Milestone 12: Alternative Clutch Testing
Centrifugal Clutch with Manual Override via Throwout Bearing
Alternative Clutch Design
Due to concerns about the longevity and tunability of the proposed electric clutch design, the Wildcat Pulling Team asked that other clutch alternatives be investigated before settling on a final clutch design. The team worked with project advisor Dr. Sama to formulate an alternative clutch design that utilizes the centrifugal Bully clutch that has proven reliable for past Wildcat pulling tractors. This alternative design utilizes a hydraulic throwout bearing to manually engage the clutch below its designated speed threshold. This allows for movements at lower ground speeds than possible through regular centrifugal actuation. This design also allows the throwout bearing to be used as a clutch lock-out, thus preventing the clutch from disengaging during high load scenarios. The clutch is actuated via a Wilwood brake pedal and actuates similarly to a inching pedal on a forklift.
Dynomometer Data
The graph above display dynamometer data collected during the proof of concept testing. The automatic engagement threshold for the clutch is 2700 RPM. During this test, a dyno pull was conducted in which the engine was idled up to 3250 RPM. The throwout bearing was engaged before applying the load to simulate a driver locking the clutch in during a pulling event. The clutch was continuously loaded well below the engagement threshold (2100 RPM). The maximum torque seen during testing (48 ft-lbs) was as expected based on previous dynamometer tests. The performance illustrated by this test has made the team confident that this design concept will provide the desired improvements in maneuverability by allowing the driver to engage the clutch at a lower RPM without diminishing the pulling capability of the vehicle.
Clutch Engagement with Hydraulics
Overall, the testing was a success. The main concern was the throwout bearing wearing out the flyweights on the clutch head. This was not observed at all. The hydraulic clutch engagement was very smooth and proves to have a high amount of potential.
Some negative observations include an incredibly high temperature that burned the grease on the needle bearings. In addition, the brass flange sleeve bearing wore out to the point that the mechanism would no longer engage. Also the pedal mechanism requires a lot force, so either a smaller hydraulic cylinder or a larger lever arm on the pedal is needed. If this design concept is selected, these failure points will be addressed in the next design iteration.