The present invention relates to an electromagnetic fuel injector system and an internal combustion engine; and, more particularly, the invention relates to an electromagnetic fuel injector system which is directly driven by a battery voltage, and an internal combustion engine equipped with said fuel injector system.
The electromagnetic fuel injector system is used in an internal combustion engine, for example, as provided in a vehicle, such as car.
The electromagnetic fuel injection valve (hereafter simply called an xe2x80x9cinjectorxe2x80x9d) of this electromagnetic fuel injector system comprises a nozzle provided with fuel injection hole, a plunger which is inserted in the nozzle in a freely reciprocating manner with a valve on the tip thereof, a return spring to give elastic force to the plunger to bias it in the direction of closing valve, and a coil to provide the plunger with electromagnetic force for opening the valve, using the power supplied from a battery. When current is applied to the coil, the plunger is attracted and the valve is released from the valve seat to open a fuel injection hole; and then fuel is jetted out of the fuel injection hole. When application of current to the coil is suspended, magnetic attraction by the coil is damped, and the valve is closed by the elastic force of the return spring.
The volume of injection by the injector is controlled by the valve opening command time. Generally, there is a delay of valve response with respect to the valve opening command time and the valve closing command time. An area where perfect linearity cannot be established occurs in the fuel injection volume characteristics showing the relationship between the valve opening command time and the injection volume. This requires the injector to have a linearity established over an extensive field. However, the injector mounted on an internal combustion engine, typically designed for reduced manufacturing costs, is required to ensure accurate injection with less fuel, and linearity with respect to a short valve opening command time is very important. To meet these requirements, a great variety of injector driving methods have been proposed.
For example, a saturated method (voltage drive) and peak hold method (current drive) are well known injector drive methods, as disclosed in xe2x80x9cElectronically Controlled Gasoline Injectionxe2x80x9d (by Fujisawa and Kobayashi, 1987, Sankaido Publishing Co., Ltd.).
Generally in the saturated method, many turns of coil are used, so that the drive current continues to increase even after the valve lifting has been terminated, until it reaches the point close to the saturated current, which is restricted by the coil internal resistance and the drive circuit internal resistance. The circuit impedance is higher than that in the peak hold method, and the rising edge of the current flowing to the coil is less sharp due to inductance. If the saturated current value is properly set by adjusting the coil internal resistance and drive circuit internal resistance, there is no need to provide a current control circuit, thereby allowing manufacture at reduced costs.
In the peak hold method, a smaller number of coil turns are used. The circuit inductance and circuit impedance are low, and the rising edge of the current during the valve opening operation is sharper than that which occurs in the saturated method. However, the coil inductance and impedance are low in this method. So, if the current is continuously applied to the coil in a specified state, excessive current will flow to the coil to damage it. To prevent this, this method uses a current limiting mechanism provided in the drive circuit. When the current flowing to the coil has reached a preset value (set peak current), the duty of voltage applied to the coil is dropped from 100%, thereby restricting the current to the value required to hold the valve.
Comparison of the above two methods shows that the peak hold method with high current response is more frequently used in order to take advantage of the linearity of injection volume with respect to valve opening command time in the low injection area.
For example, Japanese Patent Laid-Open No. 241137/1994 discloses an electromagnetic fuel injector system where the fuel pressure is detected to increase the target peak current value according to the fuel pressure or to prolong the current switching time, thereby adjusting the magnetic attraction, namely, the drive force with respect to the changes of the load applied to the valve body.
The fuel injector disclosed in Japanese Patent Laid-Open No. 241137/1994, however, is not directly driven by the battery voltage. It has a voltage boost circuit and low voltage circuit, thereby eliminating any need for consideration being given to changes in the electric circuit system during driving.
In other words, the electromagnetic fuel injector driven directly by a battery voltage requires consideration to be given not only to the changes of loads applied to the valve body, but also to the changes occurring to the electric circuit comprising the battery, coil and harness, such as the drop of battery voltage due to startup or abrupt change of electric load, to the secular change of the resistance of the harness including the coil, and to the increase of resistance due to heat generation.
With the battery voltage being applied directly to the coil, a drop of the battery voltage will delay the time for coil current to reach the preset peak current value. Moreover, a substantial drop of battery voltage may prevent the coil current from reaching the preset peak current value.
In an electromagnetic fuel injector, the voltage applied to the coil causes the coil current to be delayed by the inductance component of the coil. Delay between the input magnetomotive force (product of current and number of coil turns) and magnetic attraction is also caused by an eddy current. This delay will turn into a kind of integrating filter; therefore, not only the peak current value, but also the current application time must be taken into account in order to achieve linearity also in the low injection area with the magnetic attraction assuming an appropriate value.
In other words, when the peak hold method is used, the injector is not directly driven by the battery voltage in the prior art; therefore, the configuration thereof is not made optimum to achieving the required linearity of injection volume under each condition, with respect to the changes occurring to the electric circuit comprising the battery, coil and harness.
An object of the present invention is to provide a fuel injector system and internal combustion engine capable of maintaining the linearity of injection volume with respect to the changes in the state of the electric circuit provided to drive the electromagnetic fuel injection valve.
The above object can be attained by providing a fuel injector system which comprises a current application controller which controls the drive of the valve body, installed on an electromagnetic fuel injection valve, by controlling the current so that current flows to a coil to generate an electromagnetic force for driving said valve body until the current driving said valve body in the direction of opening the valve becomes greater than that of holding said valve body open, and by controlling current so that a change occurs to the current application time when driving said valve body in the direction of opening; wherein said current application controller allows current to be applied to reduce the maximum current in the event of increase of said current application time when driving said valve body in the direction of opening, said valve. In this case, it is preferred that current be applied to the coil installed on the electromagnetic fuel injection valve without boosting the battery voltage, and that a current application circuit to allow current to flow from the battery to the coil be provided.
The fuel injector comprises (1) a voltage detecting means to detect the voltage of the battery connected to said current application circuit, (2) a current detecting means to detect the current flowing to the coil connected to said current application circuit, and (3) a current value storage means to store the target peak current value in conformity to the battery voltage.
Here, the current application controller captures the target peak current value in conformity to the voltage detected by said voltage detecting means from said current detecting means, compares said target peak current value to the current detected by said current detecting means, and controls the current application using as a target value the current value which is smaller than said target peak current value, on conditions of agreement of said two current values.
In this case, the current storage means preferably stores the target peak current, where the current is reduced in conformity to a drop in the voltage of the battery connected to the electric circuit.
Furthermore, said injector comprises (1) a combined resistance estimating means to estimate the combined resistance, including the resistance of said current application circuit to connect the battery with the coil, and the resistance of the coil connected to said current application circuit, (2) a current detecting means to detect current flowing to said current application circuit, and (3) a current storage means to store the target peak current in conformity to said combined resistance; wherein said current application controller captures from said current storage means the target peak current in conformity to the resistance estimated by said combined resistance estimating means, compares this target peak current with the current, detected by the current detecting means, and controls current application using as a target value the current value which is smaller than said target peak current value, on conditions of agreement of said two current values.
In this case, the combined resistance estimating means is preferably configured to ensure that the estimate changes in the composed resistance, including the resistance of said current application circuit and the resistance of the coil connected to said current application circuit, from the relationship between the current value stored in said storage means and the combined resistance, using the time elapsed after start of current application and the current value after lapse of a specified time.
It is also preferred that a voltage detecting means be provided, and the storage means to store the relationship between the current and combined resistance store the relationship between the current and combined resistance with respect to voltages of multiple batteries, and configuration be designed to estimate the combined resistance including the resistance of said current application circuit and the resistance of the coil connected to said current application circuit, based on the battery voltage detected by the voltage detecting means.
It is further preferred to provide control to delay the time to switch the state of current application from the target peak current value to the holding current value, if there is an increase of the combined resistance including the resistance of the current application circuit and the resistance of the coil connected to this current application circuit.
It is also preferred that the current value storage means stores a target peak current value where the current value is reduced in conformity to an increase of the combined resistance.
Further, a fuel injector comprises (1) a voltage detecting means to detect the voltage of the battery connected to said current application circuit, (2) a current detecting means to detect the current flowing to the coil connected to said current application circuit, and (3) a timing storage means to store the time to switch in conformity to said battery voltage; wherein said current application controller operates to measure the time elapsed from the start of current application in the case of driving the valve body in the direction of opening the valve, captures from said timing storage means the time to switch in conformity to the voltage detected by said voltage detecting means, compares this switching time with said measured time, and controls the current application using as a target value the current value which is smaller for the current flowing to said coil, on conditions of agreement of said two times.
In this case, it is preferred that the timing storage means store the target switching time which is delayed in conformity to a drop of the battery voltage.
Further, the fuel injector comprises (1) a combined resistance estimating means to estimate the combined resistance including the resistance of said current application circuit to connect the battery to the coil, and the resistance of the coil connected to said current application circuit, (2) a current detecting means to detect current flowing to the coil, and (3) a timing storage means to store the time to switch in conformity to said combined resistance; wherein the current application controller operates to measure the time elapsed from the start of current application in the case of driving the valve body in the direction of opening the valve, captures from said timing storage means the time to switch in conformity to the resistance estimated by said combined resistance estimating means, compares this switching time with said measured time, and controls the current application using as a target value the current value which is smaller for the current flowing to said coil, on conditions of agreement of said two times.
In this case, it is preferred to provide control to delay the time to switch the state of current application from the target peak current value to the holding current value, if there is an increase of the combined resistance including the resistance of the current application circuit and the resistance of the coil connected to this current application circuit.
It is also preferable for that the timing storage means to store the target switching time which is delayed in conformity to the increase of the combined resistance.
The above object can also be attained by providing a fuel injector system comprising a current application controller which controls the drive of the valve body, installed on an electromagnetic fuel injection valve, by controlling the current so that current flows to a coil to generate an electromagnetic force for driving said valve body until the current driving said valve body in the direction of opening the valve becomes greater than that of holding said valve body open, and by controlling current so that a change occurs to the current application time when driving said valve body in the direction of opening; wherein said current application controller controls current to the coil, based on fuel injection command pulse having a width which is compensated when there is an increase in current application time.
Furthermore, the above object can also be attained by providing a fuel injector comprising a current application controller which controls the drive of the valve body, installed on an electromagnetic fuel injection valve, by controlling the current so that current flows to a coil to generate an electromagnetic force for driving said valve body until the current driving said valve body in the direction of opening the valve becomes greater than that of holding said valve body open, and by controlling current so that a change occurs to the current application time when driving said valve body in the direction of opening;
wherein said fuel injector comprises a combined resistance estimating means to estimate the combined resistance including the resistance of said current application circuit connected between the battery electrically connected to said coil to supply current thereto and said coil, and the resistance of said coil; and said current application controller controls current to the coil, based on a fuel injection command pulse having a width which is compensated in conformity to the resistance estimated by said combined resistance estimating means.
According to the present invention, delay in the valve closing operation is reduced by allowing current to be applied to reduce the maximum current in the event of an increase of said current application time when driving said valve body in the direction of opening said valve, thereby maintaining the linearity of the injection volume.
By controlling the current to the coil based on a fuel injection command pulse having a width which is compensated when there is can increase in current application time, it is possible to reduce the influence on the fuel injection volume given by the change in the state of the drive circuit which causes the current application time to increase. This allows the linearity of the injection volume to be maintained.
It is also possible to reduce the influence of combined resistance on the fuel injection volume by compensating the pulse width in conformity to the combined resistance, including the resistance of the current application circuit connecting the battery with the coil and the resistance of the coil. This allows the linearity of injection volume to be maintained.