Hydraulic direction control valve as a measuring orifice : Pressure compensation integrated into the main spool control

Abstract

AB3:Tämän työn tarkoituksena on kehittää hydraulisen venttiiliohjatun järjestelmän venttiilistä toimintaperiaatteeltaan mittakuristinta vastaava tilavuusvirran mittausmenetelmä integroituna venttiilin normaali toimintaan. Kehitettyä mittausmenetelmää hyödyntäen venttiiliä voidaan käyttää epäsuorana nopeuden mittausmenetelmänä. - Tässä työssä esitetty sovellus on neljän vapausasteen hydraulisen puomin mekaanisten painekompensaattorien korvaaminen itse venttilin pääkaraa toimielimenään käyttävällä sähköisellä painekompensaattonila, jonka nopeustakaisinkytkentäsignaali generoidaan venttiilin yli olevasta paine-erosta, venttiilin karan aseman mallista ja ohjaussignaalista. Työssä tehty tarkastelu kattaa kolmen keskeisen valmistajan venttiilit.- Koska työn tarkoituksena on tehostaa hydraulisen toimilaitteen manuaalista ohjausta ja koska painekompensaattori käytännössä on sidottu LS järjestelmän toimintaan, esitetään tässä yhteydessä myös sähköisen LS järjestelmän toteutus vaikeasti realisoitavassa ja testilaitteistoa vastaavissa olosuhteissa.

In this study an electrically implemented pressure compensator is developed. The hydraulic valve itself is used as a measuring orifice: The pressure difference over the valve is measured and combined to the notch relative cross-sectional area to estimate the flow through the notch. In the beginning the servo valve is used to define a goodquality valve flow model for spool type valves and to generate the velocity feedback signal for velocity servos and the inner loop of other kinds of servos. In the servo valve model the leakage flows are measured and modelled and a method to define the control notch dedicated offsets is developed.- When the control notch is opened, the through-flow of the notch begins to resemble more turbulent than laminar flow. However the change from one mode to another is not sudden, and thus modelling the interchange between the modes needs to be carried out with care, but it will still remain in many ways ambiguous. A very practical method requiring very few calibrations requiring method is developed for this purpose, keeping in mind the application.- Since the spool position, actual velocity and pressures change in different phases, and the future application includes direct pressure measurement but no knowledge of the load mass or cylinder position measurement, the corrections in the signal phases in the model are done using two different methods. Both of these methods are presented in detail.- The final application is a four-degree-of-freedom hydraulic boom pressure compensation. The load sense function is implemented electrically. The load sense control schema is presented in detail to give an overview of the studied system characteristics. In the actual boom control the pressure compensator is integrated into the main spool control while the main spool control signal is also used as an input to the pressure compensation block, so this study is actually a closed loop velocity control of a 4 DOF boom with the valve and pressure sensors as a feedback sensor. The theoretical approach is used to tune the velocity control of each DOF and then the velocity control is finally tuned in practice. The actual velocities are measured with high-resolution incremental encoders and used in the pressure compensator calibration and reference velocity. The results are shown and discussed as well as the possibilities to exploit velocities measured in this way for other purposes too.