Mercedes-Benz offers two innovative 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, the global leader in diesel passenger cars. In addition to an entire generation of super-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.
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 V6 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 V6 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.
Hybrids Ideal For Atkinson-Cycle Engine
On both hybrids, Mercedes-Benz engineers optimized the 3.5-liter V6 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, 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.
30 Percent Better Fuel Economy with S400 HYBRID
The Mercedes-Benz S400 HYBRID uses the V6 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.
A powerful computer controls the hybrid system, recalculating the best operating mode 160 times a second. Capable of up to 50 million calculations per second, the system works to maintain an ideal balance between fuel economy and performance.
Light, Powerful Lithium-Ion Battery
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. 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.
Strong Electric Motor Provides Many Benefits
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 zero to 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.
A Fuel-Saving Start-Stop Feature
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.
As soon as the driver releases the brakes or touches the gas pedal, the gasoline engine starts immediately, and works with the electric motor for good performance. Since the direct-drive electric motor operates at a much higher speed than a conventional geared starter motor, the engine starts instantly and imperceptibly, also avoiding the usually high exhaust emissions during a conventional starting mode.
It Even Recycles Energy
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.
Cleverly Located Controls
Alternating current from the three-phase motor is converted into 120-volt direct current in a converter located where the starter motor used to go. Because the current flow sometimes measures as high as 150 amperes, the system is equipped with its own cooling circuit. A transformer in the right front wheel powers an on-board 12-volt system, which includes a conventional lead-acid battery in the trunk with convenient jump leads. Since most transmission oil pumps are engine-driven, an electric auxiliary oil pump ensures lubrication of the transmission in driving modes when the gasoline engine is off.
The S400 HYBRID has the same interior room, luxury and convenience features as other S-Class vehicles. The model is differentiated by unique seven-twin-spoke 18-inch wheels and HYBRID logos on the trunk lid and dash as well as BlueEfficency badging on the front fenders. A special hybrid pictogram within the speedometer shows the energy flow, energy recovery and battery charge.
The ML450 HYBRID Boasts 30 Percent Better Fuel Economy
Considered a “full hybrid,” the Mercedes-Benz ML450 HYBRID uses the V6 gasoline engine, two magneto-electric motors and sophisticated hybrid electronics to produce more than 30 percent better fuel economy than a comparable V8-powered ML550.
Integrated within the modified automatic transmission, each electric motor serves a specific purpose. Dedicated to pulling away under electric power, the motor on the transmission output shaft generates 80 hp and 192 lb.-ft of torque. Located closer to the gasoline engine, the other electric motor is set up specifically for acceleration and is rated at 83 hp and 173 lb.-ft of torque.
Working with both electric motors when full power is needed, the gasoline engine develops 275 hp and 258 lb.-ft. of torque. The electric motors are powered by a liquid-cooled, 288-volt nickel-metal-hydride battery that’s hidden under the rear cargo floor. A powerful computer controls the hybrid system, recalculating the best operating mode 160 times a second. Capable of up to 50 million calculations per second, the system works to maintain an ideal balance between fuel economy and performance.
During parking and low-speed operation, the ML450 HYBRID runs on the electric drive only. On hard acceleration, the gasoline engine is started automatically, and it works seamlessly with the two electric motors for surprisingly good performance. The hybrid system includes a convenient start-stop function that turns off the gasoline engine – for example, when coasting up to a red light – and re-starts it during acceleration.
When the ML450 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. A Silent Start function provides noiseless starting of the gasoline engine.
During braking, the electric motor acts as a generator, slowing the SUV and recovering kinetic energy. Under heavy braking, the vehicle’s conventional brakes also come into play. Recovered energy is stored in the battery and re-used whenever the car runs only on the electric motors.
The ML450 HYBRID is differentiated by a HYBRID logo on the rear lift gate, a revised front hood with two power domes and unique five-twin-spoke 19-inch wheels. However, the HYBRID has the same interior room, convenience and safety features as other M-Class vehicles.
