Valvetrain Friction - Modeling, Analysis and
Measurement of a High Performance Engine
Valvetrain System
Michele Calabretta and Diego Cacciatore, Automobili Lamborghini
Phil Carden, Ricardo UK
www.ricardo.com
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Contents
Project Number
Introduction
Test rig and measurement system
Mathematical model
Measured results
Analysis results
Comparison between measured and calculated data
Conclusions
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Introduction
Valvetrain friction makes a significant contribution to the
whole engine friction loss, esp. at low engine speed
2.4
Auxiliaries group
The total amount depends on the valvetrain type, engine
architecture, engine speed and lubricant temperature
etc.
Crankshaft group
2
Valvetrain group
Valvetrain group contributing
– ~35% of total friction @ 1000 rpm
– Reduces with engine speed
– ~10% of total friction @ >6000 rpm
Valvetrain friction of high performance engine is
relatively high, reasons being:
1.2
1
0.8
0.4
0.2
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8000
7500
7000
6500
6000
5500
5000
4500
4000
3500
0
3000
– Large valve diameter for high performance which
leads to high valve mass. Combined with high speed
and large valve lift, leads to requirement of high
spring force
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1.4
0.6
– Use direct acting valvetrain – sliding contact between
cam and tappet
Project Number
1.6
2500
Reciprocating group
1500
Test data in general based on motored strip
measurements
1000
Whole engine - no load (bar)
1.8
2000
2.2
Engine speed (rpm)
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Contents
Project Number
Introduction
Test rig and measurement system
Mathematical model
Measured results
Analysis results
Comparison between measured and calculated data
Conclusions
Client Confidential – Client Name
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Test rig and measurement system
Cylinder head from a V12 engine was used
Intake camshaft was driven by an electric motor connected to the end of the camshaft
Camshaft operated 12 intake valves via hydraulic tappets
Drive torque was measured by electric motor
Valve motion was also measured using a laser system to verify the physical dynamic
behaviour
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Contents
Project Number
Introduction
Test rig and measurement system
Mathematical model
Measured results
Analysis results
Comparison between measured and calculated data
Conclusions
Client Confidential – Client Name
## Month 2010
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Mathematical model
Dynamic model of a single valvetrain modelled using VALDYN
Valvetrain represented as a series of lumped mass/inertia nodes
connected by stiffness and damping
Cam node connected to a stiffness element representing camshaft
bending and support stiffness
Tappet top stiffness modelled as a function of eccentricity of cam-tappet
contact
Hydraulic tappet modelled as two mass nodes connected by a HLA
element to account for the action of
– High pressure chamber
– Expansion spring
– Check valve
Tappet connected to the valve using lash stiffness element representing
the stiffness of the valve stem between the tip and the centre of mass
Valve and spring retainer modelled as a single mass node
Valve node connected to ground by another lash stiffness representing
valve head and seat stiffness
Valvetrain have double spring pack
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Mathematical model (cont.)
The cam profile designed to meet the many conflicting
requirements for
– Engine breathing
– Acceptable durability
– High speed dynamics etc.
The spring pack designed to maintain contact between cam
and follower at high engine speed
VALDYN calculated dimensions of cam tappet contact ellipse
based on Hertzian theory
MOFT at cam-tappet contact calculated using isothermal EHL
theory
Greenwood & Tripp model utilized for asperity contact friction
force prediction
Lubricant Non-Newtonian behaviour taken into account
Total friction torque calculated due to oil shear and asperity
contact effects
Camshaft bearing friction calculated using ENGDYN
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Contents
Project Number
Introduction
Test rig and measurement system
Mathematical model
Measured results
Analysis results
Comparison between measured and calculated data
Conclusions
Client Confidential – Client Name
## Month 2010
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Measured results – camshaft drive torque
Camshaft drive torque measured with
standard steel tappets
Friction torque reduced with
increasing camshaft speed
Increasing the oil supply temperature
gave increased friction at low speed
and reduced friction at high speed but
the effect was quite small
No significant change in behavior at
very high engine speed was observed
- friction torque continued to decrease
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Measured results – friction comparison
Steel tappets replaced with DLC coated ones
Comparison between whole valvetrain
measurements at 90°C
– Use of DLC gave a strong reduction in
valvetrain friction
• 24% at 350 rpm
• 33% at 1000 rpm
• 24% at 4000 rpm camshaft speed
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Measured results – camshaft bearing torque
The final build involved removal of the
valves, springs and tappets and operation
with only the camshaft present
This build measured to quantify the
losses at the camshaft bearings with low
load to assist with the understanding of
the relative contributions to the total
system friction
Drive torque increased with camshaft
speed
The highest loss occured at lowest oil
supply temperature
Bearings are operating mainly in
hydrodynamic lubrication regime
– Losses are due to oil shear effect
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Contents
Project Number
Introduction
Test rig and measurement system
Mathematical model
Measured results
Analysis results
Comparison between measured and calculated data
Conclusions
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## Month 2010
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Analysis results - 1
Calculated camshaft bearing friction torque with and without valvetrain loads
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Analysis results - 2
The cam/tappet friction power loss is a function of
– Cam-tappet sliding velocity
– Cam-tappet contact force
– MOFT between cam and tappet
At low speed
– Sliding velocity low
– Cam-tappet contact force high on the nose low
on the flanks
– MOFT low
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Analysis results - 3
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Analysis results - 4
Total power loss increased roughly linearly with speed and the largest loss occurred at
the cam/tappet contact
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Contents
Project Number
Introduction
Test rig and measurement system
Mathematical model
Measured results
Analysis results
Comparison between measured and calculated data
Conclusions
Client Confidential – Client Name
## Month 2010
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Comparison between measured and calculated data - 1
First predicted camshaft bearing friction compared with the measured data
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Comparison between measured and calculated data - 2
Comparison of measured and calculated
friction with standard steel tappets and
friction coefficient of 0.045
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Comparison of measured and
calculated friction with standard
steel tappets and variable friction
coefficient
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Comparison between measured and calculated data - 3
Coefficient of friction required for good correlation at low engine speed
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Comparison between measured and calculated data - 4
Comparison between predicted and measured data for whole valvetrain friction as a
function of oil supply temperature
– standard steel tappets (on the left) and
– DLC tappets (on the right)
Model shows the same trends as the measured data; friction increased with oil
temperature at low speed and friction decreased with temperature at high speed
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Contents
Project Number
Introduction
Test rig and measurement system
Mathematical model
Measured results
Analysis results
Comparison between measured and calculated data
Conclusions
Client Confidential – Client Name
## Month 2010
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© Ricardo plc 2010
23
Conclusion
The model indicated that friction losses are dominated by losses at the cam/tappet
contact particularly at low engine speed
Tappet/bore interactions were less important but still worth considering
Camshaft bearing losses were shown to make a very small contribution to total losses
even at high engine speed
Model shown in this paper can be used to evaluate the effect on valvetrain friction of
many variations in valvetrain design
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