Piezo injector operation. Current vs voltage

liviu2004 wrote:
You can see the circuit ecu-injector as an oscilator circuit, electrons go from ecu to inj and reverse, but voltage to ground does not change polarity. Hard to explain.

So in the first post, the diagram absolutely NOT TRUE.
And on the examples from Steve and victor2k everything is correct.
It was informative.

Hello and thank you for the posts and the feedback

Good catch on the Guided Test RYM6746 as the Technical Information suggests the Piezo Stack does not need to have a continuous supply voltage and will remain in the open state until the close command.

The close command here is the removal of voltage (by the PCM or Driver) where we see the progressive discharge of the Piezo Stack.

In our captures above, the power supply and ground is maintained across the Piezo stack throughout activation/duration which contradicts the Guided Test

I will highlight this to Technical Publications and request this be amended.

The Guided Tests are under continual review and new Guided Tests developed regularly (initially available on line) before making into the software.
https://www.picoauto.com/library/automo ... ided-tests

Thank you again for the heads up

Take care.......Steve

RYM6746 wrote:

Important note: Once the stack is in the injector open position, it does not need to have a continuous supply voltage and will remain in the open state until the close command. Hence the positive and negative current spikes in the waveform. For this reason, never disconnect the injector's multi-plug with the engine running. If the injector is in the open state it could hydraulic-lock the engine with the diesel fuel. The engine will cut out if the control module detects any faults with the injectors or driver circuit.

Surely this statement is partially incorrect in the guided test section under peizo injector technical information. when it says it does not need to have a continuous voltage and will remain in the open state?

It would appear in order to keep it in the open state a continuous voltage needs to be held even though there is no more current flow?

Theoretically, as the stack acts like a capacitor, if the injector is disconnected while it is charged (during injector "open" phase) it will stay open as the stack cannot discharge via the ECU. Is this correct or will the charge decay fairly quickly, closing the injector?

On a side note, the Bosch diesel injectors I am aware of do not actuate the nozzle needle directly with the piezo stack. The stack operates a control valve, which controls fuel pressure differential between the two ends of the needle. Worth knowing when diagnosing these injectors.

Mark

Tech Mark wrote:
Theoretically, as the stack acts like a capacitor, if the injector is disconnected while it is charged (during injector "open" phase) it will stay open as the stack cannot discharge via the ECU. Is this correct or will the charge decay fairly quickly, closing the injector?

Hello,
This simplified model not explain very well the crystal stack,the resistance(180-200 kOhm) was omitted...so you will have a self-discharge in a few minutes.But you can't be shure about the complete discharge of the crystal stack,in our captures you can't see this self-discharge current(only a few mA ,please look at the attached image for this magnified current ),this is the reason why ECU put to gnd ij+ to cut injection.
Again simplifying the entire process,you must move some electrons to excite the crystal structure and make it "fat" and after some hundreds of us you must remove the same number of electrons from the crystal structure and make it "slim".Moving and removing of electrons will give you the current,the presence of electrons on one side of crystal structure will give you the voltage... from this perspective I used the simplified model with capacitor
Anyway the big problems with this type of injectors was the shorting of the crystal stack(this can be detected by ECU or measured with a multimeter),excessive back leak,and hydraulic command of needle(back leak test with injectors unlugged or with engine running)...For me was enough to capture the current af all injectors to see if one of them work bad/not work.
If someone need more info then the solid-state physics have more answers
Regards

It would appear that the current doesn't flow into the piezo crystal stack. It flows through it. This picture has two amps clamps one on injector positive and one on injector negative.

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Could admin please move last posts to separate thread and leave this for fundamental stuff only.

I believe there is a need for several test on piezo to get facts straight. At the moment there are so many different theories here.