Testing stands for laboratory tests of hydrostatic pumps of agricultural machinery

Abstract

Abstract:In this paper, a design of testing stands for the durability tests of hydrostatic pumps of agricultural tractors is presented. The designed testing stands will be used for the laboratory verification of the influence of biodegradable oils on the durability of tractor hydrostatic pumps. The designed testing stands were built and tried out. On the basis of the results achieved in the system function tests, we can say that the testing stands are suitable for the durability tests of hydrostatic pumps. -by a strong dirty fluid -hydraulic fluid with a higher content of contamination has a greater influence on the durability of the hydrostatic pump, -by increased operating pressure, -by acceleration of the operating cycle. Laboratory tests by the acceleration of the operating cycleThe testing stand for these tests uses the selected characteristic of the cyclic pressure loading for the loading of the hydrostatic pump tested. The working principles of most frequently used types of testing stands are shown in Figure 1a and Figure 2.The tests of hydrostatic pumps can be realised by the testing stand according to Figure 1a (Radhakrishnan 2003). The characteristic of the cyclic pressure loading is given Figure 1b. This characteristic is created by the solenoid valve EHTV which is part of the circuit, Figure 1a. The solenoid valve is supplied by the voltage signal which creates the required pressure loading according to Figure 1b.The pressure loading can be realised by a flywheel which is connected to the circuit of the testing stand according to Figure 2. The loading of the hydrostatic pump is realised by flywheel Z which is mechanically connected by coupling to the hydrostatic motor HM. Three-position, four-port valve R realises a change in the rotation direction of hydrostatic motor HM. It causes the increase or decrease of pressure in compliance with the characteristic of the cyclic pressure loading Tkáč et al. 2004). MATERIAL AND METHODS Design of testing standsThe demands for the design of the testing stands issue from the parameters of hypothetically tested hydrostatic pumps and the loading process of the hydrostatic pump during the durability test (STN 11 9287 1988). The function of the suggested stands will be checked by the system function test. During the system function test and durability test, mineral oil MOL Traktol Ultra SAE 80W, API GL-4, will be used. The temperature will be 50°C ± 2%. Demands on cyclic pressure loading according to standard STN 11 9287The demands according to the standard STN 11 9287 (1988) are stated as follows: "Technical durability must be minimum 10 6 cycles under cyclic pressure loading from zero to the nominal pressure within frequency 0.5-1.25 Hz during velocity of pressure increasing 100-350 MPa/s and in nominal parameters. It this case decreasing of the volumetric Figure 3. The testing stand must be designed so that the running of the durability test corresponds to the standard STN 11 9287 (1988) Hydrostatic Gear Pumps and Hydro-motors in which the dynamic loading of...

Evaluation of tractor biodegradable hydraulic fluids on the basis of hydraulic pump wear

“…We designed the test bench so that the course of the test correspond with Standard STN 11 9287 "Gear Pumps and Motors" in which the dynamic load of gear pumps and motors is performed under cyclic pressure load. Design of test bench was published by Tkáč et al (2008). Therefore, the tests were done under cyclic pressure load from zero up to the nominal pressure with frequency from 0.5 to 1.25 Hz.…”

“…With respect to the fact that volume losses remain practically unchanged within a small range of rotation speed (1,500 ± 75 min -1 ), the flow efficiency η pr is constant, too. Therefore, it is possible to write the equation introduced by Varchola (2003): (Tkáč et al 2008) Vol. 59, 2013, No.…”

The operation of agricultural tractor with universal ecological oil

“…on the technical state of the hydraulic system parts (Žikla, Jablonický 2006;Jablonický et al 2007;Tká et al 2008). …”

The accelerated laboratory test of biodegradable fluid type "ertto"

“…The characteristics are result of regression analysis done by the MS Excel software. (Tkáč et al 2008): M -electric motor, n 1 -rpm sensor, HG 1 -tested hydrostatic pump, TV 1 -two stage pressure relief valve, TV 2 -two stage sequence valve for adjust nominal pressure in the outlet of hydrostatic pump, p 1 -pressure gauge of pressure in the inlet, p 2 -pressure gauge of pressure in the outlet, K 1 -spherical plug valve, PR -gear box, OB -control block, T -tank, RV -tree-positions, four-port slide valve with closed center which is operated electro-hydraulically, CH 1, CH 2, CH 3 -coolers, V 1, V 2, V 3 -fans, HG 2 -hydrostatic pump for cooler, t 1 -temperature sensor for tank, R -thermostatic regulator which control switching on of cooling fans…”

“…It is used in smaller and medium agriculture and construction machines. The UD hydrostatic pumps types are used in Zetor tractors and in Tatra commercial vehicles (Jihostroj, Ltd., 2007;Tkáč et al 2008). …”