Solartron Metrology, the world's leading manufacturer of gauging probes and displacement transducers, has supplied life-saving instrumentation to Richard Noble's ThrustSSC, the car designed to attempt to break the world land speed record.
There are six Solartron LVDTs (Linear Variable Differential Transformer) fitted to the vehicle: four to measure the positions of the wheels with two acting as key components in the car's Active Suspension Control System, measuring the displacement of the Active Struts. Each LVDT is powered by a Signal Conditioning Module, also supplied by Solartron, which provides the voltage output proportional to displacement.
The active Strut (hydraulic ram) Suspension System is vital to ThrustSSC to maintain stability of the car as it travels through the Transonic Region (between Mach .7 and Mach 1.2). As the car approaches the Speed of Sound, it enters the critical and dangerous Transonic Region, where the air is moving at supersonic speeds over some parts of the car's surface causing shock waves to occur. As the Mach number increases, these patterns change making it very difficult for the car to remain stable, as the close proximity of the ground influences the airflow around the car.
There are two Active Struts which control the pitch of the car. The Solartron LVDTs are mounted on each one to measure their displacement - how far they are open or closed. During a process called the Displacement Error Loop, the output signal from the LVDT and Signal Conditioning Module sends a signal to one of the car's two on-board computers, which then compares the displacement of the strut to the required position (the displacement error).
The computer will automatically send a signal to the Moog Electro-Hydraulic Servo Valve which in turn will cause the strut to move towards the required position. This process is repeated 1000 times per second and controls six tons of force to an accuracy of less than a millimetre. Without the LVDT, the Active System would not work.
The use of LVDTs during the car's testing has also provided the design team with essential knowledge of the car's suspension - knowledge which could not have been derived from a computer model. During the car's recent test runs in Jordan, the major problems to overcome were those associated with the car's rear wheel steering. The use of onboard video cameras and the LVDTs showed that the wheels were 'shimmying' from side to side, making the car unsafe at high speeds. This can be compared to the action of a supermarket trolley. During the 90 second test runs, over four megabytes of data is captured in the onboard data boxes and then downloaded onto the team's computer for in-depth analysis. The readings from the LVDTs located on the rear struts helped the team to determine that the caster angle of the rear wheels was the problem. In addition, the readings also enabled the team to adjust the suspension to a safe, softer level to improve the ride. The team was just 36 hours away from testing the new adjustments before it rained!
Jeremy Bliss, systems designer, explains the importance of the Solartron LVDTs to the safety of the car and driver, "Without the LVDTs, we wouldn't be able to run the active suspension, which is the key to the car's safety at high speed. We would also have a huge gap on our knowledge about the car's suspension. The Solartron LVDTs are the best I have ever come across - their signal to noise ratio is very small and they are incredibly robust in that they are able to stand up to one of the most adverse environments they could ever be applied to. We have experienced no problems and the support from Solartron has been excellent".
For more information, please see the Solartron-Metrology Web Site at: http://www.solartron-metrology.com
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