Patent GB-568849-A (GB)
Title: Mechanism for converting rotary into reciprocating motion and vice versa
IPC: F16H21/36
Filed: 1942-10-29
Abstract: 568,849. Converting rotary into reciprocating motion and vice versa. CULBERTSON, W. J. Oct. 29, 1942, No. 15197. Convention date, Oct. 17, 1941. [Class 80 (i)] [Also in Group XXVII] Rotary motion is converted into reciprocating or vice versa by mechanism comprising a crank-shaft, the crank-pins of which carry rotatable sleeves on each of which are rigidly fixed a pinion and an eccentric sheave, the pinions gearing through an eccentricallymounted idler ring with a fixed internal gear, and the sheaves carrying straps connected to the reciprocating part. The gears have certain relative proportions and rotate in such directions and at such relative speeds that the centre of each eccentric sheave moves in a straight line with a simple harmonic motion. In one example, a crank-shaft 1 has two crank-pins 3, 4 on which are rotatably mounted sleeves 5, 6 respectively. Two eccentric sheaves 7, 9 are integral with each sleeve, the throw of the cranks and the eccentricity of the eccentrics all being equal to one another. Pinions 8, 10 are integral with the sleeves 5, 6 respectively, the pitch diameters of the pinions being equal to one another, but greater than twice the throw of the crank-pins. The absolute angular velocity of the eccentric sheaves, pinions and sleeves is equal to that of the crank-shaft, but opposite in direction, whereby the centres 12 of the eccentric sheaves move with simple harmonic motion in straight line paths. To correctly constrain the rotation of the sheaves in relation to that of the crank-shaft, the pinions 8, 10 mesh with internal gear portions 14, 15 of an idler ring gear 16 which is composed of the side gears secured to a central part 18 having external gear teeth all mounted rotatably on the periphery 19 of an eccentrically located circular cheek 20 of the crank-shaft, the centre 21 of such cheek being at an eccentricity e from the axis 13 of the shaft. The toothed part 18 meshes with a fixed internal gear 22 concentric with the axis of the shaft and secured adjustably to the crank-case 23 by screws 24 through elongated holes 25. The pitch diameters of the gears 14, 15 and of the external gear 18 are all equal to one another. The pitch diameter of each of the pinions 8, 10 is equal to one-half of the fixed internal gear 22 and may be any amount greater than twice the crank throw. The pinions 8, 10 are driven by the combination ring 14, 15, 18 acting as an idler gear between the pinions and the fixed gear 22. Piston-rods 27 are secured to the eccentric straps 28. A twisting action on the idler ring gear is counteracted by the provision of an annular shoe 30 connected to each of the side gears 14, 15, the shoes having a bearing piece 31. which slides on the side surface of the body portion 32 of the fixed gear 22. Shims 33 are provided to take up wear. In a modification, Fig. 2a (not shown), the parts are, in the main, as described above, the variation residing in the proportions and arrangement of the pinions 8, 10, the fixed gear 22 and the external and internal gears of the combination ring gear. In a further modification, Figs. 7, 8, a sleeve 43 is rotatably mounted on the crank-pin 44 of the crank-shaft 40. Two eccentric sheaves 45 and a pinion 46 are integral with the sleeve. The sheaves have straps 47 secured to piston-rods 48. The pinion 46 is geared to a fixed internal gear 51 through three idler gears 49, 50. The gear 51 is adjustably secured to the crank-case 42 by bolts 57 and slots 58. The gears 49, 50 are rotatably mounted on stub shafts 53, 54 fixed to the side of the adjoining crank arm 55. In this form also, because of the 1 : 2 ratio of the pinion 46 and the gear 51, which ratio is unaffected by the idler gears, the pinion 46 will be caused to rotate at the same angular velocity as the crank-shaft, but in an opposite direction with the result that the centre points 56 of all eccentrics will move with simple harmonic motion in straight line paths. The Specification contains diagrammatic figures to illustrate the method of obtaining the position of the centre 21 of the combination ring gear for various values of the angle # between the line connecting the centres of the crank-pin and crank-shaft and that connecting the centre point 21 with the crank-shaft axis.