Fuel injector maximum duty cycle

[Rpmayne 0]

I've been working on an assembly machine this morning which uses a bosch fuel injector to dose cleaner onto tape which is used to clean pen refills. It's been having overheating problems since being fitted by the manufacturer.

 

Does anyone know how the fuel injectors are supposed to be operated? I thought they are oscillated at different rates to regulate the fuel and not controlled by simply holding them open for different amounts of time.

 

The machine system is a gravity fed bottle of cleaner which goes through the injector which is turned on for 100ms every second.

 

Thing which makes me wonder is I set the machine to give it a 2 second duty cycle and after about 5 minutes you couldn't touch the injector because it was so hot. Are they designed to be used like this?

 

Thanks for any comments, weird question I know.

[coolrado 0]

i would have thought the duty cycle on a car would be much shorter than that so would not give it chance to heat up at all especially with fuel being passed through it which would also keep it quite cool, would it be possible to fit a heatsink to the injector?

could you contact bosch and find out from them the maximum safe duty cycle?

[Rpmayne 0]

I was thinking that, not sure but I remember a VAG-COM equivalent saying something like 10ms injector opening times. And as you say the pressurised fuel would probably cool better aswell. In the past we've used air solenoid systems to dose the cleaner, just surprised me to see a fuel injector used like this. Rather than being a mist though it's more of a drip.

[mrbeige 0]

In a normal automotive application the duty cycle is far shorter than 2 seconds, and essentially an injector is a solenoid, so if you are holding the current high for too long, it is possible that the heat will be induced in the coil inside the injector. As far as I am aware it might be possible to modulate the current and voltage around the required value to open the injector, which may solve your problem?

[coolrado 0]

would using multiple shorter bursts have the same effect as holding the injector open for a long time without the problem of overheating?

[mrbeige 0]

would using multiple shorter bursts have the same effect as holding the injector open for a long time without the problem of overheating?

 

That should work, as the current and voltage would drop off between pulses

[Rpmayne 0]

That might work but the control over the injector is a relay output from a PLC so it's not really meant to switch that fast so it would burn out quickly. Really need a solid state relay to do that, and seeing that it's gravity fed it may not let any fluid through.

 

Just been onto Bosch technical and they're going to ring me back.

[coolrado 0]

i worked as a control panel builder for 6 years when i left school and plc's are part of the reason i left as it got a bit boring having to cut, crimp, tag and terminate several thousand individual wires for every control suite :lol:

 

are there any injectors that actually act as a pump when they fire?

 

something like the pumpe duse injectors from the newer vw diesels but i think they require mechanical force to pressurise the fuel then just open the valve electronically to control the output. http://www.boschautoparts.co.uk/pcDies6.asp?c=2&d=1

[Rpmayne 0]

We're going to have to find another way of doing it, Bosch came back and said they should be running around the 4ms cycle time, not 100ms which explains the excess heat.

 

I started out doing the panels, found the same but luckily the jobs got abit more varied since so it's not too bad. Would have liked to get into the ECU side of things but the good old VR has put me off a little. :(

[coolrado 0]

we built the control system for a machine that squirted the fragrence onto the disks you get inside those crappy round plastic air freshners that you usually see stuck on the side of bog systerns, that used a solonoid syringe pump that could fire off at a stupidly fast rate and could be controlled very precisely, not too sure who made it though but it wasnt very expensive if i remember, i will ask around tonight if i get chance.

 

i have had a look at those pumpe duse injectors but i cant work out if the pump part is solonoid driven or whether its driven off a cam? if it is solonoid driven it would probably be ideal for you as it does not require a high pressure rail.

[davidwort 0]

we built the control system for a machine that squirted the fragrence onto the disks you get inside those crappy round plastic air freshners that you usually see stuck on the side of bog systerns, that used a solonoid syringe pump that could fire off at a stupidly fast rate and could be controlled very precisely, not too sure who made it though but it wasnt very expensive if i remember, i will ask around tonight if i get chance.

 

i have had a look at those pumpe duse injectors but i cant work out if the pump part is solonoid driven or whether its driven off a cam? if it is solonoid driven it would probably be ideal for you as it does not require a high pressure rail.

 

driven off a cam IIRC, thats why they have thumping great cam belts and frequent service intervals on them, loads of strain.

 

David.

[Kevin Bacon 5]

Aye. Effective though and it means a low pressure at the rail, which is safer in an accident.

 

Electronic injectors don't like big duty cycles, the whole idea of them is finer metering with short pulses.

 

If you want big duty, you're better off with CIS type injection.....but you can't meter them as finely as you can electronic ones.

[Chris VR6nos 0]

what is CIS?>

 

 

Chris

[Henny 0]

Constant injection system = CIS

 

Basically the injectors are ALWAYS spraying fuel rather than being turned on electronically when needed and off when not... K-Jetronic is a CIS system...