EP2225133B1

(Representative patent family member)

The invention relates to a hydraulic brake system comprising a master brake cylinder (4) the at least one working chamber of which is connected to the wheel brakes of the vehicle via at least one hydraulic line, the brake piston (12a-12d) of at least one wheel brake (RBi) being adjustable by a negative pressure in the hydraulic lines to produce a brake clearance (BLS).

1. Hydraulic braking system, with a master brake cylinder (4) having
a reservoir (6), wherein the master brake cylinder (4) has at least one working space and a master cylinder piston (3) and the working space is connected by at least one hydraulic line (BL), in which a regulating valve (18) is arranged, to at least one wheel brake (11a-11d) of a vehicle, wherein by adjusting the master cylinder piston (3) a negative pressure can be generated in the master brake cylinder and the hydraulic line (BL), wherein the pressure in the hydraulic line (BL) or in the master brake cylinder (4) can be determined by means of a pressure sensor (15, 112) and the position of the master cylinder piston (3) can be determined by means of a path sensor (14), and wherein a controller (ECU) controls the master cylinder piston by taking into account the determined pressure and position of the master cylinder piston (3), characterised in that for the purpose of a defined clearance adjustment at the brake piston (12a-12d) or the brake pads, the controller (ECU) evaluates the pressure of the pressure sensor (15) and the adjustment path of the master cylinder piston (3) determined by means of the path sensor (14), and controls the master cylinder piston (3) and the regulating valve (18) in such a way that due to the negative pressure resulting therefrom a defined adjustment of the brake piston or brake pads is made.
2. Hydraulic braking system according to claim 1, characterised in that the braking system is an electrohydraulic braking system in which
the piston(s) (3, 3a) of the master brake cylinder (4) can be adjusted by means of an electric drive.
3. Hydraulic braking system according to claim 1, characterised in that the braking system is a pneumatic-hydraulic braking system in which
the master brake cylinder (4) can be pneumatically adjusted.
4. Hydraulic braking system according to any one of claims 1 to 3, characterised in that a controller adjusts or sets the clearance (BLS) as a function of the travel situation and/or the road conditions, and in particular in the case of rain and/or a wet road does not set any clearance in the wheel brakes.
5. Hydraulic braking system according to any one of the preceding claims, characterised in that switching valves (16, 16a; 118) are arranged in the connecting lines between reservoirs (6, 106) and working space or working spaces of the master brake cylinder (4, 105).
6. Hydraulic braking system according to any one of the preceding claims, characterised in that the negative pressure can be generated by means of a unit (14, 38, 49, 40, 41), in particular a driven piston-cylinder system or a pump system, wherein
the unit (14, 38, 49, 40, 41) is connected to the feed line to at least one, in particular all wheel brake(s) or at least to a feed line of the master brake cylinder (4), wherein the switching valves (16, 16a) are arranged in the connecting lines between reservoir (6) and unit (14, 38, 49, 40, 41) and a controlled regulating valve (18, 18a, 18b, 18c) is associated with each wheel brake, and this is arranged in the hydraulic line which connects the working space of the brake piston cylinder system of the wheel brake to the master brake cylinder (4) or the unit (14, 38, 49, 40, 41), wherein, when the regulating valve (18, 18a, 18b, 18c) is closed, the brake piston (12a, 12b, 12c, 12d) is held in position by the enclosed amount of hydraulic and the clearance (BLS) is therefore maintained in the wheel brake.
7. Hydraulic braking system according to any one of the preceding claims, characterised in that a device (30; 32, 35, 36, 46) exerts a force on the brake calliper (11), in particular the floating calliper, to adjust the brake calliper (11) in such a way that at the end of the braking process a clearance (BLS2) is adjusted at the brake pad (52) acting on the side of the brake disc (59) remote from the brake piston.
8. Hydraulic braking system according to any one of the preceding claims, characterised in that a supply device (F) can be connected by a feed line (ZL) to a brake line (BL) by means of a valve (108).
9. Hydraulic braking system according to claim 8, characterised in that a shut-off valve (118) is arranged in the connecting line (L) which connects a working space (A1, A2) of the brake booster to the reservoir (106).
10. Hydraulic braking system according to claim 8 or 9, characterised in that the supply device (F) is a piston-cylinder system with a spring-loaded piston (109), a spring (110) and a working space (120), wherein
the working space (120) serves as a reservoir and the spring (110) force-actuates the piston (109) in the direction of reduction of the working space (120).
11. Method for operating a hydraulic braking system according to any one of the preceding claims, characterised in that some of the volume in the master brake cylinder (105) is displaced into one or more supply chamber(s) (120) by means of the master brake cylinder (105) when the supply valve (108) is open, wherein
thereafter, when the supply valve (108) is closed and the regulating valve is open (107), the brake pistons in the wheel brakes (RB) are raised by withdrawal of the pistons (103, 104) of the master brake cylinder (105) from the brake discs to achieve brake pad clearance.
12. Method according to claim 11, characterised in that the pad clearance in the wheel brakes (RB) is adjusted successively or simultaneously or in pairs.
13. Method according to either of claims 11 or 12, characterised in that a defined stroke of the piston (103, 104) is carried out with the aid of the pressure, determined by means of a sensor (112), in the brake line (BL) or the master brake cylinder (105).
14. Method according to any one of claims 11 to 13, characterised in that the piston (109) of the supply chamber (120) is in an intermediate position, so this chamber can receive additional volume for the negative pressure control or adjustment of the pad clearance.
15. Method according to any one of claims 11 to 14, characterised in that to cancel the brake clearance, the valves (108) are closed and the valve(s) (107) are opened, after which hydraulic medium is conveyed into the wheel brake by means of the piston (103, 104) and by way of the brake line (122).
16. Method for operating a hydraulic braking system according to any one of claims 1 to 10, characterised in that to generate a clearance in a wheel brake the connection between master brake cylinder (4) and reservoir (6, 106) is closed by means of a switching valve (16, 16a) and by adjusting the piston (3, 3a) of the master brake cylinder (4) and/or by means of the unit (14, 38, 49, 40, 41) a negative pressure is generated in the hydraulic line (BL) to the wheel brake or a certain amount of the hydraulic medium is conveyed from the working space of the brake piston-cylinder system of the wheel brake (RB).
17. Method according to claim 16, characterised in that after achieving the desired clearance (BLS) the regulating valve (18, 18a, 18b, 18c) associated with the wheel brake is closed to maintain the clearance (BLS).
18. Method according to claim 16 or 17, characterised in that a defined clearance (BLS) is successively adjusted in the individual wheel brakes by means of the master brake cylinder or the unit.
19. Method according to any one of claims 16 to 18, characterised in that after adjusting the clearance the piston (3, 3a) of the master brake cylinder (4) is moved into the normal position and all valves are switched into the OPEN position.
20. Method according to any one of claims 16 to 19, characterised in that the clearance (BLS) in the individual wheel brakes is cancelled in that by generating a negative pressure in the hydraulic lines the brake pistons are adjusted in such a way that a slight braking force is adjusted by the abutment of the brake pad on the brake disc.
21. Method according to any one of claims 16 to 20, characterised in that the clearance (BLS) in the individual wheel brakes is cancelled as soon as the braking system detects with reference to the travel situation that a brake application is imminent.
22. Method according to claim 21, characterised in that the braking system detects the imminent initiation of a brake application with the aid of the movement of the accelerator pedal, in particular its speed, the speed of the foot actuating the brake, the distance of the foot actuating the brake pedal relative to the brake pedal and/or the signal of a distance warning system.
23. Method according to claim 21 or 22, characterised in that at least one distance sensor (7) determines the distance of the foot from the brake pedal in at least one, and preferably in three direction(s).
24. Method according to any one of claims 16 to 23, characterised in that the controller determines the movement of the brake piston from the course over time of the pressure signal.

[0001] The invention relates to a hydraulically acting brake system with a master brake cylinder, of which at least one working chamber is connected to the wheel brakes of the vehicle via at least one hydraulic line, according to the preamble of claim 1.

[0002] A brake system of this type is known from WO-2006/111393-A1.

[0003] After braking, in particular in braking systems with disc brakes, a residual braking effect occurs because the restoring forces at the brake piston are insufficient to lift the brake pads far enough off the brake disc. One solution to this problem was the development of a roll-back seal, which moves the brake piston and the brake pad away from the brake disc after the braking process has ended. However, the roll-back capacity of the sealing ring is limited to the brake piston and is not sufficient to fully compensate for contamination, aging and elastic deformation in the brake caliper and friction linings. Remedies with an air gap between the brake pad and the brake disc/brake piston are described in DE 44 18 701 and DE 196 01 434. The solutions proposed in the aforementioned documents have not yet been implemented because the additional effort required is disproportionate to the effect and, in addition, the air gap that is set during subsequent braking results in a loss of pedal travel, which has the disadvantage of increasing the braking distances during emergency braking.

[0004] According to the current state of brake development, mid-sized vehicles have an additional consumption of approx. 0.251 = 6g CO 2 /km due to the above-mentioned residual braking effect on the test bench when determining NEDC consumption. This value applies to a new vehicle without the effects of aging and is considerable in view of future CO2 targets.

[0005] The object of the present invention is therefore to further develop a hydraulically acting brake system in such a way that the residual braking effect is reliably avoided.

[0006] This problem is solved by the invention in that a clearance can be generated or adjusted by means of a vacuum in the hydraulic supply line of a wheel brake. Further advantageous designs of the braking system according to claim 1 result from the features of the subclaims.

[0007] The idea underlying the invention is to actively reset the brake piston of a wheel brake by means of a vacuum, wherein a defined adjustment of the piston and with it the brake lining or brake linings can be adjusted to set a defined air gap, in particular by means of the magnitude of the vacuum and its duration.

[0008] In a first embodiment of the invention, the vacuum can be applied by means of the main brake cylinder. If the drive of the main brake cylinder does not work fast enough, an additional unit for vacuum generation can be provided in accordance with a second embodiment of the invention, which is connected to the hydraulic supply line of the respective wheel brake.

[0009] For both embodiments described above, it is advantageous to provide at least one valve that is arranged between the reservoir for the hydraulic medium and the main brake cylinder and/or the unit for generating the vacuum and the main brake cylinder. This at least one valve is used to prevent hydraulic medium from flowing from the reservoir into the supply line or the main brake cylinder or the unit when the vacuum is generated.

[0010] The invention provides a simple solution for hydraulic brake systems that allows a defined air gap and is also diagnosable and adaptive. The solution according to the invention can advantageously be used in both electro-pneumatic and electro-hydraulic brake systems.

[0011] In the brake system according to the invention, the air gap can advantageously be controlled adaptively depending on the driving state of the vehicle.

[0012] In order to set the required air gap, according to the first embodiment, after the braking has ended, a vacuum is generated behind the brake piston of a wheel brake by a certain control of the tandem master brake cylinder (THZ), whereby the brake piston is moved accordingly and the air gap is generated. To adjust the wheel brake’s brake piston in a defined way, the adjustment path and optionally the pressure of the tandem master cylinder can be evaluated, since when the tandem master cylinder is adjusted relatively slowly, the brake piston path follows the tandem master cylinder piston and the air gap can be determined via the tandem master cylinder path from the ratio of the piston areas of the brake and tandem master cylinder pistons. This ensures that, with an appropriate air gap of approx. 0.1 mm, only a small residual braking effect remains, primarily due to the friction in the guide of the brake pad in the floating caliper and the floating caliper bearing.

[0013] In any case, the main component of the brake piston is no longer present. In some brake caliper designs, the brake pad is coupled to the brake piston via a spring, so that only a small amount of friction remains in the floating caliper guide.

[0014] In order to ensure that a clearance also occurs in the brake pad, which is arranged on the side of the brake disc facing away from the brake piston, in brake systems with a floating caliper, a small brake caliper clearance is generated in a further embodiment of the invention, so that no residual braking effect occurs. In a first alternative, to this end the floating caliper is moved back by means of a passive roll-back element, which acts similarly to a roll-back seal known from the prior art, to create a clearance for the brake pad attached to the floating caliper after the braking process has ended. The roll-back element can advantageously act between the brake holder and the floating caliper guide bolt. In a second alternative design, the floating caliper is actively moved by an actuator to adjust the air gap. The actuator can advantageously be an electromagnetic drive, such as a magnet or servomotor.

[0015] It is of course possible to adjust the clearance simultaneously, successively or in groups for all wheel brakes. If the vacuum can be generated quickly enough, it is advantageous to adjust or set the clearance individually for each wheel brake, i.e. one after the other. This is particularly possible with an electro-hydraulic braking system.

[0016] The air gap should not and cannot remain constant during vehicle operation. For example, when it rains, the brake pads must make light contact or even come into firm contact before braking begins when the accelerator pedal is released. Also, after driving for a long time without braking on a dry road, the brake pads must be applied briefly to clean the windshield, which can also be done with a defined small braking force in the braking system according to the invention. For this reason, the clearance must be adaptively adjustable. It is also advantageous if no clearance is set when the vehicle is stationary, e.g. when parking.

[0017] If a clearance has been set, this can mean an additional loss path or a longer response time when braking, which, depending on the actuation speed of the brake, would result in an increase in the braking distance. In the event of an emergency stop to prevent a rear-end collision, this can cost crucial meters and lead to an accident. To avoid an increase in the braking distance, the invention provides for the brake shoes to be applied to the brake disc before the brake is applied, i.e. to eliminate the clearance. The braking system must thus recognize when and whether a brake application will occur. For this purpose, it is possible to control the brake shoes with a small braking force when the accelerator pedal is quickly released, or alternatively to control this via a distance sensor from the foot to the brake pedal. The signal or data from a distance measuring system, which determines the distance to the vehicle or obstacle in front, can also be used to determine an imminent braking process. Likewise, the vehicle speed can be taken into account in the evaluation.

[0018] In the braking system, in particular an electro-hydraulic system, the volume supplied by the master brake cylinder, in particular THZ, for applying the brake pads and for eliminating the air gap, fed in by the master brake cylinder after the brake pads have been applied, and the volume is equalized via the snifting holes of the master brake cylinder. This process takes only <50 ms and is completed before the foot of the person driving the vehicle touches the brake pedal.

[0019] The advantage is that all functions of the braking system according to the invention are fully diagnosable. Thus, for example, the clearance can be tested by appropriate main brake cylinder control when the brake piston is applied to the brake pad, in particular when the vehicle is stationary.

[0020] The invention makes it possible to dispense with a brake pad wear sensor. To do this, when the vehicle is stationary, preferably in the parking position, the brake pistons are moved back to the stop and then moved forward again to make contact with the brake disc, using the above-mentioned control. This adjustment is proportional to the wear on the brake pads. An additional advantage is that the wear can be extrapolated at appropriate diagnostic intervals and recorded in the vehicle diagnostic system. This eliminates the need for additional work during vehicle inspection, e.g. by removing the wheels to inspect the brake pad wear.

[0021] The proposed solution advantageously allows a defined air gap with only a very small residual braking effect, if any, and thus a significant reduction in CO2. In addition, the braking system according to the invention is fully diagnosable and replaces and improves the brake pad wear indicator as an essential safety function. The solution is also very cost-effective.

[0022] The second embodiment described above is suitable for a rapid market launch because it is an add-on solution to existing ABS/ESP concepts with a vacuum booster, in which an electromotive suction-pressure unit with switchover valves can be attached to the existing tandem master brake cylinder with vacuum brake booster and, in addition, enables the clearance control with the ABS inlet valve using the same distributor of the individual wheel brakes. When the electromotive brake booster is launched on the market in accordance with DE 10 2005 018 649, this additional effort is no longer required, except for the switchover valves.

[0023] DE1020070628392 describes replenishment chambers that introduce additional volume into the brake circuits as required in borderline cases such as fading and high pressure and volume requirements.

[0024] The additional supply chamber can also be used for another function, to adjust the brake lining play. In the aforementioned solutions, the control of the piston and valve play is very complex if the piston cannot be moved back from the initial position, since this means additional design work for the electromotive brake booster. In contrast, it is simple with the replenishment chamber, in that a corresponding volume is briefly moved back by the HZ piston to generate the vacuum in preferably one wheel cylinder. The remaining wheel cylinders are operated in succession. In this way, a clearance can be generated in the wheel cylinders when measuring the vacuum via the pressure transducer and with corresponding control of the pressure rod piston. This brake lifting play can be eliminated again at any time during or even before braking. Thus, on the basis of an external signal, the brake pads can be applied to the brake disc again before braking begins. This so-called pre-filling makes it possible to shorten the braking distance, especially if the pre-filling pressure already reaches a pressure level of 5 bar.

[0025] In the following, the two possible embodiments of the invention and control concepts are explained in more detail with the aid of drawings.

[0026] Showing:

Fig. 1: a first embodiment of the invention; Fig. 1a: a second alternative embodiment of the invention with an additional piston-cylinder unit; Fig. 2: control process for setting a clearance; Fig. 3: control process for eliminating the play before initiating the braking process; Fig. 4: control process for determining the brake pad wear; Fig. 5: control process for minimum and maximum brake pad wear; Fig. 6: first alternative with roll-back element for floating caliper; Fig. 7: second alternative with actuator for adjusting the floating caliper to set a clearance for the brake pad, which is arranged on the side of the brake disc facing away from the brake piston; Fig. 8: third alternative embodiment, with post-delivery devices.

[0027] Fig. 1 shows a brake system with control valves 18, 18a, 18b, 18c as essentially described in DE 10 2005 018 649, and reference is made to the disclosure content of the latter. The braking system includes, among other things, the electromotive brake booster (BKV) 2, 8 with tandem master brake cylinder (THZ) 4 and its pressure rod piston (DK) 3 and floating piston (SK) 3a, the brake pedal 1, the pedal travel sensor 5, the control valves 18 to 18 c, the switchover valves 16, 16a and 17, the pressure generator 15, the wheel brakes RBa to RBd and the reservoir (ECU) 19. As described in DE 10 2005 018 649, the braking system combines brake force boosting with pressure modulation ABS and ESP.

[0028] The present invention extends the braking system of DE 10 2005 018 649 to include the active adjustment of a clearance in the individual wheel brakes.

[0029] If, after braking, the vehicle is accelerated via the (not shown) accelerator pedal or the cruise control system or driven at a constant speed, the simplest embodiment of the invention or its control system closes the changeover valves 16 and 16a so that the THZ 4 is disconnected from the reservoir 6. Then the DK piston 3 of THZ 4 is moved back from its normal position by means of the electromotive drive, causing a vacuum to form in the working chamber and the hydraulic lines. If, for example, the brake piston 12c of the wheel brake RBc is to be moved by the vacuum, the control valve 18b must be opened and the control valves 18, 18a, 18c, which are assigned to the other wheel brakes, must be closed. As long as the DC piston 3 continues to move, the brake piston 12c of the wheel brake RBc is retracted when valve 18b is open. From the area ratio of brake piston 12c and double-circuit piston 3, the necessary adjustment movement of the double-circuit piston 3 results for an air gap to be set of, for example, 0.1 mm, if the movement occurs slowly in relation to the pressure modulation for ABS and no dynamic influencing factors are acting.

[0030] The movement of the DC piston 3 can also be monitored using the pressure curve and the sensor 15. An accuracy of ± 40% is sufficient to control the air gap. Because the contact force of the brake piston is eliminated, the resulting force on the brake pad or its contact force on the brake holder, which is not shown, is also reduced. In many brake caliper designs, the brake pad is connected to the brake piston or the floating caliper by means of detent springs, so that a resetting of the brake piston automatically eliminates the brake pad from the residual braking effect. The bearing forces in the non-drawn guide pins of the floating caliper are also reduced, so that ultimately only a very small residual braking effect remains. Figures 2 to 5 explain the timing of the release clearance control in more detail.

[0031] In the illustrated position of the THZ DK piston 3 and SK piston 4, the so-called “sniffing holes” for sucking up the brake fluid from the reservoir 6 are open. This position is referred to as the normal position. Moving the DK piston 3 back from this normal position against the normal direction of actuation requires some design effort. Alternatively, it is possible to apply low pressure to two brake pistons of a brake circuit by moving the DK piston 3 forward, and then to move only the first brake piston back using negative pressure, thereby setting a larger air gap than necessary. Meanwhile, the other second brake piston remains in its position due to the closed control valve assigned to it. Subsequently, the first brake piston is moved to a smaller air gap by a corresponding DK piston movement and then the second brake piston is again controlled to the corresponding air gap by the DK piston return movement. During pressurization, i.e. valve movement, from the normal position with low pressure, the control valves 18b and 18c of the brake circuit supplied by the DK piston 3 are open, for example. The changeover valves 16 and 16a are also open. During the return movement of the double-acting piston 3, the changeover valve 16 and a control valve, e.g. 18c, are closed, whereby the brake piston 12c is moved to double the air gap. The double-acting piston 3 then remains in the “normal position” with the changeover valve 16 open and the control valve 18b also open. In this case, the brake piston 12d moves to its initial position without a clearance. In the next step, with valves 16 and 18b open, the brake piston 12c is moved to the normal clearance by the corresponding DK piston movement. The control valve 18c is closed during this process. Then the changeover valve 16 and the control valve 18b are closed and the return movement of the DK piston is activated with the control valve 18c open. This sets the clearance for the second brake piston 12d. The piston then moves to the normal position with the control valve 18c closed and the switchover valve 16 open. In the normal position, all valves are open.

[0032] Another control option for avoiding the return movement from the normal position is to move the DK piston 3 out of the normal position with low pressure applied to both brake pistons 12c and 12d with the valves open, similar to the one mentioned above. Then, with changeover valve 16 closed and control valve 18b open, the DK piston 3 is moved back until the clearance is reached in piston 12c. Then, control valve 18b is closed and control valve 18c is opened, and the DK piston 3 is moved further until the clearance is also reached at brake piston 12d. After that, control valve 18c is also closed and the DK piston 3 returns to the normal position with changeover valve 16 open. After reaching the normal position, all valves that have not yet opened are reopened. It has been found that this control is the easiest to implement.

[0033] There are various control options for controlling the clearance of the brake pistons. Another option is to arrange a changeover valve 17 in the primary circuit in the connection from THZ 4 to the wheel brakes. To control the clearance, a small pressure is generated in the corresponding brake circuit in both wheel brakes. When control valve 18 is open and control valves 18a, 18b and 18c are closed, the return movement of DK piston 3 and SK piston 3a causes a vacuum in the brake piston 12a of the RBa brake. This can be determined via pressure transducer 15. A corresponding piston movement of the DK piston 3, which can be determined by means of the sensor 14, results in the desired air gap in the wheel brake RBa, similar to the examples given above. The stroke sensor 14 can be replaced by the usual and not drawn angle of rotation sensor of the EC motor of the BKV 8. With considerable additional effort, the air gap at the brake piston can be measured and controlled directly by a sensor 37 arranged on the wheel brake.

[0034] When the brake is applied, creating a defined air gap on all four wheel brakes means an additional volume, i.e. an additional pedal travel, which in turn impairs the temporal response characteristic and means an increased braking distance in the event of an emergency stop. This volume compensation can be carried out by means of a fast brake booster BKV 2 with THZ 4 before the brake is applied. This process is described in Fig. 4. The start for this volume compensation control can be carried out when the accelerator pedal is quickly returned to its rest position. However, this solution does not work for vehicles with a cruise control system in which the foot does not have to be on the accelerator pedal. In this case, a simple distance sensor 7 can be provided on the brake pedal 1, which measures the approach distance a when the foot approaches the brake pedal. If the distance falls below a certain level, the volume compensation can then be initiated, for example.

[0035] The air gap should not be effective when it is raining. Rain or a wet road surface can be signaled to the braking system, e.g. by the control signal of the windshield wiper, which is supplied to the ECU 19 via the bus. At the same time, it is possible to use the signal of a rain sensor, for example. In addition to the aforementioned criteria, the brake disc can be cleaned by briefly braking with increased pressure of < 5 bar. If the vehicle is driven for a long period on a dry road without the brakes being applied, the disc can be cleaned by applying the brake pads for a short time.

[0036] The air gap can also be eliminated in the parking position or at low speeds. The same can apply at low temperatures, which are supplied to the ECU 19 by means of a temperature sensor in the engine compartment or the existing outside temperature sensors.

[0037] As an alternative to the preferred electromotive brake booster, a vacuum or hydraulic brake booster can also be used, which requires additional switchover valves 9 and the pressure supply line 10. However, the current state of the art is that the dynamics of these boosters are insufficient to control the clearance and volume compensation quickly enough. An add-on solution for these brake boosters is proposed in Fig. 1a. This consists of the already described switching valves 16 and 16a and a suction-pressure control 38, consisting of piston 49, spindle 41 with electric motor drive 40, as well as a distance sensor 14. Instead of this distance sensor 14, when using an electric motor, its integrated angle of rotation sensor can also be used. As an alternative to the electric motor, a linear solenoid can also be used, since the power required to achieve the necessary vacuum is not very high. If the clearance is to be adjusted, e.g. in the wheel brake 11a, all solenoid valves not shown, with electric motor 44 and pump 45 of the ABS/ESP HCU (Hydr. Computing Unit) 42 are closed. The switchover valves 16 and 16a are also closed. Piston 39 moves back a certain distance, as already described for the tandem master brake cylinder, with solenoid valve 43 being open. Here, too, the process can be monitored via pressure transducer 14. After the air gap has been set, the E-valve 43 closes. The piston 39 moves back further and sets the required air gap in the remaining wheel brakes 11b to 11d one after the other. After that, the piston 39 stops, the switchover valves and all E-valves are opened. If the clearance is now to be switched off or the braking process is initiated, the piston 39 is quickly adjusted to the initial position. In this case, the switchover valves 16 and 16a are closed. This means that the volume is equalized before braking, and there is no disadvantage in the response characteristics of the brake. The pressure level is in the range < 2 bar, so the adjustment power and the design effort as well as the weight are low. The pressure transducer 15 is present in every ESP system and may need to be extended in the measuring range for the vacuum.

[0038] Fig. 2 shows the timing process for setting a clearance according to the simple control. The diagram shows the paths of the pistons and the pressure behind the brake piston. S k is the path-time progression of the respective brake piston, S DK is the path-time progression of the double-acting piston 3, p is the pressure behind the brake piston and BLS is the size of the air gap. V16 and V18 indicate the positions of valves 16 and 18. The M curve indicates the direction of movement of the DK piston 3. At time t 0, the switchover valve 16/16a is activated and at t 1 the motor is activated to reset the DK piston 3 from the normal position, in which the snifting holes are open. Both switch points t 0 and t 1 can also be combined. When the DC piston 3 moves back, the vacuum p increases, which, after exceeding a certain value, causes the brake piston SK to move. During the movement of the DC piston 3 and the brake piston SK, the pressure remains almost constant and well below the limit value of -1 bar, indicating that the piston is moving. Full or maximum vacuum would indicate that the piston is not moving or is stuck. At time t 2, the setpoint of BLS is reached via the described correlation of piston area and corresponding path of S K and S DK. After the end of the S K movement, the vacuum decreases. There is no further movement until t 3. After that, the DK piston 3 is moved to the normal position, which is reached at time t 4. During the DK piston movement, the control valve 18 remains closed and the switchover valves 16 and 16a are opened to equalize the pressure.

[0039] At t 4, the control valve 18 is opened so that atmospheric pressure prevails on both sides of the brake piston. After t 4, the air gap can be eliminated by increasing the pressure. If the double-acting piston 3 moves further out of the normal position, the air gap for reapplying can be determined from the pressure curve and the S DK -Weg, so that the air gap is diagnosed. It is crucial that the duration of the vacuum and its level are low in order to avoid outgassing of trapped air in the brake fluid. Therefore, at time t 4, when there is no pressure increase, the DK piston 3 must be in the normal position and the switchover valves must be open so that full pressure equalization acts on the brake pistons and they remain in the clearance position. The friction forces of the roll-back seal are relatively high. With this defined clearance control, other seals can also be used, which benefits the braking behavior at low braking decelerations.

[0040] Fig. 3 describes the process of the volume compensation control. At time t 5, the accelerator pedal is quickly released, which at time t 6 leads to the activation of the motor and movement of the DC piston 3, and the brake pads are applied again after the corresponding S k travel. At time t 7 this has occurred, which leads to a pole reversal of the motor and to the opening of the switchover valves 16 and 16a. In this return movement, the control valves 18-18c are closed and the corresponding missing volume is sucked into the control chambers via the sleeves of the control piston due to the vacuum. At time t 8, the pressure is equalized again. At time t 9, the brake can then be applied normally, without a loss of volume or pedal travel to build up the pressure. Again, it is crucial that this process is completed very quickly, e.g. < 50 ms.

[0041] Fig. 4 shows the control for determining the brake pad wear. The piston travel S K for S K1 (min) and S K2 (max) wear is shown on the ordinate. The staircase-shaped curve represents the vacuum intervals for the return movement of the piston to the initial position or to the stop. This control process for the brake piston stop is described in more detail in Fig. 5. After the brake piston has reached the stop, the movement towards the brake disc contact point occurs again. With minimal wear, this occurs after ΔS K1 or ΔS 1 of the control piston. If there is a lot of wear, a single HZ full stroke is not enough, so that the entire piston movement, which is proportional to the wear, can be determined in several stages Δ S2+ Δ S2′. This test can be carried out at longer intervals, e.g. every 10,000 km. The advantage is an extrapolation of the wear values, so that the time-consuming inspection during servicing can be omitted.

[0042] Fig. 5 shows the control process shortly before the brake piston reaches the stop. The first part after t 1 corresponds to that already described in Fig. 3. At time t 10, there is an increase in the vacuum as soon as the piston reaches the stop, which is used as the starting point for measuring the brake lining wear. At t 11, the motor is switched off and the reversing valve 16, 16a is closed. At t 12, the DK piston moves back to its initial position.

[0043]Fig. 6 shows a section of the floating caliper bearing with brake holder 33, brake caliper 11a, and guide bolt 31. Here, it is suggested that a roll-back element 30 be used for a clearance of the caliper, which, after the end of the pressurization, in addition to the clearance at the brake piston, also creates a clearance on the caliper side. This means that the residual braking torque is almost zero, since the brake piston couples the brake lining with a spreading spring, thus creating a gap to the brake disc.

[0044] The solution according to Fig. 7 also has the task of creating a clearance on the caliper side. Here, a magnet armature with a bearing journal 32 is provided in the guide bolt 31 with an expanding element 34, the friction of which is greater than the friction of the two guide journals of the caliper. When braking begins, the magnet is energized by a coil and pulls the armature with brake caliper 11. On the opposite side, the reaction force of the brake piston presses the brake caliper 11 against the brake disc via the brake pad 52, thus generating the braking effect. When braking is over, the magnet 46 is switched off and the return bolt 35 with pressure spring 36 produces a defined air gap BLS 2 and thus the return of the caliper. Because the magnet is activated by a distance sensor to the brake pedal when braking begins, as shown in Fig. 1, this air gap BLS 2 does not result in an increase in pedal travel.

[0045] The above describes many realizable solutions that enable adaptive control of the clearance with the aim of keeping the braking effect very low, resulting in a high reduction in CO2 and fuel consumption. According to the inventive concept, not only on the brake piston side but also on the caliper side, a clearance can be specifically set with the solutions according to the invention, so that the residual braking effect is almost zero.

[0046] Figure 8 shows the basic structure of an electric motor BKV as described in DE 102005018649.19, DE 102006059840.7 and DE 102005003648, with this application fully adopting the content of the disclosure. When the BKV is intact, the pedal is decoupled from the main brake cylinder Hz. The pedal force is absorbed by the non-represented path simulator, which generates a familiar pedal feel. The pedal stroke sensor 113 detects the pedal stroke, which can be assigned to a desired braking pressure via a characteristic curve. Thus, when the brake pedal 101 is pressed, the brake booster 102 is activated, which acts on the pressure rod piston 103 of the main brake cylinder 105. The floating piston 104 is moved by the volume displacement and the pressure. Both pistons 103 and 104 generate pressure in the respective brake circuits. The corresponding brake fluid is provided in the reservoir. For details of the design of the known master brake cylinder, please refer to DE 102005018649.19, DE 102006059840.7 and DE 102005003648. It is known that the pedal travel and the piston travel can be different in travel simulator systems. The piston leads the pedal when braking at high friction values. When the pistons 103, 104 reach the end of the stroke, the follow-up supply process takes place. First, the control valves 107 are closed and the pressure achieved is locked in the wheel brakes. After that, the make-up valves 108 are opened. At the same time, the push rod piston 103 is retracted by the electromotive BKV, causing the pressure in the main brake cylinder to drop towards zero (0). The stored brake fluid is delivered from the already filled replenishment chambers 120 of the replenishment devices F into the working chambers A1, A2 of the master brake cylinder by means of the spring 110 and the piston 109. The booster chamber 120 is preferably pressurized, e.g. 5 bar, so that the brake fluid is actively pumped into the master brake cylinder. The booster valves 108 are then closed and the control valves 107 are opened. The brake fluid is now displaced into the brake circuits 122 by a corresponding motor control, causing the pressure in the respective brake circuits 122 to rise further, depending on the position of the valves 107. This means that a further pressure increase is possible without the pistons 103 and 104 reaching the end position (left position). Alternatively, only one brake circuit 122 can be replenished. By appropriately designing the piston area and piston stroke, the missing volume in the Hz can be stored in the replenishment chamber 120 to cover all extreme cases. The preload of the spring 110 causes the filling pressure to be 5 to 10 bar, for example, with a corresponding spring design. Together with a make-up valve 108 with a large opening cross-section, this enables a fast make-up into the working chambers A 1, A 2, in e.g. 50 ms, whereby a significant delay in the pressure increase is avoided.

[0047] The make-up valves 108 should be optimized in terms of flow and switching time. The valves 108, which are preferably designed to be closed when de-energized, can have a large valve seat cross-section. By using a conventional coil, the valve 108 can thus only open at medium pressures, such as 50 bar. This is not a disadvantage for the make-up, as the switching of the make-up valves takes place at approx. 10 bar. Thus, no expensive pressure-compensated valves are required for the make-up. Due to time constraints, it may also make sense that during the make-up, not the entire volume in the make-up chamber 120 or the working chamber is refilled in one go. If, for example, piston 103, 104 approaches the end position at 140 bar, volume can initially be supplied for a pressure build-up to 170 bar. If the pressure is to continue rising, the remaining volume for 200 bar maximum pressure, for example, can be supplied in a new post-supply step at 170 bar. Since the first post-delivery step is sufficient for the majority of cases, the dead time in the pressure build-up during the post-delivery can thus be reduced for these braking operations.

[0048] The make-up chamber 120 can be filled and diagnosed after filling at the end of the line or during servicing, each time the vehicle is started or also during acceleration phases. To do this, the maximum pressure in the make-up chamber, e.g. 10 bar, is preferably introduced in a pressure-controlled manner via the motor drive. If the make-up valve 108 is now opened, the pressure rod piston 103 must not move. If it does move, this indicates a leak in the piston seal or a leaky make-up valve 108. The differential volume can be determined via the piston displacement sK. The extent of the leakage can be determined from the differential volume and the diagnostic intervals. To do this, the maximum follow-up pressure is set in the main brake cylinder. In addition, it can now be diagnosed whether the follow-up valve 108 or the piston 109 is stuck. As soon as the follow-up block 20 is refilled, the piston 103 is retracted. The course of the pressure-volume characteristic curve can now be used to determine whether the post-delivery piston 109 is moving and whether the post-delivery valve 108 has switched.

[0049] Alternatively, the filling level of the post-delivery chamber 20 can be checked by closing the control valves 107, setting the maximum filling pressure of the post-delivery chamber 20, e.g. 10 bar, the piston position is adjusted as a control variable, the post-delivery valves 108 are opened and the pressure sensor 112 is used to monitor whether the pressure in the Hz drops.

[0050] By adjusting the post-delivery volume, it is thus possible to use the same basic system for several vehicle classes. In conventional solutions consisting of a BKV and vacuum, the dimensions have to be customized for each vehicle class, which means additional costs for logistics in production and repair.

[0051] Furthermore, the smaller piston diameter results in considerably lower pedal forces when the brake booster fails.

[0052] Since the state of the brake system’s ventilation can be regularly checked via the pressure-volume characteristic curve in the path simulator system, the total volume of the brake actuation, consisting of the main brake cylinder volume and the replenishment block displacement volume, can be reduced overall compared to conventional systems. The additional safety volume for poorly vented volumes no longer needs to be provided, as is the case with conventional systems.

[0053] Another option for monitoring the filling state of the replenishment chamber 20 is the use of an optional sensor 24. This sensor detects the position of the piston 9. The sensor 24 can be designed as a position-resolving sensor or as a switch that detects a position of the piston 9. This sensor can be used for diagnostics or for defined piston control so that sufficient volume can be provided for the function of vacuum generation.

[0054] To adjust a lining clearance between the brake disc and the brake lining, a vacuum is briefly generated in the THZ 103,104,105. This causes the brake pistons in the wheel brakes to be actively retracted, creating a gap between the brake pad and the brake disc. As a result, the residual friction between the brake pads and the brake disc can be eliminated. The feed chamber 120 can be used to generate the vacuum.

[0055] The replenishment chambers 120 are not completely filled during normal operation. They contain sufficient volume to provide brake fluid for high pressure requirements but can still take up additional volume.

[0056] At the beginning of the pad clearance adjustment, the piston 103 is advanced by the motor drive 102. The piston 104 moves analogously. With the replenishment valves 108 open, the brake fluid is thus displaced into the only partially filled replenishment chambers 120. The replenishment valves 108 are then closed. Now the solenoid valves 118 are closed and one of the control valves 107 is opened. The piston 103, which is still in the extended position, is retracted a little by the motorized spindle drive towards the initial position. This creates a vacuum which is transmitted via the brake lines 122 to the wheel brakes RB whose control valve 107 is open. Now the remaining three wheel brakes are retracted by sequentially opening the respective control valves. The travel of the piston 103 is proportional to the travel of the brake piston via the area ratio with the brake piston. In this phase, the vacuum is evaluated so that the piston movement is only evaluated under a pressure level or over time. By pressure over time, we mean that if the vacuum is constant over the piston friction, this is equivalent to a movement of the brake piston. Finally, the solenoid valves 118 are reopened. This removes the vacuum in the THZ 105. The task of the solenoid valves 118 is to prevent that during the vacuum phase in the THZ no brake fluid from the reservoir via the THZ seals into the working chambers A 1 and A 2 of the THZ. It is also possible to retract all the brake pistons of the wheel brakes RB simultaneously by opening all the control valves 107 in the vacuum phase.

[0057] As mentioned at the beginning, the replenishment chambers 120 are not completely filled during normal operation, so that these volumes of brake fluid can be used to adjust the pad clearance. The filling state can be monitored using the sensor 124. Alternatively, it is also possible to first fill the replenishment chambers completely and, with piston 103 retracted, control valves 107 closed and solenoid valves 118 open, briefly open the replenishment valves 108 to allow a defined volume to escape from the replenishment chamber. Another possibility is to empty the post-delivery chambers completely and to introduce a defined volume via the piston stroke 103. In this case, it is advantageous if the two post-delivery chambers 120 are filled separately from each other, so that one chamber is always full and the volume is available for high pressure requirements.

[0058] The set pad clearance results in an increased distance between the brake pad and the brake disc. This would interfere with braking, as it causes an additional volume to be absorbed and thus a loss path of piston 103. It is therefore important to apply the brake pads to the brake disc again before braking. This is referred to as pre-filling.

[0059] The brake fluid from the replenishment chambers 120 can be used for this purpose. First, the solenoid valves 118 are closed, the control valves 107 are opened and then the replenishment valves 108 are opened. The springs 110 thus displace the brake fluid from the replenishment chambers 120 into the wheel brakes RB via the pistons 109. The required volume can be controlled via the position of the piston 109, which is supplied by the sensor 124. Alternatively, the pre-fill volume can be set from the opening time of the replenishment valves and the filling pressure of the replenishment chamber 120. The pressure sensor 112 can also be used to detect when the brake pad clearance is eliminated. As soon as the brake pads are in contact with the brake disc, the pressure in the brake circuit increases. Pre-filling to approx. 5 bar, which is required by an external sensor, is even more effective in terms of reducing the braking distance.

[0060] A procedure that can be used if the secondary chambers 120 have emptied, e.g. due to a leak, when the pad clearance is set, involves the following steps: The top-up valves 108 initially remain closed, while the control valves 107 are open. The piston 103 is actuated by the motor drive so that volume is fed into the brake circuits until the brake pads make contact. The control valves 107 are then closed and the piston 103 is retracted again. This creates a vacuum in the working chambers A1 and A2. As soon as the piston 103 reaches its initial position, the corresponding differential volume is sucked out of the reservoir due to the vacuum.

List of reference signs

[0061] 1 Brake pedal 2 BKV 3 DK piston 3a SK piston 4 THZ, tandem master brake cylinder 5Pedal travel sensor 6Reservoir 7Distance sensor 8Electric motor-driven brake booster (BKV) 9Switchover valve 10Pressure supply line 11a-dBrake caliper 12a-dBrake piston 14DC-way sensor 15Pressure transducer in the DC circuit 16a Switchover valve 17 Switchover valve 18 Control valve 18a Control valve 18b Control valve 18c Control valve 19 Reservoir ECU 20 Temperature sensor on HCU 21 Foot 29 Brake piston seal 30 Roll-back element 31 guide bolt 32 magnet armature with bearing bolt 33 brake holder 34 expander element 35 return bolt 36 return spring 37 brake piston sensor 38 suction pressure control unit 39 auxiliary piston 40 electric motor 41 spindle 42 HCU (ABS, ESP) 43E-valve with non-return valve of ABS/ESP 44HCU motor 45HCU pump 46Magnetic circuit with coil 52Brake pad on the calliper side 59Brake disc BLSAir gap RB a -RB d Wheel brakes 101Brake pedal 102Motor drive with , path simulator 103Pressure rod piston DK 104Floating piston 105Master brake cylinder Hz 106Reservoir 107Control valves 108Post-delivery valve 109Piston 110Spring 111Pedal travel sensor 112Pressure sensor 118Solenoid valve 120Post-delivery chamber 121Inlet openings 122Brake circuit 124124 Sensor A 1 , A 2 Working chambers of the HZ BLA Brake line ZL Supply line