EMPAct and slip control: key elements to efficiency

improvement of the pushbelt CVT

Bram Veenhuizen, Bram Bonsen, Tim Klaassen, Patrick Albers (TU Eindhoven),

Christophe Changenet, Stéphane Poncy (ECAM Lyon)

2004 International Continuously Variable and Hybrid Transmission Congress

September 23-25, 2004

04CVT-49

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Contents

• Variator actuation: state of the art.

• Reference transmission efficiency analysis

• Efficiency improvement options– EMPAct system– slip control

• Loss comparison, loss reduction• Conclusions & recommendations• Next steps

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LuK/Audi control (Multitronic)

Double piston and two stage torque sensor technology

Cam disc 1

Cam disc 2

Cam disc 1

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Servo-electro-hydraulic Variator Control

• Hydraulic servo technique, driven by stepper motor.

• Closed loop ratio and pressure control.

• Over clamping still needed due to inaccuracies in torque estimation.

speed sensor

pressure sensor

pump

ECU

TCU

Torque signal

HC12

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Reference transmission

200 Nm; 110 kW

Variator

Final reduction

Oil pump

Main loss sources:

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Pump driving power

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Variator Torque loss

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Efficiency vs Safety

1500 [rpm]

over-drive

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Variator slip loss

NormalOperatingAreaslip loss: few tenths of percent

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Loss breakdown of reference transmission

1500 [rpm]over-drive

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Improvement options(actuation and control)

• Avoid over clamping completely• Avoid hydraulic limitations for low

clamping forces• Reduce actuation power rigorously• Avoid bandwidth limitationProposed system:• Servo-electromechanical actuation• Slip control

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TU/e EMPAct system

• Avoid hydraulic non-linearities

• Focus: slip control (Sf=1)Fsec=unknown!

• Force balance• Use electric

power (hybrids)• In steady state:

200 W at 200 Nm

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Traction curve: Compare with ASR

Variator Tire

Desirable operating

point

Typical traction curve in Overdrive

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Gaining efficiency with increased slip

Sf=3

Sf~1

Efficiency.gain

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Slip control test rig;pulley position sensor

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Slip control benefits

• Maximized efficiency• Lower variator load leading to

higher power density or more ratio coverage

• Increased robustness (!)• Probably leads to more dynamic

ratio shifting• Also applicable to hydraulic systems• Lower hydraulic pressure

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Loss comparison

Reference EMPAct &

slip control

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Loss reduction

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Conclusions & Recommendations

• CVT efficiency still offers room for improvement.

• Servo actuation and slip control offer great efficiency potential.

• Develop CVT-ASR.• We need small cheap servo-motors

of <200 Watt continuous, ~750 Watt peak and low power consumption at low speed.(depends on CVT spec).

• Slip sensing device is needed.

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Next steps

• Realise EMPAct proto; perform no-load tests.

• Develop control strategy (slip&ratio).

• Implement slip control on dyno.• Implement slip control in car.

In preparation for 3rd International CTI Symposium (Würzburg , Nov 30-Dec 2, 2004)

• Combine EMPAct and slip control in a car.

• Validate efficiency and fuel consumption.

First results

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TR3 Dyno (110 kW, Jatco CK2)

Implement slip control on a

dyno

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Slip Controller

More details: American Control Conference (ACC), June 8 to 10, 2005 Portland, Oregon

LVDT, mounted in CK2

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Preliminary resultsLow, controlled200 rad/sec