The Significance of Piston/Cylinder Surface

Shaping on the Performance of Axial Piston

Machines

Ashley Wondergem

Dr. Monika Ivantysynova

Purdue University

October 16, 2015

Slide 2 Ashley Wondergem

Outline

• Introduction

• Axial Piston Machines

• Theory

• Previous Research

• Method

• Fluid Structure Interaction Model

• Simulation Study First Phase

• Simulation Study Second Phase

• Simulation Study Results

• Conclusion

• Next Steps

Slide 3 Ashley Wondergem

Introduction

Piston & Cylinder

Cylinder Block & Valve PlateSlipper & Swash Plate

Overview of Main Tribological Interfaces of Axial Piston Machines

ODC (Outer

Dead Center)

IDC (Inner

Dead Center)

Bearing Function Load Carrying

Sealing Function

Functions

Viscous Friction Leakage flows

DissipationsMain source of

energy

dissipation

Goal:Investigate how to reduce energy dissipation

between the piston and the cylinder through

surface shaping of the piston

Slide 4 Ashley Wondergem

Previous Work – Surface

Shaping

• Yamaguchi (1976)

• Numerical analysis: tapered piston increased efficiency

• Ivantysynova (1983)

• Proposed a barrel like piston

• Kleist (1997)

• Surface shaping reduces friction forces

• Lasaar (2003)

• Barrel piston (analytical and experimental)

• Volumetric losses reduced

• Friction forces reduced

Loss reductions strongly dependent on

operating condition

Study made with incomplete models

Slide 5 Ashley Wondergem

Fluid Structure Interaction Model

Pressure Deformations

Kinematics / Dynamics

Lubricating Fluid Film

Macro & Micro Motion

Heat Transfer

Thermal Deformations

Pressure Field

Surface Profile

Slide 6 Ashley Wondergem

Micro Surface Shaping-Geometries Under Investigation

Sine

MRCA

λ

Flat

MRCA

Barrel

MRC

R1

R2

R3LApex

Waved Barrel

R1

R2R3

LApex

MRC

A λ

•𝐴 [µ𝑚]

𝑅𝐾 [𝑚𝑚]=0.29‰

•λ [𝑚𝑚]

𝐿𝑝𝑖𝑠𝑡𝑜𝑛 𝑙𝑒𝑛𝑔𝑡ℎ [𝑚𝑚]= 0.4

• MRC = 0.96‰

•𝑅1[𝑚𝑚]

𝑅2[𝑚𝑚]= 0.9996

•𝑅3[𝑚𝑚]

𝑅2[𝑚𝑚]= 0.9984

•𝐿𝐴𝑝𝑒𝑥[𝑚𝑚]

𝐿𝑝𝑖𝑠𝑡𝑜𝑛 𝑙𝑒𝑛𝑔𝑡ℎ[𝑚𝑚]=0.4167

• MRC = 0.96‰

•𝐴 [µ𝑚]

𝑅𝐾 [𝑚𝑚]=0.29‰

• MRC = 0.96‰

MRC

CircSine

•𝐴 [µ𝑚]

𝑅𝐾 [𝑚𝑚]=0.29‰

•λ [𝑚𝑚]𝐶𝐾 [𝑚𝑚]

= 0.167

• MRC = 0.96‰

•𝐴 [µ𝑚]

𝑅𝐾 [𝑚𝑚]=0.29‰

•λ [𝑚𝑚]

𝐿𝑝𝑖𝑠𝑡𝑜𝑛 𝑙𝑒𝑛𝑔𝑡ℎ [𝑚𝑚]= 0.4

•𝑅1[𝑚𝑚]

𝑅2[𝑚𝑚]= 0.9993

𝑅3[𝑚𝑚]

𝑅2[𝑚𝑚]= 0.9989

•𝐿𝐴𝑝𝑒𝑥[𝑚𝑚]

𝐿𝑝𝑖𝑠𝑡𝑜𝑛 𝑙𝑒𝑛𝑔𝑡ℎ[𝑚𝑚]=0.4167

• MRC = 0.96‰

Baseline:

Standard wear-in piston-cylinder from

75 cc stock unit:

• Bushing wear: max 𝑤𝑒𝑎𝑟 [µ𝑚]

𝑅𝑍 [𝑚𝑚]=1.21

• Piston wear: max 𝑤𝑒𝑎𝑟 [µ𝑚]

𝑅𝐾 [𝑚𝑚]=0.1

• MRC = 1.64‰

MRC

max wear

max wear

Slide 7 Ashley Wondergem

Simulation Studies

First phase:4 different designs compared to baseline for moderate

operating conditions in pumping mode only

Results published in:

Wondergem, A, and M Ivantysynova. 2014. "The Impact of the

Surface Shape of the Piston on Power Losses." Proceedings of the

8th FPNI PhD Symposium. Lappeenranta, Finland.

Second phase:5 different designs compared to baseline for extreme operating

conditions in pumping and motoring mode

Slide 8 Ashley Wondergem

Simulation StudyPumping Mode - 1000 rpm, 400 bar

Baseline FlatBarrel

4

6

3

1

0

Fluid Film

Gap Height

(μm)7

1000

500

0

Pressure

(bar)2000

1500

HPLP

360

Lf

0.1

0.5

1

00.1

0.5

1

360

Lf

0

0.1

0.5

1

360

Lf

0

360

Lf

0

360

Lf

0

360

Lf

0

Slide 9 Ashley Wondergem

SineBarrel

Simulation StudyPumping Mode - 2800 rpm, 400 bar

4

6

3

1

0

Fluid Film

Gap Height

(μm)7

Baseline

HPLP

0.1

0.5

1

360

Lf

00.1

0.5

1

360

Lf

0

1000

500

0

Pressure

(bar)2000

1500

360

Lf

0360

Lf

0

360

Lf

0

DC

Case

0.1

0.5

1Lf

0 360

Slide 10 Ashley Wondergem

Simulation StudyPumping Mode – Energy Dissipation

Up to 40%

reduction (flat)Flat fails at high

speeds/pressures

Circ sine and waved barrel

outperform at LP

Barrel best,

especially at HP

Up to 30% decrease

for barrelSine also fails at high

speeds/pressures

Slide 11 Ashley Wondergem

Simulation StudyPumping Mode – Leakages

Up to 70% reduction

(flat); Based on 40%

reduction in clearance

BUT fails at some

operating conditions

Around 60%

reduction (barrel)

Around 40% reduction at

higher speed/pressures

Slide 12 Ashley Wondergem

Simulation StudyPumping Mode – Overall

ϕ𝐷:𝑏𝑎𝑠𝑒 − ϕ𝐷:𝑠ℎ𝑎𝑝𝑒 ϕ𝐷:𝑏𝑎𝑠𝑒

𝑥100** Simulation failure was

penalized 1.5*baseline

Slide 13 Ashley Wondergem

Simulation StudyMotoring Mode - 2000 rpm, 225 bar

Barrel

4

6

3

1

0

Fluid Film

Gap Height

(μm)7

Baseline

HPLP

DC

Case

1000

500

0

Pressure

(bar)2000

1500

360

Lf

0

360

Lf

0

360

Lf

0

0.1

0.5

1

360

Lf

0

0.1

0.5

1

360

Lf

00.1

0.5

1

360

Lf

0

Waved

Barrel

Slide 14 Ashley Wondergem

Simulation StudyMotoring Mode – Energy Dissipation

Waved barrel and circ sine

almost 30% decrease

Waved barrel and circ sine

outperforms barrel in

motoring mode

Slide 15 Ashley Wondergem

Simulation StudyMotoring Mode – Leakages

Flat and circ sine results in

almost 50% decrease

Waved barrel and circ sine

results in larger decrease

than barrel

Trend in energy dissipation relies

on reduction in leakages

-Based on reduction in

clearance

Slide 16 Ashley Wondergem

Simulation StudyMotoring Mode – Overall

ϕ𝐷:𝑏𝑎𝑠𝑒 − ϕ𝐷:𝑠ℎ𝑎𝑝𝑒 ϕ𝐷:𝑏𝑎𝑠𝑒

𝑥100** Simulation failure was

penalized 1.5*baseline

Slide 17 Ashley Wondergem

Simulation StudyOverall Pumping & Motoring Mode

ϕ𝐷:𝑏𝑎𝑠𝑒 − ϕ𝐷:𝑠ℎ𝑎𝑝𝑒 ϕ𝐷:𝑏𝑎𝑠𝑒

𝑥100** Simulation failure was

penalized 1.5*baseline

Slide 18 Ashley Wondergem

Conclusion

Piston Surface Shaping

– Better understanding of how piston shape effects machine operation

and fluid film generation under various conditions

– Increased load support allows for reduction in clearance between the

piston and the cylinder

• Improve/maintain reliability of machine

– Improvements in the efficiency of the machine are shown over a wide

range of operating conditions

• Largely due to decreased leakages based on decreased clearances

– Overall barrel surface profile performs best under conditions studied

Slide 19 Ashley Wondergem

Next Steps• Investigate at machine limits

• Manufacture prototype

• Test on Steady State test rig

• Measure overall losses

• Test on the Tribo test rig

• Measures the friction forces at the piston/cylinder interface

• Test on the EHD test rig

• Measure the pressure and temperature distribution as the swashplate rotates

EHD Test Rig

Case

Cylinder Block

Shaft

Swashplate

Main Pistons

Tribo Test Rig

Slide 20 Ashley Wondergem

Questions

Monika Ivantysynova - mivantys@purdue.edu

Ashley Wondergem – awonderg@purdue.edu

Contact Information