CN118019900A

CN118019900A - Method for operating an internal combustion engine and corresponding internal combustion engine

Info

Publication number: CN118019900A
Application number: CN202280063559.1A
Authority: CN
Inventors: C·约布斯特; A·兰格
Original assignee: Audi AG
Current assignee: Audi AG
Priority date: 2021-09-21
Filing date: 2022-09-21
Publication date: 2024-05-10
Also published as: DE102021124416A1; WO2023046753A1; EP4405572A1

Abstract

The invention relates to a method for operating an internal combustion engine (1) having a cylinder (2), a crankshaft (3) and a camshaft (4, 5) which is drivingly coupled to the crankshaft (3) by means of a camshaft adjuster (11, 12), wherein the camshaft (4, 5) actuates a gas exchange valve (8, 9) of the cylinder (2) at least for a short time. It is provided that the camshaft adjuster (11, 12) is actuated at least briefly to change the length of the opening period of the ventilation door (8, 9). The invention also relates to an internal combustion engine (1).

Description

Method for operating an internal combustion engine and corresponding internal combustion engine

Technical Field

The invention relates to a method for operating an internal combustion engine having a cylinder, a crankshaft, and a camshaft which is drivingly coupled to the crankshaft by a camshaft adjuster, wherein the camshaft actuates a gas exchange valve (intake valve, exhaust valve) of the cylinder at least briefly. The invention also relates to an internal combustion engine.

Background

For example, document EP 1 747 366 B1 is known from the prior art. This document describes a method for operating an internal combustion engine having at least two cylinders which are provided with an intake valve and an exhaust valve, respectively. In order to increase the fresh gas filling of the cylinders during the ventilation of at least one cylinder, it is provided here that the exhaust-gas operating time and the phase of overlap of the intake-gas operating time and the exhaust-gas operating time are selected, wherein the exhaust valve is closed before the pressure on the exhaust side exceeds the pressure on the intake side.

Furthermore, DE 10 2017 200 824 A1 discloses a method for operating an internal combustion engine with a valve adjustment function, comprising the following steps: operating the internal combustion engine with a gas exchange valve operating characteristic that is dependent on a correction variable that determines a phase length of an opening phase of the gas exchange valve; switching the operating characteristics of the gas exchange valve; the correction variable is adjusted in accordance with the rotational speed profile before and after the operating characteristic of the gas exchange valve is switched.

Disclosure of Invention

The object of the present invention is to provide a method for operating an internal combustion engine, which has advantages over known methods, in particular in that a variable operation of the internal combustion engine can be achieved with high efficiency.

According to the invention, this is achieved by a method for operating an internal combustion engine having the features of claim 1. It is provided here that the camshaft adjuster is actuated at least briefly in order to change the length of the opening period of the gas exchange valve.

Advantageous embodiments and suitable developments of the invention are specified in the dependent claims.

The method is used for operating an internal combustion engine. The internal combustion engine is for example a component of a drive system for a motor vehicle, but can obviously also be present independently of the motor vehicle. Internal combustion engines are used mainly to provide a drive torque, which is intended for example to drive a motor vehicle. An internal combustion engine has at least a cylinder, a crankshaft, and a camshaft. A movable piston of the internal combustion engine is arranged in the cylinder, which piston is drivingly connected to the crankshaft, in particular by at least one connecting rod. The piston encloses a combustion chamber together with a cylinder wall of the cylinder and a cylinder head of the cylinder.

The gas exchange valve is coupled in flow communication with the cylinder, in particular with the combustion chamber. The gas exchange valve may be designed as an inlet valve or an exhaust valve. In any case, a flow-related connection exists between the environment outside the internal combustion engine and the combustion chamber, wherein the flow connection is established when the gas exchange valve is partially opened and is interrupted when the gas exchange valve is closed.

In the case of a gas exchange valve designed as an intake valve, the intake valve serves to introduce fresh gas into the combustion chamber. In this connection, fresh gas can flow from the fresh gas duct of the internal combustion engine into the combustion chamber when the gas exchange valve is at least partially opened. When closing the gas exchange valve, the flow-wise connection between the fresh gas duct and the combustion chamber is interrupted.

If the gas exchange gate is designed as an exhaust valve, the gas exchange gate is arranged in flow-through manner between the combustion chamber and the exhaust tract of the internal combustion engine. When the gas exchange valve is at least partially opened, exhaust gas can flow from the combustion chamber in the direction of the exhaust passage and then be led out of the internal combustion engine. When closing the gas exchange valve, the flow-wise connection between the combustion chamber and the exhaust tract is interrupted again.

The gas exchange valve is actuated by means of a camshaft. The camshaft has at least one cam which actuates the gas exchange valve at least briefly. The valve is opened or remains open as long as the cam acts on the valve. If the cam is far from the gas exchange valve, the gas exchange valve is closed. The cam is designed such that the gas exchange door starts to open at a first angular position of the camshaft and closes at a second angular position immediately after the first angular position of the camshaft.

The camshaft is driven by the crankshaft. For this purpose, the camshaft is connected to the crankshaft in terms of drive technology, in particular via a camshaft adjuster. There is a definite speed ratio between the crankshaft and the camshaft, in particular typically 2:1. this means that the rotational speed of the crankshaft is twice the rotational speed of the camshaft. The phase of the camshaft relative to the crankshaft can be set or changed by means of a camshaft adjuster. At a given rotational position of the crankshaft, the rotational position of the camshaft can thus be adjusted within a defined rotational angle range by means of the camshaft adjuster.

The control time of the gas exchange valve depends on the design of the camshaft and the cams. The control times are understood to mean, in particular, the opening times and the closing times, wherein the gas exchange valve is opened exactly at the opening times and closed exactly at the closing times, and is opened continuously at least partially between the opening times and the closing times. In this connection, the opening period over which the gas exchange door opens and extends from the opening time to the closing time is largely dependent on the rotational speed of the camshaft. The opening time, the closing time and the duration or length of the opening period are preferably given with reference to the rotational angle position of the crankshaft, i.e. in degrees KW.

The control time can be adjusted by means of a camshaft adjuster with reference to the rotational position of the crankshaft, wherein only a movement of the control time is possible. The length of the open period remains the same throughout. This means that the control times of the gas exchange valves can be determined when designing the internal combustion engine and can then only be moved together, in particular by correspondingly actuating the camshaft adjuster. Here, the adjustment of the opening moment is also always followed by the adjustment of the closing moment, so that the length of the opening period of the gas exchange valve cannot be adjusted. However, this enables a significant increase in the efficiency of the internal combustion engine, in particular during part-load operation of the internal combustion engine.

For this reason, it is provided that the camshaft adjuster is actuated such that the length of the opening period of the gas exchange valve is changed, in particular regularly, i.e. during a continuous operating cycle of the internal combustion engine. For example, the camshaft adjuster is actuated in such a way that the opening period is lengthened or shortened. Additionally, a camshaft adjuster can be used to advance or retard the opening of the gas exchange valve and/or to advance or retard the closing of the gas exchange valve, so that the opening and/or closing times are also adjusted.

The camshaft adjuster is therefore not used, as is the case with the known methods for operating internal combustion engines, only for shifting the opening period, but rather for changing the duration or length of the opening period. For this purpose, camshaft adjusters are considered which can correspondingly adjust the phase between the camshaft and the crankshaft, in particular for a plurality of times for each operating cycle of the internal combustion engine.

The camshaft adjuster preferably operates electrically, and thus has, for example, an electric motor by means of which the phase can be adjusted. Particularly preferably, the motor is designed as a servomotor. In the case of a camshaft adjuster, the opening period of the gas exchange valve is preferably set in such a way that the gas exchange losses of the internal combustion engine are reduced and/or the fresh gas filling of the cylinders is increased in relation to the manner in which the camshaft adjuster is not actuated to change the length of the opening period. Particularly efficient operation of the internal combustion engine can thereby be performed.

The camshaft adjuster is preferably designed on the one hand for rapid adjustment of the phase between the crankshaft and the camshaft and on the other hand for determination of the phase with great accuracy. For this purpose, for example, corresponding sensors are provided. Preferably, the camshaft adjuster is actuated by means of a controller, which sets the actual phase that is actually present between the crankshaft and the camshaft to a defined target phase. The actual phase is adjusted to the target phase, for example. The actual phase is measured in particular by means of the mentioned sensor.

The controller is arranged and designed to determine a target length of the opening period of the gas exchange valve at which maximum efficiency is achieved for the current operating point of the internal combustion engine. The camshaft adjuster is then actuated such that the length of the opening period of the gas exchange valve corresponds to the target length. Thus, the high efficiency of the internal combustion engine is achieved without additional and complicated measures (e.g., variable valve mechanisms, etc.).

The invention further provides that the gas exchange door is actuated to open in a defined and identical first angular position of the camshaft for the gas exchange door and to close in a defined and identical second angular position of the camshaft for the gas exchange door. For example, the gas exchange valve starts to open in a first angular position and closes exactly again in a second angular position. The first rotational position and the second rotational position are rotational positions of the camshaft and are not changeable. The internal combustion engine is therefore designed such that the gas exchange valve is always open in the same angular position range of the camshaft, which extends from the first angular position to the second angular position. This means that the internal combustion engine does not take complicated measures, for example, to adjust the gas exchange valve, in order to adjust the opening period based on the rotational angle position of the camshaft. Instead, the rotational position thereof relative to the camshaft is always the same.

In a further development of the invention, the camshaft adjuster is actuated when the actual rotational position of the camshaft is located before the first rotational position, such that the actual rotational position of the camshaft is adjusted in the direction of the first rotational position, in particular to a rotational position between the first rotational position and the second rotational position, so that the gas exchange valve is opened. The opening period of the gas exchange valve is only started when the actual rotational angle position reaches the first rotational angle position. However, the actual angular position can be adjusted by means of the camshaft adjuster in such a way that the gas exchange door opens in advance.

For this purpose, the actual rotational angle position is adjusted in the direction that causes the gas exchange valve to open more quickly, i.e. in the direction of the first rotational angle position or in the direction of the second rotational angle position following the first rotational angle position, past the first rotational angle position, if the actual rotational angle position of the camshaft is located before the first rotational angle position. The actual rotational position of the camshaft is preferably adjusted by means of the camshaft adjuster from the actual rotational position preceding the first rotational position such that it then corresponds exactly to the first rotational position or is located between the first rotational position and the second rotational position. Accordingly, the ventilation door opens earlier than if there were no such adjustment of the actual rotational angle.

In a further development of the invention, the camshaft adjuster is actuated in such a way that the actual rotational position of the camshaft is adjusted or kept constant in a direction opposite to the first rotational position when the actual rotational position of the camshaft is located before or corresponds to the first rotational position, so that the gas exchange door remains closed. In other words, the actual angular position of the camshaft is adjusted by means of the camshaft adjuster, so that the gas exchange door remains closed longer than if the actual angular position were not adjusted. Accordingly, when the camshaft adjuster is actuated in this way, the actual rotational position of the camshaft is either kept constant or is adjusted in a direction away from the first rotational position. This also makes it possible to simply change the opening period of the change valve by means of the camshaft adjuster.

In a further development of the invention, the camshaft adjuster is actuated such that the actual rotational position of the camshaft is adjusted or kept constant in the direction of the first rotational position, so that the ventilation door is kept open, when the actual rotational position of the camshaft is located after the first rotational position and before the second rotational position. The gas exchange door is opened if the actual rotational position of the camshaft is between the first rotational position and the second rotational position. In order to keep the gas exchange valve open, in particular longer than if the actual rotational position of the camshaft is not adjusted, the actual rotational position of the camshaft is actuated by means of the camshaft adjuster in the direction of the first rotational position, i.e. in the direction away from the second rotational position. Alternatively, the camshaft adjuster can of course be actuated again in order to keep the actual rotational angle position constantly between the first rotational angle position and the second rotational angle position. The opening period of the change valve is again changed in a simple manner by means of a camshaft adjuster.

In a further development of the invention, the camshaft adjuster is actuated such that the actual rotational position of the camshaft is adjusted in the direction of the second rotational position or beyond the second rotational position, so that the gas exchange door is closed, when the actual rotational position of the camshaft is located after the first rotational position and before the second rotational position. By the described approach, the gas exchange valve may close earlier than if the actual angular position of the camshaft was not adjusted. In the case of an actual rotational position of the camshaft between the first rotational position and the second rotational position, the gas exchange door is opened. In order to close the gas exchange valve or at least to close the gas exchange valve earlier, the camshaft adjuster is now operated in such a way that the actual rotational position of the camshaft changes in the direction of the second rotational position or beyond the latter. This means that a faster closing of the gas exchange valve is again effected only by means of the camshaft adjuster. This results in a shorter opening period of the gas exchange valve, in particular.

In one development of the invention, the actual rotational angle position is adjusted with a defined time gradient, which is selected as a function of the angular speed of the crankshaft. The higher the angular velocity of the crankshaft, the substantially higher the angular velocity of the camshaft. Accordingly, the actual rotational angle position must be adjusted at a speed which matches the angular speed of the crankshaft, in particular if the actual rotational angle position of the camshaft is adjusted by means of the camshaft adjuster, while the actual rotational angle position is between the first rotational angle position and the second rotational angle position. In this way, for example, the ventilation door can be held open in a targeted manner. The described procedure makes it possible to achieve an adjusted operation of the camshaft adjuster, so that its load is kept as small as possible and only increases at high rotational speeds of the crankshaft. Excessive wear of the camshaft adjuster is thereby avoided.

In one development of the invention, the camshaft adjuster is actuated after the closing of the gas exchange door in order to change the actual rotational angle position contrary to the previous adjustment, in particular to adjust it with the same rotational angle difference. The phase between the crankshaft and the camshaft changes based on the initial value due to the adjustment of the actual rotational angle position. The opening period of the ventilation door is changed by adjustment, in particular in the manner already described.

Since the phase changes thus occur, it is expedient or even necessary to set the phase back to its initial value. This takes place when closing the gas exchange valve, in particular in such a way that the gas exchange valve is not actuated, for example because the actual angle of rotation is adjusted too quickly. In order to set the phase to the initial value, it is preferable to change the actual rotational angle position by the same rotational angle difference as the rotational angle difference previously adjusted to change the length of the opening period of the change valve. This is particularly interesting if the internal combustion engine has a plurality of cylinders.

The improvement of the invention provides that the actual rotational angle position of the camshaft is adjusted at least once in the direction of the larger actual rotational angle position and at least once in the direction of the smaller actual rotational angle position, in particular with the same rotational angle difference, in a working cycle of the internal combustion engine. The operating cycle of an internal combustion engine includes all of the strokes, and thus, in the case of a four-stroke internal combustion engine, includes an intake stroke, a compression stroke, a power stroke, and an exhaust stroke.

In the working cycle, the actual rotational angle position of the camshaft is changed a plurality of times by means of the camshaft adjuster, i.e. once in the direction of the larger actual rotational angle position and once in the direction of the smaller actual rotational angle position, wherein the sequence is insignificant in this case. The adjustment is preferably performed with the same rotation angle difference, so that the adjustment of the actual rotation angle position is performed once and the resetting of the actual rotation angle position is performed once. It is particularly preferred to carry out this procedure for a plurality of successive operating cycles of the internal combustion engine, in particular for all operating cycles of the internal combustion engine. Thereby, a regular adjustment of the actual rotational angle position of the camshaft is achieved.

In one development of the invention, the actual rotational angle position of the camshaft is adjusted several times in the direction of a larger actual rotational angle position and likewise several times in the direction of a smaller actual rotational angle position within the operating cycle of the internal combustion engine, in particular with the same rotational angle difference, so that a pendulum-type operation of the camshaft adjuster is present. In this connection, the actual angular position is adjusted back and forth by means of the camshaft adjuster during each working cycle.

It is important here that the return of the actual rotational angle position is carried out after each adjustment, wherein for example the adjustment takes place in the direction of a larger actual rotational angle position and the return takes place in the direction of a smaller actual rotational angle position, and vice versa. The adjustment and the return are preferably carried out with the same angle difference. The pendulum operation of the camshaft adjuster is thereby carried out, so that the corresponding characteristics of the electric motor are effectively utilized.

In one development of the invention, the cylinder is a first cylinder and the gas exchange valve is a first gas exchange valve, the internal combustion engine further has a second cylinder with a second gas exchange valve, which is actuated at least briefly by the camshaft, wherein the second gas exchange valve is actuated to open in a defined and identical first angular position of the camshaft for the second gas exchange valve, and the second gas exchange valve is actuated to close in a defined and identical second angular position of the camshaft for the second gas exchange valve.

The internal combustion engine thus has a plurality of cylinders, for which the described method is implemented accordingly. Of course, the internal combustion engine may have any number of cylinders. In this regard, embodiments in this specification may be similarly applied to each of a plurality of cylinders of an internal combustion engine. The first angular position of the camshaft for the second gas exchange valve differs from the first angular position of the camshaft for the first gas exchange valve. The same applies to the second angular position. In this regard, the first and second gas exchange valves are sequentially operated by the camshaft to open.

The camshaft is designed such that the first rotational position for the second gas exchange valve follows the second rotational position for the first gas exchange valve, so that the second gas exchange valve is actuated to open only when the first gas exchange valve is closed again.

The improvement of the invention provides that the camshaft adjuster is operated such that the times during which the first and second gas exchange valves are opened are identical with respect to the rotational angle position of the crankshaft, wherein the ratio between the opening duration of the first gas exchange valve and the opening duration of the second gas exchange valve is kept constant, in particular for at least several successive operating cycles of the internal combustion engine. Provision is made for the camshaft adjuster to be actuated in order to change the opening period of each of the change valves.

Thus, for example, with the aid of a camshaft adjuster for each of the gas exchange valves, the actual rotational angle position is adjusted in the direction of the first rotational angle position by means of the camshaft adjuster when the actual rotational angle position is between the respective first rotational angle position and the respective second rotational angle position, so that the gas exchange valve remains open for a longer period. After the closing of the respective gas exchange valve, the actual rotational angle position is reset such that the respective other gas exchange valve is not affected, in particular no later opening of the gas exchange valve takes place.

The invention also relates to an internal combustion engine, in particular for carrying out the method according to the embodiments in the present description, wherein the internal combustion engine has a cylinder, a crankshaft, and a camshaft which is coupled to the crankshaft by way of a camshaft adjuster in terms of drive, the camshaft actuating a gas exchange door of the cylinder at least briefly. In this case, it is provided that the internal combustion engine is configured and designed to operate the camshaft adjuster at least briefly in order to change the length of the opening period of the gas exchange valve. The advantages of this design of an internal combustion engine and of such a method have been pointed out. The internal combustion engine and the method for its operation may be modified according to embodiments in the present description, to which reference is made in this connection.

Features and feature combinations described in the description, in particular those described in the following description of the figures and/or shown in the figures, can be used not only in the respectively given combination but also in other combinations or alone without departing from the scope of the invention. Thus, embodiments that are not explicitly shown or described in the description and/or the figures, but which are known or derived from the described embodiments, are likewise to be considered covered by the invention.

Drawings

Without limiting the invention, the invention is further illustrated by the examples shown in the drawings. The sole figure herein is as follows:

Fig. 1 shows a schematic cross-section of an internal combustion engine.

Detailed Description

Fig. 1 shows a schematic diagram of an internal combustion engine 1 having a cylinder 2, a crankshaft 3, and a camshaft 4 and a camshaft 5. The piston 6 is arranged in the cylinder 2 in a longitudinally movable manner and is coupled to the crankshaft 3, in particular to a crank pin of the crankshaft 3, by means of a connecting rod 7. The crankshaft 3 converts the linear motion of the piston 6 into rotational motion.

The camshafts 4, 5 serve to actuate gas exchange valves 8, 9 assigned to the cylinders 2. The gas exchange valves 8, 9 are in particular connected in flow connection with a combustion chamber 10, which is delimited jointly by the cylinder wall 2, the cylinder head and the piston 6. Illustratively, the gas exchange gate 8 acts as an intake valve and the gas exchange gate 9 acts as an exhaust valve. Accordingly, in terms of flow technology, the combustion chamber 10 is connected via a gas exchange valve 8 to the intake tract of the internal combustion engine 1 and via a gas exchange valve 9 to the exhaust tract, which intake tract and exhaust tract are not shown further here.

The camshaft 4 may also be referred to as an intake camshaft, and the camshaft 5 may be referred to as an exhaust camshaft, respectively. The camshafts 4, 5 are each connected to the crankshaft 3 in terms of drive technology and are driven by the crankshaft. Each of the camshafts 4, 5 is in each case connected in terms of drive technology by a camshaft adjuster 11, 12, which is only schematically shown here. The respective phase between the camshafts 4, 5 and the crankshaft 3 can be adjusted by means of the camshaft adjusters 11, 12.

It is now provided that at least one of the camshaft adjusters 11, 12 is used or actuated to change the opening period of the respective gas exchange valve 8, 9. For example, the camshaft adjusters 11 and 12 are actuated in such a way that the respective ventilation door 8, 9 remains open for a longer period of time. In this way, particularly efficient operation of the internal combustion engine 1 can be achieved using the camshaft adjusters 11, 12.

List of reference numerals

1. Internal combustion engine

2. Cylinder

3. Crankshaft

4. Cam shaft

5. Cam shaft

6. Piston

7. Connecting rod

8. Air exchanging valve

9. Air exchanging valve

10. Combustion chamber

11. Camshaft adjuster

12. Camshaft adjuster

Claims

1. Method for operating an internal combustion engine (1) having a cylinder (2), a crankshaft (3) and a camshaft (4, 5) which is drivingly coupled to the crankshaft (3) by a camshaft adjuster (11, 12), the camshaft (4, 5) actuating a gas exchange valve (8, 9) of the cylinder (2) at least for a short time, characterized in that the camshaft adjuster (11, 12) is actuated at least for a short time to change the length of the opening period of the gas exchange valve (8, 9).

2. Method according to claim 1, characterized in that in a defined and identical first angular position of the camshaft (4, 5) for the gas exchange valve (8, 9), the gas exchange valve (8, 9) is actuated open, and in a defined and identical second angular position of the camshaft (4, 5) for the gas exchange valve (8, 9), the gas exchange valve (8, 9) is actuated closed.

3. Method according to any of the preceding claims, characterized in that, when the actual rotational position of the camshaft (4, 5) is located before the first rotational position, the camshaft adjuster (11, 12) is operated such that the actual rotational position of the camshaft (4, 5) is adjusted in the direction of the first rotational position, so that the gas exchange door (8, 9) is opened.

4. Method according to any of the preceding claims, characterized in that, when the actual rotational position of the camshaft (4, 5) is located before or corresponds to the first rotational position, the camshaft adjuster (11, 12) is operated such that the actual rotational position of the camshaft (4, 5) is adjusted or kept constant in a direction opposite to the first rotational position, so that the gas exchange valve (8, 9) is kept closed.

5. Method according to any of the preceding claims, characterized in that, when the actual rotational position of the camshaft (4, 5) is located after the first rotational position and before the second rotational position, the camshaft adjuster (11, 12) is operated such that the actual rotational position of the camshaft (4, 5) is adjusted or kept constant in the direction of the first rotational position, so that the ventilation door is kept open.

6. Method according to any of the preceding claims, characterized in that, when the actual rotational position of the camshaft (4, 5) is located after the first rotational position and before the second rotational position, the camshaft adjuster (11, 12) is operated such that the actual rotational position of the camshaft (4, 5) is adjusted towards the second rotational position or beyond the second rotational position, so that the gas exchange valve (8, 9) is closed.

7. Method according to any of the preceding claims, characterized in that after closing the gas exchange valves (8, 9), the camshaft adjusters (11, 12) are actuated to change the actual angular position in opposition to the previous adjustment.

8. Method according to any of the preceding claims, characterized in that the cylinder (2) is a first cylinder and the gas exchange valve (8, 9) is a first gas exchange valve, the internal combustion engine (1) further having a second cylinder comprising a second gas exchange valve which is operated at least briefly by the camshaft (4, 5), wherein in a defined and remaining identical first angular position of the camshaft (4, 5) for the second gas exchange valve is operated open, and in a defined and remaining identical second angular position of the camshaft (4, 5) for the second gas exchange valve is operated closed.

9. A method according to any one of the preceding claims, characterized in that the camshaft adjuster (11, 12) is operated such that the duration of the opening of the first and second gas exchange valves (8, 9) is identical with respect to the rotational position of the crankshaft (3).

10. An internal combustion engine (1), in particular for carrying out a method according to one or more of the preceding claims, wherein the internal combustion engine (1) has a cylinder (2), a crankshaft (3) and a camshaft (4, 5) which is drivingly coupled to the crankshaft (3) by means of a camshaft adjuster (11, 12), the camshaft (4, 5) actuating a gas exchange door (8, 9) of the cylinder (2) at least for a short time, characterized in that the internal combustion engine (1) is configured and constructed such that the camshaft adjuster (11, 12) is actuated at least for a short time such that the length of the opening period of the gas exchange door (8, 9) is changed.