Patent GB-698739-A (GB)
Title: Improvements in change-speed gears and control means therefor
IPC: F16H3/091
Filed: 1950-09-08
Abstract: 698,739. Change-speed gear; ratchet clutches. DAIMLER-BENZ AKT.-GES. Sept. 8, 1950 [Sept. 8, 1949], No. 22239/50. Class 80 (ii). Vehicle change-speed gear, including a freewheel 33 in one ratio, has also a disc or cone friction clutch 35 in a numerically smaller ratio (higher speed), which engages automatically, by hydraulic, pneumatic or electric control, in dependence on the relative rotation between the parts of the free-wheel on overrun, under control of a member, e.g. a drag-ring 46, disposed separately from the engaging elements of the clutch 35, thus providing engine-braking in the smaller ratio. In addition, automatic control responsive to the speed of the output or countershaft may be provided to engage the clutch 35 for bi-directional drive in the smaller ratio above a predetermined speed, dependent or not. on accelerator release. Similar control is provided in alternative ratio ranges to provide sequential upshifts. The countershaft gear shown provides four forward speeds and one reverse, the former in two ranges of two ratios each including the freewheel 33 and friction clutch 35. The free-wheel 33 is between a clutch-driven input shaft 10 and an aligned intermediate shaft 11, which drives the main countershaft 18 at greatest ratio (first speed) through a wheel-pair 21, 22, drive then passing through a wheel-pair 24, 23 and synchronised double dog-clutch 25, initially in its rearward position, to an aligned final output shaft 12. The hydraulically-engaged friction clutch 35 directly connects the input 10 to a wheel 19 which would drive the countershaft at a next smaller ratio (second speed) through the wheel 20, but, in normal forward drive through free-wheeling first speed, the clutchengaging cylinder 41 is exhausted by the automatic overrun-controlled drag ring 46, which, due to a friction mounting on the input shaft 10 and a lost-motion connection 47, 48, Fig. 2, with the more slowly rotating outer clutch member 44, is dragged round (arrow x) until a groove 49 in the drag ring 46 places a passage 50 in the member 44 leading to the clutch-cylinder 41, in communication with a central shaft exhaust-duct 55 through passages 49, 51, 52, 53, and 54. If now in the first ratio, the input 10 is decelerated by throttling the engine, producing overrun at 33, the sense of relative rotation of the input 10 and outer clutch-member 44 reverses, dragging round the drag-ring 46 anticlockwise, Fig. 2, to cut off the exhaust communication 51 &c., and communicate the clutchfeed passage 50 through the drag-ring groove 49 and passages 45, 43 with an oil-pressure-supply passage 42 leading from an output-driven pump 57, Fig. 4. The clutch 35 thus engages and transmits engine-brake torque from output 12 to input 10 through the second speed train 23, 24, 20, 19. Engaging pressure on the clutch 35 at this stage is sufficient only for transmitting engine-brake torque, so that when forward drive is resumed, the clutch 35 slips and the input 10 turns the drag-ring 46 forwards to its original (Fig. 2) position, exhausting the clutch 35, so that first speed is again picked up through the free-wheel 33. To use the clutch 35 for forward - driving second ratio, its engaging pressure is automatically increased above a predetermined speed by a centrifugal governor 69, Fig. 4, driven by the output shaft or countershaft, and acting on a valve 60 to cut off an initiallyoperative line 70, leading from an output-driven pump-delivery 58 through a spring-loaded pressure-regulator valve 71 to exhaust, and to substitute a line 72 including another pressureregulator valve 73 set to maintain a higher pressure in the common clutch feed-line 42 sufficient for forward drive. Thus, if whilst travelling in first speed above the operating speed of the governor 69, the driver momentarily releases the accelerator-pedal, the free-wheel 33 overruns and causes the clutch 35 to engage for transmitting engine-brake torque in second speed, as before, but when the accelerator-pedal is again depressed to resume forward drive, the increased clutch-pressure prevents slip and a bi-directional second speed forward drive is now introduced through the clutch 35 and wheelpairs 21, 22; 24, 23, with overrun at 33. Downshift is wholly automatic when governor speed falls below the pressure-shift point. A second two-speed range, direct- and overdrive, is provided by moving the dog-clutch 25 forward to clutch the wheel 21 direct to the output shaft, either manually or automatically in response to speed or torque. At the same time, a connecting linkage opens a valve 66, Fig. 4, admitting pump-pressure beneath a piston 64 to increase the loading of the governor-spring 63, re-introducing the low-pressure regulator 71 to restore pressure conditions as for initial firstspeed drive. Direct-drive through the freewheel 33, intermediate shaft 11 and dog clutch 25 results, with overrun torque passing through wheel-pairs 21, 22; 20, 19, and the friction clutch 35, in an overdrive (forward) ratio. Release of the accelerator pedal above the new and higher vehicle speed at which the governor 69 now changes over to the high pressure regulator 73, provides, on subsequent resumption of drive, a bi-directional overdrive through the friction clutch 35 and wheel pairs 19, 20; 22, 21. Alternatively to the variable-pressure loading of the, governor-spring 63, the oil-pump 57 may be driven by the countershaft 18 or by a separate gear so that the speed ratio between it and the output automatically changes when the dogclutch 25 is. shifted, thus making the pressures the same in each ratio-range. Reverse is by a slidable idler (not shown) meshed with wheels 31, 32, drive being through the free-wheel 33 and first-speod pair 19, 20. The clutch 35 is wholly inoperative since the output-driven pump 57 produces no pressure in reverse. Due to this absence of reverse pressure the vehicle is also free to run backwards e.g. down an incline with forward gear engaged. Such action may be prevented automatically by driving the pump 57 or an additional pump from the input or other suitable shaft, so that pressure is always available and the clutch 35 then engages to lock the output shaft against this backward movement. To obtain full clutching pressure at the clutch 35 independently of the speed-control, a separate manual control may be provided to act on the governor piston 60, or the low-pressure regulator 71, or to change over from the low to the high-pressure regulator 73. In Fig. 5 (not shown), the two pressure-regulators 71, 73 of Fig. 4 are replaced by a governor-operated differential piston co-operating with a single spring-loaded pressure-regulating slide-valve having two stages of operation to produce the two pressures. The parts may be proportioned to cause the downward pressurechange to occur at a lower speed than the upward. Two separate pumps may alternatively be used to provide the two pressures, in which case upshift in the gear may occur entirely automatically without accelerator-release: In Fig. 6 (not shown), the inner member 34 of the friction clutch 35 is connected to the input shaft 10 by means permitting a limited circumferential movement against springs, which movement provides the overrun control for the drag-ring 46, whereby operation of the latter during forward take-up in a lower speed after overrun does not depend on slip in the clutch 35 itself. In this case a constant full clutchengaging pressure is used instead of the variable pressure arrangement above.