Patent GB-1250851-A (GB)
IPC: F16H61/4157
Filed: 1969-04-17
Abstract: 1,250,851. Hydrostatic transmission. POCLAIN. 17 April, 1969 [19 April, 1968], No. 19621/69. Heading F2D. A vehicle hydrostatic transmission comprises two pumps 13, 14 driving sets of motors 8, 9 and 7, 10, each set including a motor driving a front wheel connected in parallel with a motor driving a rear wheel, the front wheel of each set being on the opposite side of the vehicle to the rear wheel of that set. The pump 13 supplies motors 8, 9 through a reversing valve 17. Similarly, pump 14 supplies motors 7, 10 through reversing valve 20 and a three-position valve 22. Also, by positioning valve 22, pump 13 supplies both sets of motors and pump 14 drives a tool of the vehicle, e.g. a shovel actuator. Each motor is of a 2:1 dual capacity type having capacity selectors 7c-10c, the rear motors driving through 3 : 1 speed reducers 11 and being connected to the reducers through multi-plate friction clutches 12. Pump delivery to the rear motors is three times that to the front motors so that the wheels rotate at the same speeds. Again, the motors may have a number of incremental capacities, or may have infinitely variable capacities. The transmission provides four forward speeds and four reverse speeds with the tool inoperative, and a fifth speed with the tool operative. First speed.-Valves 17, 20 are in their forward position, and valve 22 connects pump 14 to valve 20. The pumps 13, 14 supply motors 8, 9 and 7, 10, the clutches 12 being engaged and the capacity selectors 7c-10c, in their higher capacity positions. Second speed is twice first speed and is provided by positioning the capacity selectors in their lower capacity positions. Third speed is obtained by simultaneously moving valve 22; moving a pair of valves 23, 24 to isolate motors 9 and 10; positioning the capacity selectors in their higher capacity positions; and disengaging clutches 12. The two pumps 13, 14 therefore deliver in parallel to the parallel connected front motors 7, 8. The total delivery to the front motors is thus four times that for first speed, and the vehicle speed is consequentially four times first speed. Fourth speed is eight times first speed and is obtained by positioning the selectors 7c, 8c in their lower capacity positions in third speed. To render the tool operative, all valves &c., except valve 22, are moved to their first speed position. Valve 22 is moved to connect pump 14 to the tool actuator and pump 13 supplies both motor circuits. Vehicle speed is therefore half first speed. By moving the selectors 7c-10c to their lower capacity positions, vehicle speed during tool operation may be made equal to first speed.  Reverse speeds are obtained as above, but with valves 17, 20 in their reverse positions. Control.-Valves 17, 20 are mechanically linked and manually positioned. A manually controlled distributer 34 having four positions corresponding to the four speeds, controls the capacity selectors 7c-10c, the clutches 12, and the valves 22-24. In its first position, as shown, the valve 34 connects a line 37 to sump 25 to allow a valve 36 to connect a compressed air source 38 to valves 23, 24 to maintain them open, and to the clutches to engage them for first speed. In its second position, Fig. 2 (not shown), the valve connects oil pressure in line 44 to the selectors 7 c -10 c  via lines 49 to change the selectors to their lower capacity positions for second speed. In its third position, Fig. 3 (not shown), the lines 49 are connected to sump 25 to return the selectors to their higher capacity positions. Line 37 is connected to line 44 closing valve 36 to disengage the clutches 12 and close isolating valves 23, 24. A line 42 is also connected to line 44 and moves actuator 43 for valve 22 to position the valve for third speed. In its fourth position, Fig. 4 (not shown), the valve 34 connects lines 49 again to line 44 to select the lower motor capacity for fourth speed.  To provide tool operation, the valve 34 is moved to its first position, and a valve 47 is manually moved to its second position, Fig. 5 (not shown), connecting actuator 43 of the valve 22 directly to pressure oil in line 44.  Engine braking is provided by a variable restrictor 50 in the common motor return line 26, and adjusted by the highest pump delivery pressure via a shuttle valve 27. Pump control is effected by a pressure summator 29 connected at 30 and 31 to pump delivery from pumps 13, 14, and responsive to these delivery pressures to adjust the pumps via linkage 33. An increase in delivery pressure decreasing the delivery volume so that the pumps are varied in accordance with the required power.