How Does Four-Wheel Steering Work?

Timothy

“For steering-wheel inputs of less than about 140 degrees from the straight-ahead position, the output stroke moves in one direction,” states the release. “For angles greater than that, the stroke and the relative motion at the rear gradually and smoothly diminish and eventually turn the opposite direction. Thus, the rear-steering gearbox contains a mechanism that progressively reverses the direction of output in response to the magnitude of the steering input.”

Honda adds: “Mechanically, when the steering wheel is initially turned away from the straight-ahead position, the rear wheels steer in the same direction as the front wheels. But, when the steering input is increased and the wheel is turned by more than a specified amount, about 240 degrees, the rear wheels then start to steer in the opposite direction.”

When Road & Track tested the Prelude Si 4WS in 1987, it actually outperformed a Porsche and a Ferrari in a slalom test. Honda’s 4WS system in the Prelude soldiered on in the following two generations, although the Prelude’s final generation was a Japan-only option and only in the Si and SiR models. 

Mitsubishi 3000GT VR-4/GTO

Although we only know the mighty Mitsubishi 3000GT VR-4 in the United States, its Japan-only GTO lineage can be traced to the Galant VR-4 and the introduction of Mitsubishi’s Dynamic Four system. Unlike others here, Mitsubishi’s Dynamic Four wasn’t a lone system, it also included four-wheel drive, four-wheel steer, four-wheel independent suspension, and four-wheel ABS, hence the name.

Launched in 1987, the Galant VR-4 was the genesis for not just the 3000GT but also the almighty Lancer Evolution. And this proto rally car not only spawned Dynamic Four but also Active ECS for the two-wheel-drive models, the first active suspension system on the market. Mitsubishi saw the two as opposite sides of the same coin and labeled the umbrella its Active Footwork System, which is a great name for a set of systems.

According to the Galant’s original news release: “The Active Footwork System adopted for the Galant this time is a generic name for the Active Four (four-wheel-drive models) and Active ECS (two-wheel drive), which mainly consist of the following suspension systems to create more room for driving from low to high speeds and to make driving itself easier in the age of high performance. It is a revolutionary new system that further improves the vehicle’s dynamic performance in terms of accelerating, cornering, and braking by increasing the grip between each tire and the road surface.”

As for the four-wheel-steering system, according to the release, it’s a fully hydraulic system that is sensitive to vehicle speed and steering force to further improve steering response in the medium to high speed range. How that works is through hydraulic pressure sent to the trailing-arm joints of the rear suspension up to 1.5 degrees, although that depends on the steering force and vehicle speed of more than 31 mph.

Three years later, Mitsubishi introduced the 3000GT (GTO in Japan) with Active Footwork System and the tagline, “The GTO. Designed to enable drivers of all abilities to enjoy its high levels of performance — safely, enjoyably, and as their fancy takes them.”

According to the GTO’s original Japanese press release, the four-wheel-steering system worked as such: “A hydraulic actuator is connected to an intermediate joint on the end of the trailing arm. The actuator is regulated by a rear-wheel-steering pump linked to the front-wheel power-assist hydraulic circuit, so that the rear-wheel steering angle is proportional to front-wheel steering effort. The rear-wheel steering angle is proportional to vehicle speed because the rear-wheel steering pump supplies oil in amounts relative to the rotational speed of the rear wheels.”

Paired with either a naturally aspirated V-6 or a twin-turbocharged V-6 in the 3000GT VR-4, the 2+2 sports car was built to go up against the Skyline GT-R, Supra, and RX-7, and also came with active aerodynamics both front and rear. The 3000GT/GTO’s release also came during the “gentleman’s agreement” period of Japanese performance cars, which meant that performance cars were limited to about 276 horsepower, at least on paper. A more accurate number for the 3000GT VR-4, however, was likely 300-350 horsepower.

What’s interesting is that although some of these systems transferred to the newly named Super All-Wheel Control (S-AWC) system for the Mitsubishi Lancer Evolution, the direct descendant of the Galant VR-4, it didn’t bring over the four-wheel steering system — nor did the Pajero Evo. 

General Motors Quadrasteer

Quadrasteer from General Motors is definitely the oddball of the group, but it deserves some attention as the first application to full-size pickup trucks. Unfortunately for GM, it didn’t last long.

Trucks in the U.S. are big business. That may be the understatement of the decade, but the amount of research and development spent on one-upping the competition is wild. Everything is on the table in terms of what manufacturers can offer its consumers to lure them away from other makes and models. In 2002, GM became obsessed with the idea that four-wheel steering was the next big thing. Welcome to Quadrasteer.

In the original news release from 2002, GM states: “General Motors has taken the industry lead by offering the Quadrasteer four-wheel-steering system for the first time in a full-size truck. The innovative system, which makes driving a truck safer, easier, and more convenient, will debut on the GMC Sierra Denali full-size pickup in the fourth quarter of 2002. Quadrasteer marks a milestone in full-size truck handling and control. It’s an electromechanical system that turns the Sierra Denali’s rear wheels (up to 12 degrees) in relation to the front wheels, resulting in unprecedented low-speed maneuverability and high-speed stability.”

Unlike other four-wheel steering systems, GM’s was selectable, allowing for the usual front-wheel steering as well as four-wheel steering. Along with these modes, GM also included a four-wheel-steer towing mode, all of which was actuated by a set of buttons on the dash. According to that release, “Quadrasteer operates by sensing the driver’s desired steering input by way of a steering-wheel-position sensor. This information is fed to a microprocessor that determines the appropriate rear-wheel angles, based on steering input and vehicle speed. The microprocessor feeds its data to an electric motor, which, based on algorithms, drives the rear steering rack through a planetary gearset. If a system failure is detected, Quadrasteer’s failsafe mechanisms revert to two-wheel steering.”

Despite the benefits of four-wheel steering on a full-size truck, GM killed the program after 2005. Only the GMC Sierra, Sierra Denali, and Yukon, as well as the Chevrolet Silverado and Suburban, could be equipped with Quadrasteer, which cost $5,600 at launch, although that was reduced to $1,000 before the program was axed. 

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