Spring applied, electric released drum brake

A spring-applied, electrically released drum brake, comprising:

• a rotatable brake drum,
• first and second brake shoes pivotally operable between brake-applied and brake-released positions, relative to said brake drum, with the pivot points of said first and second brake shoes being disposed, relative to the rotational axis of said brake drum, to be self-energizing in one direction of rotation of the brake drum, and partially deenergizing in the other direction,
• means for operating said first and second brake shoes including an axially displaceable rod member, and means mechanically linking said rod member and said first and second brake shoes,
• first compression spring means on said rod member, said first compression spring means being pre-compressed to bias said rod member in a first axial direction which biases said first and second brake shoes towards the brake-applied position, with a first predetermined force,
• electromagnetic means arranged for selective energization and deenergization,
• second compression spring means on said rod member,
• said electromagnetic means being arranged to compress said second compression spring means when said electromagnetic means is energized, said electromagnetic means compressing said second compression spring means without axial movement of said rod member until the stored force in said second compression spring means exceeds the stored force in said pre-compressed first compression spring means, at which time said rod member is moved in a direction opposite to said first axial direction to operate said first and second brake shoes to the brake-released position,
• and control means for controlling the release of the stored force in said second compression spring means when the electromagnetic means is deenergized and said rod member moves in the first axial direction to operate said first and second brake shoes from the brake-released to the brake-applied position,
• said first and second compression spring means being arranged relative to said rod member such that movement of said rod member in the first axial direction causes the braking force applied to said brake drum by said first and second brake shoes to be responsive to the difference between the stored forces in said first and second compression spring means at any instant, to cause the braking force applied to said brake drum to start at a low value and increase to substantially the first predetermined force according to the rate at which said control means allows the second compression spring means to release its stored force.