4-wheel steering system operation

Increasingly common in modern vehicles, whether they are sports cars, SUVs or sedans, let's find out how the rear wheel steer works. Note, however, that it was the Honda Prelude who first took advantage of this technique, and this is not new ... Let's start with some basic concepts, namely the main usefulness of this type of setup.

Here is the Aishin system (Japan)

Rear steering wheel usefulness

Obviously, the steerable rear axle system primarily allows for low speed maneuverability. By making the rear wheels moveable, the turning radius is significantly reduced, ideal for maneuvering long wheelbase machines in tight spaces (Q7). This was vital for the 911 991 (Turbo and GT3) when the engineers decided to lengthen the wheelbase to reduce understeer, which needed to be compensated for by making the rear axle moveable to maintain low speed maneuverability.

At higher speeds (50 to 80 km / h, depending on devices), the rear wheels turn in the same direction as the front. The goal here is to improve stability so that you can drive a vehicle with a longer wheelbase than it actually is.

Finally, note that the system can be used to stabilize the vehicle in the event of emergency braking, in which case both rear wheels turn inward to brake, like a skier using a snow blower. However, the system must be able to do this, because not everyone can turn the wheels in the opposite direction ...

Four wheel steering

As you can imagine, this is an electromechanical system. The central computer of the car decides in which direction and with what intensity to turn the rear wheels. It then relies on a number of parameters such as speed and steering angle. All this was tuned by the chassis engineers depending on the geometry of the chassis as well as the size of the wheelbase. If you have jailbroken your computer, you could change the way it works, but that would make the car extremely dangerous to drive as I suppose you don't know much about chassis settings ...

Please note that as far as I know there are two main systems:

With stand: one electric motor

Two main devices can be noted. The first looks like an electric power steering: a strut positioned in the center of the axle allows the rear wheels to turn left or right thanks to the threads (therefore, the rotation is carried out by an electric motor). The problem here is that you can only turn left or right, you cannot turn the wheels in the opposite direction for emergency braking.

Rear right wheels (top view)

Rear wheels turned (top view)

Close-up view (top)

Front view

Independent: two motors

The second device that we see, for example, at Porsche, is to install a small engine on the rear chassis (so the engine connects each wheel with a connecting rod). So there are two small engines here that allow you to do what you want: right / right, left / left, or even right / left (which the first system cannot).

All comments and reactions

Dernier comment posted:

haldi (Date: 2018, 09:03:12)

Thank you for this information.

Thanks

Il I. 1 reaction (s) to this comment:

• Administrator SITE ADMINISTRATOR (2018-09-04 17:03:34): My pleasure.

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