Various mechanisms for adjusting the positions of the guiding vanes of a guiding grid of variable geometry have become known, such as in U.S. Pat. Nos. 4,179,247 or 5,146,752. Just the latter illustrates how difficult and tiresome it is to mount the individual parts of the guiding grid in a housing, because various parts have to be fitted into each other and have to be mounted and fixed to one another, particularly when assembling a turbocharger or at least one turbine unit.
From U.S. Pat. No. 5,028,208, a guiding grid has become known in which levers are situated on the adjustment shafts of the guiding vanes, the free end of these levers being provided with an opening between two fork arms. In this opening, a sliding block or pin slides and has its longitudinal axis about parallel to the central axis, while being moved by the unison ring (sliding block gear). The disadvantage of this gear or mechanism is that just when the force of the turbine driving fluid or exhaust gas exerts the highest turning torque onto the guiding vanes, the turning torque exerted by the unison ring is relatively small. This is not so great a problem with combustion motors of small power; however, it is a considerable problem (also in view of wear) particularly with combustion motors of an elevated power.
This becomes then a problem too with respect to automatic adjustment, particularly when controlling the vanes during a braking operation. In this respect, reference should also be made to U.S. Pat. Nos. 5,123,246; 5,444,980 and 6,148,793 which have all an electronic control.