Status: Finished (Collaborator Student Work. Not PFC)

Introduction:

           When driving a car, everyone likes to have the maximum of possible data(speed, rpm...).  But when we talk about a competition vehicle, the information becomes crucial for the driver, always looking for better lap times.

            One of the major subjects on the Lab's Car Cross not yet undertaken was to know the selected gear.  Up to now, the driver, in addition to being concentrated on keeping the Melmac Car Cross on the track, had to memorize the last gear he had inserted. That was because our vehicle mounts a stock Honda CBR 600F six-gear sequential gearbox, like most of the FSAE and Car Cross teams do. This situation was of course very uncomfortable and we proposed to visualize the selected gear on the mounted GEMS display (http://www.gems.co.uk/). A system that carries out this function has been designed, manufactured and mounted at the Lab. It is detailed in the following lines. 

Performance:

           The gearbox of our vehicle is integrated in the own engine block using a system of three yokes guided by tappets to arrange the different combinations of gears. It gives as a result the 6 transmission relations.  The position of these tappets is determined by a drum that turns almost 360 degrees and that has three furrows for the corresponding guides. Knowing the position (rotated angle) of this drum, we know the gear inserted.

To measure this turn we use a potentiometer inserted in a purpose-built part inside the hole of the 'Neutral' switch of the engine and it receives the movement of the drum selector through gears. 

Fist of all, the drum has been mechanized creating the necessary cylindrical surface to be able to lodge tight the pinion that will be used for transmitting the turn.  This large pinion, as well as the small one, has been mechanized using wire-cutting technology. The different pieces that compose this joint are fundamentally revolution pieces maintaining the engine block hermetic and the potentiometer isolated from external elements. 

         The mechanism that adapts the potentiometer with the small pinion is made of three pieces.  The main piece, that supports the system, is screwed in the tighter part in order to being able to hitch it to the engine. In the inside part, and moving us from left to right, the first element is an axle that is joint to a small pinion making up an only piece.  This axle-pinion has two lodgings for washers that retain the oil avoiding discharges. It also has a hole that by means of an elastic pin will be used to join the axle-pinion to the interior case.

This interior case must transmit the turn of the axle-pinion to the offspring of the potentiometer. The union between case and potentiometer is carried out by means of a prisoner. 

Finally, because of assembly reasons the potentiometer is not mounted directly to the support but primarily is curled in a case that subsequently is set to the backup by means of another prisoner. 

The potentiometer works with 5 V and it revolves 4,5 turns. We take advantage of almost all the voltage (it is a 5 turn potentiometer). The signal taken from the potentiometer is conducted to the GEMS Data logger and also to the display, where it can be calibrated and easily visualized.

clic here to see the drawing