METHOD AND DEVICE FOR CONTROLLING AN INTERNAL COMBUSTION ENGINE

Abstract

A method for injecting gaseous fuel directly into a combustion chamber of an internal combustion engine in order to heat a catalytic converter, the method including: carrying out a main injection of gaseous fuel directly into the combustion chamber; carrying out a first post-injection following the main injection but prior to an ignition, and following the ignition and preferably following the end of combustion in the combustion chamber, carrying out a second post-injection of gaseous fuel into the combustion chamber.

Claims

1-11. (canceled)

12. A method for injecting gaseous fuel directly into a combustion chamber of an internal combustion engine in order to heat a catalytic converter, the method comprising: carrying out a main injection of gaseous fuel directly into the combustion chamber; carrying out a first post injection following the main injection but prior to an ignition; and following the ignition and following the end of combustion in the combustion chamber, carrying out a second post-injection of gaseous fuel into the combustion chamber.

13. The method as recited in claim 12, wherein the second post-injection is carried out when a discharge valve on the combustion chamber is open.

14. The method as recited in claim 12, wherein the second post-injection and the opening of the discharge valve begin simultaneously.

15. The method as recited in claim 12, wherein the second post-injection begins directly after the end of the combustion in the combustion chamber.

16. The method as recited in claim 12, wherein the first and the second post-injection are of equal length.

17. The method as recited in claim 12, wherein gas volumes of gaseous fuel of equal size are injected into the combustion chamber during the first and the second post-injections.

18. The method as recited in claim 12, wherein the combustion process is carried out as a lean process, at a lambda value of approximately 1.05.

19. The method as recited in claim 12, wherein if a pressure in the combustion chamber at the instant of the first post-injection is greater than a gas pressure of the gaseous fuel, the first post-injection is omitted and only the second post-injection is carried out.

20. The method as recited in claim 12, wherein the gaseous fuel is natural gas.

21. A method for injecting gaseous fuel directly into a combustion chamber of an internal combustion engine in order to heat a catalytic converter if the catalytic converter has a temperature below a threshold temperature, the method comprising: carrying out a main injection of gaseous fuel directly into the combustion chamber; and carrying out a post-injection of gaseous fuel directly into the combustion chamber following the end of a combustion in the combustion chamber to increase an exhaust-gas enthalpy.

22. A control unit for injecting gaseous fuel directly into a combustion chamber of an internal combustion engine in order to heat a catalytic converter, the control unit designed to: carry out a main injection of gaseous fuel directly into the combustion chamber; carry out a first post injection following the main injection but prior to an ignition; and following the ignition and following the end of combustion in the combustion chamber, carry out a second post-injection of gaseous fuel into the combustion chamber.

23. A control unit for injecting gaseous fuel directly into a combustion chamber of an internal combustion engine in order to heat a catalytic converter if the catalytic converter has a temperature below a threshold temperature, the control unit designed to: carry out a main injection of gaseous fuel directly into the combustion chamber; and carry out a post-injection of gaseous fuel directly into the combustion chamber following the end of a combustion in the combustion chamber to increase an exhaust-gas enthalpy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Below, a preferred exemplary embodiment of the present invention is described in detail with reference to the figures.

[0014] FIG. 1 shows a schematic illustration of a directly-injecting internal combustion engine.

[0015] FIG. 2 shows a schematic diagram that illustrates the method according to the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0016] Below, an example method according to the present invention for the injection of gaseous fuel directly into a combustion chamber 2 of an internal combustion engine 1 in order to heat a catalytic converter 7 is described in detail with reference to FIGS. 1 and 2.

[0017] The heating of catalytic converter 7 is necessary when it has a temperature below a predefined threshold temperature. In comparison with liquid fuels, a required working temperature of the catalytic converter is approximately 100 K higher for gaseous fuels and lies at approximately 420° C.

[0018] As can be gathered from FIG. 1, internal combustion engine 1 includes a piston 3 disposed in combustion chamber 2, an injector 4, and an ignition device 6 such as a spark plug.

[0019] Injector 4 is situated directly on combustion chamber 2 in order to inject gaseous fuel directly into the combustion chamber. Injector 4 is connected to a gas tank 5.

[0020] Catalytic converter 7 is provided in the exhaust tract. In the conventional manner, combustion chamber 2 has been provided with at least one inlet valve 8 and at least one discharge valve 9.

[0021] Reference numeral 10 denotes a control unit which is designed to control the internal combustion engine during a heating operation of the catalytic converter. In the following text, the method according to the present invention will be described with reference to FIG. 2.

[0022] To begin with, the example method according to the present invention includes the step of carrying out a main injection of the gaseous fuel directly into the combustion chamber of the internal combustion engine. The injected fuel quantity is determined by the driver, for instance via the operation of the accelerator. According to the present invention, once the process of main injection H has taken place, a first post-injection N1 is carried out, which takes place even before an ignition Z of the fuel-air mixture in combustion chamber 2. First post-injection N1 has the advantage of generating additional turbulence around the spark plug and of enriching this region with fuel shortly before the ignition. First post-injection N1 takes place approximately at a crank angle of 5° in advance of actual ignition Z. This facilitates an ignition in the combustion chamber, and the flame core development, and thus the subsequent combustion, are able to be stabilized.

[0023] According to the present invention, a second post-injection N2 of gaseous fuel into the combustion chamber takes place after the combustion has been completely finalized. With the aid of the second post-injection another combustion following the actual main combustion is carried out. This significantly increases an exhaust-gas temperature so that the post-connected catalytic converter 7 is able to heat up more rapidly. As can be gathered from the diagram of FIG. 2, an opening of the discharge valve and the second post-injection N2 take place simultaneously, at a crank angle W of approximately 110°.

[0024] Preferably, second post-injection N2 takes place immediately following combustion V. In addition, the first and the second post-injection are of equal length, which can be gathered from the width of the bars in FIG. 2 above crank angle W.

[0025] In addition, the method according to the present invention also offers another advantage. In the event that the first post-injection is unable to be injected, for instance when the pressure in the combustion chamber prior to the ignition instant is too high and the injection pressure is too low, which may be due to an empty gas tank, the second post-injection N2 may possibly be carried out nevertheless. As can be gathered from the diagram of FIG. 2, second post-injection N2 is carried out at a pressure of under 5×10.sup.5 Pa. As a result, despite the omittance of first post-injection N1, an exhaust-gas enthalpy is able to be increased during second post-injection N2 without causing any negative effect on the smooth running of the engine. Minimum particle emissions during the heating of the catalytic converter are also achieved in the process.

[0026] The diagram shown in FIG. 2 illustrates a pressure p over crank angle W. The positions of main injection H, first post-injection N1, combustion V, and second post-injection N2 have been plotted in the lower part of the diagram of FIG. 2. Also shown is an ignition instant Z. Moreover, in the lower part, an opening of discharge valve AV is also illustrated over the crank angle, the discharge valve opening shortly after 90° crank angle.

[0027] In addition, the present invention relates to a method for injecting gaseous fuel directly into a combustion chamber of an internal combustion engine for the purpose of heating a catalytic converter, a gas pressure of the gaseous fuel shortly in advance of a top dead center being lower at a compression in the Otto combustion cycle than a pressure in the combustion chamber, the method including the following steps: Carrying out a main injection of gaseous fuel directly into the combustion chamber, and after the compression, ignition and combustion, carrying out a post-injection into the combustion chamber in order to increase an exhaust-gas enthalpy.