These systems make working with big machines safer. Before working with hydraulic systems, consider this guide to understand the different types. Did you enjoy this article? Keep coming back for more articles on construction and industrial technology. What Is a Hydraulic System? The five most common hydraulic system examples are: 1. Hydraulic Pumps Hydraulic system components are driven by a variety of power sources.
Hydraulic Motors and Cylinders A basic hydraulic system has motors and cylinders that utilize pressurized fluid for mechanical work. Aviation Hydraulic System Another one of the hydraulic systems is the aviation system. Open Center Hydraulic System In an open-center hydraulic system, there is no pressure, but the fluid is still there.
Closed-Loop Hydraulic system In a closed-loop system, the pump operates allowing pressure for the fluids. Hydraulic System Explained Hydraulic systems are used mainly for complex and fast-moving machines.
Hose and Fitting Stores. Corporate Locations. Hydraulic Charge Pump Overview. What is a Hydraulic Charge Pump? Replenish hydraulic fluid lost from the transmission loop due to the internal leaking of the pumps and motors. The charge pump makes up for all of these internal leakages. Provides constant back pressure and lubrication of the hydrostatic pump and motors rotating group. Most manufacturers of these products require a back pressure of — psi for proper functioning.
Hydraulic systems will transmit power using the pressure of incompressible fluids. In most of the cases, the fluid is taken from a reservoir using pumps. These are simple, safe, and economic systems that can be controlled easily and accurately.
Providing constant force regardless of the speed is an advantage of the hydraulic system. Open loop hydraulic system and closed loop hydraulic system are the two types of hydraulic system. In an open loop system, when the actuating mechanism is idle, there will be fluid flow but no pressure.
For a closed loop system, when the pump operates there will be pressure for fluids. The fluid will flow continuously between the pump and the actuator without entering into the reservoir for a closed loop system. That the process is not affected during the aforementioned 0. Control error and state space representation of pressures in the working cylinder for digital Figure 6. Control error and state space representation of pressures in the working cylinder for digital control left column and displacement control right column.
Another effect that is seen in this part of the diagram is a non-monotone increase in pump speed up toFigure 6 compares approximately 25the performance rpm, which fallsofagain the two control after 0.
For instance, valves V1 and V2—which control the flow from either the can see that with digital control, the pressure ripple—even accumulator for digitalfor relatively control highthe or from motion pumpspeeds—is lower than for displacement the ripplenot control —are thatswitched occurs due to at the pump control.
This becomes clear by looking at the histograms, which same time but after a waiting time of 0. In addition, valve V3 is switched to control the flow from the show the error distribution as well astothe pump the estimate cylinder afterfor the standard another deviation 0.
The mean 5 middle error can, therefore, be improved by a reduction left , which shows constant displacement between 7. One can see that with digital control, for digital control or by compensation of pressure pulsations by means of torque control the pressure ripple—even for relatively high motion speeds—is lower than the ripple that occurs due for displacement control.
Additionally, measured pressures in digital control mode are modes. The inferior mean error of the digital controller results from the fact that a dead band controller, This error is fed back into the controller as described to in calculate a previous thesection, output was of the PWM signal.
In addition, the trajectory offset if the errorin digital is expectedcontrol mode to have themoves alongfor same sign thethelower whole red line, i.
In displacement The bottom diagrams control, it is clear in Figure that chamber 6 show the pressures B is connected pA and pB directly in Chamber to theA tank, and Bwhichof theresults piston in a certain desired pressure in chamber A to attain constant force.
In digital control mode, the controller also starts at tank pressure from the displacement controlled movement of the piston in phase I but then the pressure in pB and pA rises to a different steady state value.
The distance between the graph of the desired force and the points of the trajectory that lie outside the dead band indicates the control error. This error is fed back into the controller to calculate the output of the PWM signal. One can see that the digital controller becomes active outside of the dead band red , which drags the trajectory into the dead band again.
In addition, the trajectory in digital control mode moves along the lower red line, i. In displacement control, it is clear that chamber B is connected directly to the tank, which results in a certain desired pressure in chamber A to attain constant force. In digital control, when using a valve with two non-independent control edges the pressures in pA and pB cannot be changed independently: The valve SEC-6 is switched in ballistic mode, which results in regulation of the flow from accumulator AC1 into chamber A.
This leads to a movement of the working piston and demands for a small flow out of chamber B. As both control edges are switched at the same time, the flow out of chamber B also has to pass a ballistically actuated control edge.
This leads to a rising pressure in chamber B until the pressure difference between pB and the tank pressure results in a flow rate equal to the demanded average flow rate out of chamber B due to piston movement.
Summary and Conclusions A valve control concept for handling low speed conditions with high loads of a primarily variable pump speed controlled hydraulic drive was presented. It employs on—off valves operated in a pulse-width control mode digital mode , instead of proportional or servo valves, in order to avoid high leakage in load holding phases.
Such phases occur in several press processes. Hydraulic supply for valve control is provided by an accumulator charged by the pump in short charging cycles. The functioning of this concept in combination with rather simple control methods is demonstrated by a test rig under operating conditions with a substantial load holding phase.
Even though the motion speed in load holding was relatively large in the experiments, the force control in the digital mode achieves values that are as good as those achieved with pump control. At lower speeds, a much better performance gain can be expected. This approach intends primarily to avoid unfavorable pump operating conditions, which might impair lifespan. However, it can also reduce the energy losses of load holding by pump if such phases make up a major share of operation cycles.
To actually use this approach, valves with very low or no leakage are essential. The pump durability, and functional and energetic advantages, are opposed by additional component costs, a more complex control, and maintenance efforts for the accumulator.
The overall economic advantage of this separate control unit depends on the machine or plant specific operation scenarios and the costs of the additional components.
Future work should be done on investigating effects on the loading process of the accumulator for digital control during operation. This was not evaluated within the underlying work but could have an impact on the overall performance of the system.
Moreover, on the displacement control side, the authors are convinced that there is a great demand for pump designs that can cope with processes that require low speeds and high pressures.
Author Contributions: Funding acquisition, B. All authors have read and agreed to the published version of the manuscript. Actuators , 9, 12 of 13 Conflicts of Interest: The authors declare no conflict of interest. References 1. Thesis, Shaker Verlag, Aachen, Germany, Helduser, S.
Electric-hydrostatic drive—An innovative energy-saving power and motion contro system. Part I J. Control Eng. Minav, T. Effect of PMSM sizing on the energy efficiency of an electro-hydraulic forklift. Chiang, M. The high response and high efficiency velocity control of a hydraulic injection molding machine using a variable rotational speed electro-hydraulic pump-controlled system.
Yu, T. Hametner, G. Positioning control of a hydraulic press by a variable speed motor. Pedersen, H. Investigation of new servo drive concept utilizing two fixed displacement units. JFPS Int. Fluid Power Syst. Willkomm, J. Process-adapted control to maximize dynamics of speed-and displacement-variable pumps. Ge, L. Efficiency improvement and evaluation of electric hydraulic excavator with speed and displacement variable pump.
Energy Convers. Lovrec, D. Dynamic behaviour of different hydraulic drive concepts—comparison and limits. Determining Electric Motor Load and Efficiency. Available online: www1.
Achten, P. Kauranne, H. Michael, P. Lee, S. Effect of CrSiN thin film coating on the improvement of the low-speed torque efficiency of a hydraulic piston pump. Miller, M.
An investigation of hydraulic motor efficiency and tribological surface properties.
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