| 摘要 |
An apparatus 22 is provided for preventing shifting of a vehicle automatic transmission 10 between forward and reverse gears, except when the vehicle (e.g., an airport tractor) has stopped moving. The apparatus 22 preferably includes an assembly 24 operably coupled with the external shifting linkage 12 of transmission 10 for releasably locking the linkage 12 when the transmission 10 is in either a forward or reverse gear. Additionally, a sensing assembly 26 is provided for sensing braking system pressure, together with structure 28 interconnecting the sensing assembly 26 and locking assembly 24, in order to release the locking assembly 24 and permit transmission shifting via linkage 12. The apparatus 22 is advantageously completely mechanical, and includes an elongated rod 30 coupled with linkage 12 and engageable with a pivotal plate member 52, the latter being movable between a shift-locking position and a release position. A piston and cylinder assembly 66 is coupled to the plate member 50 and operates to move the plate member 50 to its release position, via a pressure sensitive valve 62 interposed within the vehicle braking system, when the pressure within the braking system is of sufficient magnitude to assure that the vehicle is essentially completely stopped.
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