“The new horsepower is power electronics,” an SAE 2011 World Congress session on off-roading was told by John Waraniak, Vice President of Advanced Technology for SEMA (Special Equipment Market Association). He also said that as OEs add electronics, their once-limited roles in off-roading activity have to expand, and they have to work more closely with aftermarket suppliers.
The "21st Century Off-Roading: New Powertains for an Evolving Sport" session was held April 14 in Detroit's Cobo Center as part of the annual SAE World Congress.
The Ford Raptor, an extreme-look vehicle with 35-in tall BFGoodrich tires, was cited by Jamal Hameedi, Ford SVT Chief Nameplate Engineer. It’s based on the 4WD F-150 pickup, with the 6.2-L V8. Although rated at 411 hp (306 kW) and designed to go up to 100 mph (161 km/h) off-road, it’s intended for a wider audience than the Baja 1000 in which it has been run, Hameedi said. Cargo capacity is 1000 lb (454 kg), and tow is 6000 lb/2722 kg (8000 lb/3629 kg for the crew cab).
The frame is a modified F-150, with the track widened 7.0 in (178 mm) to 73.6 in (1869 mm). He said the development program involved aftermarket suspension specialist Fox Racing Shocks to produce a vehicle that rides nicely on roads but provides control at full jounce off-road.
The program was educational for both companies. Fox had to design new shim stacks and seals to produce shocks that would meet Ford durability requirements. “We can’t have shocks that have to be rebuilt after every race," said Hameedi.
To assist suspension development, SVT obtained computer scans of extreme off-road course sections.
The Raptor has a lot of F-150 electronics, which were modified to work differently in an off-road mode, Hameedi said. The ABS was changed to lock up and plow dirt, the brake force distribution curve was reworked, and these systems were integrated with operation of other components in Ford’s Advance Trac (stability and roll control). An off-road engine throttle map and transmission shift schedule were added.
The E-Locker rear differential can be locked in 2WD, 4WD, and 4WD-Low—all the way to its top speed. This gives the Raptor rear-wheel-driving dynamics in 4WD, said Hameedi.
General Motors hybrid SUVs
General Motors was thinking fuel economy, not extreme off-roading, when it introduced two-mode hybrid SUVs with their sophisticated electrical/electronics system. The engineering team realized that the vehicle had to be prepared for customers who would take them camping, etc., without fear of “getting stuck in the woods” if the technology couldn’t take the environment, said Timothy Grewe, Chief Engineer.
There would likely be concerns about the batteries and motors in high and low ambient temperatures, in mountains, and fording streams, Grewe said, and the two-mode group had to ensure the technology would continue to work.
So GM scheduled electronics testing at -40°F (-40°C), conducted both cold starts and operation at up to 100 mph (161 km/h), not just once but reliably, and drove over Colorado Rocky Mountain roads (including the legendary Loveland Pass). These tests, as well as of other modes, included trailer towing to confirm that stability and other systems would remain balanced in those conditions.
Water testing went beyond the usual to include “fording every stream we could find when driving through the Rocky Mountains,” Grewe said. The vehicles, which have 300-V hybrid systems using nickel metal-hydride batteries, can deliver 6 kW·h electricity continuously and up to 12 kW·h peak from aftermarket converters, Grewe noted. So, the engineers exercised this capability, including “no-flame” cooking with a convection oven during the off-road drives.
Toyota’s off-road efforts have been focused on support for a 2008 Lexus LX570 campaigned in SCORE racing (including the Baja 500 and Baja 1000) by the JTGrey team of former Toyota off-road test driver Joe Bacal and including speaker Paul Williamsen of the University of Toyota. The other is a 2010 Toyota 4Runner.
Both vehicles are campaigned in stock classes, which means OE body, chassis, and powertrain, Williamsen explained. Although the suspension is largely stock, there are aftermarket springs that add about an inch of ride height and two inches of travel, remote reservoir shocks, and BFGoodrich Baja T/A radial tires. The wheels are “production”—not the OE installations but forged 17-in aluminum wheels from Toyota Racing Development.
The vehicles use aftermarket-sourced external bypass shocks, which have needle valves adjustable for rebound and compression. They’re referred to position-sensitive dampers and include a hydraulic “bump zone” to reduce bottoming at the limit of travel. The current versions are by Bilstein, made with an extruded aluminum body. They include external bypass tubes, eliminating the need to add them, Williamsen said. “They are possibilities” for production availability because “they let us drive over rocks larger than a fist” without a jarring effect.
Because the vehicles use the OE electronics and 4WD systems, the team also must ensure compatibility with suspension and tire modifications. The LX570 includes full-time AWD, a Torsen center differential, open front and electric-locking rear differentials, sequential six-speed automatic, and multiterrain control system for mud/sand, loose rock, rock crawl, and “mogul” (bumps and ruts). Also in the picture is the Lexus kinetic dynamic sway bar system, which incorporates hydraulic cylinders to virtually disconnect the sway bars for greater independent movement of each wheel in extreme off-road while providing maximum roll stiffness on-road.
At Jeep, the mantra is simple: The Wrangler is the “core” vehicle, and two-thirds of buyers use them for active off-roading. They both need and demand the most capable off-road performance, explained Ray Durham, Vehicle Line Executive at Chrysler. Size of the “core” has been declining, and the “aspirational” buyers of other Jeep models are the majority, but the core creates the image for other sales.
“The first thing the extreme off-roaders do after vehicle purchase is buy new parts,” Durham said, primarily wheels and tires. They don’t necessarily need them for where they’re going, he said, and he recalled a drive in which he kept up with a group, driving a production Wrangler Rubicon, itself the most capable OE edition.
They don’t want a lot of electronics, said Durham, noting that he received complaints even with the use of automatic temperature control.
The flood of OE electronics is unstoppable, a particular issue for the off-road market, noted Santhosh Jogi, Director of Engineering for dSPACE, which has been active in SEMA’s simulation programs for aftermarket parts—particularly their effect on vehicles meeting FMVSS 126 (stability control). He told the audience that “the impact of niche performance needs on complex systems performance” has to be evaluated with data from smaller fleets and with less testing. This means greater reliance on simulation, both at the OE level and certainly for aftermarket suppliers.
HIL (hardware-in-the-loop) simulations, in which aftermarket modules and systems are plugged into an OE overall design and run on a virtual course, were examples cited by Jogi. Although “do no harm” is an obvious requirement, the simulations also provide guidance for development of performance-only functions and modification of algorithms. For the off-road market, he said, it offers the opportunity to establish better balance with on-road operation.