Patent GB-621033-A (GB)
Title: Improvements in or relating to multi-row radial engines
IPC: F02B75/22
Filed: 1945-10-03
Abstract: 621,033. Balancing radial engines. UNITED AIRCRAFT CORPORATION. Oct. 3, 1945, Nos. 25711 and 25712. Convention dates. Sept. 1, 1944. [Class 7 (ii)] A radial engine particularly for aircraft has four radial rows A - D of cylinders, the cylinders of adjacent rows being circumferentially offset to form seven.helically extending banks, each row of cylinders having a connecting-rod assembly comprising master and link rods, and the master rods of the two middle rows being associated with circumferentially-adjacent cylinders B4M, C4M, Fig. 2, while the master rods of the end rows A, D are associated with cylinders A7M, D1M disposed at about 90 degrees in order to balance out torsional vibrations and second order inertia forces. In one form, Fig. 1, the front cylinder of one bank is offset by the same angle with respect to the rear cylinder of an adjacent bank as the anglebetween successive cylinders along a bank so that the projections of the cylinder axes are equally spaced, Fig. 2, round the crank shaft. The crank throws are arranged as shown in Fig. 4, successive throws being separated by 180 degrees plus the angle (12 6/7 degrees) of cylinder spacing. The crankshaft is balanced by pairs of counterweights 198... 201, Fig. 19. Alternatively only two counterweights 198, 200 may be used. The master rods 213 connected to pistons A7, B4, C4 and D1, are disposed so as to balance the inertia forces of the second order arising from the dissimilar piston movements due to the geometry of the master and link rod construction. The vector representing this force rotates at twice crankshaft speed. and its instantaneous position is coaxial with the master rod cylinder and directed away from the piston thereof at the top and bottom dead centre positions of the master rod. Instantaneous vector positions corresponding to cylinder rows A - D are shown in Fig. 8, the resultant of the second order inertia forces for the four connecting-rod assemblies thus being zero. Also the rocking couples produced by the two pairs of forces DB and CA approximately balance each other. The master and link rod systems also cause torque variations on the crankshaft as shown by the line 301, Fig. 9, corresponding to two revolutions of the crankshaft and relating to one row of cylinders. The curve 301 may be resolved into harmonics and the first two harmonics, corresponding to first and second order torsional forces are shown at 303, 305, respectively. The relative phases of these curves, corresponding to the four rows, and of their first and second harmonics, are given in the specification and it is shown that the resultant of the first order torsional forces for the engine is equal to .89 times the first order torsional forces in any one row. The resultant of the second order torsional forces is shown to be equal to 3.27 times the second order force for any one row. To eliminate the effect of this second order torsional force, a hydraulic damping unit 206, Fig. 4, may be provided on the crankshaft. In a modification, Fig. 13, the master rods are associated with cylinders A1, B3, C3 and D1. In this case the phases of the first order torsional forces in the different cylinders are as shown in Fig. 17, the resultant being zero. Also the resultant of-the second order torsional forces is shown to be .87 times the second order torsional force produced in any one row. The second order inertia forces have a resultant equal to 2.42 times the force for any one row and this force together with the couple due to the longitudinal spacing of the second order inertia forces, is balanced by weights 341, 347, located at opposite ends of the crankshaft, Fig. 19, and rotated at twice crankshaft speed through gears 323. Specifications 511,941, 600,376 and 605,275 are referred to.