Photos Copyright ©2009 Sam Abuelsamid / Weblogs, Inc.
We've had two previous in-motion experiences with the Volt. Last April we had the opportunity to drive one of the powertrain mules
, which put the renamed Voltec powertrain into the body shell of the Cruze that shares its platform with the Volt. In August we got to ride (not drive) in one of the pre-production Volt integration vehicle engineering release prototypes (IVERs)
with now former global chief engineer Frank Weber.
We trekked out to Dodger Stadium on Sunday afternoon before this week's press days for the LA Auto Show
for our session with the actual preproduction Volt. Chevrolet set up a driving loop in one of the parking lots where we got to try out a variety of different maneuvers with the car. This time we would get to actually drive the pre-production car from pure battery power to its charge sustaining mode.
The Volt has evolved significantly over the past three years. We've all the heard the story about the first wind tunnel evaluations of the concept and how it purportedly performed better backwards than forwards. While that may be somewhat of an exaggeration, the concept was bad in terms of aerodynamics. In production form, this new body is proclaimed to be the most aerodynamically efficient car that GM has ever built, although the company is declining to say exactly what the final coefficient of drag number is. Like the concept, the production Volt is a five-door hatchback with seating for four adults.
In the spring of 2008 when we visited the GM wind tunnel in Warren, MI, we saw a 1/3 scale model of the where the Volt design was going, but it remained covered in duct tape. We did learn then that aside from the front fascia, perhaps the most important aspect of the shape was at the trailing edge of the car where the air separates. Looking back at the EV1, that car featured a long tear drop tail to help ease the air stream off. Because of the need to make the Volt a four-seater with a real trunk, that shape was not a practical alternative.
Instead, the aerodynamicists spent many hours in the wind tunnel carefully shaping that trailing edge to get the air to come off in a controlled fashion. The result is some interesting detailing at the Volt's hind quarters. A sharp edge runs vertically down each corner while a lump in the lower body also contributes, and a full belly pan empties out into a diffuser under the rear bumper. The overall effect with the rest of the car is a fairly aggressive stance and a surprisingly attractive overall shape. The only questionable element remains the thick black border under the side windows. We'd definitely prefer more side glass and a lower belt-line.
While most compact cars of this size have three rear seat belts, the reality is that only three small children will usually fit comfortably. The Volt is limited to two rear passengers because of the battery pack down the center tunnel, so you might need to leave the third kid home. However, behind the rear seat is a surprisingly cavernous cargo area made possible in part by the tall rear deck.
The basic powertrain architecture and specifications remains unchanged, but practical realities have made changes necessary. The originally planned 1.0-liter three-cylinder turbo has been supplanted by a 1.4-liter normally aspirated four-cylinder. The four-cylinder is claimed to achieve better fuel consumption than the triple, hence the change. The engine and generator also now sit out ahead of the traction motor instead of on top of it.
While the engine and its position have changed, the operating principle has not. As far as GM is concerned, this is an electric car. Only the 110 kW traction motor ever provides drive torque to the front wheels. When the battery reaches its "depletion" point of approximately 30 percent charge, the 100-hp engine kicks in to drive a generator. For the most part, the generator sends electricity to the electric motor that's driving the wheels. The engine mainly operates at constant speeds where it can be controlled efficiently. Since power demands can fluctuate, any surplus is fed to the battery, although the engine/generator is not specifically set up to charge the battery.
Because the battery can be drawn down to provide extra power beyond the capability of the generator for hill climbing or acceleration, the charging capability is used during off-peak demand only to replenish the battery to its "depletion point."
When we arrived for our drive session, the car was plugged in to get some juice back in the battery. Vehicle chief engineer Andrew Farah rode shot gun with us as we set out with the battery gauge indicating six miles of electric range. The driving loop consisted of a number of corners of varying radius, a couple of chicanes and a fairly long back straight along with two stop signs.
The car that GM made available was one of the 80 IVER pre-production prototypes built this past summer. Unlike the other IVERs, this one was cleaned up and finished for auto show display and media drives. Most inner surfaces of these IVERs don't have the proper graining that will be on production cars or the production light clusters, but GM pulled together enough prototype parts to make them look essentially complete. In addition, unlike most of the IVERs that were finished off in primer grey, this car was painted in the same silver-green color that was the subject of GM's color contest
. The winner of the contest will be announced on Tuesday here in LA.
Like many modern cars, the Volt doesn't uses a fob instead of a key with a start/stop button on the left side of the center stack next to the shift lever. Pressing the button produces a green glow from within. We shifted into Drive and rolled out silently with the Volt running purely on battery power as we circled the loop trying to run down the battery so we could experience the charge sustaining mode.
While sucking the juice out the battery, Farah pointed out some of the features in the car. Above the start-stop button are two other buttons with Leaf and Sport labels. It turns out that the default operating mode for the Volt actually limits the maximum output of the motor to 90 kW (121 hp) in order to help maximize efficiency. The Sport mode releases an additional 20 kW bringing the output up to the full 145 hp. Even in the normal mode, the instant torque of the electric motor means that the Volt feels strong accelerating from a stop. We didn't do any official timing, but with Sport mode engaged, the Volt certainly felt like it could hit 60 mph in the mid-eight second range.
When we drove the Cruze mule last spring, the electric drive system behaved pretty flawlessly except for a couple of hiccups with the brake system, which is a fully blended system that combines friction braking with regenerative braking. We specifically looked for those hiccups in this Volt and couldn't get the brakes to misbehave. Farah acknowledged that there are still a few glitches in the brake software and calibration work is still being done. Even at this point, 11 months from Job 1, the brakes feel better than they do on many hybrids using the same system.
Another feature of the Volt is the Low position on the shift lever. The Volt doesn't actually have a transmission as such, just a reduction gear. There is no actual low gear. The Low position provides increased regenerative braking when the driver lifts off the pedal. In Drive, lifting off gives about 0.1 g of regen braking, similar to what you get in a conventional vehicle from engine braking. In Low, the lift off regen is boosted to about 0.25-0.3g, about what you get from downshifting. The main purpose of this is to save the brakes when going down a long hill.
Eventually the battery meter dipped down toward the 0 miles left point. When running on the battery, a battery meter dominates the left side of the LCD display with the ghost of a gas gauge above it. As the car switches from charge depleting to charge sustaining mode, the gauges switch place. On the right side of the display is a power gauge. A mode button on the left side of the dash swaps the energy gauge over to the other side and eliminates the power gauge for a simpler layout.
Getting into charge sustaining mode doesn't necessarily mean the engine starts up right away. In fact there is nothing in the car that tells the driver that the engine is running. According to Farah, the intent is to make everything as transparent as possible for the driver. He tells us that the Volt team is designing the car for mainstream audiences rather than the hyper-miling crowd. They wanted people to just get in the car and focus on driving rather than watching all the gauges and trying to eek out every last foot from a gallon of gas.
We didn't even realize the engine started for the first time until we came to a stop and heard it running. The most noticeable thing at first was when the engine shut off. Farah told us that the team was not yet satisfied with the engine shut-off quality and is continuing to calibrate it. While it was noticeable, we still felt the shut-down smoothness was better than many current production hybrids.
When we first talked to GM about the Volt three years ago, the thought was that the engine would simply run at a constant speed to maintain the battery charge. As development has continued, that strategy has evolved. The output of the engine/generator is based on the needs of the battery and motor, not what the driver is demanding. As the level of the battery changes, the generator is controlled to provide the necessary, electrical output. The engine speed in turn is selected to maximize the load on the engine. An engine runs most efficiently at full load. If the electrical demand is low, a lower engine speed is used in conjunction with the generator control to get the desired load.
Currently the engine can operate in a range of about 1,400-4,000 rpm. According to Farah, the maximum engine speed will likely be reduced as they finalize the calibrations, although he didn't say how much. As we continued running in charge sustaining mode, we were never able to feel the engine start and stop while the car was in motion. However, after a series of hard accelerations we were able to occasionally hear the engine running when it went into higher rpm modes. The sound was similar to or better than most other comparable compacts, but Farah was adamant that it was not good enough. Additional work is still being done both on the engine control and the general vehicle noise, vibration and harshness (NVH) properties to improve this. Farah admitted that more road noise was still coming through on these IVER vehicles, especially in the back of the car, than was desirable.
In terms of handling, the Volt felt capable but obviously we couldn't evaluate much in a parking lot. Body roll was reasonably well controlled, a behavior aided by have the 400-pound battery pack mounted low in car. In fact, according to Farah, the Volt's center of gravity ended up being about two inches lower than the Cruze. We did toss the Volt around a bit in the corners and it felt reasonably well balanced below 8/10ths, but that did turn to understeer as we pushed harder. Farah declined to say how much the Volt weighs, but he did tell us that weight reduction efforts have brought the weight of the base car (minus the battery) down to about the same as a comparable conventional car. So the Volt weighs about 400 pounds more than a Cruze, which should put it at around 3,500 pounds.
It's been a tough three years for General Motors since we first learned about the Volt. The automaker has gone through bankruptcy and emerged as a smaller company that is majority owned by the U.S. government. When we first wrote about the Volt, many of our readers groused that it was nothing more than smoke and mirrors, a simple publicity stunt. As we've followed the development since then, the proportion of people who think the Volt is vaporware has shrunk somewhat, although many still doubt whether the car can succeed commercially.
Now that we have driven the car in both charge depleting and charge sustaining modes, we can say that this car is definitely not vapor. The Volt is real and it certainly appears to work. Whether it can actually hit 40 miles on a charge, what mileage it will get in charge sustaining mode and how long the battery will last are questions that remain for another day.