INTRODUCTION
The
automobile has been providing individual mobility for more than 100 years. This
mobility is made possible first and foremost by combustion engines drawing
their power from fossil energy carriers, which, even today, provide the
foundation in generating mechanical drive power in the automobile. The primary
objectives in developing drive systems are
to curb fuel consumption and reduce CO2 emissions. In an effort to meet
this challenge, the automotive industry is developing suitable new engines. The
voluntary commitment assumed by the European Automobile Manufacturers
Association (ACEA) is to reduce the fleet emission average of all newly
introduced cars to 140g of CO2 per kilometer by 2008 .
The
first objective is to minimise emission components such as hydrocarbon, CO2 and
nitrogen oxides (NOx) subject to specific limits. At the same time,
manufacturers are seeking to minimise fuel consumption and, accordingly, CO2
emissions. All of this should be achieved with a maximum standard of comfort
and safety on the road. In the homologation of motor vehicles, Europe, Japan and the US
To
make more efficient use of the energy in fuel, the actual process of using
energy must reach a higher standard of efficiency.
Despite
modern engine technology, the process of on-going development has not yet come
to an end. Looking at the overall concept of a vehicle, the development
engineer must therefore optimize the efficiency chain formed by all of the
car’s individual components. For example, a car with a state-of-the-art spark-ignition
engine uses only about 20% of the energy consumed to actually generate driving
power and mobility in the EU test cycle. This alone demonstrates the remaining
potential.
VALVETRONIC
The Valvetronic engine is the world's first engine
without a throttle butterfly. Valvetronic
allows the engine to run without a throttle butterfly, the cylinder charge
being determined under part load as a function of the valve-opening period. The
intake and outlet camshafts are driven by variable cam adjustment, BMW’s Vanos technology.
A further advantage of this concept is that it allows worldwide use of the proven
three-way catalyst for emissions management, thus meeting even the strictest
emissions standards in the US
Innovative
technology was essential in order to reach the demanding objectives and
functional requirements desired. However, at the same time, this concept demanded
the utmost of the electronic control and management systems in the engine.
Concept
Taking nature as the role model: human
beings also apply the Valvetronic principle
A
comparison with the human being clearly explains how Valvetronic works:
Whenever we are required to make a great effort, we human beings breathe in a
deep and long process of ventilation. Whenever we need less air, we do not
throttle the supply of air by, say, closing our nose or our mouth, but simply
breathe in a shorter, flatter process of ventilation. In a conventional
combustion engine the throttle butterfly is basically comparable to a human
being keeping his nose or mouth at least partially closed. With its large valve
lift (= deep, long ventilation) and short valve lift (= flat, short process of
ventilation), Valvetronic, on the other hand, is able to breathe in the same
way as nature – always in line with current requirements, without any kind of
throttling effect and therefore with maximum efficiency.
Valvetronic
Technology
Accordingly,
the Valvetronic engine no longer requires a throttle butterfly, which has quite
literally restricted the free ventilation of the internal combustion engine
ever since its invention. Now Valvetronic replaces this conventional function
by infinitely variable intake valve lift, offering a quantum leap in technology
quite comparable to the changeover from the carburetor to fuel injection.
Its
most important feature is that it is able to save at least 10 per cent fuel
throughout the entire operating range relevant to the customer, with a
corresponding reduction in exhaust emissions, regardless of fuel quality. And a
further important point is that the efficient operation of Valvetronic does not
require any unusual types and grades of oil possibly difficult to obtain.
As
a result of these particular features the 85 kW/115bhp BMW 316ti compact with
its top speed of 210 km/h or 125 mph consumes a mere 6.9 liters of premium fuel
on 100 kilometers in the European test cycle, equivalent to 40.9 mpg Imp. This
is a significant 0.7 liters less than the former 77 kW/105 bhp compact and well
over a liter less than all competitors in this class.
The Valvetronic system is based consistently on BMW’s proven
double-VANOS (VANOS = variable adjustment of the camshafts), with infinite
camshaft adjustment to meet specific requirements. The additional, variable
valve lift adjusts the effective cam action and, accordingly, the opening
cross-section of the valves.
This
is done by a lever positioned between the camshaft and the intake valves, its
distance from the camshaft being adjusted infinitely by an additional eccentric
shaft operated by an electric motor. Depending on the position of the
Valvetronic control system, the lever converts the cam contour into a larger or
smaller valve lift, whatever may be required.
WORKING
OF VALVETRONIC ENGINE
Working
Of Ordinary Engine
In
engines without valvetronic technology fuel injection systems monitor the
volume of air passing through the throttle butterfly and determine the
corresponding amount of fuel required by the engine. The larger the throttle
butterfly opening, the more air enters the combustion chamber.
At
light throttle, the throttle butterfly partially or even nearly closes. The
pistons are still running, taking air from the partially closed intake
manifold. The intake manifold between the throttle and the combustion chamber
has a partial vacuum, resisting the sucking and pumping action of the pistons,
wasting energy. Automotive engineers refer to this phenomenon as "pumping
loss". The slower the engine runs, the more the throttle butterfly closes,
and the more energy is lost.
Working Of Valvetronic Engine
Compared
with conventional twin-cam engines with finger followers, Valvetronic employs
an additional eccentric shaft, an electric motor and several intermediate
rocker arms, which in turn activates the opening and closing of valves. If the
rocker arms push deeper, the intake valves will have a higher lift, and
vice-versa. Thus, Valvetronic has the ability to get deep, long ventilation
(large valve lift) and flat, short ventilation (short valve lift), depending on
the demands placed on the engine.
Cylinder
heads with Valvetronic use an extra set of rocker arms, called intermediate
arms (lift scaler), positioned between the valve stem and the camshaft. These
intermediate arms are able to pivot on a central point, by means of an extra,
electronicly actuated camshaft. This movement alone, without any movement of
the intake camshaft, can open or close the intake valves.
The
Valvetronic system is based on BMW's established double VANOS system, which
steplessly varies the timing of both the inlet and exhaust cams. However, the
Valvetronic system adds variable valve lift to the inlet cam, achieved by the
use of a lever positioned between the camshaft and the inlet valves. Valvetronic
varies the timing and the lift of the intake valves. The Valvetronic system has
a conventional intake cam, but it also uses a secondary eccentric shaft with a
series of levers and roller followers, activated by a stepper motor. Based on
signals formerly taken mechanically from the accelerator pedal, the stepper
motor changes the phase of the eccentric cam, modifying the action of the
intake valves. An additional eccentric shaft alters the lever's distance from
the camshaft, with the eccentric's position determined by a worm drive from an
electric motor. The position of the lever converts the cam action into a
smaller or larger valve lift, as requested by the engine management system.
Intake vale lift can be altered from a minimum of 0.25mm(!) to a maximum of
9.7mm, with the electric motor adjusting the eccentric shaft in 0.3 seconds.
Because
the intake valves now have the ability to move from fully closed to fully open
positions, and everywhere in between, the primary means of engine load control
is transferred from the throttle plate to the intake valve train. By
eliminating the throttle plate's "bottleneck" in the intake track,
pumping losses are reduced, fuel economy and responsiveness are improved.
Operating Parameters
- Valve lift is variable between 0 and
9.7 mm.
- Adjustment of the worm gear from one
extreme to the other takes 300 milliseconds.
- Combined with double-vanos valve
timing technology, the camshaft angle relative to the crankshaft can be
adjusted by up to 60°.
- The intermediate arm is finished to a
tolerance of 0.008 mm.
- The cams controlling the eccentric
shaft are machined to tolerances of a few hundredths of a
millimeter.
ENGINE
DESIGN ASPECTS
Basic engine design completely revised
Not only the cylinder head with BMW’s new Valvetronic technology,
but also the complete four-cylinder power unit featured in the BMW 316ti is an
all-new development from the ground up. The new cross-flow cooling concept with
its open deck crankcase reduces coolant flow resistance and therefore allows
use of a smaller water pump with just 60 per cent of the usual power uptake.
Made of aluminum, the engine block ends exactly on the centerline
of the crankshaft bearings. A ladder frame between the crankcase and the oil
sump connects the lower halves of the bearing bridges to form one complete unit
also accommodating the balance shaft housing and the two-stage oil pump. This
makes the entire drive unit very stiff and robust, minimizing any vibration of
other vehicle components the driver would otherwise feel on the steering wheel,
gearshift lever and pedals, and also perceive as a kind of consistent humming
noise.
All ancillaries are bolted directly to the crankcase without the
rather elaborate supports and attachments otherwise required – again an important
contribution to running smoothness with vibrations reduced to a minimum.
Throttle plate is not removed
It
is important to note however, that the throttle plate is not removed, but
rather defaults to a fully open position once the engine is running. The
throttle will partially close when the engine is first started, to create the
initial vacuum needed for certain engine functions, such as emissions control.
Once the engine reaches operating speed, a vacuum pump run off the passenger
side exhaust camshaft (on the N62 V8 only) provides a vacuum source, much as a
diesel engine would, and the throttle plate once again goes to the fully open
position. The throttle plate also doubles as an emergency backup, should the
Valvetronic system fail. In this case, the engine would enter a "limp
home" program, and engine speed would once again be controlled by the
throttle plate.
ADVANTAGES
Fuel economy increased
Valvetronic offers the
customer direct, immediate benefits, with fuel consumption and exhaust
emissions decreasing, but dynamic performance and the spontaneous response of
the engine improving accordingly. Added to this there is the even higher
standard of running smoothness, since the valves move only slightly in a
precisely controlled process.
The improvement in fuel economy ensured by this concept of
throttle-free engine load management is approximately 10 per cent in the EU
cycle and at least 10 per cent under the typical driving conditions encountered
by a customer. The basic rule is that fuel economy versus other concepts
increases with the driver running the vehicle at lower loads and engine speeds.
The consumption figures the motorist is able to achieve in this way are
comparable to the fuel economy only a diesel engine was able to offer just a
few years ago.
At the same time the new four-cylinder is even more dynamic than
its predecessor, the 316ti now accelerating well over a second faster to 100
km/h, achieving this important mark from a standstill in 10.9 seconds. The
standing-start kilometer, in turn, comes after 31.6 seconds, 1.8 seconds faster
than before, and the top speed of the 316ti is now 201 km/h or 125 mph, 11 km/h
faster than the top speed of the former model.
Another advantage is the unusually spontaneous response of the
316ti to the gas pedal. This is attributable to the simple fact that load
control, to use the technical term for "giving gas", now takes place
"right there where the action is", that is directly in the combustion
chamber. This eliminates the usual time lag between the process of "giving
gas" and the actual acceleration of the car, which used to be inevitable
due to the need to fill the intake manifold between the throttle butterfly and
the combustion chamber. In this respect, Valvetronic even outperforms the most
advanced concepts using individual throttle butterflies, thus offering an
unprecedented combination of spontaneous engine response and ultra-fine dosage
of power and performance under low loads.
Perfectly suited for all fuel grades
Another significant advantage of Valvetronic highly beneficial to
the customer is that a Valvetronic engine offers at least the same fuel economy
as the most advanced direct-injection petrol engines without the same
compromises in terms of emissions. Accordingly, the 316ti is able to do without
the elaborate and so far hardly reliable emission management technologies still
required today on a direct-injection petrol engine. And it does not require
sulfur-free fuel like a direct-injection petrol engine, achieving its superior
fuel economy with proven l =1 technology, which allows the Valvetronic engine
to run on all commercially available grades of regular petrol. In other words,
the customer enjoys all the consumption-related advantages of Valvetronic also
when driving in countries without a nationwide supply of sulfur-free fuel. The
consumption figures for the 316ti nevertheless relate to the use of premium
fuel with an octane rating of 95 RON. Together with its 63-liter (13.9 Imp gal)
fuel tank, the 316ti offers a much longer range than its predecessor, with
extra-urban fuel consumption in the European EU test cycle of just 5.3 liters
for 100 kilometers (53.3 Imp gals). This means that the driver would only have
to refuel after a very significant 1,188 kilometers or 737 miles.
Other
Advantages
·
Anti-knock
control for running on all fuel grades between 87 and 99 octane.
- Maintenance-free ignition
system with individual coils.
- Maintenance-free valve
drive with hydraulic valve play compensation.
- A Service Interval
Indicator to keep the cost of service to a minimum
- A two-mass flywheel for
maximum running smoothness
- Valve drive with roller
bearings throughout in the interest of minimum friction and fuel
consumption.
- Advanced catalysts near
the engine in special manifold design for minimum emissions.
- In Valvetronic engines coolant flows
across the head, resulting in a temperature reduction of 60%.
- The water pump size is cut in half,
reducing power consumption by 60%.
- The power steering fluid is warmed
quickly, reducing the power used by the hydraulic pump.
- Mounting the water and power pump on the same shaft and a heat exchanger between coolant and engine oil reduces oil temperature by 30%.
CONCLUSION
In summary, these innovative developments provide a combination of
product features thus far inconceivable with a spark-ignition engine. The
introduction of the world’s first intake manifold providing infinite variation
in manifold length serves to improve the torque level, which is already very
good to begin with. A particular highlight of engines with Valvetronic load
management is the significantly improved fuel/air mixture guaranteeing minimum
fuel consumption, maximum spontaneity and optimum refinement.
DFI with a stochiometric air/fuel ratio provides the highest level
of specific output as well as a combustion process helping to fulfil all
exhaust emissions standards worldwide. All-round, general use of the latest
direct-injection technology, in turn, faces some significant drawbacks such as
costs, the need to make the combustion process very robust and the potentials
in exhaust emissions treatment.
Valvetronic combines a significant improvement of fuel consumption
with excellent engine response and control, allowing optimum valve timing under
all running conditions. The result is smooth and free operation of the engine
under part load with very little throttle effect. Optimised fuel/air mixture
management ensures significant advantages in fuel efficiency compared with a
conventional four-cylinder engine, reaching the same standard as today’s
lean-burn concepts. Since such an engine with Valvetronic does not require an
NOx removal catalyst, it can be used worldwide with all types and grades of
fuel.
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