- Written By: L. S. Wynn
- Edited By: L. S. Wynn
-
Copyright Protected:
2003-2012 Conjecture Corporation
Four wheel steering is a relatively new technology that improves maneuverability in cars, trucks and trailers. It should not be confused with four wheel drive in which all four wheels of a vehicle are powered.
In standard two wheel steering vehicles, the rear set of wheels are always directed forward therefore and do not play an active role in controlling the steering. In four wheel steering systems, the rear wheels can turn left and right. To keep the driving controls as simple as possible, a computer is used to control the rear wheels.
As shown in the drawing below, most four wheel steering systems can control the rear wheels in the following fundamental ways:
- At slow speeds, the rear wheels are turned in the opposite direction of the front wheels. This can lessen the turning radius by approximately 20%.
- At faster speeds on the highway, the rear wheels are turned in the same direction as the front wheels. This improves lane changing maneuverability and is particularly beneficial for vehicles towing a trailer.
slow speeds
rear wheels are turned
in opposite direction
of front wheels
fast speeds
all four wheels
are turned in
same direction
Four wheel steering is growing in popularity and you are likely to see it in more and more new vehicles. As the systems become more commonplace you can expect the cost of four wheel steering to drop.
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Discuss this Article
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anon175006
Post 3 |
I am seriously considering using this 4 wheel steering system in my 1946 Willys Jeep. Is there a special power steering pump and oil to use? |
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anon44420
Post 2 |
what is the mechanism of four-wheel steering? |
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anon3436
Post 1 |
The concept of four wheel steering is hardly 'relatively new' as four wheel drive enthusiasts and monster trucks have been using 4WS systems for decades. Admittedly, those systems were custom, typically hydraulically controlled, and separately controlled from the front wheels.
The first production 4WS for the average American automotive consumer was offered 20 years ago on the 1988 Honda Prelude. This system was entirely self contained, automatic, and mechanical; no electronics, no speed sensors, no computers, no hydraulics; just two racks and a rod between them.
A simple tube runs from a secondary pinion on the front steering rack, transferring 1:1 steering wheel motion to the rear rack. That rear rack eccentrically transferred that rotational motion to a lateral motion.
During the first ~180 degrees (from center) of steering wheel rotation, the rear wheels are gradually steered in the same direction about 3 degrees, creating a slight under steer situation, improving straight line stability.
During the second ~180 degrees of steering wheel rotation, the rear wheels are gradually straightened back out.
From ~360 to full lock (~450), the rear wheels are gradually steered in the opposite direction about 5 degrees, creating a significant overseer situation, improving parking lot maneuverability.
That same year Mazda introduced an electronic 4WS setup on the 626 and moved it to the MX-6 in 1989. It was killed in 1990
Nissan followed suit with a hydro-electric system on the 300ZX (and other models not bound for the US), and Mistubishi developed an electric system for the 3000GT/Dodge Stealth.
Honda moved to an electric system with the fourth generation Prelude in 1992, and discontinued the concept altogether in 1994, opting to develop the "Super Handling" system in the fifth generation Prelude that has now found a home in the Acura RDX.
The 1988-1991 Prelude stands alone as the only automatic stand alone all mechanical four wheel steer system. Everything else is subject to computers and hydraulic pumps, neither of which are known for their bulletproof nature. |
