Hydrostatic Drive in the Wacker Neuson SM Series
All Wacker Neuson SM series machines, including the SM60, SM100, and SM120, feature a closed-circuit hydrostatic drive. Closed circuit drives provide the most power and efficiency to drive a loader, whether articulated or skid steer.
Other manufacturers of ‘stand-up’ mini loaders often use open circuit drives, an older technology not used on larger skid steer counterparts since the 1970s.
Let’s take a look at some of the key features differentiating the two systems:
Closed Circuit Hydrostatic Drive
Closed circuit hydrostatic drives in Wacker Neuson SM series machines work by providing flow from a hydrostatic transmission (hydraulic pump with variable flow) directly to the wheel motors. There are no valves between the hydraulic pump and the wheel motors. Speed is controlled by increasing the flow of the pump; direction is controlled by the pump flowing forward or reverse. This technology is used in all modern sit-down skid steer loaders and articulated loaders, including Wacker Neuson loaders.
Open Circuit Hydrostatic Drive
On the other hand, open circuit drives are inefficient and have low power in comparison to a closed circuit system. These drives, used in some Australian-made stand-up mini loaders, work by using the flow from a gear pump, diverting it through valves and then onto the wheel motors. Gear pumps are “fixed displacement," which means, that the flow of the pump is always the same per revolution of the engine and cannot be varied. The gear pump flows to a control valve. By pushing a lever forward on the control valve, the flow starts to bleed off to the wheel motors. The more flow that is bled off, the faster the wheel motors will turn. The output of the wheel motors then needs to travel back through the control valve and back to the hydraulic tank.
Bleeding off flow creates heat in the hydraulic fluid as it restricts the flow, leading to inefficiencies and pressure drops. Not only does heat create inefficiencies, but the hydraulic pump also flows the full amount of hydraulic fluid regardless of whether it is needed or not.