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barryforever
Joined: 15 Aug 2007
Posts: 43
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 11 May 2008 9:51 ECU 4 Hydrogen Engine Design questions |
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Hi guys ..
I have decided to build an ECU for an Hydrogen 4 cylinder inline engine .
I just have a few doubts before starting of my project.
I want to know the following things
What is the minimum voltage and current required to switch on the Injector ?
Can I use a mosfet to drive the injector ?
What artitechture should i use use a 8 bit or a 16 bit microcontroller ?
What is the switch on and switch off time of the injector ?
Should the fuel be in liquid form or gaseous form ?
Even though you cannot provide a exact answer please give me some idea .
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umery2k75
Joined: 19 Apr 2006
Posts: 247
Helped: 19
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| 11 May 2008 11:02 Re: ECU 4 Hydrogen Engine Design questions |
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http://www.edaboard.com/viewtopic.php?t=310644&highlight=
In this forum, I expect Mr_W knows much about fuel injectors as he's doing research on them.He can guide you very good.
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| What is the minimum voltage and current required to switch on the Injector ? |
A)As far voltages,current are required for injectors, they are different from one manufacture to another.
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| Can I use a mosfet to drive the injector ? |
B)You can use several semicondutors to drive the injector, like BJT,JFET p,n type,MOSFET p,n with enhancment,depletion,SCR,etc. It all depend how your circuit is made.
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| What artitechture should i use use a 8 bit or a 16 bit microcontroller ? |
C)8-bit or 16-bit doesn't reflect you toward the architecture of CPU. Architecture is distingush by the way the processor execute things, there are two basic types of them as far as I know them, Harvard and Von Neumann architecture. You can find 8-bit,16-bit,32-bit in both of these two categories.
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| What is the switch on and switch off time of the injector ? |
D)Switch ON,Switch OFF time must be within the audio frequency. You should use semiconductor that has switching max. frequency around audio range, there are VHF,UHF transistor too, that can switch at greater frequencies. It's related to the RPM of the engine, mostly vehicle engines do 8000-9000 rpm. I think every transistor has much higher switching frequency as 9000/60=150 Hz.
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| Should the fuel be in liquid form or gaseous form ? |
E)It depend on the fuel by which you are driving your engine. I have seen cars that can work both on petrol and natural gas. They have some conversion kit in them, by which user can select the fuel while driving the vehicle. I don't know whether those car has same fuel injector for gas and petrol.
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mr_W
Joined: 15 Dec 2006
Posts: 6
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| 11 May 2008 13:31 Re: ECU 4 Hydrogen Engine Design questions |
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@umery2k75
thanks for bringing me in!
Now, as for the voltage and current specs for output drivers, I've replaced original driver with BD912 which is rated for 15A and 100V. I think 15A is a bit of an overkill, since I'm using high impedance injectors - around 15 ohm, which at average automotive power supply draw around 1A of current.
100V I choose because I wasn't sure if original ECU has flyback voltage protection. Didn't know either about what voltage can flyback generate. Some sources said it was in 60V range, and some other quoted much higher. I went with 100V and assumed that there must be some sort of protection around them. Factory shouldn't be so dumb even back then not to put some.
It turned out that it works flawlessly with this driver.
Now there are other types of injectors - low impedance, which are in 2 ohm range, and they can draw much more current. However, they are operated in different manner. ECU should first allow them full current, until they open, and then limit it to lower value for the time injector is open. When operated in this way, injectors are opened faster, which results in better overall performance.
You should be able to drive injectors with about anything that is fast enough (which I assume all semiconductors are - only mechanical devices like relays are ruled out of course  .
Injector opening times are in millisecond range, which varies from engine to engine, but for petrol injected are for example 1.7msec at idle. Pulse width can go to full duty cycle at wide open throttle.
I suppose that it would be very useful for you to take a look at Megasquirt project (just google for it!) as you can use it for ideas, to get better understanding about how fuel injection works, and it could even provide complete solution for you.
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