Method for determining an aggregate state of aqueous operating liquid in an operating liquid container for a motor vehicle, and operating liquid container for carrying out the method

A method for determining an aggregate state of an aqueous operating liquid in an operating liquid container for a motor vehicle, wherein the operating liquid container has at least one capacitor which is fastened to a container wall of the operating liquid container and has a first electrode and a second electrode opposite said first electrode, the method comprising:

• applying (J) at least two different alternating voltages to the capacitor, wherein a first frequency of a first alternating voltage corresponds to a lower frequency limit (fmin) and a second frequency of a second alternating voltage corresponds to an upper frequency limit (fmax);
• determining and storing (K) a first capacitance (C1) of the capacitor for the first frequency and a second capacitance (C2) of the capacitor for the second frequency;
• determining (L) a relative deviation of the second capacitance (C2) from the first capacitance (C1);
• and
• determining (M) that the operating liquid located in the operating liquid container is in a solid aggregate state when the relative deviation of the second capacitance (C2) from the first capacitance (C1) is greater than a first capacitance deviation (ΔC1).

An operating liquid container comprising:

• an interior delimited by a ceiling wall, a bottom wall, and a sidewall which connects the bottom wall to the ceiling wall;
• at least one capacitor fastened to a container wall, the at least one capacitor including a first electrode and a second electrode;
• an electronic evaluator which is electrically connected to the first electrode and to the second electrode,
• wherein the evaluator is configured to perform a method comprising:
• applying (A) at least a first alternating voltage to the capacitor, wherein a first frequency of the first alternating voltage corresponds to a lower frequency limit (fmin);
• determining and storing (B) a first impedance of the capacitor for the first frequency;
• determining (C) a first phase angle (φ1) from the first impedance;
• and
• determining (D) that the operating liquid located in the operating liquid container is in a solid aggregate state when the first phase angle (φ1) is greater than a first critical angle (δ1).