Clutch Lever

The clutch lever is the interface  between the driver and the clutch in the engine. The clutch is used in order to engage and disengage the power transmissions.

The clutch cable was routed through a machined cable restraint. This restraint was be mounted on the steering lip with an epoxy and align with the hole in the clutch lever. With the cable restraint, we adjusted where the cable will separate from its cover. This method allowed easier installation on the car as well.

After the annual competition, there was positive feedback from drivers that the design of the clutch lever was done well. It was easier for the drivers to grip the lever with the T-shaped handle and the mechanical advantage has helped them to engage and disengage easily.

CAD Model & Specs

Weight
  • Total: 0.209 lb
  • Lever: 0.196 lb
  • Clevis: 0.013 lb
​Material
  • 6061 Aluminum (Yield Stress at 40 ksi)

​Calculated Force
  • Force needed to pull the lever: 18.8 lbf
  • Range of driver's pulling force: 15 ~ 20 lbf
  • ARG required 20 lbf to pull, but drivers did not complain in the past.
Dimensions
  • Lever:
    • 0.5'' diameter and 3.5'' height Aluminum tube welded to
    • L-shaped rod of 6.5'' long,  0.75'' wide, and 0.5'' thick.
      • Cable travel arm 1.25'' 
      • Mechanical advantage of 3.4 
      • 23.58 degrees of travel, giving 0.5'' cable travel

  • Clevis:
    • 1'' long, 0.75'' wide, 0.5'' thick bar  machine milled
​
  • Cable Length:
    • Sheath Length of 57'', Free Length 4''

Design Information

Goals
  • The clutch lever should be ergonomic, comfortable, and easy to grasp and pull.
  • The driver should be able to easily pull the clutch completely in quickly during to avoid stalling when spinning out and also to avoid accidentally applying power when  out of control.
  • The driver should be able to quickly drop the clutch for a launch.
  • The driver should be able to slowly let the clutch out with finesse in order to crawl from stand still.
  • The driver should be able to keep the clutch pulled in comfortably for at least a few minutes at a time.
Parameters
  • The pulling length of the clutch should be the same or longer than the displacement of the clutch in the engine.
  • The pulling force of the driver should be the same or larger than the force required to actuate the clutch.
  • There should be enough clearance space for the driver's hand to pull the lever with his/her gloves on.
Optimization Processes and Decisions
  • The total length of the lever should be as long as possible while the location of the cable end in the lever is close to the pivot point, allowing greater leverage, which means a greater mechanical advantage. 
  • The total length of the lever should be moderated on the other hand when regarding the space allowed in the monocoque and the weight reduction.
  • The design of the lever and the mount should be simple to manufacture.
  • In terms of reducing friction of the pivot, I changed from use of  bushings to washers due to manufacturability.
Need-to-know  Facts
  • Check the displacement of the clutch pull from that year's dynamometer.
  • Check the force needed to pull the clutch from that year's dynamometer.
  • Check the driver's pulling force to calculate minimum mechanical advantage.
  • Check how much space is available between the steering lip and the steering wheel. Also check space availability from the monocoque for the length of the lever.
  • Know how cable works: sheath length and free length.
  • Know the dimension of the cable ends.
  • Know  average clearance space needed for the driver.
  • Communicate with drivers and past designers of the part.
  • No sharp corners for manufacturing purpose.
  • Know the importance of the clutch lever: without it, the car cannot run.

Manufacturing Drawings

Simulation

  • Lever Pulling Test
  • Lever Bending Test
  • Clevis Pulling Test

Point Analysis

The length of the lever is designed that it has a  good amount of mechanical advantage.    The mechanical advantage of 3.4 should allow the driver to pull the clutch lever with no difficulty. The driver only pulls 20 lb of force. 

The lever is designed in T-shape and is behind the steering wheel so that whenever the driver need to reach for the lever, it is hard to miss it. When there is a T-shaped handle, a person naturally puts his/her index finger on the upper part of the lever and puts rest of fingers on the lower part of the lever. By gripping in such way, there is less torque generated around the other axis. If the lever was L-shaped like ARG13, then a torque from minor axis will be generated, which does no good but deforms the lever in terms of torsion.

The driver will be reaching for the lever by not reaching his/her hand, but with fingers. Finger size of each person should not differ greatly. There is about two inch space behind the steering wheel. An average person's fingers are longer than two inches, so there should be no difficulty for different drivers, unless the driver's hand is huge.

​Moreover, the retention method for the cable is much simpler compared to ARG13. ARG 13 used a coupling nut and two opposing drilled and slotted bolts. The installation of ARG13 clutch lever became an issue due to complexity. The clutch lever design for ARG15 is much simpler with a cable restraint. The cable restraint serves a wall for the cable cover to be fixed while the cable wire is pulled. 

Bill of Materials (BOM)