Patent GB-738588-A (GB)
Title: Improvements in or relating to variable ratio power transmission apparatus
Inventor: HOBBS HOWARD FREDERICK
IPC: F16H61/02
Filed: 1952-08-11
Abstract: 738,588. Change-speed control. HOBBS TRANSMISSION, Ltd. Aug. 4, 1953 [Aug. 11, 1952], No. 20162/52. Class 80 (2). [Also in Group XXIX] Speed and throttle-responsive automatic ratio-shift, with a manual ranging control and accelerator kick-down shift, in the case of a motor-vehicle, are provided by a ratio-shift piston 12, loaded in one direction, leftwards, Fig. 1, by fluidpressure supplied to one endspace 11 by an output-driven pump 37, supplying speedresponsive pressure, the cylinder-bore having at least three axially spaced exhaust outlets 16, 17, 39, at least one, 16, of which is in permanent communication with the bore, whilst the other two, 17, 39, are successively uncovered by the piston 12, which moves in steps automatically to control ratios as described below. The first and second exhaust outlets have permanently open restricted outlets 16, 17 in parallel with which, through passages 18, 19, is a common unrestricted outlet 40 controlled by a valve 20 which is opened by depression of the engine acceleratorpedal 122, to give kick-down shift. Leftward movement of the shift-piston 12 is opposed by a manually adjusted spring or by fluid-pressure supplied to a space 14 by an input-driven pump 138, which also supplies a servo main 150 providing gear-establishing pressure, and modulated if desired by speed and/or torque, or having its relief valve loading-spring 152 variably loaded in accordance with the engine throttle position. Further exhaust openings, thermostatically controlled may be provided. The ratio-shift piston 12 may control gear-shift through a fluid-pressure servo piston 30 which follows up the shiftpiston movement and controls gear shifts as by moving a control valve of the gear or by controlling ports such as 35, 36, mating with housing ports, not shown, leading to appropriate parts of the change-speed gear. The gear may be one having hydraulically actuated clutches and brakes as in Specification 738,590. Shift sequence. Initially, with the output at rest, input pump pressure 14 holds the shift piston 12 right. The right end-space 45 of the servo piston 30 is exhausted through a duct 24 opened to exhaust 39 by a groove 158 in the shift-piston 12, so that the servo piston 30 is maintained by a spring 33 in its right end position, selecting lowest ratio. With the output shaft started and increasing in speed, output pump pressure 11 exhausts through the permanently open restriction 16, and, at a predetermined value, pushes the shift piston 12 left until it uncovers-the second restricted exhaust 17, at which time a groove 157 in the shift-valve opens a pressure-supply from the input-pump 138 via 156, 28, groove 31 and axial channel in the servo piston 30, to the right end-space 45 of the latter, and also cuts off exhaust 24 therefrom. The servo piston 30 is thus moved to the left in opposition to the spring 33, until it uncovers a second outlet 23, now open to exhaust by the shift-piston groove 158. In this position the edge of the servo piston groove 31 is just beginning to close the pressure duct 28, so that the piston is arrested and introduces the next speed-ratio. Further increase in output speed causes increased output-pump pressure 11 to move the shiftpiston 12 one further leftward step until it opens a third exhaust outlet 39, checking further movement in a position in which the supply and exhaust ducts 28, 23 previously positioning the servo piston in second speed are replaced by 27, 22 respectively, thus advancing the servo piston 30 another step to the next higher ratio position. Kick-down shift. The shift speeds are all raised by overtravel of the accelerator pedal 122, which opens the valve 20 providing unrestricted parallel paths 18, 142, 40 and 19, 142, 40 for the restricted exhausts 16, 17, respectively. Manual ranging. The three different ratios selected automatically as above described may be changed for three different ratios similarly selected, by manually turning the servo piston 30 by an arm 46, which renders effective different series of the ports 35 or 36, and introduces two ranges 1, 2, 3 and 2, 3, 4 and reverse. In Fig. 2, not shown, the servo piston 30 is turned by an arm slidably keyed to it and the piston has three sets of stepped ports, which, by registering with the pressure and exhaust ducts 27, 28 and 32, 33, plus an additional pressure duct, provide two ranges of positions for the servo piston giving automatic 1, 2, 3 and 2, 3, 4, neutral, and reverse. In Fig. 3, the change-speed gear, not shown, is controlled by supplying fluid-pressure to the lines A, B, of two clutches and C, D, E of three brakes, selection being by an automatic shift valve 12, acting similarly to that in Fig. 1, and a manual valve 55, which latter has six positions giving respectively reverse, neutral, first, second and third speeds, and automatic; the last named providing automatic shifts by the piston 12 between second, third and fourth speeds. As before, output pump speed-responsive pressure 37 acts at 11 on the automatic valve-piston 12, now in opposition to a spring 50 and pressure at 51 from an input-driven pump 52 which has two relief valves 62, 53, relief from the former feeding the latter, to supply separate low and high pressure lines 54, 61 feeding respectively the lines A, B of the two clutches and C, D, E of the three brakes. Manual shifts. Moved one step up from neutral position, shown, in which all clutch and brake lines are exhausted, the manual valve 55 provides reverse by feeding clutch B from duct 54, side groove 74 in valve 55, duct 66 and passage 56 in the automatic valve 12; and brake E from duct 61 through elbow passage 75 in the manual valve 55. One step down from neutral provides first speed; clutch A, brake E, the latter through elbow passage 76, the former through side-groove 74 from duct 54. The second step down of the manual valve 55 gives second speed; clutch A through groove 74, as before, and brake D through 58 (automatic valve 12), 63, 75 (manual valve 55), 61b and 61. Throughout these steps the automatic valve 12 remains in its bottom position (second speed) with the pressure space 11 exhausted through duct 64 and the bottom of the manual valve 55 past a flat 77. The third step down of the manual valve 55, giving third speed by clutch A (through groove 74 as before) and brake C, causes also movement of the automatic valve 12 to third speed position to feed brake C as follows. The upper end of the flat 77 on the manual valve, through which the duct 64 has been exhausting in preceding positions, now closes this duct 64, which communicates with the pressure space 11 of the automatic valve 12, permitting build-up of output-pump pressure 37 so that the automatic valve 12 rises to third speed position in which the brake C is fed from the line 61 through elbow passage 58 in the automatic valve 12, and at the same time a duct 65, now uncovered by the automatic valve 12, feeds pressure from the space 11 through duct 65 and manual valve passage 79 to the line 61, whereby the output pump 37 can pressurize both lines 61, 54 for a towed engine start in the absence of pressure from the input pump 52. Automatic operation. The fourth step down of the manual valve 55 to automatic position, connects the duct 65 of the automatic valve 12 to a restricted exhaust 17 (same function as 17, Fig. 1) via elbow passage 75 of the manual valve 55, and duct 80, and the pressure-space 11 of the automatic valve 12 is also connected by ducts 64, 70 (manual valve) and 67 to a restricted exhaust 16 (as in Fig. 1). These exhausts, together with a further exhaust 39 (like Fig. 1) control the three upward steps of the valve 12 for automatic 2, 3, 4 shifts, second and third speeds being supplied as above described, whilst in the top position, for fourth speed, clutches A, B are supplied together, the former through manual valve-groove 74 as in all forward speeds, the latter through elbow-passage 58 of the automatic valve 12. Subsequent movement of the manual valve 55 to fixed second or third speeds causes the automatic valve to follow to corresponding positions, since in third speed position of the manual valve 55 ducts 65, 61 are connected and 64 shut off, reproducing the above-described conditions for shift of the automatic valve, whilst in second speed, first speed, neutral and reverse, the pressure space 11 of the automatic valve 12 is exhausted through the now-open duct 64, so that the automatic valve is moved to its lowest position. Operation of a manual valve 20 substitutes larger exhaust outlets 41, 42, for 16, 17, the effect being to raise the automatic shift speeds in the same manner as the kick-down valve 20, Fig. 1. The Provisional Specification states that the shift-piston may control the gear by electric means.