Caterpillar 24H Graders take very important roles on mining operation especially on road maintenance by ensuring road's availability and reliability to provide safe condition.

But the graders tend to frequently suffer from engine over speed.

Protection against engine over speed by OEM 

"The ECM transmission will automatically upshift the transmission above the indicated shift lever position when engine speed reaches 2675 rpm. This automatic upshift will occur from any gear. There is no limit to the number of upshift allowed. If an overspeed condition exists in 6th gear the torque converter lockup clutch will disengage. The transmission ECM will automatically downshift (after an upshift) whenever the engine speed reaches 2315 rpm and will continue to downshift until the transmission speed matches the shift lever position".

Based on above statement, engine rpm allowed to reach warning II 2500 rpm (warning II) and 2700 (warning III). Both are logged in ECM and downloadable by means of Electronic Technician (ET).

In fact, the increasing number of overspeed (logged in ECM) leads to engine failure or damage.

System Operation

OSPS module continuously monitors engine speed. Frequency analog signal is then converted into digital signal so that can be processed by module microcontroller.

When engine speed reaches 2350 rpm (before and next to overspeed) on any gear (automatic shifting), signal conditioner output signal is determined by main module as it is high enough to trigger an early warning. As part of OSPS module, output driver module is commanded by main module to produce 24 Volt output to turn a warning buzzer on alerting the operator that the machine has to reduce its speed to avoid overspeed. The warning continuously occurs until operator releases accelerator pedal or foots brake pedal to reduce speed.

if above condition is ignored by operator, engine rotation will increase and second stage of action will be taken by the protection system at 2400 rpm. Again, OSPS module’s output driver will send the second 24 VDC signal to cut out lockup solenoid power so that lockup clutch disengages / shifting the torque converter from direct drive into torque converter drive. This is supposed to protect the engine from overspeed.

Torque converter will shift back into direct drive (lockup clutch engaged) when engine rpm decreases up to 2350 rpm. Warning buzzer turns off accordingly.

System Achievement

Above graph states clearly that engine overspeed no more occurs on grader G205. Meanwhile overspeed prevention action is continuously done by the system as shown on getting taller green bar.

Yellow    =    Number of engine over speed  occurence

Green    =    Number of prevention

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