Hydraulic safety system, brake system, and operating method

Abstract

A safety system brake system comprises a hydraulic pressure-providing device having a pressure chamber connected to at least one brake circuit by a separating valve and into which pressure chamber a piston is moved to build up pressure. The pressure chamber is a two-stage pressure chamber having first and second sub-chambers. During pressure build-up the piston is moved into the first and then the second sub-chamber. The two sub-chamber are hydraulically closed off from each other when the piston is moved a specified distance into the second sub-chamber. A first check valve is connected to the first sub-chamber on a suction side and to a brake fluid reservoir on a blocking side. A second check valve is connected to the second sub-chamber on a suction side, and to the suction side of the first check valve on the blocking side.

Claims

1. A hydraulic safety system for an electrohydraulic brake system comprising: a hydraulic pressure supply device that defines a pressure chamber, the pressure chamber is connected to at least one brake circuit by at least one separating valve and into which a piston is moved to build up pressure; wherein the pressure chamber is of two-stage design with a first subchamber and a second subchamber; wherein the piston is first moveable in the first subchamber and then into the second subchamber during the pressure buildup and the two chambers are hydraulically closed off from each other when the piston is moved a specified distance into the second subchamber; a reservoir for brake fluid; a first check valve defining a suction side hydraulically connected to the first subchamber and a blocking side hydraulically connected to the reservoir; and a second check valve defining a second suction side connected to the second subchamber and a second blocking side connected to the suction side of the first check valve.

2. The hydraulic safety system of claim 1, wherein a sealing element is provided, which hydraulically seals off the first and the second subchamber from one another when the piston has entered the second subchamber.

3. The hydraulic safety system of claim 1, wherein a second subchamber cross section of the second subchamber is smaller than a first subchamber cross section of the first subchamber.

4. The hydraulic safety system of claim 1, wherein the first subchamber is connected to the reservoir by a hydraulic line into which a connecting valve is inserted.

5. The hydraulic safety system of claim 4, wherein the connecting valve is electrically switchable.

6. The hydraulic safety system of claim 4, wherein the connecting valve is hydraulically switchable.

7. A brake system comprising: a brake master cylinder, which can be actuated by a brake pedal; at least one pressure chamber of which is separably connected to wheel brakes assigned to brake circuits, having a pressure control valve arrangement for one of closed-loop and open-loop control of a wheel brake pressure input at one wheel brake; a hydraulic pressure supply device that defines the at least one pressure chamber, the at least one pressure chamber is connected to the brake circuits by at least one separating valve and into which a piston is moved to build up pressure; wherein the at least one pressure chamber is of two-stage design with a first subchamber and a second subchamber; wherein the piston is first moveable in the first subchamber and then into the second subchamber during the pressure buildup and the first and second subchambers are hydraulically closed off from each other when the piston is moved a specified distance into the second subchamber; a reservoir for brake fluid; a first check valve defining a suction side hydraulically connected to the first subchamber and a blocking side hydraulically connected to the reservoir; a second check valve defining a second suction side connected to the second subchamber and a second blocking side connected to the suction side of the first check valve; and having an electronic open-loop and closed-loop control unit for controlling one of the hydraulic pressure supply device and of the pressure control valve arrangement.

8. The brake system of claim 7, wherein a sealing element is provided, which hydraulically seals off the first and the second subchamber from one another when the piston has entered the second subchamber.

9. The brake system of claim 7, wherein a second subchamber cross section of the second subchamber is smaller than a first subchamber cross section of the first subchamber.

10. The brake system of claim 7, wherein the first subchamber is connected to the reservoir by a hydraulic line into which a connecting valve is inserted.

11. The brake system of claim 10, wherein the connecting valve is electrically switchable.

12. The brake system of claim 10, wherein the connecting valve is hydraulically switchable.

13. A method utilizing the brake system as recited in claim 7, the method comprising: cyclically checking a sealing ability of the first check valve by moving the piston from the first subchamber into the second subchamber until the first and second subchambers are hydraulically separated; opening a connecting valve; and monitoring at least one pressure in a line connecting the hydraulic pressure supply device to at least one brake circuit and power consumption of an electric motor of the hydraulic pressure supply device.

14. The method of claim 13, further comprising checking the second check valve for sealing ability every time the piston is moved.

15. The method of claim 14, further comprising switching to a hydraulic fallback level when failure of both first and second check valves is detected, and wherein during the hydraulic fallback level the pressure supply device is hydraulically separated from at least one brake circuit and the brake master cylinder is hydraulically connected to the at least one brake circuit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An illustrative embodiment of the invention is explained in greater detail by means of a drawing. In the drawing, which is highly schematic:

(2) FIG. 1 shows a hydraulic safety system in a first preferred embodiment; and

(3) FIG. 2 shows a hydraulic safety system in a second preferred embodiment.

DETAILED DESCRIPTION

(4) Identical parts are provided with the same reference signs in both figures.

(5) An electrohydraulic safety system 2 or auxiliary system shown in FIG. 1 comprises a pressure supply device 6 and a reservoir 10 for brake fluid. The pressure supply device 6 can be connected to at least one brake circuit via a hydraulic line 12. An electrically actuable separating valve 14 is inserted into the hydraulic line 12. The pressure in the hydraulic line 12 can be measured by means of a pressure sensor 18 of redundant design.

(6) The pressure supply device 6 comprises an electromechanical actuator, which comprises an electric motor 26, the rotor position of which is determined by a rotor position sensor 30 of redundant design, which detects the angle of the rotor. The rotation of the rotor is converted by a rotation-translation mechanism, which is designed as a ball screw in the present case, into the axial movement of a piston 36. For active pressure buildup, the piston 36 is moved into a pressure chamber 42 of the pressure supply device 6. The pressure chamber 42 is of stepped construction and comprises a first subchamber 46 and a second subchamber adjoining the latter. To build up pressure, the piston 36 is moved in a stroke direction 62 and, in the process, first of all enters the first subchamber 46 and then, after a further travel, the second subchamber 52.

(7) Provided in the second subchamber 52 is a sealing element 60, which seals off the first subchamber 46 and the second subchamber 52 from one another in a state in which the piston 36 has entered the second subchamber. Both subchambers 46, 52 and the piston 36 have substantially a round cross section, wherein the cross section of the second subchamber 52 is smaller than the cross section of the first subchamber 46. The piston 36 is of two-stage construction with a first stage 38, the external cross section of which corresponds to the internal cross section of the first subchamber 46, and a second stage adjoining the first stage, the external cross section of which corresponds to the internal cross section of the second subchamber 52. In this way, brake fluid can be displaced from the first subchamber 36 as the piston 36 is moved in stroke direction 62 and, as soon as the piston 36 enters the second subchamber 52, brake fluid can be displaced from the second subchamber 52, leading to a pressure buildup in the wheel brakes 64, 68, 72, 76.

(8) The safety system 2 is preferably used in a brake-by-wire brake system, in which brake pressure is built up actively by the pressure supply device 6. In the present case, the brake system has two front wheel brakes 64, 68 and two rear wheel brakes 72, 76.

(9) The safety system 2 is suitable, especially in the case of automated driving, for continuing to allow an active pressure buildup with the aid of the pressure supply device 6, even if a check valve between the pressure supply device 6 and the reservoir 10 fails. On vehicles which drive to a large extent autonomously and in which the driver does not actively steer, a relatively long delay must be expected before the driver can actively perform a braking process on a fallback level in the event of a malfunction if the active pressure buildup fails. In the case of nonautomatic driving too, however, advantages result from the fact that, as it were, a fallback level with active pressure is provided, with the result that an active pressure buildup is possible, even if a check valve fails.

(10) The first subchamber 46 is connected to the reservoir 10 by a first hydraulic reservoir line 80. Inserted into the reservoir line 80 is a first check valve 84, the suction side of which is connected to the reservoir 10. Connected in parallel with the check valve 84 is an auxiliary valve or connecting valve 88, which is closed when deenergized and which is switched mechanically. The connecting valve 88 is arranged in a hydraulic auxiliary line 92, which branches off from the reservoir line 80 at a junction 96 and reenters said line at a junction 100.

(11) A second hydraulic reservoir line 104 branches off from line 12 at a junction and opens into the first reservoir line 80 at a junction 114. Inserted into the second hydraulic reservoir line 104 is a second check valve 120, the blocking side of which is hydraulically connected to the suction side of the first check valve 84.

(12) Two scenarios are discussed below, in which one of the two check valves 84, 120 fails in each case. If the first check valve 84 fails, it is no longer possible to build up a hydraulic pressure in the first subchamber 46. However, the brake system does not have to switch to a hydraulic fallback level in which the driver builds up brake pressure by muscle power in actuating the brake pedal. As soon as the piston 36 enters the second subchamber 52, which is sealed off from the first subchamber by the sealing element 60, which is arranged in the second subchamber 52, pressure can be built up again in the second subchamberassuming the functioning of the second check valve 120.

(13) If the second check valve 120 fails, i.e. no longer blocks the flow of brake fluid from the pressure supply device 6 into the reservoir 10, pressure can nevertheless be built up when the piston 36 is in the first 46 or the second subchamber 52 since the blocking side of the second check valve 120 is connected to the suction side of the first check valve 84 via lines 104 and 80.

(14) Thus, if one of the two check valves 84, 120 fails, an active pressure buildup is therefore still possible. Only in the very improbable case where both check valves 84, 120 fail is it necessary to switch to the hydraulic fallback level.

(15) A safety system 2 is shown in a second preferred embodiment in FIG. 2. In the safety system 2 shown in FIG. 2, the auxiliary valve 88, which is closed when deenergized, is switched electrically in accordance with a signal of the pressure sensor 18 and/or of the motor position sensor 30.

(16) The functioning of the two check valves 84, 120 can be checked as follows. The leaktightness of the second check valve 120 is checkedpreferably cyclicallyby moving the piston 36 forward with the aid of the electric motor 30 until the pressure chamber 42 has been divided into two subchambers 46, 52. After the opening of the connecting valve or auxiliary valve 88, the leaktightness of the first check valve can then be checked with the aid of the pressure sensor 18 or by means of the motor current consumption. The leaktightness of the first check valve 84 is checked during each actuation of the hydraulic piston 36.

(17) The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the scope of the following claims.