The present invention relates to a gear shift mechanism for a vehicle gearblx, comprising a gear lever, which is mounted for pivoting in a first plane between two end positions, and spring means, which in one lever position on one side of a predetermined neutral position between said end positions, loads the lever towards one end position, and on the other side of said neutral position loads the lever towards the other end position.
In modem motor vehicles, especially trucks with a cab spring-mounted relative to the chassis and consequently also relative to the engine and the gearbox, problems arise at times with shift disengagement when driving on uneven surfaces and during rapid retardation, i.e. the shift lever moves unintentionally from the selected gear position to the neutral position. This can be caused by mass forces in the shift mechanism or a large relative movement between the vehicle cab and the engine/gearbox. This causes the shift lever to be affected by disengaging forces from its sealing bellows fixed to the cab.
By providing the inner controls of the gearbox with blocking balls, shift disengagement can be counteracted to some extent, but this solution is in many cases insufficient since it provides too low blocking torque.
In a known shifting mechanism of the type described by way of introduction, an outer blocking mechanism in the form of three tensile springs, so-called xe2x80x9ckick-over springsxe2x80x9d, which spring-load a shift bar joined to the shift lever towards one of the other end positions on either side of the shift lever neutral position. This solution is space-consuming, firstly, due to the fact that it requires as many as three springs and, secondly, due to the fact that the springs must be relatively long, i.e. longer than the radius of the arc along which the shift bar moves when the shift lever is moved between its end positions in the longitudinal direction of the vehicle, since the torque lever and thus the blocking torque is directed proportionally to the difference between the length of the springs and the radius of movement. For these reasons, the moment arm will be in many cases too short to provide a torque sufficient to prevent gear lever disengagement.
The purpose of the present invention is to achieve a shifting mechanism of the type described by way of introduction, which takes much less space in the longitudinal direction of the shift lever and which provides many times the torque counteracting gear shift disengagement than the above described gear shift mechanism with three long tensile springs.
This is achieved according to the invention by virtue of the fact that the spring means are fixed, firstly, to the lever or to an element joined to the lever at a distance from the pivot centre of the lever and, secondly, in an attachment point on a pivot element, which is so mounted for pivoting in a plane parallel to the pivot plane of the lever about a pivot centre fixed relative to the pivot centre of the lever, spaced from the attachment of the spring means in the lever, that abutment elements acting between the pivot element and the lever, when moving the shift lever from the neutral position, load the lever towards one or the other end position via the spring means.
By virtue of the invention there is achieved a very compact design with short springs. The torque can be controlled within wide limits in order to provide, as needed, high torque against shift lever disengagement. By selecting the proper pivot radius, spring force and placement of the pivot element, the shifting forces can be reduced maximally.