VARIABLE VALVE TIMING - Latest Seminar Topics for ... · variable valve timing engines they can vary: 1)lift of valve 2)timing of valves 3)phase shift of valve timing 4)valve overlap

VARIABLE VALVE TIMING

Guided by:

Anoop Kumar G Lecturer Dept. of Mechanical Engg

Presented by: Prashant S S7MB-112

CONTENTS

CONTENTS

1.Introduction

2.Need for VVT

Contents

1. Introduction

2. Need for VVT

3. Development of VVT

4. Types of VVT

5. Working

6. Benefits

7. Future

8. Conclusion

Introduction

Conventional engines

no relation between valve timing and engine speed

problems creep in at high rpm’s

if valve is set for high rpm problems occur at low rpm’s

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

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

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

Types of VVT

Honda VTEC – Variable valve Timing and Electronic lift Control

Toyota VVT-i – Variable Valve Timing with Intelligence

Nissan VVL - Variable Valve Lift

Porsche Vario Cam

Ferrari Valve Timing Advance

HONDA VTEC

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 rpm’s sensors send signals to ECU

ECU opens oil control valve

oil pressure couples all three rocker arms together

valves move according to third cam profile

timing is increased

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

Toyota’s VVT-i

VVT- I completely different technique

exhaust cam driven by crankshaft

intake cam driven by exhaust cam via drive gears

a cylinder behind drive gears of intake cams controls cam timing

can change cam timing by 60 degrees

controlling overlap from 0 to severe overlap at medium load to ideal for maximum power

Nissan VVL

consists of two cam lobes with different profiles

both cams operate 2 intake or exhaust valves

needle bearing roller mechanism

oil pressure pushes needle below the spring loaded slipper and follows high profile cam

BMW’s solenoid valve

BMW’s mechanical

Ferrari’s system

3-D profile

one end least aggressive cam

other end most aggressive

shaft moves by hydraulic pressure

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 closing charge does not escape

• quicker response to sudden power requirements

EGR effect

• EGR valve used in conventional engine not required here

• exhaust mixes with charge and dilutes it

• so low combustion temp. and low NOx production

• also unburnt gases in exhaust will get completely burnt

better fuel economy

• approx. 20% increase

• due to fact that smaller VTEC engine produces equal 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

Future

Electronically operated valve mechanism

Infinitely variable valve timing

conclusion

VVT is going to be affordable to the common man in a few years

Very useful technology in this age of diminishing fuel resources

Lots of R&D to be spent by companies

Thank you !