An indicator claimed to be the only known device for certain and economical obtainment of composite indicator-diagrams depicting power, offset and lower-loop effects on high-speed multi-cylinder internal-combustion engines is described, the broad field of usefulness for such an instrument in furthering the development of high-speed engines by enabling accurate investigation of the processes within the engine cylinders having long been apparent, since the ordinary indicator fails at engine speeds above 300 r.p.m. due to inertia effects on its pencil mechanism and its drum. Because of the great need for obtaining accurate indicator-cards at high engine-speed, it was determined to construct a device that would produce diagrams having little or no inertia effect included, from the cylinders of an engine operating at any speed, and to make these diagrams available for analysis immediately, without recourse to photographic or other processes.
Briefly, a standard slow-speed indicator having a drum 1½ in. in diameter is coupled directly by a standard union to the part of the device that has inside it a small poppet-valve which is opened for a very small interval of each cycle of the engine and which, when opened, completes communication between the manifold of the engine and the indicator. The indicator cylinder is filled with heavy lubricating-oil to provide a proper seal for the indicator piston and minimize gas transfer to or from the engine cylinder during each engine cycle.
Drum motion is controlled by a string threaded over a pulley and connected to a crosshead of the device which can be considered a replica of the engine piston but which moves through one stroke only for each 800 strokes of the engine piston and imparts a very slow back-and-forth movement to the indicator drum, thus nullifying inertia effects. The crosshead is controlled by a connecting-rod adjustable as to length and a graduated crank-disc, forming a train having exactly similar characteristics to those of the train that controls the engine piston. Since the connecting-rod can be varied in length, the ratio of the rod and its crank-disc can be made precisely the same as the ratio between the corresponding parts of the engine. The crosshead guide can be adjusted to simulate the offset of cylinders, if such offset exists, and the device can be made available for use on all types of internal-combustion engine and for connecting-rod to crank-throw ratios varying between 3¾ to 1 and 5½ to 1.
A shaft on the device passing vertically upward from another shaft driven at engine-speed turns at one-half engine-speed. The horizontal shaft carrying a hand crank is driven, when the clutch is engaged, at 1/40 engine-crankshaft speed. This horizontal shaft drives the vertical shaft to which the graduated crank-disc is attached through worm-gearing having a reduction of 20 to 1; so, with clutch engaged, this disc is driven by the engine at 1/800 of engine-speed and actuates the connecting-rod of the device. With the clutch disengaged, the graduated crank-disc can be operated by the hand crank in either direction.
Details and illustrations of the construction, application, procedure, and operation are included. This indicator has been in successful operation for more than 500 hr. of testing and research work at Ohio State University. The composite indicator-diagram obtained over a great number of engine cycles which, individually, are generally not alike, is claimed to be a distinct gain over anything else yet tried, since the diagram is built-up before the eyes of the testing engineer.


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