Inside the box: VDO Cruise Control Actuator - PeachParts Mercedes-Benz Forum

JamesDean · #1 03-31-2012, 03:32 AM

Hey everyone, forum member shertex was kind enough to send me a cruise control actuator. He mentioned that the unit had taken out one of his cruise control amplifiers. So I figured I'd test it out and crack it open see what all the fuss what about.

The unit tested very similar to several of my actuator. Testing current flow through pin 4 when pin 4/5 are connected to power yielded 190mA, flipping the polarity yielded 200mA.

Applying power to pin 7, ground to pin 6 to activate the solenoid yielded about 290-300mA

The transistors that supply power to these above pins are BD437/BD438 BJT transistors. They are rated at 4 amps.

The transistors are protected via a set of zener diodes and rectifier. I've not yet mapped out the full protection bit so I'm not 100% on it yet. In the event of a high current draw or inductive kickback (voltage spike) I believe they are supposed to prevent the transistors from being blown. Its possible that due to the technology available at the time VDO might not have used the most optimal components for the task. I'll look more into this avenue later.

The actuator itself is fairly simple. A motor drives a stacked gear that spins freely until the solenoid is engaged. When the solenoid engages, it tilts the stacked gear into the large gear. This large gear then contacts the partial gear which is directly connected to the actuators external arm.

On the bottom of this partial gear are two dots, these dots contact a strip on the PCB which create make a potentiometer. The potentiometer tells the cruise amplifier the position of the actuator level.

Here are some pictures:

Here's a brief video of the motor spinning and solenoid engaging (click to play):