Method for operating a brake system and brake system

Abstract

The invention relates to a brake system (100) comprising a primary brake actuator (1) and a secondary brake actuator (2), a target brake pressure (ptarget) being adjustable (603) by means of the primary brake actuator (1). The secondary brake actuator (2) monitors (604) the primary brake actuator (1) in a first monitoring phase in order to determine whether a target brake pressure is present. In the absence of the target brake pressure, the secondary brake actuator (2) hydraulically interrupts (605) the at least one hydraulic connection (22) between the primary brake actuator (1) and the secondary brake actuator (2).

Description

BACKGROUND

[0001] DE 10 2009 001 135 A1 discloses a method for operating a vehicle hydraulic brake device having an electromechanical brake force amplifier and a wheel slip control device. It is proposed to operate the vehicle brake device with the brake force amplifier in the event that the brake pedal is not operated, for example to limit the vehicle speed or to distance regulation from a vehicle in front or when parking. SUMMARY

[0002] The application proposes a method for operating a brake system having a primary brake actuator and a secondary brake actuator. A target brake pressure is to be adjusted by means of the primary brake actuator.

[0003] In a first monitoring phase, the secondary brake actuator monitors the primary brake actuator to determine whether a target brake pressure is present, i.e. whether the target brake pressure is also actually set. In the event that no target brake pressure is present, the secondary brake actuator interrupts at least one hydraulic connection between the primary brake actuator and the secondary brake actuator from a hydraulic point of view.

[0004] The primary brake actuator can be a brake-by-wire actuator, and the secondary brake actuator can be an ESP hydraulic unit which is hydraulically connected to the brake-by-wire actuator. The primary brake actuator and the secondary brake actuator together form a brake-by-wire brake system, in which there is no hydraulic or mechanical connection between the brake pedal / brake actuation unit and the primary and secondary actuators. In other words, the brake pedal / brake actuation unit and the brake actuators are constructed independently of one another hydraulically and mechanically. Both the primary and secondary brake actuators are connected to the brake actuation unit, either to a controller of the brake actuation unit or directly to a corresponding sensor system (e.g. displacement sensor, force sensor, etc.). By means of the brake-by-wire connection of the brake actuation unit, a brake specification on the driver's side or on the side of another vehicle system can advantageously be forwarded to the primary and secondary actuators in good time and quickly. In order to establish redundancy and fail safety, the brake specification can be simply converted into a target brake pressure by both actuators. By monitoring the function of the primary brake actuator on the side of the secondary brake actuator, the secondary brake actuator can react appropriately in the event of a fault in the behaviour of the primary brake actuator.

[0005] The reaction can here be firstly to close a switching valve of the ESP hydraulic unit, in order thus to lock the pressure present in the ESP system and to inhibit an undesired pressure drop in the ESP system, i.e. in the secondary brake actuator. Since the switching valve has a non-return valve connected in parallel (which enables a flow of hydraulic fluid in the direction of the wheel brakes), the primary brake actuator can continue to cause a pressure increase in the event that it should still be operational.

[0006] In a design variant of the method, the secondary brake actuator continues to monitor the primary brake actuator in the second monitoring phase in order to determine whether the target brake pressure is still not present. In the further absence, the secondary brake actuator takes over the brake function of the primary brake actuator. The safety of the overall system is thereby increased. The takeover and continuation of the braking can take place substantially unnoticed by the driver as a result of the takeover by the secondary actuator. If the brake fluid is locked by means of the closing valve under pressure and the braking is continued using the second actuator, no fluctuations or only insignificant fluctuations arise in the target brake pressure and thus in the braking effect.

[0007] It is furthermore advantageous if, in the first monitoring phase, the absence is determined if the target brake pressure is undershot, in particular by a first amount, in a first time duration. Thus, after the end of the first time phase, a deficiency of the primary brake actuator can be determined in good time when the target brake pressure is undershot, and the first measures can be taken in good time. By monitoring not only the undershooting and the first time duration, but also the amount of the undershooting, the activation of the measures (closing of the switching valve) can be adapted in terms of the point in time or the severity of the undershooting. It is also advantageous if, in the second monitoring phase, the absence is determined if the target brake pressure is undershot, in particular by a second amount, in a second time duration.

[0008] In an advantageous design variant, the second time duration is greater than the first time duration. Thus, a short first time duration can be used to respond quickly to an identified pressure drop, and thus to an assumed deficiency of the primary brake actuator, and it can then be observed over a longer time range whether the primary brake actuator is actually deficient. It is known that it is still possible to continue operating the primary brake actuator by means of the non-return valve connected in parallel to the switching valve.

[0009] In a design variant, the hydraulic interruption between the primary brake actuator and the secondary brake actuator is effected by means of at least one switching valve of the secondary brake actuator. Thus, the brake pressure can be simply maintained by means of the means which are always present in the secondary brake actuator, and can serve as a basis for the potential continued operation by means of the secondary brake actuator.

[0010] In a further design of the method, the primary brake actuator and the secondary brake actuator are actuated with the same brake preset. The brake preset is understood to be a brake desire or a brake intention, which can be set by the driver on the one hand and can come from a further vehicle system on the other hand. Here, the brake desire, the brake preset or the brake intention can each include the fact that something should be braked and additionally how strongly something should be braked. The further vehicle system, for example a congestion following drive, a distance regulation, can preset to the brake system how strongly something should be braked. It is advantageous if both brake actuators receive the same brake preset, since the secondary brake actuator can take over the brake function from the primary brake actuator and the secondary brake actuator does not have to derive, estimate or calculate the brake preset from other variables, which can lead to unnecessary time delays. Thus, the brake preset can be implemented simply and quickly in a brake-by-wire system, wherein a higher reliability is ensured. The actuation of the brake actuators takes place here electronically via corresponding signal lines or a communication network present in the vehicle.

[0011] In a refinement of the method, the target brake pressure to be adjusted by the primary and / or secondary brake actuator for the brake preset is stored in the primary and secondary brake actuators by means of a brake preset-target brake pressure relationship. The brake preset-target brake pressure relationship can be set identically in both brake actuators here. As mentioned, this has the advantage that the secondary brake actuator can reliably and quickly take over the brake function.

[0012] When the brake 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 when the secondary brake actuator is operated in order to supply hydraulic fluid. Thus, the required hydraulic fluid can be accommodated on the secondary brake actuator side, which should serve as a basis for the pressure increase.

[0013] The invention also comprises a brake system, which comprises a primary brake actuator and a secondary brake actuator and means for carrying out the method as described. The invention also comprises a computer program and a machine-readable storage medium, on which the computer program is stored, which are designed to carry out the steps of the method. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 A brake system in a first operating situation is shown.

[0015] Figure 2 A target brake pressure brake preset in relation to a recorded value is shown.

[0016] Figure 3 A brake system in a second operating situation is shown.

[0017] Figure 4The brake system is shown in a third operating situation.

[0018] Figure 5 The brake system is shown in a fourth operating situation.

[0019] Figure 6 A method flow for operating a brake system is shown. DETAILED DESCRIPTION

[0020] Figure 1 A schematic diagram of a brake system 100 is shown, 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 actuated by a control unit 5 with signals 6 and 7. The control unit 5 can detect, for example with a sensor unit 19, a current brake request of the brake system by a driver via a brake actuating element 20 of the vehicle. The signals 6 and 7 thus correspond to the current brake request.

[0021] Likewise, a brake request can be provided by other vehicle systems, for example an automatic driving system, a system for automatic following travel or an emergency brake system. Such systems are not shown here for simplicity.

[0022] The primary brake actuator 1 and the secondary brake actuator 2 are each able to generate a brake pressure in the connected hydraulic brake circuits 3 and 4 at the respectively connected hydraulic wheel brakes 21 and thus, for example, to generate a braking effect for the vehicle in a known manner by brake pads and brake discs. The two brake actuators 1 and 2 are thus able to independently increase the brake pressure on the wheel brakes.

[0023] The primary brake actuator 1 is designed as a brake-by-wire actuator, which is actuated by means of a signal, for example the signal 6 from the control unit 5. Such a primary brake actuator 1 can comprise a controller here, which actuates a motor unit. The motor unit can displace an input piston of a master brake cylinder directly or via an intermediate component, for example a spring or a further piston, by means of a transmission. The input piston limits a hydraulic chamber of the master brake cylinder. By displacement of the input piston, the hydraulic fluid located in the chamber is loaded with force and thus moved in the direction of an output line 22, by means of which the hydraulic pressure in the brake system can finally be adjusted. Other embodiments of the primary brake actuator 1, for example a pump or a reservoir, are conceivable.

[0024] The secondary brake actuator 2 can be connected to the output line 22. In Figure 1In this case, the secondary brake actuator is shown as a classic brake regulation system, the elements of which are briefly discussed subsequently. As with the primary brake actuator 1, the secondary brake actuator 2 can also be controlled and the brake pressure adjusted on the basis of signals alone, for example signals 7 from the control unit 5. To this end, the secondary brake actuator 2 has a hydraulic pump 12 in each brake circuit 3 and 4, which can be driven with an electric motor 13. If the pump 12 conveys hydraulic fluid in the direction of the individual or multiple wheel brakes 21, a brake pressure can be generated on these wheel brakes. The brake pressure can be generated on individual wheel brakes 21 by means of existing hydraulic valves. An inlet valve 8, for example an adjustable, normally open valve with a parallel connected non-return valve, is located in the hydraulic line to each wheel brake 21, which non-return valve inhibits hydraulic flow towards the wheel brake.

[0025] An outlet valve 9 in the form of a switchable, normally closed valve without a non-return valve is located leading away from the wheel brakes. The outlet valve 9 connects the wheel brakes to a hydraulic reservoir 10, which, together with the outlet valve 9, is connected to the suction side of the pump 12 by means of a non-return valve 11. The non-return valve 11 allows hydraulic flow in the direction of the pump. The outlet valve 9 is a normally closed valve. The hydraulic connection to a high-pressure switch valve 16, which is switchable, normally closed and has no non-return valve, is also connected to the suction side of the pump 12, and with its other side to one of the hydraulic lines 22 of the primary brake actuator 1.

[0026] An element 14, for example a damper and a non-return valve, which influences the hydraulic flow from the pump 12, is located on the pressure side of the pump, which non-return valve allows hydraulic flow away from the pump.

[0027] The pressure side of the pump 12 allows hydraulic flow in the direction of the inlet valve 8 from the primary brake actuator 1 via a normally open valve 15, which comprises a non-return valve, to one of the hydraulic lines 22 connected to the primary brake actuator 1. The pressure side is also connected to the associated inlet valve 8. The valve 15 is a so-called switching valve, which is adjustable, comprising the mentioned normally open non-return valve.

[0028] In the event of a brake regulation intervention being required, for example in order to implement an anti-lock function, traction control or slip protection, the brake pressure can be increased or reduced in a known manner either directly by the primary brake actuator 1 or with the involvement of the hydraulic pump 12, the reservoir chamber 10 and the correspondingly provided valves, wheel-individually.

[0029] Normally, normal braking takes place by means of the primary brake actuator 1, which can generate a brake pressure on the wheel brakes 21 by means of the hydraulic lines 22, the valve 15 and the inlet valve 8. Here, the outlet valve 9 is closed.

[0030] In the event of a brake regulation intervention being required, for example in order to implement an anti-lock function, traction control or slip protection, the brake pressure can be increased or reduced in a known manner either directly by the primary brake actuator 1 or with the involvement of the hydraulic pump 12, the reservoir chamber 10 and the correspondingly provided valves, wheel-individually. Figure 1The hydraulic circuit 23 (also including the circuit 22) highlighted in the middle shows where the associated brake pressure in the secondary brake actuator 2 is present when a pressure is generated by the primary brake actuator 1. It can be seen that the brake pressure reaches the wheel brakes 21 and cannot pass through them due to the closed valve 16 and the closed outlet valve 9.

[0031] The brake pressure p_actual that is present can thus be determined by means of the pressure sensor 17.

[0032] In order to implement the brake specification, i.e. the driver brake wish, for example, appropriately, the brake specification must be determined. This can be detected, for example, by means of the adjustment path s of the brake pedal 20, which is detected by means of the sensor system 19. This adjustment path s can be delivered as a signal 6 or 7 to the primary and secondary brake actuators 1, 2. A pre-processing of the signal is also conceivable. Likewise, a steering force, a steering pressure, a steering speed or a related variable can also be detected instead of the steering path. It is subsequently assumed for the sake of simplicity that a brake wish s is present in certain dimensions or certain degrees.

[0033] Likewise, the brake specification can be output directly by a further vehicle system, which does not necessarily use the driver specification.

[0034] The brake specification s can be associated by means of a characteristic curve 205 with the intended brake pressure p_target, which is adjusted by the primary brake actuator 1. Thus, in the case of a perfect primary brake actuator 1, a brake pressure p_target according to the marking 201 is generated for the brake specification s1. Figure 2 In the middle, a brake pressure p_target according to the marking 201 is generated for the brake specification s1.

[0035] The characteristic curve 205 is stored or present in the two brake actuators 1, 2, respectively. Thus, the two brake actuators 1, 2 know which brake pressure p_target should be adjusted for the respective brake specification s (transmitted as a signal 6, 7).

[0036] It is subsequently assumed that the primary brake actuator 1 is no longer able or no longer completely able to generate a brake pressure p_target that matches the brake specification s1. This can be represented in such a way that a lower brake pressure according to the marking 202 is adjusted, although the value according to 201 is intended.

[0037] This can be determined in the secondary brake actuator 2 by means of a controller 18 to which the brake pressure sensor 7 is connected.

[0038] Figure 3 It is shown that a brake pressure 23 is present in the system, which substantially corresponds to the brake pressure profile of Figure 1 but according to Figure 2The marker 202 in the text is lower. For example, if... Figure 1 The braking pressure present in the middle is 60 bar, then in Figure 3 Only 50 bars can exist in the middle.

[0039] If the lower braking pressure 202 persists beyond the first time interval t1, then the switching valve 15 in the secondary brake actuator 2 is closed. This locks in the remaining pressure in the hydraulic circuit of the secondary brake actuator 2. An exemplary time interval might be 10 milliseconds, after which the switching valve 15 is closed. The switching valve 15 has a parallel-connected check valve that allows hydraulic fluid to flow toward the wheel brakes. Therefore, while the primary brake actuator 1 should still be operational, it can further increase the pressure on the wheel brakes.

[0040] exist Figure 4 In the diagram, line 23a illustrates how the braking pressure generated by the primary brake actuator further decreases, according to... Figure 2 The value drops to 203. For example, a further drop to 40 bar can be achieved. In the section marked with line 23b, due to the closed valve 15, there is also... Figure 3 The braking pressure, which is related to Figure 2 The 202 mark is relevant.

[0041] If the secondary brake actuator 2 determines, with the aid of pressure sensor 17 and controller 18, that the braking pressure in the second time interval t2 is less than the expected braking pressure ( Figure 2 (201 in the original text), then it is assumed that the primary brake actuator is defective. The secondary brake actuator takes over the task of the primary brake actuator and continues braking based on the braking preset s1. Here, at the corresponding valve position ( Figure 5 As shown, the braking pressure, as expected according to characteristic curve 205, is adjusted again by pump 12. Switching valve 15 remains closed, and valve 16 is opened, allowing pump 12 to draw in hydraulic fluid. The portion of the hydraulic circuit marked 23b is then at the initial pressure level 201, which can be adjusted according to the braking expectation s1 using characteristic curve 205. The pressure level maintained by the primary brake actuator 1 can be further reduced here, even to zero if necessary. Figure 2 (marked 204).

[0042] Starting with identifying the defects in the primary brake actuator 1, all braking functions are taken over and implemented by the secondary brake actuator 2.

[0043] The method flow is described below.

[0044] In an initial step 601 a starting point is assumed in which both brake actuators, i.e. the primary brake actuator 1 and the secondary brake actuator 2, are operable.

[0045] In a subsequent step 602 the brake request s1 is detected and provided as a signal 6, 7 to the brake actuators 1, 2.

[0046] In a subsequent step 603 the brake pressure 201 is adjusted by means of the primary brake actuator 1 according to the brake request s1 by means of the characteristic curve 205.

[0047] In a monitoring step 604 it is monitored in the secondary brake actuator whether the currently prevailing brake pressure p_actual is more than 5 bar, for example, below the target brake pressure p_target set for the brake request s1 and this is the case for a first duration t > ti. If this is the case, the method continues with step 605; otherwise, the monitoring below continues for the first duration ti and the pressure is continued to be adjusted by means of the primary brake actuator 1 according to step 603.

[0048] In step 605 the monitoring function in the secondary brake actuator 2 is activated to check whether further criteria 606 are met. In addition, the valve 15 is closed in order to (as described above) lock the brake pressure which has been set by the primary brake actuator 1.

[0049] In step 606 it is checked whether the current brake pressure p_actual is more than 5 bar, for example, below the target brake pressure p_target for a second duration t > t2.

[0050] If this is the case, in step 607 the brake function is released by takeover of the secondary brake actuator 2. The valve 15 is kept closed, the valve 16 is opened and the pump 12 is actuated so that the target brake pressure is reached again by means of the operation of the secondary brake actuator 2 according to the brake request s1 by means of the characteristic curve 205.

[0051] In addition, in step 608 a warning indication can be output in the vehicle (acoustically, optically, etc.) in order to indicate a deficiency of the primary brake actuator.

[0052] Then, in step 609 the brake request is only taken over by the secondary brake actuator 2, for example in order to keep the vehicle stationary, to accelerate the vehicle again or to perform a brake initiated by the driver and a brake initiated by the system.

Claims

1. A method for operating a brake system (100), the brake system comprising a primary brake actuator (1) and a secondary brake actuator (2), wherein, The target brake pressure (p_target) can be adjusted (603) by means of the primary brake actuator (1), - and wherein the secondary brake actuator (2) monitors (604) the primary brake actuator (1) in a first monitoring phase to determine whether the target brake pressure is present, - wherein, in the absence of the target brake pressure, the secondary brake actuator (2) hydraulically interrupts (605) at least one hydraulic connection (22) between the primary brake actuator and the secondary brake actuator (1, 2).

2. The method of claim 1, wherein, The secondary brake actuator (2) continues to monitor (606) the primary brake actuator (1) in a second monitoring phase to determine whether the target brake pressure is still absent, wherein, in the absence, the secondary brake actuator (2) takes over (607) the brake function of the primary brake actuator (1).

3. The method of claim 1, wherein, In the first monitoring phase, the absence is determined if the target brake pressure is undershot, in particular by a first amount, in a first duration.

4. The method of claim 2, wherein, In the second monitoring phase, the absence is determined if the target brake pressure (p_target) is undershot, in particular by a second amount, in a second duration.

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

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

7. The method of any of the preceding claims, wherein, The primary brake actuator (1) and the secondary brake actuator (2) are actuated (602), in particular electronically, with the same brake preset (6, 7, s).

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

9. The method of claim 2, wherein, In order to take over the brake function of the primary brake actuator (1) by means of the operation of the secondary brake actuator (2), at least one high-pressure switching valve (16) of the secondary brake actuator (2) is opened to supply hydraulic fluid when the secondary brake actuator is operating.

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

11. A computer program designed to carry out the steps of the method according to any one of claims 1 to 9.

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

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