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VARIABLE VALVE TIMING

Guided by:

Anoop Kumar G

LecturerDept. of MechanicalEngg

Presented by:Prashant S

S7MB-112

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CONTENTS

CONTENTS

1.Introduction

2.Need for VVT

Contents

1. Introduction

2. Need for VVT

3. Development of VVT4. Types of VVT

5. Working

6. Benefits

7. Future

8. Conclusion

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Introduction

Conventional engines

no relation between valve timing and engine speed

problems creep in at high rpms

if valve is set for high rpm problems occur at lowrpms

VVT engines

variable valve timing engines

they can vary: 1)lift of valve 2)timing of valves

3)phase shift of valve timing

4)valve overlap

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Need for VVT

at high speeds more air for more power and

combustion

at low speeds prevention of leakage of charge and

fuel efficiency

get good mileage

clean emission

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Development of VVT

HONDA - debut in 1991 in Honda NSX

TOYOTA follower eg. Corolla

Nissan, Porsche, BMW, Ferrari followed

but not all were same with each having their own

improvisations

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Types of VVT

Honda VTEC Variable valve Timing and Electroniclift Control

Toyota VVT-i Variable Valve Timing withIntelligence

Nissan VVL - Variable Valve Lift

Porsche Vario Cam

Ferrari Valve Timing Advance

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HONDA VTEC

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3 cam lobes for 2 intake or exhaust valves

one high rpm cam - high profile

two low rpm cams low profile

correspondingly three rocker arms

center one is free to move

at high rpms sensors send signals to ECU

ECU opens oil control valve

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oil pressure couples all three rocker arms together

valves move according to third cam profiletiming is increased

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this was DOHC VTEC

Honda later developed SOHC VTEC

only intake valves had VTEC

then i-VTEC

this system induced swirl

ECU monitors : engine speed , cam position ,manifold pressure

this advances or retards the cam

reduces exhaust emissions

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Toyotas VVT-i

VVT- I completely different techniqueexhaust cam driven by crankshaft

intake cam driven by exhaust cam via drive gears

a cylinder behind drive gears of intake camscontrols cam timing

can change cam timing by 60 degrees

controlling overlap from 0 to severe overlap at

medium load to ideal for maximum power

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Nissan VVL

consists of two cam lobes with different profiles

both cams operate 2 intake or exhaust valves

needle bearing roller mechanismoil pressure pushes needle below the spring loaded

slipper and follows high profile cam

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http://www.alflash.narod.ru/D4/VVTLi.jpg

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BMWs solenoid valve

h i l

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BMWs mechanical

i

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Ferraris system

3-D profile

one end least aggressive cam

other end most aggressive

shaft moves by hydraulic pressure

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Benefits

smooth idle

valve overlap retarded to zero

so pure mixture thus stable combustion

low fuel consumption

torque improvement low to mid-range torque is increased

by increasing valve overlap

exhaust sucks charge and due to early closingcharge does not escape

quicker response to sudden power requirements

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EGR effect

EGR valve used in conventional engine notrequired here

exhaust mixes with charge and dilutes it so low combustion temp. and low NOx production

also unburnt gases in exhaust will get completelyburnt

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better fuel economy

approx. 20% increase

due to fact that smaller VTEC engine producesequal power to that of non-VTEC larger engine

Improved emission control No Nox production due to EGR effect

due to low fuel consumption low CO2 emission

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Future

Electronically operated valve mechanism

Infinitely variable valve timing

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conclusion

VVT is going to be affordable to thecommon man in a few years

Very useful technology in this age of

diminishing fuel resources

Lots of R&D to be spent by companies

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Thank you !