Patent GB-848096-A (GB)
Title: Improvements in and relating to fluid pressure control or servo systems for change speed gears
Inventor: MILLER ALBERT ARTHUR
IPC: F16H61/02
Filed: 1957-05-21
Abstract: 848,096. Change-speed control. SELF-CHANGING GEARS Ltd. May 16, 1958 [May 21, 1957], No. 16056/57. Class 80 (2). [Also in Groups XXVI and XXVIII] A main planetary change-speed gear having its ratios established by selective energization of fluid-pressure servomotors applying brakes is in series with an auxiliary planetary gear also having its ratios established by selective energization of fluidpressure servomotors applying brakes, low and high-pressure supplies of fluid for actuating the brakes being controlled by relay valves actuated by low-pressure fluid and the main gear servomotors being actuated by different pressures of fluid according to the ratio established, the pressure of the fluid applied to a simultaneously-energized servomotor of the auxiliary change-speed gear being regulated in dependence on the fluid pressure applied to establish a ratio in the main change-speed gear. As shown, the system is applied to a changespeed and reverse planetary gear, having ratio establishing brakeapplying servomotors R, F, S, T, Fig. 4, in series with a two-speed auxiliary planetary gear, having two ratioestablishing servomotors LR, HR. A lowpressure, high-capacity pump 1 supplies oil to a pipe 62 selectively connected to the desired servomotor by operation of an electromagnetic valve 61R, 61F ... which supplies oil through a non-return valve 63R &c. to a pipe 64R ... leading to the servomotor. Simultaneously, low-pressure oil is supplied to a relay piston 58R which is moved in its cylinder against spring bias to open a valve and connect a high pressure, lowcapacity pump 2 through pipes 73, 68R to the pipe 64R and the servomotor. The lowpressure oil from the pump 1 serves to produce initial engagement of the ratio establishing brake band, and the high-pressure oil completes the engagement. On closing the electromagnetically-operated valve 61R &c., the relay piston 58R is returned to the position shown, the supply of low-pressure oil thereto being exhausted through the electromagnetic valve, and simultaneously the servomotor is connected to exhaust as at 66R. The high ratio (HR) and low ratio (LR) servomotors of the auxiliary gear are controlled by an electromagnetic valve 61LR. In the position shown, low-pressure oil is supplied from the pipe 62 through a non- return valve 88 to a pipe 87b leading to the servomotor HR, and high-pressure oil is supplied through a pipe 74 to a pipe 79LR, 86 where it acts upon a pressure differential piston 83 which rises and passes high-pressure oil through a pipe 87 to the servomotor HR. Accordingly the high ratio is established. At the same time, low-pressure oil biases a relay piston 71 upwards to close an exhaust valve 72 leading to the high ratio servomotor HR. To establish the low ratio in the auxiliary planetary gear, the electromagnetic valve 61LR is energized to supply low-pressure oil from the pipe 62 through a non-return valve and a pipe 77LR to the servomotor LR. At the same time, low-pressure oil acts upon the top of the relay piston 71, which moves downwardly so that the piston groove 72 opens the pipe 87, 87a to exhaust, and releases the high ratio brake applied by the servomotor HR. Also, low-pressure oil acts upon a relay piston 55LR which is moved upwardly so that high-pressure oil from the pipe 74 is no longer supplied through the pipe 75 to the pipe 79LR, but is instead supplied to a pipe 76LR. Accordingly, high-pressure oil is now supplied to the pipe 77LR and the servomotor LR, to complete establishment of the low ratio. At the same time, this high-pressure oil is supplied through a pipe 78LR to the top of the differential piston 83, which is accordingly moved downwards to open a valve port 85 leading to a pipe 80LR. The pipe 86 leads from this pipe to the bottom of the differential piston 83, and accordingly high-pressure oil at the lower end of the differential piston tends to move the piston upwardly. A throttling effect of the port 85 is thereby obtained, in accordance with the pressure in the pipe 80LR, which finally stabilizes when the latter pressure is three times the pressure in the low ratio servomotor pipe 77LR. The pressure in the pipe 77LR is determined by which of the ratios first, second or third (F, S, T) has been established, the associated relay valves 54F, 54S, 54T having different area surfaces 55F, 55S, 55T acted upon by the ratio establishing high pressure. If, for example, the third ratio electromagnetic control valve 61T is opened, lowpressure oil is supplied to the servomotor T through the non-return valve, and the associated relay valve moves upwardly to connect the pipe 80LR with the pipe leading to the servomotor T. The pressure in the latter pipe acts downwardly against the surface 55T of the relay piston, against the low-pressure oil acting upwardly on the area of the base of this piston, and shuts off the high-pressure oil when the opposed forces reach equilibrium. The pressure of the oil supplied to the low ratio servomotor LR is then three times that of the pressure of the oil supplied through the third ratio servomotor T. If, however, the second ratio electromagnetic relay valve 61S is opened, the pipe 80LR is connected through the third ratio relay valve 54T to the second ratio relay valve 54S which acts in the same way, the relay valve stabilizing when the pressure supplied to the servomotor S is higher than the corresponding pressure supplied to the servomotor T since the surface 55S is of smaller area than the surface 55T. The pressure supplied through the pipe 77LR to the lowratio servomotor LR is again three times that supplied to the main change-speed gear servomotor S, which, since this latter is itself higher than before, is correspondingly increased. The low-pressure pump 1, Fig. 1, comprises a gear pump having inlet ports 8, 9 and outlet ports 11, 10 feeding to the inside of a filter 12, a control passage 15 leading through a bleed-hole 37 and a non-return valve 36 in parallel to a pressure-regulating piston 33 acting through a spring 23 upon a pressure-regulating valve 20. As pressure builds up in the control passage 15, the regulating valve 20 is moved leftwards against the bias of its spring 23, which bias is increased as the piston 33 moves slowly rightwards, until the outlet port 11 is connected through a port 29 to a port 30 leading back to the inlet port 8. When a predetermined pressure has been reached, the pressure-regulating valve 20 accordingly causes oil to be re-circulated through the pump. When a sudden demand for oil is made, the non-return valve 36 opens to allow rapid displacement of the control piston 33, so that a gradual return to the predetermined pressure is achieved as pressure once more builds up, by oil flowing back slowly through the bleed-hole 37. The high-pressure pump 2 comprises pistons 38, 39 reciprocated by an eccentric upon a shaft 41, and drawing oil through one-way valves 45, 46 and inlet pipes 14 to pass it through outlet pipes 49 ... 53. The low-pressure pump 1 and the high-pressure pump 2 are geared together and driven from a common input. Specifications 793,318 and 818,396 are referred to.