A Tale of Two Chevys
by Mark W. Hibben
Innovation and Follow Through
As consumers begin to take delivery of the new Chevrolet Volt, I'm reminded that GM has never lacked for innovation. Over the years, GM has pioneered numerous technologies, only to abandon them later in favor of the tried and true. One such technological adventure just passed its fortieth anniversary, the Chevrolet Vega. Introduced in September 1970, the Vega was endowed with an innovative engine that turned out to be so unreliable that many dubbed the Vega the World's First Disposable Car (use it once and throw it away). Ironically, the very same engine technology that GM failed to perfect would subsequently be adopted by automotive tech heavy weights Daimler-Benz and Porsche. Despite its enormous resources, GM had simply failed to do its development homework on the engine and then subsequently failed to address its problems and stay the course. By all indications, GM has done a more thorough development job on the Volt, but whether it can really follow through remains to be seen.
The Imperfect Car for its Time
The Vega should have been the perfect car for the times. Only a few years after its introduction as a compact car powered by an economical four cylinder engine, the US was hit by the first Arab oil embargo in 1973. As a drive, the Vega was a cut above competitors such as the Ford Pinto and the AMC Gremlin; it handled well and the body was reasonably tight and quiet. The engine featured a die cast aluminum engine block using a Reynolds developed aluminum-silicon alloy. Reynolds had patented in 1967 a surface treatment process that allowed the block to be fabricated without cylinder sleeves.
Up until then, aluminum block engines usually had sleeves made of cast iron because aluminum was too soft to withstand the wear and tear of pistons moving in the cylinders. Eliminating the sleeves reduced the cost per block. GM went a step further and developed a die casting process for the block. GM engineering had done the development work on the engine block, but production responsibility was transferred to the Chevrolet division. Here, the effort appears to have stumbled. Chevrolet was on a very tight (for the automobile industry) 36 month development schedule for the Vega, and apparently this wasn't enough time to work through the production problems with the block. The Vega became notorious for engine problems, with the block exhibiting dimensional instability making it prone to head gasket and oil leaks. There were also problems with excessive piston and cylinder wear. By 1977, GM had given up on the Vega and its innovative aluminum block engine.
In the Eighties, both Mercedes Benz and Porsche cars would feature the Reynolds aluminum alloy in sleeveless engine block designs. Starting in the 1980 model year, the Mercedes S class sedans featured aluminum V8s using the Reynolds alloy. The V8 powered Porsche 928 and the four cylinder derivative 944 also used the Reynolds alloy in sleeveless block designs. Today, most aluminum block engines are sleeveless, including those from Honda, although not all use the Reynolds approach.
Volt to the Rescue
When the Toyota Prius first popularized the hybrid car, I found the engineering approach vaguely unsatisfying. That it was neither purely electric nor purely internal combustion somehow violated my sense of engineering aesthetics. At the very least, I thought that a hybrid should dispense with the mechanical transmission of power and use electric motors for the motive force applied to the wheels, with the gasoline engine being used to generate electricity only. This is the basic concept of the diesel-electric locomotive. For the locomotive, the motivation for this approach is not so much fuel economy as the fact that electric motors can generate enormous torque even at very low rotational speeds. Just the thing to get a big freight train moving. Such a gasoline-electric hybrid affords all the advantages of the Toyota hybrid: it can recover electrical energy during deceleration (to be stored in a battery back), and it can turn off the gasoline engine while stopped in traffic, which is the Toyota hybrid's main trick for saving gas in urban driving.
But the gas-electric approach can go a step further than the conventional hybrid: since the electrical motor(s) produce enough power to drive the car, the gas-electric hybrid can function for a limited time as a pure electric vehicle. By giving the battery pack the ability to be charged from a conventional home electrical outlet, GM has created a different kind of hybrid: a car that can drive about 40 miles as a pure electric vehicle and then converts to a gas-electric vehicle for extended range driving analogous to the diesel-electric train.
Recently, it has emerged that the reality of the Volt drive train is a little more complicated than the diesel-electric analogy. First of all, at freeway speeds, 70 MPH and above, the car never functions as a pure electric vehicle, even if the batteries are fully charged. Along with the electric motors, the gasoline engine contributes directly to the powering of the drive wheels through a clutch and planetary gear system. So much for my sense of engineering aesthetic purity. Between 30 and 70 MPH, the engine can also mechanically engage the drive wheels if the battery pack is depleted. Below 30 MPH, the gasoline engine only provides electrical power to drive the wheels, if the battery pack is depleted. The mixing and matching of mechanical and electrical drive is orchestrated by the power train management computer to produce the most efficient utilization of internal combustion and electrical power and is nearly undetectable to the driver and passengers.
Even with the added complexity of the mechanical linkage between the gasoline engine and the drive train, the combination gasoline engine, generator, motor and front drive differential are remarkably compact.
In the photo at left, the electric drive unit (motor controller, electric motors, gear system and front wheel drive differential) sits approximately where the transmission would be for a normal front drive car and takes up about the same amount of space.
The lithium ion battery pack is arranged in a T along the center well of the chassis, set low to provide a low center of gravity and thereby improve the car's handling and lateral stability.
What makes the Volt drive train an especially good idea is that it can be adapted easily to a variety of power sources. In effect GM has said, “We know the future is electric, even if we don’t know exactly where the electricity is coming from.” By committing to electric motors as the primary motive force, GM can take advantage of future developments in electrical power generation and storage including more advanced batteries, flywheels, other internal combustion technologies such as diesel or gas turbine, or even fuel cells.
Developing the electric motor drive train is the crucial first step to taking advantage of future technology developments in electrical energy storage, and it's to GM's credit that they didn't wait for an electricity storage technology that would provide equivalent range to a gasoline engine. We may still have a long wait for that.
The Chevrolet Volt is perhaps the most forward-looking vehicle GM has ever produced, but therein lays the biggest question. Does GM have what it takes to stick with it and make it successful? My doubts stem in part from the short development time of the Volt, reportedly 39 months as compared with 36 months for the Vega. Short development times have not boded well at GM. Almost certainly, with so much new technology, the Volt's engineering parents will have to endure some teething pains, and the company will have to make good on significant warranty repairs or even recalls. Sticking with the Volt will not be easy.
But there's every reason to think that GM will prevail with the Volt. The GM management of the 70's could slough off failures like the Vega because it didn't make any difference to them. They couldn't conceive of GM failing as a company. The current management must surely realize that for the company failure is an option, while a second government bailout is not. GM can afford to screw up on the Volt to some degree. What it can't afford to do is walk away from it.