Smoother transmission shifting

Caterpillar’s Advanced Productivity Electronic Control Strategy (APECS) is used on several of its equipment models, including the new C and G Series trucks. APECS is a software program which controls the transmission Electronic Clutch Pressure Controls (ECPC) to improve machine performance. The system enables transmission upshift points to be performed at optimum engine operating speeds to optimize torque and improve fuel consumption. APECS also reduces cycle time by maintaining positive driving force during both upshifts and powered downshifts when ascending grades.

According to Scott Thomas, Product Application Specialist for Articulated Trucks at Caterpillar Inc., APECS provides smoother transmission shifts while maintaining torque and machine speed through the shift. With the smoother shifting, not only is there better machine performance, but also operator comfort. Operators who have tested the new G Series have found the trucks drive as smoothly and quietly as their pickup trucks due to the implementation of APECS.

APECS uses improved control algorithms to compensate shift points for machine acceleration and provide better machine control whether the truck is loaded or unloaded. Overall machine operation is made more intuitive by matching transmission shifting to operator throttle control.

Driveline durability is improved by reducing transient torque spikes during transmission shifting through the use of better clutch control algorithms, while new Shift Torque Management (STM) manages engine torque during shifts. The engine and clutch control algorithms use event-based control logic, responding in real time to any changes in transmission ratio. Reducing torque spikes during shifts helps minimize any oil spillage, as well as improve transmission component durability and increase operator comfort.

In the 725C Articulated Truck, APECS includes part throttle shifting (PTS) to provide smooth, automatic gear selection for improved acceleration, higher productivity and lower fuel consumption. APECS on the 730C and 730C EJ trucks works in tandem with Shift Torque Management (STM)—which includes PTS and improved Shift Control Logic (SCL)—to provide better shifting and greater acceleration on grades while maintaining torque through the shift changes. Thomas explains that SCL provides automatic shift selection that is specific to the desired machine operation and downshifts when necessary to maximize acceleration when increased throttle is applied. PTS enables shifting at lower speeds during part throttle operation, improving part throttle fuel economy as well as providing quieter machine operation and better maneuvering in reduced speed operating conditions.