Keeping pace with Evs
By TA News Bureau:
One of the major challenges before the automotive industry is to improve its sustainable performance. Sustainable value approach is the first value-based method for assessing corporate sustainability performance. Companies not only use economic capital but also environmental and social resources to create value. Sustainable value is created whenever a company uses its economical, environmental and social resources more efficiently than the benchmark, says Pradeep Chandrasekaran, Deputy General Manager – Vehicle Integration Centre of Excellence (Monocoque) at India’s top vehicle maker Mahindra & Mahindra. He says value contributors in the form of Co2 and Nox emissions, water use etc improve sustainability. Cars using hydrogen fuel cells , biofuels etc contribute to it. A roadmap for 2025 for sustainability is being prepared for the Indian automobile industry. Electric vehicles and tyres potentially contribute to sustainability, he says in this interview
Why do you think EVs should have specifically designed tyres?
The electric vehicles (EVs) have specifically designed tyres. EV’s torque puts immense demands on tyres because they have to be sturdy and very grippy, although not so grippy that they use up vital battery power. The silent powertrain makes tyre rumble more obvious, and therefore reducing noise is also important. The tyre needs to be hard so that when it rolls they produce Least resistance.
Low rolling resistance is the key factor in ensuring fuel efficiency and range, particularly in smaller type tyres of sizes 12 inches to 13 inches. Why do you think that it is a challenge to design such tyres?
Both 12 inch and 13 inch tyres are small series for the commercial and passenger segment. Installing smaller tyres than originally fitted will almost always result in reduced fuel economy, because the engine or motor turns more revolutions to move the car for the same distance. Running the engine/motor at more RPM than necessary results in energy wastage. The smaller tyre will roll a little easier, but not enough to make up the difference. This observation is based on actual experience .Larger tyres enable the engine to run slower, and there will be an improvement in fuel economy. Sometimes the improvement is substantial. So performance optimization is a big challenge.
Can you explain your proposition that selection of tyres for EVs depends on real world usage profile (RWUP)? Can you elaborate this concept?
Because low-rolling-resistance tyres are harder, they are also louder on the road. They provide a slightly rougher ride and that they even reduce handling performance and increase braking distances. The real world usage pattern for different categories call for different applications.
Design of tyres differs for various weather conditions as well. There are differences in winter and summer application. The tuning needs to be different for commercial and personal segment. This is actually the primary reason for tyre manufacturers to go for different variants.
For example, at low speeds tyre rolling resistance is the primary contributor to increased vehicle resistance at cold temperatures. Snow tyres have both higher resistance and a stronger dependence on temperature than low rolling resistance tyres. Lowering tyre pressure increases both resistance and temperature but this also improves traction and therefore may serve as a temporary safety measure in winter conditions.
What are the methodologies that you have followed in determining rolling resistance and its importance in mobility particularly when you expect more mileage out of each watt?
Rolling resistance is difficult to measure . One approach would be to develop individual factors for each and every rolling resistance parameter by which a tyre in question could differ with respect to the reference tyre. Some of the parameters that might require evaluation could include: diameter (rim, rolling), width (rim, tyre), number of plies (carcass, tread), type of material (carcass, rubber), tyre volume, tyre surface area, and tyre surface roughness. The total number of parameters requiring evaluation could easily exceed this list of 12 if this were the approach.
The second approach, which seeks to develop a limited number of adjustment factors (initially just 4), implicitly combines the various parameters into something more manageable. This approach begins with the formula for the tread contact area of a tyre under load. Tyre manufacturers have also developed test vehicles in standard test conditions for measuring the same.
The EV tyres are manufactured using a harder rubber compound. And since harder tyres roll easier than softer ones, this translates into fuel savings because the vehicle’s engine (or electric motor) have an easier time getting the car moving and keeping it moving — the vehicle’s rolling resistance is reduced.
Do you expect major design changes in EVs tyres? What are the major attributes of a perfect tyre for EVs?
In order to reduce tyre rolling resistance, EV tyres have reduced tread pattern thickness, a lot of rather shallow grooves and narrow sides and very good quality rubber mix. Tyre sidewalls and tread belt are very thin and flexible while tyre aspect ratio is low. In order to achieve low rolling resistance tyres for EV’s and HV’s should have as big a diameter as possible. Recent trends in tread compounding have helped in achieving tread life in competitive to the non-LRR tyres (Ie EV Tyres).
Do you think that the role of natural rubber in EV tyres is likely to increase because of its unique qualities in comparison with SR?
Performance requirements will dictate the materials that can be used. First, it is necessary to understand that almost all tyres have at least some natural rubber components. Synthetic rubber will tend to noticeably impact major tyre features like rolling resistance, quality, and handling. So NR will be for low-end tyres rather than the higher performance types, which need specialized tread materials to remain relatively unmodified.