Doosan G20P-5, Руководство по обслуживанию

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G424F(FE) Service Manual Chapter 5. Engine Management System (EMS) 146
SECM
General Description
The Small Engine Control Module (SECM) controller
has full authority over spark, fuel and air. Utilizing a
Freescale micro controller, the SECM has 48 pins of
I/O and is fully waterproof and shock hardened. To
optimize engine performance and drivability, the
SECM uses several sensors for closed loop
feedback information. These sensors are used by
the SECM for closed loop control in three main
categories:
• Fuel Management
• Load/Speed Management
• Ignition Management
The SECM monitors system parameters and stores
any out of range conditions or malfunctions as faults
in SECM memory. Engine run hours are also stored
in memory. Stored fault codes can be displayed on
the Malfunction Indicator Light (MIL) as flash codes
or read by the MI-07 Service Tool software through
a CAN (Controller Area Network) communication
link.
Constant battery power (12 Vdc) is supplied through
the fuse block to the SECM and the main power
relays. Upon detecting a key-switch ON input, the
SECM will fully power up and energize the main
power relays.
The energized main power relays supply 12 Vdc
power to the heated element of the oxygen sensors,
fuel lock-off, fuel trim valves (FTVs), gasoline
injectors, gasoline fuel pump, crank sensor, cam
sensor, and the ignition coils.
The SECM supplies voltage to the electronic throttle
actuator, oil pressure switch, fuel temperature
sensor, and the coolant temperature sensor.
Transducer or sensor power (+ 5 Vdc) is regulated
by the SECM and supplied to the manifold
temperature/air pressure (TMAP) sensor, throttle
position sensor (TPS), and the accelerator pedal
position sensors (APP1 & APP2).
The SECM provides a transducer ground for all the
sensors, and a low side driver signal controlling the
fuel lock-off, MIL, gasoline injectors, gasoline fuel
pump, and FTVs.
Fuel Management
During engine cranking at startup, the SECM
provides a low side driver signal to the fuel lock-off,
which opens the lock-off allowing liquid propane to
flow to the N-2007 regulator. A stall safety shutoff
feature is built into the SECM to close the lock-off in
case of a stall condition. The SECM monitors three
engine states:
Crank, when the crankshaft position sensor detects
any engine revolutions
Stall, when the key is in the ON position but the
crankshaft position sensor detects no engine
revolutions
Run state, when the engine reaches pre-idle RPM.
When an operator turns on the key switch the lock-
off is opened but if the operator fails to crank the
engine, the SECM will close the lock-off after 5
seconds.
To maintain proper exhaust emission levels, the
SECM uses a heated exhaust gas oxygen sensor
(HEGO) mounted before the catalyst, to measure
exhaust gas content in the LP gas system. Engine
speed is monitored by the SECM through a variable
reluctance (VR) sensor or Hall-Effect type sensor.
Intake manifold air temperature and absolute
pressure are monitored with a (TMAP) sensor.
The HEGO voltage is converted to an air/fuel ratio
value. This value is then compared to a target value
in the SECM. The target value is based on
optimizing catalyst efficiency for a given load and
speed. The SECM then calculates any corrections
that need to be made to the air/fuel ratio.
The system operates in open loop fuel control until
the engine has done a certain amount of work.
This ensures that the engine and HEGO are
sufficiently warmed up to stay in control. In open
loop control, the FTV duty cycle is based on engine
speed and load.
Once the HEGO reaches operating temperature the
fuel management is in closed loop control for all
steady state conditions, from idle through full throttle.
In closed loop mode, the FTV duty cycle is based on
feedback from the HEGO sensor. The system may
return to open-loop operation when engine load or
engine speed vary beyond a chosen threshold.
The SECM makes any necessary corrections to the
air-fuel ratio by controlling the inlet fuel pressure to
the air-fuel mixer Reducing the fuel pressure leans
the air/fuel mixture and increasing the fuel pressure
enriches the air-fuel mixture. Control is achieved by
modulating the fuel trim valves.