Transcript Thermal elastohydrodynamic simulation of a slider bearing in a heavy duty diesel engine transmission

1
Thermal elastohydrodynamic simulation of a slider
bearing in a heavy duty diesel engine transmission
Andrew Spencer
Dynamics & Acoustics
Engine Development
SCANIA
2015-10-07 14:10
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07
2
Background – V8 engine gear transmission
Camshafts
Intermediate Gear
Crankshaft
Investigation: Can we replace the Intermediate Gear roller bearing with a slider bearing?
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07
3
Why?
Motivation for a change from roller bearing to slider bearing:
1.
2.
3.
Noise reduction – lower transmission of meshing noise into the engine block
Cost reduction
Friction reduction – if the roller bearing has seals then total friction can be lower
with a slider bearing
Bearing friction measurement
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07
4
Multi-Body Dynamic model development
Multi-Body Dynamic model of the gear train developed
in AVL EXCITE Power Unit
Right
Camshaft
Left
Camshaft
Hub
• Crankshaft is driven at a constant speed
• Dynamic braking torque is applied to the left and right
camshafts, and also to the Fuel Pump, Air Compressor and
Power Steering Servo which are all driven through the
Intermediate Gear (not shown in the illustration)
• Intermediate Gear and Hub are modelled as flexible bodies
using finite elements
Intermediate Gear
Crankshaft
• Radial and Axial bearings between the hub and Intermediate
Gear modelled with Elastohydrodynamic bearings
• Different engine operating conditions are simulated
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07
5
EXCITE Power Unit model development
Elastohydrodynamic joints
Rigid bodies with brake torque applied
Flexible bodies
Crankshaft is driven at a constant speed
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
Gear joints transmit
torque and radial/axial
forces between bodies
2015-10-07
6
Condensated bodies
Condensation is performed in Nastran. The DOF’s that we want to keep (because we want to connect
a joint to them, or observe their motion in our simulations) are specified, and then Nastran is run to
reduce, or condense, the stiffness matrix down to just our specified DOF. This can hugely reduce the
DOF in our model.
Hub Flexible body
Gear Flexible body
From 16212 to 1612 DOF’s
From 18882 to 596 DOF’s
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07
7
Tribological joints
The time dependent Reynolds equation with cavitation is solved
for the radial and axial bearings.
Radial and Axial bearing pressure profile between
hub and gear
For a given separation, the pressure in the lubricant film is
calculated. This pressure is then applied to the flexible bodies and
the deformation calculated (EHD).
A full mixed lubrication model is implemented, if the separation
becomes very small then the surfaces will come into contact
(asperity contact) and the contact pressure is derived from a precalculated asperity stiffness curve. Flow factors are implemented
in the Reynolds equation.
Example of roughness used to calculate asperity stiffness
Lubricant
Supply
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07
8
Simulation of thermal effects
The Multi-Body Dynamic model presented so far is iso-thermal
Why might we want to include thermal effects?
Increase in
friction
Increase in the
temperature of
the
components
Reduction in
lubricant film
thickness
Reduction in
lubricant
viscosity
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07
9
Inclusion of thermal effects
Run MBD Model.
Results: Frictional heating & oil flow
Apply friction heating and oil flow (cooling)
from MBD to FEM thermal model
FEM: Step 1, Heat Transfer
FEM: Step 2, Thermal Expansion
Apply new temperatures and
clearances to MBD model
Evaluate Results
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07
10
Step 1 – Heat Transfer
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07
11
Step 2 – Thermal Expansion
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07
12
EXCITE & ABAQUS iterations for temperature
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07
13
Results
1. Under certain load conditions the gear is forced
backwards due to the axial loads applied through
the helical gear
Bearing
Ax. Front
Ax. Rear
Avg. Oil Flow
(l/min)
0.286
0.025
Heat flux to solid
(W/m²)
4921
11251
2. The oil flow rearwards out of the radial bearing
is very low (25 ml per minute). This is the limit
for how much oil can lubricate and cool the rear
axial bearing.
3. At the same time the rear axial bearing has the
highest heat flux into the bearing, leading to the
highest temperatures.
4. The rear portion of the hub also has higher
temperatures as there is less surrounding
material for the heat to be conducted away
through.
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07
14
Comparison with test data
A thermocouple was used to measure the temperature on the back-side of the hub – At the
highly loaded condition simulated a spike in temperature is observed during the engine test
Engine Speed
Oil Temperature
Torque transfer through
Intermediate gear
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07
15
Recommendations from simulation results
1.
Most likely cause of high temperatures in the rear axial bearing is too little oil
supplied from the radial bearing
2.
Solution would be to place axial, or spiral, grooves in the radial bearing
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07
16
Design change test results
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07
17
Conclusions and Future Work
• The use of Multi-body Dynamic simulation with thermal effects and EHD
bearing models led to a fundamental understanding of the tribological behaviour
of the system, not possible to gain from testing alone
• The model was predictive of the elevated temperatures observed during engine
testing
• Future work will entail expanding the semi-2D heat transfer and thermal
expansion FEM model to be fully 3D so that local hotspots around the
circumference of the bearing can be calculated
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07
18
Info class Public
Dynamics & Acoustics/Andrew Spencer/Tribodays 2015
2015-10-07