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).
Different instruments for studying valve-mechanism idiosyncrasies and valve motion.
| Identifier | ExFiles\Box 56\2\ Scan080 | |
| Date | 15th January 1929 guessed | |
| 2 VALVE-MECHANISM IDIOSYNCRASIES The valve motions should be studied directly. A certain amount of this can be done on an engine by observing the valve and spring motions with some sort of stroboscope, such as the Vibroscope. Engines, however, are not designed primarily to facilitate the observation of valve motions, and a special machine upon which the valve mechanism can be completed is necessary for their complete analysis. We have built such a machine and developed instruments of four different types for studying valve motions. They are: (1) Telescopic point-by-point indicator (2) Stroboscopic projector of the valve motion (3) Valve-lift-curve indicator (4) Valve-lift-curve indicator with a spring-vibration indicator Since each successive instrument did not exactly take the place of its predecessor, but was made for studying a different phase of valve operation, all four will be described. FIG. 1—DIAGRAM OF TELESCOPIC VALVE-LIFT INDICATOR TELESCOPIC POINT-BY-POINT INDICATOR Fig. 1 is a schematic diagram of the telescopic point-by-point indicator, and Fig. 2 shows it in operation. A pointer, O, is attached to the valve. In front of the valve is mounted a telescope, T, in an arm, A, which is pivoted at P. Arm A, in revolving around its pivot, P, follows arc B, on which is engraved a scale. The arm, A, is provided with a vernier, V.{VIENNA} The telescope is focused on the pointer O, and the angle can be read by means of vernier V and arc B. This angle can be translated into valve lift after a suitable calibration of the mechanism has been made. In operation, the valve and its pointer are enclosed in a comparatively dark box and are observed at selected positions of the camshaft by means of stroboscopic illumination. The Vibroscope which was used for this purpose consists of a neon lamp operated through an induction coil and breaker. The breaker was attached to the camshaft, and it could be adjusted easily so that the light would be lit for an instant at any desired point of the camshaft revolution. The position of the neon bulb for illuminating pointer O is shown at S. The breaker for operating the neon lamp S is shown at I, in Fig. 2. This apparatus is extremely accurate for measuring valve lift. As it is difficult, however, to obtain a preliminary idea of the valve action with this, it was decided to build an instrument that could be used in conjunction with the telescopic indicator for what might be called qualitative analysis of the valve motion. With this second device it was possible to watch the motion of the valve at reduced speed and enlarged scale so that the interesting speeds could be selected. The more accurate observations could then be made with the telescope at these speeds. Fig. 3 is a schematic diagram and Fig. 4 a photograph showing the arrangement of this apparatus. Again O is a pointer attached to the valve; L is a light, such as a projection bulb or an arc lamp; C is a condenser lens; and B is an objective lens which focuses an image of pointer O on screen S. A stroboscopic disc, D, is placed between the objective B and the screen S, at what is called the neck of the beam. This disc has one opening to permit the light to pass; therefore, the image of O is thrown on the screen once for each revolution of the disc. If the disc were rotated at exactly the same speed as the camshaft which operates the valve, the image of pointer O on screen S would remain at rest. It was, however, rotated at a slightly lower speed than the camshaft, through the friction-disc variable-drive U, and the image on screen S moved at a proportionately low speed. As seen in Fig. 4, it is not necessary to remove the telescope from the machine while using the screen. After making the qualitative study of the valve, the stroboscopic disc and screen can be moved out of the way easily and the telescope swung into its place for accurate readings. VALVE-LIFT-CURVE INDICATOR While the combination of these instruments gave good results, it was not possible with them to study valve performance with satisfactory speed. It was, therefore, decided to develop a valve-lift indicator that would project the valve-lift curve. The upper part of Fig. 5 is a schematic diagram of the mechanism for doing this, including the entire cam mechanism and the motor for running the camshaft. In many respects it is similar to the equipment shown in Figs. 3 and 4, as it is a projection lantern. The light is shown at A, the condenser lens at B, a small aperture at C, an objective lens at D, and a screen at E.{Mr Elliott - Chief Engineer} These parts would project an image of the aperture C, which moves with the valve. If, instead of letting the objective project the image directly upon screen E, it is deflected by means of a FIG. 2—PHOTOGRAPH OF TELESCOPIC VALVE-LIFT INDICATOR VALVE-MECHANISM IDIOSYNCRASIES 3 plain mirror, F, set at the proper angle, upon a rotating mirror, G, the resultant of two motions is projected on the screen. The vertical component is obtained from the motion of the valve, and the horizontal component from the revolving of the mirror G.{Mr Griffiths - Chief Accountant / Mr Gnapp} This mirror has eight sides and rotates at one-eighth camshaft speed. The image on screen E, therefore, will be repeated once for each camshaft revolution and, owing to the persistence of vision, appears to be continuous and in the shape of the ordinary valve-lift curve. This image curve can be observed visually for seat bouncing and increased lift, as with the stroboscopic projector; also, any irregularity of the opening and closing lines can be seen. When desired, a photographic film such as is used in the ordinary portable camera can be put in place of screen E, and the curve will be photographed. To photograph successfully, it is necessary that a mechanism be developed for holding the shutter open while only one projection of the valve lift passes across the film. FIG. 4—PHOTOGRAPH OF THE STROBOSCOPIC VALVE-MOTION PROJECTOR lens. As in the valve-lift indicator, the image of this slot is focused on the screen after being reflected by a 45-deg. flat mirror and an octagonal rotating mirror. For optical reasons, this image must be offset from the image of the aperture which makes the record of the valve motion, and correction made accordingly. In front of this slot, the width of which is adjustable, is placed a small shutter, E, which moves up and down with one of the coils of the valve-spring, F, and thereby FIG. 3—DIAGRAM OF STROBOSCOPIC VALVE-MOTION PROJECTOR The one trouble with this device was that the aperture C was magnified, as well as the motion of the valve, resulting in a heavy record line on the screen. To overcome this difficulty, we developed the apparatus shown in the lower portion of Fig. 5 to replace the plain aperture. This consists of an aperture, H, of about 1/32 in., and a strong negative lens, I, some distance away from it, both mounted in a support, J, attached to the valve. The result is that a reduced image of the aperture is used to draw the lift curve on the screen, and very thin record lines are possible. The weight of the valve must be reduced by an amount equal to the weight of the lens and its support, which must be kept at the minimum. Fig. 6 shows this valve-lift indicator complete, the parts being lettered to correspond with Fig. 5. SPRING-VIBRATION INDICATOR The spring-vibration indicator, shown on Figs. 7 and 8, is designed to project on the screen a stationary image of the wave motion of a coil of the spring. It is a part of the valve-lift indicator and uses the same projection system. By means of three small mirrors, A, B and C, a beam of light from the projection lamp is led around the valve, through a small slot, D, which is the object to be projected, and into the objective FIG. 5—(UPPER DIAGRAM) VALVE-TEST MACHINE WITH VALVE-LIFT INDICATOR. (LOWER DIAGRAM) IMPROVED OPTICAL SYSTEM OF VALVE-LIFT INDICATOR | ||