Passiv gefederte Sitze, insbesondere luftgefederte Sitze sind Stand der Technik und haben sich als ein Werkzeug zur Schwingungsreduzierung bewährt. In der Praxis tritt aber in einigen Fällen immer wieder ein Zielkonflikt zwischen der Reduzierung der Vibrationsbelastung einerseits und der Begrenzung der Relativwege zwischen der gefederten Sitzfläche und dem Kabinenboden andererseits auf, besonders bei Maschinen mit hohen Anregungsamplituden und niedrigen Anregungsfrequenzen, was seinen Ausdruck den SEAT Grenzwerten in der ISO 7096: 2000 z. B. für die Klassen EM1 und EM3 findet. Mit der hier vorgestellten aktiven pneumatischen Sitzfederung (APS) wurde eine praxistaugliche Lösung für diesen Zielkonflikt entwickelt. Das aktive Schwingsystem wurde zunächst als reines Simulationsmodell am Rechner dargestellt. Nach einem ersten Laborprototypen, mit dem die Wirksamkeit im Laborversuch nachgewiesen werden konnte, wurden zwei Versuchssitze für Fahr- und Feldversuche aufgebaut. Insbesondere die Parametervielfalt, welche Einfluss auf das Schwingverhalten hat, wurde bei dieser sehr an der Praxis orientierten Entwicklung berücksichtigt. Dieses System stellt die Weiterentwicklung luftgefederter Sitze da, bei denen eine deutliche Reduzierung der Vibrationsbelastung bei gleichzeitiger Erhöhung der Fahr- und Bediensicherheit erreicht wurde.
Passive suspended seats, mechanical as well as air suspended seats, are state of the art and have been a appropriate tool, to reduce Whole Body Vibration (WBV) in the past. Standards are defining tests for suspension seat and they are giving level for acceptance. But there is still a conflict between the reduction of the vibration on one hand and the limits of the travel between the seat cushion - the moving part of the seat - and the seat base on the other. This is most important on machines with excitation signals with high magnitudes and low frequencies. Especially for heavy construction machines, for example dumpers and heavy wheel loaders, damping is needed to avoid problems with excessive suspension travel. For these reasons SEAT-Factors of 1.0 and even higher had been defined in the ISO 7096 (2000). The setting of the damping in passive seats is a compromise between reduction of the vibration of the limitation of the suspension travel. For further developments of passive seats a dynamic simulation model had been developed and validated. The simulation results are correct in the frequency and in the time domain, in transmissibility, motions and forces. On the base of this dynamic simulation model of an air suspension system an active pneumatic suspension have been developed, by integrating a high speed valve, inflating and exhausting the air spring. The air spring, which is carrying the seat and driver weight in passive air suspension seats, is used as the active element. Due to the flat spring characteristic of the base suspension system, a small amount of asymmetry of the inflated and the exhausted air leads to change in the height of the systems. So the midride control was one of the main points, which had to taken into account. Input signals were taken from ISO 7096: 2000 (EM1 and EM3) and also a broad band excitation with different input levels. A significant vibration reduction (30% and more) had been achieved without any danger for handling and drivability - without increasing the suspension travel. The first laboratory prototype was built. The positive results were repeated and two prototype seats for driving and field tests were set up. Each step, from simulation to the laboratory prototype and also from the one axis test rig into the real situation in a vehicle or in a machine was not free from unexpected effects. The number of parameters, which have influence on the whole system are increasing. In the simulation every parameter can be changed step by step and the influence examined. In the laboratory you are testing with a real physical system, getting feed back from human test persons, but the quality of reproduction decreases. In the field you have changing conditions and more axis excitation, but that is the area were the product has to work. Many parameters like driver weight, machine and vehicle excitation in frequency and amplitude have been studied, and especially the optimisation of the mid-ride control made a high number of tests necessary. The overall results can be demonstrated by comparing this new technology with a passive seat with an adjustable damper. A Passive seat has very different vibration behaviour when loaded with a light or a heavy subject. With the active pneumatic system the improvement of the SEATFactor with the heavy drivers can nearly be realized for light drivers. In reality, the tendency for damping adjustment is more in the direction of higher forces (within the limitation of the ISO 7096:2000 requirements). The result is lower vibration reduction, with worst results for the light weighted person. Because drivers often have a higher weight compared to the heavy test person (ISO 7096). An adjustable damper with moderate hard and soft settings is a good compromise. The improvements of this new technology can even be shown with extremely hard damper settings, which produces SEAT-Factors for passive systems, much above the requirements.
Vibrationsminderung durch aktiv pneumatisch gefederte Sitze. Möglichkeiten der Reduzierung der vertikalen GKS unter Berücksichtigung der Fahrsicherheit
Vibration reduction by active pneumatic seats. Possibilities to reduce vertical WBV taking driving safety into account
2007
15 Seiten, 12 Bilder, 9 Quellen
Aufsatz (Konferenz)
Deutsch
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