Patent GB-958382-A (GB)
Title: Improvements in or relating to regulator means for variable ratio transmissions
IPC: F02D9/00
Filed: 1960-11-03
Abstract: 958,382. Change-speed control. INTERNATIONAL HARVESTER CO. Nov. 3, 1960 [Nov. 4, 1959], No. 37813/60. Heading F2D. [Also in Divisions B7, F1, G3 and H2] Variable ratio control mechanism applicable to continuously-variable-ratio or stepped-ratio mechanical gearing or to hydraulic gearing such as an hydrodynamic torque converter having stator blades of variable inclination, comprises an engine driven speed responsive means tending to produce a lower transmission ratio with decreasing engine speed and a higher transmission ratio with increasing engine speed, the device being so constructed as to maintain substantially constant the speed of a power take-off driven directly from the engine and separately from the transmission. Small fluctuations of engine speed within a predetermined range of engine speeds do not effect ratio shifts. The control mechanism may work mechanically, electrically, or by fluid pressure means. In one form, in a tractor an engine driven speed responsive device 11, Fig. 4, has a fixed flange 34 and an axially slidable flange 32 between which balls 33 are acted upon by centrifugal force to move radially outward against the bias of springs 12 and slide a ratio regulating rod 21 axially. The compression of the springs 12, and hence the engine speed at which ratio control becomes effective, is adjusted by a hand actuated rod 8 and a lever 84. The fuel injection pump control rack 9 or the carburetter throttle of the engine is biased in the direction to increase engine speed by a spring 30, movement in the engine speed increasing direction being limited by a stop 10 adjustably positioned by a hand control 7. With increasing speed of rotation of the engine driven shaft 34 and the consequential rightwards movement of the flange 32 of the speed responsive device 11, a stop 36 on the injection pump control rack 9 &c. is engaged by the flange 32 and moved against the bias of the springs 30 in such a direction as to decrease engine speed. In the form shown, the ratio control rod 21 acts through a double cam 26 and followers 55, 56 upon two switches 15, 16 controlling a circuit, Fig. 8, which energizes a reversible electric motor 14, Fig. 6, to rotate a screw 61 carrying a nut 60 acting through a link 62 upon a shaft 66 controlling the angle of inclination of the stator blades of an hydrodynamic torque converter in the transmission of the tractor. Alternatively, the rod 21 may act mechanically or through fluid-pressure servomotor means to achieve the same effect, and may act upon mechanical gearing of either stepped or stepless ratio type. The cam 26, Fig. 4, comprises steps 48, 49; 50, 51 with dwell points 52, 53 in between, the steps of the cams being off-set axially with respect to each other. The switches 15, 16, Fig. 8, in the circuit shown control the motor 14 in conjunction with limit switches 17, 18 opened mechanically when the nut 60, Fig. 6, reaches the end of its travel in either direction. The off-set cam surfaces 48 . . . 52 are so arranged that when both followers 55, 56 are, e.g. on the steps 48, 50 as shown, then the switches 15, 16 are conditioned as shown in Fig. 8 to make the circuit so that the electric motor 14 drives in such a direction as to give a reduced transmission ratio. However, with increase in engine speed, the rod 21 is slidden axially so that the follower 56 slides off the cam step 50 into the dwell point 53, this happening before the follower 55 slides off the cam step 48 into the dwell point 52. While the followers 55, 56 are in this condition, the switches 15, 16 are so actuated that no circuit is made through the motor 14, whioh accordingly remains stationary. With further rightward movement of the ratio control rod 21, accompanying further increase in engine speed, the follower 55 slides into the dwell point 52 on the cam 26, so that the two switches 15, 16 are again closed for energization of the motor 14, which now drives to give an increasing speed ratio. If the engine speed increases still further, the consequential continuing rightwards sliding of the rod 21 ultimately causes the follower 56 to ride out of the dwell point 53 on the cam 26 on to the step 47, this preceding similar motion of the follower 55. Again the ratio control motor 14 is de-energized and no change in ratio takes place. At this engine speed, the speed responsive device 11 will become effective to move the fuel injection pump rack 9 &c. in a direction to cut-off fuel supply to the engine. Should the engine speed increase still further, as by overrun of the tractor containing the transmission, then the rod 21 is slidden still further rightwards of Fig. 4 and the follower 55 rides out of its dwell point 52 in the cam 26 on to the step 46, again conditioning the two switches 15, 16 to close a circuit through the ratio control motor 14, which now rotates to give a step-down in ratio, with consequential increase of engine braking. Actuation of the hand controls 7, 8, Fig. 4, to adjust the maximum power obtainable from the engine through positioning the injection pump control &c. 9, and the compression of the spring 12, enables the control mechanism to be so adjusted that the engine works at maximum economy. A power take-off shaft 19, Fig. 7, is provided to take power from the engine before it reaches the variable ratio transmission controlled by the device. Power to drive the road wheels of the tractor mounting the transmission is then taken through gearing 20. The change-speed control is effective to maintain the speed of the power take-off shaft substantially constant, variations in load applied by the road wheels to the engine causing fluctuations in ratio which retard or accelerate the tractor, the arrangement being such that, in fact, the tractor may be brought to rest while the speed of the power take-off shaft is maintained constant. In a further form, Fig. 9 (not shown), the ratio control mechanism is applied to an existing fuel injection pump, the centrifugal device 11 comprising pairs of balls between inclined surfaces and the switches 15, 16 being contained within a casing fast with the casing of the ratio control mechanism.