PeachParts Mercedes-Benz Forum - View Single Post - Another duty cycle question, specifically for Stevebfl ...sorry

stevebfl · #2 06-22-2004, 08:14 AM

In automotive electronics polarity is a reference point. Many things are represented in ways the scientific community might express differently.

Manifold vacuum is such a concept. Even tyhe largest vacuum still represents some pressure absolute.

In the case of duty cycle my point of reference comes from that activity involved. Unfortunately by the time of KE the value on pin three had changed from the duty-cycle of the frequency valve to the mathmatical duty cycle called integrator. It now is just a representation not a true happening.

So let me explain a true duty-cycle such as used in the case of K-jet w/Lambda. Same pin. I will describe what an event cycle looks like on the scope. The picture i describe will be 30% duty cycle such as my scope pattern you reference.

The cycle starts high at battery voltage. The signal is read on the controller side of the frequency valve. It is battery voltage because the valve is constantly powered with the engine running. The other pin of the valve goes to the controller and is currently open circuited such that battery voltage appears on both sides of the frequency valve coil and nothing is happening. now the controller grounds the pin we are viewing, the voltage at the pin drops to ~0v. The duty period on the valve has started. The valve is being controlled when the signal is low since all these coil actuators are controlled on the ground side in a modern automobile (the only exception I can think of in MB are D-jet injectors they are controlled from the power side).

So when we look at a pattern on a ground control circuit and we look for the duty period it is the period when the signal is down not up.

In KE there is no direct duty cycle. It is a manufacturered signal called integrator. It still varies its signal electronically for interpretation like a true duty cycle of an activation circuit. It in this case is just a mechanism for a crude style blink code. All that matters when using it is that one gauges his perspective to that of the communications involved. KOEO = 70% worldwide except California where KOEO = 85%. Correct your point of reference to this and you won't wind up looking at the wrong fault code for 30% fixed, nor will you set the closed loop adaptation rich or lean improperly. When you turn the mixture screw in closed loop clockwise the duty cycle should go down (smaller). Thirty percent duty cycle in closed loop means that a rich mixture has been set basically and the fuel system has moved 20% (from the middle at 50%) to correct for it. And in subtracting the fuel it has kept the mixture at lambda out the exhaust.