Two Guys Rally

Electromotive Sequential Transmissions
[ June 18th, 2008 ] By: Charles Smith Posted in » Technical Articles

The standard transmission, a.k.a. manual, is found in most cars with an H-Pattern mechanical gear selector. But there are faster and easier ways to select gears. What I would like to focus on in this post is the Electromotive Sequential Transmissions.

Sequential Transmissions

First I need to explain what the difference between a standard transmission and a sequential transmission is. In the standard transmission it is possible to select any gear at any time (given enough force). However in a sequential transmission you must either select the next or previous gear from the one the transmission is using. For example, if I were in 3rd gear I could either choose 2nd or 4th. It would be impossible to skip to 5th or 1st without going through the next in the sequence, hence their name ’sequential’. I am told that this can make the mechanical workings of the transmission simpler (see motorcycle transmissions) but I wont even attempt to explain it (ask Mark).

Motorcycles are the vehicle most commonly associated with sequential transmissions. Their gear selector has 3 positions: Up Shift, Down Shift and No Change. the ‘No Change’ position is the default position. If we transition the sequential transmission into a Car nothing changes. There will be 3 positions for the gear selector, but we may make the transmission a little more complex in order to reduce weight.

Electronic Gear Selectors

Mechanical gear selectors are heavy, and depending on how they are constructed may make it harder to select gears, so we can make the gear selector electronic. That will save on weight (what is used to shift is a few thin copper wires) and allow us to place the selector anywhere in the cockpit. It also has the added benefit of reducing driver fatigue as it will be physically easier to select gears. It is not just as simple as saying “Let’s make it electronic” and then we’re done: we have to get the force to select a gear from somewhere. That somewhere can be a few places. We can use compressed air to operate a pneumatic arm that controls a short mechanical linkage on the transmission. Perhaps, if we have enough electrical current coming from the alternator we can use that to power a solenoid to operate a short mechanical shifter (on the transmission).

Both Electro-Pneumatic (Electro because the gear selector is electronic) and Electro-Mechanical Sequential Transmissions have their downsides. The Pneumatic variety require compressed air to be stored in the car, but this could be lighter than the alternate Electronic Solenoid approach. However refilling or punctures could make a less competitive race car or even end a race day. While the Electro-Mechanical types have much more weight associated with the system and are slower to respond (shift time matters!!!).

WRC vs Rally-America

Electro-whathaveyou Sequential Transmissions are a common sight in the WRC, but the H pattern is the only transmission allowed in the rules of Rally America. And that brings me to this: Why does Rally-America disallow Electromotive Sequential Transmissions? Is it a strategy to make Rally Racing cheaper and more accesible? Is it to keep the cars closer to stock so fans can say: I DRIVE THAT! ? I’d like to hear your opinions on this and I would like to go into further detail about Electro-Pneumatic Transmissions in the future.