GB2400896A

GB2400896A - A device for eliminating air from electro-hydraulic braking systems

Info

Publication number: GB2400896A
Application number: GB0408736A
Authority: GB
Inventors: Carston Pabst; Michael Blasenbrey; Matthias Hurst; Guy-Edward Michalski
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2003-04-22
Filing date: 2004-04-20
Publication date: 2004-10-27
Anticipated expiration: 2024-04-20
Also published as: DE10318114A1; GB0408736D0; GB2400896B

Abstract

A hydraulic / electro-hydraulic braking system 1, wherein a brake fluid can be directed from a storage container 2 via an inlet line 5 into a wheel brake cylinder 8 and said brake fluid can flow back to said storage container 2 via a return line 5, characterized in that an air eliminator 3 is provided in the inlet line 5 for the brake fluid. The air eliminator, which serves to remove gas / air from the brake fluid 3 may comprise a conical body 3a, and may comprise a filter mesh or screen 11. Operation of the air eliminator 3 may be measured in the vehicle or test bench by pressure volume temperature characteristics.

Description

DESCRIPTION

ELECTRO-HYDRAULIC BRAKING SYSTEM

Prior Art

al he present invention relates to an electro-hydraulic braking system, wherein a brake fluid can be directed from a storage container via inlet lines into respective wheel brake cylinders and said brake fluid can flow back into the storage container via return lines.

Electro-hydraulic braking systems are used for example in motor vehicles. Such an elcctro-hydraulic braking system is known from DE 199 23 689 Al and contains a brake master cylinder having a storage container, to which a brake pedal, actuated by a driver, is attached. Furthermore, a hydraulic assembly is provided which contains valve and pump arrangements for controlling wheel brakes. A brake pedal switch, which closes upon actuation of the brake pedal, and a measuring device for detecting displacement of the brake pedal are connected to the brake pedal. Furthermore, a pedal travel simulator is provided which simulates a counter force For the driver upon actuation of the brake pedal. Two brake circuits are connected to the brake master cylinder. A cut-off valve is inserted in each ot these brake circuits and is closed by an electrically actuated brake system by supplying current thereto. Upstream of the cutoff valve, a pressure sensor in at least one of the brake circuits measures the pressure exerted by the driver via actuation of the brake pedal. When the cut-off valves are closed, the brake master cylinder is hydraulically separated from the pressure regulating system. The pressure regulating system contains a pressure modulator for each wheel brake in order to regulate the brake pressure. When the driver presses the brake pedal, he detects a counter force which is travel-dependent. This traveldependancy is formed by means of a defined characteristic of the pedal travel simulator. When the pedal travel sensor detects desired braking, a pressure is produced in the brake master cylinder which is a result of the pedal force. This pressure is then transferred to the wheel brakes so that the brakes initiate or effect a corresponding braking action.

However, in braking systems it has proved to be disadvantageous that, owing to the hydroscopic properties of the brake fluid, air contained in the brake fluid alters the braking action. In other words, the brake fluid pressure produced by pressing the brake pedal is not] :1 but rather transferred to the wheel brakes with a known deviation owing to the air contained in the brake fluid.

In accordance with the present invention, there is an electro-hydraulic braking system, wherein a brake fluid can be directed *tom a storage container via an inlet line into a wheel brake cylinder and said brake fluid can flow back into the storage container via a return line, characterized in that an air eliminator is provided in the inlet line for the brake fluid.

The electro-hydraulic braking system in accordance with the invention permits the air contained in the brake fluid to be eliminated so that the pressure exerted on the wheel brakes is exclusively transferred by the brake fluid and not by a suspension of brake fluid and air. The air in the hydraulic assembly which separates out and rises by cooling at the end of the journey is collected and as a consequence air is prevented from flowing into the wheel lines. Owing to the hydroscopic properties of the brake fluid, minimum amounts of air are always present in the fluid. The eliminator ensures that the wheel lines are exclusively filled with brake fluid (with no air content).

In order to optimise the air elimination capacity of the air eliminator in accordance with the invention, said air eliminator may comprise a conical main body. Thus, the brake fluid flowing to the air eliminator via a suction line is caused to flow directly around the air eliminator so that the air contained and collected in the brake fluid is eliminated at the air eliminator in accordance with the invention and consequently does not flow to the wheel brakes.

In a preferred manner, at least one, preferably five, transverse ribs are formed on the conical main body which serve as deflectors and consequently direct the brake fluid in an optimal manner through the air eliminator and thus increase the air elimination capacity.

It is particularly preferred that the transverse ribs are fixedly connected to the main body and extend from the vertex of the main body along its peripheral surface to its base.

Owing to the conical shape of the main body of the air eliminator as well as the cylindrical shape of the inlet and return lines for the brake fluid, it is particularly preferred that the transverse ribs are substantially formed in the shape of a triangle.

In order to optimise the air elimination characteristics at the eliminator, the air eliminator may contain a suitable filter mesh or a suitable screen preferably having a mesh size of 200 m.

The filter mesh or the screen is preferably disposed at the vertex of the main body in such a manner that the plane of extension of the filter mesh or screen is substantially perpendicular to the normal of the main body, wherein the normal extends from the vertex to the centre point of the base of the main body. Owing to this arrangement of the filter mesh or the screen in conjunction with the conical main body, the brake fluid flows through the suction line as well as the screen or filter mesh and then back through the screen or filter mesh and then through the wheel line to the wheel brake. This dual now through the screen or filter mesh increases the rate of elimination of the air contained in the brake fluid so that it is guaranteed that no air reaches the wheel brake.

In order to assemble an air eliminator in an electro-hydraulic braking system as simply as possible, the air eliminator is preferably built as a single piece.

In order to obviate the need for additional lines for removing the air collected in the air eliminator, the eliminated air is preferably returned to the storage container via the return line by means of a flushing process.

Since the operation of the air eliminator can be impaired by any dirt in the brake fluid, but the effective operation of the brakes must also be guaranteed, the operation of the air eliminator can be preferably measured in a vehicle or on a test bench by pressure volume/temperature characteristics. Consequently as soon as an operational error in the air eliminator is detected, the eliminator can be repaired or replaced in the vehicle.

Specific embodiments of the E'rescnt invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic wiring diagram of an electro-hydraulic braking system having an air eliminator in accordance with the invention; Figure 2 shows a schematic view of the air eliminator in accordance with the invention when it is assembled in the inlet and return line; Figure 3 shows a schematic three-dimensional illustration of Figure 2; and Figures 4a and 4b show schematic illustrations of the air eliminator in accordance with the invention.

Figure 1 generally illustrates a schematic wiring diagram of an electrohydraulic braking system I having a storage container 2 for the brake fluid as well as an air eliminator 3 in accordance with the invention. The brake fluid from the storage container 2 flows following the illustrated control loop 4 via a suction line 5 into a hydraulic assembly 6. The air eliminator 3 in accordance with the invention is disposed within the hydraulic assembly 6. The brake fluid now flows through the air eliminator 3, whereby the air always present in the hydroscopic brake fluid is eliminated in the air eliminator 3 so that only brake fluid, without any air content, then flows via the wheel line 7 to the wheel brake 8 and, in accordance with the prevailing pressure, initiates a braking process for example using the electro- hydraulic braking system in a motor vehicle. It is to be noted that the braking system 1 is constantly filled with brake fluid, i.e. both in its operating state as well as in its non-operating state.

If the brake pedal of the motor vehicle is released, then the brake fluid flows lrom the wheel brake 8 via the wheel line 7 back to the air eliminator 3 and from there via a return line 9 into the storage container 2.

This reverse flow action is also used for a flushing pulse of the air eliminator 3.

For instance, when a motor vehicle is started-up a flushing pulse is effected to remove the air collected in the air eliminator 3, whereby the air collected in the air eliminator 3 is flushed out of the air eliminator 3 by means of the brake fluid and is directed to the storage container via the return line 9.

Figure 2 shows a schematic view of the air eliminator 3 in accordance with the invention in its assembled condition. The air eliminator 3 is assembled in the suction line 5 so that the brake fluid flowing through the suction line 5 and the air eliminator 3 flows directly into the wheel line 7 as illustrated by the arrow S in Figure 2.

Figure 2 shows the air eliminator 3 in accordance with the invention formed with a conical or funnel-shaped main body 3a and comprising transverse ribs 10. Brake fluid containing air is directed by the conical main body 3a to a screen 11 provided in the air eliminator 3 and preferably having a mesh size of 200 m, said brake fluid then flowing through the screen in a downward direction in Figure 2, the air being retained at the screen I I by adhesion. The transverse ribs 10 in the air eliminator 3 optimise the flow path of the brake fluid containing air so that the brake fluid containing air has to flow from the suction line 5 through the screen 11 into the chamber I la located therebehind and, when the return line 9 is closed, through a discharge valve 12, again through the screen 11 and further through the wheel line 7 to the wheel brake 8. The air is thus optimally eliminated owing to the dual flow through the screen 11.

When the brake fluid returns from the wheel brake 8 to the storage container 2, it flows t'ollowing arrows R from the wheel line to the main body 3a and Prom the main body 3a through the screen 11 and, when the discharge valve 2 is closed, through the return line 9 to the storage container 2 which is not illustrated in Figure 2.

A suitable filter mesh can also be used instead of the screen 11. Furthermore, the air eliminator 3 is to be preferably formed with five evenly distributed transverse ribs 10 so that the air eliminator 3 can be assembled in any direction.

Figure 3 shows in a three dimensional form the air eliminator 3 in accordance with the invention having a conical main body 3a and transverse ribs 10. The connection 13 for the wheel line can also be seen in the upper part of this I; igure.

The discharge valve 12 is connected to the air eliminator 3 in a substantially horizontal orientation in Figure 3, which discharge valve controls the opening and closing of the return line 9 through which the brake fluid flows back into the storage container 2 in accordance with Figure I and during a flushing process the air collected in the air eliminator 3 flows back into the storage container 2 in this manner. Consequently, as set forth above, no air is accumulated in the wheel line Figures 4a and 4b show, also on an enlarged three-dimensional scale, a preferred form ol'the air eliminator 3 in accordance with the invention. The air eliminator 3 in accordance with the invention is formed having the conical main body 3a and comprises preferably five transverse ribs 10. As explained in connection with Figures 2 and 3, the air eliminator 3 is inserted in the suction line 5 so that brake fluid flowing from the storage container 2 to the wheel brake 8 flows through the suction line 5, the air eliminator 3 as well as the wheel line 7 to the wheel brake X. The air eliminator 3 is reduced in diameter at its circumferential end to the right in Figure 4a, i.e. in the region of the base of the cone, is formed with a radius or a chamfered shape 14 and is introduced with a press-fit 15 into the corresponding bore. This ensures a reliable and leak-tight hold as the brake fluid flows through both to the wheel line and also back to the storage container. The left end of the air eliminator 3 in I;igure 4a connects to the receiving device 16 for the discharge valve 12, for example a solenoid valve.

As can be seen in particular in Figure 4a, the transverse ribs 10 are fixedly connected to the main body 3a and extend from the vertex of the main body 3a along its peripheral surface to its base. The line of connection between the transverse ribs 10 and the main body 3a is designated here with the reference numeral 1 Oa.

The transverse ribs 10 are furthermore formed substantially in a triangular shape owing to the fact that they are fitted into the two brake fluid lines 5, 7 as well as into the bore provided for the air eliminator 3 so that they direct, in the sense of deflectors, the fluid flowing though the suction line 5 optimally through the screen 11 into the chamber I 1 a located therebehind (Figure 2) as well as from the chamber I 1 a again through the screen I 1 into the wheel line 7. The rate of air elimination at the screen 11 is optimised owing to the dual flow through the screen 11 or an adequate filter mesh which means that no air reaches the wheel brake 8.

The screen 11 is inserted at the vertex of the main body 3a in such a manner that the plane of extension of the filter mesh or of the screen I 1, a circular surface in the present exemplified embodiment, as can be seen in particular in Figure 3, is substantially perpendicular to the normal of the main body 3a. The normal is defined in such a manner that it extends from the vertex of the main body 3a to the centre point of the base of the main body 3a.

Of course, instead of the circular shape of the filter mesh or of the screen 11 another shape thereof could be chosen, depending on constructive constraints. Of course, this is also true for the positioning of the filter mesh or screen 1 1 in relation to the normal of the main body 3a of the air eliminator 3 in accordance with the invention.

Figure 4b again shows schematically the arrangement of the air eliminator 3 in accordance with the invention having the five transverse ribs 10. As clearly seen in Figure 4b, as the brake fluid flows from the storage container 2 to the wheel brake 8, the air L "adheres" to the filter mesh or screen 11 and is "swept along" away from the wheel line 7 during the subsequent flushing pulse and the flow of brake fluid produced thereby and is returned to the storage container 2 from the screen 11 or filter mesh.

Although the air eliminator 3 illustrated in the Figures is assembled as a single piece, there is also the possibility, ol course, that the various components of the air eliminator 3 can be produced separately and only subsequently assembled. In addition to the conical shape of the main body 3a and depending on the application, other shapes for the air eliminator 3 have proven suitable, e.g. an approximately spherical shape.

Finally, the air eliminator consists of a brake fluid-resistant material. The material PA66 in particular has proved to be suitable 1or this purpose, which material PA66 can be produced by an injection-moulding method.

inally, the operation of the air eliminator 3 can be measured in the vehicle or on a test bench by pressure volume temperature characteristics so that the operational capacity of the air eliminator 3 in accordance with the invention can be tested continuously or at regular intervals. al

Claims

1. An electro-hydraulic braking system, wherein a brake fluid can be directed lrom a storage container via an inlet line into a wheel brake cylinder and said brake fluid can flow back into the storage container via a return line, characterized in that an air eliminator is provided in the inlet line for the brake fluid.

2. An electro-hydraulic braking system as claimed in Claim 1, charactcrised in that the air eliminator comprises a conical main body.

3. An electro-hydraulic braking system as claimed in Claim 2, characterized in that the conical main body is formed with at least one transverse rib.

4. An electro-hydraulic braking system as claimed in Claim 2, characterized in that the conical main body is formed with five transverse ribs.

5. An electro-hydraulic braking system as claimed in Claim 3 or 4, characterized in that the transverse ribs are fixedly connected to the main body and extend from the vertex of the main body along its peripheral surface to its base.

6. An electro-hydraulic braking system as claimed in any one of Claims 3 to 5, characterized in that the transverse ribs are formed substantially in the shape of a triangle.

7. An electro-hydraulic braking system as claimed in any one of Claims I to 6, characterized in that the air eliminator comprises a filter mesh.

8. An electro-hydraulic braking system as claimed in any one of Claims 1 to 6, characterized in that the air eliminator comprises a screen preferably having a mesh size of 200 1lm.

9. An electro-hydraulic braking system as claimed in Claim 7 or 8, characterized in that the filter mesh or the screen is disposed at the vertex of the main body in such a manner that the plane of extension of the filter mesh or screen is substantially perpendicular to the normal of the main body, wherein the normal extends from the vertex to the centre point of the base of the main body.

10. An electro-hydraulic braking system as claimed in any one of Claims 1 to 9, characterized in that the air eliminator is built as a single piece.

An electro-hydraulic braking system as claimed in any one of Claims I to 10, characterized in that the air eliminated in the air eliminator is returned to the storage container via the return line by means of a flushing process.

12. An electro-hydraulic braking system as claimed in any one of Claims 1 to I I, characterized in that the operation of the air eliminator can be measured in a vehicle or on a test bench by pressure volume temperature characteristics.

13. An electro-hydraulic braking system substantially as herein described with reference to, and as illustrated in, the accompanying drawings.