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 a journal discussing various types of resilient engine mountings and their performance characteristics.
| Identifier | ExFiles\Box 126\4\ scan0141 | |
| Date | 1st April 1934 | |
| 146 S. A.{Mr Adams} E.{Mr Elliott - Chief Engineer} JOURNAL (Transactions) Olds Rear-Support Designed to allow controlled close-limit deflections in three directions. Construction: Rubber vulcanized to steel shell with bolts assembled. A malleable-iron casting is inserted after molding and the shell closed over. Pontiac Side-Support Designed to allow controlled close-limit deflections in three directions. Construction: Steel forging on steel shell with bolt inserted vulcanized in rubber. Shell is closed after molding. Buick Rear-Support Designed to cushion motor with restricted motion in all planes. Construction: Three steel stampings vulcanized in rubber. Outer housing and strap riveted after molding. Pontiac Front-Support Designed to allow a restricted close-limit universal action in a horizontal plane with maximum vertical motion held to close limits. Construction: Malleable-iron casting vulcanized in rubber and inserted in steel shell which is then closed over the rubber. Olds Front-Support Designed to allow a side-rocking movement with restricted fore-and-aft movement. Construction: Malleable-iron casting and steel shell vulcanized in rubber. Bolts are inserted in steel shell before molding. Fig. 15—A Series of Inland Mfg. Co. Mountings Vol. 34, No. 4 RESILIENT MOUNTINGS 139 Fig. 3—Optical Indicator Affording a Simple Means of Recording Photographically Movements of Mechanical Units Under Operation mountings. In no case do they coincide. Fortunately, however, extreme accuracy of mounting position is not essential. Reasonable accuracy of position is necessary. Fig. 2 gives some idea of the variation of position of the true principal-axis location from our previous assumption. The intersection of the U-joint center and the center of gravity is shown as A, and the true principal axis B is obtained by hanging the engine from its end and changing the location of the point of suspension to obtain the minimum moment of inertia. Four entirely different types of engines are shown. Resistance to rotation about the principal axis, of which there are more than one, is the controlling element for engine-sensation absorption. Low resistance to rotation will result in operating smoothness. This of course may mean low internal rigidity for the mountings. Durability of the mountings depends to a great extent upon this internal rigidity. When too flexible, they may not stand up under engine movement due to road shock; therefore, we cannot blindly take advantage of the fact that low rotational resistance is beneficial, for instance, in reducing the frequency of torque reaction. Following are some figures on resistance to rotation and the resulting torque reaction of various 1932 cars: A 1500 ft.-lb. per deg. 15 m.p.h. B 2500—23 m.p.h. C 5000—35 m.p.h. A, B and C represent three ranges of resistance to rotation during 1932. The A group is the average of a fairly smooth group. Group B is the average that was barely commercial. Group C is the average that we believe to be non-commercial having a torque reaction from 5 to 35 m.p.h. The data are given here to record these values for the 1932 cars with average or less flexibility. During the early part of 1932 an investigation was made on a series of cars with extremely flexible mountings to determine the relative flexibility of these jobs as compared to the then conventional flexibility. Assuming that a flexibility of 1500 ft.-lb. per deg. was 100 per cent, the four-cylinder super-flexible job's rotational resistance was down 2145 per cent, that the four-cylinder is 2145 per cent down, the six-cylinder is 727 per cent down, and the eight-cylinder is 233 per cent down. Since these three cars were satisfactory jobs from the smoothness standpoint, the indications are that a 3:1 ratio exists for comparative results between a four and a six, and also between a six and an eight-cylinder engine. However, in 1932, it is well to note that this particular eight-cylinder engine was mounted with two and one-half times the flexibility of the average six-cylinder engine. Degree of flexibility or resistance to rotation is important, regardless of how it is obtained. However, the more accurate the location of the mountings is, the lower the resistance to rotation can be for the maximum of firmness in the mounting brackets. The resistance to rotation picture of today has changed. It is down considerably from 1932. In some cases without sacrifice of mounting firmness; in others, by application of very soft pads. Obviously, the softer the detail mountings are, the less is the need for definite location. However, we believe durability will force consideration both for decent location and limited flexibility. Checking of the rotational resistance of several 1933 cars indicated the following: Overall rotation resistance—average six-cylinder—1100 ft.-lb. per deg. Torque reaction, 5-7 m.p.h. Flexibility Ft.-lb. per Deg. Maximum, six-cylinder, 500 Average, eight-cylinder 1100 Maximum, eight-cylinder, 725 The torque reaction in the eights appeared eliminated, although, in the maximum-flexibility jobs, mountings varied considerably in construction. Durability in one case has been sacrificed materially where low resistance has been accomplished without regard to position. The mountings are forced to absorb the effects of shifting the effective principal axis, and are too soft to stand up under road shock. If the mountings due to position and resistance disturb the mass balance, then the principal axis shifts. The amount of principal-axis shift may be assumed to represent the extent of position error in the mountings. Range Smoothness Range smoothness is affected by many things; some may be offset by insulation, others by carefully designed resist- April, 1934 | ||