Thermal Management- Challenges for electric vehicles

The change to electric powertrain systems and the increasing importance of autonomous driving imply a variety of new challenges. Thermal management or rather thermal connectivity and cooling of electrical components have an important role to play.

Thermal Management for electric cars

Alternative drive systems are essential in order to meet the target of 95 g CO2/km on average for cars. If these values are exceeded, car manufacturers face massive fines. This pricing mechanism has a positive impact on low-emission cars. A global rethink has to take place in the automotive industry.

Aspects like an continuous increasing power density or higher heat flow per area (W/m2) and “high power charging” lead to an increased component temperature and consequently to a reduced lifetime in the application. Efficient thermal cooling of electrical components by connecting of the heat source to heat sink, while at the same time having an electrically insulating effect, is therefore a prerequisite for the high quality standards from the automotive sector. This connection and the levelling of appropriate component tolerances, gaps or air inclusions can be realized individually by the wide range of Thermal Interface Materials of KERAFOL, depending on the requirements for thermal conductivity (W/mK) and desired temperature difference ∆T.

Thermal Management for e-mobility

The change to electric drive systems implies completely new applications and challenges in the field of “Thermal Management.” For examples, the functional relationship between the operating temperature of a battery stack and its maximum achievable number of cycles has been sufficiently proven and can be quantified extremely precisely by the following rule of thumb:

“A reduction in operating temperature by 10°C doubles the lifetime of the battery cells”

The net reach of an electric car is also noticeably dependent on the operating temperature of the battery and thus also indirectly on the present thermal cooling. In addition to the concept for thermal connectivity of the energy source, the “car of tomorrow” also requires solutions for electrical components in the areas of LED, sensor technology, dc-dc converter, bus bars in general, battery management systems and inverter, one of the core elements of the electric powertrain.

Softtherm Gap Pads

The cross-linked silicone-based elastomers, better known as Softtherm Gap Pads, can play a crucial role in thermal cooling (power range up to 6 W/mK) of electronic components due to their variety of specifically adjustable properties.

Softtherm Pads
Basic Material Silicone
Thermal Conductivity (W/mK) 1,0 – 6,0
Breakdown Voltage (kV/mm) 2 – 16
Compression (%) up to 30
Application Temperature (°C) -60 up to +250
Hardness (Shore 00) 10 – 75

Due to the high flexibility and enormous mechanical resistance of the Softtherm Pads, large gap dimensions as well as high component tolerances can be compensated. Compared to systems based on polyurethane or epoxy, silicon-containing Pads or Tapes can absorb and compensate vibrations much better, an effect that is favoured by the high softness of the products of Kerafol.

To meet the requirements of the automotive, Kerafol did various test (internal and external) to evaluate the long-term behaviour of their products.

Test Characteristics Thermal Conductivity Hardness Breakdown Voltage
Maximum Temperature 1.000 h @ 150 °C P P P
Temperature Cycles -40 up to 125 °C P P P
Humidity/Temperature 85 % relative humidity/85 °C P P P
Vibration test according VW80000 / LV124 P (Application Test)

In addition to individual solutions, such as one-sided adhesive coating for component fixation or fibreglass reinforcement to increase mechanical stability, two-layer films (required by specific regulations) can also be of great added value to the customer.

Another important factor concerning high quality material, is the reproducible quality of the die-cut parts. Therefore, Kerafol cooperates with a specialist in the UK, the company Thermal Issues. Due to their high standard cutting technology and an outstanding service concept, samples are available next day and without additional cost for tooling.

This combination of German technology and UK supply as well as the long-term experience of both parties in the field of thermal management leads to a new type of support.

Author: Wolfgang Höfer (M.Eng), sales manager, KERAFOL GmbH & Co. KG

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