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What is Four Wheel Steering?
L. S. Wynn
L. S. Wynn
Four wheel steering is a mechanism in cars, trucks, and trailers that enables all four wheels to actually turn and rotate in response to driver commands. This is markedly different from most standard car manufacturing, which focuses only on the two front wheels. Under these more common systems the rear wheels are fixed and follow the directional lead of the others. All-wheel steering systems can make the driving experience more responsive and can help drivers make tighter turns and faster maneuvers. Having all four wheels move together can be difficult to coordinate from a mechanical perspective, though, and errors are more likely. In most cases these sorts of steering systems have to be controlled by a computer to allow for accuracy and precision. They are more common in racing vehicles than standard cars, but as the technology becomes less expensive and more user-friendly this may change.
Relationship to Drive
It’s important to note here that a car with all-wheel steering is really different from a car with all-wheel drive. Steering relates to whether the wheels actually pivot to get a car around a corner or across a diagonal plane. Drive, on the other hand, concerns how the wheels are powered and whether they have independent tractable energy.
Comparing Standard Systems
In standard two wheel steering vehicles, the rear set of wheels are always directed forward and do not play an active role in controlling the steering. As such, the steering column — which is attached to the steering wheel and responds to driver commands — typically controls only the front two wheels. When these wheels turn they propel the vehicle forward or backward, carrying the weight of the car through momentum.
In four wheel steering systems, the rear wheels can turn left and right also. This can improve the response time of tight turns. It’s more complicated from a mechanical perspective since the rear wheels must also be connected to the steering column, but has a number of benefits when it comes to actual driving efficiency and mechanical optimization.
Importance of Computer Controls
Technically speaking, a vehicle could be configured such that the rear wheels would be connected with a manual system that would require the driver’s power to operate, but this is often seen as impractical. A system like this lacks accuracy, for one thing, and is prone to user error; it is also more cumbersome to operate. In modern vehicles, to keep the driving controls as simple as possible, a computer is almost always used to control the rear wheels. The computer sends and receives signals from the steering column and directs activities accordingly.
Fundamental Processes
Most computer systems control the rear wheels using a number of “fundamental processes” or operations, including the following:
- 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.
Possible Drawbacks
Some of the earliest all-wheel steering systems entered the mainstream marketplace in the 1980s, but they were not as popular as most manufacturers had hoped. There were a couple of reasons for this, but the complex mechanics that are necessarily involved is widely believed to have been a serious contributing factor. The handling and driver requirements left a lot to be desired for many, too.
Modern computer technology has minimized a lot of these issues, but cost can still be a factor. It’s usually very expensive to engineer all-wheel driving, and cars that aren’t custom ordered to include it can’t always be retrofitted. Most of the vehicles being made with all-wheel handling capabilities are those designed for performance settings, particularly in auto racing. As the technology becomes more mainstream, though, this feature may become more common in standard passenger vehicles, too.
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![Four wheel steering is a new type of technology that's available in cars, trucks, and trailers.]()
By: Brad SauterFour wheel steering is a new type of technology that's available in cars, trucks, and trailers. -
![People who often need to drive through difficult or slippery terrain may consider a vehicle will four wheel steering.]()
By: xalanxPeople who often need to drive through difficult or slippery terrain may consider a vehicle will four wheel steering. -
![Four wheel steering is a relatively new technology.]()
By: peshkovaFour wheel steering is a relatively new technology. -
![Four-wheel steering allows the driver to turn both the front and rear tires while steering.]()
By: wellphotoFour-wheel steering allows the driver to turn both the front and rear tires while steering.
Discussion Comments
Ummm no, the GM unit is stand alone as well, and up until the recent 2017 Audi Q7 3.0 Quadratrack (which has a similar 5 degree offset as the GM units did) was the only one usable for both performance driving or towing.
The GM unit was designed for 5 degrees at low speeds, and I think 3.5 at high speeds. The system was designed to bolt in place of a a solid rear axle the truck normally came with (a 10" ring, 12-bolt I believe). There was a king ping near each wheel with a disc brake on the outside, and a u-joint at the king pin to allow the rotation... but the whole unit was technically a solid axle design with a large "shock absorber" sized servo mounted to the back of the axle housing/pumpkin, that would push laterally from a fixed spot, and against the rod/arm on each king pin to turn it. The servo was controlled by a self-contained computer module that had one sole input (I believe it was a 0-5v variable input from the truck PCM, but could also be triggered directly by the steering angle sensor output if you used it to swap into a project car... like a AWD Eldorado or a 4th gen 2WD Camaro).
A few hobbyists farmed that GMC Sierra C3 for AWS applications, though I'm not sure if anyone's actually accessed the control module to choose their own speed vs angle settings (which was the ultimate goal of many a hobbyist looking for high-speed stability, or maybe even an input from a YAW-sensor to combat body sway at high speeds). The boards were full of idea for hot rodders when that Sierra C3 came out. The early 80's and 90's AWS units paled in comparison.
There was a truck that used a four-wheel steering system back in the 1950s. It was the Eisenhauer Freighter. Not many were built, but it did work fairly well. The rear wheels would turn opposite the front at low speed, then the driver had to activate a mechanism to lock them straight at higher speed.
Trailers are also providing new technologies along with safe and sound transportation.
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?
what is the mechanism of four-wheel steering?
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.
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