The next ten years are set to see CO2 limit values increasingly tightened across key automotive markets. Customer preferences and legal requirements vary from country to country, so the new electromobility business unit of leading automotive and industrial supplier Schaeffler is already working with a range of drive solutions.
Schaeffler has achieved significant market success, developing double clutch and hybrid modules for hybrid vehicles with electrical drives located between the transmission and combustion engine.
Electric drives are more susceptible to failure than combustion engines and Schaeffler is working to address this issue through rigorous testing under extreme temperature conditions.
For example, to ensure proper, durable functioning of separating clutches, the components should be subjected to endurance testing under as realistic environmental conditions as possible, as well as fluctuating extreme temperatures.
Temperature measurement should also be performed during testing, along with measurement of drag torque at different temperatures and functional measurements.
Schaeffler’s Temperature Control Requirements
Schaeffler requires specific test environments for quality testing the separating clutch. The testing environment must offer a realistic simulation of ambient temperatures, subjecting the test specimens to temperatures that range from -40 °C to +120 °C during endurance tests.
In order to avoid extended waiting periods or downtime during specified changes in temperature, a rapid temperature change from +30 °C to -30 °C should be performed within 90 minutes. This rapid temperature change requires a compact, space saving solution that is able to effectively manage the temperature of the air within the hood.
The JULABO Approach
In order to meet Schaeffler’s requirements, an air-cooled PRESTO A85 is utilized in conjunction with a heat transfer device. The required air circulation is supplied by a powerful, specially adapted fan with variable rotational speed, allowing rotational speed to be increased for large test specimens, further improving airflow.
The heat transfer device and fan are fitted within a stainless steel chamber, while the PRESTO is connected to the heat transfer device outside and adjacent to the chamber. Testing is undertaken in a temperature range of -40 °C to +140 °C and because it offers a cool-down time from +140 °C to -30 °C in around 50 minutes, the PRESTO actually facilitates a more rapid temperature change than was initially required by Schaeffler.
Figure 1. Fan and heat transfer device are installed within a stainless steel chamber. Image Credit: JULABO GMBH
Figure 2. PRESTO A85. Image Credit: JULABO GMBH
Initial pre-tests take place using a provisional experimental setup at JULABO (Figure 3) before the heat transfer device with fan is connected to a stainless steel hood (Figure 4). The fan sucks air from above and below the heat transfer device via the front section of the chamber before pushing it through the heat transfer device slats that are temperature controlled using the PRESTO A85. This approach allows cooled or heated air to be consistently fed into the chamber containing the test specimen.
Figure 3. Provisional test setup. Image Credit: JULABO GMBH
Figure 4. Heat transfer device with fan. Image Credit: JULABO GMBH
Working with extreme temperatures in the positive and negative range results in a number of challenges.
A standard fan’s electromechanical components are not designed to accommodate the required extreme temperatures of -40 °C to +140 °C. In order to address this issue of operating temperature-sensitive parts of the fan inside the hood, JULABO’s temperature control specialists adapted the fan to meet Schaeffler’s requirements, attaching the drive motor outside of the chamber (Figure 5).
Figure 5. The fan drive motor attached to the outside of the chamber. Image Credit: JULABO GMBH
Figure 6. Heat transfer device. Image Credit: JULABO GMBH
Another common issue when working at sub-zero temperatures is condensation formation and resulting ice crystals. The air in the testing chamber only contains a low percentage of humidity due to its small volume, so in order to avoid outside air increasing the humidity, the chamber should be insulated, sealed and airtight. However, low condensation and ice crystal formation due to any existing humidity will be negligible, having no notable influence on the temperature control application.
The heat transfer device’s housing may deform due to extreme temperature changes, depending on the material in use. As temperatures increase beyond standard room temperature of 20 °C, the housing material will slowly expand and as temperatures decrease, the material will contract.
This deformation does not impact upon the temperature regulation process, but it may impede the position and fit accuracy of connections. Deformation due to changes in temperature can be prevented via appropriate reinforcement of the housing.
The use of appropriate construction measures helps to mitigate cooling or heating of the outer walls due to contact between stainless steel and the heat transfer device. Special materials are utilized to prevent points of contact between the stainless steel and the heat transfer device and these additional measures not only help ensure that touching the housing does not cause burns but that robust cooling does not lead to condensation formation.
For engineers at the industrial and automotive supplier Schaeffler, working alongside a reliable, competent partner was an essential precondition for successful realization of the project.
Numerous temperature control specialists were investigated to see if they could accommodate the special requirements that Schaeffler had, but only JULABO’s consulting team displayed sufficient willingness to develop the custom solutions required. JULABO’s expertise and many years of experience were also key factors in LUK/Schaeffler opting to work with JULABO.
With a development period of just two months, JULABO successfully constructed a heat transfer device that met all of Schaeffler’s requirements and, in some instances, far exceeded them.
By working closely with Schaeffler, a temperature control solution was developed for a universal housing in which the test specimens could be situated in precisely simulated ambient and extreme temperatures throughout functional and endurance testing (Figure 7).
Figure 7. Universal casing in which test specimens can be subject to simulated ambient and extreme temperatures. Image Credit: JULABO GMBH
This information has been sourced, reviewed and adapted from materials provided by JULABO GMBH.
For more information on this source, please visit JULABO GMBH.