1. Field of the Invention
The present invention relates to the field of engine control to induce auto-ignition combustion of fuel including gasoline, and more particularly to the field of stabilizing auto-ignition combustion without rapid increase of in-cylinder pressure.
2. Description of Related Art
According to JP-A 10-266878, it is known to vary an exhaust gas retaining duration to accomplish auto-ignition combustion of gasoline fuel over varying load request from low to middle level. Exhaust gas retaining duration extends from closure (or closing timing) of exhaust valve to opening (or opening timing) of intake valve. To meet decreasing load request, closure of exhaust valve is moved to increase the amount of advance from top dead center during exhaust or induction process, thereby to increase remaining exhaust gas content to decrease in quantity fresh intake air. Besides, opening of intake valve is moved to increase the amount of delay from top dead center during exhaust or induction process in cooperation with the movement of closure of exhaust valve to meet decreasing load request. In brevity, exhaust gas retaining duration is varied to meet varying load request. With regard to closure of intake valve, the closure is after bottom dead center during induction process. Closure of intake valve is moved to decrease the amount of delay from bottom dead center during induction process, thereby to increase compression ratio to raise in-cylinder temperature during operation with load where auto-ignition is difficult to accomplish. JP-A 10-266878 appears to contemplate an engine, which has achieved auto-ignition combustion to meet varying load request from low to middle level. However, JP-A 10-266878 does not contemplate a solution to stabilizing auto-ignition combustion without rapid increase of in-cylinder pressure against a change other than a change in load request.
It is one object of the present invention to stabilize auto-ignition combustion against a change other than a change in load request.
In accordance with the object of the present invention, in a preferred embodiment, auto-ignition combustion is stabilized against a change other than a change in load request by carrying out a method of operating an internal combustion engine having an inlet control device for controlling flow of intake air into at least one cylinder, a fuel injection device for supplying fuel into the cylinder and an outlet control device for controlling flow of exhaust gas resulting from combustion within the cylinder, which inlet and outlet control devices are adjusted to retain a portion of the exhaust gas for subjecting the retained exhaust gas to compression, the method comprising:
monitoring a parameter indicative of engine-surrounding environment; and
adjusting closing timing of the outlet control device in response to the monitored engine-surrounding environment indicative parameter, thereby to vary an exhaust gas retaining duration from the closing timing event of the outlet control device to opening timing event of the inlet control device when there is a change in the monitored engine-surrounding environment indicative parameter.
The inventors here have recognized that a change in engine-surrounding environment may cause a variation in pressure, temperature, and excess air ratio around top dead center during compression process, all of which, in turn, cause variation in ignition timing and combustion duration of auto-ignition combustion. An advantage of the above-mentioned preferred embodiment is that variation in ignition timing and combustion duration of auto-ignition combustion is prevented or at least suppressed to hold appropriate ignition timing and combustion duration against a change in engine-surrounding environment.
In another or second preferred embodiment of the present invention, auto-ignition combustion is stabilized against a change other than a change in load request by carrying out a method of operating an internal combustion engine having an inlet control device for controlling flow of intake air into at least one cylinder, a fuel injection device for supplying fuel into the cylinder and an outlet control device for controlling flow of exhaust gas resulting from combustion within the cylinder, which inlet and outlet control devices are adjusted to retain a portion of the exhaust gas for subjecting the retained exhaust gas to compression, the method comprising:
monitoring a parameter indicative of engine-surrounding environment; and
adjusting closing timing of the inlet control device in response to the monitored engine-surrounding environment indicative parameter.
A change in engine-surrounding environment may cause a drop in pressure around top dead center during compression process. Such a drop in pressure causes auto-ignition at a delayed timing, resulting in prolonged combustion duration because of descending movement of a piston during the final stage of combustion. Such combustion is low in thermal efficiency and may induce misfire event. A change in engine-surrounding environment may cause a reduction of excess air around top dead center during compression process. With the same volumetric efficiency, a drop in density of air causes a reduction of excess air ratio around top dead center during compression process. Reduction in excess air ratio may cause rapid burning during combustion after auto-ignition or may cause auto-ignition at an early time prior to appropriate timing. Rapid burning and/or early ignition may cause knock event to occur, increasing, in level, combustion noise. Reduction in excess air ratio may cause an increase in amount of NOx emission. The second preferred embodiment contemplates adjusting closing timing of the inlet control device so as to vary the volumetric efficiency. An advantage of the second preferred embodiment is that variation in ignition timing and combustion duration of auto-ignition combustion is prevented or at least suppressed to hold appropriate ignition timing and combustion duration against a change in engine-surrounding environment by varying the volumetric efficiency.
In a third preferred embodiment of the present invention, auto-ignition combustion is stabilized against a change other than a change in load request by carrying out a method of operating an internal combustion engine having an inlet control device for controlling flow of intake air into at least one cylinder, a fuel injection device for supplying fuel into the cylinder and an outlet control device for controlling flow of exhaust gas from the cylinder, which inlet and outlet control devices are adjusted to retain a portion of the exhaust gas for subjecting the retained exhaust gas to compression, the method comprising:
monitoring an engine operating temperature; and
adjusting closing timing of the outlet control device in response to the monitored engine operating temperature, thereby to vary an exhaust gas retaining duration from the closing timing event of the outlet control device to opening timing event of the inlet control device when there is a change in the monitored engine operating temperature.
A change in engine operating temperature as represented by an engine oil temperature or an engine coolant temperature may cause a variation in temperature, and excess air ratio around top dead center during compression process, all of which, in turn, cause variation in ignition timing and combustion duration of auto-ignition combustion. A variation of in-cylinder temperature may cause a variation in mass of intake air inhaled per one cycle with the volumetric efficiency held the same. An advantage of the third preferred embodiment is that variation in ignition timing and combustion duration of auto-ignition combustion is prevented or at least suppressed to hold appropriate ignition timing and combustion duration by varying an exhaust gas retaining duration to vary in-cylinder temperature during the next cycle when there is a change in engine operating temperature. During the early stages of a cold start of an engine, the engine operating temperature inhibits build-up of appropriate temperature and excess air ratio around top dead center during compression process, making it difficult to achieve stable auto-ignition combustion. The third preferred embodiment of the present invention contemplates varying exhaust gas retaining duration to retain appropriate amount of exhaust gas needed to raise in-cylinder temperature for proper combustion in the next engine cycle.
In a fourth preferred embodiment of the present invention, auto-ignition combustion is stabilized against a change other than a change in load request by carrying out a method of operating an internal combustion engine having an inlet control device for controlling flow of intake air into at least one cylinder, a fuel injection device for supplying fuel into the cylinder, and an outlet control device for controlling flow of exhaust gas resulting from combustion within the cylinder, which inlet and outlet control devices are adjusted to retain a portion of the exhaust gas for subjecting the retained exhaust gas to compression, the method comprising:
establishing a predetermined window about a desired level of combustion stability within the engine;
monitoring an actual level of combustion stability within the engine;
comparing the monitored actual level of combustion stability with the predetermined window; and
adjusting closing timing of the inlet control device in response to the result of the comparing step such that, when the monitored actual level of combustion stability falls outside of the predetermined window, the closing timing of the inlet control device is moved in such a direction as to bring the monitored actual level of combustion stability into the predetermined window.
During operation of an engine over the number of engine cycles with bad combustion stability, the cycle-by-cycle variation in combustion termination is considerably great, so the cycle-by-cycle variation in temperature of the retained exhaust gas during exhaust gas retaining duration is inevitably great. As a result, the quantity of intake air inhaled and in-cylinder temperature around top dead center during compression process vary from one to another of the engine cycles. Further, the density of unburnt fuel within the retained exhaust gas per one cycle may differ considerably from that per one of the subsequent cycles during engine operation with bad combustion stability. The density of unburnt fuel within the retained exhaust gas determines the quantity of radicals created. An advantage of the fourth preferred embodiment of the present invention is that combustion stability is monitored and closing timing of inlet control device is moved in such a direction as to bring the monitored actual level of combustion stability into a predetermined window about a desired level of combustion stability. Rather than factors deemed to induce combustion instability in combination or independently, the actual level of combustion stability is monitored according to the fourth embodiment of the present invention.