Test Environment for Realistic Testing of Electric Vehicle Batteries

In the "GRISU" project, Fraunhofer ISE, MESSRING, Linxens, and HAW Hamburg are developing a novel test environment for electric car batteries. The focus is on an innovative test device with four decoupled shakers, which is designed to simulate more realistic bending and torsion loads on complete battery storage systems. The aim is to minimize the risk of fire in the event of thermal propagation through improved test procedures, quick-release devices, and gas detection – to increase laboratory safety and validate fire protection measures.

Initial Situation

The axles of electric vehicles are subjected to varying, uneven loads while driving, which cause bending and twisting of the bodywork and battery storage. Current vibration test benches use rigid mounting surfaces and usually test individual battery modules rather than complete storage systems; moreover, they do not cover extreme axial loads (e.g., curb crossings). Existing test machines do not have automated fire protection or quick-release devices, which means that there is currently a lack of protection standards for test rooms, test equipment, and personnel.

Objective 

The "GRISU" project aims to develop and demonstrate a testing device with four individually controllable shakers that realistically simulates the bending and torsional stresses of entire battery storage systems. In addition, measurement parameters and trigger conditions will be defined that clearly identify a safety-critical condition in a battery. Based on these criteria, an automatic quick-disconnect device and suitable extinguishing concepts will be developed and tested. In addition, gas detection for the early detection of battery fires will be integrated so that test procedures can be terminated at an early stage and extinguishing measures can be initiated automatically. The aim is to significantly increase laboratory safety and to provide reproducible validation and evaluation methods for fire protection measures.

Approach

In Fraunhofer ISE's "Lab Battery Engineering, Production and Testing," a test bench consisting of four decoupled shakers is being set up. Each of the shakers should be able to simulate the load of a wheel suspension on the storage system. HAW Hamburg uses data from field measurements on electric vehicles on different road surfaces and, based on this, implements test procedures that can realistically simulate the bending and twisting of the battery storage system. The four shakers are coordinated so that they generate the different axle loads separately from each other and do not work in unison, as is the case with conventional shaker systems. This more realistic test setting is a key unique selling point of the test device developed in the project. Due to the new possibility of conducting such tests, there is also an increased risk that a battery cell will enter a safety-critical state during testing.

To mitigate this risk, our partner company, Messring GmbH, is developing a universal quick-release device. Their expertise in crash test facility construction and data acquisition will help to disconnect the equipment attached to the four shakers, including the battery storage, from the test machine as quickly as possible and without human intervention, and to initiate the deletion of the battery storage. In order to trigger the separation and deletion process in an emergency, parameters to be defined in the project are required that allow a safety-critical condition to be clearly identified. A suitable deletion concept can then be used to create a controllable situation. To this end, fire-retardant tests are being carried out at Fraunhofer ISE in close cooperation with fire protection experts for lithium-ion batteries under defined laboratory conditions. In addition, research is being conducted in cooperation with the partner company Linxens Deutschland GmbH on the early detection of battery fires through gas detection. Sensors are used to detect the gases released from battery cells in the event of a fire and analyze them in real time. This would make it possible to better identify threatening scenarios at an early stage and initiate a premature termination of the test and the extinguishing process.

Results 

Expected results of the ongoing project include a fully functional demonstrator that enables more realistic reproductions of bending and torsion loads on complete battery storage systems, thereby expanding existing test methods. In addition, measurable criteria and trigger algorithms are to be developed that reliably detect safety-critical conditions, as well as a tested quick-disconnect device that allows rapid, automatic disconnection in an emergency. Validated extinguishing concepts and a prototype gas detection system are to enable significantly earlier detection and effective containment of battery fires. This significantly expands the testing options for traction batteries in the direction of application-oriented scenarios. In addition, the procedures will be documented in a standardizable manner and preparations will be made to transfer the measures to industrial test benches with increased operational safety. 

The "GRISU" project is funded by the Federal Ministry of Economic Affairs and Energy (BMWE).