Internal-combustion engines – Combustion chamber means having fuel injection only – Combustible mixture stratification means
Reexamination Certificate
2001-09-20
2003-06-24
Dolinar, Andrew M. (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Combustible mixture stratification means
C123S406470
Reexamination Certificate
active
06581564
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an ignition time controller, an ignition time control method and engine control unit for an internal combustion engine, and more particularly, to an ignition time controller, an ignition time control method and an engine control unit for an internal combustion engine which has a cam phase changing mechanism for changing the cam phase of at least one of an intake cam for opening/closing an intake valve and an exhaust cam for opening/closing an exhaust valve to reach a target cam phase so that the engine is operated in a combustion mode switched between a uniform combustion mode which performs fuel injection during an intake stroke and a stratified combustion mode which performs fuel injection in a compression stroke.
2. Description of the Prior Art
A conventional ignition time controller for an internal combustion engine of the type mentioned above is known, for example, from Laid-open Japanese Patent Application No. 9-209895. An internal combustion engine described in this document comprises a cam phase changing mechanism which changes the phase of an intake cam (hereinafter referred to as the “cam phase”) with respect to a crank shaft. The cam phase is controlled to reach a target cam phase, as a target value, to change a valve timing of an intake valve, i.e., overlapping of the intake valve with an exhaust valve, and so on, thereby controlling the intake characteristics represented by a filling efficiency, and internal EGR. The target cam phase is determined based on the engine rotational speed and a load (an intake air mass per rotation of the engine). Also, this controller determines a basic ignition time based on the engine rotational speed and load, calculates a cam phase deviation which indicates the amount of deviation of an actual cam phase from the target cam phase, and determines a correcting amount for the basic ignition time based on the engine rotational speed, load and cam phase deviation.
Also, a recent internal engine, known as a direct injection type, directly injects a fuel into a cylinder, and is operated in a combustion mode which is switched between a uniform combustion mode and a stratified combustion mode in order to improve the fuel economy (see, for example, Laid-open Japanese Patent Application No. 11-22508). In this internal combustion engine, the stratified combustion mode is performed during an extremely low load operation such as idling, wherein a fuel injection is performed during an intake stroke with a throttle valve being substantially fully opened to supply a large amount of intake air into a cylinder for burning at an extremely leaner air/fuel ratio than the stoichiometric air/fuel ratio. On the other hand, the uniform combustion mode is performed during operations other than the extreme low load operation, wherein a fuel injection is performed during a compression stroke, and a throttle valve opening is controlled in accordance with the engine rotational speed and load to control the amount of intake air for burning at a richer air/fuel ratio than in the stratified combustion mode.
As described above, the conventional ignition time controller employs the intake air mass per rotation of engine as representative of the load which is relied on as a parameter to determine a basic ignition time. On the other hand, the load varies as the actual cam phase of the cam phase changing mechanism varies to cause a change in the filling efficiency, amount of intake air, and so on. As a result, this ignition time controller suffers from a delay in convergence of the ignition time to an optimal value due to the continuously fluctuating basic ignition time resulting from the varying actual cam phase, and therefore encounters difficulties in setting at all times an optimal ignition time in accordance with an engine operating condition.
This problem is particularly prominent when the ignition time controller is employed in the aforementioned direct injection type internal combustion engine, and particularly, when the engine is operated in the stratified combustion mode. Specifically, as described above, since the combustion is performed in an extremely lean air/fuel ratio in the stratified combustion mode, the fuel is inherently more difficult to burn in the stratified combustion mode than the uniform combustion mode. For this reason, if the ignition time delays in convergence to an optimal value, particularly, in the stratified combustion mode, the combustion state is more likely to deteriorate, thereby resulting in lower operability and exhaust gas characteristics.
OBJECT AND SUMMARY OF THE INVENTION
The present invention has been made to solve the problem as mentioned above, and its object is to provide an ignition time controller, an ignition time control method and an engine control unit for an internal combustion engine which are capable of setting an ignition time to an optimal value in accordance with a change in intake characteristics associated with a change in cam phase such that the ignition time rapidly converges to the optimal value in either of the uniform combustion mode and the stratified combustion mode in a direct injection type internal combustion engine having a cam phase changing mechanism.
To achieve the above object, according to a first aspect of the present invention, there is provided an ignition time controller for an internal combustion engine equipped with a cam phase changing mechanism for changing a cam phase with respect to a crank shaft for at least one of an intake cam for opening/closing an intake valve and an exhaust cam for opening/closing an exhaust valve such that the cam phase reaches a target cam phase, so that the engine is operated in a combustion mode switched between a uniform combustion mode in which a fuel is injected into a cylinder during an intake stroke and a stratified combustion mode in which a fuel is injected into a cylinder in a compression stroke.
The ignition time controller according to the first aspect of the present invention is characterized by comprising engine rotational speed detecting means for detecting a rotational speed of the internal combustion engine; accelerator pedal opening detecting means for detecting an opening of an accelerator pedal; required torque determining means for determining a required torque outputted by the internal combustion engine based on the detected engine rotational speed and accelerator pedal opening; fuel injection time determining means for determining a time at which a fuel is injected into the cylinder; basic ignition time determining means for determining a basic ignition time based on the engine rotational speed and the determined required torque when the engine is in the uniform combustion mode, and for determining the basic ignition time based on the engine rotational speed and the determined fuel injection time when the engine is in the stratified combustion mode; actual cam phase detecting means for detecting an actual cam phase; and ignition time correcting means for correcting the basic ignition time in accordance with a cam phase deviation which is a difference between the detected actual cam phase and the target cam phase.
The internal combustion engine is operated in a combustion mode switched between the uniform combustion mode in which a fuel is injected into a cylinder in an intake stroke and the stratified combustion mode in which the fuel is injected in a compression stroke. Also, according to the ignition time controller in the first aspect of the present invention, the basic ignition time is determined based on the engine rotational speed and required torque in the uniform combustion mode. Since the required torque is determined as a torque outputted by the internal combustion engine based on the engine rotational speed and accelerator opening, the required torque reflects an actual load, and is not affected directly by a change, if any, in the intake characteristics such as a filling efficient associated with a change in cam phase of the cam
Ogawa Ken
Tagami Hiroshi
Ueda Kazuhiro
Castro Arnold
Dolinar Andrew M.
Honda Giken Kogyo Kabushiki Kaisha
Lahive & Cockfield LLP
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