How quickly have you ever driven a car? 90, 130, or 150? Thanks to a device known as a speed limiter—sometimes known as a speed governor—nearly all cars on the road are unable to attain those kinds of high speeds. Speed limiters in contemporary fuel-injected vehicles work with the engine computer and electronic sensors.
Modern internal combustion engine vehicles are equipped with a mechanism called a rev limiter. Their purpose is to safeguard an engine by limiting its top rotational speed, expressed in revolutions per minute (RPM).
Manufacturers of engines pre-set their rev limiters. A different controller is placed on some aftermarket systems, and its RPM is customized. The manufacturer’s limit, sometimes referred to as the redline—literally, the red line on the tachometer—is prevented from being exceeded by a limiter. There’s a chance that engine damage will happen after the redline.
Operation
Limiters typically function by turning off some element—such as fuel, air, or spark—that is required for the combustion processes to take place. Electronic fuel injectors are turned off by mechanical governors or limiters in compression-ignition engines. In addition to reducing engine power by altering the spark timing, a spark-ignition engine can also cut off gasoline or cease spark ignition.
When an automatic transmission is in “drive” mode, the engine revolutions per minute (RPM) remains securely within the range selected by the transmission. Reversing the engine in “park,” “neutral,” or “manual” mode is the only situation in which a rev restriction is necessary. Before the year 2000, a tachometer was frequently absent from these cars. Engine RPM is not a worry with fully automatic transmissions because the risk of excessive engine speed is negligible. However, the redline cannot be seen without this gauge.
On the other hand, if you shift into a higher gear too late or a lower gear too early when using a manual transmission, your engine’s RPM may redline in “neutral”. A rev limiter can easily maintain engine RPM below the redline while the vehicle is in “neutral” or is shifting up too late.
A manual transmission that is engaged too soon will cause the car’s speed to push the engine past its redline. In this situation, a rev limiter will reduce engine power but won’t be able to stop the engine from running above its redline.
“Missed” shifts are possibly the worst scenario. It is possible to “miss” shifting from second to third gear in the diagram and end up in first gear when operating at a high RPM. This will cause the redline to be exceeded, and nothing will stop an engine from suffering serious damage from a connecting rod or valvetrain failure. By applying the clutch as soon as feasible, engine damage may be prevented.
Most tiny engines feature a speed governor, including those found in lawn mowers. The carburetor’s throttle plate gradually closes in response to a rise in engine RPM, limiting the quantity of fuel and air that are admitted to the engine until the engine’s RPM stabilizes. The throttle plate will automatically open to let additional fuel and air mix into the engine if the RPM falls below the set level. The governor’s spring tension is often adjusted by adjusting the throttle, allowing the engine to run at the desired speed or slower. Because most small engines don’t have a tachometer, it’s not possible to observe the redline, although there’s usually no risk of over-speeding the engine.
This is how it operates: The engine’s computer, which controls almost all of the engine’s operations, receives input from a number of sensors to determine your speed. The computer intervenes and limits the flow of fuel and air to the engine, as well as the sparks that ignite combustion, as soon as you reach a preset maximum speed. In any case, you won’t be allowed to go faster than the maximum speed set by the vehicle’s manufacturer.