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).
Page from 'Automotive Industries' magazine showing various engine performance and characteristic curves with accompanying technical text.
| Identifier | ExFiles\Box 50\3\ Scan043 | |
| Date | 27th January 1921 | |
| 166 AUTOMOTIVE INDUSTRIES THE AUTOMOBILE January 27, 1921 Fig. 9 (at left)—Characteristic curves of mechanism at engine speed of 3000 r.p.m. Fig. 10 (center, above)—Curves showing how inlet valves overlap in the six-cylinder engine. Fig. (at right)—Characteristic engine performance curves at full load. Compression ratio 4.25 to 1. Fig. 16 (center, below)—Curves showing relation between car speed and fuel consumption, with compression ratio of 4.25 to 1 coefficient of expansion of the aluminum being offset by the greater temperature range of the sleeve. The pressure on the combination cork and hydroil packing is in an axial direction only; that is, there are no radial components of pressure from the reactions of the packing to throw the sleeve out of round. This is the characteristic difference from other types of sleeve constructions and is necessary to make sleeve construction successful. Fig. 8 gives the details of the inlet and exhaust cams, both cams being identical. This is a special type of cam* having a zero opening and closing valve velocity regardless of engine speed. Fig. 9 gives the valve-mechanism characteristic curves for an engine speed of 3000 r.p.m. Attention is called to the design to obtain a high acceleration away from the cam and a low acceleration toward the cam; that is, the acceleration that must be produced by the valve spring to keep the roller following the round peak of the cam, the 0.484 in. radius shown in Fig. 8. The equivalent weight of all the accelerated parts considered placed at the valve is 0.7635 lb. The valve-spring pressure required at 3000 r.p.m. is 59.8 lb. per sq. in.; at 3200 r.p.m. it is 68 lb. per sq. in.; at 3400 r.p.m. it is 76.8 lb. per sq. in. Great care is taken to have the master cam ground to a true radius at the peak of the cam. If the cam generated has any bumps on the peak radius, it is impossible to obtain high-speed operation for two reasons. The irregularities set up synchronous vibrations in the valve springs and the accelerations are immensely increased, making the springs too weak. For instance, if the 0.484 in. peak-radius has waves on it of 3/16-in. radius, the acceleration is increased 116 per cent. These points are mentioned because they are absolutely vital to the successful application of the valve mechanism of the roller type to a valve-in-head engine operated at high speeds. Fig. 9 gives the inlet-valve timing overlap. This diagram shows that although the inlet-valve is held open fairly late, the valve of another cylinder is close to its maximum lift, preventing a blow-back into the carbureter. The valve timing is as follows: Inlet opens 4 deg. past top center and closes 60 deg. past lower center. Exhaust opens 52 deg. before lower center and closes 4 deg. past top center. Fig. 11 shows a diagram of the intake-manifold passages. These are cast within the cylinder-head, making them of the shortest possible length. The firing order is 1, 5, 3, 6, 2, 4; therefore, the flow of gas is continuous in both directions from the center. The average gas velocity at 3000 r.p.m. at manifold inlet is 181 ft. per sec.; just above the valve it is 192 ft. per sec. and at full lift of the valve it is 247 ft. per sec. The throat diameter of the valve is 1 1/2 in.; the outside diameter is 1 5/8 in.; the valve lift is 0.445 in. The area at manifold inlet is 3.39 sq. in. The tulip-shaped inlet-valve is used to lessen the resistance and keep the velocity of the gas as high as possible on entering the cylinder as an aid to turbulence. Fig. 7 shows the exhaust-gas pipe between the two center cylinders. The engine is equipped with a Delco generator and single breaker-point type of ignition, with automatic and manual spark advance. A Willard battery was charg during the tests and also was used for starting. Champion —Toledo No. A-63 metric two-piece plugs were used for all the runs. These plugs had much to do with the ease with which the tests were run. Only six plugs were used and at the end of the runs they were in perfect condition. This is saying a great deal for the spark-plugs, considering the high-compression pistons, power output and speed of this engine. Fig. 12 shows the 2-in. Johnson Model B carbureter used. The air-valve spring and strangle tube were first worked out for the low-compression piston tests. The same parts worked out nicely in connection with the 5 to 1 compression pistons, with only a slight change of adjustment on the air-valve spring. Otherwise, in each set of tests, all adjustments were kept constant for both partial and full-throttle loads. With the Sprague electrical dynamometer and the fine throttle adjustment, the proper load and speed were obtained readily. The section at AA {D. Abbot Anderson} in Fig. 13 shows the equal distribution of the cooling water to the cylinder sleeves. The water goes from the pump to the tube inside the cylinder block. Two holes for each sleeve give a uniform distribution of the water. This keeps all the sleeves at the same temperature, an important feature for equal gas distribution and smooth running. The engine cooling *A detailed description and mathematical analysis of this type of cam will be found in the 1917 S. A. {Mr Adams} E. {Mr Elliott - Chief Engineer} Transactions, Part 1, pages 328 to 337. | ||