Controlling engine speed in diesel engines

Understanding how engine speed is controlled in off-highway diesel engines is important. It’s the basis for our perception of an engine’s performance — whether it comes from objective assessment or subjective judgement. Duncan Riding, Perkins business development engineer, takes a close-up look at the separate elements that contribute to our view of an engine’s performance.

The engine is an integral part of the machine it powers. The operator depends on an engine’s ability to start and restart in all conditions, from very cold to very hot, to maintain speed under load, and to stop when it is turned off.


Cold start

Cold start

Starting and reaching its operating speed is the primary functional objective of an engine. The operator depends on the engine’s ability to start and restart in a reasonable time in all conditions.

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Speed control

Speed control

In off-highway machines, the operator makes a speed demand and then loads up the engine through the operation of the machine. The engine has a ’speed governor’ that maintains engine speed under this varying load.

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Mechanical or electronic

Mechanical or electronic speed control

In highest regulated territories, electronic engine control is required to achieve the emissions standard. However, electronic engine speed control is available for lesser regulated engines and provides a number of benefits.

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Load acceptance

Load acceptance

The ability of an engine to accept load and maintain engine speed is a function of both the engine and the machine. Maintaining speed under load affects productivity and leads to a perception of the capability of the machine and engine power.

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Torque backup

Torque backup

When a machine overloads the engine at a target speed, torque backup will help to maintain engine speed and machine operation and recover engine speed when the overload is removed.

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Automated speed controls

Automated speed controls

When an engine runs at any speed under no applied load, we say the engine is at idle, or idling. While idling, an engine burns fuel, makes noise and wears. Automated speed control strategies are designed to reduce idling time.

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