| 摘要 |
A pump (12) supplies a speed selector valve (14) via a restrictor orifice (50) so that pressure drops and builds up again whenever the valve (14) is shifted to select a different speed ratio via hydraulically actuated friction clutches and brakes A, B, C and D. The pressure is also communicated by a line (36, 54) to a forward/reverse selector valve with which is associated a modulating valve serving to ensure smooth engagement of forward and reverse friction clutches or brakes. A cut-off valve (18) cuts off the pressure to the line (54) when the pressure in a pilot line (52) downstream of the restrictor (50) drops so that forward or reverse drive is disengaged every time there is a gear change. The rate at which the modulating valve allows the drive to re-engage is controlled by the pressure in a control line (84) branched off the line (36) by way of an orifice selector valve (22) which is ganged to the speed selector valve (14) and places different size orifices (100, 102, 104, 106) in the control line (84) to adapt the said rate to the gear which has been selected. |
