This paper presents calculation and measurement results of a high-performance permanent-magnetic gear. The analyzed permanent-magnetic gear has a gear ratio of 5.5 and is able to deliver 27 N m. The analysis has shown that special attention needs to be paid to the system where the gear is to be installed because of a low natural torsion spring constant. The analyzed gear was also constructed in practice in order to validate the analysis and predict the efficiency. The measured torque from the magnetic gear was only 16 N m reduced by the large end-effects. A systematic analysis of the loss components in the magnetic gear is also performed in order to figure out why the efficiency for the actual construction was only 81%. A large magnetic loss component originated in the bearings, where an unplanned extra bearing was necessary due to mechanical problems. Without the losses of magnetic origin in the bearings and less end-effects caused by relatively short stack, an impressive efficiency estimated at 96% can be obtained. Comparison with classical mechanical gears has shown that the magnetic gear has a better efficiency and a comparable torque per volume density. Finally, it is concluded that the results in this paper may help to initiate a shift from mechanical gears to magnetic gears.Index Terms-End-effects, finite-element analysis (FEA), gearbox, high torque density, magnetic gear.
Pump-controlled hydraulic cylinder drives may offer improved energy efficiency, compactness, and plug-and-play installation compared to conventional valve-controlled hydraulic systems and thus have the potential of replacing conventional hydraulic systems as well as electro-mechanical alternatives. Since the late 1980s, research into how to configure the hydraulic circuit of pump-controlled cylinder drives has been ongoing, especially in terms of compensating the uneven flow requirements required by a differential cylinder. Recently, research has also focused on other aspects such as replacing a vented oil tank with a small-volume pressurized accumulator including the consequences of this in terms of thermal behavior. Numerous references describe the advantages and shortcomings of pump-controlled cylinder drives compared to conventional hydraulic systems or electro-mechanical drives. This paper presents a throughout literature review starting from the earliest concepts based on variable-displacement hydraulic pumps and vented reservoirs to newer concepts based on variable-speed electric drives and sealed reservoirs. By classifying these drives into several proposed classes it is found that the architectures considered in the literature reduce to a few basic layouts. Finally, the paper compares the advantages and shortcomings of each drive class and seek to predict future research tasks related to pump-controlled cylinder drives. IntroductionWith an increased industrial focus on energy efficiency, plug-and-play installation, and compactness, conventional valve-controlled hydraulic cylinder drives are increasingly being replaced by electro-mechanical alternatives, such as roller or ball screws [1], especially for small power classes. This happens despite the well-known advantages of hydraulic linear actuation such as large force/power densities, reliability, and robustness. Hydraulic actuation is, however, still the preferred solution for many applications such as industrial presses, large mobile machinery, crane manipulators, primary aircraft control etc. [2][3][4]. Among other reasons this is due to certain limitations for the electro-mechanical alternatives, such as limited reliability (e.g., shock loads damage), the difficulties of implementing overload/failure protection and/or limited force capabilities [5][6][7]. To strengthen the position regarding these applications and to make hydraulic cylinder drives competitive with electro-mechanical drives for low power applications, there is a need to enhance both the energy efficiency and the overall flexibility of hydraulic cylinder drives.The flexibility of a hydraulic system may be related to how power is being distributed between the prime mover and the actuator(s). As illustrated in Figure 1, at least three different power distribution topologies exist: hydraulic, mechanical, and electrical distribution.
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