Transmission and control system therefor

摘要

1,139,535. Change speed control. CATERPILLAR TRACTOR CO. 29 Dec., 1966 [18 Jan., 1966], No. 58138/66. Heading F2D. A control system for the transmission of a heavy duty, e.g. earth moving, vehicle, in which a gear change involves the engagement of range and speed clutches or brakes, provides a pressure fluid supply with separate means for independently modulating the pressure rise at different rates in the respective clutches or brakes. In the transmission shown an input shaft 101 is coupled to a hydrodynamic retarder or brake 171 and through gear units 211, 4611 to a hydromechanical gear comprising a torque converter 1011 and a series of ratio units controlled by clutches or brakes A ... G. The torque converter is effective only in the first two ratios. Control system details.-A pump 50 delivers pressure liquid to a pressure control valve 66 and a selector valve 55 which incorporates four spool valves 57 ... 60 controlling the liquid supply to the respective ratio clutches and brakes. The pressure valve 66 includes a first system of modulating valves & load pistons (81, 82, 83, 84), Fig. 4 (not shown), for controlling the pressure P 2 supplied by pipeline 61 to the first clutch or brake, and a second system (85, 86, 87) for controlling the pressure P 3 in line 62 applied to the second clutch or brake. In addition a further valve (91) provides in line 68 a pressure P 4 , directly proportional to P 3 , for supply to the torque converter 1011. The brake-or retarder 171 is controlled by a valve 74 actuated by a manual pneumatic valve 80. Operation.-Upon engagement of neutral or a ratio in which torque converter 1011 is eliminated (first and third traces, Fig. 9), pressures P 1 , P 3 initially rise together and then at different rates to a common maximum value. In the case of the two converter ratios (second trace, Fig. 9), valve 83 operates so that the pressures rise at their different rates to different maximum values which exceed those obtaining for the other ratios. In all cases the converter pressure P 4 is maintained at a constant proportion of the clutch or brake pressure P 3 . During any gear shift the hydrodynamic brake 171 is rendered inoperative by a cut-off valve (93) in the housing of the pressure control valve 66, Fig. 4 (not shown), and subjected to the clutch or brake pressure P 3 . Modification.-The pressure control valve may be modified to include a sequence valve (88), Fig. 8 (not shown), to provide a dual rate of rise of pressure P 2 , Fig. 10 (not shown).