Shifting device for a variable speed motor vehicle transmission

A shifting device (11, 40) with a servo-assistance mechanism (10) for a transmission (30) of a motor vehicle, the shifting device (11, 40) comprising means for selecting and engaging a gear step of the transmission (30) and control rod (20) upon which a manual shifting force to be assisted acts such that a performance characteristic curve is produced with the servo-assistance mechanism (10) which, as a function of one of the manual shifting force and a shift phase, having ranges with different gradients or proportionalities to the manual shifting force, and the servo-assistance mechanism (10) comprising:

• a hollow piston rod (22) which co-operates with means for shifting the transmission (30) and a valve (98) comprising a valve piston (82, 104) and a valve slide (80, 102),
• the control rod (20) being partially hollow,
• the shifting device (11, 40) comprising a shifting shaft (44) and a hollow shaft (52), and a trailing piston (88, 106) that co-operates with the valve (98) in the servo-assistance mechanism to produce the characteristic curve, the valve (98) being contained within the hollow piston rod (22) and surrounding the control rod (20),
• a trailing piston spring (90, 108) being present upon which a servo-pressure acts,
• a path limitation means in the control system of the servo-assistance mechanism (10) and at least one elastic element (84, 110) are at least one of provided upstream of and in the servo-assistance mechanism (10) to limit a servo-assistance force in a path-dependent manner for each gate or each gear,
• the trailing piston (88, 106) being arranged inside the piston rod (22), surrounding the control rod (20) and the valve piston (82, 104), and resting against an abutment of the piston rod (22), and
• the trailing piston spring (90, 108) resting, on one side, against an abutment of the piston rod (22) and, on another side, being connected to the trailing piston (88, 106).