Powertrain testing moves from the road to the lab

Evaluating a powertrain on the road can be both expensive and time consuming. Today, the majority of calibration and testing can be carried out through simulation or at a static workstation, writes Freddie Holmes

Gone are the days where vehicle electrification was a niche; with a growing variety of options available and across more segments than ever, the market is being flooded.

Following the trend has been a slew of new acronyms; some familiar, some less so: the mild hybrid electric vehicle (MHEV), hybrid (HEV), plug-in hybrid (PHEV), range-extended (REEV), fuel cell (FCEV) and pure battery electric vehicle (BEV). Or, as an umbrella term, ‘xEVs’. These powertrains can be expensive to design, test and calibrate, and the industry is keen to reduce the number of physical prototypes and subsequent man-hours devoted to physical tests.

“With the number of different engine, transmissions and global regulatory requirements to consider, we need to handle very efficiently the calibration and testing of all of these variants,” explained Gerald Teuschl, Senior Product Manager, Electrified Powertrains at AVL. Speaking in a recent Greenstreetsoftware.info webinar, he added that even for BEVs – which are generally considered to be less complex than an internal combustion engine – bring their own challenges. “Higher degrees of electrification can lead to increased system complexity. We need much more co-simulation and interaction between different teams to achieve the targets we are set.”

Simulation can significantly reduce powertrain development time (Source: AVL)

Vehicles with the highest levels of electrification, namely BEVs and FCEVs, are also dependent on certain infrastructure and environmental conditions – such as charging type and weather conditions – that need to be considered closely.

Considerations

Testing is not about simply producing a print out; the overall consumer experience must be evaluated. Driving attributes, for example, are a primary consideration, along with noise, vibration and harshness (NVH).

Understanding how to optimise comfort and performance is vital when it comes to launching a new vehicle, particularly in a segment where consumers are yet to be won over by unconventional powertrains. Thermal management must also be closely investigated, as it has a direct impact on how a propulsion system performs. Like most automotive systems testing, it all starts in the lab. While cars are also put to the test on roads, physical testing is typically kept to a minimum in order to reduce costs and increase productivity. In most cases, only two of six phases require a physically available powertrain.

“In our offline space, we do not need a vehicle or powertrain to be available,” explained Richard Schneider, Lead Engineer, System Evaluation and Integration at AVL. Test benches can be used to simulate real world experience from the comfort and convenience of a lab. These benches often involve a single vehicle, or even a powertrain on its own, operating in static isolation. Tests can be run without a human operator, 24 hours a day, seven days a week if necessary. Once measurements have been made on a test bed, empirical models are produced to describe how the system responds to different variations. So-called ‘optimised maps’ can then be fed back into the electronic control unit (ECU), ideally resulting in better performance.

Cutting development times

In considering the entire process of testing and calibrating an electrified powertrain, AVL says that development times can be significantly reduced, and as most of the calibration is carried out without a test vehicle, costs are also slashed. While these are notable benefits, automakers profit simply from a better end product. “We are three times faster on a test bench compared to conventional approaches,” said Schneider. “When you are only using a powertrain, you do not have to wait for a prototype vehicle to be prepared.”

Today, many Tier 1 suppliers and automakers alike carry out powertrain testing in this manner. For example, Magna Powertrain’s Austria-based Engineering Centre features huge warehouses over a 20-hectare campus. Inside, a raft of tests are carried out, sometimes pushing powertrains to their limit or fine-tuning them for optimal performance. In a visit to the site earlier in June 2018, engineers explained to Greenstreetsoftware.info how engines could be left to run over a period of weeks if necessary, often subject to harsh operating conditions simulated by hydraulic machinery or climate conditioning (EV batteries often suffer in extreme cold or heat).

Ford EV charging
Electrified powertrains bring new challenges to calibration and testing strategies (Source: Ford)

Automaker interest

Automakers have shown a keen interest in reducing physical tests. General Motors has worked with AVL in the development of its Propulsion Systems Laboratory based in Pontiac, Michigan. By increasing the amount of work carried out in a test cell using hardware and simulation, programme development time was cut by ten weeks, with a 50% increase in lab test efficiency.

A third of all testing for the upcoming Mercedes-Benz EQC – the brand’s first BEV – was carried out digitally, covering all elements of the vehicle including the powertrain. Some have taken this approach a step further, aiming to cut out the test bench altogether. In May 2018, PSA Groupe announced it would invest €4m (US$4.69m) over five years to investigate how digital simulation could assist powertrain development and testing, with long-term plans to develop a new powertrain through virtual testing only.

The trend looks set to continue, particularly given the scale of investments required to bring a growing range of electrified powertrains to market. As Steve Neads, Director of Steering and Suspension Systems at AB Dynamics, wrote for Greenstreetsoftware.info: “The attraction of virtual vehicle development is well understood – repeatable test results obtained more quickly, in greater depth and at lower cost than can be achieved with physical prototypes.”

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