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).
Article from the S.A.E. Journal discussing resilient engine mountings, dynamic balance, and material considerations.
| Identifier | ExFiles\Box 126\4\ scan0143 | |
| Date | 1st April 1934 | |
| PAGE 144 144 S. A.{Mr Adams} E.{Mr Elliott - Chief Engineer} JOURNAL (Transactions) In considering the material used in engine mounting we must deal with two important items: (a) the overall characteristic of the mounting and (b), the durability of those characteristics. Dimensional checks of deflection under load, durometer or other hardness readings, will give an adequate check on (a), but (b) is not quite as simple since in it are involved not only the compound but every move in the process of producing the mount. Until such time as the committees working on rubber specifications have definite recommendations to offer, we believe it is wise to make laboratory checks of several mountings under constant load and position, somewhat equal to operating conditions and at a temperature of about 150 deg. fahr. Under these conditions apply a stroking load at about 300 strokes per min. in a direction 90 deg. to the original static load. After each hour of stroking the rate of deflection of the sample should be checked. This will determine the comparative durability of the mounting characteristics. Cooperation with the rubber source will usually bring improvement when desired. It is interesting to note that changes for durability improvement usually do not involve compound changes, but rather changes in processing. Fig. 12—Diagrams Showing How Balanced Resistance about the Center of Gravity Can Be Accomplished Diagram A shows a single-point and direction mount as a steady rest front and rear, and universal mounts adjacent to the center of gravity tangentially placed about the principal axis, thus accomplishing relative freedom about both principal axis. Variations of the foregoing principle are indicated in Diagram C tion desired, but we also cause the minimum shift of the vertical axis. Fig. 12 includes several diagrams showing how balanced resistance about the center of gravity can be accomplished. In A, is shown a single point and direction mount as a steady rest front and rear, and universal mounts adjacent to the center of gravity tangentially placed about the principal axis. Thus, relative freedom is accomplished about both principal axes as shown in B. There can be many variations of this principle, as indicated in C. Much depends upon the chassis set-up and structure. For instance, consideration of the Hotchkiss drive and of the torque-tube drive requires separate treatment, since, with the latter, brake and drive reaction must be provided for. Sample Mountings A series of engine mountings is shown in Figs. 13 to 15. Fig. 13 represents the current Graham-Paige. Figs. 14 and 15 include a series of mountings made by the Inland Manufacturing Co., Dayton, Ohio. Material It is obvious today that insufficient knowledge of the material involved in engine mountings exists among the users of these parts. If fair control is to be exercised over the material that finds its way into our products, greater consideration must be given to the work that is going on in rubber laboratories, to establish worthwhile means of checking or inspecting material. [Image Caption] NEW X-BRACE FRAME AND FRONT ENGINE MOUNTING—GRAHAM-PAIGE STANDARD SIX AND STANDARD EIGHT [Image Caption] Fig. 13—Engine Mountings on the Graham-Paige Car [Image Caption] NEW REAR ENGINE MOUNTING—GRAHAM STANDARD SIX AND STANDARD EIGHT Vol. 34, No. 4 PAGE 141 RESILIENT MOUNTINGS 141 lutions for each shot was allowed. A stroboscopic effect can also be arranged to slow down the light beam. In Fig. 4, views A and B indicate actual paths of light beams moving with the engine. Note their relative direction with reference to the polar-axis center. There is not the slightest doubt that the engine rotation is about the principal axis. This axis is an oblique line and the excitation of the movement is from the crankshaft. The angle between the polar axis and the source of vibration causes a resultant couple about the vertical axis through the center of gravity as shown in Fig. 5, which shows also the arrangement of couples that establishes the existence of a rotating force C about the vertical axis generated by the oblique rocking action as at A.{Mr Adams} This couple causes the engine to oscillate about the vertical axis. Investigation has proved that this movement about the vertical axis is equal in importance to rotational movement about the horizontal axis, and, if not provided for by either design or accident, range smoothness cannot be had. Dynamic out-of-balance is prevalent in most engines today to some extent, and will not be eliminated until assembly balance or selected balance is in more general use. Dynamic out-of-balance is a direct force tending to turn the engine about its vertical axis. This unwelcome force adds its might to the couple produced by the angularity of the principal axis and makes essential the provision for a limited transverse rotational movement. It is extremely difficult to eliminate dynamic out-of-balance at the source, and an out-of-balance of 4 oz.-in. will penetrate the best of mountings. Consider for a moment a well balanced crankshaft held down to ½ oz.-in. on each end. If this out-of-balance is as indicated in Fig. 6-A, wherein the out-of-balance in each end is in a plane, the out-of-balance will be the small total of 1 oz.-in. However, if the out-of-balance should occur in the form of a couple as in Fig. 6-B, the out-of-balance may total 12 oz.-in.² or more, depending upon the length of the shaft. Consider further the possible out-of-balance of the harmonizer, flywheel and clutch parts. The effect of each may be low, but the accumulation and position may combine to make a considerable effect. Another source of trouble is crankpin-position tolerance, for radius and angularity. In the shaft-balancing operation, these small errors will be washed out in the correction of the balance; however, when rods are assembled to crankpins, the heavy end of the rod picks up the position error and this results in out-of-balance. The result may be static or dynamic and, added to the other possibilities, certainly gives us something to think about. Surely the effect on transverse rotational movement about the vertical axis is apparent, and so is the need for providing the offsetting flexibility. Assembly balance has been given consideration in several plants; also, selective balance, which is accomplished by assembling light and heavy sides to offset each other rather than permit the out-of-balance to accumulate. Combustion-Chamber Roughness Combustion roughness is an old offender against which considerable progress has been made. We must consider it here because it is an important factor in roughness. Engine mountings undoubtedly can overcome or absorb considerable Fig. 6—Diagrams Showing How Great Dynamic Out-of-Balance May Become Fig. 7—Simple Comparative Curves That Give the Percentage Volume of the Combustion Chamber in Various Locations as Progress is Made Across the Chamber April, 1934 | ||