Patent GB-539451-A (GB)
Title: Electrical speedometers
IPC: G01P1/04
Filed: 1939-12-11
Abstract: 539,451. Speedometers. STEWARTWARNER CORPORATION, and NORMAN, H. M. Dec. 11, 1939, No. 31972. Class 106 (iii)] [Also in Groups XXXVIII and XXXV] An electrical speedometer comprises, Fig. 11, a sending unit 10, in the form of a permanentmagnet rotor for generating 3-phase current in a set of star-connected fixed windings 22, 24, 26, a set of leads 14, 16, 20, and a receiving unit 12 in the form of an induction rotor operating an indicator needle against spring-control and a further set of fixed star-connected windings 32, 34, 36. The sending unit is located near the vehicle-engine and the indicating unit in the driver's compartment and means are provided for compensating the apparatus for the effects of temperature-change on the magnetic permeability and conductor resistance. The lead 20 is also utilized for the circuit of an odometer comprising a solenoid 76 operating a pawl and ratchet counter battery 82, a switch 84 (which may be the ignition-switch), and contacts 192, 194 operated by an engine-driven cam 196. Negative-temperature co-efficient resistances 38, 48, 58 are connected in the three leads and located as shown, one lead including also a zero-temperature co-efficient resistance 66, while a positive-temperature co-efficient calibrating resistance 68 with adjuster 70 shunts two of the indicator-windings. Fig. 1 shows the sending unit comprising a housing with compartments for the generator and the resistances 38, 48 and odometer cam 196 and contacts 192, 194 the housing being located adjacent the engine. A shaft 104 driven by the latter has a detachable coupling at 164 with a shaft 128 on which is a non-magnetic bushing 130 carrying the rotor. The latter has a disc-like part 138 having upstanding poles 140 and is formed by punching and stamping. Part of its flux is shunted by a ring 141 of Simond's or "Monsel" metal (the latter being a Registered Trade Mark) the amount being less at higher temperatures. Shaft 128 has bearing surfaces 142, 144 in a bearing 146 mounted in a bushing 150 carrying the armature laminations 170 which, Fig. 3, comprise a central hub 180 carrying nine T-shaped teeth 182 carrying the windings 22, 24, 26. The end of shaft 128 carries a worm gear 222 which by means of a further gear 224 rotates a shaft which in turn rotates the camshaft 206 through gearing 228. Fig. 7 shows the indicator unit comprising a compartmented casing for the resistances, motor, and indicator proper. The calibrating resistance 68 is wound round a wider insulating strip 278 and provided with a pivoted contact-carrying calibrating arm, Fig. 8 (not shown). The fixed windings 32, 34, 36 are distributed in the form of three pair of seriesconnected coils over six slots, Fig. 9 (not shown), in laminations 306 mounted with insulating plates 308 on the hollow end 312 of a shaft 300 secured in a bushing 292 by a nut 304. The windings produce a rotating magnetic field which acts on a cup-like rotor 40 mounted by means of a flanged bushing 330 on a shaft 328. The return flux passes through laminations 324 held in place by indented parts 326 of the housing. The shaft 328 carries a needle 372 and also has fixed to it one end of a hairspring 354, the other end of which is fixed to an adjusting member 358, the spring tending to hold an arm 336 on the rotor 40 against a stop 338. The resistances at the sender are designed to over-compensate for variations in winding- resistance produced by ambient temperature, the effect of the over-compensation being to compensate for the decrease in magnetism of the permanent-magnet rotor at high temperature and hence the resulting decrease of armature current. For very high temperature, at which the co-efficient falls off, further compensation is provided by the ring 141 which shunts less of the flux away from the rotor. The resistance 58 acts to undercompensate, but in combination with resistance 68 which shunts less current at high temperature due to its positive co-efficient, the effect is to overcompensate. Resistance 66 affects the ratio of resistance to reactance and hence the shape of the deflection/speed curve. Figures of resistance values are given in the Specification. A modified form of stator, Fig. 13, employs laminations having a hub 402 and radial parts 404 branching into parts 406, 408 so as to provide slots 412, 414. Each winding comprises an inner part, as 418, wound on a radial part 404 and connected in series with an outer part, as 416, all the inner parts being connected to a star point 428.