Internal-combustion engines – Combustion chamber means having fuel injection only – Combustible mixture stratification means
Reexamination Certificate
1999-02-19
2001-01-30
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Combustible mixture stratification means
C123S305000, C123S480000
Reexamination Certificate
active
06178943
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an engine control system for an engine for controlling the amount of fuel injection according to a target air-fuel ratio determined on the basis of a target engine load.
2. Description of the Related Art
Typically, in an engine performing stratified charge combustion to operate with a lean fuel mixture for which an air-to-fuel ratio is controlled according to according to engine operating conditions, control of the amount of fuel injection is made based on target air-to-fuel ratio determined based on a target engine load or a target value of a factor corresponding to an engine load according to engine operating conditions. A control system for a direct injection-spark ignition type of engine described in, for example, Japanese Unexamined Patent Publication No. 7-301139 determines target engine output torque meeting a target engine load on the basis of an engine speed and an throttle opening and further determines a target air-fuel ratio according to the target output torque by an operation with a map. The amount of fuel injection meeting the engine demand is calculated by using the target air-fuel ratio and the amount of intake air. The amount of intake air is controlled by means of a motor driven throttle valve whose opening is controlled according to accelerator pedal travel.
If simply controlling the amount of fuel injection on the basis of a target air-fuel ratio according to a target engine load or output torque only likely by the engine control system described in the above mentioned publication, the engine does not always produce output torque balancing a target load due to fluctuations of air charging efficiency. This is because air charging efficiency is closely related to engine output torque. For example, because the direct injection-spark ignition type of engine is designed and adapted to make stratified charge combustion by performing fuel injection in compression strokes while the engine operates with lower engine loads and, during the stratified charge combustion, the target air-fuel ratio is varied so as to provide a lean air-fuel mixture, the engine output torque drops if simply controlling the amount of intake air linearly corresponding to a change in accelerator pedal travel. In order to avoid such a drip in engine output torque, it has necessary to increase the amount of intake air while the air-fuel mixture remains lean. For this reason, it has been proposed to control the amount of intake air on the basis of a target engine load, i.e. to control throttle opening according to a target engine load, as well as the target air-to-fuel ratio. However, because, during a transitional engine operating state in which the target engine load varies due to treading on an accelerator pedal, a change in the amount of intake air occurs after a delay from the change in target engine load, it is not impossible to gain output torque balancing the target engine load even when controlling the amount of fuel injection so as to balance the target air-fuel ratio determined on the basis of the target engine load while the air charging efficiency differs from a value corresponding to the target engine load due to the delay.
SUMMARY OF THE INVENTION
It is an objective of the invention to provide an engine control system which adjust a target air-to-fuel ratio to control the amount of fuel injection so as thereby to produce engine output torque balancing a target engine load during a transitional engine operating state.
The foregoing object of the present invention is achieved by providing an engine control system for an engine equipped with a fuel injector for determining a target air-to-fuel ratio based on target loads established according to engine operating conditions and controlling the amount of fuel injection according to the target air-to-fuel ratio. The engine control system is characterized by determining a target load based on an engine speed and an accelerator pedal travel, determining a target air-to-fuel ratio based on an amount of intake air and the target load based on which the amount of fuel injection is determined.
With the engine control system which determines a target air-to-fuel ratio based on an amount of intake air and a target engine load, even when an actual air charging efficiency differs from a value corresponding to a target engine load in an ordinary operating state due to a delay of a change in the amount of intake air in responding relative to a change in the target engine load occurring in, for example, a transitional operating state, the target air-to-fuel ratio and the amount of fuel injection based on the target air-to-fuel ratio are adjusted according to the actual air charging efficiency so as thereby to provide engine output torque balancing the target engine load.
The engine control system may control operation of the engine in a plurality of operation modes in which fuel injection timing are different and which are selected according to the target air-to-fuel ratio. The fuel injection timing is determined by each operation mode according to a target engine load and an engine speed. In this instance, the fuel injection timing is adjusted to accord with the target air-to-fuel ratio determined based on an actual air charging efficiency. In the case where the engine is of a direct injection-spark ignition type and changeable in operation between a stratified charge combustion mode in which the fuel injector deliver fuel in a compression stroke to cause a stratified charge combustion and a homogeneous charge combustion mode in which the fuel injector deliver fuel in an intake stroke to cause a homogeneous charge combustion, the fuel injection timing is properly adjusted to accord with the target air-to-fuel ratio even during a transition between the stratified charge combustion mode and the homogeneous charge combustion mode. Though the direct injection-spark ignition type of engine is apt to cause a significant change in air-to-fuel ratio, and hence a change in the amount of intake air due to the change in air-to-fuel ratio, following a transition of operation mode, the engine output torque is adjusted to properly balance the target engine load.
The engine control system may employ as the target engine load either one control parameter of a virtual air charging efficiency balancing an output torque required on the assumption that the engine operates with a stoichiometric air-to-fuel ratio and a value corresponding to the virtual charging efficiency and determines the target air-to-fuel ratio based on a ratio of the one control parameter to either one control parameter of an actual air charging efficiency determined based on the amount of intake air and a value corresponding to the actual air charging efficiency. This provides easy determination of the target air-to-ratio according to the actual air charging efficiency.
The engine control system may temper the target air-to-fuel ratio with an improvement ratio of fuel consumption when the target air-to-fuel ratio is changed toward the lean side from a fuel consumption at a stoichiometric air-to-fuel ratio, which prevents the engine to cause fluctuations of output torque due to improvement of fuel consumption during lean charge combustion as compared with stoichiometric charge combustion.
The engine control system may further determine a target air-to-fuel ratio according to a predetermined relationship between the target load and the engine speed, and determine an eventual target air-to-fuel ratio based on the target air-to-fuel ratio determined based on the amount of intake air and the target engine load during a transitional operating state and based on the target air-to-fuel ratio determined according to the predetermined relationship between the target load and the engine speed during an ordinary operating state. In this embodiment, it is possible to avoid establishing a target air-to-fuel ratio at which an increase in NOx emission is caused and, however, select it while an ordinary operating state lasts. Further
Imada Michihiro
Kuroki Masayuki
Mamiya Kiyotaka
Nishimura Hirofumi
Taga Junichi
Mazda Motor Corporation
Nixon & Peabody LLP
Studebaker Donald R.
Vo Hieu T.
Yuen Henry C.
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