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Seminar Report on I VTEC HONDA (Prof. Mr. V. M. Bukka Sir)

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“intelligent-VALVE TIMING AND LIFT ELECTRONIC CONTROL”
Seminar Report
Submitted in the partial fulfillment of the requirements for the diploma of
DIPLOMA
IN
MECHANICAL ENGINEERING
In the faculty of Engineering and Technology
Government Polytechnic, Aurangabad-431005

Guided By,

Prof. Mr. V. M. Bukka Sir
(Lecturer in Mech. Engg.)
Submitted by,

Mr. Mahesh Kachru Kawade
(122041)


Department Of mechanical Engineering
Govt. Polytechnic, Aurangabad-431005.
Academic Year 2014-15

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GOVERNMENT POLYTECHNIC AURANGABAD

C E RT I FI CAT E
This is to certify that the thesis titled “intelligent- VALVE TIMMING AND LIFTELECTRONIC
CONTROL “represents the bonafide work carried out by Mr. KAWADE MAHESH KACHRU submitted in partial
fulfillment of the requirement for the diploma in “Mechanical Engg. “The work has been carried out in the Department of
Mechanical Engg. Of Government Polytechnic, Aurangabad (An Autonomous Institute Of Govt. Of Maharashtra) under
the guidance of Prof. Mr.V.M.Bukka.

Prof. V. M. Bukka Sir

Dr. A. V. Peshwe Sir

(Seminar Guide.)

(HOD of Mech. Dept.)

Dr. P.R Pattalwar Sir
(Principle)

ACKNOWLEDGEMENT


Firstly I thank none but one almighty GOD. For showering his mercy and blessing on me and being with me always,
and he is with me hence only I can finished my work successfully. Then I thank my parents for their blessing, encouragement
and moral support.

I would like to take this opportunity to express our deep sense of gratitude and respect to our guide Prof. V.M
.Bukka Sir, Lecturer in Mechanical Engineering. It was a great privilege to get his constant inspiration and guidance
during our seminar work.
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I extend word of thanks to Prof. Dr. A. V. Peshave Sir, head of the department of Mechanical Engineering
and all those teaching and non-teaching staff stood behind to help and support us.
I am also thankful to our beloved principle Dr. P. R. Pattalwar Sir for providing all necessary activities and
encouraging us throughout the work.
I am highly obliged to entire friends group providing the way in the difficult time.
Thankful I ever remain…………….

Date:
Place: Aurangabad

Mr. KAWADE MAHESH KACHRU

(122041)

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i-VTEC ENGINE

ABSTRACT

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The most important challenge facing car manufacturers today is to offer vehicles that deliver excellent fuel
efficiency and superb performance while maintaining cleaner emissions and driving comfort. This paper deals with iVTEC (intelligent-Variable valve Timing and lift Electronic Control) engine technology which is one of the
advanced technology in the IC engine. i-VTEC is the new trend in Honda’s latest large capacity four cylinder petrol
engine family. The name is derived from ‘intelligent’ combustion control technologies that match outstanding fuel
economy, cleaner emissions and reduced weight with high output and greatly improved torque characteristics in all
speed range. The design cleverly combines the highly renowned VTEC system - which varies the timing and amount
of lift of the valves - with Variable Timing Control. VTC is able to advance and retard inlet valve opening by altering
the phasing of the inlet camshaft to best match the engine load at any given moment. The two systems work in
concern under the close control of the engine management system delivering improved cylinder charging and
combustion efficiency, reduced intake resistance, and improved exhaust gas recirculation among the benefits. iVTEC technology offers tremendous flexibility since it is able to fully maximize engine potential over its complete
range of operation. In short Honda's i-VTEC technology gives us the best in vehicle performance.

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INDEX
SR.N
O
1.
2.

TOPIC NAME
INTODUCTION
OBJECTIVE
TERMS RELATED TO i-VTEC
3

VTEC
4

5.

13
4.1 Basic VTEC Mechanism
4.2 DOHC VTEC
4.3 SOHC VTEC
4.4 3-Stage VTEC

VALVE TIMING CONTROL (VTC)
i-VTEC SYSTEM
ADVANTAGES OF i-VTEC SYSTEM
DISADVANTAGES OF i-VTEC
APPLICATIONS OF i-VTEC SYSTEM
CASE STUDY OF ‘HINDA CITY’

6.
7.
8.
9.
1
10.
1

1

27

11.1 Pneumatic Valve
11.2 VTEC in Turbo
11.3 i-VTEC in Motorcycle

TOP 10 i-VTEC ENGINES
12.

19
20
23
23
24
25

10.1 Specifications OF i-VTEC Engine.
10.2 Performance

FUTURE TRENDS
11.

08
09
11

3.1 Volumetric Efficiency
3.2 Torque
3.3 Power
3.4 Camshaft
3.6 Engine Breathing
3.7 Electronic Control Unit (ECU)

3.

4.

PAGE NO.

28

12.1 B16A
12.2 B16B Type R
12.3 B18C1
12.4 B18C Type R
12.5 C32B Type R
12.6 F20C1
12.6 H22A1
12.7J37A4
12.8 K20A Type R
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12.9 K24A2

13.
14.

CONCLUSION
REFERANCE

30
31

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1. INTRODUCTION
1.1 Definition
An internal combustion is defined ‘as an engine in which the chemical energy of the fuel is released
inside the engine and used directly for mechanical work’. The internal combustion engine was first conceived
and developed in the late 1800’s. The man who is considered the inventor of the modern IC engine and the founder
of the industry is Nikolaus Otto (1832-1891).
1.2 Discovery
Over a century has elapsed since the discovery of IC engines. Excluding a few development of rotary
combustion engine the IC engines has still retained its basic anatomy. As our knowledge of engine processes has
increased, these engines have continued to develop on a scientific basis. The present day engines have advances to
satisfy the strict environmental constraints and fuel economy standards in addition to meeting in competitiveness of
the world market. With the availability of sophisticated computer and electronic, instrumentation have added new
refinement to the engine design.
From the past few decades, automobile industry has implemented many advance technologies to
improve the efficiency and fuel economy of the vehicle and i-VTEC engine introduced by Honda in its 2002 Acura
RSX Type S is one of such recent trend in automobile industry.
The VTEC system provides the engine with multiple cam lobe profiles optimized for both low and high
RPM operations. In basic form, the single barring shaft-lock of a conventional engine is replaced with two profiles:
one optimized for low-RPM stability and fuel efficiency, and the other designed to maximize high-RPM power
output. The switching operation between the two cam lobes is controlled by the ECU which takes account of engine
oil pressure, engine temperature, vehicle speed, engine speed and throttle position. Using these inputs, the ECU is
programmed to switch from the low lift to the high lift cam lobes when the conditions mean that engine output will
be improved. At the switch point a solenoid is actuated which allows oil pressure from a spool valve to operate a
locking pin which binds the high RPM cam follower to the low RPM ones. From this point on, the valves open and
close according to the high-lift profile, which opens the valve further and for a longer time.

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2. OBJECTIVE
The objective of seminar report is;
1) To know the VTC system
2) To know the components
3) To understand the construction & working
4) Operations

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i-VTEC SYSTEM:

T

he latest and most sophisticated VTEC development is i-VTEC ("intelligent" VTEC), which combines
features of all the various previous VTEC systems for even greater power band width and cleaner emissions.
With the latest i-VTEC setup, at low rpm the timing of the intake valves is now staggered and their lift is
asymmetric, which creates a swirl effect within the combustion chambers. At high rpm, the VTEC transitions as
previously into a high-lift, long-duration cam profile.
The i-VTEC system utilizes Honda's proprietary VTEC system and adds VTC (Variable Timing
Control), which allows for dynamic/continuous intake valve timing and overlap control.
The demanding aspects of fuel economy, ample torque, and clean emissions can all be controlled and
provided at a higher level with VTEC (intake valve timing and lift control) and VTC (valve overlap control)
combined.

ACTUAL DIAGRAM OF VALVE IN i-VTEC

The i stands for intelligent: i-VTEC is intelligent-VTEC. Honda introduced many new innovations in iVTEC, but the most significant one is the addition of a variable valve opening overlap mechanism to the VTEC
system. Named VTC for Variable Timing Control, the current (initial) implementation is on the intake camshaft and
allows the valve opening overlap between the intake and exhaust valves to be continuously varied during engine
operation.

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3. TERMS RELATED TO i-VTEC:
3.1 Volumetric Efficiency
The engine produces a certain force from every power stroke as a result of burning air/fuel expanding.
This force generally gets less for every power stroke as the engine revolves faster, as the air/fuel mixture has less
time to get sucked into the cylinder. The volumetric efficiency of a engine at a certain speed is the pressure of air/fuel
mixture inside the cylinder when the piston has finished sucking in the mixture, as a percentage of the atmospheric
pressure. Thus an engine with 80% volumetric efficiency at a certain speed will have a mixture pressure of 80% of
atmospheric pressure when the piston is at bottom dead centre after the intake stroke.

3.2 Torque
The torque of an engine is the total force the engine produces at a certain speed. This is a rotating force,
but the easiest way to think of torque is to imagine an engine with a drum attached to it, winching up a weight
vertically. The torque of the engine is the force that raises the weight The torque of an engine will increase as the
engine rotates faster, because the number of power strokes per time period increases. However, the volumetric
efficiency of an engine will drop after a certain speed, so each power stroke has less force. The point where the
increase in force (from the increased number of power strokes) is equal to the drop in force (because of less
efficiency) is the point of peak torque. This occurs anywhere from 2000 - 7000 rpm, depending on the engine. A
higher performance engine will generally have a higher efficiency and maintain this longer, so will have peak torque
at higher revs. In the case of my B16A VTEC engine, the torque peak is at about 7000 rpm, which is one of the
highest of any mass produced vehicle engine.

3.3 Power
The gearbox modifies torque from the engine to torque at the wheels. If one engine produces the same
torque as another, but at a higher engine speed, then force at the wheels will be higher for the first engine one the
engine speed is converted by the gearbox to the same wheel speed. The power of an engine is the measurement of the
torque of an engine at different engine speeds. Going back to our engine winching analogy, it is easy to see that if the
engine is geared down so that the drum rotates half as fast, then weight will be raised slower be more weight can be
lifted. The peak power point for an engine is the point where, ideally geared, the most force will be available at the
wheels. The peak power point will always be above the peak torque
point. In my B16A engine, the peak power occurs at about 7800 rpm.

3.4 The Camshaft
The camshaft has a very big influence on engine breathing. The camshaft controls how long the intake
and exhaust valves are open, and how high they open. The intake valves

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always open before the piston is at the top of the cylinder (and started sucking) and close after the piston is at the
bottom of the cylinder (and stopped sucking). The shape of the cam lobes limits the valve opening and closing to a
gradual opening from closed to fully open, then a gradual closing to fully shut. (Otherwise the value train will
destroy itself at high speeds) So while the value opens before the cylinder is sucking, it is not open that much. There
is a trade off in terms of efficiency with the camshaft. It is possible to open the values earlier, and have the valve
open further for a longer period while the engine is sucking in mixture (it works the same for the exhaust). The valve
will be open before the piston has reached the top of the cylinder, and some of the mixture will be pushed out of the
cylinder but the piston. Because of the momentum effect of the intake mixture, this loss is less at higher revs, and
more at lower speeds, when the intake mixture has not much momentum to overcome mixture being forced out of the
cylinder.
A camshaft that opens the values early and closes them late (called long duration, or ‘wild’ or ‘lumpy’) will be more
efficient at higher engine speeds and less efficient at lower engine speeds. A camshaft that opens later and closes
earlier (called short duration, or ‘mild’) will be more efficient at lower engine speeds and less efficient at higher
engine speeds.

3.5 ECU
The ECU (electronic control unit = the fuel injection computer) is the heart of the engine. Basically the
purpose of the ECU is to control fuel injection and ignition for the engine, for all the conditions which the engine can
be expected to run under. This is a fairly complicated job considering the number of external factors that can
influence the amount of fuel that needs to be injected into the engine, and the rate at which events happen. At 8500
rpm the ECU has to control 280 injector openings/closing per second and 280 ignition signals per second, while
coping with 2400 signals from the distributor per second. Plus there are another 16-odd signals and sensor reading
from the engine and outside world that ECU needs to know about.

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4. VTEC ENGINE:
VTEC (standing for Variable valve Timing and lift Electronic Control) does Honda Motor Co., Ltd.
develop a system. The principle of the VTEC system is to optimize the amount of air-fuel charge entering, and the
amount of exhaust gas leaving, the cylinders over the complete range of engine speed to provide good top-end output
together with low and mid-range flexibility.
VTEC system is a simple and fairly elegant method of endowing the engine with multiple camshaft
profiles optimized for low and high RPM operations. Instead of only one cam lobe actuating each valve, there are
two - one optimized for low RPM smoothness and one to maximize high RPM power output. Switching between the
two cam lobes is controlled by the engine's management computer. As the engine speed is increased, more air/fuel
mixture needs to be "inhaled" and "exhaled" by the engine. Thus to sustain high engine speeds, the intake and
exhaust valves needs to open nice and wide. As engine RPM increases, a locking pin is pushed by oil pressure to
bind the high RPM cam follower for operation. From this point on, the valve opens and closes according to the highspeed profile, which opens the valve further and for a longer time.

4.1 BASIC V-TEC MECHANISM
The basic mechanism used by the VTEC technology is a simple hydraulically actuated pin. This pin is
hydraulically pushed horizontally to link up adjacent rocker arms. A spring mechanism is used to return the pin back
to its original position.
To start on the basic principle, examine the simple diagram below. It comprises a camshaft with two
cam-lobes side-by-side. These lobes drive two side-by-side valve rocker arms.

VTEC OPERATION
The two cam/rocker pairs operates 4.1
independently
of eachWITH
other.GRAPH
One of the two cam-lobes are intentionally drawn to be
different. The one on the left has a "wilder" profile, it will open its valve earlier, open it more, and close it later, compared to the
one on the right. Under normal operation, each pair of cam-lobe/rocker-arm assembly will work independently of each other.

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VTEC uses the pin actuation mechanism to link the mild-cam rocker arm to the wild-cam rocker arm. This
effectively makes the two rocker arms operate as one. This "composite" rocker arm(s) now clearly follows the wild-cam profile
of the left rocker arm. This in essence is the basic working principle of all of Honda's VTEC engines.

VTEC, the original Honda variable valve control system, originated from REV (Revolution-modulated
valve control) introduced on the CBR400 in 1983 known as HYPER VTEC. In the regular four-stroke automobile
engine, the intake and exhaust valves are actuated by lobes on a camshaft. The shape of the lobes determines the
timing, lift and duration of each valve. Timing refers to an angle measurement of when a valve is opened or closed
with respect to the piston position (BTDC or ATDC). Lift refers to how much the valve is opened. Duration refers to
how long the valve is kept open. Due to the behavior of the working fluid (air and fuel mixture) before and after
combustion, which have physical limitations on their flow, as well as their interaction with the ignition spark, the
optimal valve timing, lift and duration settings under low RPM engine operations are very different from those under
high RPM. Optimal low RPM valve timing, lift and duration settings would result in insufficient filling of the
cylinder with fuel and air at high RPM, thus greatly limiting engine power output. Conversely, optimal high RPM
valve timing, lift and duration settings would result in very rough low RPM operation and difficult idling. The ideal
engine would have fully variable valve timing, lift and duration, in which the valves would always open at exactly
the right point, lift high enough and stay open just the right amount of time for the engine speed in use.

BASIC VTEC PRINCIPLE

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DOHC VTEC ENGINE MODEL

4.2 DOHC VTEC
Introduced as a DOHC (Double overhead camshaft) system in Japan in the 1989 Honda Integra XSi this
used the 160 bhp (120 kW) B16A engine. The same year, Europe saw the arrival of VTEC in the Honda CRX 1.6iVT, using a 150 bhp variant (B16A1). The United States market saw the first VTEC system with the introduction of
the 1991 Acura NSX, which used a 3-litre DOHC VTEC V6 with 270 bhp (200 kW). DOHC VTEC engines soon
appeared in other vehicles, such as the 1992 Acura Integra GS-R (B17A1 1.7-litre engine), and later in the
1993 Honda Prelude VTEC (H22A 2.2-litre engine with 195 hp) and Honda Del Sol VTEC (B16A3 1.6-litre engine).
The Integra Type R (1995–2000) available in the Japanese market produces 197 bhp (147 kW; 200 PS) using a
B18C5 1.8-litre engine, producing more horsepower per liter than most super-cars at the time. Honda has also
continued to develop other varieties and today offers several varieties of VTEC, such as i-VTEC and i-VTEC
Hybrid.

4.3 SOHC VTEC
As popularity and marketing value of the VTEC system grew, Honda applied the system
to SOHC (single overhead camshaft) engines, which share a common camshaft for both intake and exhaust valves.
The trade-off was that Honda's SOHC engines benefitted from the VTEC mechanism only on the intake valves. This
is because VTEC requires a third center rocker arm and cam lobe (for each intake and exhaust side), and, in the
SOHC engine, the spark plugs are situated between the two exhaust rocker arms, leaving no room for the VTEC
rocker arm. Additionally, the center lobe on the camshaft cannot be utilized by both the intake and the exhaust,
limiting the VTEC feature to one side.
However, beginning with the J37A4 3.7L SOHC V6 engine introduced on all 2009 Acura TL SH-AWD
models, SOHC VTEC was incorporated for use with intake and exhaust valves. The intake and exhaust rocker shafts
contain primary and secondary intake and exhaust rocker arms, respectively. The primary rocker arm contains the
VTEC switching piston, while the secondary rocker arm contains the return spring. The term "primary" does not
refer to which rocker arm forces the valve down during low-RPM engine operation. Rather, it refers to the rocker
arm which contains the VTEC switching piston and receives oil from the rocker shaft.
The primary exhaust rocker arm contacts a low-profile camshaft lobe during low-RPM engine operation.
Once VTEC engagement occurs, the oil pressure flowing from the exhaust rocker shaft into the primary exhaust
rocker arm forces the VTEC switching piston into the secondary exhaust rocker arm, thereby locking both exhaust
rocker arms together. The high-profile camshaft lobe which normally contacts the secondary exhaust rocker arm
alone during low-RPM engine operation is able to move both exhaust rocker arms together which are locked as a
unit. The same occurs for the intake rocker shaft, except that the high-profile camshaft lobe operates the primary
rocker arm.
The difficulty of incorporating VTEC for both the intake and exhaust valves in a SOHC engine has been
removed on the J37A4 by a novel design of the intake rocker arm. Each exhaust valve on the J37A4 corresponds to
one primary and one secondary exhaust rocker arm. Therefore, there are a total of twelve primary exhaust rocker
arms and twelve secondary exhaust rocker arms. However, each secondary intake rocker arm is shaped similar to a
"Y" which allows it to contact two intake valves at once. One primary intake rocker arm corresponds to each
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secondary intake rocker arm. As a result of this design, there are only six primary intake rocker arms and six
secondary intake rocker arms.

4.4 VTEC-E

4.4 VTEC-E

The earliest VTEC-E implementation is a variation of SOHC VTEC which is used to increase
combustion efficiency at low RPM while maintaining the mid range performance of non-vtec engines. VTEC-E is
the first version of VTEC to employ the use of roller rocker arms and because of that, it forgoes the need for having
3 intake lobes for actuating the two valves—two identical lobes for non-VTEC operation and one lobe for VTEC
operation. Instead, there are two different intake cam profiles per cylinder—a very mild cam lobe with little lift and a
normal cam lobe with moderate lift. Because of this, at low RPM, when VTEC is not engaged, one of the two intake
valves is allowed to open only a very small amount due to the mild cam lobe, forcing most of the intake charge
through the other open intake valve with the normal cam lobe. This induces swirl of the intake charge which
improves air/fuel atomization in the cylinder and allows for a leaner fuel mixture to be used. As the engine's speed
and load increase, both valves are needed to supply a sufficient mixture. When engaging VTEC mode, a pre-defined
threshold for MPH (must be moving), RPM and load must be met before the computer actuates a solenoid which
directs pressurized oil into a sliding pin, just like with the original VTEC. This sliding pin connects the intake rocker
arm followers together so that now, both intake valves are now following the "normal" camshaft lobe instead of just
one of them. When in VTEC, since the "normal" cam lobe has the same timing and lift as the intake cam lobes of the
SOHC non-VTEC engines, both engines have identical performance in the upper powerband assuming everything
else is the same.
With the later VTEC-E implementations, the only difference it has with the earlier VTEC-E is that the
second "normal" cam profile has been replaced with a "wild" cam profile which is identical to the original VTEC
"wild" cam profile. This in essence supersedes VTEC and the earlier VTEC-E implementations since the fuel and
low RPM torque benefits of the earlier VTEC-E are combined with the high performance of the original VTEC.

4.5 3-STAGES VTEC

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4.5 THREE STAGES OF ACTUATION OF VALVES

3-Stage VTEC is a version that employs three different cam profiles to control intake valve timing and
lift. Due to this version of VTEC being designed around a SOHC valve head, space was limited and so VTEC can
only modify the opening and closing of the intake valves. The low-end fuel economy improvements of VTEC-E and
the performance of conventional VTEC are combined in this application. From idle to 2500-3000 RPM, depending
on load conditions, one intake valve fully opens while the other opens just slightly, enough to prevent pooling of fuel
behind the valve, also called 12-valve mode. This 12 Valve mode results in swirl of the intake charge which increases
combustion efficiency, resulting in improved low end torque and better fuel economy. At 3000-5400 RPM,
depending on load, one of the VTEC solenoids engages, which causes the second valve to lock onto the first valve's
camshaft lobe. Also called 4-valve mode, this method resembles a normal engine operating mode and improves the
mid-range power curve. At 5500-7000 RPM, the second VTEC solenoid engages (both solenoids now engaged) so
that both intake valves are using a middle, third camshaft lobe. The third lobe is tuned for high-performance and
provides peak power at the top end of the RPM range.
 Vtec system which combines the standard Vtec and Vtec-e concepts to create a high power, fuel
efficient valve train.
 Utilizes 3 separate Camshaft Profiles. This system operates like Vtec-e closing one valve at low
speeds and then opening both valves at a standard lift and duration at a midrange rpm. It then has a
high rpm cam which opens both valves aggressively as in standard Vtec.
 Like standard Vtec one rocker arm, usually on the highest lift profile, is not attached to a valve so that
the highest lift is only used when the system is in operational Vtec range.
 In the illustration below the three significant camshaft profiles can be seen. And the sliding pins for
each stage are shown as well.

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5. VARIABLE TIMING CONTROL (VTC):
VTC operating principle is basically that of the generic variable valve timing implementation (this
generic implementation is also used by Toyota in their VVT-i and BMW in their VANOS/double-VANOS system).
The generic variable valve timing implementation makes use of a mechanism attached between the cam sprocket and
the camshaft. This mechanism has a helical gear link to the sprocket and can be moved relative the sprocket via
hydraulic means. When moved, the helical gearing effectively rotates the gear in relation to the sprocket and thus the
camshaft as well.

5. VTC PRICIPLE

The drawing above serves to illustrate the basic operating principle of VTC (and generic variable valve
timing). A labels the cam sprocket (or cam gear) which the timing belt drives. Normally the camshaft is bolted
directly to the sprocket. However in VTC, an intermediate gear is used to connect the sprocket to the camshaft. This
gear, labeled B has helical gears on its outside. As shown in the drawing, this gear links to the main sprocket which
has matching helical gears on the inside. The cam shaft, labeled C attaches to the intermediate gear.
The supplementary diagram on the right shows what happens when we move the intermediate gear along
its holder in the cam sprocket. Because of the interlinking helical gears, the intermediate gear will rotate along its
axis if moved. Now, since the camshaft is attached to this gear, the camshaft will rotate on its axis too. What we have
achieved now is that we have move the relative alignment between the camshaft and the driving cam-sprocket - we
have changed the cam timing!

6. i-VTEC SYSTEM:

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6.1 i-VTEC SYSTEM LAYOUT

Diagram explains the layout of the various components implementing i-VTEC. I have intentionally
edited the original diagram very slightly - the lines identifying the VTC components are rather faint and their
orientation confusing. I have overlaid them with red lines. They identify the VTC actuator as well as the oil pressure
solenoid valve, both attached to the intake camshaft's sprocket. The VTC cam sensor is required by the ECU to
determine the current timing of the intake camshaft. The VTEC mechanism on the intake cam remains essentially
the same as those in the current DOHC VTEC engines except for an implementation of VTEC-E for the 'mild' cam.

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6.2 VALVE ACTUATION DIAGRAM

The diagrams show that VTEC is implemented only on the intake cam. Now, note that there is an
annotation indicating a 'mostly resting (intake) cam' in variations 1 to 3. This is the 'approximately 1-valve' operating
principle of VTEC-E. I.e. one intake valve is hardly driven while the other opens in its full glory. This instills a swirl
effect on the air-flow which helps in air-fuel mixture and allows the use of the crazy 20+ to 1 air-to-fuel ratio in leanburn or economy mode during idle running conditions. On first acquaintance, variations 1 and 3 seem identical.
However, in reality they represent two different engine configurations - electronic-wise. Variation 1 is lean burn
mode, the state in which the ECU uses >20:1 air-fuel ratio. VTC closes the intake/exhaust valve overlap to a
minimal. Note that lean-burn mode or variation 1 is used only for very light throttle operations as identified by the
full load Torque curve overlaid on the VTC/RPM graph. During heavy throttle runs, the ECU goes into variation 3
Lean-burn mode is contained within variation-2 as a dotted area probably for the reason that the ECU bounces toand-fro between the two modes depending on engine rpm, throttle pressure and engine load, just like the 3-stage
VTEC D15B and D17A. In variation-2, the ECU pops out of lean-burn mode, goes back to 14.7 or 12 to 1 air-fuel
ratios and brings the intake/exhaust overlap right up to maximum. This as Honda explains will induce the EGR
effect, which makes use of exhaust gases to reduce emissions. Variation-3 is the mode where the ECU varies
intake/exhaust-opening overlap dynamically based on engine rpm for heavy throttle runs but low engine revs. Note
also that variations 1 to 3 are used in what Honda loosely terms the idle rpm. For 3-stage VTEC engines, idle rpms
take on a much broader meaning. It is no longer the steady 750rpm or so for an engine at rest. For 3-stage VTEC,
idle rpm also means low running rpm during ideal operating conditions, i.e. closed or very narrow throttle positions,
flat even roads, steady speed, etc. It is an idle rpm range. The K20A engine implements this as well.

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6.3 ACTUATION OF HIGH SPEED CAM

Variation-4 is activated whenever rpm rises and throttle pressure increases, indicating a sense of urgency
as conveyed by the driver's right foot. This mode sees the wild cams of the intake camshaft being activated, the
engine goes into 16-valve mode now and VTC dynamically varies the intake camshaft to provide optimum
intake/exhaust valve overlap for power.
On i-VTEC engines, the engine computer also monitors cam position, intake manifold pressure, and
engine rpm, then commands the VTC (variable timing control) actuator to advance or retard the cam. At idle, the
intake cam is almost fully retarded to deliver a stable idle and reduce oxides of nitrogen (NOX) emissions. The
intake cam is progressively advanced as rpm builds, so the intake valves open sooner and valve overlap increases.
This reduces pumping losses, increasing fuel economy while further reducing exhaust emissions due to the creation
of an internal exhaust gas recirculation (EGR) effect.
i-VTEC introduced continuously variable timing, which allowed it to have more than two profiles for
timing and lift, which was the limitation of previous systems. The valve lift is still a 2-stage setup as before, but the
camshaft is now rotated via hydraulic control to advance or retard valve timing. The effect is further optimization of
torque output, especially at low RPMs.
Increased performance is one advantage of the i-VTEC system. The torque curve is "flatter" and does not
exhibit any dips in torque that previous VTEC engines had without variable camshaft timing. Horsepower output is
up, but so is fuel economy. Optimizing combustion with high swirl induction makes these engines even more
efficient. Finally, one unnoticed but major advantage of i-VTEC is the reduction in engine emissions. High swirl
intake and better combustion allows more precise air-fuel ratio control. This results in substantially reduced
emissions, particularly NOx. Variable control of camshaft timing has allowed Honda to eliminate the EGR system.
Exhaust gases are now retained in the cylinder when necessary by changing camshaft timing. This also reduces
emissions without hindering performance.

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i-vtec

7. ADVANTAGES OF i-VTEC:
1)
2)
3)
4)

Better Fuel Efficiency.
High initial torque and relevant high power.
Lower emission.
Strong performance.

8. DISADVANRAGES OF i-VTEC:
1) Cost is high.
2) Available in Honda Models only.

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i-vtec

9. APPLICATIONS
Currently i-VTEC technology is available In Honda products;
1)
2)
3)
4)
5)
6)

Honda CRV
Honda CITY
Honda Civic
Honda Amaze
Honda Mobilio
Honda Accord

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