Archive for category k. Control unit and other electronics

Control unit and other electronics

A key part of the successful completion of this motorcycle is the integration of the electronic controls. Fuel injection requires a computer control system to operate. In addition to the computer control system, a handful of sensors were added, along with a complete reworking of the electrical system.

To handle the computer controls for this motorcycle, the Megasquirt II ecu system was purchased. This is a do it yourself ecu that shows up as a blank PCB board. This ecu system was chosen because of its low cost and its highly adjustable nature.

Figure ECU1: Megasquirt system ready for assembly

Figure ECU2: Assembled Megasquirt and relay board

The Megasquirt ecu must be configured in hardware for certain conditions; type of injectors, type of IACV, ignition system, etc. This system handles all of the fuel control needs, ignition control needs, and communicates with an external PC for tuning purposes. Along with the ecu, a relay board was assembled. This contains the needed fuses for the electronically controlled components of the bike, allows for a hub for all of the wiring, and provides relays to supply power to the key systems. For the operation of this system, four key sensors are added. A throttle position sensor, located on the throttle body, measures percentage of throttle opening. A manifold absolute pressure sensor, located at the ecu, fed from a vacuum port after the throttle plate, measures load on the motor and positive pressure provided by the compressor. This same vacuum port provides a vacuum signal to the blow off valve. An intake air temperature sensor in the intake pipe shortly upstream of the throttle body reads the temperature of the compressed intake air. This allows for fuel corrections based on different air densities. Finally, a wideband oxygen sensor with a separate control unit measures the oxygen content of the exhaust gases. Exhaust gas analysis is used in real time tuning of the fuel maps. This tuning is key to the vehicle operating in a reliable, efficient manner. An incorrect fuel map will lose power, increase fuel consumption, increase emissions, and can catastrophically damage the motor.

Figure ECU3: Completed electronics; TechEdge wideband controller, Megasquirt ecu, relay board

Because space is such a concern and the components in the ecu are heat sensitive, the electronics are mounted under what was the passenger seat of the motorcycle.

Figure ECU4: Tail mounting of electronics

Figure ECU5: Carbon fiber mounting plate

Figure ECU6: Carbon fiber seat cowl

A carbon fiber plate was fabricated to run under the seat for the electronics to mount on. The passenger area of the seat was hollowed out to provide ample space for the components with a carbon fiber shell added to further protect the components.

The addition of all of the piping under the seat filled the space normally taken up by the stock battery. The stock battery is a 12v lead acid battery that is extremely heavy, prone to draining in a short period of time, and occupies a lot of space. For this project, a new battery was needed. A 4 cell LiFePO4 battery was fabricated from 3.3 V cells. This provides sufficient amperage for starting and running the bike, is much safer than a lead acid battery, significantly reduces weight, and is far easier to fit on the bike. The battery tucks up nicely between the end tanks on the intercooler.

Figure ECU7: LiFePO4 battery pack

Final weight for the battery is around 1.1 lbs, about 10% of the stock battery.

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