GB2054493A - Unsprung commercial vehicle - Google Patents

Abstract

To minimise the effects of pitching and/or vertical oscillating movements of an unsprung vehicle such as an agricultural tractor, when in motion, engine 3 is mounted on the chassis or structure by means of spring elements 9, 10 effective in horizontal and vertical planes; the elements effective in the vertical plane are substantially softer then those effective in the horizontal plane and form with the motor 3 a vibratory system, which acts as a vibration absorber, having a natural frequency approximately equal to that of the vehicle plus a working implement or implements 7 (such as a plough) mounted on attachment 6. <IMAGE>

Description

SPECIFICATION Unsprung commercial vehicle This invention concerns an unsprung commercial vehicle having at least one working implement attachment point, in particular a tractor for agricultural use, and including a driving motor which is flexibly supported relative to the chassis or structure of the vehicle by spring elements effective in the horizontal and vertical planes.

Commercial vehicles used in agriculture and the building trade are usualiy equipped at front and/or rear with attachment devices for various implements, such as shovels, diggers and ploughs. No springing of the vehicle body relative to the axles is provided, since as a consequence of the considerable weight of the implements and also of forces occurring as a result of working resistance, very large strokes would arise, which would make it difficult or even impossible to carry out many jobs.

Impacts and jolting due to uneven road surfaces are softened only by pneumatic tyres.

The known attachment devices combine the vehicle and the implement into an intrinsically substantially rigid unit the mass of which, together with the tyre springing, forms a vibratory system the natural frequency of which, depending on the sizes of the vehicle and the implement, is approximately 1 to 2 Hz.

If such a vehicle moves at an acceptable speed, increases occur in the ampiitudes of the pitching and/or vertical motions to which the vehicle is always subjected even on relatively smooth roads.

This can lead to a severe periodical loading and unloading of the front axle. The dynamic loading of the axle can, as a result, be higher than the corresponding static value by a factor which is of the order of magnitued of 10. If it is desired that there should be no risk to the useful life of the axle, then this must be considerably overdimensioned. On the other hand the unloading of the axle due to the absence of springing between the vehicle structure and the axles leads to reduction of the frictional resistance between tyre and road surface which can reach such proportions that the tyre loses all contact with the road surface with the consequence that roadworthiness and steering safety are severely impaired.

However, it is not only the front axle that is excessively loaded by the strong vibrations of the vehicle; the attachment device between the vehicle and the working implement is also exposed to strong forces, which cause severe wear.

The object of the invention is so to construct an unsprung vehicle of the above-described type that the dynamic peak forces acting on the vehicle and the attachment device are significantly reduced.

To solve this problem it is proposed, in accordance with the invention, that the spring elements effective in the vertical plane are significantly softer than the spring elements effective in the horizontal plane and with the mass of the driving motor form a vibratory system the natural frequency of which is at least approximately tuned to the natural frequency of the vibratory system consisting of the vehicle with attached implement With this arrangement, it is possible to use the driving motor of the vehicle as the additional mass of a vibration absorber. Vibration absorbers in themselves are already known. The flexibly-coupled additional mass is known to reduce the amplitude of resonance of a vibratory system; instead the additional mass itself vibrates.However, its use in commercial vehicles for stabilising the whole vehicle has not hitherto been proposed.

An adjustable shock absorber may advantageously be provided in parallel with the spring elements effective in the vertical direction.

The invention will be described further, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a diagrammatic side elevation illustrating a practical embodiment of the vehicle of the invention, in the form of an agricultural tractor; and Figure 2 is a fragmentary detail of part of Figure 1, shown diagrammatically and to an enlarged scale.

The illustrated unsprung vehicle according to the invention is in the form of a tractor comprising front wheels 1, rear wheels 2, a driving motor 3, a gear unit 4 which is connected by a drive shaft 5 to the driving motor 3, and an agricultural implement attachment device 6. A plough, supported by the attachment device 6, is indicated only schematically by an arrow 7. The driving motor 3 is supported relative to chassis 8 of the tractor by means of several spring elements 9, 10. Further spring elements supporting the driving motor 3 against the chassis 8 in the horizontal plane, and which permit horizontal vibrations with amplitudes of the order of 4mm, are not shown for reasons of simplicity.

With the mass of the driving motor 3 known, and assuming that the driving motor is to act as the additional mass of a vibration absorber which vibrates at its natural frequency instead of the tractor, it is possible to determine without difficulty the load deflection curve of the spring elements 9, 10.

In comparison with the spring elements supporting the driving motor 3 in the horizontal plane against the chassis 8 the load deflection curve of the spring elements 9, 10 is very flat and the spring elements 9, 10 are thus relatively soft. The vertical vibrations performed under these circumstances by the driving motor3 have large amplitudes which, accordingly, must be taken into account in the construction of the drive shaft 5.

As mentioned above the spring elements 9, 10 are so chosen or constructed so that the driving motor 3 acts as the additional mass of a vibration absorber which makes inversely phased vibrations with its natural frequency instead of the tractor.

In the case of the majority of modern tractors this natural frequency, which is basically dependent on the mass of the vehicle and of the attached implement and on the spring behaviour of the tyres, is in the range from 1 to 2 Hz. Depending on the mass of the implement used (light or heavy plough) and on the nature of the tyres used (crop-rowortraction tyres), the natural frequency of the vehicle/imple ment combination can thus vary within the given range. In order to adapt the vibration absorber to reduce its possible frequency, adjustable dampers 11 may be provided in parallel with the spring elements 9, i0 as shown in Figure 2.

Claims (3)

1. An unsprung commercial vehicle having at least one working implement attachment point for implements, in particular a tractor for agricultural use, and including a driving motor which is flexibly supported relative to the chassis or structure of the vehicle by spring elements effective in horizontal and vertical planes characterised in that the spring elements effective in the vertical plane are considerably softer than the spring elements effective in the horizontal plane and with the mass ofthe driving motor form a vibratory system the natural frequency of which is at least approximately tuned to the natural frequency of the vibratory system consisting of the vehicle with attached implement.

2. A commercial vehicle as claimed in claim 1 characterised in that an adjustable shock absorber is provided in parallel with the spring elements effective in the vertical plane.

3. An unsprung commercial vehicle substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.