Hydraulic Fluid Power

PART I:Fundamental principles4 Objectives4 CHAPTER 1:Introduction to hydraulic control technology6 Historical perspective7 Fluid power symbology and its evolution12 Common ISO Symbols16 Problems25 CHAPTER 2:Hydraulic fluids28 Ideal vs. Actual hydraulic fluids28 Classification of hydraulic fluids31 Mineral oils (H)32 Fire resistant fluids (HF)33 Synthetic fluids (HS)34 Environmentally friendly fluids34 Water hydraulics34 Comparisons between hydraulic fluids35 Physical properties of hydraulic fluids36 Fluid compressibility: Bulk Modulus Fluid density38 Fluid viscosity42 Viscosity as a function of temperature43 Viscosity as a function of pressure47 Entrained air, gas solubility and cavitation48 Entrained air48 Gas solubility48 Equivalent properties of liquid-air mixtures50 Contamination in hydraulic fluids57 Considerations on hydraulic filters59 Filter placement64 Considerations on hydraulic reservoirs68 Tank volume68 Basic design of a tank69 Problems71 CHAPTER 3:Fundamental Equations73 Pascal’s law73 Basic law of fluid statics74 Volumetric flow rate77 Conservation of mass80 Application to a hydraulic cylinder81 Bernoulli’s Equation84 Generalized Bernoulli’s equation85 Major losses calculation87 Minor losses89 Hydraulic resistance90 Stationary modeling of flow networks92 Momentum equation96 Flow forces100 Problems106 CHAPTER 4(*):Orifice Basics111 The orifice equation111 Fixed and variable orifices115 Power loss in orifices117 Parallel and series connection of orifices119 Functions of orifices in hydraulic systems123 Orifices in pressure and return lines123 Orifices in pilot lines126 Problems131 CHAPTER 5:Dynamic Analysis of Hydraulic Systems134 Pressure build-up Equation - hydraulic capacitance134 Fluid inertia Equation - hydraulic inductance140 Modeling flow network – dynamic considerations146 Validity of the lumped parameter approach151 Further considerations on the line impedance model152 Damping effect of hydraulic accumulators153 Problems156 References160 PART II:Main hydraulic components4 Objectives5 CHAPTER 6 (**):Hydrostatic pumps and motors6 Introduction6 The ideal case7 General operating principle9 ISO symbols13 Ideal equations14 The real case16 Losses in pumps and motors17 Fluid compressibility17 Internal and external leakage20 Friction21 Other types of losses23 Volumetric and hydro-mechanical efficiency24 Trends for volumetric and hydromechanical efficiencies28 Design types34 Swashplate type axial piston machines35 Bent axis type axial piston machines38 Radial piston machines39 Gear machines40 Vane type machines43 Problems46 CHAPTER 7(*):Hydraulic cylinders50 Classification50 Cylinder analysis52 Ideal vs. real cylinder55 Problems61 CHAPTER 8(*):Hydraulic control valves63 Spring basics64 Check and shuttle valves65 Check valve65 Pilot operated check valve66 Shuttle valve67 Pressure control valves68 Pressure relief valve68 Direct acting pressure relief valve68 Pilot operated pressure relief valve72 Pressure reducing valve75 Direct acting pressure reducing relieving valve75 Pilot operated pressure reducing valve77 Flow control valves80 Two-way flow control valve80 Fixed displacement pump circuit with a two-way flow control valve83 Three-way flow control valve87 Fixed displacement pump circuit with a three-way flow control valve89 Directional control valves95 Meter-in and meter-out configurations97 Neutral position100 Actuation methods103 Servovalves107 Characteristic of servovalves112 Servovalves vs. proportional valves123 Problems126 CHAPTER 9(*):Hydraulic Accumulators132 Accumulator Types132 Weight loaded accumulators132 Spring-loaded accumulators132 Gas-charged accumulators133 Piston-type accumulators133 Diaphragm-type accumulators134 Bladder-type accumulators135 Operation of gas charged accumulators137 Typical applications138 Energy accumulation138 Emergency supply140 Energy recuperation140 Hydraulic suspensions140 Pulsation dampening – shock attenuation141 Equations and sizing142 Accumulator as energy storage device142 Accumulator as dampening device145 Problems151 References154 PART 3:Actuator control concepts3 Objectives3 CHAPTER 10 (*):Basics of actuator control5 Control methods: speed, force and position control5 Resistive and overrunning loads7 Power flow depending on the load conditions9 Problems11 CHAPTER 11:General concepts for controlling a single actuator13 Supply and control Concepts13 Flow supply – primary control18 Flow supply – metering control19 Flow supply – secondary control21 Pressure supply – primary control21 Pressure supply – metering control23 Pressure supply – secondary control25 Additional remarks26 CHAPTER 12:Regeneration with single rod actuators27 Basic Concept of regeneration27 Actual implementation32 Directional control valve with external regeneration valves32 Directional control valve with regenerative extension position33 Solution with automated selection of the regeneration mode34 Problems36 References38 PART 4:Metering controls for a single actuator3 Objectives3 CHAPTER 13:Fundamentals of metering control5 Basic meter-in and meter-out control principles5 Meter-in control Extension with resistive loads Retraction with overrunning loads Meter-out control10 Extension with resistive loads 14 Retraction with overrunning loads18 Remarks on meter-in and meter-out controls19 Actual metering control components36 Single spool proportional DCVs41 Independent metering control elements38 Usage of anti-cavitation valve for unloaded meter-out51 Problems49 CHAPTER 14:Load holding and counterbalance valves53 Load holding valves53 Pilot operated check valve61 Counterbalance valves60 Basic operating principle67 CBV architecture69 CBV detailed operation72 Effect of the pilot ratio and of the pressure setting83 Counterbalance valve with vented spring chambers85 Problems78 CHAPTER 15:Bleed-off and open center circuits80 Bleed-off circuit operation91 Energy analysis94 Basic open center system97 Operation98 Open center valve design101 Energy analysis102 Advanced open center control architectures106 Negative flow control106 Basic Schematic106 Operation107 Pump displacement setting mechanism110 Positive flow control114 Basic Schematic114 Operation115 Pump displacement setting mechanism115 Energy analysis for advanced open center architectures116 Problems118 CHAPTER 16:Load sensing systems109 Basic load sensing control concept121 LS system with fixed displacement pump122 Basic Schematic122 Operation123 Energy analysis125 Saturation conditions126 Load sensing valve127 LS system with variable displacement pump137 Basic Schematic137 Operation138 Energy analysis139 Saturation conditions140 Load sensing pump148 LS solution with independent metering valves157 Electronic load sensing (E-LS)159 Problems162 CHAPTER 17:Constant pressure systems150 Constant pressure system based on a variable displacement pump163 Basic schematic and operation163 Energy analysis166 Constant pressure system with unloader (CPU)167 Constant pressure system based on a fixed displacement pump170 Basic schematic and operation170 Application to hydraulic braking circuits173 Problems175 References PART 5:Metering control of multiple actuators3 Objectives3 CHAPTER 18:Basics of multiple Actuator Systems5 Actuators in series and in parallel5 Series configuration6 Parallel configuration8 Elimination of the load interference in parallel actuators12 Solving load interference using compensators12 Solving load interference with a volumetric coupling13 Syncronization of parallel actuators through flow dividers15 Spool type flow divider15 Spool type flow divider-combiner16 Volumetric flow divider-combiner19 Linear flow divider-combiner24 Rotary flow divider-combiner25 Problems23 CHAPTER 19:Constant pressure systems for multiple actuators27 Basic concepts for a Multi-user constant pressure system27 Basic schematic35 Flow saturation36 Energy analysis37 Complete schematic of a multi-user constant pressure system29 Problems33 CHAPTER 20:Open center systems for multiple actuators35 Parallel open center systems36 Operation46 Energy analysis48 Flow saturation49 Considerations on the open center spool design49 Opening areas39 Opening delay (valve timing)41 Load interference in open center systems41 Tandem and series open center systems47 Tandem configuration60 Series configuration63 Advanced open center circuit for multiple users: the case of excavators49 Problems52 CHAPTER 21:Load sensing systems for controlling multiple actuators53 Load sensing system without pressure compensation (LS)53 Basic circuit69 Energy analysis72 Valve implementation and extension to more actuators74 Load sensing pressure compensated systems (LSPC)61 LSPC with pre-compensated valve technology61 Basic circuit79 Energy analysis82 Valve implementation and architecture84 LSPC with post-compensated valve technology70 Basic circuit90 Energy analysis92 Valve implementation and architecture94 Flow saturation and flow sharing in LS systems79 Flow saturation with pre-compensated LSPC80 Flow saturation with post-compensated LSPC82 Pre vs. post compensated comparison84 Independent metering systems with load sensing88 Problems91 CHAPTER 22:Power steering and hydraulic systems with priority function102 Hydraulic power steering103 Classification of hydraulic power steering systems103 Hydrostatic power steering111 Hydrostatic steering unit description114 Types of hydrostatic steering units119 Priority valves121 Priority valve for a fixed displacement flow supply121 Priority valve for load sensing circuits128 Problems131 References PART 6:Hydrostatic transmissions and hydrostatic actuators3 Objectives5 CHAPTER 23:Basics and classifications6 Hydrostatic transmissions and hydrostatic actuators6 Basic definitions6 Supply concepts used in HTs and HAs9 Primary units for hydrostatic transmissions and actuators10 Constant speed prime mover and variable displacement pump10 Variable speed prime mover and fixed displacement pump10 Variable speed prime mover and variable displacement pump11 Over-center variable displacement pump11 Typical applications12 CHAPTER 24:Hydrostatic transmissions15 Main parameters of a hydrostatic transmission15 Theoretical layouts19 Pump and motor with fixed displacement (PFMF)19 Variable displacement pump and fixed displacement motor (PVMF)20 Fixed displacement pump and variable displacement motor (PFMV)21 Variable displacement pump and variable displacement motor (PVMV)23 Variable displacement pump and dual displacement motor (PVM2)25 Open circuit hydrostatic transmissions29 Open-circuit HT with flow supply: basic circuit29 Open circuit HT with flow supply: common implementation31 Open circuit displacement regulator33 Open circuit HTs with pressure supply35 Closed circuit hydrostatic transmissions40 Charge circuit and filtration41 Cross-port relief valves45 Flushing circuit47 Closed circuit displacement regulators54 Electro-hydraulic displacement regulator for closed circuit pumps54 Automotive control for closed circuit pumps56 Conceptual schematic58 Actual implementation60 Electro-hydraulic displacement regulator for motors59 Automatic pressure regulator for motors60 Problems61 CHAPTER 25:Hydrostatic transmissions applied to vehicle propulsion67 Basic of vehicle transmission67 Classification for variable ratio transmission systems71 Power-split transmissions74 Planetary gear train76 Hydromechanical power split transmission78 Analysis of an output coupled hydromechanical power split transmission Analysis of an input coupled hydromechanical power split transmission Hybrid transmissions92 Series hybrids93 Parallel hybrids95 Series-parallel hybrids (or power split hybrids)97 Sizing hydrostatic transmissions for propel applications100 Step 1: Maximum tractive effort calculation101 Step 2: Fixed or variable displacement motor selection102 Step 3: Sizing of the motor (secondary unit)104 Step 4: Sizing of the pump (primary unit)105 Step 5: Check results106 Problems112 CHAPTER 26:Hydrostatic actuators113 Open circuit hydrostatic actuators113 Closed circuit hydrostatic actuators116 Cylinder extension117 Extension in pumping mode117 Extension in motoring mode118 Cylinder retraction120 Retraction in motoring mode121 Retraction in pumping mode122 Further considerations on the charge pump and the accumulator124 Final remarks on hydrostatic actuators127 CHAPTER 27:Secondary controlled hydrostatic transmissions129 Secondary control circuit with tachometric pump132 Secondary control circuit with tachometric pump and internal force feedback135 Secondary control circuit with electronic control137 Multiple actuators139 References APPENDIX 1 – Prime movers and their interaction with the hydraulic circuit Objectives Corner power method and its limitations Diesel engine and its interaction with a hydraulic pump Diesel engine regulation Engine stall Overrunning loads Fuel consumption Electric prime movers Brushed DC electric motors DC hydraulic power units Induction motors (or asynchronous motor) Synchronous motor Power limitation in hydraulic pumps Torque limiting using fixed displacement pumps Torque limiting using variable displacement pumps References