| 摘要 |
PCT No. PCT/EP95/02265 Sec. 371 Date Dec. 12, 1996 Sec. 102(e) Date Dec. 12, 1996 PCT Filed Jun. 12, 1995 PCT Pub. No. WO95/34774 PCT Pub. Date Dec. 21, 1995A shift valve is proposed for switching the direction of travel of a powershift transmission and, in particular, a tractor, wherein a slide valve (20) fitted in a valve housing (1) can slide into a forward, a reverse or a neutral position. The slide valve (2) can be displaced by electro-hydraulic devices. Centering pistons (21, 22 and 210, 220) are provided in the valve housing (1) which, during normal operation, lie in a withdrawn or non-activated position, but during emergency operation can be hydraulically or pneumatically activated in such a way that they actuate the slide valve (20) while bypassing normal control of the latter. |
