Patent GB-1378909-A (GB)
Title: Epicyclic gear change assemblies
IPC: F16H3/54
Filed: 1972-03-18
Abstract: 1378909 Change-speed gear GKN TRANSMISSIONS Ltd 12 March 1973 [18 March 1972] 12786/72 Heading F2D A planetary over- or under-drive auxiliary two-speed gear, for installation directly in front of the rear axle or in the propeller shaft of a motor vehicle, comprises a planet carrier 18, fast to the input (or output) shaft 15; a ring gear 23, fast to the output (or input) shaft 24, and a freely mounted reaction sun 26, having a splined cone clutch-brake element 28, which can be thrust rightwardly by a diaphragm spring 33 or hydraulic actuator into clutch engagement with a coned surface 31 on the ring gear (or planet carrier) for direct drive, or braked for over- (or under-)drive at first and second coned brake surfaces 13, 43, the latter (43), when moved axially left by hydraulic pressure 35 acting on a piston 37, against return-springs 42, serving to move the clutch element 28 out of clutch engagement with the ring gear 23 and into engagement with the first brake surface 13, both brake surfaces then holding the sun. The prior engagement of the second brake surface 43 produces a smooth slipping engagement of the brake. The following two features are also essential to the invention. Firstly a one-way sprag clutch 25, directly connecting input and output shafts, takes the major part of the forward direct-drive torque. Secondly the gear teeth are helical and produce a rightward thrust on the sun 26 during direct-drive overruns or reverse, which acts through a circlip 26c on the clutch element 28, to augment the clutch engaging pressure of the diaphragm spring 33 to prevent clutch slip. As shown, the clutch element 28 is axially secured to the sun 26 in the leftward direction also, by an abutment 26b, so that when the sun is braked for the planetary ratio and the input drives the output, the tooth pressure thrust, now leftwards, augments the thrust of the brake piston 37, and is hence torque responsive. Alternatively the clutch element 28 takes only the rightward thrust of the sun 26. A control circuit for supplying hydraulic pressure to the brake cylinder 35, for shift to the planetary ratio, comprises two pumps 48, Fig, 4, arranged at a downward angle on either side of the input shaft 15, and reciprocated by an eccentric 47, Fig. 1, thereon. Pumped pressure fluid 53 passes through a solenoid valve 60, open in direct drive, and a spring-loaded valve control 54 at a low pressure (25 p.s.i.) to a lubrication main 58, 59. Closure of the solenoid valve 60, for shift to the planetary ratio, causes an increase in line pressure 53 which acts at 61, Fig. 1, below a larger lower area of a loading piston 62 of the control valve 54, which further increases line pressure to a value (200 p.s.i.) at which a previously exhausting spring-loaded check valve 65 (Fig. 3, not shown) is depressed to feed, through a line 67, the brake cylinder 35, which applies the brake, causing further pressure increase (to 450 p.s.i.). The check valve 65 produces an automatic speed responsive shift by ensuring that, below a predetermined input speed, pump pressure is insufficient to keep it open, and the ratio reverts to direct drive. Selection of reverse in the main transmission de-energizes the solenoid valve 60 for downshift.  In an equivalent circuit, Fig. 5 (not shown), the fluid pressure loading of the control valve 54 is omitted, and instead the lubrication line (158) communicates with a space (73) in the solenoid valve (74) through a ball valve (81) which is closed when the solenoid is energized, thus causing pressure increase to open the check valve (165) leading to the brake cylinder (135). A separate relief valve (86) is provided in the lubrication line (158).