| Summary: | 碩士 === 國立雲林科技大學 === 機械工程系 === 105 === In this study, a spool valve was used as the design basis because it had this advantage that the spring combined with oil pressure could generate different feedback forces on the two ends of the valve body. Nevertheless, the flow channel design near the original valve core was an orifice structure and the flow already became saturated when the opening of the valve core opened to 3-4 mm, resulting in an overly small action range for effective flow compensation. In view of this, this paper presents the change of the orifice structure to cones with different degrees of slope with reference to a poppet type restrictor for expanding the effective action range of the valve core.
The research methods were divided into simulation and static experiments for the investigation into whether changes to different viscosities affected the valve core with different oblique cones and finally the examination and analysis of various parameters via the static experiment. The COMSOL software was used for simulating the flow field of the hydraulic oil. The simulation results showed the valve core with different oblique cones was indeed affected by changes to different viscosities. At 90°, which belonged to the opening structure (or the orifice structure), the simulation showed the flow was almost unaffected by the viscosity. This also proved matching with the orifice structure formula.
First, the spring end of the valve body was designed with an open oil passage, which allowed excessive oil to exude via the high pressure end and directly return to the oil tank. The experiment showed that this type of restrictor could cause the flying height of the bearing (oil film thickness) to bounce drastically when a certain load value was reached. Compared to the orifice valve core, the non-orifice cones, with the help of the shear from fluid friction, would cause the valve to become wide open when the load was lower, thus resulting in flow spike. To achieve such flow spike by increasing the elasticity coefficient of the spring, it requires sufficiently high load and feedback pressure to happen. To sum up, flow and oil film spikes are inevitable.
To eliminate this fault, this study moderated the tendency of valve core movement by connecting the oil pressure feedback loop at the spring end and using the oil pressure conveyed from the bearing end to offset part of the force that opened the valve. The experiment showed that this design, whether with an orifice or cone valve core, could eliminate the aforementioned defect and thus generate good bearing rigidity.
Keywords：hydrostatic bearing, restrictor, spool - type, orifice- type, poppet – type
|
|---|
