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Design of hydraulic systems for lift truck
Ivan Gramatikov Design of Hydraulic Systems for Lift Trucks Second Edition Preface to the Second Edition All information contained in the first edition has been retained Some corrections and additions have been made to better serve the purpose of the book Design of Hydraulic Systems for Lift Trucks First Edition Published by Technical University- Sofia, Sofia 1000, Bulgaria ISBN: 978-954-438-730-3 Printed in Bulgaria Second Edition Copyright 2011 by Ivan Gramatikov All rights reserved No part of this book may be reproduced, stored in a retrieval system or transmitted in any form, or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the author For permissions e-mail: gramatik.publishing@abv.bg ISBN: 978-1-257-01500-9 Printed in the United States of America Front cover photos: Courtesy of Balkancar Record (http://www.balkancar-record.com) Design of Hydraulic Systems for Lift Trucks i CONTENTS Chapter 1: Introduction Preface Definitions for design and system design Regulations Calculations Systems of units Symbols used in formulae and hydraulic diagrams Chapter 2: Properties and parameters of the fluids 11 Properties Density 11 Specific weight 12 Specific gravity 13 Viscosity 13 Compressibility of fluids 16 Reynolds number and types of flow 18 Parameters Pressure 19 Flow and flow rate 20 Fluid velocity 23 Work and Power 23 Drag and pressure loss 25 Hydraulic shock 27 ii Hydraulic Lock 27 Obliteration 28 Stiction 29 Cavitation 29 The Bernoulli Equation 30 The Torricelli Equation 31 Chapter 3: Hydraulic system components 10 11 12 13 14 15 16 17 18 Flow Restrictors Pressure Relief Valves Check Valves Reduction Valves Pressure Compensated Flow Controls Directional Control Valves Hydraulic Pumps Hydraulic Motors Hydraulic Cylinders Pressure Sensors Hydraulic Accumulators Hydraulic Filters Hydraulic Reservoirs Hydraulic Lines, Fittings and Couplings Manifold blocks Hydraulic Fluid Fluid Cleanliness Electric Motors 33 34 36 37 39 40 42 48 59 60 64 66 70 77 83 88 90 95 98 Chapter 4: Management and quality of hydraulic system design process 101 Brief history of quality 101 Introduction 103 Factors 104 Design of Hydraulic Systems for Lift Trucks iii Structuring the design process 106 Definitions of tools used 108 Description of the design process steps 110 Design guidelines 116 Documenting the design activities 117 Project close-out criteria 118 Failure and failure rate 119 Patents 120 Designing around an existing patent 122 Legal aspect of the design process 123 Chapter 5: Hydraulic systems for high lift trucks 125 Elevating system 126 Hydraulic systems overview 128 Design principles 129 Design requirements 130 Hydraulic system with proportional manual directional valve 133 Calculations 146 Hydraulic system with electrically controlled proportional valves 153 Hydraulic system with emergency lowering 158 Energy recovery systems 160 Hydraulic steering system 165 Electro-hydraulic steering system 171 Integrated hydraulic system 174 Smoothness of the lifting 176 Chapter 6: Hydraulic systems for low lift trucks 181 iv Hydraulic system with independent power steering and lift circuits 183 Integrated hydraulic systems for low lift trucks 185 Integrated hydraulic system with accumulator 189 Hydraulic system for pallet trucks with long fork attachments 194 Hydraulic power-assisted steering 197 Integrated system with power-assisted steering 199 Chapter 7: Hydraulic systems for boom-type trucks 201 Hydraulic circuit for boom lift, extend and fork tilt 202 Hydraulic lift & lower circuit for telescopic boom 203 Hydraulic circuit with an automatic shut-off valve 207 High-speed extension of telescopic boom 208 Chapter 8: Selected topics I 211 Servicing the hydraulic systems 211 Troubleshooting principles System Life 212 212 Safety Rules 213 Servicing the fluid 213 Servicing filters 216 Servicing reservoirs 216 Servicing rotary pumps and motors 217 Servicing hydraulic cylinders 218 Servicing valves 219 Servicing connectors 220 Seals 221 Design of Hydraulic Systems for Lift Trucks v II Components layout- general considerations 222 III Common problems 223 IV Contamination of the hydraulic fluid 225 V The future of the hydraulics 229 Appendixes 231 Appendix A ITA classification Appendix B Physical properties of common fluids Appendix C Viscosity Classification of Industrial Lubrication Fluids Appendix D Coefficients of local resistance Appendix E Decision Matrix and QFD house Appendix F Hydraulic system calculation vi Design of Hydraulic Systems for Lift Trucks Chapter Introduction Preface The purpose of this book is to illustrate design principles and methods for designing and calculating hydraulic systems for industrial lift trucks Determining the main parameters of these systems is based on principles of hydraulics and mechanics This book is to be used as a source of information for mechanical engineers involved in designing, manufacturing and servicing hydraulic systems for mobile lift trucks This book can also be used by engineering students in Industrial Truck Programs To combine these two purposes, there is an introductory chapter, “Properties and Parameters of Hydraulic Fluid”, and a chapter on “Hydraulic Components” describing the construction and the functions of components used in mobile hydraulic systems This book will also be beneficial for engineers working in areas of design, fabrication and service of any other mobile off-highway equipment In all universities, mechanical engineering students study the theoretical foundations of fluid mechanics, fluid dynamics, and thermodynamics However few universities offer courses in hydraulics and pneumatics (also called: fluid power), which are the applications of these disciplines That is why most design engineers learn the basics of the fluid power on the job Fluid power learning time can be reduced significantly if some basic hydraulic principles are understood up front This book will describe the hydraulic principles and operation of the main hydraulic arrangements which will give you the foundation for designing any system on your own It is more difficult to design hydraulic systems for smaller lift trucks That is because these systems must have the same performance as the bigger trucks but they have to be put into a smaller space envelope The smaller design envelope is a major challenge to the design engineers To meet this and all other challenges through the design process, engineers have to follow the principles of continuous improvement and design process quality Quality of the design process depends on the proper execution of each step Chapter 1: Introduction of the process The proper execution requires knowledge in engineering and management areas The core necessary disciplines are: Mathematics, Mechanics of the Fluids, Hydraulic Circuits and Components, Management of Quality, Project Management, Design for Excellence and Professional Communication Some of these courses, in most of the engineering programs, are not part of the engineering curriculum and therefore, engineers must take extra courses in order to acquire the right set of knowledge Chapter 4, “Management and Quality of the Design Process”, describes the managerial aspect and the basic principles of the design process Definitions for design and system design • • • “The best design is the simplest one that works” Albert Einstein Design is creative problem solving System design is finding the balance in system performance that best satisfies the engineering requirements This balance has to be achieved first at the conceptual level and then maintained throughout the whole design process Design of hydraulic systems is built on knowledge of several fundamental principles Most fluid power engineers have them as background knowledge and not even think about them For people learning hydraulics, knowing the fundamental principles is the first step to designing energy and cost efficient systems The milestones of the hydraulic principles are: • Knowledge of properties and parameters of the fluids • Velocity-pressure relationship (Bernoulli equation) • Knowledge of the hydraulic components Fluid properties, fluid parameters and the Bernoulli equation are described in Chapter Chapter describes the components used in the system Good system designs would also require knowledge of: • • • The engineering requirements (parameters) for the system Factors affecting system functionality and system life Constraints- cost, space, surrounding environment When designing a system, the engineer must focus on four main aspects: A-12 Design of Hydraulic Systems for Lift Trucks Calculations Selecting cylinders Main lift (side) cylinders Maximum load on cylinders is: ( ) Lmax := n ⋅ Gmax + Gcarrige + ⋅ Gfork + Gmast1 + Gcyl.m + ⋅ Gm.chain + Gmast2 + ⋅ Gpiston + ⋅ Gex.chain Lmax = 7.076× 10 kg Calculate diameter of main lift cylinders using formula 5.2 2⋅ d1_min := Lmax⋅ g π ⋅ pmax⋅ η cyl ⋅ η mast d1_min = 0.042m We select standard size piston diameter bigger than the calculated minimum d1 := 45⋅ mm The area of the main-lift piston is: A1 := π ⋅ d1 −3 A1 = 1.59× 10 m 2 Free lift (middle) cylinder We select the diameter of the free lift cylinder so that its area is bigger than the combined area of both main lift cylinders A2_min := ⋅ A1 d2_min := d1 ⋅ d2_min = 63.6⋅ mm Select diameter size bigger than the calculated minimum d2 := 67⋅ mm Design of Hydraulic Systems for Lift Trucks A-13 The area of the free-lift piston is: A2 := π ⋅ d2 −3 A2 = 3.526× 10 m There are two main parameters which will be calculated first: follow and pressure In order to have two lift speeds (one for empty lift and one for lift with maximum load), the system requires two flow rates Mast construction has two stages (free lift and main lift) with different cylinder areas which produce different pressures Therefore, the system has four main work points: Work point Free lift without load (Maximum flow - minimum pressure) Work point Free lift with maximum load Work point Main lift without load Work point Main lift with load (Minimum flow - maximum pressure) Calculating required flow rate for desired lift speed Work point (Flow rate in free-lift cylinders, lift without load) Q1 := A2 ⋅ v2 n Q1 = 42.3⋅ L Work point (flow rate in free-lift cylinders, maximum load on the forks) Q2 := A2 ⋅ v1 n Q2 = 31.7⋅ L A-14 Design of Hydraulic Systems for Lift Trucks Work point (flow rate in main-lift cylinders, lift without load) Q3 := ⋅ A1 ⋅ v2 n Q3 = 38.2⋅ L Work point (flow rate in main-lift cylinders, maximum load on the forks) Q4 := ⋅ A1 ⋅ v1 n Q4 = 28.6⋅ L Calculate pressures Work point (pressure in free-lift cylinders, lift without load) G0 := ⋅ kg ( Zero payload on the forks ) L1 := n ⋅ G0 + Gcarrige + ⋅ Gfork + Gmast1 + Gcyl.m + ⋅ Gm.chain L1 = 854kg p1 := L1 ⋅ g A2 p1 = 2.38× 10 Pa p1 = 23.8⋅ bar Load on cylinders for work point Design of Hydraulic Systems for Lift Trucks A-15 Work point (pressure in free-lift cylinders, maximum load on the forks) ( ) L2 := n ⋅ Gmax + Gcarrige + ⋅ Gfork + Gmast1 + Gcyl.m + ⋅ Gm.chain L2 = 6854kg p2 := Load on cylinders for work point L2 ⋅ g A2 p2 = 19.1× 10 Pa p2 = 191⋅ bar Work point (pressure in main-lift cylinders, lift without load) ( ) L3 := n ⋅ G0 + Gcarrige + ⋅ Gfork + Gmast1 + Gcyl.m + ⋅ Gm.chain + Gmast2 + 2Gpiston + ⋅ Gex.chain L3 = 1076kg p3 := Load on cylinders for work point L3 ⋅ g ⋅ A1 p3 = 3.3 × 10 Pa p3 = 33⋅ bar Pressure without payload Work point (pressure in main-lift cylinders, maximum load on the forks) Lmax = 7.076× 10 kg p4 := Maximum load was calculated earlier Lmax⋅ g ⋅ A1 p4 = 21.8× 10 Pa p4 = 218⋅ bar Pressure with maximum payload of 3000 kg A-16 Design of Hydraulic Systems for Lift Trucks System Work Points- Summary Flow (Q) Points Description l/min p.1 Free lift empty 42.3 p.2 Free lift with maximum load 31.7 p.3 Main lift empty 38.2 p.4 Main lift with maximum load 28.6 Pressure (p) bar 24 191 33 218 The system power requirements must be based on minimum two work points Work points one and four are both extreems Therefore, in this example only these two points will be considered Select components Pump displacement Pump displacement is function of pump flow delivery and shaft rotational speed Gear pumps have best performance and reliability in the range of 1000 to 3000 rev/min Electric motors have best performance and reliability in the range of 1500 to 5000 rev/min Based on this, we will target rotational speed of 2200 rev/min Given Q3 = 38.2⋅ Q2 = 31.7⋅ n := 2200⋅ η vol := L L min 0.98 Maximum flow rate (lift empty) Minimum flow rate (lift with maximum load) Rotational speed - target Pump volumetric efficiency Design of Hydraulic Systems for Lift Trucks A-17 Calculate and select pump displacement (use formula 3.4) dmax := Q3 n ⋅ η vol dmax = 17.7⋅ cm dmin := Maximum pump displacement needed for empty lift at 2200 rev/min Q2 n ⋅ η vol dmin = 14.7⋅ cm Minimum pump displacement needed for lift with maximum load at 2200 rev/min Select standard pump displacement dpump := 16⋅ cm η m := Pump mechanical efficiency at 25 MPa pressure & 2000rev/min 0.90 η vol := Select to use a gear pump Pump volumetric efficiency at 25 MPa pressure & 2000rev/min 0.98 Calculate shaft rotational speed based on pump with 16 cm^3 displacement (use formula 3.4) ne := Q3 dpump⋅ η vol ne = 2434⋅ nl := Maximum pump shaft rotational speed (empty lift) Q2 dpump⋅ η vol nl = 2024⋅ Minimum pump shaft rotational speed- during lift with maximum load A-18 Design of Hydraulic Systems for Lift Trucks Select hydraulic line diameters (The diameters of the fluid lines are based on recomended fluid velocity, see Hydraulic Connectors, Chapter 3) Suction line vs := 1.5⋅ AS := m Maximum recommended fluid velocity inside suction hose s Q1 vs AS = 470.1⋅ mm 4⋅ dS := Area of inside cross section AS π dS = 24.5⋅ mm Minimum suction diameter ds := 25⋅ mm Select 25 mm diameter for suction line Pressure line vp := ⋅ Ap := m Recommended fluid velocity inside pressure hose s Q4 vp AS = 470.1⋅ mm dP := 4⋅ Area of inside cross section Ap π dP = 10.1⋅ mm dp := 10⋅ mm Recommended diameter Select 10 mm diameter for pressure line Design of Hydraulic Systems for Lift Trucks A-19 Return line vr := 2.5⋅ Ar := m Recommended fluid velocity inside pressure hose s Q1 vr AS = 470.1⋅ mm 4⋅ dR := Area of inside cross section Ar π dR = 19⋅ mm Recommended diameter for the return lines dr := 20⋅ mm Select 20 mm diameter for return line Hydraulic Losses Calculate pressure losses in two work points of the system (WP1 and WP4) Known p4 = 218⋅ bar Q4 = 28.6⋅ L ν := Flow rate during lift with maximum load Pressure p1 = 24⋅ bar Q1 = 42.3⋅ Pressure during lift with maximum load L 32⋅ 10 ⋅ stokes Maximum flow rate (lift empty) Fluid viscosity in viscosity grade 32 A-20 Design of Hydraulic Systems for Lift Trucks Losses in the hydraulic components Pressure losses are given by the manufacturer in a graph or table format Losses in the directional control valve at temperature ∆p dc := 0.08⋅ 10 ⋅ Pa ∆p fc1 := 0.26⋅ 10 ⋅ Pa ∆p fc2 := 1.5⋅ 10 ⋅ Pa Pressure drop in the flow control when lifting ∆p filter := Pressure drop in the flow control when lowering 0.07⋅ 10 ⋅ Pa Pressure drop in the suction filter (manufacturer range is from 0.05 to 0.10 MPa) Losses in the hydraulic lines There are two types losses in the hydraulic lines which result in a pressure drop: lineal (due to friction along the walls) and local (due to change of direction of the flow) Lineal losses occur in straight tubes and hoses Local losses occur in the fittings ρ := 880⋅ kg m Re := 1500 λ := Reynolds Number 64 Re Lineal losses in the suction line, use formula 2.26 Ls := 300⋅ mm AH := π ⋅ ds Suction hose length Cross area of the hose Design of Hydraulic Systems for Lift Trucks Lift empty (WP1) Lift with maximum load (WP4) ⎛ Q1 ⎞ ρ Ls ∆p s1 := ⎜ ⋅λ ⋅ ⋅ ds ⎝ AH ⎠ ∆p s1 = 0.005⋅ bar ⎛ Q4 ⎞ ρ Ls ∆p s4 := ⎜ ⋅λ ⋅ ⋅ ds ⎝ AH ⎠ ∆p s4 = 0.002⋅ bar Lineal losses in the presure line, use formula 2.26 Lp := 8000⋅ mm AP := π ⋅ dp Hose length Lift empty (WP1) Lift with maximum load (WP4) ⎛ Q1 ⎞ ρ Lp ∆p p1 := ⎜ ⋅λ ⋅ ⋅ dp ⎝ AP ⎠ ∆p p1 = 12.11⋅ bar ⎛ Q4 ⎞ ρ Lp ∆p p4 := ⎜ ⋅λ ⋅ ⋅ dp ⎝ AP ⎠ ∆p p4 = 5.54⋅ bar Lineal losses in the return line, use formula 2.26 Hose length Lr := 900⋅ mm AR := π ⋅ dr Lift empty (WP1) ⎛ Q1 ⎞ ρ Lr ∆p r1 := ⎜ ⋅λ ⋅ ⋅ dr ⎝ AR ⎠ ∆p r1 = 0.04⋅ bar Lift with maximum load (WP4) ⎛ Q4 ⎞ ρ Lr ∆p r4 := ⎜ ⋅λ ⋅ ⋅ dr ⎝ AR ⎠ ∆p r4 = 0.02⋅ bar A-21 A-22 Design of Hydraulic Systems for Lift Trucks Total lineal losses Lift empty (WP1) Lift with maximum load (WP4) ∆p L4 := ∆p s4 + ∆p p4 + ∆p r4 ∆p L1 := ∆p s1 + ∆p p1 + ∆p r1 ∆p L1 = ∆p L4 = 12.15⋅ bar 5.56⋅ bar Local losses in the fittings (use formula 2.28) ∆p loc := 2.1⋅ 10 ⋅ Pa Total losses from the pump to the lift cylinder Lift empty (WP1) Lift with maximum load (WP4) ∆p t1 := ∆p dc + ∆p fc1 + ∆p L1 + ∆p loc ∆p t4 := ∆p dc + ∆p fc1 + ∆p L4 + ∆p loc ∆p t1 = 3.66× 10 Pa ∆p t4 = × 10 Pa Pressure at pump outlet port Work poit pp1 := p1 + ∆p t1 pp1 = 6.03× 10 Pa Work poit pp4 := p4 + ∆p t4 pp4 = 24.81× 10 Pa System Work Points- Summary Pressure in Pressure Flow (Q) Points Description lift cylinders losses l/min bar bar p.1 Free lift empty 42.3 23.8 36.6 p.4 Main lift with maximum load 28.6 218 30 Pressure in pump outlet bar 60.4 248 These two points (p.1 and p.4) will be used to determine the power requirements of the system Design of Hydraulic Systems for Lift Trucks A-23 Power delivered by pump work point work poit lift without load Pemp := lift with MAX load ( pp1) ( Q3) Pmax := η vol ⋅ η m Pemp = 4.3⋅ kW pp4 ⋅ Q4 η vol ⋅ η m Pmax = 13.4⋅ kW Pemp = ⋅ hp Pmax = 18⋅ hp Motor torque (maximum load, main lift) η m := 0.90 Pump mechanical efficiency at 25 MPa pressure & 1800 rev/min work point work point lift without load lift with MAX load Te := Pemp ( ne) ⋅ ⋅ π ⋅ η m Tmax := Te = 19⋅ N·m System Work Points Work Point p.1 p.4 Description Free lift empty Main lift with maximum load Pmax ( nl) ⋅ ⋅ π ⋅ η m Tmax = 70.4⋅ N·m Hydraulic parameters Power requirements l/min 42.3 Pressure in pump outlet bar 60.4 Pump speed rev/min 2434 Pump input power kW 4.3 Pump input torque Nm 19 28.6 248 2024 13.4 70.4 Flow (Q) A-24 Design of Hydraulic Systems for Lift Trucks Notes Design of Hydraulic Systems for Lift Trucks References 10 11 12 13 14 15 16 17 Beecroft G Dennis, Management of Quality courseware Brezonick, Mike, New Flow Limiter, Velocity Fuse Target Improved Machine Safety Byrne Diane, Taguchi Shin, The Taguchi Approach to Parameter Design Casey Brendan, Hydraulic Supermarket Evans James, Lindsay William, The Management and Control of Quality Georgiev, George, Design of Lift Trucks Charles J Murray, Fluid power lessons Clausing Don P., Total Quality Development Gramatikov Ivan, Hydraulic System for High Lift Truck, Master’s thesis, Technical University of Sofia Gramatikov Ivan, Filter Selection to Maximize Hydraulic System Life, University of Toronto Jeffrey K Liker and David Meier, The Toyota Way Komitovski Michael, Components of Hydraulic and Pneumatic Systems Lazarov Stefan, Research and Improvements of the Hydraulic System for High-Lift Electric Trucks Moskov N., Lazarov C., Hydro- and Pneumatic Drives and Controls Munson, B., Yong, D., Okiishi, T., Fundamentals of Fluid Mechanics Stankov P., Antonov I., Mechanics of Fluids Lessons and Problems Vickers Mobile Hydraulics Manual Fluid Power Journal Industrial Vehicle Technology, UKiP Media Events Hydraulics & Pneumatics, Penton publication Hydraulic Supermarket (www.hydraulicsupermarket.com) Machinery Lubrication, Noria Corporation Design of Hydraulic Systems for Lift Trucks Notes ... Chapter 7: Hydraulic systems for boom-type trucks 201 Hydraulic circuit for boom lift, extend and fork tilt 202 Hydraulic lift & lower circuit for telescopic boom 203 Hydraulic circuit... illustrate design principles and methods for designing and calculating hydraulic systems for industrial lift trucks Determining the main parameters of these systems is based on principles of hydraulics... unit of length is foot (ft), the unit of force is pound (lb), the unit of mass is obscure (slug) and the unit of temperature is degree Fahrenheit (°F) Design of Hydraulic Systems for Lift Trucks