ROCHESTER, MI – Cruising along an interstate highway outside of Detroit at a tick over 75 mph (120 km/h), the new-for-’11 Chevrolet Volt electric vehicle switches from battery power to extended-range mode by firing up its internal-combustion engine.
In a split second, the Volt’s 1.4L 4-cyl. ICE starts turning a generator, which instantly makes electricity to power a traction motor and turns a gearset to continue propelling the vehicle down the highway without a blip.
Sometimes under situations like this – driving at highway speeds in extended-range mode – the 84-hp ICE pulls double duty by powering a second electric motor hooked to another gearset so the traction motor does not have to work so hard.
At the same time, the Volt’s computer tracks the state of charge in the car’s 16 kWh lithium-ion battery. If it gets too low, the ICE and generator combine to provide some juice to the pack, as Li-ion batteries perform best and last longest when kept at a relatively steady charge.
In turn, the battery wakes every now and then, as with a turbocharger, for an added jolt of torque when necessary. It also draws battery power in extended-range mode as part of the car’s start/stop technology.
Despite this elaborate orchestration of switches, gears, pistons and electrical pulses, the only hint we get that the car has made the transition to gas-generator mode is a slight tickle in the accelerator pedal.
Such a marvel of advanced engineering should come with a thunderclap. But it initially is hit with a barrage of criticism instead, as the Volt’s development team pulls back the curtain on the car’s propulsion system to reveal a strategy quite unlike those of competitive EVs powered only by batteries.
In short, a traditional EV would rely on a single electric motor to spin a fixed gearset to send the vehicle down the road. But the Volt system uses a combination of two electric motors, as well as three clutches and a planetary gearset.
The revelation that the Volt’s gas engine plays a larger role in powering the vehicle than was thought originally has caused a furor in the blogosphere among EV purists and some automotive journalists.
They loudly complain GM has been dishonest in characterizing the Volt as an electric car, rather than a complex type of plug-in hybrid. However, the ruckus is dying down as more journalists and critics drive the car and see how it functions.
Volt engineers argue their 2-motor approach maximizes system efficiency by minimizing battery drain at highway speeds and reducing the workload a single-motor EV system encounters at such times.
“In EV driving, there comes a point where it becomes highly inefficient,” says Pam Fletcher, chief engineer for GM’s Voltec propulsion system.
“Through the kinematic arrangement, we have a great way to address this, we think a very clever way to address this, and (it) gives us tremendous efficiency on the order of 10% to 15%,” she tells Ward’s.
Here’s how it works: In the first of four distinct operating modes, which GM calls “single-motor EV driving,” a primary traction motor spins a “sun gear” to propel the Volt at low speeds and during hard acceleration. In this mode, all energy comes from the battery via an inverter and provides up to 273 lb.-ft (370 Nm) of torque.
The torque arrives quickly and smoothly, making for great fun on the 2- and 3-lane roads of suburban Detroit. Stab the throttle around a tight corner, and the Volt’s tires howl their approval. The car proves quick off-the-line, too, although the torque arrives in such a linear fashion it’s impossible to perform the Motor City’s famous stoplight burnouts.
In a second mode called “2-motor EV driving,” or when the vehicle enters cruising speeds, a “ring gear” surrounding the sun gear unlocks and a second electric motor spins that outside gear using power from both the battery/inverter and generator. The traction motor continues to work the inner sun gear with power from the battery/inverter.
The blended output eases strain on the traction motor and provides a boost of two extra miles (3.2 km) of pure electric range in highway driving, GM says.
Speeding past 80 mph (129 km/h) out on the interstate, the Volt hums along like a big-block Chevy. Unlike a traditional compact car, where under wide-open-throttle the ICE sounds ready to burst from the engine bay in a cartoonish explosion of springs and washers, the Volt’s propulsion system remains poised and unstrained.
There’s also plenty of punch left to dart in and out of slower-moving traffic.
A third mode, or “single-motor-extended-range driving,” occurs after the battery reaches its minimum state of charge and at low speeds. Here, the ICE drives the generator, providing power to the traction motor through the inverter. The ring gear remains locked.
In the fourth mode, called “2-motor-extended-range combined driving,” the outside ring gear is engaged, turned by power from the motor/generator originating at the ICE. Power from the generator also is sent through the inverter to power the traction motor.
A planetary gearset blends power from the two motors and transfers torque to the final drive.
“You’re balancing the power on the planetary to drive the output,” Fletcher says. “You get the same effect as you had in 2-motor EV driving, where now you’ve brought the speed of the traction motor down significantly and brought the efficiency of high-speed driving up.”
Critics of the Volt say turning that outside ring gear with the ICE makes the car more of a hybrid than an EV. It’s difficult to argue against this. GM could also have been clearer about key technical data earlier, especially when the recently bankrupt auto maker needs to build good will.
In GM’s defense, the auto maker has said since the Volt concept car bowed in 2007 that a range-extending ICE would help propel the car electrically after the battery exhausted its range of 40 miles (64 km). It now estimates battery range of between 25 and 50 miles (40/80 km), depending on factors such as driver aggressiveness, ambient temperature and terrain.
“We said it was going to be an EV with a range-extender, and that’s exactly what it is,” says Doug Parks, vehicle line executive for the Volt.
Parks admits on some levels the idiosyncrasies of the Volt’s propulsion strategy, which GM kept quiet for competitive reasons, might matter to rivals and techies. But not among consumers, who will be the ultimate judge of the system’s success.
“The vehicle cannot be driven without electricity or without the battery,” he adds. “If you somehow got the engine to spin, it could not directly drive the vehicle. The wheels are driven by electricity at all times.”
But many in the EV community feel jilted that GM did not reveal those important details about the ICE’s level of assistance, and their fervor has overshadowed news some journalists have achieved well over 50 miles of battery-electric range.
Putting the Volt through its paces, we logged a middling 29 miles (47 km) off a full charge. Underscoring how important driver behavior is to the efficiency of any vehicle, more sedate testing after just two hours on a 240V charging station delivered 30 miles (48 km). In range-extended mode, we averaged 39 mpg (6.0 L/100 km).
“Some (EV) people feel like they put their credibility on the line,” says Chelsea Sexton, an EV advocate and consultant based in Los Angeles. “GM didn’t handle it very well, either. They didn’t have to stomp their feet so hard whenever it was called a plug-in hybrid.”
Sexton, a former GM marketer with the EV1 and one of 15 people chosen by the auto maker to take early deliveries of a Volt, doubts the powertrain controversy will make a difference with buyers.
| Vehicle type | 4-passenger, 5-door, front-wheel-drive extended-range electric vehicle |
| Engine | 1.4L DOHC 4-cyl. |
| Electric Motors | 111 kW drive motor, 54kW generator motor |
| Max Power | 149 hp |
| Max Torque | 273 lb.-ft. (368 Nm) |
| Wheelbase | 105.7 ins. (268.5 cm) |
| Overall length | 177.1 ins. (449.8 cm) |
| Overall width | 70.4 ins. (178.8 cm) |
| Overall height | 56.3 ins. (143 cm) |
| Curb weight | 3,781 lbs. (1,715 kg) |
| Base price | $41,000 |
| Fuel economy | NA |
| Competition | Toyota Prius, Nissan Leaf |
| Pros | Cons |
|---|---|
| Emissions-free driving | Sacrifices to save weight |
| Excellent ride, handling | GM’s reticence untimely |
| It’s a hatchback | Some styling overdone |
“It does not matter,” she says. “Most people could not tell you how their current car works.”
In our test drive, the Volt works exceptionally well. The range-extender alleviates any anxiety over running out of power. More importantly, there only are a few trade-offs, compared with a conventional car, which are aimed mostly at chopping weight.
For example, interior door panels feel chintzy because they are, but they’re also very lightweight.
In a conventional vehicle priced at $41,000, you also would expect power seats, but manual controls weigh less and don’t draw precious electricity. However, leather-seating surfaces are available, a seemingly strange option for a vehicle designed to be the ultimate in environmental friendliness.
Other disappointing interior details are a pass-through to the rear-cargo area that is sealed with a flimsy square cover secured with cheap Velcro fasteners, and an overlay atop the instrument panel cover that’s meant to enhance Chevy’s trademark dual-cockpit interior but instead looks overdone.
At the same time, a human-machine interface intended to resemble a docked iPod looks modern and high-tech, providing the driver with a catalogue of nifty vehicle functions. HMI switches also look and feel sophisticated and respond to the slightest touch.
More technical data, such as battery range and fuel economy, is viewable on the instrument panel. Drivers monitor their efficiency with a bouncing green ball inside the IP. Keeping it stable leads to greater efficiency.
And while the Volt provides roomy seating for four, instead of five, a hatchback design heightens its utility. We also enjoy GM’s solution to alerting pedestrians when the Volt is creeping around parking lots and city streets in its stealthy single-motor EV mode – pull the turn signal toward you and the horn discreetly honks three times.
The Volt drives like a real car, too. Aside from slightly grabby regenerative brakes that require some getting used to, the car boasts a spot-on electric-power-steering system.
A wide track, long wheelbase and 5.5-ft. (1.7-m) 435-lb. (189.5-kg) T-shaped battery down the center of the car give it a low center of gravity, great balance and substantial road feel. On this front, it’s more sports car than electric car.
Until the next major advance in battery technology, an event plenty of experts do not expect anytime soon, the Chevy Volt seems the most practical approach to EVs.
It’s too bad its debut has been marred by controversy, but that’s usually the case with major breakthroughs.
