Spring-loaded brake actuator

Abstract

Spring-loaded brake actuator (1) for a vehicle, in particular a commercial vehicle, wherein the spring-loaded brake actuator (1) has a service brake pressure (p B) pressurised service brake chamber (25), a push rod assembly (21) movable in a stroke direction with a working surface (23) which is designed to absorb a force resulting from the pressurised service brake chamber (25) and which defines a first movable wall (63) of the service brake chamber (25), and a spring-applied brake piston (27) with a contact surface (33) which is designed to transmit force to the working surface (23).The invention provides that the contact surface (33) is a first surface, wherein the spring-applied brake piston (27) additionally has a free surface (35) as a second surface, wherein the contact surface (33) and the free surface (35) are offset from each other in the stroke direction such that the free surface is spaced away from the working surface (23) when the service brake chamber (25) is unpressurized, and the contact surface (33) and the free surface (35) together define a second movable wall (65) of the service brake chamber (25).

Description

[0001] The present invention relates to a spring-applied brake actuator for a vehicle, in particular a commercial vehicle, wherein the spring-applied brake actuator comprises a service brake chamber that can be pressurized with a service brake pressure, a pushrod assembly movable in a stroke direction with a working surface which is configured to absorb a force resulting from the pressurized service brake chamber and which defines a (first) movable wall of the service brake chamber, and a spring-applied brake piston with a contact surface which is configured to transmit force to the working surface.

[0002] Spring-applied brake actuators of this type are well-known. They are primarily used in the commercial vehicle sector, for example, in trucks and rail vehicles, and serve as either a parking brake or an auxiliary brake, depending on the application. With spring-applied brake actuators, simultaneous application of the service brake and parking brake functions can lead to a phenomenon known as compounding. During compounding, the service brake force and the spring brake force acting on the pushrod assembly overlap. This can result in a high force being applied to the brake components and, in extreme cases, can prevent the brake pads from being released from the brake discs solely by the service brake pressure – against the spring brake force. For safety reasons, anti-compound measures are implemented in spring-applied brake actuators to prevent excessive force build-up and damage to the brake components.

[0003] A pneumatic approach to preventing compounding is known from the prior art. This approach involves creating an additional pneumatic control circuit. With the spring brake engaged and the spring brake actuator vented, the spring brake is pressurized with a control pressure from the service brake circuit. This introduces pressure into the parking brake chamber to release the brake. Disadvantages of this approach include the additional piping required and the potential for force reduction or increase during dynamic switching phases. Another disadvantage is the inability to control individual wheels, as the additional pneumatic control circuit is based on the service brake circuit and therefore provides the same control pressure for all wheels.

[0004] Furthermore, a software-controlled anti-compounding system is known from the prior art. In this approach, a sensor detects whether the spring brake is engaged or not. If the sensor detects the engaged spring brake, it reports this condition to a control unit, and the service brake pressure at the individual wheels is then held back by the service brake system when the vehicle is stationary. A disadvantage of this approach is that it cannot be used in the event of redundancy braking, as only one brake system is active at any given time.

[0005] Against this background, the invention was based on the objective of developing a solution for a spring-applied brake system based on an existing spring-applied brake actuator, which overcomes the disadvantages described in the prior art as far as possible. In particular, the invention was based on the objective of providing a spring-applied brake system that reduces compounding and enables low installation effort without compromising reliability and performance.

[0006] The invention solves the underlying problem in a spring-applied brake actuator of the type described above according to a first aspect by being designed according to claim 1. In particular, the invention proposes that the contact surface is a first surface, wherein the spring-applied brake piston additionally has a free surface as a second surface, wherein the contact surface and the free surface are offset from each other in the stroke direction such that the free surface is spaced away from the working surface when the service brake chamber is unpressurized, and wherein the contact surface and the free surface together define a (second) movable wall of the service brake chamber facing the spring-applied brake piston, preferably opposite the first wall.By offsetting the two surfaces in the stroke direction, a gap is created between the free surface and the contact surface. This gap gives the first wall of the service brake chamber a depth profile that forms an annular gap when the contact surface rests against the working surface or any intervening diaphragm. When pressurized, this allows force to be simultaneously applied to both the pushrod assembly and the spring-applied brake piston, even when the profile peaks, formed by the contact surface, are in contact with the working surface, the second wall of the service brake chamber. This latter force acts as a counterforce on the spring-applied brake piston if it is partially or fully deflected in the stroke direction, thus reducing the overall force acting on the pushrod assembly and effectively counteracting compounding.Consequently, by constructively redesigning the second movable wall of the service brake chamber, which consists of a contact surface and a free area, it is possible to add another function to the profiled surface without additional pneumatic or control-related effort.

[0007] The invention is advantageously further developed in that the free surface is dimensioned such that, when the service brake chamber is subjected to a predetermined service brake pressure, for example 6.0 bar or more, preferably 8.0 bar or more, it exerts a counterforce on the second movable wall which is at least 50% of the maximum spring braking force of the spring-applied brake actuator, preferably 75% or more. The maximum spring braking force depends on the selection or dimensioning of the spring of the spring-applied brake actuator, which is known from the actuator design. It preferably corresponds to the force that the spring-applied brake actuator exerts in the stroke direction when the spring-applied brake piston is pre-tensioned and retracted. In this way, the spring-applied brake actuator is automatically prevented from exerting an impermissible force increase.

[0008] In a preferred embodiment, the counterforce on the second movable wall, which comprises the free surface and the contact surface, corresponds to at least 50%, preferably 75% or more, of the force exerted by the service brake pressure on the first wall or the diaphragm. A clear differentiation in the magnitudes of the individual forces ensures that they act independently of one another and that an undesirable or even impermissible addition of spring brake force and service brake force can be avoided.

[0009] In a preferred embodiment, the contact area is less than 25% of the free area, more preferably less than 10%, and particularly preferably 3% to 5% of the free area. By precisely designing the size of the free area during manufacturing, a precise counterforce to the spring force can be generated, given the known operating pressure in the service brake chamber. The installation space of the spring-applied brake actuator can simultaneously be kept compact.

[0010] In a preferred embodiment, the contact surface has a surface normal that is oriented essentially parallel to the effective axis of the spring. This embodiment ensures that the contact surface transmits the spring force to the working surface, and thus to the pushrod assembly, with optimal force transmission. This also promotes a compact design in the stroke direction.

[0011] The term "essentially parallel" shall be understood to mean an angle between the surface normal and the effective axis of 5° or less, preferably 2° or less, including an angle of exactly 0°. Furthermore, in a preferred embodiment, the effective axis is arranged collinearly with the lifting axis.

[0012] In another preferred embodiment, the free surface has a surface normal that is oriented essentially parallel to the effective axis of the spring. This orientation also promotes a compact design in the stroke direction.

[0013] In a preferred embodiment, the working surface has a surface normal that is oriented essentially parallel to the effective axis of the spring. This enables direct force transmission from the spring piston to the pushrod assembly in the event of parking braking. Furthermore, the pushrod assembly and the spring brake piston preferably have the same direction of action, which centers the braking effect on the same position at the respective wheels and also keeps the installation space compact.

[0014] Preferably, the free surface is a radially extending area that further preferably extends to the circumference of the spring-applied brake piston. The spring-applied brake piston preferably extends to the inner wall of the housing. Preferably, one or more seals are arranged between the spring-applied brake piston and the inner wall of the housing. In preferred embodiments, a diaphragm seal or a dynamic seal is used.

[0015] A surface of "radial extent" refers to a circular or annular area characterized by an outer radius at its maximum extent. For an annular area, the inner radius is greater than a length of zero. For a circular area, the inner radius is equal to zero.

[0016] Preferably, the contact surface is a radially extending surface. The radial extension of the contact surface enables a central and uniform force transmission from the spring force via the working surface to the pushrod assembly.

[0017] In a preferred embodiment, the contact surface is arranged on a (first) end face of the spring-applied brake piston, and the clearance surface is designed as a recess provided on the (first) end face, preferably recessed into the contact surface, which is further preferably aligned parallel to the contact surface. In other words, the contact surface forms an end face of the spring-applied brake piston. The parallel alignment of the clearance surface to the contact surface allows the distance between the clearance surface and the contact surface to be kept small, while still ensuring uniform compressed air pressure. Uniform and complete compressed air pressure on the clearance surface guarantees maximum utilization of the area as a pressure-acting surface.

[0018] In a further preferred embodiment, the free surface is formed in multiple parts and has two or more surface segments separated by spacer elements. The spacer elements are designed to ensure a distance between the working surface and the free surface when the contact surface rests against the working surface (or an intermediate seal, such as a membrane). The spacer elements are preferably arranged circumferentially around the stroke axis of the spring-applied brake actuator, preferably with uniform distribution. The spacer elements thus reliably guarantee a distance between the free surface and the working surface, particularly when the working surface is covered by a membrane. Furthermore, the spacer elements prevent the free surface from adhering to the working surface, which may be designed as a membrane, over a large area.

[0019] In another preferred embodiment, the contact surface and the free surface are aligned concentrically. This concentric alignment enables a uniform distribution of the free surface area around the contact surface. This allows for a force effect that is parallel to the direction of action of the spring and does not experience any deflection at an angle.

[0020] Preferably, the spring-applied brake piston is designed in multiple parts and comprises a counter-piston and a spring piston. This multi-part design allows for cost-effective yet precise manufacturing of the spring-applied brake piston, as well as good assembly.

[0021] Preferably, the counter-piston extends from the first end face of the spring-applied brake piston towards a second end face of the spring-applied brake piston on the spring side. The counter-piston is designed to absorb the counterforce generated in the service brake chamber when pressurized.

[0022] In another preferred embodiment, the spring piston extends from the spring-side second end face of the spring-applied brake piston towards the first end face of the spring-applied brake piston. The spring piston absorbs the spring force and the pressure from the parking brake chamber.

[0023] In a preferred embodiment, the counter piston and the spring piston are joined together in a connection area, wherein the connection area has the same cross-sectional area in both the area of ​​the counter piston and in the area of ​​the spring piston. The identical cross-sectional area allows for a stepless transition between the counter piston and the spring piston.

[0024] In a further preferred embodiment, the cross-sectional area of ​​the connection area is smaller than the spring contact area with respect to the direction of the spring's effective axis; preferably, the cross-sectional area of ​​the connection area is 5% to 8% of the spring contact area with respect to the direction of the spring's effective axis. This ratio of cross-sectional areas to each other creates a sufficiently load-bearing connection area for force transmission, and the installation space for the end faces remains as large as possible.

[0025] Preferably, the spring-applied brake piston, and preferably the counter-piston, has one or more stops, the stop(s) preferably being ring-shaped. This design reduces the stop to the smallest possible area, thus minimizing wear. Furthermore, a dimension for the stop can be defined by spacing it from the rear side of the clearance surface, thereby determining the maximum extension of the service brake chamber in the direction of spring action.

[0026] In a preferred embodiment, the counter-piston and the spring piston are joined together using one of the joining methods: screws, presses, shrink-fitting, or clamping. All of the aforementioned joining methods create a positive-locking connection between the counter-piston and the spring piston, ensuring precise alignment of the counter-piston with the spring piston and thus guaranteeing sufficient force transmission both in the direction of the spring and in the direction of the pushrod assembly.

[0027] In a further preferred embodiment, the spring-applied brake actuator has a housing which features a stop rib on its inner wall between the stop and the spring contact surface of the spring-applied brake piston, preferably with a seal provided between the stop rib and the spring-applied brake piston. Furthermore, the stop rib forms an abutment, i.e., a counterpart, for the stop.

[0028] In a preferred embodiment, the inner wall of the housing, together with the counter-piston and the stopper bridge, forms a counter-piston chamber, wherein the inner wall of the housing, together with the pushrod assembly, forms a brake chamber, and wherein the spring piston, together with the inner wall of the housing, forms a spring chamber. This embodiment provides the spring-applied brake actuator with an additional chamber in the form of the counter-piston chamber, resulting in additional functionality for the spring-applied brake actuator.

[0029] In another preferred embodiment, the brake chamber, the counter-piston chamber, and the spring chamber are fluidly connected to the environment and thus exhibit ambient pressure. This ambient pressure can be easily displaced by the forces acting from the service brake pressure and parking brake pressure and requires no additional sealing against the environment.

[0030] This prevents overpressure in the chambers not subjected to service brake pressure or parking brake pressure, and thus avoids premature material fatigue.

[0031] In a preferred embodiment, the brake chamber and the counter-piston chamber are fluidly connected to each other, preferably by means of a first ventilation passage integrated into the housing.

[0032] Furthermore, in a preferred embodiment, the counter-piston chamber and the spring chamber are fluid-conductingly connected to each other, preferably by means of a second ventilation passage integrated into the housing.

[0033] The invention has been described above in a first aspect relating to a spring-applied brake actuator. In a second aspect, the invention further relates to a vehicle, in particular a commercial vehicle, with a spring-applied brake actuator.

[0034] The invention solves the underlying problem in such a vehicle by designing the spring-applied brake actuator according to one of the aforementioned embodiments. The installation of a spring-applied brake actuator according to the invention guarantees reliable operation of both the service brake and parking brake functions. Force multiplication due to the combination of an acting service brake force and an acting parking brake force is reliably prevented, since an applied service brake exerts a pressure-induced counterforce on the spring-applied brake piston, thus returning the spring to its compressed position.

[0035] The invention utilizes the insights and advantages of the spring-applied brake actuator according to the first aspect. Preferred embodiments of the first aspect are therefore also preferred embodiments of the second aspect and vice versa, which is why, to avoid repetition, reference is made to the explanations regarding the first aspect.

[0036] The invention is described in more detail below with reference to the accompanying figures and a preferred embodiment. The figures show: Fig. 1 a schematic sectional view of a spring-loaded brake actuator according to the invention in a preferred embodiment, and Fig. 2 a schematic view of the first end face of a spring-applied brake piston of the actuator according to Fig. 1.

[0037] In Fig. Figure 1 shows a spring-applied brake actuator 1 according to a preferred embodiment of the invention. The spring-applied brake actuator 1 for a vehicle, in particular a commercial vehicle, has a spring-applied brake section 79 and a service brake section 81, which are enclosed by a common housing 3. The housing 3 further has an inner wall 5. In the embodiment shown, the spring-applied brake section 79 is separated from the service brake section 81 by a second wall 65 of a service brake chamber 25. Furthermore, a spring-applied brake piston 27 extends through the spring-applied brake section 79 to the service brake section 81.

[0038] The spring accumulator area 79 has a spring 17 arranged on a housing base 83 of the housing 3. Opposite the housing base 83, a spring contact surface 43 is formed on the spring accumulator brake piston 27.

[0039] Fig. Figure 1 further shows that the spring-applied brake piston 27 is formed in multiple parts and comprises a counter-piston 29 and a spring piston 31. The counter-piston 29 extends from the first end face 55 of the spring-applied brake piston 27 towards a spring-side second end face 57 of the spring-applied brake piston 27. The spring piston 31 extends, opposite to the counter-piston 29, from the spring-side second end face 57 of the spring-applied brake piston 27 towards the first end face 55. Consequently, the counter-piston 29 and the spring piston 31 meet at a joint 39 and are joined together at the joint 39.

[0040] Furthermore, it shows Fig. 1. The spring contact surface 43 is arranged on the second end face 57 of the spring-applied brake piston 27. The spring contact surface 43 extends with its outer diameter to the inner wall 5 of the housing. One or more seals 45 are arranged at the common interface of the spring-applied brake piston 27 in the area of ​​the spring contact surface 43 and the inner wall 5 of the housing. The sealing point is designed as a dynamic seal.

[0041] The spring piston 31, as part of the spring-applied brake piston 27, forms a spring chamber 13 with the inner wall 5 of the housing. The spring chamber 13 has a vent to the environment and consequently contains ambient pressure pu.

[0042] The spring accumulator area 79 further comprises a locking bolt 19, as shown in the exemplary embodiment. The locking bolt 19 engages, preferably by means of a threaded connection, in the spring accumulator brake piston 27 at the spring contact surface 43. Furthermore, the central axis of the locking bolt 19 lies on the stroke axis 61 and thus on the effective axis of the spring 17.

[0043] Referring to the described joint 39, it is disclosed Fig. 1. The counter-piston 29 and the spring piston 31 are joined together in a connection area 51. The connection area 51 has the same cross-sectional area in both the area of ​​the counter-piston 29 and the area of ​​the spring piston 21. The cross-sectional area of ​​the connection area 51 with a surface normal lying on the stroke axis 61 is smaller than the spring contact area 43. Preferably, the cross-sectional area of ​​the connection area 51 is 5% to 8% of the spring contact area 43.

[0044] Furthermore, the spring-loaded brake actuator 1, as shown in Fig. Figure 1 shows a stopper 15 on the inner wall 5 of the housing. The stopper 15 is formed as a wall extending into the housing 3 and has a passage for the connection area 51 of the spring-applied brake piston 27. Preferably, the passage is cylindrical. The inner diameter of the stopper 15 and the outer diameter of the connection area 51 are the same size.

[0045] Furthermore, one or more seals 45 are arranged between the connection area 51 and the inner housing wall 5. This embodiment enables a dynamic seal between the inner housing wall 5 and the connection area 51 of the spring-applied brake piston 27.

[0046] A parking brake chamber 41 is formed by the dynamic seals, firstly between the stopper bridge 15 and the connection area 51, and secondly between the spring-applied brake piston 27 in the area of ​​the spring contact surface 43 and the inner wall of the housing 5. Furthermore, a supply line 49 to the parking brake chamber 41 is arranged in the housing 3 and is located in the spring-applied area 79.

[0047] Furthermore, it shows Fig. 1, that the spring-applied brake piston 27, preferably the counter-piston 29, has one or more stops 37. The stop 37 is preferably annular in shape. Furthermore, the stop 37 is spaced apart from the rear side of the second wall 65 of the service brake chamber 25 and has a larger inner diameter than the outer diameter of the connection area 51. Due to the spacing of the stop 37 from the second wall 65 of the service brake chamber 25 and the inner diameter of the stop 37, which is also radially spaced from the outer diameter of the connection area 51, a collar is formed on the rear side of the second wall 65 of the service brake chamber 25 in the illustrated embodiment.

[0048] The inner wall of the housing 5, together with the counter-piston 29 and the stopper bridge 15, forms a counter-piston chamber 11, which is at ambient pressure pu. The counter-piston chamber 11 and the spring chamber 13 are fluid-conductingly connected to each other by means of a ventilation passage 8.

[0049] The service brake section 81 has a pushrod assembly 21 that is movable in the direction of travel. The pushrod assembly 21 lies with its central axis on the stroke axis 61 of the spring-applied brake actuator 1. Furthermore, the pushrod assembly 21 comprises a pushrod 75, a spring plate 77, and a return spring 73. The pushrod 75 extends through a cylindrical opening in a pushrod-side housing wall 85 of the housing 3. A bellows 71 is arranged on the pushrod-side housing wall 85 of the housing 3, which slidably surrounds the pushrod 75 at its outer diameter.

[0050] Within the housing 3, the pushrod 75 forms an end section 76 with a larger outer diameter than the rest of the pushrod 75. A first part 23a of the working surface 23 is arranged spring-side to the end section 76. This part 23a of the working surface can be extended by a spring plate 77. The spring plate 77 is mounted on the pushrod 75 in the region of the smaller diameter and is bell-shaped over the end section 76 of the pushrod 75. An end section 78 of the spring plate 77 forms a second part 23b of the working surface 23, which is arranged in a plane E with the first part 23a of the working surface 23. The working surface 23, whether formed in one piece or in multiple parts, forms a first wall 63 of the service brake chamber 25. Furthermore, the surface normal N Ar the working surface is essentially parallel to the effective axis of the spring 17 and lies on the lifting axis 61.

[0051] The work surface 23 is a surface with radial spread. In the Fig. In the embodiment shown in Figure 1, the working surface 23 is preferably covered by a membrane 69. An end region 22 of the pushrod assembly 21, which includes the end region a of the pushrod 75 and the end region 78 of the spring plate 77, extends to the inner wall 5 of the housing. One or more seals 45 are arranged between the end region 22 and the inner wall 5 of the housing. Furthermore, the working surface 23 defines a first movable wall 63 of the service brake chamber 25, which is arranged on the side of the end region 22 opposite the brake chamber 9.

[0052] Fig. Figure 1 further shows that the return spring 73 is arranged on the pushrod-side housing wall 85, specifically on the inner housing wall 5. The return spring extends, for example conically, along the pushrod 75 to the spring plate 77. Additionally, the inner housing wall 5, together with the pushrod assembly 21, particularly the end region 22, forms a brake chamber 9. The brake chamber 9 is at ambient pressure pu and is vented to the environment. Furthermore, the brake chamber 9 is fluidly connected to the counter-piston chamber 11 via a vent passage 7.

[0053] Furthermore, the service brake chamber 25 has a supply line 47 for the service brake pressure p B on, which passes through the housing 3 and enters the service brake chamber 25 on the inner wall of the housing.

[0054] Fig. Figure 1 further shows that a contact surface 33 is arranged on the second wall 65 of the service brake chamber 25. The contact surface 33 has a surface normal N. An on, which is essentially aligned parallel to the effective axis of the spring 17 and lies on the lifting axis 61.

[0055] The contact surface 33 is a first surface of the spring-applied brake piston 27. Additionally, the spring-applied brake piston 27 has a clearance surface 35 as a second surface. The contact surface 33 and the clearance surface 35 are offset from each other in the stroke direction such that the clearance surface 35 is spaced away from the working surface 23 when the service brake chamber 25 is unpressurized. The contact surface 33 and the clearance surface 35 together define the second movable wall 65 of the service brake chamber 25, which is preferably arranged opposite the first wall 63. The second movable wall 65 of the service brake chamber 25 is part of the spring-applied brake piston 27. The contact surface 33 is a surface with radial extension.

[0056] The contact surface 33 is arranged on a first end face 55 of the spring brake piston 27 and the free surface 35 is designed as a recess 59 provided on the first end face 55, preferably recessed into the contact surface 33. Fig. Figure 1 shows that the installation area 33 and the open area 35 are preferably aligned parallel to each other.

[0057] The free surface 35 is also a surface with radial extension. The radial extension of the free surface 35 reaches to the inner wall of the housing 5. The free surface 35 has a surface normal N Fr on, which are essentially aligned parallel to the effective axis of the spring 17 and lie on the lifting axis 17.

[0058] Fig. Figure 2 shows the view of the first end face 55 of the spring-applied brake piston 27. The clearance surface 35 is formed in multiple parts and has two or more surface segments 67 separated by spacer elements 53. The spacer elements 53 are designed to ensure a distance between the working surface 23 and the clearance surface 35 and are preferably arranged circumferentially around the stroke axis 61 of the spring-applied brake actuator 1, preferably evenly distributed. Fig. 2 The lifting axis 61 runs through the center of the first end face 55 shown and orthogonally to the first end face 55. In the illustrated embodiment, the spacer elements 53 are designed as webs which extend radially outwards from the outer diameter of the contact surface 33 to the outer diameter of the clearance surface 35 and thus to the inner wall 5 of the housing.

[0059] Furthermore reveals Fig. 2 a concentric arrangement of the mounting surface 33 and the free space 35. This concentric arrangement can also be expressed from Fig. Read 1.

[0060] During operation, the parking brake chamber 41 is pressurized with a parking brake pressure p P applied. The parking brake pressure p P is sufficiently dimensioned to hold spring 17 in a compressed position. The parking brake pressure p PPressurized air can be supplied to or discharged from the parking brake chamber 41 via the supply line 49. The seals 45 between the spring-applied brake piston 27 and the inner housing wall 5, as well as the stopper rib 15, ensure a fluid-tight seal between the parking brake chamber 41 and the spring chamber 13 (which is at ambient pressure pu) and the counter-piston chamber 11. The return spring 73, arranged on the spring plate 77, secures the brake in the released state, i.e., when the service brake chamber 25 is closed.

[0061] During service braking, the service brake is applied. The service brake chamber 25 is pressurized with a service brake pressure p. B The pressure is applied and the volume of the service brake chamber 25 increases. This causes the pushrod assembly 21 to extend to actuate a brake mechanism (not shown), overcoming the return spring 73.

[0062] During a parking brake operation, the parking brake is applied. The parking brake pressure p P The compressed spring 17 is released from the parking brake chamber 41. It expands, transmitting the spring force to the spring surface 43 and displacing the spring-applied brake piston 27 along the stroke axis 61 towards the pushrod assembly 21. If the service brake chamber 25 is depressurized, the spring-applied brake piston 27 comes into contact with the working surface 23 via its contact surface 33. The spring force is transmitted to the pushrod assembly 21 via the contact surface 33, causing the pushrod assembly 21 to deflect. To terminate the parking brake operation, pressurized air is introduced into the parking brake chamber 41 via the supply line 49.

[0063] The following considers the situation in which both a parking brake operation and a service brake operation are initiated. In addition to a deflection of the spring brake piston 27 against the pushrod assembly 21, a service brake pressure p is applied. B The brake cylinder, located in the service brake chamber 25, acts against the spring-applied brake piston 27 even when the latter is in contact with the working surface 23. The free surface 35 is dimensioned such that it exerts a sufficiently large counterforce on the second movable wall 65 of the service brake chamber 25. When the parking brake pressure p is applied in the parking brake chamber 41... PWhen pressurized air is supplied again via the supply line 49, the spring-applied brake piston 27 compresses the spring 17 back to its initial position. The additional pressure-bearing surface in the form of the free surface 35 reduces, and ideally prevents, double loading of the pushrod assembly 21. In other words, the free surface 35 ensures that the service brake pressure p B A counterforce can always be generated on the spring-applied brake piston 27 when it is in a deflected position, at least partially. As long as the spring-applied brake piston 27 is fully in the retracted position, these counterforces are transferred into the housing 3 via the stop 37 and stopper 15. Reference symbol (part of the description) 1 spring-loaded brake actuator 3 cases 4 Outer housing wall 5 Inner wall of the housing 7 Ventilation passage 8 Ventilation passage 9 brake chamber 11 Counter-piston chamber 13 Spring chamber 15 Stopper bridge 17 spring 19 locking bolts 21 Pushrod assembly 22 End area of ​​the push rod assembly 23 work surface 23a first part of the work area 23b second part of the work area 25 Service brake chamber 27 spring-loaded brake pistons 29 Counter-pistons 31 spring pistons 33 Plant area 35 open space 37 attacks 39 Joint 41 Parking brake chamber 43 Spring mounting surface 45 Seal 47 Supply line for service brake pressure 49 Supply line for parking brake pressure 51 Connection area 53 spacer element 55 first front 57 second front 59 Exclusion 61 Lifting axle 63 first wall 65 second wall 67 Area segment 69 Membran 71 Bellows 73 Return spring 75 Pushrod 76 End area of ​​the push rod 77 spring plates 78 End area of ​​the spring plate 79 Spring storage area 81 Service braking area 83 Case base 85 Housing wall, pushrod side Level E N An Surface normal of the installation area N Ar Surface normal of the work surface N Fr Surface normal of the free area PU ambient pressure p B Service brake pressure p P Parking brake pressure

Claims

Spring-applied brake actuator (1) for a vehicle, in particular a commercial vehicle, wherein the spring-applied brake actuator (1) comprises: - a service brake chamber (25) that can be pressurized with a service brake pressure (pB), - a pushrod assembly (21) movable in a stroke direction with a working surface (23) which is configured to absorb a force resulting from the pressurized service brake chamber (25) and which defines a first movable wall (63) of the service brake chamber (25), - a spring-applied brake piston (27) with a contact surface (33) which is configured to transmit force to the working surface (23), characterized in that the contact surface (33) is a first surface, wherein the spring-applied brake piston (27) additionally has a free surface (35) as a second surface, wherein the contact surface (33) and the free surface (35) are offset from each other in the stroke direction such thatthat the free area in the unpressurized service brake chamber (25) is spaced away from the working surface (23), and wherein the contact surface (33) and the free area (35) together define a second movable wall (65) of the service brake chamber (25), preferably opposite the first wall. Spring-loaded brake actuator (1) according to claim 1, characterized in that the free surface (35) is dimensioned such that, when the service brake chamber (25) is subjected to a predetermined service brake pressure (pB), for example 6.0 bar or more, preferably 8.0 bar or more, it exerts a counterforce on the second movable wall (65) which is at least 50% of a maximum spring brake force of the spring-loaded brake actuator (1), preferably 75% or more. Spring-loaded brake actuator (1) according to claim 1 or 2, characterized in that the counterforce on the second movable wall (65), which comprises the free area (35) and the contact surface (33), corresponds to at least 50%, preferably 75% or more, of the force exerted by the service brake pressure (pB) on the first wall (63) or the diaphragm (69). Spring-loaded brake actuator (1) according to one of the preceding claims, characterized in that the contact surface (33) is less than 25% of the free area (35), more preferably less than 10%, particularly preferably 3% - 5% of the free area (35). Spring-loaded brake actuator (1) according to one of the preceding claims, characterized in that the contact surface (33) has a surface normal which is oriented substantially parallel to the effective axis of the spring (17). Spring-loaded brake actuator (1) according to one of the preceding claims, characterized in that the free surface (35) has a surface normal which is oriented substantially parallel to the effective axis of the spring (17). Spring-loaded brake actuator (1) according to one of the preceding claims, characterized in that the working surface (23) has a surface normal which is oriented substantially parallel to the effective axis of the spring (17). Spring-loaded brake actuator (1) according to one of the preceding claims, characterized in that the working surface (23) is a surface with radial extension, which preferably extends to an inner housing wall (5), and wherein one or more seals (45) are arranged between the spring-loaded brake piston (27) and the inner housing wall (5), preferably in the form of a diaphragm. Spring-loaded brake actuator (1) according to one of the preceding claims, characterized in that the free surface (35) is a surface with radial expansion, which preferably extends to a circumference of the spring-loaded brake piston (27), wherein the spring-loaded brake piston (27) preferably extends to the inner wall (5) of the housing, and wherein one or more seals are arranged between the spring-loaded brake piston (27) and the inner wall (5) of the housing. Spring-loaded brake actuator (1) according to one of the preceding claims, characterized in that the contact surface (33) is a surface with radial expansion. Spring-loaded brake actuator (1) according to one of the preceding claims, characterized in that the contact surface (33) is arranged on a first end face (55) of the spring-loaded brake piston (27) and the free surface (35) is formed as a recess (59) provided on the first end face (55), preferably recessed into the contact surface (33), which is further preferably aligned parallel to the contact surface (33). Spring-loaded brake actuator (1) according to claim 10, characterized in that the free surface (35) is formed in multiple parts and has two or more surface segments (67) separated by spacer elements (53), wherein the spacer elements (53) are arranged to ensure a distance between the working surface (23) and the free surface (35), and wherein the spacer elements (53) are preferably arranged circumferentially around the stroke axis (61) of the spring-loaded brake actuator (1), preferably evenly distributed. Spring-loaded brake actuator (1) according to one of claims 10 or 11, characterized in that the contact surface (33) and the free surface (35) are aligned concentrically. Spring-loaded brake actuator (1) according to one of the preceding claims, characterized in that the spring-loaded brake piston (27) is designed in multiple parts and has a counter-piston (29) and a spring piston (31). Spring-loaded brake actuator (1) according to claim 14, characterized in that the counter-piston (29) extends from the first end face (55) of the spring-loaded brake piston (27) towards a spring-side second end face (57) of the spring-loaded brake piston (27). Spring-loaded brake actuator (1) according to one of the preceding claims, characterized in that the spring-loaded brake piston (27), preferably the counter-piston (29), has one or more stops (37), wherein one stop (37) is preferably annular in shape. Spring-loaded brake actuator (1) according to one of the preceding claims, characterized in that the spring-loaded brake actuator (1) has a housing (3) which has a stopper web (15) on the inner wall (5) of the housing between the stop (37) and the spring contact surface (43) of the spring-loaded brake piston (27), wherein preferably the inner diameter of the stopper web (15) and the outer diameter of the connection area (51) have the same size, and wherein one or more seals (45) are arranged between the connection area (51) and the inner wall (5) of the housing. Spring-loaded brake actuator (1) according to one of the preceding claims, characterized in that the brake chamber (9) and the counter-piston chamber (11) are fluidly connected to each other, preferably by means of a ventilation passage (7) integrated into the housing (3). Spring-loaded brake actuator (1) according to one of the preceding claims, characterized in that the counter-piston chamber (11) and the spring chamber (13) are fluidly connected to each other, preferably by means of a ventilation passage (8) integrated into the housing (3). Vehicle, in particular a commercial vehicle, characterized in that the vehicle has a spring-loaded brake actuator (1) according to one of the preceding claims.

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