Robust, Cost-Effective Sealing is Key to Success for Preventing Coolant Leakage for Busbars in EV Drivetrains

In electric vehicles, designers often need to deal with situations where e-motors are cooled by immersion in either oil or water, but also need robust electrical connections to external inverters or other power electronics modules.

Managing busbar interfaces in EVs where coolant is present on one side and a dry, electrically robust connection is required on the other side presents several challenges.

Figure 1 – Importance of Controlling Coolant Leakage Between Motor and Inverter

Some of the key issues to consider include:

1. Sealing and Isolation

  • Leakage Prevention: Ensuring that the coolant does not leak into the dry side is critical. This requires robust sealing mechanisms that can withstand temperature variations, vibrations, and pressure differentials without degradation over time.
  • Electrical Isolation: The interface must maintain high dielectric strength to prevent any electrical current from inadvertently flowing through the coolant. This typically involves selecting materials with high insulating properties and ensuring that the design maintains adequate creepage and clearance distances.

2. Material Compatibility

  • Corrosion Resistance: The materials used in the busbar and sealing components must be compatible with both the coolant and the electrical environment. Corrosive interactions could compromise both the mechanical integrity and the electrical performance of the interface.
  • Thermal Expansion: Different materials expand and contract at different rates with temperature changes. This can lead to gaps or stresses at the interfaces, potentially leading to leakage or electrical failure.

3. Thermal Management

  • Heat Dissipation: Busbars typically carry significant currents and therefore generate heat. The design needs to ensure that the heat is effectively dissipated without affecting the integrity of the seals or performance of the coolant system.
  • Temperature Gradients: Managing temperature differences between the coolant side and the dry electrical side is crucial to avoid condensation, which could lead to moisture ingress and electrical leakage.

4. Mechanical Integrity

  • Vibration and Shock: EVs are subject to significant mechanical stresses, including vibrations and shocks. The busbar interface must be mechanically robust to prevent the coolant from penetrating the dry side or compromising the electrical connection.
  • Pressure Management: Variations in pressure due to changes in altitude, temperature, or coolant flow could stress the seals. The design must account for these variations to prevent leakage.

5. Manufacturing Tolerances

  • Precision Engineering: The interface must be designed with tight manufacturing tolerances to ensure that all components fit perfectly. Even minor deviations could lead to gaps that might compromise sealing or electrical performance.
  • Quality Control: Strict quality control is essential during manufacturing to ensure that the sealing and insulation are applied consistently and effectively.

6. Maintenance and Longevity

  • Durability: The materials and design need to be durable over the vehicle’s lifetime. The interface should be resistant to wear, chemical degradation, and thermal cycling.
  • Serviceability: If maintenance or inspection is required, the interface design should allow for easy access without compromising the integrity of the seal or the electrical connection.

Existing Sealing Methods

Conventional sealing methods include:

  • Potting This method involves applying a potting material, such as epoxy or silicone adhesive after the busbars have been over-molded with resin. The potting material is applied around the busbars, forming a protective barrier that seals the assembly
  • O-Ring Seals – Typically made from elastomers like nitrile rubber (NBR), fluorocarbon (FKM), or silicone, which are selected based on their compatibility with the coolant and temperature range. O-rings are placed in a groove between two mating surfaces to provide a flexible, yet tight seal.

However, these approaches present challenges regarding either the high cost and time for secondary processes and/or issues with leakage over the lifetime of the assembly.

Our New ENNOVI-SealTech Approach

As leaders in connectivity innovation for automotive applications over the past 60 years, we have addressed the issue of cost-effective sealing with a new approach called ENNOVI-SealTech, which can be used seamlessly along with injection molding of the interface.

Figure 2 – ENNOVI-SealTech Shrink Tubing

ENNOVI-SealTech Shrink Tubing Method offers a unique approach using a double-walled shrinkable tube. This method consists of two layers:

  • Inner Glue Layer: This layer melts during the shrinking process, allowing the tube to adhere firmly to the metal busbar.
  • Outer Polyolefin Layer: This cross-linked layer blends into the molded parts during the injection molding process, ensuring a tight and durable seal.

Unlike traditional methods, this shrink tubing approach integrates smoothly into the assembly line before injection molding, eliminating any need for additional post-processing. As a result, it reduces time, costs, and labor without compromising sealing performance.

ENNOVI-SealTech Adhesive Tape is an alternative for applications where shrink tubing might not be suitable. This is a robust adhesive tape solution where the tape can be applied via automation equipment and boasts excellent adhesion to both metal and plastic. It maintains its elasticity and temperature resistance during the injection molding process, compressing under pressure and bouncing back to form a strong seal after the pressure is released.

This alternative provides flexibility in manufacturing processes and, like the shrink tubing method, eliminates the need for extra post-processing steps.

Figure 3 – ENNOVI-SealTech on a 3-Phase Busbar

ENNOVI SealTech is rigorously tested to ensure it meets the specific requirements of each design. We perform high-temperature and humidity endurance (HTHE) tests, with voltage bias applied, to simulate long-term environmental conditions and ensure the integrity of the sealing. Additionally, thermal shock testing with oil or water is carried out to validate the performance of the seal under extreme temperature variations. By customizing our testing processes to the exact specifications of each part, we ensure that ENNOVI SealTech delivers reliable and durable sealing solutions for high-demand applications.

As shown in Figure 4, the ENNOVI-SealTech shrink tubing process integrates smoothly into the assembly sequence prior to injection molding and does not require any secondary processing steps.

Figure 4 – ENNOVI-SealTech Integration into Pre-Injection Molding Steps

Summary

Once again, ENNOVI is proactively addressing a key challenge in EV powertrain design with an innovative solution the improves both production efficiency and quality results.

Key benefits of ENNOVI-SealTech include:

  • Design freedom with two options, shrink tube or adhesive tape.
  • Cost advantages in comparison to traditional post-processing potting methods.
  • Space savings that works in tight spaces with no additional material needed.
  • Simple process that eliminates unnecessary steps and secondary operations.
  • Good sealing performance with tests confirming no leakage at 7 bar, even after thermal cycling and aging.

ENNOVI has a proven track record with the top Tier-1s and OEMs, along with a global and local strategy that includes a vast engineering network covering key regions such as Europe, America, India and China. This leveraging of local production and design support has consistently demonstrated success in exceeding customer expectations through early engagement, tailored solutions, and ramp up to high volume production.

Discover how ENNOVI-SealTech supports your busbar sealing needs at a lower cost.

Newsletter

Stay up to date on all the latest ENNOVI news.

Discover More