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Automatic Transmissions, Braking Force, and Sudden Acceleration
Automobiles made in the past decade or so are very different from the cars that were on the roads not long ago. The introduction of computer-based systems has revolutionized car design, allowing all of a vehicle’s systems to respond more intelligently. When something fails to work correctly, such as a vehicle’s accelerator, the vehicle’s other systems try to maximize the driver’s control. Unfortunately this does not always work as planned.
Transmissions exist to control the relationship between the power generated by the vehicle’s engine and the force applied to the wheels. Low gears maximize the engine’s ability to pull weight, such as when climbing a hill, but it is much more difficult to go fast. Shifting into a higher gear means having less “pulling” power, but allows a vehicle to go faster when it is already moving.
In newer vehicles, pressing the brake pedal has no direct effect on the brakes. Instead, the position of the pedal instructs a computer to apply braking force. The computer then triggers the vehicle’s brakes as necessary, changing the braking force on each wheel to match road conditions. In vehicles with automatic transmissions, the computer may also use other sources of braking force.
A vehicle’s transmission can also be used to bring it to a halt. Using a technique known as engine braking, the automobile’s transmission can contribute to stopping force. In short, engine braking works by shifting into a lower gear. This increases vacuum pressure in the engine, causing the engine and the wheels to turn more slowly.
Engine braking is a familiar technique for people who frequently drive vehicles with manual transmissions. Many people who do not ordinarily drive vehicles with manual transmissions may be not be aware of engine braking and how it works. Most recent-model vehicles with automatic transmissions already automatically utilize engine braking.
For drivers of vehicles with automatic transmissions that already use engine braking, an engine that is accelerating out of control cannot provide any additional braking force. A malfunctioning acceleration system simply negates the vehicle’s braking system’s ability to utilize engine braking, and therefore reduces the driver’s odds of bringing the vehicle under control.
A number of recent-model Toyota vehicles have been linked with sudden uncontrolled acceleration. Drivers of newer vehicles may be at risk of experiencing Toyota sudden acceleration -and if they do, their brakes may not work as effectively as they should.
