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14 September 2004

Air Spring Systems Expanded with New Sensor

A contactless functioning height and pressure sensor that has been integrated into the air spring is being showcased by ContiTech Air Spring Systems at the InnoTrans in Berlin (hall 1.2, booth 136).

Air suspension is becoming ever-more common as secondary suspension on modern passenger train cars since air-sprung chassis offer optimum riding comfort. The advantage of air suspension when it comes to comfort is that the spring characteristics can be adjusted to a constant spring height, depending on the static load being carried. At present, the train car height is controlled with the help of pneumatic valves, which are actuated via a lever linkage between the bogie frame and the vehicle body.

With its integrated height and pressure sensor, ContiTech Air Spring Systems has created the technical prerequisite for using electronically controlled air spring systems with electrically operated valves. This will make it possible for future rail vehicles to benefit from the advantages that road vehicles have profited from for so long:

  • Low air loss
  • Precise level adjustment
  • Adjustment of variable target level

The conventional level control results in greater air loss because it is active at all times, adjusting dynamic changes in level while the vehicle is in motion. To reduce this effect, the mechanically actuated pneumatic valves have a “passive” zone around their neutral position, in which air is neither applied to nor removed from the air spring.

The electronic control reduces the number of adjustment processes significantly because it adjusts the height only if the load has changed as a result of passengers getting on or off. In contrast to the conventional control system, which sets only the target height determined by the lever linkage, the electronic control can initiate various target values to adjust the height of the vehicle to the heights of different station platforms.

The ultrasound sensor introduced by ContiTech is integrated in the air spring, providing the actual values of the spring height and the air spring pressure to the electronic control unit, which then actuates the solenoid valves to apply air to or remove air from the system.

A combined height and pressure sensor in a casing for this application would already qualify as a technological quantum leap. ContiTech has taken things a step further, though. The ultrasonic signal for the height measurement is used to determine air spring pressure. No other sensor component is involved.

Complicating development of the ultrasonic sensor was the fact that sonic waves in a spring spread differently depending on pressure and temperature conditions. A reference sensor at a constant distance from the sensor solved the problem of continually varying environmental conditions. The height is calculated on the basis of the ratio of the transit times from sensor to reference reflector and from sensor to the reflector on the base of the air spring piston.

ContiTech ended up making a virtue of necessity in that it was possible to derive the spring pressure directly from the amplitude of the reference signal.

The ultrasonic sensor is nearing production readiness. For use in commercial vehicles on the road, it is currently undergoing testing in vehicles from various manufacturers and has been producing very good results. “Our system can be designed for compatibility with all control devices currently on the market,” declares developer Dr.-Ing. Siegfried Reck. “With its built-in intelligence, the sensor can easily be adapted to customer demands,” he adds, referring to a powerful micro-controller that takes the measurements and serves as interface to the control device.

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