Eccentric Screw Pump Threaded Rotor Coupling
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Solution Overview
Problem
Existing uniaxial eccentric screw pumps face challenges in efficiently coupling flexible rods to rotors without causing rattling, fretting wear, stress concentration, and corrosion, particularly due to inadequate coupling methods that require significant time, effort, and equipment for maintenance, and are prone to fluid ingress leading to corrosion.
Innovation Solution
A uniaxial eccentric screw pump design featuring a threaded shaft part that engages with a threaded groove and facially contacts the coupling shaft, allowing for secure coupling without rattling and reducing stress concentrations, while preventing fluid ingress through the threaded interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shrink fit method is used to join flexible rod to shaft body, then the joined part achieves strong connection without rattling, but heating is required for separation during maintenance which consumes considerable time and effort
Solution Approach 1:
The coupling structure is divided into separate components: a coupling member with external threads on the flexible rod side and a corresponding internal threaded hole in the shaft body. This segmentation allows the flexible rod to be detached from the shaft body by simply unscrewing the threaded connection, eliminating the need for heating and enabling quick maintenance while maintaining reliable operation during use.
2Ease of manufacture
If adhesive coupling with serration is used, then assembly is simplified, but the reliability of adhesive strength is insufficient
Solution Approach 1:
The adhesive coupling method is replaced with a mechanical threaded coupling system. The coupling member features external threads that engage with internal threads in the shaft body's threaded hole, providing reliable mechanical strength without requiring adhesives. This mechanical engagement maintains assembly simplicity while significantly improving connection reliability.
3Ease of manufacture
If tapered shaft end insertion method is used, then assembly is simplified, but it is difficult to form the shaft end part into the tapered shape in constant quality and fretting wear occurs
Solution Approach 1:
The tapered shape parameter is replaced with standardized thread parameters (pitch, diameter, thread profile). Instead of requiring precise tapered machining, the coupling uses standard threaded forms that can be manufactured with consistent quality using conventional threading processes. This parameter change eliminates the difficulty of maintaining constant tapered shape quality while preventing fretting wear through proper thread engagement.
4Ease of operation
If threaded engagement is used to couple flexible rod to rotor, then assembly and disassembly become easy, but stress concentration at thread roots causes cracks
Solution Approach 1:
A fillet (rounded transition) is provided at the root of the external threads on the coupling member and at the root of the internal threads in the shaft body's threaded hole. This preliminary geometric modification eliminates stress concentration points that would otherwise cause cracks under operational loads. The fillets distribute stress evenly, allowing the threaded coupling to maintain both ease of operation and structural strength.
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3(a)~3(c)
AI summary
The purpose of the invention is to provide a uniaxial eccentric screw pump which can easily couple a flexible rod to a rotor so that rattling is not caused therebetween, and can prevent inconveniences such as fretting wear, breakage of the shafts associated with a stress concentration, and corrosion by entering of fluid. In the uniaxial eccentric screw pump, a flexible rod 62 is connected with a rotor 30 via a structural coupling part 100. The structural coupling part 100 is formed by inserting and threadedly engaging a threaded shaft part 104 provided at a tip end of the flexible rod 62 into/with the shaft insertion hole 110 formed in an end face 112 of the rotor 30. In the structural coupling part 100, a flange part 102 on the flexible rod 62 side facially contacts an end face on the rotor 30 side.