Gearbox for motor vehicle

Mechanical stepped gearbox comprises a number of gear wheel pairs which interact with one another and are arranged on an input shaft, an output shaft, and a first side shaft. The gear wheel pairs can be selectively coupled in order to form different gear ratios.

In addition to this, the gearbox comprises, arranged on a second side shaft, a gear wheel which is used both in order to bring about a reverse gear and in order to transmit driving force to the first side shaft. The gearbox can thus be designed with short axial extend even when the gearbox comprises many gear steps.

Gearboxes for use in passenger cars are dimensioned in order to permit driving at different speeds while utilizing combustion engines that permit the most economical driving within a limited engine speed range. In association with an increased requirement for performance and at the same time a requirement for economical driving, there is an increased requirement for more gear steps in the gearboxes.

More gear steps can be arranged by mounting more gear wheels in the gearbox on its existing shafts. This means that the gearbox is given an axially longer extent. For vehicles with a longitudinally mounted gearbox, this is no great problem. On the other hand, for vehicles with a transverse gearbox, the space in the transverse direction of the vehicle is critical, since an increased gearbox length is not usually possible without the width of the vehicle having to be increased. The use of a transverse gearbox affords the possibility of building the gearbox together with the drive engine of the vehicle, so that a complete drive aggregate is obtained. This in turn makes it possible to build the drive aggregate compactly and to use the available space in the vehicle effectively. The possibilities for increasing the number of gears while retaining the axial length of the gearbox are limited and presuppose that it is possible in another manner to reduce the axial length of other components in order thus to create new space for more gear wheels in the gearbox. For modern vehicles, which to a great extent are already optimised in said respect, there are problems in creating such space. This problem is further aggravated by the fact that it is usually the cars with the most powerful engines which, with a view to increasing the maximum speed of the vehicle, it is most important to provide with more gear steps. Since these cars can transmit a very high driving torque, gear wheels, couplings and other components in the gearbox must be dimensioned for these torques, which further increases its axial extent.

A known manner of reducing the axial extent of a gearbox is to replace the conventional synchronising couplings with other, narrower types of non-synchronised couplings in order thus to make space to further gear wheels. However, the requirement thus arises to arrange synchronising in another manner, for example by suitable engine control or by arranging so-called central synchronising arrangement. Such solutions comprise both expensive and complicated control systems and have not come into practical use in series-produced vehicles.

The aim of the invention is to make it possible that a gearbox can be designed with more gear steps without its axial extent increasing. The gearbox is particularly advantageously to be capable of being used in transverse drive aggregates for use in motor vehicles. Moreover, the gearbox is to be capable of comprising synchronising couplings which are usual for gearboxes, as well as also being constructed around conventional and proven components. The gearbox is to be based on usual gear wheel technology with its possibilities for manufacturing the gearbox at low cost and to have a high degree of efficiency, at least in the majority of driving conditions.

Within the scope of the attached patent claims, the invention can be modified and designed differently from what is indicated in the above exemplary description. For example, the couplings for the different gear positions R, 1 to 6 inclusive, and the gear wheels likewise, can be arranged in another manner. Similarly, the gearbox can be modified for both fewer and more gear steps than the number in the example.