Internal-combustion engines – Spark ignition timing control – Electronic control
Reexamination Certificate
2002-01-11
2004-08-03
Solis, Erick (Department: 3747)
Internal-combustion engines
Spark ignition timing control
Electronic control
C123S0780AA, C123S090160
Reexamination Certificate
active
06769404
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a combustion control system for a spark-ignition internal combustion engine employing a variable piston stroke characteristic mechanism (a variable compression ratio mechanism capable of varying a compression ratio &egr;) and a variable valve operating mechanism capable of varying a valve lift characteristic (a valve lift, a working angle, a phase of a central angle of the working angle) of an intake valve.
BACKGROUND ART
A compression ratio often denoted by Greek letter &egr; (epsilon) is generally defined as a ratio (V
1
+V
2
)/V
1
of the full volume (V
1
+V
2
) existing within the engine cylinder and combustion chamber with the piston at bottom dead center (BDC) to the clearance-space volume (V
1
) with the piston at top dead center (TDC). On the other hand, an effective compression ratio denoted by &egr;′ is generally defined as a ratio of the effective cylinder volume corresponding to the maximum working medium volume to the effective clearance volume corresponding to the minimum working medium volume. These two compression ratios &egr; and &egr;′ are thermodynamically distinguished from each other. A compression ratio is one of basic parameters for enhanced thermal efficiency. In fixed compression-ratio spark-ignition internal combustion engines, compression ratio &egr; is set to as high a ratio as possible, taking into account the frequency of detonation or knock. There are several options to avoid such fixed compression-ratio engines from knocking. One way to avoid a combustion chamber knock condition is to simply retard ignition-spark timing, when combustion knock occurs in the engine. Another way to avoid knocking is to vary intake-valve operating characteristics, thereby varying effective compression ratio &egr;′. Moreover, a variable compression ratio device can be added as an antiknock means. In designing combustion control systems, it is important to balance two contradictory requirements, that is, high thermal efficiency and high-response knock control. As is generally known, there is an increased tendency for combustion knock to occur at severe engine operating conditions, such as at high-temperature high-load operation. Knocking occurs under certain conditions wherein the temperature of intake air introduced into the engine cylinder goes high enough owing to heat of compression and heat exchange between the intake air and the cylinder wall and piston, and the last part of compressed air-fuel mixture or end gas explodes suddenly or self-ignites before flame propagation is completed and thus the combustion velocity increases, thereby creating knocking noise and higher thermal and mechanical stresses on internal combustion engine components. As discussed above, engine knock tends to occur owing to a temperature rise in the compressed air fuel mixture. There is an increased tendency for knocking to occur, in particular when the engine coolant temperature rises during continuous high-load operation. Setting compression ratio &egr; to a low value contributes to knocking avoidance, but results in reduced thermal efficiency, that is, deteriorated fuel economy. In recent years, fixed spark-ignition compression-ratio engines usually employ a knock sensor or a detonation sensor in order to detect cylinder ignition knock and retard the ignition spark-timing, to avoid engine knock while setting compression ratio &egr; to a relatively high value. Ignition-timing retardation, by way of which a relatively high knocking control response can be attained, is suitable for knocking avoidance. However, ignition-timing retardation deteriorates fuel economy and results in an exhaust-temperature rise. This deteriorates the durability of an exhaust-system catalytic converter. For knocking avoidance, ignition-timing retardation can be combined with variable phase control. In case of the integrated knocking-avoidance control based on both ignition-timing retardation and variable phase control, under a condition that there is an increased tendency for the engine to knock, effective compression ratio &egr;′ is lowered by retarding the phase of the camshaft (in other words, by retarding the intake valve closure timing often abbreviated to “IVC”), and as a result the charging efficiency and the temperature of air-fuel mixture on compression stroke can be decreased, thereby preventing an exhaust-temperature rise. One such knocking-avoidance system has been disclosed in Japanese Patent Provisional Publication No. 8-338295. Japanese Patent Provisional Publication No. 11-36906 has disclosed a knocking-avoidance system capable of variably controlling a working angle of an intake valve. For improved fuel economy, an integrated control based on both the variable working-angle control and the variable phase control has been proposed. A variable piston stroke characteristic mechanism, which is capable of variably adjusting a compression ratio &egr; by varying at least one of a TDC position and a BDC position, has been disclosed in pages 706-711 of the issue for 1997 of the paper “MTZ Motortechnische Zeitschrift 58, No. 11”.
SUMMARY OF THE INVENTION
The variable piston stroke characteristic mechanism or the variable compression ratio mechanism is effective to avoid engine knock. However, the variable piston stroke characteristic mechanism is inferior to the ignition-timing control in control response. To enhance the control response, the variable piston stroke characteristic mechanism requires a comparatively large-size actuator having a large torque capacity. In contrast to the above, with compression ratio &egr; kept constant, it is possible to reduce the pumping loss by lowering effective compression ratio &egr;′ by way of the intake valve closure timing (IVC) control, for improved fuel economy. In general, the ignition-timing control is superior to a so-called valve operating control containing variable intake-valve working-angle control and variable phase control, in control response for knocking avoidance. The valve operating control is superior to the variable piston stroke characteristic control, in knocking-avoidance control response. Under a particular condition where a comparatively high knocking-avoidance control response is required, such as during rapid acceleration, it is desirable to properly combine the IVC control having a relatively high control response with the other control. In the case that high engine output torque is required, the quantity of intake air has to be increased. However, the increased intake-air quantity is not always reconciled to a drop in effective compression ratio &egr;′. The IVC control has to be utilized suitably depending on engine/vehicle operating conditions, from the viewpoint of the correlation of knocking avoidance with improved fuel economy and enhanced driveability.
Accordingly, it is an object of the invention to provide a combustion control system for a spark-ignition internal combustion engine with a variable piston stroke characteristic mechanism and at least one of a variable valve lift and working angle control mechanism and a variable phase control mechanism, which avoids the aforementioned disadvantages.
It is another object of the invention to provide an integrated combustion control system for a spark-ignition internal combustion engine with a variable piston stroke characteristic mechanism and at least one of a variable valve lift and working angle control mechanism and a variable phase control mechanism, which is capable of setting a compression ratio and operating conditions of an intake valve optimally depending upon engine/vehicle operating conditions, and of balancing a plurality of requirements, that is, knocking avoidance, improved fuel economy, and enhanced driveability by way of integrated control based on an operating mode selected from a variable piston-stroke characteristic control mode (or a variable compression-ratio control mode), a variable intake-valve working-angle control mode, and a variable intake-valve phase control mode,
Aoyama Shunichi
Moteki Katsuya
Foley & Lardner LLP
Nissan Motor Co,. Ltd.
Solis Erick
LandOfFree
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