Spring brake actuator

Abstract

A spring brake actuator for braking a vehicle wheel. The spring brake actuator comprises an axially elongated housing having a parking brake chamber and a service brake chamber. The parking brake chamber houses a main compression spring, a flexible diaphragm, and a pressure plate axially positioned between the main compression spring and the flexible diaphragm. The flexible diaphragm has a shaped profile that inhibits radial movement of the pressure plate relative to the flexible diaphragm.

Description

Technical Field

[0001] The present disclosure relates to vehicle braking systems and, more particularly, to a pneumatic spring brake actuator for engaging wheel brakes. Background Art

[0002] Trucks, trailers, and other vehicles often have pneumatic spring brake actuators that provide the braking force needed to stop the vehicle. A brake pedal, located on the floor of the vehicle's cab, draws compressed air from an air reservoir into the spring brake actuator when activated. This, in turn, causes a pushrod to extend from the spring brake actuator and activate the wheel brakes. Wheel brakes typically have brake shoes with brake lining material that press against a brake drum at the end of the vehicle's wheel, thereby braking the vehicle. Wheel brakes often include slack adjusters that rotate a cam roller via a camshaft to force the brake shoes into engagement with the brake drum and brake the vehicle. Releasing compressed air from the air chamber allows a spring within the chamber to retract the pushrod to its original position.

[0003] U.S. Patent Publication No. 2018 / 0281767, incorporated herein by reference, discloses a known spring brake actuator. The spring brake actuator includes a push rod assembly having a base located in a service brake chamber and a push rod extending from the service brake chamber. Pneumatic activation of the spring brake actuator causes the push rod to extend further out of the service brake chamber, thereby engaging the wheel brakes on the vehicle's wheels. Pneumatic deactivation of the spring brake actuator causes the push rod to retract into the service brake chamber, thereby disengaging the wheel brakes from the vehicle's wheels.

[0004] The following U.S. patents further describe the prior art and are also incorporated herein by reference in their entirety: U.S. Patent Nos. 10,059,322; 9,297,392; 9,050,958; 8,522,666; 6,394,462; 6,314,861; 6,405,635; 5,791,232; and 5,285,716. Summary of the Invention

[0005] This Summary is provided to introduce a selection of concepts that are further described below in the Detailed Description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used to help limit the scope of the claimed subject matter.

[0006] In an example disclosed herein, a spring brake actuator is used to brake a vehicle wheel. The spring brake actuator comprises an axially elongated housing having a parking brake chamber and a service brake chamber; a main compression spring in the parking brake chamber; a flexible diaphragm in the parking brake chamber; and a pressure plate axially positioned between the main compression spring and the flexible diaphragm. According to the present invention, the flexible diaphragm has a shaped profile that advantageously inhibits radial movement of the pressure plate relative to the flexible diaphragm.

[0007] A spring brake actuator assembly for braking a vehicle wheel is also provided. The assembly includes a flexible diaphragm for positioning within a parking brake chamber of the spring brake actuator, and a pressure plate for positioning between a primary compression spring of the spring brake actuator and the flexible diaphragm. The pressure plate has a hub, a radial outer diameter, and a flange extending radially from a center post to the radial outer diameter. The flexible diaphragm includes a contoured portion that abuts and surrounds the entire radial outer diameter, thereby inhibiting radial movement of the pressure plate relative to the flexible diaphragm, at least when the primary compression spring is in an extended position. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Examples of work machines are disclosed herein with reference to the following drawings.Throughout, like reference numerals are used to refer to similar features and components.

[0009] Figure 1 is a perspective view of a spring brake actuator according to the present disclosure.

[0010] Figure 2 is an exploded view of the spring brake actuator.

[0011] Figure 3 is a perspective view of an assembly for a spring brake actuator including a flexible diaphragm and a pressure plate.

[0012] Figure 4 is a cross-sectional view of the flexible diaphragm.

[0013] Figure 5 is a cross-sectional view of the spring brake actuator showing its parking brake chamber in a pressurized state.

[0014] Figure 6 is a cross-sectional view of a spring brake actuator showing both its parking brake chamber and service brake chamber in a pressurized state.

[0015] Figure 7 is a cross-sectional view showing the spring brake actuator with the main compression spring activated and both the parking brake chamber and the service brake chamber depressurized. DETAILED DESCRIPTION

[0016] Figure 1A spring brake actuator 10 for braking a vehicle wheel is shown. The spring brake actuator 10 has an axially elongated housing 12 formed by opposing cup-shaped end portions 14, 16 and an intermediate portion 18 located axially between the cup-shaped end portions 14, 16. The cup-shaped end portions 14, 16 each have a peripheral flange 20, 22 that seals with an opposing peripheral flange 24, 26, respectively, on the intermediate portion 18. Ports 28, 30 are located on the intermediate portion 18 and are configured to allow compressed air to enter and release compressed air from the housing 12 during operation of the spring brake actuator, as will be described further below.

[0017] like Figure 2 and 5 As shown in FIG. 7 , the intermediate portion 18 has an inner wall 32 that divides the interior of the housing 12 into a parking brake chamber 34 and an opposing service brake chamber 36. A flexible diaphragm 38 is positioned within the parking brake chamber 34 and has a radial outer diameter 40 that is clamped and compressed between the cup-shaped end portion 14 and the peripheral flanges 20 and 24 of the intermediate portion 18. A flexible diaphragm 42 is positioned within the service brake chamber 36 and has a radial outer diameter 44 that is clamped and compressed between the cup-shaped end portion 16 and the peripheral flanges 22 and 26 of the intermediate portion 18. The flexible diaphragm 38 divides the parking brake chamber 34 into an upper chamber 46 and a lower chamber 48. The flexible diaphragm 42 divides the service brake chamber 36 into an upper chamber 50 and a lower chamber 52.

[0018] A main compression spring 54 is positioned in the upper cavity 46 of the parking brake chamber 34 and has a first end pressed against an inner end wall 56 of the cup-shaped end portion 14 and an opposite second end pressed against a pressure plate 58 axially positioned between the main compression spring 54 and the flexible diaphragm 38. The pressure plate 58 has a hub 59 and a radial flange 61 extending from the hub 59 to a radial outer diameter 63. Conversely, the second end of the main compression spring 54 surrounds the hub 59 and abuts the radial flange 61.

[0019] The push rod assembly 60 has a first end 65 adjacent to the flexible diaphragm 38 and an opposite second end 67 extending into the service brake chamber 36. The second end 67 is pivotally connected to a lever arm 64 of a conventional slack adjuster or cam roller. A portion of the lever arm 64 is shown in the figure. The slack adjuster and / or cam roller are configured to convert the reciprocating motion of the push rod assembly 60 to the cam roller and wheel brakes for the vehicle, as is conventional, and therefore will not be described further herein. The type and configuration of the push rod assembly may vary from that shown. In the example shown, the push rod assembly 60 includes a rod 68 that is located in the lower cavity 52 of the service brake chamber 36 and extends through a central hole in the end wall 69 of the cup-shaped end 16. In this way, the rod 68 is partially disposed within the interior of the service brake chamber 36 and partially disposed outside the service brake chamber 36. Radial end flanges on the rod 68 form a pressure plate 70 that abuts the flexible diaphragm 42 so that the rod 68 further reciprocates in and out of the lower chamber 52 of the service brake chamber 36 as the flexible diaphragm 42 flexes back and forth within the chamber as will be further described below.

[0020] The push rod assembly 60 further includes an extension rod 72 that extends through a central aperture in the inner wall 32 of the intermediate portion 18 of the housing 12 and, in particular, through a boss 76 containing an O-ring seal 78, which forms an airtight seal along the sliding extension rod 72. An end plate 80 is coupled to one end of the extension rod 72 via fasteners. End plate 80 abuts the flexible diaphragm 38 opposite the pressure plate 58. An end plate 84 is coupled to the other end of the extension rod 72 via fasteners. End plate 84 abuts the flexible diaphragm 42 opposite the pressure plate 70. The pressure plate 58 defines a central cavity 71 within which the end plate 80 nests, effectively engaging the end of the extension rod 72 with the pressure plate 58 and sandwiching the flexible diaphragm 38 therebetween. A return spring 86 is positioned within the lower cavity 48 of the parking brake chamber 34 and has a first end that presses against the end plate 80 and an opposing second end that presses against the inner wall 32 of the intermediate portion 18 of the housing 12. A return spring 88 is located in the lower cavity 52 of the service brake chamber 36 and has a first end pressed against the pressure plate 70 and an opposite second end pressed against the inner end wall 69 of the cup-shaped end portion 16 .

[0021] Figure 5-7 The spring brake actuator 10 is depicted during various operating conditions. Figure 5 The spring brake actuator 10 is shown in a state where the wheel brakes are released and the vehicle can be driven. Compressed air is supplied to the lower chamber 48 of the parking brake chamber 34 via the port 28. The air pressure pushes the flexible diaphragm 38 upward in the figure, thereby compressing the main compression spring 54 and retracting the extension rod 72 into the lower chamber 48, as shown. The return spring 88 pushes the flexible diaphragm 42 upward in the figure, thereby retracting the rod 68 into the lower chamber 52 of the service brake chamber 36, as shown by the arrow 92.

[0022] Figure 6 The spring brake actuator 10 is shown in a state in which the vehicle driver has depressed the wheel brake pedal, which causes compressed air to be provided to the upper chamber 50 of the service brake chamber 36 via the port 30. This causes the flexible diaphragm 42 to move downward in the figure, compressing the return spring 88. As a result, the rod 68 moves downward in the figure, as indicated by arrow 94, and outward relative to the lower chamber 52 of the service brake chamber 36, thereby pivoting the lever arm 64 of the slack adjuster or cam roller and causing the wheel brakes to be applied.

[0023] Figure 7 The spring brake actuator 10 is shown in a condition where the vehicle is stopped and / or air is being pumped from the housing 12. When this occurs, the primary compression spring 54 pushes downward against the pressure plate 58 in the figure, thereby pushing the push rod assembly 60 downward in the figure, as shown by arrow 96, thereby applying the wheel brakes. The spring brake actuator 10 can be used in conjunction with a variety of conventional brake assemblies, including both brake drum assemblies and brake disc assemblies.

[0024] Thus, pressurizing the parking brake chamber 34 compresses the main compression spring 54, thereby retracting the push rod assembly 60 into the service brake chamber 36 and disengaging the designated wheel brakes from the vehicle's wheels. Depressurizing the parking brake chamber 34 allows the main compression spring 54 to move the push rod assembly 60 out of the service brake chamber 36, thereby engaging the wheel brakes with the vehicle's wheels.

[0025] Through research and experimentation, the present inventors sought to improve conventional spring brake actuators of all makes and models, specifically to provide an improved spring brake actuator that exhibits less wear over time and is therefore more robust and durable than the prior art. Through research and experimentation, the present inventors have determined that the flexible diaphragm located in the parking brake chamber is a component that can resist wear over time. This can lead to performance degradation, including, for example, allowing the pressure plate to shift relative to the diaphragm (i.e., radial movement). This pressure plate shift can make it difficult to effectively service the brake actuator, for example by preventing manual access to the pressure plate with a release bolt. Through further research and experimentation, the present inventors determined that pressure plate shift can be prevented by securing the pressure plate to the diaphragm using one or more adhesives. However, the present inventors also discovered that the application of adhesives is labor-intensive and must be performed under carefully monitored conditions. The present inventors further recognized that this radial movement can be prevented by mechanically attaching the pressure plate to the diaphragm using one or more fasteners. However, again, the installation of these fasteners is labor-intensive and therefore costly.

[0026] The present disclosure is the result of the inventors' recognition of the aforementioned design challenges and their efforts to provide an improved, more robust and durable spring brake actuator that is less expensive to manufacture and less susceptible to wear over time, particularly wear of the diaphragm in the parking brake chamber and the resulting displacement of the pressure plate relative to the diaphragm.

[0027] According to this disclosure, Figure 3 and Figure 4 The flexible diaphragm 38 is shown removed from the spring brake actuator 10 and in a relaxed, natural state. In accordance with the present disclosure, the flexible diaphragm 38 has a novel contoured portion 100 that advantageously inhibits radial movement of the pressure plate 58 as described above. More specifically, the flexible diaphragm 38 has a radial center portion 102 axially adjacent the pressure plate 58 and an intermediate portion 104 radially located between the outer diameter 40 of the flexible diaphragm 38 and the radial center portion 102. The intermediate portion 104 has an angled sidewall 106 that tapers radially inwardly from the radial outer diameter 40 to the contoured portion 100. The contoured portion 100 is located along the intermediate portion 104 and defines a pocket 108 (see FIG. 1 ) in which the radial outer diameter 63 of the pressure plate 58 is disposed. Figure 4 ).

[0028] like Figure 5-7 As shown in the comparison, when the main compression spring 54 moves to its compressed position ( Figure 5 ) and its extended position ( Figure 7 ), and in the process of moving between the two, the shaping contour portion 100 will deform. Figure 5 and 7 As shown in contrast, movement of the main compression spring from the compressed position to the extended position causes the flexible diaphragm 38 to axially invert relative to the radial outer diameter 40 of the flexible diaphragm 38. In certain embodiments, when the main compression spring 54 is fully compressed, the contoured portion 100 deforms such that the recess 108 is nested from the outer diameter 40 into the recessed portion 108 (see FIG. Figure 4 and Figure 7 ) into a convex shape forming the radially outer shoulder of the extended flexible diaphragm 38 (see Figure 5-6 However, at least when the main compression spring 54 is fully compressed, the shaped profile 100 advantageously inhibits radial movement of the pressure plate 58 relative to the flexible diaphragm 38. When the main compression spring 54 is extended ( Figure 7 ), the recess 108 abuts and wraps around the entire radial outer diameter. That is, the shaped profile 100 abuts the entire radial outer diameter 40, or the radial outer side surface 40, thereby inhibiting the aforementioned radial movement.

[0029] Throughout this description, certain terms are used for the sake of brevity, clarity, and understanding. No unnecessary limitations are to be implied beyond those required by the prior art, as these terms are used for descriptive purposes only and are intended to be broadly interpreted. The various devices described herein may be used alone or in combination with other devices. Various equivalents, alternatives, and modifications may be made within the scope of the appended claims.

[0030] The terms are as follows:

[0031] 1. A spring brake actuator for braking a vehicle wheel, the spring brake actuator comprising an axially elongated housing having a parking brake chamber and a service brake chamber, a main compression spring within the parking brake chamber, a flexible diaphragm within the parking brake chamber, and a pressure plate located between the main compression spring and the flexible diaphragm, wherein the flexible diaphragm includes a shaped profile that inhibits radial movement of the pressure plate relative to the flexible diaphragm.

[0032] 2. A spring brake actuator according to claim 1, wherein the main compression spring is axially movable to a compressed position and an extended position, and axially movable between the compressed position and the extended position, and wherein the shaped profile portion inhibits radial movement of the pressure plate at least when the main compression spring is in the extended position.

[0033] 3. A spring brake actuator according to claim 1, wherein the main compression spring is axially movable to a compressed position and an extended position, and axially movable between the compressed position and the extended position, and wherein the pressure plate is nested within the shaped contour portion at least when the main compression spring is in the extended position.

[0034] 4. A spring brake actuator according to claim 1, wherein the main compression spring is axially movable to a compressed position and an extended position, and axially movable between the compressed position and the extended position, wherein the pressure plate has a radial outer diameter, and wherein at least when the main compression spring is in the extended position, the shaped contour portion is adjacent to the radial outer diameter of the pressure plate, thereby inhibiting radial movement of the pressure plate.

[0035] 5. A spring brake actuator according to clause 4, wherein the flexible diaphragm includes a radial outer diameter that is sealed to the boundary of the parking brake chamber, and wherein movement of the main compression spring from the compressed position to the extended position causes the flexible diaphragm to invert relative to the radial outer diameter of the flexible diaphragm.

[0036] 6. A spring brake actuator according to clause 1, wherein the flexible diaphragm includes a radial center portion axially adjacent to the pressure plate and an intermediate portion radially located between a radial outer diameter of the flexible diaphragm and the radial center portion, and wherein the shaped contoured portion is located along the intermediate portion.

[0037] 7. The spring brake actuator of clause 6, wherein the intermediate portion comprises an angled sidewall that converges radially inwardly from a radially outer diameter of the flexible diaphragm toward the shaped contoured portion.

[0038] 8. The spring brake actuator of clause 7, wherein, at least when the primary compression spring is in an extended position, the shaped contour defines a recess in which the radially outer diameter of the pressure plate is disposed.

[0039] 9. The spring brake actuator of clause 8, wherein, at least when the primary compression spring is in the extended position, the recess abuts and wraps around the entire radial outer diameter.

[0040] 10. A spring brake actuator according to claim 1, wherein the main compression spring is axially movable to a compressed position and an extended position, and axially movable between the compressed position and the extended position, wherein the pressure plate has a radial outer diameter, and wherein, at least when the main compression spring is in the extended position, the shaped contour defines a recess in which the radial outer diameter of the pressure plate is arranged.

[0041] 11. The spring brake actuator of clause 10, wherein, at least when the primary compression spring is in the extended position, the recess abuts and wraps around the entire radial outer diameter.

[0042] 12. The spring brake actuator of clause 1, wherein the flexible diaphragm has a relaxed state when removed from the housing, and wherein the shaped contour defines a recess when the flexible diaphragm is in the relaxed state.

[0043] 13. The spring brake actuator of clause 1, further comprising a push rod assembly having a first end adjacent the flexible diaphragm and an opposing second end extending out of the service chamber.

[0044] 14. The spring brake actuator of clause 13, wherein the pressure plate comprises a hub, a radial outer diameter, and a flange extending radially from a central post to the radial outer diameter.

[0045] 15. The spring brake actuator of clause 14, wherein a primary compression spring surrounds said central post and abuts said flange.

[0046] 16. The spring brake actuator of clause 15, wherein the pressure plate includes a cavity that mates with the first end portion of the push rod assembly and the center portion of the diaphragm.

[0047] 17. The spring brake actuator of clause 16, wherein the first end of the push rod assembly includes an end plate disposed within the recessed cavity such that the diaphragm is sandwiched between the end plate and the central cavity of the pressure plate.

[0048] 18. A spring brake actuator according to claim 13, wherein pressurizing the parking brake chamber compresses the main compression spring, thereby retracting the push rod assembly into the service brake chamber and disengaging the wheel brakes from the wheels of the vehicle, and wherein depressurizing the parking brake chamber allows the main compression spring to move the push rod assembly out of the service brake chamber, thereby engaging the wheel brakes with the wheels of the vehicle.

[0049] 19. A spring brake actuator assembly for braking a vehicle wheel, the assembly comprising a flexible diaphragm for positioning in a parking brake chamber of the spring brake actuator, and a pressure plate for positioning between a main compression spring of the spring brake actuator and the flexible diaphragm, wherein the pressure plate comprises a hub, a radial outer diameter, and a flange extending radially from a center post to the radial outer diameter, and wherein the flexible diaphragm comprises a contoured portion that abuts and wraps around the entire radial outer diameter, at least when the main compression spring is in an extended position, thereby inhibiting radial movement of the pressure plate relative to the flexible diaphragm.

[0050] 20. The assembly of clause 19, wherein the flexible diaphragm has a relaxed state when removed from the housing, and wherein the shaped contour defines a recess into which the outer diameter nests when the flexible diaphragm is in the relaxed state.

Claims

1. A spring brake actuator for braking a vehicle wheel, the spring brake actuator comprising an axially elongated housing having a parking brake chamber and a service brake chamber, a main compression spring within the parking brake chamber, a flexible diaphragm within the parking brake chamber, and a pressure plate located between the main compression spring and the flexible diaphragm, wherein: The flexible diaphragm includes a shaped contoured portion that inhibits radial movement of the pressure plate relative to the flexible diaphragm; wherein the primary compression spring is axially movable to and between a compressed position and an extended position, wherein the pressure plate has a flat radial outer diameter, and wherein the shaped contour abuts the flat radial outer diameter of the pressure plate at least when the primary compression spring is in the extended position, thereby inhibiting radial movement of the pressure plate; wherein the flexible diaphragm includes a radial outer diameter that seals against a boundary of the parking brake chamber, and wherein movement of the main compression spring from the compressed position to the extended position causes an inversion of the flexible diaphragm relative to the radial outer diameter of the flexible diaphragm; wherein the flexible diaphragm includes a radial center portion axially adjacent the pressure plate and an intermediate portion radially between a radial outer diameter of the flexible diaphragm and the radial center portion, and wherein the contoured portion is located along the intermediate portion; wherein the intermediate portion comprises a flat angled sidewall that tapers radially inwardly from the radially outer diameter of the flexible diaphragm toward the shaped contour portion; and wherein the shaped profile inhibits radial movement of the pressure plate at least when the main compression spring is in the extended position; and wherein the shaped contour defines a recess in which the flat radial outer diameter of the pressure plate is disposed at least when the main compression spring is in the extended position, wherein the recess abuts and wraps around the entire flat radial outer diameter at least when the main compression spring is in the extended position.

2. The spring brake actuator according to claim 1, wherein: The pressure plate nests within the contoured portion at least when the main compression spring is in the extended position.

3. The spring brake actuator according to claim 1, wherein: The flexible diaphragm has a relaxed state when removed from the housing, and wherein the shaped contour defines the recess when the flexible diaphragm is in the relaxed state.

4. The spring brake actuator of any one of claims 1 to 3, further comprising a push rod assembly having a first end adjacent the flexible diaphragm and an opposite second end extending out of the service brake chamber.

5. The spring brake actuator according to claim 4, wherein: The pressure plate includes a hub, the flat radial outer diameter, and a flange extending radially from the hub to the flat radial outer diameter.

6. The spring brake actuator according to claim 5, wherein: The main compression spring surrounds the hub and abuts the flange.

7. The spring brake actuator according to claim 6, wherein: The pressure plate includes a recessed cavity that mates with the first end portion of the push rod assembly and a central portion of the flexible diaphragm.

8. The spring brake actuator according to claim 7, wherein: The first end of the push rod assembly includes an end plate disposed within the cavity such that the flexible diaphragm is sandwiched between the end plate and the cavity of the pressure plate.

9. The spring brake actuator of claim 4, wherein: Pressurizing the parking brake chamber compresses the main compression spring, thereby retracting the push rod assembly into the service brake chamber and disengaging the wheel brakes from the wheels of the vehicle, and, wherein depressurizing the parking brake chamber allows the main compression spring to move the push rod assembly out of the service brake chamber, thereby engaging the wheel brakes with the wheels of the vehicle.

10. A spring brake actuator assembly for braking a vehicle wheel, the assembly comprising a flexible diaphragm for positioning in a parking brake chamber of the spring brake actuator, and a pressure plate for positioning between a main compression spring of the spring brake actuator and the flexible diaphragm, wherein: the pressure plate includes a hub, a flat radial outer diameter, and a flange extending radially from the hub toward the flat radial outer diameter, and wherein the flexible diaphragm includes a shaped contoured portion that abuts and wraps around the entirety of the flat radial outer diameter to inhibit radial movement of the pressure plate relative to the flexible diaphragm, at least when the primary compression spring is in an extended position; wherein the shaped contour defines a recess in which the flat radial outer diameter of the pressure plate is disposed at least when the main compression spring is in the extended position, wherein the recess abuts and wraps around the entire flat radial outer diameter at least when the main compression spring is in the extended position.

11. The assembly according to claim 10, wherein The flexible diaphragm has a relaxed state when removed from the housing, and wherein the shaped contour defines the recess into which the flat radial outer diameter nests when the flexible diaphragm is in the relaxed state.

12. A spring brake actuator for braking a vehicle, the spring brake actuator comprising a housing having a parking brake chamber and a service brake chamber, a main compression spring within the parking brake chamber, a flexible diaphragm within the parking brake chamber, and a pressure plate located between the main compression spring and the flexible diaphragm, in, The main compression spring is axially movable to a compressed position and an extended position, wherein the pressure plate includes a flange extending radially to a flat radial outer diameter, wherein the flexible membrane comprises a radially central portion adjacent to the flange and a shaped contoured portion, and wherein the shaped contour defines a recess in which the flat radial outer diameter of the pressure plate is disposed at least when the main compression spring is in the extended position, and wherein the recess abuts and wraps around the entire flat radial outer diameter of the pressure plate at least when the main compression spring is in the extended position and thereby inhibits radial movement of the pressure plate at least when the main compression spring is in the extended position.

13. The spring brake actuator of claim 12, wherein: The pressure plate is nested in the recess at least when the main compression spring is in the extended position.

14. The spring brake actuator of claim 12, wherein: The flexible diaphragm has a relaxed state when removed from the housing, and wherein the shaped contour defines the recess when the flexible diaphragm is in the relaxed state.

15. The spring brake actuator of any one of claims 12 to 14, further comprising a push rod assembly having a first end adjacent the flexible diaphragm and an opposing second end extending out of the service chamber.

16. The spring brake actuator of claim 15, wherein: The pressure plate includes a recessed cavity that mates with the first end portion of the push rod assembly and a central portion of the flexible diaphragm.

17. The spring brake actuator of claim 16, wherein: The first end of the push rod assembly includes an end plate disposed within the cavity such that the flexible diaphragm is sandwiched between the end plate and the cavity.

18. The spring brake actuator of claim 17, wherein: Pressurizing the parking brake chamber compresses the main compression spring to retract the push rod assembly into the service brake chamber and disengage the wheel brakes from the wheels of the vehicle, and wherein depressurizing the parking brake chamber allows the main compression spring to move the push rod assembly out of the service brake chamber to engage the wheel brakes with the wheels of the vehicle.

19. A spring brake actuator for braking a vehicle, the spring brake actuator comprising: a housing having a first chamber and a second chamber; a flexible diaphragm within the first chamber; a main compression spring, the main compression spring being within the first chamber and movable to a compressed position and an extended position; as well as a pressure plate positioned between the main compression spring and the flexible diaphragm, the pressure plate having a flange with a flat radial outer diameter; wherein the flexible diaphragm includes a shaped contoured portion defining a recess in which the flat radial outer diameter is disposed at least when the main compression spring is in the extended position, the recess abutting and wrapping around the entire flat radial outer diameter at least when the main compression spring is in the extended position, thereby inhibiting radial movement of the pressure plate at least when the main compression spring is in the extended position.

20. The spring brake actuator of claim 19, wherein: The flexible diaphragm has a relaxed state when removed from the housing, and wherein the shaped contour defines the recess when the flexible diaphragm is in the relaxed state.

21. The spring brake actuator of claim 19, wherein: The primary compression spring abuts the flange and surrounds the hub of the pressure plate.

22. A spring brake actuator according to any one of claims 19 to 21, wherein: The pressure plate includes a concave cavity adjacent a central portion of the flexible diaphragm.

23. The spring brake actuator of claim 22, further comprising a push rod assembly having a first end adjacent to the flexible diaphragm and an opposing second end extending out of the second chamber.

24. The spring brake actuator of claim 23, wherein: The first end of the push rod assembly includes an end plate disposed within the cavity such that the flexible diaphragm is sandwiched between the end plate and the pressure plate.

25. The spring brake actuator of claim 24, wherein: Pressurizing the first chamber compresses the main compression spring, thereby retracting the push rod assembly into the second chamber and disengaging the brake from the vehicle, and wherein depressurizing the first chamber allows the main compression spring to move the push rod assembly out of the second chamber, thereby engaging the brake with the vehicle.

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