MEC 461 IC Engines: VTEC and VVTL Technologies with Cam Phasing

This assignment provides a detailed comparison of Variable Valve Timing and Lift Electronic Control (VTEC) and Variable Valve Timing and Lift (VVTL) technologies used in internal combustion engines. It explains the working principles of both systems, highlighting their mechanisms, advantages, and differences. VTEC, developed by Honda, enhances volumetric efficiency by using multiple camshaft profiles selected hydraulically, optimizing engine performance at both low and high RPMs. VVTL, used by Toyota, adjusts valve lift events through camshaft rotation, improving power output across different engine speeds. The assignment concludes with an argument favoring VTEC due to its low RPM drivability, electronic switch activation, and good power at high RPM, supported by relevant figures and references. Desklib provides access to this and other solved assignments.

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Introduction
In most modern engines, they are fitted with variable valve timing systems to help in
improving the engine operations. It increases the flexibility of the engine under different
conditions which can result in better performance or the increased fuel economy. The engines
discussed below namely Variable Valve Timing and Lift Electronic Control (VTEC) and Variable
Valve Timing and Lift(VVTL). The VTEC was used by Honda while the VVTL was being used by the
Toyota. The Variable valve timing in the vehicle engine involves hydraulic and mechanical
processes and each manufacture variable valve timing varies to some extent but most
operation are on the similar basic guidelines (Duncan, 2008, p. 78)
Variable Valve Timing and Electronic Control (VTEC)
The system mentioned above (VTEC) is an electric and mechanical structure established
by Honda to enhance the efficiency of volumetric in a four-stroke internal combustion engine
causing a higher performance at high RPM and lower fuel consumption at low RMP.VTEC
engines constitute additional intake cam which retains the intake valve open lengthier, unlike
the other cam profile. Two or three camshafts profiles are used by the VTEC system and the
profiles are selected hydraulically. The VTEC is different from Variable Valve Timing (VVT) since
VVT system only changes valve timing and do not change valve lift or camshaft. This system
offers a valve timing to the engine heightened for both low and high RPM operations and also
attempts to conglomerate the low-RPM fuel proficiency and steadiness with high-RPM
operation (Handfield, 2009, p. 279).

Fig1: Showing VTEC engine (Gilles, 2018)
How does it work? The VTEC system simply permits the engine to have several camshafts. The
valves simply allow the engine to receive air and also the exhaust out of the engine with the
help of camshaft which assists in controlling the valves. The rotating lobes are used by the
camshaft to push the valves to open and close. There is a connection between the manner the
lobes are ground on the camshafts and the manner the engines are performing in dissimilar
rotations per minutes. The Variable Valve Timing ( VTEC) system also gives the engine a valve
timing enhanced for both low and high RMP operation (Emadi, 2015, p. 67).
In Variable Valve Timing Electronics(VTEC) when RPM is increased, the camshaft
configuration will not work well and in case the system is operating at 4000 rpm while the
opening and closing of the valves is 2000 times every single minute or forty times per second.
At higher rpm ranges, if there is need to open the intake valve earlier at the intake stroke and
back in the exhaust stroke therefore by the time the time piston begins moving down in the
intake stroke, the opening of valves take place and the movement of air is allowed easily into
the cylinder throughout the whole intake stroke. For supreme engine operation at little engine

speed, the opening and closing of the valve need to be different than they do at higher engine
speeds. If a camshaft of a decent low speed is put, it hurts the performance of the engine at
high speed while a decent low-speed camshaft hurts the performance of the engine at high
speeds. (Emadi, 2015, p. 366).
Variable Valve Timing and Lift (VTL)
This system mentioned above is involved in the camshaft rotation above a range of 60
degrees to check or boost valve lift events such that, opening of the valve at 5 degrees and
closing at 185 degrees after and before the top dead center. If the valve timing confines the lift
events by 10 degrees, the valve will open and close at 10 degrees later correspondingly. It will
assist the engine in producing better power at high RPM while advancing the timing which will
improve the power at low RPM (Adwera, 2013, p. 345)
Fig 2: Showing VVTL engine (Handfield, 2009)

How does it work? When the valve timing needs to be adjusted, it only requires varying
the position of the gang lever post of phase regulator (Emadi, 2015, p. 178). The pumping of oil
begins when the cam lift is pending and since the pre-tightening force of the valve spring is
more than that of the phase regulator spring, the oil pumped from the cam cylinder would flow
first into phase regulator cylinder until the gag lever post stops the regulator piston. At this
stage, the valve stay still and when the gag level post is zero it opens (Handfield, 2009, p.
67)The working principle is opposite when the cam is operating in cams fall curve since the
force of the valve spring is bigger compared to the phase of regulator spring force and this, will
make the oil in the valve cylinder to move back to the cam cylinder until the valve seat. The
cam keeps on rotating and also the phase regulator oil returns to the cam cylinder under the
effect of phase regulator spring until the cams go back to the base circle segment. This makes
the valve to be closed earlier than the adjustment of the gang level post is zero. The continuous
adjustment of the valve advance angle is realized by the system, when the valve duration angle
and valve retard angle by controlling the time taken by oil to flow into and out of the valve
cylinder (Handfield, 2009, p. 129).
The lift regulator piston, under the spring effect, will be in the fronts position of lift
regulator cylinder while the cam working in the base circle segments for the gang lever post.
The valve needs only to vary the position of the gag lever post of the lift regulator in order to be
adjusted. The valve opens when the cam working in its oil pressure of the system and lifts has
attained the point in which the value lift regulator spring pre-tightening force is bigger
compared to that of the valve spring and the lift will be in idle state thus oil is pumped right
from the cam cylinder and will only flow to valve which is opened (Emadi, 2015, p. 345).

The lifting piston starts moving under the influence of oil pressure immediately when
the system pressure continue increasing and get to the point that it is overcoming the lift
regulator spring pre-tightening force. The oil continues flowing into the lift regular cylinder until
the piston is stopped by the lift regulator gang lever post. Therefore, there will be a decrease in
the volume of the liquid flowing into the valve cylinder and the valve lift will also decrease
(Duncan, 2008, p. 234).
The working process is opposite when the cam is working in the cam fall curve. Since the
lift regulator is operating in the opening of the valve, the valve timing is not influenced by the
lift adjustment. It is obvious that the system can realize the continuous valve adjustment by
controlling the volume of the liquid flowing into the lift regulator and valve cylinder which can
be done by adjusting the position of lift regulator gag lever post. When adjustment of the lift
and the valve timing need to be done at the same time, the system can obtain a reasonable
valve timing and lift by simply adjusting the lift regulator piston and the phase regular piston to
their reasonable position based on the engine working conditions (Adwera, 2013, p. 321)
If choosing I was to choose variable valve timing, I would go for VTEC since it has numerous
advantages such a;
 The VTEC engine has low RPM drivability since it includes a camshaft with a profile
intended to offer better fuel economy and better low-end torque and power.

 The VTEC is capable of detecting the circumstance under which the high-performance
camshaft is essential, activation of electronic switch takes place and switching of valve
process to a different camshaft by the use of hydraulic pressure.
 The VTEC has good power at high RPM.

References
Adwera, P. (2013). Automotive Engineering International. HarperCollins.
Duncan, I. (2008). Automotive Engineering International. Adventure Works Press.
Emadi, A. (2015). Handbook of Automotive Power Electronics and Motor. OLMA Media group.
Gilles, T. (2018). Automotive Engines. Hauffe Gruppe.
Handfield, C. (2009). Todays Technician. Ridders Digest.