Patent GB-998215-A (GB)
Title: Hydraulic system and method for starting engines
IPC: F02N15/00
Filed: 1963-05-31
Abstract: 998,215. Hydraulic transmissions. NEW YORK AIR BRAKE CO. May 31, 1963 [June 8, 1962; Aug. 28, 1962], No. 21853/63. Heading F2C. In an hydraulic starting means for an engine 8 comprising a fixed (Fig. 2, not shown) or, as shown, variable displacement hydraulic motor 2 connected to the engine through a one-way clutch 11, the supply of motor energizing fluid, at substantially constant pressure and at a rate varying to a maximum value, is terminated by closure of a start valve 27 in response to decrease in motor energizing pressure due to motor flow demand exceeding said maximum supply rate when the engine reaches starter cut-out speed. The maximum supply rate may be determined by a limited supply pump capacity or, as shown, where a supply pump is larger than required by the motor, by a flow limiter 29. As shown, a variable delivery, discharge pressure compensated pump 23, driven by an auxiliary engine 24, and the motor 2 are of the variable displacement, rotary cylinder barrel, longitudinally reciprocating piston type. The pump feeds an auxiliary apparatus system through a line 28 and the motor 2 through the start valve 27 opened by energization of a solenoid 27a, the flow limiter 29, and a line 5. The motor 2 comprises an angularly adjustable swashplate 12 the minimum displacement position of which is defined by a stop 14 at a position greater than zero displacement to prevent motor over-speeding. The swash-plate 12 is biased towards its minimum displacement position by a spring 15 and is acted on, to increase displacement, by a servo cylinder 16 energized from the line 5 through a pilot valve 19 responsive to motor energizing pressure and thus to motor flow demand. In operation, the operator closes a switch 32 connecting a battery 31 to the solenoid 27a to open the valve 27. Fluid discharged by the pump then flows to the line 5 the rising pressure in which acts on a piston 34 to hold the switch 32 closed, and the pilot valve 19 to move it to its supply position to energize the servo cylinder 16 and move the swash-plate 12 to its maximum displacement position. The energized motor rotates the engine through the one-way clutch 11. As the motor accelerates the engine, its increased flow demand is met by the pump which maintains the supply pressure constant whilst increasing its delivery. The maximum supply rate determined by the flow limiter 29 is arranged to equal the motor flow demand at a predetermined speed which is engine ignition speed or preferably, to avoid the necessity for precise ignition initiation, a speed higher by, say, 1000 r.p.m. Therefore, as the engine commences to develop assisting torque and to accelerate from said predetermined speed, motor flow demand exceeds the supply rate and motor energizing pressure tends to decrease. The pilot valve 19 senses this pressure decrease and by controlling the venting of the servo cylinder 16 and thereby the movement of the swash-plate 12 towards its minimum displacement position, reduces the motor displacement to maintain motor flow demand constant at the said predetermined speed rate. When the engine reaches starter cut-out speed, the motor swash-plate will have been moved to its minimum displacement position against the stop 14, and since at this time both the displacement of, and the flow to, the motor are limited, motor acceleration begins to lag behind engine acceleration and motor output torque decreases. The resultant drop in motor energizaing pressure in the line 5 permits a spring 33 to open the switch 32 to close the valve 27 and interrupt energization of the motor which comes to rest and remains idle until the operator again closes the switch 32. In Fig. 2 (not shown), the motor swash-plate is fixed, the pilot valve 19 and servo cylinder 16 being dispensed with, and the maximum supply rate determined by the flow limiter is arranged to equal the motor flow demand at starter cutout speed.