GB392586A - Improvements in or relating to variable speed power transmission mechanism - Google Patents

Abstract

392,586. Controlling motor vehicles. HAYES, F. A., Middletown Township, New Jersey, U.S.A. Aug. 19, 1931, No. 18897/32. Divided on 392,570, [Group XXIV.] [Class 79 ( v).] Variable-speed power-transmission mechanism for driving a vehicle comprises a piston 70 for controlling the speed ratio operated automatically by fluid at a speed dependent on the engine speed, an operator-operated throttle control or accelerator pedal 74a, and a relief valve 71i controlled from that pedal to relieve the pressure behind the control piston 70 when the throttle is open and the piston is in a high speed position and thereby prevent increase of the speed ratio beyond a pre-determined value corresponding to that at which the engine can drive the vehicle at maximum velocity. Oil pumped by the engine 75 enters at 74 and presses on a piston 78 in a cylinder 77 which applies the usual clutch (not shown) arranged either before or behind the variable gearing, which may comprise precessional rollers as described in Specifications 344,061 and 392,570, [both in Group XXIV]. The oil passes by a pipe 71a to a ratio control cylinder 71 corresponding to the cylinder 10 of Specification 388,129. The pressure in the cylinder 71 depends thus on the opening of a throttle 75a by the pedal 74a. In the side of the cylinder 71 is a port 71b registering with a port 70a in the skirt of the piston 70 in the low-speed position shown. A pipe 71c leads to the sump past a control valve 71d. The pipe 71a is also connected by a pipe 71e to a port 71f in a relief valve cylinder 71g having a drain 71h to the sump. In this cylinder is the sliding sleeve relief valve 71i provided with a port 71k and connected by a rod 75b to the accelerator pedal 74a. The control cylinder 71 also has a port 71m connected by a pipe 71n to a port 71p in the valve cylinder 71g into register with which the port 71k in the sleeve valve can be brought by depressing the pedal 74a. The control piston 70 has a port 71r in its skirt which opens the port 71m when the piston reaches a certain position in its rightward movement. With the engine idling and the control valve 71d open, oil entering at 74 escapes freely at the valve 71d and cannot develop pressure to move the piston 78 to engage the main clutch, but the engine is warmed up. To start the vehicle, the control valve 71d is set partially closed, as shown, and the accelerator pedal 74a depressed. The clutch is engaged at once, and as the car gains speed, the operator depresses the pedal fully, giving the throttle 75a its widest opening and bringing the port 71k of the valve 71i into register with the port 71p. The inertia of the -car keeps the engine speed down. As the car velocity increases, the engine speed increases, so that the piston 70 advances, increasing the speed ratio so that the car accelerates rapidly. The advancing control piston 70 opens the port 71m permitting oil to escape through the still open relief port 71p so as to prevent further advance of the piston and to keep the ratio gearing so that the engine can drive the car at maximum velocity. If the velocity so attained is too high, the operator allows the pedal 74a to rise, as he naturally would, the first effect of which is to move the valve sleeve 71i rightwardly to close the port 71p. The control piston 70 then moves farther to the right bringing the ratio gearing into an over-drive. This operates the car at maximum engine torque but reduced engine speed, resulting,in high economy of operation. If the engine on overdrive ratio still drives the car faster than is desired, the operator raises the accelerator pedal farther, thus closing the throttle until the desired car velocity is attained. If the pull of the engine on overdrive is insufficient to drive the car at the desired velocity, the operator raises the accelerator pedal so as partially to open the port 71p p allowing the control piston 70 to recede till a lower ratio is attained in the transmission proper to increased engine speed and increased pull on the driving wheels. If the engine then slows down, the decrease of oil pressure lets the piston 70 move back and open the port 70a. This allows the control piston to move back farther still, making it still easier for the engine to carry the load. If the engine does not maintain the desired car velocity with the accelerator 74a fully depressed and the port 71p therefore wide open, the continued decrease of engine speed may permit the control piston to move back far enough to close the port 71m. With increasing load, the control piston may move right back so that maximum pull is delivered to the load wheels. If at any time before the port 71m is closed, the car velocity increases too much, the operator lets the accelerator pedal rise, thereby restricting the port 71p, causing increased oil pressure, increased speed ratio, decrease of engine speed, and consequent decrease of car velocity. These movements of the accelerator pedal 74a for opening and closing the port 71p and so controlling the car velocity have very little effect on the throttle 75a which thus remains practically wide open. To stop the car, it is only necessary to let the accelerator pedal rise and apply the brakes. A sudden stop may leave the control piston advanced with the ports 71b, 71p both closed and the main clutch held engaged by entrapped oil so that the engine cannot be restarted. To prevent this, a release pedal 75f is provided preferably positioned for operation with the left foot in place of the conventional clutch pedal. Before starting the engine, this pedal is depressed causing a pin 75g to lift the accelerator pedal 74a against a stop 75e and thereby shift the valve sleeve 71i to bring the port 71k into register with the port 71f, thereby allowing the clutch and control cylinders 77, 71 to empty, disengaging the clutch and bringing the transmission to lowest speed. The relief pedal 75f may be the brake pedal.