Braking system for a motor vehicle and method for controlling such a braking system

Abstract

The present invention relates to a brake system (2) for a motor vehicle comprising a brake pressure generator (4) actuated by an electrically controlled motor (16) with a working chamber (10) delimited by a cylinder (6) and a piston (8), a wheel brake (18) with a brake cylinder (20), a brake piston (22) which interacts with a first friction partner (28) of the wheel brake (18) to bring the first friction partner (28) into frictional engagement or out of frictional engagement with a second friction partner (30), and a pressure chamber (24) delimited by the brake cylinder (20) and the brake piston (22) which is fluid-connected to the working chamber (10) via a pressure medium channel (26), and an electronic control device (50). The brake pressure generator (4) is designed to create a vacuum in the pressure chamber (24) in order to move the brake piston (22) by means of a vacuum-induced restoring force acting on the brake piston (22).Furthermore, the invention relates to a method for controlling such a braking system (2).

Description

State of the art

[0001] The present invention relates to a braking system for a motor vehicle. Furthermore, the present invention relates to a method for controlling such a braking system.

[0002] Brake systems for motor vehicles with hydraulically actuated wheel brakes are known from the prior art. The wheel brake is designed as a caliper brake, either a fixed caliper or a floating caliper brake. At least one brake piston is provided on the caliper housing, which, together with the caliper housing, defines a pressure chamber that can be pressurized with hydraulic pressure. The brake piston interacts with a first friction partner in the form of a brake pad. The brake piston is movable in a closing direction to press the first friction partner against a second friction partner in the form of a brake disc, thus achieving a braking effect.To move the brake piston in the opposite direction to the closing direction at the end of the braking process, a spring element in the form of a sealing ring is provided. This seals the pressure chamber between the brake caliper housing and the brake piston and deforms elastically when the brake piston is moved in the closing direction, thus exerting a restoring force on the brake piston in the opening direction. Furthermore, the first friction partner is supported on the brake caliper housing by another spring element. This allows the first friction partner to be separated from the second friction partner by means of a corresponding elastic restoring force, thereby establishing a clearance between the friction partners when the braking process is complete.

[0003] DE 10 2023 129 216 A1 describes a previously known example of a brake system with a hydraulically operated caliper brake. Disclosure of the invention

[0004] The present invention allows the clearance between the friction partners of a wheel brake to be adjusted with particular precision using minimal equipment.

[0005] According to the invention, a braking system for a motor vehicle with the features of claim 1 and a method for controlling such a braking system with the features of claim 7 are therefore provided.

[0006] Accordingly, a braking system for a motor vehicle is provided. The braking system comprises a brake pressure generator, actuated by an electrically controlled motor, with a cylinder, a piston, and a working chamber bounded by the cylinder and the piston. The piston can be moved by the motor, optionally with the interposition of a gearbox, in a pressure build-up direction by reducing the volume of the working chamber and in a pressure release direction opposite to the pressure build-up direction by increasing the volume of the working chamber. Furthermore, at least one wheel brake is provided, comprising a brake cylinder, a brake piston that interacts with a first friction partner of the wheel brake to bring the first friction partner into or out of frictional engagement with a second friction partner, and a pressure chamber bounded by the brake cylinder and the brake piston.The wheel brake is preferably designed as a caliper brake, for example as a fixed caliper brake or a floating caliper brake. The first friction partner is preferably a friction lining or a friction lining carrier to which a friction lining is attached. The second friction partner is preferably a brake disc, particularly preferably an internally ventilated brake disc. The pressure chamber is fluid-connected to the working chamber via a pressure medium channel; a hydraulic fluid is preferably provided as the pressure medium. The brake pressure generator is configured to increase, maintain, or decrease the pressure in the pressure chamber, and furthermore includes an electronic control unit for controlling the motor and other components of the brake system, such as valves.In order to precisely adjust the clearance between the friction partners, the brake pressure generator is designed to create a vacuum in the pressure chamber in order to move the brake piston by means of a vacuum-induced restoring force acting on the brake piston.

[0007] Furthermore, a method for controlling such a brake system is provided. In this method, the wheel brake clearance is adjusted or achieved by moving the piston, driven by the motor, from a first position to a second position in the pressure reduction direction and holding it in the second position. This is accomplished by generating a vacuum in the working chamber and consequently also in the pressure medium channel and the pressure chamber of the wheel brake, such that the brake piston is moved by a vacuum-induced restoring force from a contact position, in which the first friction partner contacts the second friction partner of the wheel brake, to a clearance position and held in the clearance position, in which a predetermined clearance exists between the first and second friction partners.

[0008] One aspect of the invention lies in the particularly precise adjustment of the clearance between the friction partners in order to avoid residual braking torque when the wheel brake is open, to minimize brake wear, to improve the transition between recuperation and hydraulic braking in electric or hybrid drives, and to prevent the friction partners from sticking to each other after the vehicle has been switched off.

[0009] Advantageous designs and further developments result from the sub-claims as well as from the description with reference to the figures.

[0010] According to a preferred embodiment of the brake system according to the invention, the brake pressure generator is configured to move the piston from a first position in the pressure reduction direction to a second position while generating a vacuum in the pressure chamber, and to hold it in the second position. This allows the brake piston to be moved by the restoring force from a contact position, in which the first friction partner contacts the second friction partner of the wheel brake, in an opening direction to a ventilation position, and held in the ventilation position in which a predetermined clearance exists between the first and second friction partners. The predetermined clearance, which is preferably 0.1 mm to 0.5 mm, is thus determined by the ventilation position of the brake piston.

[0011] According to a further preferred embodiment of the brake system according to the invention, the first friction partner is attached to the brake piston, wherein the movements of the brake piston and the first friction partner are preferably coupled such that the displacement of the brake piston corresponds to a displacement of the first friction partner, in order to precisely determine the clearance by the brake piston's open position. Alternatively or additionally, no spring elements are provided for directly acting on the brake piston and / or indirectly acting on the brake piston via the first friction partner with a force acting in the opening direction. For example, the usual spring-loaded sealing ring for resetting the brake piston can be omitted in favor of a simple sealing ring. Alternatively or additionally, the usual spring elements for resetting the friction pad carrier or friction pad can also be omitted.

[0012] According to a further preferred embodiment of the brake system according to the invention, a rotational position sensor is provided for detecting the rotational position of the motor, wherein a first rotational position, in which the piston assumes the first position, and a second rotational position, in which the piston assumes the second position, can be stored or are stored in the control unit in order to control the motor by the control unit to achieve the respective rotational position. Alternatively or additionally, a pressure sensor is provided for detecting the pressure in the working chamber, and thus also the pressure in the pressure medium channel and the pressure chamber.

[0013] In a preferred embodiment of the method according to the invention, the first position is determined by the control device through a first rotational position of the motor in which the piston assumes the first position, and the second position through a second rotational position of the motor in which the piston assumes the second position. It is preferred that, prior to setting the clearance, the first position of the piston is determined by moving the piston through the motor in the pressure build-up direction, measuring the pressure in the working chamber, and recording the rotational position of the motor. The recorded rotational position is then stored in the control device as the first rotational position if the measured pressure exceeds a predetermined value and / or increases abruptly.The latter is particularly the case when the friction partners touch after overcoming a clearance, causing the pressure to increase sharply or abruptly as the piston is moved further in the pressure build-up direction. This allows the piston's initial position for adjusting the clearance to be determined very precisely. The pressure in the working chamber can be measured by a pressure sensor; alternatively, a value representative of the pressure in the working chamber can be measured, for example, the motor's current draw representative of the pressure in the working chamber. The detected rotational position is then stored as the first rotational position in the control unit when the measured motor current draw exceeds a predetermined value and / or increases abruptly. The second position is then determined by calculating it from the stored first rotational position and storing it in the control unit.The calculation is simple insofar as a translation between the rotational movement of the motor and the translational movement of the piston, and the dimensions of the piston, working chamber, brake piston and pressure chamber are known.

[0014] In a further advantageous embodiment of the method according to the invention

[0015] The invention is explained in more detail below with reference to exemplary embodiments and the accompanying drawings. These show: Fig. 1 a hydraulic circuit diagram of an embodiment of the brake system according to the invention and Fig. 2 a flowchart to illustrate an embodiment of the inventive method for controlling the brake system according to Fig. 1.

[0016] The accompanying figures are intended to provide a further understanding of the embodiments of the invention. They illustrate embodiments and, in conjunction with the description, serve to explain the principles and concepts of the invention. Other embodiments and many of the advantages mentioned will become apparent with reference to the drawings. The elements of the drawings are not necessarily shown to scale.

[0017] In the figures of the drawing, identical, functionally equivalent and similarly acting elements, features and components - unless otherwise stated - are each provided with the same reference symbols.

[0018] Fig. Figure 1 shows a hydraulic circuit diagram of an embodiment of the brake system 2 according to the invention within a motor vehicle.

[0019] The brake system 2 includes a brake pressure generator 4. The brake pressure generator 4 essentially consists of a cylinder 6 and a piston 8, wherein the cylinder 6 and the piston 8 define a working chamber 10 of the brake pressure generator 4. The piston 8 can be moved in a pressure build-up direction 12 by reducing the volume of the working chamber 10 and in a pressure release direction 14 opposite to the pressure build-up direction 12 by increasing the volume of the working chamber 10.

[0020] The piston 8 can be actuated by an electrically controlled motor 16. A transmission (not shown), for example a spindle or ball screw drive, can be arranged between the motor 16 and the piston 8 to convert the rotary motion of a drive shaft of the motor 16 into a translational motion of the piston 8 in the pressure build-up or pressure release direction 12, 14. Since the transmission ratio is known, a rotational position of the motor 16 can always be assigned to a corresponding position of the piston 8 in the cylinder 6.

[0021] Furthermore, the brake system 2 includes a wheel brake 18. The wheel brake 18 is preferably designed as a caliper brake, for example as a fixed caliper or floating caliper brake. The wheel brake 18 thus has at least one brake cylinder 20 and a brake piston 22 guided in the brake cylinder 20, wherein the brake cylinder 20 and brake piston 22 define a pressure chamber 24. The working chamber 10 of the brake pressure generator 4 is fluidically connected to the pressure chamber 24 of the wheel brake 18 via a pressure medium channel 26, so that the brake pressure generator 4 is configured to increase, maintain, or decrease the pressure in the pressure chamber 24 via the pressure medium channel 26.

[0022] The brake piston 22 interacts with a first friction partner 28, preferably a brake pad or a brake pad carrier, of the wheel brake 18 to bring the first friction partner 28 into frictional engagement or out of frictional engagement with a second friction partner 30, preferably a brake disc. For this purpose, the brake piston 22 is translationally movable or displaceable in the brake cylinder 20 in a closing direction 32 and in an opening direction 34 opposite to the closing direction 32.

[0023] The brake system 2 further comprises a pressure medium reservoir 36 for storing pressure medium, which is preferably a hydraulic pressure medium or a hydraulic fluid. A supply channel 38 extends from the pressure medium reservoir 36 to the brake pressure generator to supply the working chamber 10 with pressure medium. A plunger charging valve 40 is provided in the supply channel 38 to control the flow direction, blocking flow from the working chamber 10 to the pressure medium reservoir 36. In a simple embodiment, the plunger charging valve 40 is designed as a check valve. Alternatively, however, the plunger charging valve can also be designed as a controllable switching valve, as shown in Fig. 1 is indicated by the separately shown plunger charging valve 40'. For example, the plunger charging valve 40' can be selectively controlled to switch between a closed position and an open position, thus making the plunger charging valve 40' lockable in the flow direction from the working chamber 10 to the pressure medium reservoir 36.

[0024] Furthermore, a relief channel 42 is provided through which pressure medium can flow from the working chamber 10 into the pressure medium reservoir 36. In the illustrated embodiment, the relief channel 42 opens for this purpose on one side into the working chamber 10, the pressure medium channel 26 or the pressure chamber 24, and on the other side into the pressure medium reservoir 36 or the supply channel 38. The outflow through the relief channel 42 can be controlled by an electrically actuated relief valve 44.

[0025] The brake system 2 has a rotational position sensor 46 assigned to the motor 16 for detecting the rotational position of the motor 16. In addition, a pressure sensor 48 is provided for detecting the pressure in the working chamber 10, and thus also the pressure in the hydraulic fluid channel 26 and the pressure chamber 24. The rotational positions and pressure values ​​detected by the rotational position sensor 46 and the pressure sensor 48 can be received and processed by an electronic control unit 50. Besides receiving and processing the data, the control unit 50 also controls the motor 16, the plunger charging valve 40', and the relief valve 44.

[0026] The brake pressure generator 4 is configured to generate a vacuum in the pressure chamber 24 in order to move the brake piston 22 by means of a vacuum-induced restoring force acting on the brake piston 22 in the opening direction 34. More specifically, the brake pressure generator 4 is configured to move the piston 8 from a first position in the pressure reduction direction 14 to a second position and hold it in the second position by generating the vacuum in the working chamber 10 and, via the pressure medium channel 26, also in the pressure chamber 24. This is achieved by the restoring force moving the brake piston 22 from a contact position, in which the first friction partner 28 contacts the second friction partner 30 of the wheel brake 18, in the opening direction 34 to a ventilation position, and holding it in the ventilation position in which a predetermined clearance a exists between the first and second friction partners 28, 30. The predetermined clearance a is preferably 0.1 mm to 0.5 mm.

[0027] The rotational position sensor 46 can detect a first rotational position, in which the piston 8 assumes the first position, and a second rotational position, in which the piston 8 assumes the second position, and store this information in the control unit 50. Based on the stored first and second rotational positions, the control unit 50 can actuate the motor 16 to achieve the respective rotational position and thus also the corresponding first and second positions of the piston 8.

[0028] The brake pressure generator 4 is designed such that the piston 8 can be moved in the pressure build-up direction 12 to a first end position and in the pressure release direction 14 to a second end position, while the aforementioned first and second positions of the piston 8 are designed as intermediate positions between the end positions.

[0029] The first friction partner 28 of the wheel brake 18 is attached to the brake piston 22 such that the movements of the brake piston 22 and the first friction partner 28 are coupled, such that the displacement of the brake piston 22 corresponds to a displacement of the first friction partner 28 in the opening and closing directions 34, 32. Furthermore, it is preferred that a sealing ring 52 between the brake piston 22 and the brake cylinder 20 exerts no or at most a minimal restoring force in the opening direction 34 on the brake piston 22 when it is displaced in the closing direction 32. Instead of the usual sealing ring designed as an elastomer spring, a simple sealing ring 52 without a restoring function should be used to simplify the design and to achieve the restoring effect primarily through the vacuum. In general, spring elements for directly applying a force to the brake piston 22 in the opening direction 34 are preferably omitted.Alternatively or additionally, spring elements for indirectly applying a force in the opening direction 34 to the brake piston 22 via the first friction partner 28 are omitted, for example, by not holding the first friction partner 28 to the wheel brake housing by means of a spring element as is customary in the prior art. The latter is unnecessary anyway with the aforementioned attachment of the first friction partner 28 to the brake piston 22, thus simplifying the design of the wheel brake 18.

[0030] Fig. Figure 2 shows a flowchart to illustrate an embodiment of the inventive method for controlling the brake system 2 according to Fig. 1.

[0031] To precisely adjust the air clearance a and thus achieve the aforementioned advantages, the required initial position of the piston 8 is first determined. For this purpose, in process step A, the motor 16 is actuated by the control unit 50 such that the piston 8 is moved by the motor 16 in the pressure build-up direction 12. This occurs starting from an open wheel brake 18. The relief valve 44 and the plunger charging valve 40 or 40' are closed, so that the amount of hydraulic fluid in working chamber 10, hydraulic fluid channel 26, and pressure chamber 24 remains unchanged, and the pressure in working chamber 10, hydraulic fluid channel 26, and pressure chamber 24 can increase. The pressure in working chamber 10 is measured by the pressure sensor 48, and the rotational position of the motor 16 is also detected by the rotational position sensor 46. The pressure increase in the pressure chamber 24 displaces the brake piston 22 in the closing direction 32 relative to the brake cylinder 20.Alternatively, a value representative of the pressure in the working chamber 10 can be measured, for example a current consumption of the motor 16 representative of the pressure in the working chamber 10, so that the pressure sensor 48 could basically be dispensed with. The detected rotational position is stored as the first rotational position in the control unit if the measured current consumption of the motor exceeds a predetermined value and / or increases abruptly.

[0032] In process step B, it is continuously determined whether the measured pressure exceeds a predetermined value and / or increases abruptly, or alternatively, whether the measured current draw of the motor 16 exceeds a predetermined value and / or increases abruptly. If this is not the case, the piston 8 is moved further in the pressure build-up direction 12. However, if the measured pressure, or alternatively the measured current draw of the motor 16, exceeds a predetermined value and / or increases abruptly, this is considered an indication that the brake piston 22 has reached a contact position (touch point) in which the first friction partner 28 contacts the second friction partner 30. The rotational position detected by the rotational position sensor 46 at this time is then stored in process step C as the first rotational position in the control unit 50.

[0033] In process step D, the second position of piston 8 is then determined by calculating the second rotational position from the stored first rotational position and storing it in the control unit 50. This is done based on the known transmission ratios from the motor 16 to the brake piston 22. In particular, the transmission ratio between motor 16 and piston 8, the piston area of ​​piston 8, and the piston area of ​​brake piston 22 are known, which allow the calculation of the second rotational position to which motor 16 must be turned from the first rotational position in order to achieve a predetermined adjustment travel of the brake piston 22 by means of the vacuum, which preferably corresponds to the ventilation clearance a.

[0034] The aforementioned steps A to D should be repeated periodically to take account of any wear that may have occurred in the meantime on the friction partners 28, 30 and in particular to ensure an exact adjustment of the air gap a over the entire service life of the wheel brake 18.

[0035] To precisely adjust the air clearance a based on the values ​​determined above after a braking operation, motor 16 is controlled by the control unit 50 in process step E such that the piston 8 is moved from the first position in the pressure reduction direction 14 to the second position and held there. The first position is determined by the first rotational position of motor 16, and the second position by the second rotational position of motor 16, as determined by the control unit 50. The amount of hydraulic fluid in working chamber 10, hydraulic fluid channel 26, and pressure chamber 24 remains unchanged, resulting essentially in a volume shift, especially since the plunger charging valve 40 or 40' and the relief valve 44 are closed or will be closed in the flow direction to working chamber 10.

[0036] This occurs by generating a vacuum in the pressure chamber 24, so that the brake piston 22 is moved by a vacuum-induced restoring force from the contact position in which the first friction partner 28 contacts the second friction partner 30, into the position in Fig. The ventilation position shown in Figure 1 is shifted. By holding the piston 8 in the second position, the brake piston 22 is also held in the ventilation position, in which the predetermined air gap a exists between the first and second friction partners 28, 30. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2023 129 216 A1

[0003]

Claims

[1] comprising a braking system (2) for a motor vehicle a brake pressure generator (4) actuated by an electrically controlled motor (16) with a cylinder (6), a piston (8) and a working chamber (10) bounded by the cylinder (6) and the piston (8), wherein the piston (8) can be displaced by the motor (16) in a pressure build-up direction (12) by reducing the volume of the working chamber (10) and in a pressure release direction (14) opposite to the pressure build-up direction (12) by increasing the volume of the working chamber (10), a wheel brake (18) comprising a brake cylinder (20), a brake piston (22) which interacts with a first friction partner (28) of the wheel brake (18) to bring the first friction partner (28) into frictional engagement or out of frictional engagement with a second friction partner (30), and a pressure chamber (24) bounded by the brake cylinder (20) and the brake piston (22), which is fluidically connected to the working chamber (10) via a pressure medium channel (26), wherein the brake pressure generator (4) is configured to increase, maintain or decrease a pressure in the pressure chamber (24), and an electronic control unit (50), characterized by , that the brake pressure generator (4) is designed to create a vacuum in the pressure chamber (24) in order to move the brake piston (22) by means of a vacuum-induced restoring force acting on the brake piston (22). [2] Brake system (2) according to claim 1, in which the brake pressure generator (4) is arranged to move the piston (8) from a first position in the pressure reduction direction (14) by generating the vacuum in the pressure chamber (24) to a second position and to hold it in the second position, so that the brake piston (22) is moved by the restoring force from a contact position in which the first friction partner (28) contacts the second friction partner (30) of the wheel brake (18) in an opening direction (34) to a ventilation position and is held in the ventilation position in which a predetermined air gap (a) exists between the first and second friction partner (28, 30). [3] Brake system (2) according to one of the preceding claims, wherein the first friction partner (28) is attached to the brake piston (22), wherein the movements of the brake piston (22) and the first friction partner (28) are preferably coupled such that the displacement path of the brake piston (22) corresponds to a displacement path of the first friction partner (28), and / or the wheel brake (18) does not have any spring elements for directly acting on the brake piston (22) and / or indirectly acting on the brake piston (22) via the first friction partner (28) with a force acting in the opening direction (34). [4] Brake system (2) according to one of the preceding claims, in which a rotation position sensor (46) is provided for detecting the rotation position of the motor (16), wherein a first rotation position in which the piston (8) assumes the first position and a second rotation position in which the piston (8) assumes the second position can be stored or is stored in the control device (50) in order to control the motor (16) by achieving the respective rotation position by the control device (50), and / or a pressure sensor (48) is provided for detecting the pressure in the working chamber (10). [5] Brake system (2) according to one of the preceding claims, wherein the brake pressure generator (4) is arranged to move the piston (8) between two end positions, the first and second positions being intermediate positions between the end positions. [6] Brake system (2) according to one of the preceding claims, further comprising a pressure medium reservoir (36) for storing hydraulic pressure medium, wherein preferably a relief channel (42) through which pressure medium can flow from the working chamber (10) into the pressure medium reservoir (36), wherein the outflow through the relief channel (42) can be controlled by an electrically controllable relief valve (44), and / or a supply channel (38) for supplying the working chamber (10) with pressure medium is provided, wherein a plunger charging valve (40, 40') is provided for controlling a flow direction in the supply channel (38), which blocks or can be blocked in the flow direction from the working chamber (10) to the pressure medium reservoir (36). [7] Method for controlling a brake system (2) according to one of the preceding claims comprising the method steps of adjusting the air clearance (a) of the wheel brake (18) by moving the piston (8) by the motor (16) in the pressure reduction direction (14) from a first position to a second position and holding the piston (8) in the second position by generating a vacuum in the pressure chamber (10) such that the brake piston (22) is moved by a vacuum-induced restoring force acting on the brake piston (22) from a contact position in which the first friction partner (28) contacts the second friction partner (30) of the wheel brake (18) to a ventilation position and is held in the ventilation position in which a predetermined air clearance (a) exists between the first and second friction partner (28, 30). [8] Method according to claim 7, wherein the first position is determined by the control device (50) by a first rotational position of the motor (16) in which the piston (8) assumes the first position, and the second position is determined by the control device (50) by a second rotational position of the motor (16) in which the piston (8) assumes the second position. [9] Method according to claim 8, wherein, prior to adjusting the air clearance (a), the first position of the piston (8) is determined by moving the piston (8) through the motor (16) in the pressure build-up direction (12), measuring the pressure in the working chamber (10), and detecting the rotational position of the motor (16), wherein the detected rotational position is stored as the first rotational position in the control device (50) when the measured pressure exceeds a predetermined value and / or increases abruptly, and the second position is determined by calculating the second rotational position from the stored first rotational position and storing it in the control device (50). [10] Method according to one of claims 7 to 9, wherein the brake system (2) is controlled when adjusting the air clearance and / or when determining the first position such that the amount of pressure medium in the working chamber (10), pressure medium channel (26) and pressure chamber (24) remains unchanged, wherein when adjusting the air clearance (a) preferably the plunger charging valve (40, 40') and / or the relief valve (44) are blocked or become blocked in the flow direction to the working chamber (10) and / or when determining the first position preferably the plunger charging valve (40, 40') and / or the relief valve (44) are blocked or become blocked in the flow direction to the pressure medium reservoir (36).

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