The start/stop control is responsible for coordinating the sequence for engine start-up and shutdown. There are seven steps to the sequence:
- Off
- Prestart
- Cranking
- Run
- Cooldown
- Coast
- Postlube
The "Off mode" allows the control system to be powered up with the engine in a controlled shutdown condition.
In the "Off mode", the control ensures that the following driver circuits from the ECM are off:
- Fuel shutoff valve
- Starting motor solenoid
- Driver circuit for the ignition
- Service meter
In the "Off mode", the system monitors the control command signal. The system will remain in the "Off mode" until "Run" is requested. If a "Run" command is requested, the system will exit "Off mode" and the system will enter "Pre-start mode". In the "Off mode", it is safe to turn off power to the control.
The "Prestart mode" provides protection against cranking the engine when it could be harmful to the engine. The "Prestart mode" performs the following three tasks:
- Optional prelube cycle
- Optional crank inhibit due to low temperature of the coolant water
- Driven equipment crank inhibit
In "Prestart mode", any control command signal other than "Run", returns the system to the "Off" mode.
Prelube Cycle and postlube Cycle Feature
The prelube cycle applies lubricating oil to the bearings before the engine is cranked. The postlube cycle lubricates the turbocharger after the engine shuts down. Prelube must be enabled with Caterpillar Electronic technician (ET). A postlube duration time is programmable with Cat ET.
Low Coolant Water Temperature Start Inhibit
The "Low coolant water temperature start inhibit" function is optional. If the temperature of the coolant water is below the set point, an event is generated and starting is inhibited.
Driven Equipment Start Inhibit
This function allows the customer to connect a switch input to auxiliary equipment in order to delay starting of the engine until the equipment is ready. Monitoring a pressure switch for driven equipment is an example of this input.
The following is part of the cranking mode process: fuel purge procedure, crank cycle, rest cycle and subsequent crank and rest cycles.
The following steps describe the process:
- The indicator for the run relay is energized.
- The "Engine Purge Cycle Time" allows any unburned fuel to exit through the exhaust system prior to ignition. This helps prevent combustion in the exhaust system.
- The driver circuit for the starter solenoid is energized. The system remains in the cranking mode until either the engine starts, or the cycle crank time is exceeded. If the cycle crank time elapses without the engine starting, the starter solenoid and the fuel shutoff valve are de-energized. The system enters the rest cycle.
- During the rest cycle, the starter and the fuel shutoff valve remain de-energized. The system remains in the rest cycle for the cycle crank time. After the cycle crank time has elapsed, the system goes back to the fuel purge procedure. The cycle will repeat.
- A timer starts as soon as the system enters the cranking mode. During the cranking mode, if the timer exceeds a user defined total crank time, an overcrank event is generated. This causes the system to change to the off mode.
When the engine speed exceeds a set crank terminate speed, the engine is defined as being started. The following actions take place when the crank terminate speed is achieved:
- The starter solenoid is de-energized.
- The crank terminate indicator is energized.
- The service meter is started.
- The system enters the run mode.
In run mode, the control monitors the engine during normal operation.
The cooldown mode allows the engine to run at a reduced load before shutdown. The system remains in the cooldown mode until the cooldown period elapses or until the control command signal changes from cooldown mode.
The system monitors engine speed as the engine is coasting to a stop. In coast mode, the control monitors the engine during deceleration after the fuel has been shut off. In the coast mode, the system will generate a fault code if the fuel shutoff valve is not functioning correctly.
The postlube mode lubricates the turbocharger bearings after engine shutdown. The system runs the pump for a programmable period of time after shutdown in order to lubricate the turbocharger bearings.