Load sensing

from Wikipedia, the free encyclopedia

The load sensing system (LS system), also known as the load pressure reporting system , is a hydraulic control in which the pressure and / or volume flow of the hydraulic pump is adapted to the conditions required by the consumer.

In conventional hydraulic circuits, the volume flow to the engine is throttled by pressure limiting or pressure regulating valves. The hydraulic pump always delivers at maximum power even when the volume flow is restricted , which in some cases causes high power losses.

The load sensing system, on the other hand, ensures that the pump only delivers the volume flow that is currently required for all active consumers.

description

LS system (open center)

LS systems can be designed as an open center with constant pumps or as a closed center with variable displacement pumps . The pump pressure is regulated with so-called pressure balances . If the consumer is switched off, the pump only delivers enough to operate the pressure compensator. In an open center system, this means that the excess volume flow is diverted to the tank. In the closed center system, the pressure compensator actuates the adjustment piston of the pump, the delivery volume of the pump is reset. The pump pressure levels off in such a way that the pressure difference between the control line ( LS ) of the pressure compensator and the delivery pressure of the pump always remains the same. , also LS pressure , is determined by the spring force of the pressure compensator.

If the control valves for the consumer are opened, the pressure is passed on to the pressure compensator via the LS line. The LS pressure acts in the same direction as the compression spring , the pressure to actuate the pressure compensator increases. In the open center system, this means that less hydraulic fluid is fed to the tank, the pump delivers more to the consumer. The variable displacement pump in the closed center system is swiveled out and delivers more. The delivery volume of the pump is only corrected upwards until the set pressure difference is restored.

If there are several consumers, shuttle valves are installed between the consumers for the feedback via the LS line , which always pass on the highest pressure occurring in the system.

A load sensing system with a variable displacement pump is often used in conjunction with a power limitation and pressure cut-off .

In addition to the purely hydraulic control, a load-sensing system can also be implemented electrohydraulically . For this, the proportional valves and the hydraulic pump are controlled electrically. Instead of a pressure compensator, a pressure sensor records the pressure in the system. is determined by an electrical control unit and the pump is regulated accordingly.

function

  • Engine is off

  • Motor is on, valves closed

  • Motor on, valve open

  1. The drive motor and the pump are off.
    • The pump is set to maximum delivery by the spring pressure of the adjusting cylinder.
  2. The pump is driven. The valves are closed.
    • The pump begins to deliver hydraulic fluid. If the pressure is high enough, the pressure regulator is moved. This acts on the adjusting piston and resets the pump. There is a balance between the pump pressure and the pressure to operate the pressure regulator.
  3. The pump is driven. The valves are opened.
    • Hydraulic fluid flows to the consumer. An LS line leads back to the pressure regulator via shuttle valves. The pressure from this line and the valve spring press together against the pressure side of the pump. If the valve is opened further, the pressure also increases in the LS line. The greater the pressure, the wider the pressure regulator is opened. The adjusting piston sets the pump to a higher delivery rate.

Individual evidence

  1. ^ Dubbel: Pocket book for mechanical engineering. 19th edition, Springer-Verlag, Berlin, p. H18.
  2. ↑ HAWE Fluid Lexicon