EVs: Challenges for tyre makers
By Louis Rumao:
Even if Electric Vehicles (EV) match internal combustion-powered cars in total cost of ownership, will it be enough for the projected revolution? An inadequate charging infrastructure could limit growth of EVs
The long-awaited, oft-delayed electric vehicle revolution is now projected to happen in the near future. Britain recently said it would “end the sale of all conventional petrol and diesel cars” by 2040, following similar proposals by France earlier this month to reduce nitrogen dioxide (NO2) pollution. China issued plans last year requiring that 12 per cent of cars sold be battery-powered or plug-in hybrids by 2020, while India has said it wants to replace all vehicles with EVs by 2030. Norway hopes to end sales of new petrol and diesel cars by 2025, and other countries such as Sweden, Denmark and Finland have expressed similar ambitions to phase out fossil fuel engines.
This month Volvo Cars became the first mainstream automaker to sound the death-knell of the internal combustion (IC) engine, saying that all models it introduces starting in 2019 will be either hybrids or powered solely by batteries.
“Given the rate of improvement in battery and electric vehicle technology over the last ten years, by 2040 small IC-powered private cars could well have disappeared without any government intervention,” said Alastair Lewis, professor of atmospheric chemistry at the University of York. “Nonetheless this is highly symbolic since it signals to both the public and to manufacturers that there is no turning back from electrification,” he added.
According to a report from research firm Bloomberg New Energy Finance, in less than ten years, the biggest obstacle to the sale of EVs—their high cost —will be gone and cars that run on electricity will cost less than those that run on fossil fuels. “By 2022,” the report says, “the unsubsidised total cost of ownership of BEVs (battery electric vehicles) will fall below that of an IC-powered vehicle.” From there, the report projects a steadily increasing rate of adoption, reaching global sales of 41 million—25 per cent of total market share—by 2040. That’s a remarkable prediction given that today, EVs make up less than 1 percent of new car sales in the US, mostly with government subsidies and mandates. But the change is coming, according to the Bloomberg report. “We project that the cost of manufacturing electric vehicles will fall dramatically, and faster than most people realize,” says Salim Morsy, the author of the study. At present, battery pack accounts for about a third of the cost of the entire vehicle. Between 2010 and 2015, the average cost per kilowatt hour (kWh) dropped from $1,000 to $350—a 65 per cent plunge – and could drop to $120/kWh by 2030! Additional cost reductions will come from moderate improvements in production processes, battery chemistry, economies of scale as manufacturing expands, and “aggressive pricing” by producers eager to sign contracts with major automakers. “We believe that between now and 2020, cost will continue to drop significantly,” Morsy says. Even when the ownership cost of EVs becomes comparable to the fossil fuel-powered vehicles, their widespread use may still be hindered if the charging infrastructure is inadequately developed.
Tyres for EVs
For EVs, advanced battery packs, efficient motors, and cutting edge thermal management systems often steal the spotlight, but that does not mean that tyres on an electric car are being overlooked. Tyres are a carefully crafted compromise for every vehicle, a compromise that emphasizes some attributes over others, because you can’t have it all. Great-handling tyres have poor durability. Durable tyres are noisy. Quiet tires suffer from poor handling. The EV manufacturers have challenged the tyre industry to make tyres that have low rolling resistance, low noise, but can still handle the instant torque of an electric motor. EVs complicate things further – they lack the roar of I-C engines which hide the noise of tyre rubber on pavement, so quiet matters. For EVs, range is also crucial, and tyres need to play their part in squeezing every mile from every watt. A “sticky” tyre would grip road better and thus better handle the instant torque of an electric motor, but will sap the car’s electric range due to high rolling resistance. Likewise, a tyre that is durable enough to handle the instant torque will likely be a loud tyre.
So, tyre engineers juggle more than 200 variables—rubber compounds, construction methods, sidewall design, belt arrangement, tread design, groove width, and so on—to find the best combination for a given manufacturer and model. Tyre manufacturers strive to create customized compounds and construction that stiffens tyre without degrading comfort. Some EV tyres also are self-sealing in the event of a puncture, eliminating the need for a spare or even an inflation kit. That saves weight, which also helps boost range. Acoustics are another important factor in the tyres’ design—down to tweaking tread patterns, block sizes, and groove widths to minimize noise. The Michelin Energy Saver A/S tyres that come standard on the all-new Chevrolet Bolt EV are custom built specifically for that car.
Michelin makes tyres for 45 per cent of EV’s built in the US, including Tesla’s Model S and Model X, the Nissan Leaf, and Chevy’s Volt. And it’s the sole provider of tyres for Formula E, the electric racing series. The lessons learned with one program—improvements in longevity, rolling-resistance, etc.—carry over to others. Tesla has challenged Michelin in a variety of ways. “We’re pretty proud of the work we’ve done with them,” says tyre engineer Ed Gliss. “Smaller electric cars mostly care about rolling resistance to extend their range, but Tesla wants that plus good handling and low noise,” Gliss says. “But the Tesla is heavy, with all the batteries under the floor. So, the weight-loading is a bit bizarre. You can’t just take a tire off the shelf and expect it to handle the Model S. We had to reconfigure it to be able to absorb all those forces.” For Tesla, Michelin created a compound that minimizes heat buildup, allowing the tyre blocks to retain their rigidity and not bend or flex excessively while driving. That offers the best mix of rigidity and adhesion, minimizing rolling resistance while maximizing handling. Goodyear Eagle Touring/TO tyres, also marketed for EVs, feature a foam liner for enhanced tire-noise reduction while maintaining durability and grip.
Hankook too has developed the Enfren Echo tyres that feature low rolling resistance coupled with an environmentally-friendly manufacturing process. These new tyres are arguably on the cutting edge of tyre technology. They are quiet, durable, and sticky without sacrificing too much range.
Pushing the tyre boundaries for future electric cars—achieving that desirable balance between performance and EV tranquility—will require plenty of new science, research, and many thousands more hours on test tracks. It’s where the rubber truly meets the road for the EV revolution happening now!
(Photo courtesy: experimentalev)