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I've seen the term yaw rate several times in the catalogs of luxury vehicles but I always
wondered what it meant.
Yaw originated in the aviation industry as yaw, pitch and roll must be controlled for the
successful flight of an aircraft but the yaw rate is now an essential part of automotive safety.
Yaw is simply an indication of a vehicle's rotation from it's vertical axis or how far is the
vehicle angled to the left or right away from its center or how far has the vehicle deviated from it's
straight course.
Roll (body roll) which is used to indicate when a vehicle tilts to the left or right especially
during cornering is also important to the automotive industry as roll is eliminated from vehicles as much
as possible.
There are sensors in many high end vehicles to measure the yaw rate and this information is used in
stability control systems.
This measurement by itself is not much help to the stability control system of the vehicle because
a vehicle could have deviated, lets say 30 degrees left from it's straight course but that could have
been the intention of the driver.
So when does the information become useful for you and the vehicle?
The information sent by the yaw rate sensor is compared to the steering wheel angle and the angle
of the tires and only then can the system come up with a useful decision.
As I said earlier a vehicle may deviate 30 degrees to the left but if the tire angle for instance
indicates that the vehicle should be turning at 30 degrees the system does nothing.
If the vehicle is deviating 30 degrees to the left but tire angle indicates that the vehicle should
be turning at 45 degrees the differences is sent to an ECU which
would realize that the vehicle is understeerinng and use the necessary
actions to correct the understeer.
The yaw rate is something that is continuously measured by the yaw sensors and compared with the
tire angle but the system only acts when the necessary action is required.
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