Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2002-05-21
2004-03-30
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C361S154000
Reexamination Certificate
active
06712048
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to driving circuitry for an electromagnetic fuel injection valve for use in a direct-injection gasoline engine in which fuel is injected directly into the engine cylinder.
2. Discussion of Related Art
For the purpose of improving the combustion efficiency of a gasoline engine, it has been attempted to inject fuel directly into the engine cylinder from an injector (electromagnetic fuel injection valve) provided for the cylinder. The direct injection of fuel into the cylinder allows all the gasoline fuel injected from the injector to be supplied into the cylinder and hence makes it possible to realize combustion closer to the stoichiometric one. Accordingly, it is possible to enhance fuel economy and to reduce NO
x
, HC and so forth in exhaust gas.
In the case of the direct injection, where the gasoline fuel is injected is a space formed by the cylinder block, the piston and the cylinder head. Considering the fuel injection performed during compression stroke, the fuel has to be injected under a very high pressure in comparison to port injection in which fuel is injected into the intake manifold. Further, there is no sufficient space and time to allow the injected fuel to diffuse satisfactorily. Accordingly, in order to obtain combustion conditions comparable to those of the port injection engine under the above-described conditions, it is necessary to increase the pressure of gasoline fuel supplied to the injector so that the fuel is satisfactorily diffused from the moment it is injected into the cylinder.
An injector driving circuit
1
for a direct-injection gasoline engine as shown in
FIG. 3
has heretofore been known [see Japanese Patent Application Unexamined Publication (KOKAI) No. Hei 11-351039]. The injector driving circuit
1
excites a solenoid L of an injector (INJ) of an engine to drive the injector. The solenoid L excited by the injector driving circuit
1
is contained in the injector (electromagnetic fuel injection valve). Although detailed illustration of the arrangement of the injector is omitted in the figure, the injector has a plunger slidable inside the solenoid L, a needle valve secured to the plunger, and a spring for urging the needle valve in the direction in which it is closed.
The injector driving circuit
1
in
FIG. 3
includes a high-voltage application part
2
, a timing control part (TC)
3
, a constant-current control part
4
, switches SW
1
to SW
3
, and so forth. The high-voltage application part
2
comprises a high-voltage charge control part (HVC)
20
and a capacitor C for charging. The high-voltage charge control part
20
is connected between a battery B (power supply) and the capacitor C to convert the battery voltage (+B, e.g. 12 V) to a high voltage of the order of 200 V and to control charging of the capacitor C. The timing control part
3
on-off controls the switches SW
1
to SW
3
individually at predetermined timing on the basis of an injection command signal output from an engine control unit (ECU; not shown). It should be noted that the ECU judges the operating condition of the engine on the basis of detection signals input thereto from various sensors and outputs an injection command signal and so forth to each control part of the engine according to the judged operating condition.
The constant-current control part
4
comprises a comparator circuit
41
, resistors
42
and
43
, and reference voltage generating resistors
44
and
45
. The non-inverting input terminal of the comparator circuit
41
is supplied with a reference voltage obtained from the reference voltage generating resistors
44
and
45
. The inverting input terminal of the comparator circuit
41
is supplied with a detected value (voltage) from a resistor R
4
for detection. The switch SW
3
is on-off controlled by a signal from the timing control part
3
or an output signal from the comparator circuit
41
. On the basis of a control signal from the timing control part
3
, or when the injector current is not in excess of a predetermined value, the switch SW
3
is turned on to apply the battery voltage (+B) to the injector solenoid L (including an internal resistor R
1
). The electric current produced by the battery voltage is supplied to the injector solenoid L through a holding current supply circuit
7
. It should be noted that reference symbol D
1
denotes a diode for preventing backward flow of the electric current produced by the applied voltage.
Control signals transmitted from the timing control part
3
through resistors R
2
, R
3
and resistors
43
and
42
are input to the switch control parts of the switches SW
1
to SW
3
, and thus the switches SW
1
to SW
3
are on-off controlled, respectively. The switch SW
1
controls the application of the high voltage to the injector solenoid L. The high-voltage current is supplied to the injector solenoid L through a switch circuit
6
. The switch SW
2
controls the electric current supplied to the injector solenoid L. That is, the drive of the injector INJ is controlled through the switch SW
2
. A Zener diode ZD
1
and a diode D
3
form an arc-suppression circuit.
The operation of the injector driving circuit
1
shown in
FIG. 3
will be described below with reference to the timing chart of FIG.
4
. Let us assume that the capacitor C has been charged by the high-voltage charge control part
20
, and the solenoid applied voltage V
d
is high V
c
as shown in (f) of FIG.
4
. In response to an injection command signal, the timing control part
3
operates to turn on the switches SW
1
to SW
3
simultaneously at time t
1
, as shown in (b) to (d) of FIG.
4
.
As the switch SW
1
turns on, the high voltage stored in the capacitor C is applied to the injector solenoid L. An injector solenoid excitation current (hereinafter referred to as “excitation current”) I
SOL
flows through the injector solenoid L in the mode as shown in (e) of FIG.
4
. Consequently, the needle valve begins to open. At time t
2
when the excitation current value exceeds a preset current (large current) value I
th
for fully opening the needle valve of the injector, the switch SW
1
turns off to terminate the application of the high voltage to the injector solenoid L.
Because the switch SW
3
is turned on at time t
1
, the battery voltage (+B) is applied to the injector solenoid L during the period between time t
2
and time t
3
at which the switch SW
3
is turned off. Regarding the application of the battery voltage (+B), the on-state of the switch SW
3
is continued for the period &tgr;
2
between time t
1
and time t
3
, as shown in (d) of FIG.
4
. The needle valve is held in a substantially full open position during the period between time t
2
and time t
3
.
As shown in (f) of
FIG. 4
, the solenoid applied voltage V
d
is a rectangular wave-shaped high voltage during the period between time t
1
and time t
2
at which the switch SW
1
is turned off, i.e. during the period t
1
shown in (b) of FIG.
4
. It should be noted that the voltage waveform shown in (f) of
FIG. 4
does not show the terminal voltage of the injector solenoid L but the voltage applied to the solenoid L, i.e. the waveform of the composite voltage on the voltage application side. The period &tgr;
1
is set as a period of time (constant value) sufficient to fully open the needle valve with reliability.
At time t
3
, the switch SW
3
is turned off to terminate the application of the battery voltage (+B) to the solenoid L. During the period &tgr;
3
between time t
3
and time t
4
at which the injection command signal is switched off, the switch SW
3
is of-off controlled at predetermined intervals to apply a pulsed battery voltage (+B) to the solenoid L. That is, as shown in (e) of
FIG. 4
, a constant excitation current I
SOL
(holding current) smaller than the preset current value I
th
flows through the solenoid L to hold the fully opened needle valve in a substantially full open position.
At time t
4
when the fuel injection signal
Aoki Tsuneaki
Okada Atsushi
Yoneshige Kazuhiro
Aisan Kogyo Kabushiki Kaisha
Argenbright Tony M.
Baker & Botts LLP
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