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Chassis Design: Principles and Analysis

 

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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