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Automotive Industry

Engineering the LX; Chrysler Group builds a quintessentially American car: a large, rear-wheel-drive car with just a touch of Mercedes

Automotive Design & Production, April, 2004 by Christopher A. Sawyer

DaimlerChrysler's decision to scrap the front-drive LH line and replace it with the rear-drive LX large car platform is very astute. The 120-in. wheelbase gives plenty of interior room, the rear-drive chassis and fully independent suspension provide the base for a pair of very credible performance vehicles, optional all-wheel-drive takes care of Snow Belt worries, Chrysler can borrow parts--like the five-speed automatic transmission that is mated to the Hemi V8--from Mercedes, and the layout is different than anything the domestic competition has to offer. Obviously, someone in Auburn Hills has been thinking.

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UNDER THE SKIN

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"Thirty-seven percent of the LX body-in-white is high-strength steel," says Tom Seel, supervisor, Body-in-White Engineering, Premium Vehicle Platform Team at DaimlerChrysler, "which is 17% greater than the amount we used in the 1998 LH." According to Seel, dual-phase steel is used for the front rails; load management and durability parts are stamped from 280 Mpa steel; the passenger safety cage utilizes 340 Mpa sheet; the front rails are stamped from DP590 and the rear rails from 550 Mpa steel. A geometric assessment of the body sections resulted in the use of two-piece welded octagonal front rails, a double C-section rear rail (inner and outer), a load-bearing cross-car roof bow, and a three-layer body side. "The LX chassis has a one-piece outer ring supplemented by a two-piece inner ring and reinforcements," says Jack Broomall, director of DaimlerChrysler's Vehicle Development, Activity and Premium Product Team. "And the spare tire is mounted on an angle (down at the front, up at the rear) so it stands up in a crash to help absorb the energy."

The bare body shell weighs 914.8 lb, has a torsional stiffness of 13,200 lb-ft/degree, a claimed first torsional moment of 40 Hz and a first bending moment of 48 Hz. "Not only does this give a solid base on which to mount the fully independent suspension," says Seel, "it helps the LX's crash performance as well. A 35-mph head-on barrier crash brings almost no intrusion into the passenger compartment, while a 40-mph offset has minimal intrusion." By using a "tire catcher" section along the A-post, engineers are able to redirect the front wheels away from the passenger compartment, feed this energy into the reinforced lower rails, and use the tire sidewall to absorb some of the energy. In addition, the LX was designed to meet future rear crash standards, including a 50-mph offset rear crash. "We used multiple impact zones, including the spare tire and well, to protect the fuel tank," says Seel. To reinforce his point, Seel adds that the LX body-in-white has 4,277 spot welds and 22,366 cm of adhesive holding it together.

But anyone can do a stiff structure if money is no object. The trick is to build a strong, light structure that doesn't break the bank. "Compared to the LH platform," says Seel, "we've reduced equalized variable costs by 15% and capital tooling costs by 40%. Plus, we've designed the structure around strategic subassemblies that will allow us to build new models and variants quickly, easily, and inexpensively." The latter confirms an open secret: the LX platform will not only add high-performance versions of the 300C and Magnum RT, but distinct new models as well.

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UNDER THE ALUMINUM HOOD

The base engine for the LX is the 190 hp 2.7-liter V6 found in the mid-size Chrysler Sebring and Dodge Stratus. Next up, and standard in the 300 Touring 300 Limited and Magnum SXT, is a 3.5-liter V6 with a triple-plenum intake manifold that produces 250 hp and 250 lb-ft of torque. It is mated to the four-speed automatic, and is the volume engine/transmission combination for the LX line. At the top of the heap sits the 5.7-liter Hemi V8 with its 340 hp and 390 lb-ft of torque, more than enough to push about 4,000 lb down the road quickly. And it is the first high-volume American production engine to offer an integrated cylinder deactivation system.

The MDS (Multi-Displacement System) unit replaces a conventional roller cam follower with a hydraulically pressurized design consisting of an outer sleeve and piston unit to which a roller follower is attached. When the pressure in the solenoid is released, the outer housing slides over the piston, which prevents the transfer of energy to the pushrod. "By trapping air in the cylinders," says Broomall, "we're able to reduce the pumping losses and increase the sealing force on the deactivated valves without introducing any temperature spikes into the system." Buyers will see fuel economy improvements of 10% to 20% depending on conditions, but MDS has little to no effect on EPA fuel economy numbers due to the dearth of situations in which the system can engage. The transformation from V8 to V4 operation takes just 40 milliseconds.

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Automotive Industry

Engineering the LX; Chrysler Group builds a quintessentially American car: a large, rear-wheel-drive car with just a touch of Mercedes

Automotive Design & Production, April, 2004 by Christopher A. Sawyer

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