Patent GB-947208-A (GB)
Title: Improvements in or relating to time sweep indicating arrangements
Inventor: HUNT JOHN CHARLES
IPC: G01M15/06
Filed: 1959-07-23
Abstract: 947,208. Cathode-ray oscilloscopes. STANDARD TELEPHONES & CABLES Ltd. July 22, 1960 [July 23, 1959], No. 25266/59. Heading H4T. [Also in Division G1] Relates to indicators for compression-expansion reciprocating machinery having no rotating parts. According to the invention a displayed distance scale is produced by an oscillating plate having a centre of oscillation as its centre of curvature and adapted to be fitted to oscillate with an oscillating member of the machine, the periphery of the plate being divided at least over its whole range of oscillatory travel into teeth so spaced apart as to represent equal increments of travel of a reciprocating machine member coupled to the oscillating member, and an electromagnetic pick-up responds to the passage of the teeth. The invention is described as applied to a free-piston diesel engine composed of opposing pistons 1, 2 operating in line in a cylinder and linked by crossheads 5, 6 connected to rocking shafts 13, 14 and driving compressor pistons 7, 8. Oscillatory motion of rocking shaft 13 is used to provide an indication of the positions of the pistons between inner and outer dead points (I.D.P., O.D.P.); at I.D.P. and O.D.P. the diesel pistons are closest together or furthest apart respectively and vary with the load and the apparatus of the invention provides traces such as those shown in Figs. 5A . . . 5D, the millimetre distances being from a position representing " pistons touching " position. The wheel shown in Fig. 2 is attached to shaft 13 and carries teeth 1 ... 86 cut at varying angular positions around its periphery, the shallow slots corresponding to 10 mm. piston stroke intervals and the deep ones to 2 mm. intervals; and the arc 1-86 is made to correspond to at least the maximum piston stroke. The wheel carries projection X for triggering the trace and projection Y for position-marking, in co-operation with fixed magnetic pick-up heads. The wheel is aligned with the rocking lever such that when the diesel pistons touch slot 1 is directly under the pole tip of the stroke marker electromagnetic pick-up. Fig. 3 (not shown). The wheel is enclosed within a casing by means of a pair of concentrically mounted " phasing plates " each mounting normally to its surface a pick-up for co-operation respectively with the X and Y projections on the wheel face; the phasing plates may be locked in any angular position relative to the casing to enable " trigger " and " position " signals to become effective at any desired point in the engine cycle. To afford one effective triggering impulse per engine cycle a divide-by-two circuit as described in Specifications 693,950 and 722,673 is provided. Typical millimetre and indicator traces are shown, Figs. 6 and 7 (neither shown); and the millimetre trace may be interpreted so as to locate the I.D.P. and to assist locating the O.D.P. three shallow slots in succession are provided around tooth 41, Fig. 2. To obtain an approximately constant amplitude for the millimetre trace, the pick-up output is integrated. To avoid continual switching from the cylinder diagram to the millimetre trace and back again to identify the position of an event, the position may be marked on the cylinder diagram by deflection or intensity modulation.