The invention relates to an axle construction for vehicle, especially for off-the-road vehicle or tractor, comprising a rigid, centrally pivoted oscillating axle suspended in relation to the frame of the vehicle at its central part.

In off-the-road vehicles and tractors it is common to use a rigid- oscillating axle, centrally directly pivoted to the frame of the vehicle without any suspension. One of the disadvantages of this axle construction is poor driving comfort which makes the said axle construction unsuitable for high speeds. Previously known is also a rigid oscillating axle directly mounted with bearings to the frame and comprising suspension in its shoulder axles. This axle construction is however not suited for driving wheels and the construction becomes complicated and expensive.

Concerning the patent literature related to this invention, reference is made to US patents 1.120.036 and 3.572.748. In the former US patent an axle construction is disclosed in which the front axle of the vehicle is fixed in a yielding way to the frame of the vehicle. This axle construction comprises interposed members parallel to the axle of the vehicle and associated at both ends with leaf springs by means of which the oscillating centrally pivoted axle is fixed in a yielding way to other structures of the vehicle.

In the US patent no. 3.572.748 a suspended axle system construction of the steerable wheels of a vehicle is disclosed, consisting of a telescopic construction having a rectangular cross-section. This telescopic construction comprises a lower part to which the axle of the vehicle is fixed in a centrally pivoting way, an upper part fixed to the frame of the vehicle, and a helical spring assembly disposed between the mentioned parts. As a disadvantage of both of the afore-mentioned constructions may be regarded the fact that all the loads of the oscillating axle, also horizontal loads, are conveyed to the frame of the vehicle by means of the spring assembly,

and thus the spring assembly or assemblies must be so constructed as to permit loads with a horizontal constituent also, which leads to a heavy construction of the spring assembly and prevents the planning of the spring assembly entirely with regard to optimal suspension characteristics.

It is an object of the present invention to create a simple and cheap axle construction so that same axles can be used as in previously known solutions where direct fixing through bearings to the frame has been used. An object is to create 'tractors or off-the- road vehicles with better driving comfort than in unsuspended ones. It is an object to improve by means of suspension and shock- absorbing the driving characteristics of tractors and other off-the- road vehicles especially at higher driving speeds. An additional object of the invention is to create such an axle construction of the type in question in which the above-discussed disadvantages of the solutions disclosed in the said US patents are avoided.

In order to achieve the objects mentioned afore and becoming apparent later, this invention is mainly characterized in that the axle construction comprises an auxiliary frame to which are fixed axle bearings permitting the rocking of the said axle, that between the said auxiliary frame and the frame of the vehicle is disposed a spring assembly permitting the vertical yield of the auxiliary frame and the axle fixed thereto, and that the said auxiliary frame is fixed at its one end to the frame of the vehicle by means of fulcrum pins transverse to the moving direction of the vehicle, or by a corresponding joint assembly.

In the following the invention is described in detail by referring to an embodiment of the invention shown in the attached figures, to the details of which the invention is however not restricted.

Fig. 1 shows a side elevation of an axle construction according to the invention. Fig. 2 shows a front elevation of the same as Fig. 1.

According to figures 1 and 2 the axle construction has a rigid

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oscillating axle 10 which in this case is steerable and has driving wheels 11. The axle 10 is in the previously known way centrally pivoted through the axle bearings 12a and 12b, longitudinally dis ^¬ posed in relation to the vehicle and fixed to the auxiliary frame 13. The auxiliary frame 13 again is pivoted at its one end by means of transverse fulcrum pins 14 to the frame 15 of the vehicle. Between the free end of the auxiliary frame 13 and the frame a spring 16 is disposed which in the embodiment shown by the figures is pneumatic. Between the auxiliary frame 13 and the frame 15, as such previously known shock-absorbers.17 may further be disposed.

The movement of the auxiliary frame 13 is restrained by means of restraining members 18 in the auxiliary frame and rubber cushions 19a and 19b in the frame 15.

The pressure of the pneumatic spring 16 and thus the space to move between the auxiliary frame 13 and the frame 15 of the vehicle is regulated by means of the height adjustment valve 20 placed in the frame 15. By means of the lever system 21 the said valve 20 communi- cates with the auxiliary frame 13. The automatic height adjustment of the frame 15 and also manual height adjustment are possible. Compressed air is led from a compressor through hoses 22 to the pneumatic spring 16.

The oscillating axle shown in the figures is also a driving axle and in Fig. 1 is shown a power transmission shaft 23. In Fig. 1 can also be seen the vertical members 24 by means of which the axle bearings 12a and 12b have been connected to the auxiliary frame 13.

According to a preferred embodiment of the invention the auxiliary frame 13 is disposed under the power transmission shaft 23 and in this way the auxiliary frame itself forms or thereto can be advantageously attached a bottom armour which is an essential element in some off-the-road vehicles.

In the figures a compressed-air spring is shown as the spring assembly 16, but also other types of springs can be used within the

invention. Thus leaf springs, helical springs, torsion bar springs, rubber springs or other corresponding springs and combinations of different spring types can be used as the spring assembly 16.

According to Fig. 1, power is transmitted to the driving axle 10 by means of a cardan shaft 23 through the axle bearing 12b. If the joint of the cardan shaft is disposed in alignment with the fulcrum pins 14 of the auxiliary frame 13, no axial space to move is required in the cardan shaft.

In Figs 1 and 2 only one axle 10 of the two axles of the vehicle has been shown, in this embodiment being provided with both steerable and driving wheels. As the other axle, for example a bogie axle can be used.

In the following the claims are presented defining the concept of invention within which the different details of the invention may vary.

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