Brake system for motor vehicles and method for operating the brake system

#This application claims priority to German Patent Application Nos. 10 2011 075 325.7, filed May 5, 2011, 10 2011 075 330.3, filed May 5, 2011, 10 2011 075 331.1, filed on May 5, 2011, 10 2012 205 962.8, filed on Apr. 12, 2012, and PCT/EP2012/056894, filed Apr. 16, 2012.

#The invention relates to a brake system for motor vehicles and to a method for operating a brake system of this type.

#Hydraulic vehicle brake systems are known which are configured as power-assisted brake systems and, in addition to a brake master cylinder which can be actuated by muscular force, to which wheel brakes are connected hydraulically and which provides pressure and volume for actuating wheel brakes, include a further, electrically controllable pressure and volume provision device which actuates the wheel brakes in a “brake-by-wire” operating mode. If the electrically controllable pressure and volume provision device fails, actuation of the wheel brakes takes place solely by way of the muscular force of the vehicle driver (non-boosted fallback operating mode).

#Further preferred embodiments of the invention result from the subclaims and the following description using figures, in which, diagrammatically:

#FIG. 1 shows a first exemplary embodiment of a brake system according to the invention,

#FIG. 2 shows a second exemplary embodiment of a brake system according to the invention, and

#FIG. 1 diagrammatically shows a first exemplary embodiment of a brake system according to the invention. The brake system substantially includes a hydraulic actuating unit 2 which can be actuated by means of an actuating or brake pedal 1, a displacement simulator or simulation device 3 which interacts with the hydraulic actuating unit 2, a pressure medium storage vessel 4 which is under atmospheric pressure and is assigned to the hydraulic actuating unit 2, a first electrically controllable pressure provision device 5, a second electrically controllable pressure provision device 49, an electronic control and regulating unit 12 and an electrically controllable pressure modulation device.

#According to the example, the pressure modulation device includes, per wheel brake 8, 9, 10, 11 of a motor vehicle (not shown), an inlet valve 6a-6d and an outlet valve 7a-7d which are connected together hydraulically in pairs via central connectors and to which wheel brakes 8, 9, 10, 11 are connected. By means of brake circuit supply lines 13a, 13b, the inlet connectors of the inlet valves 6a-6d are supplied with pressures which are derived in a “brake-by-wire” operating mode from a system pressure which prevails in a system pressure line 38 which is connected to a pressure space 37 of the first electrically controllable pressure provision device 5. In each case one nonreturn valve which is not designated in further detail and opens toward the brake circuit supply lines 13a, 13b is connected in parallel to the inlet valves 6a-6d. In a non-boosted fallback operating mode, the brake circuit supply lines 13a, 13b are loaded via hydraulic lines 22a, 22b with the pressures of the pressure spaces 17, 18 of the actuating unit 2. The outlet connectors of the outlet valves 7a-7d are connected in pairs via return lines 14a, 14b to the pressure medium storage vessel 4. A pressure sensor 19 which is preferably of redundant configuration is provided for detecting the pressure which prevails in the system pressure line 38. According to the example, the wheel brakes 8 and 9 are assigned to the left-hand front wheel and the right-hand rear wheel, respectively, and the wheel brakes 10 and 11 are assigned to the left-hand rear wheel and the right-hand front wheel, respectively. Other circuit divisions are likewise conceivable.

#In a housing 21, the hydraulic actuating unit 2 has two pistons 15, 16 which are arranged behind one another and delimit hydraulic chambers or pressure spaces 17, 18 which, together with the pistons 15, 16, form a two-circuit brake master cylinder or a tandem master cylinder. The pressure spaces 17, 18 are connected firstly via radial bores which are formed in the pistons 15, 16 and corresponding pressure equalizing lines 41a, 41b to the pressure medium storage vessel 4 (via the return lines 14a, 14b), it being possible for said pressure spaces 17, 18 to be shut off by way of a relative movement of the pistons 17, 18 in the housing 21, and are connected secondly via the hydraulic lines 22a, 22b and the second pressure provision device 49 to the abovementioned brake circuit supply lines 13a, 13b. Here, a parallel connection of a normally open (NO) diagnosis valve 28 with a nonreturn (check) valve 27 which closes toward the pressure medium storage vessel 4 is contained in the pressure equalizing line 41a. The pressure spaces 17, 18 accommodate restoring springs which are not denoted in greater detail and position the pistons 15, 16 in a starting position when the brake master cylinder 2 is not actuated. A piston rod 24 couples the pivoting movement of the brake pedal 1 as a consequence of a pedal actuation to the translatory movement of the first (master cylinder) piston 15, the actuating travel of which is detected by a displacement sensor 25 which is preferably of redundant configuration. As a result, the corresponding piston displacement signal is a measure of the brake pedal actuating angle. It represents a braking request of a vehicle driver. A pressure sensor 20 which is connected to the line section 22b detects the pressure which is built up in the pressure space 18 as a result of a displacement of the second piston 16.