METHOD FOR CHECKING THE AVAILABILITY OF A HYDRAULIC FALLBACK LEVEL IN A POWER BRAKE SYSTEM WITH ELECTRONIC SLIP CONTROL; ELECTRONIC CONTROL DEVICE FOR A POWER BRAKE SYSTEM WITH ELECTRONIC SLIP CONTROL, AND POWER BRAKE SYSTEM WITH ELECTRONIC SLIP CONTROL HAVING AN ELECTRONIC CONTROL DEVICE

Abstract

A method for checking the availability of a hydraulic fallback level in a power brake system with electronic slip control, an electronic control device, and a power brake system with electronic slip control. In normal operation, power brake systems perform braking procedures without a driver participating in building up braking pressure. A requirement for braking is detected by an electronic control device and associated with a braking pressure which is set by electrical control of the drive of a primary pressure generator. Power brake systems are often equipped with a secondary pressure generator, connected with the wheel brakes, in parallel with the primary pressure generator, which can be used to perform the building up of pressure at a hydraulic fallback level. For safety reasons, the availability of the hydraulic fallback level is checked at particular time intervals during normal braking operation of the power brake system.

Claims

1-9. (canceled)

10. A method for checking availability of a hydraulic fallback level in a power brake system with electronic slip control, of a motor vehicle, the power brake system configured to supply connected wheel brakes with pressurized medium under braking pressure and including a plurality of pressure generators, of which respective drives are controllable separately from one another by at least one electronic control device, the power brake system being set up for operation in a normal operation in which a necessary braking event is detected by the electronic control device and associated with a braking pressure which can be set at the wheel brakes by corresponding electrical control of the drive of a primary pressure generator, and at least one electrically controllable secondary pressure generator being provided configured to adapt the braking pressure to a respective wheel slip that currently prevails at wheels associated with the wheel brakes, and the power brake system being set up for operation at a hydraulic fallback level at which the braking pressure can be set at the wheel brakes of the power brake system by a corresponding electronic control of the drive of the secondary pressure generator as a result of a fault occurring in the generation of braking pressure by the primary pressure generator, the method comprising: during the normal operation of the power brake system, checking availability of the hydraulic fallback level at determinable time intervals.

11. The method as recited in claim 10, wherein the availability of the hydraulic fallback level is checked in that, during the normal operation of the power brake system, when a braking request is made, the electronic control device suppresses a drive of the primary pressure generator and controls the drive of the secondary pressure generator electrically in order to build up braking pressure in the wheel brakes.

12. The method as recited in claim 10, wherein the availability of the hydraulic fallback level is checked in that, during the normal operation of the power brake system, a drive of the secondary pressure generator is controlled electrically in an absence of a braking request when, at the latest on electrical control of the drive of the secondary pressure generator, a hydraulic connection between the secondary pressure generator and the wheel brakes is broken, by electrical control of a valve device.

13. The method as recited in claim 10, wherein the availability of the hydraulic fallback level is checked after the motor vehicle equipped with the power brake system has come to a standstill, a drive of the secondary pressure generator being controlled electrically during the standstill to build up a braking pressure in at least one of the wheel brakes.

14. The method as recited in claim 10, wherein a conclusion is drawn that there is availability of the hydraulic fallback level when the braking pressure generated by the secondary pressure generator is equal to or greater than a specifiable limit value for the braking pressure which is stored in the electronic control device of the power brake system.

15. The method as recited in claim 10, wherein the braking pressure in the power brake system that is generated by the electrically controlled secondary pressure generator is measured and evaluated directly, or the braking pressure that has built up is deduced indirectly based on a characteristic of power consumed by the drive of the secondary pressure generator.

16. The method as recited in claim 15, wherein the power of the secondary pressure generator is detected by measuring current flowing to the drive of the secondary pressure generator.

17. An electronic control device for a power brake system with electronic slip control, of a motor vehicle, the electronic control device configured to check availability of a hydraulic fallback level in the power brake system, the power brake system configured to supply connected wheel brakes with pressurized medium under braking pressure and including a plurality of pressure generators, of which respective drives are controllable separately from one another by the electronic control device, the power brake system being set up for operation in a normal operation in which a necessary braking event is detected by the electronic control device and associated with a braking pressure which can be set at the wheel brakes by corresponding electrical control of the drive of a primary pressure generator, and at least one electrically controllable secondary pressure generator being provided configured to adapt the braking pressure to a respective wheel slip that currently prevails at wheels associated with the wheel brakes, and the power brake system being set up for operation at a hydraulic fallback level at which the braking pressure can be set at the wheel brakes of the power brake system by a corresponding electronic control of the drive of the secondary pressure generator as a result of a fault occurring in the generation of braking pressure by the primary pressure generator, the electronic control device configured to: during the normal operation of the power brake system, check availability of the hydraulic fallback level at determinable time intervals.

18. A power brake system with electronic slip control, which is equipped with an electronic control device, the electronic control device configured to check availability of a hydraulic fallback in the power brake system, the power brake system configured to supply connected wheel brakes with pressurized medium under braking pressure and including a plurality of pressure generators, of which respective drives are controllable separately from one another by the electronic control device, the power brake system being set up for operation in a normal operation in which a necessary braking event is detected by the electronic control device and associated with a braking pressure which can be set at the wheel brakes by corresponding electrical control of the drive of a primary pressure generator, and at least one electrically controllable secondary pressure generator being provided configured to adapt the braking pressure to a respective wheel slip that currently prevails at wheels associated with the wheel brakes, and the power brake system being set up for operation at a hydraulic fallback level at which the braking pressure can be set at the wheel brakes of the power brake system by a corresponding electronic control of the drive of the secondary pressure generator as a result of a fault occurring in the generation of braking pressure by the primary pressure generator, the electronic control device configured to: during the normal operation of the power brake system, check availability of the hydraulic fallback level at determinable time intervals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention is explained in detail in the description below, with reference to the figures.

[0025] FIGS. 1A and 1B show the hydraulic layout of a power brake system providing the basis for the present invention.

[0026] FIG. 2 shows a flow chart of a first variant embodiment of the present invention.

[0027] FIG. 3 shows a flow chart of a second variant embodiment of the present invention.

[0028] FIG. 4 shows a flow chart of a third variant embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0029] FIGS. 1A and 1B show, with the aid of hydraulic circuit symbols and their hydraulic connections with one another, the basic layout and organization of a power brake system providing the basis for the present invention. For details of this power brake system, reference is made to the description in German Patent Application No. DE 10 2018 222 488 A1; the description below goes again into certain points for an understanding of the present invention.

[0030] As mentioned above, the power brake system (10) providing the basis for the present invention is organized into two assemblies (12; 14), which, for example, are constructed separated from one another and brought into in hydraulic contact with one another. The two assemblies (12; 14) are connected hydraulically and in parallel with one another, and supply, for example, four wheel brakes (16) of power supply brake (10) with pressurized medium under braking pressure. In each case, two of these four wheel brakes are grouped together in one of a total of two brake circuits of power brake system (10).

[0031] First assembly (12) comprises, among other things, an actuation element (18) by way of which a brake request can be specified by the driver of a motor vehicle. Actuation element (18) is illustrated as a pedal, but could also be a manual lever. Moreover, first assembly (12) comprises a primary pressure generator (20) which can be actuated by an electrically controllable drive (22). The electric control is determined by an electronic control device (24), which ascertains control signals that correspond to the brake request and passes them on to drive (22) of primary pressure generator (20). Driven pressure generator (20) then supplies wheel brakes (16) of power brake system (10) with pressurized medium at a uniform braking pressure.

[0032] Connected hydraulically and in parallel with first assembly (12), and in contact with wheel brakes (16), is second assembly (14), which is equipped with a second or secondary pressure generator (30). In addition to secondary pressure generator (30) and its drive (32), second assembly (14) comprises a valve device (34) made up of a plurality of multiway valves for controlling power brake system (10). Like drive (32) of secondary pressure generator (30), these multiway valves can be controlled electrically. It is the task of second assembly (14) to adjust the braking pressure at each wheel individually and at the same time to adapt it to the slip conditions currently prevailing at the wheels associated with wheel brakes (16). If needed, a corresponding electrical control of drive (32) of secondary pressure generator (30), and where appropriate of the multiway valves of valve device (34), is likewise determined and performed by electronic control device (24).

[0033] The power brake system (10) constructed in this manner can be operated in normal operation, as described above, or at a hydraulic fallback level. In the case of the hydraulic fallback level, there is a fault in pressure generation in first assembly (12), and the build-up of braking pressure is performed by an electrical control of secondary pressure generator (30) of second assembly (14). At the same time, an alert is output to the driver to have power brake system (10) repaired.

[0034] Second assembly (14) accordingly safeguards functionality of power brake system (10) at the hydraulic fallback level, and for this reason should be checked for functionality from time to time, for safety reasons. Methods to this purpose are illustrated in the figures below.

[0035] A first method, on which the present invention is based, for checking the availability of a hydraulic fallback level in a power brake system (10) with electronic slip control is shown in FIG. 2. This method requires power brake system (10) to be operating in normal mode, so the first method step S1 of this checking method consists in a query to this effect.

[0036] If the query result is positive, a query is made in step S2 as to whether there is a current need for braking or a braking request. If this is the case, electronic control device (24) ascertains a braking pressure that corresponds to the braking request and outputs a corresponding control signal for controlling secondary pressure generator (30) and its drive (32) (step S3). At the same time, an electrical control of drive (22) of primary pressure generator (20), which generates the braking pressure in normal operation, is suppressed.

[0037] In step S4, which now follows, the build-up of braking pressure in power brake system (10) that takes place is detected by electronic control device (24). There, a logic system provided for this purpose evaluates, for example, the speed of pressure build-up and/or the pressure level reached within a timeframe. If a comparison (step S5) with the setpoint values stored in control device (24) gives the result that the build-up of braking pressure has occurred in the manner expected, the conclusion is drawn that the hydraulic fallback level is available, and the method ends. If by contrast the build-up of braking pressure does not correspond to expectations, the conclusion is drawn that there is a fault in the hydraulic fallback level, and an alert such as an acoustic and/or visual signal is output to the driver.

[0038] If the queries in either of steps S1 or S2 give a negative result, the method is aborted, and is executed again from the beginning after a determinable time interval has elapsed.

[0039] FIG. 3 illustrates a second, alternative method.

[0040] First of all, in this method, step S1b is carried out and a query made regarding normal operation.

[0041] If normal operation applies, in the following step S2b there is a query as to whether there is a need for braking, and—unlike the method according to FIG. 2—the method is only continued if there is no braking request. In step S3b, secondary pressure generator (30) of power brake system (10) is actuated, and at the same time as the beginning of this actuation the pressurized medium connections to wheel brakes (16) are broken. For this, advantageously the valves of valve device (34) of second assembly (14) may accordingly be controlled electrically. Consequently, braking pressure is applied only to a region of power brake system (10) located between secondary pressure generator (30) and wheel brakes (16), but not to wheel brakes (16) themselves. Thus, braking of the vehicle does not take place.

[0042] In step S4b, the build-up of braking pressure is once again detected and evaluated by electronic control device (24). If a comparison with the setpoint values stored in control device (24) gives the result that the build-up of braking pressure corresponds to expectations, then in S5b the conclusion is drawn that the hydraulic fallback level is available, and the method ends. If by contrast the build-up of braking pressure does not correspond to expectations, the conclusion is drawn that there is a fault in the hydraulic fallback level, and an alert such as an acoustic and/or visual signal is output to the driver.

[0043] If the query in step S1b gives a negative result, or if the query in step S2b gives a positive result, the method is in either case aborted, and is re-started after a determinable time interval has elapsed.

[0044] FIG. 4 illustrates a second alternative for a checking method, of which the flow chart corresponds to that of the method according to FIG. 2.

[0045] In this second alternative, there is a query in step S1c as to whether the power brake system is in normal operation. If it is, there is a query as to whether the vehicle is at a standstill. (Step 2c). The method only continues if the returned message is positive; otherwise it is aborted and re-started later.

[0046] In step S3c, the drive of secondary pressure generator (30) undergoes electrical control by electronic control device (24), as a result of which pressure is built up in power brake system (10), including its connected wheel brakes (16). The build-up of pressure is detected electronically and evaluated in electronic control device (24) in step S4c. Steps S4c and S5c correspond to steps S4, S5 and S4b, S5b as described above.

[0047] It goes without saying that modifications or additions to the described methods are possible without departing from the basic concept of the present invention.

[0048] In this context, it should be pointed out that, in all the described variants, the build-up of pressure by secondary pressure generator (30) is detected and evaluated directly, in that a pressure measurement is carried out in the hydraulic circuits of power brake system (10) with the aid of the braking pressure adjusting sensor system provided.

[0049] However, in principle it is possible that the pressure is detected indirectly. For this purpose, it is possible to take account of the power that is consumed by drive (32) of secondary pressure generator (30) during pressure build-up. This power can be deduced from the electrical current flowing to drive (32), and is in proportion to the generated braking pressure.

[0050] The checking method that is described in each case is repeated at intervals. In this context, the time intervals between two checking cycles can be determined however desired, and may vary for example depending on the amount of use made of the power brake system in the intervening period.