Motor vehicle gearbox

Motor vehicle gearbox, comprising an input shaft and two countershafts having six pairs of interengaging gears for first to sixth gear. The disengageable gear for the first gear speed engages a disengageable gear on the fourth shaft for reverse.

Motor vehicle gearbox comprising a housing with an input shaft and two countershafts lying in a plane offset from the input shaft and having gears in engagement with gears on the input shaft, at least one gear of each pair of mutually engaging gears on said shafts being disengageable from its shaft, one of said disengageable gears being mounted on one countershaft and being disposed to transmit torque in a first gear speed to a final drive unit, wherein the input shaft has at least five gears in engagement with gears on the countershafts for transferring torque to the final drive unit for forward drive with at least five different gear ratios and wherein each of said at least five gears on the input shaft meshes with only one of said gears on only one of the countershafts, so that only one power path is provided for each of said at least five different gear ratios, and wherein the one of said disengageable gears for transmitting torque in the first gear speed engages an additional gear, which is disengageably carried on a fourth shaft and is disposed to transmit reversing torque to the final drive unit and wherein the countershafts and the fourth shaft have final drive gears non-rotatably joined to their respective shafts, each of said final drive gears engaging a crown wheel of a differential.

The present invention relates to a motor vehicle gearbox comprising a housing with an input shaft and two countershafts lying in a plane offset from the input shaft and having gears in engagement with gears on the input shaft, at least one gear of each pair of mutually engaging gears on said shafts being disengageable from its shaft, one of said disengageable gears being mounted on one countershaft and being disposed to transmit torque in the first gear speed to a final drive unit.

A gearbox of the above described type is known, for example, by SE-A-8601247-3. It has five gear speeds forward and one reverse. The torque is transmitted in reverse from the input shaft via one countershaft to the other countershaft. In this way, the need for a separate shaft for the idler gear for reverse is eliminated. Instead, the first mentioned countershaft is used as a reverse gear shaft. This provides a particularly compact, simple and inexpensive design, which, with its axially small dimensions is particularly suited for use together with transverse engines.

The purpose of the present invention, starting from the above described gearbox, is to achieve a gearbox, which in a five-speed version can be made even shorter, and, in a six-speed version, will be as short as the known five-speed gearbox.

This is achieved according to the invention by virtue of the fact that the input shaft has at least five gears in engagement with gears on the countershafts for transferring torque to the final drive unit for forward drive with at least five different gear ratios, and that the disengageable gear for transmitting torque in the first gear speed engages an additional gear which is disengageably carried on a fourth shaft and is disposed to transmit reversing torque to the final drive unit.

In a six-speed embodiment of the gearbox according to the invention, the input shaft has six gears in engagement with gears on the countershafts.

In this embodiment, a disengageable gear for the sixth gear speed can assume the place taken by the reverse disengageable gear in a five-speed gearbox, and the reverse disengageable gear can instead be carried by an extra shaft. In comparison with the above mentioned known five-speed gearbox, one gear is eliminated in the drive train in reverse by virtue of the fact that the reverse disengageable gear on the fourth shaft engages directly the disengageable gear for the first gear speed and now, as in the known design, a gear solidly joined to the hub of the disengageable gear for the first gear speed. This also provides optimally small masses to be synchronized and a suitable gear lever shift pattern is obtained.

The invention has been described above with reference to preferred embodiments for a transverse engine, but the principle of the invention can of course also be applied to a gearbox for a longitudinally mounted engine. An advantage of using the disengageable gear for the first gear speed as an intermediate gear for reverse is that a high gear ratio is obtained.