Method for calibrating a slope sensor

• US 8,386,123 B2
• Filed: 03/12/2010
• Issued: 02/26/2013
• Est. Priority Date: 06/03/2009
• Status: Active Grant

• Current Assignee: ZF Friedrichshafen AG (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Original Assignee: ZF Friedrichshafen AG (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Wurthner, Maik, Staudinger, Joachim, Sauter, Ingo
• Primary Examiner(s): Nguyen, Kim T
• Application Number:
  US13/321,335
• Publication Number:
  US 20120065835A1
• Time in Patent Office: 1,082 Days
• Field of Search: 701/29.1, 701/29.7, 701/30.3, 701/30.5, 701/30.8, 701/30.9, 701/31.1, 701/33.1, 701/33.3, 701/33.4, 701/33.7, 701/33.9
• US Class Current: 701/33.1
• CPC Class Codes: B60W 2520/06 Direction of travel
• CPC Class Codes: B60W 2520/10 Longitudinal speed
• CPC Class Codes: B60W 2520/105 Longitudinal acceleration
• CPC Class Codes: B60W 2520/30 Wheel torque
• CPC Class Codes: B60W 2530/10 Weight
• CPC Class Codes: B60W 2530/16 Driving resistance
• CPC Class Codes: B60W 2540/12 Brake pedal position
• CPC Class Codes: B60W 2552/15 Road slope, i.e. the inclination of a road segment in the longitudinal direction
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices
• CPC Class Codes: G01C 9/06 Electric or photoelectric indication or reading means
• CPC Class Codes: G01D 18/008 with calibration coefficients stored in memory

Abstract

A method for automatically determining a current offset value for the zero-point correction of a vehicle inclination sensor including the steps of while driving in a first driving direction, the current driving resistance is determined repeatedly, without regard to the sensor and stored temporarily, and a current raw signal value of the sensor is noted. Upon a change in the driving direction, the last-noted raw signal value is stored temporarily and while driving in the second driving direction. The current driving resistance is determined repeatedly, without regard to the sensor and stored temporarily. Then, if the difference between the two stored driving resistances agree with a tolerance threshold, the noted raw signal value is stored as the offset value for the zero-point correction of the inclination sensor.

Claims

1. A method of calibrating an inclination sensor, which is arranged in a motor vehicle (1) with a semi-automatic transmission (3) for determining road inclination (α

_Fb) and inclination-related resistance (F_Steig) and being connected for signal transmission purposes with a transmission control unit (4) of the transmission (3) such that, under certain operating conditions of the motor vehicle, a current offset value (x_Offset) for the zero-point correction of the inclination sensor (5) is determined automatically, the method comprising the steps of;

once operation of the motor vehicle (1) begins, repeatedly determining and temporarily storing, while the motor vehicle is driving in a first driving direction, a current first driving resistance (F_Fw1) without regard to the inclination sensor (5) and noting a current raw signal value (x_Ns0) of the inclination sensor (5);

recognizing a change of driving direction from the first driving direction to a second driving direction;

temporarily storing the raw signal value (x_Ns0) of the inclination sensor (5) that was last determined;

repeatedly determining and temporarily storing, while the motor vehicle is driving in an opposite, second driving direction, a current second driving resistance (F_Fw2) without regard to the inclination sensor;

comparing the first driving resistance (F_Fw1) determined for driving in the first driving direction with the second driving resistance (F_Fw2) determined for driving in the second driving direction; and

if the first and the second driving resistances (F_Fw1, F_Fw2) are in agreement with a specified tolerance threshold (Δ

F_Ts), permanently storing the stored raw signal value (x_Ns0) of the inclination sensor as the offset value (x_Offset) for the zero-point correction of the inclination sensor (x_Offset=x_Ns0).

2. The method according to claim 1, further comprising the step of determining each of the first and the second driving resistances (F_Fw1, F_Fw2) from either a traction or a thrust force (F_Rad) of a drive engine acting on drive wheels and from an acceleration resistance (F_B) calculated from a mass (m_Fzg) of the motor vehicle and driving acceleration (a_F) (F_B=m_Fzg*a_F) in accordance with an equation (F_Fw=F_Rad−

F_B).

3. The method according to claim 1, further comprising the step of subjecting each of the first and the second driving resistances (F_Fw1, F_Fw2) to a plausibility check, and only storing and using plausible first and second driving resistances (F_Fw1, F_Fw2) for determining the offset value (x_Offset) of the inclination sensor (5).

4. The method according to claim 3, further comprising the step of, if the first and the second driving resistances (F_Fw1, F_Fw2) are within an expected range defined by appropriate limit values (F_Fw_min, F_Fw_max), recognizing that the first and the second driving resistances (F_Fw1, F_Fw2) determined are plausible.

5. The method according to claim 3, further comprising the step of checking the plausibility of the first and the second driving resistances (F_Fw1, F_Fw2) by determining a respective gradient of the first and the second driving resistances (d/dt F_Fw1, d/dt F_Fw2), and checking whether the respective driving resistance gradient (d/dt F_Fw1, d/dt F_Fw2) lies within an appropriate tolerance threshold during an appropriate observation period.

6. The method according to claim 3, further comprising the step of checking the plausibility by checking whether a difference between the respective currently determined driving resistance value (F_Fw1, F_Fw2) and the respective driving resistance value (F_Fw1, F_Fw2), last determined in the same driving direction, lies within an appropriate tolerance threshold close to zero.

7. The method according to claim 1, further comprising the step of comparing a last value of the first driving resistance (F_Fw1) determined in the first driving direction with a first value of the second driving resistance (F_Fw2) determined in the second driving direction.

8. The method according to claim 7, further comprising the step of smoothing with a suitable filter function the first and the second driving resistance values (F_Fw1, F_Fw2) determined successively in each driving direction.

9. The method according to claim 1, further comprising the step of determining the first and the second driving resistances (F_Fw1, F_Fw2) by averaging a plurality of several successively determined first and second driving resistance values (F_Fw1, F_Fw2).

10. The method according to claim 1, further comprising the step of determining the permanently stored offset value (x_Offset) of the inclination sensor as an average of a plurality of offset values (x_Offset) determined after successive driving direction changes.

11. The method according to claim 1, further comprising the step of determining at least one of a steering angle of the steering system of the vehicle and a transverse acceleration of the vehicle, and interrupting the determination of the first and the second driving resistances (F_Fw1, F_Fw2) and of a current offset value (x_Offset) of the inclination sensor (5) for a duration (Δ

t_U) of recognized while driving round a curve.

12. The method according to claim 11, further comprising the step of continuing the determination of the first and the second driving resistance (F_Fw1, F_Fw2) and the current offset value (x_Offset) of the inclination sensor (5) after the interruption, if the duration (Δ

t_U) of the interruption is less than a duration limit (Δ

t_Gr) (Δ

t_U<

Δ

t_Gr), and discontinuing if the duration (Δ

t_U) of the interruption either reaches or exceeds the duration limit (Δ

t_Gr) (Δ

t_U≧

Δ

t_Gr).

13. The method according to claim 1, further comprising the step of detecting at least one of unevenness of a road, a transverse inclination of the motor vehicle and an engagement of an off-road gear in the transmission, and interrupting the determination of the first and the second driving resistances (F_Fw1, F_Fw2) and of the current offset value (x_Offset) of the inclination sensor (5) for a duration (Δ

t_U) of recognized off-road driving.

14. The method according to claim 1, further comprising the step of detecting a shift status of the transmission (3), and interrupting the determination of the first and the second driving resistance (F_Fw1, F_Fw2) and the current offset value (x_Offset) of the inclination sensor (5) for a duration (Δ

t_U) of a recognized gearshift.

15. The method according to claim 1, further comprising the step of detecting a degree to which a starting clutch, that connects a drive engine to the transmission (3), is open, and interrupting the determination of the first and the second driving resistance (F_Fw1, F_Fw2) and of the current offset value (x_Offset) of the inclination sensor (5) for a duration (Δ

t_U) of an at least partially disengaged starting clutch.

16. The method according to claim 1, further comprising the step of detecting an actuation status of service brakes, and interrupting the determination of the first and the second driving resistance (F_Fw1, F_Fw2) and the current offset value (x_Offset) of the inclination sensor (5) for a duration (Δ

t_U) of recognized actuation of the service brakes.

17. The method according to claim 1, further comprising the step of determining a current driving speed (v_F), and interrupting the determination of the first and the second driving resistance (F_Fw1, F_Fw2) and the current offset value (x_Offset) of the inclination sensor (5) for a duration (Δ

t_U) of a driving speed (v_F) which is above an appropriate speed limit (v_Gr) (v_F>

v_Gr).

18. The method according to claim 1, further comprising the step of noting a gear (G_F) currently engaged, and interrupting the determination of the driving the first and the second resistance (F_Fw1, F_Fw2) and the current offset value (x_Offset) of the inclination sensor (5) for a duration (Δ

t_U) during which a gear (G_F) that is higher than a limit gear (G_Gr) remains engaged (G_F>

G_Gr).

19. The method according to claim 1, further comprising the step of noting an operating status of the motor vehicle, and interrupting the determination of the first and the second driving resistance (F_Fw1, F_Fw2) and the current offset value (x_Offset) of the inclination sensor (5) for a duration (Δ

t_U) of a recognized pause in operation.

20. The method according to claim 1, further comprising the step of determining either a mass of the vehicle (m_Fzg) or a laden mass of the vehicle (m_Ldg) and discontinuing the determination of the first and the second driving resistance (F_Fw1, F_Fw2) and the current offset value (x_Offset) of the inclination sensor (5) if a numerical value of a change (Δ

m) of either the mass of the vehicle (m_Fzg) or the laden mass of the vehicle (m_Ldg) is greater than a mass difference limit (Δ

m_Gr>

0) (|Δ

m|>

(Δ

m_Gr).