The Drive By Wire (hereafter referred to as DBW) system is the electronically throttle control system. It controls a throttle valve in order to aim at a suitable throttle position according to an engine operating condition and a demand of driver or rider. This system is basically composed of a throttle body with driving motor, an Accelerator Position Sensor (hereafter referred to as APS), and an Electronic Control Unit (hereafter referred to as ECU). The DBW system is spreading to motorcycle field as replacement of existing mechanical intake control system. This is because there are some advantages as the following especially in the large displacement model: capability for installation of several functions, flexibility in adaptation to recent environmental regulations, and effect on reduction of system cost, etc.
In general, the motorcycle has some unique features compared with the automobile. Among them, important features for the DBW system are following three points. The first, dynamic behavior of the motorcycle is controlled by adjustment of engine power, which is based on the dynamics of single-track vehicle. The second, response of engine power to the throttle operation is fast, this is because the motorcycle has an air-intake pipe with short length at each cylinder. The third, engine layout of the motorcycle is great variety, and mounting space of intake devices is very limited because of the compact frame structure. Thus, requirements of the DBW system for the motorcycle are two points as the following: firstly, the throttle valve control should be more responsive and more accurate, and should be robust to various disturbances compared with the automobile; secondly, the design of the DBW throttle body should have flexibility so as to satisfy various required layout.
Therefore, the DBW system for the motorcycle was developed in order to satisfy special requirements of motorcycle above. This development was achieved by two key technologies as the following: firstly, the throttle valve control which is superior on response, accuracy, and robustness to disturbances by the feedback control with a disturbance estimator; and secondly, modularization of the DBW unit which transmits motor torque to a throttle shaft.