Andrew Spencer Dynamics & Acoustics Engine Development SCANIA 2015-10-07 14:10 Thermal...

Info class Public Dynamics & Acoustics/Andrew Spencer/Tribodays 2015

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Andrew Spencer

Dynamics & Acoustics

Engine Development

SCANIA

2015-10-07 14:10

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

2015-10-07


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Background – V8 engine gear transmission

2015-10-07

Investigation: Can we replace the Intermediate Gear roller bearing with a slider bearing?

Intermediate GearCamshafts

Crankshaft


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Why?

Motivation for a change from roller bearing to slider bearing:1. Noise reduction – lower transmission of meshing noise into the engine block

2. Cost reduction

3. Friction reduction – if the roller bearing has seals then total friction can be lower with a slider bearing

2015-10-07

Bearing friction measurement


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Multi-Body Dynamic model development

2015-10-07

Crankshaft

Right Camshaft

LeftCamshaft

Multi-Body Dynamic model of the gear train developed in AVL EXCITE Power Unit

• 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

• Radial and Axial bearings between the hub and Intermediate Gear modelled with Elastohydrodynamic bearings

• Different engine operating conditions are simulated

Intermediate Gear

Hub


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EXCITE Power Unit model development

2015-10-07

Crankshaft is driven at a constant speed

Rigid bodies with brake torque applied

Flexible bodies

Gear joints transmit torque and radial/axial forces between bodies

Elastohydrodynamic joints


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Condensated bodies

2015-10-07

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 18882 to 596 DOF’s

From 16212 to 1612 DOF’s


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2015-10-07

The time dependent Reynolds equation with cavitation is solved for the radial and axial bearings.

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 pre-calculated asperity stiffness curve. Flow factors are implemented in the Reynolds equation.

Tribological joints

Example of roughness used to calculate asperity stiffness

Radial and Axial bearing pressure profile between hub and gear

Lubricant Supply


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Simulation of thermal effects

The Multi-Body Dynamic model presented so far is iso-thermal

Why might we want to include thermal effects?

2015-10-07

Increase in friction

Increase in the temperature of

the components

Reduction in lubricant viscosity

Reduction in lubricant film

thickness

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Inclusion of thermal effectsRun 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

2015-10-07Info class Public Dynamics & Acoustics/Andrew Spencer/Tribodays 2015

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Step 1 – Heat Transfer


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Step 2 – Thermal Expansion


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EXCITE & ABAQUS iterations for temperature


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1. Under certain load conditions the gear is forced backwards due to the axial loads applied through the helical gear

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.

Results

Bearing Avg. Oil Flow (l/min)

Heat flux to solid (W/m²)

Ax. Front 0.286 4921Ax. Rear 0.025 11251



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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

2015-10-07

Engine Speed

Torque transfer through Intermediate gear

Oil Temperature

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Recommendations from simulation results1. 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



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Design change test results

2015-10-07


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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

2015-10-07


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2015-10-07

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Andrew Spencer Dynamics & Acoustics Engine Development SCANIA 2015-10-07 14:10 Thermal...

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