Patent GB-596379-A (GB)
IPC: F04C2/10
Abstract: 596,379. Making gear-type pumps. EATON MANUFACTURING CO. Oct. 24, 1944, No. 20613. Convention date, June 1. [Classes 83 (ii) and 83 (iii)] [Also in Group XXVI] In the production of gear-type fluid pumps consisting of inner and outer toothed. members 10, 12, Fig. 1, wherein the outer member has one tooth more than the inner member and rotates on an axis 20 eccentric to the axis of rotation 18 of the inner member, the outer member has teeth 16 formed as circular arcs and the teeth 14 of the inner member are generated by a rotary cutter having a radius equal to that of the teeth 16 and moved bodily with a rolling circle which rolls on a base circle concentric with the inner member, the ratio of diameters of the base and rolling circles being equal to the number of teeth 14. In setting out the form of the teeth 14 where the wheel 10 has six teeth and the wheel 12 has seven teeth, a base circle B\ Fig. 2, having a centre 18 and a radius B is selected and the rolling circle R<1> having a radius R one-sixth of B is made to roll thereon. A point P on a circle E<1 >having a radius E equal to the eccentricity of the wheels 10, 12, rolls with the circle R<1> and traces out a cycloid GP which forms the locus of the centre P of the generating circle G<1>. The circumference of the latter then traces out the enveloping surface 14 of the required tooth. The Specification describes in detail the method of determining the dimensions B, E, G, R<1> and R for a pump of given capacity and overall dimensions having teeth which have a flat contact between them, a small pressure angle and minimum slip and which provide clearance at 82 to prevent jamming by foreign matter in the fluid being pumped. The teeth 16 of the outer wheel 12 are formed by a broaching or other machining operation using a form cutter, and teeth 14 are generated by a milling or grinding tool. In the former method, a cylindrical milling-cutter has a radius G equal to that of the generating circle and whilst being rotated about its own axis P, this axis is caused to rotate on a radius E while the wheel 10 rotates on its own axis 18, the ratio of these last two rotations being equal to the number of teeth to be generated in the wheel 10, the cutter thus tracing out the tooth curve 14. When generating by grinding a grinding-wheel 64, Fig. 3, is used, rotating on an axis 66 transverse to that of the work 10, and having an arcuate edge 68 of radius equal to that of the generating circle G. The wheel 10 is carried by a spindle 40 rotated in a bearing 42 through a shaft 46 from an electric motor 50, the spindle and shaft being connected by an Oldham coupling 52. The bearing 42 is rotated in a block 44 about an axis eccentric to the axis of spindle 40 by the amount E and is driven by gearing 56, 58, 60, 62 from the shaft 46 at a speed six times that of the spindle for a sixtoothed workpiece 10, the grinding-wheel axis being reciprocated in the direction of arrow 70 to traverse the thickness of the work. In each method of generation, the work may perform several revolutions and the cutter or grinding- wheel be fed in after each revolution until the finished size is attained.