Patent GB-1176715-A (GB)
Title: Hydrostatic Transmission.
IPC: G05D13/00
Filed: 1967-04-21
Abstract: 1,176,715. Variable speed hydrostatic transmissions; linkwork. SUNDSTRAND CORP. 21 April, 1967 [31 Aug., 1966], No. 18601/67. Headings F2D and F2K. An hydrostatic transmission for the drive of a motor vehicle comprises a reversible variable displacement swash-plate pump 11 driving a variable displacement swash-plate motor 12, and a manual control lever 24 which, when moved from its neutral position towards its maximum speed position in either direction, is operative through a linkage assembly 23, Fig. 2, to increase the pump displacement while the motor is held in its maximum displacement position until the pump approaches its maximum displacement position when the motor displacement is decreased to its minimum position while the pump displacement is increased to, and held in, its maximum position. The lever 24 reciprocates a rod 27 pivoted at 56 to one end of a lever 48 carrying a follower roller 54 which runs in a cam slot 47 in a stationary cam plate 43, and a follower roller 53 which runs in a cam slot 46 in the plate 43, the other end of lever 48 being pivoted to a rod 35 which acts on the control lever 37 of a servo valve 21 to adjust the displacement of motor 12. A follower roller (72), Fig. 3 (not shown), is mounted on the same spindle as follower 54 and runs in a cam slot in a pivotable cam plate 70 fast with a shaft (71) on which is also rigidly mounted, at one end, a lever 29, the opposite end of which is pivoted to a rod 30 acting on the control lever 32 of a servo valve 20 to adjust the displacement of the pump 11. The cam slot 47 has a central circular portion 65 of a radius equal to the distance between the followers 53, 54 on the lever 48, so that initial movement, e.g. raising, of the lever 48 from its neutral position, as shown, raises the cam plate 70 through the action of follower (72), and hence pivots lever 29 to increase the displacement of pump 11 whilst maintaining the motor displacement at a maximum. When the follower 54 reaches the end of the portion 65 of the cam slot 47, the inner surface 75 of the upper leg of the cam slot in plate 70 is just not in line with the surface 78 on the upper leg 66 of the cam slot 47, and the pump displacement is just below maximum. The camfollower 54 then enters a transition arc 92, in slot 47, having a radius equal to one-half the width of the cam slot 47 taken at the centre line, causing the follower 53 to move along slot 46 and hence moving rod 35 to the right to decrease the motor displacement while the pump displacement is still not at a maximum, thus eliminating the possibility of a stage during which no displacement in either pump or motor occurs. On raising the lever 48 further to the end of the transition arc 92, the follower (72) aligns the cam surface 75 with surface 78, locking the cam plate 70 against a stop 80, and the pump displacement is at a maximum. With further raising of the lever 48, follower roller 54 moves in portion 66 of cam slot 47, reducing the displacement of motor 12 to a minimum, whilst maintaining the displacement of pump 11 at a maximum. Again, Figs. 4-6 (not shown), the cam slot in cam plate 70 is pearshaped, and the plate 70 is pivotably mounted about an axis closer to the axis of follower 54 to reduce the portion of the manual lever throw that is utilized to stroke the pump. The linkages and cams may provide dissimilar operation of the transmission in opposite directions of rotation. The control levers 32, 37 of the pump and motor may be directly connected to their respective pivoted displacement control cams to eliminate the need for the servo valves 20, 21 and their associated servomotors.