Optimising Dynamic Oil Volume in a 2-Stage EV Transmission

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At Hewland, we recognize that effective oil flow management is a critical factor in designing robust and efficient transmission systems. With pitch line velocities and e-machine speeds on the rise, the design and simulation of transmission oiling systems is more important than ever to ensure adequate oil penetration into mesh and that churning losses are minimised. We are committed to supporting our customers by providing optimal solutions tailored to their specific design requirements.

By utilizing Particle Works meshless CFD software, we can predict how oil behaves within a transmission system. This allows us to make informed design decisions early on; before costly casings are patterned, cast, and machined. Through iterative design and analysis revisions during the concept phase, we ensure that the final product performs reliably and efficiently whilst reducing the time spent testing & developing the physical hardware.

Case Study: Optimising Dynamic Oil Volume in a 2-Stage EV Transmission

The following case study shows an example of how Meshless CFD simulation performed during the concept phase enabled an oil management issue to be rectified before committing to costly hardware. The initial analysis revealed a diminishing sump volume that negatively impacted the transmission’s operating requirements. This issue was addressed by installing baffles to return oil more efficiently to maintain the sump oil level.

A before and after snapshots from the simulation shows how implementing a baffle reduced oil hang up around the gear train and improved oil replenishment to the sump.

Initial analysis

Baffle development analysis

We characterised the issue by probing and tracking oil sump volume. Our analysis predicted that the initial design would exhaust the sump after just one minute, which would risk insufficient lubrication and result in operational failure.

To address this, we applied our extensive experience in transmission design and development by strategically placing and optimising oil baffles. These baffles help capture and direct the oil back to the sump as early as possible, significantly reducing oil retention in the gear cavity.

The result is clearly visible in the revised analysis, where particle density (represented by orange areas) in the gear cavity is reduced. The effectiveness of the baffle is further highlighted by the increased particle density above the input shaft, where the baffle was positioned, indicating the oil is being captured and directed to the sump.

This intervention led to a dramatic improvement in the sump return flow, which in the revised design is sufficient to support the extreme dynamic events experienced during operation. The delta between the analysis revisions is plotted below:

The raw data is depicted by the red (initial) and green (revised) lines, representing the return oil flow over time. Additionally, the orange line highlights the peak performance of the pump, corresponding to its continuous flow rate. The data suggests that when baffles are in place, the system achieves equilibrium, where the return rate matches the pump outflow, at approximately 17.5 seconds.

This result bolsters the stabilising effect of the baffles on the system, as they promote a steady return rate and alignment with pump demand, critical for optimum efficiency.

The improvements in dynamic oil level were not the only benefits of this redesign. By ensuring reliable oil scavenging through a more consistent oil level in the sump, we also reduced the risk of aeration and cavitation. This resulted in a more stable and continuous oil supply to critical transmission components, improving the system’s reliability.

Furthermore, reducing the retained oil volume in the gear cavity minimized churning losses, leading to better efficiency. These enhancements contributed to the creation of a superior oil delivery system that not only meets the transmission’s demanding requirements but also provides our customers with increased confidence and a reduced development time.

How Can Hewland Support You?

At Hewland, we are equipped to help you tackle oil flow management challenges. From 1D analysis to full-scale clear case validation on our dedicated test rig, our team is ready to support your design journey. If you’re facing oil management issues or need help optimizing your transmission systems, don’t hesitate to reach out—we are here to help you achieve the best results with efficient, cutting-edge solutions.