Toyota COMPUTER-CONTROLLED SYSTEM Training Manual page 71

EFI - Fuel Syste m
CURRENT CONTROL METHOD (for 4A-GE
engine with D-type EFI )
In injectors that use this method, the solenoid
resistor is eliminated, and a low-resistance
injector is connected directly to the battery .
Current flow is controlled by switching a
transistor in the Engine ECU on and off .
When the injector plunger is pulled in, a heavy
current flows, causing the amperage to rise
quickly . This causes the needle valve to open
quickly, resulting in improved injection response
and reduced ineffective injection duration .
While the plunger is held in, the current is
reduced, preventing the injector coil from
generating heat, as well as reducing power
consumption .
On
Injection Of f
signal ~
Voltage 12 V, 20kHz
waveform
0V i
~CT
BA
Amperage
waveform
®
This current builds up until the potential at point
"A" reaches a certain value, then the injector
drive circuit switches Tri off . The switching on
and off of Tr, is repeated at a frequency of
roughly 20 kHz over the duration of the
injection . In this way, the current to the injector
solenoid coils is controlled (when the +B voltage
is 14 V, the current pulling in the injector plunger
is approximately 8 A, while it is about 2 A while
the plunger is being held in) .
Tr2 absorbs counter-electromotive force from the
injector solenoid coil while Tri is being switched
on and off, thus preventing sudden reductions in
current .
If an extremely large current flows to the
injectors for any reason, the fail-safe main relay
goes off, cutting off the flow of current to the
injectors .
REFERENCE
The current control method was used in the
4A-GE engine with D-type EFI, which was
produced between August, 1983, and May,
1987 .
Ineffective
injection duration
OHP 50
The drive circuitry for this injector is as shown in
the figure at the right . Battery voltage is applied
to the ignition switch, then to the fail-safe main
relay or INJ fuse, then to the injectors, and
finally to the Engine ECU .
The fail-safe main relay is connected in such a
way that it is grounded through the injector
drive circuitry via the FS terminal of the Engine
ECU . The relay therefore goes on when the
ignition switch is turned on . This turns on Tr, in
the Engine ECU, letting current flow to the
injector solenoids .
Ignition
Fail-safe
switch main relay
*
Engine EC U
OHP 5 0
*In vehicles produced between August, 1984,
and May, 1987, an INJ fuse was used in place
of the fail-safe main relay .
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