Patent GB-1233686-A (GB)
IPC: B62D11/04
Filed: 1970-02-26
Abstract: 1,233,686. Steering by differential driving. GENERAL MOTORS CORP. 26 Feb., 1970 [17 June, 1969], No. 9266/70. Heading B7H. [Also in Division F2] In a vehicle transmission including a pair of hydrostatic transmissions on opposite sides of the vehicle, comprising axial-piston pumps 58, 59 feeding similar motors 60, 61, and each in parallel with a mechanical transmission having LO, INT, and H1 ratios provided by the engagement of corresponding friction devices, the hydrostatic transmission is controlled by a servomotor 34 which turns a pair of cam drums 688 of a ratio control 62 to adjust the displacement of the pumps 58, 59, opposite sides of the piston 361 of the servo 34 being subjected to displacement increasing or decreasing signals 335, 336, from a ratio control valve 33 subjected to opposing throttle position and engine speed signals, and the hydraulic control circuit including a neutral shuttle valve 26 and a neutral hold valve 25 which utilize the increase and decrease signals when a neutral automatic valve 24 is in neutral to maintain and/or establish the pump displacements at zero. Function summary.-During the initial or low range of operation, the engine power is transmitted purely hydraulically through the hydrostatic transmission, the pump displacements being increased automatically under opposing throttle position and engine-speed signals to maximum forward. The mechanical transmission then upshifts to its INT ratio, the hydrostatic transmissions providing the reaction, and the power is transmitted through splittorque paths as it is in the high range to which the mechanical transmission upshifts when the pump displacements are reduced through zero to maximum reverse. The motors have two operating positions, a high and low, between which they are shifted in accordance with high operating pressure. The transmissions on opposite sides of the vehicle may operate in different ranges for steering. Hydraulic pressure supply and regulation.- Engine-driven pumps 11, 13, 14 and 15, and a rear pump 12 provide the control and lubricating hydraulic fluid for the system. The pump 11 provides the main pressure fluid 66 regulated by a main valve 16 selectively connecting the fluid to exhaust under opposing spring and main fluid pressure. A second valve 17 regulates the pressure fluid 66 to provide low pressure regulated fluid 87. The second pump 13 provides make-up fluid pressure 93 to the hydrostatic transmissions through make-up valves 19, 21 and 22, 23, and provides pressure fluid to the control pump 15 providing servo control fluid 96 for the pump adjustment servo valves 97, 98, the pressure of the fluid being adjusted by a valve 18 under opposing control fluid pressure 96 and a pressure signal 105 responsive to the high pressure in the hydrostatic transmissions. The pump 14 provides lubrication for vehicle brakes and rear pump 12 provides main pressure 66 during push starts. Shift control pressures. Hydrostatic transmission.-The pump displacement increase or decrease pressures 335, 336 are produced by a ratio control valve 33, the spool of which is acted on at one end by a spring 322 reacting against a stop 321 positioned by an engine throttle link. The opposite end of the spool is subjected to a force from centrifugal masses 326 rotated by the engine shaft. The spool selectively connects low-pressure regulated fluid 87 to either line 335 or 336 in accordance with the opposing engine speed and throttle signals. Mechanical transmission.-The left and right shift valves 39, 38 are upshifted from LO to INT, and from INT to H1 by low-pressure regulated fluid 87 acting in lines 444, 444a, 445, 445a, 477 and 477a, the presence of pressure in these lines to effect an upshift being controlled by cam grooves in the end of the hydrostatic cam control drums 688. Again, Fig. 10 (not shown), the hydrostatic transmission may be controlled by cams on the drum ends, and the mechanical transmissions by cams on the drum surface. Operation. Neutral.-A solenoid B is manually energized to vent the top of the neutral automatic valve from low-pressure regulated fluid 87 so that the valve is held in its neutral position shown. Low-pressure regulated fluid is also directed in line 279 to shift a push-start inhibit valve 28 to connect main pressure 66 through the valve to a push-start blocking passage 281 which holds a push-start valve 32 in its upward position preventing push-starts. The ratio control valve produces a displacement increase or decrease signal 335, 336 connected to the neutral shuttle valve via the neutral hold valve 25 or directly, respectively. The shuttle valve output 406 is connected to a directional valve 40 which connects the signal in line 406 to both or one of the displacement decrease lines 385, 386 for forward or reverse respectively, depending on the presence of low-pressure regulated pressure 87 in forward and return lines 368, 367 connected to exhaust grooves in the piston-rod 362 of the pump displacement servomotor 34. The signal in line 385, 386 is transmitted to the respective side 373, 374 of the piston 361 via shuttle valves 55, 56 and the push-start valve 32, causing the piston to return to neutral when communication of the respective forward or reverse line 368, 367 with its exhaust groove in piston-rod 362 is broken to return the valve 40 to its central position pressurizing both sides of piston 361 equally. Drive.-A solenoid A in the neutral automatic valve, and a solenoid E or F in the forward/reverse valve 31 are manually energized to provide forward or reverse drive. On energizing solenoid A, the neutral automatic valve is vented at the bottom to shift the valve down to connect main pressure 66 to a mechanical transmission apply line 472 to the left and right shift valves 39, 38 to engage the LO friction devices. Main pressure is also connected through the valve 24 to the top of a plug valve 135, in the valve 24 to hold the valve in its downshifted position, and to a line 158 to the neutral hold valve 25 to shift it to its drive position connecting the displacement increasing signal 335 to the forward/reverse valve 31. Energization of solenoid E or F moves the valve 31 to its forward or reverse position connecting lowpressure regulated fluid 87 via a shift inhibitor valve 29 and line 256 to either of two lines 426 or 427 connected to opposite ends of a forward/ reverse clutch valve 35 which selectively connects main pressure 66 to a forward or reverse clutch and to the top or bottom of left and right relay valves 37, 36 through lines 431, 428. The reverse line 431 is also connected to the end of left and right intermediate valves 42, 41. The push start valve 32 and its inhibitor valve 28 are again shifted to prevent push-starts. A pump displacement increase signal 335 is now transmitted through the neutral hold valve 25 to the forward/reverse valve 31 and then to either of lines 384 or 387 to the shuttle valves 55, 56 and push-start valve 32 to the adjustment motor 34. A pump displacement decrease signal 336 is again transmitted to the directional valve 40 via the neutral shuttle valve 26 to act on the motor 34. The motor 34 then increases the pump displacement to a maximum when the pump adjustment cam follower 631 reaches the point 747 in cam groove 641. At that time, forward and reverse lines 444, 444a, and 445, 445a respectively, are disconnected from exhaust cam grooves in the end faces of the cam drums 688 to allow low-pressure regulated fluid 87 to build up therein and act on the end of shift valves 38, 39 via left and right relay valves 36, 37 to effect a shift to INT. The function of fluid motors 60, 61 changes to that of rotating reaction members, and to compensate for this, a slight adjustment of the pump displacement is effected through intermediate valves 41, 42 and lines 496, 497 or 496a, 497a for forward or reverse respectively, the pressure fluid being directed to an adjustable hydraulic link 501 between the pump adjustment servos 97, 98 and the cam followers 631. Continued increase in speed rotates the drums 688 further to decrease pump displacement until cam followers 631 reach the points 479 in the cam grooves when lines 477, 477a are disconnected from exhaust grooves in the cam drums 688 to shift the mechanical transmission into H1. A shift inhibitor valve 29 prevents reversal of the mechanical transmission in INT or H1. Push-starts in forward only are effected by energizing solenoids B and D in the neutral valve 24 and push-start valve 32 so that main pressure 66 and low-pressure regulated fluid 87 produced by the rear pump 12 provide for neutral steer and shift the push-start valve 32 down by developing push-start pressure in line 369. Lowpressure regulated fluid is then connected through valve 32 to the adjustment motor 34 which moves up to connect push-start pressure line 369 to exhaust, the valve 32 then acting to throttle the low-pressure regulated fluid 87. With solenoid D energized, line 279 is exhausted so that the inhibitor valve 28 remains in its unshifted position. Steering.-Three modes of steering are provided: (a) Neutral or push-start: Main pressure 66 provided by the engine-driven pump 11 or the rear pump 12, is directed through the neutral automatic valve 24, line 744, pivot steer valve 27, line 743, steer selector valve 732 and a line 729, to a pair of manually actuated valves 711 under the control of a lever 715 selectively connecting the pressure line 729 to either of right and left brakes 712, 713 for the ground engaging wheels or tracks; (b) Pivot steer: Solenoids B and C are manually energized to position neutral valve 24 in its neutral position and to shift pivot steer valve 27 down to cut-off fluid supply to neutral steer valves 711. Main pressure 66 is connected through pivot steer valve 27 to hold the valve down, and through a line 705 to a pivot steer engage valve 63 and via neutral valve