Throttle
Throttles are a part of the Intake system used to modulate Engine output.
Contents
Throttle Form Factors
Butterfly
Butterfly valves are the most common throttle valves used in industry and automotive racing.[1]
As butterfly valves open, the cross sectional area does not increase linearly with the throttle open percent. The opening ideally changes as a function where is throttle angle. In the real world, the throttle valve must be attached to a shaft that becomes the dominant obstruction to airflow at higher throttle angles. Where the shaft becomes the significant obstacle depends on both the throttle and shaft diameters[2]. The relationship between your throttle angle and true air flow can be found on a flow bench or a validated simulation if the manufacturer cannot supply the data.
The truncated cosine function gives the butterfly valve an inherent progressive throttle response: the rate of throttle opening increases as the pedal is pushed. This translates to fine control at low throttle angles and a quick response to high throttle angles. However, some drivers may desire a more progressive less progressive throttle than inherent to your system. This is a tunable parameter by swapping out the cam on the throttle bod itself or adding a cam to the pedal. A progressive throttle response combined with certain engine tunes or tuning strategies can produce a jump in torque felt throughout pedal travel known as throttle snatch. This can be tuned out or "tamed" with a cam on the throttle body or pedal. Commercial cams and cam-tamers are available for motorcycles and can easily be mimiced or adapted for use in FSAE.
An electronic throttle control system (ETC) can be used to create and easily modify a function of throttle pedal % to of any desired shape.
Barrel
Barrel Throttle are not as common in FSAE but have been used. Teams who run them usually cite the lack of restriction at the higher end of throttle angles present in butterfly valves. This means a smaller barrel throttle body can be used than a comparable butterfly valve. They also have a more linear inherent throttle response compared to the progressive nature of the butterfly. They are harder to manufacture as they require tighter tolerances over larger areas. Barrel throttle's are also heavier and the valve itself has a higher rotational inertia.
Slide
Iris
Cabling
If using a cable actuated throttle, the choice and routing of cable are important considerations. A push-pull cable has negligible stretch/flex over time and will give the greatest consistency [citation needed for stretch comparison].
Other popular choices are shifting and brake cables used on bicycles. Brake cables are often thicker than shifter cables[1]. A steel cable will always have some stretch, and a thicker gage will stretch less. The housings supplied for brake and shifter cables are also different. Bicycle brake cable housing has steel reinforcement wrapped in a spiral along the length of the housing. Shifter cable housing has longitudinal reinforcement that leads to the cable being incompressible, but the minimum bend radius can be compromised..
Cable fittings are either swage or swageless. Swage fittings are permanently attached by crimping (swaging). Swawgeless fittings can be attached to the cable in a number of ways including set screws or collets. [citation for fittings] Swageless fittings allow for a degree of adjustment as the cable stretches.
[insert image of swageless v swage fittings]
Dry lube like graphite or molybdenum disulfide are the best go to for high quality cable sheathing. However, if the cable is in a wet/humid environment or the sheathing is old or slightly damaged, a liberal dose of a high quality oil such as motor oil is desirable[citation needed]. Non-synthetic oils like mineral oil can degrade the cable housing [citation needed]. WD-40 may also degrade the housing and will dissolve the lubricant applied to the cable by the manufacturer [citation needed].
Further reading here: https://www.sheldonbrown.com/cables.html
Electronic Throttle Control
- Main page: Electronic Throttle Control
overview and driving rationale how it fits into system
not specific design info
- ↑ https://www.jenvey.co.uk/support/faqs/donec-at-velit-massa/
- ↑ Bordjane, Mustapha, and David Chalet. Journal of Multidisciplinary Engineering Science and Technology (JMEST), vol. 2, no. 12, Dec. 2015, pp. 3532–3541., http://www.jmest.org/wp-content/uploads/JMESTN42351286.pdf?msclkid=591985f1b68911ec9bab58abc221607d.
