The principles of using one variable pump to distribute oil flow to several hydraulic functions appeared with the first hydraulic load-sensing systems in the 1970s. Since then, technological developments have refined and extended the functional opportunities. Sauer-Danfoss supplies complete load-sensing solutions with a full range of performance-optimising, flexible, energy-saving and noise-reducing benefits.
Regardless of the load, or how many functions are in operation at the same time, an hydraulic load-sensing (LS) system guarantees consistent, high performance. That is why so many manufacturers of agricultural, construction and material-handling vehicles have already chosen to replace their standard work hydraulics with LS, and why many more are considering a similar move.
Load-sensing steering systems, Series 45 open circuit axial piston pumps and the PVG 32 range of proportional valves are key elements in Sauer-Danfoss's load-sensing package, supplemented by priority valves, hydraulic integrated circuits (HICs) and joysticks.
Competitive issues
Today, the growing focus on LS has highlighted functional benefits that go beyond the obvious - the sheer practical advantage of using one pump to serve all - and respond to many of the most pressing competitive issues for vehicle manufacturers.
Flexibility is one of them. In vehicles designed for a variety of purposes and working conditions, LS lends itself to tailor-made solutions. The result is compact, energy-efficient and easy-to-operate vehicles. On top of it all, LS systems are easy to extend with additional functions.
Controlled performance
PVG 32 proportional valves are built together to ensure high performance in relation to a variety of lifting and rotating functions. In some cases, PVG 32 valves and HIC blocks are combined - the aim being to secure an optimum solution for each individual machine.
Performance relies on the individual load-sensing signals, which can control single compensators. The largest of these signals is transmitted to a variable pump via an hydraulic connection. Informed of the load, the pump then supplies the pressure required for all functions, plus a little extra to allow for natural loss. Low-noise and compact, Series 45 pumps are designed to work with PVG 32 valves in such highly responsive LS systems.
Compared to traditional hydraulic systems, the simultaneous operation of functions is improved due to the close match between pressure supplied and pressure required. At the same time, a minimum of excess flow is returned to the tank, and loss of fluid is significantly reduced. This, in turn, generates less heat and reduces the need for cooling capacity - again saving space in the vehicle construction.
Meeting greater needs
A large number of work functions may exceed the ability of the pump to provide sufficient oil flow to all functions simultaneously. Because of this, the installation of a priority valve may be the solution, giving highest priority to selected functions while borrowing from others. But there are still occasions where a variety of functions on one vehicle can detract from its energy-efficient performance, particularly when the functions have widely differing pressure requirements. In reality, the ultimate energy efficiency can only be obtained by installing a separate variable pump for each function, but the extra cost of doing so will often outweigh the performance improvement. A compromise solution is the best alternative.
By grouping the work functions according to their pressure needs, it is often possible to achieve optimal efficiency using one variable pump to serve each group. For the vehicle driver, operating the work functions is still as easy as ever, with a joystick enabling control of most functions with one hand.
Responsive steering
In addition to meeting the pressure needs of the work functions, the pump can also supply an LS steering unit. Sauer-Danfoss has three standard LS units in its range: OSP LS Static, OSP LS Dynamic and OSPF LS Dynamic. As with the work functions, the steering unit sends a load-sensing signal to a priority valve and the pump, which then controls the oil flow. Drivers benefit from light and responsive steering.
Technological developments within LS are ongoing. Today, the load-sensing signal is sensed by an hydraulic line. Sauer-Danfoss is looking to a future when LS will be synonymous with intelligent systems that adapt vehicle performance automatically to working conditions.
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