GB992242A - Improvements in or relating to vehicle change-speed transmissions - Google Patents

Abstract

992,242. Change-speed control. BROCKHOUSE ENGINEERING Ltd. Aug. 8, 1961 [May 5, 1960], No. 16847/60. Headings F2C and F2D. In a motor vehicle forward-reverse gear control wherein a manually operated selector valve 38 controls the energization of forward and reverse hydraulically operated friction clutches CF, CR, engagement of the forward or reverse clutch above a predetermined vehicle speed (5-10 m.p.h.) in a reverse or forward direction is prevented by hydraulically operated inhibitor means supplied with liquid at a pressure proportional to vehicle speed by output driven pump means. Gear arrangement.-In Fig. 1 a countershaft gear providing two ratios in both forward and reverse is arranged behind a hydrodynamic torque converter 20. An input member carries the impeller 22 of the torque converter, the turbine 23 of which is fast with a shaft G1 which can be frictionally clutched at CR, CF to gears G14, G15 respectively meshing directly and through a reversing idler a gear pair G16 fast with a countershaft G3. The countershaft G3 can be frictionally clutched at G11 to high- or low-speed gears G13, G12 meshing gears fast on an output shaft G2. Friction clutches.-The clutches CF, CR are engaged by supplying liquid pressure through lines 44a, 45a, Fig. 2, G9, Fig. 1, to annular pistons G4 which are connected together by rods G8 and biased to a central position in which both clutches are disengaged by springs G10. Fluid system.-An input pump 21 normally supplies system pressure 34 and feeds through a pressure regulating valve 60 the torque converter 20, outflow from which passes through a heat exchanger 64 to a passage 65 which supplies oil to lubricate the gearing, excess pressure being relieved at 66 to sump. A manual selector valve 38 supplies system pressure to the clutches CR, CF. In Fig. 2 two output driven pumps 24, 25 supply pressure liquid to reverse and forward inhibitor valves 30, 31 during forward and reverse travel respectively. At a predetermined vehicle speed in either forward or reverse the liquid pressure is sufficient to raise the valve 30 or 31 against its spring loading 33 whereupon system pressure 34 is supplied to the selector valve port 46 or 47. The predetermined speed is dependent upon the spring loading 33 and the size of a restriction 48. As shown the circuit is conditioned for neutral with the vehicle stationary, both clutch servos CF, CR being supplied with system pressure and the springs G10 maintaining the pistons G4 in a central neutral position. For forward travel the selector valve spool 39 is moved left to vent the reverse clutch CR at 31g through line 37 and valve 31 whilst still supplying system pressure to the forward clutch CF. During forward travel above the predetermined speed rightward movement of the selector valve spool supplies system pressure to the reverse clutch CR and the forward clutch CF is still supplied with system pressure through the now raised valve 30, line 36 and port 46 whereupon the springs G10 neutralizing the gear. Engagement of reverse ratio is thus prevented until the vehicle speed falls below the predetermined speed whereupon the valve 30 moves down and the forward clutch CF is vented at 30g through line 36. Engagement of forward ratio from reverse is prevented in a similar way by supplying system pressure to port 47 through vlave 31 and line 37 above the predetermined speed. If the interconnected forward-reverse clutches shown in Fig. 1 are replaced by two separate hydraulically operated friction clutches the system is modified in the following way. The forward and reverse clutches are respectively connected to the valves 31, 30 at 31g, 30g, the valve ports 45, 44, 30e, 31e are omitted and the ports 47, 46, which now supply the forward and reverse clutches through lines 37, 36, valves 31, 30 and ports 31g, 30g, are moved closer together. In this arrangement rightward movement of the selector valve spool 39 engages the forward clutch and leftward movement the reverse clutch. Raising the valve 30 or 31 now blocks the connection between the line 36 or 37 and ports 30g or 31g thus preventing system pressure from engaging the reverse or forward clutch above the predetermined speed. In Fig. 7 a single output driven pump 71 supplies pressure liquid to a chamber 41a during forward travel and to a chamber 41b during reverse travel. At a predetermined vehicle speed the pressure in the chamber 41a or 41b is sufficient to overcome centralizing springs 72 and move left or right a piston 68 which in turn moves a locking plunger 70 or 69 into a recess 39f or 39e in the valve spool 39 which is thus prevented from movement into the reverse or forward position until the vehicle speed falls below the predetermined speed. The length of the recesses 39e, 39f is sufficient to permit the valve spool 39 to move into a neutral position whilst preventing further movement in forward or reverse ratios. In Fig. 10 liquid pressure is supplied to a chamber 78 and always acts on both plungers 69, 70. At the predetermined vehicle speed the pressure in the chamber 78 moves the plunger 69 or 70 into a recess 39e or 39f in an extension 77 of the selector valve spool whilst the other plunger 70 or 69 abuts the extension 77 intermediate the recesses 39e, 39f. The length of the recesses 39e, 39f is sufficient to permit the extension 77 moving to the neutral position, as shown, whereupon the other plunger engages its recess and locks the valve spool in the neutral position until the vehicle speed falls below the predetermined speed. In Fig. 14 (not shown) the plungers engage slots in a plate fast with the linkage between the executive lever 40 and the valve spool 39. The linkage also includes a spring loaded lost motion coupling so that the executive lever may be moved to the new gear ratio above the predetermined speed whilst the plungers prevent the corresponding movement of the valve spool. The valve spool is then moved under the action of the spring loading into the new ratio position when the vehicle speed falls below the predetermined speed. Tow starting -In Fig. 2 for tow starting the output pump 24 or 25 may supply the system pressure through one-way valve 58 or 57 and after the valve 30 or 31 has been raised supplies the torque converter 20 through a valve 52.