For over 45 years Hewland Engineering has made automotive gearboxes for racing purposes. They have had immense success in Formula 1, World Rally, FIA Sportscars, IMSA, Le Mans, Grand AM, Trans AM, Japan GT, F3000 and countless other series. I have decided to design a 6 speed sequential gearbox to mate with an engine I designed in the third semester. Sequential gearboxes work in a different way then regular H-pattern gearboxes; although the basic idea is the same, the shifting mechanism is different.
The gearbox will be based on the Hewland TLSa model. This gearbox is for mid-engine rear wheel drive cars because of its small compact design; it also eliminates the need for a differential as it is built into the transmission. The shifting order is, R-N-1-2-3-4-5-6; with the option for an additional neutral gear after the 6th gear, used mainly in racing applications. The power comes from the engine through the input shaft on which the input gears are located. The input gears are connected to the output gears on the output shaft. While the output gears rotate freely on the output shaft because it is in the neutral. When the driver pulls the shift lever back it send an electric signal to a solenoid which is activated to turn the selector barrel; when it rotates it moves the selector fork forward. When the selector fork is moves forward, the fork disc makes contact with the output gears through dogteeth. Now the output shaft has a "direct contact" with the output shaft and it turns transmitting the power out. At the end of the output shaft another gear is there to change the sense of the rotation; this can be accomplished two way either by the use of a worn gear and a spur gear, or by using two bevel gears. The approach used in the final is drive is similar when either approach is taken to convert the rotation perpendicular. When a worm gear and spur drive are used; the spur gear is directly connect to another larger spur gear which is in contact with another larger spur gear, this converts the rotation making the car move forward instead of backwards. It is the same design when two bevel gears are used; but in this situation the smaller spur gear is directly connected to the second bevel gear instead of a spur gear; from there on it is the same operation. It is extremely hard to explain and understand the operation of the gearbox without an animation.
