Improvements relating to gear-changing arrangements for non-positively changed planetary change-speed gearings, in particular for motor vehicles

摘要

831,058. Change-speed control. DAIMLERBENZ A.G. Nov. 20, 1957 [Nov. 20, 1956; July 26, 1957], No. 36200/57. Class 80 (2). A gear-changing element for a non-positively changed gear is shifted automatically from partial to full operation in dependence on torque reversal. The gear-changing element may comprise a plate clutch having limited rotational freedom on its shaft against the loading of a spring, or may be a band brake 6 acting on a drum 5 as in Fig. 1. The brake is operated by a brake cylinder 8 and push-rod 7 against a push-rod 10 supported by a spring 11 from an abutment 12. The spring 11 is matched to suit the increase in loading on the rod 10 when the torque on the drum 5 reverses. A modulating slide valve 13 is connected by a linkage 14 to the end 9 of the brake band, and controls the admission of fluid pressure to the cylinder 8 from the pipe 15. When the drum 5 is rotating in an anti-clockwise direction and the valve 13 is moved to the left to the position shown by the broken lines, fluid applied by pipe 15 to engage the brake is permitted a partial escape by the control faces 16, 17 and the brake is applied lightly by a low pressure in the cylinder 8. As the engine speed is increased for synchronism of a downward change, the drum slows until at synchronism it stops. At this moment there is a sudden rise in force at the end 9 of the brake band, which overcomes the spring 11 and causes linkage 14 to move the valve 13 to the right to prevent spill of fluid pressure and allow full pressure to reach the cylinder 8 for full engagement of the brake. In a modification, the valve 13 is moved by fluid pressure applied to its left-hand end when movement of the rod 10 closes a bleed valve. In another modification in which the partial engagement effect of the brake is maintained after shift has been completed, the reaction support push-rod 10 is actuated by a second brake cylinder connected by a pipe to the first cylinder, the direction of fluid flow in the connecting pipe caused by brake reaction controlling the pressure reducing valve. Alternatively the position of the brake band may be sensed mechanically. This arrangement may be expanded to provide a residual pressure in the disengaging gear control until the next engaging gear has been fully shifted. In another embodiment, Figs. 4 and 5, the brake cylinder 8 has a double acting piston 26 with a short-circuit valve 31 contained in the piston-rod 27, the valve 31 comprising a spring- loaded disconnecting-piston 43 and a checkpiston 44. In the position shown in Fig. 4 the brake is held released by pressure from a pipe 36 passing through restrictor 37, valve 34 and pipe 35 to the left hand side of the piston 26. On application of pressure to cause gear-shifting through a pipe 38, the valve 33 moves to the left to connect the right hand side of the piston with the source 36 through pipe 32 and at the same time passes pressure fluid through a restrictor 42 to a valve 18 controlled by the reaction support 10. Since the pressures on the two sides of the piston are equal, the piston-rod is moved to the left to gently apply the brake under the force of a spring 28 and pressure entering the piston-rod through opening 49, and check piston 44, moves the piston 43 to the left to open ports 50 to ensure a balance of pressure across the piston 26. On torque reversal in the brake band, the valve 18 is closed and pressure build-up on the face 40 of the valve 34 moves that valve to shut off the pressure supply to the left-hand face of piston 26, which then engages the brake under full pressure. The check piston 44 moves to the left to shut off the flow through the ports 50 and the short-circuiting valve is rendered inoperative. The brake is released when the pressure in the pipe 38 is released. In a modification the check piston is replaced by a spring-loaded disc valve.