Carbon fiber reinforced plastic Composites

ABSTRACT

            Composites are the 21^st century material to meet the stringent demands of light weight, high strength, corrosion resistance & near-net shapes. Carbon Fiber Reinforced Plastic Composite is new class of materials has recently emerged as a leading contender for numerous application in automobile, aerospace, electronic and wear industries. in brake disks of aircraft or Formula 1 / Indy race cars. These type of composite can operate at temperatures up to approx. 900ºC or higher. Useful properties of carbon fibres are their durability, resistance to fatigue and that they are chemically inert and still exhibit high  strength at high temperatures.Although they were know to mankind since prehistoric times, the concept and technology have undergone a sea change with better understanding of the basics like the bonding mechanism between the matrix and fiber. Technologically composites are artificially produced multiphase materials having desirable combination of best properties of the constituent phases. Since carbon is a high performance fiber material that is most commonly used reinforcement in advanced Polymer- matrix composites known as CFRP.

Keywords: - CFRP, Carbon fiber, PMC.

INTRODUCTION

             Many of our modern technologies require material with unusual combination of properties that can not be met by the conventional metal alloys, ceramics & polymeric materials. Composites are one of the most widely used material because of their adaptability to different situations & the relative ease of combination with other material to serve specific purposes & exhibit desire properties. “A composite material is a combination of two or more chemically distinct & insoluble phases.” Its properties & structural performance are superior to those of the constituents acting independently. The plastic posses mechanical properties that are generally inferior to those of metal & alloys-in particular low strength, stiffness & creep resistance. These properties can be improved by imbedding reinforcement of various types (such as glass or graphite fibers) to produce reinforced plastic.

Many composite materials are composed of just two phases ; one is termed the matrix, which is continuous & surrounds the other phase often called dispersed phase another is discontinuous phase & termed as fiber. The properties of composites are a function of the properties of the constituent phase, their relative amounts, & the geometry of fibers.

FIBERS:-

In a continuous fiber reinforced composite, the fibers provide virtually all of the load carrying characteristics of the composites, the most important of which are strength and stiffness. The multiple fibers in a composite make it a very redundant material because the failure of even several fibers results in the redistribution of load on to other fibers rather than a catastrophic failure of the part.

On the basis of diameter & character, fibers are grouped into three different classifications; whiskers, fibers, & wires.

Fig.  Common forms of fiber reinforcement

Matrices:-

The purpose of the matrix is to bind the reinforcements together by virtue of its cohesive and adhesive characteristics, to transfer load to and between reinforcements, and to protect the reinforcements from environments and handling. The matrix also provides a solid form to the composite, which aids handling during manufacture and is typically required in a finished part. This is particularly necessary in discontinuously reinforced composites, because the reinforcements are not of sufficient length to provide a handle able form. Because the reinforcements are typically stronger and stiffer, the matrix is often the “weak link” in the composite, from a structural perspective. As a continuous phase, the matrix therefore controls the transverse properties, interlaminar strength, and elevated-temperature strength of the composite. However, the matrix allows the strength of the reinforcements to be used to their full potential by providing effective load transfer from external forces to the reinforcement.

                                                             Fig: Types of matrices
 

CARBON FIBER RAINFORCED PLASTIC (CFRP)

In this type of composite carbon/graphite fiber is embedded in polymer matrix. Carbon is a high performance fiber material that is most common in used reinforcement in advanced (i.e. non-fiber glass) polymer- matrix composites. The reason for this is as follows:

1. Carbon fibers have the highest specific modulus & specific strength of all reinforcing fiber materials.
2. They retain their high tensile modulus & high strength at elevated temperatures: high temp. Oxidation however may be a problem.
3. At room temp. Carbon fibers are not affected by moisture or a wide variety of solvents, acids, bases.
4. These fibers exhibit a diversity of physical & mechanical characteristics, allowing composites in corporating these fibers to have specific engineered properties.
5. Fiber & composite manufacturing processes have been developed that are relatively inexpensive & cost effective.

CARBON FIBERS

Classification of Carbon Fibers:-

Carbon fibers are classified by the tensile modulus of the fiber. Tensile modulus is a measure of how much pulling force a certain diameter fiber can exert without breaking. Carbon fibers classified as "low modulus" have a tensile modulus below 240 million kPa. Other classifications, in ascending order of tensile modulus, include "standard modulus," "intermediate modulus," "high modulus," and "ultrahigh modulus." Ultrahigh modulus carbon fibers have a tensile modulus of 500 million-1.0 billion kPa. As a comparison, steel has a tensile modulus of about 200 million kPa. Thus, the strongest carbon fiber is about five times stronger than steel.  The term graphite fiber refers to certain ultrahigh modulus fibers made from petroleum pitch. These fibers have an internal structure that closely approximates the three-dimensional crystal alignment that is characteristic of a pure form of carbon known as graphite.

Raw Materials

The raw material used to make carbon fiber is called the precursor. About 90% of the carbon fibers produced are made from polyacrylonitrile. The remaining 10% are made from rayon or petroleum pitch. All of these materials are organic polymers, characterized by long strings of molecules bound together by carbon atoms. The exact composition of each precursor varies from one company to another and is generally considered a trade secret. During the manufacturing process, a variety of gases and liquids are used. Some of these materials are designed to react with the fiber to achieve a specific effect. Other materials are designed not to react or to prevent certain reactions with the fiber. As with the precursors, the exact compositions of many of these process materials are considered trade secrets.

MANUFACTURING PROCESS

           The manufacturing process for producing carbon fibers involved highly controlled steps of heat treatment and tension to form the appropriately ordered carbon structure. Rayon, Pitch has been largely supplanted as a precursor by Polyacrylonitrile (PAN). Polyacrylonitrile precursors produce much more economical fibers because the carbon yield is higher and because PAN-based fibers do not intrinsically require a final high-temperature “graphitization” step. Polyacrylonitrile-based fibers having intermediate- modulus values of about 240 to 310 GPa (35 to 45 _ 106 psi), combined with strengths ranging from 3515 to 6380 MPa (510 to 925 ksi), are now commercially available. Because carbon fibers display linear stress-strain behavior to failure, the increase in strength also means an increase in the elongation-to-failure. The commercial fibers thus display elongations of up to 2.2%, which means that they exceed the strain capabilities of conventional organic matrices. The diameter of carbon fibers typically ranges from 8 to 10 lm (0.3 to 0.4 mils).

              The process for making carbon fibers is part chemical and part mechanical Plastics are drown into long strands or fibers and then heated to a very high temperature without allowing it to come in contact with oxygen. Without oxygen, the fiber cannot burn. Instead, the high temperature causes the atoms in the fiber to vibrate violently until most of the non-carbon atoms are expelled. This process is called carbonization and leaves a fiber composed of long, tightly.

Fig: Manufacturing of carbon fibers.

PYROLYSIS PROCESS:-

Fig:Pyrolysis processes for PAN precursors

Pyrolysis is the processes of inducing chemical changes by heat-for a instance, by burning a length of yarn & causing the material to carbonize & become black in color. The temperature of carbonizing range up to about 1500°C; for graphitizing to 3000°C,    Here is a typical sequence of operations used to form carbon fibers from polyacrylonitrile.

Spinning:-

1.  Acrylonitrile plastic powder is mixed with another plastic, like methyl acrylate or methyl methacrylate, and is reacted with a catalyst in a conventional suspension or solution polymerization process to form a polyacrylonitrile plastic.
2.  The plastic is then spun into fibers using one of several different methods. In some methods, the plastic is mixed with certain chemicals and pumped through tiny jets into a chemical bath or quench chamber where the plastic coagulates and solidifies into fibers. This is similar to the process used to form polycyclic textile fibers. In other methods, the plastic mixture is heated and pumped through tiny jets into a chamber where the solvents evaporate, leaving a solid fiber. The spinning step is important because the internal atomic structure of the fiber is formed during this process.
3.  The fibers are then washed and stretched to the desired fiber diameter. The stretching helps align the molecules within the fiber and provide the basis for the formation of the tightly bonded carbon crystals after carbonization.

Stabilizing:-

4.  Before the fibers are carbonized, they need to be chemically altered to convert their linear atomic bonding to a more thermally stable ladder bonding. This is accomplished by heating the fibers in air to about 390-590° F (200-300° C) for 30-120 minutes. This causes the fibers to pick up oxygen molecules from the air and rearrange their atomic bonding pattern. The stabilizing chemical reactions are complex and involve several steps, some of which occur simultaneously. They also generate their own heat, which must be controlled to avoid overheating the fibers. Commercially, the stabilization process uses a variety of equipment and techniques. In some processes, the fibers are drawn through a series of heated chambers. In others, the fibers pass over hot rollers and through beds of loose materials held in suspension by a flow of hot air. Some processes use heated air mixed with certain gases that chemically accelerate the stabilization.

Carbonizing:-

5.  Once the fibers are stabilized, they are heated to a temperature of about 1,830-5,500° F (1,000-3,000° C) for several minutes in a furnace filled with a gas mixture that does not contain oxygen. The lack of oxygen prevents the fibers from burning in the very high temperatures. The gas pressure inside the furnace is kept higher than the outside air pressure and the points where the fibers enter and exit the furnace are sealed to keep oxygen from entering. As the fibers are heated, they begin to lose their non-carbon atoms, plus a few carbon atoms, in the form of various gases including water vapor, ammonia, carbon monoxide, carbon dioxide, hydrogen, nitrogen, and others. As the non-carbon atoms are expelled, the remaining carbon atoms form tightly bonded carbon crystals that are aligned more or less parallel to the long axis of the fiber. In some processes, two furnaces operating at two different temperatures are used to better control the rate de heating during carbonization.

Treating the surface:-

6.  After carbonizing, the fibers have a surface that does not bond well with the epoxies and other materials used in composite materials. To give the fibers better bonding properties, their surface is slightly oxidized. The addition of oxygen atoms to the surface provides better chemical bonding properties and also etches and roughens the surface for better mechanical bonding properties. Oxidation can be achieved by immersing the fibers in various gases such as air, carbon dioxide, or ozone; or in various liquids such as sodium hypochlorite or nitric acid. The fibers can also be coated electrolytically by making the fibers the positive terminal in a bath filled with various electrically conductive materials. The surface treatment process must be carefully controlled to avoid forming tiny surface defects, such as pits, which could cause fiber failure.

Sizing:-

7.  After the surface treatment, the fibers are coated to protect them from damage during winding or weaving. This process is called sizing. Coating materials are chosen to be compatible with the adhesive used to form composite materials. Typical coating materials include epoxy, polyester, nylon, urethane, and others.
8.  The coated fibers are wound onto cylinders called bobbins. The bobbins are loaded into a spinning machine and the fibers are twisted into yarns of various sizes.

Fig: sizing

. Capabilities:-

• Excellent air flow uniformity
• Easy internal access to facilitate maintenance
• Electric or gas fired
• Optimal temperature uniformity
• Operator isolation from effluent

Features

• Multiple temperature control zones
• Proven alternating cross flow design
• Adjustable louvers and diffuser plates for precise temperature adjustment
• Excellent float end seals for positive sealing, minimized infiltration of ambient atmosphere and improved temperature uniformity
• Aluminized steel construction
• Plug fans to facilitate maintenance.

TYPICAL PROPERTIES OF REINFORCING FIBER

1. The advantages of carbon fibre products over different woods and metals come to      prominence when a rigid, strong but also lightweight material is needed

2. Further useful properties of carbon fibres are their durability, resistance to fatigue   and that they are chemically inert and still exhibit high strength at high temperatures.

3. It is often preferred to other fibre composites due to the tensile strength and modulus of the high quality fibres which perform better than fibreglass or Kevlar.

TYPE	TENSILE  STRENGTH        (MPa)	ELASTIC MODULUS    (GPa)	DENSITY      ( kg /  m3 )		RELATIVE COST
Boron	3500	380	2600		Highest
Carbon
High strength	3000	275		1900		Low
High modulus	2000	415	1900		Low
Glass
E  type	3500	73	2480		Lowest
S  type	4600	85	2540		Lowest
Kevlar
29	2800	62	1440		High
49	2800	117	1440		High

POLYMER MATRIX COMPOSITES

        It consists of a polymer resin as the matrix, with the fiber as the reinforcement medium. Polymer makes ideal matrix materials as they can be processed easily possess lightweight, inlight of their room temperature properties, & cost. The various types of PMCs are classified according to reinforcement type (i.e. glass, carbon, aramid & boron)

The two main kinds of polymers are Thermosets & Thermoplastics.

Thermosets:-

Thermosets have qualities such as a well bonded three dimensional molecular structure. The most common resins of these types are epoxies, phenolics, polyimides & cyanate esters. The epoxies are more expensive & in addition to commercial application are also utilized extensively in PMCs for aerospace application. For high temperature applications polyimide resins are employed.

Thermoplastics:-

Thermoplastics have one or two dimensional molecular structure & they tend to soften at an elevated temperature & show exaggerated melting point. High temperature thermoplastic resins offer the potential to be used in future aerospace application; such material include Polyetheretherketone (PEEK), Polyphenylene sulfide (PPS) & Polyethereimide (PEI).

APPLICATIONS

1. . Most sports now use carbon fibres in their equipment whether it is to reinforce the traditional materials or create new ones. Golf clubs, tennis rackets and bicycles all use the strength and durability of modern composites to enhance the quality of the sport. Formula One and other motor sports use carbon fibre composites in order to protect the driver in the event of a crash.

2. Reinforced plastic are used for automobile parts. The fatigue properties of the materials & low weight, ability to sustain strains from the engine heat & low frequency road vibrations are features that favors composites in truck & other vehicles.
3. Carbon/graphite is also used as a moderator in both reactor & non-reactor system & exhibit good moderating characteristics. They are also used in space application due to thermal conductivity & strength.
4. Fiber epoxy composites have been used in aircraft engine to enhance the performance of the system
5. The aerospace and automotive industry also use the excellent properties to their advantage and are always researching and developing further improvements in the quality of the fibres.

 

Fig: The Boeing 7E7

CONCLUSION

            There are many fibers which embedded in PMCs & to increase the strength & desired properties of material. Out of which carbon & boron fibers are mostly used but economical point of view carbon has low cost as compared to boron. Polymer matrix are used in large quantities, in light of there room temperature properties, ease of fabrication & cost. Carbon fibers are produced by many processes by using Reyon, Pitch or PAN as a precursor. Pyrolysis of PAN produces fibers of high strength & stiffness. As CFRP is light in weight they are used in aerospace & space application

i-VTEC ENGINE

Abstract

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 i-VTEC(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. i-VTEC 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.

1.         RECENT ADVANCES IN AUTOMOBILE ENGINES

q  Common Rail Diesel Injection System(CRDI)

q  Direct Injection System(DI-System)

q  Multi Point Fuel Injection(MPFI)

q  Digital Twin Spark Injection(DTS-I)

q  Quantum Core Engine

q  16 Valve Engine

q  Programmed Electronic Fuel Injection(PGM-FI)

q  Six Stroke Engine

2.      INTRODUCTION:-

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).

                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.     

q  i-VTEC:-

                The 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.

The i stands for intelligent: i-VTEC is intelligent-VTEC. Honda introduced many new innovations in i-VTEC, 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. This allows for a further refinement to the power delivery characteristics of VTEC, permitting fine-tuning of the mid-band power delivery of the engine.

q  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 high-speed profile, which opens the valve further and for a longer time.

q  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.

The two cam/rocker pairs operates independently of each other. 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.

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.

q  DIFFERENT VARIANTS OF V-TEC:-

q  VARIABLE TIMING CONTROL (VTC)

                                  VTC operating principle is basically that of the generic variable valve timing implementation (this generic implementation is also used by 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.

Fig.3-VTC principle

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, labelled 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 camshaft, labelled 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 acheived now is that we have move the relative alignment between the camshaft and the driving cam-sprocket - we have changed the cam timing!

q  i-VTEC SYSTEM:-

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.

 

                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 lean-burn 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 to-and-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.  

          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(er) 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.

3.APPLICATIONS :-                                                                                                                                    Currently i-VTEC technology is available on three Honda products;

Ø  2002 Honda CRV

Ø  2002 Acura RSX

Ø  Honda Civic 2006

q  CASE STUDY  OF ‘HONDA  CIVIC  2006’  WITH  1.8 liter  ENGINE

          The new i- VTEC system in Honda civic 2006 uses its valve timing control system to deliver acceleration performance equivalent to a 2.0-liter engine and fuel economy approximately 6% better than the current 1.7-liter Civic engine. During cruising, the new engine achieves fuel economy equivalent to that of a 1.5-liter engine.

          In a conventional engine, the throttle valve is normally partly closed under low-load conditions to control the intake volume of the fuel-air mixture. During this time, pumping losses are incurred due to intake resistance, and this is one factor that leads to reduced engine efficiency.

             The i-VTEC engine delays intake valve closure timing to control the intake volume of the air-fuel mixture, allowing the throttle valve to remain wide open even under low-load conditions for a major reduction in pumping losses of up to 16%. Combined with friction-reducing measures, this results in an increase in fuel efficiency for the engine itself.

            A DBW (Drive By Wire) system provides high-precision control over the throttle valve while the valve timing is being changed over, delivering smooth driving performance that leaves the driver unaware of any torque fluctuations.

          Other innovations in the new VTEC include a variable-length intake manifold to further improve intake efficiency and piston oil jets that cool the pistons to suppress engine knock.

         In addition, lower block construction resulting in a more rigid engine frame, aluminum rocker arms, high-strength cracked connecting rods, a narrow, silent cam chain, and other innovations make the engine more compact and lightweight. It is both lighter and shorter overall than the current Civic 1.7-liter engine, and quieter as well.

q  SPECIFICATIONS  OF   1.8l i-VTEC ENGINE

Ø  Engine type and number of cylinders         Water-cooled in-line 4-cylinder

Ø  Displacement                                               1,799 cc

Ø  Max power / rpm                                          103 kW (138 hp)/ 6300

Ø  Torque / rpm                                                 174 Nm (128 lb-ft)/4300

Ø  Compression ratio                                        10.5:1

q  PERFORMANCE :-

This new engine utilizes Honda's "VTEC" technology, which adjusts valve timing and lift based on the engine's RPM, but adds "VTC" - Variable Timing Control - which continuously modulates the intake valve overlap depending on engine load. The two combined yield in a highly intelligent valve timing and lift mechanism.In addition to such technology, improvements in the intake manifold, rearward exhaust system, lean-burn-optimized catalytic converter help to create an engine that outputs 103kW (140PS) @ 6300rpm,and provides ample mid-range torque. It also satisfies the year 2010 fuel efficiency standard of14.2km/Landreceives the government standard of "LEV" .

4.     FUTURE TRENDS :-                                                                                                     

               From now onwards, there is all likelihood that Honda will implement i-VTEC on its performance engines.  Again what i-VTEC does allow is for Honda to go for the sky in terms of specific power output but yet still maintaining a good level of mid-range power. Already extremely authoritative reviewers like BEST motoring have complained about the lack of a broad mid-range power from for e.g. the F20C engine. In a tight windy circuit like Tsukuba and Ebisu, the S2000 finds it extremely tough going to overtake the Integra Type-R in 5-lap battles despite having 50ps or 25% more power. To get the extreme power levels of the F20C, the wild cams' power curve are so narrow that there is effectively a big hole in the composite power curve below 6000rpm. What i-VTEC can do to this situation is to allow fine-tuning of the power curve, to broaden it, by varying valve opening overlap. Thus this will restore a lot of mid-range power to super-high-output DOHC VTEC engines allowing Honda, if they so desire, to go for even higher specific outputs without too much of a sacrifice to mid-range power.                

5.CONCLUSION: -                                                                                                  i-VTEC system is more sophisticated than earlier variable-valve-timing systems, which could only change the time both valves are open during the intake/exhaust overlap period on the transition between the exhaust and induction strokes. By contrast, the i-VTEC setup can alter both camshaft duration and valve lift.  i-VTEC Technology gives us the best in vehicle performance.  Fuel economy is increased, emissions are reduced, derivability is enhanced and power is improved.