Electronic Throttle Controls

The drive-by-wire technology you might already have

accelerator pedal
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Until recently, throttle control systems were almost always very straightforward. The gas pedal was connected mechanically to the throttle, and pressing down on it would cause the throttle to open. Most vehicles accomplish that feat with a throttle cable and linkage, though there have been some that made use of more complicated systems of rigid bars and levers. In any case, there was always a direct, physical connection between your foot and the throttle.

Electronic engine controls complicated matters during the 1980s, but components like throttle position sensors were just designed to allow the computer to make adjustments. Throttle controls remained entirely mechanical, and physical cables and linkages were still the order of the day.

How Does Electronic Throttle Control Work?

Electronically-controlled throttles work just like traditional throttles, but there is no physical cable or linkage connecting the gas pedal to the engine. When the gas pedal is pressed in a vehicle that uses drive-by-wire technology, a sensor transmits data about the position of the pedal. The computer is then able to use that information to change the position of the throttle.

In addition to the actual position of the gas pedal, the computer can also rely on a variety of other information to determine the best course of action. Rather than simply opening or closing the throttle as a direct response to the position of the pedal, the computer may analyze the current speed of the vehicle, the temperature of the engine, the altitude, and other factors before opening or closing the throttle.

Why Is Electronic Throttle Control Needed?

Like many other advancements in the field of automotive technology, the main purpose of electronic throttle control is to increase efficiency. Since electronic throttle control technology can rely on numerous sensor inputs, these systems can operate with a much higher degree of efficiency than vehicles that use traditional throttle controls.

The use of electronic throttle control technology can result in improved fuel economy and reduced tailpipe emissions, largely due to the greater control it affords over air/fuel mixtures. That, of course, is due to the fact that these systems are capable of both setting the position of the throttle and adjusting the amount of fuel, while traditional systems can only tweak the amount of fuel to match the position of the throttle.

Electronic throttle control can also be seamlessly integrated with technologies such as cruise control, electronic stability control, and traction control, which can improve handling and increase safety.

Is Electronic Throttle Control Safe?

Whenever any form of technology is placed in between a driver and the vehicle he is in control of, it creates the potential for at least some level of risk. When you drive a vehicle that uses traditional throttle controls, you are typically relying on a Bowden cable to actuate the throttle. This type of cable consists of a wire inside a plastic sheath, and they fail regularly. The cable can become stuck in the sheath, or it can wear through and ultimately break. The end of a Bowden cable can also snap off, which will render it useless.

In most cases, a failed throttle cable will result in a vehicle that is unable to accelerate. If that occurs at freeway speeds, it can result in a very dangerous situation. However, it is relatively rare for a traditional throttle cable to become stuck in the open position.

With electronic throttle controls, the main worry is the throttle being stuck in the open position, or the computer erroneously ordering the throttle to open. Modern electronic throttle controls are designed with the express purpose of avoiding that type of situation, but a number of high-profile cases have raised concerns.

Electronic Throttle Control and Sudden Unintended Acceleration

When a vehicle accelerates without any intentional input from the driver, it is referred to as “sudden unintended acceleration.” Some potential causes of sudden unintended acceleration include:

  • Driver error
  • Pedal entrapment
  • Stuck throttle
  • Mechanical or electronic failure

Many cases of sudden unintended acceleration are due to pedal entrapment, which can easily occur if a floor mat slides forward and interferes with the normal operations of the pedal. This can depress the gas pedal, but it can also cause the brake pedal to malfunction.

According to the NHTSA, a number of SUA cases also occur when a driver accidentally presses the gas instead of the brake. That was the case with an Audi recall during the 1980s that resulted in the German automaker increasing the distance between its gas and brake pedals.

With electronic throttle controls, the concern is that the computer may open the throttle regardless of whether the brake pedal is being depressed. That would create an incredibly dangerous situation, especially in a vehicle that also used brake-by-wire technology, though it is still just a hypothetical concern. While Toyota did recall a number of vehicles that used ETC systems due to an issue with SUA in 2009 and 2010, there was no conclusive proof that their electronic throttle control technology was at fault.