A continuously variable transmission, or CVT, is composed of a hydraulic motor combined with a hydraulic pump that provides smooth and continuous speed variation.
The CVT design combines the benefits of a mechanical transmission and a hydrostatic transmission in the same machine. It allows the DL420CVT-5 to automatically transition from hydrostatic power at low speed to the mechanical system at higher speeds.
By combining the two types of transmission, the CVT technology ensures high loads can be carried at low engine speeds with high dynamics for an optimum wheel loader operating cycle, Doosan says.
The DL420CVT-5 therefore provides an increase in machine performance for operators working in digging, loading and lifting applications, the manufacturer claims.
With a maximum bucket capacity of 4.2 m3, the DL420CVT-5 wheeled loader is intended to meet a wide range of material-handling needs from loading and transporting sand and gravel to industrial, construction, demolition, mining and quarrying applications.
For most tasks, operators will use the hydrostatic part of the transmission, which is more fuel efficient in low-speed applications. The combination of the two transmissions is automatic and fully transparent for the operator, Doosan says.
The complete driving range, forwards and in reverse, is controlled by the CVT system. Low engine speeds ensure a high efficiency and the best driving comfort irrespective of the traction speed. The power splitting continuously variable technology facilitates moving off softly and hydraulically. Furthermore, with the CVT, a fuel saving of up to 15% can be achieved.
The ability to split hydrostatic and mechanical power has allowed Doosan to move to the Scania DC09 engine in the DL420CVT-5, as the CVT system maintains the machine’s efficiency even at low engine rpm. With an output of 232 kW (311 hp) of power at 1800 rpm, the Scania DC09 engine provides generous torque at low rpm and meets Stage IV emission regulations without the need of a diesel particulate filter (DPF), through the use of cooled exhaust gas recirculation (EGR) and selective catalyst reduction (SCR) after-treatment technologies.
As with all Doosan Stage IV wheel loaders, there’s a programmable auto idling feature and operators can also select between different driving modes that adjust maximum engine rpm based on preference and application. ‘Normal’ balances fuel consumption for everyday digging, grading and lifting tasks while ‘Economy’ reduces fuel consumption for low-demand applications.
Two new modes have been introduced: ‘Digging’ mode is available at speeds below 3 km/h and by pressing a button, the machine exerts the maximum torque to the transmission to ensure the best performance; ‘Drive’ mode ensures the best traction and decrease the fuel consumption. When the machine travels forward at over 14 km/h (or backwards at over 5.4 km/h), with the front pressure stabilised, the loader recognises that the task is driving only and thus shifts automatically into the Drive mode.
A ‘Creep’ setting is also available with the CVT system. This enables the operator to drive the machine at low speed with no need to press on the accelerator pedal when shifting into forward or reverse. Four Creep settings are available: 0 km/h, 1 Km/h, 2 km/h or 3.1 km/h. This function also avoids the transmission autobrake.