Finally Supercharged Success!

By Clinton HulleyVW Polo Classic Project Car
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Now that all the hardware was done in the car I had to work out a strategy. How am I going to control the clutch of the supercharger and also the electronic bypass valve? I have seen other setups with this charger that the guys just fit a switch on the dash. They can switch the charger on and off by will. I was not too fond of this. I like the equipment in the car must be automated. Everything must come on at the right time and be off when not in use.

Coming up with a strategy!

After some thinking and doing some looking at driving patterns I came up with a strategy. This will give me power on demand and also will give me a good fuel economy. If I could have the bypass valve fully open when the car is started. The engine will consume air through the bypass valve. This makes it a naturally aspirated system, there are no restrictions sucking air through as supercharger that is not active. Once the pedal position reaches 50% the charger clutch must engage. The bypass throttle must close to approximately 50%. The engine will be in a state were the supercharger will blow the boost out the bypass valve. It will also supply the engine with air it needs.


The airflow into the engine will be equal to the air supplied by the charger. The excess will just be blown back into the intake of the supercharger, basically recycling the air. The boost gauge reading will still be on a vacuum or maybe 0 bar. Once the pedal is taken passed the 50% mark the electronic bypass valve would close further linear to the input from the pedal. So basically once the pedal reached 100% the bypass valve will be closed 100%. All the pressure will enter the engine. When you close the throttle for gear shifts the charger will disengage. The bypass valve will open up fully to dump the pressure. This basically acts as a dump valve unloading the charger and taking the load off the charger belt.

How to control the electronic bypass valve!

Now that I had a strategy it was great, and I was really excited about it. The problem that I had was I did not have a fancy programmable controller. I also did not have money to buy a fancy ECU that could control the electronic bypass valve. To make something mechanical to switch the charger on and off did not sound like too much of an issue. The problem was the electronic throttle body. I did some research on the electronic throttle bodies. Found out that they need to be controlled via a pulse width modulated signal. That sounds like a mouth full. It basically just means a fixed frequency signal. If you vary the amplitude (voltage) of the signal the butterfly will move. The throttle motor will increase the force against the spring of the throttle opening the throttle.

Solution?

I had a chat with one of the guys that worked with me. He had some electronic experience and especially with electronic throttles as he had do build a simple throttle controller for engines at work a few weeks earlier. He built me a controller. It had input from the Throttle Position Sensor(TPS) on the throttle bodies. This would tell the little black box where the throttle is currently at. The little back box had two settings on it. One was at what throttle angle the charger should engage. The other setting was, till what position the throttle should close when charger engaged.


Once the controller was completed I installed it into the Polo. Now being very excited about how this was going to work. I switched on the ignition of the car. I heard the humming sound of the throttle. The bypass throttle was standing fully open as it should. Suddenly I smelled something burning and the throttle just shut closed. I quickly shut all power off again.

Having more issues…

I traced the smell of burning to the little black box. The component that was driving the throttle overheated as it was driving the throttle to its stop limit. It took the controller back to my friend and he replaced the burnt part. I had to keep this part cool. I added an old PC CPU Heat sink and fan to the new driver. The heat sink and fan were a bit of an overkill for the application. But I had it and the chip was running nice and cool now.

Once I got home I refitted the little back box back to the car. The ignition was put on but the engine was not running yet. I played with the throttle pedal a bit. I could hear the supercharger clutch kick in and see the bypass throttle closing and opening. Now that the function was there I just had to set the 2 settings. I got it to more or less what I thought it should be.


Now the time had come to start the car with the new supercharger setup all set up and connected. I started the car and it sounded standard. I increased the throttle to 50% and the charger kicked in, the car actually sounded very healthy. It was a weird but nice sound coming from the supercharger. No screaming noises. Then I gave the throttle a sudden blip, and the boost went up to 0.4 bar boost. I was really relieved that the control system was doing its job.

Now I had a working Supercharged 2.0 Polo…


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