Dynamic Performance Analysis of a Full Toroidal IVT

- a theoretical approach -

2004 International CVT and Hybrid Transmission Congress

CVT2004

R. Fuchs, Y. Hasuda

Koyo Seiko Co. Ltd.

I. James

Torotrak Development Ltd.

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Performance Analysis of a Full Toroidal IVT- a theoretical approach -

Content

• Motivations

• Approach

• Dynamics of the full toroidal variator

• Interaction variator-hydraulic

• Variator system damping

• Conclusion

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Motivations

• IVT dynamic in the frequency domain

• Prediction of system behavior

• System design

• Transmission and driveline control

Performance Analysis of a Full Toroidal IVT- a theoretical approach -

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Approach

InteractionVariator-hydraulic

InteractionVariator-driveline

(engine side)

InteractionVariator-driveline

(vehicle side)

Performance Analysis of a Full Toroidal IVT- a theoretical approach -

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The Full Toroidal Variator

Dynamic model(4 inputs, 4 outputs)

Variator(roller)

i

o

Pe

Pp

Ti

To

xp

dxp/dt

Performance Analysis of a Full Toroidal IVT- a theoretical approach -

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Variator Dynamic: 2 Main Mechanisms

2 mains mechanisms dictates variator stability

Performance Analysis of a Full Toroidal IVT- a theoretical approach -

② Castor angle roller self-alignment. castor angle and disc

rotational direction linked.

① Traction drive power transmission. basic control law for piston

and endload forces.

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Variator Dynamic: Static Response

Soft nonlinearities only due to toroidal geometry Linearization possible

Torque controlPiston position

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Variator Stability: Frequency ResponseThe full toroidal variator is a nonlinear MIMO system.

Performance Analysis of a Full Toroidal IVT- a theoretical approach -

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Variator Dynamic: Parametric Study

Dominant parameters

Roller speed, dxp /dt /Fp

100Hz

Performance Analysis of a Full Toroidal IVT- a theoretical approach -

Castor angle, dxp/dt/Fp

• Castor angle Damping

• Endload force Gain• Roller speed Stiffness

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Hydraulic Interaction: Closed-Loop

Mechanism of interactionVariator ratio change produces pressure perturbation.

Performance Analysis of a Full Toroidal IVT- a theoretical approach -

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Performance Analysis of a Full Toroidal IVT- a theoretical approach -

Block diagram

Variator

Hydrauliccircuit Pressure

demand

T

xp, dxp/dtFe, Fp

Hydraulic Interaction: Closed-Loop

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Hydraulic Interaction: 2 Circuit Concepts

Pressure control circuits based on flow control valve and pressure reducing valve

xp

u

Flow control valve　 (FCV)

Valve spool not sensitive to pressure perturbation.

FCVxp

u

Pressure-reducing valve (PRV)

Valve spool sensitive to pressure perturbation.

PRV

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Hydraulic Interaction: Frequency Response

Comparison of frequency response of hydraulic circuit: Fp/dxp/dt

bandwidth

damping

Pressure reducing valve

• Low pass.• Resonance peak.• Load compliance dependent

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• Low pass.• Load pressure dependent.

gain

bandwidth

Flow control valve

Hydraulic Interaction: Variator-FCV Circuit

Stable interactionHydraulic damping when variator resonance frequency is higher than hydraulic cut-off frequency

Stability

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Closed-loop: Hydraulic damping

Hydraulic Interaction: Variator-PRV Circuit

Valve stability can be guaranteed usingconventional hydraulic design techniques

Stable example

Performance Analysis of a Full Toroidal IVT- a theoretical approach -

Closed-loop: Hydraulic damping

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Hydraulic Interaction: Summary

2 basic circuits

Performance Analysis of a Full Toroidal IVT- a theoretical approach -

Flow control valve circuit• Interaction stable.• Hydraulic damping.• Technically not optimum for control.

Pressure reducing valve• Interaction stable for high load compliance.• Hydraulic damping.• Technically good for control.

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Importance of sub-system designfor system stability.

System Damping: 2 Methods

Performance Analysis of a Full Toroidal IVT- a theoretical approach -

u1

FCV1

Pp1

u2

FCV2

xp

Pp2

Fp1Fp22Ft

Flow control valve　 (FCV)

PRV1u1u2

PRV2

Pp1Pp2

Fp1Fp22Ft

xp

Pressure-reducing valve (PRV)

• Differential hydraulic (major effect for FCV circuits)• Damping orifices (major effect for PRV circuits)

Damping orifice Damping orifice Damping orifice Damping orifice

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System Damping: FCV Differential Circuit

Performance Analysis of a Full Toroidal IVT- a theoretical approach -

Frequency responses Fp/dxp/dt for null differential pressures

FCV hydraulic

As pressures increases:• Hydraulic gain increases & bandwidth decreases• System damping

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Variator + FCV hydraulic

System Damping: PRV Circuit with Restriction

Performance Analysis of a Full Toroidal IVT- a theoretical approach -

Frequency responses Fp/dxp/dt for different restriction areas

PRV hydraulic Variator + PRV hydraulic

As the area decreases:• Hydraulic gain & damping increase• System damping

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Conclusion

The variator-hydraulic system is stable• For a given variator design, the system performance is determined by the hydraulic circuit.• Additional response tuning possible with control.

Performance Analysis of a Full Toroidal IVT- a theoretical approach -

System design• This analysis is a key step in a theoretical approach of system design.• It should be applied at the design stage to provide a system optimised for fast but well damped response.

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Outlook

Extension to the complete IVT driveline• Complete theoretical investigation including dynamic response of the driveline.

Experimental validation and implication on driveability• Using test rigs and prototype vehicles.

>> Future publications

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