Brake system, automobile, and method for operating brake system

Abstract

To provide a concept of operating an electric hydraulic brake system.SOLUTION: In particular, it is proposed to switch from such a braking mode for each of the identical axles as supplying an axle, to which higher pressure is added, with hydraulic pressure by an actuator having a lower pressure construction inclination to such a further braking mode as supplying the axle, to which higher pressure is added, with hydraulic pressure by an actuator having a higher pressure construction inclination, in a brake system.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a braking system, in particular a braking system for a motor vehicle. The present invention further relates to a motor vehicle equipped with such a braking system. The present invention further relates to a method for operating a braking system. [Background technology]

[0002] background Brake systems for motor vehicles can be realized, for example, as electrohydraulic brake systems, where so-called brake-by-wire systems are also increasingly used, as described, for example, in U.S. Patent Application Publication No. 2015 / 0021978.

[0003] In an electrohydraulic braking system, an actuator piston can operate a master brake cylinder to generate hydraulic pressure that can act on wheel brake cylinders located on the wheels of the vehicle to brake the vehicle.

[0004] Furthermore, the brake circuit may include additional components, such as an Electronic Stabilization Program (ESP), which may include, in addition to a number of valves, an electrically driven pump, which may also provide a volumetric flow for operating the brake cylinders.

[0005] This may allow, for example, individual axle braking to be achieved, with a primary actuator, for example in the form of an electrically operated master brake cylinder, providing a first brake pressure for the axle to which a lower pressure is applied, and a pump within the ESP system providing a higher pressure to drive the brake cylinders of further axles to which a higher pressure is applied.

[0006] DE 10 2017 205 209 A1 describes a method for compensating for excessively low actuator dynamics of mechanical brakes in motor vehicles.

[0007] DE 10 2019 200 820 A1 discloses a method for distributing the braking torque requested by the driver to the front and rear axles of a motor vehicle.

[0008] WO2020224814 shows a braking system and a method for controlling the braking system.

[0009] DE 102020110013 A1 discloses a method for operating a braking system of a vehicle. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] US Patent Application Publication No. 2015 / 0021978 [Patent Document 2] German Patent Application Publication No. 102017205209 [Patent Document 3] German Patent Application Publication No. 102019200820 [Patent Document 4] International Publication No. 2020224814 [Patent Document 5] German Patent Application Publication No. 102020110013 Summary of the Invention [Means for solving the problem]

[0011] Disclosure of the Invention The present invention provides a brake system for a motor vehicle, a motor vehicle and a method for operating the brake system with the features set forth in the independent claims. Further advantageous embodiments are the subject of the dependent claims.

[0012] Therefore, the following is envisaged:

[0013] Specifically, a brake system for a vehicle is envisioned, the brake system including a first actuator and a second actuator. The first actuator is configured to provide a first hydraulic brake pressure. The first hydraulic brake pressure may be provided by the first actuator having a first maximum pressure gradient. The second actuator is disposed downstream of the first actuator. In this case, the second actuator is configured to provide a second hydraulic brake pressure. The second hydraulic brake pressure may be provided by the second actuator having a second maximum pressure gradient, the first maximum pressure gradient being greater than the second maximum pressure gradient. For example, the first actuator may be an electromechanically operated master brake cylinder of a brake mechanism. The second actuator may be a hydraulic pump, such as a hydraulic pump of an ESP system. The brake system is configured such that, in a first operating mode, hydraulic brake pressure for a higher pressure primary axle of the vehicle is provided by the second actuator. The brake system is further configured such that in the first operating mode, hydraulic brake pressure for a lower pressure applied secondary axle of the vehicle is provided by the first actuator, and in the second operating mode, hydraulic brake pressure for a higher pressure applied primary axle of the vehicle is provided by the first actuator, and hydraulic brake pressure for a lower pressure applied secondary axle of the vehicle is provided by the second actuator, In particular, the brake system is configured to switch from the first operating mode to the second operating mode when a predetermined switching condition is met.

[0014] In addition, the following is envisaged:

[0015] The present invention relates to a vehicle equipped with a brake system according to the present invention, which may in particular be an at least partially electrically driven vehicle, in which case, in addition to deceleration by means of the hydraulic brake system, the desired deceleration can also, if necessary, be achieved at least partially by regeneration.

[0016] Finally, the following is envisaged:

[0017] Specifically, a method is contemplated for operating a brake system including a first actuator and a second actuator, wherein the first actuator of the brake system is configured to provide a first hydraulic brake pressure. The first hydraulic brake pressure may be provided at a first maximum pressure gradient. The second actuator is disposed downstream of the first actuator and is configured to provide a second hydraulic brake pressure. The second hydraulic brake pressure may be provided at a second maximum pressure gradient, the first maximum pressure gradient being greater than the second maximum pressure gradient. The method includes a first mode of operation, wherein hydraulic brake pressure for a higher pressure applied primary axle of the vehicle is provided by the second actuator and hydraulic brake pressure for a lower pressure applied secondary axle of the vehicle is provided by the first actuator. The method further includes a second mode of operation in which hydraulic brake pressure for a higher pressure applied primary axle of the vehicle is provided by the first actuator and hydraulic brake pressure for a lower pressure applied secondary axle of the vehicle is provided by the second actuator. The method further includes detecting a predetermined switch condition and switching from the first mode of operation to the second mode of operation when the predetermined switch condition is detected.

[0018] In hydraulic braking systems, part of the required deceleration can be achieved by braking the front axle, and another part by braking the rear axle. Furthermore, in vehicles that are at least partially electrically driven, a further part of the desired deceleration can possibly be achieved by recuperation using the electric drive system. On the one hand, in this case, for example, the brake pressure for the primary axle to which higher pressure is applied can be provided by a first actuator, such as an electromechanically operated plunger of the master brake cylinder, which allows pressure build-up in a very large pressure gradient. Alternatively, braking of each axle is also possible, with this first actuator having a larger pressure build-up gradient providing the brake pressure for the axle to which lower pressure is applied, and additionally, a second actuator, such as a pump operated by the ESP motor, providing the brake pressure for the axle to which higher pressure is applied.

[0019] The invention is based on the recognition that in this case the secondary actuator, for example the ESP pump, is limited by additional considerations such as the maximum pump speed for trouble-free operation, particularly in terms of noise.

[0020] The idea of ​​the present invention is therefore to take this knowledge into account and provide a switching of operating modes, which allows a reliable operation of the brake system to achieve particularly large pressure build-up gradients, while maintaining basic conditions such as, for example, noise-free operation of the ESP pump.

[0021] For this purpose, it is envisaged that the assignment of the first and second actuators to the respective axles can be adjusted in a suitable manner. In particular, for example, for a quick pressure buildup, the first actuator with a larger pressure buildup gradient can be assigned to the axle to which higher pressure is applied, if this assignment has not been performed beforehand during braking of each individual axle. In this way, operation of the ESP pump in a speed range that is unfavorable in terms of noise generation can be avoided.

[0022] According to one embodiment, the predetermined switching condition comprises a brake force request with a target pressure gradient greater than a given maximum pressure gradient of the second actuator, which in this case can correspond to a pressure gradient that can be provided by the second actuator while maintaining trouble-free operation, in particular in terms of noise. If the brake force request and the target pressure gradient, in particular related to the brake force request, exceed this value, a switchover to a second operating mode can be performed, in which the first actuator can provide brake pressure for the axle to which more pressure is applied, with a greater maximum pressure gradient.

[0023] According to one embodiment, the maximum pressure gradient of the second actuator can be determined using a given maximum rotational speed of the pump in the second actuator. This maximum rotational speed of the pump can be, in particular, the rotational speed up to which the pump operates without any noise problems. Additionally or alternatively, for example, to determine the maximum pressure gradient for the second actuator, the capacity of the brake for the primary axle can also be taken into account. This capacity can be determined in advance, for example, by a suitable method.

[0024] According to one embodiment, the brake system is further configured to reduce or prevent a pressure drop in the brake pressure for the secondary axle before switching to the second operating mode, thereby assisting in preparation for the transition from the first operating mode to the second operating mode.

[0025] According to one embodiment, the predetermined switching condition for the transition from the first operating mode to the second operating mode comprises detecting that the brake pressure for the secondary axle is at most a given threshold value. The threshold value may in particular be zero bar or at least approximately zero bar. Once the brake pressure on the secondary axle has been reduced almost completely, further reduction is technically impossible. Accordingly, under this operating condition, switching from the first operating mode to the second operating mode is very easy.

[0026] According to one embodiment, the switch from the first operating mode to the second operating mode is further performed depending on the available regenerative capacity of the vehicle. For example, the switch may be performed, in particular, when the maximum regenerative capacity of the electric drive system has been exhausted. Similarly, the absorption of electrical energy during regeneration may be limited or even impossible due to, for example, the state of charge of an electrical energy storage device for the electric drive system or other operating conditions of the electrical energy storage device. Accordingly, even under these basic conditions, the demands on the hydraulic brake system increase, which may require a switch in operating mode. Furthermore, for example, a decrease in driving speed may also reduce the regenerative braking performance and thus require more powerful braking by the hydraulic brake system, which may also require a switch in operating mode. Furthermore, further vehicle dynamics parameters may also be taken into account when switching between operating modes.

[0027] The first actuator may be, for example, a plunger, in particular a plunger of a brake-by-wire braking system or a decoupled electronic braking system, and the second actuator may be, for example, a hydraulic pump, in particular a hydraulic pump of an ESP system.

[0028] The above-described embodiments and developments can be combined with each other in any way that makes sense. Further embodiments, developments and implementations of the invention also include not-explicitly mentioned combinations of the features of the invention that are explained above or below with reference to the examples. In particular, a person skilled in the art will add individual aspects to the respective basic form of the invention as improvements or supplements.

[0029] Further features and advantages of the invention will be explained below with reference to the drawings. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a schematic diagram of a principle diagram of a brake system according to an embodiment; [Figure 2] FIG. 2 is a schematic diagram illustrating switching of an operation mode in a brake system according to an embodiment. [Figure 3] 10 is a schematic diagram illustrating further switching of operating modes in a brake system according to an embodiment. FIG. [Figure 4] 1 is a flowchart underlying a method for operating a braking system in one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0031] Description of the embodiment FIG. 1 shows a schematic diagram of a brake system 1 for a motor vehicle according to one embodiment. The brake system 1 is, in particular, an electrohydraulic brake system. In this case, hydraulic brake pressure is generated by both actuators 10 and 20, possibly adjusted for each axle or wheel. In this way, a desired braking effect can be set at brakes 41, 42, 51, 52 provided on axles 40, 50 of the vehicle. In particular, the brake system 1 can be a so-called brake-by-wire brake system or a brake system with decoupled power actuators (DPB). In this case, a request for deceleration can be output from an input device, for example, an electronic brake pedal, or from a control device, such as a driver assistance system. In response to this request, a brake pressure can be generated by the first actuator 10 and / or the second actuator 20, possibly set for each wheel, to achieve the desired braking effect. In some cases, for example in the case of a fully or at least partly electrically driven vehicle, the required braking effect can also be at least partly realized by regeneration using the electric drive system, in which case the required braking performance can in particular be divided between a regenerative share and a hydraulic brake system 1 share.

[0032] The first actuator 10 may be, for example, an electromechanically operated master brake cylinder. In this case, an electric actuator can be used to operate a so-called plunger in order to provide the desired hydraulic brake pressure. However, the embodiment shown here with two separate hydraulic circuits is not limiting of the invention. In principle, brake systems with a different number of brake circuits are also possible. Such an electrohydraulic actuator 10 can provide the required brake pressure with a very large pressure gradient. In other words, pressure build-up can be achieved within a very short period of time.

[0033] The brake system 1 further includes a second actuator 20. This second actuator 20 can include, for example, a hydraulic pump of an ESP system. The second actuator 20 can further include further components, in particular further valves (not shown). These valves (or other suitable components) allow the brake pressure at the individual brakes 41, 42, 51, 52 to be adjusted individually for each wheel, if necessary. It is also possible, for example, to apply hydraulic brake pressure provided by the first actuator 10 to the brakes 41, 42 or 51, 52 of one axle 40 or 50, while adjusting, in particular boosting, the brake pressure at the other axle 40, 50, respectively, by the second actuator 20. In this way, braking of the individual axles of the vehicle can be achieved. In particular, the brake pressure for each axle 40, 50 can be set differently. In this case, the braking pressure of the axles 40, 50 supplied directly by the first actuator 10 is limited to the braking pressure of the first actuator 10, while the braking pressure can be additionally increased by the second actuator 20 at the respective other axle.

[0034] In this configuration, to increase the braking action, additional brake pressure must be generated by the hydraulic pump of the second actuator 20. The volumetric flow rate that can be provided by such a pump is determined by the product of the pump speed, the pump's discharge capacity per revolution, and the pump's efficiency. In addition to other basic conditions, noise generation increases as the speed of the hydraulic pump in the second actuator 20 increases. Therefore, for example, a maximum speed can be defined for the hydraulic pump of the second actuator 20, which should not be exceeded in order to avoid or at least limit noise disturbances, particularly for vehicle occupants. This maximum pump speed thus determines the maximum achievable volumetric flow rate that can be provided by the hydraulic pump of the second actuator 20. Furthermore, if the storage volume for hydraulic fluid in the brakes 41, 42 or 51, 52 of the respective axles 40, 50 is also known, the maximum achievable brake pressure gradient can be determined from this. The brake pressure gradient that can be achieved by the hydraulic pump of the second actuator 20 is in this case essentially smaller than the brake pressure gradient that can be achieved by the first actuator 10. Therefore, during individual axle braking (first operating mode), the axle 40 or 50 to which a lower brake pressure is applied can be supplied with brake pressure by the first actuator 10, while the axle 40, 50 to which a desired higher brake pressure is applied is supplied with brake pressure by the second actuator 20. Therefore, due to the above-mentioned limitations, if additional braking torque is required at the axle 40, 50 to which a higher pressure is applied, only the relatively small brake pressure gradient of the second actuator 20 can increase the brake pressure. However, if a pressure build-up is to be performed with a larger brake pressure gradient, it is necessary to first switch to the second operating mode, i.e., to the second operating mode in which the brake pressure for the axle 40, 50 to which a higher pressure is applied can be supplied by the first actuator 10.Such a switchover from the first to the second operating mode of braking for each axle may be performed, for example, when a corresponding switchover condition is fulfilled, such as a brake pressure demand with a large pressure buildup gradient, in particular a pressure buildup gradient that is larger than the maximum pressure buildup gradient of the second actuator 20.

[0035] When switching from the first operating mode to the second operating mode in this way, the axles 40, 50 to which higher pressure is applied, i.e. the axles to which higher braking pressure should be applied, are assigned to the first actuator 10. This allows the build-up of braking pressure at the axles to which higher pressure is applied to be achieved with a greater pressure build-up gradient at the first actuator 10. Before switching the assignment, a possible pressure drop at the axles to which lower pressure is applied can be slowed down or prevented as the case may be, in order to take preparatory measures for the transition.

[0036] FIG. 2 shows a schematic diagram illustrating the switching from the first operating mode to the second operating mode of the brake system 1 according to one embodiment. Curve 100 represents the required brake pressure in this case. Curve 210 represents the pressure at the axle 40 or 50 to which higher pressure is applied, and curve 220 represents the pressure at the axle 40, 50 to which lower pressure is applied. Finally, curve 300 represents the target pressure of the first actuator 10. In phase A, the brake pressure for both axles 40, 50 is uniformly provided by the first actuator 10. Subsequently, in phase B, the brake pressure at the axle to which lower pressure is applied is reduced. In this phase, for example, part of the braking effort can be achieved by regeneration in the vehicle's electric drive system. The target brake pressure of the primary actuator 10 is also reduced accordingly. The brake pressure at the axle to which higher pressure is applied is maintained by the second actuator 20. In phase C, the transition of braking for each individual axle from the first operating mode to the above-mentioned second operating mode can be prepared. In this case, for example, the pressure drop on the axles to which lower pressure is applied can be slowed down or completely prevented. Finally, in phase D, the switchover to the second operating mode is carried out. In this case, the brake pressure for the axles to which higher pressure is applied is provided by the primary actuator 10. The adjustment of the brake pressure on the axles to which lower pressure is applied is then carried out, for example, by components in the second actuator 20. After the transition to the second operating mode is completed, in phase E, the pressure build-up on the axles to which higher pressure is applied can be carried out using a larger pressure build-up gradient of the first actuator 10.

[0037] In addition to switching from the first operating mode to the second operating mode when a (anticipated) demand for brake pressure with a large pressure build-up gradient occurs, further possible switching conditions are also possible. For example, switching from the first operating mode to the second operating mode can be performed when the brake pressure at the axle to which lower pressure is applied has completely or at least almost completely dropped. This may be the case, for example, when the braking performance at this axle is completely taken over by regeneration. In such a case, further reduction of the brake pressure is technically impossible. Such a process is exemplarily shown in FIG. 3. The same reference numerals as those already used in FIG. 2 apply here.

[0038] As exemplarily shown in Figure 3, the switch from the first to the second operating mode during phase D may possibly be performed more slowly than in the above-described example of Figure 2. During the switch to phase D, in particular, the brake pressure at the axles to which less pressure is applied may be maintained or increased as needed, possibly by appropriate control of valves in the second actuator 20. After the transition is complete, the first actuator 10 is again assigned to the axles 40, 50 to which more pressure is applied, in phase E.

[0039] In addition to the above-mentioned switching conditions of a brake pressure demand with a large pressure build-up gradient and of a brake pressure at the axle to which lower pressure is applied being zero or at least approximately zero bar, further criteria for a possible switchover can also be considered. In this regard, in particular, the regenerative capacity of a fully or at least partially electrically driven vehicle can also be taken into account. For example, the switchover can be initiated when the vehicle's maximum regenerative capacity has been completely or at least almost completely used up. For example, the switchover can also be performed in preparation for braking the vehicle to a complete standstill, since at low speeds no regenerative braking force or only very little regenerative braking force can be used. Furthermore, it is also possible to take into account possible regeneration levels, which can depend, for example, on the state of charge or operating state of an electrical energy storage device in the electric vehicle. Furthermore, the switchover can be performed even if, for example, relevant effects that could oppose such a switchover on driving dynamics are not currently anticipated.

[0040] 4 shows a flowchart underlying a method for operating a brake system 1 according to an embodiment. The brake system 1 may in particular be one of the brake systems 1 described above. Correspondingly, the method described below may include any method steps that may be suitable for realizing the functionality of the brake system 1 described above. Likewise, the brake system 1 described above may also include any components that may be suitable for realizing the method described below.

[0041] The method includes a first mode of operation M1 in which hydraulic brake pressure for the vehicle's higher pressure applied primary axles 40, 50 is provided by the second actuator 20 and hydraulic brake pressure for the vehicle's lower pressure applied secondary axles 40, 50 is provided by the first actuator 10. In a second mode of operation M2, hydraulic brake pressure for the vehicle's higher pressure applied primary axles 40, 50 can be provided by the first actuator 10 and hydraulic brake pressure for the vehicle's lower pressure applied secondary axles 40, 50 can be provided by the second actuator 20.

[0042] In step S1, a predetermined switching condition can be detected. Such a switching condition can be, for example, an (anticipated) demand for braking pressure with a large braking pressure gradient. In particular, the braking pressure gradient can be larger than a given maximum pressure build-up gradient of the second actuator 20. Furthermore, the switching condition can also include, for example, the detection of an at least almost complete drop in braking pressure at the secondary axle 40, 50 to which lower pressure is applied. If such a switching condition is detected, a switch from the first operating mode M1 to the second operating mode M2 ​​can be performed in step S2.

[0043] In summary, the present invention relates to a concept for operating an electrohydraulic braking system, in particular it is proposed to switch the braking system from an individual axle braking mode, in which the axles to which higher pressure is applied are powered by actuators with a smaller pressure build-up gradient, to a further operating mode, in which the axles to which higher pressure is applied are powered by actuators with a larger pressure build-up gradient.

Claims

1. A braking system (1) for a motor vehicle, comprising: The brake system (1) a first actuator (10) configured to provide a first hydraulic brake pressure at a first maximum pressure gradient; a second actuator (20) disposed downstream of the first actuator (10) and configured to provide a second hydraulic brake pressure at a second maximum pressure gradient; Equipped with the first pressure gradient is greater than the second pressure gradient; In a first operating mode, hydraulic brake pressure for the vehicle's higher pressure applied primary axles (40, 50) is provided by the second actuator (20) and hydraulic brake pressure for the vehicle's lower pressure applied secondary axles (40, 50) is provided by the first actuator (10); in a second operating mode, hydraulic brake pressure for the higher pressurized primary axles (40, 50) of the vehicle is provided by the first actuator (10) and hydraulic brake pressure for the lower pressurized secondary axles (40, 50) of the vehicle is provided by the second actuator (20); The brake system (10) is configured to switch from the first operating mode to the second operating mode when a predetermined switching condition is met. Brake system (1).

2. the predetermined switching condition comprises a brake force request with a target pressure gradient greater than a given maximum pressure gradient of the second actuator (20); A braking system (1) according to claim 1.

3. the given maximum pressure gradient of the second actuator (20) is determined using a given maximum rotational speed of a pump in the second actuator (20) and / or a brake capacity for the primary axle (40, 50); A braking system (1) according to claim 2.

4. The brake system (1) is further configured to reduce or prevent a pressure drop in the brake pressure for the secondary axle (40, 50) before switching to the second operating mode. A braking system (1) according to claim 2 or 3.

5. the predetermined switching condition comprises detecting that the brake pressure for the secondary axle (40, 50) is at most a given threshold value, in particular zero bar or at least approximately zero bar; A braking system (1) according to any one of the preceding claims.

6. The switching from the first operating mode to the second operating mode is further performed depending on the available regenerative capacity of the vehicle. A braking system (1) according to any one of the preceding claims.

7. The first actuator (10) comprises a plunger, in particular a plunger of a brake-by-wire system or a decoupled electronic braking system. A braking system (1) according to any one of the preceding claims.

8. The second actuator (20) comprises a hydraulic pump, in particular a hydraulic pump of an ESP system. A braking system (1) according to any one of the preceding claims.

9. A motor vehicle, in particular an at least partly electrically driven motor vehicle, equipped with a brake system (1) according to any one of claims 1 to 8.

10. A method for operating a brake system (1), comprising: The brake system (1) a first actuator (10) configured to provide a first hydraulic brake pressure at a first maximum pressure gradient; a second actuator (20) disposed downstream of the first actuator (10) and configured to provide a second hydraulic brake pressure at a second maximum pressure gradient; Equipped with the first maximum pressure gradient is greater than the second maximum pressure gradient; The method includes a first operating mode (M1), in which hydraulic brake pressure for a higher pressure applied primary axle (40, 50) of the vehicle is provided by the second actuator (20) and hydraulic brake pressure for a lower pressure applied secondary axle (40, 50) of the vehicle is provided by the first actuator (10); The method includes a second operating mode (M2), in which hydraulic brake pressure for the higher pressure applied primary axles (40, 50) of the vehicle is provided by the first actuator (10) and hydraulic brake pressure for the lower pressure applied secondary axles (40, 50) of the vehicle is provided by the second actuator (20); The method comprises: Detecting a predetermined switching condition (S1); When the predetermined switching condition is detected, switching from the first operation mode (M1) to the second operation mode (M2) is performed (S2); The method further comprises:

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