Abstract
To accurately calculate the flow rate of cycloid rotary pump as well as to correctly understand its trapped oil phenomenon, firstly the instantaneous flow rate formula of cycloid rotary pump was established based on the method of swept area, and then it was compared with the two present approximate formulas by an example. Secondly, based on the established flow rate formula and the created trapped oil model in the present literature, the trapped oil pressure of a single cavity near the minimum volume position was simulated. It was pointed that for cycloid rotary pump as an example, the flow non-uniform coefficient was 6.45%, and in contrast, the flow non-uniformity coefficient of external gear pump was 21.2%. Relative to the accurate results, the two present approximate errors of flow rates were 1.93% and 2.90%; and the present approximate error of flow non-uniform coefficient was 7.13%; when the minimum position angle was added by 0.5° or 1° or 2°, relative to discharge pressure of the pump, the corresponding maximum peak of trapped oil pressure increased by 1.6% or 6.0% or 21.7%. The results indicate that the flow characteristics of cycloid rotary pump are better than the external gear pump, the two present approximate errors of flow rate are little but the present approximate error of flow non-uniform coefficient is higher. Also, there is a trapped oil phenomenon in cycloid rotary pump which is not obvious.
Highlights
As an internal cycloid gear pump (“cycloid rotor pump” for short) having a mesh with tooth difference, its characteristics include taking the equidistant curve of complete curtate epicycloid as the inner rotor tooth profile, and the outer rotor tooth profile as circular arc profile conjugated with it
According to the literature [2], the tooth profile envelope forming method of the cycloid pump was studied on the basis of the envelope theory in the differential geometry; the production method of cyclical toothing and spiral rotor and their geometry were studied with the gear pump and the cycloidal toothing on the roots blower [3]; the geometric correction method of the cycloidal profile was proposed [4]; a study was carried out on the curve and the formation of its envelope line with the principle of gear meshing and differential geometry theory from different aspects [5,6,7,8,9,10,11]
The formed meshing points of a working cavity are set as n1 and n2 respectively, the volume is set as V1, the inner rotor is called the wheel o1, and the outer rotor is called the wheel o2, wherein the wheel o1 and the wheel o2 refer to the corresponding wheel centers
Summary
Fig. (1) describes three positions of the cycloid rotor pump in a complete oil absorption process. (1a) indicates the minimum volume position of a working cavity, called minimum position; in Fig. 450 The Open Mechanical Engineering Journal, 2015, Volume 9 position of a working cavity is indicated, called maximum position; and in Fig. (1b), one unspecific volume position of a working cavity between the maximum and minimum is indicated, called one unspecific position. (1b), the angles of the wheel o1 and o2 turn are set as dφ and dφ in the small time dt. (1c), the total output flow Qsh of the pump is the sum of all positive or negative DV1 in a circle according to the volume of z2 single working cavities in a circle as the wheel o2 rotates, namely If φ2=π/z2 in Fig. (1a) and φ2=π+π/z2 in Fig. (1c), the total output flow Qsh of the pump is the sum of all positive or negative DV1 in a circle according to the volume of z2 single working cavities in a circle as the wheel o2 rotates, namely
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