A method for indicating fading in thermally loaded brakes.

Abstract

To provide a method for pointing out fading of a brake under a thermal load.SOLUTION: According to the present invention, a method controls an automobile brake device of a hydraulic brake-by-wire automobile brake system including a sensor system for detecting a brake pedal operation amount and an actuator for providing hydraulic pressure to a wheel brake, and a control value of the actuator is generated on the basis of the brake pedal operation amount and a stored pedal characteristic curve. A fading phenomenon is detected to avoid a dangerous state during the fading phenomenon, and a volume monitoring part determines a present pressure-volume characteristic curve to determine a quantitative fading value, compares the present pressure-volume characteristic curve with a stored pressure-volume characteristic curve, generates a control value adjusted for the actuator on the basis of the brake pedal operation amount, the stored pedal characteristic curve, and a quantitative fading value of when the fading phenomenon is confirmed, and controls the actuator by using the adjusted control value.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a hydraulic brake-by-wire braking system for a motor vehicle and to a method for controlling such a system, which comprises a sensor system for detecting at least one brake pedal actuation quantity and at least one actuator for supplying hydraulic pressure to at least one wheel brake, in which a control value for the at least one actuator is generated on the basis of the brake pedal actuation quantity and a stored pedal characteristic curve. [Background technology]

[0002] Hydraulic brake systems for automobiles are typically implemented with dual circuits, either permanently or switchably, to provide some degree of fault redundancy. The two circuits are connected in an X-pipe configuration or a front-to-rear split configuration. In a brake-by-wire system, an electric actuator is responsible for the actual pressure setting, and the driver is connected to a simulator via the brake pedal. The brake pressure demand is generated based on brake pedal operation and converted by the actuator. The brake pressures on the front and rear axles are generally equal, but may differ from each other depending on various conditions.

[0003] In a brake-by-wire system, the driver is thus decoupled from the wheel brakes. The simulator provides the driver with a consistent pedal feel, independent of the actual wheel brake conditions and method. However, with a conventional hydraulic wheel brake system, heavy braking leads to a reduction in braking effectiveness. This reduction in braking effectiveness is called fade. The brake friction coefficient decreases and the brake volume absorption increases. The driver immediately notices this, as more force is required via the brake pedal to achieve the same level of deceleration. By decoupling the driver from the wheel brakes, a brake-by-wire braking system eliminates this feedback. Therefore, due to the lack of direct feedback, the driver may unknowingly overuse the wheel brakes.

[0004] In racetrack driving, wheel brakes may not be properly cooled or may not have enough cooling air flowing around them, which can cause the brake fluid in the brake caliper to reach its boiling point at high temperatures, causing the brake fluid to degas and create bubbles, or air bubbles, in the brake caliper.

[0005] US Pat. No. 5,699,499 discloses a method for monitoring brake fluid volume, whereby a volumetric discharge amount is determined that is useful for indicating leaks.

[0006] From the unpublished patent application EP 1 099 563 A1 a method is known for determining an air estimate in the case of an inaccurate pV curve, where an actual pV curve is determined which differs from the nominal pV curve due to heavy braking.

[0007] From patent document 3, a method for operating a hydraulic vehicle braking system is known, which modifies the ratio between the driver's brake application and the resulting wheel brake pressure in the event of a malfunction. The aim here is to provide feedback to the driver that the braking force of the brake system has been reduced. This is achieved by modifying a predetermined pedal characteristic. In a first embodiment, the progression of the pedal characteristic is modified so that, upon application, the wheel pressure initially increases relatively small and then increases significantly. The curves of the different pedal characteristics are selected so that they intersect. In a further embodiment, the change in the pedal characteristic is combined with a warning (visual, acoustic, etc.). In this case, the pedal characteristic is modified so that the vehicle deceleration is smaller. At an actuation point of a pedal force F of 500 N, the vehicle deceleration is 2.44 m / s 2 The progression of the curve is made flatter so that a vehicle deceleration of 0.05 s is achieved, but the actual degree of the fade phenomenon is not taken into account. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] German Patent Application Publication No. 102019215418A1 [Patent Document 2] German Patent Application Publication No. 102022209170 [Patent Document 3] German Patent Application Publication No. 102018212852A1 Summary of the Invention [Problem to be solved by the invention]

[0009] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a brake system and a method for controlling the brake system that suppress problems caused by the fade phenomenon. [Means for solving the problem]

[0010] This problem is solved by a volume monitoring unit that determines a current pressure-volume characteristic curve, compares the current pressure-volume characteristic curve with a stored pressure-volume characteristic curve, and, when a fade phenomenon is detected, generates an adjusted control value for at least one actuator based on the brake pedal depression amount, the stored pedal characteristic curve, and the quantitative fade value, and controls the actuator with the adjusted control value to supply pressure to at least one wheel brake. This gradually adjusts the behavior of the brake system as the fade phenomenon increases, allowing the driver to receive accurate feedback regarding the state of the brake system, enabling the driver to appropriately adjust their driving behavior.

[0011] In a preferred embodiment of the invention, the sensor system comprises at least one sensor for brake pedal travel, brake pedal force, and / or brake pedal pressure. The brake pedal pressure is in particular the master cylinder pressure, i.e., the pressure generated by the driver's muscle force via the brake pedal. In particular, by combining several of these quantities, accurate and reliable inductive inferences can be drawn about the driver's braking needs.

[0012] In a further preferred embodiment of the invention, the actuator is a linear actuator and / or a piston pump, in particular a linear actuator allows very precise control of both pressure increase and pressure decrease.

[0013] In a further preferred embodiment of the present invention, the volume monitoring section is formed by a leak monitoring unit which detects a leak when the difference between the current pressure-volume characteristic curve and the stored pressure-volume characteristic curve is greater than a threshold value, and switches to a fallback mode when a leak is detected.

[0014] In a further preferred embodiment of the invention, the fade value comprises a volume difference, in particular an offset between the current pressure-volume characteristic curve and the nominal pressure-volume characteristic curve, a slope of the current pressure-volume characteristic curve, and / or a coefficient between the stored pressure-volume characteristic curve and the current pressure-volume characteristic curve.

[0015] In a further preferred embodiment of the invention, at least one intermediate value is determined from the brake pedal actuation amount and the stored pedal characteristic curves to determine the adjusted control value, and the intermediate value is modified by a quantitative fade value. For example, a deceleration demand or a pressure demand can be calculated as the intermediate value. Therefore, it is also possible to use pedal characteristic curves, which can be selected depending on the driver's input, for example, in a sport mode.

[0016] In a further preferred embodiment of the invention, the adjusted control value provides a lower pressure to the wheel brakes than the control value that would be used without fade detection, thereby making the reduced braking effect more apparent to the driver.

[0017] In a further preferred embodiment of the invention, the intermediate value is multiplied by the fade value as a factor, in particular as a factor less than one.

[0018] In a further preferred embodiment of the present invention, the fade value is subtracted from the intermediate value as an offset.

[0019] In a further preferred embodiment of the invention, when a fade phenomenon is confirmed, an audible and / or visual warning message is additionally output to the driver, the warning message being output immediately upon detection of the fade phenomenon and / or after the fade value exceeds a threshold value, so that the driver can adjust his / her driving behavior at an early stage.

[0020] In a further preferred embodiment of the invention, the adjustment of the control value during a fade phenomenon is carried out only if the method is activated via the driver interface, so that such a function can be used in particular for test drives.

[0021] The object is further achieved by a hydraulic brake-by-wire vehicle braking system, comprising a sensor system for detecting at least one brake pedal actuation amount, at least one actuator for supplying hydraulic pressure to at least one wheel brake, and a control device configured to generate a control value for the at least one actuator based on the brake pedal actuation amount and a pedal characteristic curve stored in a storage device of the control device. The control device is further configured to perform volume monitoring, determining a current pressure-volume characteristic curve and comparing the current pressure-volume characteristic curve with the stored pressure-volume characteristic curve in order to detect a fade phenomenon and determine a quantitative fade value. When a fade phenomenon is detected, an adjusted control value for the at least one actuator is generated based on the brake pedal actuation amount, the stored pedal characteristic curve, and the quantitative fade value, and the actuator is controlled by the adjusted control value to supply pressure to the at least one wheel brake.

[0022] Further features, advantages and possible applications of the present invention are apparent from the following description of exemplary embodiments and the drawings, in which all features described and / or shown belong to the subject matter of the present invention both individually and in any combination, independently of their abstracts in the claims or their references. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a diagram showing a brake device operating in a normal operating mode using a brake-by-wire system; [Figure 2] FIG. 10 is a diagram illustrating driver request detection. [Figure 3] 1 is a graph showing a pressure-volume characteristic curve. [Figure 4] FIG. 10 is a diagram illustrating a calculation logic for detecting a driver's request. DETAILED DESCRIPTION OF THE INVENTION

[0024] FIG. 1 shows a brake system 1 operating in a normal operating mode with a brake-by-wire system. Brake fluid is stored in a reservoir or brake fluid tank 2 and is delivered to the individual wheel brakes 6, 7, 8, and 9 by a master brake cylinder 3 or linear actuator 5. In normal driving mode, the master brake cylinder 3 is isolated from the individual wheel brakes 6, 7, 8, and 9 by a shut-off valve (MCV) 11 or master brake cylinder valve and is used solely for detecting the driver's braking request. Instead, a simulator valve 10 is open, establishing a connection between the master brake cylinder 3 and the simulator 4 via the simulator valve 10. When the brake pedal connected to the master brake cylinder 3 is actuated, brake fluid moves from the master brake cylinder 3 to the simulator 4 to simulate a proper pedal feel. The master brake cylinder pressure generated by the driver via the master brake cylinder 3 is measured by a pressure measuring device 17. Furthermore, the position of the brake pedal is detected by a suitable measuring device, in particular by a pedal stroke measurement. Based on the measured master brake cylinder pressure and / or brake pedal position, a linear actuator 5 is controlled, which is connected to each of the wheel brakes 6, 7, 8, and 9 via an open supply valve (PFV) 12. The brake circuit of the hydraulic brake system 1 is divided or can be divided into two partial circuits by a circuit isolation valve (CSV) 13. The wheel brakes 8 and 9 of the rear axle are assigned to a first partial circuit, and the wheel brakes 6 and 7 of the front axle are assigned to a second partial circuit. The circuit isolation valve 13 further isolates the second partial circuit from the linear actuator 5. Each of the wheel brakes 6, 7, 8, and 9 has an inlet valve 14 and an outlet valve 15. In normal driving mode, the circuit isolation valve 13 is open, thereby supplying hydraulic pressure supplied via the linear actuator 5 to all four wheel brakes 6, 7, 8, and 9.

[0025] 2 next shows driver request detection, which determines a first deceleration request based on a pedal stroke sensor 21 and a first pedal characteristic curve 22. A second deceleration request 26 is determined based on a master cylinder pressure sensor 17 and a second pedal characteristic curve 25. The first deceleration request 23 and the second deceleration request 26 are processed to form a joint deceleration request 27 which is used as the basis for the subsequent control of the linear actuator 5. In addition to this, a further transformation cascade can follow, including, for example, the pressure to be delivered, the required volume, the torque, the motor current, etc.

[0026] Heavy braking during driving causes a thermal load on the brakes (brake fade phenomenon), which increases the volumetric consumption. Because the brake pedal and the braking system are decoupled, the driver does not receive immediate feedback from the system about a decrease in braking effectiveness. The volume monitoring function (VDM) in the brake system's control and regulation unit (ECU) detects any increase in volumetric consumption caused by deviations of the actual pressure-volume characteristic curve (pV curve) 32 from a stored or nominal pressure-volume characteristic curve 31 (Figure 3).

[0027] By analyzing the pressure-volume characteristic curves 31, 32, several pieces of information regarding the fade phenomenon can be determined, in particular the volume difference (offset), the slope of the actual pressure-volume characteristic curve 32, and the coefficient between the actual pressure-volume characteristic curve 32 and the nominal pressure-volume characteristic curve 31.

[0028] If the difference (coefficient or slope) between the actual pressure-volume characteristic curve and the nominal pressure-volume characteristic curve increases, the present invention provides the driver with feedback regarding the deceleration behavior. For this purpose, information regarding the state of the brakes and the state of the volumetric absorption is provided by the monitoring function (VDM), as shown in Figure 4.

[0029] To achieve a gradual adjustment of the deceleration demand depending on the degree of the fade phenomenon, a correction factor can be used in the driver's request detection. For this purpose, different input values ​​are detected by the volume monitoring function (VDM), which influences the correction factor.

[0030] For example, the correction factor can be based on the ratio of the actual volumetric absorption to the nominal volumetric absorption. a korr =a nom *1 / F pv where a korr is the corrected deceleration demand, a nom is the nominal deceleration demand, and F pv is the ratio of the actual volumetric absorption to the nominal volumetric absorption.

[0031] From experience, the pV coefficient F pv reaches values ​​between 1.0 and 2.0, where a pV factor of 1.0 corresponds to an ideal match between the nominal and real pV curves.

[0032] Additionally, an offset may also be provided, which may be inferred, for example, from a table of values. In this manner, an offset in the deceleration demand may be determined based on the current volume difference.

[0033] [Table 1]

[0034] The nominal deceleration demand is corrected by this offset. a korr =a nom -a x In this case, the overall adjustment may have a limited effect, and on the one hand, it must not result in under-braking, and on the other hand, the change during braking must not be so large as to annoy the driver. For example, the change in the deceleration demand amount may be adjusted by the correction value to reduce the service brake performance by 6.43 m / s. 2It cannot be less than 3 m / s (for example, at full deceleration). 2 The adjustment must be limited so that the difference does not exceed

[0035] Information from the volumetric driver monitor (VDM) is used to influence the vehicle's deceleration behavior. This influence is achieved as a change in the calculation logic for driver demand detection, as shown in FIG. 4. The change is not made to the characteristic curve of the pedal response; rather, it is intervened in the downstream calculation of the deceleration demand. This allows essentially infinite adaptation, despite the limited computing power and memory capacity of the vehicle control unit. Furthermore, other functions, such as the driving mode selector, that involve the selection of the characteristic curve are not affected. According to the present invention, the volumetric driver monitor (VDM) provides information about the presence and extent of the fade phenomenon.

[0036] The downstream calculation in the driver's request detection can adjust the deceleration demand based on the fade information, thereby affecting the deceleration behavior. For example, a correction factor in the calculation algorithm is used to adapt the deceleration demand to the degree of fade, so that as fade increases, deceleration decreases. In this embodiment, the volume monitoring function outputs a (pV) factor, which represents the degree of fade according to the relationship between the actual volumetric absorption and the nominal volumetric absorption. As a result of reducing or adjusting the deceleration demand to the degree of fade, as fade increases, the deceleration demand decreases. This indicates a decrease in braking performance to the driver, allowing the driver to adapt their driving style to the system. The stored pedal characteristics do not change in this case. To compensate for the reduced deceleration due to fade, the driver must control the pedal to a higher operating point. The driver's indication of the decreased braking effect due to the changed deceleration behavior can be supplemented by a visual or audible warning message. For example, a text message (e.g. "heavy braking") can be shown on the display, complemented by a warning light. Fade is usually a reversible system condition. As the wheel brakes cool down, the degree of fade decreases, i.e. the wheel brake volume requirement decreases again. This requires the system to recover and the correction value to be reduced again.

[0037] As with conventional braking systems where the driver has direct access to the wheel brakes, the driver experiences a gradual change in deceleration behavior and can adapt their driving style. If the fade phenomenon decreases due to an adjusted driving style or reduced brake use, the correction factor for the deceleration demand is reduced again. In this case, the fade phenomenon itself is not generally interpreted as a brake system malfunction or failure state. However, if the driver does not recognize the change in system behavior at an early stage, the fade phenomenon can lead to brake system malfunction and deterioration.

[0038] Taking quantitative fade into account can improve racetrack suitability through early warning measures in the event of brake fade, as well as enhance vehicle driving safety, especially during test runs, thereby preventing potential risks of premature system degradation due to increased volume consumption.

[0039] In an alternative embodiment, the modification of the deceleration behavior is not performed during driver demand detection, but directly in the control logic of the actuator (pressure regulator, SPC). This means that the pressure demand is modified instead of the deceleration demand due to the fade phenomenon. As in the previous embodiment, the modification is performed depending on the manifestation of the fade phenomenon. This has the same effect at the system level.

[0040] The current volumetric absorption of the system is detected and normalized to the actual volumetric absorption of the system. A normalization factor can be derived from this and used in the pressure regulator. The control strategy can then be adjusted or changed. The normalization factor is used to set a control differential proportional to the system volume difference. The greater the actual volumetric absorption relative to the nominal volumetric absorption, the greater the control differential. The control differential causes the driver to press the pedal harder to obtain a higher actual pressure (the actual pressure does not reach the target pressure due to the control differential). Due to the increasing volume demand, the driver must constantly adjust his / her operation to achieve the desired deceleration. In this way, the fade phenomenon is "simulated" or indicated to the driver. The present invention may also include the following aspects: 1. A method for controlling a hydraulic brake-by-wire vehicle braking system comprising a sensor system for detecting at least one brake pedal actuation quantity and at least one actuator for supplying hydraulic pressure to at least one wheel brake, the method comprising generating a control value for the at least one actuator based on the brake pedal actuation quantity and a stored pedal characteristic curve, a volume monitoring unit determining a current pressure-volume characteristic curve and comparing the current pressure-volume characteristic curve with a stored pressure-volume characteristic curve to detect a fade event and determine a quantitative fade value; generating an adjusted control value for the at least one actuator based on the brake pedal depression amount, the stored pedal characteristic curve, and the quantitative fade value when a fade phenomenon is identified; and controlling the actuator with the adjusted control value to supply pressure to at least one wheel brake. 2. The method according to claim 1, wherein the sensor system comprises at least one sensor for pedal stroke, brake pedal force, and / or brake pedal pressure. 3. The method according to 1. or 2. above, wherein the actuator is a linear actuator and / or a piston pump. 4. A method according to any one of 1. to 3. above, characterized in that the volume monitoring unit forms a leak monitoring unit, and the leak monitoring unit detects a leak when the difference between the current pressure-volume characteristic curve and the stored pressure-volume characteristic curve is greater than a threshold value. 5. A method according to any one of 1. to 4. above, characterized in that the fade value includes a leakage value, a volume difference, and / or a slope of the current pressure-volume characteristic curve, and / or a coefficient between the stored pressure-volume characteristic curve and the current pressure-volume characteristic curve. 6. A method according to any one of items 1 to 5 above, characterized in that in order to determine the adjusted control value from the brake pedal operation amount and the stored pedal characteristic curve, at least one intermediate value is determined and the intermediate value is modified by the quantitative fade value. 7. A method according to any one of claims 1 to 6, characterized in that the adjusted control value provides a lower pressure to the wheel brake than the control value that would be used without checking for fade. 8. The method according to any one of the above items 1 to 7, characterized in that the intermediate value is multiplied by the fade value as a coefficient, in particular as a coefficient less than 1. 9. The method according to any one of 1. to 8. above, characterized in that the fade value is subtracted from the intermediate value as an offset. 10. When a fade phenomenon is confirmed, an audible and / or visual warning message is additionally output to the driver; The method according to any one of 1. to 9. above, wherein the warning message is output immediately upon detection of a fade phenomenon and / or after the fade value exceeds a threshold value. 11. A method according to any one of items 1 to 10 above, characterized in that the adjustment of the control value in the event of a fade phenomenon is performed only if the method is activated via the driver interface. 12. A hydraulic brake-by-wire type automobile braking device, 1. A motor vehicle braking system comprising: a sensor system for detecting at least one brake pedal actuation quantity; at least one actuator for supplying hydraulic pressure to at least one wheel brake; and a control device configured to generate a control value for the at least one actuator based on the brake pedal actuation quantity and a pedal characteristic curve stored in a memory device of the control device, the controller is further configured to perform volume monitoring, determining a current pressure-volume characteristic curve and comparing the current pressure-volume characteristic curve with a stored pressure-volume characteristic curve to detect a fade event and determine a quantitative fade value; generating an adjusted control value for the at least one actuator based on the brake pedal depression amount, the stored pedal characteristic curve, and the quantitative fade value when a fade phenomenon is identified; and wherein the actuator is controlled by the adjusted control value to supply pressure to the at least one wheel brake. [Explanation of symbols]

[0041] 1 Brake device 5 Linear Actuators 6, 7, 8, 9 Wheel Brakes 17 Master cylinder pressure sensor 21 Pedal stroke sensor 22 Pedal characteristic curve 31 Stored pressure-volume characteristic curve 32 Actual (current) pressure-volume characteristic curve

Claims

1. 1. A method for controlling a hydraulic brake-by-wire vehicle braking system comprising a sensor system for detecting at least one brake pedal actuation quantity and at least one actuator for supplying hydraulic pressure to at least one wheel brake, the method comprising generating a control value for the at least one actuator based on the brake pedal actuation quantity and a stored pedal characteristic curve, a volume monitoring unit for determining a current pressure-volume characteristic curve and comparing the current pressure-volume characteristic curve with a stored pressure-volume characteristic curve to detect a fade event and determine a quantitative fade value; generating an adjusted control value for the at least one actuator based on the brake pedal depression amount, the stored pedal characteristic curve, and the quantitative fade value when a fade phenomenon is identified; controlling said actuator with its adjusted control value to supply pressure to at least one wheel brake.

2. 2. The method according to claim 1, wherein the sensor system comprises at least one sensor for pedal travel, brake pedal force and / or brake pedal pressure.

3. 3. The method according to claim 1 or 2, characterized in that the actuator is a linear actuator and / or a piston pump.

4. 3. The method according to claim 1, wherein the volume monitoring unit forms a leak monitoring unit, which detects a leak if the difference between the current pressure-volume characteristic curve and the stored pressure-volume characteristic curve is greater than a threshold value.

5. 3. The method according to claim 1 or 2, characterized in that the fade value comprises a leakage value, a volume difference, and / or a slope of the current pressure-volume characteristic curve, and / or a coefficient between the stored pressure-volume characteristic curve and the current pressure-volume characteristic curve.

6. 3. The method according to claim 1, further comprising determining at least one intermediate value from the brake pedal actuation quantity and the stored pedal characteristic curve to determine the adjusted control value, and modifying the intermediate value by the quantitative fade value.

7. 3. A method according to claim 1 or 2, characterized in that the adjusted control value provides a lower pressure to the wheel brakes than the control value used without checking for a fade phenomenon.

8. 7. A method according to claim 6, characterized in that the intermediate value is multiplied by the fade value as a factor, in particular as a factor less than one.

9. 7. The method of claim 6, wherein the fade value is subtracted from the intermediate value as an offset.

10. When a fade phenomenon is confirmed, an audio and / or visual warning message is additionally output to the driver; 3. A method according to claim 1 or 2, characterized in that the warning message is output immediately upon detection of a fade phenomenon and / or after the fade value exceeds a threshold value.

11. 3. The method according to claim 1, wherein the adjustment of the control value in the event of a fade phenomenon is carried out only if the method is activated via a driver interface.

12. A hydraulic brake-by-wire type automotive brake device, 1. A motor vehicle brake system comprising: a sensor system for detecting at least one brake pedal actuation quantity; at least one actuator for supplying hydraulic pressure to at least one wheel brake; and a control device configured to generate a control value for the at least one actuator based on the brake pedal actuation quantity and a pedal characteristic curve stored in a memory device of the control device, the controller is further configured to perform volume monitoring, determining a current pressure-volume characteristic curve and comparing the current pressure-volume characteristic curve with a stored pressure-volume characteristic curve to detect a fade event and determine a quantitative fade value; generating an adjusted control value for the at least one actuator based on the brake pedal depression amount, the stored pedal characteristic curve, and the quantitative fade value when a fade phenomenon is identified; 10. A hydraulic brake-by-wire vehicle braking system, characterized in that the actuator is controlled by the adjusted control value to supply pressure to the at least one wheel brake.

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