Braking Mechanism for a Motor Vehicle, and Method for Controlling the Braking Mechanism when Different Force Components are Combined

Abstract

A method for performing a parking brake application process in a motor vehicle with a service brake and a parking brake includes combining a hydraulic force component and a mechanical force component to obtain a total clamping force for the parking brake application process. The two force components are combined in each parking brake application process.

Claims

1. A method for carrying out a parking brake process with a motor vehicle that includes a service brake and a parking brake, the method comprising: combining a hydraulic force component and a mechanical force component to achieve a total clamping force for the parking brake process, the superposition of the two force components carried out for every parking brake process.

2. The method as claimed in claim 1, wherein an electromechanical force component is generated by an automated parking brake and an electrohydraulic force component is generated by the hydraulic service brake, and wherein the generation and the superposition of the two force components is carried out for every parking brake process.

3. The method as claimed in claim 1, wherein the parking brake process includes at least one force build-up phase, and wherein the superposition of the force components is essentially carried out during the entire force build-up phase.

4. The method as claimed in claim 2, wherein on the activation of the parking brake process, the electrohydraulic force component is generated in a first step.

5. The method as claimed in claim 1, wherein a defined hydraulic pressure is generated during the parking brake process.

6. The method as claimed in claim 4, wherein the electromechanical force component is generated in a second step, the second step carried out after or simultaneously with the first step.

7. The method as claimed in claim 2, wherein on activation of the parking brake process, the hydraulic service brake is activated in a first step and the automated service brake is activated in a second step, the second step carried out after or simultaneously with the first step.

8. The method as claimed in claim 2, wherein an increase in the electromechanical force component is carried out until the total clamping force is reached.

9. The method as claimed in claim 8, wherein the actuation to achieve the electrohydraulic force component is removed after reaching the total clamping force.

10. The method as claimed in claim 8, wherein after reaching the total clamping force, the actuation to achieve the electromechanical clamping force as well as the actuation to achieve the electrohydraulic force component are removed essentially simultaneously.

11. A control unit for carrying out a parking brake process in a motor vehicle that includes a service brake and a parking brake, the control unit comprising: a device configured to carry out a method for carrying out the parking brake process, the method including: combining a hydraulic force component and a mechanical force component to achieve a total clamping force for the parking brake process, the superposition of the two force components carried out for every parking brake process.

12. An automated parking brake for a motor vehicle with a hydraulic service brake, the parking brake comprising: a device configured to carry out a method for carrying out a parking brake process, the method comprising: combining a hydraulic force component and a mechanical force component to achieve a total clamping force for the parking brake process, the superposition of the two force components carried out for every parking brake process.

Description

[0039] Further features and functionality of the invention are revealed by the description of exemplary embodiments using the accompanying figures.

[0040] FIG. 1 shows as prior art a schematic sectional view of a braking mechanism with an automatic parking brake of a “motor on caliper” design;

[0041] FIG. 2 shows a flowchart of the process according to the invention; and

[0042] FIG. 3 shows a schematic representation of the force profile during and after the clamping phase of a parking brake process according to the invention.

[0043] FIG. 1 shows a schematic sectional view of a braking mechanism 1 for a vehicle according to the prior art. The braking mechanism 1 comprises in this case an automated (automatic) parking brake that can exert a clamping force for holding the vehicle stationary by means of an actuator 2 (brake motor). For this purpose, the actuator 2 of the parking brake drives a spindle 3 supported in an axial direction, in particular a threaded spindle 3. On the end thereof facing towards the actuator 2, the spindle 3 is provided with a spindle nut 4 that rests against the brake piston 5 in the clamped state of the automated parking brake. In this way, the parking brake transfers a force to the brake linings 8, 8′ or the brake disk 7 electromechanically. In this case, the spindle nut rests against an inner end face of the brake piston 5 (also known as the rear of the brake piston base or the inner piston base). The spindle nut 4 is displaced axially during a rotary displacement of the actuator 2 and a resulting rotary displacement of the spindle 3. The spindle nut 4 and the brake piston 5 are supported in a brake caliper 6 that engages around a brake disk 7 in a pincer-like manner.

[0044] A respective brake lining 8, 8′ is disposed on each side of the brake disk 7. In the case of a clamping process of the braking mechanism 1 by means of the automated parking brake, the electric motor (actuator 2) rotates, whereupon the spindle nut 4 as well as the brake piston 5 are moved in the axial direction towards the brake disk 7 in order thereby to produce a predetermined clamping force between the brake linings 8, 8′ and the brake disk 7. Because of the spindle drive and the self-locking means connected thereto, a force produced with the parking brake by actuating the electric motor is also maintained when the actuation is ended.

[0045] The automated parking brake is for example designed as shown as a “motor on caliper” system and is combined with the service brake. This could also be considered as being integrated within the system of the service brake. Both the automated parking brake and also the service brake engage the same brake piston 5 as well as the same brake caliper 6 in this case, in order to build up a brake force on the brake disk 7. However, the service brake comprises a separate actuator 10. The service brake is designed as a hydraulic system in FIG. 1, wherein the actuator 10 can be represented by the ESP pump or a so-called iBooster. During service braking, a predetermined clamping force is built up hydraulically between the brake linings 8, 8′ and the brake disk 7. To build up a brake force by means of the hydraulic service brake, a medium 11, in particular an essentially incompressible brake fluid 11, is compressed in a fluid chamber bounded by the brake piston 5 and the brake caliper 6. The brake piston 5 is sealed against the surroundings by means of a piston sealing ring 12.

[0046] The actuation of the brake actuators 2 and 10 is carried out by means of a final stage, i.e. by means of a control unit 9, which can be for example a control unit of a driving dynamics system, such as an ESP (electronic stability program) or another control unit.

[0047] In the case of the actuation of the automated parking brake, first the free travel or the air gap must be overcome before a brake force can be built up. For example, the distance that the spindle nut 4 must overcome by the rotation of the spindle 3 in order to come into contact with the brake piston 5 is referred to as free travel. The distance between the brake linings 8, 8′ and the brake disk 7 in disk brake systems of motor vehicles is referred to as an air gap. As a rule, said process lasts a relatively long time in relation to the overall actuation, in particular for the automated parking brake. At the end of such a preparation phase, the brake linings 8, 8′ are in contact with the brake disk 7 and the force build-up starts upon further actuation. When applying the brake linings 8, 8′, it is therefore important within the scope of this invention not to impose a brake force, or to set the brake force that is imposed during application as low as possible in order not to produce any undesired premature braking effects. FIG. 1 shows the state with the free travel and air gap already overcome. Here the brake linings 8, 8′ are in contact with the brake disk 7 and all brakes, i.e. the parking brake and also the service brake, can immediately build up a brake force on the corresponding wheel in the event of subsequent actuation. The descriptions of the free travel or the air gap also apply analogously to the service brake, wherein however overcoming the free travel represents less time than with the parking brake because of the highly dynamic pressure build-up.

[0048] FIG. 2 shows a flow chart of a possible embodiment of the process according to the invention. S1 refers to the starting point of the method. The process is for example started if a parking brake request, for example a parking situation, is detected. After detecting the parking situation, a pressure supply by means of the hydraulic service brake is activated in step S2. With the pressure supply, a defined hydraulic pressure is produced and is controlled in the brake system. The magnitude of said pressure is for example 40 bar. Because of the provided hydraulic pressure, the vehicle can be held at first hydraulically, even if only with a smaller force. The supply of pressure can be carried out by means of electrified components of the hydraulic service brake system, for example by means of an electrified pressure booster, of a so-called iBooster. In the case of the use of such components, the pressure supply can be carried out relatively rapidly, because no liquid has to be sucked in (such as for example with a classic ESP pump). The pressure supply is carried out by means of an iBooster alone by displacement of the fluid volume. In a next step S3, the electromechanical actuator is actuated. This must first overcome the existing air gap in a known manner. Once the spindle nut contacts the base of the spindle, however, a steep increase in force is carried out, because the brake system is already preloaded. From this point in time, the electrohydraulic force and the electromechanical force work together. By the combination of the two force components, a total force results that produces a clamping force in the brake system. The force produced, or the total clamping force, is checked in a further step S4 as to whether it corresponds to a defined, required force. If this is not the case (N), the force component produced by means of the electromechanical actuator is increased. If it is detected that the required force is reached (Y), the electromechanical actuator is turned off in a next step S5. Likewise, turning off the electrohydraulic actuator is carried out in a step S6. Hereby the two steps S5 and S6 are also carried out at the same time, which means switching the actuators off can be carried out at the same time. The final step 7 indicates the end of the method.

[0049] FIG. 3 shows a schematic representation of the force profile F during and after a clamping process according to the invention. Whereas FIG. 2 provides a procedural representation of the process, FIG. 3 illustrates the same method by means of a time perspective t. The method starts at the point in time t1. The build-up of a defined hydraulic pressure value is carried out first. For this purpose, an actuator of the service brake system is actuated. This is for example the iBooster. In the phase P1, the free travel and the air gap of the service brake are overcome. In a phase P2, the generation of the electrohydraulic force component F.sub.hydr is carried out. For this purpose, a defined pressure value is produced. Once the pressure value has been produced, this now only has to be maintained during the further course of the process. In the present example, the actuator of the parking brake system is also actuated simultaneously with the actuation of the actuator of the service brake system. Overcoming the free travel of the parking brake is carried out in the phase P3. After overcoming the free travel of the parking brake, i.e. if the spindle nut is in contact with brake piston, a steep increase in force is carried out with a further deflection of the spindle nut, because the brake system is already preloaded by means of the hydraulic service brake. In said phase P4, the actual superposition of the parking brake and the service brake is carried out. The electromechanical force component F.sub.mech is produced by the actuation of the parking brake. This is superimposed on the existing electrohydraulic force component F.sub.hydr and increases the achieved total clamping force F.sub.ges. The actuation of the actuator of the parking brake is carried out until the required total clamping force F.sub.ges is reached. An increase of the fluid volume between the brake caliper and the brake piston results from the actuation of the parking brake by the displacement of the brake piston. Because of said increase in the fluid volume, the hydraulic pressure may have to be adjusted by means of the service brake. This can be carried out in a targeted manner by means of an iBooster system that is equipped with a suitable force sensing system and means for pressure monitoring. On reaching the required total clamping force F.sub.ges, removal of the actuation is carried out, which means that turning off the electromechanical and electrohydraulic actuators is carried out at the point in time t2. This prevents a further build-up of force. Removal of the electromechanical force component F.sub.mech as well as the electrohydraulic force component F.sub.hydr is carried out by turning off the actuators.

[0050] The total clamping force F.sub.ges that is built up is, however, also maintained after the end of the clamping process, because the exemplary parking brake as described is provided with a self-locking means, as is represented in phase P5. Only active actuation of the parking brake in the reverse direction causes releasing of the parking brake, which is not shown in FIG. 3 however.