Method for detecting belt slip

1. A method for detecting belt slip of a belt drive driving a generator of an internal combustion engine, the belt drive including: i) a belt wrapped around a crankshaft pulley arranged on a crankshaft of the internal combustion engine, ii) a generator pulley arranged on a generator shaft of the generator, and, iii) a belt tensioner that can be adjusted in operation of the belt drive and adjusts a pre-tensioning force of the belt according to detected belt slip, the method comprising:

recording a rotational speed profile of the crankshaft during an angular window of the crankshaft, defined by an equation m·360°, and forming an average value of crankshaft rotational speed from said rotational speed profile of the crankshaft,

recording a rotation speed profile of the generator shaft, temporally independently of the recording of the rotational speed profile of the crankshaft, during an angular window of the generator shaft defined by an equation n·ü −1 ·360°, and forming an average value of generator shaft rotational speed from said rotational speed profile of the generator shaft,

whether a rotational speed relationship between the average value of the crankshaft rotational speed and the average value of the generator shaft rotational speed is within a nominal range,

adjusting the belt tensioner if the rotational speed relationship is outside the nominal range, and

wherein m and n are real numbers and ü is a transmission ratio between the crankshaft pulley and the generator pulley.

2. The method as claimed in claim 1 , wherein m and n are natural numbers.

3. The method as claimed in claim 2 , wherein m=n=2.

4. The method as claimed in claim 1 , wherein the internal combustion engine is controlled by an engine ECU, the generator is controlled by a generator ECU, and the belt tensioner is controlled by a belt tensioner ECU, and the engine ECU, the generator ECU and the belt tensioner ECU communicate with one another via a data bus system.

5. The method as claimed in claim 4 , wherein the average value of the crankshaft rotational speed is formed by the engine ECU, and the average value of the generator shaft rotational speed is formed by the generator ECU, and the belt tensioner ECU; i) forms the rotational speed relationship between the average value of the crankshaft rotational speed and the average value of the generator shaft rotational speed, ii) checks whether the rotational speed relationship is within the nominal range, and iii) controls the belt tensioner for a purpose of adjusting said tensioner if the rotational speed relationship is outside the nominal range.

6. The method as claimed in claim 1 , wherein the average value of at least one of the crankshaft rotational speed or the generator shaft rotational speed is an arithmetic mean, geometric mean, or root mean square value.

7. A method for detecting belt slip of a belt drive, the belt drive including:

a crankshaft pulley arranged on a crankshaft of an internal combustion engine,

a generator pulley arranged on a generator shaft,

a belt wrapped around the crankshaft pulley and the generator pulley, and

a belt tensioner arranged to adjust belt tension during operation of the belt drive according to detected belt slip, the method comprising:

recording a rotational speed profile of the crankshaft during a first angular window,

forming an average value of crankshaft rotational speed from the rotational speed profile of the crankshaft,

recording a rotational speed profile of the generator shaft during a second angular window,

forming an average value of generator shaft rotational speed from the rotational speed profile of the generator shaft,

checking whether a rotational speed relationship between the average value of the crankshaft rotational speed and the average value of the generator shaft rotational speed is within a nominal range, and

adjusting the belt tensioner if the rotational speed relationship is outside the nominal range.

8. The method as claimed in claim 7 , wherein the second angular window is equal to the first angular window in terms of time.

9. The method as claimed in claim 8 , wherein in the second angular window, a number of rotations of the generator shaft exceeds a number of rotations of the crankshaft within the first angular window by a factor of ü −1 , wherein ü is a transmission ratio between the crankshaft pulley and the generator pulley.

10. The method as claimed in claim 8 , wherein the first angular window is offset from second angular window in terms of time.

11. A belt tensioner for a belt drive system including a crankshaft and a generator, the belt tensioner configured to adjust belt tension during operation of the belt drive system according to detected belt slip determined by checking a rotational speed relationship between an average value of crankshaft rotational speed obtained from a first angular window to an average value of generator rotational speed obtained from a second angular window.

12. The belt tensioner of claim 11 , wherein if the rotational speed relationship is outside of a nominal range, the belt tensioner is adjusted to increase the belt tension.

13. The belt tensioner of claim 11 , wherein the belt tensioner includes an actuator that adjusts the belt tension during operation of the belt drive system.