2002 GMC Sierra Denali
2002 GMC Sierra Denali
Click image to enlarge

by Greg Wilson

General Motors’ GMC Truck division recently unveiled three new technologies for light trucks, one that vastly improves the manoeuvrability and trailer towing ability of pickups, and two more that significantly improve the fuel consumption of big V8 engines.

Four-wheel-steering, an idea that GM dabbled with in the 80’s without success, will be standard equipment on the 2002 GMC Sierra Denali (formerly the C3), an upscale half-ton extended cab, short box pickup truck.

“Full-size truck customers can now get the kind of small car manoeuvrability and on-highway control, whether trailering or not, that has never been offered before,” said Sierra Brand Manager, Sam Mancuso at the vehicle’s introduction. “GMC and Sierra Denali are poised to forever change public perception that big trucks are hard to handle.”

The Sierra Denali’s new ‘Quadrasteer’ system, developed by GM’s supplier Delphi Automotive Systems, is an electro-mechanical rear-steer system that turns the rear wheels as a percentage of the front wheels up to a 12 degree angle. Below 60 km/h, the rear wheels turn in the opposite direction to the front wheels, and above 60 km/h the rear wheels turn in the same direction as the front wheels. The Sierra Denali’s turning diameter has been reduced by 21% to 11.3 metres (37.1 ft.) – about the same as a compact Saturn coupe.

2002 GMC Sierra Denali
2002 GMC Sierra Denali
Click image to enlarge

The advantages for truck buyers are numerous – at slow speeds, tight turns such as parallel parking and U-turns, are much easier and require less effort than before. At higher speeds, particularly when towing a trailer, the Sierra Denali’s four-wheel-steering improves stability, handling, steering control and overall safety.

A button on the dashboard allows the driver to choose between 2WS (only front wheels turn) 4WS (all four wheels turn), and 4WS Tow (steering angle is adjusted for easier trailer towing). This feature allowed me to compare the truck’s manoeuvrability in both 4WS and 2WS. In 2WS, I attempted to parallel park into a space just a little bit longer than the truck – I couldn’t manage it. But in 4WS mode, I was able to accomplish it. In another test, I tried turning 90 degrees (frontways) into a narrow parking stall – I couldn’t do it in 2WS but I could in 4WS.

2002 GMC Sierra Denali
2002 GMC Sierra Denali
Click image to enlarge

Perhaps the biggest benefits of four-wheel-steering are for recreational trailer owners. The four-wheel-steering system allows significantly better control on the freeway and makes driving long distances much more relaxed. I towed a 30 foot, 7000 lb. recreational trailer at speeds up to 120 km/h on the freeway, and found it much easier to control the trailer’s side-to-side motions – 4WS reduces that rocking, high-centre-of-gravity feeling found in two-wheel-drive trucks. Lane-changing at high speeds required less steering input and was accomplished more quickly and easily. In a slow speed manoeuvrability test, I was able to turn more than 180 degrees with a 30 foot trailer in tow while in 4WS mode.

GM will have exclusive use of Delphi’s Quadrasteer system for two years, and it will be offered first in the 2002 Sierra Denali this October.

Chevy PHT Silverado
Chevy PHT Silverado

Another new GMC truck scheduled to arrive in 2004 is the Parallel Hybrid Truck, a V8-powered pickup with an electric motor that gets 10 to 15% better fuel consumption than a standard truck with the same engine.

“This is a hybrid with a twist,” said Tom Stephens, VP of Vehicle Integration. “Unlike our competitors who are looking to use the electric motor as a power assist on a small powertrain and giving up some utility to accomplish that, we give you all the acceleration, towing and hauling capability… using a truck V8 engine. Energy captured through regenerative braking and being able to shut the engine off at idle, improves fuel economy by up to 15 percent.”

Instead of a conventional starter motor and alternator, the PHT truck has an electric motor integrated into the drivetrain between the engine and the transmission. To save fuel, the engine automatically shuts off when the truck is stopped, and automatically starts again when the accelerator pedal is pressed. During my test-drive, I found it difficult to tell when the engine had stopped – the easiest way to tell is by looking at the tachometer and oil pressure gauge – they both drop to zero when the engine shuts off! There is only a slight ‘bump’ when the engine starts again, almost seamless.

PHT Outlet
PHT Outlet
PHT Outlets

The PHT truck features a 42 volt battery pack (soon to be standard on new vehicles), electric power steering, an electric water pump, and the ability to generate 110 volt power. Two 110 volt outlets, one under the rear seat and the other in cargo box, allow truck owners to run 110 volt items like laptop computers, heaters, power tools, external lights, microwaves, TV’s, stereos or other electrical accessories. For this purpose, the engine can be left running with the keys removed from the ignition. GM expects this feature to appeal to campers and contractors who use noisy, dirty gas-powered generators.

The 2004 Parallel Hybrid Truck will be based the GMC Sierra/Chevy Silverado with a 5.3 litre V8 – the hybrid propulsion system will be available as an option.

Another fuel-saving technological innovation expected to arrive in 2004 is Displacement-On-Demand, a cylinder deactivation system that automatically varies cylinder firing between eight cylinders and four cylinders, depending on engine load and power requirements. The system is expected to improve fuel economy by an average of 8%, and up to 25% in certain driving conditions.

This is a different system to Cadillac’s infamous 4-6-8 system introduced in 1981. “The Cadillac system was like an early IBM AT computer compared to today’s powerful modern computers,” said Chris Meagher, Assistant Chief Engineer for the project. “The new system has electronic controls which are much more sophisticated.”

The new Displacement-on-Demand system always starts on eight cylinders, but switches to four cylinders in third and fourth gears on level or descending grades. The engine doesn’t run on four cylinders at idle because the engine would vibrate more. “Our #1 goal is to make it totally invisible to the customer,” said Meagher.

6.0L V8 LQ4 with Mechanical Throttle Control
6.0L V8 LQ4 with Mechanical Throttle Control

Indeed, during my test-drive, I could not tell when the engine switched between four and eight cylinders, and I didn’t detect any loss of power. Upon returning to my starting point, Meagher’s laptop computer which was connected to the engine’s computer, indicated that there had been 46 “changeovers” between four and eight cylinders during my 15 kilometre drive.

Displacement-on-Demand will be offered first in GM’s large trucks and SUV’s, and later in a new generation of four and six cylinder engines.

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