|
|
|
|
|
01/01/2005
 Email to a friend
 Comment on this article
|
Roger Bishop reports on the development of a composite spring/actuator with automotive potential that promises all the controllability of advanced electronic spring-damper systems without their electromechanical complexity.
Roger Bishop reports on the development of a composite spring/actuator with automotive potential that promises all the controllability of advanced electronic spring-damper systems without their electromechanical complexity
The composite spring may be coming of age. The research arm of one of the world’s leading Tier One organisations is testing a ‘smart’ system that has no moving parts or mechanisms yet can provide a car with the full range of spring-damper suspension responses including anti-roll control, anti-yaw, and load compensation.
Described by its developers — UK-based TRW Conekt — as a quarter elliptic composite spring, it in fact comprises two elliptical elements placed back to back. One end is connected to the vehicle and the other to the axle via metal bushes.
Between the two ‘leaves’ are two elements about which TRW Conekt is prepared to say very little. However, the primary function of the section closest to the axle is to link the two sub-leaves while the purpose of the other is to control the load transfer in bending, tension and shear from the axle, through the sub-leaves and into the chassis. It is developments in this region that hold the secret to ‘smart’ active control of spring rate and damping.
So far, the technology has been under development for three years. Mark De Cooper Jones, the engineer behind the invention, believes it may be another six or seven years before an application is seen on a production vehicle, even though some initial discussions are now taking place.
He says installed in a micro car — a Smart, for example — the system should weigh less than half that of conventional spring-damper combination and, as the illustration clearly shows, the design is equally applicable to motorcycles. It is also highly relevant to vehicles requiring adjustment for load, given the load-compensating capabilities claimed.
Jones says glass, carbon fibre and Kevlar are the target materials for the system—a hybrid using different materials in areas of the suspension requiring specific properties.
“Units are designed so that wheel movement remains within the fatigue life of the materials,” he says. “This relies on our proprietary strain management approach which is highly dependent on the lay-up of the materials and the geometry of the part. If we get it right—and we believe we can—the life of the system can be infinite.”
TRW Conekt believes the ‘holistic approach’ taken to the design and manufacture of the spring will be key to its ultimate success.
“From the outset we only considered designs that could be produced by volume production methods and have evolved what we believe to be the lowest cost manufacturing process for medium volume production,” says Jones. “This will enable us to produce a family of products with different mechanical and performance properties from a common manufacturing line and part geometry.”
Again, he would not be persuaded to reveal further details except to confirm that it did not rely on pre-pregs and to say that was a “high volume continuous process using fabrics and resins aimed at achieving the lowest process cost”.
So how are Jones and his colleagues bringing to their design the range of chassis control features that vehicle OEMs expect now, let alone in the future?
“Our system was designed from the outset to be an active suspension,” says De Cooper Jones. “A variable stiffness element is part of the structure and embedded within this are sensors that provide programming signals, to determine deflection and to provide condition monitoring of the whole system. Inputs can be put into this element via an actuator to adjust spring rate in real time.” (The insulating layers of composite materials are excellent hosts for embedded sensors.)
The biggest benefit, though, comes from the capability of the system to separate variable spring rate from variable damping and to control these as independently as possible. “Combining variable spring rate with active damping in a highly decoupled system provides very high levels of control,” he says.
Ride height adjustment is possible and systems could range between lightweight passive arms offering great durability or active (smart) designs with variable active damping operating either in ‘real time’ or in a programmed manner — for example a ‘sports mode’ setting. Only one additional moving part would be required.
Weight-saving and its potential to influence vehicle dynamics may not be the only reasons that persuade vehicle-makers ultimately to consider this remarkable technology seriously. With only three load points it could be attached to a vehicle body with just two bolts, with obvious advantages to vehicle assembly operations.
Further (patent applied for) proprietary research and development has taken place to protect systems against automotive fluids and also a strategy to protect components from damage caused by flying stones, road debris and so on.
European Automotive Design has seen this technology demonstrated on rig resembling the rear trailing suspension arm of a micro car. It uses a full-sized 14in wheel and tyre and has a composite spring element that is 500mm long and 100mm wide.
|
|
| |
Author
Roger Bishop
|
| |
| |
Copyright European Automotive Design.
See Terms and Conditions.
One-off usage is permitted but bulk copying is not.
For multiple copies contact the sales team.
|
| |
|
|
| |
To access the whitepaper section you need to complete our 60 second registration process. Once completed this then allows you to download any and all white papers, register for e-zines and access our detailed supplier directory for FREE.
If you are all ready a registered user then enter your e-mail address and login.
You will need to have logged in prior to entering your comments in the boxes provided.
|