Patent Application
20100269684
The present invention relates to a vacuum brake booster for a motor vehicle brake system, having a force input element that is connectable or connected to a brake pedal, a chamber arrangement comprising a vacuum chamber and a working chamber that are separated from one another by a movable wall, a control valve with a valve element for selectively connecting and separating vacuum chamber and working chamber, and a force output element for transmitting an output force to a master cylinder, wherein the force input element is workingly connectable or connected to a transmission piston arrangement disposed in the control valve, wherein the control valve is settable in accordance with a displacement of the transmission piston arrangement along a longitudinal axis by means of the force input element.
Such vacuum brake boosters are prior art. For example, the document DE 40 21 304 A1 discloses a vacuum brake booster, in which by means of the force input element the transmission piston arrangement is displaceable against the resistance of a resetting spring. On the transmission piston arrangement a first valve seat is provided, which interacts with a valve element. As a result of the displacement of the transmission piston arrangement this valve seat is lifted off the valve element, thereby leading to a connection of the working chamber to the atmosphere and hence to a pressure build-up at the movable wall. As a result of the pressure difference arising at the movable wall, the control valve housing is correspondingly re-displaced until the open valve seat closes again. The vacuum brake booster is then situated once more in a state of equilibrium, wherein an output force corresponding to the displacement of the force input element is transmitted by the force output element to a master cylinder arrangement. If the force input element is released, it is moved together with the transmission piston arrangement back in the direction of its initial position owing to the action of the resetting spring. In this case, a second valve seat is opened, with the result that a pressure compensation may be effected between the vacuum chamber and the working chamber. The control valve housing consequently moves back into its initial position. For this purpose, the resetting spring has to be designed in such a way that it overcomes all of the pressure-related counterforces that arise.
A substantial drawback of this vacuum brake booster is that during operation at the valve element a differential pressure arises, which is caused by the fact that at a side of the valve element facing the force input element atmospheric pressure is permanently applied, whereas upon a brake pedal actuation the pressure prevailing in the working chamber is applied to the opposite side of the valve element. In many operating situations this pressure is lower than atmospheric pressure, thereby resulting in the pressure difference at the valve element. During the return of the control valve housing to its initial position, this pressure difference counteracts a movement of the valve element. It has to be overcome in order to open the second valve seat. As the resetting movement is effected solely by the resetting spring, the resetting spring has to have a sufficiently high spring constant. However, this in turn means that correspondingly high forces are also needed for the actuation of the vacuum brake booster and for the compression of the resetting spring associated therewith. In other words, the differential pressure arising at the valve element causes an increase of the actuating forces and therefore influences the response characteristic of this vacuum brake booster. This conflicts with the requirement for comfortable actuation of the brake system.
As further prior art, reference is made to the documents EP 0 830 276 B1, and corresponding U.S. Pat. No. 5,799,559, both of which are incorporated by reference herein, and EP 0 655 039 B2, and corresponding U.S. Pat. No. 5,546,846, both of which are incorporated by reference herein. These documents also disclose in each case vacuum brake boosters of prior art, in which a force input element is connected to a transmission piston arrangement, wherein at the valve element during operation a differential pressure may build up and leads to the increase of the actuating forces that are to be summoned up.
To combat this problem of the high actuating forces, the document DE 42 27 879 A1, and corresponding U.S. Pat. No. 5,546,846, both of which are incorporated by reference herein, proposes that in a bellows-like valve element a plurality of axial openings be provided, by means of which a pressure compensation may occur. This means however that the valve element manufactured from elastomer material has to be pierced a plurality of times and, in order to retain its stability, has to be strengthened elsewhere. The valve element as a whole is however nevertheless more susceptible to failure.
A desired feature of the invention is to provide a vacuum brake booster of the initially described type, in which for a low constructional outlay and without increasing the susceptibility to failure the actuating forces may be reduced compared to the conventional solutions of prior art.
This feature is achieved by a vacuum brake booster of the initially described type, in which the transmission piston arrangement is provided with at least one pressure compensation channel, by means of which during operation a pressure compensation is effected at the valve element.
The effect achievable by providing at least one pressure compensation channel is that a differential pressure that builds up during operation at the valve element may be kept to a minimum or such a differential pressure build-up may even be entirely prevented, with the result that the valve element during operation is displaceable in a substantially “pressure-neutral” manner inside the control valve. It is thereby possible to avoid having to design the resetting spring strong enough in terms of its spring force to be able to cope additionally with the differential pressure during a resetting movement. Because of the weaker design according to the invention of the resetting spring, a driver upon an actuation of the brake pedal experiences lower counterforces, thereby on the whole enabling a more comfortable actuation. By virtue of preventing the development of such a differential pressure because of the provision of at least one pressure compensation channel in the transmission piston arrangement, i.e. in a dimensionally stable component, it is moreover possible to prevent the vacuum brake booster from being more susceptible to failure. The valve element manufactured from an elastomer may be formed free of holes and is therefore, on the one hand, easier to produce and, on the other hand, less susceptible to faults.
In a variant of the invention it may be provided that the control valve comprises a control valve housing, wherein the transmission piston arrangement is guided in the control valve housing so as to be displaceable relative thereto and relative to the valve element. The valve element in this case is formed in a bellows-like manner from an elastomer and ensures a sealing abutment with corresponding valve seats. According to an embodiment of the invention it is provided that the transmission piston arrangement has an axial guide portion, which is guided sealingly in the valve element. In this connection, according to the invention it may be provided that a first pressure compensation channel is provided in the guide portion that extends substantially in axial direction from a pneumatic region connected to the working chamber into a first pneumatic region delimited by the valve element. In addition or alternatively thereto, a development of the invention provides that a second pressure compensation channel is provided in the guide portion that extends substantially in radial direction from a pneumatic region connected to the atmosphere into a second pneumatic region delimited by the valve element. The valve element may therefore be kept substantially pressure-neutral, with the result that its displacement, in particular by means of a resetting spring, is possible with a low expenditure of force.
To guarantee a sealing guidance of the guide portion relative to the valve element, according to the invention it may be provided that the valve element has first sealing means, by which the guide portion is guided sealingly in the valve element. The valve element in turn may have second sealing means, by which it is sealingly guided in the control valve housing.
As already stated above, the valve element may be of a bellows-like construction, wherein it then comprises a displaceable part and a part that is fixed in the control valve housing. In this connection, according to the invention it may be provided that the valve element is held in the control valve housing by means of a retaining element. In this case, the guide portion may be guided sealingly relative to the retaining element. With regard to the displaceable part, according to the invention it may be provided that it is preloaded into an initial position by means of a resetting spring.
Instead of an integral valve element of a bellows-like construction, the valve element may be of a multi-part construction. A development of the invention therefore provides that the valve element comprises a dimensionally stable carrier element with an elastomer coating, wherein the valve element interacts with the retaining element. Unlike in the case of the valve element of a bellows-like construction, the sealing relative to the control valve housing is achieved for example in that additional sealing means are attached to the retaining element.
It has already been indicated above that the vacuum brake booster according to the invention, exactly like conventional vacuum brake boosters, comprises two sealing seats, by means of which the working chamber may be connected selectively to the vacuum chamber or to the ambient atmosphere. In this connection, an embodiment of the invention provides that a first sealing seat is provided on the control valve housing for interaction with the valve element and that a second sealing seat is provided on a component of the transmission piston arrangement or valve element for interaction with the respective other component of the transmission piston arrangement or valve element. According to the invention the geometry of the valve seats may be selected differently. For example, the valve seats may in each case take the form of a circumferential annular projection on the control valve housing or on the transmission piston arrangement and interact sealingly with a corresponding planar sealing face on the valve element. It may however alternatively be provided that planar sealing faces are provided on the control valve housing or/and on the transmission piston arrangement, wherein corresponding sealing projections or edges are formed on the valve element.
With regard to the design of the guide portion relative to the transmission piston arrangement it may be provided that these are formed integrally with one another. As an alternative to this, the transmission piston arrangement may however be of a multi-part construction, for example such that the guide portion is formed as a separate component separately from the transmission piston arrangement but connected sealingly thereto. Manufacture of the transmission piston arrangement as a whole may therefore be simplified because for example the relatively complex geometry of the mechanically less highly loaded guide portion may be manufactured by a suitable manufacturing method preferred for this purpose, such as for example by injection moulding. The piston element, which because of the pressure loading during actuation is mechanically loaded to a greater extent and which during operation comes into interaction with a rubber-elastic reaction element, may then be designed for example as a correspondingly solid component. In this connection, it may further be provided that the guide portion and the transmission piston arrangement are manufactured from different materials.
Given a multi-part construction of the transmission piston arrangement, it is necessary for the individual parts to be connected reliably and sealingly to one another. According to a variant of the invention the transmission piston arrangement has a fastening formation for sealingly receiving the guide portion. Thus, the guide portion of a bush-like construction may for example be inserted into an annular recess in the transmission piston arrangement that is tuned to the guide portion. Optionally, for this purpose an edge-formed fastening may additionally be provided in order to fix the guide portion securely to the transmission piston arrangement.
In order to guarantee an adequate sealing in the case of a multi-part transmission piston arrangement, it may be provided that at least one sealing element is provided between the transmission piston arrangement and the guide portion in the region of the fastening formation.
Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.
In
The control valve 14 has a control valve housing 18, which is guided in a brake booster housing 20 so as to be displaceable along the longitudinal axis A. In the brake booster housing 20 a chamber arrangement 22 comprising a working chamber 24 and a vacuum chamber 26 is provided, wherein the working chamber 24 is separated from the vacuum chamber 26 by a movable wall 28. The movable wall 28 is connected for joint movement in a fixed manner to the control valve housing 18. Such a movement of the control valve housing 18 as well as a movement of the transmission piston arrangement 16 that is induced by a movement of the force input element 12 are transmitted via a rubber-elastic reaction element 30 to a force output element 32. The force output element 32 is workingly connectable to a non-illustrated master cylinder arrangement.
There now follows a detailed description with reference to
It is evident from
The transmission piston arrangement 16 further has a guide portion 36, which is integrally connected to the piston portion 34. The guide portion 36 is guided in a sealingly displaceable manner in a valve element 38 as well as in a retaining element 40 that fixes the valve element 38 in the control valve housing 18. For this purpose, on the valve element 38 in a flexible bellows-like region a sealing lip 42 is provided, which slides sealingly along a cylindrical outer surface of the guide portion 36. There is further provided in the retaining element 40 a further sealing element 44, which likewise interacts sealingly with the cylindrical outer surface of the guide portion 36. It is evident that the flexible bellows-like portion 46 of the valve element 38 is preloaded in
It is further evident that by means of a spring arrangement 56 the retaining element 40 is held in the position shown in
In the embodiment shown in
Finally, in
The vacuum brake booster 10 according to
As soon as the force input element 12 is released, because of the resetting forces stemming from the non-illustrated master cylinder arrangement at the force output element 32 and because of the resetting action of the resetting spring 56 a backward movement of the transmission piston arrangement 16 together with the force input element 12 occurs. The flexible part of the valve element 38 is therefore driven in
As a result of opening of the sealing seat 54, the vacuum chamber 26 is connected to the working chamber 24 so that the pressure difference at the movable wall 28 is reduced and a pressure compensation to the pressure level of the vacuum chamber 26 may be effected. This leads to a backward movement of the movable wall 28 together with the control valve housing 18 until the valve seat 54 is applied once more onto the valve element 38. The vacuum brake booster 10 then returns to its initial position shown in
The advantage of the present invention in terms of designing the transmission piston arrangement 16 with a guide portion 36, in which the pressure compensation channels 60 and 66 are disposed, is therefore that the valve element 38 is guided in the control valve housing 18 in a substantially pressure-neutral manner, namely independently of the respective operating state. This means that in the pneumatic region 64 there can be no development, as is the case in the prior art, of for instance a differential pressure that has to be overcome during a resetting movement by a stronger design of the resetting spring 56. Rather, by means of the pressure compensation channels 60 and 66 a pressure compensation occurs, so that a differential pressure counteracting a resetting movement cannot develop at the valve element 38. This however also means that the resetting spring 56 may be of a weaker design, with the result that the total actuating forces that are perceptible to the driver may be reduced. The unwanted occurrence of increased response forces, such as may occur in the prior art, may therefore be prevented by providing the pressure compensation channels 60 and 66. In other words, pressure-dependent disturbance variables, which depending on the actuating situation may occur in systems of prior art, may be avoided by virtue of the present invention.
The formation of the pressure compensation channels in the guide portion 36 allows the measures described above to be achieved without weakening the valve element or expensively redesigning the valve element in some other way.
A second embodiment of the invention is represented in
The embodiment according to
The embodiment according to
Otherwise the vacuum brake booster 210 according to
The embodiment according to
On the whole, it is possible to achieve a construction that is simplified compared to
A further advantage of the embodiment according to
A further effect achieved by the reduced diameter of the guide portion 336 is that the load at the transmission piston arrangement 316, upon which the pressure of the atmosphere acts, is diminished, thereby reducing the load acting upon the transmission piston arrangement 316.
The embodiment according to
Otherwise the embodiment according to
The embodiment according to
In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 049 122.2 | Oct 2007 | DE | national |
This application is a national stage of International Application No. PCT/EP2008/008318 filed Oct. 1, 2008, the disclosure of which is incorporated herein by reference, and which claimed priority to German Patent Application No. 10 2007 049 122.2 filed Oct. 12, 2007, the disclosure of which is incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/008318 | 10/1/2008 | WO | 00 | 6/21/2010 |
