"Smart" Stepper Motors
Until the E38 was introduced, the stepper motors used in IHKR and IHKA climate control systems did not contain electronic components, and only 3 part numbers were needed to service all the motor assemblies. As described earlier in this Handout, the motors consisted of copper wire coils wrapped around iron cores (pole pieces), and permanent magnet rotors, all attached to a high-reduction mechanical gearbox. The system electronic control components were located inside the climate control module assembly.
Starting with the E38 climate control system, some of the control module electronics were moved into the stepper motors, making the E38 motors (except the fresh air flaps motor) substantially different from the "conventional" stepper motors we've already discussed.
The circuits feeding these new "smart" stepper motors also changed - for one thing, there are only three circuits:
- power
- ground
- signal
Also, all 9 smart stepper motors used on the E38 system share the same set of power, ground, and signal circuits. (Left and right branches are connected inside the control module.) The fresh air flaps "conventional" stepper motor has its own separate circuits.
These stepper motors have the same type gear box, permanent magnet rotor, and 4 field coils as a "conventional" stepper motor. Plus, it still receives operating signals from the system control module.
An E38/E39/E46 stepper motor constantly receives power and ground on two of the terminals, and operating instructions on the third.
The operating instructions are digital signals which "tell" the stepper motor whether to open or close a flap. The microprocessor inside the stepper motor receives the instructions and converts them into pulses to operate the permanent magnet rotor.
Notice that this 3-wire arrangement (referred to as the M-Bus ) allows the control module to operate the motor using only 1 signal circuit instead of the 4 control circuits used previously.
And, since all 9 smart stepper motors are connected to the same signal circuit, a total of 35 separate circuits between the control module and the motors can be eliminated.
But how can the system operate with just one signal circuit for all 9 motors?
- Each of the 9 stepper motors is different (and has its own part number).
- The control module identifies which motor it want to operate before it issues the commands.
The part number is clearly marked on every stepper motor, and every stepper motor must be installed in the correct location on the climate control housing.
The operating instructions issued to the smart stepper motors by the control module are much more sophisticated than with conventional stepper motors. The sequence of events appears below:
- The control module determines that a flap position must change
- It issues a "wake-up call" to alert the stepper motors that a command is coming
- It "names" the motor that is to respond to the command
- It issues the command signal, e.g. "move 15 steps clockwise"
- All the stepper motors "hear" the command
- Only the stepper motor that "hears its name" follows the command
- The "named" stepper motor then informs the control module that it has carried out the command