Accelerated Lifetime Tests
Hybrid power technology development is ramping up globally in today’s ultra competitive automotive industry – and these technologies of the future demand vibration test solutions that can efficiently perform accelerated lifetime tests even on large and fully operational assemblies.
General Motors’ 3000 sq.m battery test laboratory at The Alternate Energy Center, Michigan, USA tests battery cells and packs for the Chevrolet Volt electric vehicle. An LDS Vibration Test System is used for electric vehicle preproduction qualification and functional test of a complete T-shaped battery assembly designed to be mounted underneath the car.
The Chevrolet Volt – Impressive Performance
The Chevrolet Volt is an electrical vehicle. Hailed as the spiritual and technological successor to the EV1, it will be launched in November 2010 as a 2011 model and has a “Voltec” extended range propulsion system. At the core of this is a T-shaped battery pack weighing over 400 lbs (190kg). The packs are water-cooled and have a capacity of about 400 amps at 400 volts. In the laboratory they are tested under extreme conditions – high and low temperatures, extremes of humidity, and different road conditions – to determine whether they will last for the life of the car. The Chevrolet Volt can manage 32 miles (51.5 km) on pure electric propulsion. When the battery is depleted, a 1.4 litre engine generator kicks in to sustain the battery charge and provide up to 482 km of electric propulsion
Anthony (Tony) Cullen has worked for GM for 20 years, mainly for the Milford Proving Ground Group. He has been involved with the GM-Volt battery vibration test lab since it came online in the second quarter of last year. Today, he is Lead Test Engineer for the vibration room in the laboratory.
Tony says, “The development of the Volt is unique with its on-board generator. It uses kinetic energy to charge the lithium-ion batteries and a standard Volt in urban driving conditions will do 40 miles [64 km] on a full battery charge”. He continues, “Once the energy in the battery reaches a specific level, the on-board 1.4 litre gasoline engine takes over and powers a generator to supplement the battery. The engine and generator now supply power for the vehicle, and everything is automatically controlled by sophisticated on-board computer systems”.
The LDS Vibration Test System
Tony Cullen explains his team’s tasks, “The main purpose of the vibration lab is to test the battery’s durability by simulating its lifecycle. The targeted lifetime of the battery is ten years. In addition to vibration, various other tests such as thermal and mechanical fatigue are carried out. The random vibration test lasts for 48 hours, that is, 48 hours of random vibration input and shock pulses. The data to power the shaker is acquired from a Volt on the GM proving ground. They test the battery in the x, y and z axes – one at a time – and each axis test takes 16 hours.”
Vibration testing also takes place in a climatic chamber where temperature and humidity are strictly and closely controlled. The environment in the climatic chamber can range from – 30°C to +78°C, and each 16-hour axis test is carried out under controlled temperature and humidity conditions.
To meet GM’s testing demands, the system used had to be high-performing and versatile and easily adaptable to several test demands on large heavy payloads in multiple axes. The LDS Vibration Test System delivered perfectly fulfils GM’s requirements for a heavy-duty system, able to perform accelerated durability test simulating the lifetime of the car. This includes several days of continuous testing at very high vibration levels and extreme temperatures.
Of the system, Tony says, “One of the major advantages of the vibration system is that it takes typically less than two hours to change the slip table from horizontal to a vertical position. Alignment is critical. The testing profiles in the horizontal and vertical axes are slightly different”. The head expander and assembly airlifts six inches from the armature via airbags between the head expander guidance frame and the shaker base. It is then a matter of moving the test specimen, rotate the shaker and fix it to the slip-table. Normal procedure would be to remove all head expander bolts and frame bolts – completely remove the entire head expander and guidance assembly and rebuild to the new configuration.
GM’s commitment to hybrid technology is far reaching and has extended to GM’s wholly-owned subsidiary, OPEL, and its production of the Ampera electric car in Europe. The prototype Ampera was built in Michigan and its battery tested at The Alternare Energy Center. It is hoped that the Ampera will hit the European markets in 2011.
GM’s commitment is, furthermore, reflected in its plans to be the first major U.S. automaker to design and manufacture electric motors, a core technology for hybrids and electric vehicles, and which will debut in GM’s 2-mode hybrid vehicles (which operate on engine power, electric power, or a combination of both) in 2013.
In a 2010 Press Release GM stated that the move to the 2-mode hybrid cars would “lower costs and improve performance, quality, reliability and manufacturability of electric motors”.
Tom Stevens, GM Vice Chairman for global product operations added, “In the future, electric motors might become as important to GM as engines are now. By designing and manufacturing electric motors in-house, we can more efficiently use energy from batteries as they evolve, potentially reducing cost and weight – two significant challenges facing batteries today.”