Method for operating a brake system and control device configured to carry out said 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 a power brake and driving dynamics control after detecting a drop below a minimum fill level in a brake fluid reservoir of the brake system, and also to a brake system capable of carrying out such a method. [Background technology]

[0002] Modern power-operated 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 demand is recognized throughout the system via this input rod, and pedal feel is realized in the form of a force-stroke characteristic curve (Kraft-Weg-Kennlinie). In this case, pressure is boosted via a piston hydraulically decoupled from the driver's foot. Then, at a fallback level, the driver's foot is coupled to the wheel brake cylinders by muscle-operated brake cylinders, allowing the driver to apply brake pressure with their foot. This allows the vehicle to continue to be braked in the event of a fault.

[0003] Patent document 1 discloses an electrohydraulic powered vehicle braking system for an autonomous land vehicle, which has two redundant powered brake pressure generators, so that in the event of the self-propulsion and failure of one powered brake pressure generator, 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 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem on which the invention is based is to provide a method which makes it possible to keep the braking system safe for a longer period of time when a minimum fill level is detected in the brake fluid reservoir. [Means for solving the problem]

[0006] The above problem is solved by a method for operating a brake system having the features of claim 1. Preferred embodiments emerge 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 detecting a brake fluid reservoir below a minimum fill level of the brake system. After detecting a brake fluid reservoir below the minimum fill level, it is assumed that a leak exists in the brake system and that some brake fluid has already been lost due to this leak. The method then includes the steps of detecting a brake signal, advancing a power piston to a position where the required brake pressure is achieved, and determining a stroke of the power piston from a home position to a current position. The stroke is the value of the power piston's feed stroke, which can be expressed, for example, in mm. The home 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 period, the power piston is advanced by a further correction stroke. In this case, the decrease in brake pressure may be caused by a loss of brake fluid due to leakage. Therefore, in order to be able to keep the brake pressure constant despite the leakage, the power piston is moved in the direction of the outlet of the power cylinder to compensate for the loss of brake fluid.

[0009] After the braking process is completed, the power piston is retracted by a determined stroke amount. Therefore, the power piston is retracted by the same stroke amount as the brake pressure was initially reached. Therefore, the power piston is not retracted by an additional correction stroke. Correspondingly, the piston does not reach its previous base position before the next braking. This prevents air from entering the brake system, which may have been lost due to leakage during the braking process. This allows the brake system to remain safe for a longer period of time, so that it does not have to be degraded when a drop below the minimum fill level is detected.

[0010] The brake system is degraded when a limit value for the forward position of the powered piston is reached. In this case, the limit value can be fixedly specified or can be variably adapted. Degradation of the brake system is understood to mean that it goes into emergency operation in which its full functionality is no longer available. This allows the brake system to continue operating in a degraded state in a timely manner before the braking capacity is lost, so that limited braking is still possible. This makes it possible to ensure that the brake system is operated in a degraded mode in a timely manner even during relatively long operation of the brake system. This continues to guarantee the 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 at which no further pressure buildup by the power piston is possible. In this case, the front end position of the power piston is the position at which the power piston reaches its maximum stroke. This can be, for example, the position at which the power piston reaches 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 in a safe and undegraded state for the maximum time, so that full braking capacity is available.

[0012] In another preferred embodiment of the present invention, the degradation of the brake system is performed directly by reaching a limit value, which may prevent additional brake pressure from being generated. In order to be able to continue braking the vehicle if the brake pressure is reduced due to leakage, this is immediately degraded, thereby providing sufficient safety for braking the vehicle.

[0013] Preferably, the stroke before the end position is reached is selected as the limit value of the pre-position, so that after the limit value is reached, the braking process can be terminated using a corrective stroke before the end position is reached. Therefore, after the limit value is reached, despite the corrective stroke, there is still enough brake fluid in the power cylinder for the current braking process, so that the braking process can be safely terminated. Advantageously, a specific value is assumed for the corrective stroke. This prevents the brake system from degrading during the braking process. Since degradation during the braking process would result in a loss of braking force, the current braking process can be terminated with full braking force. This increases the safety of the braking process.

[0014] In an advantageous development, the correction stroke from the previous braking is used to determine the limit value. Since the correction stroke depends on the type and size of the leak, the fixed assumed correction stroke may be too small in some cases. However, several braking cycles are usually performed before the limit value is reached. Based on the correction stroke required during these braking cycles, the correction stroke can be better estimated for determining the limit value, and this method can thereby keep the brake system in a safe state for a longer period of time.

[0015] Advantageously, the degrading of the brake system is performed after the braking process is completed, so that degrading of the brake system does not have to be performed during braking, thereby increasing the safety of the brake system.

[0016] In another advantageous embodiment, a circuit isolation valve is closed in the unbraked state to isolate the brake circuits of the driving dynamics control. The two brake circuits are isolated from each other by the circuit isolation valve. This prevents the other brake circuit from becoming empty in addition to the circuit with the leak. Therefore, at least in this degraded state, there is one brake circuit that can apply braking force to the vehicle brakes.

[0017] According to a suitable embodiment, a warning is issued to the user after detecting a drop below a minimum fill level in the brake fluid reservoir of the brake system. Thus, the driver is informed of a problem with the brake system early on before the brake system deteriorates, so that the driver can still safely drive to the nearest repair shop. In this case, the warning is preferably issued optically, acoustically, and / or tactilely.

[0018] In particular, after the brake system is degraded, brake pressure is applied via the driving dynamics control and / or the master brake cylinder. Therefore, brake pressure is not applied via the power cylinder after the degraded state. This allows brake pressure to continue to be applied in emergency situations despite the power piston being positioned in the front end position, thereby ensuring the safety of the brake system.

[0019] Advantageously, after the brake system is degraded, the brake circuits of the driving dynamics control are isolated via a circuit isolation valve. The degraded state eliminates pressure generation by the powered piston, which means that the circuit isolation valve does not need to be opened. This limits the effect of leakage on the brake circuits, so that braking is possible using at least one brake circuit in emergency situations. This increases the failure safety of the brake system.

[0020] The problem on which the invention is based is additionally solved by a brake system comprising a power-operated brake, a driving dynamics control and a control device which is configured to execute a method for operating the brake system when detecting a drop below a minimum fill level in a brake fluid reservoir of the brake system, which provides the above-mentioned advantages of the method and thus allows the brake system to remain safe for a longer period of time. [Brief explanation of the drawings]

[0021] [Figure 1] 1 illustrates an exemplary embodiment of a braking system for performing the method during braking. [Figure 2] 1 is a diagram of a method of operating a braking system according to an exemplary embodiment of the present invention. [Figure 3] 1 is a diagram of a powered piston stroke-time graph in relation to brake pressure. DETAILED DESCRIPTION OF THE INVENTION

[0022] Exemplary embodiments of the invention are illustrated in the drawings and explained in detail in the following description.

[0023] 1 shows an exemplary embodiment of a brake system 1 for carrying out the method. The brake system 1 is shown during braking. The brake system 1 comprises a power brake 4 and a driving dynamics control 8. The power brake 4 comprises a brake fluid reservoir 12, the fill level of which can be determined by means of a fill level sensor (not shown). In the brake system 1 shown here, a signal 16 is present indicating that the fill level is below a minimum fill level.

[0024] The brake system 1 additionally comprises a master brake cylinder 20, which can be operated by the driver via a brake pedal 24 and is supplied with brake fluid from the brake fluid reservoir 12. The stroke of the brake pedal is correspondingly 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 in 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, 48b are closed. By means of the master brake cylinder isolation valves 48a, 48b, the master cylinder 20 is connected to the brake circuits 40a, 40b of the driving dynamics control 8 so that brake pressure can be applied to the vehicle brakes 52a, 52b, 52c, 52d of the brake system 1. In the example shown, the pressure in the master brake cylinder 20 is used to operate a brake feel simulator 56, which generates a braking feel for the driver.

[0026] The power brake 4 additionally comprises a power cylinder 60 in which a power piston 64 is arranged, which is movable axially of the power cylinder 60 via a motor 68 in order to generate brake pressure. In the illustrated view, the power piston 64 is shown in its forward end position. The power cylinder 60 is fluidly connected to the brake fluid reservoir 12 via a power cylinder valve 72. The brake pressure generated via the power piston 64 is measured via a brake pressure sensor 76. The power cylinder 60 is connected to the two brake circuits 40a, 40b of the driving dynamics control 8 via two circuit isolation valves 80a, 80b.

[0027] To supply brake fluid to the brake circuits 40a, 40b of the driving dynamics control 8, these brake circuits 40a, 40b are directly connected to the brake fluid reservoir 12 via one check valve 84a, 84b, respectively. The driving dynamics control 8 can draw brake fluid from the brake fluid reservoir 12 via the check valves 84a, 84b when needed. To control the driving dynamics and deliver brake pressure to the vehicle brakes 52a, 52b, 52c, 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 has a control device 94, which is connected in signal technology to the power brakes 4 and the driving dynamics control 8. This control device 94 receives the measured values ​​of the sensors and controls the valves of the power brakes 4 and the driving dynamics control 8 and the movement of the power piston 64. The method according to the invention according to FIG.

[0029] 2 shows a diagram of a method for operating the brake system 1 according to an exemplary embodiment of the present invention. In a first step A, a drop below a minimum fill level in the brake fluid reservoir 12 is detected. In a subsequent step B, a warning is issued to the driver, which can be achieved by illuminating a warning lamp. Correspondingly, the brake system 1 operates in a corresponding leakage mode. Since such a leakage would result in a loss of brake fluid, in a next step, the circuit isolation valves 80a, 80b are closed during non-braking conditions to isolate the brake circuits 40a, 40b. This prevents both brake circuits 40a, 40b from becoming empty due to leakage, so 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, 80b are opened again, thereby ensuring that the brake pressure generated via the powered piston 64 can be applied to the brake circuits 40a, 40b and thus to the vehicle brakes 52a, 52b, 52c, 52d. Correspondingly, in the following step F, the powered piston 64 is advanced to a forward position in accordance with the brake signal, thereby applying the required brake pressure p soll is generated.

[0031] Subsequently, in step G, the stroke amount Δ of the power piston 64 from the base position to the current position is calculated. SF This can be determined via a rotation sensor 96 attached to the motor 68 for driving the powered piston 64. The required brake pressure p soll After reaching the required brake pressure p, it is held in the next step H. If the brake pressure p measured via the master brake cylinder pressure sensor 44 should decrease during the hold due to leakage, the powered piston 64 will increase the required brake pressure p soll, which causes the corrected stroke S of the powered piston 64 to K occurs.

[0032] End of braking process B END Then, in step J, the power piston 64 is moved to the base position where the brake pressure p is not present by the stroke amount Δ SF In that case, the new base position is the corrected stroke S K Finally, the limit value S for the forward position of the powered piston 64 is Max is reached, and no further braking can be performed. If this is not the case, the method can continue. In that case, step C is started again, in which first the circuit isolation valves 80a, 80b are closed.

[0033] In this case, the limit value S of the forward position of the powered piston 64 Max The method can be performed a number of times until the test result is that the brake pressure p is reached, in which case the brake system 1 is degraded, whereby the brake pressure p is applied via the driving dynamics control 8 and / or the master brake cylinder 20.

[0034] In Figure 3, a diagram of the stroke vs. time graph s / t of the powered piston 64 in relation to the braking pressure p / t is shown. The graph shows multiple braking cycles 100, where the upper curve shows the stroke s of the powered piston 64, while the lower curve shows the braking pressure p. When the powered piston 64 advances, the required braking pressure p soll It can be seen that the braking pressure p increases until the braking pressure p soll Even though the brake pressure p is constant, the stroke s of the powered piston 64 continues to change. This is because the leakage causes the powered piston 64 to advance further to compensate for the pressure loss. Without the leakage, the required brake pressure p sollThe stroke of the powered piston will not change when

[0035] The loss of brake fluid occurs due to leakage. Therefore, after the minimum fill level in the brake fluid reservoir 12 falls below the minimum fill level, a warning is issued at point F1 and the leakage mode is activated. Correspondingly, in the next braking cycle 100, after the end of the braking process of the power piston 64, the required brake pressure p soll The stroke amount Δ required to initially reach SF Therefore, the brake pressure p soll Correction stroke S required to hold K Therefore, the new base position is determined by this corrected stroke S K It has just been shifted forward.

[0036] In this case, in the leakage mode, the powered piston 64 is at the forward position limit S Max A number of 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 Max Once CFM is reached, it will only operate in degraded mode. [Explanation of symbols]

[0037] 1. Brake system 4 Power brakes 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 circuits 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 valve 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 time FLI point S Max Limit S K Correction Stroke Δ SF Stroke volume

Claims

1. A method for operating a braking system (1) from a power brake (4) and a driving dynamics control (8) after detecting a brake fluid level below a minimum level in a brake fluid reservoir (12) of said braking system (1), comprising the steps of: - a step (D) of detecting a braking signal; - Required brake pressure (P ｓｏｌｌ (F) advancing the powered piston (64) to a position where the above-mentioned (1) is achieved; - the stroke amount (Δ ＳＦ (G) determining a step (H) of holding the brake pressure (p) and, if the brake pressure (p) decreases during the holding step (H), moving the powered piston (64) to a corrected stroke (S Ｋ (I) further advancing the - After the braking process is completed, the powered piston (64) is moved by the determined stroke amount (Δ ＳＦ ) step (J); - the limit value (S Ｍａｘ and (K) degrading said braking system (1) when said brake pressure is reached.

2. Limit value (S Ｍａｘ 2. The method according to claim 1, characterized in that as the pressure increase (p) of the powered piston (64) a front end position of the powered piston (64) is selected in which no further pressure increase (p) by the powered piston (64) is possible.

3. The degradation (K) of the brake system (1) is Ｍａｘ 3. The method of claim 2, wherein the method is performed directly by reaching

4. The front position limit value (S Ｍａｘ ) is selected as the stroke (s) before reaching the end position, so that the limit value (S Ｍａｘ ) and then a correction stroke (S Ｍａｘ 2. The method of claim 1, wherein the braking process can be terminated using a

5. The limit value (S Ｍａｘ ) for the determination of the correction stroke (S Ｋ 5. The method of claim 4, wherein a

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

7. 7. The method according to claim 1, wherein a circuit isolation valve (80a, 80b) is closed (C) in the unbraked state to isolate the brake circuit (40a, 40b) of the driving dynamics control (8).

8. 8. The method according to claim 1, wherein a warning (B) is issued to the user after detecting a drop below a minimum fill level in a brake fluid reservoir (12) of the brake system (1).

9. 9. The method of claim 8, wherein the warning is emitted optically, acoustically and / or tactilely.

10. 10. The method according to claim 1, wherein after the degradation (K) of the brake system, the brake pressure (p) is applied via a driving dynamics control (8) and / or a master brake cylinder (20).

11. 11. The method according to claim 1, wherein after the degrading (K) of the brake system (1), the brake circuits (40a, 40b) of the driving dynamics control (8) are isolated via circuit isolation valves (80a, 80b) in order to isolate the brake circuits (40a, 40b).

12. 12. A braking system (1) comprising a power-operated 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 11 when detecting a drop below a minimum fill level in a brake fluid reservoir of the braking system.

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