Shift Rod for a Manual Transmission

The invention relates to a shift rod for a manual transmission.

A shift rod of this type that is known from German Published Examined application Ser. No. (DE-AS) 21 65 629 consists of two segments that are connected with one another by means of a fork joint. For uncoupling the fork joint from vibrations, it is equipped with an elastic bush. If this type of a bush is made to be very flexible in order to achieve a good disconnection from the vibrations, the shift rod, as a whole, becomes so flexible that no precise coordination is obtained between the movement of the manual gear shift lever and the position of the shift fork in the transmission.

It is an object of the invention to develop such a shift rod having a damping body in such a way that a good uncoupling from vibrations as well as a precise shifting becomes possible.

This objective is achieved by developing a vibration coupling joint between two shifting rod segments which is softly resilient over a predetermined short distance and stiffly connected thereafter with a very stiff transfer of twisting forces. If the damping body that is inserted into the shift rod, in longitudinal direction of the shift rod, is developed to be softly resilient over a short distance, the vibrations that are introduced into the shift rod by the engine transmission unit are damped effectively. Since subsequently the spring progression of the damping body rises steeply, a quasi-rigid coordination is ensured between the movement of the manual gear shift lever and the shifting movement in the manual transmission so that the transmission gears can be shifted very precisely. In twisting direction of the shift rod, the damping body is developed to be every stiff with respect to torsion so that also for the preselection of the gears, an exact coordination is achieved between the selecting movement of the manual gear shift lever and the preselection position of the respective transmission components.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

FIG. 1 schematically depicts a shift rod between an engine transmission unit and a manual gear shift lever constructed in accordance with a preferred embodiment of the present invention;

FIG. 2 is a longitudinal enlarged sectional schematic view of the shift rod and the damping body of FIG. 1;

FIG. 3 is a cross-sectional view of the damping body of FIG. 1;

FIG. 4 is a top view of FIG. 2; and

FIG. 5 is a schematic view similar to FIG. 2, showing an alternative embodiment of the coordination between the damping body and the shift rod.

A shift rod 2 engages in an engine transmission unit 1 and, with a manual gear shift lever 3, can be twisted for the preselection of the transmission gears, and can be slid longitudinally for the shifting of the transmission gears. The shift rod 2 is composed of two rod segments 4 and 5, and rod segment 4 that engages into the engine transmission unit 1, via a damping body 6, being pivoted at the other rod segment 5 that leads to the manual gear shift lever 3. The damping body 6 consists of a damping plate 7 and a metal plate 8 that is bent around this damping plate 7 as an interlacing means. The damping plate 7 is made of rubber having a textile ply 9 and, at one of its sides, is equipped with a cylindrically thickened joint receiving device 10 that extends over the whole width of the plate.

A metal sleeve 11 is vulcanized into a bore of the joint receiving device 10 that is located in the center with respect to the joint receiving device 10 and in the center with respect to the longitudinal course of the shift rod 2 this metal sleeve 11, at its front faces, is held between the forks 12 and 13 of a fork head 14 that is welded to the rod segment 5. By means of a hexagon cap screw 15 that is screwed through the metal sleeve 11 and the forks 12 and 13 and by means of a screw nut 16, the damping body 6 is pivotally fastened at the rod head 14.

The metal plate 8 is bent around the joint receiving device 10 of the damping plate 7 in such a way that all around it has a radial distance s from it. The two ends of the metal plate 8 are connected with the damping plate 7 flush with its underside by means of a tubular rivet 17. The rod segment 4 that leads to the engine shift lever transmission block 1 is fitted into a sleeve 18 welded to the metal plate 8 and is connected with it by means of a radial tight-fit screw 19.

In the unloaded condition, the damping body 6, because of its softness, allows the absorption of axial vibration and movement amplitudes in the range of several millimeters. As soon as, during a shifting operation, the damping body 6 is loaded by higher axial forces, the housing receiving device of the damping plate 7 comes to rest against the metal plate 8. The resulting higher effective springs rate provides a good shifting feel. A resulting impaired insulation from vibrations during the shifting process is accepted because the damping body 6, after the manual shift lever 3 is released, automatically adjusts itself again in the central position with a radial gap s on both sides with respect to the metal plate 8. All compensating movements will be carried out by the elastic deformation of the damping plate 7 without any sliding or rolling friction. This results in freedom from maintenance and insensitivity to dirt and corrosion.

The damping body 7 is developed to be very stiff with respect to torsion in order to, by the twisting of the shift rod, be able to carry out the preselection of the transmission gears in a precise way. In a predetermined manner, the stiffness with respect to torsion can be influenced by the dimensioning of a textile reinforcement 9 that is vulcanized into the damping plate 7.

The rod segment 4 at the transmission is exposed to strong vibrations, the direction 20 of their movements extending tangentially with respect to a circle drawn around the engine crankshaft 21 and forming an angle of about 45.degree. with respect to the longitudinal axis of the shift rod 2. These vibrations can be optimally damped according to certain preferred embodiment, if the damping body 6 is arranged at an angle of about 45.degree. with respect to the shift rod 2 in such a way that the longitudinal axis 6' of the damping body 6 is located vertically with respect of the direction 20 of the movement of the vibrations of the engine transmission unit 1.

In FIG. 5, it is assumed that the direction of vibration movement extends along the length of the rod segments 4 and 5. In this embodiment the damping body extends at a 90.degree. angle to these rod segments 4, 5.

Although the present invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only, and is not to be taken by way of limitation. The spirit and scope of the present invention are to be limited only by the terms of the appended claims.