* The Engine: The engine is the primary source of power for acceleration.

* Transmission: The transmission (gearbox) modifies the engine's power delivery to suit different driving situations.

* Brakes: While braking is deceleration, it's still a change in velocity, therefore acceleration.

* Steering Wheel: Turning the steering wheel also causes acceleration, as the car changes direction.

* Differential: This component allows the wheels to turn at different speeds, contributing to acceleration during cornering.

Therefore, you could argue that the number of devices is greater than 4, but it depends on how you define "device." You could even argue that the tires themselves are a "device" contributing to acceleration, as their interaction with the road surface is what actually propels the car forward.

The key point is that multiple systems work together to produce acceleration in an automobile.