Torque vectoring simulation for EVs
Driving simulators are helping to make electric cars safer and development programs more efficient.
Electric vehicles can provide more than a cleaner form of transport: they can offer additional safety, too. In cases where there is more than one electric motor on an axle, torque vectoring can be used to ensure the right amount of power is always delivered to the wheel, no matter whether it has lots of grip, or very little. Torque vectoring works instantaneously to enhance the stability of the vehicle during cornering, react to slippery surfaces and help steer the car out of trouble during emergency manoeuvres.
Electric drives have the potential to function as the ultimate electronic stability control (ESC) system. In traditional, internal combustion engine (ICE)-powered vehicles, the comparatively slow response from the powertrain means that ESC systems typically only use the brakes to stabilize the car. But an electric motor can apply more torque much faster than an ICE and work together with the brakes to stabilize the car. With two motors on an axle, torque vectoring can improve the steering response and theoretically steer the car without the driver having to turn the steering wheel, opening up new possibilities for active safety. Driving simulators support the development of torque vectoring by integrating advanced, physics-based vehicle and tyre models that run in real time.
The driver’s role
No matter how sophisticated its systems, a car never acts in isolation. A driver will remain at the wheel for the foreseeable future, so to ensure that torque vectoring systems work properly, they must be tested and validated in conjunction with the driver’s attempts to control the car.
As with many advanced technologies, torque vectoring sounds great as an engineering concept. But the underdevelopment of active-safety systems can lead to poor consumer acceptance: after all, the idea of the car turning without steering application could easily make the driver feel uncomfortable. To gain the driver’s trust, it must be smoothly integrated into the overall driving experience, so that they are confident in its abilities and know that the system is working with them, not against them.
Driving simulators contribute to presenting innovations like torque vectoring to the driver in a way that makes them feel safe. This is achieved by enabling human drivers to experience the intervention of new systems at an early stage of their development, long before a physical prototype car is available. By evaluating and fine-tuning the performance of torque vectoring and other chassis control or driver-assistance systems in the simulator, engineers ensure that fewer prototype vehicles must be built for final validation, making the development program faster, more cost-effective and more sustainable.
Simulator setup for torque vectoring tests
On the hardware side, the driving simulator’s motion system must be capable of transmitting the higher-frequency inputs generated from a detailed road surface model. For this application, driving simulator specialist, Cruden has developed an eight-actuator ‘octopod’ concept that provides the necessary tight control loop and high-frequency bandwidth while remaining a very cost-effective solution.
Recent developments at Cruden have resulted in a driving simulator that is suitable not just for ride and handling development, but also for the precise evaluation of secondary ride. Secondary ride – how the vehicle reacts to rapid, high-frequency inputs from the road surface – is crucial for torque vectoring development because for the powertrain to react correctly to the situation, it must have precise information about a tyre operating at the edge of its grip while also dealing with uneven road surfaces.
For example, a tyre will lose friction when it encounters small bumps during a turn, and the motor controller may need to respond by sending more torque to the outer wheel and reducing the torque to the inner wheel, to prevent understeer.
Physics-based models
This level of advanced simulation requires a high-fidelity, physics-based tyre model such as FTire from cosin. Traditionally an offline simulation tool, FTire can now run in real time and be used in a driving simulator to get much more realistic tyre behavior into the wider vehicle model. When combined with a high-fidelity model of the road surface – typically a LIDAR scan of a real track surface – this provides a more accurate “picture” of the road, and the tyre’s detailed response to it. That is crucial not just for the control software under development, but also for the human driver in the simulator, who is now in a more immersive environment and, as a result, reacts in a realistic way. Realistic interactions with advanced technologies are key to successful development in the simulator.
It’s important to ensure not just that the tyre model runs in real time, but also the model of the powertrain controller that will handle torque vectoring, as well as the vehicle model. In this type of test, a simulator would typically be integrated with a dSPACE or Concurrent real-time system on which to run the controller model. On the full-vehicle model side, Adams has long been popular with OEMs. The development of Adams Real Time means that users can now compile their physics-based model to a real-time solver, adding to the fidelity of the systems being modeled.
The use of physics-based models for online simulation is a growing trend in the automotive industry, with one example being the more frequent deployment of FTire rather than an empirical, model like MF-Tyre. In Cruden’s experience, EV manufacturers tend to be more CAE-driven than legacy car makers, which accelerates their development programs and reduces the number of physical vehicle prototypes by consolidating the tool chain. By running engineering tools previously confined to offline simulation in real time, the same tools can be used in the driving simulator to start collecting early subjective feedback quickly and easily, without the complication and risk of parallel development paths using different tools.
The team has worked hard behind the scenes to ensure that the Panthera control software at the heart of its simulators integrates seamlessly with its customers’ favoured engineering tools – whether that’s a vehicle model, a tyre model or something else. This means that not only may the simulator be used to test a model of the motor controller for a torque vectoring system, but even to test the motor itself, running as hardware-in-the-loop, if the customer so wishes.
“Our simulation technology helps ensure that advanced systems, now and in the future, will make EVs safer than the cars we’ve been driving up to now,” sums up Maarten van Donselaar, Cruden’s CEO. “If electric cars are safer because of torque vectoring and intelligent electric motor control, then consumers will have additional reasons to buy them. The more advantages EVs offer, then the greater the benefit will be to the environment from increased sales.”
Dennis Marcus, manager at Cruden
