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The paper addresses some aspects of an ongoing research on a commercial compact excavator. The interest is focused on the analysis and modelling of the whole hydraulic circuit that, beside a load sensing variable displacement pump, features a stack of nine proportional directional control valves modules of which seven are of the load sensing type. Loads being sensed are the boom swing, boom, stick and bucket, right and left track motors and work tools; instead, the blade and the turret swing users do not contribute to the load sensing signal. Of specific interest are the peculiarities that were observed in the stack. In fact, to develop an accurate AMESim modelling, the stack was dismantled and all modules analysed and represented in a CAD environment as 3D parts. The load sensing flow generation unit was replaced on the vehicle by another one whose analysis and modelling have been developed using available design and experimental data.

The rapid and ever increasing development of microprocessor based controllers in a wide and diversified range of applications leads to consider their candidacy on spacecraft systems. Easy programmability, potentials for implementing the most complex logical control laws, and their “adaptivity” form the backbone of their many interesting features. In this perspective, the paper illustrates an application of adaptive control, within a closed air loop, for thermal conditioning of a typical biochemical experiment cell to be flown in space and addresses some aspects specific to the underlying control philosophy.

The present paper details an original investigation based on the attainment of performance predictions of a radiator panel that is in itself a subsystem of the Technology Demonstration Model, an advanced heat rejection device conceived, and built, by AERITALIA SpA under Contract to ESA (European Space Agency) Since at the time of writing this report experimental results we re not available, expected correlations and contrasts will form the object of future communications. In this perspective, the feasibility of simulating via computer assisted analysis the aforementioned subsystem is demonstrated; this being achieved by an accurate build-up of the mathematical model and subsequent development of appropriate software tools grounded on the finite element method.

A rigorous study of physical phenomena that characterize the energy transfer in a radiative panel, presents serious problems when, aiming at optimizing feasible design solutions, is oriented to the prognostic evaluation of the overall system performance. Different thermal interaction modes among constitutive components (i.e. headers, tubes, fins, honeycombs) and an intrinsically complex geometry make extremely cumbersome, if not impossible, to operate with a mathematical model featuring infinite degrees of freedom, as is the case for the real system. The need thus arises to build up a model possessing limited degrees of freedom, capable of approximately portraying, yet with specifiable accuracy, the bulk of physical phenomena that actually evolve in the heat rejection system. In the given frame this work elucidates how the objective may be attained by utilizing the finite element method and how it is also possible to deal with non-linearities stemming from existing boundary conditions.

Effective methodologies are detailed to help synthesising better hydraulic systems in terms of efficiency and control characteristics. In principle, by considering the system dissected in “Multipole Blocks” with appropriate linking strategies, the approach enlightens the role of digital computers and the viability of problem oriented Software when proper strategies and techniques receive adequate implementation. The entire study and the ensuing computer code are both grounded on the programming language “APL”. Based on a reference system, an extensive analysis is detailed finally leading to the presentation of optimization procedures to help demonstrate, on practical bases, the versatility of the proposed approach. An unconstrained optimization APL code is reported in the Appendix, illustrating a remote terminal session to solve a typical test problem.

The paper contributes to the analysis of hydrostatic vehicles looking at controlling and sizing aspects in terms of productivity goals. Three significant stages are developed: (1) an open circuit hydrostatic transmission model with a variable displacement pump actuating two fixed displacement motors; (2) a tracked vehicle locomotion model interfacing transmission and soil characteristics; (3) a comprehensive evaluation of the system behaviour based on the “overall productivity efficiency”. Productivity concepts are considered as useful yardsticks to decide on optimal sizing and controls of transmission and vehicle components under specific constraints. Computational case-studies, based on a conversational program, are described to illustrate applications and potentials of this approach.

In view of a rational appraisal of mobile hydraulics design, a simple yet significant example system is considered and a detailed static analysis is performed by means of a conversational computer program, basically modular in concept, and flexible enough to allow the implementation of potentially feasible refinements and extensions. A representative and meaningful number of applications is detailed within the major topics of energy transmission and system control characteristics. The paper delineates the development of the mathematical model and presents results of the analysis by adopting two intrinsically different methods of attack: the parametric search and the stochastic approach. Relative merits of these methods are contrasted in the light of their informative yield capabilities and adequacy in accurately reflecting system performances. Output data are then scrutinized and proper inferences are made.

Efficiency characteristics are considered of simple control types (constant pressure and constant power) applied to a variable displacement pump as single unit or in connexion with a fixed displacement motor or a dummy actuator (having efficiency features of a transmission line). The most efficient way to implement a specific control is identified in terms of speed and displacement, while basic control parameters result from the optimization of maximum or mean efficiency. Some effects of controls on driving engine fuel consumption and sizing are also discussed. Computations are based on efficiency models devised by authors as approximation of a number (sometime large) of reference data, and carried out with an original Non-Linear Programming code (FALL77).

The X77 Hydrostatic Research Vehicle was completed in the present form during 1977 and officially presented at the International Agricultural Fair in Verona (Italy). This paper reviews some of the major design concepts, features and specifications for this new vehicle. In this context, particular emphasis is applied in presenting favorable aspects of an integral hydrostatic power transmission in the light and perspective of actual and potential transmission controls. Problem areas and development options of this approach are also discussed.

The hydrodynamic transmissions found in much of today's earthmoving machinery provide distinct advantages in overall functional facilities, but there is a great need for improvement in their converter efficiencies. This paper explains a new method, based on optimization techniques and utilizing computer analysis, which has been developed to help solve this problem. Computational case studies are described to illustrate its use in selecting and identifying optimal values for basic transmission parameters. The immediate and potential applications of this approach are also discussed.