Method for hydraulically boosting an electric parking brake of a vehicle
A method for hydraulically boosting a vehicle electric parking brake having a hydraulic service brake and an electric parking brake. Application forces electically generated by the parking brake function is superimposed on the boosting brake force generated by a hydraulic boosting brake pressure provided by the service brake to the brake actuator. When the parking brake is actuated to generate a predetermined application force, the force generated by the brake actuator is detected as the actual value, if an actual value of the measured value is smaller than a first target value a boosting brake pressure value is applied to the brake actuator, and by means of the parking brake function an adjustment function for the tension of the brake actuator to which the hydraulic boosting brake pressure is applied is carried out to achieve the predetermined application force.
1. A method for hydraulic boosting of an electric parking brake of a vehicle comprising providing at least one brake actuator ( 2 c , 2 d ), which for electric and hydraulic operation of the at least one brake actuator ( 2 c , 2 d ) includes a hydraulic service brake function and an electric parking brake function, wherein an application force (F) electrically generated with the parking brake function is superimposed with a boosting brake force generated by subjecting the brake actuator ( 2 c , 2 d ) to a hydraulic boosting brake pressure (P u ) provided by the service brake function,
operating of the parking brake to generate a specified application force, detecting the application force generated by the brake actuator ( 2 c , 2 d ) as the actual value (I actual ) by means of a measurement variable (I) representing the actual value,
for a measurement of the actual value (I actual ) that is smaller than a first target value (I 1,target ) representing a first target force value (F 1,target ) of the application force, the brake actuator ( 2 c , 2 d ) is subjected to a hydraulic boosting brake pressure (P u ) that corresponds to a specified target boosting brake pressure value, (P u,target ) and
performing by means of the parking brake function a further application function for further application of the brake actuator ( 2 c , 2 d ) that is subjected to the hydraulic boosting brake pressure (P u ) to achieve the specified application force.
2. The method as claimed in claim 1 , further comprising the steps of to generate the hydraulic boosting brake pressure (P u ) a means of generating pressure ( 3 ), is controlled by means of the service brake function.
3. The method as claimed in claim 2 , further comprising in that the target boosting brake pressure value (P u,target ) is set to a value at which the resulting boosting brake force corresponds to the first target force value (F 1,target ),
following the generation of the hydraulic boosting brake pressure (P u ) corresponding to the target force value (F 1,target ) the means of pressure generation ( 3 ) is switched off, and
the boosting brake pressure (P u ) applied to the brake actuator ( 2 c , 2 d ) is hydraulically confined within the brake actuator ( 2 c , 2 d ).
4. The method as claimed in claim 2 , further comprising in that the target boosting brake pressure value (P u,target ) corresponds to a specified inlet pressure target value (P u, inlet ), wherein the resulting boosting brake force is smaller than the first target force value (F 1,target ), and
following the generation of the hydraulic boosting brake pressure (P u ) the means of generating pressure ( 3 ) is not switched off and the brake actuator ( 2 c , 2 d ) is further subjected to the boosting brake pressure (P u ).
5. The method as claimed in claim 3 , further comprising in that for further application of the parking brake the brake actuator ( 2 c , 2 d ) is controlled by the boosting brake pressure (P u ) by means of the parking brake function until the actual value (I actual ) of the measurement variable (I) of the application force corresponds to a target value (I 2,target ), which is smaller than the first target value (I 1,target ) corresponding to the first target force value (F 1,target ).
6. The method as claimed in claim 4 , further comprising in that for further application of the parking brake by means of the parking brake function a displacement control is activated, wherein a brake piston of the brake actuator ( 2 c , 2 d ) that is subjected to the boosting brake pressure (P u ) is controlled to a target position corresponding to the specified application force using a stored displacement-force characteristic.
7. The method as claimed in claim 6 , further comprising in that an error message is generated if the brake piston target position is not reached by a determined actual position.
8. The method as claimed in claim 4 , further comprising in that
the further application function ( 2 c , 2 d ) includes further application of the brake actuator by means of the parking brake function and thereby the actual value (I actual ) of the measurement variable (I) representing the application force generated by the brake actuator ( 2 c , 2 d ) is detected, and
the further application is terminated if the actual value (I actual ) of the measurement variable (I) reaches a second target value (I 2,target ) corresponding to a second target force value (F 2,target ) wherein the second target force value (F 2,target ) is reduced relative to the first target force value (F 1,target ) by a force value corresponding to the boosting brake pressure (P u ).
9. The method as claimed in claim 8 , further comprising in that an error message is generated if the actual value (I actual ) of the measurement variable (I) does not reach the second target value (I 2,target ).
10. The method as claimed in claim 8 , further comprising in that prior to performing the further application, the brake actuator ( 2 c , 2 d ) that is subjected to the boosting brake pressure (P u ) is controlled by a small displacement amount in the direction of releasing the parking brake by means of a displacement control.
11. The method as claimed in claim 1 further comprising in that the hydraulic boosting brake pressure (P u ) is reduced following performance of the further application function.
12. The method as claimed in claim 1 , further comprising in that the brake actuator ( 2 c , 2 d ) for performing the parking brake function is driven by an electric motor ( 2 d ) and the motor current of the electric motor ( 2 d ) is detected as the measurement variable (I) representing the application force.