Post on 27-Mar-2020
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 !