A joint development between Continental and the bus manufacturer VDL Bus & Coach has yielded prototypes for electric bus tyres. The prototypes offer impressive wet handling on the Contidrom test track and face complex technical trade-offs and new requirements.
Electric Bus Tyre Prototypes Tested at Continental’s Contidrom
Automotive and commercial vehicle manufacturers are not alone in changing their processes to accommodate electric mobility. Tyre manufacturers must also come up with new concepts to accommodate this new form of drive. A particularly demanding field, in terms of technology, is the development of tyres for electric city buses. Hence why Continental and VDL Bus & Coach, a leading manufacturer of electric buses, have pooled their expertise and jointly developed initial tyre prototypes that are currently being tested on Continental‘s Contidrom test track.
VDL Bus & Coach introduced its first Citea electric city bus in 2013. Since then, its electric vehicles have traveled more than 75 million kilometers across numerous European cities, cutting the emission of 11 million metric tons of CO2.
“Like all other electric vehicles, these bus tyres are exposed to higher torque when starting and accelerating,” explained Ben Hudson, Automotive Engineer at Continental Truck Tires. But, as he goes on to say, with electric city bus tyres there are other considerations involved, beyond those experienced in previous exterior vehicle projects: ‘Particulary in urban traffic, vehicles need to run very quietly so that the comfort of quiet electric drive is not jeopardised by the loud noise of the tyres on the road.”
Furthermore, the slowdown in urban traffic is a key factor in the energy recovery process for electric buses. Here, the electric motor acts as a generator and, driven by the deceleration of the bus, produces energy to charge the battery. This provides a marked increase in the range of the vehicle. Compared to conventional brake management systems, this recovery process puts additional pressure on the drive axle tyres.
Consequently, electric bus tyres have to face stricter requirements than those for buses with combustion engines. “They must offer the same mileage and meet the same safety standards as conventional powertrain bus tyres,” Hudson said. Trade-offs between mileage, braking performance and handling are technically demanding. “Here we are faced with new requirements”, he added, “but we are not going to accept any compromise in robustness or braking performance. Safety is our top priority.”
Currently, VDL vehicles at the Contidrom still run on tyres made by the Hannover-Stöcken Prototype department, with hand-carved drawings. As a general rule, the tyre development cycle, from initial prototype to series production, takes three to five years. For electric bus tyres, the goal is to shorten that cycle. “In developing this tyre prototype, we are not limited to previous creations,” said the Continental Truck Tires automotive engineer. “That gives us the freedom to try completely new concepts and ideas. If they are successful, we will implement them very quickly and include them in the development of the next tyre range. This can lead to significantly shorter development cycles, which means that Continental can react faster to market requirements.” In the search for the best possible solution, time is a key factor: given the dizzying progress in the electric mobility segment, the demand for suitable tyres is growing rapidly.