Patent GB-607384-A (GB)
Title: Improvements in eddy current dynamometers
IPC: H02K49/04
Filed: 1946-02-01
Abstract: 607,384. Rotary-absorption dynamometers. WINTHER, M. P. Feb. 1, 1946, No. 3233. Convention date, June 17, 1943. [Class 106 (ii)] In a water-cooled eddy current dynamometer having an electromagnetic member provided with imbricated polepieces, and members secured to the stator to form a water-tight compartment surrounding the rotor, and at least one annular coil carried by the stator with annular sealing rings in the stator to prevent water contacting the coil, a plurality of annular belts of magnetic poles extends inwardly from the stator towards the rotor adjacent opposite sides of the coil, the latter producing a toric flux field passing through the rotor and stator and through adjacent belts of poles. The rockable stator S, carrying the magnetic poles, forms with the end plates 7 a water-tight enclosure for the rotor. The rotor R comprises end hubs 19 and a central spider 29 carrying two hollow cylindrical eddy current drums 31. The stator comprises two outer cylinders 41 into which are fitted intermediate rings 43, end rings 45, and centre rings 47. Each ring 43, Figs. 4 and 5, comprises an annulus of T-shaped section with the trunk 53 of the T radial, and in the spaces between the rings is an annularly wound field coil 57 protected from water by a welded sealing ring 61. The internal flange 51 of each ring 43 has teeth 63 formed thereon, the bases being of the same width as the trunk 51, but the upper parts being flared out, the ends 69 being flat, and the side edges chamfered at 67. The base area A+B of each tooth where it joins the trunk 51 of the ring 43 is 1.3 times the end area 71 of the tooth. - As shown in Fig. 4 the end areas of the teeth in adjacent rows overlap axially ; the teeth on the end rings 45, 47 similarly overlap. This produces high torque at low speeds. Water is supplied to the space between the rotor and stator from a manifold 89, supported by one end pedestal bearing 1, supplying a bank of flexible hoses 85 connected to a manifold 77. Pipes 75 fitted in holes 73 in the rings 43 pass through the manifold 77, the water passing through perforations 83 in the pipes. Each end plate 7 is dish-shaped at 95, and provided with a sump 99 connected by flexible hoses 105 and pipes to a suction pump. Aligned recesses at the bottom of the rings 43, 45, 47 allow any water that has leaked past the sealing rings 61 for the coils 57 to escape. The flow of water through the holes 73 is controlled to prevent the space between rotor and stator being filled, the water being repeatedly flung by the drums 31 of the rotor against the teeth 63 and splashed. back again on to the rotor before escaping at the end plates 7. Some water is thrown through openings 25 in end plates 21 of the rotor and escapes through holes 39 to the outside of the rotor, thus cooling the rear faces of the drums 31. The coils 57 are energized with direct current to produce toric flux fields F, the current in adjacent coils flowing in opposite peripheral directions so that adjacent bands of teeth 63 are of opposite polarity. To prevent damage to the dynamometer in case the drums 31 of the rotor overheat and distort, a feeler device adapted to operate a sensitive electric switch is arranged in one of the teeth 63 so that the end of the feeler is just clear of the rotor. The switch may operate an audible or visible signal, or cut off the. current to the ignition circuit of the engine under test if an engine of this type is being tested. Inspection holes may also be provided to enable the surface of the drums 31 to be seen. Specification 576,689 is referred to.