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Article citation info: (*) Tekst artykułu w polskiej wersji językowej dostępny w elektronicznym wydaniu kwartalnika na stronie www.ein.org.pl KAmińsKi Z, KuliKowsKi K. Determination of the functional and service characteristics of the pneumatic system of an agricultural tractor with mechanical brakes using simulation methods. Eksploatacja i Niezawodnosc -maintenance and Reliability 2015; 17 (3): 355-364, http:// dx.doi.org/10.17531/ein.2015.3.5. Zbigniew KAmińsKi Krzysztof KuliKowsKiDetermination of the functional anD service characteristics of the pneumatic system of an agricultural tractor with mechanical brakes using simulation methoDs wyznaczanie metoDami symulacyjnymi właściwości funkcjonalnoużytkowych pneumatycznej instalacji ciągnika rolniczego z hamulcami mechanicznymi* IntroductionIn agricultural tractors, a variety of friction braking mechanisms are used, including band brakes, drum brakes, and dry or wet multidisc brakes [5]. To transfer the energy needed to run the service brakes of a tractor, a mechanical, hydraulic or an air drive is used. Selection of the drive type and the energy source depends on the design and weight of the tractor. In low-and medium-power tractors, manually operated hydraulic brake systems are used, which are relatively inexpensive and simple. Because of their cost, mechanically actuated brakes are still attractive in low-power tractors.Agricultural tractors with mechanical or hydraulic brakes are equipped with a pneumatic system designed to run the air braking systems of towed trailers and agricultural machines. So called combined systems are currently used [32], which have the capability to operate with the single-and dual-line braking systems of towed vehicles.A typical combined pneumatic system of a farm tractor consists of two major parts: an energy supply unit and a control device. The function of the energy supply unit is to compress and purify air and to maintain the adequate pressure in the tractor and trailer reservoirs in order to ensure the required trailer braking performance. The role of the control device is to provide the follow-up control of the single-or dual-line braking system of a towed vehicle in a manner that enables the synchronous braking of the both vehicles. Control devices differ mainly in the type of the trailer brake control valve, which can be actuated either mechanically, hydraulically or pneumatically, deEksploatacja i NiEzawodNosc -MaiNtENaNcE aNd REliability Vol.17, No. 3, 2015 356 sciENcE aNd tEchNology pending on the tractor brakes [32]. A schematic diagram of a tractor's pneumatic system with a mechanically actuated brake valve is shown in Figure 1.Because of the road safety, agricultural vehicles braking systems must meet several specific requirements [8,9] for braking performance, high operation speed during rapid braking (the response time should not exceed 0.6 s) and the compatibility of the tractor and towed vehicle braking systems [27] (the synchrony of operation of individual circuits). Research by Scarlett [28] reveals that ...

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Abstract. The paper presents a description of a new DTFC3L3A (direct torque and flux control three levels three areas) control method of induction machine as well as its comparison with the DTC method. The basis for the comparison is the switching frequency of described methods. The proposed method is optimized to reduce number of switchings (which is proportional to switching power losses) in static state, as well as it takes into account the δ angle which makes it possible to obtain a sinusoidal shape of flux within range of low angular frequencies of an asynchronous machine. The paper includes the results of experiments performed on a three level DC/AC inverter for both control methods.

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