MONTVALE, NJ - Mercedes-Benz offers two hybrid models for the 2011 model-year - the S400 HYBRID premium luxury sedan and the ML450 HYBRID sport/utility vehicle.
Hybrid power is one of several fuel-efficient choices offered by Mercedes-Benz. In addition to an entire generation of clean, quiet BlueTEC diesel cars, Mercedes-Benz also leads the industry in development of fuel cell vehicles and offers cars powered by compressed natural gas in a number of global markets, according to the automaker.
Characterized as a "mild hybrid," the S400 HYBRID (335 total hp, 381 lb.-ft. of torque) comes with the world's first lithium-ion battery designed specifically for automotive use. The light-weight, high-capacity lithium-ion battery powers a 20-horsepower electric motor, which works with a 275-hp V-6 gasoline engine to provide impressive fuel economy.
On the SUV side of the Mercedes-Benz family, the ML450 HYBRID comes with two electric motors and a 275-hp V-6 gasoline engine that work together to provide impressive hybrid power with fuel economy estimated at 21 miles per gallon around town and 24 mpg on the highway.
On both hybrids, Mercedes-Benz engineers optimized the 3.5L V-6 engine for good fuel economy by taking advantage of the Atkinson principle. By delaying the closing of each intake valve, the intake stroke effectively becomes longer than the compression stroke, increasing thermal efficiency, which reduces fuel consumption and exhaust emissions.
Although Atkinson engines inherently produce less low-speed torque and throttle response, according to Mercedes, they are ideal for hybrid vehicles because the electric motor compensates for this disadvantage by working with the gasoline engine to provide excellent throttle response on acceleration. The Atkinson-cycle V6 has different cylinder heads, pistons and camshafts as well as modified variable valve timing control and a low-load oil pump for good fuel economy.
The Mercedes-Benz S400 HYBRID uses the V-6 gasoline engine, a magneto-electric motor and sophisticated hybrid electronics to produce 30-percent better fuel economy than a comparable S550 model. Not only does the electric motor make 20 horsepower, but it also produces an impressive starting torque of 118 lb.-ft., while the gasoline engine develops 275 hp and 258 lb.-ft. of torque.
The 120-volt lithium-ion battery weighs less than most other batteries and takes up less space, but has high energy density for its size, according to the manufacturer. As a result, it can be installed in the engine compartment, so the car's ample trunk capacity and spacious interior are not affected. The lithium-ion battery has a high-strength steel housing, a separate cooling circuit, and its cells sit in a special gel that dampens jolts and vibration.
Characterized as a "mild hybrid," the S400 HYBRID gasoline engine and electric motor work together for responsive performance, and its driveline includes a specially configured seven-speed automatic transmission, a transformer to power the 12-volt vehicle system and intelligent operating electronics. Acting both as the starter and generator, the disc-shaped electric motor is mounted in the torque converter housing, between the engine and transmission. A 120-volt, three-phase AC external-rotor magneto motor, its high torque is especially significant during acceleration, which is otherwise one of the highest fuel consumption modes. The electric motor also helps to dampen drivetrain noise and vibration, which means even better ride comfort.
The S400 HYBRID accelerates from 0-60 miles per hour in 7.2 seconds and reaches an electronically limited top speed of 155 mph. Fuel economy is even better than an S-Class sedan powered only by a conventional V6 engine, and CO2 emissions are 21 percent lower.
The hybrid system includes a fuel-saving start-stop feature that turns off the gasoline engine below nine mph when braking to a stop. When the S400 HYBRID is at a traffic light, for example, the gasoline engine is off, but the AC compressor and steering pump are operated electrically, so air conditioning and power steering are fully operational.
During braking, the electric motor acts as a generator, recovering kinetic energy and storing it in the lithium-ion battery. Under heavy braking, the vehicle's conventional brakes also come into play. Recovered energy is stored in the battery and re-used whenever the electric motor is running.
During deceleration with no braking, the electric motor already acts as a generator, recovering energy and helping to slow the car. When the driver just touches the brake pedal, the generator output increases, which feels like heavier braking. Only when more brake pedal pressure is applied do the conventional wheel brakes come into action. These three stages are controlled seamlessly, so the driver perceives the system simply as smooth, responsive braking.
Originally posted on Green Fleet Magazine