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Aims of integrating and modularizing the throttle body and ECU |
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In conventional motorcycle FI systems, the ECU is mounted
to the vehicle body. Also, various sensors for detection of
the control information are located at various places in the
engine or vehicle body as an independent component. Because
of that, many wire harnesses are required to connect various
sensors to the ECU. Consequently, the conventional system is
complex, and difficult to apply to a small motorcycle having
a 50cc-125cc single cylinder engine. In an attempt to practically
apply a compact PGM-FI in place of a carburetor, the throttle
body, which controls the intake air volume, and the ECU module,
which controls engine operating conditions, have been integrated
into one unit. With the wire harnesses eliminated, the size
of the module has been reduced to the same size as a carburetor.
| Example
of conventional FI system for motorcycles |
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Cut
model of FI for small motorcycles |
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Outlines of system |
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The newly developed compact PGM-FI system has a two-split
configuration consisting of the throttle body and the ECU module.
This configuration allows for replacement of a throttle body
having a bore size suitable for a particular engine displacement,
thus realizing a FI system applicable to various models with
a high level of application freedom. The throttle body and ECU
module incorporating various sensors are connected with 4 bolts.
The idle air passage is grooved on the mating surface, and by
sealing with an O-ring, the idle air passage is formed, thus
contributing to the integration and down-sizing. The ECU module
unit consists of the plastic box (device body), ECU board, and
the cover. Various sensors are housed in the device body, and
the ECU board is connected directly to the input and output
terminals of the sensors. Applying the cover from above, the
inside is packed with potting resin to secure the internal parts
and to prevent water entry.
Layout
of sensors
The throttle body module has 3 sensors in the device body.
| 1. |
Intake air temperature (Ta) sensor: To allow measurement
of intake air temperature, the sensing tip of the sensor
is exposed in the intake air passage before the throttle
valve. For down-sizing, the sensor terminals are directly
mounted on the ECU board. |
ECU module component |
| 2. |
Throttle position sensor (TPS): Located on the end of
the throttle shaft, directly detects the throttle opening.
The throttle shaft and the sensor rotor are connected
via a spring to eliminate a hysteresis in the operation.
The TPS is directly fit into the device body and sealed
from outside by potting. |
| 3. |
Manifold vacuum (Pb) sensor: The sensor terminals are
directly mounted on the ECU board, and connected to the
connecting passage provided after the throttle valve in
the throttle body. |
ECU
board
The ECU board used in the PGM-FI system for small motorcycles
is exclusively designed for single cylinder engines. The size
is reduced by providing an injector driver circuit and an ignition
circuit for one cylinder, allowing mounting on the side of the
throttle body. The CPU used for the controller is a 16bit CPU.
The large parts such as the power supply condenser are located
in the space between various sensors in the device body, contributing
to reduce the overall width to the same level as a conventional
carburetor. The ECU board is a 4-layer structure to reduce the
surface area for various circuits. In addition, the harness
connector, which takes a large amount of space in a conventional
ECU, has been down-sized to approximately 1/2 from the conventional
one by using a terminal-to-terminal pitch of 2.6mm·32
pin design. The reduction of terminal-to-terminal pitch becomes
possible by using an adhesive gel sheet to seal the connector
from water. To allow application of additional function such
as an immobilizer, the number of pins is set at 32.
Idle air
control device
| Compared to a large motorcycle, less volume of intake
air has to be controlled for a small displacement motorcycle
engine. To cope with the stringent exhaust emission regulations,
delicate control capabilities are also required. At the
same time, to make an FI system applicable to small motorcycles,
down-sizing is the key. To satisfy these demands, the
slide-valve-type air control valve (SACV) driven by a
stepping motor is applied to the PGM-FI system for small
motorcycles. In conventional direct drive type, a stepping
motor of ø20mm was required to maintain the operating
torque to overcome the intake vacuum. In this system,
the size of the stepping motor has been reduced to ø14mm
by using the slide valve design. |
Comparison of idle-air control valve
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FI system control |
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The PGM-FI system for small motorcycles controls the fuel
injection volume, injection timing and the ignition timing based
on signals from the throttle position sensor (TPS) in the ECU
module, the manifold vacuum (Pb) sensor, and the crank position
sensor that detects the rotation angle. The fuel injection volume,
the injection timing and the ignition timing are further compensated
by the engine temperature, intake air temperature and the atmospheric
pressure to ensure optimum controls under various environmental
conditions.
Fuel
injection control
| For the control of fuel injection volume,
two kinds of maps are stored in the ECU and an appropriate
map is selected and used depending on the throttle opening
and the engine revolutions. |
| 1. |
When the loads are low, the delicate changes in throttle
opening are detected by the manifold vacuum, and the manifold
vacuum map determined by the manifold vacuum and the engine
revolutions is used. |
| 2. |
When the loads are high, the throttle map determined
by the throttle opening and the engine revolutions is
used. |
Ignition
timing control
For ignition timing, the map control determined by the throttle
opening and the engine revolutions is executed to control the
ignition timing at the optimum timing.
O2
feedback control
To efficiently use the 3-way catalyst in the exhaust muffler,
the feedback system using an O2 sensor
is applied to control the mixture near the stoichiometric ratio.
Control
of idle air control device
The idle air control valve regulates the intake air volume depending
on the operating conditions such as the starting, warming up
and idling. When starting, the intake air is supplemented by
opening the idle air control valve depending on the engine temperature
for easy starting. The opening of the air control valve is regulated
depending on the increase of the engine temperatures to control
the intake air volume at the optimum level. After the engine
reaches the prescribed temperature, the intake air volume is
controlled to maintain idling at a constant speed by the revolution-feedback
control. This feedback control eliminates the conventionally
required idle speed adjustment, thus eliminating the need of
maintenance to compensate for the secular distortion.
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