A method for operating a brake system, and a control device configured to perform that method.

Abstract

The present invention relates to a method for operating a brake system (1) from a power brake (4) and driving dynamics control (8) after detecting a brake fluid reservoir (12) of the brake system (1) below a minimum fill level. In that case, the method comprises the steps of detecting a brake signal (D) and calculating a required brake pressure (P soll Step (F) of advancing the powered piston (64) to a previous position where the stroke amount (Δ SF ) step (G), a step (H) of holding the brake pressure (p), and if the brake pressure (p) decreases during the holding step (H), the powered piston (64) is moved to a corrected stroke (S K and (I) further advancing the powered piston (64) by a determined stroke amount (Δ SF ) and the limit value (S Max and (K) degrading the brake system (1) if the brake pressure reaches the threshold (P).

Description

[Technical Field]

[0001] The present invention relates to a method for operating a brake system from the power brake (Fremdkraftbremse) and driving dynamics control (Fahrdynamikregelung) after it is detected that the brake fluid reservoir of the brake system has fallen below a minimum fill level. The present invention also relates to a brake system capable of performing such a method. [Background technology]

[0002] Modern powered braking systems are characterized by their mechanical and / or hydraulic coupling to the driver. This is done via a brake pedal connected to an input rod. The driver's braking request is recognized throughout the system via this input rod, and the pedal sensation is realized in the form of a force-stroke characteristic curve (Kraft-Weg-Kennlinie). In this case, pressure is increased via a piston hydraulically disconnected from the driver's foot. Then, at the fallback level, the driver's foot is coupled to the wheel brake cylinder by a muscularly operated brake cylinder, thereby allowing the driver to apply brake pressure with their foot. This ensures that the vehicle remains able to brake in the event of a malfunction.

[0003] Patent Document 1 discloses an electrohydraulic powered vehicle braking system for autonomous land vehicles. In this case, such an electrohydraulic powered vehicle braking system comprises two redundant powered brake pressure generators, so that in the event of self-propulsion (Selbstfahrt) or failure of one of the powered brake pressure generators, the other powered brake pressure generator can brake the vehicle without driver intervention. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] German Patent Application Publication No. 102018222488 Specification [Overview of the project] [Problems that the invention aims to solve]

[0005] The problem on which this invention is based is to provide a method for keeping the brake system safe for a longer period of time when it is detected that the brake fluid level in the brake fluid reservoir has fallen below the minimum fill level. [Means for solving the problem]

[0006] The above problem is solved by the method of operating a brake system having the features of claim 1. Preferred embodiments will become apparent from the dependent claims.

[0007] The present invention provides a method for operating a brake system from a power brake and driving dynamics control after it is detected that the brake fluid reservoir in the brake system has fallen below a minimum fill level. After it is detected that the brake fluid has fallen below the minimum fill level, it is assumed that there is a leak in the brake system and that some of the brake fluid has already been lost due to this leak. In this case, the method includes the steps of detecting a brake signal, advancing a power piston to a position before the required brake pressure is achieved, and determining the stroke amount (Wegbetrag) of the power piston from its base position to its current position. The stroke amount is the value of the feed stroke of the power piston and can be expressed in millimeters, for example. In this case, the base position is the position of the power piston where no brake pressure is generated.

[0008] In the next step, the brake pressure is maintained, and if the brake pressure decreases during this maintenance, the powered piston is advanced further by a corrective stroke (Korrekturweg). In this case, the decrease in brake pressure may be due to loss of brake fluid due to leakage. Therefore, to ensure that the brake pressure can be kept constant despite leakage, the powered piston is slid toward the outlet of the powered cylinder to compensate for the loss of brake fluid.

[0009] After the braking process is complete, the powered piston is retracted by a predetermined stroke. Thus, the powered piston is retracted by the same stroke amount to which the brake pressure was first reached. Therefore, the powered piston is not retracted by an additional corrective stroke. Correspondingly, the piston does not reach its previous base position before the next braking (Bremsung). Thus, air is prevented from entering the brake system, as brake fluid may have been lost due to leakage during the braking process. This allows the brake system to remain safe for a longer period, and thus does not need to be degraded when it is detected that the minimum fill level has fallen below the required level.

[0010] The brake system degrades when the forward position of the powered piston reaches its limit. This limit can be fixed or variably adapted. Brake system degradation is understood as a transition to an emergency operation where its full functionality is no longer available. This ensures that the brake system continues to operate in a degraded state in a timely manner before complete loss of braking capability, thereby allowing for continued limited braking. This ensures that the brake system operates in degraded mode in a timely manner, even during relatively prolonged operation, thereby guaranteeing the continued safety of such a brake system.

[0011] In a preferred embodiment of the present invention, the limit value is selected as the front end position of the power piston where further pressure increase by the power piston is not possible. In this case, the front end position of the power piston is the position where the power piston reaches its maximum travel stroke (Verfahrweg). This can be, for example, the position where the power piston arrives at the bottom of the power cylinder. In this case, there is no brake fluid in the power cylinder that can increase the brake pressure. By selecting this limit value, the brake system can be kept safe and undegraded for the maximum possible time, thereby making full braking capability available.

[0012] In another preferred embodiment of the present invention, the degradation of the brake system is performed directly by reaching a limit value. By reaching the limit value, it may be impossible to generate additional brake pressure. This is immediately degraded in order to allow the vehicle to continue braking even if the brake pressure decreases due to leakage. This provides sufficient safety for braking the vehicle.

[0013] Preferably, the stroke before reaching the end position is selected as the limit value for the forward position, so that after reaching the limit value, a corrective stroke can be used to terminate the braking process before reaching the end position. Therefore, after reaching the limit value, despite the corrective stroke, the brake fluid in the power cylinder is sufficient for the current braking process, thereby allowing the braking process to be safely terminated. Advantageously, a specific value is assumed for the corrective stroke. This eliminates the need for the brake system to degrade during the braking process. Since degradation during the braking process leads to a loss of braking force, the current braking process can be terminated with full braking force. This enhances the safety of the braking process.

[0014] In an advantageous development form, in order to determine the limit value, the correction stroke from the preceding braking is used. Since the correction stroke depends on the type and magnitude of the leakage, the correction stroke assumed fixedly may be too small in some cases. However, usually, a plurality of braking cycles are performed before reaching the limit value. Based on the correction stroke required during this braking cycle, the correction stroke can be better estimated to determine the limit value, whereby the braking system can be kept in a safe state for a longer time by such a method.

[0015] Advantageously, the degradation of the braking system is carried out after the completion of the braking process. Therefore, there is no need for the degradation of the braking system during braking. Thereby, the safety of the braking system is enhanced.

[0016] In another advantageous embodiment, in order to separate the brake circuit of the driving dynamics control, the circuit separation valve is closed in the non-braked state (ungebremsten Zustand). The two brake circuits are separated from each other by the circuit separation valve. Thereby, it is prevented that in addition to the circuit with leakage, the other brake circuit also becomes empty. Therefore, thereby, at least in this degraded state, there is one brake circuit capable of applying a braking force to the vehicle brake.

[0017] According to an expedient embodiment, a warning is issued to the user, and a warning is issued to the user after it is detected that the minimum filling level in the brake fluid reservoir of the braking system is fallen below. Therefore, the driver is informed early that there is a problem with the braking system before the degradation of the braking system, whereby the driver can still drive safely to the nearest repair shop. In that case, the warning is advantageously issued optically, acoustically and / or haptically.

[0018] In particular, braking pressure is applied via the driving dynamics control and / or the master brake cylinder after degradation of the braking system. Therefore, the braking pressure is not applied via the power cylinder after degradation. Thereby, in an emergency operation, the braking pressure can continue to be applied even though the power piston is positioned at the front end position, thereby continuously ensuring the safety of the braking system.

[0019] Advantageously, after degradation of the braking system, the brake circuit is separated via a circuit separation valve in order to separate the brake circuit of the driving dynamics control. Due to the degradation, the pressure generation by the power piston disappears, whereby there is no need to open the circuit separation valve. Thereby, the effect of leakage into the brake circuit is limited, whereby in an emergency operation, braking is possible using at least one brake circuit. Thereby, the fail-safety of the braking system is enhanced.

[0020] The problem on which the present invention is based is additionally solved by a braking system comprising a power brake, a driving dynamics control, and a control device configured to execute an operating method of the braking system when it is detected that the minimum filling level in the brake fluid reservoir of the braking system is undershot. Such a braking system provides the above advantages regarding the method. Therefore, such a braking system can be kept in a safe state for a longer time.

Brief Description of the Drawings

[0021] [Figure 1] It is a diagram showing an exemplary embodiment of a braking system for executing the method during braking. [Figure 2] It is a diagram of an operating method of a braking system according to an exemplary embodiment of the present invention. [Figure 3] It is a diagram of a stroke-time graph of a power piston related to braking pressure.

Embodiments for Carrying Out the Invention

[0022] Exemplary embodiments of the present invention are shown in the drawings and described in detail below.

[0023] Figure 1 shows an exemplary embodiment of a brake system 1 for implementing the present method. In this case, the brake system 1 is shown in braking mode. The brake system 1 comprises a power brake 4 and a driving dynamics control 8. The power brake 4 includes a brake fluid reservoir 12, the fill level of which can be determined using a fill level sensor (not shown). The brake system 1 shown herein includes a signal 16 when the fill level is below a minimum fill level.

[0024] The brake system 1 additionally includes a master brake cylinder 20, which is operable by the driver via a brake pedal 24 and supplied with brake fluid from a brake fluid reservoir 12. Correspondingly, the stroke of the brake pedal is measured via a stroke sensor 28. The master brake cylinder 20 has first and second brake pistons 32, 36, which can be used to control separate brake circuits 40a, 40b, respectively. The pressure generated within the master brake cylinder 20 is measured by a master brake cylinder pressure sensor 44.

[0025] In the control operation of the brake system 1, the master brake cylinder isolation valves 48a and 48b are closed. Using the master brake cylinder isolation valves 48a and 48b, the master cylinder 20 is connected to the brake circuits 40a and 40b of the driving dynamics control 8, and brake pressure can be applied to the vehicle brakes 52a, 52b, 52c, and 52d of the brake system 1. In the example shown here, the brake sensation simulator 56 that gives the driver a braking sensation is operated using the pressure of the master brake cylinder 20.

[0026] The powered brake 4 is further equipped with a powered cylinder 60, within which a powered piston 64 is located, which is movable axially in the powered cylinder 60 via a motor 68 to generate brake pressure. In the figure shown here, the powered piston 64 is shown in its front end position. The powered cylinder 60 is fluidly connected to the brake fluid reservoir 12 via a powered cylinder valve 72. The brake pressure generated via the powered piston 64 is measured via a brake pressure sensor 76. The powered cylinder 60 is connected to two brake circuits 40a and 40b of the travel dynamics control 8 via two circuit isolation valves 80a and 80b.

[0027] To supply brake fluid to the brake circuits 40a and 40b of the driving dynamics control 8, these brake circuits 40a and 40b are directly connected to the brake fluid reservoir 12 via check valves 84a and 84b, respectively. The driving dynamics control 8 can draw brake fluid from the brake fluid reservoir 12 via these check valves 84a and 84b when necessary. To control driving dynamics and to deliver brake pressure to the vehicle brakes 52a, 52b, 52c, and 52d, the driving dynamics control 8 has several inlet and outlet valves and a brake fluid pump 92 driven via a pump motor 88.

[0028] Furthermore, the brake system 1 additionally includes a control device 94, which is signal-technically connected to the power brake 4 and the travel dynamics control 8. This control device 94 receives sensor measurements and controls the valves of the power brake 4 and the travel dynamics control 8, as well as the movement of the power piston 64. In this case, the method according to the present invention shown in Figure 2 is performed on this control device 94.

[0029] Figure 2 shows a diagram illustrating how to operate the brake system 1 according to an exemplary embodiment of the present invention. In the first step A, it is detected that the brake fluid level in the brake fluid reservoir 12 falls below the minimum fill level. In the following step B, a warning is issued to the driver. In this case, the warning can be given by the illumination of a warning lamp. In response, the brake system 1 operates in the corresponding leak mode. Because brake fluid is lost due to such leak, in the next step, the circuit isolation valves 80a, 80b are closed while the vehicle is not being braked in order to isolate the brake circuits 40a, 40b. This prevents both brake circuits 40a, 40b from becoming empty due to the leak, thereby ensuring that at least one of the brake circuits 40a, 40b remains available for braking the vehicle.

[0030] In the next step D, it is detected whether a brake signal is present. If a brake signal is present, in the next step E, the circuit isolation valves 80a and 80b are opened again. This ensures that the brake pressure generated via the powered piston 64 can be applied to the brake circuits 40a and 40b, and consequently to the vehicle brakes 52a, 52b, 52c, and 52d. Correspondingly, in the following step F, the powered piston 64 is moved forward to its forward position in accordance with the brake signal, thereby generating the required brake pressure p soll This is generated.

[0031] Following this, in step G, the stroke amount Δ of the powered piston 64 from its basic position to its current position is determined. SF This is determined. This can be determined via a rotation sensor 96 attached to a motor 68 for driving the powered piston 64. The required brake pressure p soll Once this is reached, it is held in the next step H. If the brake pressure p measured via the master brake cylinder pressure sensor 44 decreases due to leakage during holding, the powered piston 64 will press the required brake pressure p sollis further advanced until it exists again. Thereby, the modified stroke S of the power piston 64 K occurs.

[0032] End B of the braking process END After that, in step J, the power piston 64 moves to the basic position where there is no braking pressure p by the stroke amount Δ determined in step G SF only in the backward direction. In that case, the new basic position may be further forward based on the modified stroke S K Finally, it is checked whether the limit value S of the forward position of the power piston 64 Max is reached, and further braking is no longer possible. If this is not the case, the method can be continued. In that case, a new step C is started, in which case the circuit isolation valves 80a, 80b are first closed.

[0033] In that case, the method can be executed multiple times until the test result indicates that the limit value S of the forward position of the power piston 64 Max is reached. In this case, the braking system 1 is degraded, and thereby the braking pressure p is applied via the driving dynamics control 8 and / or the master brake cylinder 20.

[0034] In FIG. 3, a diagram of the stroke-time graph s / t of the power piston 64 related to the braking pressure p / t is shown. A plurality of braking cycles 100 are shown in this graph. In that case, the upper curve shows the stroke s of the power piston 64, while the lower curve shows the braking pressure p. In that case, when the power piston 64 moves forward, it can be recognized that the braking pressure p soll increases until the required braking pressure p soll is achieved. Although the braking pressure p sollThe stroke of the powered piston will not change even when it reaches that point.

[0035] Brake fluid loss occurs due to leakage. Therefore, after the brake fluid level in the brake fluid reservoir 12 falls below the minimum fill level, a warning is issued at point FLI and the leak mode is activated. Correspondingly, in the next brake cycle 100, after the completion of the braking process of the powered piston 64, the required brake pressure p soll The stroke amount Δ needed to reach the initial point SF It will not reverse. Therefore, brake pressure p soll The correction stroke S required to hold K It is not moved backward. Therefore, the new base position is this corrected stroke S K It is shifted forward by only that much.

[0036] In that case, in the leakage mode, the powered piston 64 moves to the limit value S of the forward position. Max Many braking cycles can be performed until the limit value S is reached. This front position can be located at the front end position as shown in Figure 3. The braking system can reach the limit value S. Max Once this condition is reached, the system will only operate in degraded mode from CFM onward. [Explanation of Symbols]

[0037] 1. Brake System 4. Power brake 8. Driving Dynamics Control 12 Brake fluid reservoir 16 signals 20 Master brake cylinder 24 Brake pedal 28 Stroke Sensor 32 First brake piston 36. Second brake piston 40a, 40b Brake Circuit 44 Master Brake Cylinder Pressure Sensor 48a, 48b Master brake cylinder isolation valve 52a, 52b, 52c, 52d Vehicle brakes 60 Powered Cylinder 64 Powered Piston 68 Motor 72 Powered Cylinder Valve 76 Brake pressure sensor 80a, 80b Circuit isolation valves 84a, 84b Check valve 88 Pump motor 92 Brake fluid pump 94 Control device 100 Brake cycles p Brake pressure s stroke B END End of braking process P soll Required brake pressure CFM (Conditioning of the Market) FLI point S Max Limit value S K Correction stroke Δ SF Stroke amount

Claims

1. A method for operating the brake system (1) from a power brake (4) and a driving dynamics control (8) after it is detected that the brake fluid reservoir (12) of the brake system (1) has fallen below the minimum fill level, comprising the following steps: - Step (D) of detecting the brake signal, - Required brake pressure (P ｓｏｌｌ Step (F) involves advancing the powered piston (64) to a position before the ) is achieved, - The stroke amount (Δ) of the powered piston (64) from its basic position to its current position. ＳＦ The step (G) of determining ) - A step (H) to maintain the brake pressure (p), and if the brake pressure (p) decreases during the maintaining step (H), the powered piston (64) is moved to a correct stroke (S Ｋ ) and step (I) which is to advance further, - After the braking process is completed, the powered piston (64) is moved by the determined stroke amount (Δ ＳＦ A step (J) that moves backward by only that much, - Limit value of the forward position of the powered piston (64) (S Ｍａｘ A method comprising the steps of: (K) degrading the brake system (1) when the threshold is reached.

2. Limit value (S Ｍａｘ The method according to claim 1, characterized in that a front end position of the powered piston (64) is selected such that further pressure increase (p) by the powered piston (64) is not possible.

3. The degradation (K) of the brake system (1) is the limit value (S Ｍａｘ The method according to claim 2, characterized in that it is directly performed by reaching ).

4. The limit value (S Ｍａｘ ) of the front position, the stroke (s) before reaching the end position is selected, so that after reaching the limit value (S Ｍａｘ ), the braking process can be terminated using a correction stroke (S Ｍａｘ ) before reaching the end position. The method according to claim 1, characterized in that.

5. The aforementioned limit value (S Ｍａｘ ) In order to determine the corrective stroke (S) from the preceding braking, Ｋ The method according to claim 4, characterized in that ) is used.

6. The method according to claim 4 or 5, characterized in that the degrading (K) of the brake system (1) is performed after the completion of the braking process.

7. The method according to any one of claims 1 to 5, characterized in that, in order to isolate the brake circuits (40a, 40b) of the driving dynamics control (8), circuit isolation valves (80a, 80b) are closed when the brakes are not applied (C).

8. The method according to any one of claims 1 to 5, characterized in that a warning (B) is issued to the user after it is detected that the brake fluid reservoir (12) of the brake system (1) has fallen below the minimum fill level.

9. The method according to claim 8, characterized in that the warning is emitted optically, acoustically, and / or tactilely.

10. The method according to any one of claims 1 to 5, characterized in that, after the degrade (K) of the brake system, the brake pressure (p) is applied via the driving dynamics control (8) and / or the master brake cylinder (20).

11. The method according to any one of claims 1 to 5, characterized in that, after the degradation (K) of the brake system (1), the brake circuits (40a, 40b) of the driving dynamics control (8) are separated via circuit separation valves (80a, 80b).

12. A brake system (1) comprising a power brake (4), a driving dynamics control (8), and a control device (94) configured to perform the method according to any one of claims 1 to 5 when it detects that the brake fluid reservoir of the brake system has fallen below a minimum fill level.

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