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<p>As a widely used downhole drilling tool, the universal joint assembly of positive displacement motors is prone to failure while transmitting torque and speed in ultra-deep wells. To address these issues, static and dynamic models of petal-type and spherical-hinge universal joints for the 7LZ172 PDM were established. Finite element and numerical analyses evaluated their strength, failure mechanisms, and the effects of five rotational speeds on alternating strain, contact forces, and axial displacement. A novel cross-flex universal joint was proposed for comparison. Results show that, under the same load, the maximum Mises stress of the petal-type joint is 2–3 times that of the cross-flex joint, while the spherical-hinge joint exceeds 3 times. The cross-flex universal joint exhibits the smallest strain, contact force, and deformation, ensuring minimal wear, higher reliability, and longer service life.</p>

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Study on the failure mechanism and dynamic characteristics of universal joints in positive displacement motors

  • 期刊论文

  • 发表日期：

    2025年12月4日

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  • Changshuai Shi,
  • Lun Ni,
  • Xiaohua Zhu

摘要

As a widely used downhole drilling tool, the universal joint assembly of positive displacement motors is prone to failure while transmitting torque and speed in ultra-deep wells. To address these issues, static and dynamic models of petal-type and spherical-hinge universal joints for the 7LZ172 PDM were established. Finite element and numerical analyses evaluated their strength, failure mechanisms, and the effects of five rotational speeds on alternating strain, contact forces, and axial displacement. A novel cross-flex universal joint was proposed for comparison. Results show that, under the same load, the maximum Mises stress of the petal-type joint is 2–3 times that of the cross-flex joint, while the spherical-hinge joint exceeds 3 times. The cross-flex universal joint exhibits the smallest strain, contact force, and deformation, ensuring minimal wear, higher reliability, and longer service life.