by Lem Bingley
At first glance, the 2016 Chevrolet Volt might seem like a superficial update. Under swoopy new bodywork, the second generation of General Motors’ pioneering extended-range electric car still resembles its predecessor. It remains a sleek five-door hatchback powered by twin electric motors, a big lithium-ion battery and a petrol engine.
However, all the major components of the new car’s underlying Voltec powertrain have been reassessed and replaced in search of superior efficiency. According to Chevrolet, the projected outcome is a 30% increase in range on batteries and 11% better fuel economy in range-extender mode. Chevrolet estimates the Volt’s 38-mile official US rating will increase to 50 miles per charge when the new car goes on sale later this year.
Contributing to that increase is the Volt’s lithium-ion battery, which is still made (in America) by South Korea’s LG Chem. It is now formed from two rather than three parallel banks of 96 cells connected in series, dropping the total cell count from 288 to 192. Each cell has grown, with the battery now rated at 18.4kWh, compared with 17.1kWh for the outgoing Volt.
The old battery proved highly reliable, with fewer than two faults per million cells, according to Chevrolet. The company will be hoping for similar dependability from the new battery, which remains liquid cooled to keep its cells in the pink.
As before, the battery is T-shaped in plan, running along the Volt’s spine and branching out under the rear seats, although Chevrolet says the weight is carried lower than before.
Many rival electric cars – including Tesla’s Model S, Nissan’s Leaf and BMW’s i3 –put their cells lower still, with a flatter battery mounted beneath the cabin floor. Chevrolet’s layout allows a low roofline for aerodynamic efficiency, but divides the cabin with a bulky center tunnel. The new Volt will be offered as a five-seater, unlike the four-seat original, but middle passengers may feel short of places to put their feet.
When the battery’s plug-in power runs low, the Volt can fire up its internal combustion engine to generate fresh electricity. Combined range from socket to filling station should reach 400 miles, a modest increase over the 380 miles of today’s Volt.
While BMW’s motorcycle division provided a compact 650cc, two-cylinder petrol engine for the i3’s range extender, Chevrolet has stuck with four cylinders and has actually increased capacity from 1.4 to 1.5 litres in the new Volt. The new engine’s peak power output is consequently higher at 102PS (75kW) compared with 85PS (63kW) beforehand.
Chevrolet engineers have revealed that they tested a variety of alternative engines, including small turbocharged three-cylinder units, but settled on a surprisingly large engine because it improved efficiency in the Volt’s unique setting. Battery charging demands sustained high torque, and is a world away from the variable load and fluctuating speeds of conventional cars.
Unlike the engine, the main electric motor has been made slightly smaller than before. Peak power and torque ratings are 87kW and 280Nm, down from 111kW and 370Nm in the outgoing Volt. The big drive motor can now double as a generator, while the Volt’s smaller motor-generator can now contribute up to 48kW and 118Nm to propulsion. Again, that’s a level that has fallen compared with the older car, which used a small motor with 55kW and 186Nm ratings.
Despite both motors being less beefy than before, the revised Volt can actually outpace its predecessor. The sprint from zero to 60mph is now 7% quicker, Chevrolet says, at 8.4 seconds, while the 2.6-second surge from rest to 30mph is faster by almost a fifth. This seemingly contradictory result is possible because the two motors can be linked together more of the time, combining their efforts more effectively to give the Volt a brisk turn of speed.
It also helps that the second-generation Volt is 110kg lighter overall, with a kerb weight of 1,607kg, down from 1,717kg. The revised motors contribute to the weight loss, accounting for 12kg, while the drive unit as a whole is 45kg lighter.
The motors use permanent magnets and are supplied with alternating current, synthesised from the battery’s direct current by a box of electronics called an inverter. In the new Volt the inverters are integrated directly into the drive module rather than bolted on as a separate black box. This dispenses with the need for thick orange connecting cables, which has trimmed weight and cut complexity on the production line.
The same drive unit also houses the planetary gears and hydraulic clutches that selectively direct drive from the two motors to the front axle. Each motor now has its own planetary gear set, allowing greater flexibility in how each is deployed – for example allowing the larger motor to act as a generator, which was not possible with the original Volt’s single gear set.
Chevrolet has said that one of its key goal has been to reduce the Volt’s reliance on rare-earth elements. Both motors in the outgoing Volt used magnets containing neodymium and dysprosium, exotic metals with extremely strong magnetic properties but which are expensive and subject to volatile price swings. Only the larger motor in the new Volt still needs these metals – and in reduced quantities. The smaller motor-generator now uses commonplace ferrite magnets, trimming the overall rare-earth requirement by about three quarters.
As well as controlling production costs, cutting the need for rare-earth elements makes the second generation Volt a more sustainable product, with less call for the destructive, energy intensive mining and refinement that yields these materials. And that’s a change that should go down well with the Volt’s eco-minded target audience.
While the new Volt is scheduled to go on sale in the US in the second half of this year, Chevrolet is no longer active in the UK and, reportedly, there is no plan to produce a Vauxhall-Opel Ampera directly based on it. Whether pieces of the powertrain will show up in some other car for Europe remains to be seen.
Leaner and greener: inside Chevrolet’s Volt version 2
30 May 2015
by Lem Bingley