Patent GB-1280987-A (GB)
Title: Improvements in or relating to transmission assemblies
Inventor: ABBOTT RANDLE LESLIE
IPC: F02B1/04
Filed: 1968-09-17
Abstract: 1280987 Variable-speed gear GKN TRANSMISSIONS Ltd 12 Sept 1969 [17 Sept 1968] 44038/68 Heading F2D In an automatic control for a steplesslyvariable gear on a vehicle, e.g. a toric-disc friction gear or a hydrostatic gear, responsive to engine speed and the setting of the engine power control (throttle), means are provided whereby if the power control is set to a low value (e.g. engine idle) whilst engine speed remains above a predetermined value after said setting, the gear ratio is held to the same value as before the change of setting, the hold continuing until engine speed reaches a predetermined value. In addition, if the engine speed attempts to rise above a permitted safe maximum the hold is discontinued and upshift is permitted. Gear arrangement.-In the toric-disc gear shown in Figs. 1 and 2, toric discs 24, 33, rotating with a driving shaft 17, driven through a gear-pair 15, 16 by a main input 12, drive through non-planetary rollers 36, 39, a centre disc 32, fast to a ring gear 66 of a torquesplitting train, planets of which are carried by an intermediate output shaft 70, whilst the sun 63 is fast to the gear driving shaft 17. The final output shaft 64 is driven through a bevel reverse gear 80 controlled by a dog clutch 74, although this reverse gear may be eliminated by using the full range of adjustment of the rollers to obtain reverse. As shown in Fig. 1. the adjustment range includes only forward ratios and neutral. For traction pressure the front toric disc 24 is formed as a piston slidable in a cylinder 26 to which fluid pressure is supplied through a passage 29 and line 140, Fig. 3. For ratio adjustment cages 42 carrying the individual rollers 36, 39, are supported tangentially to the toric discs at their ends by ball- and-socket connections 43, 45 with arms 30, 49 of three-armed levers 46, mounted on fixed pivot pins 47, and each having a third arm 51 engaging adjusting sleeves 53, 54 on the shaft 17, one inner sleeve 54 serving to adjust the rear rollers 39, and one outer sleeve 53 the front 36. The sleeves 54, 53 are simultaneously turned in opposite directions, for ratio shift, through arms 61, 55 by rams in a cylinder 62 and a similar cylinder 90, Fig. 3, at the opposite side of the gear. Turning the sleeves 53, 54 makes the shift by moving the rollers tangentially to take their spindles out of the radial plane and thus induce precessional tilting movement to new ratio settings. This control arrangement is such that the drive torque-reaction on the friction rollers 36, 39 is taken by the hydraulic rams, and, in the absence of pressure in the rams, the rollers will be unconstrained and will then automatically precess to a setting giving overall neutral and so no drive. In a modification, ratio adjustment is by a single double-acting ram, and a similar ram may also adjust the swash-plate of the pump in a pump-motor hydrostatic drive. A fluid-pressure supply pump 22 and governor 21 are driven by the input wheel 16. Fluid supply and regulation.-A single enginedriven pump 22 supplies a main line 143, 145 at a pressure controlled by a main regulator valve 148, combined with a lubricating valve 147, the respective valve spools 150, 151 being inwardly spring loaded and separated by a sliding spacer 167. Leak-off is to a lubricating line 159 and the arrangement is such that in any position of the valves one or other is supplying the lubricating line. In addition to the leftward spring bias, the regulator valve 148 is loaded leftwards by shift control pressure 130 (described below) through a line 160, in opposition to line pressure 145 acting between the valves so that the regulator valve 148 maintains a constant pressure differential between line and shift-control pressure, relieving the pump when shift pressure is low. Neutral valve.-Shift control pressure 130, described below, reaches the roller shift-rams 133, 136 through a two-position neutral valve 92, which, in its neutral setting shown, exhausts shift-control pressure 130 and both sides of the rams through a wide centre port 126 and exhaust 125. In the absence of constraint the rollers assume the overall neutral setting, as described above. In its second setting FR, the neutral valve 92 blocks the exhaust 125, so that the left ends of the shift rams can receive shift control pressure 130 whilst their right ends communicate with a line 131. Balance (shift) valve 91 meters the shiftcontrol pressure line 130 to line pressure 145 or exhaust 104 under the influence of rightward thrust by governor pressure 113, and leftward thrust of a spring 96 loaded through a plunger 95 and cam 171 linked to the engine throttle control. Governor pressure is provided by a two-stage engine-driven governor 21 with sequential centrifugal masses 115, 116 not described. Variation in governor pressure 113 and for throttle setting thus produces pressure variation in the shift-control line 130 and causes the friction rollers 136, 139 to precess towards new ratio settings in which torquereaction on the rollers balances the changed shift-pressure 130. Hold control.-The ratio hold control, referred to above, forming the main feature of this invention, is as follows. The condition envisaged is that of a vehicle completing the ascent of a gradient at a relatively low ratio and starting a descent. The driver would normally close the engine throttle to idle, which would, apart from this provision, cause an immediate increase in ratio (upshift) with consequent loss of enginebrake torque. This upshift is prevented as follows. In the preceding lower ratio condition, the balance valve 91 would be in a relatively leftward setting, exhausting at 109 the line 131 leading through the neutral valve 92 to the right sides of the ratio shift rams 62, 90. Idling the engine-throttle removes leftward loading from the balance valve 91, which, under the influence of unchanged governor pressure 113, moves right, blocking the line 131. At the same time the drive undergoes torque-reversal, so that roller torque-reaction is transferred from the left to the right sides of the shift rams 62, 90. However, the closure by the balance valve 91 of the line 131 places an hydraulic lock on the right sides, so that the rightward upshift movement of the rams under overrun torquereaction is prevented and the original ratio setting is held. Overspeed prevention.-If, under the preceding condition, engine speed should rise above a safe limit, governor pressure 113 shifts the balance valve 91 further right into positive abutment with the plunger 95, thereby exhausting the line 131 at 107, thus removing the hydraulic lock and permitting upshift.