Brake Pedal Arm

Introduction

The objective of this project was to design and optimize a brake pedal arm that could withstand a load of 100 lbf (444.8 N). Under load, the pedal arm must not deflect any more than 3” (76.2 mm) on the end and upon lifting the load, the point of contact with the Instron probe must not have deflected any more than 0.020” (0.5 mm). The pedal arm must fit onto a 0.50” diameter mounting pin, it must rotate onto a 0.50” diameter stopping area, and the load will be applied to a ball bearing with a diameter of 9/32”. Minimizing the weight of the pedal arm is the priority.

Design

The design was created in SolidWorks. It was made with straight but angled edges which are moderately difficult to machine but removes a considerable amount of material, reducing weight. For the creation of the design, a basic layout of the pedal arm that included all of the given parameters was first sketched. Its key components included a hole for the mounting pin, a curve for the stopping area, a load area, and a “bridge” between the mounting area and the load area. A pedal arm thickness of 1 inch was determined to be optimal, as it allows for the pedal to rotate and rest onto the curved stopping area for support. Material was cut away from areas that were not providing significant support to withstand the load. These areas included the section under the load area and the sections around the stopping area and mounting pin. The removal of material not only focused around reducing weight but also around fitting into a smaller and cheaper stock size. The width of the “bridge” was then adjusted to provide a minimum safety factor of 1.5 and to maintain the residual vertical deformation below 0.02”.

Fabrication

The pedal was fabricated in the UMass Amherst Mechanical and Industrial Engineering Machine Shop using a Bridgeport milling machine. The stock used was a 1.25” thick by 3” wide by 6” long block of 6061-T6511 aluminum.

For failure analysis, the shear and von Mises strength theories were considered since they apply to ductile materials like aluminum. The minimum safety factor using shear theory is 1.492. The minimum safety factor is 1.555 using von Mises theory.

Testing

The pedal was tested using an Instron machine which applied a load to a ball bearing placed in the 9/32" ball bearing hole. The force and deflection data were recorded by LabVIEW software. The pedal was first gradually loaded until the force applied reached 445N (100 lbf). The vertical deformation under this load was recorded along with the residual deformation after the load was removed. Then, the pedal was loaded to its failure load, which is defined as the load value at which the instantaneous slope of the pedal’s load curve decreases to 50% of its average slope.

The pedal arm passed all the testing requirements. The deflection under the 445N (100 lbf) load was 2.07 mm, whereas the requirement was below 76.2 mm. The residual deflection was 0.22 mm, while the requirement was below 0.5 mm. Finally, the failure load was approximately 2180 N (490 lbf), which is nearly 5 times the required load bearing ability of 445 N (100 lbf).