Challenge: To Break the Durability Limitations of the New Generation High-Torque DP-EPS (Dual Pinion - Electric Power Steering‌)

A Tier-1 steering system integrator for mainstream global Automakers faced an ultimate test: the next generation of high-torque Dual Pinion steering systems required a 40-70% increase in worm gear output torque with no size change —

But the chassis space was fixed and must fit within the existing gearbox housing:

✓ Fixed center distance,

✓ Outer diameter of worm shaft & worm wheel cannot be increased

✓ Tooth width cannot be increased

Solution: A Two-Stage Strategy in Tooth Profile Design

Stage 1: Optimised Helical Tooth Profile leads to a 40% torque increase

The team relied on Nylacast Automotive’s in-house Application Engineering skills and experience and design processes utilising a KISSsoft gear design platform to complete the basic calculations of core parameters coupled with Finite Element Analysis (FEA) technology to accurately verify the stress distribution in key areas. Through multiple iterations and validations of design schemes, they successfully found the optimal balance between bending, shear and contact stresses, balancing the predicted life of the various failure modes. The solution used a highly optimsed helical gear paired with Nylacast high durability polymer. Simulation tests confirmed that this solution could significantly increase the system's torque capacity by approximately 40%.

"After successfully passing the Customer durability validation with a 40% torque increase, the R&D team seized the momentum and shifted their focus to the more challenging globoidal worm gear solution."

Stage 2: A Globoidal Worm Gear Shatters the 70% Ceiling

The Customer initially rejected the globoidal worm gear solution due to limitations in existing assembly processes, but their attitude showed a clear turning point—if the solution could achieve the 70% torque increase target in actual tests, they would be willing to reconsider modifying the assembly process. In the technical solution comparison, the semi-globoidal option offered assembly compatibility without conflicts but had limited stress optimization potential. In contrast, the globoidal worm gear, though requiring targeted adjustments to production processes, could maximize stress reduction effects. CAE predictions indicated that the globoidal worm gear fully met the 70% torque increase and lifespan goals, ultimately convincing the Customer to approve this higher-performance globoidal gear solution. The solution was then successfully validated by the Customer,

Nylacast Automotive Durability Test Rig 

Case Summary

This case achieved a 40% torque increase through the integration of helical tooth profiles and Nylacast polymer technology. A further development using a globoidal worm gear solution, resulted in a 70% torque increase compared to the original design, with an additional 30% stress reduction. The theoretical design was transformed into practical performance through Nylacast’s precision manufacturing processes:

Worm Gear

·        High-Precision Hobbing: Using high quality hobs to achieve ISO Class 9 gear accuracy, eliminating residual stress to ensure tooth profile stability, and optimizing load distribution to reduce tooth stress.

·        Polymer-Metal Interface Reinforcement: Through controlled Nylacast processes, a seamless physicochemical bond is formed, achieving four major safety advantages: vibration damping, dimensional stability, efficiency improvement, and compatibility with complex structures.

·        Durability test rig (DTR) data validated the design so the Customer could justify modifying the assembly process. Ultimately Nylacast Automotive were able to push the boundary, setting a new benchmark of "design-driven performance" in high-torque DP-EPS applications.

Dr. Tom Hardy from Nylacast Automotive, with 17 years of experience in Automotive gear design, commented: "This is a step change in torque density attained by combining an optimsed tooth profile, globoidal gear, highly durable polymer and high precision manufacturing and keeps Nylacast Automotive at the forefront as the industry moves to ever higher loads!"