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Novel fluid simulation software enables longer range for EVs by reducing losses in drivetrain

Driveline engineering consultancy Drive System Design (DSD) has partnered with software specialists Altair and FluiDyna to develop and enhance FluiDyna’s computer modeling technique, nanoFluidX, that significantly improves the analysis of lubrication flow. nanoFluidX utilizes a Smoothed Particle Hydrodynamics (SPH) methodology and increases the accuracy of analysis while reducing the simulation time from weeks to just a few days, when compared to traditional methods.

Smoothed-particle hydrodynamics (SPH) is a numerical method used for simulating the dynamics of continuum media, such as solid mechanics and fluid flows. Originally invented for astrophysical problems, it can also be successfully applied to free-surface flows and complex multi-phase problems with interfacial effects such as surface tension.

Using SPH, a continuum phase is discretized with Lagrangian discretization points (particles) and the dynamics of this phase result from interaction forces between neighboring particles. This generalized approach offers the flexibility to model (almost) any physical phenomenon as these interaction forces can be formulated as complex as necessary. FluiDyna points out an important advantage of SPH is the meshless nature of the method—no cumbersome grid generation is necessary.

Origins of the code stem from Technical University of Munich’s (TUM) Chair of Aerodynamics and Fluid Mechanics (Lehrstuhl für Aerodynamik und Strömungsmechanik), and the company remains in close relationship with TUM.

DSD is using nanoFluidX to improve electric vehicle (EV) range by reducing losses in the drivetrain, identified as the largest energy draw on the battery pack at steady speeds up to approximately 80 km/h (50 mph)—even greater than the vehicle’s aerodynamic drag. Improving efficiency at these lower speeds is essential to achieve worthwhile improvements in real-world driving range.

SPH
SPH model in nanofluidX showing lubrication flow in a passive pump EV transmission. Click to enlarge.

Bearing, gear and seal losses are well understood by the industry; the interaction between rotating components and the transmission lubricant however has been too complex to explore within a typical project timescale. Practical tests using transparent casings have some value but it is difficult to visualise what is going on deep within the rotating components. The hardware lead times can also be prolonged; Finite Volume CFD (Computational Fluid Dynamics) analysis typically involves extensive run times, with each test point requiring several weeks’ computing just to generate a couple of seconds of real time data.

—Matt Hole, Head of Design Engineering, Drive System Design

DSD has overcome these difficulties working alongside Altair and FluiDyna further to develop and to enhance the software to make it suitable to solve drag and fluid visualisation in transmission applications. In a recent project DSD used nanoFluidX to optimize an EV planetary transmission design.

Using nanoFluidX enabled us to accurately visualise and analyse the behaviour of the transmission lubricant and its interaction with the rotating assemblies. The improved understanding meant we could develop a highly optimized, passive lubrication system, iterating the design with specifically targeted improvements. In all, we reduced drag losses by almost 30 percent while maintaining satisfactory lubrication of all the transmission elements.

—Matt Hole

Better visualization allowed DSD to improve thermal management by increasing the oil volume without incurring high churning and windage losses. Instead, a segregated oil cavity was created within the transmission case, from which oil is directed by baffles to strategic areas, such as the planet bearings and pins which are often very difficult to lubricate reliably.

nanoFluidX offers a level of interaction with, and analysis of, the results that is not available with conventional testing, and those results can be achieved in a much shorter time frame than is possible with either physical testing or fixed volume CFD approaches. It means we can achieve a much higher level of design optimization within the timescale of a typical customer program.

—Matt Hole

Drive System Design will demonstrate its use of the software in conjunction with its development engineering when the company exhibits at the Future Powertrain Conference in Solihull, UK, this week. Visitors to DSD’s stand will see an ultra-compact, highly efficient electric drive unit, recently developed on behalf of a global manufacturer, demonstrating the benefits of the methodology.

Comments

Arnold

Something like pre WW11 (Chev) splash feed bottom with pressure feed top end engines that we see in so many small engines today?
The idea seem to be to continue the move away from conventional semi-imersed gears without using conventional pumps as such.
Surely any splash shares the same physics with an ideal pump such as centrifugal. It would seem that to reduce drain down and supply good cold start lube with the low viscosity oils we see in the market an electric pump could be utilised for cold start.
Using lower viscosity oil would seem to be an important contribution to reducing drag in every friction area including bearings seals as well as the viscosity fluid impact losses.
The take away idea is not new but the specialised activity of putting in numbers during the design process is.

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