Well...I got bored so I decided to pull my throttle body apart, well, not quite.
It appeared that the engine had a slight surge, between about 55 to 60 KMH. I decided that it potentially could be the electronic throttle body. So lets pull the throttle body apart and see what we can see.
This engine (TU3JP 1.4l petrol) has what is known as a fly-by-wire throttle. That means that the engine ECU actually controls how the throttle moves and the engine throttle is not directly connected to the throttle peddle. This is a fairly common way to control the engine in cars now days.
This arrangement has several advantages including; the ability for the engine ECU to directly control the speed of the car making a cruise control system simpler.
The engine ECU can over ride the drivers throttle commands if the commands would result in a negative impact on the engine performance. For example if the driver mashes the throttle peddle to the floor when going up a hill. If the engine is incapable of the power requested of the driver the engine ECU "backs off" on the throttle because it's a waste of time and fuel!
The engine ECU can reduce throttle in a skid situation if the car has ESP.
On the outside the throttle body looks fairly unassuming and common. This electronic throttle body is manufactured by VDO
Lets take the top off and have a look. First, there is tab to cut off.
It looks like a synchronous AC motor but it cant be! A synchronous motor goes round and round but the butterfly valve shaft only goes backwards and forwards!
Typically the throttle contains a DC motor that drives reduction gears to the butterfly valve. The DC motor can run in either direction, thereby moving the throttle butterfly, backwards and forwards.
This is obviously very different!
To be frank with you I have not seen this technology before, well not used like this! The P-3C engine oil cooler gill flap position indicators (that I used to work on) had a 3 phase version of this. They were very simple. This is only single phase but requires a lot more electrickery to get it to work! But I digress.
There is a round permanent magnet on the end of the butterfly valve shaft and an electromagnet surrounding it. No gear reduction. Just one moving part! How cool is that? (nerd alert!)
Lets dig a bit deeper. I removed the electromagnet armature.
So how does this thing work? How does it move the butterfly valve?
Basically there is a permanent magnet stuck on the end of the shaft of the butterfly valve.
Around this magnet is an electromagnet! The intensity of the electromagnet can be changed and the rotation position of the permanent magnet can be changed by attracting or repelling the poles of the two magnets. The engine ECU can tell the position of the magnet by the feed back from the potentiometers. It can tell from this if the magnetic flux is strong enough to hold the permanent magnet in position. The butterfly valve and shaft are connected to a return spring that tends to pull the valve back to idle. This is also a safety feature. If power is cut, the butterfly snaps back to idle.
That is a VERY simplistic over view.
The current in the coil is actually pulsed at a high frequency. If you own one of these little engines you now know why you get a "squeal" from the engine when you turn it on or off. It's the high frequency current passing through the coil of the electromagnet that is making the noise. The current will always be pulsing through the coil. Only the length of the pulse will vary. longer pulses will produce more power and deflect the magnet (and valve) further.
One of the disadvantages of the DC motor and gears type of throttle is the gears becoming damaged. Have a look on Youtube at the number of videos for throttle body repairs! AS you can see this throttle can not suffer that problem.
Well I hope you found something interesting in that? I know I discovered something new.
Oh! Did I find anything wrong with the throttle? well I used a dry cotton bud to clean the carbon tracks but I didn't find any large amounts of dross. A small amount on one track. The car still surges a small amount but I cant say for sure that cleaning the tracks made a big difference.
