Patent GB-1035822-A (GB)
Title: Infinitely variable transmission
Inventor: KEMPSON BERTRAM CARL
IPC: F02D1/00
Filed: 1963-01-11
Abstract: 1,035,822. Hydraulic transmission. DOWTY HYDRAULIC UNITS Ltd. Jan. 3, 1964 [Jan. 11, 1963], No. 1424/63. Headings F2C and F2D. [Also in Division B7] In a control for a diesel engine 1 and an hydrostatic variable speed gear 18, 22 in a vehicle, wherein a conventional engine-driven centrifugal governor 3 acts on a fuel injection pump 2 to control fuel flow to the engine to tend to maintain engine speed within a predetermined range, a further engine-driven centrifugal governor 45 acts to reduce the hydrostatic gear ratio when engine speed is reduced below a speed within said predetermined range. The engine speed governor 3 is loaded by a spring 9 which is adjusted to vary the engine speed range by a lever 15. The gear ratio centrifugal governor 45 is loaded by a spring 57 which is adjusted by a lever 58 having a handle 61. The levers 15 and 58 are connected by a link 62. The hydrostatic gear comprises an engine-driven variable displacement pump 18 connected in closed circuit, by flow and return pipes 19, 21, with a fixed displacement motor 22 driving the road wheels. To compensate for leakage loss an enginedriven make-up pump 38 feeds the pipes 19, 21 through a pipe 24 and a non-return valve assembly 25. The pump 18 displacement is varied by a double-acting, spring-centred servomotor 28 actuated, through restrictors 39, 41, pipes 35, 36, a driver-operated forward-reverse valve 34 and pipes 32, 33, by pressure drop across a restrictor 37 in the pipe 24. The governor 45 slides a waisted valve member 49 controlling ports 53, 54 of the pipes 35, 36. In operation, when idling the pressure drop across the restrictor 37 produced by the pump 38 is too small to actuate the servomotor 28 and a spring 57 acts to move the valve member 49 to connect the lines 35, 36 thereby preventing such pressure drop. To move the vehicle the valve 34 selects, e.g., forward, and the handle 61 is rightwardly moved to increase the loading of the springs 9, 57. Consequent engine acceleration, and increase in delivery of the pump 38, causes a substantial pressure drop across the restrictor 37 and increased force by the governor 45 restricts the port 53 so that the servomotor 28 is actuated to forwardly displace the pump 18.  With the handle 61 at maximum setting, curve A (Fig. 3), both springs 9, 57 are given maximum loading. Between points a and b the governor 45 closes the port 53 to give maximum pump displacement. From point a increasing torque reduces engine speed until at point b the governor 3 has increased fuel injection to a maximum. With increase in torque demand engine speed drops from point b until at point c the spring 57 starts to move the valve member 49 against the weights of the centrifugal governor 45 to slightly open the port 53 to reduce the displacement of the pump 18, this displacement reduction continuing to point d as torque increases. The engine works at maximum fuel injection and therefore maximum efficiency between the points c, d. With the handle 61 at minimum setting, curve B, the governor 45 starts to reduce the displacement of the pump 18 at a point f lying within the speed range of the governor 3, maximum fuel injection never being reached over the portion of the curve f to g. The levers 15, 58 act through cam surfaces thereon so arranged that for selected engine speeds below and above half maximum speed the governor 45 should begin to reduce pump 18 displacement respectively within and below the " droop " of the engine speed governor 3. For engine braking of the vehicle, the lever 58 may be moved to select a lower engine speed. Under such a condition the engine is driven at a speed higher than that selected by the governor 3 so that fuel flow is substantially zero and the hydrostatic gear is at high ratio. To increase braking there may be provided a pedal-operated braking valve 54 arranged to  controllably short-circuit the pipes 35, 36 and reduce the pump 18 displacement in response to pedal depression.