Internal-combustion engines – Cooling – Automatic coolant flow control
Reexamination Certificate
2002-11-08
2004-09-14
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Cooling
Automatic coolant flow control
C123S041440, C123S568120
Reexamination Certificate
active
06789512
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of operating an internal combustion engine which has a cooling circuit.
Modern internal combustion engines achieve high levels of thermodynamic efficiency. This results in new conflicts of objectives with regard to the heat budget of the engines. On the one hand, a rapid heat-up phase after the cold start is desirable, in order to reduce the friction by heating of the oil and to achieve optimum combustion as quickly as possible. However, implementing measures aimed at achieving high engine efficiency, delays the heating of the interior of the vehicle, since the coolant which flows through a heater is not heated sufficiently quickly, to achieve a satisfactory heating comfort. It is therefore necessary to provide secondary heating means.
German laid-open specification DE 197 28 351 A1 discloses a method for regulating heat in an internal combustion engine in which component temperatures and output characteristic variables of the internal combustion engine are monitored and are taken into account in the control of the coolant flow. Speed-controlled pumps, fans, electrically actuable valves and shutters can be used to implement the control.
It is the object of the present invention to provide a method of operating an internal combustion engine, and a motor vehicle, with which a satisfactory heating comfort is achieved without the need for secondary heating means.
SUMMARY OF THE INVENTION
In a method for operating an internal combustion engine, and a motor vehicle to be heated by the engine coolant, wherein the internal combustion engine has a cooling circuit, a heating mode can be established in which operating parameters of the internal combustion engine, while satisfying required output set values, are set for the maximum possible introduction of heat into the coolant and the exhaust gas in order to reach or hold a desired coolant temperature.
The coolant can be heated rapidly if, during the startup phase, the internal combustion engine is briefly switched to an operation with a thermodynamic efficiency, which is as bad as possible while still ensuring proper operation while the required output set values are satisfied. Consumption and exhaust-gas limit values can be maintained by switching to the heating mode only for a short period. Switching to the heating mode makes it possible to avoid the need for secondary heating means.
In a particular embodiment of the invention, in order to increase a combustion-chamber surface temperature during the startup phase, combustion is temporarily advanced with respect to the standard operation, while a maximum possible combustion-chamber pressure is maintained.
Advancing the combustion and/or maintaining the flow of coolant allows the combustion-chamber surface to be heated as quickly as possible. This is a required condition for operation with the worst possible thermodynamic efficiency, since misfiring can only be avoided with a high combustion-chamber surface temperature. Therefore, if the combustion-chamber surface temperature sensed is below a predetermined threshold value, above which the engine can be operated with a poor thermodynamic efficiency, the combustion timing is initially advanced or the flow of coolant is shut off or reduced in order to increase the combustion-chamber surface temperature. The point in time at which the general combustion takes place is considered to be the point in time when a fuel conversion rate of 50% of the charge has been reached.
In another embodiment of the invention, in the heating mode, the combustion is temporarily delayed with respect to standard operation, while predetermined limits for a combustion-chamber surface temperature are maintained.
Delaying the combustion results in a high exhaust-gas temperature and a poor thermodynamic efficiency of the internal combustion engine. It is ensured that predetermined limits for a combustion-chamber surface temperature are maintained, in order to avoid misfiring and to allow the internal combustion engine still to run smoothly. The high exhaust-gas temperature and the poor thermodynamic efficiency result in a high heat output and a maximum generation of heat in the internal combustion engine. As a result, the coolant can be heated rapidly in order to achieve a satisfactory heating comfort. In addition to a particular cold-start mode, these measures can also be carried out in partial-load mode in order to prevent the engine from cooling down. Such a cooling of the engine may result from the fact that cooling systems are generally designed for maximum demands, for example when driving uphill with a trailer in full-load operation at high ambient temperatures.
In still another embodiment of the invention the idling speed is increased in the heating mode as compared to standard operation, while the oil temperature and the coolant temperature are monitored.
This measure also contributes to the coolant temperature being increased to a level which ensures a satisfactory heating comfort.
In a further embodiment of the invention, in the heating mode, the flow of coolant through the internal combustion engine is blocked for a predetermined period of time after a cold start.
In this way, a combustion-chamber surface temperature can be rapidly increased to a level which allows the internal combustion engine to be operated with poor thermal efficiency as quickly as possible after a cold start. A blockage of the flow of coolant through the internal combustion engine is achieved, for example, by shutting down an electric cooling-water pump or by diverting the flow.
In a refinement of the invention, in heating mode, the flow of coolant through the internal combustion engine is controlled as a function of the combustion-chamber surface temperature and of the engine operating point.
In this way, it is possible to maintain a combustion-chamber surface temperature within a predetermined range.
In a further refinement of the invention, in the heating mode, an exhaust-gas re-circulation rate in an exhaust-gas re-circulation device of the internal combustion engine is set to a maximum possible value within predetermined limit values.
The limit values for the exhaust-gas re-circulation rate are determined by the smooth running of the engine, emission of pollutants and fuel consumption. A high exhaust-gas re-circulation rate results in a high thermal output from an exhaust-gas re-circulation heat exchanger. A high exhaust-gas re-circulation reduces the mass flow of cold fresh air, and leads to reduced heat losses on account of the reduced mass flow of exhaust gas being discharged. An exhaust-gas re-circulation rate is advantageously increased to such an extent that a cloudiness value of the exhaust gas remains just below the visibility limit.
In a further refinement of the invention, in order to increase the exhaust-gas re-circulation rate in the heating mode, the charging pressure of a supercharging device of the internal combustion engine is increased.
In this way, the amount of heat which can be removed from the engine and an exhaust-gas re-circulation cooler can further be increased. In addition, the dynamic properties of the vehicle can be improved, since the exhaust-gas temperatures are significantly higher than during standard operation, so that the charge pressure can be built up with less delay because of greater turbine output.
In a further refinement of the invention, in the heating mode the air flow through a charge-air cooler of a supercharging device of the internal combustion engine is set to zero (bypass).
This measure also contributes to the internal combustion engine or the coolant in the internal combustion engine being heated as quickly as possible.
Furthermore, in the heating mode, a radiator shutter is closed.
In still another refinement of the invention, in order to shift the combustion timing in the heating mode with respect to standard operation, a change is made to the injection quantities and/or injection times of a pre-injection, main injection and/or after-injection. Furthermore, in the he
Duvinage Frank
Klingebiel Matthias
Pfaff Ruediger
Sass Helko
Welte Lothar
Bach Klaus J.
Daimler-Chrysler AG
Wolfe Willis R.
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