| The tooth shape of gear pump has important influence on machining and characteristics of pumps, such as flow rate, fluctuation rate and noise etc. First, the working principle of TATSUNO combined pumps is analyzed in this article. Secondly, the advantages and disadvantages of TATSUNO dual-circle-arced gear pumps are analyzed. To overcome the disadvantage of TATSUNO combined pumps and to improve the characteristics of the pumps, a new kind of pump with the fixed transmission ratio is proposed, the teeth of which are circle-arc and its envelope. With the new-simple method, the equation of circle-arc-enveloping curve are deduced. Also the relationship between the arc radius , the radius of center distribution and the distance of centers is given to avoid undercutting. The parameters of inner meshed gear pump with external circle-arc and its envelope teeth are optimized by the method of the genetics algorithms. Although the flux per revolution of the optimized pumps is a little smaller than that of TATSUNO combined pumps, other characteristics, such as fluctuation rate, maximum pressure angle and velocity fluctuation rate etc, are much better.The methods to cut gears are proposed in the theory for the practical produce in the future. The gearing machine tool of the model Y3150E is modified and a new milling head is designed to cut the envelope tooth of the pinion using allelomorph method. A assembled drawing of clamp for cutting the tooth shape of circle-arc gear is also presented.
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