Lecture 5 - College of Engineering, Purdue University

Design and Modeling of Fluid Power Systems ME 597/ABE 591

Lecture 5

Dr. Monika Ivantysynova MAHA Professor Fluid Power Systems MAHA Fluid Power Research Center Purdue University

Displacement Machines Study different design principles and learn about the following topics Axial piston pump design solutions (swash plate and bent axis) Radial piston pumps and motors – piston support Gear Pumps – internal and external – axial and radial gap compensation Vane pumps – advantage and disadvantage of this design Please study the appropriate chapters in Ivantysyn, J. and Ivantysynova, M. (2001), Hydrostatic Pumps and Motors. Akademia Books International. New Dehli. ISBN-81-85522-16-2 Aim: - To be able to select the right design for your system application! - Knowledge about limitations of each basic design - To apply models on system level for each design © Dr. Monika Ivantysynova

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Design and Modeling of Fluid Power Systems, ME 597/ABE 591

Displacement Machines Swash Plate Machines

Axial Piston Machines Piston Machines F In-line Piston Machines

Bent Axis machines with external piston support

Radial Piston Machines with internal piston support External Gear

F Gear Machines

Internal Gear Annual Gear F Screw Machines

Vane Machines Fixed displacement machines © Dr. Monika Ivantysynova

others

Variable displacement machines 3

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Bent axis axial piston pumps Synchronization of cylinder block Driving flange Cylinder block Using a bevel gear

Using a universal joint

© Dr. Monika Ivantysynova

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Bent axis axial piston pumps Synchronization of cylinder block

connecting rod

piston

Piston rod Cardan joint

Synchronization by piston rod Synchronization by pistons


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Kinematics of bent axis pumps Four link 3D mechanism Frame (1)

Five link 3D mechanism Frame (1)

Cylinder (4)

Cylinder (4) Piston rod (5)

Piston (3) Piston (3)

Driving flange (2)

Driving flange (2)

Assuming a fixed connection between link 2 and link 4, achieved by synchronization the mechanism has finally three mechanism has finally two degrees degrees of freedom of freedom Piston can rotate about z -axis and 3

Piston can rotate about z 3 -axis © Dr. Monika Ivantysynova

piston rod can rotate about z5-axis 6

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Piston Design Long piston with piston rod

Short piston with piston rod

Synchronization by universal joint or bevel gear

Synchronization by pistons or piston rods

Spherical piston with piston ring

Conical piston with piston rings


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Design Examples Pump control device

Driving flange bearings

Spherical valve plate


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Design Examples Driving flange bearings

Fixed displacement pump Conical piston

Spherical valve plate


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Radial Piston Pumps with external piston support

with internal piston support

Rotating cylinder body Stroke ring

Suction

Stationary cylinder body Delivery

Suction Delivery eccentricity

Rotating cam or crankshaft

Displacement volume adjustable by changing eccentricity e © Dr. Monika Ivantysynova

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Radial Piston Pumps Multiple stroke radial piston pumps with external piston support

with internal piston support

Rotating cylinder body

Stationary cylinder body

Rotating cam

Stationary stroke ring

Only fixed displacement pumps realizable! © Dr. Monika Ivantysynova

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Piston support on outer stroke ring

Plane valve plate

Stroke ring Stroke ring

Piston

Rotating cylinder body


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Piston rotation enforced by friction force Ff Design and Modeling of Fluid Power Systems, ME 597/ABE 591

Piston support on outer stroke ring Stroke ring

Piston

Piston roller guide

Stroke ring borne in roller bearings © Dr. Monika Ivantysynova

Piston sliding bearing 13

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Piston support on outer stroke ring Stroke ring

Slipper support

Hydrostatically balanced slipper

Hydrodynamically balanced slipper

Slipper pocket

Ball joint inside the piston © Dr. Monika Ivantysynova

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Stroke ring support Using a sliding carriage

supported using line contact

Stroke ring mounted on a pivot

Change of eccentricity by pivoting the stroke ring about pivot axis


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Design Example Pump control system

Slipper

Piston

Control journal © Dr. Monika Ivantysynova

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Stroke ring Design and Modeling of Fluid Power Systems, ME 597/ABE 591

External gear pump Basic principle Radial gaps between teeth addendum circle and housing Housing

Inlet

Outlet

Driving gear

Qe = V ⋅ n -Qs

Driven gear

Axial gaps between housing and the gear pair must be very small to seal the displacement chamber © Dr. Monika Ivantysynova

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Two stage gear pump Inlet 1 p1

Driven gear

Outlet 2 p4

p2

p3

Outlet 1

Driving gear

Driven gear

Inlet 2

Outlet 1 and inlet 2 can be connected or the pump can have two separate outlets

p2 = p3 p1 = p3

the driving gear is pressure balanced! © Dr. Monika Ivantysynova

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Internal gear pump Internal gear (ring gear)

Pinion

Advantages: Better suction ability Higher efficiency More compact design Less noise emission Suction zone

Pressure zone

Crescent shaped divider

Using teeth of standard involute design requires a combination where the pinion has two or more fewer teeth than the ring gear! Pinion and ring gear are then separated by a crescent shaped divider. Longer duration of teeth meshing leads to better sealing function © Dr. Monika Ivantysynova

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Internal gear pump Crescent shaped divider

Many different tooth profiles have been applied in the recent past. © Dr. Monika Ivantysynova

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Annular gear pumps Applying specially generated tooth curves it can be achieved, that the inner rotor (the pinion) has only one tooth less than the ring gear, thus eliminating the crescent-shaped divider. Ring gear (z2) Outlet

Inlet

Each tooth of the pinion maintains continuous sliding contact with a tooth of the ring gear, providing fluid tight engagement.

Relative sliding velocity between pinion and ring gear is very small Pinion (z1) quiet operation and long service life Gerotor pump © Dr. Monika Ivantysynova

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Annular gear pump – Orbit principle 2 Pressure port

Ring gear (z2) fixed

Rotating pinion (z1)

1 Suction port

Outlet

Inlet

Multiple delivery of each tooth space

Rotating distributor


Displacement volume is given by z1 times z2 tooth spaces

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Pressure compensated axial gaps Sealing ring

Pressurized area A

Sliding bearing

Shaft seal

Gear pair Axial gap

FZ FZ

End cap

Bearing bushings housing Front cover

Only one direction of shaft rotation possible! © Dr. Monika Ivantysynova

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Pressure compensated axial gaps Driving gear

Axial gap – pressure compensated Pressurized area

Sealing 2FZ

Sliding bearings © Dr. Monika Ivantysynova

Driven gear

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Improved volumetric efficiency Design and Modeling of Fluid Power Systems, ME 597/ABE 591

Pressure compensated radial gaps Radial gap compensation

Axial gap compensation Pressurized area Bearing bushing

Small pressure zone achievable © Dr. Monika Ivantysynova

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Gear pump – design example Driving gear

Shaft seal

inlet

outlet

Driven gear

Bearing bushing performing a radial and axial gap compensation


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Internal gear pump- design example Internal gear pump with axial and radial gap compensation Pinion Ring gear special shaped divider inlet

Pressurized area

outlet

Moveable bearing shell Radial gap compensation


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Screw Pumps With two meshing screws outlet

inlet


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Screw Pumps outlet t…thread pitch

inlet

outlet

With three meshing screws


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Vane Pumps Classification of vane pumps Unbalanced vane pump Stator Rotor

Balanced vane pump

Only fixed displacement pump

Fixed and variable pump design © Dr. Monika Ivantysynova

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Vane pumps- basic working principle Single stroke vane pump – variable displacement volume

inlet

Overcenter pump – the direction of flow can be reversed by change of eccentricity, i.e. without changing the direction of rotation of the drive shaft

outlet

no flow!

Relatively high friction between axial moveable vanes and rotor & between vanes and stator

outlet

Large radial forces exerted on the rotor

inlet

Limitation of max. operating pressure (20 MPa) © Dr. Monika Ivantysynova

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Vane pumps- classification Multiple stroke vane pump

Rigid vane pump

Rotor


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Fluid distribution External fluid distribution

Internal fluid distribution

outlet stator

rotor

Distributor - fixed control journal

inlet


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Rigid vane pump Stator ring

Displacement volume:

Rotor

Pulsation free flow 1st rotor


2nd rotor

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vane
