Hydraulic Systems_2

Hydraulic Systems_2 - Hydraulic Systems Chapter 11 Material...

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1 Hydraulic Systems Chapter 11 Material taken from Goering, 2003, Of -Road Vehicle Engineering Principles Hydraulic Actuators ± A hydraulic actuator is a device for converting hydraulic power into mechanical power. ± There are two types of actuators: rotary and linear. ± Rotary actuators are called hydraulic motors, while linear actuators are called hydraulic cylinders. Hydraulic Motors ± Hydraulic motors are similar in appearance to hydraulic pumps. ± If care is taken to avoid damaging the seal, pumps and motors can often be used interchangeably.
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2 Hydraulic Motors con’t ± The theoretical speed of a hydraulic motor is calculated using: ± N mt = (1000Q ma ) / D m ± Where N mt = theoretical motor speed, rpm ± Q ma = liquid flow rate into the motor, L/min ± D m = motor displacement, cm3/rev Hydraulic Motors con’t ± Internal leakage from the inlet port to the outlet port causes the actual motor speed to be less than the theoretical speed. ± The volumetric efficiency of a motor is defined as: ± e mv = N ma / N mt = Q ma / (Q ma + Q ml ) ± Where e mv = motor volumetric efficiency, decimal ± N ma = actual speed of motor, rev/min ± Q ml = internal leakage in motor, L/min Hydraulic Motors con’t ± The equation for calculating the theoretical torque produced by a motor is similar to T pt = pD p / 2 π , except that the p-subscripts are replaced by m: ± T mt = pD m / 2 π ± Where T mt = theoretical torque from motor, N*m ± p = pressure drop across motor, Mpa ± D m = motor displacement
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3 Hydraulic Motors con’t ± Internal friction causes the actual torque production to be less than the theoretical torque. Motor torque efficiency is: ± e mt = T ma / T mt = (T mt –T mf ) / T mt ± Where e mt = motor torque efficiency, decimal ± T ma = actual motor torque, N*m ± T mf = motor friction torque, N*m Hydraulic Motors con’t ± P h = Q p / 60 calculates the hydraulic power into a motor, given the actual flow into the motor and the pressure drop across the motor. ± The power efficiency of a hydraulic motor is: ± e mp = P ms / P mh = e mv e mt ± Where e mp = power efficiency of motor, decimal ± P ms = shaft power out of motor, kW ± P mh = hydraulic power into motor, kW ± The volumetric, torque, and power efficiencies of a hydraulic motor vary in a manner similar to the next figure for hydraulic pumps. Goering, 2003, Of -road Vehicle Engineering Principles Motor Efficiencies •e pp = pump power efficiency •e pt = pump torque efficiency •e pv = pump volumetric efficiency
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4 Hydraulic Cylinders ± When oil is forced into the port on the left, the cylinder is forced to extend while expelling oil from the port on the right. ± Conversely, the cylinder retracts and
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Hydraulic Systems_2 - Hydraulic Systems Chapter 11 Material...

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