Patent GB-513274-A (GB)
Title: Improvements in and relating to means for controlling variable-speed transmissions
IPC: F16H61/02
Filed: 1938-04-01
Abstract: 513,274. Fluid - pressure servomotor - control systems. FLEISCHEL, G. April 1, 1938, No. 10084. Convention date, April 8, 1937. [Class 135] [Also in Groups XXIV and XXXIV] A step-wise change-speed gearing, particularly for motor-vehicles, has individual progressive brakes or clutches, e.g., E, F, G, H, J, Fig. 3, actuated by pairs of servomotors E', F', G<1>, H', J, controlled by selector-valves 39, 40, 41, 42, 44, respectively, the stems of which are pivotally connected by links which form a chain L along which a roller 45 is adapted to be selectively moved so as to deform the chain and lift the valve of the selected brake or clutch lying opposite the roller. The arrangement is such that, as the roller moves from a position opposite one selector-valve to the next, it constitutes a shifting fulcrum for the intervening link which acts as a lever, so that the valve of the brake or clutch to be next engaged is progressively lifted in proportion as the valve of the previously operative brake or clutch is being released, resulting in a gradual transition of speed. A fixed pivot 58 provides a neutral position for the roller 45, between first and reverse speeds. To provide for a gear engagement if the oil-pressure fails, as for starting the engine by pushing the vehicle, the direct-drive clutch J, contrary to the brakes, is disengaged when pressure-oil is supplied to its servo J<1> and engaged when the pressure is released. For this purpose its valve 44 is actuated through a reversing link 60 on a fixed pivot 61. When the selecting- roller 45 is moved to the direct-drive position shown, the valve 44 is moved to its lower closed position, against a return-spring 62, thereby venting the servo J' and engaging the direct-drive clutch J. In all other positions, the spring 62 raises the valve 44, and energizes the servo J' for release of the direct-drive clutch. The valves 39 &c. are " pressuresensitive " i.e. the force f<1>, Fig. 5, required to raise them to the open position is rendered proportional to the effective servo-pressure at any moment, by the provision of a stem-port 55, which allows the servo delivery-pressure to have access to a chamber above the valve-stem and at the same time produces a differential-area effect, thereby subjecting the valve to an unbalanced downward force P<1> which is proportional to the delivery-pressure. Thus the effective servo-pressure at any instant is proportional to the force f<1> which the selecting-roller 45 exerts upwardly on the valve, whereby progressive actuation of the brakes takes place. Pressure-sensitive valves of this kind are fully described in Specification 496,754. The valves 39 &c. have a common inlet-conduit M' connected to a pump M, and an exhaustconduit M<2>. To provide for release of any brake or clutch which happens to be engaged, thus in effect declutching the transmission, the selecting- roller 45 can be withdrawn perpendicularly from the chain L, by turning a squared shaft 47 on which slides a member 46 carrying the selecting- roller, such turning being effected by downward pressure on a lever-arm 48, secured to the shaft 47, and pressed upwardly by a spring 49. The downward pressure on the lever 48 may be applied manually or by a manually or automatically controlled servomotor 57. Due to the pressure-sensitivity of the valves 39 &c., the available servo-pressure and thus the brake- or clutch-engaging force is directly proportional to the upward force exerted on the selecting- roller by the spring 49, and, in order to render this force variable in accordance with the load on the engine, the spring 49 is opposed by enginesuction acting below a diaphragm 63. Thus at light loads (heavy suction) the spring force is weakened and the engaging-pressure of the brakes or clutch is reduced, whilst at heavy loads (light suction) the spring 49 is unopposed, and the maximum servo-pressure is available at the brakes and clutch. As shown in Fig. 4, each brake comprises a double band operated by a pair of servomotors E' &c. A main-clutch K, with pedal and servo control K<1>, K<2>, is used with this transmission. The Specification as open to inspection under Sect. 91 describes also several automatic control systems and alternative selector arrangements. In the automatic control shown in Fig. 1, Cancelled, an engine-driven centrifugal governor G, opposed by a spring-loaded lever system, actuates distributing-valves one DE controlling a single-acting servomotor C for the main-clutch, when provided, whilst another DV controls a double-acting servomotor F, operating the selector shaft 1 of a progressively-variable speed gear. The two valves DE, DV may be formed integrally, or, as shown, are linked together, and are actuated by a lever 70 carried on a fixed pivot 71, the lever being directly actuated to the right of Fig. 1 by the stem 98 of the governor G, and to the left by a spring 103, which supplies a constant opposing force. Mounted on the same fixed pivot 71 is an additional lever 104 abutting on the lever 70 and biassed to the left, for a travel limited by a stop 110, by springs 105, 106, which constitute a variable opposition to the governor, and are subject to variable compression respectively by a linkage connection 107, 115 with the servo speed-changing lever 57, and by a freely mounted arm 111 having an abutment 112, which is picked up by an abutment 116 on the engine accelerator-pedal A when this latter is moved beyond the full-open position of the engine-throttle 13. A yielding connection 18 with the throttle allows the accelerator-pedal A to have this supplementary travel. At initial idling speeds both valves DE, DV are in a position to the left of that shown, and pressure oil from an engine-pump B (described below) passes directly through pipes 80, 84 to the clutchservo C, causing disengagement of the mainclutch. Increasing engine-speed causes the governor G to move both valves DE, DV to the right until the former cuts off the clutch servo from pressure at 80 and opens it to exhaust at 82, thus allowing the clutch to engage. In order that clutch engagement shall be gradual, the control valve DE is rendered " pressuresensitive " by the provision of a central boring 130 or peripheral groove, which, as above described, unbalances the valve, so that, to maintain pressure in the clutch-servo C, the said leftward force applied to the valve must always be proportional to the pressure in the servo C. During the entire clutch-actuating period, such leftward force is supplied only by the constant governoropposing spring 103, the lever 104 of the variablesprings 105, 106 having been detained in a further rightward position by the stop 110. Thus as the governor G gradually overcomes the spring 103, the pressure in the clutch-servo is reduced in like proportion and the clutch engages gradually, clutching being initiated and completed between the positions a and b of the lever 70. In order to provide for rapid disengagement of the mainclutch on reduction of speed, the lever 104 acts on the lever 70 through a bellcrank M pivoted to the latter and having a roller 135, Fig. 2, Cancelled, tracking a cam 137, a hump on which retards the lever 70 at the position c during a speed decrease only, thereby allowing the speed to drop sufficiently for the lever to pass rapidly from the position c to the position a, giving rapid clutch disengagement. During the clutchengaging interval on speed-increase, the speedchanging valve DV is supplying pressure-oil through the conduit 89 to the left face of the servo-piston 52, holding the selector-lever 57 in the lowest-ratio position I. With further speedincrease at position c the lever 70 picks up the lever 104 from its stop 110, whereafter the variable springs 105, 106 provide additional opposition to the governor in its subsequent speed-changing movement. With the lever 70 at position d, as shown, the valve DV vents both sides of the speed-changing piston 52 resulting in a balanced position of the selector-lever 57. With further speed-increase between the positions d and e of the lever 70, the valve DV energizes the right-face of the speed-changing piston 52, moving the selector-lever 57 between its lowest and highest ratio positions I, II respectively. The lever 70 thus moves between positions c and e to set the selector-lever 57 in the particular position between I and II demanded by control conditions, restoring balance in such setting by returning to the position d. The strengths of the governor-opposing springs 103, 105, 106 are chosen by reference to the maximum economy and maximum power curves of the engine, Fig. 8, Cancelled. During the " first phase " of governor operation, i.e. before the accelerator-pedal A has been given its supplementary stroke to introduce the loading-spring 106, the engine is arranged to work on the maximum economy curve, K, Fig. 8 (i.e. the curve of power for maximum economy against engine speed), the intersection of selected ordinates of this curve with the parabola L of governor-loading against speed, giving the strengths Of<2>, f<2> f<4>, of the springs 103, 105 to produce such a result. At the point h<2> where the maximum economy curve blends into and continues with the maximum power curve H, the engine is working on its maximum gearratio, so that no further speed-increase is possible until the governor is caused to enter its " second phase" of working by introducing the supplementary stroke of the accelerator-pedal, thereby loading the governor with the additional spring 106, and causing a reduction in gear-ratio to allow further in vehicle-and engine-speeds increase, this time along the combined maximum power and economy curve. Ordinates of this curve determine the strength f<4> f<5> of the spring 106 to produce this result. The engine thus works always at maximum economy. In a modification the three springs 103, 105, 106, Fig. 1, Cancelled, are repl