Advanced wheel hub drive passes extensive driving tests
The consortium tested two wheel hub drives, mounted at the rear axle of a Fraunhofer-developed demo vehicle under various difficult road surface conditions. The wheel hub drive generated a torque of up to 900 Nm per wheel. Tests included dynamic turning manoeuvres on wet surface, directional stability on slick, icy roads as well as during heavy braking – and all of them in combination with various system malfunctions which have been controlled selectively by the scientists. Subject to the test were innovative concepts of drive monitoring and error handling of fault-tolerant drive technologies under the aspect of operational safety.
In a first phase, the project partners collected and analysed data on possible effects of errors. By means of measurements on test rigs and numerical simulations, they determined the brake torque during short circuits in the coils as well as during failures of sensors and other components. Based on this knowledge they could develop specific hardware and software concepts for failure management. In this context, they developed a novel error recognition method that enables localising any errors reliably.
Failures of the current sensor and the angle sensors can be detected safely through a comparison of values obtained though measurements and through model-based calculation. In the case of an error, the model data are used. Handling of complications like short circuits in the windings or converters is based on a fault-tolerant design of the entire drive system. Towards this end, the electric motor consists of multiple redundant subsystems, enabling designers to isolate any errors and to compensate brake torque resulting from a failure, guaranteeing safely stopping the vehicle and even continue operation in emergency mode.
The test proved that in particularly during rides at the physical limits under difficult road and weather conditions the implementation of the project results led to significant safety improvements. At any operational situation the formation of improper brake torques could be avoided. Even during fast turns and wet or even slippery road conditions, the vehicle remained controllable. First assessments as to the economics of the concepts showed that the safety measures can be integrated into electric drives without added cost, which makes it possible to transfer the results into series vehicle production.
The project consortium included Fraunhofer IFAM and the institute for drive systems and power electronics of the Hannover university. It was funded in part by the German federal ministry for economy and energy.