As for the engine torque control of an internal combustion engine controller for automobiles, so-called “torque base (torque demand) type engine control” in which target engine torque is computed from the angle of an accelerator and the speed of an engine and throttle control, fuel control and ignition control are carried out to achieve the target engine torque and the target air-fuel ratio has recently been implemented.
The torque base (torque demand) type engine control of the internal combustion engine has advantages that a torque difference at the time of switching between uniform charge combustion and stratified charge combustion in a stratified charge lean combustion system can be reduced and that traction control and engine torque demanded from an external device such as an auto-cruise or AT can be processed smoothly by adding an interface for external demand torque to a logic for computing the above target engine torque.
The above torque base type engine control has an advantage that torque control can be carried out while the target air-fuel ratio is maintained as torque control is basically carried out by controlling the quantity of air sucked by an electrically controlled throttle. However, it has a problem that its response for achieving desired torque is low due to a phenomenon that the supply of intake air into cylinders is delayed. To cope with this problem, when high-speed response is desired for traction control or VDC (vehicle dynamics control), for example, other torque control means is used in combination to improve the torque response. As one example of this, there is known technology making use of a fuel cut or ignition retard when torque is reduced (deceleration).
Another technology concerning the torque response is disclosed by JP-A H11-72033, for example. In this technology, when high-speed torque response is desired in a stratified charge lean combustion system, the torque response is improved by correcting the ignition time at the time of uniform charge combustion and the air-fuel ratio at the time of stratified charge combustion. In this technology, torque correction is carried out by correcting the ignition time as the purification efficiency of a three-way catalyst is reduced to deteriorate exhaust gas when the air-fuel ratio is corrected at the time of uniform charge combustion, and torque correction is carried out by correcting the air-fuel ratio in the case of stratified charge combustion as the variable range of ignition time is small.
Meanwhile, as for the recent exhaust gas purification control of an automobile internal combustion engine, there is generally known technology for improving the exhaust purification ratio with a three-way catalyst by carrying out air-fuel ratio feed-back control, using a detection signal from an O2 sensor installed in the exhaust pipe, so that the air-fuel ratio becomes a value close to the theoretical air-fuel ratio.
However, the three-way catalyst has an O2 storage effect (effect of storing oxygen in a catalyst) and the function of reacting with an exhaust component in the catalyst so that the stored O2 cancels a shift from the theoretical air-fuel ratio in exhaust from the engine. Therefore, when air-fuel ratio feed-back control is carried out by using information only from the O2 sensor without considering the exhaust purification function of the stored O2, the correction quantity of fuel becomes inappropriate and over-correction occurs, thereby deteriorating the exhaust gas. To cope with this problem, for example, technology disclosed by JP-A H2-230935 is to prevent the deterioration of the purification of exhaust gas by adjusting the amount of air-fuel ratio feed-back control based on an estimated value obtained by O2 storage quantity estimation means for estimating the storage quantity of O2 in a three-way catalyst provided in an internal combustion engine controller.
For the torque base type control of the conventional internal combustion engine controller for automobiles, technology for improving the torque response by using other high-speed torque control means is used to compensate for a delay in the supply of intake air when high-speed torque response is desired. In a uniform charge stoichiometric combustion system which is operated at a value close to the theoretical air-fuel ratio, there has not been proposed appropriate torque assist means when high-speed torque increase is demanded during non-idling.
One of the reasons for this is that torque increase is impossible at the time of non-idling by further advancing the ignition time as a value (MBT) at which the ignition time is advanced to enable the generation of the maximum torque is generally set as a standard ignition time even when torque assist is tried by changing the ignition time.
Another reason is that when the air-fuel ratio is simply made rich, the purification of exhaust gas may be deteriorated (specifically, increases in the quantities of CO or HC) as the air-fuel ratio must be maintained at a value close to the theoretical air-fuel ratio due to the exhaust gas purification properties of the three-way catalyst used in a uniform charge stoichiometric combustion system though it is commonly known that the torque can be increased by making the air-fuel ratio rich (for example, power air-fuel ratio of about 12) as for the technology of assisting torque by the air-fuel ratio control of an internal combustion engine.
It is an object of the present invention which has been made in view of the above problems to provide an internal combustion engine controller for automobiles which can realize torque increasing performance and exhaust gas purification performance in a well-balanced manner even when a high-speed torque increase is demanded in uniform charge stoichiometric combustion which is operated at a value close to a theoretical air-fuel ratio in the torque base type engine control of an internal combustion engine.