Page 181 - The Mechatronics Handbook

10

Fluid Power Systems

10.1 Introduction
Fluid Power Systems • Electrohydraulic
Control Systems
10.2 Hydraulic Fluids
Density • Viscosity • Bulk Modulus
10.3 Hydraulic Control Valves
Principle of Valve Control • Hydraulic Control Valves
10.4 Hydraulic Pumps
Principles of Pump Operation • Pump Controls
and Systems
10.5 Hydraulic Cylinders
Cylinder Parameters
Qin Zhang 10.6 Fluid Power Systems Control
System Steady-State Characteristics • System Dynamic
University of Illinois
Characteristics • E/H System Feedforward-Plus-PID
Carroll E. Goering Control • E/H System Generic Fuzzy Control
University of Illinois 10.7 Programmable Electrohydraulic Valves

10.1 Introduction

Fluid Power Systems
A fluid power system uses either liquid or gas to perform desired tasks. Operation of both the liquid
systems (hydraulic systems) and the gas systems (pneumatic systems) is based on the same principles.
For brevity, we will focus on hydraulic systems only.
A fluid power system typically consists of a hydraulic pump, a line relief valve, a proportional direction
control valve, and an actuator (Fig. 10.1). Fluid power systems are widely used on aerospace, industrial,
and mobile equipment because of their remarkable advantages over other control systems. The major
advantages include high power-to-weight ratio, capability of being stalled, reversed, or operated inter-
mittently, capability of fast response and acceleration, and reliable operation and long service life.
Due to differing tasks and working environments, the characteristics of fluid power systems are
different for industrial and mobile applications (Lambeck, 1983). In industrial applications, low noise
level is a major concern. Normally, a noise level below 70 dB is desirable and over 80 dB is excessive.
Industrial systems commonly operate in the low (below 7 MPa or 1000 psi) to moderate (below 21 MPa
or 3000 psi) pressure range. In mobile applications, the size is the premier concern. Therefore, mobile
hydraulic systems commonly operate between 14 and 35 MPa (2000–5000 psi). Also, their allowable
temperature operating range is usually higher than in industrial applications.

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