U.S. patent application number 10/818406 was filed with the patent office on 2004-10-07 for method for operating an internal combustion engine having two inlet valves.
Invention is credited to Dunstheimer, Jens, Kramer, Ulrich, Phlips, Patrick J..
Application Number | 20040194745 10/818406 |
Document ID | / |
Family ID | 32842835 |
Filed Date | 2004-10-07 |
United States Patent
Application |
20040194745 |
Kind Code |
A1 |
Phlips, Patrick J. ; et
al. |
October 7, 2004 |
Method for operating an internal combustion engine having two inlet
valves
Abstract
The invention relates to a method for controlling an internal
combustion engine, which has a first inlet valve (P) and a second
inlet valve (S) per cylinder, which can be operated independently
of one another between maximum operation (P1, S1) and minimum
operation. The change of the inlet valves takes place preferably by
engine oil pressure, in a basic state (P1+S2) the first inlet valve
(P) is in maximum operation (P1) and the second inlet valve (S) is
in minimum operation (S2). From the basic state, the valve control
device switches the first inlet valve (P) into a minimum operation
(P3) at low engine rotational speeds/engine torques and sufficient
engine oil pressure and switches the second inlet valve (S) into
maximum operation (S1) at high engine rotational speeds/engine
torques.
Inventors: |
Phlips, Patrick J.; (Koeln,
DE) ; Kramer, Ulrich; (Bergisch Gladbach, DE)
; Dunstheimer, Jens; (Koeln, DE) |
Correspondence
Address: |
FORD GLOBAL TECHNOLOGIES, LLC.
SUITE 600 - PARKLANE TOWERS EAST
ONE PARKLANE BLVD.
DEARBORN
MI
48126
US
|
Family ID: |
32842835 |
Appl. No.: |
10/818406 |
Filed: |
April 5, 2004 |
Current U.S.
Class: |
123/90.15 |
Current CPC
Class: |
F02D 2013/005 20130101;
F02D 13/0207 20130101; Y02T 10/12 20130101; F02D 13/0257 20130101;
Y02T 10/18 20130101; F02D 13/0226 20130101; F02B 31/085 20130101;
Y02T 10/146 20130101 |
Class at
Publication: |
123/090.15 |
International
Class: |
F01L 001/34 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 4, 2003 |
EP |
03100895.6 |
Claims
1. A method of operating an internal combustion engine with at
least one cylinder, the cylinder having a primary intake valve and
a secondary intake valve disposed therein, the method comprising:
operating the primary valve at a first lift profile and the
secondary valve at the second lift profile as a default condition
wherein the primary valve is capable of being switched between said
first lift profile and a third lift profile and the secondary valve
is capable of being switched between said second lift profile and a
fourth lift profile and the primary and secondary valves are
independently controllable.
2. The method of claim 1 wherein said first lift profile has a
taller valve stroke than said third lift profile and said fourth
lift profile has a taller valve stroke than said second lift
profile.
3. The method of claim 1 wherein said first lift profile has a
longer opening duration than said third lift profile and said
fourth lift profile has a longer opening duration than said second
lift profile.
4. The method of claim 1 wherein a valve stroke of the secondary
valve operating with said second lift profile is less than 40% of a
valve stroke of the primary valve with said first lift profile.
5. The method of claim 1 wherein said third lift profile of the
primary valve and said fourth profile of the secondary valve are
caused to be selected by oil pressure acting on a valve change
device.
6. The method of claim 1 wherein the primary valve operates with
said first lift profile and the secondary valve operates with said
second lift profile when oil pressure is below an actuation
pressure.
7. The method of claim 1, further comprising: operating the primary
valve at said first lift profile and the secondary valve at said
fourth lift profile in response to at least one of engine speed and
torque.
8. The method of claim 1, further comprising: operating the primary
valve at said first lift profile and the secondary valve at said
fourth lift profile when engine speed and torque are in a higher
range.
9. The method of claim 1, further comprising: operating the primary
valve at said second lift profile and the secondary valve at said
third lift profile in response to at least one of engine speed and
torque.
10. The method of claim 1, further comprising: operating the
primary valve at said second lift profile and the secondary valve
at said third lift profile when engine speed and torque are in a
lower range.
11. An internal combustion engine, comprising: at least one engine
cylinder; a primary inlet valve disposed in each of said cylinders;
a secondary inlet valve disposed in each of said cylinders; a first
variable valve control device allowing switching of the primary
inlet valve between a first and a third lift profile; a second
variable valve control device allowing switching of the secondary
inlet valve between a second lift profile and a fourth lift
profile; and an engine control unit coupled to the engine and to
said first and second variable valve control devices, said engine
control unit controlling said variable valve control devices based
on a speed and torque of the engine.
12. The engine of claim 11 wherein said variable valve control
devices are actuated by engine oil pressure.
13. The engine of claim 11 wherein said engine control unit manages
oil pressure actuation of said variable valve control devices.
14. The engine of claim 11 wherein a default operating condition is
when said primary inlet valve is operated at said first lift
profile and said secondary valve at said second lift profile as a
default condition.
15. The engine of claim 14 wherein said first lift profile has a
taller valve stroke than said third lift profile and said fourth
lift profile has a taller valve stroke than said second lift
profile.
16. The engine of claim 14 wherein said first lift profile has a
longer opening duration than said third lift profile and said
fourth lift profile has a longer opening duration than said second
lift profile.
17. The engine of claim 14 wherein said default operating condition
is requested by said engine control unit when engine speed and
torque is in a medium range.
18. The engine of claim 14 wherein said engine control unit causes
switching of said first valve control device to said third lift
profile at a lower range of engine speed and torque.
19. The engine of claim 14 wherein said engine control unit causes
switching of said second valve control device to said fourth lift
profile at a higher range of engine speed and torque.
Description
FIELD OF THE INVENTION
[0001] The invention is a method for operating an internal
combustion engine having a first and a second inlet valve in one
cylinder, which are capable of being changed independently between
maximum operation and minimum operation. The invention relates,
furthermore, to an internal combustion engine for carrying out a
method of this type.
BACKGROUND OF THE INVENTION
[0002] Motor vehicle engines with spark ignition, which, in
practice, use almost exclusively gasoline as fuel, are operated
predominantly with a stoichiometric air/fuel mixture, which allows
highly efficient treatment of the exhaust gas emissions. Torque
control is provided by throttling. In part load operation of such
an engine, however, fuel consumption increases due to throttling
and to stoichiometric operation. These losses can be reduced by
homogeneous or stratified lean operation, although this has the
disadvantage that the NOx emissions of the engine cannot be treated
at high efficiency by a conventional three-way catalytic converter.
Three-way catalysts with NOx trapping capability are considerably
more costly than conventional three-way catalytic converters are
used to remove nitrogen oxides for lean burning systems.
Furthermore, when stratified direct injection is employed, the
systems for the provision of air, fuel, exhaust gas recirculation,
and ignition are also all considerably more complex and costly than
in a conventional engine. Even pressure charging, for improving
fuel consumption in stoichiometric operation, is more costly due to
the turbocharger with intermediate cooler.
SUMMARY OF THE INVENTION
[0003] A more cost-effective approach to improving engine
efficiency is by variable valve control in which the opening
durations, closing times, and/or valve stroke of the inlet valves
and/or the exhaust valves is adjusted. One alternative to provide
variable valve control is for the valve control device to have two
or three valve opening profiles (referred to briefly below as
"valve profiles"), which differ in terms of duration and/or valve
stroke.
[0004] Furthermore, in internal combustion engines having two or
more inlet valves per cylinder, the inlet valves of a cylinder may
be equipped in each case with variable valve controls, which are
independent of one another, thus allowing a multiplicity of control
possibilities for engine operation.
[0005] Against this background, the object of the present invention
was to provide means for efficient operation of an internal
combustion engine having a plurality of inlet valves per cylinder,
which can be changed independently of one another between minimum
operation and maximum operation.
[0006] A method operate an internal combustion engine which has at
least one cylinder with at least one first and one second inlet
valve is disclosed. Preferably, the first inlet valve is arranged
in a primary inlet duct, via which the main quantity of fresh air
is supplied, and the second inlet valve is arranged in a secondary
inlet duct, via which a smaller quantity of air for swirling is
supplied. The inlet valves are capable of being changed
independently from each other between:
[0007] (a) maximum operation, which is defined by a larger valve
stroke and/or a longer opening duration, and
[0008] (b) minimum operation, which is defined by a smaller valve
stroke and/or a short opening duration.
[0009] The shorter valve opening durations in minimum operation
preferably are such that they lie completely within the valve
opening durations in maximum operation. Moreover, the valve opening
duration in minimum operation is preferably shorter than the intake
stroke of the internal combustion engine. The method is defined in
that, in a basic state, the first inlet valve is used in maximum
operation and the second inlet valve in minimum operation.
[0010] In the method described, by the relatively simple changeover
of valve operation between two types of operation (minimum
operation, maximum operation), a broad spectrum of control
possibilities can be covered since two inlet valves of a cylinder
can be changed independently. In theory, by a combination of the
various types of operation of the two inlet valves, a minimum of
four operating modes can be set for the internal combustion engine.
According to the method, an operating mode, in which the first of
the inlet valves is used in maximum operation and the other inlet
valve is used in minimum operation, serves as a basic state, which
is assumed during most of the time of the "normal" driving
operation of a motor vehicle, i.e., the most commonly used
rotational speed and torque ranges. The advantage of a basic state
of this kind, with mixed maximum and minimum operation of the inlet
valves, is that this constitutes an optimum starting point both for
an increase in power of the internal combustion engine and for a
transition to minimum power requirements, for example during
idling. Furthermore, owing to the maximum operation of one of the
inlet valves, the basic state makes available a certain minimum
performance of the internal combustion engine, which ensures a
reliable functioning of connected assemblies such as, for example,
an alternator, or of pressure pumps, and therefore the
controllability of the motor vehicle functions. At the same time,
due to the minimum operation of the other inlet valve, an
asymmetric air inlet and consequently a high swirling in the
cylinder are achieved. This leads to a good mixing of air and fuel
and to good combustion. The basic state thus has advantageous
properties also with regard to fuel utilization and engine
efficiency. The basic state is preferably implemented automatically
by the inlet valves in the event of the absence of active (that is
to say, energy requiring) control of the inlet valves. That is to
say, the basic state is a default state which is assumed
automatically in the event of a possible anomaly of valve control
owing to the mixing of maximum operation and minimum operation,
reliable engine operation is ensured in the basic or default
state.
[0011] Alternatively, the changeover of the inlet valve between
minimum operation and maximum operation is brought about by the
pressure of the engine oil. In the event of a low engine oil
pressure below a predetermined threshold value, the inlet valves
are operated in the basic state. The basic state is therefore
assumed automatically whenever the available engine oil pressure is
insufficient for switching the inlet valves, for example because
the engine has been idling for a relatively long time, because
there is a high oil temperature or because the oil system is
disrupted. In the basic state, a spontaneous increase in power of
the internal combustion engine is therefore possible from idling,
the increased power subsequently ensuring an increase in the engine
oil pressure and thus ensuring the complete switchability of the
valve control.
[0012] In one embodiment, the capacity of the inlet valves to
change independently of one another is used to operate the engine
optimally according to the following. In the case of a low to
medium engine rotational speed and a low to medium engine torque,
both inlet valves can be used in minimum operation. When both inlet
valves are in minimum operation, the air quantity supplied and
consequently also the associated fuel consumption are minimum. If,
as described above, the changeover of the inlet valve takes place
with the aid of the engine oil pressure, the operating state of
minimum operation of both inlet valves is carried out preferably
only in the case of a sufficiently high engine oil pressure or in
the case of an engine oil temperature which has not increased, so
that the capability of the inlet valves to change over and
consequently the transition into another operating state remain
possible at any time. In the case of a high engine rotational speed
and/or a high engine torque, both inlet valves are used in maximum
operation to provide as much air as possible.
[0013] The transition from one operating mode to another operating
mode of the inlet valves preferably takes place in such a way that
only one of the inlet valves changes its type of operation.
Thereby, changes in engine behavior associated with the inlet valve
mode change are kept as small as possible, so that they are noticed
to the least possible extent by the driver or can be compensated
relatively simply by other devices such as a change in the throttle
setting, spark timing or in fuel injection. An operating mode
change of this kind due to a change in the type of operation of
only one inlet valve is implemented in the chain of the
above-described operating modes (both inlet valves in minimum
operation; basic state; both inlet valves in maximum
operation).
[0014] The valve stroke and/or the valve opening duration of the
first inlet valve in minimum operation are/is preferably shorter
than the corresponding size when the second inlet valve is in
minimum operation. In particular, the maximum valve stroke of the
first inlet valve in minimum operation may be less than 40%,
preferably less than one third, of the maximum valve stroke of the
second inlet valve in minimum operation. Thereby, when both inlet
valves are in minimum operation, most air is sucked in through the
second inlet valve, thus ensuring high swirling in the cylinder due
to the asymmetry.
[0015] The valve stroke of the second inlet valve in the minimum
operation is preferably less than 40%, particularly less than one
third, of the valve stroke of the first inlet valve in the maximum
operation. During the basic state, therefore, the predominant
fraction of the inlet air flows through the first inlet valve with
a relatively low flow resistance. By contrast, considerably less
air flows through the second inlet valve, although the
corresponding quantity advantageously brings about swirling in the
cylinder.
[0016] The invention relates, furthermore, to an internal
combustion engine which contains the following components:
[0017] a) At least one cylinder with at least two inlet valves.
[0018] b) A variable valve control device which can changeover the
inlet valves independently of one another between (a) maximum
operation with a larger valve stroke and/or a longer opening
duration and (b) minimum operation with a small valve stroke and/or
a shorter opening duration. The valve control device may contain,
in particular, a camshaft with different inlet cams for minimum
operation and maximum operation, between which the changeover can
be made.
[0019] c) An engine control which is connected to the valve control
device and is set up to operate the internal combustion engine
according to a method of the type explained above. That is to say,
in a basic state, the first inlet valve is used in maximum
operation and the second inlet valve in minimum operation. The
internal combustion engine or the engine control may be developed
in such a way that it can also implement the variants of said
method.
[0020] According to the preferred development of the internal
combustion engine, the valve control device is connected to the
engine oil system of the internal combustion engine and is designed
to change over the inlet valves by means of selective action by an
engine oil pressure. The use of the engine oil pressure for
switching purposes has the advantage that known hydraulic methods
can be adopted. Preferably, furthermore, the valve control device
is set up to operate the first inlet valve in maximum operation and
the second inlet valve in minimum operation when the engine oil
pressure lies below a predetermined threshold pressure. This
setting thus constitutes a default state which is assumed when, for
any reason, the engine oil pressure is not sufficient for
changeover operation.
[0021] The invention is explained in more detail below by way of
example with the aid of the Figures of which:
[0022] FIG. 1 is a graph of valve stroke versus crank angle for
inlet and exhaust valves .smallcircle. an internal combustion
engine showing three operating states;
[0023] FIG. 2 is a graph of the full torque curves in an engine
state graph of the torque versus engine rpm for the three operating
states of the inlet valve, as illustrated in FIG. 1;
[0024] FIG. 3 is a schematic of the first and second inlet valves
in the port of an internal combustion engine and graphs of the
associated types of operation according to the invention of the
valves; and
[0025] FIG. 4 is a graph of the full torque curve in an engine
state graph of the torque versus engine rpm showing the engine
control, according to the present invention, indicating operating
mode.
DETAILED DESCRIPTION
[0026] FIG. 1 shows diagrammatically the valve profiles of an
exhaust valve EX and of an inlet valve IN of the valve stroke H
(vertical axis) against crankshaft angle (horizontal axis) where
TDC is top dead center and BDC is bottom dead center of piston
travel. The inlet valve, which is of interest in the present case,
is operated by means of a valve control device capable of being
changed over between three states 1, 2, 3, so that three valve
profiles of the inlet valve are possible:
[0027] 1: Maximum operation under full torque, the valve opening
duration being longer than the intake stroke;
[0028] 2: Intermediate operation for medium torques, the valve
opening duration being shorter than the intake stroke;
[0029] 3: Minimum operation for engine idling with a very short
opening duration and with a small maximum valve stroke.
[0030] With reduced valve opening duration in intermediate
operation 2, the pumping loss normally associated with throttling
of the engine can be reduced. Since the inlet valve is open for a
shorter duration and/or stroke, the manifold pressure is raised.
Consequently, the pressure drop across the throttle is less and the
engine performs less pumping work to induct the desired amount of
air into the cylinder.
[0031] FIG. 2 shows, in an engine state graph of torque, T, of the
internal combustion engine versus engine rotational speed, n, the
three full torque curves 1, 2 and 3 for wide open throttle
operation for valve operation modes 1, 2 and 3, according to FIG.
1. Reduced valve stroke and valve opening duration reduces the
achievable torque at all engine speeds. The minimum operation 3 of
the inlet valve can be utilized, for example, only in a small
region of area around the idling rotational speed n0. The
intermediate operation 2 of the inlet valve affords the greatest
advantages in the range of medium engine rotational speeds and of
low torques. By contrast, maximum operation 1 opens up the entire
operating field of the internal combustion engine, but has no
advantages with regard to fuel consumption.
[0032] At idle, therefore, the minimum operation 3 of the inlet
valve is preferable, and, in the event of an actuation of the
accelerator pedal by the driver as command for spontaneous
acceleration, a rapid changeover into intermediate operation 2 or,
if a particularly sharp acceleration were required, even into
maximum operation 3. However, in hydraulically switched valve
control devices used conventionally, such a valve control leads to
problems, since, during idling, engine oil pressure is typically
insufficient for changing over the actuators. This is exacerbated
by increased oil temperatures such that a sufficient engine oil
pressure for changing over the actuators becomes available only at
medium engine rotational speeds.
[0033] This could be overcome, in principle, by an oil pump having
a higher performance than otherwise be used. However, this would
largely nullify the advantages achieved by variable valve control.
Thus, a valve control device which can change over between (at
least) two types of operation of the inlet valves (minimum
operation, maximum operation) is desired.
[0034] In this regard, FIG. 3 shows the valve device on which the
solution according to the invention is based. The upper part of
FIG. 3 illustrates a part of a cylinder head of an internal
combustion engine with a first inlet valve P and with a second
inlet valve S. Fresh air is supplied to the inlet valves via an
intake manifold 10, the intake manifold 10 being divided into a
primary inlet duct 11 to the first inlet valve P and a secondary
inlet duct 12 to the second inlet valve S. The configuration of the
ducts and the inlet valves P, S is preferably such that the air
supplied through the second inlet valve S generates swirl in the
cylinder to create turbulence to enhance the ensuing combustion of
the air and fuel.
[0035] The two inlet valves are capable of being changed
independently of one another between various types of operation
with the aid of the engine oil pressure. The lower part of FIG. 3
illustrates these types of operation of the two inlet valves P, S
as valve profiles in the graph of the valve stroke H against the
crankshaft angle. Accordingly, the two inlet valves P, S have a
maximum operation P1 and S1 with a large maximum valve stroke and
with a long valve opening duration. In particular, the valve
opening duration is preferably longer than the intake stroke of the
internal combustion engine. The valve profiles P1 and S1 of the two
inlet valves are otherwise similar to one another.
[0036] Furthermore, the two inlet valves may also be operated in
each case in minimum operation P3 and S2. In this case, they have
very much smaller maximum valve strokes and/or shorter valve
opening durations than in maximum operation P1 or S1. In
particular, the valve opening duration is shorter than the intake
stroke of the internal combustion engine.
[0037] Moreover, FIG. 3 indicates that
[0038] in minimum operation, P3, of the first inlet valve, P, the
maximum valve stroke is only about one third of the maximum valve
stroke of the second inlet valve S in minimum operation S2 of the
latter; and
[0039] the maximum valve stroke of the second inlet valve S in
minimum operation S2 of the latter is only about one third of the
maximum valve stroke of the first inlet valve P in maximum
operation, P1, of the latter.
[0040] FIG. 4 shows an engine state graph (corresponding to FIG. 2)
for the internal combustion engine or valve control discussed above
with reference to FIG. 3. The possibility of being able to change
over two inlet valves, P, S, of a multi-valve internal combustion
engine independently between various cam profiles affords
additional advantageous possibilities, as compared with the system
of FIGS. 1 and 2.
[0041] In the combination of maximum operation, P1, of the first
inlet valve P with minimum operation S2 of the second inlet valve
S, designated in brief as "P1+S2", the full torque of the internal
combustion engine is available in the lower half of the rotational
speed range, whereas, at higher rotational speeds, considerable
losses of torque and power occur. However, in terms of fuel
consumption, the asymmetric minimum/maximum operation of the inlet
valves is also advantageous, since an asymmetric flow of the inlet
air with turbulence is thereby generated, this being conducive to
rapid and complete combustion. This, in turn, makes the engine
tolerant to dilution with fresh air (lean combustion) or residual
gases (exhaust gas circulation, variable camshaft control), which
improve fuel efficiency.
[0042] In the lower rpm range, the P1+S2 combination satisfies,
torque, acceleration response and allows for sufficient oil
pressure for the valve control device. At the same time, advantages
arise in regards to combustion stability and fuel consumption over
double maximum operation P1+S1. The operating mode P1+S2 is
suitable as a basic state or a standard setting not employing
engine oil pressure. The basic state, P1+S2, is the "default
state," since this state is assumed in the absence of engine oil
pressure (for whatever reasons), and sufficient driveability of the
motor vehicle, while providing good fuel efficiency.
[0043] Investigations with motor vehicles show that four-cylinder
gasoline engines with manual shift transmissions are operated
predominantly between 1500 and 3000 rpm. Speeds between idling
(approximately 700 rpm.) and 1500 rpm are not used often. Under
normal operating conditions, that is to say with no excessively
high oil temperature, oil pressure is much higher at 1500 rpm than
during idling and is, therefore, sufficient to change over the
actuators of the valve control device. According to FIG. 4,
therefore, preferably the first inlet valve P is changed from
maximum operation, P1, to minimum operation, P3, when the engine
speed reaches approximately 1500 and approximately 3000 rpm and
engine torque is light to medium. The zone of this operating mode,
designated by "P3+S2," is reached from the basic state, P1+S2, by
changing one of the inlet valves, P.
[0044] At high engine speed, the second inlet valve S, too, is
adjusted to maximum operation, S1, to provide a maximum of fresh
air. At a predetermined medium engine rotational speed, therefore,
the valve control device changes the second inlet valve S into.
maximum operation S1, that is, the operating mode changes from
P1+S2 to P1+S1. In the hydraulic valve control device described,
this change takes place by pressure upon the inlet camshaft to the
second inlet valve S.
[0045] According to FIG. 4, a distinction is thus made between
three operating modes: the basic state or default operating
condition, P1+S2 (achievable without engine oil pressure), the low
torque operating state P3+S2 (requires engine oil pressure for the
first inlet valve P), and the high torque operating mode P1+S1
(requires engine oil pressure for the second inlet valve S). It is
advantageous that, in each operating mode, the use of engine oil
pressure is necessary at most for one of the inlet valves.
[0046] Furthermore it is particularly advantageous that the
transitions among operating modes is executed by only one of the
inlet valves changing. In general, the transitions between the
various operating modes, P3+S2 P1+S2 P1+S1 require not only a valve
change, but also adjustment in the throttle valve position and
spark timing to ensure a constant torque of the engine through the
change. In the method described, such a transition control is made
easier in that only the changeover is of a single inlet valve.
[0047] In summary, a preferred embodiment of the invention thus
relates to a method for operating a four-stroke internal combustion
engine having two inlet valves, P, S, per cylinder and a
corresponding primary inlet duct 11 and secondary inlet duct 12,
each inlet valve P, S being operated by an independent changeover
device which provides either a higher and longer valve profile or
lower and shorter valve profile, the lower/shorter profile lying
completely within the higher/longer valve profile. The changeover
among valve profiles is achieved using an engine oil pressure above
a threshold value, by means of two independent oil control valves
for the first and second inlet valves P, S of a cylinder bank. In a
basic state, which doesn't relay on oil pressure, the first inlet
valve, P, of each cylinder is operated with a maximum valve stroke,
P1, and the second inlet valve, S, with a minimum valve stroke, S2,
and with a shorter valve opening duration than the intake stroke
duration. In the case of insufficient engine oil pressure for a
changeover, it becomes possible, at low engine speeds, to have full
torque by the provision of a full valve opening duration of the
first inlet valve, while at the same time the combustion properties
are improved by the generation of swirl as a result of the reduced
opening of the second inlet valve.
[0048] The maximum valve stroke in minimum operation, S2, of the
second inlet valve, S, is preferably smaller than the maximum valve
stroke of the first inlet valve, P, in maximum operation, P1, of
the latter, so that the predominant fraction of the fresh air
supply takes place via the first inlet valve, P.
[0049] Under typical operating conditions with heated-up engine
oil, at moderate engine speed and torque, the valve control device
for the first inlet valve, P, is acted upon by pressure, so that
these are changed over to minimum operation, P3, with a short valve
stroke and a short valve opening duration, which are both smaller
than the corresponding sizes in the case of the second inlet valve,
S, in minimum operation, S2, of the latter. The second inlet valve,
S, remains without action upon it by pressure and therefore in
minimum operation, S2. The short valve opening durations of the two
inlet valves, P, S, reduce the pumping losses in low-torque
operation, and the asymmetric valve openings ensure swirls and
turbulence in the cylinder to assist combustion.
[0050] The maximum valve stroke of the first inlet valve, P, in
minimum operation, P3, preferably amounts to one third of the
maximum valve stroke of the second inlet valve, S, in minimum
operation, S2, of the latter, so that, owing to the very much
higher flow resistance of the first inlet valve, P, the predominant
fraction of the inlet air flows through the second inlet valve.
Furthermore, under typical operating conditions of medium engine
speed and medium engine torque, but an increased engine oil
temperature and therefore a reduced engine oil pressure which is
not sufficient for changing over the valve control device, the
control device of the two inlet valves, P, S, operate in the basic
state P1+S2. This makes it possible to have full engine torque and
at the same time is conducive to obtaining the oil pressure in the
rest of the engine.
[0051] During idling or at a low engine speed, the engine oil
pressure is typically not sufficient for changing over the valve
control device, so that it likewise remains in the basic state
P1+S2, ensuring the availability of a full engine torque.
[0052] At medium to high engine rotational speeds, engine oil
pressure is sufficient for changing the valve control device, so
that the actuators for the second inlet valves, S, can be acted
upon by pressure, so that the second inlet valves, S, can be used
in maximum operation (similar to the maximum operation of the first
inlet valve, P). The full torque and power potential of the
internal combustion engine at high rotational speed is thereby
available.
* * * * *