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Valvetrain dynamics can greatly influence engine characteristics such as NVH, thermodynamics and durability. Thus it’s important to gain system knowledge on the dynamic behavior at a rather early point in the design process. With the growing availability of numerical tools, such as 1D system simulation and MBD simulation accessing data on valvetrain dynamics has become more comfortable. MBD and 1D models greatly vary in terms of calculation time, model building and the ability of applying multiple physics like mechanics and hydraulics (especially important for the modeling of valve clearance compensators). Regarding the necessity of easy to use models and justifiable calculation times, at Hatz we were running a comparison between a 1D model and a MBD model regarding result quality, calculation times and model building efforts. To evaluate the results we conducted dynamic valve lift measurements on a test engine.
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Valvetrain dynamics A comparison between 1D model, MBD
and measurement
Tobias Winter
Hatz Diesel
Agenda
2
• About Hatz
• 1D Valvetrain dynamics – model building and results
• 3D Valvetrain dynamics – model building and results
• Measurement of dynamic valve train behavior
• Comparison between different modeling approaches and measurements
Hatz – the company
3
Hatz CZ
Headquarters at Ruhstorf, Germany New Diesel, Italy
… branch offices all over the world (France, Italy, GB, Spain, USA, Australia, …)
Hatz – the company
4
Light-Duty-1B-Engine Family
• low fuel consumption
• reliable start-up at very low termperatures
• tightly arranged & low weight
• high torque and output power
• multi-purpose usability
…
Heavy-Duty-1D-Engine Family
• long lasting
• easy startup with crank-handle
• vertical crankshaft available
• multi purpose usability
…
2G40/2G40H
• extremely fuel economic
• very good power/weight ratio
• direct drive of hydraulic pumps
• multi purpose usability
…
L/M-Series as 2, 3 & 4 Cylinder
• extremely long lasting, easy to service
• highly reliable due to mechanical and electronic
surveillance
• mutli purpose usability
...
Hatz – the company
5
H50 engine family
• Water cooled
• Turbo charged with intercooler
• EGR, DOC TIER IV final
• Side PTO
• 500h service intervalls
• …
1D Valvetrain dynamics
6
AmeSim Model for 1D dynamics
• Multiphysics approach
• Special attention to the hydraulic lash
adjusters
• No 3D setup for the rods available
• Stiffness of rocker arms etc. from FEM
model or analytic calculations
1D Valvetrain dynamics
7
1D Valvetrain dynamics
8
Intake valve
Lift
Velocity
Acceleration
@3000 rpm
1D Valvetrain dynamics
9
Difference between designed liftcurve and dynamic liftcurve @3000 rpm
1D Valvetrain dynamics
10
Difference between liftcurves at idle speed and max operating speed
3D Valvetrain dynamics
11
Multi Body Dynamics model using Altair Motionsolve/Motionview
Flexbody
Rigid body
Part Flexbody Rigid Body
Camshaft •
HLA-Housing •
Pushrods •
Rocker Arms •
Valve •
Bolt (rockers) •
Bolt mounting •
3D Valvetrain dynamics
12
Multi Body Dynamics model using Altair Motionsolve/Motionview
Contact
Joint
Connection Type
Cam-Follower CTC
HLA-Housing
Piston
Nonlinear spring
HLA-Piston
Pushrod
Joint
Pushrod
Rocker arm
Joint
Rocker arm
axis
Joint
Rocker arm
Valve
Contact
Valve seatring Contact
3D Valvetrain dynamics
13
Modeling details on the HLA and it‘s components
• Cam follower is
represented by a rigid
body
• Needle bearing is
represented by a stiffness
value
• No contact interface
between cam and
follower, CTC-constraint
was used instead
3D Valvetrain dynamics
14
Modeling details on the HLA and it‘s components
• All of the inner parts of the
HLA are represented by
rigid bodies
• Working piston is
connected to the rest of
the HLA by a nonlinear
spring characteristic
• Spring characteristic is
taken from a 1D Model
• But what about the
damping?
3D Valvetrain dynamics
15
Results for Intake valve @ 3000 rpm
Measuring valve train dynamics
16
Testbench for measuring lift and speed (acceleration is calculated)
Measuring valve train dynamics
17
Measurement results for intake valve
Comparison
18
Comparison for intake valve @ 3000 rpm
Comparison
19
Timing deviations (according to a valve lift of 0.5mm) @ 3000 rpm in °CA
Results from Delta IVO Delta IVC
1D +2,7° -2,1°
3D +3,0 -3,0
Measurement +2,8 -2,2
Both modeling approaches bring good results in terms of timing deviation
3D model accuracy suffers from underestimated HLA damping
Discussion of results
20
Some additional comments on the results:
• Both simulations were conducted without measurement results available
especially in the 3D model no tuning of contact dampings etc. was possible
• Overprediction of valve lift of the 1D model was a known issue from the start,
as the inclination of push rods wasn‘t taken into account (would be possible by
using „planar mechanics“ library, wasn‘t available in our license package)
• HLA has vital influence on the dynamic behaviour of the valve train (was a new
insight for us, as this was our first engine with HLA)
Discussion of results
21
Some additional comments on models:
• The main advantage of the 1D approach is the detailed modeling of the HLA
(multiphysics)
• Result quality of 3D model surely can be increased by using a 1D-3D
cosimulation to give a detailed modeling of the HLA
• Additional information in the 3D model (component stresses, visualization)
• Calculation times of 3D model aren‘t that much longer on todays desktop
workstations than those of the 1D model (~90s for 3D vs. ~4s for 1D)
3D modeling approach with a 1D cosim for the HLA seems to be best practice
to access highly accurate valve train dynamic behavior. Nevertheless both
approaches bring good results in terms of timing deviation
Discussion of results
22
Improving dynamic behavior of valve train:
• Bringing more stiffness to the valve train is difficult as the HLA is the „weakest
link“
• Redesign of intake cam brings improvement
Thank you for your
attention
Tobias Winter
Hatz Diesel
