Jeep remakes Grand Cherokee

Jeep remakes Grand Cherokee – Cover Story

Lindsay Brook

Building a real 4×4, rather than just a `snow car,’ is a dirty job, but somebody’s got to do it. Jeep still does.

WITH THE ’99 GRAND CHEROKEE, JEEP faces a uniquely difficult problem. They have the strongest brand image in the SUV market to protect, yet the definition of an SUV has changed since the ’92 model. It’s far less about ability to traverse the Rubicon Trail as it is to function as a luxury passenger carrier. Jeep’s still gotta build vehicles to cross the Rubicon, but doing so compromises the more important requirement, in areas like rear seat packaging. That’s gonna hurt the Grand Cherokee. With this new vehicle, Jeep can only protect its image at the cost of unit volume.

— Eric Noble, AutoPacific.

THE NEW GRAND CHEROKEE HAS stronger front-end styling, a little more macho. The rest of the body doesn’t look different, but won’t offend anyone. The new powertrain and driveline is an impressive step up from the old pushrod six and V-8, and will help make the Jeep more carlike. Sales should be strong — we’re looking at over 300,000 per year once the plant is cranking. And it’s up against carryover models from Chevy and Ford. The only reason our prediction is conservative is because the market is crowded.

— Sam Fiorani DRI/Standard & Poor’s.

These two auto analysts’ counterpoints say a lot about the 1999 Jeep Grand Cherokee — and the challenges it faces. After six years and over 1.6 million units sold, Chrysler’s profit-raking sport-ute is being reborn into a market that’s still growing, but is far more competitive than it was in 1992, when the original ZJ Grand Cherokee debuted.

Blink too quickly, and the new WJ seems only a mild departure from the old, angular ZJ it replaces. However, those evolutionary outer panels cover a truly all-new vehicle, with just 130 parts, mostly small items, carrying over from the ZJ.

“Customers told us not to make the Grand Cherokee bigger overall,” notes executive engineer Glenn House. “Instead, they asked for improved interior packaging, a quieter ride, better interior fit/finish and higher overall quality.”

WJ thus rides on the same wheelbase as the ZJ, but is four inches longer (one inch in front and three in the rear) and two inches higher, overall. Track is wider by an, inch. Step-in has been lowered an inch, and there’s an inch more headroom in front, half an inch in the rear. More important, rear seat hip room (a real weakness in the ZJ) has been boosted three inches.

Not all is ergonomically sound, however. The new body carries over a design detail that remains as problematic as it was on the ZJ. Rear wheelhouse intrusion into the door apertures makes ingress/egress into the rear seat area awkward, compared with Explorer and other competitors. This seems to be a compromise in favor of off-road prowess.

The drastically stiffer body helps reduce noise and harshness — Lincoln Continental was the NVH benchmark — and it improves ride, and handling by allowing more precise suspension tuning. The body architecture also enables a widely requested change: moving the full-size spare tire out of the rear cargo area. It’s now in a well under the floor.

There’s a trick new 4-wheel drive system that may be the industry’s new benchmark (see p. 83). WJ is also the lead platform to get Chrysler’s first overhead-cam V-8 and a new 4-speed/5-ratio automatic. (The 4.7L is Chrysler’s first entirely new V-8 since JFK’s presidency.) The new Jeep also features a new multi-link rear suspension, and new braking and steering systems.

All of this will benefit Grand Cherokee as it defends its turf from present and future interlopers. Ford’s Explorer may be laughable in the dirt, but it dominates the U.S. SUV market, outselling Grand Cherokee by 120,000 units last year. Most of the newcomers seeking their slice of the segment also lack serious off-road credentials, but their makers claim customers don’t care. Jeep, along with fellow SUV pioneers Land Rover and Toyota’s Land Cruiser, continue to disagree, but they’re stubborn holdouts.

Jeep engineers quietly deride the growing genre of mainly car-based, highway-biased 4x4s, dubbing them “snow cars.” Yet Toyota’s Harrier/Lexus RX300, BMW’s upcoming E53 (based on the 5-Series wagon) and others are increasingly seen as the “formula for future SUVs,” AutoPacific’s Eric Noble believes. They sit you up high, offer a feeling of security — and they’re hunting in Grand Cherokee’s $27,000 to $35,000 price range.

Jeep Engineering general manager Craig Winn admits that the WJ team worried when the RX300 and Mercedes’ M-Class bowed — until they tested both vehicles against WJ mules at Chrysler’s proving ground. “We were relieved by the results,” Winn tells AI. “Here were two new vehicles that clearly couldn’t match us off road and, we felt, weren’t superior on-road, either.”

For customers who value them, WJ’s approach, departure, and breakover angles are the same as ZJ’s, as is the V-8 model’s 6,500-pound towing capacity The turning radius is one foot shorter, and axle articulation (already world-class for a solid-axled SUV) is slightly better. Jeep uses the infamous Rubicon Trail in California’s Sierra Nevada mountains as a development bogey, and even the luxury WJ had to prove its “Rubiconibility.”

There’s a reason for that beyond brand image. Remarkably, nearly 15% of Grand Cherokee owners take their vehicles “seriously” off-road, says WJ Development Manager Dan Knott. That’s three times more than any competitor in the segment. And over 10% have attended a Jeep Jamboree.

“Jeep will remain the leader in 4wheel drive authenticity,” promises House. The $2.3 billion WJ program is betting 350,000 customers a year will buy into that philosophy, rather than opt for a “snow car.”

The Program

The total WJ program outlay breaks down as follows, according to Chrysler:

Design/engineering: $550 mil.

Tooling and U.S. plant: $750 mil.

New engines and trans. $700 mil.

Graz plant, RDH tooling: $300 mil.

Chrysler (or more accurately, Daimler-Chrysler AG) is getting more bang for the WJ program buck than meets the eye. The modular sohc V-&V-6 engines will soon be shared by Dodge trucks and Chrysler minivans. Ditto for the new 45RFE 4-speed automatic and NV247 transfer case, which go into Rams and Dakotas. And key elements of the WJ’s body architecture will form the basis of Jeep’s 2001 KJ (Cherokee) platform.

The program was run by six “functional engineering” managers, responsible for body, chassis, powertrain, interior, electrical and vehicle development. These were the day-to-day leaders, reporting to program manager Bill Grabowski (and to Bob Hardin, who took over later). The program manager met weekly with Winn, who held regular ride-and-drives. Development of the new powertrain paralleled the rest of the program.

An advanced manufacturing team was put together for WJ, to “integrate product and process into one,” according to Mike Doman, body systems engineering manager. WJ was the first Jeep model (and the third Chrysler product, after Durango and the LH cars) to be designed 100% digitally on CATIA. The new 3-link rear suspension was designed using an Adams CAD suspension model. Using these tools, the designers were able to reduce the number of packaging bucks required, but not the number of driveable prototype vehicles — “we probably built more of them,” recalls Dan Knott. Both he and Doman agree that dovetailing the product and manufacturing groups paid off in measurably better fit/finish on preproduction vehicles.

A sophisticated Transfer Path Analysis was run on Chrysler’s Cray supercomputer. The analysis correlates component and system design with the resulting paths of vibration and harshness through the vehicle. It then shows designers where to stiffen and isolate for best results. The WJ’s transmission crossmember and front control arms — typical telegraphs of vibration in any vehicle — were both improved by a factor of five using the TPA.

(The challenge of changing over the plant and launching the new Jeep is discussed by columnist Jim Harbour on p. 247, and will be presented in further detail in a future issue of AI.)

Body/Chassis

Engineering the WJ’s body-in-white and chassis presented many cost-versus- performance tradeoffs. Porsche Engineering, in Troy, Mich., was brought in at the beginning of the program to optimize the body structure for strength, mass and cost. “They applied `holistic’ design practices,” says Mike Doman, “using the entire body-in-white to counteract load inputs.” Porsche’s six-month involvement created a virtual production engineering team comprised of Porsche senior and CAD engineers, their counterparts at Jeep, “and even some of our Tier 1s hired Porsche people to design stamped components,” notes Doman.

Steel unibody architecture was a given, because it provides “the best balance between on-road feel, off-road-ability, and light weight,” according to Dan Knott. From there, the choices began: Slipplane construction, one-piece bodysides, nine applications of laser-welded tailored steel, and hydroformed radiator closure and front suspension control arms (the latter done by Magna) all require more up-front investment. But the payoffs include greater dimensional control, greater overall stiffness and less fabricating.

For example, the one-piece bodysides give better door fit and seal control. Stamped at Chrysler’s Warren, Mich., plant, they are claimed to be the longest continuously laser-welded panels in the auto industry. Their inners are triple-gauge and replace five separate parts on the old model. Likewise, the single-blank front wheelhouse replaces five pieces. Tailored blanks are also used on the liftgate and doors.

The front rails and door beams are high-strength steel (+40 ksi yield), the rails forming an engine box that’s 40% more rigid than ZJ’s, for better on-center steering feel. Front and rear crossmembers are now welded in. Overall, WJ’s body-in-white, at 6,543 lb-ft/degree, is 26% torsionally stiffer than ZJ’s.

Aluminum was considered for certain outer panels, and for the U-shaped radiator closure, but was nixed on cost. Although slightly heavier, due partly to increased length, the steel bodyshell has far fewer pieces than the ZJ.

WJ development was well along when the issue of SUV bumper heights was created by the insurance industry/crusader media Axis. Jeep engineers are studying ways to possibly “crash-soften” the vehicle, including taking mass out in the future.

Many different independent rear suspensions were evaluated, but Dana’s proven solid axle was chosen, in a new set-up featuring two lateral trailing arms and a single hydroformed A-arm above the axle. Coil springs are again used, with Tokico shocks. “IRS is not necessarily a cost penalty any more,” explains Knott. “Our question was, what does this Jeep really need? We achieved better axle articulation and on-road ride quality, and still reduced unsprung weight, using solid axles.” (Ford will use IRS on its 2001 Explorer.)

The front suspension is a modified version of the previous ZJ system. ITT Automotive developed a new ABS for the `99 Grand Cherokee that features electronic brake distribution (EBD). This system eliminates the front/rear proportioning valve, is lighter, simpler, has less pedal pulsation and improved front/rear balance, Chrysler engineers claim. Foundation brake rotors have grown by an inch in diameter, giving 22% more swept area. At 12.0 (front) and 12.2 inches, they’re touted as the largest SUV rotors in the industry.

Powertrain

Replacing the ancient ohv 5.2L and 5.9L V-8s in the Grand Cherokee will be the lighter, quieter, smoother and more fuel-efficient 4.7L modular V-8. Its V-6 cousin will arrive in late 2000 to replace the 4.0L inline six. Both V-8 and V-6 are sohc, two-valve-per-cylinder designs, with iron cylinder blocks, aluminum heads, chain-driven hollow camshafts operating roller followers, and coil-on-plug ignition. Composite intake manifolds and magnesium cam covers help make the 4.7L more than 50 pounds lighter than the old 5.2L

The new V-8 (rated at 240 hp and 295 lb-ft of torque) will be California LEV-certified and is said to be much, much smoother, particularly at highway speeds. The engine was developed as a system with the all-new 45RFE, a 4-speed automatic that actually offers five ratios. Its computer decides between two 2nd gear ratios (1.50:1 or 1.67:1), depending on load and throttle position.

The V-8 powertrain gives 2 mpg over the previous one, allowing WJ to use a 2.5 gallon smaller fuel tank to deliver the same driving range as ZJ. WJ’s built in Graz, Austria and South America will offer VM Motori’s new 3.1L 5-cylinder turbodiesel. Manual 5-speed gear-boxes are also fitted to Euro-spec Jeeps.

NVH and Interior

With a stouter body, smoother and quieter engines and new rear suspension, the WJ team was able to reduce the amount of sound-deadening mastics used in ZJ by 50%. Still, the new Jeep contains 11 pounds more rubber sealers, and denser carpet and instrument panel backing, to cut noise.

Grand Cherokee became Chrysler’s most multiplexed vehicle in 1996, and WJ’s electrical system improves on it. Designed on SAE’s new J1850 protocol, the Yazaki-supplied harness features databusses for all communications. This helped simplify the harness and reduce the number of “pass-throughs” in NVH- and reliability-critical areas such as the firewall.

Our seat-time in the new Jeep has been minimal to date — we don’t get to drive production models until August — so we can only offer a brief review of the interior. It’s a refinement over ZJ, with attention paid to the IP’s handsome center-stack layout, upgraded switchgear feel, a programmable overhead console (by Prince Corp.) and a new dual-zone HVAC system. The Denso-supplied system uses infra-red technology to measure driver- and passenger-area, temperatures.

With the SUV ranks filled with poseurs designed for slush-filled parking lots and little else, it’s reassuring that Jeep still believes in building a well-appointed vehicle that can go anywhere — even if it’s never asked to do so. There’s still a big market for genuine 4x4s, and the `99 Grand Cherokee is definitely one.

COPYRIGHT 1998 Cahners Publishing Company

COPYRIGHT 2000 Gale Group