Method for checking availability of hydraulic fallback level in an electronically slip-controllable power brake system, electronic controller for an electronically slip-controllable power brake system, and electronically slip-controllable power brake system with electronic controller

Abstract

The present invention relates to a method for checking the availability of a hydraulic fallback level in an electronically slip-controllable power brake system, an electronic controller, and an electronically slip-controllable power brake system. [Solution] The power brake system 10 performs braking operations during normal operation, even without the driver's involvement in brake pressure boosting. Braking requirements are detected by an electronic controller 24 and correlated to brake pressure, which is then adjusted by electrically activating the drive 22 of the primary pressure generator 20. For example, to individually adapt the brake pressure to the prevailing wheel slip conditions, the power brake system 10 includes multiple electrically activatable secondary pressure generators 30. The secondary pressure generators contact the wheel brakes 16 in parallel with the primary pressure generators 20 and can be used to provide brake pressure boost at a hydraulic fallback level. For safety reasons, it is proposed to check the availability of this hydraulic fallback level at specific time intervals during the normal braking operation of the power brake system 10.

Description

[Technical field]

[0001] The invention relates to a method for checking the availability of a hydraulic fallback level in an electronically slip-controllable power brake system according to the preamble of claim 1. Furthermore, the invention relates to an electronic controller for an electronically slip-controllable power brake system according to the preamble of claim 8 and to an electronically slip-controllable power brake system with an electronic controller according to the preamble of claim 9. [Background technology]

[0002] The invention is based on an electronically slip-controllable power brake system known from the prior art, for example from DE 10 200 03 133 A1.

[0003] The known power brake system comprises a service brake which is actuated without human power and an auxiliary brake which can be actuated by muscle power. The service brake allows the braking process to be carried out under normal conditions without the driver's involvement in brake pressure build-up. For this purpose, the need for braking is set or recognized by the driver or a vehicle sensor device and communicated to an electronic controller. The controller calculates the required brake pressure and correspondingly activates the drive of the pressure generator. The auxiliary brake is provided so that the driver can slow down the vehicle by muscle power in the event of a service brake failure.

[0004] The known power brake system is composed of several assemblies, which are for example manufactured separately from one another and are in hydraulic contact with one another, due, inter alia, to the small space situation in a vehicle and the possibility of arranging several assemblies at different locations with this non-integrated construction. A first assembly is provided for detecting the braking request given by the driver. For this purpose, the first assembly comprises the above-mentioned brake actuation element and a primary or first pressure generator for boosting the required brake pressure. The primary pressure generator has an electrically activatable drive, the activation of which is carried out by an electronic control.

[0005] The second assembly is used under normal conditions to adapt this adjusted brake pressure wheel-by-wheel to the slip situation currently prevailing at the wheel of the vehicle associated with the wheel brake, and for this purpose comprises an electrically controlled actuable secondary or second pressure generator as well as a valve mechanism which can also be electrically actuated, which valve mechanism includes a number of switchable directional control valves.

[0006] Both assemblies are in parallel hydraulic contact with the wheel brakes of the vehicle.

[0007] Said known power brake system can be operated in various operating modes: In a first operating mode (normal operation), the brake pressure as described above is provided by a primary or first brake pressure generator and, if necessary, regulated individually for the wheels by a secondary or second pressure generator.

[0008] In the second operating mode of the power brake system (hydraulic fallback level), the pressure generation by the first assembly is inhibited and the wheel brakes are energized with brake pressure by using a secondary pressure generator that remains functional. The second assembly is therefore provided to protect the power brake system against possible failure of the first assembly, in addition to the wheel-specific brake pressure regulation described above. Due to the redundancy in pressure generation, the power brake system is suitable for use in vehicles capable of autonomous driving or self-piloting.

[0009] Since under normal conditions the second assembly is rarely operational, a malfunction of this second assembly may not be recognized in time and therefore the hydraulic fallback level may not be available when needed. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] DE 102018222488 Summary of the Invention

[0011] In order to recognise a fault in the second assembly in time and possibly to warn the driver, claim 1 proposes checking the availability of the hydraulic fallback level and thus the functionality of the second assembly by means of its secondary or secondary pressure generator at regular intervals for safety reasons during normal operation of the power brake system. The time intervals between the individual check cycles can be set arbitrarily and can be varied, for example depending on the load placed on the power brake system.

[0012] The proposed method is carried out without the driver's involvement, i.e. independently of the driver, and ensures that the vehicle can be safely slowed down to a stop in the event of a malfunction in the correct functioning of the first assembly, in particular of the primary pressure generator, regardless of whether this malfunction is due to mechanical causes, for example in the pressure generator, or due to electrical causes, for example in the drive of this pressure generator and / or due to electronic causes in the start-up of said drive.

[0013] Advantageous further developments of the proposed checking method are claimed in the dependent claims.

[0014] Claim 2 proposes, for example, that during normal operation, if there is a request for braking, the drive of the primary pressure generator is inhibited by the electronic control and instead the drive of the secondary pressure generator is electrically activated, in other words, if a braking process is selected, the brake pressure is not generated by the primary pressure generator as usual, but by the secondary pressure generator, via which its functionality is checked.

[0015] If the brake pressure boost by the secondary pressure generator is performed as expected, i.e. if the brake pressure boosts as expected and reaches the desired brake pressure within the expected time span from the start of the electrical activation of the secondary pressure generator, then it can be assumed that the hydraulic fallback level is in the normal state. The braking process following the one according to claim 2 can then be performed as normal, again with the primary pressure generator.

[0016] Alternatively, the method according to claim 3 proposes that the secondary brake pressure generator is electrically activated in the absence of a braking request and that the hydraulic connection between this secondary brake pressure generator and the wheel brakes in contact with it is interrupted at the latest simultaneously with this electrical activation of the secondary pressure generator, for which the valve mechanism of the second assembly can advantageously be used.

[0017] In this method, therefore, no brake pressure build-up takes place in the wheel brakes and therefore no braking process of the vehicle takes place: only the hydraulically situated area of ​​the power brake system between the secondary pressure generator and the wheel brakes is energized with brake pressure.

[0018] The pressure build-up in this region can be detected and evaluated, for example, by a sensor for the brake pressure regulation of the power brake system already provided. The method according to claim 3 can likewise be carried out during normal driving operation of the vehicle, as long as no braking event is required.

[0019] A particular advantage of the method according to claim 3 is that the noise generated by the start-up of the secondary pressure generator due to existing road and environmental sounds is not annoyed to the occupants or, ideally, the progress of the checking method is not noticed by the occupants.

[0020] Claim 4 proposes to carry out the method when the vehicle is at a standstill. In contrast to the method according to claim 3, the wheel brakes are also actuated with brake pressure. In this case too, the process of brake pressure build-up can be monitored and evaluated, but for this purpose the connection between the secondary pressure generator and the wheel brakes does not have to be interrupted. The method is therefore characterized in that only a small number of electrically actuable actuators of the power brake system can be operated, or in that this requires only small amounts of power for carrying out the method.

[0021] The vehicle is stopped after a stopping process in normal driving operation, or when parked or when the prime mover is switched off, i.e. the method according to claim 4 does not necessarily presuppose that the vehicle drive is running or that a driver is present.

[0022] According to claim 5, it is proposed as one possible criterion for determining the availability of a hydraulic fallback level to compare the brake pressure generated by the secondary pressure generator (actual brake pressure) with a limit value for this brake pressure (target brake pressure) stored in the electronic control. The availability of the hydraulic fallback level exists if the generated brake pressure is equal to or greater than this limit value. As already mentioned, the pressure detection can be performed by means of a sensor device for adjusting the brake pressure that is already present in the power brake device, so that no additional component costs arise.

[0023] Claim 6 proposes, as an alternative, to evaluating the power consumption of the drive during brake pressure boosting by means of a secondary pressure generator, instead of the generated pressure, since the power consumption is proportional to the boosting pressure. The power consumption of the drive of the secondary pressure generator can be detected by the electronic control of the power brake system by measuring the strength of the current flowing to the drive (claim 7).

[0024] Other advantages or advantageous further configurations of the invention will become apparent, if necessary, from the following description of the invention. [Brief description of the drawings]

[0025] The invention is explained in more detail in the following description with the aid of the drawings, which for this purpose contain several figures. [Figure 1A] 1 is a hydraulic layout diagram of the power brake system on which the present invention is based; [Figure 1B] 1 is a hydraulic layout diagram of the power brake system on which the present invention is based; [Diagram 2] 1 is a flowchart of a first embodiment of the present invention. [Diagram 3] 5 is a flowchart of a second embodiment of the present invention. [Figure 4] 10 is a flowchart of a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] 1 shows, by means of hydraulic circuit symbols and their mutual hydraulic connections, the basic construction and layout of the power brake system on which the present invention is based. For details of this power brake system, reference is made to the disclosure in DE 10 2018 222 488 A1. The following description revisits the matters necessary for understanding the present invention.

[0027] The basic power brake system (10) is divided, as mentioned at the beginning, into two assemblies (12; 14) which are, for example, structurally separate from one another and hydraulically in contact with one another. The two assemblies (12; 14) are hydraulically connected in parallel and supply, for example, four wheel brakes (16) of the power brake system (10) with pressure medium under braking pressure. Two of these four wheel brakes are grouped together in one of the two brake circuits of the power brake system (10).

[0028] The first assembly (12) comprises, among other things, an operating element (18) via which a braking request can be given by the driver of the motor vehicle. The operating element (18) is illustrated as a pedal, but may also be a hand lever. Furthermore, the first assembly (12) comprises a primary pressure generator (20) operable by an electrically actuable drive (22). Electrical actuation is determined by an electronic control (24), which detects an actuation signal corresponding to the braking request and transmits it to the drive (22) of the primary pressure generator (20). Based on this, the actuated pressure generator (20) supplies the wheel brakes (16) of the power brake device (10) with pressure medium at the same brake pressure.

[0029] A second assembly (14), hydraulically connected in parallel with the first assembly (12) and in contact with the wheel brakes (16), comprises a second or secondary pressure generator (30). In addition to the secondary pressure generator (30) and its drive (32), the second assembly (14) also comprises a valve mechanism (34) consisting of a number of directional control valves for controlling the power brake device (10). These directional control valves, like the drive (32) of the secondary pressure generator (30), can be electrically actuated. The task of the second assembly (14) is to control the brake pressure individually for the wheels and thereby to adapt it to the currently prevailing slip behavior of the wheels associated with the wheel brakes (16). The corresponding electrical actuation of the drive (32) of the secondary pressure generator (30) and, if necessary, of the directional control valves of the valve mechanism (34) is likewise determined by the electronic control (24), if necessary.

[0030] The power brake system (10) constructed in this manner can be operated in normal operation as described above, or can be operated in a hydraulic fallback level in which, if there is a failure in the pressure generation in the primary assembly (12), brake pressure boosting is provided by electrical activation of the secondary pressure generator (30) in the second assembly (14) and a warning is issued to the driver to allow the power brake system (10) to be repaired.

[0031] The second assembly (14) therefore protects the functionality of the power brake device (10) at the hydraulic fallback level and therefore for safety reasons it is necessary to check its functionality from time to time. The following diagram explains how this is done.

[0032] The first method for checking the availability of a hydraulic fallback level in an electronically slip-controllable power brake system 10, on which the present invention is based, is shown in Figure 2. The prerequisite for this method is that the power brake system 10 is in normal operating mode, and therefore the first method step S1 of this checking method consists in an inquiry to that effect.

[0033] If the result of the inquiry is positive, in step S2, an inquiry is made as to whether there is a current need or desire for braking. If there is, the electronic control unit (24) detects and outputs (step 3) a brake pressure corresponding to the braking desire and a corresponding start signal for starting the secondary pressure generator (30) or its drive unit (32). At the same time, electrical start-up of the drive unit (22) of the primary pressure generator (20), which generates brake pressure during normal operation, is inhibited.

[0034] In the next step S4, the brake pressure build-up taking place in the power brake device (10) is detected by the electronic control (24), where a logic provided for this purpose evaluates, for example, the speed of build-up and / or the pressure level achieved over a certain time span. If the comparison with the target values ​​stored in the control (24) (step S5) shows that the brake pressure build-up is taking place as expected, it is assumed that there is a hydraulic fall-back level availability and the method is terminated. On the other hand, if the brake pressure build-up does not correspond to the expectation, it is assumed that there is a failure of the hydraulic fall-back level and a warning signal, for example of the acoustic and / or optical type, is sent to the driver.

[0035] If the inquiry in step S1 or step S2 leads to a negative result, the method is respectively interrupted and is carried out anew from the beginning after the expiration of a configurable time interval.

[0036] FIG. 3 illustrates a second alternative method.

[0037] First, the method performs step S1b to inquire whether normal operation is occurring.

[0038] In the case of normal operation, the next step S2b is a query as to whether there is a need for braking, which, in contrast to the method of FIG. 2, continues only if there is no desire to brake. Step S3b now operates the secondary pressure generator 30 of the power brake system 10, and at the same time interrupts the pressure medium connection to the wheel brakes 16 with the start of this operation. For this purpose, advantageously, the valves of the valve mechanism 34 of the second assembly 14 can be correspondingly electrically activated. As a result, only the area of ​​the power brake system 10 between the secondary pressure generator 30 and the wheel brakes 16 is energized with brake pressure, but the wheel brakes 16 themselves are not energized. Therefore, no braking process of the vehicle takes place.

[0039] The brake pressure buildup is again detected and evaluated by the electronic control (24) in step S4b. If the comparison with the target value stored in the control (24) shows that the brake pressure buildup corresponds to the expectation, then in step S5b the availability of the hydraulic fallback level is presumed and the method is terminated. On the other hand, if the brake pressure buildup does not correspond to the expectation, then a failure of the hydraulic fallback level is presumed and a warning signal, for example of an acoustic and / or optical type, is sent to the driver.

[0040] If the interrogation in step S1b leads to a negative result, or if the interrogation in step S2b leads to a positive result, the method is respectively terminated and started anew after the expiration of a configurable time interval.

[0041] FIG. 4 illustrates a second alternative embodiment of the checking method, the flow chart of which corresponds to that of the method of FIG.

[0042] In this second alternative embodiment, step S1c inquires whether the power brake system is in normal operation. If so, an inquiry is made as to whether the vehicle is stationary. The method continues only in the case of a positive response, otherwise it is stopped or restarted later.

[0043] Thereafter, in step S3c, the electronic control 24 electrically starts the drive of the secondary pressure generator 30, while in parallel the pressure boost in the power brake system 10, including the wheel brakes 16 connected thereto. Electronic detection and evaluation of the boost is performed in the electronic control 24 in step S4c. Steps S4c and S5c correspond to steps S4 and S5 or steps S4b and S5b described above.

[0044] Of course, modifications or additions to the described method are conceivable without departing from the basic idea of ​​the invention as claimed in the independent claims.

[0045] In this regard, it should be noted that in all of the embodiments described, pressure measurements in the hydraulic circuit of the power brake device (10) are performed using existing brake pressure adjustment sensor devices, thereby directly detecting and evaluating the pressure increase provided by the secondary pressure generator (30).

[0046] However, in principle, indirect pressure detection is also possible. For this purpose, the drive unit (32) of the secondary pressure generator (30) is driven by the Consumed in This power can be derived from the strength of the current flowing to the drive 32 and is proportionally related to the generated brake pressure.

[0047] The respective described check methods are repeated at time intervals, the time interval between two check cycles being freely definable and being variable, for example, depending on the load of the power brake system which is taking place in the meantime. [Explanation of symbols]

[0048] 10 Power brake device 12 First Assembly 14 Second Assembly 16 Wheel brakes 20 Primary or primary pressure generator 22 Primary or secondary pressure generator drive 24 Electronic Controller 30 Secondary or secondary pressure generator 32 Secondary or secondary pressure generator drive 34 Valve mechanism

Claims

1. A method for checking availability of a hydraulic fallback level in an electronically slip-controllable power brake system (10) of a motor vehicle, comprising: said power brake device (10) having a plurality of pressure generators (20; 30) for supplying pressure medium under braking pressure to connected wheel brakes (16), the respective drives (22; 32) of which can be activated separately from one another by at least one electronic control (24); The power brake system (10) is operated in normal operation by sensing a required braking event by the electronic controller (24) and relating adjustable brake pressure to the wheel brakes (16) by correspondingly electrically activating the drive (22) of the primary pressure generator (20); at least one electrically actuable secondary pressure generator (30) is provided for adapting the brake pressure, which is respectively just prevailing at the wheel associated with the wheel brake (16), to the wheel slip, the power brake system (10) is operated at a hydraulic fallback level, the brake pressure of which can be adjusted in the wheel brakes (16) of the power brake system (10) by corresponding electronic activation of the drive (32) of the secondary pressure generator (30) upon failure of brake pressure generation by the primary pressure generator (20); In the method, performing a check of the availability of the hydraulic fallback level at configurable time intervals during the normal operation of the power brake device; and checking the availability of the hydraulic fallback level by inhibiting the drive (22) of the primary pressure generator (20) and electrically activating the drive (32) of the secondary pressure generator (30) to build up brake pressure in the wheel brakes (16) by the electronic controller (24) during the normal operation of the power brake system (10) when a braking request is detected.

2. A method for checking availability of a hydraulic fallback level in an electronically slip-controllable power brake system (10) of a motor vehicle, comprising: said power brake device (10) having a plurality of pressure generators (20; 30) for supplying pressure medium under braking pressure to connected wheel brakes (16), the respective drives (22; 32) of which can be activated separately from one another by at least one electronic control (24); The power brake system (10) is operated in normal operation by sensing a required braking event by the electronic controller (24) and relating adjustable brake pressure to the wheel brakes (16) by correspondingly electrically activating the drive (22) of the primary pressure generator (20); at least one electrically actuable secondary pressure generator (30) is provided for adapting the brake pressure, which is respectively just prevailing at the wheel associated with the wheel brake (16), to the wheel slip, the power brake system (10) is operated at a hydraulic fallback level, the brake pressure of which can be adjusted in the wheel brakes (16) of the power brake system (10) by corresponding electronic activation of the drive (32) of the secondary pressure generator (30) upon failure of brake pressure generation by the primary pressure generator (20); In the method, performing a check of the availability of the hydraulic fallback level at configurable time intervals during the normal operation of the power brake device; checking the availability of the hydraulic fallback level after a vehicle equipped with the power brake device (10) has come to a standstill, and during this standstill, performing an electrical activation of a drive (32) of the secondary pressure generator (30) for increasing the brake pressure in at least one of the wheel brakes (16).

3. 3. The method according to claim 1 or 2, characterized in that the availability of the hydraulic fallback level is presumed when the brake pressure generated by the secondary pressure generator (30) is equal to or greater than a preconfigurable limit value for this brake pressure stored in the electronic control (24) of the power brake device (10).

4. 4. The method according to claim 1, further comprising the steps of: directly measuring and evaluating the brake pressure generated by the electrically activated secondary pressure generator (30) in the power brake device (10); or indirectly estimating the brake pressure boost achieved on the basis of a characteristic value for the power consumed by the drive (32) of the secondary pressure generator (30).

5. 5. The method according to claim 4, characterized in that the detection of the power of the secondary pressure generator (30) is based on the measurement of the intensity of the current flowing to its driver (32).

6. An electronic controller (24) for an electronically slip-controllable power brake system (10), configured to carry out the method according to any one of claims 1 to 5.

7. An electronically slip-controllable power brake system (10) comprising an electronic controller (24) according to claim 6.

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