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O+P Fluidtechnik 5/2017

O+P Fluidtechnik 5/2017


CONTROLS AND REGULATIONS FORSCHUNG UND ENTWICKLUNG PEER REVIEWED 02-4 Load quadrants of hydraulic cylinders 84 O+P Fluidtechnik 5/2017

CONTROLS AND REGULATIONS low pressure rail (LP) between MP and TP is installed at the return flow side. In this study the pressure level of LP p lp is set at 35 % of p mp . The combinations using LP are shown in the diagrams using dotted lines. The arm cylinder is operated mainly in the Quadrants I and III. The combinations of MP→MP and MP→HP are effective for the frequent load forces between -50 to 150 kN, when the arm cylinder is extended. While the arm cylinder is contracted, the combination of TP←MP produces the smallest throttling losses. Because the combinations configured by LP do not produce the valid cylinder forces while the arm cylinder is contracted, the LP is not connected. The load forces of the bucket cylinder are concentrated between 25 and 150 kN while the bucket begins the digging action and the combinations of MP→LP and MP→HP are effective in this range. When the bucket cylinder is retracted to release the soil in the bucket, the load forces concentrate between ±25 kN and the combination of TP←MP is suitable, therefore the combinations using MP at the return side are not used at all for the bucket cylinder. The combinations for all actuators are summarized in Table 2-2. Actuator Boom Arm Buckert Optional Connections LP or TP HP, MP or TP HP, LP or TP Table 2-2 Optional Connections of the Return Sides Next the hydro-mechanically controlled valve system selecting these pressure combinations is introduced, which is installed in parallel downstream of the pressure compensator. Two pressure signals and a spring force are acting on each switching valve. For example, upstream pressure of compensator p out is acting on the right side of the valve SV4. The p lp and the spring force are acting on the other side. This valve is closed when p out F > plp + A SV SV ( 2) and the return flow flows into LP through the check valve. Here, F SV is the spring force and A SV is the area exposed to pressure signals. Because the flow rate through the proportional valve is determined by the opening area of the valve and its pressure difference produced by the pressure compensator, the operating speed of the actuator does not depend on the combination of pressure rails, however a quick switching of the valves makes pressure impact and it causes discontinuities of the cylinder velocity [11], therefore the relatively long switching time of the valves is given in this study. 2.3 LINEAR TRANSFORMER 02-5 Linear transformer Whereas the recuperated energies in MP and HP can be reused directly to drive the actuators, the recuperated energy in LP cannot be reused, because the pressure level is not high enough to drive the actuators. There is no accumulator in LP and the return oil into LP is directly boosted to the p mp by a linear transformer. The linear trans- 02-6 Pressures in operation of upper structure O+P Fluidtechnik 5/2017 85


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