Patent GB-909792-A (GB)
IPC: F16H61/46
Abstract: 909,792. Hydraulic transmission of power. INTERNATIONAL HARVESTER CO. July 18, 1961 [Oct. 28, 1960], No. 25966/61. Class 69 (2). [Also in Group XXXI] In an hydrostatic power transmission system for a vehicle, comprising an engine, a variable displacement fluid pump driven from the engine and a fluid motor or motors connected in fluid communication with the fluid pump, there is provided governor means comprising speedresponsive mechanism driven by the engine and power-actuated means operatively connected to mechanism for varying the displacement of the pump and controlled by the speed-responsive mechanism, the arrangement being such that the power-actuated means is actuated in a direction to decrease the displacement of the pump when the speed of the engine operating at maximum fuel supply is less than a predetermined speed. A tractor 10 is provided with an engine 15, the crank-shaft 19 of which drives a variable displacement hydraulic pump 18, which drives, by means of the system shown in Fig. 4, hydraulic motors 25, 26 which are mounted on the tractor frame 24 and are in driving connection with the rear wheels. The pump 18 comprises a casing 34 having a rotating carrier 35 provided with a plurality of pistons, two of which 37, 38 are shown. A swash plate 39, pivotally mounted at 40, is movable under the action of a piston 43 controlled by a valve 45 operated by a rod 46. If rod 46 is moved downwardly, valve 45 opens to admit fluid under pressure to chamber 47, thus driving piston 43 downwardly and turning swash plate 39 in an anti-clockwise direction. Pistons 37, 38 ride on the face of swash plate 39 which thereby causes reciprocal movement of the pistons, thereby pumping fluid from port 41 to port 42. The displacement capacity of pump 18 depends on the position of swash plate 39 which is determined by the setting of the manually operated lever 28 through the linkage shown. Port 42 communicates through conduits 50, 53 and a normally open spring-loaded stop valve 51 with the inlet side of motor 25, and through conduits 57, 58 and valve 55 with the inlet side of motor 26. The exhaust fluid from motors 25, 26 passes through conduits 54, 66 respectively to inlet port 41 of pump 18. Valves 51, 55 are provided so as to allow the tractor operator to terminate energization of either or both of the motors, which will assist steering the tractor in sharp turns. Fluid leakage from valves 51, 55 are returned to a sump 59 through conduits 60, 61 and 62, 61 respectively. To prevent damage due to excessive pressure in conduits 50, 57 relief valves 63, 65 are provided to open at a predetermined figure. The outlet sides of valves 53, 65 communicate with sump 59. For draining leakage fluid from motors 25, 26, and pump 18, conduits 67, 68 and 69, respectively connected thereto, are provided, which are connected to sump 59 through conduits 64, 61. A normally closed valve 79 connecting conduits 50, 54 provides means for de-energizing both motors. A pump 48 draws fluid from sump 59 and discharges through conduit 71 to the inlet side of an oil filter 72, the outlet side of which communicates through conduits 75, 76 with check valves 73, 74, communicating respectively with conduits 53, 66 through conduits 53a, 66a. The purpose of valves 73, 74 is to permit replenishment of oil in the working circuit lost through leakage flowing in conduits 67, 68, 69. A pressure gauge 77 is provided to observe the fluid pressure in the secondary circuit. Excessive fluid pressure in this circuit is prevented by a relief valve 78 communicating with conduit 71 and with sump 59 through conduit 80. Conduit 71 also supplies pressure fluid through conduit 71a to a governor-controlled valve 81 having two outlets communicating respectively with power-actuated means 83 through conduit 82 and with sump 59 through conduits 84, 64 and 61. Means 83 comprises a ram 49 whose connecting rod 85 is secured to a lost-motion member 86 having a recess 87 adapted to receive a rod 88 pivoted at its other end to the upper arm 93 of a bell crank 91 which is urged by spring 94 in the direction to move rod 46 downwardly to obtain maximum displacement of pump 18 in the forward direction. A valve 89 in conduit 82 permits unrestricted flow into ram 49, but restricts flow back to conduit 82. The means for shifting bell crank 91 by actuation of means 83 is shown in Fig. 3. Governor-controlled valve 81 is of the solenoid-actuating type and comprises a casing 102 having a bore 103 in which slides a plunger 104 connected to armature 105 of solenoid 106. Casing 102 has three ports connecting bore 103 to conduits 71a, 82, 84. Plunger 104 has a groove 108 which always registers with the port leading to conduit 82. In Fig. 3, solenoid 106 is deenergized and fluid flows from conduit 82 to conduit 84. In this position ram 49 retracts and the fluid therefrom returns to sump 59. When solenoid 106 is energized, conduits 71a, 82 are in communication and pressure fluid energizes ram 49 expansively. The carburetter 109 controls the fuel supply to engine 15 by means of an element 110 having projections 111, 112. A stop member 113 limits rotation of element 110 in a clockwise direction corresponding to the position of maximum fuel supply. The idling speed adjustment for engine 15 is determined by screw 115. A spring 128 urges element 110 in a direction towards maximum throttle position. Pivoted at 116 to element 110 is a rod 117 whose other end slides in a bore 124 of a lost-motion device 118. Rod 117 can move relative to casing 119 of device 118 through the axial distance between face 127 and face 126 of nut 125 mounted on the end of rod 117. Casing 119 is pivotally connected at 130 to a lever 131 of a speed-responsive mechanism 132, shown in detail in Fig. 5. Journalled for rotation in the casing 133 is a shaft 134, driven by the crankshaft of engine 15 and having an axially slidable sleeve 136 provided with flanges 137, 138. A yoke member 142 secured to shaft 134 has pivoted thereto a plurality of inertia elements, two of which 143, 144 are shown. Fingers 147, 148 provided on elements 143, 144 engage the outer face of flange 137, so that as the speed of shaft 134 increases, sleeve 136 is driven to the right. The outer surface of flange 138 is engaged by the lower portion of a bifurcated element 140 which forms part of lever 131 which is pivoted to casing 133 at 139. A spring 141 connected to lever 131 and either to a stationary part of the tractors or to throttle control 29 urges element 140 into engagement with flange 138. Referring to Fig. 3, a microswitch 149 fixed to the tractor has a switch lever 152 and in alignment therewith a strip of spring metal 153. The electrical circuit comprises an ignition switch 154, distributer 156 and light 157, solenoid 106 being energized through leads 159, 160. If control lever 28 is in neutral position the displacement of pump 18 is zero, and the engine readily attains high speed since there is no load thereon. As soon as engine 15 reaches optimum speed, inertia elements 143, 144 drive sleeve 136 to the right moving lever 131 anticlockwise about pivot 139. This moves lostmotion device 118 to the left against the action of springs 124, 141 and rotates element 110 anticlockwise, thereby reducing the rate of delivery of fuel to engine 15. The governor mechanism thus stabilizes element 110 in the position in which the speed of engine 15 is maintained at a constant optimum. If lever 28 is set to the position in which pump 18 delivers fluid under pressure to motors 25, 25 at one-half its maximum fluid displacement and if the tractor is connected to a plough, for example, which engages hard ground which imposes a load on engine 15 so great that element 110 has reached maximum fuel delivery position, the speed of engine 15 is reduced below optimum. This allows lever 131 to move in a clockwise direction thus moving casing 119, sleeve 121 and bushing 122 of device 118 to the right independently of rod 117. This action moves metal strip 153 to the right, thus closing switch 149 and illuminating lamp 157 to inform the operator of an overload condition. At the same time solenoid 106 is energized and plunger 104 moves to the right, thus terminating the flow in conduit 84, and bringing conduits 71a, 82 in communication thereby energizing expansively the ram 49. This will rotate bell crank 91 clockwise and move rod 46 upwardly to reduce the displacement of pump 18. The reduced speed of the tractor will reduce the applied load on the engine and as soon as its speed reaches optimum device 132 will act to allow the microswitch to return to its open position which extinguishes light 157 and de-energizes solenoid 106. Conduits 82, 84 are brought into communication and the fluid in ram 49 returns to sump 59, the rate of flow being retarded by valve 89. Bell crank 91 and rod 46 move, at a retarded rate, to increase the displacement of pump 18 and increase the speed of the tractor to the speed setting of lever 28. This arrangement prevents rapid increase in the loading of the engine. In the modification of Fig. 5, all electrical components are eliminated and the solenoid-operated valve 81 is replaced by a spool valve 811.