Contents of the Journal of Mechanical Engineering 48, 2 (1997)

ORAVSKY, V.: Determination and relation of various efficiencies 
of a symmetric hydrostatic transmission at periodic load (in Slovak)      69


MURIN, J., HUCKO, B.: A weakly coupled thermo-mechanical problem - 
solution by the finite element method (in Slovak)                         86


ZIGO, M.: Determination of extreme properties of springs created
from two mutually symmetrically sloped rubber prisms (in Slovak)          97 


STEFANIK, P., VOLNAR, L., CHUDY, V., SEBO, P.: Flexible joints made 
of polymer composites for load transfer in measuring systems             
(in Slovak)                                                              106


HOMISIN, J., JURCO, M.: Application   of differential   pneumatic 
clutches with and without autoregulation in torsionally oscillating 
mechanical systems (in Slovak)                                           116


ONDROVIC, P., JELEMENSKY, K.: Hydrodynamics and heat transfer 
in helical ducts with rectangular cross-section (in Slovak)              126



Report

KOUDELKA, M., ZAK, R., TALANDA, M.: Characteristics and exploitation 
of an electromechanical sensing unit (in Slovak)                         136

In the paper one starts from the dimensionless dynamic model of a linear symmetric hydrostatic transmission HsT with a constant driving moment at input (hydrogenerator, HG) and a harmonic loading moment at output (hydromotor, HM). The model is of the 7th order and contains besides others angular velocities \omega_G, \omega_M, moments M_G, M_M and 8 dimensionless parameters as well. Also split submodels X and Y of the 3rd and 4th order are presented enabling simpler solution of the original model.
After survey of literature several efficiencies (based on powers and works, full and reduced, quasi-static and dynamic) are introduced, classified and defined and their mutual relations are examined.
Quasistatic efficiency is determined and analysed more in detail whereby some simpler cases (ideal, critical) are derived from the general HsT. Influence of parameters of HsT upon quasistatic efficiency is investigated both analytically and graphically.

The aim of this paper is to present a simple theory of weakly coupled thermo-mechanical problems. The plastic strains caused by an external loading generate heat which represents an additional source of it, i.e. the temperature field is changing. Because of thermo-mechanical coupling the shape of a thermal field domain is also changing. The presented theory is illustrated by upsetting of a cylinder.

A method for calculation and production of springs created from two mutually symmetrically sloped rubber prisms inserted between two consoles, has been previously described in [1]. This type of rubber spring can be created in an arbitrary size irrespective of the produced type of rubber-metal springs. Therefore, in this paper we describe how to choose physical properties and shape of this type of rubber spring, to reach its extreme values which warrant optimal dynamic properties of the resilient support created by this spring.

A new construction of a flexible joint is described. The functional section of the joint is made of unidirectional carbon fibre/epoxy resin composite. Using the joint, an effective transfer of axial force of given intensity is ensured with optimal spatial deflection and minor rotation.

It is possible to lower dangerous torsional oscillations to an acceptable level by tuning mechanical systems, i.e. by adjusting the stiffness and absorption parameters of flexible shaft clutches. The research staff of our department has recently devoted deep attention to development and research of pneumatic flexible shaft clutches. From the results of the theoretical research characterizing the influence of pneumatic clutches upon the size of the torsional oscillations of a model mechanical system, it is clear that a differential pneumatic clutch is suitable for mechanical systems which run with constant working revolutions, whereas autoregulative pneumatic clutches can be classified as mechanical systems running in a broad range of running revolutions.

The aim of the work is to expand knowledge in the field of hydrodynamics and heat transfer in helical ducts with rectangular cross-section and to investigate effects of the duct geometry. Experiments were performed in six channels with various simplexes d_e/D and b/h. In the experiments the influence of the helical lead or relative lead s/D on the hydrodynamics and heat transfer was not studied. Working media were water and air. In water experiments both heating and cooling operations were studied. Our results are presented in the form of criterial equations.

One way how to objectively evaluate condition of human motion apparatus in biomechanics is to measure the affect power. By its analysis we obtain not only the state of the motion apparatus but also information about healing progress or rehabilitation, the necessity of its correction as well as for the diagnosis itself. In the paper a new electromechanical sensing unit on base of an optounit is described, its principle, characteristics, its advantages over another unit used until now, as well as its preferences and exploitation. Some of the diagrams obtained during verification of its characteristics as well as progress plots of power obtained from function tests are given.