Pressure Test Systems: Assessing Thermal Management & Cooling Circuit for E-Mobility
Johannes Montag
Climate control systems such as in electronic vehicles must be able to withstand extreme load changes during their lifetime. To ensure component safety and efficiency, manufacturers can use test stands for measuring the strength and durability of components in automotive engineering as well as other industries.
To prove the quality of media-carrying vehicle components, drive units (e-motors), valves, cooling and heating systems, hose lines, pipes, pressure vessels and other components are pressurized during testing – whether for dynamic pressure cycling tests, static pressure holding tests, flow measurements or classic burst pressure tests. The focus here is on efficient energy management and performance under changing temperature conditions.
Pressure changes at -60 to +160°Celsius
In a typical test, the component is inserted into the test chamber of the pressure cycling test bench. This can be an auxiliary heater for an electric car or valves, hoses and other hollow bodies that need to withstand more than 100,000 load changes over the lifetime of the vehicle (which can last up to 15 years). The test medium is a water-glycol mixture or pure glycol (for example Glysantin G40, G44, G48). The cooling circuit is tested at -40°C to +20°C (-40°F to +68°F) while a heating circuit is tested in temperatures from +20°C to +140°C (68°F to 284°F). A specially developed closed test media circuit uses pressure to prevent the formation of alcoholic vapours (which create a risk of explosion). A system can also be analysed in a climate chamber.
The flow rate of the test medium can vary from 1-50 l/min at a pressure of 0.2-12 bar or higher. The load changes are freely programmable with sinusoidal or trapezoidal rise at a test frequency of 0.2-2 Hz or faster. The test stand can be used for complete systems, assemblies and components made of various plastics, metals, and sealants. Weak points in the material combination – for example around a weld seam – can be optimized early in the development process as well as during serial production.
Time lapse for long-term tests
A long-term test usually takes between 20-30 days, depending on the frequency of the various load changes. The temperature and volume flow of the test medium as well as the ambient temperature (if the test takes place in the climatic chamber within the test stand) vary according to the test specification. The temperature at the inlet and outlet of the test object is measured continuously, as well as the flow rate, pressure and pressure drop, and current and voltage (both in the high and low range). The focus lies on the thermal and electrical performance of the heating and cooling unit under varying environmental conditions. Thermal sensors can be mounted on the product to indicate when energy is lost (thermal bridges) during the test or when the component becomes very hot and thus presents a fire hazard.
The test chamber consists of welded stainless steel with a high-strength polycarbonate safety window allowing for visual inspection. Any test sequences created on the PC can simply be called up manually via coded recipe management or by a handheld scanner. The integrated software enables efficient data acquisition and visualization. Test procedures and data are automatically stored on the system and can be exported to the network for evaluation. The open software structure makes it possible to integrate additional sensors and data during testing.
A modern technology for more energy-efficient testing
Most pressure cycling test stands use a pneumatic or hydraulic actuator. This has the disadvantage that the heat generated in the process necessitates the use of cooling water. Additionally, mineral oil must also be used for operation with these drives. To enable its customers to test components for electromobility more energy-efficiently in the future, Poppe + Potthoff Maschinenbau has developed a new electromechanical servo drive for its pressure cycling test stands. Due to the drive by means of a roller thread, high forces can be generated during the tests, which are sufficient for use in pressure cycling test stands – especially for testing components for e-mobility. “This new drive is particularly durable and can therefore be used for longer periods with little maintenance required” says Johannes Montag, CEO. “The newly developed test method enables us to offer our customers a more energy-efficient pressure cycling test stand. This means that a contribution to reducing the overall energy consumption can already be made in the development and production of components for electromobility”.
Testing energy efficiency in battery operation
In addition, the company has developed a function test bench for electrical appliances in e-vehicles such as cooling and heating units, control valves and pumps. Power consumption and performance are typically tested at alternating temperatures – optionally with a low- or high-voltage power supply to simulate operation via onboard battery and generator or the traction accumulator.
In many EVs, the heating and cooling systems drain the battery and thus negatively affect the vehicle’s range. Comparison of test results before and after a load test on the pressure cycling test bench can show how power consumption and performance change over the vehicle’s service life. The test object is connected to the power supply (low voltage 0-20VDC/5A) or high voltage (0-600VDC/150A) and the test media circuit. The test medium is circulated at a temperature of between -40°C to +100°C (-31°F to +212°F) and a flow rate of 1-50 l/min. The test can also be carried out in a climatic chamber at -60°C to +160°C (-76°F to +320°F) (and even higher temperatures) simulating various changing ambient temperatures.
Johannes Montag, CEO/Sales, Poppe + Potthoff Maschinenbau GmbH, Nordhausen
