ELECTROHYDRAULIC POWER BRAKE SYSTEM FOR A MOTOR VEHICLE TRAVELING AUTONOMOUSLY

Abstract

An electrohydraulic power brake system for a motor vehicle traveling autonomously. An auxiliary brake unit is connected to a service brake unit in such a manner, that in the event of failure of the service brake unit, the vehicle brake system may be operated by the auxiliary brake unit. In order to be able to build up a brake pressure rapidly, using the auxiliary brake unit, in the case of cold and viscous brake fluid, as well, check valves, via which hydraulic pumps of the auxiliary brake unit are connected to a brake fluid reservoir of the service brake unit, are provided in the service brake unit.

Claims

1. An electrohydraulic power brake system for a motor vehicle traveling autonomously, comprising: a service brake unit that has a brake fluid reservoir, to which at least one hydraulic wheel brake is connected, and that has a brake pressure generator configured to generate a brake pressure; and an auxiliary brake unit, which is connected to the service brake unit, so that in the event of failure of the service brake unit, the at least one wheel brake may be actuated by the auxiliary brake unit, the auxiliary brake unit including an externally-powered brake pressure generator configured to generate a brake pressure to actuate the at least one hydraulic wheel brake, the externally-powered brake pressure generator being connected to the brake fluid reservoir of the service brake unit via a check valve; wherein the service brake unit includes a wheel-brake pressure control valve set-up configured to regulate a wheel brake pressure applied to the at least one wheel brake.

2. The electrohydraulic power brake system as recited in claim 1, wherein the check valve is situated in the service brake unit.

3. The electrohydraulic power brake system as recited in claim 1, wherein the service brake unit includes a master brake cylinder which may be actuated by muscle power and is connected to the brake fluid reservoir through the check valve and connected to the auxiliary brake unit in such a manner, that the externally-powered brake pressure generator of the auxiliary brake unit is connected to the brake fluid reservoir of the service brake unit via the check valve and through the master brake cylinder.

4. The electrohydraulic power brake system as recited in claim 1, wherein the vehicle brake system includes a plurality of brake circuits, and the auxiliary brake unit has a plurality of externally-powered brake pressure generators in different ones of the brake circuits, which are connected to the brake fluid reservoir of the service brake unit via check valves.

5. The electrohydraulic power brake system as recited in claim 1, wherein the service brake unit includes a master brake cylinder which may be actuated by muscle power and is connected to the brake fluid reservoir via a test valve.

6. The electrohydraulic power brake system as recited in claim 5, wherein the brake fluid reservoir includes a plurality of chambers, and the check valve is connected to the same chamber of the brake fluid reservoir as the test valve.

7. The electrohydraulic power brake system as recited in claim 6, wherein the check valves are connected to different chambers of the brake fluid reservoir.

8. The electrohydraulic power brake system as recited in claim 1, wherein the brake fluid reservoir includes a plurality of chambers, the service brake unit includes an externally-powered brake pressure generator, and the externally-powered brake pressure generator of the service brake unit is connected to a chamber of the brake fluid reservoir different from the check valve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In the following, the present invention is described in greater detail in light of specific example embodiments shown in the figures.

[0014] FIG. 1 shows a hydraulic circuit diagram of a service brake unit of an electrohydraulic power brake system according to an example embodiment of the present invention;

[0015] FIG. 2 shows a hydraulic circuit diagram of an auxiliary brake unit of the electrohydraulic power brake system from FIG. 1.

[0016] FIG. 3 shows a hydraulic circuit diagram of the service brake unit of the electrohydraulic power brake system according to an example embodiment of the present invention, modified in comparison with FIG. 1.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0017] The electrohydraulic power brake system 1 of the present invention represented in the figures is intended for a motor vehicle, namely, a passenger car, traveling autonomously up to Level 4 or 5. Level 4 means autonomous driving, where a driver may be called upon to take action, and Level 5, the highest level, means autonomous driving, which does not require any intervention by a driver.

[0018] Power brake system 1 includes a service brake unit 2 and an auxiliary brake unit 3. Service brake unit 2 is intended for actuating the brakes, and auxiliary brake unit 3 is intended for actuating the brakes in the case of a defect or failure of service brake unit 2. Hydraulic wheel brakes 4 are connected to service brake unit 2 by brake lines, in the exemplary embodiment, four brake lines. Auxiliary brake unit 3 is connected to service brake unit 2 by brake lines in such a manner, that wheel brakes 4 may also be actuated by auxiliary brake unit 3. In each instance, service brake unit 2 and auxiliary brake unit 3 are separate modules, which may be situated in different places, such as in an engine compartment of the passenger car. In the following, the brake lines, which connect auxiliary brake unit 3 to service brake unit 2, are also referred to as forward lines V1, V2 and return lines R1, R2.

[0019] The vehicle brake system 1 of the present invention is constructed as a dual-circuit brake system, and its brake units 2, 3 are constructed as dual-circuit brake units. In each instance, two wheel brakes 4 are assigned to a brake circuit. In each brake circuit, auxiliary brake unit 3 is connected to service brake unit 2 by a forward line V1, V2 and by a return line R1, R2. In service brake unit 2 and in auxiliary brake unit 3, connecting points of forward lines V1, V2 and return lines R1, R2 are denoted consistently by V1, V2, R1 and R2.

[0020] Service brake unit 2 includes a piston-cylinder unit 5, whose piston 6 is displaceable in a cylinder 9 by an electric motor 7 via a screw drive 8, in the form of a rotation-to-translation conversion gear. Electric motor 7, screw drive 8, and piston-cylinder unit 5 form an externally-powered brake pressure generator 10 of service brake unit 2 for generating a brake pressure for service braking. Service braking is the usual and intended brake actuation. Externally-powered brake pressure generator 10 is connected to the two brake circuits via service-brake valves 11, between separating valves 12 and intake valves 13.

[0021] For each wheel brake 4, service brake unit 2 includes an intake valve 13 and an exhaust valve 14, with the aid of which wheel brake pressures in each wheel brake 4 may be adjusted individually. Due to this, the wheel brake pressures in wheel brakes 4, and consequently, the braking forces of wheel brakes 4, may be adjusted without slippage during normal vehicle operation. In addition, traction control systems, such as antilock and drive slip control, electronic stability programs, which are also referred to colloquially as anti-skid control systems, automatic braking, adaptive cruise control, and the like, are more possible. Such control systems are conventional and are not explained here in more detail. Intake valves 13 and exhaust valves 14 may also be viewed as wheel-brake pressure control valve set-ups 13, 14.

[0022] In addition to externally-powered brake pressure generator 10, service brake unit 2 includes a master brake cylinder 15, which may be actuated by muscle power, and to which wheel brakes 4 are connected via separating valves 12 and intake valves 13. Service brake unit 2 includes a separating valve 12 in each brake circuit, as well as an intake valve 13 and an exhaust valve 14 for each wheel brake 4. In the case of operation by a driver, master brake cylinder 15 is used as a setpoint adjuster for the wheel brake pressures to be set in wheel brakes 4 during service braking. The brake pressure is generated by externally-powered brake pressure generator 10 during both operation by a driver and autonomous driving. During service braking, master brake cylinder 15 is separated hydraulically from wheel brakes 4, by closing separating valves 12.

[0023] As mentioned, master brake cylinder 15 is used as a setpoint adjuster for the wheel brake pressures in the event of service braking during operation by a driver, where the brake pressure is generated by externally-powered brake pressure generator 10 of service brake unit 2. In the event of a failure of externally-powered brake pressure generator 10, the brake pressure may be generated by actuating master brake cylinder 15. This is so-called auxiliary braking by muscle power, and therefore, master brake cylinder 15 may also be viewed as a muscle-powered brake pressure generator.

[0024] In order for brake fluid to be able to displaced from master brake cylinder 15, and for pistons of master brake cylinder 15 and a brake pedal 16 to be able to be moved when separating valves 12 are closed, service brake unit 2 includes a pedal travel simulator 17, which is connected to a brake circuit of master brake cylinder 15 via a simulator valve 18. Pedal travel simulator 17 is a piston-cylinder unit having a spring-loaded or also, for example, gas-pressurized, piston.

[0025] In the specific embodiment of the present invention described and shown, in their currentless initial states, separating valves 12 and intake valves 13 are open 2/2-way-solenoid valves; and in their currentless initial states, service brake valves 11 of externally-powered brake pressure generator 10, exhaust valves 14, and simulator valve 18 are closed 2/2-way solenoid valves.

[0026] The hydraulic components of service brake unit 2 of the electrohydraulic power brake system 1 according to the present invention, namely, valves 11, 12, 13, 14, 18, externally-powered brake pressure generator 10, master brake cylinder 15, pedal travel simulator 17, and further components, such as pressure sensors, are situated in receptacles of a hydraulic block 19 of service brake unit 2 and are interconnected by holes drilled into hydraulic block 19 in accordance with the shown hydraulic circuit diagram of vehicle brake system 1 and/or of service brake unit 2.

[0027] An unpressurized brake fluid reservoir 20, as is in conventional master brake cylinders, is mounted on hydraulic block 19, and master brake cylinder 15 is connected to the brake fluid reservoir, and externally-powered brake pressure generator 10 is connected to the same via a check valve 28. In one of the two brake circuits, a test valve 21 is provided between brake fluid reservoir 20 and master brake cylinder 15. In the exemplary embodiment, the test valve is also a 2/2-way solenoid valve open in its currentless initial state. A check valve 29, through which flow may occur in the direction of master brake cylinder 15, but which is not present in all variants of the present invention, is connected hydraulically in parallel with test valve 21.

[0028] In each of its two brake circuits, auxiliary brake unit 3 includes a hydraulic pump 22, which may be driven by a common electric motor 23. Hydraulic pumps 22 are piston pumps, although other hydraulic pumps, such as gear pumps, are possible as well. Hydraulic pumps 22 form, together with electric motor 23, an externally-powered brake pressure generator 24.

[0029] Suction sides of hydraulic pumps 22 of auxiliary brake unit 3 are connected to the two brake circuits of master brake cylinder 15 of service brake unit 2 via suction valves 25 and the above-mentioned brake lines, namely, forward lines V1, V2, with the aid of which auxiliary brake unit 3 is connected to service brake unit 2. Pressure sides of hydraulic pumps 22 of auxiliary brake unit 3 are connected to the two brake circuits of master brake cylinder 15 of service brake unit 2 via pressure valves 26 and forward lines V1, V2. In addition, the pressure sides of hydraulic pumps 22 of auxiliary brake unit 3 are connected to separating valves 12 of service brake unit 2 via brake lines, namely, return lines R1, R2, by which auxiliary brake unit 3 is connected to service brake unit 2. Due to this, it is possible to actuate wheel brakes 4 by generating brake pressure, using hydraulic pumps 22 of auxiliary brake unit 3, which form its externally-powered brake pressure generator 24. Wheel brake pressures in wheel brakes 4 may be adjusted, using intake valves 13 and exhaust valves 14 of service brake unit 2, which form the wheel-brake pressure control valve set-ups, provided these valves 13, 14 and their control systems are functional. In the case of a defect or a failure of service brake unit 2, the brake pressure is generated by the hydraulic pumps 22 of auxiliary brake unit 3, which form externally-powered brake pressure generator 24. Such braking is referred to as auxiliary braking.

[0030] In the specific embodiment of the present invention described and shown, suction valves 25 of auxiliary brake unit 3 are constructed as 2/2-way solenoid valves closed in their currentless initial states, and pressure valves 26 are constructed as 2/2-way solenoid valves open in their currentless initial states. In the case of auxiliary braking, suction valves 25 are open, so that hydraulic pumps 22 of auxiliary brake unit 3 may draw in brake fluid from brake fluid reservoir 20 of service brake unit 2, through master brake cylinder 15. In addition, pressure valves 26 are closed, in order to apply a brake pressure to wheel brakes 4.

[0031] In the case of service braking, a brake pressure generated by externally-powered brake pressure generator 10 of service brake unit 2 is applied to wheel brakes 4 through open pressure valves 26 of auxiliary brake unit 3 and, in this case, through to-be-opened service brake valves 11 of service brake unit 2; or a brake pressure generated by master brake cylinder 15 is applied to the wheel brakes through open pressure valves 26 of auxiliary brake unit 3 and open separating valves 12 of service brake unit 2.

[0032] To build up brake pressure rapidly during auxiliary braking, hydraulic pumps 22, which form externally-powered brake pressure generator 24 of auxiliary brake unit 3, are connected to brake fluid reservoir 20 of service brake unit 2 via check valves 30, which, in the exemplary embodiment, are situated in the hydraulic block 19 of service brake unit 2.

[0033] Variants of electrohydraulic power brake system 1 of the present invention, which have only one of the two check valves 30 between brake fluid reservoir 20 and hydraulic pumps 22 of auxiliary brake unit 3, are also possible; in this case, the check valve 30 in the primary circuit and/or the check valve 30 in the brake circuit, in which test valve 21 is also provided, being preferably present. The primary circuit is the brake circuit, which is operated directly via a pedal rod, using brake pedal 16.

[0034] The check valve 29, which is connected in parallel with test valve 21 between brake fluid reservoir 20 and master brake cylinder 15, may be omitted, in particular, if hydraulic pumps 22 of auxiliary brake unit 3 in the two brake circuits are connected to brake fluid reservoir 20 of service brake unit 2 via a check valve 30.

[0035] The hydraulic components of auxiliary brake unit 3, namely, hydraulic pumps 22, valves 25, 26, and further components, such as pressure sensors, are situated in a hydraulic block 27 of auxiliary brake unit 3 and are interconnected by holes drilled into hydraulic block 27 in accordance with the shown hydraulic circuit diagram, which may also be referred to as the interconnection configuration of hydraulic components 22, 25, 26.

[0036] Brake fluid reservoir 20 includes a chamber 31′, 31″ for each brake circuit, as well as a further chamber 31″ for externally-powered brake pressure generator 10 of service brake unit 2, thus, a total of three chambers 31′, 31″, 31″. The check valve 30, via which a hydraulic pump 22 of auxiliary brake unit 3 is connected to brake fluid reservoir 20, is connected to the same chamber 31′ of brake fluid reservoir 20 as test valve 21. Hydraulic pumps 22 of auxiliary brake unit 3, that is, the two check valves 30, via which hydraulic pumps 22 of auxiliary brake unit 3 are connected to brake fluid reservoir 20, are connected to different chambers 31′, 31″ of brake fluid reservoir 20. Externally-powered brake pressure generator 10 of service brake unit 2 is connected to a separate chamber 31″, that is to a chamber 31″ of brake fluid reservoir 20 different from those of hydraulic pumps 22 of auxiliary brake unit 3.

[0037] In comparison with FIG. 1, in FIG. 3, forward line V1 of the one brake circuit, in the exemplary embodiment, the primary circuit, is not connected directly to brake fluid reservoir 20 via check valve 30, but via master brake cylinder 15. In all other respects, FIGS. 1 and 3 are consistent.