WO2008071499A1

WO2008071499A1 - Method for controlling an internal combustion engine and internal combustion engine

Info

Publication number: WO2008071499A1
Application number: PCT/EP2007/061762
Authority: WO
Inventors: Gerhard Eser; Kia Hsu; Frank Weiss
Original assignee: Continental Automotive Gmbh
Priority date: 2006-12-12
Filing date: 2007-10-31
Publication date: 2008-06-19
Also published as: DE102006058571B4; DE102006058571A1

Abstract

In order to optimize the fuel consumption and the driving comfort, according to the invention in a method for controlling an internal combustion engine (1), which comprises an intake valve (10), the lift of which is variable, the lift of the intake valve (10) is changed when a switching condition (USB) is fulfilled. The uneven operation (LR) of the internal combustion engine (1), which is caused by the change of the lift, is determined and the switching condition (USB) is changed as a function of the uneven operation (LR).

Description

Method for controlling an internal combustion engine and internal combustion engine

The invention relates to a method for controlling an internal combustion engine with an intake valve whose stroke is variable, and an internal combustion engine with a control device which is designed such that it can perform the method.

Modern internal combustion engines are becoming increasingly stringent in terms of fuel consumption, exhaust performance and comfort. One way to meet these requirements is the use of variable valve controls, by means of which both the stroke and the timing of the intake valves and possibly also the exhaust valves of the internal combustion engine can be changed. The variable valve control makes it possible to control the load of the internal combustion engine in the lower and middle load range essentially via the valve lift and the valve control times. In this case, the valve lift is set correspondingly small, whereas the throttle valve is wide open. This causes a significant reduction in throttle losses during the intake stroke and improved combustion mixture formation. For larger load requirements, however, must be switched in principle to a larger valve lift, the load control is done here mainly by means of the throttle.

Numerous mechanical and electromechanical systems for implementing the variable valve control are known from the prior art. In some mechanical systems, the number of possible strokes that can be achieved is limited to two or three. Basically, the switching between the various valve strokes for the driver should be barely noticeable. At the same time, however, for reasons of saving fuel consumption, it is desirable to carry out the load control with a small valve lift via the camshaft adjustment in the largest possible operating range of the internal combustion engine. This is possible by means of modern, code-based control functions, but their calibration is performed on a few test motors. Due to manufacturing tolerances or series production, however, it can lead to uncomfortable driving behavior when switching between the different valve lifts.

It is therefore an object of the present invention to provide a method and an internal combustion engine, which allow a substantial reduction in fuel consumption while comfortable handling.

This object is achieved by the method and the internal combustion engine according to the independent claims. Advantageous embodiments of the invention are the subject of the dependent claims.

A control method according to claim 1 relates to an internal combustion engine having an intake valve whose stroke is variable. In this case, the lift of the intake valve is changed upon fulfillment of a changeover condition. Furthermore, the running noise of the internal combustion engine, which is caused by the change in the stroke of the intake valve, determined and changed the switching condition as a function of the Lau funruhe.

The idea underlying the invention is to be seen in the switching condition, in the fulfillment of which a change in the stroke of the intake valve takes place and to bring the rough running of the internal combustion engine in a functional context. The running noise of the internal combustion engine can be detected and evaluated with known methods, such as the monitoring of the rotational speed or the indicated torque of the internal combustion engine. As a result of this functional connection, the switchover condition can be changed in such a way as to depend on the rough running of the internal combustion engine, so that system tolerances can be compensated. This is It is possible to exhaust as much as possible for each internal combustion engine individually and over the entire operating time, the operating range in which the load control of the internal combustion engine is carried out over the valve lift, without having to accept sacrifices in terms of comfort.

In an embodiment of the method according to claim 2, in the event that the running noise exceeds a predetermined rough running limit, the switching condition is changed in the sense that the running noise caused by the change of the stroke is reduced, and otherwise the switching condition is changed in the sense of that the uneven running caused by changing the stroke increases.

According to the configuration of claim 3, the switching condition may be based on a load limit value for the load applied to the internal combustion engine, and in the case where the rough running exceeds the rough running limit value, the load limit value is decreased, and otherwise the load limit value is increased.

In a further embodiment of the method according to claim 4, the switching condition based on a speed limit for the speed of the internal combustion engine, wherein in the event that the running noise exceeds the rough running limit, the speed limit is reduced, and otherwise the speed limit is increased.

Due to these refinements, the region in which the load control of the internal combustion engine takes place with a small valve lift via the camshaft adjustment can be extended as far as possible. This is done in independence of series variations as well as of changed environmental conditions, which affect the absorption behavior of the engine. Since the uneven running is usually permanently monitored, it is possible to respond quickly and flexibly to changing circumstances. Because the switching condition on a load limit value and / or based on a speed limit, a very quick and easy adjustment of the switching condition to changed conditions can be made. The load and the speed of the internal combustion engine are particularly well suited as a switching condition due to their ease of measurement and their high relevance to the control of the intake valve.

According to a further embodiment of the method according to claim 5, the switching condition for different operating points of the internal combustion engine is determined individually.

This refinement further increases the flexibility of the valve control. The determination of the operating range, in which the load control of the internal combustion engine is controlled via the valve lift, can be set optimally for each operating point.

The embodiment of the method according to claim 6 is directed to an internal combustion engine in which in addition the timing of the intake valve can be changed. Thus, with a change in the switching condition, the timing of the intake valve is adjusted so that, when the stroke is changed, the difference in the air mass introduced through the intake valve caused thereby is minimal.

In the case of small valve strokes, the air mass introduced via the inlet valve is particularly strongly dependent on the time of the maximum valve lift or on the valve opening and closing times. Basically, at the switching point between a large valve lift and a small valve lift, the difference between the air mass, which is supplied at a large valve lift, and the air mass, which is supplied at a small valve lift, should be as low as possible in order largely to avoid torque jumps and thus uncomfortable driving behavior. Since, according to the method of claim 1, the switching condition is changed, according to the Designs according to claim 6, the timing of the intake valve adjusted accordingly. This ensures that at the switching time, the timing of the intake valve is selected at a small stroke so that a maximum air flow at this stroke is introduced via the inlet valve. In this way, it is ensured that the best possible driving comfort is achieved even during a change in the valve lift, even if the changeover condition changes.

An internal combustion engine according to claim 7 comprises an intake valve, an adjusting mechanism by means of which the lift of the intake valve is variable, a means for determining the running noise of the internal combustion engine, and a control device which is coupled to the adjusting mechanism and the means for determining the rough running. The control device is designed such that the lift of the intake valve is changed upon fulfillment of a changeover condition, a smooth running of the internal combustion engine, which is caused by the change of the stroke, is determined, and the changeover condition is changed depending on the smoothness.

With regard to the advantages of such an internal combustion engine, reference is made to the comments on claim 1.

In the following the invention will be explained in more detail with reference to the attached figures. Show it:

1 shows a schematic representation of an internal combustion engine,

FIG. 2 shows a diagram for illustrating the valve lift changeover and the change of the valve control times,

FIG. 3 shows the dependence of the fresh air mass flow as a function of the valve control times, 4 shows a flow chart of an embodiment of the method according to the invention. characters

5 and 6 are diagrams for explaining the method according to the invention.

1 shows an internal combustion engine 1 is shown schematically. For the sake of clarity, the representation is made much simpler.

The internal combustion engine 1 comprises at least one cylinder 2 and a piston 3 movable up and down in the cylinder 2. The internal combustion engine 1 further comprises an intake tract 4, downstream of an intake opening 5 for sucking in fresh air, an air mass sensor 6, a throttle valve 7 and a suction pipe 8 are arranged. The intake tract 4 opens into a combustion chamber 9 delimited by the cylinder 2 and the piston 3. The fresh air required for combustion is introduced into the combustion chamber 9 via the intake tract 4, the fresh air supply being controlled by opening and closing an inlet valve 10. The internal combustion engine 1 shown here is an internal combustion engine 1 with direct fuel injection, in which the fuel required for the combustion is injected directly into the combustion chamber 9 via an injection valve 11. The combustion exhaust gases are discharged via an exhaust valve 13 into an exhaust gas tract 14 of the internal combustion engine 1 and cleaned by means of an exhaust gas catalytic converter 15 arranged in the exhaust gas tract 14. The inlet valve 10 has an adjusting mechanism 16, by means of which the stroke and the valve control times are variable.

The power transmission to a drive train of a motor vehicle (not shown) takes place via a crankshaft 17 coupled to the piston 3. The internal combustion engine 1 also has a rotational speed sensor 18 for detecting the rotational speed of the engine. Number of crankshaft 17 and a combustion chamber pressure sensor 19 for detecting the combustion pressure in the combustion chamber. 9

The internal combustion engine 1 has a fuel supply system which has a fuel tank 20 and a fuel pump 21 arranged therein. The fuel is supplied by means of the fuel pump 21 via a supply line 22 to a pressure accumulator 23. This is a common pressure accumulator 23, from which the injection valves for a plurality of cylinders 2 are supplied with pressurized fuel. In the supply line 22, a fuel filter 24 and a high pressure pump 25 are further arranged. The high-pressure pump 25 serves to supply the fuel delivered by the fuel pump 21 at relatively low pressure (about 3 bar) to the pressure accumulator 23 at high pressure (typically up to 150 bar). The high-pressure pump 25 is thereby driven by means of its own drive (not shown), for example an electric motor, or by corresponding coupling with the crankshaft 17.

The internal combustion engine 1 is associated with a control device 26 which is connected via signal and data lines with all actuators and sensors of the internal combustion engine 1. In the control device 26, characteristic-based engine control functions (KF1 to KF5) are implemented by software.

Based on the measured values of the sensors and the map-based engine control functions, control signals are sent to the actuators of the internal combustion engine 1 and of the fuel supply system. Specifically, the controller 26 is coupled via data and signal lines to the fuel pump 21, the air mass sensor 6, the throttle valve 7, the spark plug 12, the injection valve 11, the combustion chamber pressure sensor 19, the speed sensor 18 and the intake valve 10 adjusting mechanism 16.

In Figure 2, the operation of the adjustment mechanism 16 for the intake valve 10 in the form of a diagram which the Valve lift over the valve timing represents, explained in more detail. It can be seen from the diagram that the inlet valve 10 can be switched by means of the valve adjusting mechanism between a small stroke H 1 and a large stroke H 2. Furthermore, the valve timing of the intake valve 10 can be varied by means of the valve adjusting mechanism. As the valve timing, the timing at which the intake valve 10 is closed with respect to the upper intake end point OT of the piston will be understood below. In the diagram of Figure 2, the valve lift curves of the intake valve 10 at the small stroke Hl for 3 different valve timing, tl, t2 and t3 are shown. In this case, tl is the time closest to the upper intake dead center OT, whereas the valve control times t2 and t3 are scheduled later.

In the following, the terms "late" and "early" are always to be understood relative to the upper intake dead center OT of the piston.

In FIG. 3, the air mass flow MAF, which is referred to as the load MAF of the internal combustion engine via the intake tract 4 and the intake valve 10, is shown schematically over the valve control time t at a small stroke Hl, constant rotational speed N and constant throttle valve opening angle TPS. It can be seen from the diagram that the fresh air mass supplied to the combustion chamber 9 becomes larger the later the valve control time is. This makes it possible, with a constant throttle valve opening angle TPS, to influence the fresh air mass supplied to the combustion chamber 9 only to a certain extent by the change in the valve control times of the inlet valve 10.

The variable valve control brings in particular in the lower and middle load range of the internal combustion engine 1 consumption advantages. This is due to the fact that the internal combustion engine 1 is operated in the lower and middle load range with a small valve lift Hl of the intake valve 10 and only in the upper load range with the large valve lift H2. By the possibility of limiting the combustion chamber 9 supplied fresh air mass at a small valve lift Hl can in the operating areas in which the internal combustion engine 1 is operated at a small valve lift Hl, the internal combustion engine 1 significantly more de-throttled, ie with more open

Throttle 7 are operated. If the internal combustion engine 1 were operated at the same operating point with a large valve lift H2, the limitation of the air mass supplied to the combustion chamber 9 would have to be effected by the throttle valve 7, which would manifest itself in a significantly smaller throttle valve opening angle TPS and considerably greater throttle losses. The consumption advantage in operation of the internal combustion engine 1 with a small valve lift Hl compared to operation with a large valve lift H2 is therefore justified by the fact that due to the smaller throttle effect on the throttle valve 7 on the inlet side a significantly higher pressure at the inlet valve 10 is present than in a strong throttling in the Case of operation of the internal combustion engine 1 with the large valve lift H2. In addition to the lower intake losses, the smaller opening cross-section at the inlet valve 10 has a positive effect on mixture formation with a small valve lift H1.

However, since the fresh air mass supplied to the combustion chamber 9 is limited at a small valve lift H 1, it is necessary to switch over to operation of the internal combustion engine 1 with a large valve lift H 2 at a higher load requirement. However, due to the fuel economy potential during operation of the internal combustion engine 1 with a small valve lift H1, it is desirable to extend this operating range as far as possible. The switching condition, which determines the switching time between the small valve lift Hl and the large valve lift H2, is stored in the control device 26 of the internal combustion engine 1 in the form of a characteristic map. The switching condition is dependent on the operating point of the internal combustion engine 1, i. from the applied load, which flows through the incoming

Fresh air mass MAF is represented, and the engine speed N. Such a map is shown schematically in FIG.

As already explained above, when the switching condition is met, it is necessary to switch over between the small valve lift H 1 and the large valve lift H 2. Furthermore, it has already been mentioned that the combustion chamber 9 is supplied with the same throttle valve opening angle TPS and large valve lift H2 a significantly larger air mass than at a small valve lift Hl. In a switching between the large and the small

Valve lift results in the problem that the combustion chamber 9 supplied air mass changes abruptly. Although this change in the air mass over the opening angle of the throttle valve 7 is corrected, but this Korrekturmaß- would take effect due to the flow dynamics in the intake manifold 8 only with noticeable delay. Without additional measures, there would thus be a sudden change in the torque produced by the engine, which has a negative effect on driveability and comfort. Therefore, it is necessary to temporarily make a Zündwinkeleingriff when switching between the small valve lift Hl and the large valve lift H2 until the correction via the throttle valve 7 takes effect.

Basically, the valve lift switching is controlled by means of the control device 26. All manipulated variables which are necessary for the changeover gear, such as, for example, the setpoint values for the adjusting mechanism 16 of the intake valve 10, the adaptation of the throttle valve opening angle TPS and the ignition angle intervention, are implemented in the control device 26 by software. However, the control functions and maps are usually parameterized using only a small number of test motors. This leads to the fact that due to the series scattering or manufacturing tolerances in the production or due to deviating environmental conditions in which the

Internal combustion engines 1 are operated, despite the most careful calibration of the software in the valve lift to noticeable torque jumps and can lead to an uncomfortable driving behavior.

On the other hand, however, it is also possible for internal combustion engines 1 to be able to be operated in a further operating range with a smaller valve lift H 1 than the test engines due to the segregation. In this case, the possible savings potential of these internal combustion engines 1 would not be fully exploited on account of the control unit 26 being charged.

Against this background, the idea underlying the present invention and a concrete exemplary embodiment will now be explained in more detail with reference to FIGS. 4 to 6. The embodiment of a method for controlling a

Internal combustion engine 1 is shown in Figure 4 in the form of a flow chart.

After starting the process in step 400, it is checked in step 401 whether the switching condition USB is satisfied. As mentioned above, the switching condition USB is met, for example, when a predetermined load limit value and / or a speed limit value are exceeded or fallen short of. Step 401 is repeated until the switchover condition USB is fulfilled. In this case, in step 402, a switching between the small valve lift Hl and the large valve lift H2 is performed. In step 403, a rough running value LR of the internal combustion engine 1 is determined. The rough-running value LR can be determined by evaluating the signal of the rotational speed sensor 18 and / or the signal of the combustion chamber pressure sensor 19. By evaluating these signals, sudden changes in the torque generated in a combustion chamber 9 can be detected and quantified during or due to the valve lift reversal. The rough-running value LR thus represents a measure of the uneven running of the internal combustion engine 1 caused by the valve lift reversal circuit. In step 404, the rough-running value LR _is compared with a rough running limit value LR _THRES . Is the running value LR RESIZE ^¬ SSER than the predetermined uneven running threshold _THRE LR s, so the uneven running counter Z is incremented in step 406 by a certain amount. Otherwise, the running noise counter Z is decremented by a certain amount in step 405. Advantageously, the running noise counter Z is decremented by a larger amount than incremented.

In step 407, a correction factor F is then determined as a function of the unevenness counter Z, the speed N present at the time of changeover, and the load MAF. This correction factor F is then used in step 408 to change the switching condition USB, which is stored in the form of a characteristic diagram (see FIG. 5) as a function of the load MAF and the rotational speed N of the internal combustion engine 1, based on the determined uneven running.

The change in the switching condition USB is carried out according to the principle shown schematically in Figure 5.

With an increasing value of the rough-running counter Z, that is, with a rough-running value LR of greater than the limp-home limit value LR _{THRES /} , the switching condition USB in becomes

Direction of a smaller load MAF and / or shifted in the direction of lower speeds N of the internal combustion engine 1. This is shown in Figure 5 by the dashed line a. This means that the switchover between the large valve lift H2 and the small valve lift Hl is already carried out at a lower load MAF and lower rotational speed. In order to display a lower load MAF, the throttle valve opening angle TPS is also smaller when the internal combustion engine 1 is operating with the small valve lift Hl than at higher loads. When switching over to the large valve lift H2, the difference between the valve lift Hl and the low valve lift Hl is therefore small large valve lift H2 supplied fresh air mass and thus lower between the torque generated by the internal combustion engine 1. A compensation of the sudden torque excess when switching from the small valve lift Hl to the large valve lift Hl can thus be more reliably compensated with a corresponding Zündwinkeleingriff. The same applies in analogous form for switching from the large valve lift H2 to the small valve lift Hl.

As the value of the running rest counter Z becomes smaller, that is, in the case where the rough running value LR is less than or equal to the rough running limit LR _THRES , the switching condition USB is shifted toward a larger load MAF and / or a higher speed N of the engine 1, as it is is shown by the dashed line b in Fig. 5. This is possible, for example, in internal combustion engines 1, in which a larger fresh air mass flow can be supplied due to the series dispersion and manufacturing tolerances compared to the test specimens with the same throttle position and maximum retardation of the valve timing. Another reason for such a shift may also be the change in environmental conditions, such as the ambient pressure and the ambient temperature, which have an influence on the aspirated fresh air mass. Operation with a small valve lift Hl can be extended in these cases without impairing ride comfort.

It should be noted that the switching condition USB can be changed either for different operating points individually or as a whole for the entire operating range.

After changing the switching condition USB in step 408, in step 409, the valve timing t is adjusted to the change of the switching condition USB such that, when the stroke is changed, the difference in the air mass MAF introduced through the intake valve 10 is minimal. The valve timing is, as shown in FIG. shown stored in the control device 26 as a map in dependence on an air mass desired value MAF_SP. With an extension or narrowing of the switching condition USB, as shown in FIG. 5, the switching also takes place to different air mass desired values MAF_SP. In FIG. 6, the solid line corresponds to the valve timing, which is optimized for the switching condition USB shown in FIG. 5 with a solid line. At these valve timing, a maximum fresh air mass is introduced into the combustion chamber 9 at a given throttle valve opening angle. In this context, reference is again made to Figure 3, in which the supplied air mass is shown in dependence on the valve timing. In the event of a change in the switching condition USB, the valve control times are therefore also adapted in accordance with step 409 such that correspondingly optimized valve control times of the intake valve are predetermined even at the changeover time in accordance with the changed switchover condition USB. This ensures that the fresh air mass supplied to the combustion chamber 9 via the inlet valve 10 at the small valve lift H2 is maximal even when the switchover condition USB is changed, so that the torque jump when switching to the large valve lift H2 or vice versa is minimal. As a result, uncomfortable operating behavior due to undesired torque jumps can be reliably avoided. The

Adjustment of the valve timing is done by a dynamic change of the map for the valve timing under consideration of the factor F, by means of which even the switching condition USB is changed dynamically. By considering the same factor, a correspondingly uniform adaptation is ensured.

In step 410, the process has completed a full run and may be terminated or restarted here. Reference / list of terms:

1 internal combustion engine

2 cylinders

3 pistons

4 intake tract

5 intake opening

6 air mass sensor

7 throttle

8 intake manifold

9 combustion chamber

10 inlet valve

11 injection valve

12 spark plug

13 exhaust valve

14 exhaust tract

15 catalytic converter

16 adjustment mechanism

17 crankshaft

18 speed sensor

19 combustion chamber pressure sensor

20 fuel tank

21 fuel pump

22 supply line

23 accumulator

24 fuel filters

25 high pressure pump

26 control device

MAF air mass flow / load

N speed

MAF SP Setpoint of air mass flow

LR running noise value

LRTHRE _S Smoothing limit

USB switching condition

TPS throttle opening angle

Claims

claims

1. A method for controlling an internal combustion engine (1) with an inlet valve (10) whose stroke is variable, wherein the stroke of the inlet valve (10) is changed upon fulfillment of a changeover condition (USB), the running noise (LR) of the internal combustion engine (1) , which is caused by the change of the stroke, is determined, the changeover condition (USB) is changed depending on the rough running (LR).

2. The method of claim 1, wherein in the case that the rough running (LR) is a predetermined rough running limit

(LRTHRE _S ), the switching condition (USB) is changed in the sense that the running noise (LR) caused by the change of the stroke is reduced, and otherwise the switching condition (USB) is changed in the sense that the Incident (LR) caused by the change in the stroke increased.

3. The method of claim 2, wherein the switching condition

(USB) is based on a load limit value for the load applied to the internal combustion engine 1, and in the case that the rough running (LR) is the rough running limit value

(LRTHRE _S ), the load limit is lowered, and otherwise the load limit is increased.

4. The method of claim 2, wherein the switching condition (USB) is based on a speed limit for the number of revolutions (N) of the internal combustion engine (1), and in the case that the uneven running (LR) exceeds the rough running limit (LRTHRE _S ), the speed limit is reduced, and otherwise the speed limit is increased.

5. The method of claim 1, wherein the switching condition (USB) for various operating points of the internal combustion engine (1) is determined individually.

6. The method of claim 1, wherein additionally the control times (t) of the intake valve (10) are variable and at a change of the switching condition (USB), the timing (t) of the intake valve (10) are adapted such that in a change of the stroke causing the difference in the air mass introduced via the inlet valve (10) is minimal.

7. internal combustion engine (1) with an inlet valve (10), - an adjusting mechanism (16) by means of which the lift of the inlet valve (10) is variable, a means for determining the rough running (LR) of the internal combustion engine (1), and a control device (26), which is coupled to the Verstellme- mechanism (16) and the means for determining the uneven running (LR), and which is designed such that o the stroke of the intake valve (10) upon fulfillment of a

Changeover condition (USB) is changed, o a running noise (LR) of the internal combustion engine (1), which is caused by the change of the stroke, is determined, o the switching condition (USB) depending on the

Running Rest (LR) is changed.