MERCEDES-BENZ TAKES WRAPS OFF NEW V6 V8 ENGINE
New Engine Is 40 Percent Cleaner, 25 Percent Lighter and 13 Percent More Fuel-Efficient
The 3.5 liter M112 gasoline V6 engine was introduced in 1998. The M113 V8 followed a year later and is based on the same technology.
Mercedes-Benz is launching many of its 1998 models including the new M-Class all-activity vehicle and the CLK coupe with a new-generation V6 engine which is more fuel-efficient and lighter in weight, with lower exhaust emissions and a broader torque range than the previous in-line six-cylinder engine. The new Mercedes-Benz powerplant will be among the very few engines capable of meeting future Ultra-Low-Emission-Vehicle (or ULEV) standards.
The First Production V6 From Mercedes-Benz
Mercedes-Benz is replacing its proven in-line sixes in most models with the company's first production V6 powerplants. The 90-degree "V" cylinder layout provides very compact packaging, low engine weight and high safety in frontal collisions. The new engine uses an aluminum cylinder block and cylinder heads as well as magnesium valve covers and intake manifold, and features the first use of cylinder sleeves made of an innovative low-friction silicon-aluminum alloy. The new Mercedes V6 weighs just under 330 pounds, about 100 pounds less than the previous in-line powerplant.
Another Mercedes-Benz First Low-Friction Silicon-Aluminum Cylinder Sleeves
Mercedes-Benz is the world's first automaker to use innovative silicon-aluminum cylinder sleeves with a low-friction surface that allows piston-ring spring tension to be reduced by 50 percent. Thanks to a number of such friction-reducing measures, the internal "drag" of the new engine is 45 percent lower than other V6 engines. The efficiency pay-off for low internal friction means both fuel savings and increased power. PEAK Werkstoff GmbH produces the liners using their patented Osprey spray compacting process.
The new sleeve technology is also designed to provide exceptional block stiffness while minimizing weight. The new sleeves are more than a pound lighter than conventional iron sleeves, and overall, the new aluminum cylinder block weighs only 57 pounds over 50 percent lighter than its predecessor's cast-iron block.
Three-Valve Technology Reduces Emissions by 40 Percent
The new Mercedes-Benz V6 engine features innovative three-valve-per-cylinder technology which can reduce exhaust emissions dramatically over 40 percent particularly during the critical warmup stage, before the catalytic converter usually begins to operate. Catalysts must heat up to work effectively, and this takes nearly two minutes with most modern engines. Increasingly strict emissions limits mean this converter light-off time must be reduced to about one minute, and the new Mercedes-Benz V6 meets this tough criteria. There's about 30 percent less surface area at the exhaust port, relative to a comparable four-valve engine, which dramatically reduces exhaust heat losses between the engine and the catalytic converter. This translates to higher exhaust temperature (about 70 degrees Centigrade or 125 degrees Fahrenheit) and converter "light-off" about 12 seconds earlier.
In the new V6, combustion heat in each of the large, single exhaust valves is dissipated through a sodium-filled valve stem, while exhaust heat is retained and insulated by double-wall piping in the exhaust manifold. The seamless double-wall manifold is made by using high-pressure liquid-forming technology, for greater durability and lighter weight.
There is no tradeoff in horsepower and torque with the new three-valve technology compared to a four-valve design. In any efficient, well-designed engine, exhaust valve size needs to be somewhat smaller than the intake valve area, simply because the "leftovers" of combustion (especially in a modern, clean-burning engine) take up less space than the incoming fuel-air mixture.
A One-Two Punch For Spark Plugs
Using one less exhaust valve also makes room for two spark plugs per cylinder, and an innovative offset-phase twin-plug ignition system matched to the new three-valve technology actually improves performance in the new engine.
Among other things, the new dual ignition system allows an extremely lean fuel-air mixture and late ignition timing during warm-up (retarded by 5-10 crank degrees), which further increases exhaust gas volume and temperature. In this way, the tri-metal catalytic converter is heated up more quickly and begins converting pollutants even sooner. In addition, the dual ignition system activates the two spark plugs in each cylinder one after the other in quick succession (rather than simultaneously), depending on engine load and speed. This "phase-shifted" twin-plug sequence (as well as the basic ignition timing) can change after each combustion cycle for extremely precise control of the combustion process. This also enables combustion chamber pressures to be closely controlled to minimize combustion noise without sacrificing efficiency.
Modern Modular Assembly
Not only did Mercedes-Benz engineers decide that genuine progress would mean a new-from-the-ground-up engine, but their analysis also showed that an entirely new engine factory with the most advanced equipment would make the best sense in terms of both quality and cost efficiency.
Key to this approach is the ability to manufacture six- and eight-cylinder engines under the same roof, with as many standardized components as possible. This strategy provides for increased output, which further reduces costs. As a result, a full range of V6 and V8 engines all with a standard distance between cylinders of 106 millimeters or 4.2 inches is being produced at the new engine plant in the Stuttgart suburb of Bad Canstatt. Details of a new V8 engine will be revealed at a later date. The Mercedes-Benz S600 sedan and coupe and SL 600 coupe/roadster will continue to use the current 389-horsepower 6.0-liter V12 engine.
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This coin vibration test is especially difficult due to the convex cover surface. Notice the low idle with just under 600 rpms. Sweet. |
Balance Shaft Ensures Smoothness
These plans also spelled the end of the in-line six engine family produced since 1984. With the proposed side-by-side manufacture of modular V6 and V8 engines, Mercedes engineers faced a basic conflict: while a 90-degree cylinder angle is ideal for V8 power, a 90-degree V6 design was chosen, and without compromising vibration and noise.
The new V6 incorporates a balance shaft in the block, nestled between the cylinder banks about where the camshaft in a pushrod-type "vee" engine might be located. Fitted with two small off-center weights, the balance shaft counter-rotates at crankshaft speed, compensating first order and second order moments inherent in 90-degree V6 engines.
The wide, 90-degree block layout also provides good rigidity for exceptionally low vibration. Mercedes engineers placed special emphasis on minimizing vibration frequencies in the 500 to 1500 Hertz range, where the human ear is particularly sensitive.
The Longest Intake Runners In The Industry
The Mercedes-Benz V6 engine features the longest intake pipes in the industry, a plus which provides outstanding low- and mid-range power. Cast into the super-lightweight magnesium intake manifold are long intake passages which spiral around to each cylinder. Incorporated into the manifold are two flaps that are closed below about 3,700 rpm, forcing intake air to take the "long route" through the manifold and build up pressure waves which boost the intake process and improve low- and mid-range torque.
At higher speeds, the two flaps open, allowing intake air to take a shortcut a more direct route to the cylinders for maximum high-speed power and efficiency. The electronic engine control unit determines precisely when the flaps are open and closed. The new 3.2-liter V6 produces 221 horsepower at 5,500 rpm, while peak torque is rated at 233 lbs.-ft. @ 3,000-4,600 rpm, depending on the specific model, and e.g. catalytic converter volume. The 2.8-liter version of the new V6 in the C280 sport sedan produces 194 horsepower and 195 lbs.-ft. of torque.
Summarizing The Building Blocks
Putting all the pieces together underscores the efficient design of the new Mercedes-Benz V6 engine. An exceptionally stiff forged-steel crankshaft (with four main bearings and six offset rod bearing journals) is at the heart of the new engine, and it's bolted into a pressure-cast aluminum block or crankcase housing. An aluminum oil pan also contributes to block rigidity. Aluminum pistons are mounted on the connecting rods, then slid into the silicon-aluminum sleeves which are an integral part of the block.
Connecting rods must be made in two pieces for assembly on the crank, and the new V6 uses hollow, forged steel rods which are made in one piece, then "cracked" hydraulically, instead of being machine-cut and reground. The irregular fracture provides a very strong, durable fit, even at high engine speeds, and shortens the production process since re-grinding isn't necessary. The two cylinder heads come next, each with a single, hollow camshaft driven by double roller chains and silent, rubber-coated sprockets. Twin rocker shafts in each head hold low-friction, roller-tip aluminum rocker arms to actuate the valves, and housed in the end of each rocker arm is a small hydraulic lifter which ensures quiet, maintenance-free valve operation.
Super-lightweight magnesium valve covers, the intake manifold and the double-wall sheet-steel exhaust manifolds complete the assembly of the basic engine. The double walled exhaust manifolds also reduces heat radiation to surrounding components.
Motronic Magic
The new Mercedes V6 engine is managed by a high-performance Motronic ME 2.0 electronic management unit. Not only does it handle both fuel injection and the new phase-shifted dual ignition, but the engine control unit is also networked via a CAN data bus with other micro-computers for the automatic transmission and the traction control and Electronic Stability Program (ESP). In this way, data is constantly exchanged at lightning speed to ensure good fuel economy and performance, low emissions, and outstanding handling safety.
Wide Acclaim
Starting in 1995 engine experts at Ward's Automotive select The Ten Best Engines every year. The Mercedes-Benz V6 has won this distinguished award four consecutive times since its introduction, in 1998, 1999, 2000 and in 2001, more often than any other Mercedes engine. In 2002 the MB V8 (M113) in the ML 500 was thus honored. Overall V6 engines received this prestigious award more often than any other engine configuration, closely followed by the popular V8s.
Several AMG engines are based on these three valve engines. From the C32 AMG, the ML55 AMG to the G55 AMG. In 2003 the Mercedes-Benz AMG 55 was recognized as the best performance engine by the UK based International engine of the year awards.
written in April 2003
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Veni, vidi, M. |