Patent GB-1271387-A (GB)
Title: Electro-hydraulic control apparatus
IPC: F16H61/40
Filed: 1969-05-06
Abstract: 1,271,387. Hydrostatic transmission control; two-disc brakes; fluid pressure brakes. BROWN BOVERI & CIE A.G. 6 May, 1969 [21 May, 1968; 29 March, 1969], No. 23090/69. Headings F2C, F2D, F2E and F2F. [Also in Division F1] In a hydrostatic transmission wherein a reversible electric motor 1 drives a fixed displacement gear-type pump 2 in closed circuit 5, 6 with a fixed displacement piston or vanetype motor 3, means are provided to hold the motor output shaft 4 stationary when the driving electric motor 1 is inoperative. The speed of the motor 3 is controlled by a variable throttle valve 19 in a by-pass line 18. Make-up liquid is drawn from a reservoir 7 through oneway valves 10, 11. The lines 5, 6 are additionally connected through one-way valves 16, 17 to a high pressure relief valve 15. If the high pressure exceeds a predetermined value a pressure sensitive element 20 opens a switch 21 in the circuit to the driving electric motor 1. In Fig. 1 electromagnetically operated valves 24 on each side of the motor 3 are closed when the driving electric motor 1 is de-energized and thus hydraulically lock the motor 3 when the motor 1 is inoperative. Limit switches 22 may be provided to de-energize the electric motor 1 when the hydraulic motor 3 has completed a predetermined rotation. In Fig. 2 (not shown) pressure responsive valves on either side of the motor 3 block the lines 5, 6 and provide an hydraulic lock for the motor 3 when the pump supply pressure is below a predetermined value. The pressure responsive valves may be manually overridden to permit rotation of the motor 3 when the driving electric motor and pump are inoperative. In Fig. 4 rotation of the motor 3 is prevented when the driving electric motor 1 and pump 2 are inoperative by a brake 68. The brake 68 is applied by a spring 84 and is disengaged by circuit pressure supplied through one-way valves 65 and lines 71, 69 to a release cylinder 58. The pressure in the release cylinder 58 acts on a piston 80 in opposition to the spring 84. Exhaust from the release cylinder 58 is controlled by a valve 70 which is biased to an open position by a spring 85. When the pump is operative circuit pressure acts on the lower end of the valve 70 to close the latter and permit brake release. The brake 68 may be a multidisc brake connected to the rotor of the motor 3 or may comprise two fluted disc one of which is secured to the motor rotor whilst the other is axially slidable but non-rotatable in the motor housing. In Fig. 3 the brake 68 may be disengaged whilst the driving motor 1 and pump 2 are stationary by pressure liquid supplied to the cylinder 58 from an hydraulic accumulator 68 through a control valve 61. The hydraulic accumulator is charged during pump operation from the high pressure relief line 12 through a one-way valve 63. Alternatively or additionally an hydraulic lock may be provided for the motor 3 comprising one-way valves 66, 66<SP>1</SP> which prevent flow from the motor 3. During drive the flow from the motor 3 by-passes the valve 66 (or 66<SP>1</SP>) through lines 74, 75 (or 74<SP>1</SP>, 75<SP>1</SP>) controlled by valves 73, 73<SP>1</SP> responsive to the pump supply pressure. In order to permit rotation of the motor 3 in the event of failure of the driving motor supply current a motor by-pass line 77 includes an electromagnetically controlled valve 78 which opens in the event of current failure. In Fig. 5 (not shown) the supply of circuit pressure to a brake release cylinder (49) is controlled by a valve (45). The valve (45) may be controlled by a solenoid (46) which opens the valve (45) to supply pressure liquid to the brake release cylinder (49) when the driving electric motor (1) is energized. Alternatively the valve (45) may be controlled by a pressure responsive cylinder (48) which opens the valve (45) when the pump supplies pressure liquid through the circuit. The cylinder (48) may be controlled by dynamic pressure responsive tubes (47) or by the pressure drop across an orifice. In these cases initial flow from the pump (2) passes through the relief valve (15) to the reservoir until the brake is disengaged. In Fig. 6 (not shown) rotation of the motor (3) is permitted in the event of failure of the driving electric motor supply current by a by-pass (57) including a throttle valve (53) and a solenoid controlled valve (55) which latter is opened when the supply current fails. In Fig. 7 (not shown) the brake may be disengaged whilst the driving electric motor and pump are stationary by pressure liquid supplied through the valve (45) to the brake release cylinder (49) from a spring-loaded hydraulic accumulator (56).