Fluid-operated spring brake atuator with funnel-shaped pressure plate

In a fluid-operated diaphragm spring brake actuator, having a service brake actuator in combination with a spring brake actuator, the service brake actuator having a 2housing, an elastomeric service diaphragm suspended in the housing to divide the interior thereof into a first service chamber and a second service chamber, a service housing pressure plate in the second service chamber adjacent the service diaphragm, a push rod abutting the service pressure plate and connected to a brake mechanism;

• the spring brake actuator having a housing, an elastomeric spring diaphragm suspended in the housing to divide the interior thereof into a first spring chamber and second spring chamber, a spring pressure plate adjacent to the spring diaphragm in the first spring chamber, a spring in the first spring chamber between the spring pressure plate and the housing, and an actuator rod in the second spring chamber for actuating the brake mechanism in response to movement of the spring diaphragm and spring pressure plate, the actuator extending into the first spring service chamber and contacting the service diaphragm, the improvement wherein:
• the spring pressure plate has a tubular portion adjacent to the actuator rod at an end of the actuator rod in the first spring chamber and a flared portion extending obliquely away from the tubular portion.

In a fluid-operated diaphragm spring brake actuator having a housing with first and second opposing walls, an elastomeric diaphragm suspended in the housing to divide the interior of the housing into first and second chambers, the first wall partially defining the first chamber and the second wall partially defining the second chamber, a pressure plate in the first chamber and adjacent to the diaphragm, a spring in the first chamber between the pressure plate and the first wall, and an actuator rod in the second chamber for actuating a brake mechanism in response to movement of the diaphragm and the pressure plate from a retracted position, the improvement wherein:

• the pressure plate generally has the shape of a hollow cone with a vertex pointed toward the first wall and a flared portion extending generally toward the second wall, the area of the flared portion forming a significant part of the total surface area of the pressure plate, wherein a portion of the diaphragm generally follows the contour of the pressure plate with the actuator rod being received within the hollow of the cone whereby to minimize the maximum volume of fluid in the second chamber when the diaphragm and pressure plate are in the retracted position.