A brake system, a method for operating the brake system, a computer program for performing the method, and a storage medium in which the computer program is stored.

Abstract

The present invention relates to a brake system (100) comprising a primary brake actuator (1) and a secondary brake actuator (2), wherein the primary brake actuator (1) can set a target brake pressure (p_target) (603). [Solution] In the first monitoring phase, the secondary brake actuator (2) monitors the primary brake actuator (1) to see if a target brake pressure exists (604). If the target brake pressure is not present, the secondary brake actuator (2) hydraulically shuts off at least one hydraulic connection (22) between the primary brake actuator (1) and the secondary brake actuator (2) (605).

Description

Technical Field

[0001] The present invention relates to a method of operating a braking system and a braking system.

Background Art

[0002] Patent Document 1 discloses a method of operating a hydraulic vehicle braking device having an electromechanical brake force booster and a wheel slip control. Patent Document 1 proposes operating the vehicle braking device by means of the brake force booster in situations where the brake pedal is not being operated, for example in order to limit the vehicle speed, or to control the distance from a preceding vehicle, or when parking.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] The present invention starts from a method of operating a braking system, the braking system having a primary brake actuator and a secondary brake actuator. The primary brake actuator should set a target brake pressure.

[0005] In a first monitoring phase, the secondary brake actuator monitors the primary brake actuator as to whether the target brake pressure is present, that is, as to whether this target brake pressure is actually applied. In the absence of the target brake pressure, the secondary brake actuator hydraulically interrupts at least one hydraulic connection between the primary brake actuator and the secondary brake actuator.

[0006] The primary brake actuator is a by-wire actuator, and the secondary brake actuator may be an ESP hydraulic unit hydraulically connected to the by-wire actuator. Together, the primary and secondary brake actuators form a by-wire brake system, in which there are no hydraulic or mechanical connections between the brake pedal / brake operating unit and the primary and secondary actuators. In other words, the brake pedal / brake operating unit and the brake actuators are hydraulically and mechanically independent of each other. Both the primary and secondary brake actuators are connected to the brake operating unit, where they are connected to the brake operating unit's control unit or directly to the corresponding sensor system (e.g., stroke sensor, force sensor, etc.). The by-wire connection of the brake operating unit advantageously allows brake presets to be transferred instantly and quickly from the driver side or another vehicle system side to the primary and secondary actuators. To form redundancy and failure safety, the brake presets can be easily converted to target brake pressure by both actuators. By monitoring the function of the primary brake actuator from the secondary brake actuator side, the secondary brake actuator can react appropriately when there is an undesirable behavior in the primary brake actuator.

[0007] One possible response is to first close the switching valve of the ESP hydraulic unit. This confines the pressure present within the ESP system, preventing an unintended pressure drop within the ESP system, i.e., within the secondary brake actuator. The switching valve has a check valve connected in parallel, which allows the flow of hydraulic fluid toward the wheel brake, so that the primary brake actuator can continue to generate pressure if it is still functional.

[0008] In the configuration described above, the secondary brake actuator further monitors the primary brake actuator in the second monitoring phase to ensure that the target brake pressure is still not present. If it remains absent, the secondary brake actuator takes over the braking function of the primary brake actuator. This improves the reliability of the overall system. Based on the takeover by the secondary actuator, the takeover and continuation of braking can be carried out without the driver noticing. When the pressurized brake fluid is contained by the closure of the valve and braking is continued by the second actuator, there are no fluctuations within the target brake pressure, and consequently within the braking action, or if there are, they are only undetectable.

[0009] More advantageously, in the first monitoring phase, if the target brake pressure falls below a certain duration, particularly by a certain magnitude, its absence is confirmed. This allows for immediate confirmation of a primary brake actuator malfunction if the target brake pressure remains below the target after the first time phase has elapsed, and the first corrective action can be taken immediately. By monitoring not only the degree of the failure but also the magnitude of the failure, the implementation of the above corrective action (closing the switching valve) can be adapted to the timing or severity of the failure. Similarly advantageously, in the second monitoring phase, if the target brake pressure falls below a certain duration, particularly by a certain magnitude, its absence is confirmed.

[0010] In a favorable configuration, the second duration is longer than the first duration. Thus, the relatively short first duration allows for a rapid response to the perceived pressure drop, and consequently, the suspected malfunction of the primary brake actuator, while subsequently, over a relatively longer timescale, it is possible to observe whether an actual malfunction has occurred in the primary brake actuator. It is still possible, as is well known, to continue operating the primary brake actuator via a check valve connected in parallel to the switching valve.

[0011] In one configuration, hydraulic isolation between the primary and secondary brake actuators is achieved by at least one switching valve in the secondary brake actuator. Thus, the brake pressure is easily maintained by means present in the secondary brake actuator anyway, and can serve as the basis for any possible continued operation by the secondary brake actuator.

[0012] In an alternative configuration of the above method, the primary and secondary brake actuators are controlled by the same brake preset. A brake preset can be understood as a brake request or brake intention, which may be set by the driver on the one hand, and may originate from another vehicle system on the other hand. In this case, the brake request, brake preset, or brake intention may include not only the fact that braking should be performed each time, but also the fact that braking should be performed with a certain force. Similarly, another vehicle system (e.g., traffic jam following, distance control, etc.) may set the brake system for the force with which braking should be performed. It is advantageous for both brake actuators to receive the same brake preset. This is because, in this case, the secondary brake actuator can take over the braking function of the primary brake actuator without the secondary brake actuator needing to derive, estimate, or calculate the brake preset from another variable. If it were necessary to derive, estimate, or calculate from another variable, it could lead to unintended time delays. Thus, brake presets can be easily and quickly converted within the brake-by-wire system, ensuring improved failure safety. The operation of the brake actuator is controlled electronically via a corresponding signal line or a communication network present within the vehicle.

[0013] In an advanced version of the above method, the target brake pressure to be set relative to the brake preset by the primary and / or secondary brake actuators is stored within the primary and secondary brake actuators based on the brake preset-target brake pressure relationship. In this case, the brake preset-target brake pressure relationship may be identically provided within both brake actuators. As mentioned above, this is advantageous in that the secondary brake actuator can take over the braking function with high reliability and speed.

[0014] When the braking function of the primary brake actuator is taken over by the operation of the secondary brake actuator, at least one high-pressure switching valve of the secondary brake actuator is opened during its operation to supply hydraulic fluid. In this way, the hydraulic fluid required on the secondary brake actuator side and which should serve as the basis for pressure increase can be contained.

[0015] The present invention further includes a brake system comprising a primary brake actuator, a secondary brake actuator, and means for carrying out the method described above. The present invention also includes a computer program configured to carry out the steps of the above method, and a machine-readable storage medium in which the computer program is subsequently stored. [Brief explanation of the drawing]

[0016] [Figure 1] This is a diagram showing the braking system in the first driving situation. [Figure 2] This diagram shows the relationship between the target brake pressure and the brake preset, along with the entered values. [Figure 3] This is a diagram showing the braking system in the second driving situation. [Figure 4] This is a diagram showing the braking system in the third driving situation. [Figure 5] This is a diagram showing the braking system in the fourth driving situation. [Figure 6] This is a diagram showing the flow of how to operate the brake system. [Modes for carrying out the invention]

[0017] Figure 1 shows a schematic diagram of the brake system 100, which comprises a primary brake actuator 1 and a secondary brake actuator 2. The primary brake actuator 1 and the secondary brake actuator 2 are controlled by an operation unit 5 using signals 6 and 7. The operation unit 5 can detect, for example, that the driver has operated the brake system via the vehicle's brake operating element 20, for example, using a sensor unit 19. Signals 6 and 7 correspond to the brake requests that arise as a result.

[0018] Brake presets may also be provided by other vehicle systems, such as automated driving systems, automatic follow-me systems, or emergency braking systems. Such systems are not illustrated here for simplicity.

[0019] Both the primary brake actuator 1 and the secondary brake actuator 2 generate brake pressure in the connected hydraulic wheel brakes 21, respectively, within the connected hydraulic brake circuits 3 and 4, thereby generating a braking action for the vehicle in a known manner, for example, through the brake lining and brake disc. In this case, both brake actuators 1 and 2 can independently generate brake pressure in the wheel brakes.

[0020] The primary brake actuator 1 is provided as a by-wire brake actuator, and the by-wire brake actuator is operationally controlled based on a signal, for example, signal 6 on the operation unit 5 side. Such a primary brake actuator 1 can, in this case, have a control device, and the control device operationally controls the motor unit. Through a transmission mechanism, the motor unit can move the input piston of the master brake cylinder directly or via an intervening component, such as a spring or another piston. The input piston defines the hydraulic chamber of the master brake cylinder. By moving the input piston, a force is applied to the hydraulic liquid present in the chamber, and thus this hydraulic liquid is pushed out towards the output pipeline 22, whereby ultimately the hydraulic pressure can be set within the brake system. Another configuration of the primary brake actuator 1, such as a pump or an accumulator, is also possible.

[0021] The secondary brake actuator 2 can be connected to the output pipeline 22. In FIG. 1, the secondary brake actuator 2 is shown as a conventional brake control system, and its elements will be briefly described below. Similar to the primary brake actuator 1, the secondary brake actuator 2 is also operationally controlled based only on a signal, for example, signal 7 of the operation unit 5, and can set the brake pressure. For this purpose, the secondary brake actuator 2 has a hydraulic pump 12 for each of the brake circuits 3 and 4, and the hydraulic pump 12 can be driven by a motor 13. When the pump 12 pumps the hydraulic liquid towards the individual or multiple wheel brakes 21, brake pressure can be generated in these wheel brakes 21. Appropriate brake pressure generation in each of the multiple wheel brakes 21 can be implemented by the existing hydraulic valves. In the hydraulic pipeline leading to each wheel brake 21, an inlet valve 8, for example, a controllable non-energized open valve, is present in parallel with a check valve that blocks the hydraulic flow towards the wheel brake.

[0022] At the point where it exits the wheel brake, there is an outlet valve 9 in the form of a switchable non-energized closed valve without a check valve. The outlet valve 9 connects the wheel brake to the hydraulic accumulator 10, and the hydraulic accumulator 10 is connected to the suction side of the pump 12 via the check valve 11 together with the outlet valve 9. The check valve 11 permits the hydraulic flow towards the pump. The outlet valve 9 is a non-energized closed valve. Also, on the suction side of the pump 12, a hydraulic connection leading to the high-pressure switching valve 16 is connected, and the high-pressure switching valve 16 is switchable, non-energized closed, without a check valve, and on the other side of the high-pressure switching valve 16, it is connected to one of the hydraulic lines 22 of the primary brake actuator 1.

[0023] On the discharge side of the pump, there are elements 14 that affect the hydraulic flow coming out of the pump 12, such as dampers, and a check valve that permits the hydraulic flow coming out of the pump.

[0024] The discharge side of the pump 12 is connected to one of the hydraulic lines 22 of the primary brake actuator 1 via a non-energized open valve 15 having a check valve that permits the hydraulic flow from the primary brake actuator 1 towards the inlet valve 8. Also, the discharge side is connected to the assigned inlet valve 8. The said valve 15 is a so-called switching valve, and this switching valve is controllable, non-energized open, and has the above-mentioned check valve.

[0025] For example, in situations where brake control intervention is required to implement an anti-lock function, traction control, or anti-slip, the brake pressure for each wheel can be formed, eliminated, increased, or decreased in a known manner directly via the primary brake actuator 1 or with the involvement of the hydraulic pump 12, the accumulator chamber 10, and the correspondingly setable valves.

[0026] Typically, normal braking is performed by the primary brake actuator 1. The primary brake actuator 1 can generate brake pressure in the wheel brake 21 via the hydraulic pipeline 22, valve 15, and inlet valve 8. At this time, the outlet valve 9 is closed.

[0027] The hydraulic pipeline 23 highlighted in Figure 1 (which also includes pipeline 22) shows where the corresponding brake pressure is applied within the secondary brake actuator 2 when pressure is generated by the primary brake actuator 1. It can be seen that the brake pressure reaches the wheel brake 21 and cannot pass through valves 16 and 9 due to the closed valve 16 and the closed outlet valve 9.

[0028] The brake pressure p_actual, which is thus dominant, can be determined by the pressure sensor 17.

[0029] To properly implement a brake preset, that is, a driver brake request, the brake preset must be determined. A brake preset or driver brake request can be determined, for example, based on the operating stroke s of the brake pedal 20, which is determined by a sensor system 19. This operating stroke s can be supplied as a signal 6 or 7 to the primary brake actuator 1 and the secondary brake actuator 2. Signal preprocessing is also possible. Similarly, instead of the operating stroke, an operating force, operating pressure, operating speed, or a correlated variable may be determined. For simplicity, the following will begin with brake requests s existing of a certain size or scale.

[0030] Similarly, brake presets may also be output directly by a separate vehicle system. This vehicle system does not necessarily rely on the driver's preset.

[0031] The brake preset s can be assigned the expected brake pressure p_target, which is set on the primary brake actuator 1 side, as indicated by the characteristic curve 205. If the primary brake actuator 1 is functioning correctly, then the brake pressure p_target, indicated by the marking 201, will be generated for the brake preset s1 in Figure 2.

[0032] The characteristic line 205 is stored or present within each of the brake actuators 1 and 2. This allows both brake actuators 1 and 2 to know which brake pressure p_target should be set for the current brake preset s transmitted as signals 6 and 7.

[0033] The following assumes that the primary brake actuator 1 can no longer generate, or can no longer fully generate, the brake pressure p_target that matches the brake preset s1. This can occur because a lower brake pressure, indicated by marking 202, is set, even though the value indicated by 201 is expected.

[0034] This can be determined by the control device 18 within the secondary brake actuator 2. A brake pressure sensor 17 is connected to the control device 18.

[0035] Figure 3 substantially corresponds to the brake pressure distribution shown in Figure 1, but shows a lower dominant brake pressure 23 within the system, corresponding to the marking 202 shown in Figure 2. For example, if the applied brake pressure was 60 bar in Figure 1, it may be only around 50 bar in Figure 3.

[0036] When this lower brake pressure 202 persists for longer than the first time span t1, the switching valve 15 in the secondary brake actuator 2 is closed. This confines the still dominant pressure within the hydraulic line of the secondary brake actuator 2. An exemplary time span can be 10 milliseconds, after which the switching valve 15 is closed. The switching valve 15 has a check valve connected in parallel, which allows the flow of hydraulic fluid toward the wheel brake. Thus, if the primary brake actuator 1 is still functional, the primary brake actuator 1 can continue to generate pressure in the wheel brake.

[0037] Figure 4 shows how the brake pressure generated on the primary brake actuator side, based on line 23a, further decreases to value 203 according to Figure 2. This further decrease may occur, for example, to 40 bar. At the point marked by line 23b, based on the closed valve 15, the brake pressure shown in Figure 3 (corresponding to marking 202 in Figure 2) continues.

[0038] When the secondary brake actuator 2, using the pressure sensor 17 and control device 18, confirms that the brake pressure is lower than the expected brake pressure (201 in Figure 2) during the second time span t2, it is presumed that there is a malfunction in the primary brake actuator. The secondary brake actuator takes over the role of the primary brake actuator and continues braking based on the brake preset s1. In this case, the pump 12 therefore sets the expected brake pressure again to the corresponding valve position (shown in Figure 5) according to the characteristic line 205. The switching valve 15 remains closed, and the valve 16 is opened, allowing the pump 12 to draw in hydraulic fluid. The portion of the hydraulic line marked by line 23b is therefore again at the original pressure level 201 that should be set by referring to the characteristic line 205 based on the brake request s1. The pressure level maintained by the primary brake actuator 1 may have dropped further at this point, possibly even to zero (marked 204 in Figure 2).

[0039] All braking functions are taken over and implemented by the secondary brake actuator 2 after a malfunction of the primary brake actuator 1 is detected.

[0040] The process described above can be expressed as a method flow as follows:

[0041] In the starting step 601, we begin from a starting point where both brake actuators, namely the primary brake actuator 1 and the secondary brake actuator 2, are functioning.

[0042] In the subsequent step 602, the brake preset s1 is detected and provided to the brake actuators 1 and 2 as signals 6 and 7.

[0043] In the subsequent step 603, the brake pressure 201 is set by the primary brake actuator 1 based on the characteristic curve 205 according to the brake preset s1.

[0044] In monitoring step 604, the system monitors whether the currently controlled brake pressure p_actual in the secondary brake actuator is, for example, above 5 bar and below the target brake pressure p_target scheduled for brake preset s1, and whether this continues for a first duration (t>t1). If this is true, the system proceeds to step 605. Otherwise, monitoring continues for a first duration t1, and the pressure is then set by the primary brake actuator 1 according to step 603.

[0045] In step 605, a monitoring function in the secondary brake actuator 2 is activated to check whether another criterion 606 is met. Furthermore, as described above, the valve 15 is closed to contain the brake pressure already applied by the primary brake actuator 1.

[0046] In step 606, it is checked whether the current brake pressure p_actual is below the target brake pressure p_target by, for example, 5 bar for a second duration (t>t2).

[0047] If this condition is met, in step 607, the secondary brake actuator 2 begins to take over the braking function. Valve 15 is kept closed, valve 16 is opened, and the pump 12 is controlled to achieve, thereby again achieving the target brake pressure based on the brake preset s1 derived from the characteristic curve 205 through the operation of the secondary brake actuator 2.

[0048] Additionally, in step 608, a warning signal is output within the vehicle (auditoryly, visually, etc.) to indicate a malfunction of the primary brake actuator.

[0049] In step 609, the brake request is then taken over solely by the secondary brake actuator 2, which makes it possible to, for example, keep the vehicle stopped, accelerate the vehicle again, or perform driver-initiated and system-initiated braking. [Explanation of symbols]

[0050] 1. Primary brake actuator 2. Secondary brake actuator 3,4 Hydraulic brake circuits 5. Operation Unit 6,7 signal 8 Inlet valve 9. Outlet valve 10. Hydraulic accumulator, accumulator chamber 11 Check valve 12. Hydraulic pump 13 Motors 14 Factors affecting hydraulic flow 15 valves, switching valves 16 High-pressure switching valve 17 Pressure Sensor 18 Control device 19. Sensor Units, Sensor Systems 20 Brake operation elements, brake pedal 21 Hydraulic wheel brakes 22 Output pipelines, hydraulic pipelines 23. Hydraulic pipeline, brake pressure 100 Brake System 201-204 Markings, brake pressure values 205 Characteristic Line Steps 601-609 p_actual brake pressure p_target Expected brake pressure s Actuation stroke, brake request, brake preset s1 Brake preset, brake request t1 First time span t2 Second time span

Claims

1. A method for operating a brake system (100), wherein the brake system (100) comprises a primary brake actuator (1) and a secondary brake actuator (2), and the primary brake actuator (1) can set a target brake pressure (p_target) (603). The secondary brake actuator (2) monitors (604) the primary brake actuator (1) in the first monitoring phase to determine whether the target brake pressure exists. When the target brake pressure is not present, the secondary brake actuator (2) hydraulically disconnects at least one hydraulic connection (22) between the primary brake actuator (1) and the secondary brake actuator (2) (605). How to operate the brake system (100).

2. The method according to claim 1, wherein the secondary brake actuator (2) further monitors the primary brake actuator (1) in the second monitoring phase to see if the target brake pressure is still absent (606), and if absent, the secondary brake actuator (2) takes over the braking function of the primary brake actuator (1) (607).

3. The method according to claim 1, characterized in that, in the first monitoring phase, if the target brake pressure falls below a certain threshold for any first duration, particularly by any first magnitude, its absence is confirmed.

4. The method according to claim 2, characterized in that, in the second monitoring phase, if the target brake pressure (p_target) falls below a certain second duration, particularly by a certain second magnitude, its absence is confirmed.

5. The method according to claims 3 and 4, wherein the second duration is longer than the first duration.

6. The method according to any one of claims 1 to 5, wherein the hydraulic shutoff between the primary brake actuator (1) and the secondary brake actuator (2) is performed by at least one switching valve (15) of the secondary brake actuator (2).

7. The method according to any one of claims 1 to 6, wherein the operation of the primary brake actuator (1) and the secondary brake actuator (2) is controlled by the same brake preset (6, 7, s) (602), particularly electronically.

8. The method according to claim 7, wherein the target brake pressure (p_target) to be set for the brake preset (6, 7, s) by the primary brake actuator (1) and / or the secondary brake actuator (2) is stored in the primary brake actuator (1) and the secondary brake actuator (2) based on the brake preset-target brake pressure-relationship (205), and in particular, in both brake actuators (1, 2) based on the same brake preset-target brake pressure-relationship (205).

9. The method according to claim 2, wherein at least one high-pressure switching valve (16) of the secondary brake actuator (2) is opened during operation to supply hydraulic fluid, so that the braking function of the primary brake actuator (1) is taken over by the operation of the secondary brake actuator (2).

10. A brake system comprising a primary brake actuator (1) and a secondary brake actuator (2), and means (18, 19) for carrying out the method according to any one of claims 1 to 9.

11. A computer program configured to carry out the steps of the method described in any one of claims 1 to 9.

12. A machine-readable storage medium in which the computer program described in claim 11 is stored.

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