Method and device for controlling an armature solenoid

A device for controlling an armature solenoid for generating a predefined force to be exerted by the armature solenoid for use in a vehicle operating unit with haptic feedback, which armature solenoid has a potentially changed air gap width in an idle state, the device comprising:

• a DC voltage source for exciting an exciter coil of an armature solenoid,
• at least one buffer capacitor connected in parallel to the DC voltage source and having a known capacitance,
• a first switch arranged between the DC voltage source and the buffer capacitor,
• the exciter coil of the armature solenoid and a second switch arranged in series therewith being connected in parallel to the buffer capacitor, and
• a control and evaluation unit for controlling the first switch, as well as the second switch and for evaluating a measurement voltage dropping over the exciter coil,
• wherein the control and evaluation unit, when the buffer capacitor is in a charged state, opening the first switch and closing the second switch and determining, from the measurement voltage, the frequency of the resonant circuit having the capacitance of the buffer capacitor and the inductance of the armature solenoid,
• the inductance of the armature solenoid being determinable by the control and evaluation unit based on the determined frequency,
• the air gap width of the armature solenoid being determinable by the control and evaluation unit based on the determined inductance of the armature solenoid, and
• based on a look-up table or a mathematical modelling of the electromagnetic behavior of the armature solenoid, the control and evaluation unit can apply to the second switch the PWM control signal with which, with consideration to the air gap width determined, the armature solenoid is operable to generate a predefined force to be applied by the armature solenoid.