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Review of Chassis
Design: Principles and Analysis
by "Flutenews"
The magazine of the Vauxhall Owners Club 1903 to 1957
January 2004
Maurice
Olley was one of the outstanding automobile engineers of the twentieth
century, who made invaluable contributions to the understanding of vehicle
ride and handling, and to the development of car suspension during the
30's, 40's and 50's. He was born in Scarborough, North Yorkshire, in 1889,
and from the age of four grew up in North Wales. His career as an
automobile engineer started when he worked for Henry Royce, both in Derby
and at Royce's winter retreat in the south of France, and for ten years
from 1920 he was Chief Engineer at the Rolls-Royce factory in Springfield,
Massachusetts, USA.
In 1930 he
joined Cadillac in Detroit, working on vehicle suspension and ride, and
during the ensuing years was responsible for introducing independent front
suspension on all General Motors cars. He also spent time from 1936 onwards
in England, introducing the Dubonnet IFS on to the Vauxhall models.
A few
years after "officially" retiring from GM in 1955, Olley returned
to Chevrolet on an informal basis and proceeded to write a series of
monographs describing his lifetime's work in chassis engineering. These
were acquired by Bill Milliken and were being readied for publication in
1969 when General Motors decided that in view of the litigation issues to
which the Chevrolet Corvair had been subjected
from 1963 to 1968, it would not be prudent to publish such information on
vehicle handling, and the project was stopped.
Thirty
years later, father and son Bill and Doug Milliken, who are themselves
eminent vehicle dynamicists, and the authors of
"Race Car Vehicle Dynamics", again approached GM, and this time
permission to publish was granted.
Bill
Milliken had worked in association with Maurice Olley from 1952 until Olley's death in 1972, and together with colleagues at
the Cornell Aeronautical Laboratories had been the first to apply some of
the principles and techniques used in aeronautical engineering to the
analysis of road vehicle stability and transient handling, in a project
sponsored by General Motors.
"Chassis
Design - Principles and Analysis" contains over six hundred pages, and
covers all aspects of vehicle suspension, ride and handling. As a textbook,
it develops the subject matter from first principles, supported by a vast
number of easily understood diagrams; the authors have also added their own
explanatory notes in places to clarify some aspects and to aid
understanding. Those of us for whom school is but a distant memory may
prefer to skip through much of the mathematics, but the erudite manner in
which Olley discusses the conclusions drawn from his theoretical and
practical work makes fascinating reading for anyone interested in how and
why motor cars behave in the way that they do. Any young engineer starting
work in this field, with arrays of computer aided design and data
acquisition packages at his disposal, would be well advised to first study
the contents of this book, to obtain a tangible feel for the subject and to
help to avoid some of the "rubbish in - rubbish out" pitfalls of
the electronic age.
This is
not just a textbook however. Sections are devoted to Olley's
reminiscences, descriptions of early motoring in Britain and his views on
the future. It even includes four rather "Thurberesque"
cartoons drawn by Olley. In short, it forms a comprehensive review of the
accomplishments of an engineer described by the authors as a "creative
and inspired individual" whose work "has had a positive effect on
the ride and handling of every car on the road".
For owners
of late pre- and early post-war Vauxhalls, the information on Dubonnet
suspension should be particularly interesting, including a practical
analysis of the "caster wobble" exhibited by a Chevrolet fitted
with Dubonnet IFS. The book makes clear distinctions between wheel fight,
shimmy, (which cannot occur with IFS) and caster wobble, (which can). In fact the book states that "nose-wheel shimmy"
on aircraft is actually an example of caster wobble. To this I could also
add the wheel wobble of some early generation supermarket trolleys!
As the
owner of the LM 14-40 once owned by Brian Frank, I was particularly
interested in wheel wobble. In correspondence with "Flutenews" about twelve years ago, Mr Frank suggested reducing the camber angle (!) and
increasing the caster angle, (perhaps the intuitive thing to do, to
increase the self-centring), to cure wheel
wobble, but finished up fitting a steering damper between the track-rod and
the axle.
In the
book Olley states that, on the Chevrolet, increasing the caster increased
the violence of the wobble, but had little effect on the frequency, and
that caster wobble can be damped out by decreasing the caster or by
a small increase in king-pin friction - friction applied elsewhere in the
steering linkage is less effective and more liable to spoil the handling.
On my car, the damper certainly made the steering feel dead, but when I
removed it, the first bump in the road hit at about 15mph set off a violent
wobble. I then fitted some wedges, tapering from 3/16ins to 1/16ins over a
4ins length, between the springs and the axle, so as to reduce the caster
angle (as described on page 29a of Supplement No 2 to the 14-40 HP Vauxhall
Chassis Shop Manual, kindly sent to me by fellow VOC member and 14-40 owner
Alan Livingstone).
The result
is steering which feels decidedly "lively", with plenty of
feedback, but despite severe provocation from badly surfaced local roads
the wobble has not returned.
"Chassis
Design - Principles and Analysis" (ISBN 0-7680-0826-3) is published by
Society of Automotive Engineers Inc., Warrendale, PA 15096-0001, USA, and
is available in UK from Professional Engineering Publishing Ltd, Bury St.
Edmunds, IP32 6BW. at £62.00 (with a discount for Institution of Mechanical
Engineers members).
-Brian Shilton
Flutenews
The magazine of the Vauxhall Owners Club 1903 to 1957
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