle cab 22, a single-axle configuration 24 which in this case comprises a steerable front axle 26 of the engine- powered vehicle 2, and vehicle frames 28, 30.

In the position depicted in Fig. 1 of the axles 12, 14, 16, 18, 20 of the multi-axle configurations 8, 10, the rear axle 16, 20 of each multi-axle configuration 8, 10 is raised by its respective axle lift device (not depicted in this drawing). Alternatively, only one of the two multi-axle configurations 8, 10 depicted might be provided with an axle lift device, or only one of the two multi-axle configurations 8, 10 depicted might be provided with more than one axle lift device, or both of the multi-axle configurations 8, 10 depicted might be provided with more than one axle lift device so long as at least one axle 12, 14, 16, 18, 20 of each multi-axle configuration 8, 10 is not raised but still bears on the running surface 32 via wheel rims 34 and tyres 36, although the axle which bears on the running surface might also be provided with an axle lift device which is not being used at the time. It is therefore not necessarily the rear axle 16, 20 of a multi-axle configuration 8, 10 which is raisable by an axle lift device as depicted by way of example in the drawing, since any of the axles 12, 14, 16, 18, 20 of a multi-axle configuration 8, 10, e.g. at least the furthest forward or at least the midmost axle might be provided with an axle lift device of the kind described in more detail below.

By way of example, in the embodiment depicted in the drawing, the axles 12, 14, 16 of the multi-axle configuration 8 of the engine-powered vehicle 2 are powered axles 12, 14, 16, whereas the axles 18, 20 of the multi-axle configuration 10 of the engineless vehicle 6 are not powered. Alternatively, the powered and unpowered axles might be arranged in some other way, e.g. only the furthest forward axle 12 of the engine- powered vehicle 2 might be powered. The axle lift device according to the invention is applicable on powered or unpowered axles, as described in more detail below.

Fig. 2 depicts schematically part of a vehicle frame 28, 30 and an axle lift device 38 for an axle 11 according to an embodiment of the invention, with the axle 1 1 lowered. In this example the axle 1 1 is a powered axle (compare the axles 12, 14 and 16 in Fig. 1), the construction of which is more complicated than an unpowered axle, but the axle 11 in the drawing may alternatively be unpowered (compare the axles 18, 20 in Fig. 1). An unpowered axle differs from that depicted in Fig. 2 in that an unpowered axle has no axle driving devices 40, e.g. no toothed gearing, so a powered axle with axle driving devices occupies a larger volume, since the axle casing 42, which in the case of a powered axle may be an axle bridge comprising axle driving devices, can be made smaller for an unpowered axle. The axle 11 may therefore be part of a multi-axle configuration 8, 10 of a vehicle 2, 6 comprising axles 12, 14, 16, 18, 20 which are either powered or unpowered. The drawing depicts a multi-axle configuration 8, 10 with at least two axles 1 1, 21, the axle 21 being in this example an axle which has not been raised but bears on the running surface 32 via wheel rims 34 and tyres 36. The drawing shows only the outer wheels 44; 34, 36 on each axle 1 1, 21 to make it easier to illustrate the axle lift device 38, and for the same reason only the outer part of the frame 28, 30 of the vehicle 2, 6 is depicted.

As may be seen in the drawing, the axle lift device 38 comprises at least one frame- mounted bracket 46 and one axle casing-mounted bracket 48, between which at least one lift unit 50 is disposed, preferably in the form of at least one air bellows. As the axle 1 1 in this example is a powered axle, it is connected to an engine (not depicted) via a power train 52 which may for example comprise drive devices 54 for a powered axle and a gearbox (not depicted). The axle 1 1 is suspended in any desired way relative to the frame 28, 30 of the vehicle 2, 6. An example of axle suspension takes the form of a spring unit 58, e.g. a leaf spring unit, which supports the axle casing 42 in a bracket 60 disposed between a frame-mounted bracket 62 and an air spring unit 64, which air spring unit 64 is itself attached to a frame-mounted bracket 66. As may further be seen in the drawing, the frame-mounted bracket 46 is connected to the lower end 68 of the lift unit 50, and the axle casing-mounted bracket 48 is connected to the upper end 70 of the lift unit 50, which means, in cases where the lift unit 50 takes the form of at least air bellows, that the one or more air bellows is/are in a compressed state when the axle 1 1 is lowered towards the running surface 32, while the air spring unit 64 is pressurised to push the axle 1 1 away from the frame 28, 30 of the vehicle 2, 6. Although the drawing shows it comprising only one element, the lift unit 50 preferably comprises at least two elements, e.g. two air bellows, each disposed on their respective side of the axle casing-mounted bracket 48 so as to result in a more compact construction while at the same time minimising the bending moment at the connection between the lift unit 50 and the axle casing-mounted bracket by achieving laterally uniform loading on the axle casing-mounted bracket 48. In cases where the lift unit 50 takes the form of at least one air bellows, two smaller air bellows may be used for the purpose instead of a single larger air bellows. As may also be seen in the drawing, the axle casing-mounted bracket 48 is mainly subject to tensile loading.

Fig. 3 depicts schematically part of a vehicle frame 28, 30 and an axle lift device 38 for an axle 1 1 according to Fig. 2, with the axle 11 raised. As illustrated in the drawing, raising of the axle 11 takes place as follows: The pressure is released from the air spring unit 64, followed by the lift unit 50 being activated, which in cases where the lift unit 50 takes the form of at least one air bellows means that the one or more air bellows is/are pressurised, with the result that the lift unit 50, being disposed between the frame- mounted bracket 46 and the axle casing-mounted bracket 48 as described above, is pushed apart, thereby raising the axle casing-mounted bracket 48, and hence also the axle casing 42 and the axle 11, towards the frame 28, 30. Since the axle casing 42 is fastened to the spring unit 58 which is arranged for rotation relative to a frame-mounted bracket 62, the axle 1 1 performs a pivoting movement about the fastening point 71 of the spring unit 58 in the frame-mounted bracket 62, as illustrated by the arrow A. Thus the axle casing 42 is fastened to a spring unit 58 which supports the axle casing 42 in a bracket 60 disposed between a frame-mounted bracket 62, about which the spring unit 58 is arranged for rotation, and an air spring unit 64 fastened to the axle lift device 58, which air spring unit 64 is itself attached to a frame-mounted bracket 66, so that the axle 11 is adapted to performing a pivoting movement A about the fastening point 71 of the spring unit 58 in the frame-mounted bracket 62 during raising and lowering of the axle 1 1, 12, 14, 16, 18, 20. At the same time as the axle 11 is raised, the air spring unit 64 is compressed. Lowering of the axle 1 1 is effected by the lift unit 50 being deactivated, which means, in cases where the lift unit 50 takes the form of at least one air bellows, that the pressure is released from the one or more air bellows. As illustrated in the drawing, the connections between the lift unit 50 and the frame-mounted bracket 46 and between the lift unit 50 and the axle casing-mounted bracket 48 are rigid, leading to the lift unit 50 being subject to bending when the axle 1 1 is raised, which means in cases where the lift unit 50 takes the form of at least one air bellows that the latter is bent somewhat compared with when the axle 11 is lowered. At the same time, or alternatively, at least some connections between the lift unit 50 and the frame-mounted bracket 46 and between the lift unit 50 and the axle casing-mounted bracket 48 may be articulated or flexible.

As illustrated in Figures 2 and 3, the axle lift device is protected from external influences such as dirt and impacts by the frame 28, 30 of the vehicle 2, 6 when the axle 11 is lowered or raised, while at the same time the axle lift device is of compact construction. The fact that the lift unit 50 is positioned obliquely relative to the vertical direction of the vehicle 2, 6 also results in a relatively longer travel of the lift unit 50 protected by the frame 28, 30 of the vehicle 2, 6 as compared with a traditional axle lift situated with its travel in the vehicle's vertical direction.

Fig. 4 depicts schematically part of a vehicle frame and an axle lift device for an axle according to a further embodiment. As illustrated in the drawing, the axle lift device is particularly suited to powered axles 11 of vehicles 2, 6 in cases where the lift unit 50 comprises at least two elements 72, 74, e.g. two air bellows. The fact that the lift unit 50 is positioned obliquely relative to the vertical direction of the vehicle 2, 6 as mentioned above, and that the lift unit 50 comprises two elements 72, 74, makes it possible for two elements 72, 74 to be connected between a substantially T-shaped axle casing-mounted bracket 48 with its stem 49 disposed partly between the two elements 72, 74 of the lift unit 50, and a substantially U-shaped or π-shaped frame-mounted bracket 46 disposed above the axle casing 42, whereby the two elements 72, 74 of the lift unit can each be situated on their respective side of axle driving devices 40, e.g. a toothed gear, and drive devices 54, e.g. a bogie propeller shaft for a bogie with two powered axles.

Fig. 5 depicts schematically part of a vehicle frame and an axle lift device for an axle according to a further embodiment. As illustrated in the drawing, the axle lift device is particularly suitable for powered axles 1 1 of vehicles 2, 6 in cases where the lift unit 50 comprises at least two elements 72, 74, e.g. two air bellows. The fact that the lift unit 50 is positioned obliquely relative to the vertical direction of the vehicle 2, 6 as mentioned above, and that the lift unit 50 comprises two elements 72, 74, makes it possible for the two elements 72, 74 to be connected between a substantially U-shaped or π-shaped frame-mounted bracket 46 disposed above the axle casing 42 and a substantially U-shaped axle casing-mounted bracket 48 with its limbs 45, 47 disposed on the outside of the two elements 72, 74 of the lift unit 50, whereby the two elements 72, 74 of the lift unit can each be situated on their respective side of axle driving devices 40, e.g. a toothed gear, and drive devices 54, e.g. a bogie propeller shaft for a bogie with two powered axles.

The lift unit 50, e.g. in the form of one or more air bellows, is preferably disposed at a large angle relative to the vertical plane, i.e. with its travel alignment at the frame fastening at an angle of preferably 15-55°, more preferably 25-45°, e.g. about 35° relative to the horizontal plane, in order thereby to achieve sufficient travel and maximum possible leverage without protruding too far outside the frame as seen in its vertical direction. As previously mentioned, a sloping lift unit means that the axle casing-mounted bracket 48, e.g. the stem 49 of the T-shaped bracket or the limbs 45, 47 of the U-shaped bracket, is subject more to tensile loading than to bending moments, so the axle casing-mounted bracket can be made relatively flat.

The arms of the frame-mounted bracket should not be made too long, so as to minimise the loading and at the same time keep the lifting device substantially protected by the vehicle's frame during both raising and lowering of the axle 1 1.

The frame-mounted bracket 46 is preferably a torsionally rigid member disposed across the frame 28, 30, fastened high up in the frame 28, 30 and comprising arms 76, 78 which extend downwards and connect to the respective elements 72, 74 of the lift unit 50 at the lower end 68 of the lift unit 50.

The invention relates to an axle lift device for at least one axle 1 1, 12, 14, 16, 18, 20 of a multi-axle configuration 8, 10 of a vehicle 2, 6 with frame 28, 30, such that the axle 1 1, 12, 14, 16, 18, 20 is fastened to the vehicle 2, 6 via at least one axle casing 42, the axle lift device 38 comprises at least one frame-mounted bracket 46 connected to a lift unit 50 at the latter' s lower end 68, and at least one axle casing-mounted bracket 48 connected to the lift unit 50 at the latter' s upper end 70, and the lift unit 50 is positioned obliquely relative to the vertical direction V of the vehicle 2, 6, so that the axle lift device 38 is adapted to using the lift unit 50, which is substantially protected within the frame 28, 30 of the vehicle 2, 6, to raise and lower the axle 1 1, 12, 14, 16, 18, 20, resulting in an axle lift device which is protected from external influences while at the same time being of compact construction. The invention is in no way limited to the embodiments described but may be varied freely within the scopes of the claims. The axle lift device may therefore be situated at a front edge, at a rear edge or on top of an axle casing, but it is generally most practical for it to be situated at a front edge of an axle casing so that a powered axle can be raised without the power train having to be of complicated construction, e.g. such that a bogie propeller shaft need only be angled about one point instead of the whole of it being moved up and down laterally. It is also preferable for the powered axles raised first to be as far as possible away from the engine in order thereby also to simplify the construction of the power transmission. It is also appropriate to disconnect a raised powered axle in order to disconnect the drive and thereby avoid various power transmission losses and hence also reduce the fuel consumption which may be involved with a known kind of gear.