Predicting flow performance and contact stresses … · Predicting flow performance and contact...

Predicting flow performance and contact stresses

in a gerotor pump

Neenad Wamane

November 14, 2016

Stanadyne Confidential

Predicting flow performance and contact stresses in a gerotor

pump

Copyright © Stanadyne 2016

Outline

Introduction

Objective of the work

Method to achieve the objectives

Model configuration in GT-SUITE

Flow model

Test setup and instrumentation

Model results and validation

Dynamic pressure and flow match

Pressure regulator selection

Power breakdown – viscous drag and fluid power

Mechanical model for Hertz contact stress prediction

Inputs to mechanical model

Contact forces and Hertz stress

Summary and conclusions

2Stanadyne Confidential


Introduction

Gerotors are widely used in automotive for oil and fuel supply systems

Cost effective and works well with wide range of fluid viscosities

Gerotor operating principle

Fluid drawn into and squeezed out of cavity formed by inner and outer rotor


Outer rotorInner rotor

Outlet

kidney

Inlet kidney


Objective of the work


To size the gerotor and regulator to achieve low speed and high speed

pump performance requirements

Challenges

Low speed leakage and flow output

Flow regulation at high speed

Over stressing of teeth at high speed


Method to achieve the objectives

1. Flow model

Modeling of the gerotor pump and regulator performance

Validation of the model with test data

Study the dynamics of pressure and flow pulsations for pressure regulator

sizing

2. Mechanical model

Apply loading from flow model to the gerotor teeth

Predict the Hertzian contact stresses

To select appropriate material



Flow model generation from CAD geometry


3D CAD model imported

to GT-SPACECLAIM

Volume and area profile

generation in GEM3D

1D GT model


GT-SUITE flow model


Flow model

Delivery pressure (bar)

Flow (L/min)

Orifice diameter varied to meet the average delivery

pressure targets at different speeds


Test setup and instrumentation

High speed pressure transducers to study

pressure ripple

High resolution flow rate measurement

Gerotor isolated from pump for testing

A valve is used to impose the desired outlet

pressures at different speeds


Pump Speed

(rpm)

Pressure

(psi-a)

500 50

1000 81

1500 88

2000 93

2500 102

3000 105

Pressure

measurement

Flow meter

Valve to

create load


Instantaneous pressure comparison


Good consistency between

simulation and measured

delivery instantaneous

pressures

Fluid parameter "Time

Constant for free =>

dissolved“ tuned for high

speeds


Flow comparison


The flow correlates well for all conditions Volumetric efficiency within 2% of test data


Pressure regulator selection

Calibrated flow model used to optimize

pressure regulator

- Spool valve geometry

- Piston diameter

- Spill hole size

- Spring selection

- Rate

- Preload

- Will be looking into resonant

frequencies of the regulator valve



Power breakdown prediction – viscous drag and fluid power


Viscous drag increases with decrease in

temperature

Gerotor friction object to calculate the viscous drag


Mechanical model for Hertz contact stress prediction

Objective

To predict the Hertzian stresses to understand the pressure withstanding limits of gerotor

Methodology

Feed the mechanical model with loading inputs from the flow model

Inner rotor tooth profile

Outer rotor approximated circle

Material properties of inner and outer rotor

Run the model to see contact forces and stresses



Inputs to mechanical model


Forces on the shaft

imposed on inner

and outer rotor

Approximated

circle

Single tooth

profile

Material properties

for both rotors

1D flow

model


Contact forces and Hertz stress


Resultant force vectors show majority

of the load is taken by the bearings

The 150 N spikes at the contacts correspond to the

240 MPa (34,800 psi) contact stress


Summary and conclusion

GT-SUITE 1D model was built and prediction of dynamic pressure and flow correlated

well with experimental results.

The time constant for free air to dissolve in liquid, significantly affected the dynamic

pressure amplitude.

Time constant of 2 seconds best matched experimental results.

The pressure regulator was designed and optimized using the flow model.

Regulator testing results matched the predicted performance from GT-SUITE.

Loading contact forces are carried mostly by the bearings.

Hertzian contact stresses were predicted using mechanical modeling and the gerotor

material was found to be suitable to withstand those stresses.



Thank you

Thank you for your attention

Special thanks to -

Mark Cavanagh and Peter Hasiuk from Stanadyne

Rodrigo and Pete from GT support


Predicting flow performance and contact stresses … · Predicting flow performance and contact...

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