DE102014210804B4 - Master brake cylinder for a vehicle's braking system and method for operating a vehicle's braking system - Google Patents

Abstract

Master brake cylinder (10) for a braking system of a vehicle with:
at least one first pressure chamber (12) comprising at least one first partial volume (12a) which is limited by a first piston wall (14a) of at least one adjustable piston (16) and in which at least one first return spring (13a) is arranged such that the first partial volume (12a) can be reduced by adjusting the first piston wall (14a) from its initial position along a braking direction (15) under a deformation of at least the first return spring (13a) and the first piston wall (14a) can be returned to its initial position by means of the first return spring (13a);
characterized by
a simulator spring (18) which, in addition to the first return spring (13a), is arranged in the first partial volume (12a) such that, during the adjustment of the first piston wall (14a) from its initial position along the braking direction (15) by a predetermined initial adjustment path (x1), the simulator spring (18) remains in its initial shape despite the deformation of the first return spring (13a), and by adjusting the first piston wall (14), which has already been adjusted by at least the initial adjustment path (s1), along the braking direction (15) by a further adjustment path (x2), the simulator spring (18) can be deformed from its initial shape.

Description

The invention relates to a master brake cylinder for a vehicle's braking system, a braking device equipped therewith for a vehicle's braking system, and a corresponding braking system for a vehicle. Furthermore, the invention relates to a method for operating a vehicle's braking system.

State of the art

1 shows a schematic representation of a conventional braking system for a vehicle, which is known to the applicant as internal prior art.

The in 1 The schematically represented conventional brake system has a master brake cylinder 10 with a first pressure chamber 12, a rod piston 16 delimiting the first pressure chamber 12, a second pressure chamber 20, and a floating piston 22 arranged between the pressure chambers 12 and 20. The pressure chambers 12 and 20 of the master brake cylinder 10 are connected to a brake fluid reservoir 26 of the conventional brake system via vent holes 28. Furthermore, a first brake circuit 30 with at least one first wheel brake cylinder 32 is hydraulically connected to the first pressure chamber 12, and a second brake circuit 34 with at least one second wheel brake cylinder 36 is hydraulically connected to the second pressure chamber 20. Each of the brake circuits 30 and 34 is connected to its respective pressure chamber 12 or 20 via a separating valve 54a and 54b, respectively. Each of the brake circuits 30 and 34 is additionally connected to a plunger 44 via a further isolating valve 52a and 52b.

In addition, the conventional braking system of the 2 The simulator unit 60 comprises a pressure chamber 62, a spring chamber 64, and a piston 66 adjustable between the pressure chamber 62 and the spring chamber 64, which can be moved into the spring chamber 64 against the spring force of at least one simulator spring 68. The pressure chamber 62 is selectively connected via a line 70 to either the first pressure chamber 12 or the second pressure chamber 20. The simulator unit 60 can be decoupled from the conventional brake system by means of a further isolating valve 72.

Additionally, the DE 102 23 799 A1 A master brake cylinder of a vehicle's braking system with at least one first pressure chamber, which comprises at least one first partial volume bounded by a first piston wall of at least one adjustable piston. A first return spring is arranged in the first partial volume. The first partial volume can be reduced by adjusting the first piston wall from its initial position along a braking direction, thereby deforming the first return spring, while the first piston wall can be returned to its initial position by means of the first return spring.

Furthermore, the DE 26 42 078 A1 A load-dependent brake pressure regulator, used in addition to a master brake cylinder in a vehicle's braking system equipped with one. One end of a control spring of the load-dependent brake pressure regulator is supported on a cam of a shaft, the shaft being rotatable by means of a lever connected to a vehicle axle. The control spring can be two-part, i.e., consisting of two individual springs. In particular, two individual springs of different lengths can be nested inside one another.

Disclosure of the invention

The invention provides a master brake cylinder for a vehicle braking system with the features of claim 1, a brake device for a vehicle braking system with the features of claim 8, a brake system for a vehicle with the features of claim 10 and a method for operating a vehicle braking system with the features of claim 12.

Advantages of the invention

The present invention provides cost-effective ways to improve the brake pedal feel for a driver. Furthermore, the present invention can be combined with a variety of known brake system components. The present invention is also risk-free. As explained in more detail below, the present invention can also be used in brake systems with an advantageous safety standard without compromising the safety standard or making fault detection in the respective brake system more difficult.

The present invention provides, in particular, possibilities for ensuring a (standard) brake actuation characteristic (pedal characteristic) that is advantageous for the driver. In particular, a pedal characteristic that is perceptible to the driver as a jump-in can be ensured in this way without having to change the connection of the brake actuation element (brake pedal) to the master brake cylinder.

The invention provides an integrated simulator function within an (otherwise conventional) master brake cylinder by means of an additional simulator spring. This eliminates the conventional need to mount a separate simulator on a brake system. The present invention thus allows for a more compact and lightweight brake system design. Furthermore, the present invention reduces the labor required for assembling a brake system.

The integration of the simulator into the master cylinder, as achieved by the present invention, can be carried out without a (significant) increase in the size and weight of the respective master cylinder. In most embodiments of the invention, the weight of the respective master cylinder increases only by the weight of the simulator spring. Since a simulator that is conventionally arranged externally on the master cylinder is usually already connected to the respective master cylinder via a valve/isolation valve, this valve for the hydraulic connection of the simulator to the master cylinder can also be eliminated by the present invention. Thus, the simulator valve can be used instead of the conventionally required valve for the hydraulic connection of the simulator to the master cylinder. Apart from the simulator spring, no additional component is generally required on a master cylinder/brake unit/brake system to implement the present invention.

Advantageously, the simulator spring arranged in the first partial volume has a maximum simulator spring length that is shorter by the initial adjustment travel than the maximum return spring length of the first return spring arranged in the first partial volume. In this way, it is easily ensured that deformation of the simulator spring only occurs once the first piston wall is moved from its initial position along the braking direction by the initial adjustment travel.

In a preferred embodiment, the first return spring has a spring constant up to its elastic limit that is smaller than the spring constant of the simulator spring up to its elastic limit. From the moment the first piston wall is moved from its initial position by the initial adjustment travel, a more pronounced feedback effect during further braking is thus tactilely perceptible to the driver, at least in the first partial volume.

The master brake cylinder can, for example, have at least one rod piston as well as at least one adjustable piston. Alternatively or in addition, the at least one adjustable piston can also be at least one floating piston.

In an advantageous embodiment, the master brake cylinder has a stepped bore within which at least the first pressure chamber is formed. The master brake cylinder comprises a stepped piston as the at least one rod piston, which, with its first piston wall, defines the first partial volume and, with its second piston wall, defines a second partial volume of the first pressure chamber. The second partial volume can be reduced by adjusting the second piston wall along the braking direction. Alternatively, the second partial volume of the first pressure chamber can also be separated from the first partial volume of the first pressure chamber by means of at least a partial partition. The two partial volumes can, for example, be hydraulically connected to each other via at least one opening in the partial partition and/or via an externally routed line. In all the cases listed here, the advantages of a subdivided first pressure chamber can be utilized for the present invention. However, it should be noted that the formation of a second partial volume in the first pressure chamber is not a prerequisite for the use of the invention.

Preferably, the master brake cylinder comprises a second pressure chamber and a floating piston adjustable between the first and second pressure chambers, which is supported in its initial position by a second return spring arranged in the second pressure chamber. Thus, a tandem master brake cylinder can be used for the present invention in particular.

In a further development of the present invention, a further simulator spring can be arranged in the second pressure chamber, which, during an adjustment of the floating piston from its initial position along the braking direction by a predetermined initial adjustment path of the floating piston (despite the deformation of the second return spring), is in its initial form, and can only be deformed from its initial form after an adjustment of the floating piston by at least the initial adjustment path by means of a further adjustment of the floating piston along the braking direction by a further adjustment path.

The simulator spring (located in the first partial volume) can be attached to the floating piston, to an inner wall of the master cylinder opposite the first piston wall, or to the first piston wall itself. Thus, a Great design freedom is ensured when attaching the simulator spring in the first partial volume.

A brake control unit for a vehicle's braking system with such a master cylinder and a simulator valve, through which the first partial volume can be hydraulically connected to an external or brake control unit-integrated brake fluid reservoir, also provides the advantages described above. The simulator valve can be used to prevent brake pressure build-up in the first partial volume of the first pressure chamber despite the movement of the first piston wall from its initial position along the braking direction. For this purpose, the simulator valve simply needs to be controlled to at least a partially open state. By at least partially opening the simulator valve while the first piston wall is moved from its initial position along the braking direction by the initial travel, virtually force-free movement of the first piston wall is achieved. (Typically, in such a situation, the adjustment movement of the first piston wall is counteracted only by the spring force of the first return spring and the frictional force of the first piston wall.) The driver can therefore brake directly into the first partial volume of the first pressure chamber without applying significant driver braking force. The simulator valve thus ensures, in particular, a standard brake feel (pedal feel) for the driver.

Advantageously, the braking device includes operator electronics designed to control the simulator valve so that, during normal operating mode, the simulator valve is at least temporarily in a partially open state and, in a fallback mode, in a closed state. Thus, in normal operating mode, the operator electronics can ensure, by controlling the simulator valve, that the movement of the first piston wall from its initial position along the braking direction is counteracted only by spring forces, not by pressure. In normal operating mode, the master cylinder can therefore be used as a simulator, while pressure build-up in at least one wheel cylinder can be achieved independently of the driver's actuation of the brake pedal. Simultaneously, in the fallback mode, the driver can use the master cylinder to prime the at least one wheel cylinder. The operator electronics thus reliably realize the advantageous brake actuation feel (pedal feel) for the driver in the normal operating mode of the braking device and additionally ensures a high safety standard.

A suitable braking system for a vehicle also guarantees the advantages already mentioned above.

Furthermore, the described advantages can be realized by implementing the corresponding method for operating a vehicle's braking system. This method can be further developed according to the embodiments of the master brake cylinder, the brake device, and/or the braking system described above.

Brief description of the drawings

• 1 eine schematische Darstellung eines herkömmlichen Bremssystems für ein Fahrzeug;
• 2 eine schematische Darstellung einer Ausführungsform des Hauptbremszylinders, bzw. des damit ausgestatteten Bremssystems; und
• 3 ein Flussdiagramm zum Erläutern einer Ausführungsform des Verfahrens zum Betreiben eines Bremssystems eines Fahrzeugs.

Further features and advantages of the present invention are explained below with reference to the figures. They show:

• 1 a schematic representation of a conventional braking system for a vehicle;
• 2 a schematic representation of an embodiment of the master brake cylinder, or of the brake system equipped with it; and
• 3 A flowchart to explain one embodiment of the method for operating a vehicle's braking system.

Embodiments of the invention

2 shows a schematic representation of an embodiment of the master brake cylinder, or of the brake system equipped with it.

The in 2 The master brake cylinder 10, shown schematically, has at least one first pressure chamber 12, which comprises at least one first partial volume 12a. At least one first return spring 13a is arranged in the first partial volume 12a. Furthermore, the first partial volume 12a is bounded by a first piston wall 14a of at least one adjustable piston 16 such that the first partial volume 12a (i.e., a volume of the first partial volume 12a that can be filled with brake fluid) can be reduced by adjusting/displacing the first piston wall 14a from its initial position along a braking direction 15, thereby deforming at least the first return spring 13a. Thus, to adjust/displacing the first piston wall 14a from its initial position along the braking direction 15, at least a restoring force of the first return spring 13a must be overcome by means of a braking force exerted/transmitted on the at least one adjustable piston 16. The first piston wall 14a can be returned to its initial position by means of the first return spring 13a (when the braking force is less than the restoring force of the first return spring 13a). The initial position of the first piston wall 14a is preferably understood to be its position when the braking force is zero. In particular, the first piston wall 14a can be in its initial position when no (not shown) brake actuation element/brake pedal of the braking system is actuated.

The master brake cylinder 10 also includes a simulator spring 18, which, in addition to the first return spring 13a, is arranged in the first partial volume 12a such that, during the adjustment of the first piston wall 14a from its initial position along the braking direction 15 by a predetermined initial adjustment path x1, the simulator spring 18 remains in its initial shape despite the deformation of the first return spring 13a. Furthermore, by adjusting the first piston wall 14a, which has already been adjusted by at least the initial adjustment path x1, along the braking direction 15 by a further adjustment path x2, the simulator spring 18 (together with the still deformed first return spring 13a) can be deformed from its initial shape. The initial shape can be understood, for example, as the shape of the simulator spring 18 in which it exists in the first partial volume 12a without the application of any force. In particular, the simulator spring 18 can have its maximum simulator spring length in its initial form. Preferably, the deformation of the simulator spring 18 from its initial form is achieved by compression of the simulator spring 18.

During the adjustment of the first piston wall 14a from its initial position along the braking direction 15 by the initial adjustment travel x1, no additional force is required to deform/compress the simulator spring 18. Therefore, the driver can brake into the first partial volume 12a with a comparatively low braking force (e.g., for an initial pressure build-up in the first partial volume 12a). At the same time, it is ensured that from the moment the first piston wall 14a is adjusted from its initial position along the braking direction 15 by the initial adjustment travel x1, an increased force is required for further pressure build-up (to jointly deform/compress the first return spring 13a and the simulator spring 18). A driver braking into the first partial volume 12a thus experiences a feedback that is at least similar to a standard brake actuation characteristic (standard pedal characteristic). A particularly advantageous way to achieve a favorable/standard brake actuation feel (pedal feel) for the driver will be discussed in more detail below.

Preferably, the first return spring 13a has a spring constant up to its elastic limit that is smaller than the spring constant of the simulator spring 18 up to its elastic limit. The spring constant of the simulator spring 18 can be greater than the spring constant of the first return spring 13a by a factor of 2, preferably by a factor of 3, and more preferably by a factor of 4. This provides the driver with an advantageous brake feel (pedal feel) during braking into at least the first partial volume 12a.

The simulator spring 18 arranged in the first partial volume 12a can have a maximum simulator spring length that is shorter by the initial adjustment travel x1 than the maximum return spring length of the first return spring 13a arranged in the first partial volume 12a. In this way, it is easily ensured that deformation/compression of the simulator spring 18 only occurs from the point at which the first piston wall 14a is moved from its initial position along the braking direction 15 by the initial adjustment travel x1.

The master brake cylinder 10 of the 2 It has at least one rod piston 16 as the at least one adjustable piston 16. The at least one adjustable piston 16 can, however, also be designed as a floating piston.

In the embodiment of the 2 The first pressure chamber 12 is subdivided, or subdivisible, into a first partial volume 12a and a second partial volume 12b. The second partial volume 12b is also limited by a second piston wall 14b of the at least one adjustable piston 16 such that the volume of the second partial volume 14b that can be filled with brake fluid can be varied by adjusting/displacing the second piston wall 14b. The partial volumes 12a and 12b can, for example, be designed as two separate chambers or as chambers that can be hydraulically separated by means of a valve component.

For example, the master brake cylinder 10 of the 2 A stepped bore is formed within which at least the first pressure chamber 12 is located. The stepped bore can have a first (inner) internal diameter d1 oriented perpendicular to the braking direction 15 of the at least one adjustable piston 16, which is smaller than a second (outer) internal diameter d2 of the stepped bore oriented perpendicular to the braking direction 15. Furthermore, the master brake cylinder 10 has a stepped piston 16 as the at least one rod piston 16, which, with the first piston wall 14a, forms the first partial volume 12a and, with the second piston wall 14b, the second partial volume 12b of the first pressure chamber 12. limited, wherein the second partial volume 12b (or the volume of the second partial volume 12b that can be filled with brake fluid) can be reduced by adjusting/moving the second piston wall 14b along the braking direction 15.

In the embodiment of the 2 The master brake cylinder 10 comprises a second pressure chamber 20 and a floating piston 22 adjustable between the first pressure chamber 12 (e.g., the first partial volume 12a of the first pressure chamber 12) and the second pressure chamber 20. The floating piston 22 is preferably supported by a second return spring 13b located in the second pressure chamber 20. The master brake cylinder 10 can thus also be used as a "modified" tandem master brake cylinder. However, it should be noted that a design of the master brake cylinder 10 with two pressure chambers 12 and 20 is optional.

The first partial volume 12a and/or the second pressure chamber 20 can have the first/inner diameter d1 perpendicular to the braking direction 15, while the second partial volume 12b has the second/outer inner diameter d2 perpendicular to the braking direction 15. The second partial volume 12b can therefore also be configured as an annular volume. However, it should be noted that the in 2 The depicted design of the master brake cylinder 10 is to be interpreted merely as an example.

The simulator spring 18 can be attached to the floating piston 22, to an inner wall of the master cylinder 10 opposite the first piston wall 14a, or to the first piston wall 14a itself. The simulator spring 18 fulfills its advantageous function in all mounting positions described here. The first return spring 13a can be supported on one side by the first piston wall 14a and on another side by the floating piston 22 or by an inner wall of the master cylinder 10 opposite the first piston wall 14a. If present, the second return spring 13a can be supported on one side by the floating piston 22 and on another side by an inner wall of the master cylinder 10 opposite the floating piston 22.

Preferably, the master brake cylinder 10 is used together with a simulator valve 24, via which the first partial volume 12a can be hydraulically connected to or is connected to a brake fluid reservoir 26. The master brake cylinder 10 can, for example, be installed together with a simulator valve 24 in a brake unit as a compact unit. In the embodiment of the 2 The master brake cylinder and the simulator valve 24 are each installed as separate structural units in a brake system.

The in 2 The depicted brake system also includes the brake fluid reservoir 26. Brake fluid can be drained from the first partial volume 12a into the brake fluid reservoir 26 by at least partially opening the simulator valve 24. This allows the brake pressure present in the first partial volume 12a to be selectively reduced despite adjustment of the first piston wall 14a, thereby improving the brake feel (pedal feel).

Preferably, the braking system also has operator electronics 25, which are designed to control the simulator valve 24 (by means of at least one control signal 25a). Preferably, the control is such that the simulator valve 24 is at least temporarily (advantageously always) in a partially open state during normal operating mode of the braking system and is in a closed state in a fallback state of the braking system. If the simulator valve 24 remains continuously in the partially open state during normal operating mode of the braking system, the driver only feels the forces exerted by the springs 13a and 18 during their braking request. Thus, despite the absence of a mechanical free travel/jump-in area in the brake system, the brake actuation feel/pedal feel of a standard brake system (with a mechanically formed free travel/jump-in area) is ensured by inserting the master brake cylinder 10, the simulator valve 24, and the operator electronics 25. At the same time, a good safety standard is guaranteed as a fallback.

In a possible further development, the control in normal operating mode can be implemented such that, during the adjustment of the first piston wall 14a from its initial position along the braking direction 15 by the predetermined initial adjustment travel x1, the simulator valve 24 is at least partially open, and during the adjustment of the first piston wall 14a, which has already been adjusted by at least the initial adjustment travel x1, along the braking direction 15 by the further adjustment travel x2, the simulator valve 24 is at least partially closed. If desired, the operator electronics 25 in normal operating mode can also be configured to control the simulator valve 24 to its at least partially open state during the entire adjustment of the first piston wall 14a from its initial position along the braking direction 15 by the predetermined initial adjustment travel x1. and only during the adjustment of the first piston wall 14a, which has already been moved by at least the initial adjustment travel x1, along the braking direction 15 by the further adjustment travel x2, does the simulator valve 24 close. This prevents a pressure build-up in at least the first partial volume 12a during the adjustment of the first piston wall 14a from its initial position along the braking direction 15 by the predetermined initial adjustment travel x1. The adjustment movement of the first piston wall 14a from its initial position along the braking direction 15 by the predetermined initial adjustment travel x1 is thus only opposed by the restoring force of the first return spring 13a (and possibly the second return spring 13b). Only after the initial adjustment travel x1 has been overcome does the pressure build-up begin in at least the first partial volume 12a. The driver therefore only feels a significant reaction from the braking system during brake application after overcoming a free travel/jump-in range corresponding to the initial adjustment travel x1.

It is also noted that the advantageous brake actuation feel/pedal feel can be achieved without a conventional simulator designed as a separate structural unit. Instead, a simulator is integrated into the master brake cylinder 10. This reduces the installation space required and the weight of the brake system. Furthermore, the integration of a conventional simulator into the master brake cylinder 10 simplifies the installation of the brake system.

The control of the simulator valve 24 by the operator electronics 25 can be carried out taking into account at least one brake actuation force signal provided to the operator electronics 25. For example, an adjustment travel of the respective brake actuation element, such as a pedal travel, a driver brake pressure and/or a driver brake force, can be taken into account when controlling the simulator valve 24 by the operator electronics 25.

Preferably, at least the first partial volume 12a can also be hydraulically connected to the brake fluid reservoir 26 via a vent hole 28. Likewise, the second partial volume 12b and/or the second pressure chamber 20 can each be connected to the brake fluid reservoir 26 via a vent hole 28.

The braking system also has at least one first brake circuit 30 with at least one first wheel brake cylinder 32, wherein the first brake circuit 30 is hydraulically connectable to the first partial volume 12a. Preferably, a second brake circuit 34 with at least one second wheel brake cylinder 36 is also hydraulically connectable to the second pressure chamber 20. However, the braking system described here is not limited to a design with two brake circuits 30 and 34. Likewise, the number of wheel brake cylinders 32 and 36 that can be used in a brake circuit 30 and 34 is relatively freely selectable. Furthermore, a variety of different hydraulic components, such as pumps and/or valves 37a and 37b, can be used in the brake circuits 30 and 34. The equipment of brake circuits 30 and 34 with two wheel inlet valves 37a and two wheel outlet valves 37b each is to be interpreted only as an example.

The braking system, in its embodiment, features 2 An electrically controlled valve 38 is also provided, through which the second sub-volume 12b is connected to the brake fluid reservoir 26. In this case, the electrically controlled valve 38 is positioned between the second sub-volume 12b and the brake fluid reservoir 26 in such a way that, when the electrically controlled valve 38 is open, the second sub-volume 12b remains depressurized despite any movement of the second piston wall 14b. However, the inclusion of the electrically controlled valve 38 in the brake system is optional.

The brake system also has a pressure relief valve 40, through which the second sub-volume 12b is connected to the brake fluid reservoir 26. The pressure relief valve 40 can, in particular, be arranged in a bypass line running parallel to the electrically controlled valve 38. Furthermore, the brake system includes a check valve 42, through which the second sub-volume 12b is connected at least to the first brake circuit 30 in such a way that brake fluid can be transferred from the second sub-volume 12b to the first brake circuit 30 via the check valve 42. Due to the advantageous configuration of the brake system with the valves 40 and 42, when the electrically controlled valve 38 is in its closed state, a pressure build-up up to a mechanically predetermined limit pressure can be achieved in the second sub-volume 12b by adjusting/displacing the second piston wall 14b. Furthermore, brake fluid can be transferred into the first brake circuit 30 via the check valve 42. This ensures that, despite further adjustment/displacement of the second piston wall 14b, the limit pressure in the second partial volume 12b is prevented from being exceeded. The limit pressure can be, for example, between 1 and 3 bar, particularly at 2 bar. A pressure threshold above which brake fluid from the second partial volume 12b at least into the The flow rate in the first brake circuit 30 can be around 0.5 bar.

Due to its advantageous design, the braking system can be operated in a normal operating mode in which the driver only applies pressure to the first pressure chamber 12 by means of the first surface of the first piston wall 14a, which delimits the first partial volume 12a. This is ensured by controlling the electrically controlled valve 38 in its open state. This can also be described as follows: in the normal operating mode, the second partial volume 12b is short-circuited to the brake fluid reservoir 26 by opening the electrically controlled valve 38. The timing of this activation can be delayed in the event of detected rapid deceleration, such as during emergency braking, in order to improve the pressure build-up dynamics in this operating condition. After the electrically controlled valve 38 opens, the movement of the second piston wall 14b together with the first piston wall 14a does not result in any pressure build-up in the second partial volume 12b. Therefore, in normal operating mode, due to the comparatively small braking area for braking, the driver has a pleasant braking feel (pedal feel) at least in the first pressure chamber 12, which is the same as the first surface.

The braking system can also be operated in a fallback mode in which the break-in area (for break-in, at least into the first pressure chamber 12) is increased compared to the normal operating mode. By (automatically) controlling the electrically controlled valve 38 in its closed state, an additional pressure build-up in the second partial volume 12b can be achieved. The (total) break-in area effective in the fallback mode (for break-in, at least into the first pressure chamber 12) thus corresponds to the sum of the first area and the second area of the second piston wall 14b, which delimits the second partial volume 12b. By increasing the break-in area (for break-in, at least into the first pressure chamber 12) to the sum of the first and second areas, the gear ratio of the master brake cylinder 10 is increased, so that the driver can achieve even higher brake pressures in the wheel brake cylinders 32 and 36 of the braking system with a given braking force.

At the same time, it is ensured that the pressure present in the second partial volume 12b (barely) exceeds a mechanically predetermined limit pressure. Thus, even in fallback mode, it is guaranteed that the driver perceives the actuation of their brake actuator as pleasant. Furthermore, by transferring brake fluid from the second partial volume 12b at least into the first brake circuit 30, the brake pressure that can be built up in the at least one first wheel brake cylinder 32 of the first brake circuit 30 can be increased.

The braking system can operate in fallback mode, particularly in the event of a partial or complete failure of at least one electrical component of the braking system, or in the event of a failure of the vehicle's electrical system. This ensures that even in such a fault situation, the driver can still comfortably bring the vehicle equipped with the braking system to a standstill.

The electrically controlled valve 38 is controlled in its closed state in the fallback mode/mechanical fallback level. If the electrically controlled valve 38 is designed as a normally closed valve, this can be achieved automatically by interrupting the power supply to the electrically controlled valve 38.

Preferably, the braking system also includes an external power braking device 44, by means of which the brake pressure build-up in the wheel brake cylinders 32 and 36 can be performed or supported during normal operating mode. The external power braking device 44 can be pneumatic, electric, or electro-hydraulic. Thus, during normal operating mode, the driver only needs to apply a relatively low braking force and a comparatively small initial contact area with the master brake cylinder 10.

In the embodiment of the 2 The external force braking device 44 is a plunger 44 whose pressure chamber 46 is limited by a piston 50 adjustable by the operation of a motor 48. The pressure chamber 46 of the plunger 44 is hydraulically connected to the brake circuits 30 and 34 via a line, each containing a separating valve 52a and 52b. The plunger 44 is preferably self-locking.

Furthermore, the first brake circuit 30 is connected to the first partial volume 12a and the second brake circuit 34 to the second pressure chamber 20 via further isolating valves 54a and 54b, respectively. The master brake cylinder 10 can thus be decoupled from brake circuits 30 and 34 by closing the isolating valves 54a and 54b. In this way, it is ensured that, when the brake system is in normal operating mode, brake pressure is built up in the wheel brake cylinders 32 and 36 solely by means of the plunger 44, while in the fallback mode... The master brake cylinder 10 can be used to build up the desired high brake pressure in the wheel brake cylinders 32 and 36. Normally open valves 52a and 52b can be used as isolating valves, and normally closed valves 54a and 54b can be used as isolating valves. This ensures that the brake system can be automatically switched from normal operating mode to fallback mode in the event of a failure of the vehicle's electrical system.

The simulator valve 24 can be arranged in parallel with the isolating valve 54a of the first brake circuit 30. This allows a common bore to be used for the hydraulic connection of the simulator valve 24 and the first brake circuit 30. A cost-effective isolating valve can be used as the simulator valve 24. However, a continuously variable/adjustable valve can also be used as the simulator valve 24.

It is reiterated that a simulation can be realized using the simulator spring 18, which is only perceived by the driver as a force after braking into the first partial volume 12a of the first pressure chamber 12 with at least the initial adjustment travel x1. A jump-in range can thus be simulated using the simulator spring 18. Simultaneously, the floating piston 22 of the master brake cylinder can be opened by opening the simulator valve 24. 2 held in its starting position. In this case, the floating piston 22 remains in its starting position despite further adjustment of at least the first piston wall 14a. Additionally, the isolating valve 54b, through which the second brake circuit 34 is connected to the second pressure chamber 20, can also be closed.

The length of the jump-in range can be easily adjusted using the length of the initial adjustment travel x1. For example, the length of the initial adjustment travel x1 can be approximately one quarter of the master cylinder stroke, or one half of the stroke of the at least one adjustable piston 16.

In a fallback mode, for example after a failure of the vehicle's electrical system, the driver can also apply a comparatively small counterforce directly to the master brake cylinder 10, thereby generating pressure in the at least one connected wheel brake cylinder 32 and 36. Preferably, the simulator valve 24 is designed as a normally closed valve for this purpose. (In this case, the brake system does not require the operator device 25.) With a comparatively small braking force, the driver can then generate significant pressure in the at least one wheel brake cylinder 32 and 36, achieving rapid and powerful deceleration of the vehicle.

3 shows a flowchart to explain one embodiment of the method for operating a vehicle's braking system.

The method described below can be carried out, for example, with the brake system shown in the preceding figure. However, it should be noted that the feasibility of the method is not limited to the use of such a brake system. Instead, the method can be carried out with (almost) any brake system that has a master brake cylinder with at least one pressure chamber comprising at least a partial volume with a return spring and a simulator spring, wherein the partial volume is limited by a piston wall of at least one adjustable piston such that the partial volume is reduced by adjusting the piston wall from its initial position along a braking direction by a predetermined initial adjustment travel, deforming at least the return spring while the simulator spring remains in its initial shape, and by a further adjustment travel, deforming both the return spring and the simulator spring.

A process step S1 is executed in a normal operating mode of the brake system. In process step S1, a hydraulic connection between the partial volume and a brake fluid reservoir of the brake system is opened. This can also be described as short-circuiting the partial volume. If the master brake cylinder includes another pressure chamber, this can be blocked during process step S1.

Another process step, S2, takes place in a (mechanical) fallback level of the braking system. In process step S2, the hydraulic connection between the partial volume and the brake fluid reservoir is closed. This (mechanical) fallback level thus eliminates the short circuit of the partial volume, allowing it to be used to transfer brake fluid into a connected brake circuit. Simultaneously, brake fluid can be moved from the (possibly present) additional pressure chamber of the master cylinder into a connected additional brake circuit using the driver's braking force. Therefore, after process step S2 has been executed, the driver can immediately achieve braking effect using their own braking force (without having to brake in a simulator).

Process steps S1 and S2 also realize the advantages described above. However, a further description of these advantages is omitted here.

In process step S1, the hydraulic connection can be opened by controlling a simulator valve, through which the partial volume is hydraulically connected to the brake fluid reservoir, into a partially open state. Similarly, in process step S2, the hydraulic connection can be closed/sealed by controlling the simulator valve into a closed state.

Claims (13)

Master brake cylinder (10) for a brake system of a vehicle with: at least one first pressure chamber (12) comprising at least one first partial volume (12a) which is limited by a first piston wall (14a) of at least one adjustable piston (16) and in which at least one first return spring (13a) is arranged such that the first partial volume (12a) can be reduced by adjusting the first piston wall (14a) from its initial position along a braking direction (15) under a deformation of at least the first return spring (13a) and the first piston wall (14a) can be returned to its initial position by means of the first return spring (13a); characterized by a simulator spring (18) which, in addition to the first return spring (13a), is arranged in the first partial volume (12a) such that, during the adjustment of the first piston wall (14a) from its initial position along the braking direction (15) by a predetermined initial adjustment path (x1), the simulator spring (18) remains in its initial shape despite the deformation of the first return spring (13a), and by adjusting the first piston wall (14), which has already been adjusted by at least the initial adjustment path (s1), along the braking direction (15) by a further adjustment path (x2), the simulator spring (18) can be deformed from its initial shape. Master brake cylinder (10) after Claim 1 , wherein the simulator spring (18) arranged in the first partial volume (12a) has a maximum simulator spring length which is shorter by the initial adjustment travel (x1) than a maximum return spring length of the first return spring (13a) arranged in the first partial volume (12a). Master brake cylinder (10) after Claim 1 or 2 , wherein the first restoring spring (13a) has a spring constant up to its elastic limit which is smaller than a spring constant of the simulator spring (18) up to its elastic limit. Master brake cylinder (10) according to one of the preceding claims, wherein the master brake cylinder (10) has at least one rod piston (16) as the at least one adjustable piston (16). Master brake cylinder (10) after Claim 4 , wherein the master brake cylinder (10) has a stepped bore within which at least the first pressure chamber (12) is formed, and wherein the master brake cylinder (10) comprises a stepped piston (16) as the at least one rod piston (16) which, with the first piston wall (14a), defines the first partial volume (12a) and, with a second piston wall (14b), defines a second partial volume (12b) of the first pressure chamber (12), wherein the second partial volume (12b) can be reduced by adjusting the second piston wall (14b) along the braking direction (15). Master brake cylinder (10) after Claim 4 or 5 , wherein the master brake cylinder (10) comprises a second pressure chamber (20) and a floating piston (22) adjustable between the first pressure chamber (12) and the second pressure chamber (20), which is supported in its initial position by means of a second return spring (13b) arranged in the second pressure chamber (20). Master brake cylinder (10) according to one of the preceding claims, wherein the simulator spring (18) is attached to the floating piston (22), to an inner wall of the master brake cylinder (10) opposite the first piston wall (14a) or to the first piston wall (14a). Brake device for a vehicle brake system comprising: a master brake cylinder (20) according to one of the preceding claims; and a simulator valve (24) via which the first partial volume (12a) can be hydraulically connected to or is connected to an external or brake device-specific brake fluid reservoir (26). Brake device after Claim 8 , wherein the brake device includes operator electronics (25) designed to control the simulator valve (24) such that the simulator valve (24) is at least temporarily in a partially open state during a normal operating mode of the brake device and is in a closed state in a fallback level of the brake device. Braking system for a vehicle with: a master brake cylinder (10) after one of the Claims 1 until 7 ; a brake fluid reservoir (26); and a simulator valve (24) via which the first partial volume (12a) is hydraulically connected to the brake fluid reservoir (24). Brake system according to Claim 10 , wherein the braking system comprises operator electronics (25) which are designed, at least in one operating mode, to control the simulator valve (24) such that, during the adjustment of the first piston wall (14a) from its initial position along the braking direction (15) by the specified initial adjustment travel (x1), the simulator valve (24) is at least partially open, and during the adjustment of the first piston wall (14a), which has already been adjusted by at least the initial adjustment travel (x1), along the braking direction (15) by the further adjustment travel (x2), the simulator valve (24) is at least partially closed. Method for operating a vehicle braking system with a master brake cylinder (10) having at least one pressure chamber (12) comprising at least one partial volume (12a) with a return spring (13a) and a simulator spring (18), which is limited by a piston wall (14a) of at least one adjustable piston (16) such that the partial volume (12a) is reduced by adjusting the piston wall (14a) from its initial position along a braking direction (15) by a predetermined initial adjustment travel (x1) with deformation of at least the return spring (13a) while the simulator spring (18) remains in its initial shape, and by a further adjustment travel (x2) with deformation of the return spring (13a) and the simulator spring (18), comprising the steps: - Opening a hydraulic connection between the partial volume (12a) and a brake fluid reservoir (26) of the braking system in a normal operating mode of the braking system (S1); and - Closing the hydraulic connection between the partial volume (12a) and the brake fluid reservoir (26) in a fallback level of the brake system (S2). Procedure according to Claim 12 , wherein the hydraulic connection is controlled to be open by controlling a simulator valve (24), via which the partial volume (12a) is hydraulically connected to the brake fluid reservoir (26), into a state that is at least partially open, and the hydraulic connection is closed by controlling the simulator valve (24) into a closed state.