FLINT, Mich. -- As is usually the case with advanced engineering, supercharging did not spring to life ready for consumption overnight. In fact, supercharging predates the automobile as we know it today.
Fundamentally, all internal combustion engines are energy conversion devices: fuel and air are drawn in, power flows out. When more power is desired, there are three alternatives:
- Use a larger converter capable of processing greater quantities of fuel and
- Speed up the conversion process by spinning the engine faster.
- Pack in more fuel and air for processing.
In its 95-year history, Buick has used all three approaches several times. The first is the "larger hammer" approach: for years, if a maker wanted more power, it was a simple matter to bore out the cylinders or to stretch the stroke a fraction of an inch to increase piston displacement. Power and torque rose proportionately.
Today, however, no car manufacturer is pursuing that path to increased power because of fuel efficiency, emissions, and overall vehicle efficiency concerns. Instead, engineers are busy exploring ways to make small engines perform like large ones when their drivers tap the accelerator pedal.
The second method is more sophisticated, like deftly wielding a small ball-peen hammer. By using overhead camshafts, properly tuned intake and exhaust systems, four-valve combustion chambers, a higher compression ratio, and internal components that are both lighter and stronger, it's possible to raise the speed potential of any engine. Current Formula 1 engines routinely spin more than 16,000 rpm to produce 750 horsepower from 3.0 liters (183 cu. in.) of piston displacement. Small engines are attractive for two reasons: Even the largest cars in the vehicle fleet have been downsized. And today's customers demand packaging efficiency -- ample room for passengers and parcels, leaving little space for propulsion gear.
The third approach to increased power is as old as internal combustion. In 1885, only eight years after Nikolaus Otto patented the four-stroke engine and nine months before Carl Benz patented his three-wheeled automobile, Gottlieb Daimler received a German patent for supercharging. It stated, "With this engine, greater amounts of combustible mixture are delivered into the cylinder and at the same time the exhaust gases are more effectively removed. This is done by means of a pump alongside the cylinder."
Supercharging means forcing more air and fuel mixture into an engine than it can naturally breathe. As Gottlieb Daimler specified, an external fan, pump, or compressor is used to pack the charge into the engine.
Of course, the supercharger must itself be driven by some means. One approach is to use exhaust energy; such a device is called a turbo-supercharger, or more commonly, a turbocharger. Alternatively, the supercharger can be driven by the engine's crankshaft through a rubber belt or a system of gears and shafts.
Due to technological limitations and the sheer difficulty of building automobiles in the 19th century, Daimler had no success with his supercharged engine patents. Instead, it was up to others to exploit the concept. Lee Chadwick of Pottstown, Pa., made the first noteworthy advancements in 1908 when he constructed a supercharged Vanderbilt Cup racer which was clocked at 100 mph. The marriage of a spinning air compressor to a gasoline engine worked and the all-American high-performance automobile was born.
Chadwick began with an eight-inch-diameter fan driven by a leather belt to spin at five times crankshaft speed. Louis Renault had patented this centrifugal supercharger concept in France in 1902. Chadwick's second-generation design used three fans in series spinning at six times crankshaft speed blowing through the carburetor. When the Indianapolis Motor Speedway opened in 1909, Len Zengle won the inaugural 10-mile race in a Chadwick with what reporters called the most hair-raising performance of the afternoon. (Fifteen Buicks were entered in the same race, one driven by Gaston Chevrolet. Buick swept the first three places in the 231-300 cubic inch class.)
Racing success did not, however, boost Chadwick's commercial prospects. Customers weren't interested in his $375 factory-installed option, guaranteed to raise the top speed of a Chadwick Runabout or Tourabout to more than 100 mph.
During World War I, military strategists realized that air superiority could be achieved if an aircraft engine's natural loss of power with altitude could be eliminated. Supercharging was rigorously investigated in pursuit of that goal. Engineers began investigating both superchargers and turbochargers in earnest.
Alfred Buechi, a Swiss engineer, first proposed the turbocharger to his employers Brown-Boveri in 1906. Testing followed but the idea went nowhere until Frenchman Auguste Rateau applied the concept to aircraft in 1916. Two years later, General Electric, another turbo pioneer, successfully demonstrated that a Liberty aircraft engine which produced 346 horsepower at sea level would deliver only 222 horsepower atop Pikes Peak (14,109 foot altitude). But with turbocharging, the same engine's high-altitude output rose to 356 horsepower, a 10-horsepower gain over the sea-level rating.
When the Armistice was signed only one month later, government research contracts were abruptly canceled. (Buick manufactured 1,320 V-12 overhead cam Liberty aircraft engines during World War I. The V-12 was the only American-made engine to be used in combat, mainly in DeHavilland DH4s. The Buick-built Liberty which powered the first nonstop transcontinental flight of the United States is now on display at the Smithsonian Institute's National Air and Space Museum.)
There was no such interruption in Europe. Paul Daimler, son of Gottlieb Daimler, wasted little time applying his findings to production automobiles. Two supercharged four-cylinder Mercedes models were unveiled at the 1921 Berlin Motor Show.
During the ensuing four years, more than 500 of the supercharged Mercedes models were produced. Later six and eight-cylinder models, better suited to supercharging, were built and sold in larger numbers.
Instead of the centrifugal approach used by Renault and Chadwick, Mercedes favored a Roots-type blower. Philander and Francis Roots of Connersville, Indiana, invented this device to pump water in 1859. That application failed but the Roots brothers didn't give up. After demonstrating that the blower moved air well in a foundry, various patents were issued in 1860.
The Roots supercharger consists of two double-lobed rotors which spin in opposite directions inside a sealed housing. Each rotor has an hour-glass-shaped cross-section. The tip of one rotor nestles adjacent to the waist of the other and there are phasing gears to maintain that orientation while the rotors spin.
Air is swept through the housing within cavities defined by each rotor's lobes and the housing wall. There is no flow between the tightly nestled rotors.
In 1921 Max Sailer won the Cappa Florio in a 6-cylinder Mercedes, the first road-racing victory for a supercharged car. In 1923, Fiat took the first Grand Prix victory for a supercharged car at Monza, Italy.
American efforts were not far behind. Fred Duesenberg rolled out four entries for the 1924 Indianapolis 500, three of which were centrifugally supercharged.
While the Duesies were not the fastest cars at the brickyard that year, Joe Boyer and L.L. Corum shared the victory laurels in one of the Duesenberg Specials powered by a supercharged 122-cubic-inch straight 8.
From these meager beginnings, racers quickly learned how to tune superchargers to deliver major increases in power. They were used whenever the rules allowed them by Fiat and Mercedes -- and most of their competition. During the '20s, Sunbeam, Bugatti, Delage and Talbot in Europe and Harry Miller in America used superchargers to boost their oval and road racing efforts and their speed-record attempts. And Mercedes made its translation from racer to roadster with five supercharged models for 1926.
In Europe, Bugatti, Alfa Romeo, Bentley, MG and Squire all produced memorable supercharged sports-touring cars during the 1930s. In America, the cause was fostered by prestige makers Auburn, Cord, Duesenberg, Graham and Stutz before the war. The very sight of a "Supercharged" script on the fender of a prestige marque was enough to strike awe in the heart of the beholder.
Practically all military aircraft engineered for high altitude missions exploited supercharging during World War II. Buick erected the world's largest aluminum foundry to cast Pratt & Whitney cylinder heads -- just one of the division's 37 war production operations.
Nearly 75,000 Pratt & Whitney engines were manufactured in a plant built and operated by Buick near Chicago.
Many B-24 bombers, the highest-volume aircraft produced during WWII, were powered by Buick-built engines that delivered 1200 horsepower at 25,000 feet. Buick-built R-2000s powered the Douglas C-54 Skymaster transoceanic transports.
After peace resumed, most auto manufacturers ignored what had been learned about supercharging and turned to large-displacement, high-compression V-8s as a simple and inexpensive source of high performance. Buick, on the other hand, took a more ambitious path; in 1951, it created a 335-horsepower supercharged hemi-head aluminum V-8 for its remarkable LeSabre and XP-300 dream cars. That paved the way to the division's first V-8 for production models in 1953.
While American manufacturers' interest in supercharging was short lived during the fifties (including forays into the market by Ford and Kaiser-Frazer), Studebaker selected that approach as the center pillar of its 1960s performance image. Paxton Products was purchased in 1962 as part of the firm's diversification effort. Before the last Studebaker rolled off the South Bend assembly line, superchargers were used to increase the speediness of Hawk, Lark, and Avanti models.
The Granatelli family of Indy 500 and STP fame used supercharged Studebakers to set a host of speed records at Bonneville. One twin-blower Avanti producing 575 horsepower ran 196.62 mph on the salt flats in 1963. When Studebaker ceased manufacturing in the United States, Paxton Superchargers turned to the aftermarket.
Midway through the 1962 model year, two GM divisions tried turbocharging with modest success. More than a decade later, Buick helped relaunch the turbo era, this time achieving excellent results.
Buick's compact V-6 responded especially well to the addition of a turbocharger. Chief Engineer Lloyd Reuss (later Buick's general manager, 1980-84, and GM's president, 1990-92), directed the construction of the first turbocharged Indy 500 pace car, an experimental 1976 Buick Century T-roof coupe producing 305 horsepower from 231 cubic inches.
That experience led to two turbocharged V-6 production engines for 1978, one rated at 150 horsepower and the other at 165 horsepower. Buick returned to the Brickyard in 1983 with an even more remarkable pace car, a 450-horsepower twin-turbo Riviera convertible. Turbocharged Buick V-6 racing engines campaigned at the Memorial Day classic won pole positions in record-time performances 1985 and 1992. And twice in the 1990s, Buick stock-block racing powerplants earned a third or more of the 33 starting positions in the Indy 500, with the best finish a third place by Al Unser Sr. in 1992.
Success with boosted engines prompted research into any and every means of pressurizing the intake tract throughout the 1980s. The supercharger tree has sprouted at least eight branches to date.
First, turbocharging uses the engine's exhaust energy to power a fan-like compressor wheel which force-feeds air to the intake passages of the engine.
A second approach called pressure-wave supercharging (trade name: Comprex) applies exhaust pressure directly against intake air within the honeycomb-like passages of a rotating drum.
A belt from the crankshaft is used to spin the drum. Opel and Mazda both used the Comprex approach for diesel models not imported to the United States.
The six remaining approaches might be considered classical paths to supercharging since all use a pump of some sort driven by a belt from the engine's crankshaft.
In 1980, Bendix (now part of AlliedSignal Automotive) attempted to perfect a sliding vane type pump similar to auxiliary air injection pumps in use since the 1960s. That effort was not successful.
Centrifugal superchargers use a rapidly spinning impeller that looks something like a pinwheel to supercharge air into an engine. In essence, this device is identical to the compressor half of a turbocharger; air enters at the center of the wheel's axis of rotation and is exhausted tangentially. Unlike a turbo, the impeller is rotated by either a belt or shaft-drive from the parent engine. Since this type of compressor is efficient only at very high rpm, some system of gearing must be employed to step up crankshaft rpm to a speed suitable for the compressor wheel (hence the two-speed supercharger of WWII.) Paxton superchargers, still sold in the aftermarket, are of the centrifugal type.
Various manufacturers have toyed with rotary-piston compressors invented by Felix Wankel during the 1960s without commercial success.
The sixth type of supercharger nearly defies categorization. Called the G-Lader and used to date only by Volkswagen, this device shares certain characteristics with the aforementioned rotary piston compressors.
A moving rotor fits within a fixed housing. Both the rotor and the housing have spiral walls that intermesh to provide a maze-like air passage.
The rotor oscillates on an eccentric shaft and the constantly changing internal volume between the spiral walls provides a pumping effect. Air enters at the periphery of the spiral walls and is exhausted near the central axis.
Another unusual design is the screw-type compressor patented by Svenska Rotor Maskiner (SRM) in Sweden in 1936. Two interlocking and counter-rotating screw-shaped rotors move air axially through a housing with a claimed 10-percent efficiency advantage over Roots-type blowers. SRM's sister company, Opcon Autorotor, has developed automotive applications in more than a dozen countries. Whipple Industries of Fresno, Calif., currently imports these superchargers for aftermarket use.
The eighth contender, the Roots-type blower, keeps returning to popularity in spite of all the aforementioned challengers that have arisen over the years. Simple to the extreme, the Roots blower and variations on that original theme provide a very efficient means of moving high volumes of air.
One of the most common applications of the Roots blower is not for supercharging. Detroit Diesel engines have used the devices for scavenging -- flushing out exhaust residue and charging each cylinder at atmospheric pressure -- for 60 years. Ingenious hot rodders found the Roots-type blowers to their liking for drag racing and have used the design for decades. Several west coast companies manufacture copies of the Detroit Diesel blower originally designed by GM.
While turbochargers are still in use today, most manufacturers interested in boosting the output of small to medium-sized engines have taken the mechanically driven supercharger path. The reasons why are revealed in a comparison of the strengths and weaknesses of each device.
Both approaches supply additional quantities of air to the intake side of the engine. Since a turbo is driven by exhaust gas, it has certain response characteristics that can be detrimental to performance. At low loads and low rpm, there isn't sufficient exhaust energy to keep a turbo spinning fast enough to appreciably boost the supply of intake air. If the driver steps into the throttle with the engine rpm too low and the transmission in an upper gear, not much happens for a couple of seconds. The turbo motor doesn't feel instantly eager to charge ahead.
With an engine-driven supercharger (all types except centrifugal), the pump is always primed. Throttle response is virtually instantaneous and this is the supercharger's trump suit over the turbocharger.
Superchargers can be tailored very readily to the engine's characteristics by simply adjusting the unit's size (volumetric output per revolution) and drive ratio (supercharger revolutions per engine revolution).
Both devices add to cost and require careful engineering so it's easy to see why car manufacturers make their choices with great deliberation. Turbos and superchargers both take up space under the hood, another concern. Most makers feel that packaging a turbo is simpler than accommodating a supercharger.
The turbo is more compact and it can be located in various positions on or next to the engine. Belt-driven superchargers demand some space at the front of the engine, one area that's already quite congested. Fitting a supercharger and its associated hardware under a low hoodline is a major engineering headache.
While turbos spin at very high speeds -- typically more than 100,000 rpm -- and contain hot exhaust gases, superchargers are relatively slow turning (no more than 15,000 rpm) and much cooler. Both have to be supplied with lubrication, though this task is somewhat simpler with the supercharger because of its speed and temperature characteristics. Turbo bearings are typically water cooled for durability, a complication that isn't necessary with a supercharger.
Any under-hood device can be a source of noise, presenting yet another engineering problem to solve. Other than an occasional distant whine, turbos do their work in silence. In sharp contrast, the Roots blowers used by Mercedes automobiles in the twenties and thirties shrieked like tormented banshees.
The shrill report comes from pressure pulses as air is pumped into the engine and from the gears that keep the two rotors in proper mesh. Tuning a supercharger for silent operation is a significant engineering challenge.
Superchargers impose a significant parasitic loss on the engine since they are turned by power from the crankshaft. The loss may be less than one horsepower while cruising but 50 or more horsepower at full load. This is why bypass systems are provided to route induction air around (instead of through) the supercharger when no boost is demanded -- during idle and cruise modes.
Since all air compressors operate at less than 100 percent efficiency, it's impossible to raise the pressure of intake air without also raising its temperature. For this reason, both superchargers and turbochargers benefit from intercoolers. These radiator-like devices dissipate heat to the atmosphere and cool the intake air stream before it enters the combustion chamber.
The use of an intercooler imposes cost and packaging penalties but on this particular issue, turbos and superchargers share equal footing.
With tightening exhaust emissions standards, heat energy in the exhaust stream has become a precious commodity. What used to be considered waste energy is now used to warm catalytic converters to operating temperature and to continue the oxidation of combustion by-products outside the engine. Since superchargers don't depend on this exhaust heat energy to operate, they enjoy a major advantage over the turbo approach in the era of ultra-low emissions.
Buick's final turbocharged V-6 was built in 1987 because something better was in the offing. Engineers had concluded that a supercharged V-6 offers an excellent combination of virtues: compactness, durability, reliability, fuel efficiency, smoothness, and plenty of power potential. Efforts to perfect a modern supercharger for automotive use began at Eaton Corp. in 1977 between the first and second energy crises. By 1991, both Buick and Eaton were ready to introduce what has become the most successful supercharged automotive engine in history.
Since it was reintroduced for the 1975 model year, the Buick 3800 V-6 has enjoyed continuous refinement:
- Adoption of a split-pin crankshaft facilitated smoother even firing in 1977.
- Larger valves and new intake and exhaust ports raised power in 1979.
- Direct fire ignition and electronic port-type fuel injection were added in 1984.
- Single-serpentine-belt accessory drive was introduced in 1985.
- Reduced-friction, roller-type hydraulic lifters and sequential fuel injection came in 1986.
- Low-drag piston rings, digital exhaust gas recirculation, direct-impingement fuel-injection targeting, and a quick-start ignition were added in 1988. A new counter-rotating balance shaft eliminated the second-order rocking couple inherent to all V-6 engines.
- Tuned-port induction boosted horsepower and torque in 1990.
- Roller rocker arms, a higher compression ratio, and reduced piston ring tension improved efficiency in 1993.
In 1995, Buick thoroughly overhauled the successful 3800 V-6 in anticipation of rising customer expectations. The latest advancements in design, materials, and manufacturing were invested in the new engine, now designated 3800 Series II V-6.
Key features are as follows:
- A low deck height cylinder block trims 8.8 pounds of weight and reduces the exterior dimensions.
- Cross-bolted main-bearing caps and a deep-skirt design improves stiffness to reduce noise radiated from the engine.
- Lightweight pistons with floating pins and low-tension rings in combination with shorter cast-steel connecting rods reduce reciprocating mass and internal friction.
- More rigidly mounted external accessories (alternator, power steering pump, AC compressor) are smoother and quieter in operation.
- Replacing the balance shaft's front roller bearing with a pressure-lubed sleeve bearing reduces noise.
- Cylinder heads with symmetric ports and combustion chambers balance power output, improving smoothness and reducing emissions.
- Larger valves, less restrictive intake and exhaust ports, a larger throttle body and mirror-smooth passages in the molded composite intake manifold improve volumetric efficiency. Lighter, stiffer valvetrain components facilitate a 6000-rpm redline.
- More aggressive valve timing improves both low and high rpm output.
- Horsepower, torque and fuel efficiency are improved by a higher 9.4:1 compression ratio.
- The addition of dual knock sensors permits optimum spark timing and protection against detonation.
- Oil pan, crankshaft, and water pump seals are improved to yield a lifetime leak-free engine.
- A constrained-layer oil pan design (sound-deadening material between two layers of steel) quiets noise at the bottom of the engine.
- Exhaust manifolds and connecting pipes are designed to minimize the radiation of both heat and noise for quiet operation and rapid warm-up of the catalytic converter.
- A foam-lined top acoustical cover mutes injector click and intake system noise.
Nearly all of the Series II refinements invested in the normally aspirated
3800 V-6 were passed on to the supercharged version in 1996. In addition, the supercharger's internal displacement was increased from 62 to 90 cubic inches.
Driving the blower 1.8 times faster than crankshaft speed yields a maximum full-throttle boost of 7.5 psi and impressive output: 240 horsepower at 5200 rpm and
280 lb-ft of torque at 3600 rpm.
That's more torque than any other manufacturer offers in a six-cylinder engine, including Porsche's new 911.
Delivering a supercharged engine that's as smooth, quiet, efficient, and trouble-free as the 3800 Series II is no easy feat. The entire powertrain must be treated as one interrelated system to meet a long list of demands without compromise.
The air induction tract must be tuned from the mouth of the air cleaner all the way to the intake valve for quiet operation with maximum performance.
Two helmholtz resonators eliminate induction boom. Cavities are also positioned in the supercharger's cast aluminum housing to quiet induction noise. Each rotor has three lobes which are twisted 60 degrees along their length to smooth pressure build up and air flow. These extruded-aluminum rotors are powder-coated with epoxy for lifetime durability.
Since the rotors seal without contact, there is no chance for wear in normal service. An axial entry port at the rear of the housing and a bottom exit port are carefully configured to hush the siren sound with no loss of flow capacity.
Sealed lubricant reservoirs at both ends of the supercharger provide lifetime maintenance-free reliability. During idle and cruise operation, a valve controlled by the powertrain computer bypasses intake air around the supercharger to minimize drag.
That helps deliver excellent fuel efficiency: The Buick Regal GS achieves
18 mpg in EPA city driving and 27 mpg in highway ratings. The Buick Park Avenue Ultra and the Riviera both score 18 mpg in the city and 27 mpg on the highway. Buick's balance of supercharged performance and efficiency beats virtually every V-8-powered automobile on the U. S. market.
In summary, the supercharging road is long and winding with side trips high into the sky. But this much is inarguable: supercharging the 3800 V-6 engine is a marriage made in engineering heaven.
Source: Buick Motor Division
copyright © all rights reserved