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 planar radially outer diameter, and wherein the contoured portion abuts the planar radially outer 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 outer 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 outer diameter of the flexible diaphragm;
• wherein the flexible diaphragm comprises a radial center portion that axially abuts the pressure plate and an intermediate portion located radially between the radially 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 planar angular sidewall that radially inwardly funnels from the radially outer diameter of the flexible diaphragm to the contoured portion;
• and
• wherein the contoured portion inhibits the radial shifting of the pressure plate at least when the main compression spring is in the extended position.