As the demand for electric vehicles (EV) increases, more automakers have been working on developing their vehicle systems and, in particular, their powertrain systems. Motion control is one area that is evolving due to the electrification of the powertrain, with the high-precision control capability of electric drives finding a new purpose as part of this complex science.
A major challenge with EVs is managing their weight, especially the impact of that weight on their dynamics. New ideas and techniques that reduce the cost, packaging volume and complexity of the systems required for this task are finding a welcome audience.
Only now, when vehicle manufacturers have achieved a reasonable spread of EV models, are the time and resources available to consider how electric powertrains can add value to other vehicle systems. “This is a field where motion control is very much in play,” says Intertek’s EV Services Director, Patrick Havers.
Intertek provides engine and powertrain performance testing services with global labs across the Americas and Europe to support the global transition to EV. These testing facilities offer an impressive research portfolio across ICE, EV, hybrid-electric vehicle (HEV) and hybrid propulsion systems (HPS). To name just a few, its facilities include powertrain in the loop testing, high-speed eMotor dyno, EV fluids, hybrid transmission and battery simulation or real battery integration to powertrain testing.
Based in Milton Keynes, UK, Intertek’s research-quality new four-wheel-drive laboratory (4WD) is part of its new EV powertrain test facility. When the Intertek team specified the company’s 4WD laboratory for EV powertrain development, it chose hub dynamometers (rather than a rolling road) to eliminate tyre variability—together with a very high torque and transient capability.
This was complemented by high fidelity data capture into MHz levels. “What we hadn’t anticipated,” continues Havers, “is that this is exactly what is required to develop and calibrate a number of chassis and active safety systems.”
When the 4WD vehicle-in-the-loop laboratory opened early in 2022, the Intertek team discovered that programmes were extended to oversee technologies such as torque vectoring, complex blending, and transient control required when active safety systems intervene.
“EV high mass and high torque capability contribute considerably to the dynamics and related motion control challenges, often leading to a range of complex and costly additional systems being packaged,” explains Will Parkinson, Intertek’s test facility development specialist. “We are seeing that while very precise individual wheel control—or even simple axle torque control—is not a substitute for sophisticated motion control systems, the technique offers significant potential for simplification and de-costing of the motion control development package.”
As an example, Harry Tregartha, Intertek’s vehicle-in-the-loop specialist, points to maximising traction by providing a swift response to changing levels of grip. He also raises the controversial topic of tyre particulates. “People disagree about the scale of the problem caused by the high torque and high weight of EVs, but most agree that additional tyre particulate emissions are a problem that needs addressing,” he comments.
“Thoughtful control of transients, wheel slip and body motion will make a significant contribution—it’s a relatively new area of research, but one that I think has great potential now that we can offer sector specialists a research-quality 4WD laboratory.”
To help its clients develop these techniques, Intertek can measure wheel speed and slip very precisely in real-world driving or on track for motorsport applications and then replicate those conditions in the laboratory.
High-speed torque control
It’s not a simple equation, as Havers explains, “Individual wheel control can add cost and packaging challenges because of the requirement for individual motors and inverters. And there may also be implications for the design of the inverters—very high-speed torque control requires minimum overshoot in the control signal. That can require some clever hardware optimisation as well as rigorous calibration.”
However, the capacity for EVs to deliver very high torque loads very quickly is already leading to more manufacturers specifying 4WD, often with at least one axle delivering individual wheel motors.
Havers says that every project through the laboratory so far has taken a different approach. “This creates opportunities for a much more sophisticated strategy for high-level integration of motion control, dynamics optimisation, active safety and tyre particulate management,” he concludes. “The result will be reduced complexity of motion control systems alongside improvements in performance in each area.”