Patent GB-711293-A (GB)
Title: Improvements relating to control means for change-speed gearing
IPC: F16H61/00
Filed: 1951-09-04
Abstract: 711,293. Change-speed control. DAIMLERBENZ AKT.-GES. Sept. 4, 1951 [Sept. 4, 1950], No. 20839/51. Class 80 (2) A torque-speed responsive automatic hydraulic control of ratio-selecting clutches I ... IV of a change-speed gear, is supplied by input- and output-driven oil-pumps P1, P2, through a change-over valve U operating in response to speed and torque, and serving not only to change over the supply from one pump to the other, but also to connect different ratio clutches to the supply, thus causing a simultaneous ratio-shift at pump change-over. The torque factor is engine - manifold depression acting on a diaphragm M, and both speed and torque also modulate the servo pressure supplied to the ratio selecting friction clutches. Conjoint manual control is provided by a shift lever movable in the gate-pattern shown in Fig. 2. With the manual lever in position III the pump change over valve U causes automatic shifts between second and third speeds at change-over, and in position IV, between third and fourth. The change-speed gear, not shown, may be that described in Specification 699,039, wherein the first three ratios only drive through a fluid coupling FC, which is mechanically bridged by the fourth speed clutch. Clutches II. III and IV are multi-disc friction, clutch I, which remains in for all forward ratios, being positive and driving through a free-wheel which overruns in higher speeds. Torque-overlap in the 2-3 and 3-4 upshifts provides uninterrupted power shifts without excessive free-engine speed, whilst the corresponding downshifts have a definite neutral break-period to allow time for the engine speed to rise to synchronism. Manual movement into the positive reverse R is subject to a temporary lock Rh during which the second- and thirdspeed clutches are engaged simultaneously to brake the output shaft and avoid idle drag. The lower channel of the shift-lever gate-pattern, Fig. 2, includes a mechanical positive park lock P (not described), in addition to neutral N and reverse R. Fluid system components.-These are as follows, their functions being as described below. Input- and output-driven oil pumps P1, P2 supplying the system: pressure-regulating valve D having two pistons Dl, D2 with spring and torque-responsive fluid loading therebetween; the suction-controlled torque modulator valve M, a manual selector valve W having two butting piston-valves W1, W2, the former operated stepwise by the I .. IV movements of the manual shift lever; a cress-shift valve Gs, operated by the through-the-gate movements of the manual shift lever; a gear shift valve unit S having three pistons S1, S2, S3, which effects the shifts after preselection at W; a pump change-over valve U effecting pump-change and automatic shift; a reverse-lock valve Rh, preventing coupling drag; forward speed clutches I .. IV. and the fluidcoupling FC; and a transmission and engine lubricating-line Lub. Initial starting.-With the engine running the vehicle may be started in alternative manners as follows. The manual shift lever may be simply moved through the gate from N to L, in which case, on acceleration of the engine, the vehicle starts in second speed followed by automatic upshift to third, all as described below. The alternative sequence for a normal start in low is as follows. The manual shift lever is moved through the gate from N and along to position I. The through-the-gate movement moves the cross-shift valve Gs to the left, connecting ports 26, 41, whilst the longitudinal movement to position I steps the piston W1 of the manual selector valve W two steps to 'the left from its III position shown in Fig. 1. Pressure from the input pump PI acts rightwards on the left piston D1 of the regulator valve D against a spring fd, supplying, through a port 12, the lubricating line lub, and through ports 16, 19, the fluid-coupling FC. Pressure also passes upwards through ports 23, 24 of the pump change-over valve U (positioned as shown), connected ports 26, 41 of the cross-shift valve Gs, and a restrictor d1, to the low-speed clutch I. Pressure in the lowspeed clutch I also passes a metering port 44 into a chamber 52 of the torque-modulator valve M where its pressure is thus modulated in accordance with engine suction acting on the spring-loaded diaphragm M, and is led to a chamber 56 between the two pistons D1, D2 of the regulator-valve D, thus assisting the spring fd in loading both pistons, and regulating supply pressure in accordance with torque, i.e. increasing the pressure at low engine-suctions (high torques), and vice versa. This torquemodulation applies to the output - pump regulator-piston D2 (as described below) as well as to that of D1 of the input pump. Manual 1-2 shift.-A line 53 connects the torque-modulating pressure chamber 52 of the valve M with a port 54 of the manual selectorvalve W. Assuming that vehicle speed in low is not yet sufficient for the output pump P2 to take over (as described below), movement of the shift lever from I to II steps the selector-valve piston W1 one step to the right (one step left of Fig. 1), which connects ports 54, 57, passing pressure from the torque-modulator valve M to the left of the gear-shift valve S, moving two of its pistons S1, S2 to the right, which connects ports 50, 60, passing pressure from the feed-line of the clutch I through the reverse-lock valve Rh to the second-speed clutch II which engages. Clutch I, remaining engaged, is overrun in its free-wheel. Shift movement to position III (selector valve position shown) has no further effect unless the output pump P2 has taken over as described below. Output pump take-over.-A throttle reliefvalve d2' ensures that the output pump P2 develops pressure which is proportional to the square of the vehicle speed. Output pump pressure acts leftwards on the right face of the pump change-over valve U, in opposition to a spring fu and input pump pressure acting rightwards at 23. As output pump pressure increases with vehicle speed it eventually moves the valve U .to the left, cutting off an exhaust outlet O, to which the output pump P2 was previously connected through a restrictor d2; blanking off the port 23 through which the input pump PI had been previously supplying the system, and itself (P2) now supplying the same system feedline 27 through a port 29. Pressure from the output pump P2 now builds up and, acting at 34 on the right face of the regulator valve piston D2, moves that piston to the left. connecting additional ports 17, 21 and 18, 14 through which the input pump P1 can supply respectively the fluid-coupling FC and lubrication line lub. This increase in flow-passage breaks down the pressure of the input pump P1 with-the result that the regulator-piston D1 also moves to the left whereafter the input pump P1 continues to feed only the fluid-coupling and lubricating lines and the change-over valve U. Outputpump pressure is also torque-modulated by pressure in the chamber 52 of the modulatorvalve M and 56' of the regulator valve D, so that both vehicle speed and engine torque determine the pump take-over and shift point. The restrictor d2 ensures return of the change-over valve U at a lower pressure, to prevent hunting. In second speed pressure from the clutch II also passes to the right face of a small piston D2<SP>1</SP> of the regulator valve D so that change-over to the output pump P2 occurs at a lower speed in second than in higher speeds. Shift to third speed.-With the shift lever in position III (selector-valve position shown), and the vehicle travelling in second speed below pump change-over speed, an automatic shift to third speed occurs at the change-over, since leftward movement of the pump change-over valve U now interconnects ports 67, 68 providing passage from the pressurized selector-valve port 65 to the right face of the piston S3 of the gearshift valve S, moving that piston S3 to the left to connect ports 51, 71, providing passage for pressure from the feed-line of the low-speed clutch I, through the reverse-lock valve Rh, directly to the third-speed clutch III. At the same time the third-speed clutch pressure passes from the port 71 to a port 77 on the right of the piston S1 of the gear-shift valve, now, as also with the piston S2 in its right position, supplying the second-speed clutch II, due to continued pressure on the left face of the piston S1. The opposing pressures balance and a spring fs is then able to move both pistons S1, S2 to the left, which exhausts the second-speed clutch II through ports 60, O controlled by the piston S1. Disengagement of the second-speed clutch II cannot therefore commence until after pressure has been built up on the third-speed clutch III, resulting in a torque-overlapped 2-3 shift. Negative torque-overlap for downshift is described below in relation to the 4-3 shift. Manual shift to high.-In position IV the shiftlever moves the selector-valve piston W1 one step to the right of its Fig. 1 position, which also takes along the butting piston W2, connecting ports 47, 79 and providing passage from the pressurized first-speed clutch I, through the' connected ports 83, 84 of the pump change-over valve U (assuming that the output pump P2 has already taken over), to the fourth-speed clutch IV, which now bridges the fluid coupling for allmech,and,cal high-speed drive. As pressure builds up in the clutch IV it also passes from the change-over valve-port 84 (through a restrictor if required), to a chamber 87-of the gear-shift valve S, moving the piston S3 to the right to exhaust the third-speed clutch III through the reverse-lock valve Rh and ports 71, O of the gear-shift valve S. Torque-overlap is thus obtained on the 3-4 shift. The 4-3 downshift, manual or automatic (the latter as described below) occurs-similarly, but due to the gradual decrease of pressure acting in the gear-shift valve-chamber 87 with decrease of pressure in the disengaging clutch IV. engage-