Patent GB-649577-A (GB)
Title: Improvements in or relating to clutches, brakes and power transmission apparatus
Inventor: HOBBS HOWARD FREDERICK
IPC: F16D65/28
Filed: 1947-02-19
Abstract: 649,577. Friction clutches; change-speed gear. HOBBS TRANSMISSION, Ltd. Feb. 19, 1947, No. 4803. [Class 80(ii)] [Also in Groups XXIX and XXXIV]  A friction clutch 6 which is used in conjunction with a similar reaction-brake 13, in an automatic change-speed transmission, e.g. of a battery-electric vehicle, which also prevents overspeeding of the driving motor, comprises a rotary input member 1 providing a space 2 to receive pressureliquid for engaging the driven disc 6, through a flexible diaphragm 3, heatinsulator plate 4 and pressure-plate 5, the pressure-space 2 having a constantly open exhaust-port 15 at an inner radius to retain the space partly filled with liquid the centrifugal pressure of which produces speedresponsive engagement at least in part, the exhaust port 15 being so dimensioned as to permit an externally-pumped liquidsupply to fill the space 2 for complete engagement, the space 2 having also a second exhaust opening at an outer radius controlled by a centrifugally-balanced spring- closed valve 40, opened by an externally controlled pressure-supply through a duct 39, for completely emptying the pressurespace 2 for clutch disengagement when required. The clutch is used in a two-speed or forward-reverse planetary train and connects a reaction sun 48 to the input planet-carrier 1 for direct drive, whilst a similar disc-brake 13 holds the reaction-sun 48 for reduced or reverse drive. The stepped planets 45 mesh also a driven sun 46 fast on the final output shaft 47. Initial depression of a single control-pedal 53 switches on the driving motor and at this time there is sufficient liquid in the clutch pressure-space 2 to effect gradual engagement of the direct-drive clutch 6 and thus prevent overspeeding of the motor. At the same time a continuously-driven pump 17, by virtue of duplicated suction and delivery valves 19. supplies pressure independently of its direction of rotation, to a duct 18, the magnitude of the pressure being determined by a centrifugal valve 22 which slides in a radial bore in the driving drum 1 and has its outer face communicating with the pressure-duct 18 so as to relieve the duct to exhaust 23 at low speeds. Increase of speed causes the centrifugal valve to effect progressive reduction of the opening to exhaust 23, and pressure, building up in the duct 18, acts on a spring-loaded piston shiftvalve 26 to snap it to the left (position shown) completing a fluid-circuit from the pressure-duct 18 through a valve 24, under graduated control of the single pedal 53. a duct 25, valve-groove 36 and ducts 27, 29 to the clutch pressure-space 2. Initial openings of the pedal-valve 24 supplies fluid at a rate less than the escape capacity of the clutch exhaust-port 15 so that the clutchengaging load is only that due to the centrifugal force on the liquid remaining at radii greater than that of the exhaust-port 15, but as the valve 24 is opened further by depression of the pedal 53, the supply exceeds the exhaust and finally full circuitpressure is added to centrifugal pressure to complete engagement of the direct-drive clutch. If the output torque requirements reduce the motor speed sufficiently to cause the centrifugal valve 22 to reduce the pressure in the pressure-duct 18 to a predetermined value, a loading spring 30 snaps the shift-valve 26 to the right completing a pressure-supply from the duct 18 through the pedal-valve 24, duct 25, valve-groove 36 and duct 35 to thepressure-space 9 of the reaction-brake 13, and also through further ducts 37, 39 to the spring-loaded centrifugally - balanced valve 40, which is forced inwards by the pressure to exhaust the clutch-space 2 at 42. The clutch 6 thus disengages and the reaction-brake 13 engages, so that reduced drive supersedes direct. Pressure in the brake-space 9 will be determined by the centrifugal valve 22, the pedal-valve 24 and its fixed exhaust port 16. Shift back to direct-drive occurs automatically when the speed increases sufficiently to permit the centrifugal valve 22 to build up pressure in the duct 18 so as to snap the shift-valve 26 back to the left. A spring-detent 31 locks the shift-valve 26 in its two operative positions, or, in more than two positions where additional clutches and brakes are provided for additional ratios. Alternatively additonal interlocked shift-valves may be provided for this purpose; To protect the motor against overspeed in direct-drive the shiftvalve 26 houses a secondary spring-loaded. valve 43, and at a predetermined speed higher than the shift speed, when the pressure in the duct 18, as controlled by the centrifugal-valve 22 exceeds a predetermined value with the shift-valve 26 in its leftward direct-drive position, this secondary valve 43 is moved to the left, opening the pressure-duct 18 to the brake-duct 35 whereby the reaction-brake 13 is applied, without disengaging the direct-drive clutch 6, to reduce vehicle-speed. Slipping of both clutch and brake under control of the pedal 53 is possible and they are both cooled and lubricated by liquid escaping at the exhaust ports 15, 16.