 Variable Gear Ratio Steering
There are transmissions that have not only each an input and output, but a total of three of them, whereby it is not clear which of these are only outputs and which inputs. The simplest example is the axle drive
of a motor vehicle. Here the torque coming from the transmission output and is allocated to the two drive wheels.
The matching construction may be a transfer case with bevel gears or even one with planetary wheels. And just such one we use now for superimposition of the steering. So there is in addition to the input,
coming from the steering column or the steering wheel a second, computer-controlled electric motor.
This brings us to the term 'Active Steering', for example, very important for autonomous driving. With certainty the described here belongs to it. Of course, the electric power steering has already intervened
actively in the steering action. So to speak, the steering wheel would rotate therewith by itself, while the Variable Gear Ratio Steering could steer even if the driver holds tight
the steering wheel.
But the crucial difference is that the electric power steering can only strengthen or steer alone, while the variable transmission ratio steering changes the gear ratio during normal operation. This means, you
drive through the city and can fully turn the front wheels with only one turn at the steering wheel. If you drive then onto the highway, so you would already need half a steering wheel turn to change only the lane.
The responsible control unit has thus taken the speed as a parameter, to change the transmission ratio between the steering and swivel angle. Of course, it is not content with it. Since all possible sensors
data are able to incorporate, for example, the yaw moment or ESP data. So also active accident prevention would be possible with this system. Incidentally, it is structurally independent of the type of power
steering.
1: Steering shaft input, 2: Steering shaft output, 3: Electric motor with worm gear drive for ring gear, 4: Planetary gear
To understand the construction, imagine a planetary gear relatively far down on the steering column. Whose upper part is, for example, connected to the sun gear, the lower to the planet carrier. Additionally,
the ring gear has an outer toothing, in which the electric motor shown below, engages with its worm gear.
So it can move the ring gear during steering operation or also with the steering holding tight. By the way, if the electronic control should fail, then it stops in the worst case and the driver must drive to the
workshop with the transmission ratio available at that moment.
The steering can also be superimposed on the steering wheel, but this is currently only practiced by American manufacturers. If you look at the picture below, you too will be wondering how you can
accommodate all of this into a steering wheel complete with a full-size airbag. It is unclear what exactly the electric motor and its worm drive are used for. Typical USA, would be an even greater relief when
maneuvering.
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