From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Description of an apparatus designed to measure pressure variations within the combustion chamber of an internal combustion engine.
| Identifier | ExFiles\Box 165\4\ img040 | |
| Date | 28th March 1928 guessed | |
| 10 indicates a plug having its lower end threaded for reception on a threaded aperture 12 in a wall of the chamber within which it is desired to study the pressure variations. Our improved apparatus is especially designed to indicate pressure variations in the combustion chamber of an internal combustion engine, and we have indicated such chamber at 14. The plug 10 is provided with a central bore 16 the lower end of which is closed by a diaphragm 18. To the center of the diaphragm is rigidly secured the thrust member 20. The diaphragm 18 is secured to the plug 10 and the thrust member 20 in such manner as to provide gas-tight joints. We prefer to accomplish this by welding or brazing. The indicating mechanism is of the type known as a telemeter but in it we have embodied an improvement to be later pointed out. The indicating mechanism comprises a frame 22 within which carbon pile rheostats 24 and 26 are clamped between adjusting screws 28 and 30. Between the adjacent ends of the rheostats is located an arm 32 and to this arm is rigidly connected the thrust element 20. The arm 32 is relatively rigid and is preferably an integral extension of the frame 22. However, it is inherently flexible or yielding within narrow limits. The adjusting screws 28 and 30 are provided with conical heads as shown and between the heads and the end pressure pleates of the rheostats are interposed insulating members 34 preferably in the form of mica discs. The adjacent pressure plates are similarly provided with conical lugs engaging the yielding arm 32. If preferred the rheostats may be insulated from the arm 32 but we have preferred to include the arm in the indicating circuit in the manner to be described. 36 indicates a battery applying current through the conductors 38 and 40 and a variable resistance 42 to a wheatstone bridge indicated at 44. The arms 46 and 48 of the bridge include balanced fixed resistances in the usual manner. The arms 50 and 52 of the bridge include carbon pile rheostats 24 and 26 respectively. 54 indicates the bridging element connected at one end at a point between the arms 46 and 48 and at the other end to the adjacent ends of the carbon pile rheostats. This connection is preferably made through frame 22, arm 32 and the contacting pressure plates of the rheostats. In the bridging element 54 is interposed the oscillograph element which, as is well-known, produced movement of a mirror in synchronism with the current fluctuations in the conductor 54 causing a light ray to be projected on a travelling photographic roll. The apparatus operates as follows: Pressure variations in the combustion chamber 14 cause reciprocating movement of the thrust member 20 causing corresponding flexing of the arm 32 varying the pressure on the carbon piles and consequently the resistances in the corresponding arms of the wheatstone bridge. This in turn varies the potential at the rheostat and of the bridging conductor 54 causing a flow of current therethrough in either one direction or the other. This flow operates the oscillograph. By this means the rapid fluctuations of pressure in the -2- | ||