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).
Function and practicality of suction operated ignition control.
Identifier | ExFiles\Box 133\2\ scan0139 | |
Date | 8th February 1935 | |
To E.{Mr Elliott - Chief Engineer} Suction Operated Ignition Control. The function of controls of this type is to advance the ignition when the car is running under partially closed throttle conditions. Theoretically, suction and speed operated controls working in conjunction should give the most economical spark advance under any engine conditions. In practice, the economy due to suction control does not appear to be realized. We attach curves showing the characteristics of the Delco-Remy control on the Graham cars. The connection to the suction control unit is taken from a point which is on the throttle edge for small throttle openings, but which is clear of the throttle on the upstream side when the latter is closed. The suction operating on the control is therefore a maximum when the throttle is open sufficiently to maintain a speed of 35 m.p.h. on a level road, and falls at openings greater and less than this. Careful road tests made on the car, both under constant 35 m.p.h. and "give and take" conditions, have revealed that the control has no effect on fuel economy. We attach figures showing the results of these tests. At middle speeds the Bentley engine requires about 12° more advance at 1/4 load than at full load for maximum power. As shown on the attached curves, however, the power drop which results from fixing the ignition at the best for full throttle is only 2% at half load and 3% at quarter load. In view of the foregoing we do not anticipate that we shall get any appreciable benefit from the use of suction ignition controls on our cars. What the Americans gain is also problematical. Hs{Lord Ernest Hives - Chair}/Smth. | ||