The constant velocity joint was patented in 1928 by Alfred Rzeppa, it
was designed for use in submarines, then know as "ball type universal
joint".
In 1959 Alex Issigonis developed the constant velocity joint to drive
the front wheels of the Austin and Morris Mini Minor, he also made the fatal
mistake of using the shaft to retain the wheel.
Over the ensuing 44 years front wheel drive has become the dominant
means of propulsion with 85% of all light vehicles now using front wheel
drive or four wheel drive, all using constant velocity joints, had this type
of drive been monitored at anytime over this period, the practice of using
the shaft to affix the wheel would have been consigned to the scrap-heap
long ago. Fracture
Pictures
Either the Constant Velocity Joint drive shaft has reached a pinnacle
of engineering excellence unheard of in any other field of engineering or
something has gone terribly wrong, it is feared the latter is the case, a
failed shaft is to hand.
Sometime ago a senior lecturer at one of Englands Universities
specializing in auto safety contacted the web-master of this site to ask if
he could use material from the site, of course permission was given, he
wants to use the fractography images to "ensure future engineers don't
make the same mistakes"
With the request from the lecturer and information acquired over the
last 2 years, it has become obvious that those charged with vehicle safety
have no knowledge of fatigue failure and it's implications, so this shaft
has been fitted to vehicles for the last 44 years and it's suitability has
never been questioned.
Vehicle safety relies on reporting defects to The Trading Standards "Home
Authority" in other words the Trading Standards Department which covers
the area that is home to the headquarters of the manufacturer, in the case
of Volkswagen it's headquarters are at Milton Keynes in the UK. It may be
expected that such a department with the important role of vehicle safety
with a manufacturer who sells hundred of thousands of vehicles annually
would have some knowledge of such a safety-critical defect, this knowledge
has yet to be detected at Trading Standards.
The Police who should identify such defects in crashed vehicles don't
appear to have received any training in identifying fatigue failure or any
other material failure mode, it is a matter of speculation how many motorist
have been killed and injured, others will have been prosecuted who in
reality are all victims: because of this lack of basic knowledge.
Metal fatigue is caused by repeated cycling of of the load. It is a
progressive localized damage due to fluctuating stresses and strains on the
material. Metal fatigue cracks initiate and propagate in regions where the
strain is most severe.
The process of fatigue failure consists of three stages: Initial crack
propagation. Progressive crack migration across the part. Final sudden
fracture of the remaining cross section, in the case of the constant
velocity joint shaft it will remain in it's intact state until the side load
on the wheel is sufficient to separate the bearing allowing the wheel to
detach.
In the car industry there are many excuses made for defective vehicles,
overtightened, impact damage, bad batch even bad driving etc. However in
this case it is down to extremely bad design, the prevalence of driveshaft
failures is well known among engineers, the motor industry has continued to
put life at risk by using these shafts as a cheap method of wheel
attachment.
Your safety as a car user is held in the hands of a bunch of inept "safety
experts" who impose penalties and restrictions on drivers without the
slightest idea of what they are doing. The drive in Britain to reduce
accident figures is to reduce the speed of traffic, Gatso cameras and so
called traffic calming humps along with other dangerous road structures are
installed, they have been so successful that the death rate in Staffordshire
up to September 2003 is greater than in the whole of 2002 and still rising.
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