Braking system for a vehicle and method for operating the braking system

Abstract

Braking system (10) for a vehicle, comprising: - a master brake cylinder (30) with at least one pre-filling ring chamber (40) designed as a second independent volume, wherein the master brake cylinder (30) has at least two hydraulically effective surfaces (46, 47) that can be fluidically coupled to one another and act on a hydraulic fluid located in the master brake cylinder; - a hydraulic fluid reservoir (50) which is fluidically coupled to the master brake cylinder (30); and - at least one first and one second brake circuit, which are each fluidically coupled on the one hand to chambers (31, 32) of the master brake cylinder (30), and on the other hand are each fluidically coupled to brake torque-generating wheel brake cylinders, wherein the wheel brake cylinders are coupled to wheels of the vehicle, - furthermore comprehensively a pedal feel simulator (600) which can be operated over the entire brake pedal travel that can be actuated by the driver or sections thereof, - wherein the pedal feel simulator (600) is fluidically coupled on the input side via a fluid line (100) which is fluidically coupled to the first brake circuit and / or the second brake circuit, to a chamber (32) of the master brake cylinder (30), and the pedal feel simulator (600) is fluidically coupled on the output side via a fluid line (60) in which a normally closed valve (70) is arranged, to both the pre-filling ring chamber (40) and the hydraulic fluid reservoir (50).

Description

State of the art

[0001] WO 2009 / 121645 A1 describes a hydraulic vehicle braking system. The master brake cylinder of the hydraulic vehicle braking system comprises a first pressure chamber and a second pressure chamber. Additionally, the master brake cylinder has an integrated pedal travel simulator 22 at an end that widens towards the brake pedal. The volume of this simulator, which can be filled with brake fluid, is hydraulically connected to a brake fluid reservoir via a simulator valve. The brake fluid-fillable volume of the pedal travel simulator and the adjacent first pressure chamber are delimited by a rod and simulator piston designed as a stepped piston.

[0002] Furthermore, DE 10 2011 006 327 A1 discloses a brake system of the "brake-by-wire" type, comprising a master brake cylinder with two pistons slidably arranged therein, wherein one piston is designed as a stepped piston with at least two hydraulically actuated surfaces of different sizes, resulting in an annular volume that can be filled with hydraulic fluid or brake fluid due to the stepped piston shape. In "brake-by-wire" operating mode, when the master brake cylinder is actuated by the driver, the smaller actuated surface is effective for generating a braking torque at the vehicle wheels, and in a fallback scenario, i.e., if a malfunction occurs, the larger actuated surface is used, with the switch from the smaller actuated surface to the larger actuated surface depending on the hydraulic pressure in a pressure chamber in the master brake cylinder or the applied pedal force.

[0003] DE 10 2013 004 549 A1 also discloses an electro-hydraulic braking system comprising a master cylinder, two hydraulic circuits, a pump with motor, an accumulator, and various valves in a single unit. To generate a familiar pedal feel for the driver, a pedal simulator is also provided, connected to a reservoir via a simulation valve. This simulation valve is designed as a normally closed solenoid valve and opens only when activated, thus filling a simulation chamber with oil and providing realistic pedal feedback.

[0004] In externally driven braking systems, it is possible to design the fallback level independently of the hydraulic fluid volume to be pumped during operation by decoupling the pedal stroke and pedal force. Typically, the hydraulically effective area for such a fallback level is determined by the volumetric capacity of the braking system, taking into account certain operating conditions. Disclosure of the invention

[0005] The invention provides a braking system for a vehicle with the features of claim 1 and, in a dependent claim, a method for operating the braking system.

[0006] This braking system for a vehicle comprises a master brake cylinder with at least one pre-filling ring chamber designed as a second independent volume, wherein the master brake cylinder has at least two hydraulically effective surfaces that can be fluidically coupled to one another and are hydraulically effective on a hydraulic fluid located in the master brake cylinder; a hydraulic fluid reservoir which is fluidically coupled to the master brake cylinder;and at least one first and one second brake circuit, each of which is fluidically coupled to chambers of the master brake cylinder on the one hand, and each of which is fluidically coupled to brake torque-generating wheel brake cylinders on the other hand, wherein the wheel brake cylinders are coupled to wheels of the vehicle, further comprising a pedal feel simulator which can be operated over an entire brake pedal travel actuated by the driver or sections thereof, wherein the pedal feel simulator is fluidly coupled on the input side via a fluid line which is fluidically coupled to the first brake circuit and / or the second brake circuit, to a chamber of the master brake cylinder, and the pedal feel simulator is fluidly coupled on the output side via a fluid line in which a normally closed valve is arranged, to both the pre-filling ring chamber and the hydraulic fluid reservoir. Advantages of the invention

[0007] The invention provides for operating a braking system in such a way that, in the event of a partial or complete failure, for example, a failure and / or malfunction of the integrated braking system, the driver has direct access to two connectable hydraulically active surfaces. By cleverly coupling them, i.e., activating one of the surfaces until a certain pressure is reached, the effects of various operating conditions can be reduced, and it is thus possible to achieve higher pressures and therefore greater deceleration with a given force.

[0008] This measure significantly increases the deceleration achievable in a mechanical fallback position without adversely affecting the pedal travel through operating conditions. In contrast to previously known braking systems from the prior art, which also utilize the aforementioned operating principle, the present braking system is able to achieve the same functions with fewer switching valves. This advantageously reduces not only the effort required to control the switching valves but also the overall cost of the braking system.

[0009] Furthermore, the elimination of the switching valves previously used upstream of the pedal feel simulator in the present braking system offers the advantage of increased user comfort, as the use of a switching valve is generally associated with inertia in the hydraulic system due to its operation, as well as noise when actuated. Additionally, the elimination of the switching valves in the present braking system reduces its weight, thereby lowering the vehicle's fuel consumption.

[0010] According to the present invention, the pedal feel simulator is fluidically coupled to a chamber of the master brake cylinder via a fluid line, which is fluidically coupled to the first brake circuit and / or the second brake circuit. According to a further preferred embodiment of the present brake system, the pedal feel simulator is directly fluidically coupled to a chamber of the master brake cylinder via a fluid line, which is fluidically coupled to the first brake circuit and / or the second brake circuit. Here, direct fluidic coupling is understood to mean a fluidic connection between two components in which no other components influence the fluidic connection. In other words, no other components should be arranged or acting between the directly fluidically coupled components.

[0011] Furthermore, according to the present invention, the master brake cylinder can be provided with at least one first pressure chamber, which can be subdivided into a first volume and a second volume, wherein the first volume is limited by a first piston wall of a rod piston in such a way that the volume can be varied by moving the first piston wall, and the second volume is limited by a second piston wall of the rod piston in such a way that the second volume can be varied by moving the second piston wall, wherein the first volume and the second volume are fluidically coupled to a hydraulic fluid reservoir, and a first brake circuit is fluidically coupled to the first volume via a first fluid line.

[0012] According to a further embodiment of the present brake system, the normally closed valve can implement the functionality of several valves in a single component. In this respect, with regard to a known brake system from the prior art, the previously arranged, in particular on the input side of the pedal feel simulator, is to be replaced in the present brake system. Fig. 1 normally closed solenoid valve 35, and that according to Fig. The valve 610, also known as a simulator separating valve, is now combined into a single normally closed valve, thereby achieving the advantages described above for the present brake system. In addition, the present brake system offers advantages over the known configuration of a prior art brake system, such as that described in [reference to relevant document]. Fig. 1 discusses saving the check valve 210, which is fluidically coupled to the pedal feel simulator on the input side.

[0013] According to a further embodiment of the present brake system, a check valve can also be provided, which is fluidically coupled at one end to the fluid line of the pedal feel simulator via a fluid line, and at the other end to the pre-filling ring chamber. Due to the additional volume provided by the pre-filling ring chamber, the check valve advantageously improves the braking performance from a depressurized brake state by more quickly overcoming a so-called dead volume in the respective connected brake circuit.

[0014] According to a further embodiment, the present brake system includes a controllable check valve which is fluidically coupled to the normally closed valve via a fluid line downstream of the normally closed valve. The flow into the respective brake circuits of the brake system and the return flow into the hydraulic fluid reservoir are controlled by the closing pressures of the controllable check valve. The controllable check valve defines the maximum permissible pressure in the annular piston volume 40, i.e., it thus serves as a pressure limiter.

[0015] According to a further embodiment of the present brake system, the pedal feel simulator can be fluidically coupled to one of the chambers of the master brake cylinder at its output side, the master brake cylinder having a corresponding vent bore for this purpose. This advantageously improves the design of the present brake system compared to the prior art, since a previously used so-called 'jump-in valve', which is used to represent the characteristic curve in the area of ​​the pedal feel simulator's entry point, can now be implemented using the master brake cylinder. Brief description of the drawings

[0016] The present invention is explained with reference to the accompanying drawings. These show Fig. 1: a schematic hydraulic circuit diagram of a brake system according to the state of the art, Fig. 2: a schematic hydraulic circuit diagram of a brake system according to a first embodiment of the invention, and Fig. 3: a schematic hydraulic circuit diagram of a brake system according to a second embodiment of the invention. Embodiments of the invention

[0017] Before describing embodiments of the invention, the basic configuration of a brake system with an annular piston chamber in the master brake cylinder, which is applicable in principle to all embodiments of the present brake system, will first be explained. Then, with reference to the Fig. 2 and Fig. 3. The specification of the individual embodiments will be described in addition to or in modification of this basic configuration.

[0018] Fig. Figure 1 shows a schematic representation of a hydraulic circuit diagram of a brake system 10 according to the prior art, wherein essential components for the operation of the brake system 10 are housed in a unit marked with reference numeral 11 and provided with a dash-dotted border.

[0019] The aforementioned approach with a stepped piston 45 forming a ring volume, the operation of which is described in more detail below, shifts additional brake fluid volume into the first brake circuit 100 when the pressure in the ring volume piston chamber is limited and low, and the first brake circuit is designated with reference numeral 100. This additional quantity increases the brake pressure achievable in the first brake circuit 100 during full braking in the mechanical fallback system, and thus the maximum possible vehicle deceleration.

[0020] Furthermore, this effect compensates for any air bubbles that may be present in the first brake circuit, which allows for a higher maximum brake pressure in the fallback level, and thus a relatively shorter stopping distance of the vehicle.

[0021] The additional volume also improves braking performance from a depressurized brake state by more quickly overcoming a so-called dead volume in the first brake circuit 100. This well-known principle corresponds to that in Fig. 1 hydraulic path or fluid line marked with reference numeral 15 with check valve 20. All of these advantages mentioned above can also be realized with the present brake system.

[0022] According to Fig. 1. A primary chamber or pre-filling ring chamber 40 is positioned upstream of the two pressure chambers 31, 32 of a conventional master brake cylinder 30. The volume of this primary chamber can be varied by the stepped piston 45 with one of the two hydraulically effective surfaces 46 and 47, as will be explained further below. A brake input element 48 is coupled to the stepped piston 45 in a known manner and is pivotable about a point 49.

[0023] In normal operation (i.e., by-wire), the pre-filling ring chamber 40 is short-circuited to a brake fluid (hydraulic fluid) reservoir 50 by controlling a (normally closed) solenoid valve 35.

[0024] The timing of this activation can be delayed if rapid braking is detected (for example, during emergency braking) to improve pressure build-up dynamics in this operating condition. In the 'mechanical fallback' mode, solenoid valve 35 remains closed (as it is usually not energized).

[0025] The flow into brake circuits 100 and 200 and the return flow into reservoir 50 are controlled by the closing pressures of check valves 210, 110, and 55. Check valve 55 defines the maximum permissible pressure in the annular piston volume 40 (pressure limit), while check valves 210 and 110 in brake circuits 100 and 200 define a minimum pressure differential between brake circuits 100 and 200 and the annular piston volume or the pre-filling ring chamber 40, respectively.

[0026] If the pressure in the annular piston volume 40 exceeds this pressure threshold, brake fluid flows from the annular piston area 40 into the brake circuits 100 and 200. This condition persists until either the pressure threshold is undercut by an increase in the brake circuit pressures or until the maximum pressure in the pre-filling ring chamber 40, specified by the check valve 55, is exceeded. By implementing a parallel hydraulic path 115, this effect is also utilized in brake circuit 200.

[0027] For the sake of completeness, it should be mentioned at this point that switching valves 105, 205 are arranged in the fluid lines 100, 200 (normally open) in a known manner, which allow a direct connection (i.e. a supply with hydraulic fluid) to a wheel modulation 300.

[0028] In Fig. 1 is an arrangement generally known as wheel modulation, designated by reference numeral 300, wherein the wheel modulation 300 comprises vehicle wheels (not shown separately here), wheel brake cylinders assigned to them, and inlet and outlet valves, the functions of which are known to those skilled in the art and are therefore not to be explained here for the sake of brevity.

[0029] Furthermore, in Fig. 1 with reference numeral 400 is an actuator which, in the configuration shown, is in Fig. 1. The actuator 400 is to be electro-hydraulically operable, for example, via an electric motor marked "M". The actuator 400 is supplied with hydraulic fluid from reservoir 50 via a fluid line 425. The electric motor M can be controlled such that it can move a piston 405 back and forth in a housing via a forward or reverse drive 415 in order to compress, i.e., pressurize, hydraulic fluid located in a volume 410, in order to transfer hydraulic fluid via fluid lines 430, 440 to feed connections 450, 460 into the wheel modulation 300 (for example, as an ESP function), independently of any actuation of the master brake cylinder 30.As is known, switching valves 470 and 480 are arranged in the fluid lines 430 and 440, respectively, with filter devices 475 and 485 upstream (i.e., viewed from the actuator 400), as are other locations in the brake system 10, which will not be discussed in detail here, as this is assumed to be common knowledge. For the sake of completeness, it should also be mentioned that pressure sensors are arranged at various locations in the brake system 10, the function of which should also be known to those skilled in the art. The one in [reference to relevant section] serves as an example. Fig. 1 pressure sensor marked with reference number 500 at the end of fluid line 440 is listed.

[0030] Furthermore, a pedal feel simulator device 600 is described, comprising a pressure accumulator 605, a switching valve 610, and a bypass fluid line 615 with a check valve 210. A switching valve 620 is arranged in parallel. However, it should be emphasized that the pedal feel simulator device 600 is already known to those skilled in the art.

[0031] Fig. Figure 2 shows a schematic hydraulic circuit diagram of a brake system 10 according to a first embodiment of the invention.

[0032] The Fig. 2 and Fig. Figure 3 each shows a detailed view of a part of the braking system 10. Fig. 1, namely the part which shows the master brake cylinder 30 in conjunction with the pedal feel simulator 600.

[0033] Fig. Figure 2 shows a cross-sectional view of the master brake cylinder 30 (a so-called 'parallel plunger') as well as the rod piston 45 with the hydraulically effective and coupling surfaces 46 and 47, the pre-filling ring chamber 40, the pressure chambers 31, 32, a floating piston 33 which separates the pressure chambers 31 and 32 from each other, and the hydraulic fluid reservoir 50.

[0034] Furthermore, fluid lines 100, 200 of the first and second brake circuits with the corresponding valves 105, 205 are provided, wherein the fluid lines 100, 200 run 'downwards' (relative to the drawing) to the wheel modulation (not shown here) and are coupled to it.

[0035] The hydraulic fluid reservoir 50 is fluidically coupled to the pressure chambers 31, 32, 40 of the master brake cylinder 30 via vent holes 34a, 34b, 34c. Furthermore, the vent holes 34a, 34b, 34c are equipped with corresponding seals 41, 42, 43, which seal the master brake cylinder 30 against the environment.

[0036] In the event of a malfunction of the brake system 10, the driver still has the option of moving the rod piston 45 to the left in the drawing by applying a force indicated by arrow 900, i.e., by pressing the brake pedal (not shown here). This builds up pressure in the pressure chambers 31, 32, which is then transmitted directly via the fluid lines 100, 200 to the wheel modulation (not shown here) to generate braking torque at the wheels. This is possible because the pressure building up in the pre-filling ring chamber 40 by the hydraulically effective surface 46, which would make effective braking very difficult and against which the driver would have to exert a correspondingly large force, is reduced by (opening) the valve 55, so that the driver ultimately 'brakes' using the hydraulically effective surface 47. Therefore, the hydraulically effective surfaces 46, 47 are functionally coupled to each other.

[0037] The pedal feel simulator 600 of the brake system 10, which can be operated over the entire brake pedal travel that can be actuated by the driver or sections thereof, is fluidically coupled on the input side via a fluid line 100, which is fluidically coupled to the first brake circuit and / or the second brake circuit, to the pressure chamber 32 of the master brake cylinder 30, and the pedal feel simulator 600 is fluidically coupled on the output side via a fluid line 60 in which a normally closed valve 70 is arranged, to both the pre-filling ring chamber 40 and the hydraulic fluid reservoir 50.

[0038] Furthermore, the brake system 10 includes a check valve 20, which is fluidically coupled at one end via a fluid line 15 to the fluid line 60 of the pedal feel simulator 600, and at the other end to the pre-filling ring chamber 40. The brake system 10 also includes an adjustable check valve 55, which is fluidically coupled via a fluid line 71 downstream of the normally closed valve 70 to the normally closed valve 70.

[0039] Fig. Figure 3 shows a schematic hydraulic circuit diagram of a brake system 10 according to a second embodiment of the invention.

[0040] Since the basic structure of the brake system 10 is similar to that of the first embodiment of Fig. In the following, only the difference between version 2 and the first embodiment will be explained.

[0041] Here, the pedal feel simulator 600 is fluidically coupled at its output side to one of the pressure chambers 32 of the master brake cylinder 30, the master brake cylinder 30 having a corresponding sniffing bore 81 for this purpose. The sniffing bore 81 is fluidically coupled via a fluid line 82 to the fluid line 15 downstream of the check valve 20. The sniffing bore 81 has a corresponding lip seal 84 in the master brake cylinder 30, which, when the rod piston 45 is positioned in the area of ​​the sniffing bore 81, enables a so-called "engagement" behavior to be demonstrated without the pedal feel simulator 600.

Claims

[1] Braking system (10) for a vehicle, comprising: - a master brake cylinder (30) with at least one pre-filling ring chamber (40) designed as a second independent volume, wherein the master brake cylinder (30) has at least two hydraulically effective surfaces (46, 47) that can be fluidically coupled to one another and act on a hydraulic fluid located in the master brake cylinder; - a hydraulic fluid reservoir (50) which is fluidically coupled to the master brake cylinder (30); and - at least one first and one second brake circuit, which are each fluidically coupled on the one hand to chambers (31, 32) of the master brake cylinder (30), and on the other hand are each fluidically coupled to brake torque-generating wheel brake cylinders, wherein the wheel brake cylinders are coupled to wheels of the vehicle, - furthermore, a comprehensive pedal feel simulator (600) which can be operated over the entire brake pedal travel that can be actuated by the driver or sections thereof, - wherein the pedal feel simulator (600) is fluidically coupled on the input side via a fluid line (100) which is fluidically coupled to the first brake circuit and / or the second brake circuit, to a chamber (32) of the master brake cylinder (30), and the pedal feel simulator (600) is fluidically coupled on the output side via a fluid line (60) in which a normally closed valve (70) is arranged, to both the pre-filling ring chamber (40) and the hydraulic fluid reservoir (50). [2] Braking system (10) according to claim 1, characterized by , that the normally closed valve (70) realizes the functionality of several valves in a single component. [3] Braking system (10) according to claim 1 or 2, characterized by, that furthermore a check valve (20) is provided which is fluidically coupled at one end to the fluid line (60) of the pedal feel simulator (600) via a fluid line (15), and is fluidically coupled at the other end to the pre-filling ring chamber (40). [4] Braking system (10) according to one of claims 1 to 3, characterized by , that normally open switching valves (105, 205) are arranged in the first brake circuit and in the second brake circuit, wherein the pedal feel simulator (600) is fluidically coupled upstream of the first normally open switching valve (105) of the first brake circuit to the first normally open switching valve (105) of the first brake circuit. [5] Brake system (10) according to one of claims 1 to 4, further comprising a controllable check valve (55) which is fluidically coupled to the normally closed valve (70) via a fluid line (71) downstream of the normally closed valve (70). [6] Braking system (10) according to claim 5, characterized by , that the fluid line (71) for the controllable check valve (55) is designed as a by-pass fluid line, wherein the controllable check valve (55) is fluidically coupled at one end to the fluid line (60) of the pedal feel simulator (600) and is fluidically coupled at the other end to the pre-filling ring chamber (40). [7] Braking system (10) according to any of the preceding claims, characterized by , that the pedal feel simulator (600) is fluidically coupled at its output side to one of the chambers (32) of the master brake cylinder (30), the master brake cylinder (30) having an associated sniffing bore (81) for this purpose. [8] Braking system (10) according to any of the preceding claims, characterized by , that the brake system (10) is designed such that hydraulic fluid can be supplied to only one of the brake circuits. [9] Braking system (10) according to any of the preceding claims, characterized by , that the master brake cylinder (30) has at least two hydraulically effective surfaces (46, 47) and / or at least three pressure chambers (31, 32, 40) that can be filled with hydraulic fluid, which are fluidically separated from each other by a floating piston (33) and a rod piston (45), wherein the rod piston (45) is designed as a stepped piston which can be coupled to a brake input element (48) that can be actuated by the driver. [10] Method for operating a braking system (10) according to claims 1 to 9, wherein in the event of a malfunction of the braking system (10) the brake input element (48) is actuated by the driver, and the normally closed valve (70) is opened, so that hydraulic fluid flows into the hydraulic fluid reservoir (50), so that braking in a fallback level is possible.

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