Hi all.

For my A-Level electronics project I have decided to design a turbo timer (couldn't think of anything else ).

I am thinking of using the idea of measuring the temperature of the turbo and when it drops below a suitable level the engine is switched off.

Now I need to know a few things to get me started.

What sort of temperatures does the tubro reach - anybody know/like to make a guess? I know they get red hot, but how hot is red hot?

What is a safe temperature to turn the engine off? Again, anybody know/like to make a guess?

What part of the turbo needs to be measured for the temp, and why exactly is it that it has to be cooled? Something to do with the oil that cools the turbo?



Anybody know of any good info about the workings of a turbo?

Thanks for any help.
Richard

 

I think the temp of the turbo is not that important, what is important is:

1. If you have been driving hard and turn the engine off without letting the engine idle, the turbo can take a while to spin down, but oil is not circulating around the bearings. We're talking maybe fractions of seconds, but the cumulative effect can be serious.

2. The turbo gets very hot, and idling lets some of this intense heat dissipate to adjacent parts of the engine, such as the exhaust and manifold. The result is to reduce the temp of the oil and bearings when you eventually switch off the engine.

Good luck with your project!

<standing by to be technically corrected !>

 

Goto

http://www.howstuffworks.com/turbo1.htm

Ton's of links as well or do a search on turbo timers on this site and you'll find loads of good info.

 

Richard,

turbo operating temperature depends on the type of use...

On a steady high speed cruise you'de expect to see somewhere between 500 and 900 degrees C. On a charge you'de ideally like to keep the temps down to about 850 degrees C, but if you're not too concerned about turbo like (ie a works team that replaces them every day) then maybe up to 1200 degrees C. I have my antilag system set to reduce the boost enhancement when the turbo gets up to 950 degrees C (since I don't have the time, inclination or budget to keep on replacing the darn thing ).

The turbo timer is *NOT* there to keep an oil feed to the turbo to allow it to stop rotating with a lack of an oil supply. It is there because without a flow of oil through the bearings the oil would be "burnt" turning it into a gum/varnish type substance by the heat. This is rather bad for the bearings as you can no doubt imagine.

The solution, thus, is to allow the exhaust housing to cool down to such a temperature that thermal conduction of the residual heat energy in the housing into the bearing core would result in a temperature rise of the core which would be insufficient to allow the oil to get destroyed.

Generally, when I drive home I see about 630 degrees C on cruise, then when I come off the dual carriageway, I drive for about a minute or two through a 30 limit. By the time I get home the temps are down to about 360 degrees C. It takes a LONG time for it to cool down much more with the engine running, and even then it's unlikely to fall much below 200 degrees...

I usually turn off with the temps at about 330 to 350 degrees. I dunno if this is cool enough but.... I used to run an MHI TD-05H turbo and gave it hell... Antilag on track, full throttle shifts (makes well over 2 bar and 6 foot blue flames!). When I got a bigger turbo I had the -05H rebuilt (I don't like to sell bits without being certain they're OK). When taken to bits for inspection the bearings were absolutely perfect, with no oil varnish or anything. So I guess that 350 is OK *ON THAT TURBO*. Others may need to cool down less, whereas some may need more. It all comes down to how much the bearing core gets heated by the exhaust housing....

For measuring the temps, I have a K-type thermocouple in the exhaust housing (yes, this does require the drilling of a hole in the housing!). I did it this way since it will give me true readings of how hot the turbo is getting. You can get an integrated thermocouple amplifier device from Analogue Devices (I forget the part number)... this does all the hard work (ie compensation, cold junction reference etc) so you don't have to What you could do is feed the output of that into a PIC (would be REALLY cool if they have released the PIC16F010, it's an 8 pin device with A/D converters... just the ticket ). Then just write a little bit of code for it and hey presto, a turbo timer (OK, you'll need a relay, but that's not rocket science).

For more info on the devices mentioned take a look at www.microchip.com and www.analog.com .

Hope this helps,

Pat.

 

Pat's right - the point of the oil flow is to help cool the bearing housing and stop the residual oil there from overheating.

So why not just measure the temperature difference between the oil going into and out of the of the turbo bearing housing - much easier than drilling and tapping the turbo housing itself.

When the temp increase of the oil across the bearing is lower than a certain level (corresponding to a 'safe' turbo temperature) the timer could turn off.
Alternatively, wait until the oil temp difference is steady - but this is probably overconservative.

Nick