DRIVE GP-FINAL 2883462 - Caterpillar

Hydramechanical Protective System
The hydramechanical protective system is designed as a self contained system separate from the engine governor. This system is used to activate an alarm or shutdown an engine for low oil pressure, high coolant temperature or engine overspeed conditions.Overspeed
In general, an overspeed condition is the result of a fuel system that fails to operate correctly. This in turn allows the combustion system to get more fuel than the engine load needs. The excess fuel can accelerate the engine to a point that engine failure can be the result.The rate of engine acceleration is controlled by several factors. Friction horsepower, attached inertial loads and operating loads make up the main affects on acceleration. In most all cases, the protective system must have a response time of less than one second. Response time is the time interval between the overspeed and the actuation of the protective system. The protective system must provide this response under different conditions such as engine start up at extreme ambient temperatures and under full load operation.For an overspeed condition the fuel control linkage is moved to the "SHUTOFF" position and the engine combustion air supply is stopped.Low Engine Oil Pressure
As engine speed increases, the required oil pressure for main bearing protection increases. The engine oil pump is a positive displacement type pump, therefore, engine oil pressure varies in direct proportion to speed until the pump goes on controlled bypass. From Figure 1, it can be seen that if only the low range oil pressure protection level was used for the full speed range, the engine could operate at rated speed with oil pressure below the required level. Also, if only the high range oil pressure protection level was used for the full speed range, the system would shutdown the engine at low idle, since the engine oil pump develops lower pressure at that speed. Therefore, the protective system must operate between the required oil pressure curve and the engine oil pressure curve. This is done with a step action of pressure versus speed.The hydramechanical protective system operates within the two ranges of engine oil pressure. As engine speed increases, the minimum oil pressure needed at the main bearings also increases. At low engine speed, an alarm or fuel shutoff actuator will activate when oil pressure is reduced to within 140 35 kPa (20 5 psi). At high engine speeds, an alarm or fuel shutoff actuator will activate when oil pressure is reduced to within 205 35 kPa (30 5 psi).For a low oil pressure condition, the protective system activates an alarm or moves the fuel control linkage, through the governor, to the "SHUTOFF" position. The combustion air supply is not shutoff for this condition.High Coolant Temperature
If the coolant temperature of an engine goes above a set limit, the protective system activates an alarm or moves the fuel control linkage to the "SHUTOFF" position to shutdown the engine. The combustion air supply is not stopped under this condition.System Components
The system