Spring brake actuator

A spring brake actuator for braking a wheel of a vehicle, the spring brake actuator comprising 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 located between the main compression spring and the flexible diaphragm, wherein the flexible diaphragm comprises a contoured portion that inhibits radial shifting of the pressure plate with respect to the flexible diaphragm;

• wherein the main compression spring is axially movable into and between a compressed position and an extended position, wherein the pressure plate has a hub portion and a radial flange that is planar and radially extends from the hub portion to a planar radially outermost diameter, and wherein the contoured portion abuts the planar radially outermost diameter of the pressure plate, at least when the main compression spring is in the extended position, thereby inhibiting the radial shifting of the pressure plate;
• wherein the flexible diaphragm comprises a radially outermost diameter that is sealed to perimeter 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 radially outermost diameter of the flexible diaphragm;
• wherein the flexible diaphragm comprises a radial center portion that axially abuts the radial flange of the pressure plate and an intermediate portion located radially between the radially outermost 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 planar angular sidewall that radially inwardly funnels from the radially outermost diameter of the flexible diaphragm to the contoured portion;
• and
• wherein the contoured portion has a uniform thickness and defines a pocket in which the planar radially outermost diameter of the pressure plate is disposed, at least when the main compression spring is the extended position, and wherein the contoured portion wraps around an entirety of the planar radially outermost diameter of the pressure plate at least when the main compression spring is in the extended position and thus inhibits the radial shifting of the pressure plate at least when the main compression spring is in the extended position.