Patent GB-990371-A (GB)
Title: Improvements relating to tractor hydraulic control systems
IPC: A01B63/111
Filed: 1961-08-08
Abstract: 990,371. Tractor power-lift mechanisms. MASSEY-FERGUSON Inc. Aug. 8, 1961 [Aug. 26, 1960], No. 28556/61. Heading A1P. A hydraulic control system for a tractor having automatic draft control includes a main control valve 57 which is positioned by joint manual and automatic means to determine the working depth of an implement carried on the power lift linkage of the tractor and a by-pass valve 56 which, when open, diverts incoming hydraulic fluid from the system to exhaust conduits 69 and which is operable by the power lift through a mechanical connection 190 to hold the by-pass valve closed throughout the range of operation of the power lift up to the transport position at which the connection permits the by-pass valve to open. The hydraulic system. A continuously driven pump 40 supplies fluid along conduit 47 to a pressure relief valve 49 and along conduit 48 through a filter 50 (with a bypass 51) to a by-pass valve 56 which, in its closed position shown in Fig. 7 forms a stop for the fluid which then passes via non-return valve 59 to the main control valve 57. If the by-pass valve moves to the left, in the Figure, under the action of its spring 71, annular passageway 67 is joined to annular passageway 68 which communicates with exhaust passageway 69, thus reducing pressure in the system. When the by-pass valve is closed fluid is supplied, in the position shown in the Figures through the main control valve to a flow control valve 58 which permits unrestricted fluid flow to the operating cylinder 31 whilst restricting the exhaust of fluid by regulating the pressure drop across the orifice valve 60. Fluid entering the flow control valve passes into chamber 98 in which it builds up pressure until the plunger 90 is moved against the action of the spring 100 to allow fluid to pass into chamber 93 and thence through conduit 101 to the ram cylinder 31. If, however, fluid flow ceases, plunger 90 returns to the position shown in the Figures so that fluid can return through the flow control valve only via an orifice valve 60, the hollow centre of the plunger 90 and holes 99<SP>1</SP> therein. This flow can be controlled by adjustment of the orifice valve 60. When the main control valve 57 is moved to the right in the Figures it connects the fluid pressure system with the exhaust conduit 69. The movement of this valve is damped by a piston 84 sliding in a cylinder 83 connected to a fluid filled chamber 81 by a conduit 85 controlled by an adjustable valve 86. A temperature controlled valve 125 in the exhaust conduit 69 operates to divert fluid through a cooler 121. The pressure relief valve 49 consists of a valve member 137 which, at a predetermined pressure, pushes piston 138 against the action of the spring 140 to uncover a port 134 whereby when the sleeve 145 is in the position shown fluid is exhausted through passageway 149. If, however, the sleeve 145 is moved to the left in the Figures the port 134 communicates with a port 143 so that the pressure of the fluid is distributed over the area of the piston 138 thus moving the piston to uncover exhaust ports 144, 148 at a much lower pressure than in the normal operation of the valve. Operation. The top control link 21 of the three point hitch mechanism is pivoted at 25 to a rocker 26 which has a pivot shaft 27. A spring 205 resists movement of the rocker. The lower draft links are connected by drop links to lift arms 36 secured to a rock shaft 35 which is rocked by the power lift unit 30. For automatic draft control (see Fig 1) the hand lever 170 is moved to the required position between the two positions shown in Fig. 1 whereby the projection 201 on the draft control lever 184 which is mounted on an eccentric 181 engages the main control valve 57 to open it so that the hydraulic system is opened to exhaust whereby the lift links drop. When compression takes place in the top link 21 this is transmitted by a rod 210 and a roller 215 to a projection 204 on the draft control lever 184 so that the draft-responsive mechanism assumes control whereby the main control valve 57 is closed to establish balance between the draft load and the force applied by the power lift unit. When the hand lever 170 is moved to the transport position i.e. lever 184 is moved to allow valve 57 to close, cam 178, which normally holds the by-pass valve 56 closed is turned because of its connection through rod 190 with rock shaft 35 until it allows lever 196 to move outwardly thus opening the by-pass valve which unloads the hydraulic system. For position control (see Fig. 5) the lever 170 is moved through more than 27‹ to the left of the position shown in Fig. 1 whereby lever 184 is moved by its eccentric 181 out of engagement with valve 57 and a position control lever 185 is moved by an eccentric 182 into engagement with this valve, the plunger 75 of which is shown in Fig. 5. One arm 222 of lever 185 engages a cam surface 224 on the rock shaft 35 so that, depending on the setting of lever 170, the valve 57 is moved until hydraulic balance is achieved. When in the transport position (Fig. 5) the ram 32 of the power lift unit 30 engages a rod 150 connected to the sleeve 145 of the pressure relief valve 49, thus setting the valve to maintain a low pressure in the system. This is an additional safety device. Under normal conditions the by-pass valve 56 opens to unload the system in the transport position. The hydraulic system can be adapted to operate an auxiliary cylinder 230 (Fig. 7) by locking the rock shaft 35, and therefore the piston 32 in the power lift unit, in the transport position by rotating a locking pin 231 (Fig. 5). The hydraulic pressure is then transferred to the cylinder 230. Specifications 990,372, 990,373 and 990,374 are referred to.