×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Current Vs Voltage Piezzo diesel injector
2

Current Vs Voltage Piezzo diesel injector

Current Vs Voltage Piezzo diesel injector

(OP)
Hello

I connected my scope to the two wires of a Siemens piezzo diesel injector. One chanel reading voltage and the other reading current with a current clamp.

I get voltage growing around to 50v, stepping up and then falling to zero (This is normal).
In exactly the same time, current starts going up from zero to around 10 Amps and then falls to zero for a while but (here is were i don't understand...) it goes negative the same amount it has been positive before and goes back to zero.
I have a picture that is more explicit but I don't know how to post it here.

In a book that I have, Bosch has the same pattern for the same kind of injector (so, its a normall pattern) but does not explain how it works.

Question: How can I have, at the same time, in the same circuit, voltage in one sense and current that reverses?


Best regards
Carlos Reis
Lisbon, Portugal

RE: Current Vs Voltage Piezzo diesel injector

CarlosReis,

The Piezo elements that are being driven have a very large capacitance.  In order to change their shape, you apply voltage.  This voltage has to "charge" their capacitance, which you see as "positive pulse" current.  In order to return them to their original shape, that capacitance has to be "drained" away.  Hence, the "reverse pulse" current.

-Tony Staples
www.tscombustion.com

RE: Current Vs Voltage Piezzo diesel injector

(OP)
Thanks for the reply(s).

As far as I have understand, the piezo works like a capacitor and the feed circuit "discharge" it at the end of each cycle in order to close the injector.

Did I got it?

Thanks
Carlos Reis

RE: Current Vs Voltage Piezzo diesel injector

Fabrico, thanks for the great reference.  What it doe not explain fully is that the piezo stack expands when you apply the voltage to turn on the injector. When you turn off the injector the piezo stack contracts and generates voltage. To prevent extremly high voltages and to control the turn off time,  the injectors are discharged into a controlled impedance which develops the reverse current.

RE: Current Vs Voltage Piezzo diesel injector

Carlos,

You've got it! Good luck!

-Tony Staples
www.tscombustion.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources