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Piezo Injector (Common Rail)
Function
With the introduction of the Piezo technology, the injector has also been newly designed. It has become smaller and allows a continuous high pressure with every new injection cycle. The dead-weight inertia of the
nozzle needle has shrunk to one quarter of its previous size. Together with a higher pulse rate there are more injections than before, pre-injection and very late post-injections. Also varying pressures within a cycle are
possible. Compared with magnetic valves, not only can higher-, but also lower injection pressures be reached. With this technology, in the future, Euro-V threshold values can be upheld by engines with a particle filter
and possibly, perhaps post-injection for regeneration.
How it works
To be able to see the innovation in the injector, the above figure must be enlarged to the max. by clicking. No longer a magnetic valve, but approx. 200 layers of crystalline material influence the nozzle needle. Up to now
the Piezo crystal is known only from the sensor side, e.g., as a knock sensor where a voltage change
is achieved through pressure. In this case it's exactly the opposite. Voltage generates movement. This happens very quickly because crystal structures react very quickly. Indeed, the linear expansion is only very slight.
To achieve the required dilations, 200 of these crystalline layers and a certain lever ratio are necessary. The effect that the linear expansion corresponds precisely to the voltage laid on, is also upheld in this
construction.
In the meantime, the first variation has already appeared, namely, one with direct drive. The Piezo drive is connected with the nozzle needle making it possible to call up data about the position of the nozzle needle. It
thus, almost takes over the role of the nozzle motion sensor of former systems. Hereby progress is possible concerning the injection control and perhaps also in the error analysis. 05/08
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