Method for operating hydraulic external vehicle brake system for autonomous driving

Abstract

In order to operate a hydraulic external-force vehicle brake system for autonomous driving, the invention proposes that a brake pressure is generated by a second external-force brake pressure generator if no brake pressure is generated by the first external-force brake pressure generator after a predetermined first time period (t1) or a sufficient brake pressure is not generated. If there is no failure notification from the first external force brake pressure generator within a second time period (t2) longer than the first time period (t1), the process of generating brake pressure with the second external force brake pressure generator is interrupted.

Description

[0001] This application is a divisional application of Chinese invention patent application filed on April 28, 2020, with application number 202080051554.8 and invention title "Method for operating hydraulic external force vehicle braking device for autonomous driving". Technical Field

[0002] This invention relates to a method having the features of the preamble of claim 1, for operating a hydraulically operated external vehicle braking device for autonomous driving of land vehicles at or below level 4 or 5 on public roads. The term "autonomous driving" refers to a feasible scheme of autonomous driving, but the vehicle braking device according to the invention can also be used for non-autonomous driving or autonomous driving at lower levels of land vehicles. Background Technology

[0003] To enable autonomous driving at levels 4 (where driver intervention is required) and 5 (the highest level; no driver required), redundant external vehicle braking systems are needed that can prevent complete failure of the vehicle braking system with a probability adjacent to safety, without requiring driver intervention.

[0004] Publication DE 10 2014 220 440 A1 discloses an electro-hydraulic external force vehicle braking device with two braking units. Each braking unit has an external force braking pressure generator and a braking pressure regulating valve device for each wheel brake, wherein the external force braking pressure generator has an electrically actuated pressure source. One braking unit is connected to the other, and a hydraulic wheel brake is connected to one of the braking units, allowing the wheel brake to be operated using both the other and one braking unit. Thus, in the event of a failure or malfunction of one braking unit, the wheel brake can be operated using the other braking unit without driver intervention. The correspondingly active braking unit regulates the wheel braking pressure in the wheel brake. Summary of the Invention

[0005] The objective of this invention is to minimize the time lost during external braking if the first external braking pressure generator fails to generate braking pressure or, in any case, fails to generate sufficient braking pressure, in order to establish braking pressure using a second external braking pressure generator. However, in principle, it is not advisable to operate two external braking pressure generators, but rather to always operate only one external braking pressure generator whenever possible.

[0006] A vehicle braking device configured according to the method of the present invention has two external braking pressure generators, which are capable of generating braking pressure for operating the hydraulic wheel brakes of the vehicle braking device. The external braking pressure generator can have a hydraulic pump or a piston-cylinder unit, wherein the hydraulic pump can be driven by an electric motor, and the piston of the piston-cylinder unit can be moved within the cylinder by an electric motor, for example via a helical gear transmission mechanism and, if necessary, via an inserted mechanical reduction gear mechanism. Another feasible embodiment of the external braking pressure generator is a master brake cylinder, which can be operated by a controllable negative pressure-braking force amplifier or an electromechanical braking force amplifier. This example is exemplary and not exhaustive.

[0007] According to the present invention, if the first external force braking pressure generator fails to generate a predetermined braking pressure after a predetermined first time period from the receipt of the braking signal and the braking signal still exists, then the second external force braking pressure generator is used to generate braking pressure. If external braking is required, the braking signal can be generated through braking operation performed by the vehicle driver. The braking signal can also be generated independently of the vehicle driver, for example, independently of autonomous vehicle control devices, independently of the distance adjustment mechanism of the vehicle ahead, or when approaching another vehicle or other obstacle too quickly.

[0008] If a malfunction of the first external braking pressure generator is detected within a second time period longer than the first time period from the receipt of the braking signal, the wheel brakes can be operated using the braking pressure generated by the second external braking pressure generator. The time from the end of the first time period until the malfunction of the first external braking pressure generator is detected is saved. If no malfunction of the first external braking pressure generator is detected within the second time period, the process of generating braking pressure with the second external braking pressure generator can be interrupted in one embodiment of the method according to the invention. This avoids operating the vehicle braking device with the second external braking pressure generator, even though a braking signal is present, because the vehicle braking device should not or should not be operated by generating braking pressure with the first external braking pressure generator. For example, the vehicle braking device can be operated with a third external braking pressure generator, for example, by manually or externally operating the master brake cylinder, or the vehicle equipped with the vehicle braking device can decelerate in other ways, for example, by generating current by operating a generator using an electric motor, and therefore the hydraulic wheel brakes are intentionally not operated. The electric motor is, for example, an electric motor or generator operating as a generator.

[0009] For example, if the first external braking pressure generator generates a predetermined braking pressure within a second time period after receiving the braking signal (but still does so), or if the vehicle equipped with the vehicle braking device stops or has come to a standstill, then the process of generating braking pressure with the second external braking pressure generator can also be interrupted by other interruption criteria.

[0010] The subject matter of the dependent claims is the improvement and advantageous design of the invention described in the independent claims.

[0011] All features disclosed in the specification and drawings can be implemented individually or in virtually any combination in embodiments of the invention. The following embodiments of the invention are possible in principle, having not all, but only one or more, features of the claims or embodiments of the invention. Attached Figure Description

[0012] The invention will now be explained in detail with the aid of embodiments shown in the accompanying drawings.

[0013] Figure 1 A simplified hydraulic circuit diagram of an externally driven vehicle braking device for implementing the method according to the invention is shown; and Figure 2 A flowchart of the method according to the present invention is shown. Detailed Implementation

[0014] exist Figure 1 The electro-hydraulic external-force vehicle braking device 1 shown is installed for autonomous driving of land vehicles, i.e., passenger cars, on public roads at levels 4 or 5 and below. Level 4 means autonomous driving, in which driver intervention is required, while level 5, the highest level, means autonomous driving without driver intervention. Lower levels and non-autonomous driving are also possible.

[0015] The vehicle braking device 1 is configured as a dual-circuit vehicle braking device with four hydraulic wheel brakes 2, wherein each pair of hydraulic wheel brakes is connected to one of two braking circuits I and II. Braking circuit I with two hydraulic wheel brakes 2 is shown, and the other braking circuit II is configured similarly.

[0016] For external force actuation, the vehicle braking device 1 has two external force braking pressure generators 3 and 4, which can independently operate the wheel brakes 2. The first external force braking pressure generator 3 has a piston-cylinder unit 5. The piston 6 of this unit can be moved in a cylinder 9 by a first electric motor 7 via a helical gear transmission mechanism 8, such as a ball screw transmission mechanism, to generate braking pressure. A mechanical reduction transmission mechanism (not shown), such as a planetary gear transmission mechanism, can be inserted between the first electric motor 7 and the helical gear transmission mechanism 8. Two braking circuits I and II are hydraulically connected in parallel to the cylinder 9 of the piston-cylinder unit 5 of the first external force braking pressure generator 3 via a first release valve 10; only one of the release valves is shown in the figure.

[0017] The second external braking pressure generator 4 has a hydraulic pump 11, which can be driven by a second electric motor 12. The hydraulic pump 11 is, for example, a piston pump or an internal gear pump. Two braking circuits I and II are connected to the second external braking pressure generator 4 in hydraulic parallel connection. In this embodiment, the two braking circuits I and II are connected to the pressure side of the hydraulic pump 11. The two braking circuits I and II can be directly connected to the second external braking pressure generator 4 without an insertion valve. In this embodiment, the two braking circuits I and II are connected to the second external braking pressure generator 4 via a check valve 24 to prevent brake fluid from flowing back from or through the braking circuits I and II into the second external braking pressure generator 4. No controllable valve, such as a solenoid valve, is provided between the second external braking pressure generator 4 and the two braking circuits I and II (not shown), but this is possible. Not only the piston-cylinder unit 5 of the first external force braking pressure generator 3, but also the hydraulic pump 11 of the second external force braking pressure generator 4 are connected to the pressureless brake fluid storage container 13. The brake fluid storage container is placed on the dual-circuit master brake cylinder 14 that can be operated manually. The two brake circuits I and II are connected to the dual-circuit master brake cylinder in a hydraulic parallel manner through the second separation valve 15.

[0018] Between the first and second separation valves 10 and 15 and the wheel brake 2 and the second external force braking pressure generator 4, a third separation valve 16 is arranged in each brake circuit I and II, and a check valve 25 that can flow in the direction of the wheel brake 2 is hydraulically connected in parallel with the third separation valve.

[0019] Each external force braking pressure generator 3, 4 has its own power supply device 17—in this embodiment, a battery—and its own electronic control device 19.

[0020] Each wheel brake 2 has an inlet valve 20 through which it is connected to brake circuits I and II of the vehicle braking system 1, and the wheel brake is associated with brake circuits I and II. Each wheel brake 2 is connected to a pressureless brake fluid reservoir 14 via an outlet valve 21. The inlet valve 20 and outlet valve 21 form a wheel brake pressure regulating valve device, which allows for individual regulation of the wheel brake pressure in each wheel brake 2, where "regulation" can also mean control. In addition to regulating the wheel brake pressure during external braking, slip regulation can also be performed using the inlet valve 20, outlet valve 21, and one of the two optional external braking pressure generators 3 and 4. Such slip regulation is anti-lock braking, traction control, and driving dynamics regulation, or electronic stability program, commonly abbreviated as ABS, ASR, and FDR or ESP. Such slip regulation is well known to those skilled in the art and will not be explained here.

[0021] In this embodiment, the separation valves 10, 15, 16, inlet valve 20, and outlet valve 21 are 2 / 2-passage solenoid valves, wherein the second and third separation valves 15, 16, and inlet valve 20 are open in their non-energized basic position, and the first separation valve 10 and outlet valve 21 are closed in their non-energized basic position. Valves and valve positions different from those described are also possible. For example, inlet valve 20 and outlet valve 21 can be combined into a 3 / 3-passage solenoid valve (not shown). Valves 10, 13, 16, 20, and 21 of the illustrated brake circuit I are shown respectively; the unillustrated brake circuit II is constructed similarly and has the same valves 10, 15, 16, 20, and 21.

[0022] Figure 2 The flowchart illustrates the process of autonomous external braking according to the invention, starting in region 500. An autonomous vehicle control device 22, not necessarily part of the vehicle braking device 1, is present for autonomous driving and sends braking signals in step 501 to the electronic control devices 18 and 19 of the two external braking pressure generators 3 and 4. The braking signals indicate that the vehicle braking device 1 should be operated with external force. Next, the first electric motor 7 moves the piston 6 within the cylinder 9 of the piston-cylinder unit 5, thereby generating braking pressure with the first external braking pressure generator 3 (step 502). The first disconnect valve 10 and the third disconnect valve 16 remain open, allowing the wheel brakes 2 to be operated with the braking pressure generated by the first external braking pressure generator 3. The second disconnect valve 15 is closed, causing the wheel brakes 2 to be hydraulically separated from the master brake cylinder 15, and external braking can be performed with the braking pressure generated by the first external braking pressure generator 3.

[0023] The electronic control unit 19 of the second external braking pressure generator 4 monitors the braking pressure generated by the first external braking pressure generator 3 by means of a pressure sensor 23 connected to cylinder 9 of the piston-cylinder unit 5 of the first external braking pressure generator 3 (step 503). In addition to sending its pressure signal to the electronic control unit 19 of the second external braking pressure generator 4, the pressure sensor 23 also sends its pressure signal to the electronic control unit 18 of the first external braking pressure generator 3 and the autonomous vehicle control device 22.

[0024] If the first external force braking pressure generator 3 does not generate braking pressure during the first predetermined time period t1 from the start of the self-braking signal, or does not generate the predetermined braking pressure in any way, or if the braking pressure establishment gradient is too low and if the braking signal of the autonomous vehicle control device 22 is also present, then the second external force braking pressure generator 4 generates braking pressure by driving the hydraulic pump 11 with the second electric motor 12 (step 504).

[0025] If, within a predetermined second time period t2, longer than the first time period t1, starting from the start of the self-braking signal, the electronic control device 19 of the second external braking pressure generator 4 receives a fault notification from the first external braking pressure generator 3 (step 505), then the first disconnect valve 10 of the first external braking pressure generator 3 is closed, and the wheel brake 2 is operated using the braking pressure generated by the second external braking pressure generator 4 (step 506). The fault notification from the first external braking pressure generator 3 means that the first external braking pressure generator 3 has malfunctioned or is incapable of generating sufficient braking pressure for a sufficiently short time. In addition to the electronic control device 18 of the first external braking pressure generator 3, the fault notification can also come from, for example, an autonomous vehicle control device 22.

[0026] If the electronic control device 18 of the second external braking pressure generator 4 does not receive a fault notification from the first external braking pressure generator 3 within the second time period t2, the process of generating braking pressure with the second external braking pressure generator 4 is interrupted (step 507). The reason for no fault notification may be that, despite the presence of a braking signal, the braking pressure should not be generated by the first external braking pressure generator 3. This is, for example, if a vehicle equipped with the vehicle braking device 1 uses an electric motor operating as a generator to obtain electrical energy, or uses a generator to generate current, and thus sufficiently decelerates using the electric motor or generator. In this case, operating the wheel brake 2 with the second external braking pressure generator 4 would cause interference.

[0027] If the first external force braking pressure generator 3 generates sufficient braking pressure during the second time period t2 from the start of the braking signal, even if no braking pressure is generated or the braking pressure is too low, the vehicle can still be sufficiently decelerated or stopped or has already come to a standstill, then the process of generating braking pressure with the second external force braking pressure generator 4 can be interrupted.

[0028] If a fault notification for the first external force braking pressure generator 3 exists at the start of the braking signal or within the first time period t1 from the start of the braking signal (step 502), then braking pressure is generated using the second external force braking pressure generator 4 from the start of the braking signal or from the date of receiving the fault notification (step 506). If the first external force braking pressure generator 3 is unavailable for reasons other than a fault or in any case without a fault report, then braking pressure is also generated using the second external force braking pressure generator 4 from the start of the braking signal (steps 502 and 506).

Claims

1. A method for operating a hydraulic external-force vehicle braking device for autonomous driving, the hydraulic external-force vehicle braking device having a first external-force braking pressure generator (3) and a second external-force braking pressure generator (4), wherein hydraulic wheel brakes (2) are connected to the first external-force braking pressure generator and the second external-force braking pressure generator, characterized in that, The electronic control device (19) of the second external force braking pressure generator (4) monitors the situation of the first external force braking pressure generator (3) generating braking pressure (p1) by means of a pressure sensor (23) on the cylinder (9) of the piston-cylinder unit (5) connected to the first external force braking pressure generator (3). If the predetermined braking pressure (p1) is not generated after a predetermined first time period (t1) from the receipt of the braking signal from the first external force braking pressure generator (3) and the braking signal still exists, then the second external force braking pressure generator (4) generates braking pressure in the case of the braking signal.

2. The method according to claim 1, characterized in that, If the first external force braking pressure generator (3) generates a predetermined braking pressure or the vehicle equipped with the external force vehicle braking device (1) stops within a predetermined second time period (t2) longer than the first time period (t1) from the date of receiving the braking signal, the process of generating braking pressure with the second external force braking pressure generator (4) is interrupted.

3. The method according to claim 1 or 2, characterized in that, If the first external force braking pressure generator (3) is not yet ready to generate braking pressure, the second external force braking pressure generator (4) is used to generate braking pressure immediately upon receiving a braking signal.

4. The method according to claim 1 or 2, characterized in that, If there is a fault notification from the first external force braking pressure generator (3), the second external force braking pressure generator (4) is used to generate braking pressure immediately upon receiving a braking signal.

5. The method according to claim 1 or 2, characterized in that, If the predetermined braking pressure is generated in a manner different from that generated by the first external force braking pressure generator (3) and / or the vehicle equipped with the external force vehicle braking device (1) decelerates at a predetermined deceleration in a manner different from that generated by the external force vehicle braking device (1), then the method is not performed.

6. The method according to claim 1 or 2, characterized in that, The external force braking pressure generators (3, 4) have electronic control devices (18, 19).

Images