Patent GB-1009183-A (GB)
Title: Improvements in transmission arrangement for tractor loaders and the like
IPC: B62D5/07
Filed: 1963-05-03
Abstract: 1,009,183. Hydrostatic transmissions. FRANK G. HOUGH CO. May 3, 1963 [May 4, 1962], No. 17543/63. Heading F2C. A transmission system for tractors and like vehicles comprises one or more engine-driven hydraulic transmission pumps supplying one or more vehicle-driving motors, there being at least two of either pump or motor, control means whereby either one or more of such pumps or motors can be interconnected for fluid flow so that different ratios of pumping capacity can be selected, and a further enginedriven pump and associated control means to supply power to motor means for actuating an engine-powered appliance. The invention is described as applied to a front-end tractor loader as described in Specifications 862,525 and 1,002,289. General arrangement.-The engine drives a loader pump 13, and large and small transmission pumps 14, 15, the output from pump 13 passing via a flow divider 20a to the power steering mechanism 23a, 24a or to the control valve 19 of the loader mechanism 34, 35. The pumps 14, 15 are connected by pipelines 42, 45 to a transmission control valve 33, and by pipelines 49, 50 to a motor 47 driving the wheels 51 through bevel and spur gearing 52 . . . 56. The accelerator pedal 67 actuates a solenoid valve 59 in a connection 58 between the valve 33 and pump suctions 40, 41, while the brake pedal 76 operates a pressure switch 81 connected to the contacts of the solenoid valve 59. Control valve 33 is provided with a spool 115 operable by a hand lever for low and high forward and reverse speeds. In the low speed setting the small pump 15 only is connected to motor 47, while for high speed both pumps 14, 15 are connected to the motor. An unloading valve 100 with pilot valve 111 prevents engine stalling when the pumps are receiving full engine power. A relief valve 88 fitted between the brake line 80 and pump suction line 58 acts to relieve either pump at less than maximum engine power, while non-return valves 136, 137 prevent cavitation, e.g. when coasting. A modified arrangement, Fig. 3 (not shown) incorporates one pump and two drive motors. Operation.-If the spool 115 of control valve 33 is moved to the right to the high speed forward drive position the output from both pumps 14, 15 passes from passage 107 through grooves 125, 124 and passages 134, 49 to drive motor 47, returning to the pumps via passages 50, 135, grooves 129 and passages 95, 32, 31, 40, 41. If the tractor wheels 51 meet an obstruction or other resistance the liquid in passage 108 acts upon poppet valve 111 to open the unloading valve member 102 to vent and unload the larger pump 14, valve 109 then closing so that only the output from the smaller pump 15 passes to motor 47. If the obstruction or resistance continues relief valve 88 opens to remove the load on pump 15. Upon reduction and removal of the obstruction the operation of the valves is reversed to render pump 15 and then pump 14 effective for driving. Hence with the valve spool 115 positioned in the forward travel position the control valve 33 can be automatically disconnected and reconnected to drive the wheels through the action of 100, 88 without stalling the engine at maximum power. To slow or stop the tractor brake pedal 76 is applied and solenoid valve 59 energized to open relief valve 88 and the combined flow of pumps 14, 15 is then vented through the latter valve. Upon releasing the brake pedal and depressing the throttle pedal 67 the solenoid valve 59 and relief valve 88 are closed to restore the flow from pumps 14, 15. If the spool 115 is positioned for low speed forward travel and brake pedal 76 operated the small pump 15 is vented through relief valve 88, the flow being restored upon release of the pedal. With valve spool 115 positioned for forward travel the loader control valve 19 may be operated, since if pump 13 is loaded by operation of valve 19 the unloading valve member 102 of control valve 33 automatically unloads the large pump 14 to prevent engine stalling and to drive the tractor at low speed. If spool 115 is set for reverse drive liquid from passage 108 passes through grooves 128, 129 and passages 135, 50 to drive motor 47, and the throttle and brake controls 67, 76 operate with relief valve 88 in the manner already described to prevent engine stalling.