WO1997010134A1

WO1997010134A1 - Hydraulic brake system with a pre-pressure generator

Info

Publication number: WO1997010134A1
Application number: PCT/EP1996/003706
Authority: WO
Inventors: Helmut Steffes; Peter Volz
Original assignee: Itt Automotive Europe Gmbh
Priority date: 1995-09-16
Filing date: 1996-08-22
Publication date: 1997-03-20
Also published as: DE19534456A1

Abstract

The prior art already includes hydraulic brake system with a pre-pressure generator in the master-cylinder reservoir. To simplify the design, the invention proposes that the storage chambers (21, 22) themselves in the reservoir (20) are acted on by pressure so that it is not necessary to fit complex piston/cylinder assemblies inside the reservoir. Generating the pre-pressure inside the reservoir (20) makes it possible to prime the fluid-return pump (16) in the brake system even when the brake pedal is not being actuated. Such priming makes rapid brake operation possible in active braking.

Description

Hydraulic brake system with pre-pressure generator

The present invention is based on a hydraulic brake system according to the preamble of claim 1. Such a brake system is described in DE 41 28 091 AI. The known brake system is suitable for brake slip control and for drive slip control. So that a quick build-up of pressure in the wheel brakes can take place in the case of a traction control system, in spite of the self-priming return pump in the brake circuit, a pre-pressure generator is arranged in the reservoir, which has a small-volume loading chamber delimited by a piston, the piston being actuable via a vacuum source and the pressure medium being released can displace the loading chamber in the master cylinder. Since the pressure medium connection of the master cylinder is thus connected to the loading chamber and not to the substantially larger storage chamber of the storage container, care must be taken to ensure that pressure medium can always flow from the storage chamber into the loading chamber if this is necessary for brake actuation. The constructive design of the pre-pressure generator with piston, prestressing spring, actuating rod for the piston and vacuum socket and with a feed line for the vacuum source which can be blocked by means of a solenoid valve is relatively complex and structurally difficult to get to grips with.

The object of the present invention is therefore to create a structurally simpler solution for generating the pre-pressure in the container, starting from a brake system of the type mentioned at the outset. This object is achieved in conjunction with the characterizing features of claim 1. The principle of the invention therefore consists in dispensing with a separate loading chamber which is connected to the master cylinder. The pre-pressure is generated in the pantry itself.

In order to build up a corresponding upstream pressure, there are common pumps whose delivery pressure only has to be a few bar.

When using a hydraulic pump, no media separation between the conveyed medium and brake fluid is required if the hydraulic pump conveys the pressure medium used in the brake system into the storage chamber of the storage container. It then goes without saying that a pressure equalization between the storage chamber and the atmosphere is either not present or is interrupted.

An alternative solution is the use of a pneumatic pump. An air chamber, which is delimited by the storage chamber and is fluid-tight, can be used, which is arranged in the storage container. As the volume of the air chamber increases, the volume of the storage chamber decreases accordingly. Air as a pressure medium can simply be taken from the atmosphere and released into the atmosphere.

If an air bag is used as the air chamber, this can also cover a pressure compensation opening in the inflated state, so that no additional valve for interrupting the pressure compensation between the storage chamber and the atmosphere is required. A more detailed explanation of the concept of the invention will now be given on the basis of the description of four embodiments of the invention in five figures. It shows

1: a brake system according to the invention with a hydraulic pump for generating pressure,

2: a section of a brake system according to the invention with a hydraulic pump with a different design,

3: a brake system according to the invention with a pneumatic pump for generating the initial pressure,

4: a first variant of a storage container with an air bag and

5: a second variant of a storage container with an air bag.

The brake system according to FIG. 1 can be exchanged below the master cylinder 1 for that of FIG. 3 or other embodiments. It has two hydraulic brake circuits I and II, which are constructed identically. Each brake line 2 passes through a separating valve 3 and branches into two brake branches 4 and 5. Each brake branch 4 and 5 is provided with an inlet valve 6 and 7 and leads to a wheel brake 8 and 9, respectively. Of the wheel brakes 8 and 9 lead return branches 10 and 11 via an outlet valve 12 and 13 to a low-pressure accumulator 14. The low-pressure accumulators 14 are each connected via a check valve 15 to the suction side of a self-priming return pump 16. Furthermore, the return pumps 16 each have a suction line 17 to the brake line 2 of the respective brake circuit, this suction line 17 connecting to the brake line 2 between the master cylinder 1 and the isolation valve 3. The pressure sides of the return pumps 16 are each connected via a pressure line 18 to the brake line 2, but between the isolating valve 3 and the inlet valves 6, 7.

In the brake system shown, the suction lines 17 have no separate changeover valve for separating the suction side of the return pumps 16 from the brake line 2. This brings savings by reducing the number of valves used. However, if it is to be avoided that the master cylinder pressure propagates up to the suction side of the respective return pump 16, then a changeover valve can be inserted into the suction lines 17, for example according to FIG. 3. This changeover valve does not necessarily have to be a normally closed solenoid valve, but hydraulically operated versions are also possible, even in the open basic position.

A storage container 20 is arranged above the master cylinder 1. It has two pressure medium connections 21 and 22 to the master cylinder 1, one for each brake circuit 1.11. The storage container 20 is divided by a horizontal partition 23 into two separate rooms. The upper space 24 has a pressure equalization to the atmosphere above the container lid. The lower room 25 is divided into two pantries 26 and 27. The storage chamber 26 feeds the brake circuit I, while the storage chamber 27 supplies the brake circuit II. The suction side of a hydraulic pump 28 is connected to the space 24, which is filled with pressure medium. The pressure side of the hydraulic pump 28 is connected to the room 25 via a switching valve 29. The switching valve 29 is a 3/2-way valve actuated hydraulically by the delivery pressure of the pump 28, the two spaces 24 and 25 being connected to one another in the basic position for pressure equalization. The switching position of the switching valve 29 set by pump pressure connects the pressure side of the pump 28 to the space 25 via a check valve. The space 24 is then separated from the space 25.

So that the switching valve 29 can return to its basic position after precharging, the pressure side of the pump 28 is short-circuited with its suction side via a throttle 30. The throttle 30 enables a small leakage, so that when the pump is switched off, the pressure on the pressure side of the pump gradually increases is reduced and the control pressure for switching the switching valve 29 is finally fallen below.

The storage chambers 26 and 27 are only separated from one another by a half-high wall. If the pump 28 thus conveys pressure medium into the space 25, it first reaches the chamber 27. However, since there is pressure equality in the chambers 26 and 27, the brake circuits I and II are connected via the connections 21 and 22 supplied with the same form. If the pressure medium level in the storage chamber 27 exceeds the height of the half-high wall due to the delivery of the pump 28, pressure medium flows into the storage chamber 26.

Generating pressure in the storage chambers themselves has the advantage that the storage container 20 can be constructed in a relatively simple manner. All that is required is a horizontal partition 23. Fig. 2 shows a constructive measure to limit the delivery pressure of the pump 28. Fig. 2a shows the constructive solution, while Fig. 2b shows the corresponding circuit symbols. The arrangement shown can replace the symbol for the pump 28 in FIG. 1, for example.

2a, two cylindrical cavities 31 and 32 are arranged relative to one another in such a way that the cavity 32 of smaller diameter opens radially into the cavity 31 with one end face. A piston 33 is guided in a sealed, displaceable manner in the cavity 32 and, as indicated by the arrows shown, can be pushed back and forth by an eccentric or the like. In the cavity 31 two plate pistons 34 and 35 are arranged, each of which has such a seal to the wall of the cavity 31 that a pressure medium flow from top to bottom along the plate piston 34 and 35 is possible, but not in the opposite direction. The upper plate piston 34 is acted upon in the downward direction by a compression spring 38, which is stronger than the compression spring 39 arranged between the two plate pistons 34 and 35. The lower plate piston 35 lies against the lower end face of the cavity 31 and has a spacer 40, which defines a minimum distance between the two plate pistons 34 and 35, so that the opening 36 to the cavity 32 can never be passed over by the seal 36 of the plate piston 34.

The upper pressure medium connection 41 of the cavity 31 is connected to an unpressurized storage container, for example the space 24 from FIG. 1. The lower pressure medium connection 42 of the cavity 31 can be connected to a storage container and corresponds, for example, to the pressure side of the hydraulic pump 28 from FIG. 1.

The mode of operation of this arrangement from FIG. 2a is clear in connection with FIG. 2b. From a functional point of view, the seals 36 and 37 form check valves, corresponding to a suction valve and a pressure valve of a pump. Since the plate pistons 34 and 35 are not rigidly coupled to one another, when the pressure builds up in the chamber spanned by the compression spring 39, the plate piston 34 can move upward and swallow volume. This takes place only when the delivery pressure of the pump is sufficient to compress the compression spring 38. The pressure prevailing in the chamber spanned by the compression spring 39 can therefore never exceed a value which corresponds to the compression force of the compression spring 38 divided by the area of the plate piston 34.

As already mentioned in connection with FIG. 1, in FIG. 3 the brake system connected below the master cylinder 1 can also be exchanged for that of FIG. 1. The changeover valves 43 in the suction lines 17 of the return pumps 16, which are present once per brake circuit I and II in FIG. 3, can also be omitted according to FIG. 1 or be designed differently. A storage container 20 is in turn arranged above the master cylinder 1, but in this case is supplied with pressure by a pneumatic pump 44. The reservoir 20 has a pressure compensation throttle in the closure, which can be closed, for example according to FIGS. 4 and 5, for the purpose of generating the pre-pressure.

4 and 5 illustrate alternative solutions in which way an airbag which can be filled by the pneumatic pump 44 can be arranged within the container 20. Part a of the 4 and 5 each show the airbag in the depressurized state, while part b shows the filled airbag.

First, the features common to FIGS. 4 and 5 are described. A filler neck 46 is attached to the container ceiling 45 for filling the container with pressure medium. A container closure is schematically indicated, which has a compensation throttle for pressure compensation of the container with the atmosphere. The pressure medium level within the container is approximately at the level of the container seam 48, so that both storage chambers 49 and 50 have a common pressure medium level. Compressed air socket 51 is formed on the side of the container wall above the pressure medium level and extends outward and inward approximately in a cylindrical manner. An airbag 53 is fastened to the inner extension 52 of the compressed air socket by means of a clamp. A pneumatic pump can be connected to the outer extension 54 of the compressed air connection.

In the relaxed state, the almost empty airbag 53 floats on the pressure medium level.

If the storage container 20 is constructed in accordance with FIG. 4, the upper airbag skin lies against the container ceiling 45 when the airbag 53 is inflated and thus closes the compensating throttle 47. As the airbag 53 increases in volume, the pressure in the storage container 20 increases since the volume of the storage chambers 49 and 50 decreases as the volume of the airbag increases. The maximum pressure in the storage container 20 is thus determined by the delivery pressure of the pneumatic pump which is connected to the compressed air connection 51. Since there is the same pressure in the entire airbag 53, so are the both storage chambers 49 and 50 exposed to the same pressure, so that the same pressure is built up in both brake circuits.

5, a horizontal partition 55 is drawn in above the airbag 53, which is provided with a central opening 56. If the airbag 53 is inflated in the case of a container of this type, it does not lie against the container ceiling 45, but rather against the partition 55. Instead of the compensating throttle 47, the opening 56 is closed, which has the same effect as in FIG. 4, namely that a pressure is built up in the storage chambers 49 and 50 when the airbag 53 increases in volume.

The pre-pressure generated in the reservoir 20 - in whatever way - is propagated via the brake lines 2 to the suction side of the return pumps 16. For this purpose, the isolating valves 3 in the brake lines 2 are closed and, if necessary, the changeover valves 43 in the suction lines 17 are opened. Rapid active braking is also possible with such a pre-pressure generation. Active braking means that it is a brake intervention without actuating the brake pedal. The need for braking can be recognized on the basis of different criteria by means of sensor signals. Active braking can be carried out, for example, for traction control, for yaw moment control or for distance control of a vehicle.

Embodiments of the invention are not limited to the examples shown. For example, a pneumatic pump without an airbag or other chamber separation can also be used if it is ensured that air is not pressed into the master cylinder 1 by the pneumatic pump.

Claims

claims

1. Hydraulic brake system with a master cylinder (1) actuated by a brake pedal, which is connected to a pressure medium reservoir (20) with at least one storage chamber (21, 22, 49, 50) and via at least one brake circuit 1, 11 with at least one Wheel brake (8, 9) is connected, the master cylinder (1) being permeable to pressure medium when the brake pedal is not actuated, and with a pre-pressure generator in the reservoir (20), characterized in that at least one reservoir chamber (21, 22, 48,49) can be pressurized.

2. Brake system according to claim 1, characterized in that the pressure is applied by a pump (28,44).

3. Brake system according to claim 2, characterized in that it is a hydraulic pump (28) which promotes pressure medium into the Vorrats¬ chamber (22,21) from an unpressurized space (24).

4. Brake system according to claim 2, characterized in that it is a pneumatic pump (44) which pumps air into an area within the storage container (20).

5. Braking system according to claim 4, characterized in that the pneumatic pump för¬ changes air into an air chamber (53) va¬ riablen volume within the storage container (1), the volume of the storage chamber (48,49) by increasing the volume of the air chamber ( 53) decreases. Brake system according to claim 5, characterized in that the air chamber is formed by an air bag (53).

Brake system according to claim 6, characterized in that the air bag, when filled, rests against a ceiling (45, 55) delimiting the storage chamber (48, 49) and closes a pressure compensation opening (47, 56) therein.