Simulation Model And Application Research Of Screw Motor Meshing

Downhole motor is one of power motors which is widely used in the oil drilling engineering. The power assembly,which is consisted of stator and rotor,is the core component of mudmotor. The operational principle of mudmotor is that the drilling fluid with high pressure drive the rotor to rotate and the bit to break rock,which converting the hydraulic power to mechanical energy. Improving the performance of downholel motor can significantly improve the drilling efficiency and reduce the cost of drilling.The design of stator and rotor is the core content of motor design and manufacture, firstly, the basic theory of stator and rotor's profile was studied and paved the way for mudmotor's design; The main factor that is the cavity pressure influencing the mudmotor's performance was analyzed and the basic principles of interferences between the stator and rotor were determined; Based on the meshing model of stator and rotor, a evaluation method of the stator and rotor profile was constructed in order to design the reasonable interferences between the stator and rotor and improve the sealing and output performance of mudmotor, at last, through the mudmotor's performance tests, the evaluation method of the stator and rotor profile was proved more reasonable. The main research contents are as follows:(1) Theoretical study on the profile of stator and rotor in the mudmotor. Cycloid is the foundamental curve of mudmotor's profile. Based on the theory of plane coordinate transformation, the general formulas of many kinds of cycloids were obtained. Because the profile of stator and rotor is a pair of conjugate curves, two methods of generating conjugate curves,i.e., the tooth profile normal method and the envelope method, are analyzed. Traditionally, the profile of stator and rotor is the outer equi-distant curve of hypocycloid, a new profile to replace the equi-distant curve by arc and elliptic arc was proposed and an in-depth analytical study of involute profile was conducted in this paper.(2) Study on the distribution and change rules of cavity between the stator and rotor. The high pressure drilling fluid has great effect on the catity sealing, so the distribution and change rule of cavity was studied, then the basic principles for the subsequent designing of reasonable interferences between the stator and rotor was proposed in order to ensure that the differential pressure of adjacent cavity is less than the contact pressure caused by the interferences between the stator and rotor, which could improve the sealing performance of mudmotor.(3) Research on the meshing model of stator and rotor. In this article, ignoring the dynamics and other factors and just considering the contact force and based on Hertz contact theory,the meshing model of stator and rotor was established,so that the rotor is in the theoretical equilibrium state. Based on the above research, the criteria of interferences between the stator and rotor was defined.(4) Evaluation method of stator and rotor profile and mudmotor performance test. Through the cavity pressure analysis and meshing model of stator and rotor, the evaluation method of stator and rotor profile was established, when the interferences between the stator and rotor are in a range of 0.16mm-0.21mm and fluctuate smoothly, the mudmotor will get good performance. Through the mudmotor trial-production and the performance tests,the evaluation method of the stator and rotor profile was proved more reasonable.Through the research in this paper, a new method to design the interferences between the stator and rotor was formed, which can effectively reduces the premature leakage of drilling fluid and improves mudmotor's sealing performance. The new method can be used to guide the fine designing of mudmotor's profile and have significantly application values to improve the product quality.