CAMLESS ENGINES A NEW APPROACH IN I.C.ENGINES
Ms. A. Sushma
Mr. M. Sunil
Email:
[email protected] Email:
[email protected] Pre-Final Mechanical Engineering, Bapatla Engineering College. Address to Communicate: A. Sushma
M. Sunil;
D/o A.V. Prasad;
Door No 5-39;
D.No: 15-7-3;
Mahatmajipuram;
Besthapalem;
Opp Bapatla Engineering College;
Bapatla-522101.
Bapatla-522101.
Contact: 09392399662
09391673727 finds its place in the market with latest design
Abstract The internal combustion engine (ICE)
modifications
components economy
to and
in
improve overall
various efficiency,
performance.
However, one component has remained
unchanged in the
internal combustion
objects that comprise the valve train
engine development i.e., the camshaft,
hardware in your pride and joy. Camless
has been the primary means of controlling
engine technology is soon to be a reality
the valve actuation and timing, and
for
therefore,
overall
camless valvetrain, the valve motion is
performance of the vehicle. Camless
controlled directly by a valve actuator -
technology is capturing the future of
there's
internal combustion engines. It has been
mechanisms. Various studies have shown
known to man that if valves could be
that a camless valve train can eliminate
controlled independently in an Internal
many otherwise necessary engine design
Combustion Engine then there would be
trade-offs.Automotive engines equipped
benefits like increased power, reduced
with camless valvetrains of the electro-
emissions and increased fuel economy. In
hydraulic and electro-mechanical type
the camless technology valve motion is
have been studied for over twenty years,
operated by valve actuators of electro-
but production vehicles with such engines
mechanical and electro-hydraulic type. In
are still not available.
influencing
the
mass-produced
no
vehicles.
camshaft
or
In
the
connecting
this paper we compare camless valve operation
with
conventional
valve
operation and we deal with the valve actuating mechanisms of camless engine by considering the electromechanical and electrohydraulic
actuators
as
the
important types of actuating valves in camless engines. Keywords: Valve actuation, Electromechanical actuators, Electrohydraulic actuators. Introduction Cams, lifters, pushrods... all these things have up until now been associated with the internal combustion engine. But the end is near or these lovely shiny metal
The issues that have had to be addressed in the actuator design include: •
reliable valve performance
•
cost
•
packaging
•
power consumption
•
noise and vibration Noise has been identified as the main
problem
with
the
electromechanical
actuator technology, arising from high contact velocities of the actuator's moving parts. For this noise to be reduced, a so-
soft-landing is mechanically embedded
called soft-landing of the valves has to be
into the shape of the camshaft lobe.
achieved. In a conventional valvetrain, the
Conventional Valvetrain
The valvetrain in a typical internal
profile. Usually , it is fixed to deliver only
combustion engine comprises several
one specific cam timing. The cam lobes
moving components. Some are rotating
have to be shaped such that when the
and some are moving in a linear manner.
valve travels up and down at the engines
Included are poppet valves that are
maximum speed it should still be able to
operated by rocker arms or tappets, with
slow down and gently contact the valve
valve springs used to return the valves to
seat. The valves crashing down on their
their seats. In such a system the parasitic
valve seats results in an engine that is real
power losses are major - power is wasted
noisy and has a short life expectancy.
in accelerating and decelerating the
Having different cam profiles will
components of the valvetrain. Friction of
result in different engine characteristics.
the camshaft, springs, cam belts, etc also
While high-rpm power and low rpm-
robs us of precious power and worsens
torque
fuel economy, not to mention contributing
compromise is required to obtain the best
to wear and tear. The power draw on the
of both in the same engine. With Variable
crankshaft to operate the conventional
Valve Timing (VVT) technologies the
valve train is 5 to 10 percent of total
compromise is getting better and better -
power output.
reasonable low down torque and high-
Another factor working against the conventional valve train is that of the cam
can
be
each
optimised,
a
speed power are being produced by many sub 2-litre engines.
But the problem remains that the
manufacturers.
cam grind is still a fixed quantity - or two fixed quantities in the case of Honda V-
1. Electromechanical Poppet Valves
TEC
the
This type of system uses an armature
is
attached to the valve stem.The outside
considered the next evolution of VVT.
casing contains a magnetic coil of some
With the potential to
dial in any
sort that can be used to either attract or
conceivable valve timing at any point of
repel the armature, hence opening or
the combustion cycle for each individual
closing the valve.
engines.
Electromechanical
That's Valve
why Train
cylinder, valves can be opened with more lift and/or duration , as the computer
Most early systems employed solenoid
and
magnetic
deems necessary. Camless Valvetrain Operation The types of camless variable valve actuating systems being developed can be classed in two groups: electrohydraulic and electromechanical. When it comes to electromechanical valve trains, there are several designs that are being trialed. Most developers are using the conventional poppet valve system (ie valves that look the same as in today's engines) but an alternative is a ball valve set up. Both use electromagnets in one way or another to open and close the valve. Originally created for the Apollo space program, the electrohydraulic valve
actuator
works
by
sending
pressurised hydraulic fluid to the engine valve to move it open or closed. These systems are mainly retain poppet valves and are preferred by truck engine
attraction/repulsion actuating principals using an iron or ferromagnetic armature. These types of armatures limited the performance of the actuator because they resulted in a variable air gap. As the air gap becomes larger (ie when the distance between the moving and stationary magnets or electromagnets increases), there is a reduction in the force. To maintain high forces on the armature as
the size of the air gap increases, a higher
valve stem. Depending on the direction of
current is employed in the coils of such
the current supplied to the armature coil,
devices. This increased current leads to
the valve will be driven toward an open or
higher energy losses in the system, not to
closed
mention non-linear behaviour that makes
electromechanical valve actuators develop
it
higher and better-controlled forces than
difficult
to
obtain
adequate
position.
designs
These
mentioned
latest
performance. The result of this is that
those
previously.
most such designs have high seating
These forces are constant along the
velocities (ie the valves slam open and
distance of travel of the armature because
shut hard!) and the system cannot vary
the size of the air gap does not change.
the amount of valve lift. The
electromechanical
valve
Referring now to Figures 1 to 4, an
actuators of the latest poppet valve design eliminate
the
iron
or
ferromagnetic
armature. Instead it is replaced with a current-carrying
armature
coil.
A
magnetic field is generated by a magnetic field generator and is directed across the fixed air gap. An armature having a current-carrying armature coil is exposed to the magnetic field in the air gap. When a current is passed through the armature coil and that current is perpendicular to the magnetic field, a force is exerted on the armature.When a current runs through the armature coil in either direction and perpendicular to the magnetic field, an electromagnetic vector force, known as a Lorentz force, is exerted on the armature coil. The force generated on the armature coil drives the armature coil linearly in the air gap in a direction parallel with the
electromechanical valve actuator of the poppet valve variety is illustrated in conjunction with an intake or exhaust valve (22). The valve (22) includes a valve closure member 28 having a cylindrical
valve
stem
(30)
and
a
cylindrical valve head (32) attached to the end of the stem (30). The valve actuator (20) of the poppet valve system generally
includes
a
housing
assembly
(34)
consisting of upper and lower tubular
without valve springs as shown in Figure 1
housing members (36) and (42), a magnetic field generator consisting of upper and lower field coils (48) and (52), a core (56) consisting of upper and lower core member (58) and (68), and an armature (78) suitably connected to the valve stem (30). The armature coil is preferably made from aluminium wire or other electrically conductive lightweight material, which is highly conductive for its mass. Minimising the armature mass is especially important in view of the rapid acceleration forces placed on it in both directions. The ability of the electromechanical valve actuator to generate force in either direction and to vary the amount of force applied to the armature in either direction is an important advantage of this design. For instance, varying the value of the current through the armature coil and/or changing the intensity of the magnetic field can control the speed of opening and closing of the valve. This method can also be used to slow the valve closure member to reduce the seating velocity, thereby
or can equally be equipped with them as shown in Figures 6 & 7 2. Electromechanical Ball Valves An alternative to the conventional poppet valve for use in camless valve trains is a ball valve. This type of electromechanical valve system consists of a ball through which a passage passes. If the ball is rotated such that the passage lines up with other openings in the valve assembly, gas can pass through it. (Exactly like the ball valves many of us use to control our boost.) Opening and closing the valve is accomplished
by
electromagnets
positioned around its exterior.
lessening wear as well as reducing the resulting noise.
Referring to Fig, the valve housing (7) is shown in two pieces. Ball valve (8)
This system is able to operate
has two rigidly attached pivots (12). The
the ball valve needs only to rotate on its axis
to
achieve
the
desired
flow
conditions, rather than be accelerated up and down in a linear fashion. A partially open ball valve state may also be able to be used to create more turbulence. Electromechanical
valve
train
implementation would not be possible disc (10) is permanently attached and indexed to the ball valve and contains permanent magnets around its perimeter. The electromagnets (11) are situated on both sides of the ball valve (8) and they are fixed to the valve housing. through the ECU. A crank trigger sensor on the crankshaft provides information about the position of the pistons relative to top dead centre. Thus, at top dead centre of the power stroke, the ECM could be used to fix the polarity of both electromagnets so that they are of opposite polarity to the magnets in the ball valve, rotating the ball valve to the closed position. substitution in
electrical system as the next automotive standard. Electrohydraulic Poppet Valves electrohydraulic valves comprise poppet valves moveable between a first and second position. Used is a source of pressurised hydraulic fluid and a hydraulic actuator coupled to the poppet valve. The motion between a first and second position is responsive to the flow of the pressurised hydraulic fluid. An electrically operated hydraulic valve controls the flow of the pressurised hydraulic fluid to the hydraulic actuator. In one design, the
of
a
simple,
efficient ball valve and valve housing arrangement
automotive industry has chosen a 42V
In general terms, present designs of
The electromagnets are controlled
The
with a normal 12V electrical system, the
a
a
four
stroke
reciprocation piston engine eliminates all the independent moving parts in the valve train. This may even be an improvement over the poppet valve camless system -
provision is made for a three-way electrically operated valve to control the flow of the pressurised hydraulic fluid to the actuator. This supplies pressure when electrically pulsed open, and dumps actuator oil to the engine oil sump when the valve is electrically pulsed to close.
The use of engine oil as the hydraulic
oil sump (34). The pump output pressure
fluid simplifies and lowers the cost of the
is also limited by an unloader valve (36),
design by removing the need for a
as controlled by an accumulator (38)
separate hydraulic system.
connected to the oil pressure rail. With this design the hydraulic pump could be periodically disconnected, such as under
Electrohydraulic Poppet Valves The
basic
design
of
braking, so that the valve train would run the
electrohydraulic valvetrain hardware is illustrated in
off the stored accumulator hydraulic pressure.
Fig. The engine poppet
As is the trend with all modern
valves (22) and the valve springs (24) that
engine systems, the camless engine has an
are used to reset them are shown. The
even greater reliance on sensors. The
poppet valves are driven by hydraulic
valve
actuation
and
control
system
typically needs a manifold pressure sensor, a manifold temperature sensor, a mass flow sensor, a coolant temperature sensor, a throttle position sensor, an exhaust gas sensor, a high resolution engine position encoder, a valve/ignition timing decoder controller, injection driver electronics, valve coil driver electronics, ignition coil driver electronics, air idle speed control driver electronics and actuators (26), which are controlled by electrically
operated
power down control electronics.
electro-hydraulic
A valve developed by Sturman
valves (28) supplying hydraulic fluid to
Industries is said to be about six times
the actuators via conduit (29). The
faster than conventional hydraulic valves.
preferred hydraulic fluid is engine oil,
To achieve such speeds, it uses a tiny
supplied to the electro-hydraulic valves by
spool sandwiched between two electrical
the pressure rail (30). An engine-driven
coils. By passing current back and forth
hydraulic pump (32) supplies the oil
between the coils, a microprocessor-
pressure, receiving the oil from the engine
based controller can quickly move the
spool back and forth, thereby actuating
increase overall valvetrain efficiency by
the engine valves in accordance.
eliminating the frictional losses of the
Benefits of Camless Engines
camshaft mechanism, the weight of the
The benefits of camless valve actuator
mechanism and the cam mechanism's
systems are numerous. The most obvious
drain of power from the crankshaft.
one - infinitely variable valve timing. More torque is made available through
Valve
out the rev-range due to the valve timing
mechanical cam shaft and camless
changes
engine actuation
enabling
efficiency.
optimal
This
volumetric
comparision
between
engine
The improvement in the speed of
fuel
operation valve actuation and control
consumption, also decreasing harmful
system can be readily appreciated with
emissions,
reference to Fig..
performance
increases
speed
and increasing
decreases durability
and
engine life, and allowing compensation for different types of fuel and varying altitudes. Cylinder deactivation (ie an eight cylinder can become a six as needed!) is also
possible,
with
the
associated
reduction in emissions. Further fuel consumption
reductions
could
be
obtained by combining camless valve technology with a high-pressure direct fuel injection system. The amount of engine oil required would also be dramatically
reduced
because
no
lubrication would be required for the traditional
complex
camshaft
valve
system. Cold start wear would also be minimal to the valve train hardware. There is also a general consensus that electromechanical valve actuation will
It shows a comparison between valve speeds of a mechanical camshaft engine and the camless engine valve actuation. The length of the valve stroke in inches versus degrees of rotation of a mechanical camshaft is illustrated. When graphed, the cycle of opening and closing of a valve driven by a mechanical camshaft will display a shape similar to a sine curve. The opening period
(as
measured
in
crankshaft
degrees) remains constant for any engine load or rpm. However, the cycle of
opening and closing of valves driven by
engine operation difficult to achieve
the electromechanical valve actuators
during low load, and more precisely,
operates much faster. Designed to match
during idle conditions.
valve-opening rates at the maximum
Using
camless
valve
actuators
engine rpm, the electromechanical valve
permits reprogramming to allow the engine
actuators open the valve at this same rate
to
regardless of engine operating conditions.
can be done by simply inverting one input
Because of this improved speed, greater
wire
flexibility in programming valve events is
advantageous in marine equipment having
possible, allowing for improved low-end
dual outdrives or T-drives. This feature
torque, lower emissions and improved
would also eliminate the need for reverse
fuel economy. The massive opening
gear in the transmission since forward
period for the electromechanically driven
gears would be used to operate in either
valve can also be seen!
vehicle
Controlling the intake valve event can also eliminate the need for throttled
operate in reverse . This pair.
Reverse
direction.
operation
This
provides
is
an
opportunity for multiple reverse gears without the added hardware.
operation in petrol engines, thereby
However, the future is not necessarily
reducing pumping losses and improving
as rosy as the above states. There are many
fuel economy - the throttle butterfly
problems
becomes redundant. In the un-throttled
electronically
camless engine, the intake valves' opening
problems lie not only in the software
duration is used for cylinder airflow
required but also the mechanisms of the
regulation, rather than a throttle or air-
actuators. Coil transient response times and
bypass valve. A simplification of the
saturation effects at high rpm are just some
induction system results and a more
of the issues.
compact engine design is thus possible.
Conclusions
This leads to valve specific intake
The main difference between camless
trumpets with less restriction to give the
engine and conventional engine arose
best breathing capabilities. Although, it
when we deal with the valve actuating
needs to be said that there are reported
methods in both of these engines. In
problems with respect to idle control of a
conventional engines the valves are
throttleless design, with stable unthrottled
actuated by using camshafts, lobes and
to
be
overcome
controlled
with
valves.
the The
gears. But in camless internal combustion engines all these are eliminated by using actuators like electro-hydraulic or electromechanical type by which we can overcome the problems with conventional i.c.engines. The benefits like reduced emission, increased power, increased fuel economy can be obtained by applying camless
technology
to
internal
combustion engines. From all these we can conclude that by applying camless technology to internal combustion engines the overall performance of the vehicle will enhance. References: 1. Fundamentals of
I.C.Engines by
J.B.Heywood. 2. Kim D, Anderson M. A dynamic model of
electrohydraulic camless
valve train system SAE article. 3. Schechter MM, Levin MB Camless engine. SAE article. 4. Article in autospeed on camless engines. 5. A
Website
www.autospeed.com,
article on camless engines.
