Internal-combustion engines – Engine speed regulator – Responsive to deceleration mode
Reexamination Certificate
1999-11-11
2001-02-27
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Engine speed regulator
Responsive to deceleration mode
C123S568140
Reexamination Certificate
active
06192858
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
Priority is claimed with respect to German Application No. 198 04 988.9-13 filed in Germany on Nov. 13, 1998, the disclosure of which is incorporated herein by reference.
The invention relates to a method for operating a four-stroke internal combustion engine, in particular a four-stroke internal combustion engine with exhaust-gas retention and exhaust-gas throttling.
An internal combustion engine is taken to be a machine which burns mixtures of air and fuel in a number of variable volumes and converts the energy released into mechanical energy by way of the gas pressure generated in the volumes. The mixtures are formed within a combustion chamber.
At least at idle and/or at part load, combustion is initiated by compression ignition. With lean mixtures, this offers good potential for burning air/fuel mixtures with good efficiency and little formation of nitrogen oxides. At the compression ratios customary in engines, this type of combustion can only be implemented by exhaust-gas retention and exhaust-gas activation. Here, exhaust-gas activation refers to an activating injection of fuel into hot compressed exhaust gas. It is only possible to implement such combustion stably within a narrow range of the characteristic map. However, stable combustion requires rapid control, particularly in the case of non steady-state operation. Mechanical control systems such as flaps or valves are too slow for this purpose and are too expensive for a cylinder-selective design.
Compression ignition is effected by increasing the temperature of the air/fuel mixture. The temperature of the fresh mixture is increased by mixing it with the exhaust components of the preceding cycle and by the subsequent geometrical compression of the enclosed maximum initial volume to a residual volume. The temperature in the remaining compressed volume rises to a level such that it ignites the mixture. By virtue of the energy released, the combustion process which follows the compression ignition of lean mixtures is a self-sustaining or self-reinforcing process. This combustion can be initiated and controlled by variable compression by means of variable closure of the inlet or by way of variable exhaust-gas retention with activating injection. A knock-free increase in load can be achieved by vaporization cooling with fuel injected at a late stage.
The combustion of the homogeneous air/fuel mixture is dependent on the proportions in the mass in the combustion chamber of retained exhaust gas together with the excess air from the preceding cycle, the cold fresh air fed in and the fuel introduced directly into the combustion chamber. The particular composition of the mixture influences the beginning and hence progress of the release of energy. The high proportion of retained exhaust gas influences the next cycle. Pilot control of combustion is possible by selective injection in the context of activation.
For this purpose, fuel is injected into the exhaust gas retained in the combustion chamber, thereby bringing about a predominantly endothermic preliminary reaction of the fuel fed in by means of the heat of the exhaust gas and the hot residual air, a reaction which influences the subsequently compressed full charge when the exothermic reaction is initiated.
U.S. Pat. No. 6,105,550 which is not a prior publication, describes an internal combustion engine of the same generic type in which the mechanical concept required for the implementation of compression ignition in engines is explained. The exhaust-gas retention required is achieved by mechanical pilot control by means of a camshaft that can be switched in binary fashion and the switched-over cam shape of which leads to shorter valve timings (valve closure overlap) and hence to compression of the exhaust gas retained. The quantity of exhaust gas is controlled by means of an exhaust throttle valve downstream of the outlet members. This valve controls the quantity of exhaust gas retained in the combustion chamber by means of the back pressure and the resulting pressure difference with respect to the combustion chamber.
An activating injection into the exhaust gas retained and spark ignition of homogeneous stoichiometric mixtures are furthermore provided for full-load operation.
However, retention of exhaust gas by causing an exhaust-gas build-up downstream of the combustion chamber is subject to inertias associated with the dynamics of gases and cannot be pilot-controlled in a cylinder-selective manner. Cyclic compensation of previous influences or pilot control for selective rapid and dynamic changes in the load and engine speed can be controlled only with difficulty from the exhaust end of the engine and is complex in terms of control because of dead times and hystereses.
Cylinder-selective fitting of the individual exhaust lines with individual butterfly valves is thermally problematic in load mode and is complex in terms of design. Moreover, the inner cylinders of a multi-cylinder engine suffer less heat loss and hence exhibit higher gas temperatures, leading to differences in the quantity and density of the exhaust gas retained in the individual combustion chambers. As a result, the progress of combustion in the inner cylinders is different from that in the outer cylinders, something which permanently prejudices the smoothness of running of the engine and nonsteady-state operation.
SUMMARY OF THE INVENTION
The object on which the invention is based is to specify a method for a multi-cylinder internal combustion engine of the generic type by means of which the combustion-chamber pressure at the end of exhaust-gas compression can be equalized in a cylinder-selective manner consistent with the cycle.
The object is achieved by a method with the following features.
Exhaust-gas retention is controlled as a function of the speed and load of the internal combustion engine by just one exhaust throttle valve in the exhaust line. For low loads and engine speeds, this valve is closed to the maximum extent, with the result that the largest possible proportion of exhaust gas is retained in the combustion chambers. As the engine speed rises, the exhaust throttle valve exposes a larger cross section and thus allows a higher mass flow. As the load rises, the temperature of the exhaust gas increases, with the result that less exhaust gas has to be retained and hence less exhaust-gas throttling is required to initiate the reaction. The exhaust throttle valve is accordingly used for pilot control of the operating point and can be controlled to a limited extent in a nonsteady-state manner.
By skilful variation of the activating injection, it is possible to influence the pressure in the combustion chamber when the inlet member is opened. The activating injection is divided into an early and a late injection, depending on the injection point. In the case of the early activating injection, the reaction activity releases energy during the activation phase. The combustion-chamber pressure rises in comparison with exhaust-gas retention without activation. As a result, a lower vacuum relative to the surroundings is obtained when the inlet members are opened, thereby reducing the filling of the combustion chambers.
Late injection alters the pressure variation during the expansion of the exhaust gas only due to the cooling brought about by the vaporization of the fuel since chemical reactions are retarded because of the rapid pressure drop in the rapidly expanding combustion chamber. Early injection, in contrast, increases the pressure in the combustion chamber even during the expansion phase of the exhaust gas retained, because of the release of energy in the exhaust gas. If this is not desired, the exhaust gas in the combustion chamber can be cooled by the vaporization of additional fuel injected at a later stage. The higher density or lower pressure of the cooled mass allows a larger charge. Activating injection is therefore a suitable means of selectively changing the pressure prevailing in the combustion chamber when the inlet member is opened. The pr
Coughlin William J.
Daimler-Chrysler AG
Gimie Mahmoud
Yuen Henry C.
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