Patent GB-624636-A (GB)
Title: Improvements in or relating to variable-ratio power transmission apparatus
IPC: F16H61/02
Filed: 1946-10-21
Abstract: 624,636. Change-speed gear ; claw clutches. HOBBS TRANSMISSION, Ltd., and HOBBS, H. F. Oct. 21, 1946, Nos. 31204 and 36995. [Class 80 (ii)] A change-speed gear between aligned input and output shafts 1, 14, includes concentric intermediate shafts 5, 6, connected to the output shaft 14 by one sun 17 and the carrier 13 respectively of a stepped planet train 15, and driven by a pair of nested friction disc-clutches 27, 28 in the driving drum 1 which are selectively operable, separately and simultaneously, to drive the intermediate members 5, 6 either directly (Fig. 8, not shown) or through an additional steppedplanet train 7 as. shown, to provide four, five or seven forward ratios and one or two reverse ratios in conjunction with at least one reaction disc-brake 39 and a balked positive detent 45 or a one-way roller detent assisted by a disc-brake for overrun load only. A one-way detent may also be provided in parallel with the disc-brake 39 to share its load. As shown there is also a double dog-clutch 25, connecting the output shaft 14 with either the ring-gear 16 or sun 18 of the output train 15 and the teeth or splines of this clutch may have a small helix angle, to produce an end-thrust which aids the clutch-operating pressure in causing disengagement of the dog-clutch during a shift, in some cases under full forward drive torque, in others under overrun torque, as described below. The clutches, brake and detent are all actuated hydraulically under control of a rotary selector-valve 68, with pressure supplied by engine- and vehicle-driven pumps 64, 164, so that on a vehicle, the engine can be cranked by towing. Gear train. Fig. 1 provides three reduced ratios, direct-drive, overdrive and two reverse ratios, the input train comprising stepped planets 7 carried by the driving drum 1, a driven sun 10 integral with the outer intermediate shaft 5 and a reaction-sun 11 on an outer sleeve 12 which can be held by the disc-brake 39 for reduced drive of the intermediate shaft 5 or clutched to the driving member for solid drive thereof by the disc-clutch 28. The other disc-clutch 27 directly drives the inner intermediate shaft 6, integral with which is the carrier 13 for the stepped planets 15 of .the output train, the driving sun 17 of which is fast on the outer intermediate shaft 5, whilst its driven sun 18 or ring-gear 16 can be selectively clutched to the final output-shaft 14 by the dogclutch 25. The gear-teeth in both trains may be helical, of angles such as to balance end-thrusts. Ratios. With the output-train carrier 13 bidirectionally locked by the positive detents 45, and the ring-gear 16 dog-clutched to the output shaft 14, two reverse ratios are obtained, first by engaging the brake 39 alone to drive the connected suns 10, 17 at a low forward speed, and second by engaging the clutch 28 alone to lock the input train solid and drive the connected suns 10, 17 forwards at engine-speed, reverse being obtained in the output-train in each case. The two lowest forward speeds are obtained with the same friction clutch and brake combination, but with the output-shaft 14 dog-clutched to the sun 18 instead of the ring-gear 16. Third speed is by engaging the brake 39 to drive the connected suns 10, 17 at reduced forward speed ; by releasing the output-train carrier-detent 45 and engaging the clutch 27 to drive the carrier 13 forward at enginespeed, whereby the sun 18, still dog-clutched to the output shaft 14, rotates forwards at reduced speed. Fourth speed, direct drive, is by engaging both discclutches 27, 28 together and releasing the brake 39 to lock both trains for a one-to-one solid drive. Overdrive fifth speed is by dog-clutching the ring- gear 16 to the output shaft 14 and engaging the clutch 27, to drive the carrier 13 directly, and the brake 39 to hold the sun 17. Fig. 9, not shown, provides seven speeds viz. an additional overdrive and an additional reduced drive by a further disc-brake on the outer intermediate shaft 5, whilst Fig. 8, not shown, provides four speeds by dispensing with the input planet train 7. The positive detent for the planet-carrier 13 of the output train, comprises two radially sliding detents 45 engaging notches 47, Fig. 2, in the carrier under control of a balk-ring 52, frictionally mounted on the carrier 13 and having notches 56 with steps engaged by the detents in their inward movement to retain them in a balked position until rotation of the carrier ceases and it begins to reverse, whereupon the steps are dragged away from the detents 45 which are thus free to move into the carrier notches as they come into alignment. The surfaces between the carriernotches 47 are inclined to assist engagement and also to prevent engagement if the detents should come into contact with the surfaces while the carrier 13 is rotating forwards. The detents 45 are moved to an outer released position against engaging-springs 48 by oil-pressure on the inner faces of pistons 48, which (Fig. 10, not shown) may slide on the detents, disengaging them positively through outer shoulders, and moving separately by independent springs to the inner engaged position, leaving the detents to follow with a snap action when permitted by the balk-ring 52, as described in Specification 590,607. Clutches and brake. The disc-clutches 27, 28 and brake 39 are engaged by hydraulic pressure applied to spaces 35, 36, 44 behind diaphragms e.g. 33, acting on presser-plates 29 through insulator-plates 31. Lubricating-oil, applied through shaft-ducts by the servo-supply, is diverted to the friction-surfaces when disengaged, and away from them, through grooves between the presser and insulator plates, when engaged. Hydraulic control. Control is by a rotary distributing-valve 68, Fig. 3 (and detailed in Fig. 4, not shown), the pressure-inlet 101 of which is supplied by two pumps one, 64, engine-driven, the other, 164, vehicle driven, the delivery of the latter, 164, being connected to the suction 100 of the former, 64, so that if the engine-driven pump 64 is idle, the vehicledriven pump 164, drawing from a common supply 99, will build up pressure in the engine-pump suction line, opening a spring-closed valve 102 which then passes the pressure-supply to the distributer-valve feed-line 101, in which is a common relief-valve 104 which, before exhausting, relieves to a lubricating duct 179. Pressure from the distributer-valve 68 reaches the clutches 27, 28 through annular grooves e.g. 74 in a part rotating with the driving drum 1, the final supply to each clutch including a centrifugallybalanced valve 122, which is closed (position shown) by a spring 123 to cut off the pressure-supply line and exhaust the clutch at 125 when the pressure-supply is stopped at the distributer-valve 68. A similar automatic exhaust valve 110 is also provided in the pressure-line to the disc-brake 39. To provide for automatic disconnection of the drive (automatic de-clutching in effect) in all ratios at low engine-speeds, a centrifugally-closed valve 114, rotating with the driving drum 1, is moved inwards by a spring 115 at low engine-speeds. to open to exhaust 116 a duct 76, 73, 112, leading to the diaphragm-pressure space 44 of the reaction-brake 39, whilst a similar centrifugal valve 117 relieves the clutch 28. A similar valve for the clutch 27 is unnecessary since this clutch is never used alone. To cancel the de-clutch effect automatically when the engine is to be cranked by towing the vehicle, the change-over valve 102, operated by the delivery of the vehicledriven pump 164 in the absence of pressure from the engine-driven pump 64, also cuts communication between the ducts 73, 112 leading to the centrifugal valve 114 of the reaction-brake 39. The dog-clutch 25 is operated by a double-acting piston 59, (through snap-action springs if desired) provided, in addition to distributer-valve supply-ducts 61, 63 to each end, with a similar supply duct 62 to a centre port which supplies the dog-clutch piston alone in fourth ratio (direct-drive) only, the pressure passing through one or other of two piston-grooves 127, 128 to reach that end-face of the piston which was under pressure in the ratio which was effective immediately prior to engaging fourth ratio, so that the piston is not moved. Thus in a shift from third to fourth ratio, the centre duct 62 is pressurised instead of the previously pressurised duct 61, so that the piston remains undisturbed at the right. In a shift from fourth (direct) to fifth (overdrive), the duct 63 is pressurised alone and the piston moves to the left. In the return downshift from fifth to fourth, since it is immaterial whether for fourth speed, solid drive, the output shaft is clutched to the ring gear 16 or the sun 18, it is preferred to leave the dog-clutch unmoved, whereby shifts from overdrive to direct and back again (a frequent operation) do not involve operation of the dog-clutch, but only changes of the friction clutches and brake, which is a simple operation. On this particular downshift therefore, pressure is transferred from the duct 63 to 62, which, leaves the dog-clutch undisturbed. In the distributer-valve 68 the ducts 61, 62, and 63 supplying the dog-clutch and 151 supplying the positive detent 45, are fed directly from a duct 108 which is separate from that, 109, feeding the clutch and brake ducts 72,105,177, the-latter (109) including a valve 106 so that reductions of pressure in-the clutch and brake ducts (as for automatic de-clutching) do not affect the dog-clutch and detent ducts. Dog-clutch helix action. As stated above the teeth 22, 23 of the dog-clutch 25 or its spline 26, have a small helix angle (10 degrees), left-hand, whereby forward drive torque produces an end-thrust tending to move the clutch-member 25 to the right, and overrun torque tends to move it to the left, these tendencies being normally resisted by the pressure on the dog-clutch piston 59. In the construction shown, sh