At Home Mechanic

The Brake and Clutch pedal are easy to understand because they are really connected to the items they are named for. OK, you nitpickers could drag me over the coals for not disclaiming that the Brake and Clutch pedal in most modern street cars are actually attached to a hydraulic system that in turn activates the Brakes and Clutch. But when you step on "The Brakes" friction materiel will convert motion into heat and in turn stop the car. If you have a car with a Clutch Pedal, stepping on it will activate the clutch, which is mechanical connection between the engine's flywheel and the transmission.

Mash down on the Gas Pedal and the car goes. But what is the pedal physically attached to? In the days before fuel injection, the gas pedal was physically linked through the car's firewall to the carburetor by a Rube Goldberg system of levers and rods that pushed, pulled and rotated to make the butterflies flutter open (perhaps the most poetic operation in all of mechanical engineering) in the throat of the carb to allow air to flow into the carburetor. Also invited to this party in the carb is gasoline, which arrives from by fuel jets that deliver pressurized fuel from a small pump in the carb. The swirling action of air and fuel meeting in the carb stirs the mixture to an explosive combination that is then delivered to the cylinders via the intake manifold. The spark plugs ignite this brew, explosions occur in the cylinders, pistons are thrust up and down, the crankshaft spins, power is transmitted to the wheels and the car goes. So way back in the day, the Gas Pedal was actually attached to the Gas (which was actually metered and mixed with air by the carburetor.)

That old-fashioned connection between the gas Pedal and the Carburetor of a series of rods and levers was perfectly adequate as long as it stayed aligned and lubricated. But as time passes the well-oiled connections in the linkage would get sticky and normal engine and road vibration could put the carefully arranged pieces out of whack. It was not uncommon for throttle linkages to get stuck, sometimes at open throttle with disastrous results. As a legacy of those times, technical inspectors for amateur car racing make a point of inspecting the throttle linkage of competing cars to insure safe operation.

The first improvement to the Gas Pedal to Carburetor connection was the introduction of the throttle cable to replace the linkage. A simple braided wire cable was used to supplant all that tricky throttle linkage. The throttle cable simplified the manufacturing process and made life for home hobbyists some much easier. One of my earliest memories was watching my Dad spread out the various linkage bits from a new four-barrel carburetor on the kitchen table so he could re-engineer it to work with the car he was trying to modify. If the throttle cable had been an available option to him the process would have taken minute rather than hours.

The Gas pedal stopped being attached to the fuel system when the electronic fuel injection system became common on modern automobiles. The Gas Pedal in the car's cabin was still attached to the engine compartment by a wire cable, but stepping on that pedal did not DIRECTLY (a special qualifier) induce more gas to enter the fuel mix. Stepping on "the gas" only opened a valve that allowed more air to enter the intake manifold. "Give her more gas": in fact became "Give her more air" The clever electronic fuel injection can sense the extra air entering the system and in turn order the fuel injection nozzles to squirt high pressure sprays of gas which atomizes and create a nearly perfect air/fuel mixture. The great leaps forward in fuel economy, performance and environmental protection that modern cars enjoy is largely due to advancements in fuel injection and precision ignition control that modern automobiles have enjoyed for the last 20 years.

The latest development in the "Gas Pedal" completely breaks the direct connection between the thingy down on the floor and the engine compartment. The very latest cars use a technology that was pioneered by NASA for the Apollo Program, refined in fighter jets and eventually trickled down to consumer use in our cars. Called Fly-by-Wire, the gas pedal no longer uses a wire cable or linkage to control the engine; instead a data stream is created by a sensor at the gas pedal that is sent to a central processor that evaluates a huge number of variables to sent a data message to the engine management system to add just the right amount of air and fuel to be mixed for the engine's needs. Pressing down on the "gas" is really just sending a signal to a computer that can be located anywhere in the car (usually hidden in the passenger compartment) and so that old-fashioned direct physical connection between the Gas Pedal and the Engine is completely broken.

Military Aircraft Manufactures are working hard to create a telepathic link between pilot and plane; a person would only have to think of the command and the aircraft will respond without any kind of physical input from a human. Eventually this technology could trickle down to consumer terrestrial vehicles. But hopefully the software will include a buffer to filter out random thoughts of road rage during commuting hours.