Electrohydraulic vehicle braking system

Abstract

Electrohydraulic vehicle brake system, with an externally powered service brake system and with a human-powered auxiliary brake system, wherein the externally powered service brake system has an external energy source (12), at least one wheel brake cylinder (22) connected to the external energy source (12), and a brake value sensor, and wherein the human-powered auxiliary brake system has a master brake cylinder (44), at least one wheel brake cylinder (22) connected to the master brake cylinder (44), and a reservoir (34) for brake fluid, to which the master brake cylinder (44) is connected, characterized in that the vehicle brake system (10) has an isolating valve (52) arranged between the master brake cylinder (44) and the reservoir (34), which is controllable independently of actuation of the master brake cylinder (44) and by means of which the master brake cylinder (44) can be separated from the reservoir (34).

Description

State of the art

[0001] The invention relates to an electrohydraulic vehicle brake system having the features of the preamble of claim 1.

[0002] Known vehicle braking systems of this type comprise a power-assisted service braking system and a human-powered auxiliary braking system. The service braking system and auxiliary braking system are not entirely separate but use some of the same components, such as wheel brake cylinders. The power-assisted service braking system comprises an external energy source, usually a hydraulic pump, to which a hydraulic accumulator is connected. Where there are multiple brake circuits, there is an external energy source for each brake circuit. At least one, and usually several, wheel brake cylinders are connected to the external energy source. To control or regulate wheel brake pressure in the wheel brake cylinders, known vehicle braking systems comprise a brake pressure build-up valve upstream of the wheel brake cylinder and a brake pressure reduction valve downstream of the wheel brake cylinder.

[0003] These valves also enable anti-lock, traction control, and / or vehicle dynamics control (ABS, ASR, FDR). This is known per se and will therefore not be explained in detail here. The wheel brake pressure can be controlled or regulated individually for each wheel or for several or all vehicle wheels together. Since other options for controlling or regulating wheel brake pressures are fundamentally possible, the invention is not intended to be limited to one specific option. A target value for the wheel brake pressures is specified using a brake value transmitter, which is usually a foot brake pedal or a handbrake lever, the position of which is detected by a sensor.

[0004] If the service brake system fails, the braking system can be actuated conventionally using the muscle-powered auxiliary braking system, which has a master brake cylinder to which the wheel brake cylinder(s) is / are connected. In known electrohydraulic vehicle braking systems, the master brake cylinder is hydraulically separated from the vehicle braking system by a separating valve when the service brake system is actuated. The master brake cylinder of known vehicle braking systems is connected to a brake fluid reservoir, from which the external energy source typically also draws brake fluid. An example of a known electrohydraulic vehicle braking system of the type described above is disclosed in DE 197 01 070 A1.

[0005] The published patent applications DE 196 32 130A1 and DE 195 23 946 A1 disclose hydraulic auxiliary vehicle brake systems with a master brake cylinder that has a vacuum brake booster. Braking is performed by the driver's muscle power, assisted by an auxiliary force from the brake booster. For pre-charging, the known vehicle brake systems have a hydraulic pump known as a pre-charging pump, which can be used to pressurize the rear side of a primary or rod piston of the master brake cylinder. By pre-charging, wheel brake clearance can be eliminated and friction brake pads can be applied to brake discs in anticipation of a brake application. Pre-charging also enables pressure to build up on the suction side of a return pump of a slip control system. The purpose in this case is a rapid pressure buildup at low temperatures and, as a result, viscous brake fluid.To build up the pre-charge pressure, a solenoid valve is located between the brake fluid reservoir and a follow-up chamber of the master cylinder. The follow-up chamber is located on the rear side of the primary piston and, as already mentioned, can be pressurized by the pre-charge pump.

[0006] German Patent Application DE 101 64 355 A1 discloses a hydraulic power-operated vehicle brake system with a muscle-operated master brake cylinder, which is connected to a pressureless brake fluid reservoir in each brake circuit via a shut-off valve, and with a power-operated brake pressure generator, which is connected to the master brake cylinder in each brake circuit via a main shut-off valve. A pedal travel simulator is connected to the master brake cylinder, the rear of which is connected to the reservoir via a shut-off valve. A check valve, an overpressure or proportional safety valve, and a throttle orifice are connected in parallel to the shut-off valves in one brake circuit, which is why the master brake cylinder cannot be separated from the reservoir by closing the shut-off valves. Explanation and advantages of the invention

[0007] The vehicle brake system according to the invention with the features of claim 1 has a separating valve, preferably designed as a solenoid valve, which is arranged between the reservoir for brake fluid and the master brake cylinder and which is controllable independently of actuation of the master brake cylinder. This separating valve should not be confused with the separating valve of known vehicle brake systems, which is connected downstream of the master brake cylinder and with which the master brake cylinder is hydraulically separated from the vehicle brake system when the service brake system is actuated. With the separating valve according to the invention, the reservoir can be emptied more quickly, i.e.with a shorter piston travel of a piston in the master brake cylinder, separate from the master brake cylinder than with known master brake cylinders, where the piston of the master brake cylinder has to pass over a sniffer bore or a central valve integrated into the piston of the master brake cylinder has to close in order to separate the master brake cylinder from the reservoir. The central valve closes mechanically by moving the piston and requires piston travel to close. The isolating valve according to the invention can be closed, for example, by means of a so-called brake light switch with minimal pedal travel of a foot brake pedal. In order to close the isolating valve even earlier, the placement of a foot on the foot brake pedal or the gripping of a handbrake lever with one hand can be sensed and the isolating valve can thus be closed without the piston travel of the master brake cylinder.This has the advantage that no piston travel is lost to build up pressure in the master cylinder. Another advantage is improved pedal feel because no mechanical valve closing processes occur during braking. Another advantage is the possibility of simplified fault testing of the master cylinder. The (unactuated) master cylinder is separated from the reservoir by means of the inventive isolating valve and pressurized using the external energy source of the service brake system. If the brake fluid is free of air bubbles and the master cylinder is leak-tight, the pressure rise is rapid due to the incompressibility of the brake fluid. If the brake fluid is compressible due to air bubbles or leaks, the pressure rise is slower.Another advantage of the invention is that no mechanical shutoff devices for the master brake cylinder from the reservoir, such as the aforementioned sniffer hole or the aforementioned central valve, are necessary. This allows for the use of a simplified and consequently more cost-effective master brake cylinder. However, a master brake cylinder can also be used for the vehicle brake system according to the invention that has a mechanical shutoff device for the brake fluid reservoir of the aforementioned type.

[0008] The subclaims relate to advantageous embodiments and further developments of the invention defined in claim 1. drawing

[0009] The invention is explained in more detail below with reference to an exemplary embodiment illustrated in the drawing. The single figure shows a hydraulic circuit diagram of an electrohydraulic vehicle braking system according to the invention. Description of the embodiment

[0010] The electro-hydraulic vehicle brake system 10 according to the invention shown in the drawing has a power-operated service brake system and a human-powered auxiliary brake system. The service brake system has an external energy source 12 with two hydraulic pumps 14 connected hydraulically in parallel and a hydraulic accumulator 16 connected to their pressure side. The two hydraulic pumps 14 are driven by a common electric motor 18. For safety reasons, two hydraulic pumps 14 are provided; in principle, the service brake system also functions with a single hydraulic pump 14. A pressure sensor 20 is connected to the pressure side of the hydraulic pumps 14 and the hydraulic accumulator 16. A check valve 24 through which flow toward the wheel brake cylinders 22 is connected downstream of the external energy source 12. The wheel brake valves 22 are connected to the check valve 24 via brake pressure build-up valves 26.The check valve 24 prevents brake fluid from flowing back into the hydraulic accumulator 16 from the direction of the wheel brake cylinders 22. The wheel brake cylinders 22 are connected via brake pressure reduction valves 28 to a common return line 30, which leads to a brake fluid reservoir 34 via a shut-off valve 32. The shut-off valve 32 is designed as a 2 / 2-way solenoid valve that is closed in its de-energized basic position.

[0011] A suction side of the hydraulic pumps 14 is connected to the reservoir 34.

[0012] Each wheel brake cylinder 22 is assigned a brake pressure build-up valve 26 and a brake pressure reduction valve 28, with which a wheel brake pressure in the wheel brake cylinder 22 can be controlled or regulated in a manner known per se. A pressure sensor 36 is connected to each wheel brake cylinder 22 to measure the wheel brake pressures. By providing a brake pressure build-up valve 26 and a brake pressure reduction valve 28 for each wheel brake cylinder 22, wheel-individual control or regulation of the wheel brake pressures is possible. If wheel-individual control or regulation of the wheel brake pressures is not desired or necessary, several or all wheel brake cylinders 22 can be connected to a brake pressure build-up valve 26 and a brake pressure reduction valve 28. Anti-lock braking, traction control, and / or vehicle dynamics control (ABS, ASR, FDR) are also possible with the brake pressure build-up valves 26 and brake pressure reduction valves 28.This is known per se and will therefore not be explained in detail here. The brake pressure build-up and reduction valves 26, 28 are designed as 2 / 2-way proportional solenoid valves. In the described and illustrated embodiment, the brake pressure build-up valves 26 are closed in their de-energized basic position and the brake pressure reduction valves 28 are open in their de-energized basic position. However, this is not mandatory.

[0013] The electrohydraulic vehicle brake system 10 includes a foot brake pedal 38 as a brake value sensor, the position of which can be measured with a pedal travel sensor 40. In addition, a so-called brake light switch 42 is provided, with which the actuation of the foot brake pedal 38 can be detected.

[0014] The auxiliary brake system has a master brake cylinder 44, which can be actuated by the foot brake pedal 38, which forms the brake value sensor of the service brake system. The master brake cylinder 44 is connected to the brake pressure reduction valves 28 via an isolating valve 46, and via these to the wheel brake cylinders 22. In the illustrated and described embodiment, the connection of the wheel brake cylinders 22 to the master brake cylinder 44 via the brake pressure reduction valves 28 was chosen because the brake pressure reduction valves 28 are open in their de-energized basic position. If, as is usual in known vehicle brake systems, the brake pressure build-up valves 26 are designed as solenoid valves that are open in their de-energized basic position, the wheel brake cylinders 22 are preferably connected to the master brake cylinder 44 via the brake pressure build-up valves 26.It is also generally possible to connect the wheel brake valves 22 directly to the isolation valve 46, bypassing the brake pressure build-up and brake pressure reduction valves 26, 28. When the vehicle brake system 10 is actuated with the externally powered service brake system, the master brake cylinder 44 is hydraulically separated from the vehicle brake system 10 by closing the isolation valve 46.

[0015] A pressure sensor 48 is connected to the master brake cylinder 44, the signal of which can also be used to form a target value for the wheel brake pressures to be set in the wheel brake cylinders 22 when actuated by external power.

[0016] The master brake cylinder 44 can, as shown, be a single-circuit master brake cylinder, or a dual- or multi-circuit master brake cylinder can be used. A so-called pedal travel simulator can be integrated into the master brake cylinder; as shown, a pedal travel simulator 50 designed as a separate component can also be connected to the master brake cylinder 44. The pedal travel simulator 50 enables movement of the foot brake pedal 38 when the isolating valve 46 is closed, i.e., when the vehicle brake system 10 is actuated by external power. Without a pedal travel simulator 50, movement of the foot brake pedal 38 would not be possible due to the incompressibility of brake fluid when the isolating valve 46 is closed.

[0017] The master brake cylinder 44 is connected to the reservoir 34, with the master brake cylinder 44 being connected to a different chamber of the reservoir 34 than the hydraulic pumps 14. A further isolating valve 52 is connected between the master brake cylinder 44 and the reservoir 34. This isolating valve 52 is designed as a 2 / 2-way solenoid valve that is open in its de-energized basic position. The isolating valve 52 makes it possible to isolate the master brake cylinder 44 from the reservoir 34 regardless of its actuation. In particular, it is possible to isolate the master brake cylinder 44 from the reservoir 34 without or with a significantly shortened travel of a piston of the master brake cylinder 44. Without the isolating valve 52, a piston travel would be required to override a sniffer bore of the master brake cylinder 44 or to close a central valve integrated into a piston of the master brake cylinder 44.The isolation valve 52, when closed, also enables a test of the unactuated master brake cylinder 44 by pressurizing it using the external energy source 12 by opening at least one brake pressure build-up valve 26 and by the open, associated brake pressure reduction valve 28. If the brake fluid is free of air bubbles and the master brake cylinder 44 is tight, a rapid pressure increase results; if gas bubbles or leaks are present, the pressure increase is delayed.

[0018] A pressure-limiting device such as a so-called bursting disc or a pressure-limiting valve, which connects the pressure side of the external energy source 12 to the reservoir 34 and thereby limits the pressure in the hydraulic accumulator 16 and at the brake pressure build-up valves 26, can be omitted, since excessive pressure can be reduced or limited by opening at least one of the brake pressure build-up valves 26 through the associated, open brake pressure reduction valve 28 and by opening the shut-off valve 32. Damage, in particular to the brake pressure build-up valves 26, can thus be avoided.

[0019] In the illustrated and described embodiment of the invention, a piston of the pedal travel simulator 50 can be pressurized on both sides. On one side, it is pressurized by the master brake cylinder 44; the other side is connected by a first simulator valve 53 to a brake line leading from the check valve 24 to the brake pressure build-up valves 26, and by a second simulator valve 54 to the return line 30 leading from the brake pressure reduction valves 28 via the shut-off valve 32 to the reservoir 34. In the illustrated and described embodiment, the two simulator valves 53, 54 are designed as 2 / 2-way solenoid valves, with the first simulator valve 53 being open in its de-energized basic position and the second simulator valve 54 being closed in its de-energized basic position. The pedal travel simulator 50 is connected to the first simulator valve 53 via a throttle 56.By closing both simulator valves 53, 54, the pedal travel simulator 50 can be "locked." Since no brake fluid can be displaced from the pedal travel simulator 50 when the simulator valves 53, 54 are closed, no brake fluid can be displaced from the master brake cylinder 44 into the pedal travel simulator 50 in this state. This eliminates the need for an otherwise conventional shut-off valve between the master brake cylinder 44 and the pedal travel simulator 50. Furthermore, an active reset of the pedal travel simulator 50 is possible by opening one of the two simulator valves 53, 54. For the second simulator valve 54, an additional requirement is that pressure is present in the return line 30, which is the case when the wheel brake pressure in the wheel brake cylinders 22 is reduced by opening the brake pressure reduction valves 28.In addition, there is the possibility of recovering a volume of brake fluid displaced from the master brake cylinder 44 into the pedal travel simulator 50 by opening one of the two simulator valves 53, 54. The brake fluid displaced from the master brake cylinder 44 into the pedal travel simulator 50 by depressing the foot brake pedal 38 flows through the opened simulator valve 53, 54 in the direction of the wheel brake cylinders 22. By opening the second simulator valve 54, the wheel brake cylinders 22 can be pressurized with pressure from the pedal travel simulator 50 through the brake pressure reduction valves 28.

[0020] The simulator valves 53, 54 can be used to represent an active pedal travel simulator by applying pressure to the pedal travel simulator 50 via the simulator valves 53, 54 depending on the pedal travel or position of the foot brake pedal 38 and the pressure in the master brake cylinder 44. Since the pedal travel simulator 50 communicates with the master brake cylinder 44, the pressure in the master brake cylinder 44 can be controlled or regulated in this way using the simulator valves 53, 54. For better control / regulation of the pressure in the master brake cylinder 44, proportional valves should be used as simulator valves 53, 54 instead of the switching valves shown.

[0021] The muscle power actuation of the vehicle brake system 10 is carried out with the master brake cylinder 44 through the open isolating valve 46 and the open brake pressure reduction valves 28. The designation of the valves assigned to the wheel brake cylinders 22 as brake pressure build-up and reduction valves 26, 28 therefore refers to the service brake system and does not exclude a brake pressure build-up in the wheel brake cylinders 22 by the brake pressure reduction valves 28 or, conversely, a brake pressure reduction in the wheel brake cylinders 22 by the brake pressure build-up valves 26.

Claims

[1] Electrohydraulic vehicle braking system, with an externally powered service braking system and with a human-powered auxiliary braking system, wherein the externally powered service braking system has an external energy source (12), at least one wheel brake cylinder (22) connected to the external energy source (12) and a brake value transmitter, and wherein the human-powered auxiliary braking system has a master brake cylinder (44), at least one wheel brake cylinder (22) connected to the master brake cylinder (44) and a reservoir (34) for brake fluid to which the master brake cylinder (44) is connected, characterized by that the vehicle brake system (10) has a separating valve (52) arranged between the master brake cylinder (44) and the reservoir (34), which is controllable independently of an actuation of the master brake cylinder (44) and by means of which the master brake cylinder (44) can be separated from the reservoir (34). [2] Electrohydraulic vehicle braking system according to claim 1, characterized by that the isolation valve (52) is a solenoid valve. [3] Electrohydraulic vehicle braking system according to claim 1, characterized by that the externally powered service brake system has a reservoir (34) for brake fluid, to which at least one wheel brake cylinder (22) is connected via a shut-off valve (32). [4] Electrohydraulic vehicle braking system according to claim 1, characterized by that a check valve (24) through which flow can take place in the direction of the wheel brake cylinder (22) is arranged between the external energy source (12) and the at least one wheel brake cylinder (22). [5] Electrohydraulic vehicle braking system according to claim 1, characterized bythat a pedal travel simulator (50) is connected to the master brake cylinder (44), which is designed as a media separator and pressure transmitter, which transmits a pressure from the master brake cylinder (44) to the externally powered service brake system and vice versa and which hydraulically separates the master brake cylinder (44) from the externally powered service brake system. [6] Electrohydraulic vehicle braking system according to claim 5, characterized by that the vehicle brake system (10) has a simulator valve (53, 54) which is interposed with the pedal travel simulator (50) of the externally powered service brake system.

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