Analysis of E-Motor Oil Cooling using Smoothed Particle Hydrodynamics (SPH)

Posted on 7th August 2025

Johannes Becker, Dive Engineering Software, Inc.
Felix Pause, dive solutions GmbH

Drivetrain electrification across the automotive and commercial vehicle industry drives increasingly power-dense electric motor designs, which require well-engineered cooling systems. Front-loading e-motor thermal simulations in the early design stage can de-risk prototypes and unlock more innovative designs.

The Role of Smoothed-Particle Hydrodynamics in Drivetrain Development

As the automotive industry is shifting towards electrification, the design of electric motors is key for optimizing vehicle performance. Balancing increased power and longevity with compactness and simplicity necessitates the use of sophisticated cooling strategies to maintain optimal operating temperatures. Various simulation methods have been explored in the past, ranging from traditional Volume of Fluid (VOF) techniques to particle-based approaches.

In response to increasing market pressure for faster, more efficient product development under constrained resources, Smoothed Particle Hydrodynamics (SPH) offers a flexible and powerful simulation approach, particularly suited for early-stage design. Unlike traditional CFD, SPH − as the name suggests − simulates fluids as a collection of small particles and does not require mesh generation (see Figure 1). This provides significant pre-processing and numerical efficiencies in cases where mesh generation and remeshing are a bottleneck in VOF methods, allowing engineers to explore large numbers of design variations quickly and cost-effectively. For that reason, SPH has become a widely used method of analyzing lubrication and cooling performance in drivetrain engineering, due to its ability to accurately model free surface and multiphase flows, as well as its efficacy in handling complex geometries and moving components. Consequently, SPH is increasingly applied in the design of electric motors as well.

Modeling Heat Transfer in Complex Geometries with SPH

Correctly predicting cooling performance in simulation fundamentally requires accurate modeling of surface wetting by the coolant, i.e. a good surface tension model, and consideration of the (often significant) temperature-sensitive viscosity of coolant oils [1]. SPH enables detailed simulation of how coolant oil absorbs and transfers heat across complex geometries like coil windings, accounting for temperature-dependent viscosity layers. By applying adaptive particle refinement [2] and realistic boundary conditions, SPH captures both transient and steady-state heat transfer behaviors. This allows engineers to evaluate heat transfer coefficients, optimize cooling strategies, and support thermal network models − especially in areas where empirical data is lacking.

This article presents findings from simulations of a simplified, actively cooled e-motor employing SPH. The results are validated against experimental data, demonstrating the method’s efficacy in predicting oil dynamics and heat transfer.

Experimental Reference and Simulation Setup

To validate the applicability of SPH in real-world designs, we examined an experimental e-motor cooling case by Davin et al. [3] as our reference scenario. Davin et al. investigated a 40kW radial flux machine equipped with 12 coils and examined different cooling configurations. Here, we focus on investigating a setup utilizing 5 inlets to distribute oil onto the coil windings. Since the experimental setup is symmetrical, our simulation model encompasses only half of the domain, with symmetry boundary conditions applied to the center plane. The setup is illustrated in Figure 2.

To validate the method against the experimental references, the inlet mass flows and inlet temperature of the coolant are varied. Since the properties of the coolant oil were not reported in the original work, some assumptions had to be made. As viscosity was given at 50 and 75°C, the following exponential law was used to interpolate between these two points and account for the influence of reduced viscosity with increasing temperature:

The density, thermal conductivity, specific heat capacity, surface tension coefficient and contact angles of the coolant used in the experimental work were not reported. Thus, typical values for coolant oils were applied (see Figure 2).

Results

For each of the six operating points, the heat flow rates on the coils are obtained and compared with the experimental results. The simulation generally follows the experimental trend in [3] of increasing heat transfer rates with increasing volume flow rates and decreasing inlet temperatures. Moreover, a 77 % to 96 % match with experimental reference is found for the 6 operating points (see Figure 3). Given the accuracy of an experiment and the assumptions made, this indicates that the simulation can capture the complex multiphase flow present in the e-motor.

The method can therefore be used to test different design variations. In Figure 4, a snapshot of oil distribution predicted by the simulation is given. Here, the oil flow could be optimized by changing the nozzle position or design, ensuring that all coils are adequately cooled.

Figure 4: Oil distribution and heat flux at 368 l/h and 75°C.

Conclusions

The Smoothed-Particle Hydrodynamics method is widely applied and extensively validated in different sectors and applications. I can reliably predict complex multiphase flows in drivetrain, automotive, manufacturing, and more. Our results show accurately predicted heat transfer in the e-motor case, with deviations from experimental data ranging from 4 to 23 %.

Initial setup time was around 2 − 3 hours and only minutes for every additional operating point, the computational effort for each operating point was around 3 − 6 hours. By integrating SPH within a scalable, cloud-based platform, conducting extensive parametric studies, such as testing different nozzle types, orientations, placements, and coolant flow rates, can be parallelized. Automated DoE configuration and parallel execution of simulation and data analysis (i.e., simulating all operating points in parallel) allow for rapid design space exploration [4] − enabling engineers to investigate the effect of nozzle types, positions, inlet conditions (temperature/flow rate) or other design changes with same-day turnaround.

As the automotive industry accelerates toward more compact, powerdense electric drivetrains, SPH offers a critical simulation tool to meet thermal management challenges early in the design cycle − supporting faster innovation, reduced prototyping costs, and more robust e-motor designs.

 

Sources:

[1] G. A. Mensah, P. Sabrowski, and T. B. Wybranietz, “Practical guidelines on modelling electric engine cooling with SPH,” in 2023 International SPHERIC Workshop, 2023.
[2] B. Legrady, “Particle-Based CFD Study of Lubrication in Power Transmission Systems Using Local Refinement Techniques,” Power Transmission Engineering,
vol. February 2024, 2024.
[3] T. Davin, J. Pellé, S. Harmand, and R. Yu, “Experimental study of oil cooling systems for electric motors,” Applied Thermal Engineering, vol. 75, pp. 1–13, 2015.
[4] B. Legrady, “Efficient Numerical Assessment of Thermal Effects in a Gearbox Using Smoothed Particle Hydrodynamics,” in American Gear Manufacturers Association,
in Fall Technical Meeting, vol. 24FTM25, 2024.

 

HOERBIGER emDOC – Smart Clutch System for Compact, Wear-Free Actuation and Scalable e-Drive Integration

Posted on 6th August 2025

With emDOC, HOERBIGER offers a compact and innovative dog clutch system with electromagnetic actuation – engineered for tight spaces and smart integration into next-generation electric drivetrains.

Electrification increases complexity in drivetrain integration – demanding compactness, durability, and responsiveness. HOERBIGER meets these requirements with emDOC, an electromagnetically actuated dog clutch system, optimized for space-saving, wear-free-actuation, and scalable use in e-drive architectures.

The HOERBIGER emDOC is designed to fit:

• Optimized for tight packaging constraints
• wear-free actuation principle – no mechanical contact during shifting
• Engineered for low maintenance and long service life
• Available in mono-, bi-, or tri-stable versions for maximum safety and flexibility

emDOC supports applications such as disconnect clutches for e-axles, multi-speed electric drives, and differential locker or parking break. Integrated sensors enable precise position control, while low energy consumption and high torque density ensure system efficiency.

Another key benefit is the fast development cycle:

• Week 1: Initial concept and pricing indication
• Week 2: Application-specific feasibility concept
• Month 3: Finalized, order-ready design

HOERBIGER delivers more than technology, we deliver structure:

With 130 years of engineering experience and over 60 years as a proven automotive supplier, we deliver robust system integration – from design and simulation to validation and series production. As a certified, foundation-owned group, we are stable and diversified across industries.

Whether you’re designing for performance, packaging or lifecycle cost – emDOC is ready to integrate into your system.

World’s First Disconnect and Locker Combo Differential (DL ComboTM)

Posted on 31st July 2025

JJE’s New Solution for High-Efficiency, High-Capability eAWD

Dr. Yang Cao, Transmission Manager, JJE Technologies

JJE Technologies proudly presents the DL Combo™, the industry’s first fully integrated disconnect and locker differential system. By combining eDisconnect and eLocker functionalities into a single, compact unit, this innovation provides electrified all-wheel-drive (eAWD) vehicles uncompromised off-road capability and low energy consumption.

Introducing the DL Combo™ Differential

JJE launched its DirectFlux™ eLocker in 2021, now in use by several OEMs including in the newly introduced Beijing Automotive BJ60e and BJ40e extended-range off-road SUVs. This eLocker utilizes JJE’s unique electromagnetic clutch technology to lock up 6000 Nm of half-shaft torque within just 70 milliseconds.

JJE’s Disconnect & Locker Combo Differential, or DL ComboTM Differential

In 2022, JJE introduced the DirectFlux™ eDisconnect, offering both mono-stable and bi-stable configurations. This system enables real-time AWD/2WD switching at any vehicle speed, improving energy efficiency and electric range by 7–10 %.

Now, with an innovative, highly integrated mechanical design, JJE’s new DL Combo™ Differential merges these two systems into a compact differential with the same envelope as a conventional differential − making it fully interchangeable for OEM applications.

Compact. Capable. Integrated.

The DL Combo™ features a deeply integrated, nested mechanical structure that leverages JJE’s DirectFlux™ electromagnetic clutch configuration. As a result, the DL Combo™ differential maintains the same envelope as a conventional unit while offering dual functionality − eDisconnect and eLocker − within a single package.

Compared to standalone solutions, this design allows standard layout, significantly reducing the complexity and weight of the eDrive system with such dual functions. It allows vehicle OEMs to offer different drivetrain functions − conventional, disconnect only, locker only, or combined disconnect and locker − with standard mechanical interfaces.

JJE’s eDifferential Family & Roadmap

For OEMs, balancing efficiency against off-road and dynamic capabilities has long been a challenge. JJE’s DL Combo™, built upon its proven DirectFlux™ clutch technology, eliminates that offering below  features:

• eDisconnect for 4×2 mode and drag loss reduction
• eLocker for 4×4 mode with 100 % torque transfer and maximum traction

Already validated in production vehicles, the DL Combo™ marks a major leap in electrified drivetrain systems.

Ideal for Secondary Axles

The DL Combo™ is especially suited for secondary drive axles − for instance, enabling a 4×4 off-road SUV to seamlessly switch to 4×2 for efficiency, while  maintaining full locking capability when additional taction is needed.

Technical Breakthroughs

The DL Combo™ integrates two subsystems:

• eDisconnect: Electronically decouples the secondary axle in <70 milliseconds, reducing drag losses by up to 95 % and increasing electric range by 7 − 10 %
• eLocker: Delivers rigid locking between left and right half shafts for full torque transfer − even in extreme off-road scenarios

Both functions can be configured as bi-stable or mono-stable, depending on application needs. Two typical configurations meet different functional safety targets:

• Front axle: Bi-stable eDisconnect + Mono-stable eLocker. The bi-stable eDisconnect is fail-safe. It keeps the system in the state that the vehicle needs at the moment of failure, e.g., loss of 12V power supply. The mono-stable eLocker lets the front secondary axle default to open in case of a failure − the vehicle will be easier to steer when unlocked, but the vehicle will lose front axle’s power.
• Rear axle: Bi-stable eDisconnect + Bi-stable eLocker. eLocker’s bistable function allows the differential to stay locked for torque safety, which is especially important under critical conditions such as climbing rocky steep grade and pulling up heavy trailer on low-traction surface. This configuration is ideal for rear axle, which bears more driving force, and does not affect steering when locked up.

One additional benefit of bi-stable device is energy efficiency − the bi-stable electromagnetic clutch does not require any current to hold its state, enhancing system’s efficiency.

The DL Combo™ can be applied to provide several practical driving modes based on the vehicle’s need:

• 4×2 Mode (Economy): the eDisconnect disengages the secondary axle, eliminating the drag and maximizing efficiency. A mechanical interlock ensures the eLocker will not engage accidentally.
• 4×4 Mode (Sport): the eDisconnect in the secondary axle is engaged, but the eLocker stays open. This is the normal 4×4 mode.
• 4×4 Locked Mode: With the eDisconnect engaged, the eLocker is further engaged to secure the axle’s traction.

 

Vehicle Test

The DL Combo™ has been successfully demonstrated in the Beijing Automotive BJ40e, China’s iconic off-road SUV. The vehicle demonstrated 7 − 10 % EV range improvement by seamlessly switching between 4×2 and 4×4 at any speed. The offroad capability remains uncompromised as the eLockers function when needed.

BJ40e Test Vehicle with JJE’s DL ComboTM Differential & Drag Loss Chart

Setting a New Benchmark for eAWD

By addressing both efficiency and capability, the DL Combo™ Differential enables automakers to offer the next generation of electrified AWD with best-in-class efficiency and uncompromised traction security.