WO2004055345A1

WO2004055345A1 - Method for control of a switching process on an internal combustion engine

Info

Publication number: WO2004055345A1
Application number: PCT/DE2003/003424
Authority: WO
Inventors: Frank Weiss; Hong Zhang
Original assignee: Siemens Aktiengesellschaft
Priority date: 2002-12-16
Filing date: 2003-10-15
Publication date: 2004-07-01
Also published as: DE10258803B4; DE10258803A1

Abstract

According to the invention, a jump in torque on a switching of valve lift in discretely adjustable inlet valves or a switching between stoichiometric and lean operation in an internal combustion engine can be avoided, whereby a device for the pulse charging of the cylinder is operated such that a jump in torque caused by switching process can be avoided or at least reduced by means of a corresponding counteracting change in torque generated by impulse charging.

Description

description

Method for controlling a switching process of an internal combustion engine

The present invention relates to a method for controlling a switching operation in the operation of an internal combustion engine provided with an electronic operating control device.

Internal combustion engines with intake valves, the valves of which can be adjusted, for example, between a small and a large value, that is to say discretely, by an adjusting mechanism, are being used more and more frequently in motor vehicles. B. DE 195 20 117 and MTZ Motortechnische Zeitschrift 61 (2000) 11, pp. 730 to 743. Since the air mass in the cylinders and the amount of fuel injected change suddenly when the valve lift is switched, there is a corresponding jump Change in torque if this is not prevented by a control intervention. One way to prevent such a torque jump is to operate the cylinders immediately after a valve lift switchover, for example from a smaller to a larger value with a reduced efficiency, for example by adjusting the ignition angle, in order to reduce the excess torque that occurs during the valve lift switchover , Such a switchover strategy would, however, have to be bought through increased fuel consumption.

A similar problem occurs when switching between stoichiometric operation and lean operation of an internal combustion engine. Since a gradual transition between these two operating modes is out of the question to avoid increased pollutant emissions, a gradual transition is required. Change in the air mass flow through a corresponding position of the throttle valve, the injected fuel close and the ignition angle suddenly changed to to switch from one operating mode to the other operating mode. This would also lead to a corresponding jump in torque if this were not prevented by a control intervention in the form of a reduction in efficiency, which in turn would result in an increase in plastic consumption and pollutant emissions.

The present invention is based on the object of specifying a method for controlling a corresponding switchover operation in the operation of the internal combustion engine, in which a torque jump is avoided in the most fuel-efficient and low-pollutant manner possible.

The inventive method for solving this problem is defined in claim 1.

In the method according to the invention, a device for pulse charging the cylinders of the internal combustion engine is used to avoid or at least reduce a jump in torque caused by the switching process by a corresponding change in the opposite direction of a torque generated by pulse charging.

Devices for pulse charging, also called MIC (Meta Impuls Charger), are known, cf. z. B. DE 37 37 824 AI and DE 37 37 826 AI. These devices consist of an additional valve arranged in the intake tract, the so-called air cycle valve, which closes the intake cross section of the intake tract for a short time and releases it again. This leads to an increased vacuum in the cylinder for a short time, which creates a pressure wave when the air cycle valve is opened, which causes a corresponding “pulse charging” of the cylinder.

The pulse charging has a very high dynamic, ie it responds immediately to a control intervention and it allows a practically infinite change in the suction Air mass and the torque made available thereby. The method according to the invention takes advantage of this by switching the pulse charging on or off before the switching process and suddenly resetting it to its original state during the switching process. In this way, a deterioration in efficiency can be avoided or at least reduced by changing the ignition angle and / or air / fuel ratio during the changeover process.

The switchover process can be the switchover of the valve stroke of discretely adjustable intake valves or the switchover between stoichiometric and lean operation of the internal combustion engine.

If, for example, the valve lift of the intake valves is switched from a small value to a large value, a torque generated by pulse charging is increased before the valve lift switchover by switching on the device for pulse charging and thereby providing part of the air mass flow through the pulse charging. The device for pulse charging is then switched off at the same time as the valve lift switchover, so that the torque provided by pulse charging is eliminated. This compensates or at least reduces the increase in the air mass flow or torque caused by the valve lift switchover.

If the valve lift of the intake valves is switched from a large to a small value, a torque generated by pulse charging is reduced before the valve lift switchover and simultaneously increased again with the valve lift switchover.

In an analogous manner, when switching between stoichiometric and lean operation of the internal combustion engine, the device for pulse charging is controlled accordingly to compensate for a torque jump caused by the changeover by a corresponding opposite change in the torque provided by the pulse charging. The term "lean operation" is to be understood in its most general form, ie it includes a homogeneously lean operation, a stratified lean operation and also a so-called HCCI operation. HCCI (homogeneous-ous charge compression ignition) means an operating mode , in which the ignition of the air / fuel mixture takes place not by spark ignition, but by controlled auto-ignition, see for example US 6 260 520, US 6 390 054, DE 19927479 and WO 98/10179.

Since with the help of pulse charging the torque can be increased continuously and practically decelerated by up to approx. 50% under otherwise unchanged conditions, the method according to the invention enables a torque-neutral switching process in which an adjustment of the ignition angle and / or the air / fuel ratio to Avoiding a torque jump is avoided completely or at least partially.

In a further embodiment of the invention, it is provided that the method according to the invention for controlling a changeover process is initially carried out for only a first part of the cylinders and, for this purpose, is delayed for a second part of the cylinders. This is possible without any problems in the method according to the invention, since the pulse charging operates in a cylinder-selective manner. The advantage of a step-by-step implementation of the reversing method according to the invention is that only a small change in torque occurs in each case during the changeover processes, which change can be compensated for more easily and more economically by a corresponding control intervention.

Further refinements and modifications of the method according to the invention result from the subclaims. Exemplary embodiments of the invention are explained in more detail with reference to the drawings. It shows:

1 shows a schematic illustration of an internal combustion engine;

2 shows a flowchart for a method for controlling the switching of the valve lift of the intake valves;

3 shows a flowchart for a method for switching the internal combustion engine from stoichiometric operation to leaner operation.

1 schematically shows an internal combustion engine 1 of the Otto type with a plurality of cylinders 2 (only one of which is indicated), an intake tract 3, an exhaust tract 4, an intake valve 5, an exhaust valve (not shown), one Actuator with an adjustment mechanism 6 for the discrete adjustment of the valve lift of the intake valve 5, an injection valve 7 for injecting fuel, a spark plug 8 with an ignition angle adjustment mechanism 9, and a throttle valve 10 arranged in the intake tract 3 in the form of a throttle valve.

Furthermore, a device 11 for pulse charging (MIC) in the form of a so-called air cycle valve is arranged in the intake tract 3 between the throttle valve 10 and the inlet valve 5. As already explained at the beginning, the air cycle valve of the device 11 can be briefly closed and opened again during an intake cycle (that is to say when the inlet valve 5 is open) in order to generate a pulse charge of the cylinder 2 by the pressure pulse caused thereby. For further details, reference is made to the publications DE 3737824 AI and DE 37 37826 AI mentioned at the beginning.

Further devices known to the person skilled in the art for the operation of the internal combustion engine are not shown, since they are not required for an understanding of the present invention.

The operation of internal combustion engine 1 is regulated by an electronic operating control device 12. As indicated by dashed lines, the operating control device 12 is connected to the intake valve or the adjustment mechanism 6, the injection valve 7, the spark plug 8, the ignition angle adjustment mechanism 9, the throttle valve 10 and the device 11 for pulse charging in order to operate them in dependence on To regulate control signals. Since control methods of this type are fundamentally known to the person skilled in the art, this is dealt with only to the extent that it is necessary for an understanding of the method according to the invention for controlling changeover processes.

The invention will first be described with reference to a method for switching the valve lift of the inlet valves 5 by the adjustment mechanism 6 between a small and a large valve lift. Here, reference is made to the flowchart of FIG. 2, which represents the steps for switching from a small to a large valve lift of the inlet valves 5.

The large valve lift of the inlet valves 5 leads, for example, to 50% more filling in the cylinders 2 and thus to a corresponding increase in the torque of 50%. It is assumed that the target torque to be delivered by the internal combustion engine 1 to its clutch (not shown) is 100 Nm before the switching process. If the valve stroke is adjusted without further control intervention, a clutch torque of 150 Nm would result with a large valve stroke. This jump in torque is avoided by the method according to the invention as follows.

If the program determines that you want to switch from the small to the large valve lift (step 13), then next, the device 11 for pulse charging (MIC) is activated and the throttle valve 10 is adjusted in the closing direction (step 14). The throttle valve 10 is expediently set by the operating control device 12 to an opening degree (target value), at which a torque of 100 Nm results after the switching process, when the valve stroke for all cylinders 2 has been adjusted to the large value. The filling of the cylinders 2 and, accordingly, the torque are thus only partially provided by the throttle valve 10 (for example 66.7 Nm), while the remaining part (for example 33.3 Nm) is supplied by the device 11 for pulse charging (MIC) becomes.

In the flow chart of FIG. 2 it is assumed that the target value of the throttle valve is equal to the minimum value of the throttle valve. As soon as the minimum value of the throttle valve is reached (step 15), the intake valves 5 are switched over to the large valve lift. At the same time, the device 11 for pulse charging is switched off. Both processes take place synchronously and without time delay.

The air mass flow additionally provided by the large valve lift leads, as already mentioned, to an increase in torque by 50%, i. that is, in the above numerical example from 66.7 Nm to 100 Nm. The loss of the torque of 33.3 Nm provided by the pulse charging completely compensates for the increase in torque caused by the valve lift adjustment, so that the torque does not change when the valve lift is switched.

If the torque change caused by the valve lift switchover is greater than can be compensated for by pulse charging, the remaining torque jump can be compensated for by a deterioration in the efficiency of the combustion in the cylinders. This is achieved, for example, by adjusting the ignition angle from a basic ignition angle in the direction of a later ignition time. point (a so-called retreat angle) or by adjusting the air / fuel ratio.

If the minimum value of the throttle valve has not yet been reached in step 15, a step 17 asks whether the switchover must take place immediately. If this is not the case, the program returns to a point between steps 14 and 15. However, if the switchover must take place immediately, the program proceeds to step 16.

It goes without saying that the switchover from the large valve lift to the small valve lift takes place in an analogous manner, the device 11 for pulse charging being switched on simultaneously with the valve lift adjustment in order to compensate for the torque drop caused by the valve lift adjustment by a corresponding pulse charging.

An embodiment of the method according to the invention for switching from stoichiometric to lean operation is now explained using the flowchart in FIG. 3.

When switching from stoichiometric to lean operation, the throttle valve 10 is usually first adjusted in the opening direction in order to provide the additional air mass flow required for the lean operation. The changeover to the lean operation then takes place suddenly by the fuel supply and the ignition angle being adjusted accordingly. The resulting torque jump is compensated or at least reduced in principle according to the invention in the same way as was described in connection with the valve lift adjustment.

As soon as the program determines that the switch should be made from stoichiometric to lean operation (step

17), the device 11 for pulse charging, if it was switched on, is switched off and the throttle valve 10 in Opening direction adjusted (step 18). The throttle valve 10 is expediently set here to an opening degree (target value) which is required for optimal lean operation.

When the throttle valve 10 has reached the target value (step 19), the system switches over to the lean operation by adjusting the injection valve 7 and the ignition accordingly. At the same time, the device 7 for pulse charging (MIC) is activated or switched on (step 20).

This compensates for the drop in torque caused by the changeover to the lean operation due to the pulse charging and the additional torque generated thereby.

In this case too, an additional torque compensation can be carried out by adjusting the ignition angle or the air / fuel ratio if the available pulse charging is not sufficient to completely compensate for the torque jump.

Since the pulse charging works in a cylinder-specific manner and thus the method according to the invention for controlling the valve lift switchover or operating mode switchover can also be carried out specifically for the cylinder, the method according to the invention for controlling a switchover process can initially only be carried out for a part of the cylinders and with a time delay for a second part Carry out cylinder. The switchover process is thus to a certain extent divided into two or more switchover processes, so that with each switchover process only a minor change in torque has to be compensated for by a corresponding change in the pulse charge.

Claims

claims

1. A method for controlling a switchover process in the operation of an internal combustion engine (1) provided with an electronic operating control device (12), which comprises a device (11) for pulse charging of the cylinders (2), in which process a torque jump caused by the switchover process a corresponding opposite change in a torque generated by pulse charging is avoided or at least reduced.

2. The method according to claim 1, so that the switchover process involves switching the valve stroke of discretely adjustable inlet valves (5) of the internal combustion engine (1).

3. The method according to claim 2, wherein the valve lift of the inlet valves (5) is switched from a small value to a large value, characterized in that before the valve lift switchover, a torque generated by pulse charging is increased and, at the same time, the valve lift switchover is reduced again ,

4. The method according to claim 2, wherein the valve lift of the inlet valves (5) is switched from a large value to a small value, dadurchgekennzeic hn et that before the valve lift switchover a torque generated by pulse charging is reduced and at the same time increased again with the valve lift switchover becomes.

5. The method according to claim 1, characterized in that it is in the switching process to switch between a stoichiometric and lean operation of the internal combustion engine (1).

6. The method according to claim 5, in which a switchover from stoichiometric operation to lean operation of the internal combustion engine (1) takes place, so that a torque generated by pulse charging is reduced before the switchover process and simultaneously increased again with the switchover process.

7. The method according to claim 5, in which a switchover from lean operation to stoichiometric operation of the internal combustion engine (1) takes place, so that a torque generated by pulse charging is increased before the switching operation and simultaneously reduced again with the switching operation.

8. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that it is first carried out for a first part of the cylinder and delayed for this for a second part of the cylinder.