Patent GB-1118982-A (GB)
Title: Hydraulic controls
IPC: B62D11/14
Filed: 1965-11-19
Abstract: 1,118,982. Change-speed gear. G. G. TURNER (Caterpillar Tractor Co.). 19 Nov., 1965, No. 49372/65. Headings F2D and F2F. In a track type vehicle in which the tracks are each driven through an hydraulically actuated two speed, e.g. planetary, gear, 32, 33, and 34, 35, the driven shafts 29, 31 of which can be braked 36, 37, steering of the vehicle is effected by turning a steering wheel 100, and application of a brake pedal 95 during straight line driving and steering is effective to maintain engaged at the same pressure those of the elements 32-37 previously engaged, and to engage at a low pressure, e.g. less than 100 p.s.i., to allow slipping, those of the elements 32-37 not previously engaged. The power train of the vehicle, Fig. 1, provides ten forward gears and four reverse gears by means of, (a) a front transmission 11, operative in two conditions, mechanical overdrive 21 or split drive through a torque converter 19, (b) a range transmission including speed clutches 22, 23 and range clutches 24, 25 and 26, and (c) a cross drive transmission comprising the elements 32-37. The speed and range clutches are actually brakes holding ring gears of planetary trains. Two manual ratio selector levers 82, 81, the shift patterns of which are illustrated in Fig. 3, (not shown), operate on the front transmission, and the rest respectively. The hydraulic control system for the power train comprises a pump 41 which directs hydraulic fluid to a regulating valve unit 43, which directs the fluid to two main sections: (a) that controlling the front transmission and comprising the regulator valve unit 43, a dump and fill valve 51 for the torque converter, and a torque divider selector valve 104, and (b) that controlling the rest of the power train and comprising the unit 43, a lubrication relief valve 56, a pressure control valve unit 63, speed selector and range selector valve units 66 and 71, steering pressure control valve unit 61 and steering selector valve unit 84. Straight line driving.-The regulating valve unit 43 comprises a first flow control valve (119), Fig. 5 (not shown), which maintains the pressure to main trunk line 48 at a desired pressure P3 (e.g. 410 p.s.i.), some of the excess fluid from the pump being passed to conduit 49 to supply the fill and dump valve with a pressure source, and some being passed to maintain the pressure in a regulated compartment (131) for the torque converter at a desired level (e.g. 60 p.s.i.), the excess passing via conduit 52 to a cooler 53 and conduit 54 to lubrication relief valve 56. Valve 56 provides conduit 57 with lubrication pressure (e.g. 20 p.s.i.) which is passed to valve unit 61 and to lubrication distributing conduits 60. The dump and fill valve 51 is supplied with pressure fluid from valve unit 43 via conduit 49 and directs it in the overdrive condition to an outlet conduit (316), Fig. 16 (not shown), which limits the flow to a desired quantity and passes it to the fluid converter 19. A conduit (109) connects the converter back to the valve 51 which communicates with a dump line 105 preventing build up of converter pressure. Conduit (316) also connects with a conduit (328) of valve 104 via a one way valve (329), but the pressure is insufficient to move a spool (332) in the valve 104 and communication exists between the conduit 107 from valve unit 66 and the overdrive clutch 21. On moving the spool (312) of valve 51 upward by lever 82 to the split drive position, conduit 49 is connected to an unrestricted output conduit (336), and the pressure in conduit (328) is sufficient to move the spool (332) to block the communication between conduit 107 and clutch 21. Conduit (336) also communicates with the torque converter and as conduit 109 is now instead communicated with an output conduit (111) which leads to the compartment (131), Fig. 5 (not shown), in valve unit 43, the pressure in the converter builds up, and some of the vehicle driving power may pass therethrough. The valve unit 63 receives the pressure fluid from valve unit 43 via conduit 62, and comprises a modulating reducing valve (341), Fig. 20 (not shown), a pressure differential valve (342) and a safety reset valve (343). On receiving a pressure fluid signal from speed selector valve unit 66 via conduit 76 signifying that the lever 81 is in a neutral position, the safety valve (343) opens to allow valve (341) to deliver modulated pressure fluid to units 66, 71 to ensure gradual engagement of the respective selected valves, valve (342) ensuring that the pressure of the fluid delivered to unit 71 is always greater than that delivered to unit 66 to ensure that the speed clutches of the range transmission 12 pick up the load of the vehicle. Selector valve units 66, 71 include a speed selector valve spool (141), Fig. 6 (not shown), and a range selector valve spool (146) together with a directional selector valve spool (149) respectively, each spool having a number of lands co-operating with recesses in their associated valve bores to direct pressure fluid to a selected clutch. Valve unit 61 also includes a flow control valve (161) which receives fluid pressure from conduit 69 and delivers it at a controlled flow rate to torque divider selector valve 104 via conduit 107 when the front transmission is shifted from split drive to overdrive. The shift pattern of lever 81 has five vertical and three horizontal positions, and spools (141), (146) are positionally dependent on the vertical positions of lever 81 whilst valve spool (149) is positionally dependent on the horizontal positions. In all positions except neutral, the pressure fluid from conduit 64 is directed to either clutch 22 or 23 depending on the position of spool (141), whilst in the neutral position pressure fluid is directed to conduit 76 to provide a signal to control valve unit 63. When lever 81 is in the fourth or fifth gear or neutral position, spool (146) is positioned to direct pressure fluid from conduit 74 to clutch 25, but in all other gears clutch 25 is blocked, and clutch 24 or 26 is engaged depending on the position of spool (149). Unit 71 is also effective to select the cross drive clutches 32-35 which are engaged by providing, in first gear forward and all reverse gears, a pressure signal in conduit 88 which leads to valve unit 84 via branch conduits 89 and 91 and causes valves therein to be positioned such that pressure fluid P1 from valve unit 61 is directed to clutches 32 and 35. When clutch 25 is engaged, (in neutral, fourth, and fifth gear) a pressure signal exists in conduit 83 and pressure fluid P1 is directed to clutches 33, 34. In second and third gear, no signal exists in conduits 83 or 88, and clutches 33, 34 are again engaged. Steering pressure control valve unit 61 includes a flow limit valve (181), Fig. 7 (not shown), which communicates with a spring loaded modulating reducing valve (183) and is provided with P3 pressure fluid from conduit 92. Valve (183) further communicates with a selector vale spool (187) which communicates with a check valve spool (192). As fluid is pumped into the unit 61 it passes through flow limit valve (181) and past selector valve spool (187) and into conduit 97 which provides 'the source of P1 pressure to steering selector valve unit 84. As the clutches supplied by conduit 97 fill up, check (192) moves up, blocking the connection to dump line (208), the pressure P1 begins to rise providing gradual engagement of the clutch, until the maximum desirable P1 pressure is reached. A second source of P3 pressure is directed to unit 61 by conduit 93. A Brake valve (207), under the control of a manually operated brake pedal 95, determines the amount of this P3 pressure which is allowed to be built up in conduit 94, to supply P4 pressure to steering selector valve unit 84, with a maximum of, e.g. 100 p.s.i. A conduit 103, directs pressure fluid to unit 84 and is also in connection through the unit with conduit 94. Thus the pressures P2 and P4 are the same for straight line driving The steering selector valve unit 84 comprises a pair of shuttle valve spools (231), (232), Figs. 11-13, (not shown) between which are disposed left and righthand selector valve spools (237), (238) spring biased to a downward position and providing various paths of communication between the bores of the shuttle spools, which paths are fixed and unaltered by a gear change when the vehicle is driven in a straight line. The P1 pressure fluid carried by conduit 97 from valve unit 61 is directed via the shuttle spool bores into one the clutches or brakes associated with each track. The shuttle spools are spring biased to a central position in their bores, the ends of the bores communicating with conduits 88, 83 via branches 89, 91 and 86, 88 respectively and are positioned by the respective control signals 'therein to engage the selected clutch or brake. The brake engaging fluid P4 carried by conduit 94 enters the valve bore of shuttle vale (232) which is in constant communication with the bore of shuttle valve (231), and hence whenever P4 pressure exists, it is present in both shuttle valve bores, the position of the respective shuttle valve determining whether the pressure is delivered. Thus depression of the brake pedal 95 results in establishment of a a P4 pressure (the magnitude of which depends on the amount of brake pedal dopression) which in turn gives rise to a P2 pressure of the same magnitude during straight line driving, resulting in the' engagement of the disengaged clutches, and the brakes. The vehicle steering has two major conditions, that which occurs on turning the steering wheel one half revolution, and that on rotating it a full revolution. Steering wheel turned one half revolution.- One half turn of the vehicle Steering wheel 100 results in selector valve spool (187), Fig. 9 (not shown), moving upwardly, reducing the P1 pressure in conduit 97 and establishing a P2 pressure of the same magnit