Demonstration of a variable compression ratio cylinder head.
| Identifier | ExFiles\Box 158\3\ scan0004 | |
| Date | 29th August 1939 | |
| 1345 To By. {R.W. Bailey - Chief Engineer} from Rm {William Robotham - Chief Engineer} /NRC. {N. R. Chandler} c. Da {Bernard Day - Chassis Design} /Jnr. {Charles L. Jenner} c. E. {Mr Elliott - Chief Engineer} Rm {William Robotham - Chief Engineer} /NRC. {N. R. Chandler} 2/MH. {M. Huckerby} 29.8.39. Mr. Bradburn of Wolverhampton called this morning on the introduction of F.B.S. He brought a 6-cyl. Morris truck with a special cylinder head fitted to the standard side valve petrol engine, the object being to provide a variable compression ratio with a constant compression pressure, for which he claims a saving of some 25% in fuel at light loads, and a substantial saving over the operating range of the truck under average running conditions. Briefly described, the device consists of a special cylinder head, having a piston working in a cylinder arranged vertically above each main cylinder, I would guess the dia. of the control cylinders at about 2". (See sketch). Each piston is controlled by a connecting rod mounted on an eccentric shaft running along the entire length of the engine, and a small angular motion of the eccentric shaft raises or lowers the pistons, thereby altering the C.R. On the engine shown, the rotation of the eccentric shaft is controlled by a tension spring working on the end of a torque arm, so that when the engine is at rest the pistons are at the bottom of their stroke, thus giving an abnormally high C.R. and a compression pressure approximating that at full throttle. As the throttle is opened, the rise in pressures acting on the control pistons causes a small rotation of the eccentric shaft against the pull of the spring, so that all six pistons rise together, thus reducing the C.R. and maintaining an approx. constant compression pressure, the "all out" C.R. being about the same as that of a normal engine. The eccentric shaft may alternatively be controlled by hand or other means, but as demonstrated, is entirely automatic. I saw the engine running, and when idling there was no movement of the eccentric shaft, the pistons remaining in the high compression position, but on opening the throttle the pistons rose a little and remained up during the period of acceleration. Mr. Bradburn claims that on this truck the fuel consumption has improved from 12 to 16 m.p.g. | ||
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).