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O+P Fluidtechnik 5/2017

O+P Fluidtechnik 5/2017


CONTROLS AND REGULATIONS FORSCHUNG UND ENTWICKLUNG PEER REVIEWED 03-5 Pressures of each accumulator 03-6 Operating points of ICE and main pump for the LS-System tion. The soil density is about 900 kg/m 3 . Figure 03-3 shows the displacements and loads of the actuators. The cycle time is 13.7 s and it is repeated 4 times in the simulation. Rated Power of ICE Hybrid 125 kW Rotation Speed 1100 min -1 1800 min -1 Max. Torque 700 Nm 633 Nm Available max. Power Output 81 kW 120 kW Pump Displacement 180 cm 3 /rev 210 cm 3 /rev Table 3-1 Parameters of both systems 3.2 SIMULATION RESULTS Figure 03-4 shows the operating points and their frequency for the ICE (left) and the main pump (right) of the hybrid system. LS The ICE consistently experiences operation at high torque of approximately 650 Nm. As shown in the right figure, the pump’s operating points are concentrated along the pump output power limit. The MP rail is charged during most of the cycle time, because the loads of this simulated cycle were relatively light. The total efficiencies of the ICE and main pump were 40.3 % and 87.4 % respectively. When the accumulators are fully charged the efficiencies of the ICE and the main pump take on their lowest values, however, as the output power was also very low at this time, these low efficiencies affect the total fuel consumption very little. The pressures in each accumulator are shown in Figure 03-5. Figure 03-6 shows the operating points and their frequency for the LS-System. The main pump operates according to the pressure and displacement ratio and causes an equal distribution of the torque as shown in the left figure. It is obvious that such pump operation causes poor efficiencies. The total efficiencies of the ICE and main pump were 34.0 % and 81.2 % respectively. 88 O+P Fluidtechnik 5/2017

CONTROLS AND REGULATIONS LS-System with one pump. To reduce throttling losses, it is effective, for example to increase the number of the pressure rails and switching valves, however this solution would increase the costs and complexity of the system. The next challenge in this study is to decrease the throttling losses without increasing the number of components. The latest LS-Systems often use more advanced system, e.g. pump rotation speed adjustment based on total flow requirement, therefore the comparison with such an advanced LS-system will be done in the next step, and moreover the influence on emissions of harmful substances like NOx from the ICE is also taken into consideration. 5 NOMENCLATURE 03-7 Fuel Consumptions of both systems A SV D pump F SV T pump.max p charge.low Area Pump Displacement Spring Force Available Torque Expected lowest Pressure The total fuel consumption in one cycle of both systems is shown in Figure 03-7. The hybrid system consumed 2200 kJ which is 20.2 % less fuel than the LS-System. Because most of the energy savings were realized by the lower energy loss of the ICE, it can be stated that the ICE is the most important factor to improve the efficiency of the machine. The energy losses of the main pumps were considerably low in comparison to the total consumed energy. However, it is predicted that the pump loss of the LS-System would be higher, in case when the load is light, e.g., in a levelling cycle. On the other hand, because there is no correlation between the load conditions and pump operation, the main pump of the hybrid system is always operating at high efficiency. Moreover the energy recuperation of the swing deceleration and boom lowering is done in the hybrid system and the energy is reused to drive the actuators. The most important result is that slightly more energy was consumed in the hydraulic system of the hybrid system than that of the LS-System for the same working cycles. It means the throttling losses in the hybrid system were larger than in the LS-System with one variable displacement pump. 4 SUMMARY / OUTLOOK Using the basic ideas of STEAM, a new hydro-mechanically controlled system was proposed. In this system, the ICE and the main pump rotate at a lower engine speed than conventional systems to benefit from the excellent efficiency of the ICE in this region. The pump displacement was determined by the lowest supply pressure and the maximum available torque for the pump. The pump displacement ratio is changed along the approximated limit power. The hydro-mechanically controlled valve system, the pressure rails and the arrangement of the switching valves were designed by analysing three different working cycles. To compare the fuel consumption of the hybrid system with the one pump LS-System, simulations were conducted. The results show that the hybrid system consumes 20.2 % less energy than the LS-System and that most of the energy saving is produced by the difference in ICE and main pump operation. On the other hand, it was found that the throttling losses of the hybrid system are, in fact, larger than that of the η pump.HM 6 BIBLIOGRAPHY Hydro-Mechanical Pump Efficiency [1] Zimmerman, J.; Invantysynova, M.: „Hybrid displacement controlled multi-actuator hydraulic systems“, Proc. of the 12th Scandinavian International Conference on Fluid Power, Tampere, Finland, 2011 [2] Inderelst, M.: „Efficiency Improvements in Mobile Hydraulic System“, Ph.D. Thesis, Aachen, Germany, 2013 [3] Busquets, E.; Invantysynova, M.: „The world´s first displacement-controlled excavator prototype with pump switching – a study of the architecture and control“, Proc. of the 9th JFPS International Symposium on Fluid Power, Matsue, Japan, 2014 [4] Sugimura, K.; Murrenhoff, H.: „Hybrid Load Sensing – Displacement Controlled Architecture for Excavators“, Proc. of the 14th Scandinavian International Conference on Fluid Power, Tampere, Finland, 2015 [5] Inoue, H.: „Development of Hybrid Hydraulic Excavators“, Proc. of the 9th JFPS International Symposium on Fluid Power, Matsue, Japan, 2014 [6] N, N.: „CAT336E H Hydraulic Excavator“, CAT Product Brochure, USA, 2013 [7] Young-Bum, K.; Pan-Young, K.; Murrenhoff, H.: „Boom Potential Energy Regeneration Scheme for Hydraulic Excavators“, Proc. of the BATH/ASME 2016 Symposium on Fluid Power and Motion Control, Bath, UK, 2016 [8] Leifeld, R.; Vukovic, M.; Murrenhoff, H.: „STEAM – the best of both worlds“, Proc. of the 7th Workshop on Digital Fluid Power, Linz, Austria, 2015 [9] Vukovic, M.; Leifeld, R.; Murrenhoff, H.: „STEAM – Ein hydraulisches Hybridsystem für Bagger“, 6. Fachtagung Baumaschinentechnik 2015, Technische Universität Dresden, 2015 [10] Vukovic, M.; Leifeld, R.; Murrenhoff, H.: „STEAM – a hydraulic hybrid architecture for excavators”, Proc. 10th International Fluid Power Conference, Dresden, Germany, 2016 [11] Sgro, S.: „Concept of Hydraulic Circuit Design Integrating the Combustion Engine“, Ph.D. Thesis, Aachen, Germany, 2014 [12] Murrenhoff, H.; Eckstein, L.: „Fluidtechnik für mobile Anwendung”, Schaker, Aachen, Germany, 2011 Autors: M.-Sc. K. Sugimura and Prof. Dr.-Ing. H. Murrenhoff, Institut für fluidtechnische Antriebe und Steuerungen (IFAS) O+P Fluidtechnik 5/2017 89


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