Patent GB-1177328-A (GB)
Title: Process for Minimizing Tyre Deflection Variation
IPC: G01M17/02
Filed: 1968-05-08
Abstract: 1,177,328. Grinding vehicle tyres. FORD MOTOR CO. Ltd. 8 May, 1968 [11 May, 1967], No. 21774/68. Heading B3D. [Also in Division B7] A process for minimizing deflection variations of a loaded vehicle tyre made at least in part of elastomeric material comprises: (a) mounting the tyre on an axle so that the tread contacts a loading means, (b) loading the tyre to a load sufficient to deflect the tyre, (c) rotating the tyre so that different portions are deflected by the load of the loading means, (d) measuring the variation in deflection of each portion as that portion is deflected by the loading means, and (e) removing material from the tyre to minimize the variation in deflection. An inflated pneumatic tyre 10 is mounted on a metal rim and hub assembly 16 fastened to an axle 18 rotatable in bearings 20, 22. A loading roll 26 has its axle 28 supported in bearings 30, 32 and rotated by an electric motor 49. Bearings 30, 32 are connected to pistons 34, 36 located in hydraulic cylinders 38, 40 connected to a fluid-pressure source. A grinding wheel 50 is positioned near the tyre tread 14. Grinding wheel 50 has a concave grinding surface 52 shaped to the desired crown of the tread; the wheel axle 54 is mounted through gimbals 56, 58 to bearings 60, 62 and is driven by a motor 64. Bearings 60, 62 are connected to pistons 66, 68 located in hydraulic cylinders 70, 72 with which are associated control valves 86, 106. Cylinders 70, 72 are connected to pistons 74, 76 located in hydraulic cylinders 78, 80 with which are associated control valves 116, 126. Pressure transducers 46, 48 located in cylinders 38, 40 to sense the fluid pressure in each cylinder are connected to inputs 132, 134 of a magnetic storage drum 24 fastened on the axle 18. Outputs 136, 138 positioned around the drum to pick up the signals stored on the drum by the inputs are connected to control valves 116, 126. Position sensors 140, 142, located rotatably anterior to grinding wheel 50 to sense the positions of the shoulders 13 as they approach the grinding wheel, are connected to control valves 86, 106. Operation.-Hydraulic fluid is pumped into cylinders 46, 48 to move loading roll 26 against tyre tread 14 with a force sufficient to deflect the tyre. The roll diameter must be sufficient to simulate the deflection produced by a road surface; the diameter may be approximately equal to the tyre diameter. The distance between axles 18, 28 necessary to obtain the desired load for a given tyre size is determined empirically and hydraulic fluid is pumped into cylinders 46, 48 to achieve this distance at each side. Motor 49 rotates roll 26 to rotate tyre 10, e.g. at 3 r.p.m. As each sector of the tyre comes into contact with the loading toll that sector deflects under the force applied by the roll. Variations in deflection laterally across the tyre and from sector to sector result in signals from transducers 46, 48 which are applied to drum 24. When the tyre has rotated approximately 180 degrees the signals are removed from the drum and applied to control valves 116, 126 to position grinding wheel 50 so that it removes material from those portions having high deflection. Due to the sensors 140, 142 no correction for run-out is effected. Erase heads are located on drum 24 posterior to outputs 136, 138 but anterior to inputs 132, 134 to permit continuous signal transmission from transducers 46, 48 to control valves 116, 126. A prior deflection sensing operation is usually used to determine whether the deflection variations can be corrected without removing large amounts of material that would damage or otherwise decrease the life of the tyre. A supported belt can be used instead of the roll for loading. Magnetic tape or any other data storage devices can be used instead of the magnetic drum. Deflection variations may be measured at one stage of an assembly line and tyre material removed at a later stage. Electrical or electromechanical means may be used instead of hydraulic means for positioning the grinding wheel. Position sensors (linear transducers) may be used instead of pressure transducers 46, 48. The grinding wheel may be more concave so that material is removed only from the tyre shoulders, or a smaller grinding wheel may be located on each side of the tyre to remove material from the side walls or shoulders. The load may be within 25% of the service load; for higher quality tyres, the load is within 10% of the service load, the latter being preferably the weight of the vehicle containing its average load.