Method for monitoring the signal value of a vacuum sensor

1. A method for monitoring a signal value of a vacuum sensor of a vacuum system in a vehicle, wherein

a vacuum generator and a brake booster are provided in the vacuum system,

an upper error threshold (−p_vac_errorthreshold) is calculated as a function of the operating states of the vacuum generator and of the brake booster, wherein

an error is identified when the signal value of the vacuum sensor exceeds a current value of the error threshold, wherein

when the vacuum generator is active and the brake booster is not activated, a value of the error threshold (p_vac_errorthreshold) which increases with a predefinable gradient (p_grad_evac) is calculated on the basis of a starting value, and wherein the starting value is a high negative value at the system start, and otherwise is the value of the error threshold respectively calculated last.

2. The method as claimed in claim 1 , wherein the vacuum generator is an intake duct of an internal combustion engine and/or a vacuum pump.

3. The method as claimed in claim 1 , wherein a driver warning signal is output, by a warning lamp, when the value of the vacuum sensor signal exceeds the value of the calculated upper error threshold (−p_vac_errorthreshold).

4. The method as claimed in claim 1 , wherein the gradient (p_grad_evac) has a variable value as a function of a number, design and performance of the activated vacuum generator or generators.

5. The method as claimed in claim 1 , wherein when the vacuum generator is inactive and the brake booster is not activated, the value of the error threshold is kept constant.

6. The method as claimed in claim 1 , wherein the value of the error threshold is limited to a predefinable maximum value (p_vac_max), wherein this limiting value is selected on the basis of a maximum achievable vacuum of the vacuum generator which is used.

7. The method as claimed in claim 6 , wherein a maximum value of the error threshold (p_vac_max) has a variable value as a function of a number, design and performance of the activated vacuum generator or generators.

8. A method for monitoring a signal value of a vacuum sensor of a vacuum system in a vehicle, wherein

a vacuum generator and a brake booster are provided in the vacuum system,

an upper error threshold (−p_vac_errorthreshold) is calculated as a function of the operating states of the vacuum generator and of the brake booster, wherein

an error is identified when the signal value of the vacuum sensor exceeds a current value of the error threshold,

wherein when the vacuum generator is inactive and the brake booster is not activated, the value of the error threshold is reduced by a predefinable difference value (delta_p_vac).

9. The method as claimed in claim 8 , wherein the calculation of the difference value (delta_p_vac) is carried out as a function of the hydraulic brake pressure (p_tmc) taking into account a volume capacity characteristic of a brake system of the vehicle.

10. The method as claimed in claim 8 , wherein a maximum value of the hydraulic brake pressure (p_tmc) which is achieved during an activation of the brakes is used to calculate the difference value (delta_p_vac).

11. The method as claimed in claim 8 , wherein an accumulated value of the hydraulic brake pressure (p_tmc) in an activation of the brakes is used to calculate the difference value (delta_p_vac).

12. The method as claimed in claim 8 , wherein the difference value (delta_p_vac) is calculated as a function of a hydraulic brake pressure (p_tmc) which occurs owing to activation of the brakes.

13. The method as claimed in claim 12 , wherein the hydraulic brake pressure (p_tmc) is detected by a pressure sensor in an ESC (electronic stability control) system of the vehicle.

14. The method as claimed in claim 12 , wherein a travel distance of a diaphragm in the vacuum brake booster is used to calculate the difference value (delta_p_vac).

15. The method as claimed in claim 14 , wherein a maximum value of the travel distance of the diaphragm in the brake booster which is achieved during an activation of the brakes is used to calculate the difference value (delta_p_vac).

16. The method as claimed in claim 14 , wherein an accumulated value of the travel distance of the diaphragm in the brake booster within an activation of the brakes, which is achieved during an activation of the brakes, is used to calculate the difference value (delta_p_vac).

17. The method as claimed in claim 14 , wherein the travel distance of the diaphragm in the vacuum brake booster is detected by means of a diaphragm travel sensor in the brake booster.

18. The method as claimed in claim 14 , wherein the travel distance of the diaphragm in the vacuum brake booster is detected by means of a deflection sensor (distance or angle) on a brake pedal of the vehicle.

19. The method as claimed in claim 14 , wherein the travel distance of the diaphragm in the vacuum brake booster is detected by means of a travel sensor in or on a master brake cylinder of the vehicle.