Us4470259a closed center, load sensing hydraulic system. Troubleshooting insufficient flow in closed center load. Denison hydraulics open loop pump controls series p140 amod. The load sensing concept load sensing is a hydraulic circuit configuration which allows the load, as sensed at the control valve, to modulate pump output in relation to system demand. With marketleading features like priority flow sharing and patented load sense bleedoff, the cls load sensing sectional mobile valve gives you the power to prioritize work functions, improve machine efficiency and enhance performance like never before. When the system is idle, it drops the pressure considerably, typically to about 200300 psi. Here is an axial piston, variable displacement pump, its camplate and camplate control piston. The most common hydraulic systems on mobile equipment are based on two designs. Hydraulic loadsense directional control valves parker na. One type of hydraulic control system in widespread use, but not well understood, is loadsensing control. Home resources articles and white papers load sensing methods for mobile hydraulic systems 855.
Oct 15, 2016 load sensing pumps are one of the most interesting subjects in industrial hydraulics. Valve, available from 1 to 10 sections, is used for systems with fixed displacement pumps open centre version or load. Load sensing principle of operation 4 very simply stated, it is a hydraulic system that senses and provides only the pressure and flow required by the hydraulic system. Lspc the load sensing pressure compensated hydraulic system. The components required to accomplish the characteristics of the load sensing system are. Hydraulics, opencenter, pressure compensated pc 21. Transmission of large forces using small components, i. Load sensing control for hydraulic system eaton corporation. Apr 29, 1980 a load sensing hydraulic system is disclosed of the type in which a load signal is communicated from downstream of a main flow control orifice to a device which is operable to vary the fluid delivery rate in response to changes in the load signal. The service valves and intermediate sections avalibility, make dpc38 valve suitable for agricultural machines, drilling rigs, etc. Open center load sensing hydraulic system john deere.
Then when a load is sensed, raises the pressure to the compensator setting. A load sensing circuit typically comprises a variable displacement pump, usually axialpiston design, fitted with a load sensing controller, and a directional control valve with an integral load signal gallery exhibit 1. Therefore on each consumer or valve block pressure sensors are. Us6216456b1 load sensing hydraulic control system for. Nov 02, 2017 parker variable flow opencenter vfo takes a big step towards realizing these objectives. Generate pdf catalogue your quickprint catalogue is generated on demand based on your product selection. Reductions in energy consumption and noise reduction. The orifice is usually a directional control valve with proportional.
Another benefit is that efm can use wellestablished components, such as variable pumps with electrohydraulic loadsensing valves. As you can see the two malfunctions have similarities. The traditional loadsensing hydraulic system is an energysaving fluid power transmission, which supply ondemand flow at a prescribed pressure margin greater than the highest load pressure. The carefully designed features and integrated electrohydraulic control ensure a highly compact and optimised layout. Slow or rapid movements are done with precision, due to the constant adjustment of pump flow rate. Dec 19, 2016 the customer stated that this load sensing hydraulic valve was creating pressure in a port when the b port was on.
Controlling both flow and pressure at the pump allows for a significant reduction in valving losses and circuit inefficiencies. A load sensing hydraulic control system for use in a work machine and adaptable for controlling the displacement of a variable displacement hydraulic pump. Structure of load sensing systems variation in the ls circuit. Loadsensing describes a type of variable pump control used in open circuits. Electronic load sensing main control valve danfoss. Flow control systems are studied as an alternative to load sensing. The 20 bar 290 psi spring of the compensator forces the pressureflow compensator spool towards the left when there is no pressure in the system. Load sensing methods for mobile hydraulic systems crossco. Jul 20, 2017 schematic and symbolic representations of a pump compensator in a load sensing hydraulic pump operation of a load sensing system the load sensing system for the control of a hydraulic actuator consists of a variabledisplacement pump, a compensator block, and a load sensing closedcentre directional control valve. This, in turn, improves system response, and it increases stability with respect to disturbance variables. Directional control valves getting started it is wellunderstood that efficiency is paramount and machine developers are always seeking ways to make machines operate faster or move a greater load while decreasing the output of the prime mover. The control system includes a signal duplicating valve connected in fluid communication with both the pump controller and a fluid pressure source, and a sensor positioned and located for sensing the fluid pressure to the pump controller and. Load sensing systems are now found on a large percentage of mobile machinery, due to the efficiencies that they offer.
The load signal gallery ls, shown in red is connected to the load signal port x on the pump controller. Load sensing hydraulic systems fluidsys training centre. With just a few tweaks to a typical pressure compensator, you get a surprising improvement in efficiency and. Hydac nordhydraulic load sensing directional control valves are available with 1 to 10 sections. A closed center, load sensing hydraulic system is disclosed which contains a primary work circuit which has priority in flow demand over a secondary work circuit. A small hydraulic line connects the ls port on the load sensing compensator to the ls port on the valve that diverts flow to one or more functions. In both cases the malfunction symptom is insufficient equipment speed, caused by insufficient flow.
Hydraulic load sensing control explained load sensing is a term used to describe a type of pump control employed in open circuits. Load sensing pump controls typically incorporate a pressure limiting control, also referred to as a pressure cutoff or pressure compensator. Whats more, it presents a nominal flow rate up to 200 lmin and maximum operating pressure of 420 bar. It is also termed this because the loadinduced pressure downstream of an orifice is sensed and pump flow is adjusted to maintain a constant pressure drop and therefore flow across the orifice. This means that regardless of load conditions the flow will remain constant for a given orifice opening. Introducing a load sensing valve that eliminates compromise. A variable volume piston pump, that has a compensator that will allow the pump to standby at. In principle els replaces the hydraulic load pressure signal with an electronic pressure signal. Designing for loadsensing becomes tricky with multiple demands on a hydraulic supply. Hydraulic load sensing and control devices power hydraulics. The fundamental difference compared to load sensing systems is that the pump is controlled based on the operators. The traditional load sensing hydraulic system is an energysaving fluid power transmission, which supply ondemand flow at a prescribed pressure margin greater than the highest load pressure. Whats more, it presents a nominal flow rate up to 200 lmin and.
This comparison reveals some important advantages of hydraulics. It also supports new functions for automated, monitored workflows and simplified operation. In both cases we have closed center load sensing systems, which use the same type of pump. It is so called because the loadinduced pressure downstream of an orifice is sensed and pump flow adjusted to maintain a constant pressure drop and therefore. Hydraulic pumpmotor division load sense control piston pump controls psi gpm the load sense comp will increase or decrease the output flow to maintain a constant delta across the load orifice. One, load sensing ls, uses an upstream pressure compensator. Hydraulic load sensing control insider secrets to hydraulics. Flow versus pressure control of pumps in mobile hydraulic systems. In this video, the operation and setting procedure is explained in simple terms so that you may get the maximum efficiency from your load sensing pump system. We tested the valve while the a port was open to the tank and when it was. This is done by sensing the pressure drop across an external orifice. Pdf the paper describes the major research contributions made in the research of hydraulic load sensing systems throughout the last decades find, read. A conventional hydraulic system with a fixeddisplacement pump provides a constant flow through the system. Aug 07, 2017 the load sensing system for the control of a hydraulic actuator consists of a variabledisplacement pump, a compensator block, and a load sensing closedcentre directional control valve.
For the development of control strategies of nonlinear hydraulic systems, the use of linearised models is well established. As a consequence, the system generates tremendous amount of heat. Loadsensing controls to ensure that flow matches demand, system designers specify control valves with pressure compensators that control flow rates or distribution. How to adjust a load sensing pump gpm hydraulic consulting. Sensing variable displacement pumps closed centre version. In order to direct the oil flow from the hydraulic pump to the equipment to be driven, load sensing and control devices, which are built up in modular construction segments, are used. Simulation of an electrohydrauliclload sensing system with ac motor and frequency changer proc. Disclosed is an open centertype load sensing hydraulic system for securing operability and responsiveness of the open centertype hydraulic system, and for bypassing a discharge volume of a hydraulic pump to a hydraulic tank when a control valve is in a neutral state. The pressure compensator limits maximum operating pressure by reducing pump displacement to zero when the set pressure is reached. Accessories and integral valve options can increase the versatility of gear pumps, in some cases leading to substantial cost savings over systems using variabledisplacement pumps. The backbone of a highly efficient hydraulic system is the load sense network. Installing a txv variable displacement pump will transform your hydraulic equipment. Application of hydraulic sensors for electronic load sensing and main control valve hydraulics.
Oct 12, 2015 yet, the hydraulics must be ready to respond at the instant when the operator moves a valve lever. Cls loadsensing sectional mobile valve mobile hydraulic. The eaton pressureflow and load sensing hydraulic system. In the load sensing control, the vent flow is modulated by a valve which senses load pressure and establishes the pump compensator pressure at 21 bar above load pressure. Wo2012165674a1 open centertype load sensing hydraulic. Parkers vpl series is a stackable, multisection, loadsensing, pressurecompensated directional valve for mobile equipment. This is done by sensing the pressure drop across an external orifice and adjusting displacement to maintain a constant pressure drop across the orifice. The flow sharing technology applied to the standard load sensing system characterizes the new control. A load sensing system with a variable pump will often be subordinate to some form of power limiter with pressure limitation. Energy efficient variable flow opencenter vfo hydraulic. Eaton pvh variable displacement piston pumps vickers product line. Hydac nordhydraulic loadsensing directional control valves are available with 1 to 10 sections. That is, the working hydraulics are more agile and less susceptible to oscillations. Modeling and experimental evaluation of a loadsensing and.
This thesis deals with innovative working hydraulic systems for mobile machines. Electrohydraulic load sensing with a speedcontrolled hydraulic. Mobile working hydraulic system dynamics diva portal. One way to accomplish this objective is with a load sensing system. If there is no valve in the circuit specifically designed to communicate a load sense signal, then connecting the line beyond the valve and near the actuator is acceptable. Process time depends on the models selected and the resulting file size. With eloadsensing els, bosch rexroth proudly presents the next generation of hydraulic systems.
Load sensing principle of operation 5 how load sensing works this is best accomplished by using a simplified system so that the underlying theory and principles of operation can be clearly seen. Pdf on load sensing fluid power systems researchgate. The electronically controlled system makes the comprehensive management of the tractor and various attachments possible. The system includes a variable displacement pump fluidly connected between a reservoir and a control valve with the primary work circuit. Electronic loadsensing for tractors rwth publications. Mobile working hydraulic system dynamics load sensing and negative load sensing, where the pump is controlled in order to maintain a constant opencentre.
1189 1486 54 439 1486 915 203 305 590 554 1224 1403 635 535 893 297 205 509 880 157 960 1046 491 412 662 1529 1364 15 1128 1205 1459 1 547 1577 364 662 76 1260 760 1309 836 324 1348 566 926