This invention relates to control of a fuel injection quantity of an internal combustion engine mounted in a vehicle, and particularly to a fuel injection system for controlling a fuel injection quantity of a direct injection type internal combustion engine for directly injecting fuel into a cylinder.
With reference to control of a fuel injection quantity of an internal combustion engine, various techniques are conventionally disclosed, and a control method suitable for a so-called MPI injector for injecting fuel into an intake passage of the internal combustion engine at multi points is disclosed in, for example, the Examined Japanese Patent Application Publication No. Hei 4-23100. When a valve of an electromagnetic drive injector is conventionally opened to inject the fuel into the internal combustion engine, it is known that a valve opening current of a large current value is passed through a solenoid of the injector in the case of opening the valve to speed operation of opening the valve and the current is switched to a valve opening hold current of a small current value necessary to maintain a valve opening state after the completion of opening the valve and this valve opening hold current is passed through the solenoid for a predetermined period of time to control a fuel injection quantity, but the fact that a relationship between current-carrying time T1 of the valve opening current and valve opening required time T0 from a current-carrying start to full opening of the valve is set to T1 greater than T0+0.1 ms and a switch to a holding current is made after a lapse of this current-carrying time T1 of the valve opening current is disclosed in the conventional example described above.
In a mechanism of a needle valve used for such an electromagnetic drive injector, a stopper for limiting the amount of movement of a plunger for fixing a valve element is provided in order to regulate an opening of the valve, and a bounce due to a collision of the plunger with this stopper occurs and this bounce interferes with linearity of characteristics of the fuel injection quantity to injection time to adversely affect accuracy of the control of the fuel injection quantity, so that in the conventional example described above, the current-carrying time of the valve opening current is made longer than the valve opening required time to apply a strong electromagnetic attraction force to the plunger and the bounce is controlled while its extended time is regulated to 0.1 ms in order to ensure the minimum value of the fuel injection quantity per one action.
Also, another example of conventional art for controlling this bounce phenomenon to improve controllability of the fuel injection quantity is disclosed in the Examined Japanese Patent Application Publication No. Hei 3-7834. The technique disclosed in this publication is constructed so that the current-carrying time T1 of the valve opening current is set shorter than the valve opening required time T0 and the current is once broken or the current is switched to a low level of a current value to reduce a valve opening speed and immediately before the plunger collides with the stopper, namely reaches the valve opening required time T0, a current with a value larger than a hold current is passed to control the bounce and the current is switched to the hold current after an opening of a valve has stabilized, and by performing the control in this manner, a speed of a collision between the plunger and the stopper is reduced and further an attraction force in the case of occurrence of the bounce is strengthened to control the bounce.
Since a cylinder injection injector for directly injecting fuel into a cylinder of an internal combustion engine, (a so-called DI injector) is premised on a stratified-charge combustion within the cylinder, the mass mixture ratio of air to fuel is normally set larger than 14.7 of the theoretical mixture ratio and for this reason, the minimum injection quantity of fuel needs to be set small compared with that of the MPI injector. Also, even when it is not premised on the stratified-charge combustion, a predetermined quantity of fuel needs to be injected in a shorter time for the cylinder injection and a flow gain of the injector is largely set, so that the injection quantity per time becomes large and there is a problem that injection time in the case of injecting the minimum injection quantity of fuel needs to be more reduced. In order to obtain the minimum injection quantity of this injector as an stable value, it is found from experimental results that an injection pulse width needs to be set to the substantially same time as the valve opening required time T0 or longer than or equal to the time T0, and the bounce phenomenon needs to be controlled in a manner similar to the conventional example.
Also, in construction of the valve used for the injector, valve closing required time until closing the valve after the passage of current through the solenoid is broken exists, and this valve closing required time is affected by a damping factor of a magnetic flux applied to the plunger as the electromagnetic attraction force other than mechanical inertia of a valve mechanism. The damping factor of this magnetic flux damps according to a time constant determined by various specifications of the plunger and is commonly called a residual flux or a response delay of the magnetic flux, and the delay time from a current break to a start of valve closing operation depends on a strength of a magnetomotive force in the case of the current break, and the residual flux becomes larger with an increase in the magnetomotive force and it takes time to extinction of the magnetic flux, so that this delay time of the valve closing operation becomes long and accordingly, the valve closing required time becomes long and the minimum injection quantity also increases.
In the technique disclosed in the Examined Japanese Patent Application Publication No. Hei 4-23100 of the conventional example described above, the current-carrying time T1 of the valve opening current is made longer than the valve opening required time T0 by 0.1 ms to control the bounce and along with the delay time of the valve closing operation, an extension of this valve opening time of 0.1 ms has a great influence on the control of the minimum injection quantity and it is difficult to control the injection quantity to a predetermined value or less. Also, in the technique disclosed in the Examined Japanese Patent Application Publication No. Hei 3-7834, since the valve opening speed is reduced, the valve opening required time T0 becomes long and further, it is constructed so as to pass a current with a large value immediately before arrival at T0 and hold this until the opening of the valve stabilizes, so that the valve opening time becomes long and it is impossible to reduce the minimum injection quantity, and any of the techniques do not suit the direct injection type internal combustion engine.
An object of the invention is to obtain a fuel injection system which allows a decrease in the minimum injection quantity and control of a bounce in a simple control configuration and has the control contents suitable for a cylinder injection injector for directly injecting fuel into a cylinder of an internal combustion engine.
A fuel injection system according to the invention comprises an injector to be electromagnetically driven, injection control means for outputting a drive signal having first current-carrying time and second current-carrying time to this injector, and injector drive means for passing a large current to open a valve of the injector during the first current-carrying time and passing a small current to hold the injector in a valve opening state during the second current-carrying time, and is constructed so that the first current-carrying time is set to the time shorter than valve opening required time from a current-carrying start to full opening of the injector and this time difference is set to the value shorter than valve closing operation delay time from a current break in the case of breaking a current in the first current-carrying time to a start of valve closing operation by the injector.
Also, the fuel injection system is constructed so that current-carrying stop time for making a current-carrying stop is set between the first current-carrying time and the second current-carrying time and this current-carrying stop time is set to the value substantially equal to the time difference between first valve closing required time to the valve closing after the current break of the first current-carrying time and second valve closing required time to the valve closing after the current break of the second current-carrying time.