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Global Viewpoints
Dodge's mild hybrid

The Dodge ESX3 "mild hybrid" prototype achieves an average 3.3 L/100 km (72 mpg) gasoline-equivalent fuel efficiency.

Delphi Automotive Systems provided its Energen hybrid electric propulsion system for the ESX3 and developed the battery safety system in conjunction with other program partners.

The main structure of the ESX3 has only 12 injection-molded thermoplastic pieces, compared to as many as 100 metal parts in a conventional car.

The ESX3's IP, supplied by Johnson Controls, is constructed from expanded polypropylene and houses two liquid-crystal displays. One replaces the typical instrument cluster, the other climate control and radio functions.

Drawing on technology developed for the Partnership for a New Generation of Vehicles (PNGV), Daimler-Chrysler has developed what it terms a "mild hybrid" concept car—the Dodge ESX3. The car builds upon experience gained by Chrysler Corp. from the Dodge Intrepid ESX of 1996 and the ESX2 of 1998.

According to Tom Gale, Executive Vice President, Product Development and Design for Daimler-Chrysler, "While we've achieved tremendous gains in fuel efficiency with the ESX3, we've put that technology in a dynamic design that is clean and safe, has the comfort, utility, and performance consumers demand, and is closing in on affordability." With the ESX3, Daimler-Chrysler engineers and designers have cut the cost penalty for PNGV-type vehicles in half in just two years. The ESX2 cost about $15,000 more than a comparable gasoline-powered car; with the ESX3, the cost differential is about $7500. (The ESX in 1996 carried a cost penalty of $60,000.)

The progress in fuel efficiency and cost stem from several improvements in technology. The ESX3's mild hybrid electric powertrain combines a diesel engine, electric motor, and lithium-ion batteries to achieve an average 3.3 L/100 km (72 mpg) gasoline-equivalent fuel eficiency—close to the PNGV's goal of 2.9 L/100 km (80 mpg). Delphi Automotive Systems provided its Energen hybrid electric propulsion system and developed the battery safety system in conjunction with other program partners, as well as a new high-power connection system. The car's electromechanical automatic transmission provides the fuel efficiency of a manual transmission with automatic shifting. Its lightweight body is designed to make use of injection-molded thermoplastic technology for significant improvements in weight and cost. The ESX3 has a mass of just 1020 kg (2250 lb), but still meets all federal safety standards and providing the room of a typical family sedan.

The ESX3 sees only a slight improvement over the Dodge Intrepid ESX2, but the new car accelerates faster and provides a smoother, quieter ride while being less aerodynamic than its predecessor, according to Tom Moore, Vice President, DaimlerChrysler Liberty & Technical Affairs. Much of the driving pleasure is the result of the ESX3's electromechanical automatic transmission (EMAT), which combines two separate clutches in tandem with a computer-controlled, six-speed unit. The EMAT is a vital link in helping DaimlerChrysler achieve the fuel-efficiency target, according to Tom Kizer, Director of Advanced Powertrain and Electrical Engineering at Daimler- Chrysler Liberty.

The ESX3's powertrain is a further development of the ESX2's and uses a 1.5-L three-cylinder direct-injected engine and 15-kW (20-hp) peak power electric motor. As in the ESX2, the electric motor and battery capture braking energy and reuse it to power accessories and provide an acceleration boost in some situations. For added efficiency, the engine automatically shuts off when the vehicle is stopped, and is restarted by the electric motor when the accelerator pedal is pressed.

The car's 48-kg (106-lb) lithium-ion battery pack from French company Saft is said by DaimlerChrysler to weigh less and be more compact than other battery options, while providing more energy. It has integrated cooling and control systems and fits between the rear seat, trunk, and rear wheel housings, but still allows a 450-L (16-ft3) trunk. Mass saving was a focus for the entire powertrain. The engine has a mass of less than 113 kg (250 lb), the air-cooled motor less than 33 kg (76 lb). The complete powertrain has a lower mass than a conventional single-combustion-engine powertrain.

To reduce body mass, DaimlerChrysler designed the ESX3 to use injection-molded thermoplastic body technology similar to that of Chrysler's 1997 Composite Concept Vehicle. However, the ESX3 was actually built with hand-made thermoset materials that match the properties of the injection-molded thermoplastic design.

DaimlerChrysler said it has made advances in material strength, color, and affordability, in combination with design and manufacturing innovations, that allow the injection-molding technology to be applied to vehicles that can meet tough safety standards and customer expectations. The main structure of the car is made of only 12 parts, compared to as many as 100 metal panels in a conventional car. The body is estimated to have a mass 46% less and cost 15% less to manufacture than a comparable metal body. The low-cost, lightweight material also helps offset the cost of the powertrain. Daimler-Chrysler intends to patent the proprietary mix of thermoplastic, aluminum, and lightweight structural foam intended for the ESX3's body.

Computer-simulated crash tests were used to show that the ESX3 could pass federal tests. Aluminum tubular sections are combined with the injection-molded thermoplastic body sections to give the body added strength. This body structure is actually stiffer than today's Intrepid. "We refer to the thin aluminum sections as the 'sparseframe' to distinguish it from currently available vehicles that simply hang plastic body panels over a conventional, metal spaceframe," explained Larry Oswald, Director, Advanced Body Engineering, Daimler-Chrysler Liberty & Technical Affairs. Continued testing and improvements in generating a high-gloss surface color without conventional paint are required before complete vehicles are made with the thermoplastic material.

ESX3 developers used several technologies to avoid interior temperature extremes so the heating, ventilation, and air conditioning (HVAC) systems can run more efficiently. Solar reflective glass and paint reduce the amount of sunlight and heat that enter the car. Interior temperatures are monitored when parked, with fans expelling hot air if necessary. The ventilation system can instantaneously provide heat on a cold day using a new electric heater design. These energy-efficient technologies allow the complete HVAC system to be 40% lighter than in a conventional mid-size car.

Interior supplier Johnson Controls had a major role in creating the ESX3's interior. Serving as the interior developer/integrator for the vehicle, it created the lightweight seats, instrument panel, overhead system, and door trim panels.

The car's TechLight front seats have fewer parts and significantly lower weight than conventional seats, according to Johnson Controls. They feature tubular aluminum frames and aluminum cushion pans, an integrated heating and ventilation system, and mesh suspension materials that enhance "breathability" and boost rear-seat legroom. The seat-back panels, finished in a nonreflective color, are designed to reduce heat retention. The rear seats have a thin profile that cuts weight, reduces complexity, and increases legroom. Their structure is molded into the floorpan and rear compartment, creating a single contoured unit that is trimmed with thin foam pads. Johnson Controls' I-Seating technology is used for the driver's seat. Said to be a major step forward in seat control and electrical architecture, it reduces weight, wiring, and complexity.

The lightweight instrument panel (IP) is constructed from expanded polypropylene materials. Replacing the typical instrument cluster is a reconfigurable, liquid-crystal display that allows viewing of multiple levels of information sequentially. For climate control and radio functions, another display in the center of the IP is controlled by three knobs on the floor console, which adjusts fore and aft to meet the driver's ergonomic needs. The knobs control the vehicle's DVD, CD, climate, seat, navigation, and instrument cluster reconfiguration systems. Periscope mirrors integrated in the A-pillars reduce aerodynamic drag and provide rear-view images that are displayed on the left and right top corners of the IP.

The four door panels are made from EcoCor, a Johnson Controls material that contains significant amounts of fiber recycled from consumer and industrial uses. The overhead system also uses a headliner substrate made from one of the most-recycled plastic resins in the world—polyethylene terephthalate.

Kevin Jost

AEI May 2000

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