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1-Newbie

Finding the Actual Force and Brake Capacity of a Long-Shoe Internal Drum Brake

This worksheet will:

• Determine the actuating force and the brake capacity of a long-shoe internal brake
• Apply to mechanical engineering and the automotive industry
• Perform using brake geometry, coefficient of friction, maximum pressure, actuating force, braking capacity, assumed pressure distribution, friction force moment, normal force moment, torque, etc.

This worksheet using PTC Mathcad shows you how to determine the actuating force and the brake capacity of a long-shoe internal brake. For this particular worksheet the long-shoe brake is actuated by a device that exerts the same force on each shoe and the shoes are identical in form and are symmetrically position about the vertical centerline. The worksheet begins by listing the parameters of the brake geometry and the brake line properties. These include:

• Face width of shoe
• Distance from the center of the drum and vertical axis of symmetry to the shoe pivot
• Moment arm distance of actuating force to the shoe pivot
• Angle from shoe pivot to heel and toe of lining
• Coefficient of friction
• Maximum allowable pressure

To solve, the worksheet first shows you how to calculate for the assumed pressure distribution for the long-shoe brake. Because the clockwise drum rotation causes the right-hand shoe to be self-energizing, you can determine the actuating force on the basis that the maximum allowable pressure will occur there. The worksheet then shows you how to calculate for the friction force moment, the normal force moment, the torque applied to the drum, and the actuating force.

Next, the worksheet shows you how to calculate for the pressure on the left-hand shoe, along with the torque applied to drum and the brake capacity. All images, notation, formulas, calculations, data, and solutions are provided to aid you in your own calculations.