Issue: Feb 2005


DieselTech - Diesel Hybrids



OEMS are combining the two fuel saving technologies to meet both demands for better fuel economy and lower emissions.

by Bill Siuru

As the rivalry continues between the American-favored hybrid electric vehicles and European-favored diesels, Ford, General Motors and DaimlerChrysler brought prototypes that combine both technologies to the 2005 North American International Auto Show (NAIAS).

These are the Mercury Meta One, Opel Astra Diesel Hybrid and Mercedes-Benz S-Class Hybrid. Diesels are already the most common power source in hybrid electric trucks and buses, driven partly by military interest in hybrids running on a single battlefield fuel, JP-8, that can be used in both ground and air vehicles.

Mercury Meta One

The Mercury Meta One, a showcase for many advanced technologies, features a 2.7L V- 6 diesel mated to a Modular Hybrid Transmission (MHT). The twin-turbocharged, intercooled, DOHC, 24-valve, 60- degree V-6 has a compacted graphite iron block and aluminum heads.









 
The Mercury Meta One concept not only carries some of Fords state-of-the-art safety technology, but serves as a rolling laboratory for using hybrid technology to help clean diesels meet stringent emissions regulations.
 
This engine is used in the new Jaguar S-Type Diesel sold outside North America. With the MHT, the torque converter of the 6-speed automatic transmission is replaced by a high-voltage electric motor and two hydraulic clutches so the motor can operate independently of, or with, the diesel engine. The 35-kW, three-phase motor also serves as the flywheel, starter, alternator and traction motor to drive the front wheels. The layout required minimal change to the base transmission, thus reducing the complexity and cost compared to other hybrid systems.

The MHT can operate in an assist mode to supplement the engines output for additional power for acceleration and under conditions where a diesel pollutes most. For example, there is a short burst in soot emissions as a typical diesels turbocharger speeds up when accelerating. Tuning a diesel engine to minimize this spike usually compromises throttle response. The MHT provides a momentary burst of power for a quick takeoff with very low emissions. Electrical energy is stored in a 325-Volt, 6-Amp-hour nickel metal hydrid (NiMH) battery. Working together, the diesel and electric motor, the 2.7L V-6 makes 248- hp at 4,000 rpm and 431 ft. lb. of torque at 1,900 rpm almost as much as the Fords 6.8L Triton V-10 but sips rather than guzzles fuel.

Also helping fuel economy is a start-stop system that shut down the diesel engine during stops. The Mercury Meta One is the first diesel hybrid that meets stringent Partial Zero Emission Vehicle (PZEV) requirements accomplished by combining hybrid and advanced exhaust after-treatment technologies. The latter includes (1) dual pre-turbo metallic oxidation catalysts for faster light-off and reduced cold-start emissions, (2) oxidation catalysts to reduce hydrocarbon and carbon monoxide, (3) urea selective catalytic reduction system to control nitrogen oxide, (4) catalyzed particulate filter, (5) dual-wall, airgap exhaust pipes to retain heat in the aftertreatment system and improve its efficiency, and (6) hands-free, capless fuel filler. According to Graham Hoare, director of Powertrain Research and Advanced Engineering, By applying our full arsenal of advanced emissions-reduction technologies, we have demonstrated that it is possible for diesel engines to have emissions even lower than many gasoline engines on the road today. With its tremendous low-end torque, this turbo-diesel packs a strong, but clean, punch.

The Mercury Meta Ones engine can run on a biomass-based diesel fuel that minimizes carbon dioxide emissions being explored by Ford in partnership with BP. The renewable fuel is produced via the Fischer-Tropsch process from feedstocks like grasses, waste wood, food crop residues and municipal solid waste. This fuel can be blended with conventional diesel fuel to reduce life cycle greenhouse gas emissions. Since the fuel comes from biological feedstocks that absorb carbon dioxide while growing, the fuel closes the carbon loop as the carbon dioxide emissions are offset by the carbon dioxide absorbing fuel production. Unlike biodiesel, this fuel is not susceptible to water contamination and microbial growth in storage tanks. It is also naturally sulfur-free, vital for use with emission control catalysts and filters.

With a focus on preventing and reducing the severity of accidents, Ford has developed several active safety technologies included in Meta One. These include Lane Departure Warning providing a visual, audible and vibration in the drivers seat if the vehicle departs from a lane without activation of a turn signal.

A Crash Mitigation by Braking system uses a video camera and radar to sense vehicles on the road ahead. If the on-board system determines an imminent collision and the driver fails to react, brakes are applied automatically. Other high-tech electronics include a Reconfigurable Display so drivers can customize the size and location of displays, Wi-Fi integrated radio and SIRIUS satellite video that provide streaming video entertainment to passengers. The SmartNav system not only receives real-time traffic and weather information, but also communicates with roadside sensors about traffic and weather conditions that in turn communicate with a central computer system. This system informs all SmartNav-equipped vehicles in the region to suggest alternate routes.

Opel Astra Diesel Hybrid

The Opel Astra Diesel Hybrid is one of the first results of the collaboration between GM and DaimlerChrysler to develop hybrid vehicles starting with GMs two-mode full hybrid technology. Hans H. Demant, GMs European engineering vice president and Opels managing director, says, We decided to use a dieselpowered car as a starting point because in the mid-term, we dont see a demand for gasoline hybrids in Europe. The diesel is a 1.7L, 4-cylinder, 92-kW (125-hp), CDTI (Common Rail Diesel Turbo Injected) engine. The concept vehicle is based on the Opel Astra GTC already on sale in Europe. Externally, the only change from the production Astra GTC is the unique panoramic glass roof. Inside, the tachometer has been replaced by a display providing information on the operation of the hybrid system.









 
The hybrid Astra will prove that GMs two-mode hybrid bus system can be scaled down to fit in front-drive applications.
 
The two-mode hybrid system, based on GMs Allison EV Drive used in hybrid electric buses, is essentially an electrically variable transmission with two hybrid drive modes. In this parallel hybrid configuration two electronically controlled electric motors, 30- and 40-kW, drive a series of gears to create an infinitely variable drive system. During the input split mode the vehicle can operate on electric, mechanical or a combination of the two. This mode is used for starting from a stop and lowspeed driving. The compound split mode is used primarily at higher speeds to provide efficient cruising. Switching between modes is seamless.

The diesel engine is shut off at low speed and under light loads. Operating only on electric power is key to reducing fuel consumption in stop and go traffic. Depending on the driving conditions, the electric motors propel the Astra on full electric power or supplement the turbodiesel engine to deliver performance expected only from a larger-displacement engine. The Astra Diesel Hybrid is projected to be 25 percent more fuel-efficient than comparable diesel models achieved partly via full engine stop at idle and full electric propulsion at launch.

A sophisticated controller determines when the vehicle should operate in either mode of the two-mode drive system based on the necessary torque for the particular driving conditions The engine and electric motors transfer torque to a series of gears in the transmission, which multiply torque similar to a conventional automatic transmission.

But unlike conventional continuously variable transmissions, the two-mode full hybrids electrically controlled system uses no mechanical belts or bands. Shifts between the two modes are synchronous, which means no engine speed changes are necessary for the mode shift to occur, resulting in ultra smooth accelerations.

A 1.3-kW NiMH battery pack located in the spare tire well supplies power to the electric motors. The diesel engine recharges the battery as does regenerative braking. There are two separate on-board electrical systems, the high-voltage drive system and a 12-volt system for lights, HVAC, audio system and other safety and creature comforts. The Astra Diesel Hybrid demonstrates how hybrid components can be integrated into a compact car without compromising passenger comfort and the vehicles utility. The two-mode hybrid system fits within the space occupied by a conventional automatic transmission.

Mercedes-Benz S-Class Hybrid

As part of the GM-DaimlerChrysler collaboration, Mercedes-Benz is focusing on using the two-mode hybrid propulsion technology in rear wheel- drive, luxury passenger cars. The twomode concept can be used with front-, rear-, and all-wheel drive vehicles with either gasoline and diesel engines in sizes ranging from compact cars to trucks and even 60-foot transit buses.
 








 
 
Mercedes-Benz hybrid S-Class will be the first car to get a jointly-developed DCX/GM two-mode hybrid system.
The Mercedes-Benz S-Class Hybrid shown at the 2005 NAIAS combines a two-mode hybrid drive system with a Mercedes-Benz 4L, V-8 CRDI (Common Rail Direct Injection) diesel engine. This combination results in a new record for power output in a hybrid car 241 kW (330- hp). The diesel engine contributes 191-kW(260 hp) while the two electric motors contribute 50 kW (70 hp). A 1.9 kilowatt-hour NiMH (nickelmetal hydride) battery located in the trunk supplies power to the electric motors. The battery is recharged by both the diesel engine and energy recouped from regenerative braking.

Combining the P1/2 hybrid transmission, as it is called by Mercedes-Benz, with a 7G-Tronic automatic transmission ensures that the SClass Hybrid always operates in the most fuelefficient range. This includes when accelerating from standstill in bumper-to-bumper traffic, when traveling slowly and cruising at a constant speed. With a second electric motor, the diesel can be started at any time without transition, independently of driving mode. The compact dimensions of the system means minimum impact on interior space and the design of the drivetrain is surprisingly simple but highly efficient. The bottom line is performance expected in an S-Class sedan 0 to 100 km/h (62.1 mph) in 7.6 seconds combined with fuel economy not expected in a S-Class sedan 34 mpg.

These prototypes add the strengths of the diesel good fuel economy and gobs of torque to the advantages of hybrid electric vehicles. They could bridge the gap between the hot diesel market in Europe and the rapidly growing demand for hybrids in the U.S. With the exhaust emission reductions already demonstrated by the Mercury Meta One, diesel hybrids could even be sold in all 50 states.


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