Patent GB-472317-A (GB)
Title: Improvements in or relating to transmission dynamometers
IPC: G01L3/10
Filed: 1936-02-21
Abstract: 472,317. Magnetic tests. MUIR, N. S. Feb. 21, 1936, No. 5273. [Class 37] [Also in Group XIX] Two springs forming part of a power transmission system and connected in series with one another are arranged between the driving and driven members one spring being damped, and the deflection of the other being measured by magnetic means. Keyed to the engine shaft A between the engine and the boss A<1> of an air screw is a hub B having formed integral therewith radial blade spokes B<1> springy in a plane perpendicular to the axis of the shaft. The outer ends of the spokes B<1> are connected to an annular rim B<2> which may be integral with the spokes but as shown is provided with slotted rotatable trunnions B<3> to receive the ends of the spokes. The rim B<2> has rigidly connected thereto a set of inwardly projecting radial spokes B<4> interleaved between spokes B<1>, as shown, two spokes B<4> between each spoke B<1> and the next. The inner ends of the spokes B<4> unite to form a boss B<5> attached by bolts B<6> to an annular flange A<2> on the air screw boss. The springs B<1> are damped by two frusto-conical brake rings C, C<1> connected to hub C<4> keyed to the shaft A and to the rim B<2> respectively. The damping is adjustable and may be automatically relieved by the air screw thrust. Deflection measurement. Between the rim B<2> and boss A<1> is connected the means for measuring their relative rotation This is preferably electrical as described in Specification 472,313. An annular plate D of laminated magnetic material rigid on a non- magnetic ring D<1> connected to bosses B<5> has six radial arms D<2> each formed rigid with an arcuate cross member with ends D<3>, D<4> forming poles co-operating with armatures D<5> mounted on an annular spider E bolted to the rim B<2>. Each arm D<5> is laminated and of T-shape. Air gaps F, F', and F<2> are thus formed. Angular movement between inner ends of spokes B<4> and the rim B<2> lengthens one gap F and decreases the other F<2>. These systems are magnetized by alternating current from a source G, Fig. 5. Primary coils E are arranged so that each armature D<5> forms part of one magnetic system, and each system has two circuits. The coils E<1> are connected in series and the secondary coils E<2> are connected in opposition in pairs as shown, the units being arranged alternately. When the air gaps are equal there is no secondary output, but when they differ due to torque a current passes. The opposed pairs E<2> are connected in series so that the voltages are additive and when the applied voltage is constant the output may be measured by a voltmeter calibrated in terms of torque. Oscillations of the apparatus in the plane of the paper produce variations in the width of the gaps F<2>, but with the symmetrical arrangement shown these cancel each other out. The connections to the coils are made through slip rings H, H<1>, H<2>, H<3> mounted on a tubular member H<4> arranged to rotate with the shaft A. The indication is preferably effected by a null method. The deflection measuring apparatus is duplicated as shown in Fig. 5. regarding the first apparatus as "transmitter" it is connected as shown to another system made with similar characteristics mav be termed the receiver. The air gaps in this are varied by hand preferably through a reduction gear. When no torque is transmitted the instrument C<1> gives no reading but when torque is transmitted a reading is given and the instrument brought each to zero by rotating the armature carrying elements relatively to the polecarrying elements.