GDI/FSI Injector driver for Injector cleaning

Discussion in 'Automotive Electronics' started by dave18, Mar 8, 2018.

  1. dave18

    Thread Starter New Member

    Mar 8, 2018
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    Hi, new to the forum and had a search but couldn't find any relevant info. I've been looking at injector cleaning equipment and it seems that machines for gasoline direct injection are very hard to come by apart from one major manufacturer. I have the equipment for standard indirect injection but would like to find someone interested in modifying the existing driver or building a driver circuit to pulse GDI injectors. The engine ecu opens the injectors with battery voltage but once running the injectors induce a flyback voltage which is stored in capacitors and then allows a brief voltage of up to 120V with a 12a spike, holding current is also controlled while the injector is open. As far as I know the old type petrol injectors are just pulsed at vehicle voltage. I've seen GDI adapter boxes are available to convert old equipment but they are still a huge expense. Anyone interested? :)
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Welcome to AAC!
    Are you asking for a circuit to pulse an injector at 12V only, or something more complicated involving 120V and 12A spikes?
     
  3. dave18

    Thread Starter New Member

    Mar 8, 2018
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    [​IMG] Hi, thanks for replying. The problem is new direct injection petrol injectors are triggered differently to the old indirect type. The cleaning machine still needs to pulse a variable duty cycle at 12V which the old machines do but the new injectors induce voltage back to capacitors in the vehicles ecu which is then used to trigger them at a higher voltage when the engine's running. I'd need to look into the exact workings but it's just an idea to build a converter for the old machines. There is one manufacturer but their adapter is £1800 and only available to owners of their equipment and the machine that contains the driver for these injectors is around £7000+vat. The machines that could be converted are £300, just thinking there is a demand for this and if someone with some electronics knowledge would be interested in designing something. I'm not after making money from it, I already run a small business in the motor trade but to be honest quit electronics engineering before becoming a mechanic. I'd just like small independent garages like myself to be able to carry out this service without being bent over by one company that seems to have a monopoly when it comes to supplying the equipment to do it. ;)
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I get that the voltage feedback and high voltage stuff is appropriate for a fast-running engine, but surely not for a cleaning machine? Are you saying that in order to clean the new type injectors you need the high voltage (>100V) just to get them to open? Or does the cleaning machine also test the injectors by simulating their normal drive arrangement? As you can guess, my injector/automotive knowledge is sadly lacking.
     
    Last edited: Mar 9, 2018
  5. dave18

    Thread Starter New Member

    Mar 8, 2018
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    No problem :) The injectors aren't tested at working pressure as they work at up to 100 bar of pressurised petrol on the vehicle and visually inspecting the spray patterns is more precise at low pressure. The switch times need to be controlled to simulate the rev range. Appreciate the interest.

    gdicleaner2.jpg
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    So, you want a circuit to generate the pulse form shown? What will the pulse repetition frequency be? What are the injector inductance and resistance values?

    Edit: Can you post a link to the spec/datasheet/manual of the cleaning machine and its adapter?
     
    Last edited: Mar 10, 2018
  7. dave18

    Thread Starter New Member

    Mar 8, 2018
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    Sorry I haven't been on for a while, there aren't many details of the machine apart from the waveform above, possibly to make it harder to make a copy which is understandable.
    I was thinking the other night though about using an old ECU which are easy enough to get hold of. Setting input sensor values with fixed resistors and have spoken to an engine tuner to code out anything that will cause the ECU to shut down the injectors due to fault codes with ignition system being open circuit. The ecu would only need a 12V supply and a variable crankshaft signal to trigger the injectors which is a square wave with a reference point for TDC. Switching the sensor values such as air mass, boost, throttle angle would simulate idle through to full load injection rates. The injection signal would vary from idle - 800rpm 6hz to full speed - 7000rpm 58Hz.
    I was just thinking it would be easier to simulate the crankshaft signal and input that to the ecu.
     
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Those pulse rates are appropriate for a single injector, but doesn't your machine test/clean multiple injectors at a time? If so, the pulse rates woud be multiplied by the number of cylinders/injectors.
    Would you be happy with a gizmo entirely separate from your existing machine, or will it have to interface with the machine the same way the OEM adapter does?
    Do you have a spare ecu which can cope with the new GDI injectors?
    Does it provide all the necessary voltages/currents/timing parameters?
    How variable are those parameters from one injector brand to another.
    I've designed a circuit which can be the basis for a stand-alone gizmo, but it would need refining and calibrating. This is an analogue approach, but a digital approach would be more versatile and have a lower parts count. Digital isn't my forte.
    Here's the circuit:
    GDI_injector_driver.PNG
    And here's the simulated output:
    GDI-injector_waveform.PNG
    I've also attached the simulation file in case anyone wants to play.
    By way of explanation, the parts in the blue rectangle form a DC boost converter to step up the 12V supply to something in the 60V-90V region (adjustable with VR1), which is held on C6.
    A hex Schmitt inverter IC (U2, CD40106) does the timing. The pulse repetition period is set with VR2. The width of the highest peak is set with VR3. The widths of the intermediate and lower current levels are set by VR4 and VR5 respectively.
    NOR gates U3 control the timed switch-on of MOSFET M2 during those three pulse stages.
    R16/17 set a current limit during the highest peak stage when C6 discharges through the injector. Current limits during the second and third stages (when the current source is primarily the 12V supply) are set by VR6 and VR7.
    When any of the U3 outputs is high, diodes D12/13/14 pull R20 high to enable the ouput opamp U8 to drive push-pull pair Q1,Q2 and hence M2. The source current of M2 is sensed with R9 to give a feedback signal to comparator U7. When the set limit is exceeded U7 output goes low and M2 switches off.
     
    Last edited: Mar 13, 2018
  9. dave18

    Thread Starter New Member

    Mar 8, 2018
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    That is amazing work! I did find a PDF on injector driver design but it is a design for vehicle use so there is probably more involved with accuracy and signal noise. The GDI/FSI driver could be used in a standalone box to cost effectively convert existing petrol injector testers to view the spray pattern and delivery rate rate of these modern injectors.
     
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