Patent Description:
The purpose of brake actuators in commercial vehicles such as trucks and buses is to produce a braking force at the wheel brakes using compressed air. As soon as the compressed air, or any other suitable fluid, enters the actuator, the force on a piston is transmitted through a push-rod onto a brake lever or a hydraulic master cylinder. When the pressure is released, a spring pushed the piston, or a diaphragm back to its running condition.

<CIT> describes an air-operated diaphragm spring brake wherein a push-rod extends through an aperture. Since the aperture is in open communication with the interior of a brake actuator, dust shields are frequently employed to prevent contaminants from entering the interior of the brake actuator. Such dust shields are typically flexible neoprene or rubber boots which move as the pushrod reciprocates and articulates. However, a minimum size, in particular length, of the push-rod is limited by the size of the dust shield.

A further brake actuator is described in <CIT>.

It would be therefore beneficial to provide a brake actuator with the same functionality and a reduced size.

According to the first aspect of the present invention, a brake actuator is described. The brake actuator comprises a housing having an inlet port for receiving a fluid, in particular compressed air, and a push-rod aperture. The housing arranged and configured to accommodate a first chamber connected to the in-let port, and a second chamber that includes the push-rod aperture. The first chamber and the second chamber are separated by a movable separation element arranged at the housing, such that a volume amount of the first chamber increases, and a volume amount of the second chamber decreases, when the fluid, in particular the compressed air, enters the first chamber via the inlet and actuates the separation element. The brake actuator further comprises a push-rod having a proximal end connected to the movable separation element, and a distal end protruding outside the housing via the push-rod aperture. The brake actuator further comprises a boot defining a boot inner volume for accommodating a middle section of the push-rod, the boot having a proximal end section connected to the push-rod at a region proximate the proximal end of the push-rod, and a distal end section connected to the housing at the push-rod aperture. The boot has at least one foldable boot segment in a longitudinal direction.

According to the invention, a cross-sectional area amount of the boot inner volume at the distal end section of the boot is larger than a maximum cross-sectional segment area of a first boot segment proximate the distal end section such that, in a folded state of the boot, the first boot segment is at least partially fitted inside the distal end section, thereby reducing an effective length of the boot in the actuated state. This, in turn, enables a reduction of the length of the push-rod. Thus, by using a push-rod with a reduced length, the size of the second chamber can be reduced compared to typical brake actuators and the brake actuator in accordance with the first aspect of the invention can be advantageously implemented in pneumatic systems where there is limited space available.

The functionality of the brake actuator of the first aspect of the present invention is fundamentally identical to known brake actuators that include a boot or bellow for dust protection, but the design of the boot enables the reduction of the length of the push road, which is limited by the effective length of the boot in the actuated stare. By allowing a degree of overlap between the distal end section of the boot and the boot segment proximate or adjacent to said distal end, the effective length of the boot is reduced, compared to the boots of the prior art, that have a substantially constant effective diameter, such that in an actuated state, each of the boot segments rests on top of the previous one, without any overlapping.

The configuration of the boot enables the use of a push-rod with a reduced length, which in turn enables a reduction of a longitudinal extension of the second chamber. This results in a reduced overall size of the brake actuator.

In the following, developments of the brake actuator of the first aspect of the present invention will be described.

In a preferred development, the fluid used for actuating the push-rod is compressed air. However, any other suitable fluid (gas or liquid) can be used in any of the developments.

In a preferred development, the boot is an elastic boot, in particular a boot consisting of or comprising an elastic material, such as rubber. However, in another development, the boot is made of rigid segments connected to each other, for instance through a mechanical bearing such as a hinge, and that allows a rotational movement between two adjacent segments.

In a development, the boot comprises a plurality of boot segments, and the cross-sectional area amount of the boot inner volume at the distal end section of the boot is larger than the maximum cross-sectional segment area of any boot segment of the plurality of boot segments. In yet another development, the maximum cross-sectional segment area of the respective boot segments decrease with increasing distance from the distal end section, such that there is a possible overlapping of any segment with the segment adjacent to it in the direction of the distal end section.

In another development wherein the movable separation element is an elastic separation element, in particular a diaphragm. When the compressed air enters the first chamber with the required pressure, the elastic element moves to accommodate the incoming compressed air. This movements actuate the push-rod, which is moved in the longitudinal direction such that a larger section thereof protrudes from the housing via the push-rod aperture. This is referred to as a diaphragm brake actuator and can be pneumatically or hydraulically driven. In a preferred development, the proximal end of the push-rod is connected to a piston that is attached to the elastic separation element. This provides a more effective transfer of the force exerted by the fluid in the first chamber to the push-rod.

In an alternative development, wherein the movable separation element is a rigid separable element, in particular a piston. This is referred to as a piston type brake actuator, which can be pneumatically or hydraulically driven. It is particularly preferred that a piston brake actuator further comprises a sealing member arranged and configured to seal the first chamber from the second chamber, in particular when the piston is actuated. The sealing member is preferably a toric joint or an o-ring arranged between the piston and an inner side of the housing.

In another development, which may also include any of the technical features described with respect to the previous developments, the boot comprises a transition section connecting the distal end section of the boot to the first boot segment, and wherein the transition section has a longitudinal component in the longitudinal direction when going from the distal end section to the first boot segment that is directed towards the distal end section. The longitudinal component is understood as the projection of the transition section on a longitudinal direction substantially corresponding to a longitudinal axis of the push-rod. When starting from that end of the transition section that is connected to the distal end section and moving towards the opposite end of the transition section, which is connected to the first boot segment, the projection on the longitudinal direction shifts towards the distal end section, i.e. away from the proximal end section of the boot or, in other words, away from the proximal end of the push-rod and toward the distal protruding end thereof.

Such an arrangement of the transition section favors the insertion, at least the partial insertion, of the first boot segment in the inner volume at the distal end section of the boot.

In a development, the boot comprises a proximal connection unit arranged at the proximal end section for connecting the boot to the push-rod. For example, in a development, the brake actuator comprises fasteners such as clamps, braces, retaining clips, bolts, rivets, screws or any other type of mechanical connectors known to the ordinary skilled in the art. In another development, the boot is glued to the push-rod.

Optionally, and also preferably, the push-rod comprises a cooperating connection unit arranged proximate the proximal end and configured to form a connection, preferably a releasable connection, with the proximal connection unit of the boot. For example, the push-rod may comprised threaded orifices and the boot may comprise orifices such that the it be effectively connected to the push-rod by means of screws.

Additionally, or alternative, wherein the boot comprises a distal connection unit arranged and configured to be connected to the housing at the or in the vicinity of the push-rod aperture. In a development, the boot is connected to the housing around the push-rod aperture by gluing. In an alternative development, the brake actuator includes a mechanical connector such as clamps, braces, retaining clips, bolts, rivets, screws or any other type of mechanical connectors known to the ordinary skilled in the art for connecting the distal end section of the boot to the housing such that the push-rod aperture directly connects the exterior of the brake actuator with the boot inner volume.

In a preferred development, the distal end section of the boot comprises a slot, in particular in a direction transversal to the longitudinal direction. The slot is arranged and configured to house a rim of the push-rod aperture, i.e. that section of the housing that defines or borders the push-rod aperture. The rim is then fitted in the slot to provide a tight connection between the distal end section of the boot and the housing. In another development, the housing rim comprises a slot in which the distal end section of the boot can be inserted for fixating the boot to the housing.

In another development, the brake actuator is further configured as spring-brake actuator, wherein the housing further accommodates a parking brake chamber comprising a spring loaded parking brake piston that is configured to actuate the movable separation element upon reception of a parking brake signal. Thus, the movable separation element can be actuated in two different ways, i.e. either pneumatically by means of the fluid (e.g., compressed air) entering the first chamber, or mechanically, by means of the spring loaded parking brake piston, that is provided in the parking brake chamber. The housing comprises a dividing wall section between the fist chamber and the parking brake chamber, which has an opening such that the spring loaded parking brake piston, in particular a piston rod connected thereto, can actuate the mov-able separation element, which is preferably but not necessarily an elastic separation element such as a diaphragm.

A second aspect of the invention is directed to a boot, in particular to an elastic boot, for use in a brake actuator in accordance with the first aspect of the invention. The boot defines a boot inner volume for accommodating a middle section of a push-rod. The boot has a proximal end section that is connectable to the push-rod at a region proximate a proximal end of the push-rod, and a distal end section connectable to a housing of the brake actuator at a push-rod aperture. The boot has at least one foldable boot segment in a longitudinal direction L.

In the boot according to the second aspect of the invention, a cross-sectional area amount of the boot inner volume at the distal end section of the boot is larger than a maximum cross-sectional segment area of a first boot segment proximate the distal end section, such that, in a folded state of the boot, the first boot segment is at least partially fitted inside the distal end section.

In a preferred embodiment, the boot further comprises a transition section connecting the distal end section of the boot to the first boot segment, and wherein the transition section has a longitudinal component in the longitudinal direction that is directed towards the distal end of the boot when going from the distal end section to the first boot segment.

A third aspect of the invention is directed to a use of a boot in accordance with the second aspect of the invention in a brake actuator, in particular in a brake actuator of a commercial vehicle, and preferably in a brake actuator according to the first aspect of the invention.

A fourth aspect of the invention is formed by a braking system, in particular a braking system of a commercial vehicle, and wherein the braking system comprises a fluid supply unit, in particular a compressed air supply unit, for supplying fluid for operation of the braking system, a brake actuator in accordance with the first aspect of the invention, wherein the inlet port is connected to the fluid supply unit for receiving the fluid for filling the first chamber and actuating the movable separation element, and a braking unit connected to the distal end of the push-rod of the brake actuator and configured to apply, when the push-rod is actuated, a braking force on a movable element, in particular on a wheel of the commercial vehicle.

The embodiments of the invention are described in the following on the basis of the drawings in comparison with the state of the art, which is also partly illustrated. The latter is not necessarily intended to represent the embodiments to scale. Drawings are, where useful for explanation, shown in schematized and/or slightly distorted form. With regards to additions to the lessons immediately recognizable from the drawings, reference is made to the relevant state of the art. It should be borne in mind that numerous modifications and changes can be made to the form and detail of an embodiment without deviating from the scope of the invention, which is defined by the appended claims. The features of the invention disclosed in the description, in the drawings and in the claims may be essential for the further development of the invention, either individually or in any combination.

<FIG> shows a schematic cross-sectional view of a known brake actuator <NUM> typically used in braking systems of commercial vehicles. The brake actuator <NUM>, comprises a housing <NUM> having an inlet port <NUM> for receiving a fluid, in this particular case compressed air, and a push-rod aperture <NUM>. The housing is formed by a first, proximal, housing section <NUM> and a second, distal, housing section <NUM> In this particular comparative example, the inlet port <NUM> is arranged as an opening in the first housing section <NUM> and the push-rod aperture is arranged as an opening in the second housing section <NUM>. Both housing sections are connected to each other by means of a connection element <NUM>, such as a connecting clamp. The housing <NUM> is arranged and configured to accommodate a first chamber <NUM> connected to the inlet port <NUM>, and a second chamber <NUM> that includes the push-rod aperture <NUM>. The first chamber <NUM> and the second chamber <NUM> are separated by a movable separation element <NUM> arranged at the housing <NUM>, in particular held in place by the connection element <NUM>, such that a volume amount V1 of the first chamber <NUM> increases, and subsequently, a volume amount V2 of the second chamber <NUM> decreases (given that the housing defines a fixed inner volume V1 +V2), when the fluid, i.e. the compressed air, enters the first chamber <NUM> via the in-let <NUM> and actuates the separation element <NUM> by driving it towards the push-rod aperture. The brake actuator <NUM>, further comprises a push-rod <NUM> that has a proximal end 112a connected to the movable separation element <NUM>, in this particular example via a piston <NUM>, and a distal end 112b protruding outside the housing <NUM> via the push-rod aperture <NUM>. Thus, when the compressed air enters the first chamber and the movable separation element is driven the piston is moved along a longitudinal direction L such that a larger section thereof protrudes from the push-rod aperture. This movement is performed against an elastic force exerted by a spring element <NUM> arranged in the second chamber such that, when the compressed air in the first chamber <NUM> is exhausted, the spring element <NUM> returns the push rod <NUM> to the unactuated position shown in <FIG>. During the actuation, the air in the second chamber <NUM> is exhausted via exhaust opening <NUM>, through which air is also drawn when the push-rod <NUM> returns to its unactuated position. This exhaust opening <NUM> may be connected to the environment such that dust or dirt may enter the second chamber <NUM>. In order to shield the push-rod <NUM> and the push-rod aperture <NUM> from this dirt, the brake actuator comprises a boot for accommodating a middle section 112c of the push-rod <NUM>. The boot <NUM> has a proximal end section 14a connected to the push-rod <NUM> at a region proximate the proximal end 112a of the push-rod <NUM>, and a distal end section 14b connected to the housing <NUM> at the push-rod aperture <NUM>. The boot <NUM> of <FIG> has <NUM> fold-able boot segments <NUM> in the longitudinal direction L.

In an actuated state, i.e., in a state where compressed air fills the first chamber <NUM> and the push-rod <NUM> is moved to a final actuated position, the effective length of that section of the push-rod <NUM> that remains within the second chamber <NUM> is limited by the minimum effective length of the boot <NUM> in a completely folded position. In the case shown in <FIG> and for a given constant boot wall thickness of "d" mm, this minimum effective length is at least "<NUM> x d", since each of the four boot segments contributed with two segment sections, each corresponding to one of the two flank portions of the corresponding segment. A flank portion of a boot segment links a root portion with a corresponding crest portion of the boot segment.

The brake actuator <NUM> may be also configured as a spring-brake actuator, wherein the housing <NUM> further accommodates a parking brake chamber comprising a spring loaded parking brake piston that is configured to actuate the movable separation element upon reception of a parking brake signal (not shown). The spring loaded parking brake piston actuates a brake piston rod that is arranged inside the additional opening <NUM> for actuating the movable separation element <NUM>, which in this particular example is an elastic separation element in the form of a diaphragm.

The brake actuator <NUM> can be attached to an external structure by means of suitable connection elements <NUM> such as screws.

<FIG> shows a schematic cross-sectional view of a first embodiment of a brake actuator <NUM> according to the invention where the effective length of the push-rod <NUM> can be reduced in comparison to the brake actuator <NUM> of <FIG>. The following discussion will focus on those technical feature that differ from those shown in <FIG>. Those technical features having an identical or similar function will be referred to using the same reference numbers. The brake actuator <NUM> is substantially similar to the brake actuator <NUM> of <FIG>. However, in the boot <NUM>, a cross-sectional area amount A1 of the boot inner volume V3 deter-mined at the distal end section 114b of the boot <NUM>, is larger than a maximum cross-sectional segment area A2 of a first boot segment 116a (see <FIG>) proximate the distal end section 114b such that, in a folded state of the boot <NUM>, the first boot segment 116a is at least partially fitted inside the distal end section 114b. Thus, the minimum effective length of the boot <NUM> in a completely folded position can be reduced due to the fact that, in the folded, actuated position, at least part of the boot, in particular at least part of that boot segment 116a proximate or adjacent the distal end section 114b is inserted in the volume delimited by the distal end section 114b. Exemplary values for the diameter of the circular sections given raise to the cross sectional areas A1, A2, A2 and A4 are <NUM> for cross sectional area A1, <NUM> for cross sectional area A2, <NUM> for cross sectional area A3 and <NUM> for cross sectional area A4.

The operation of the brake actuator <NUM> of <FIG> is similar to that of brake actuator <NUM> of <FIG>. When a service braking system is actuated, compressed air provided by an external compressed air supply flows through the inlet port <NUM> and into the first chamber <NUM>. The pressure building up in said first chamber acts on the movable separation element <NUM>, in this example a diaphragm, and pushes it, together with the piston <NUM>, towards the push rod aperture <NUM>, against the force of the pressure spring <NUM>. A force, being pressure times sur-face, is being transferred via the push rod <NUM> onto an external braking unit (not shown). for example to a piston of a flanged master brake cylinder. The air present in the second chamber <NUM> exits it via the exhaust openings <NUM>. When the braking process is ended, the pressure in the first chamber <NUM> is reduced, for instance by an upstream brake valve. At the same time, the spring element <NUM> returns both the piston <NUM> and the diaphragm <NUM> to their original positions. Air from an exterior penetrates in the second chamber via exhaust openings <NUM> when the diaphragm, as a movable separation element <NUM>, the push-rod <NUM> and the piston <NUM> return to their original positions. The boot <NUM> shields the inner boot volume V3 from dust or dirt present in the air. In some embodiments, the diaphragm actuators can have a wear and/or stroke indicator fitted for the driver to see which condition the wheel brakes are in.

The boot <NUM> has a proximal end section 114a, a distal end section 114b and three boot segments <NUM> arranges between them. A largest cross sectional area of the boot <NUM>, perpendicular to the longitudinal direction, corresponds to the distal end section 114b and is indicated as A3 in <FIG>. The boot inner volume V3 has a largest cross-sectional area also in the region of the distal end section 114b, and it is indicated as A1. The difference between A3 and A1 thus corresponds to a maximum thickness of the boot <NUM> in the distal end section 114b. Further, the value A2 corresponds to the maximum cross-sectional segment area A2 of the boot segments <NUM>, and the value A4 corresponds to the minimum cross-sectional segment area of the boot segments <NUM>. The minimum cross sectional area of the boot <NUM> corresponds to the cross sectional area of the push-rod <NUM> and is located in the proximal end region 114a.

The inventive configuration of the boot <NUM> enables the use of a push-rod <NUM> with a reduced length compared to that of the push rod of <FIG>. This, in turn, enables a reduction of a longitudinal extension of the second chamber <NUM>, i.e., an extension in the longitudinal direction L. Thus, the actuator <NUM> can have a reduced overall size compared to know actuators, such as actuator <NUM> of <FIG>.

The configuration of the boot <NUM> is shown more clearly in <FIG>, which shows a schematic cross-sectional view of a first embodiment of a boot <NUM> for use in a brake actuator according to the invention. The boot <NUM> of <FIG> includes a proximal end section 114a configured and dimensioned to be in contact with the push-rod, and a distal end section 114b for connection to the housing <NUM> at the push-rod aperture <NUM>. The housing <NUM> is shown in <FIG> in an un-mounted state. The boot <NUM> comprises three boot segments 116a, 116b and 116c. Boot segment 116a is proximate the distal end section 114b, boot segment 116c is proximate the proximal end section 144a and boot segment 116b is arranged between boot segments 116a and 116c. Three is not a limitative number of boot segments, and other suitable boots may include any number of boot segments. Each of the boot segments, for example 116c start at a first root portion <NUM>, includes a first flank portion <NUM> that ends at a crest portion <NUM> and the includes a second flank portion <NUM> that ends at a second root portion <NUM> that also corresponds to the first root portion of the neighboring boot segment <NUM>. A respective maximum cross-sectional segment area A2a, A2b and A2c is defined by the periphery of the boot <NUM> at the crest portions <NUM> of the respective boot segments 116a, 116b, 116c.

In the boot in accordance with the invention, a cross-sectional area amount A1 of the boot inner volume V3 at the distal end section 114b of the boot <NUM> is larger than a maximum cross-sectional segment area A2 of the first boot segment 116a proximate the distal end section 114b such that, in a folded state of the boot <NUM>, the first boot segment 116a is at least partially fitted inside the distal end section 114b. The relation between the cross-sectional area amount A1 and the maximum cross-sectional segment area A2a of the first boot segment 116a is such that a projection of the first boot segment 116a on a plane defined by the distal end section 114b and perpendicular to the longitudinal direction L lies completely within the cross-sectional area A1 of the boot inner volume V3 at the distal end section 114b. In this exemplary embodiment, the cross-sectional area amount A1 of the boot inner volume V3 at the distal end section 114b of the boot <NUM> is larger than the maximum cross-sectional segment area A2a, A2b, A2c of any boot segment 116a, 116b, 116c of the plurality of boot segments, in particular, the a cross-sectional area amounts A2a, A2b and A2c of the three boot segments 116a, 116b and 116c are equal. However, in other embodiments, the cross-sectional area amounts may differ. In some embodiments (not shown), the cross-sectional area amount A2b, A2c of a boot segment 116b, 116c that is not proximate the distal end section 114b can be larger than the cross-sectional area amount A1 of the boot inner volume V3 at the distal end section 114b.

The boot <NUM> of <FIG> also comprises a proximal connection unit <NUM> arranged at the proximal end section 114a for connecting the boot <NUM> to the push-rod (not shown). In this particular embodiment, the proximal connection unit <NUM> is a clamp. In alternative embodiments the proximal connection unit comprises other fasteners such as braces, retaining clips, bolts, rivets, screws or any other type of mechanical connectors known to the ordinary skilled in the art. In another embodiment, the boot <NUM> is glued to the push-rod at the proximal end section 114a.

Optionally, as exemplarily shown in <FIG>, the push-rod <NUM> comprises a cooperating connection unit <NUM> arranged proximate the proximal end 112a and configured to form a connection, preferably a releasable connection, with the proximal connection <NUM> unit of the boot <NUM>. In <FIG>, the cooperating connection unit <NUM> comprises a recess arranged and configured to receive the proximal end section 114a of the boot <NUM> and to hinder a movement of the proximal end section 114a relative to the push-rod <NUM>.

Also, the boot <NUM> comprises a distal connection unit <NUM> arranged and configured to be connected to the housing <NUM> at the or in the vicinity of the push-rod aperture <NUM>. In particular, the distal end section 114b of the boot <NUM> comprises a slot <NUM> arranged and configured to house a rim <NUM> of the push-rod aperture <NUM>.

<FIG> shows a schematic cross-sectional view of a second embodiment of a brake actuator <NUM> according to the invention. The following discussion will focus on those technical features of the brake actuator <NUM> that differ from those of the brake actuator <NUM> shown in <FIG>. Those technical features having an identical or similar function will be referred to using the same reference numbers. The brake actuator <NUM> is a piston type actuator wherein the movable separation element is a rigid separation element such as a piston <NUM> instead of an elastic separation element as the diaphragm <NUM> of <FIG> and <FIG>. The brake actuator <NUM> further comprises a sealing member <NUM> that arranged and configured to seal the first chamber <NUM> from the second chamber <NUM>, in particular when the piston <NUM> is actuated. The sealing member <NUM> is arranged between the piston <NUM> and the housing <NUM>, and is preferably a toric joint. The piston <NUM> may include a retaining structure for holding the sealing member in place with respect to the piston <NUM> during operation. In this particular embodiment, and to ensure a tight sealing, the first housing section <NUM> and the second housing section <NUM> are connected at a position that is not within the movement range of the piston <NUM>.

In the case of the piston type brake actuator <NUM>, when a service braking system is actuated, compressed air from provided by a compressed air supply (not shown) flows through the inlet port <NUM> and into the first chamber <NUM>. The pressure building up there forces the piston <NUM> towards the push-rod aperture <NUM> against the force of the pressure spring <NUM>. A Force being pressure times sur-face, is transferred via the push rod <NUM>, for example onto a piston of a flanged master brake cylinder. The air present in the second chamber <NUM> exits it via the exhaust opening <NUM>. When the braking process is ended, the pressure in the first chamber <NUM> is reduced, for instance by an upstream brake valve. At the same time, the spring element <NUM> returns the piston <NUM> to its original position. Air from an exterior penetrates in the second chamber via exhaust opening <NUM> when the piston <NUM>, and the push-rod <NUM> connected thereto return to their original positions. The boot <NUM> shields the inner boot volume V3 from dust or dirt present in the air.

<FIG> shows a schematic cross-sectional view of a second embodiment of a boot <NUM> for use in a brake actuator according to the invention. The following discussion will focus on those technical features of boot <NUM> of <FIG> that differ from those of the boot shown in actuator <NUM> shown in <FIG>. Those technical features having an identical or similar function will be referred to using the same reference numbers. The boot <NUM> of <FIG> comprises a transition section 114c connecting the distal end section 114b of the boot <NUM> to the first boot segment 116a, wherein the transition section 114c has a longitudinal component LC in the longitudinal direction L, determined from the distal end section 114b to the first boot segment 116a, that is directed towards the distal end section 114b. The longitudinal component LC is understood as the projection of the transition section 114c on the longitudinal direction L. When starting from that end of the transition section 114c that is connected to the distal end section 114b, and moving towards the opposite end of the transition section 114c, which is connected to the first boot segment 116a, the projection on the longitudinal direction L shifts towards the distal end section 114b, i.e. away from the proximal end section of the boot 114a.

Such an arrangement of the transition section 114c favors the insertion, at least the partial insertion, of the first boot segment 116a in the boot inner volume V3 at the distal end section 114b of the boot <NUM>.

<FIG> shows a schematic cross-sectional view of a third embodiment of a brake actuator <NUM> according to the invention. The brake actuator <NUM> is formed by a brake actuator <NUM> according to <FIG> and a parking brake chamber <NUM> comprising a spring loaded parking brake piston <NUM> that is configured to actuate the movable separation element <NUM> upon reception of a parking brake signal S. Thus, the movable separation element <NUM>, in this particular nonlimiting example, an elastic separation element, can be actuated in two different ways, i.e. either pneumatically by means of the fluid (e.g., compressed air) entering the first chamber <NUM>, as explained with reference to <FIG>, or mechanically, by means of the spring loaded parking brake piston <NUM>, that is provided in the parking brake chamber <NUM>. The housing <NUM> comprises a dividing wall section <NUM> between the fist chamber <NUM> and the parking brake chamber <NUM>, which has an opening <NUM> such that the spring loaded parking brake piston <NUM>, in particular a piston rod <NUM> connected thereto, can actuate the movable separation element <NUM> through the opening <NUM>.

The brake actuator <NUM> has therefore a combined spring brake-diaphragm brake chambers and can be referred to as a spring brake actuator. It can be used to generate the brake force for the wheel brakes. It includes a diaphragm portion for the service braking system (see <FIG> and <FIG> and the corresponding description) and the spring loaded portion (parking brake chamber <NUM>) for the auxiliary and parking braking systems.

For operation of the service braking system, when the service braking system is actuated, compressed air flows into the first chamber <NUM> via inlet port <NUM>, acting on diaphragm <NUM> as explained above. The brake chambers, i.e., the first <NUM> and second <NUM> chambers operate independently from its spring-loaded portion.

For operation of the parking brake, when the parking brake is actuated, a parking brake signal is received that causes the pressure in the parking brake chamber <NUM> to be fully or partially released via a release port (not shown). In this process, the force of the relaxing compression spring <NUM> acts on the wheel brake via the spring loaded parking brake piston <NUM> and the push-rod <NUM> connected thereto. The maximum braking force of the spring-loaded portion is achieved when the parking brake chamber <NUM> is pressureless. Since this braking force is achieved exclusively by mechanical means, i.e. by compression spring <NUM>, the spring-loaded portion may be used for the parking brake. When the brake is released, the pressure is once again increased in the parking brake chamber <NUM> via an input port, which can be the same as the release port (not shown).

<FIG> shows a schematic block diagram of a commercial vehicle <NUM> including a braking system <NUM>, pneumatic, or hydraulic, in accordance with the invention. The braking system <NUM> comprises a fluid supply unit, in particularly a compressed air supply unit <NUM>, such as a compressor, for supplying compressed air <NUM> for the braking system <NUM>. It also comprises brake actuators <NUM>, <NUM>, wherein the inlet port <NUM> is connected to the fluid supply unit <NUM> for receiving the compressed air that is used for filling the first chamber <NUM> and actuating the movable separation element <NUM>. The braking system <NUM> also includes braking units <NUM> connected to a respective distal end 112b of the push-rod <NUM> of the brake actuators <NUM>, <NUM> and configured to apply, when the push-rod <NUM> is actuated, a braking force on a movable element, in particular on a wheel <NUM>, of the commercial vehicle <NUM>.

Preferably, the compressed air is dried and optionally filtered at an air processing unit comprising an air dryer <NUM>. The dried compressed air <NUM> is preferably stored in an air-reservoir unit <NUM> comprising one or more air reservoirs.

When the brake valve (e.g. brake pedal) <NUM> is actuated, compressed air flows, preferably via an ABS solenoid control valve (not shown) into the first chambers of the brake actuator <NUM> and the spring brake actuator <NUM>. The pressure in the brake cylinders generating the force required for the wheel brake de-pends on the amount of force applied to the brake valve <NUM>. Also, the air reservoir unit <NUM> is connected via a hand brake valve <NUM> to the spring-loaded portion of the spring brake actuator <NUM>. When the hand brake valve <NUM> is actuated and locked, the spring-loaded portions of the spring brake actuators <NUM> are exhausted fully. The force needed for the wheel brake is now provided by the heavily preloaded springs <NUM> of the spring brake actuators.

In summary, The invention is directed to a brake actuator comprising a housing with an inlet port for receiving a fluid, and a push-rod aperture, and configured to accommodate a first chamber connected to the inlet port and a second chamber that includes the push-rod aperture. The first chamber and the second chamber are separated by a movable separation element to which a push-rod is connected that protrudes outside the housing via the push-rod aperture. A boot defining an inner volume has a proximal end section connected to the push-rod and a distal end section connected to the housing, wherein a cross-sectional area amount of the inner volume at the distal end section is larger than a cross-sectional segment area of a boot segment, thus enabling a reduction of a length of the push rod.

Claim 1:
Brake actuator (<NUM>, <NUM>, <NUM>), comprising a housing (<NUM>) having an inlet port (<NUM>) for receiving a fluid, particularly compressed air (<NUM>, <NUM>), and a push-rod aperture (<NUM>), the housing (<NUM>) arranged and configured to accommodate
- a first chamber (<NUM>) connected to the inlet port (<NUM>); and
- a second chamber (<NUM>) that includes the push-rod aperture (<NUM>), and
wherein
the first chamber (<NUM>) and the second chamber (<NUM>) are separated by a movable separation element (<NUM>) arranged at the housing (<NUM>), such that a volume amount (V1) of the first chamber (<NUM>) increases and a volume amount (V2) of the second chamber (<NUM>) decreases when the fluid enters the first chamber (<NUM>) via the inlet (<NUM>) and actuates the separation element (<NUM>);
the brake actuator (<NUM>), further comprising:
- a push-rod (<NUM>) having a proximal end (112a) connected to the movable separation element (<NUM>), and a distal end (112b) protruding outside the housing (<NUM>) via the push-rod aperture (<NUM>); and
- a boot (<NUM>) defining a boot inner volume (V3) for accommodating a middle section (112c) of the push-rod (<NUM>), the boot (<NUM>) having a proximal end section (114a) connected to the push-rod (<NUM>) at a region proximate the proximal end (112a) of the push-rod (<NUM>), and a distal end section (114b) connected to the housing (<NUM>) at the push-rod aperture (<NUM>); the boot (<NUM>) having at least one foldable boot segment (<NUM>) in a longitudinal direction (L);
characterized in that
a cross-sectional area amount (A1) of the boot inner volume (V3) at the distal end section (114b) of the boot (<NUM>) is larger than a maximum cross-sectional segment area (A2) of a first boot segment (116a) proximate the distal end section (114b) such that, in a folded state of the boot (<NUM>), the first boot segment (116a) is at least partially fitted inside the distal end section (114b).