机电技术专业英语课件作者徐起贺张庆良pataalessonsix.pptVIP

尚辅网 / 机电技术专业英语 Lesson Six Text Hydraulic drives are used in preference to mechanical system when power is to be transmitted between points too far apart for chains and belts1，high torque at low speed is required, a very compact unit is needed, a smooth transmission, free of vibration, is required, easy control of speed and direction is necessary, or out speed must be varied steplessly. Electrically driven oil pressure pumps establish an oil flow for energy transmission, which is fed to hydraulic motor or hydraulic cylinder, converting it into mechanical energy. The control of the oil flow is by means of valves. The pressurized oil flow produces linear or rotary mechanical motion. The kinetic energy of the oil flow is comparatively low, and therefore the term hydrostatic driver is sometimes used. There is little constructional difference between hydraulic motor and pumps. Any pump may be used as a motor. The quantity of oil flowing at any given time may be varied by means of regulating valves or the use of variabledelivery pumps2. Hydraulic Power Transmission In general terms, hydraulic drives may be divided into rotary and linear types. Rotary drives produce a rotating motion, whilst linear devices in the form of piston and cylinder units produce a reciprocating movement. All hydraulic motors function broadly is in accordance with the same basic principle. A pressurized fluid is alternately forced into and removed from a chamber. The filling cycle begins with minimum chamber volumes. When the chamber reaches its maximum volume (the maximum capacity) the filling is ended by isolating the chamber from the supply line. The oil is then returned to the oil pump through the return lines and at the same time the next chamber is filled with oil. Lesson Six New Words and Expressions Lesson Six Notes 1. Hydraulic drives are used in preference to mechanical system when power is to be transmitted between points too far apart for chains or b