Class #6Hydraulic PumpsME 4232:FLUID POWER CONTROLS LAB2Notes• Next Friday: – Van de Ven Traveling– Servo Hydraulic Overview & System Dynamics Review• Upcoming Labs:– Lab 11/12: Synchronous / Asynchronous &Tandem / Parallel Connections– Lab 13: Power Steering– Lab 14: Integrated Lab (Part I)3Agenda• Feedback: Lab Sections• Power Steering Valve• Pump Classification– Positive Displacement Types• Pump Theory– Flow Ripple– Inefficiencies– Aeration/Cavitation• Hydrostatic Transmissions– Types / Characteristics– Hybrid Vehicle Architectures4Feedback: Lab Sections• Overall Going Well– Helpful / Knowledgeable TAs (right amount of guidance)• Issues:– Some labs tight on time– Sometimes confusion– Lab assignments vague5Power Steering Valve (Lab 13) Open center steering Power beyond steering6Pumps - Introduction7Non-Positive Displacement Pump8Types of Positive Displacement Pumps• Gear pump (fixed displacement)– internal gear (gerotor)– external gear• Vane pump – fixed or variable displacement– pressure compensated• Piston pump– axial design– radial design– bent-axis design9External Gear Pump• Driving gear and driven gear• Fluid trapped between gear teeth and housing10Gerotor pump• Internal/External Gear Pair• Inexpensive• Low-Pressure Applications• Low Flow (0.1 – 11.5 in3)Inlet portOutlet port11Vane Pump• Vanes in slots in rotor• Vanes loaded against cam ring• Eccentricity determines displacement•Quiet• Limited Pressure12Pressure Compensated Vane Pump• Spring determines P-Q curve13Axial Piston Pump• Pistons rotate with cylinder block• Pistons translate against swash plate• Displacement determined by swash plate angle• Fluid enters/exits through valve plate14Radial Piston Pump• Cam moves pistons radially• Displacement determined by cam profile• Displacement variation can be achieved by moving the cam (not common)• High pressure capable, and efficient• Pancake profile15Bent Axis Pump• Drive shaft coupled to cylinder block• Stationary valve plate• Low piston side load• High efficiency16Pumping Theory - Flow Ripple17Pumping Theory – Power Variable Calculations18Pumping Theory – Efficiency1920Aeration and Cavitation• Disastrous Events • Aeration– air bubbles enter pump at low pressure side• Cavitation– Dissolved air cavitation– Vapor cavitation• Bubbles expand in low pressure• Bubbles collapse in high pressure– Micro-jets formed  Rapid Erosion21Cavitation Videohttp://www.youtube.com/watch?v=eMDAw0TXvUo22Hydraulic Motor / Actuator• Hydraulic motors / actuators are basically pumps run in reverse• Input = hydraulic power• Output = mechanical power23Hydrostatic Transmission24Closed Circuit Hydrostatic Trans25General Consideration - Hydrostats• Advantages:– Wide range of operating speeds/torque– Infinite gear ratios - continuous variable transmission (CVT)– High power, low inertia (relative to mechanical transmission)– Dynamic braking via relief valve– Engine does not stall– No interruption to power when shifting gear• Disadvantage:– Lower energy efficiency (80% versus 92%+ for mechanical transmission)– Leaks !26Hydraulic Hybrid Vehicle CircuitsParallelSeriesPros: Retains existing mechanical drive trainCons: Does not allow optimal engine managementPros: Allows optimal engine management Four-Wheel Drive Capable  Independent Wheel Torque ControlCons: Hydraulic Efficiency Losses  Pump/Motor Operation27Hydraulic Accumulators• Energy Storage Device• Oil Compresses a Pre-Charged Gas (Nitrogen)28Hydro-Mech w/ Wheel Torque Control• High Efficiency & Decoupling• 2 Power Paths: Mechanical & Hydraulic– Leverage Highly Efficient Mechanical Branch– Infinite Speed Variability with Hydraulic Branch• Independent Wheel Torque ControlEngineClutchAccumulatorAxle GearboxMechanicalTransmissionPlanetary Differential29Hydraulic Transformer• Used to change pressure in a power conservative way• Pressure boost or buck is accompanied by proportionate flow decrease and increase• Note: Hydrostatic transmission can be thought of as a mechanical transformerQ1Q230Why Are Pumps Inefficient at Low X?Volumetric:Mechanical: 211xVxBppxCDxQrsxCpxCxpDTfv1Source: http://www.emeraldinsight.com/content_images/fig/0180560404021.png31Improving Pump Efficiency• Mechanical: – Variable Displacement Linkage• Low Friction Pin Joints• Volumetric:– Rolling Diaphragm Seal• No Leakage• Minimal FrictionSource: www.diacom.comSource: Sandor, G.N. and Erdman, A.G., Advanced Mechanism Design: Analysis and Synthesis, Volume 2, Prentice-Hall, 1984.32Linkage Synthesis• VideoVideo: http://www.youtube.com/watch?v=ovVGkjuXdvE33Configuration AnalysisOptimized Solution: •R3= 1.8, R4= 1.8• Max Displacement = 2.11• Footprint = 8.38• Minimum Transmission Angle of Slider = 56°• Minimum Timing Ratio = .72Overlapped Case at R1,max1.522.531.522.530.140.160.180.20.220.24|R4| UnitlessStroke/Footprint|R3| Unitless-1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4-1.5-1-0.500.511.5234First Generation Prototype• Variable Pump/Motor– Design Speed: 1750 RPM– Design Flow Rate 2.6e-4 – Design Max Pressure: 6.9 MPa (1000 psi)35First Generation Prototype36First Generation Prototype37Quantifying Energy Loss• Leakage:• Viscous Friction:• Compressibility:• Pin Friction: 󰇛6Δ3󰇜12 Δ         Δ      ∗    󰇛󰇜()compPVE PdV dPP()deadVdV dPP38Energy Loss Model0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1024681012141618Displacement d/dmaxEnergy Loss (J/rev)System Energy Loss 1800 RPM 6.9 MPa k = 0.173 LeakageViscous FrictionCoulomb FrictionCompressibility LossesTotal Losses0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9