Patent GB-653912-A (GB)
Title: Improvements in or relating to electrical apparatus for indicating cyclically varying phenomena in an internal combustion power plant
IPC: G01M15/12
Filed: 1948-05-12
Abstract: 653,912. Testing ignition and working conditions. SPERRY CORPORATION. May 12, 1948, No. 13038. Convention date, May 15, 1947. [Classes 7(ii) and 7(iv)] [Also in Groups XXXVI and XXXVIII] For indicating cyclically varying phenomena in an internal combustion power plant by means of a cathode ray oscillograph switching devices are provided, one for each engine of the power plant, that have as many switching positions as there are engine cylinders, and each of which serves to select for display, or for display in a particular portion of the sweep path of the electron beam, the phenomena associated with the firing period of one or another of the engine cylinders. As shown the oscillograph 39 indicates the primary magneto voltage or the vibration pick-up voltage of one or more aircraft engines as ordinates and timing' degrees as abscissa, the abscissa being synchronised' with the actual rotational position of the engine crankshaft by means of a trip action sweep generator circuit controlled by means of individual engine driven switches. Connections are shown to one of the magnetos 20 of a dual magneto power plant, the voltage across the primary 23 of which is applied through switches 40, 34 to the vertical deflection plates 48, 49 of the oscillograph 39. Vibration pick-ups 50, 51 are mounted on each cylinder and the voltage output is also applied to the plates 48, 49 through the switches 40, 34. A multiple selector point engine driven switch 32 is individually provided for each engine and has as many selector points as there are cylinders for the engine. This switch is used to trigger a time-base circuit 38 which initiates a time-base sweep only when effective contact is made with a predetermined selector point. The switch 32 is connected to a section 33 of the switch 34 which selects the point in the engine timing diagram at which the sweep is initiated and thus determines the initial point of the timing diagram to appear on the screen. The other section 35 of the switch 34 selects any chosen cylinder vibration pick-up for observation, and the section 33 thus determines the portion of the engine diagram to appear on the oscillograph screen. The speed of the sweeping beam may be varied so that it traverses a sweep across the screen once per whole cycle or per fraction of a cycle as desired, by varying the time constants of the sweep circuit 38, e.g. by switching a capacitance in or out by a push-button 37 actuating a switch 37<SP>1</SP>. The sections 33, 35 of the switch 34 may be locked together by means of a friction coupling or a pin coupling so that both sections may be rotated simultaneously to observe a particular function (e.g. combustion), of each cylinder in turn. The switch 40 is used to select for observation the desired engine of the aircraft and the condition for which the performance of the engine is to be tested and analysed. By means of leads 41 the switch 40 is connected to any desired magneto primary through a protective resistance 42 to earth. Any departure from normal operation of the ignition system alters the shape of the voltage-time curve on the oscillograph. By observing these characteristic patterns it is possible to detect and locate faults such as fouled spark plug, open or short circuit in ignition system or magneto condensers, improper breaker adjustment, setting of spark plug gaps, or low output magnetos. Specification 598,360, [Group XXXIX], is referred to.