Development of the ECU-integrated throttle body module
To allow for application to a small motorcycle, the FI system had to be simplified and down-sized considerably from the conventional one. The development team packed various functions into the compact yet simple system that could be installed in the place of a conventional carburetor by modularizing the throttle body, various sensors, and the engine control unit (ECU) into an integral unit.
|Aims of integrating and modularizing the throttle body and ECU|
|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.
|Outlines of system|
|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.
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
|FI system control|
|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
Fuel injection control
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.