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).
Programme outlining tests and modifications for a single-cylinder unit, focusing on back pressure and camshaft design.
Identifier | ExFiles\Box 134\2\ scan0127 | |
Date | 27th August 1937 | |
CHASSIS SINGLE CYLINDER UNIT The following is the programme it is intended to follow on the above unit. As soon as possible we are anxious to try out a head and block of the type to be used on the full scale Phoenix, but in the meantime a few smaller points can be cleared up. (1) Back Pressure Tests. Tests which have to date been run on the single cylinder unit tend to indicate that exhaust valve timing has a great effect on the power loss at back pressure, a long duration being superior. It has also been suggested that the following points might influence the response to back pressure. (a) Rate of exhaust valve opening, the existing one being too fast. (b) Valve overlap, and its relation to blow by.{R.W. Bailey - Chief Engineer} We should therefore like an exhaust camshaft for the single cylinder unit, which will give us a longer duration than the present one, and in order that existing cam formers may be used, suggest the Ph.II. exhaust form, with a duration of 240°. Further, to check on the first of the above items, the construction of the single cylinder valve gear lends itself to giving the valve the impression of a slow lift with a rapid return. The duration control is effected by varying the angular velocity of the camshaft, and at present phasing is such that the peak of the valve lift curve occurs at a change over speed of the camshaft, giving a symmetrical diagram. If, however, a new camshaft were made with the keyway displaced through 90°, the cam would be subject to a steadily increasing angular speed throughout the valve lift, giving the effect desired. We should be glad, therefore, if cams could be made with this modification. This scheme could, of course, be improved by making serrations instead of a key way, when any desired camshaft position could be adopted, but as the altered position of the keyway involves only one new part, we should like to try this first. continued | ||