Vtech (Ts Doc)

7/21/2019 Vtech (Ts Doc)

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1. INTRODUCTION

The classic problem facing high-performance street cars has always been

how to maximize performance without sacricing drivability. Short of power-

adders like turbo or nitrous oxide, signicant power increases are only

achieved by extending the engines rpm operating range, usually with some

combination of intake, exhaust, camshaft, and cylinder head changes. !ut

any signicant gains upstairs inevitably cause a loss of low-speed

performance, decreased fuel e"ciency, and increased emissions.

The conundrum of camshaft selection is one of the key determinants in

altering the power band. #acing engines have longer intake$exhaust timing,

a higher valve lift, and a narrower lobe displacement angle %&'() than

standard engines, which for low-speed response and power tend to have

short durations, low valve-lift numbers, and a wide &'(. !eginning with the

*+ onda ntegra in apan and the +/ (cura 0S1 supercar in the 2.S.,

onda implemented a novel solution to the problem, e3ectively combiningthe attributes of both passenger-car and race-car cam timing with its uni4ue

5T67 system. The initials stand for 5ariable 5alve Timing and &ift 6lectronic

7ontrol, and as the name implies, a 5T67 engine can actually alter the cam

timing while the engine is running.

VTEC%Variable Valve Timing and Lift Electronic Control) is a system

developed by ondato improve the volumetric e"ciency of a four-

strokeinternal combustion engine. The 5T67 system uses two camshaft

proles and hydraulically selects between proles. t was invented by onda

engineer Ikuo Kajitani, and was the rst system of its kind. t is distinctly
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di3erent from standard 55T %variable valve timing) which advances the valve

timing only and does not change the camshaft prole or valve lift in any way.

5T67, the original onda variable valve control system, originated from #65

%#evolution-modulated valve control) introduced on the 7!#8//in 9+*:

known as ;


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5T67 was initially designed to increase the power output of an engine to 9//


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5T67 is one of ondas greatest invention. Though an undisputed expert in

turbo-charging as evidenced by years of Aormula-9 domination while onda

was active in the sport, ondas engineers feels that turbo charging has

disadvantages, primarily bad fuel economy that made it not totally suitable

for street use. (t the same time, the advantages of working with smaller

engines meant that smaller capacity engines with as high power output as

possible %very high specic-output engines) are desirable for street engines.

Thus onda invented 5T67 which allows it to extract turbo level specic

output from its engines without having to su3er from the disadvantages of

turbocharging.

5ariable 5alve Timing and &ift 6lectronic 7ontrol, more commonly known as

5T67, is an electronic and mechanical system that allows the engine to draw

in more air while minimizing fuel consumption. (s the engine moves into the

upper rpm range, the engines computer activates alternate lobes on the

camshaft to increase the lift of the valves. 2ltimately, 5T67 is a way of

e3ectively having multiple camshafts.


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The 5T67 system provides the engine with multiple cam lobe proles

optimized for both low and high # operations. n basic form, the single

barring shaft-lock of a conventional engine is replaced with two prolesB one

optimized for low-# stability and fuel e"ciency, and the other designed to

maximize high-# power output. The switching operation between the two

cam lobes is controlled by the 672which takes account of engine oil

pressure, engine temperature, vehicle speed, engine speed and throttle

position. 2sing these inputs, the 672 is programmed to switch from the low

lift to the high lift cam lobes when the conditions mean that engine output

will be improved. (t the switch point a solenoid is actuated which allows oil

pressure from a spool valve to operate a locking pin which binds the high

# cam followerto the low # ones. Arom this point on, the valves open

and close according to the high-lift prole, which opens the valve further and

for a longer time. The switch-over point is variable, between a minimum and

maximum point, and is determined by engine load. The switch-down back

from high to low # cams is set to occur at a lower engine speed than the
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switch-up %representing a hysteresiscycle) to avoid a situation in which the

engine is asked to operate continuously at or around the switch-over point.

The older approach to timing ad@ustments is to produce a camshaft with

a valve timingprole that is better suited to high-# operation. The

improvements in high-# performance occur in trade for a power and

e"ciency loss at lower # ranges, which is where most street-driven

automobiles operate a ma@ority of the time. 7orrespondingly, 5T67 attempts

to combine high-# performance with low-# stability.

C.9. 7(>S(ATS (0' &?!6SB

The camshafts of a 5T67 engine have extra lobes. ?n an average cam, there

are only two lobes for each cylinder -- one intake and one exhaust. (s the
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crank turns, it spins the timing chain, which turns the cam. The 5T67 system

uses extra lobes to operate more than one valve at a time. This process is

called 5T67 crossover. ts the point at which some of the rocker arms are

linked together to change the running characteristics of the engine.

C.C. #?7D6# (#>SB

#ocker arms are the levers that pivot to push down on the valve stems,

opening the valves to allow air and fuel into the combustion chambers, and

to let exhaust out. onda 5T67 rocker arms have hydraulically-actuated

interlocking pins that, when activated, @oin the arms together, enabling the

simultaneous opening of multiple valves by a single cam lobe.


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C.:. 60E06 7?0T#?& 20TB

The 672, or 6ngine 7ontrol 2nit, monitors all of the engines vital statistics.

(s the name suggests, it also operates all the servo-mechanisms on which

the engine relies for normal operation.

". VTEC !EC#$NIS!S%

".1. DO#C VTEC%Fith an electronically-controlled variable valve timing and lift mechanism,

this Gsuper sportsH engine delivered high performance in all areas. ondaIs

engineers, pursuing high #s and high output on a par with racing engines,

developed the incredibly high-powered '?7 %'ouble overhead camshaft)

5T67 engine, taking both high-speed and low-speed performance to a new

level.

Fith an electronically-controlled variable valve timing and lift mechanism,

this Gsuper sportsH engine delivered high performance in all areas. ondaIs

engineers, pursuing high #s and high output on a par with racing engines,


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developed the incredibly high-powered '?7 5T67 engine, taking both high-

speed and low-speed performance to a new level.

ntroduced as a '?7system in apan in the 9+*+ onda ntegra 1Si which

used the 9J/ bhp %9C/ kF) !9J( engine. The same year, 6urope saw the

arrival of 5T67 in the onda 7#19.Ji-5T, using a 9K/ bhp variant %!9J(9).

The 2nited Statesmarket saw the rst 5T67 system with the introduction of

the 9++9 (cura 0S1, which used a :-litre '?7 5T67 5J with CL/ bhp

%C// kF). '?7 5T67 engines soon appeared in other vehicles, such as the

9++C (cura ntegra ES-#%!9L(9 9.L-litre engine), and later in the

9++: onda


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(s popularity and marketing value of the 5T67 system grew, onda applied

the system to S?7%single overhead camshaft) engines, which share a

common camshaft for both intake and exhaust valves. The trade-o3 was that

ondas S?7 engines benetted from the 5T67 mechanism only on the

intake valves. This is because 5T67 re4uires a third center rocker

armand cam lobe%for each intake and exhaust side), and, in the S?7

engine, the spark plugs are situated between the two exhaust rocker arms,

leaving no room for the 5T67 rocker arm. (dditionally, the center lobe on the

camshaft cannot be utilized by both the intake and the exhaust, limiting the

5T67 feature to one side.

owever, beginning with the :L(8 :.L& S?7 5J engine introduced on all

C//+ (cura T& S-(F' models, S?7 5T67 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 5T67 switching piston, while the secondary

rocker arm contains the return spring. The term OprimaryO does not refer to

which rocker arm forces the valve down during low-# engine operation.

#ather, it refers to the rocker arm which contains the 5T67 switching piston

and receives oil from the rocker shaft.

The primary exhaust rocker arm contacts a low-prole camshaft lobe during

low-# engine operation. ?nce 5T67 engagement occurs, the oil pressure

=owing from the exhaust rocker shaft into the primary exhaust rocker arm

forces the 5T67 switching piston into the secondary exhaust rocker arm,

thereby locking both exhaust rocker arms together. The high-prole camshaft

lobe which normally contacts the secondary exhaust rocker arm alone during

low-# 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-prole camshaft lobe operates the primary rocker arm.
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The di"culty of incorporating 5T67 for both the intake and exhaust valves in

a S?7 engine has been removed on the :L(8 by a novel design of theintake rocker arm. 6ach exhaust valve on the :L(8 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. owever, each secondary intake rocker arm is shaped similar to a O;O

which allows it to contact two intake valves at once. ?ne primary intake


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rocker arm corresponds to each secondary intake rocker arm. (s a result of

this design, there are only six primary intake rocker arms and six secondary

intake rocker arms.

".". " & ST$'E VTEC%

:-Stage 5T67 is a version that employs three di3erent cam proles to control

intake valve timing and lift. 'ue to this version of 5T67 being designed

around a S?7 valve head, space was limited and so 5T67 can only modify

the opening and closing of the intake valves. The low-end fuel economy

improvements of 5T67-6 and the performance of conventional 5T67 are

combined in this application. Arom idle to CK//-:/// #, depending on load

conditions, one intake valve fully opens while the other opens @ust slightly,

enough to prevent pooling of fuel behind the valve, also called 9C-valve

mode. This 9C 5alve mode results in swirl of the intake charge which

increases combustion e"ciency, resulting in improved low end tor4ue and

better fuel economy. (t :///-K8// #, depending on load, one of the 5T67

solenoids engages, which causes the second valve to lock onto the rst

valves camshaft lobe. (lso called 8-valve mode, this method resembles a

normal engine operating mode and improves the mid-range power curve. (t

KK//-L/// #, the second 5T67 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 # range.

".(. I & VTEC%


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The last evolution of ondas 5T67 system was back in 9++K where they

introduced the now-famous :-stage 5T67 system. The :-stage 5T67 was

then designed for an optimum balance of super fuel economy and high

power with drivability. Aor the next K years, onda still used the regular

'?7 5T67 system for their top power models, from the !9J! right up to the

AC/7 in the SC///. 0ow onda have announced the next evolution of their

legendary 5T67 system, the i-5T67.

The GiH stands for intelligentB i-5T67 is intelligent-5T67. onda introduced

many new innovations in i- T67, but the most signicant one is the addition

of a variable valve opening overlap mechanism to the 5T67 system. 0amed

5T7 for 5ariable Timing 7ontrol, 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 renement to the power delivery characteristics of 5T67,

permitting ne-tuning of the mid-band power delivery of the engine.

i-5T67 is the technology used in the latest family of onda engines. The

engines incorporate a host of innovative features designed to deliver a

cutting-edge combination of performance, e"ciency and low emissions. The

technology combines 5T7 %variable Timing 7ontrol) - which continually

ad@usts camshaft timing - with 5ariable 5alve Timing and &ift 6lectronic

7ontrol %5T67), which changes valve lift, timing and duration. The result is

impressive horsepower and high tor4ue with outstanding fuel economy and

low emissions. n addition, the new engines are rotated 9*/ degrees from the

traditional onda layout, bringing the exhaust manifold closer to the catalyst

for improved operating temperature and reduced emissions at start-up.


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onda i-5T67 has 5T7 continuously variable timing of camshaft phasing on

the intake camshaft of '?7 5T67 engines. The technology rst appeared

on ondas D-seriesfour-cylinder engine family in C//9 %C//C in the 2.S.). n

the 2nited States, the technology debuted on the C//C onda 7#-5.

5T7 controls of valve lift and valve duration are still limited to distinct low-and high-# proles, but the intake camshaft is now capable of advancing

between CK and K/ degrees, depending upon engine conguration.


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(. O)TI!I*IN' EN'INE +RE$T#IN'% VTEC

,OR-IN'

(n elegant, simple mechanism Switching between high and low valve lift

using two cam proles and two rocker arms per cylinder.

The switch is made using hydraulic pressure to push$release the sliding pin,

locking$unlocking the middle rocker arm and the other rocker arm.

(t low engine speeds, the pin is retracted, disengaging the middle rocker

arm. The valves are operated by the two outside, low-prole cams for a low

valve lift.


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(t higher engine speeds, increased hydraulic pressure pushes the pin,

engaging the middle rocker arm. The valves are operated by the middle, high

prole cam for high valve lift.

. $))LIC$TIONS

7urrently i-5T67 technology is available on many onda products likeB

C//C onda 7#5

C//C (cura #S1

C//J onda 7ivic

.1. /#OND$ CIVIC 200 ,IT# 1.3 LITER EN'INE%

The new i- 5T67 system in onda civic C//J uses its valve timing

control system to deliver acceleration performance e4uivalent to a C./-liter

engine and fuel economy approximately JP better than the current 9.L-liter

7ivic engine. 'uring cruising, the new engine achieves fuel economy

e4uivalent to that of a 9.K-liter engine.


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n a conventional engine, the throttle valve is normally partly closed under

low-load conditions to control the intake volume of the fuel-air mixture.

'uring this time, pumping losses are incurred due to intake resistance, and

this is one factor that leads to reduced engine e"ciency.

The i-5T67 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 ma@or reduction in pumping

losses of up to 9JP. 7ombined with friction-reducing measures, this results

in an increase in fuel e"ciency for the engine itself.

( '!F %'rive !y Fire) 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 tor4ue

=uctuations.


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?ther innovations in the new 5T67 include a variable-length intake

manifold to further improve intake e"ciency and piston oil @ets that cool the

pistons to suppress engine knock.

n 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. t is both lighter and shorter overall than the current 7ivic 9.L-

liter engine, and 4uieter as well.

.1.1. S)ECI4IC$TIONS O4 1.3L I&VTEC EN'INE%

6ngine type and number of cylinders - Fater-cooled in-line 8-

cylinder

'isplacement - 9,L++ cc

>ax power $ rpm - 9/: kF %9:* hp)$ J://

Tor4ue $ rpm - 9L8 0m %9C* lb-ft)$8://

7ompression ratio - 9/.KB9


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.1.2. )ER4OR!$NCE%

This new engine utilizes ondas O5T67O technology, which ad@usts valve

timing and lift based on the engines #, but adds O5T7O - 5ariable Timing

7ontrol - which continuously modulates the intake valve overlap depending

on engine load. The two combined yield in a highly intelligent valve timing

and lift mechanism. n addition to such technology, improvements in the

intake manifold, rearward exhaust system, lean-burn-optimized catalytic

converter help to create an engine that outputs 9/:kF %98/


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J. T6 A2T2#6

From now onwards, there will no doubt be countless attempts to second-guess at what Honda

will do to i-VTEC. There is all likelihood that Honda will implement i-VTEC on its performance

engines. The most probable benefiaries will be the Integra and the Ciic, the two models which

hae alwa!s been at the forefront to carr! Honda"s high-performance flag.

#t this point, it is important to highlight again that the basic $%HC VTEC s!stem is more than

capable of deliering e&tremel! high specific power outputs. i-VTEC is notneeded. 'itness the

()*ps+litre power delier! of the F)C used on the ). #gain what i-VTEC doallow is for

Honda to go for the sk! in terms of specific power output but !et still maintaining a good leel of

mid-range power. #lread! e&tremel! authoritatie reiewers like ET /%T% 0ing hae

complained about the lack of a broad mid-range power from for eg the F)C engine. In a tightwind! circuit like Tsukuba and Ebisu, the ) finds it e&tremel! tough going to oertake the

Integra T!pe-0 in *-lap battles despite haing *ps or 25%more power. 'atching the "battle"

brings one point painfull! clear. There is a dire need of power from the F)C below 1rpm.

Eer! time the ) sneaks up behind the IT0, it fails to engage in a good oertaking moe

because the power from the F)C is surprisingl! insufficient. The reason for this is because

$%HC VTEC makes do with merging two distinct power cures. To get the e&treme power

leels of the F)C, the wild cams" power cure are so narrow that there is effectiel! a big hole

in the composite power cure below 1rpm. 'hat i-VTEC can do to this situation is to allow

fine-tuning of the power cure, to broaden it, b! ar!ing ale opening oerlap. Thus this will

restore a lot of mid-range power to super-high-output $%HC VTEC engines allowing Honda, if

the! so desire, to go for een higher specific outputs without too much of a sacrifice to mid-

range power.


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