GB1132473A - Variable ratio friction transmission and control system therefor - Google Patents

Abstract

1,132,473. Variable-speed friction gear and control; gearing for stopping and starting machinery. J. R. YOUNG. 15 Nov., 1965, No. 48456/65. Headings F2D and F2L. in a continuously variable friction gear, particularly for an automotive vehicle, driving and driven discs 30, 32, respectively rotatable about the axis of, and secured to, shafts 28, 34, have mutually facing surfaces frictionally engageable with substantially point contact 96, and the distances from the centres of the disc surfaces to the cantact point are both variable throughout ranges at least equal to major portions of the respective radii of the discs. Gear arrangement. - The driving disc 30, serving as the flywheel of a driving engine 26 and preferably provided with starter teeth, has a spherical engagement surface of large radius. The engagement of surface of the driven disc 30 may be plane as shown, or, where the relative angularity of the shafts 28, 34 is maintained nearly or exactly constant, may comprise a central plane portion surrounded by an annular surface revolution generated by an arc (Fig. 15, not shown). The discs 30, 32 are preferably metallic and their engagement surfaces are unyielding, being metallic or ceramic. The shafts 28, 34 are respectively rotatably mounted in an outer housing 22 and an inner housing 24 movably mounted therein. Below and parallel to the shaft 34 an output shaft 36 is rotatably mounted in the inner housing 24 and projects rearwardly from the outer housing 22 through a flexible seal 38 between the two housings. The output shaft 36 is connected to the rear road wheels through a universal joint, a telescopic propeller shaft and the usual differential, and is located where relative movement of the two housings axially of the output shaft 36 is at a minimum. An engageable and disengageable driving connection between the shafts 34, 36 comprises stepped planets 66, 68 respectively meshing a sun 56 fast with the shaft 34 and a sun 58 geared at 60, 62 (if required, through an idler) to the output shaft 36. The steps of each planet have only slightly different pitch diameters and either one may be the larger. The planet carrier 64 drives an eccentric gear pump 40, the output of which is (1) progressively throttled to restrain the carrier and thereby provide a drive to the output shaft, and (2) provides an output torque responsive fluid pressure used for a disc traction pressure loading as described below. To provide for torque reversals, the pump is provided with suitable check valves. The disc traction pressure or loading means comprises tiltable cam members 84 between races 78, 80 urged together by springs 82 and respectively fixed to the inner housing 24 and acting axially on the shaft 34 through ball-bearings 86. The race 80 has teeth meshing a rack 88 which is moved to rotate, and hence axially move, the race 80, and load the discs, by fluid pressure acting on a Loader Actuator 44 connected to the rack. The inner housing 24 may be so moved as to move the disc contact point 96 through Reduced Reverse range and Reduced, Direct and Overdrive Forward range positions. For Reverse range the contact point 96 is between the centres of the driving and driven disc centres whilst for Forward range the surface centres are on the same side of the contact point, the latter lying substantially on a line extending through said centres. Between the Forward and Reverse ranges there is a non-driving position which is referred to as the "Re-Zero" range, and in this position, in the immediate vicinity of the centre of the driving disc, the discs are disengaged, as described below, to prevent overheating. For guidance in its movement, the inner housing 24 has three follower rollers 50 engaging three track grooves 48. The inner housing 24 is movable for ratio change by a gear (112) meshing teeth 110 on said housing. The Specification includes details (Fig. 9, not shown) of means by which the track grooves 48 and the teeth 110 may be cutter-generated to meet the desired relationship of the distances from the disc surface centres to the point of contact throughout the movement of the inner housing. A power take-off 54 comprising a telescopic shaft and universal joints connects the output shaft 36 to the exterior of the outer housing and may drive a combined speedometer and odometer and an output pump 190 for the control system described below. Whilst the inner housing 24 and the control system both use the same fluid having good lubricating qualities, the space between the inner and outer housings contains a low lubricity coolant fluid to achieve a high coefficient of friction between the discs. CONTROL. Summary of main functions.-The control of the gear is combined with that of the engine carburetter throttle (210) so as to adjust the gear ratio so as to permit the engine to be operated at the most economical speed at which it will develop the power desired by the operator and is also combined with that of the conventional hydraulic braking system (338) so as to downshift the gear at such a rate as to produce a vehicle retarding effect in proportion to the rate the operator desires to resist the vehicle motion. Between zero output power and a fraction of the engine maximum power output, the engine speed increases somewhat above its idling speed depending upon the specific engine design while the throttle changes from the minimum opening to full opening. Between the above-mentioned fraction of maximum power and the maximum power, the throttle opening remains at its full position while the power developed increases in proportion to engine speed. The throttle opening is automatically reduced when engine speed exceeds a limit. Means are provided for engine starting by pushing or towing the vehicle or by permitting down-hill vehicle motion. Until the engine commences normal power development a vehicle control pedal (260) may influence the gear ratio to modify starting. In the changeover from Forward to Reverse range and vice versa the discs are automatically separated in the "Rezero" range. Other functions are mentioned below in connection with the control system components. Operator's control inputs include:-The vehicle control pedal (260) actuating a Power Selector Cam (264) and, through a Linkage Telescoper (258), the Carburetter Throttle (210); the pedal being fully released for Deceleration and depressed slightly to a point offering a sharp increase in resistance to pedal movement to commence its Drive movement the first part of which opens up the Throttle; a Neutral- Forward-Reverse Drive Selector Lever (186); an Electrical Starter Switch; a Brake Pedal for the conventional hydraulic braking system (338); and a Push Start Lever (398). Control system components: Engine Driven Pump (160): piston, gear, vane or roller, positive, fixed displacement pump driven in direct proportion to engine speed. Output Driven Pump (190): positive, fixed displacement pump driven by the power takeoff 54. Engine-Speed-Variable Orifice (162): provides a pressure drop increasing with flow but at a rate less than that with a fixed orifice, and on excessive engine speed directs flow to an Engine Throttle Decreaser (164). Vehicle-Speed- Variable Orifice (394): pressure drop as orifice 162, and on excessive vehicle speed directs flow to the Engine Throttle Decreaser (164). Shift-Lock-and-Starter Interrupter (176): responsive to both engine and output speed pressures to lock the Drive Selector Lever (186) and break the starter circuit. To allow shifting at higher speeds when the temperature is unusually low, an engine temperature responsive mechanism may be included. Slip Pump Throttle (192): responsive to engine speed pressure to control Slip Pump flow, the Throttle gradually closing to establish drive through the gear on increase in engine speed, and to a signal from a Push Start Shift-up switch valve (202). Excess Torque Switch Valve (204): responsive to Slip Pump pressure to direct the latter to the Engine Throttle Decreaser (164). Engine Throttle Decreaser (164): reduces engine power to protect against excessive engine speed, vehicle speed and torque, and damps throttle movement. Neutral Switch Pressure Regulator (220): spring-biased to regulate engine speed pressure for supply to a Drive-Decelerate Switch Valve (226), and shifted in Neutral by the Drive Selector Lever (186) to exhaust both the engine pump flow and a traction pressure Pre-Load line (320). Position -Proportional Pressure Generator (240): in forward drive modifies Slip Pump pressure as a function of the contact radius of the driven disc 32 by shifting a helically grooved piston as a function of the position of the inner housing 24; in Reverse drive provides unmodified Slip Pump pressure. Loader Pressure Regulator (254): regulates Slip Pump pressure in response to pressure from the Position-Proportional Pressure Generator (240) for supply to the Loader Actuator 44, and blocks Slip Pump pressure and exhausts said supply to the Loader Actuator in Neutral. Loader Actuator 44: a double piston means responsive to both the Pre-Load pressure in the line (320) for initial disc driving contact for minimum tractive effort, and to pressure from the Loader Pressure Regulator (254) for torque responsive traction pressure. Drive-Decelerate Switch Valve (226): responsive to the position of the Power Selector Cam (264) to switch pressure from the regulator (220) between (a) a Deceleration-Downshift-Rate selector (312) and, through a check valve 314, the Pre-Load side of the Loader Actuator 44, and (b) a Ratio Change Determiner (316) and said Pre-Load side. In the "Re-zero" range, pressure in an override line from a Ratio Range Switch Valve (304) blocks flow from the regulator (220) and Pre-Load pressure is exhausted. Power Selector Cam (264): provides a mechanical position signal, as a function of the engine power desired, to the Ratio Change Determiner (316) and