One of the major themes at the IFK 2018 fluid power conference in Aachen, Germany, is machine efficiency. In a presentation by researchers from the Technical University Darmstadt, “Integrated Fluid Dynamic Vibration Absorber for Mobile Applications,” researchers discussed how the setup of a suspension always leads to a compromise between comfort and safety. To counteract this in a passive approach, one could attach a structural extension in the form of a dynamic vibration absorber to the axle. Thus, energy of the wheel vibrations diverts into the vibration absorber instead of the body. In comparison to a classic dynamic vibration absorber, which increases weight, the new Fluid Dynamic Vibration Absorber (FDVA) reduces the dynamic mass by using a hydrostatic transmission.
The authors examined how the dynamic vibration absorber can be integrated into the suspension strut and mitigate oscillations. Simulation of the new concept shows that it is possible to improve driving safety without, or only slightly, affecting driving comfort. Measurements presented show that the vibration absorber fulfills its function and that the hydraulic transmission of the vibration absorber inertia works quite well.
Next, they plan to optimize the design of the FDVA by adjusting the vibration absorber spring and natural frequency. Further, it’s possible to make a more compact, semi-active version of the units with electrically actuated valves, to adapt it for use in racing cars. This means that the absorber can be adapted to high-speed driving situations.
In a presentation, “A new Approach on a Hydrostatic Motor for Applications in Mobile Cranes,” researchers from Graz University in Austria discussed how designers could improve the performance and flexibility of mobile booms, for example in concrete pumping applications, by replacing hydraulic cylinders with hydraulic motors in the boom and arm joints furthest from the cab.
They offered a new approach with a hydrostatic rotational motor characterized by low weight and high torque. The motor as a direct drive in the joints of mobile cranes offers new possibilities in terms of kinematics and the construction of booms, and can improve the overall power to weight ratio.
“Performance Investigation of a Hydro-pneumatic type Accumulator used in a Hydrostatic Drive System of Off-road Vehicles” was discussed by officials from the Indian Institute of Technology in Jharkhand, India. They studied the performance of a hydropneumatic type accumulator on the response of hydrostatic drive systems, and offered recommendations on the proper selection of accumulators in typical mining equipment.
Efficient performance and energy saving in construction and mining machinery has become a preeminent issue due to higher fuel price and increasing demands of production, said the presenters. In hydraulic systems commonly used in a typical working cycle of mining equipment, potential and kinetic energy are dissipated as heat. This technique makes maximum use of regenerative energy to further improve fuel consumption and also to ensure higher system control performance. One of the possible solutions is the incorporation of hydraulic accumulators in a hydraulic main.
They analyzed the characteristics of a hydropneumatic type accumulator on the responses of a hydraulic drive system, especially a typical open-circuit hydrostatic system with an accumulator used in a mining vehicle. The simulation model of the physical system was made using MATLAB/Simulink validated through experiments with different characteristics of the system. They looked at factors like various sizes, loads and precharge pressures, and offered possible efficiency improvements and recommendations based on different application criteria.
For instance, drive efficiency decreases when differential pressure across the flow control valve increases, while an accumulator can increase system efficiency. The right-sized accumulator should be used at optimum precharge pressure (near about system operating pressure). The future scope of this work will be to analyze the energy stored in the accumulator owing to pressure surge which needs additional simulation and experimentation work. The authors believe that the studies made in this article may be useful for selecting a proper size of accumulator for a given application.
Researchers from Chongqing University in China conducted a talk on the topic, “Active damping improvement of the electrohydraulic control system with dual actuators for mobile machinery.” They said the low damping property of hydraulic systems has been a remarkably troublesome issue for a few decades. Owing to flexible structures and less-than-ideal damping of hydraulic manipulators, the oscillation tendency is a major issue for mobile machinery characterized by large size and heavy load, such as excavators, hydraulic cranes and turntable ladders. There are disadvantages of safety hazards, actuator wear and physical discomfort of the operators caused by system oscillations.
Poor damping with two actuators or more is still intractable due to the complex coupling effect of different loads. They proposed a decoupling compensator based on pump/valve combined control for the system with dual actuators for mobile machinery.
The proposed system is for active damping improvement of an electrohydraulic system with dual actuators. Using decoupling control of different load branches, the coupling hydraulic circuit with dual cylinders is transformed into two separate single-cylinder circuits with dynamic compensation. They carried out compound motion tests on a 2-ton hydraulic excavator, and results indicated that the proposed compensator reduced velocity and pressure oscillations under different working conditions.
The decoupling control concept also opens up an opportunity to solve the poor damping issue of multiple actuators to reduce vibrations of mobile machinery. Future work will focus on auto-tuning decoupled methods to deal with parameter uncertainties so that the dynamic behavior in multi-actuator systems can be optimized under resistive or overrunning load conditions