Air brake with collet locked push rod and excessive force reducer

A pressurized fluid actuated brake comprising:

• a brake housing defining a service brake chamber and a collet brake chamber;
• a push rod mounted to the housing for movement in brake on and brake off axial directions towards brake on and brake off positions;
• means, including a service brake diaphragm operably coupled to the push rod and responsive to the presence of a pressurized fluid within the service brake chamber, for driving the push rod towards the brake on position when the service brake chamber is at a first pressurized state;
• and
• collet means, operably coupled to the push rod and responsive to the presence of a pressurized fluid within the collet brake chamber, for selectively restricting movement of the push rod towards the brake off position, said push rod restricting means including:
• a collet having a bore and a radially deflectable portion surrounding at least a portion of the bore, said radially deflectable portion including an external surface;
• said housing defining an axially movable collet bore portion having an internal surface sized and positioned for mating engagement with said external surface, at least one of said internal and external surfaces being tapered;
• a collet brake diaphragm partially defining the collet brake chamber;
• means for mounting the collet to the collet brake diaphragm for movement of the collet in response to the presence of pressurized fluid within the collet brake chamber so to bias said collet away from said collet bore portion to disengage said external and internal surfaces when the collet brake chamber is at a second pressurized state;
• said push rod including a movement limited bar partially housed within said collet bore portion and sized for complementary sliding engagement within the collet bore portion;
• spring means for driving the collect into the collet bore portion when said collect brake chamber is in a third pressurized state to lock the movement limiting bar in place thereby restricting movement of the push rod towards the brake off condition;
• and
• means for axially biasing the collect bore portion in the brake on axial direction, whereby the collect moves the collet bore portion in the brake off acial direction when an excessive force is applied to the push rod so to reduce such excessive force on the push rod.