Electro-Hydraulic Actuators

Klaus Stadlbauer∗ , Florian Poltschak∗† , David Rafetseder∗ and Wolfgang Amrhein∗†
∗ JKU † Austrian
HOERBIGER Research Institute for Smart Actuators, Linz, Austria Center of Competence in Mechatronics (ACCM), Linz, Austria
978-1-4673-1301-8/12/$31.00 ©2012 IEEE 511
life cycle [1]. A brief literature review shows many different ways to calculate the temperature distribution of a machine. They can be classified in three main groups: The first possibility is the method of Finite Elements (FEM) [2]. It allows parameterized modeling but in general the effort to create and simulate the model is time consuming, especially if 3D models are used. On the other hand these models have the advantage to allow the coupling of thermal and electro-magnetical issues. The second group of models solve the thermal differential equations analytically. These analytical results directly show the dependency of the parameters and therefore give the maximum possible insight into the geometrical influences on the temperature distribution. Unfortunately the differential equations can be directly solved only for very simple geometries. This strongly limits the usability of such models. The third and biggest group is positioned between the previously described ones and uses an electrical network representation for modeling the thermal behavior. The challenge is here to define the parameters of the elements of the equivalent circuit (i.e. resistors, capacitors, ...). However the results for both transient and steady state analysis can easily be obtained. Now different kinds of models can be realized using electric networks which depict mathematically lumped parameter models because of their discretized spatially calculated properties. On the one hand there are geometrically distributed parameter models [3], [4] and on the other hand there are geometrically lumped descriptions [5], [6], [7], [8], [9]. Latter models outline a system by showing only parameters for summarized parts. For example to model an electrical motor parts like the stator, rotor, etc. are identified and represented by equivalent resistors and capacitors for each part. The major disadvantage of geometrically lumped models is that further assumptions have to be made because the system of equations is often under-determined. On the other hand an advantage is the use in combination with real time estimation of temperature for integration in feed-backward control strategies because of its fast speed [8]. Lumped parameter models with geometrically distributed elements are often found for calculation of thermal
Abstract—In highly exploited and integrated mechatronic systems the thermal design and management defines the maximum load case. The trend to move to higher power densities needs precise andห้องสมุดไป่ตู้reliable thermal models of electrical machines to determine the limits of new and thermally demanding use cases and/or gives design guidelines for future generations of the product. For the electro-hydraulic system investigated in this paper a mathematically lumped parameter model with geometrically distributed elements has been developed. The thermal properties of the elements are calculated with physical material properties according to their geometric sizes. This allows to implement a comfortable parameterized interface that facilitates an easy change of geometrical dimensions and material properties. Moreover sub-sections of the system can be grouped which allows modularized modeling - this possibility shows its strength when an electrical sub-system is combined with a hydraulic sub-system. Together with automated model generation the resulting SPICE model is well suited for parameterized optimization. The model applies to both transient and/or steady state temperature including the effects of heat radiation and air convection. Thus, fast and accurate calculation of the temperature distribution and heat flow is possible and has been validated by measurements on a test rig. Index Terms—electric network, electro-hydraulic actuator, geometrically distributed elements, lumped parameter model, thermal model.
I. I NTRODUCTION Along with advancing power density and optimization the temperature distribution in an electro-hydraulical system gains importance. However it is mainly not the overall thermal behavior of a system that limits the performance, but the temperature at specific points or in specific areas. These areas contain components or materials with a defined maximum operating temperature which limits the safe operational area of the system. In the demand to increase the operational area it is crucial to understand not only the thermal distribution but also the interconnections of the involved subsystems. The main focus rests here on the calculation of the temperature distribution in the electrical, mechanical or hydraulic sub-systems due to internal heat losses. Since the beginning of the developement of electrical machines it is recognized that an efficient cooling of a system/machine is absolutely necessary to maintain its