1Copyright © 2012 Mahindra & Mahindra Ltd. All rights reserved. 1

Mahindra Automotive

2Copyright © 2012 Mahindra & Mahindra Ltd. All rights reserved.

22 August 2013

Effect of Spring Preload Optimization on Friction of 3 Cylinder Variable Valve Timing Gasoline Engine.

Presented By:

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Presented By:

Anshul Agarwal

Mahindra & Mahindra Ltd.

Presentation Plan

Design Criteria

AVL Excite TD model

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3

2

4

Dynamic Simulation Result Analysis

Methodology For spring Optimization

Conclusion

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5

Components of Valve train Assembly

CamshaftHydraulic Lash Adjuster

Cam Phaser

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Roller Finger FollowerValves

Valve SpringSpring retainers Valve Lock

Methodology

START

Preliminary spring

design calculation

AVL excite Timing drive

analysis

YESNO

� Preliminary spring calculations are performed.

� The outcome of mathematical calculation is

used for generating inputs for spring

element in simulation tool.

� Based on simulation results spring

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Spring

optimization

Dynamic Analysis

END

� Based on simulation results spring

optimization is done.

� overall effect of valve spring on valvetrain

system dynamics is analyzed.

AVL Excite TD Model

Valve train model� Intake cam shaft

� Timing and contact geometry

� Cam contour.

� Lubrication element

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� Roller Finger follower

� Valve spring

� Valve

� Hydraulic lash adjuster,

� Radial and Thrust bearings for support.

Assumptions & Considerations

• Constant part of stiffness is considered for the analysis.

• Stiffness of valve train parts are calculated by FEA.

• Stiffness of the Valve Face is as per AVL software manual .

• The relative damping has been taken as per AVL guidelines.

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• The relative damping has been taken as per AVL guidelines.

• An oil aeration of up to 5% at max. speed of the hot engine is assumedfor the oil in HLA.

Spring Dynamic Analysis Result

Cam to follower contact stress ( Hertz-stress)

240 245 250 255 260

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The amplitude of hertz stress is less on nose portion as compared to flank portion

as inertia forces in flank portion are on higher side as compared to nose portion.

Spring Dynamic Analysis Result

Valve acceleration curve

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Reason for low force factor at cam nose portion is higher valve deceleration

forces.

Spring Dynamic Analysis Result

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� The min. calculated axial forces for intake valve train which is above

the limit to avoid pump up losses.

� The maximum side force is also lower than the permissible limit.

Spring Dynamic Analysis Result

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Engine speed v/s Camshaft instantaneous torque

Effect of spring preload on Camshaft instantaneous torque

Spring Dynamic Analysis Result

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• Contact between two adjacent active coils during operation is commonly

termed as coil clash.

• Condition of spring surge and resonance effect within the valve spring are

checked .

• Coil to coil contact should be prevented.

Conclusion

S. No Parameter Effect for 188N preload w.r.t 250 N preload

1. Hertz stress Reduced by 10 % for 188 N valve spring preload

2. Surplus spring force Reduced by 10 % for 188 N valve spring preload

3. HLA pump up force Reduced by 14 % for 188 N valve spring preload

4. Camshaft Torque Reduced by 11.2 % for 188 N valve spring preload

5. Normal spring force Reduced by 12 % for 188 N valve spring preload

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5. Normal spring force Reduced by 12 % for 188 N valve spring preload

�A mathematical model for analysis of different valve spring preloads has been

developed and results are very well co-relating with theoretical explanations

and theories.

�It can be safely concluded that The valve spring preload reduction results in

friction reduction in the valvetrain, as valve opening load and camshaft torque

is reduced by 11 % and 11.2 % respectively.

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