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The paper deals with influence of combined load of engine on drawbar properties of a tractor. The aim was focused on determination of power consumed via PTO and the impact on drawbar pull. During the development of the tractor is assumed that certain work will transfer operations from 60 to 60% over the PTO. Combined loading of engine power significantly reduces driving force as well as drawbar pull. In general, any change in power distribution will affect power balance and overall efficiency. Nevertheless, decreasing of drawbar force enables higher efficiency due to lower resistance in transmission to PTO. Previous researches have shown that the overall loss can achieve at the most 15 %. Ordinary efficiency of pulling tractor will not cross the limit of 70 %. The contribution brings the results of experimental work where the load was changed. The combined load can be simulated with using of chassis dynamometer along with a dynamometer connected over the PTO. Basic levels of absorbed power over the PTO were set to 50, 70 and 90 kW. These points usually presents needs for main field operations. Settings of the test were carried out of constant power transferred over the PTO. Variable part of engine power is consumed to movement what means change in tractor velocity. The results of experiment have been evaluated using spreadsheet editor and statistical software and were built into plots.

Within the frame of this paper the key theoretical knowledge to the selected topic is described, the presentation of partial results and discussion on the issue of the psychological aspects of managerial work, focusing on stress and its manifestations are submitted. The aim of this research was to identify the most frequent stress symptoms in the physiological, emotional and behavioral field and to define the main factors which cause them in work and private life terms. For the purpose of this research of stress effects on health area a questionnaire technology of our own design was chosen. For a deeper understanding of sources of an increased psychological stress in managerial activities a technique of interviews with the top managers was used. Research investigation has showed the action of stress on the senior managers, particularly increased during the current economic recession. The most significant signs of stress are manifested in physiological area, especially by fatigue, headache, digestion problems and sleep disturbances, as in the emotional area by anxiety, excessive concern and overall irritability. At the same time stress impacts also the behavioral area, where it has a negative impact to the work and family life. In the course of processing this subject, an absolutely obvious need occurred for a deeper processing of this large area of work stress, which will be subsequently dealing with, and whose output will be, the methodology of anti-stress strategy for HR (Human Resources) managers and Senior Executives of companies to prevent stress, promote health and quality of living conditions in the workplace.

The goal of the experimental measurement was determination of relation among weight load of the tractor together, hitch height changes and drawbar characteristic. The measurement was realized on chassis dynamometer at MUAF in Brno. The first step consisted of rated speed characteristics measurement in conformity with OECD demands. The drawbar characteristic was measured under two selected gears. Adding 980 kg to the nominal wight of the tractor brought increasing maximal drawbar power and drawbar force together with decreasing of slip. The highest differences were observed during the mesurement of fifth gear shifted. The drawbar force grew up to 18.9% as well as the maximal drawbar power (15.2%). The maximal drawbar power at ninth gear gave 62.8 kW. The hitch height was setting to 0.54 m; 0.64 m and 0.74 m. When the hitch height was set from 0.54 m to 0.74 m the drawbar force an power on front axle was lower by reason of load reduction. As can be noticed from the final drawbar characteristics, both curves are identical up to border of maximal drawbar power. Small differences in the area of the highest slips can be ascribed to the rolling resistance.