Trucks, Jeeps

Li’l Blue: the amazing independent-suspension Jeep Wrangler experiment

“Li’l Blue” was a “cost no object” demonstration of how an independent suspension can exceed the mobility of a live-axle or Hotchkiss suspension. It was one of three prototypes competing to become the 1997 Jeep TJ:

  1. Li’l Blue, built mainly by Bob Sheaves and Evan Boberg of the Pre-Program Group, with the Parkway plant’s Quality Control staff;
  2. Red Devil, a medium-cost link-coil mule made under Craig Love’s leadership in Vehicle Development; and
  3. Screaming Yellow Chicken, a low-cost, long-leaf design built by the Production group at Jeep-Truck Engineering (JTE).

li'l blue - a suspension mule car

All of these prototypes would increase the TJ’s mobility, and each one was rooted in Jeep engineering:

  1. The Screaming Yellow Chicken was essentially an adaptation of the current Wrangler;
  2. The Red Devil was based on the Cherokee and Grand Cherokee; and
  3. Li’l Blue had its roots in the 1963 Jeep Wagoneer, the world’s first independent-suspension 4x4.

Bob Sheaves wrote,

It was very rare to have an internal competition, such as the one that spawned Blue, and rare to have a “cost no object” option. Evan and I knew we had no chance of her ever making it into production, but we showed what could be done.

Before we even started, we got out into the field and recorded, with film and paper, exactly what people were doing with the CJs and YJs all over the US, Canada, and Baja Sur/Baja Norte, Mexico. We did not identify ourselves as factory people, but acted as newbies to see how the true Jeepers treated their cars, but how they treated each other, and how they encouraged or discouraged people towards or away from the “family.” Since Evan and I were doing Li’l Blue, we concentrated on the hardcore people, even taking our personal vacations in Moab to learn.

How Li’l Blue worked

Why would they even bother to make a Jeep with an independent suspension? Generally, because:

  • The Hotchkiss suspension used by CJ and Wrangler had a large amount of unsprung weight; in general, the higher the unsprung weight, the worse the on-road handling.
  • The wheels can react independently, so that one wheel hitting an obstacle does not affect both sides (one cause of wheel shimmy, or “the death wobble”).
  • Having the wheels react independently to obstacles also means that all four of the wheels are always on the ground, in normal on-road and most off-road driving (within the limits of suspension travel). This helps to maintain stability and steering control.
  • Independent suspensions can generally be built as a unit and shipped to the factory, speeding installation and sometimes cutting costs.

side viewThere were good reasons for using a Hotchkiss suspension on the CJ and Wrangler, as well:

  • Lower cost
  • Vertical wheel travel (articulation) is harder to increase in an independent suspension, due to the limits of powered joints — the angles of the joints are firmly limited.
  • When the wheels travel independently, ground clearance is reduced when the car rebounds from a bump.
  • With the Hotchkiss design, simple methods can be engineered to increase to increase ground clearance

The team working on Li’l Blue started by researching the 1963 Jeep Wagoneer design; its independent front suspension was the first of its kind, but it did have shortcomings, which Evan Boberg, Bob Sheaves, and Gerry Hentschel addressed. They started out with a deDion independent suspension, but, to increase wheel travel and ground clearance, connected the differential to the suspension so that it travelled with the wheel. This is illustrated by the following patent drawings; Evan Boberg and Gerald Hentschel were registered as inventors for Chrysler Corporation in the 1993 application.

isometric view

One of the clever aspects of the system is that in cases where one wheel was particularly loaded, e.g. if one side of the vehicle was going over a rock or into a ditch, the differential would be pulled up by that wheel, providing better ground clearance regardless of which side was higher. This helps to counter the independent suspension’s issues with jounce and rebound.

bouncing differential

Evan Boberg wrote, in his book Common Sense Not Required, that for an independent front suspension to have the same off-road capability as a Hotchkiss design, wheel travel had to be increased to about 12 inches.

The challenge in achieving this much wheel travel in an independent design is the universal joint angle design limits in the drive shafts [if the joint is too severe, it will quickly break under power]. Off-road racecars use very exotic joints and achieve large amounts of travel, but do not put torque through these joints except when necessary.

... We invented an IFS design which did not compromise the drive shaft angles and had 12 inches of travel. This design had off-road capability equal to the beam axle design. It did increase unsprung mass about 25 percent vs. a shorter travel independent front suspension, although it still had lower unsprung mass than a beam axle design [our italics]. The cost to manufacture this suspension was about that of the Dakota IFS at the time [which was] more than double the cost of the Grand Cherokee front suspension.

Bob Sheaves wrote,

side viewWe used custom coil-over shocks mounted on the lower control arm, similar to the WK Grand Cherokee or early-1990s Honda Accord; but they were attached even further outboard. The junkyard 16” wheels we used had a deep offset which allowed the knuckles and wheel bearings to be positioned for zero scrub.

The axle was mounted on three points; left and right were connected to the lower control arms with a “shackle” on the right side, to allow the axle to move laterally as the lower control arms moved vertically. The third point was a Camaro-style torque arm that went from the pinion mounting (a Dakota housing with the pinion mounts) rearward to the frame at the transfer case front U-joint centerline. We used a Ram 360 (5.9 V8) voided-bushing engine mount to allow for the fore and aft travel we needed to keep from binding up the suspension.

McPherson struts have too much geometry change at the extremes of travel. The floating axle design of Lil Blue allowed greater control — that was the key to the design.

One of the advantages was the ability to take bumps in stride, which would have thrown the CJ off kilter. Crossing a parking-lot curb at 30 mph, at a 45° angle, would flip a CJ; Li’l Blue was tested at 60 mph “and we didn’t even feel it.” The calculated speed to roll when hitting the curb at 45° was 84 mph. The suspension would have boosted the off-road capability beyond the CJ series, eliminated the instability problems, and dramatically improved on-road handling.

Even the light CJ-5 had well over 300 pounds of unsprung weight. with the same width, the new “Long Travel” independent suspension slashed unsprung weight down to roughly a third —116 pounds.

There were downsides — among other things, conventional lift kits would not work, and getting even better ground clearance would have been very expensive, if it could be done at all. The major limit of the suspension is the ability of the powered joints to hold together; the joints can only bend so far while under power.

Li’l Blue vs the KL Cherokee and other IFS designs

Former Jeep/Truck engineer “JTE” wrote:

To package a floating differential system, as in Li’l Blue, the differential must be close to the vehicle’s center line while not infringing on its range of motion, so the largest radius arc can be struck by the axle shafts, which translates into greater wheel travel. Allowing the differential to rise during jounce and drop during rebound creates an even larger window for wheel travel while maintaining axle angularity. When one wheel is in jounce and the other in rebound, the differential hits its optimal position, maximizing articulation and CV joint life.

Once the differential and axles are in place, it needs to be driven. Here too, a longer radius for the drive shaft will promote longer life for the U-joints and greater travel.

What is a north-south engine?
If the engine is mounted so that the crankshaft(s) and center line of the engine are parallel to the “long side” of the car — it’s north-south. In a north-south engine, the spark plugs face the side of the engine bay, not the grille or cabin. Nearly all vintage cars (1930s-1970s) had north-south engines. The other option is “east-west” (or “west-east,” depending on where the flywheel housing is.)

The floating differential IFS (independent front suspension) system, though, requires a narrow north-south mounted engine to package it closer to the center line, and it requires a traditional transmission and transfer case arrangement to give a good radius for drive shaft longevity.

In today's fixed-differential, north-south IFS systems, the differential’s location is close to the center line and will give an equal area to fit a long axle shaft as the floating differential does. However, the wheel travel and articulation will be reduced by the amount that the floating differential moves vertically.

In today's fixed differential, east-west IFS systems, the differential (transaxle) location is pushed off to one side behind the engine, shortening the space available to the axle shafts, and the shortest distance determines the length of both shafts. This lessens the wheel travel and articulation benefits of a longer axle shaft.

The shocks’ leverage ratios (the distance they would travel for each inch in vertical ground travel) were 87% with the body partly loaded (all fluids, full tank, half payload, 150-lb driver and passenger), 101% at rebound, and 99% at jounce, as I remember.

The Jeep 4.0 liter engine was offset to the right side of the frame rail, to provide clearance for the steering gear and left-hand frame inner web and lower frame. The limit of jounce travel was set by the sweep of the engine crankshaft (the 4.0 was raised by 1.25 inches from stock). Mr. Sheaves wrote, “We took a ‘Ford fixer’ (big hammer) to the oil pan to clear the mounting ears; these changes let us set the bottom of the frame rails to not interfere with engine roll or various supension parts under full torque or other extreme conditions.”

There was no question about the performance, according to Mr. Sheaves:

We greatly exceeded Jeep standards and exceeded on-road standards. We applied for 17 patents on the design, which had a floating axle to eliminate the main issue of an independent drive axle—that of half shaft joint angularity.

Why it was not produced — and whether it still could be

PPED was the advanced engineering group, which did the “what if” studies for Jeep and truck, such as the Jeep Dakar and Dodge T-Rex. Fully 90% of the stuff we looked at never even became mule builds. The group was there to answer “what if” questions, and come up with 80% feasible vehicles to hand off to production groups when approved.
Dodge Durango came from an idea of taking the Dakota and making a smaller version of the already-nixed Mexican “Adventurer,” or Ramcharger replacement. It took Tom Gale to tie it all together by using minivan taillights and other off-the-shelf parts, to get under the budget and actually start a program.

Bob Sheaves wrote that the estimated production cost for the components alone was about $210 per vehicle more than the YJ Hotchkiss suspension, based on a production build quantity of 50,000 vehicles per year for five years. The retail cost for the 1997 Wrangler would have been around $1,000 over and above the normal retail price — which started at $12,000. At the time, that cost penalty was hard to overcome; today, it would likely be lower.

Mr. Sheaves wrote, “In those days, a four-inch lift kit would cost around $350 (installed) to fit the same size tires. The suspension we designed was modular and could have been sold by Mopar Performance at the time. Evan and I even talked to Shep and Jerry, and did a cost projection for them — $5,000 [in 1996 dollars] for the kit. It was deemed too expensive for Mopar Performance; they believed it would not sell.”

That leads to the question of whether it would be practical today — and the answer, surprisingly, is that it might be. The Wrangler’s popularity has grown despite price hikes; the off-road-focused Rubicon model has been much more popular than product planners thought it would be. The factory could assemble both versions on the assembly line, so that the independent suspension could be offered as an option, either on Rubicon or a special model. Advances since 1993 could cut costs somewhat; and, if all Wranglers were built that way, the factory might be able to boost its speed, since suspension modules could be built elsewhere and shipped in.

Mr. Sheaves added:

If I were to do the job today with new axle components, I would use the new Cherokee pattern of double reduction axles. I could then make the ring gear smaller (in diameter), and place the second stage reduction gearset out on the hub ends. Shrinking the ring gear diameter would allow increasing the ground clearance. If I were to use a bevel gear set, the aftermarket could offer less expensive gearsets to change the overall axle ratio.

In the JK Wrangler design, there is a single reduction axle, so there is only one place where you can reduce the ratio of the powertrain speed to the axle shaft speed. Cherokee has two places to do this, spreading the geartooth bending stress out over a greater number of teeth. The downside is greater mechanical complexity and wear.

One method which allows longer half shafts with an east-west powertrain is to use a 3 gear (to keep the wheels turning in the same direction) drop box at each shaft flange on the transaxle. By lowering the attachment of the halfshaft, and canting the boxes (to allow the halfshafts to pass by each other to drive the opposite side), you can increase the length of the shafts by around 12 inches, lessening the angularity of the inner tripod joint, and thereby allowing grester travel. There are downsides to this, however, not the least of which is much higher cost.

The big question, other than convincing Jeep and Chrysler leaders to give a green light, is whether the system could work with the current powertrain. From a straight-six engine with plenty of room on the sides, Wrangler has gone to a V6; packaging everything in would be quite a challenge, though Mr. Sheaves wrote, “You can use a V-type engine as long as you watch out for the packaging. If it has a long stroke, you either jack the engine higher on the frame or body, or you modify the ring gear and carrier housing.”

Li’l Blue was a mind-stretching exercise in 1993, which ended up ready for actual production. It’s been biding its time, but it remains a practical alternative to the more traditional designs used in Wrangler today.

Postscript

In October 2013, Bob Sheaves added:

The suspension was designed as a module to be used at either end of the vehicle. The parts that would change between modules would be the axle housing and gearset; control arm bushings; torque arm and torque arm mounting and bushings.

[As for the retail cost increase], Several items affect the retail cost. The lower number is the incremental cost of the parts including the hardware. The higher number includes the labor to assemble, training for assembly, plant process incremental costs, part number and other associated costs. Profit margin is not included.

This design is intended as a maximum offroad mobility design so any Jeep vehicle that would require such performance and still have good manners onroad would benefit.

The patents are still in effect and are owned by Chrysler.

Comments? Want to learn more? Visit our Li’l Blue forum thread.


Related Jeep Wrangler pages

Inside the Wrangler

Years

Background

Variants and related...

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weight, strength, and safetytransmissionsengines

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