| 摘要 |
1,237,564. Variable ratio hydrostatic transmission. CATERPILLAR TRACTOR CO. 14 June, 1968 [14 June, 1967], No. 3982/70. Divided out of 1,237,561. Headings F2C and F2D. In a hydrostatic transmission having ducts 33, 34 connecting an hydraulic motor and pump to form a closed loop, there is a relief unit 240 comprising a central chamber 242 in a housing 200 having ports 243 connecting the housing ends with the ducts 33, 34, the housing ends being closed by spring biased poppet valves 246, each movable to open a line 247 to the drain, and having an orifice 253 leading to a balance chamber 250, the chamber 242 being divided into two compartments 241a by a shuttle spool 242 having projections 242a and movable under the pressure difference between ducts 33, 34 to open one of the valves 246, which also open under excess pressure in one of the ducts 33, 34, the permissible maximum pressure being determined by spring biased poppet valves 252 closing openings 251 to drain in chambers 250. The housing 200 may also include a replenishing unit 201 supply fresh cooled fluid under pressure at 40 to make up fluid lost through leakage and the relief unit 240. The unit 200 only replenishes the hydraulic loop when lines 213 are pressurized, closing valves 209 to drain from balance chambers 208, preventing de-pressuring of the hydraulic loop via lines 205, 207, 208a. Line 213 is pressurized from line 40 via a unit 220 when spool 223 is correctly positioned when the hand brake 222 of a vehicle comprising the transmission is off, and by spool 229 being correctly set initially whence it retains its position so long as the system is pressurized. Spool 229 is initially set by the variable displacement pump of the transmission being set to zero displacement. The unit is dislosed in a hydrostatic transmission with the control systems claimed in copending Specification 1,237,561 and Specification 1,237,563. The valve of copending Specification 1,237,562 is also disclosed. |
