The present invention relates to a front axle arrangement for a heavy vehicle and its cooperation with the vehicle chassis and also with the vehicle engine.
Heavy vehicles, which here means, for example, trucks, buses and similar freight and utility vehicles, incorporate according to conventional technology a longitudinal chassis element in the form of two frame side members which are connected to one another by means of a number of cross-members. The frame side members extend parallel with one another along substantially the whole length of the vehicle and support vehicle components such as the engine, the driver""s cab and a load surface which takes the form of, for example, a load platform or a superstructure. In addition, the vehicle""s front and rear axles are suspended in the frame side members.
In heavy vehicles such as trucks, the frame side members and the cross-members act as the main loadbearing parts of the vehicle in order to provide strength and rigidity. In heavy vehicles such as buses, the bodywork also contributes to vehicle rigidity and strength. Conventionally designed support devices are nevertheless built so as to be relatively unresistant to bending and torsion in order to be able to cope with heavy loads and varying road conditions, comprising a complete range from forest roads or no roads to smooth motorways. Relatively low resistance to bending and torsion does entail, however, certain problems with regard to riding comfort and vehicle running characteristics. The chassis element having relatively low resistance to torsion and the wheel axles being made of steel result in not entirely satisfactory riding comfort, particularly on long journeys and on good roads. Nor is it possible for riding comfort and vehicle running characteristics to be improved to any appreciable extent by more sophisticated suspension systems. As heavy vehicles are to an ever increasing extent travelling on smooth roads, riding comfort and vehicle running characteristics are an increasingly important factor. In addition to riding comfort being naturally advantageous for the vehicle""s driver and passengers, it is also important to reduce the amount of damage to freight, particularly when carrying goods which are easily damaged. Conventional frame side members and steel wheel axles result in any road surface unevenness being propagated in the support device and having adverse effects on substantially the whole vehicle.
The conventional superstructure of a heavy vehicle also has the disadvantage of its manufacture being relatively expensive because such a design involves many different components which cannot be standardised for different vehicle variants. For example, the vehicle""s front and rear axle arrangements may involve many different components depending on whether the respective wheels are to be steerable or not, powered or not, how many rear axles the vehicle is to have, the type of suspension, etc. Such a conventionally constructed heavy vehicle also requires a relatively large amount of assembly work.
DE-A-4322716 describes a vehicle chassis for heavy-duty vehicles. The chassis incorporates a rear axle arrangement, a box-like central chassis element and a front axle arrangement. The rear and front axle arrangements are of conventional design in that they incorporate two longitudinal frame members which are connected to one another by means of cross-members. The wheel suspension seems to incorporate a steel wheel axle and the forces acting upon the wheels will be led on into the central box-like chassis element.
The object of the present invention is to eliminate the abovementioned problem. What is particularly intended is a front axle arrangement which contributes to a more comfortable ride and better running characteristics. It is also desirable that it be possible for the front axle arrangement to be made of components which are largely standardised and are easy to assemble.
This object is achieved with the front axle arrangement indicated in the introduction which has a frame with a box-like structure in cross section across the vehicle axis. The frame is separably received at the vehicle chassis and it also receives and separably supports the engine unit.
Such a front axle unit incorporating a box-like frame structure which supports vital components of the vehicle in the region of the front axle makes it possible to create a unit which forms a front axle module which can be used for many different vehicle variants. The box-like structure also means that the front axle unit according to the invention is so constructed as to be, in all essentials, self-supporting and designed to absorb at least substantially all the vertical forces which act upon the front wheels.
According to one embodiment of the invention, the engine unit is arranged in the front axle unit in such a way as to be at least partially extractable from it. This makes it possible for the engine unit to take the form of a uniform module which can be used for many different vehicle variants. The engine unit being extractable from the front axle module renders the engine readily accessible for maintenance and servicing without having, as with previous technology, to tilt the vehicle""s cab.
In accordance with a further embodiment of the invention, the frame structure as viewed in the direction of the longitudinal axis has a central aperture. This means that the engine unit can with advantage extend in through the central aperture. In this way the engine, which is of considerable weight, will be situated over an imaginary rear wheel shaft, which is a favourable situation from the load distribution point of view. The frame structure as viewed in the direction of the longitudinal axis forms with advantage a substantially closed ring round the central aperture and has a substantially quadrilateral shape. Such a ringlike configuration enables the frame structure to absorb substantially all the vertical forces which act upon the front wheels. Such a frame structure is of great rigidity and strength In addition, the chassis element, as viewed in the direction of the longitudinal axis, may also have a substantially quadrilateral shape, while the frame structure has an outer contour which in all essentials corresponds to an inner contour of the chassis element. Such a quadrilateral box-like chassis element has a relatively high resistance to torsion. At the same time, the quadrilateral frame structure is easy to fasten in such a chassis element and the chassis element""s resulting torsional rigidity can also be maintained with respect to the front axle unit.
According to a further embodiment of the invention, the frame structure incorporates a substantially horizontal lower portion. In addition, the frame structure may incorporate two side portions which extend upwards from the lower portion, and an upper portion which extends between, and connects, the two side portions. The result is a substantially quadrilateral closed ring configuration.
According to a further embodiment of the invention, said two wheels are individually suspended in the frame structure. This improves the vehicle""s riding comfort and running characteristics in that vertical forces acting upon a front wheel of the vehicle will be absorbed by the frame structure and will not act upon other parts of the vehicle. This means that each of said two wheels can be suspended by means of a lower link arm and an upper link arm which are pivotingly connected to the frame structure. With advantage, the lower link arms are pivotingly connected to the lower portion and each of the upper link arms to a respective side portion. In addition, the front axle unit may incorporate a spring device for each wheel, each spring device being connected to the upper portion and a respective lower link arm.
According to a further embodiment of the invention, the front axle unit is designed to carry a driver""s cab of the vehicle. This enables the driver""s cab to rest on substantially fixed support elements of the frame structure, resulting in stable mounting of the driver""s cab on the substantially self-supporting front axle unit.
According to a further embodiment of the invention, the drive unit includes the vehicle""s engine, the engine""s radiator core and two support members which extend substantially parallel with the vehicle""s longitudinal axis and on which the engine and the radiator core are mounted, the radiator core being situated in front of the engine in the direction of forward movement. Such an embodiment substantially facilitates maintenance and servicing in that the engine and radiator core can be extracted from the front axle unit in the form of a single joint unit, i.e. the engine""s cooling circuit can remain intact during normal maintenance work. At the same time, said support members are at least partially intended to rest on the lower portion when the engine unit is in place in the front axle unit and to support the engine and the radiator core when the engine unit is extracted from the front axle unit.
According to a further embodiment of the invention, the engine unit is intended to be connected via a driveshaft to a gearbox which is situated at a distance from the engine unit and adjacent to powered rear wheels of the vehicle. This provides the vehicle with a favourable weight distribution.