GB688753A - Improvements in or relating to friction clutches for power transmission for use in mechanically propelled vehicles - Google Patents

Abstract

688,753. Clutches; variable-speed gearing. AUTOMATIC TRANSMISSIONS, Ltd. May 4, 1950 [May 26, 1949], No. 8328/49. Class 80 (ii). Friction clutches for use in variable speed transmissions for vehicles are adapted to be operated by fluid pressure generated by compact readily withdrawable pump units carried by one of the clutch members. A double clutch assembly is shown in Fig. 1 having a driven shaft 24 and a driven sleeve 15 adapted for operating corresponding members of a gearbox shown in Fig. 2. Driven friction plates 5a and 5d are adapted to be clutched to a composite driving member 1, 6, 11 by means of annular pistons 7a and 7b respectively when supplied with pressure fluid from separate pumps, only one of which 10a is shown, mounted for rotation with the driving member 1, 6, 11. The pump 10a is actuated by a cam surface 5c on the hub of driven plate 5a whilst the pump for plate 5d is actuated by a cam surface 5f on the hub 5e thereof. The actual engagement and disengagement of each clutch is controlled by centrifugally operated valves, only one 12a of which is shown. These valves control the return passage of fluid between the pressure chamber of the pistons 7a or 7b and reservoir chambers 9a, 9b to regulate the actuating pressure, and are weighted and spring-loaded to operate at desired speeds. When used in conjunction with the gearbox in Fig. 2 the two driven members 24, 15 carry gears 24b, 15b meshing with gears 18a and 16 on a countershaft 18. A freely rotatable gear 20 on the countershaft 18 is adapted to be clutched thereto by a sliding dog clutch 19 and a freely rotatable gear 21 on a driven shaft 22 is adapted to be clutched thereto by a synchronising dog clutch 23a, b. With these two clutches engaged first and second speeds are automatically obtained through the successive engagement of the clutches 5d and 5a as the engine and driving member; 1 is speeded up, the gear 16 over-running on second speed by reason of a one-way clutch device 17. For third and fourth speeds the clutch 19 is disengaged and the clutch 23a, b is coupled to the gear 24b and the automatic engagement of clutches 5d and 5a. gives a drive through gears 15b, 16, 18a to 24b or a direct drive. The centrifugal valves provide for automatic disengagement of the clutches 5a or 5d to effect a change-down or complete disengagement of the drive on a fall of engine speed sufficient to effect this but the valves are preferably arranged so that the change-down takes place at a somewhat lower speed than the change-up. Reverse speed is obtained when dog clutch 23a, b is engaged with gear 21 and a gear 19b on the dog clutch 19 engaged with a reverse idler 48a which is on a layshaft geared to the gear 21, the drive being obtained through the automatic clutch 5d. Manually operable release valves 13a, 13b, the latter only being shown are provided for releasing the pressure on either or both clutch as required by means of a sliding sleeve 14b. A double automatic clutch assembly as above described may be combined with a third mechanically operating radial centrifugal clutch so that three different ratios may be obtained by the successive energisation of such clutches or when combined with a gearbox still further ratios can be obtained. In the arrangement described above the pumps cease to operate when the clutches are engaged since there is then no relative velocity between the driving and driven parts and to overcome any slip that is likely to arise in these conditions the pumps are also adapted to be operated by a further cam sleeve on the shaft 24 which is driven separately from the gearbox at a speed different from shaft 24 or suitably braked to rotate at a different speed. This ensures that the clutch pressures are maintained after engagement and release valves are provided to relieve such pressure if it becomes too great. In a modified arrangement of two clutches particularly for co-operation with an epicyclic gear one of the clutches has two separate operating pistons controlled by separate centrifugal valves so that one clutch can come into operation first, then the second clutch, at the same time releasing the pressure on the first clutch, then both clutches together, which operations correspond to driving first one member then another of an epicyclic train, then locking the train solid to provide three ratios. An arrangement for replenishing the reservoir chamber for the pumps from a further auxiliary chamber through a float controlled valve is also described. Specification 688,820 is referred to.