Patent GB-865570-A (GB)
Title: Speed ratio governor
IPC: F16H47/06
Filed: 1958-01-27
Abstract: 865,570. Change-speed control. TWIN DISC CLUTCH CO. Jan. 27, 1958 [July 1, 1957], No. 2674/58. Class 80 (2). A mechanism for detecting a change from a predetermined speed ratio between a pair of shafts comprises a screw 27 and nut 30 driven synchronously with the respective shafts and at the same speed when at said speed ratio, whereby any change from said speed ratio causes axial movement of the screw 27. As shown applied to the transmission of a tractor, power shovel, truck or locomotive, the pair of shafts are the input and output shafts of an hydraulic torque converter and the axial movement of the screw 27 operates a valve causing shift in a following two-speed constant mesh gear having clutches, operated by pressure air, liquid or mechanically, the shift taking place automatically at a predetermined point on the efficiency-speed ratio curve of the converter to maintain maximum efficiency of the latter. Two such mechanisms may (Fig. 7, not shown) be used to control two shifts, one on each side of the peak of the efficiency curve of the converter. The screw 27 and nut 30 are driven through gears, chains or belts at 16, 15 respectively, the drive connections to the nut 30 including a permanent magnetic coupling 23, 30 with or without air gap, which slips after axial movement of the screw. The valve operated by the screw controls the gear shift through a snapaction valve 50 and relay valve 69. Pressure oil is supplied by a pump 62 to a chamber 60 and through a throttling orifice 65 to passages 45 . . . 48 and hence returned to a sump. When, at the predetermined shift point, the speed of the valve 27 drops below the speed of the nut 30, the valve 27 is moved left, closing ports 39, 40 and thereby arresting flow in the passages 45, 46 and throttling the flow through the port 41 which throttling raises the pressure in the passages 45, 46, 47, 66 and in a passage 54 to move the snap-acting piston 50 right against a pin 57 biased to the left by the pressure in the chamber 60, to close port 52 and finally to close with a snap-action a port 53 against a joint resistance from the pin 57 and a sleeve 58. Hence the pressure in the passage 66 rises rapidly and shifts a relay valve 68 to engage a high gear clutch for effecting upshift. When the torque converter speed ratio rises above the shift point the above sequence reverses and the low gear clutch is engaged for downshift. In Fig. 6 (not shown), the nut is geared to the armature of the magnetic coupling to provide a fixed speed ratio therebetween. In Figs. 7 to 10 (not shown), two screw-nut units as above are connected in parallel by gearing giving different fixed ratios to provide an upshift and downshift at two different predetermined ratios. The shift pressure signals operate a frictionally-located valve 193, Fig. 11, which, as shown, is in its rightward setting for high speed ratio, an air supply 205 being connected to the high gear clutch line 204 and low gear clutch line 203 being exhausted at 206. When, due e.g. to increased load the converter speed-ratio increases to the lower shift point the low speed screw-nut unit pressures, as above described, a line 181 and pressure passes through a non- return valve 195 to shift left the valve 193, exhausting the high gear clutch line 204 and pressurizing the low-gear clutch line 203. When on reduced load, the converter speed-ratio reduces to the upper shift point the high-speed screw-nut unit pressures a line 188 and shifts the valve 193 back to the position shown for high gear. Fig. 12 (not shown), gives an efficiency vs speed-ratio curve for the torque converter, with lower and upper shift points at ratios of 0.3 and 0.75 respectively on each side of the curve peak.