Throttle Control Malfunction
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FEATURE
Throttle Control Malfunction Jonathan R. Raush Æ John R. Liechty
Published online: 29 August 2008 Ó Engineering Design & Testing Corp. 2008
‘‘The Vehicle Got Away from Me’’ We have all heard stories about runaway vehicles that accelerate uncontrollably and collide with other vehicles, crash into buildings or run people over. The circumstances often sound familiar and are sometimes tragic. The vehicle accelerates for no apparent reason and the driver is said to have been rendered helpless in an out-of-control machine. It seems as if a demon has taken control of the vehicle. Although such episodes do happen, the actual malfunction of the vehicle leading to unintentional acceleration is less common than one would think. To get a grasp on the demon and the out-of-control machine, it is best to first gain an understanding as to how the speed of a vehicle is controlled. The ways that speed is controlled can be complicated, but—fortunately—can be condensed to a few basic concepts. Once the basic concepts are understood, the approaches taken in investigating a sudden acceleration incident can also be better appreciated.
The Driver, the Accelerator and the Engine On every vehicle, control of the engine is managed by the driver’s use of the accelerator—known in common language as the ‘‘gas pedal’’ (as in ‘‘step on the gas’’). Stated another Reprinted from The Stress Point, 2008, 21(2), pp. 8–11, with permission from Engineering Design & Testing Corp. J. R. Raush (&) J. R. Liechty Engineering Design & Testing Corp., P.O. Box 610406, Birmingham, AL 35216-0406, USA e-mail: [email protected] J. R. Liechty e-mail: [email protected]
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Definitions Accelerator
A pedal at the driver’s position that is operated by the right foot of the driver and that, along with the brake pedal, gives the driver control over the speed of the vehicle.
Engine throttle
Mechanical and/or electrical devices on the engine itself that deliver air or a fuel–air mixture to the engine for efficient combustion of the fuel within the combustion chambers of the engine. A valve, typically a butterfly valve, housed in the throttle body that regulates the amount of air entering the engine.
Throttle valve
Throttle control system
The link (mechanical and/or electrical) between the accelerator and the throttle valve so as to respond to driver input to increase or decrease the flow of air or a fuel–air mixture to the engine.
way: the speed of the vehicle, by way of the engine throttle, is managed with the accelerator. The engine throttle is a mechanical and/or an electrical configuration that is a part of the engine and delivers air or a mixture of fuel and air to the engine. When the driver depresses the accelerator, more air is delivered to the engine, and the engine throttle responds to the driver. The speed of the vehicle should then increase. Releasing or relaxing the depression of the accelerator reduces the flow of air to the engine, and the speed of the vehicle should then decrease. The connection between the engine throttle
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