DESIGN AND TIMING ANALYSIS OF VARIABLE VALVE TIMING (VVT)
FOR INTERNAL COMBUSTION ENGINE
MOHD EFENDI BIN HUSIN
This report are submitted to the Faculty of Mechanical Engineering
As a partial to fulfill the requirement of
Bachelor of Mechanical Engineering (Automotive)
Faculty of Mechanical Engineering
Universiti Teknikal Malaysia Melaka
April 2008
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“I hereby to declare that the work is my own except for summaries and quotations which
have been duly acknowledged “
Signature : ………………………………
Author : MOHD EFENDI BIN HUSIN
Date : ………………………………
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Dedicate to my family, my friends and all compatriots.
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ACKNOLEDGEMENT
Alhamdulillah, thanks to God because with His blessing, I can finish this project
with successful. I would like to express my gratitude and appreciate to my PSM
supervisor, Mr. Herdy Rusnandi because he gives many valuable suggestion and advice
throughout the project. He also help in obtaining the reference and read through the
manuscript of this report.
Thanks should also to be forwarded to UTeM for their cooperation especially to
staff and librarian because give support and provide facilities and references in
completing this research.
Also to take this opportunity to thanks my family and friends who have been my
sides throughout this time for their moral support and loyalty. Thanks to you all.
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ABSTRACT
This project is focusing about design and analysis variable valve timing (VVT)
mechanism for spark ignition engine. This VVT mechanism will be applied to Proton
Wira 1.6 L with 4G92 SOCH engine as a car model to develop which does not have
VVT system yet. VVT is a system which that allows for more varying time at which
valve open, duration and valve overlap period. Design of this VVT system is based on
three parameters which are the configuration, dimension and complexity of the engine.
The timing analysis wil be done to get the suitable mechanism for this system.
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ABSTRAK
Projek ini memfokuskan tentang rekabentuk dan analisis mekanisma VVT untuk
enjin S.I. Mekanisma VVT ini akan di masukkan pada Proton Wira 1.6 L yang
menggunakan enjin 4G92 SOHC sebagai model kerata yang ingin dibangunkan. Sistem
VVT ini membenarkan masa untuk bukaan dan tutupan injap masukan berubah-ubah
mengikut kesesuaian kelajuan enjin. Rekabentuk system VVT ini adalah dengan
mengambil kira konfigurasi, dimensi dan kerumitan sesuatu enjin. Analisis masa akan
dilakukan untuk menentukan masa dan tempoh yang sesuai dengan mekanisma VVT.
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TABLE OF CONTENT
CHAPTER CONTENT PAGE
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRAK v
ABSTRACK vi
TABLE OF CONTENT vii
LIST OF TABLE xi
LIST OF FIGURE xii
CHAPTER I INTRODUCTION
1.1 Project overview 3
1.2 Problem statement 3
1.3 Objective 4
1.4 Project scope 4
CHAPTER II LITERATURE REVIEW
2.1 Introduction of VVT 5
2.2 The conventional valve timing 7
2.3 Categories of VVT 8
2.3.1 Variable phase control (VPC) 8
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CHAPTER CONTENT PAGE
2.3.2 Combined valve lift and phase
control (VLPC) 8
2.3.3 Variable event timing (VET) 9
2.4 Principles of current VVT 10
2.4.1 Axial movement of a piston with
helical gear teeth 11
2.4.2 Camshaft chain adjustment 11
2.4.3 Vane Type Systems 12
2.5 Advantages of VVT 13
2.6 Application of VVT 13
2.6.1 MIVEC by Mitsubishi 13
2.6.2 Valvetronic by BMW 15
2.6.3 VTEC by Honda 16
2.6.4 VVTL-i by Toyota 16
2.7 Mechanism of VVT 18
2.7.1 Rocker Arm 18
2.7.2 Camshaft 19
2.7.3 Poppet Valve 20
CHAPTER III METHODOLOGY
3.1 Introduction 21
3.2 Research on the problem involving
4G92 engine. 21
3.3 Analysis of engine system 23
3.3.1 Car specification 23
3.3.2 Engine Specification 24
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CHAPTER CONTENT PAGE
3.4 Research on the problem involving
conventional 4G92 SOCH engine. 25
3.5 Research for VVT system 25
3.6 Research the potential VVT system 25
for existing engine
3.7 Design cam profile 25
3.7.1 Prescribed rocker arm motion 27
3.8 Conceptual Design 29
3.8.1 Example drawings with
Catia software 29
CHAPTER IV RESULT AND DISCUSSION 31
4.1 Introduction 31
4.2 Concept of VVT design 31
4.3 Timing analysis 32
4.3.1 Timing of opening and closing
exhaust valve 32
4.3.2 Timing of opening and closing
intake valve 34
4.3.2.1 Intake valve for
conventional timing 34
4.3.2.2 Engine speed at low RPM 38
4.3.2.3 Engine speed at high RPM 41
4.3.3 Comparison of conventional,
low speed and high speed RPM 44
4.4 Cam profile design 45
4.4.1 The low RPM camshaft profile 47
4.4.2 The high RPM camshaft profile 48
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CHAPTER CONTENT PAGE
4.5 Full design 49
CHAPTER V CONCLUSION AND RECOMMENDATION 51
5.1 Conclusion 51
5.2 Recommendation 52
5.2.1 Fully variable valve timing
without camshaft 52
5.2.2 Variable Valve Event and Lift (VVEL) 53
REFERENCES
BIBLIOGRAPHY
APPENDICES
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LIST OF TABLE
NUMBER TITLE PAGE
2.1 Basic function principle of variable valve 7
timing concept
3.1 Proton Wira Specification 23
3.2 4G92 SOCH Engine Specification 23
4.1 Exhaust valve displacement for conventional 32
4.2 Valve timing for conventional 34
4.3 Intake valve displacement for conventional engine 35
4.4 Valve timing at low engine speed 38
4.5 Intake valve displacement for low engine speed 39
4.6 Valve timing at high speed engine 41
4.7 Intake valve displacement for high engine speed 42
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LIST OF FIGURES
NUMBER TITLE PAGE
2.1 VVT diagram 6
(Source: Ed. M, (2000))
2.2 Valve timing diagram 7
2.3 The inlet opening point for VPC 8
(Source: Garrett, T. K. (2001))
2.4 Stepped cams provide variable lift and 9
timing (VLTC) with rocker actuated valve
(Source: Garrett, T. K. (2001))
2.5 Curves of variable event (VET) timing 10
without phase change
(Source: Garrett, T. K. (2001))
2.6 Helical spline system 11
(Source: Jost, K. (2002))
2.7 Camshaft chain adjuster 12
(Source: Jost, K. (2002))
2.8 Vane Type system 12
(Source: Jost, K. (2002))
2.9 Mivec mechanism 14
2.10 Vanos VVT mechanism 15
2.11 Toyota VVTL-i cover engine 17
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2.12 Rocker arm 18
2.13 Camshaft 19
2.14 Poppet valve 20
3.1 Flow chart project 22
3.2 Cam profile design – flat face follower. 29
3.3 Poppet valve 29
3.4 Rocker arm 30
3.5 Camshaft 30
4.1 Valve timing diagram for conventional engine 35
4.2 Timing diagram for conventional engine 37
4.3 Timing diagram at low engine speed 38
4.4 Timing diagram for low engine speed 40
4.5 Timing diagram at high engine speed 41
4.6 Timing diagram for high engine speed 44
4.7 Comparison between conventional,
low speed and high speed engine 45
4.8 Cam profile for low engine speed 47
4.9 Cam profile for high engine speed 48
4.10 The full mechanism of VVT 49
4.11 The variable camshaft 50
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CHAPTER 1
INTRODUCTION
Nowadays, technology in automotive was blooming. Many automotive
manufacturer produce may invention to conquer the market. These inventions are
including producing the engine. Many consumer want cars with low capacity engine but
have high performance and low fuel consumptions. As example, VVT (Variable Valve
Timing) can give the small engine the high performance.
Variable valve timing is a system that allows for more efficient engine operation
by varying the time at which valves opens, duration of opening, and valve overlap
period. Some manufacturer called this mechanism in various name such as VVT-i, i-
Vtec, Mivec, VTC, CVVT and others. Common camshaft was designed with the
tolerance between low RPM for better fuel economy and high RPM for better
performance.
When we increase the rpm, this configuration for the camshaft does not work
well. If the engine is running at 4,000 rpm, the valves are opening and closing 2,000
times every minute. When the intake valve opens right at the top of the intake stroke, it
turns out that the piston has a lot of trouble getting the air moving into the cylinder in the
short time. Therefore, at higher rpm ranges we want the intake valve to open prior to the
intake stroke, so that by the time the piston starts moving downward in the intake stroke,
the valve is open and air moves freely into the cylinder during the entire intake stroke.
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For maximum engine performance at low engine speeds, the valves need to open longer
and close differently than they do at higher engine speeds.
So, VVT engine have an ability to vary the valve timing and opening duration in
both low and high speed operation. New technology such as i-Vtec mechanism allow
camshaft to operate at best performance on any speed.
Example car use VVT engine
BMW - Valvetronic
Honda - i-VTEC
Mitsubishi - MIVEC
Proton - Campro CPS
Toyota - VVT-i
Daihatsu - DVVT
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1.1 Project Overview
This project is about to design the new variable valve timing (VVT) system
which wants to applied for internal combustion engine. The design must be suitable for
spark ignition(S.I) engine.
To design this VVT, the mechanisms must be design first. To design this
mechanism, all of aspect must be known to ensure mechanisms can be applied to the
system.
Beside that to design this system, all the calculation for the mechanism must be
calculate to get the theoretical result and the graphs.
1.2 Problem statement
In Malaysia, Proton Wira is the most seller car. It maybe this car is cheap and
comfortable. But according to fuel consumption and power, it left out compare to other
similar car because this car is using more fuel and its power is lower.
The factor of this problem is this car used regular engine with old technology.
Now, almost of new car used the new technology such as turbocharged, VVT, hybrid
and others. This technology will give the car’s engine more energy in performance and
used low fuel consumption.
Now, Proton Wira must use the new engine to walk together with other cars. The
engine must more powerful with low consumption like VVT system. VVT can be
applied at Proton Wira engine because that engine is based on Mitsubishi engine (4G92).
Now Mitsubishi have Mivec which is one of VVT type system.
With VVT in Proton Wira, Proton Berhad which is the manufacturer of this car
can be advance and able to compete with other car manufacturer in worldwide market.
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1.3 Objective of Project
The main objective of this study is:
To design and timing analysis VVT mechanism for Spark Ignition Engine
(SI engine).
1.4 Scope of Project
The scopes of this project generally involve the following:
Analyze the valve timing
Conceptual design for 4 stroke engine passenger car with SI engine.
Drawing VVT mechanism with CAD software.
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CHAPTER 2
LITERATURE REVIEW
2.1 Introduction of VVT
Variable valve timing (VVT) is a generic term for an automobile piston engine
technology. VVT allows the lift or duration or timing of the intake or exhaust valves to
be changed while the engine is in operation. Two-stroke engines use a power valve
system to get similar results to VVT.
Piston engines normally use poppet valves for intake and exhaust. These are
driven by cams on a camshaft. The cams open the valves for a certain amount of time
during each intake and exhaust cycle. The timing of the valve opening and closing is
also important. The camshaft is driven by the crankshaft through timing belts, gears or
chains. The profile, position and shape of the cam lobes on the shaft, is optimized for a
certain engine rpm, and this tradeoff normally limits low-end torque or high-end power.
VVT allows the cam profile to change, which results in greater efficiency and power.
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Figure 2.1: VVT diagram (Source: Ed. M, (2000))
At high engine speeds, an engine requires large amounts of air. However, the
intake valves may close before all the air has been given a chance to flow in, reducing
performance. On the other hand, if the cam keeps the valves open for longer periods of
time, as with a racing cam, problems start to occur at the lower engine speeds. This will
cause unburned fuel to exit the engine since the valves are still open. This leads to lower
engine performance and increased emissions. Pressure to meet environmental goals and
fuel efficiency standards is forcing car manufacturers to turn to VVT as a solution. Most
simple VVT systems advance or retard the timing of the intake or exhaust valves. Others
like Honda's VTEC switch between two sets of cam lobes at a certain engine RPM.
Table 2.1: basic function principle of variable valve timing concept
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TDC
BDC
DC
00
1800
2700 900
160 ATDC
140 BTDC
580 ABDC
520 BBDC
Intake
valve
Intake
valve
2.2 The conventional valve timing
The valve timing for the conventional engine is fixed and not variable. It’s that
means the valve timing is same when the engine run in low RPM and high RPM. For the
4G92 SOCH engine, the valve timing open 140 before top dead center (BTDC) and close
at 580 after bottom dead center (ABDC). For the exhaust valve, it open at 52
0 before
bottom dead center (BBDC) and close at 160 after top dead center (ATDC).
Figure 2.2: Valve timing diagram
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2.3 Categories of VVT
Variable valve timing (VVT) has three main categories. They are variable phase
control (VPC), combined valve lift and phase control (VLPC), and variable event timing
(VET) systems.
2.3.1 Variable phase control (VPC)
Variable phase control, VPC implies varying the overlap so that low speed
torque and, with it, specific fuel consumption is improved over most of the speed range.
Since the duration of opening remains constant, wide-open throttle power is unaffected.
Figure 2.3: The inlet opening point for VPC. (Source: Garrett, T. K. (2001))
The inlet opening point can be retarded to reduce the overlap which, during
idling, ensures stability and low emissions with VPC. For good low-speed torque and
low fuel consumption, the inlet opening should be advanced, to increase the overlap.
2.3.2 Combined valve lift and phase control (VLPC)
VLPC offer further performance enhancement, but is more costly than VPC. It
has axially stepped cams, the variation being effected by shifting the followers from step
to step, but such a mechanism is complex. Tapered cams, such as the Fiat Tittolo system
combining variable lift and event timing, are an alternative but this means virtually point
contact, between cam and follower and, if the duration of opening is kept constant, the
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cam is extremely difficult to manufacture. Moreover, the axial loading introduced is
about 10% of the force between the cam and follower, so a powerful controller is
needed.
Figure 2.4: Stepped cams provide variable lift and timing (VLTC) with rocker actuated
valves. (Source: Garrett, T. K. (2001))
From the figure above, at the lower lifts, friction is reduced, charge swirl
enhanced and fuel consumption improved. The curves represent three steps, though up
to ten are practicable
2.3.3 Variable event timing (VET)
Varying the valve event timing (VET) is the changing of the duration of lift
while keeping the timing and magnitude of maximum lift constant. In other words, only
the opening and closing points are varied. This improves part load emissions and
economy, leaving the wide-open throttle condition unchanged, and has the advantage
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that the ramps on the cam remain effective both as the valve begins to lift and when it
re-seats.
Figure 2.5: Curves of variable event (VET) timing without phase change. (Source:
Garrett, T. K. (2001)).
Valve lift remains constant and the variation is effected continuously. Part-load
emissions and economy are improved, and the wide-open throttle condition is
unimpaired
2.4 Principles of current VVT
After the first patent application for a rotary displacement of a SI engine
camshaft was submitted in 1918 by Haltenberger, hundreds of patents for camshaft
adjustment systems have been issued, but only three construction principles have made
their way to series production. These systems use either mechanical or hydraulic
functional principles.
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2.4.1 Axial movement of a piston with helical gear teeth
The system is obtained from the functional principle of a spur/helical gear sleeve.
When the engine was in idle mode, a return spring keeps the system safely in the first
valve timing position. When engine oil pressure acts on the piston against the load
exerted by the spring, the helical cut gear spline teeth will translate the axial
displacement of the piston into a rotational movement. This causes rotation of the
camshaft relative to the drive sprocket and thus relative to the crankshaft.
Figure 2.6: Helical spline system (Source: Jost, K. (2002))
2.4.2 Camshaft chain adjustment
These systems employ a small chain between the intakes and exhaust camshaft.
The chain tensioner will moving upwards or downwards by oil pressurized piston will
vary the phase angle between the shafts. In this arrangement, the exhaust camshaft is
directly driven by the crankshaft and the intake camshaft can be repositioned by the
adjuster. This system is quite compact and costeffective, but permits only one camshaft
to be adjusted.