Neutral self-centering, function

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Self-centering of neutral position at shift control unit and gear or gate shift cylinder

5 Shift control unit

7 Shift cylinder

N Neutral position with no positional error

N1 Neutral position with positional error at shift cylinder

N2 Neutral position with positional error at shift control unit

Function

Self-centering occurs in the shift control unit (5). This function resets the gearshift lever if its neutral position does not correspond to the neutral position of the transmission. This can be caused by uneven volume ratios in the hydraulic circuits (gear/gate) e.g. due to fluid expansion or fluid contraction caused by temperature fluctuations, or due to minor inner leakages, fluid changes and repair work on the hydraulic circuit or gearshift.

In each case the system must be self-centered.

Self-centering is actuated by moving the gearshift lever beyond the actuation point to the limit stop several times in the gear and gate directions. This allows hydraulic fluid to be replenished through the equalizing holes in the housing and the axial grooves. The surplus oil in the opposing circuit can flow back through the pressure relief valves.

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The replenishment function of the self-centering feature is made possible by the combination of axial grooves (3.1) of a certain length in the pistons (3) and the location of the primary cup seal (7.1) with its one-way valve function. The axial grooves (3.1) in the pistons (3) are arranged so that they just touch the primary cup seal (7.1) in all normal positions. If the gearshift lever is outside its normal range of positions, the axial grooves (3.1) in one of the pistons (3) extend beyond the primary cup (7.1) and open the connection between the hydraulic circuit and the expansion reservoir. The fluid is replenished.

When the gearshift lever is moved back again, the first movement is merely an adjustment in which the fluid is passed from one of the circuits via the axial grooves (3.1) to the expansion reservoir and from the expansion reservoir via the one-way lip of the primary cup seal (7.1) to the opposing circuit.

This guarantees that the gearshift lever is always in the correct position.