Patent Description:
Pneumatic brake actuators of the aforementioned kind are commonly used in the commercial vehicle industry. It is the aim of such pneumatic brake actuator to generate a braking force which is, in turn, transmitted to the vehicle wheel. A pneumatic brake actuator according to the state of the art is known from <CIT>.

State of the art pneumatic brake actuator comprise a housing which comprises a pressure chamber and a piston chamber having a piston mounted therein. The piston is configured to reciprocatingly move between a retained position and an extended position as a function of pressure inside the pressure chamber. The piston is connected to a piston rod which is guided through an out of the actuator housing via a rod opening.

To ensure that the interior of the brake caliper remains free from contamination, for example dirt or water, a rod boot is utilized for sealing the rod opening. The rod boot is connected to the rod opening and the piston rod.

Although such actuators are commonly used and well-proven, there is still room for improvement. One major drawback associated with these kinds of actuators is that the actuator housing needs to provide an accommodation volume for accommodating the rod boot, in particular when the piston is in its extended position and the rod boot is compressed. Furthermore, the compressed rod boot generates a counterforce acting towards the retained position which needs to be overcome by an additional degree of pressure inside the pressure chamber. When the pressure inside the pressure chamber is limited, the maximum stroke of the piston rod might not be available due to the above.

As a consequence, it was an object of the invention to provide a pneumatic brake actuator of the initially mentioned type which overcomes the aforementioned problems as much as possible. In particular, it was an object of the invention to provide a pneumatic brake actuator which comprises a smaller total length and requires less actuation pressure to operate the piston rod into its maximum stroke position.

The invention attains the aforementioned object by suggesting a pneumatic brake actuator according to claim <NUM>. According to the invention, it is proposed that the second section of the rod boot is inverted inwardly relative to the first section, wherein a longitudinal dimension of the first section and a longitudinal dimension of the second section vary with respect to each other as a function of a relative position of the first section to the second section.

The invention is based upon the finding that by utilizing a rod boot having one section inverted inwardly relative to the other section, the rod boot is moved with the respective section of the piston rod out of the actuator housing when the piston rod is moved into its extended position. Thus, the rod boot requires a considerable less installation volume within the actuator housing. Furthermore, due to the rod boot design, no counterforce is generated when the piston rod is in the extended position, since the rod boot would not be compressed inside the actuator housing. For a given pressure inside the pressure chamber, this results in a better output regarding the maximum extended position, also called "maximum stroke". Furthermore, the new design allows for a reduction of the overall length of the actuator.

According to a preferred embodiment, the rod boot extends out of the actuator housing through the rod opening, when the piston is moved towards its retained position.

According to a preferred embodiment, a diameter of the mantle tappers from the first section to the second section. This ensures that the length of the first section and the second section can vary as a function of the relative position of the first section of the second section without substantial friction between the sections.

Preferably, the mantle comprises a varying thickness. The thickness of the mantle can be used as another means to ensure that the first section and the second section can be moved conveniently with regard to one another. Moreover, the thickness of the mantle may be locally increased for those sections of the mantle that are heavily stressed during operation. Furthermore, the stiffness of certain sections of the mantle may be adjusted as required.

According to yet another preferred embodiment, the mantle comprises at least one rib. The rib is used to adjust the stiffness of the mantle. This is in particular beneficial for those embodiments at which the mantle tappers from the first section to the second section. With the help of the rips, it can be ensured that the stiffness of the mantle remains constant although the mantle surface is reduced from the first section to the second section.

Preferably, said rib extends along the longitudinal axis. According to another preferred embodiment, the mantle comprises four rips, said rips being equidistantly spaced around said mantle. Preferably, the at least one rib is arranged at the inside of said mantle.

According to another preferred embodiment, the mantle comprises at least one groove. The groove is utilized for adjusting the stiffness of the mantle. Like the rips, the groove can also be utilized to compensate for a changing surface area of the mantle from the first section to the second section. Preferably, the groove is arranged at the outside of the mantle. According to yet another preferred embodiment, the groove is arranged adjacent to the at least one rib. Forming a rib at the inside of the mantle may lead to the formation of a groove at the outside.

According to yet another preferred embodiment, the first section comprises a flange section for securing said first section to the rod opening. The flange section is used to ensure a proper sealing of the piston chamber against the surroundings of the housing. According to a preferred embodiment, the flange section comprises a circumferential groove, which is configured to form a seal with the rod opening. With the help of said groove, the rod boot can be easily installed at the housing while it is at the same time ensured that the boot forms a durable connection with the housing.

According to yet another preferred embodiment, the second section comprises a shoulder for engaging with a corresponding shoulder of the piston rod to form a seal therewith. This design ensures a durable connection between the rod boot and the piston root to seal the piston chamber of the actuator.

Preferably, the second section is secured to said piston rod by means of a clamping ring. With the help of said clamping ring, the durability of the connection between rod boot and piston rod is improved.

The invention as herein above has been described according to a first aspect relating to the inventive brake actuator. According to a second aspect, the invention however also relates to a rod boot for sealing a rod opening for a pneumatic brake actuator of a commercial vehicle, wherein said rod boot is configured to be connected to a rod opening and a piston rod, said rod boot comprising a mantle, said mantle having a first section and a second section opposite from the first section, and wherein the first section is connected to a rod opening of a pneumatic brake actuator and the second section is connected to a mounting section of a piston rod of the actuator.

The invention suggests that the second section is inverted inwardly relative to the first section, wherein a longitudinal dimension of the first section and a longitudinal dimension of the second section vary with respect to each other as a function of a relative position of the first section to the second section.

The inventive rod boot accordingly shares the technical advantages and preferred embodiments of the inventive brake actuator. In this regards, reference is made to the description above and the preferred embodiments described therein.

According to a third aspect, the invention relates to the use of a rod boot according to the previous embodiments for sealing a rod opening of a pneumatic brake actuator of a commercial vehicle. The inventive use of a rod boot accordingly shares the technical advantages and preferred embodiments of the inventive brake actuator and the inventive rod boot. In this regard, reference is made to the description above and preferred embodiments described therein. For a more complete understanding of the invention, the invention will now be described in detail with reference of the accompanying drawings. The detailed description will illustrate and describe what is considered as a preferred embodiment of the invention.

The invention is limited only within the scope of the appended claims. In particular, any reference signs in the claims shall not be construed as limiting the scope of the invention. The wording "comprising" does not exclude other elements or steps. The word "a" or "an" does not exclude a plurality.

The invention will now be described with reference to the accompanying drawings which illustrate, by way of example and not by way of limitations, one of several possible embodiments of the spring brake actuator proposed herein, and wherein:.

<FIG> shows a vehicle braking system <NUM>. The vehicle braking system <NUM> comprises a pneumatic actuator <NUM>. The pneumatic actuator <NUM> comprises an actuator housing <NUM>. The actuator housing <NUM> comprises a pressure chamber <NUM> and a piston chamber <NUM>. In the piston chamber <NUM>, a piston <NUM> is mounted. The piston <NUM> is configured to reciprocatingly move between a retrained position <NUM> and in extended position <NUM> (shown in <FIG>) as a function of pressure inside the pressure chamber <NUM>.

A piston rod <NUM> is connected to piston <NUM>. The piston rod <NUM> is guided through and out of the actuator housing <NUM> via a rod opening <NUM>. The pneumatic brake actuator <NUM> moreover comprises a compression spring <NUM>. The compression spring <NUM> is effective to push the piston <NUM> towards the retained position <NUM>. The pneumatic brake actuator <NUM> moreover comprises a rod boot <NUM>. The rod boot <NUM> is configured for sealing the rod opening <NUM>. The rod boot <NUM> is connected to the rod opening <NUM> and the piston rod <NUM>.

The rod boot <NUM> comprises a mantle <NUM>. Said mantle <NUM> has a first section <NUM> and a second section <NUM>. The second section <NUM> is opposite from the first section <NUM>. The first section <NUM> is connected to the rod opening <NUM>. The second section <NUM> is connected to a mounting section <NUM> of the piston rod <NUM>. The second section <NUM> of the rod boot <NUM> is inverted inwardly <NUM> relative to the first section <NUM>. A longitudinal dimension l<NUM> of the first section <NUM> and a longitudinal dimension l<NUM> of the second section <NUM> vary with respect to each other as a function of a relative position of the first section <NUM> to the second section <NUM>. The braking system <NUM> moreover comprises a caliper box <NUM>. In the caliper box <NUM> a lever <NUM> is arranged.

<FIG> shows the actuator of <FIG> in an extended position <NUM>. It can be seen, that the rod boot <NUM> now extends out of the actuator housing <NUM> through the rod opening <NUM> at into the caliper box <NUM>. The volume that is now occupied by the rod boot <NUM> inside the actuator housing <NUM> is minimal.

<FIG> and <FIG> show perspective views of the rod boot <NUM> in perspective views. The rod boot comprises the mantle <NUM>. The diameter <NUM> of the mantle <NUM> tapers from the first section <NUM> to the second section <NUM>. Furthermore, the mantle <NUM> comprises a varying thickness. The mantle comprises four ribs <NUM>. Said ribs <NUM> extend along a longitudinal axis <NUM>. The ribs <NUM> are equidistantly spaced around the mantle <NUM>. The ribs <NUM> are arranged at the inside <NUM> of the mantle <NUM>. Furthermore, the mantle comprises groves <NUM>. The groves <NUM> are arranged at the outside <NUM> of the mantle <NUM>. The groves <NUM> are arranged adjacent to the ribs <NUM>. The mantle <NUM> comprises four groves <NUM>. A rib <NUM> at the inside <NUM> of the mantle <NUM> forms a grove <NUM> at the outside <NUM> of the mantle <NUM>. The mantle <NUM> has a thickness <NUM>.

Claim 1:
A pneumatic brake actuator (<NUM>) for a vehicle, in particular a commercial vehicle, comprising:
- an actuator housing (<NUM>) having a pressure chamber (<NUM>) and a piston chamber (<NUM>),
- a piston (<NUM>) that is mounted inside the piston chamber (<NUM>) and configured to reciprocatingly move between a retained position (<NUM>) and an extended position (<NUM>) as a function of pressure inside the pressure chamber (<NUM>),
- a piston rod (<NUM>) connected to the piston (<NUM>), wherein said piston rod (<NUM>) is guided through the actuator housing (<NUM>) via a rod opening (<NUM>),
- a compression spring (<NUM>) being effective to push the piston (<NUM>) towards the retained position (<NUM>), and
- a rod boot (<NUM>) for sealing the rod opening (<NUM>), wherein said rod boot (<NUM>) is connected to the rod opening (<NUM>) and the piston rod (<NUM>),
said rod boot (<NUM>) comprising a mantle (<NUM>), said mantle (<NUM>) having a first section (<NUM>) and a second section (<NUM>) opposite from the first section (<NUM>), and wherein the first section (<NUM>) is connected to the rod opening (<NUM>) and the second section (<NUM>) is connected to a mounting section (<NUM>) of the piston rod (<NUM>),
characterized in that the second section (<NUM>) is inverted inwardly (<NUM>) relative to the first section (<NUM>), wherein a longitudinal dimension (l<NUM>) of the first section (<NUM>) and a longitudinal dimension (l<NUM>) of the second section (<NUM>) vary with respect to each other as a function of a relative position of the first section (<NUM>) to the second section (<NUM>).