Razmere v režah hidravličnih ventilov

J. Pezdirnik

Vzdrževalec 60 (1997) 33–35.

Abstract

S funkcionalno-konstrukcijskega vidika oziroma z vidika kontakta med gibajočim se in mirujočim elementom ločimo v hidravliki ventile na ventile sedežnega in ventile drsniškega tipa. Batni drsniški ventil je najbolj pogosto uporabljani tip ventila v pogonsko-krmilni hidravliki. Cilindrični bat oscilira linearno v aksialni smeri v puši ali direktno v izvrtini ohišja. Zaradi tehničnih razlogov je pri tem tipu ventilov vedno prisotna določena reža velikosti vsaj nekaj mikrometrov med steno izvrtine in batom. Kadar se pojavijo različni tlaki med obema stranema reže pride do lekažnega toka skozi režo. V prispevku je podana razmeroma splošna enačba, ki omogoča izračun tega lekažnega toka skozi režo. Bata z idealno cilindrično obliko ni mogoče izdelati. Zato se pod določenimi pogoji pojavijo različni padci tlaka v krožni reži med obema elementoma in sicer v vzdolžni - aksialni smeri. Kot je znano, se večinoma pojavijo v slučaju, ko ima bodisi bat bodisi izvrtina ali pa oba skupaj obliko prisekanega stožca namesto idealne cilindrične oblike. V slučaju, da je to npr. bat, je razlika v premerih bata na enem in drugem koncu največ do nekaj mikrometrov ali celo manj od enega symbol 109 f "Symbol"s 12 m. Kljub temu je to dovolj, da nastopijo prečne sile, ki so pri določenih parametrih lahko pomembno velike. Prečna sila deluje na bat in preko njega na steno izvrtine. V prispevku so podane enačbe, ki omogočajo izračun prečnih sil. Zaradi nepravilnih cilindričnih oblik bata in/ali izvrtine obe drsni površini nista v celoti v kontaktu. Zato se prečna sila prenaša z bata na steno izvrtine samo preko nekaj mikrokontaktnih ploskvic, ki nastanejo na vršičkih izstopajočih iz obeh površin. Upoštevaje višino posameznega vršička lahko izračunamo kot med teoretičnim in realno nastopajočim mikrokontaktom. Ustrezne enačbe za izračun tega kota so podane v prispevku.

From the design-functionally point of view and the point of view of the contact between the moving and the stationary element respectively, we divide hydraulic valves into seat-type and spool-sliding type of valves. The spool-sliding valve is most frequently applied type of valve in power-control hydraulics. The cylindrical spool oscillates linearly in axial direction in a bushing or directly in a bore made in a housing. Because of the technical reasons a certain gap of at least few micrometers between the bore and the spool is always present at this type of valves. In the case of the different pressures between the both sides of the gap, a leakage flow through the gap occurs. Rather universal equation, which enables the calculation of the leakage flow, is given in this paper. An ideal cylindrical shape of the spool or of the bore cannot be manufactured. Therefore, under certain circumstances, different pressure drops occur along the axial direction in a circular gap between both elements. As already known, they mostly occur when either a spool or/and a bore is truncated cone-shaped instead of possessing an ideal cylindrical shape. The error difference of spool cross-section diameters due to the cone-shaped spool is normally up to a few micrometers or even less than one symbol 109 f "Symbol" s 12m. Nevertheless, it is sufficient to consequently give rise to a transverse force which, for certain parameters, may be significantly great. The transverse force acts on the spool and beyond it on the wall of its bore. In the paper the equations to calculate the transverse forces are given. Due to incorrect cylindrical shapes of the spool and/or its bore both sliding surfaces are not completely in contact. The transverse force is therefore transmitted from the spool to the bore wall only over a few microcontact areas resulting in the asperities which protrude from one or both surfaces. With regards to the height of a single asperity the angle between the theoretical and the real microcontact can be calculated and the adequate equations for the calculation are given in the paper.

Keywords: pogonsko-krmilna hidravlika, hidravlični batni drsniški ventil, reža, oblika drsnih površin, prečna sila, power-control hydraulics, hydraulic spool-sliding valve, gape, shape of sliding surfaces, transverse force

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