After developing the MDSOS system to manage $2M worth of calibration equipment, I joined Delphi’s Valvetrain Group to work on the Active Fuel Management (AFM) system for General Motors (GM). At the time, the project was called CD, or Cylinder Deactivation, as it would “shut off” 4 cylinders of the big V-8 truck engine to save fuel. While I completed my work on this system in 2001, I’m proud to say that this system is still in use and now prolific on most GM vehicles.
The system performance is impressive. It gains as much as 13% in fuel economy with no compromise in engine power. It’s also a very low-cost solution, adding less than $100 to an engine build’s cost – which, compared to competitors, is about 5-10x lower. It also has a very smooth transition on and off, as it activates under low-load conditions – like idle or while on cruise control – and instantly returns full power whenever needed.
My job was to design and test the solenoid that activated the system when the engine computer (ECU) sent the electrical signal to the solenoids. Each solenoid held oil pressure from the engine on the input side and, when activated, passed it through to the specially-designed AFM lifters that compressed (rather than transferred the motion) under cam pressure to keep the cylinder’s valves closed. Below is an image of the incredible lifter design that my brilliant colleague came up with:
My test team had a series of tests to run on the system to ensure that it performed reliably and smoothly under a variety of conditions – high temperature, low oil pressure; low temperature, high oil pressure; and so on. We used a test bench similar to this one:
What was interesting was that the system was passing all but one test, and we were nearing the deadline to send the design to GM for production. We collected a massive amount of data from the tests, creating plots and performing analyses (e.g. Fourier transform) to try to find the culprit. As the deadline passed, and GM hounded us for our final product, the team continued tweaking the system and running tests. Finally, about a week past the deadline, we found it – one of the o-rings was undersized by 1/64″! Once corrected, all tests passed and the system went into production, and is still in use today.
