Alternator electrical circuit in a automotive - Basics of control engineering, this and that

・Running resistance

・Vehicle acceleration

・Alternator

・Fuel injection amount

・IMEP vs BMEP

・MY, CY, FY

・Turning Radius

・Roll, Pitch, Yaw

・Torque and power

・Engine vs vehicle speed

・WLTP, WLTC

・OBD

・Tire size

・Failsafe, failproof

・Water,Buttock,Transverse Line

・Gears, splines

■What is an automobile alternator?

An alternator is a generator that generates 3-phase alternating current and is mainly installed in automobiles. As shown in the figure below, alternating current is converted to direct current (AC-DC conversion) and power is supplied to electrical devices.

＜B terminal＞
The current output from the B terminal is connected in parallel with the battery and supplied to the electrical device. The reason for connecting in parallel with the battery is:When the battery capacity is low, the alternator supplies current to the electrical devices while charging the battery, or the alternator is temporarily stopped to improve fuel efficiency while the battery supplies current to the electrical devices. The voltage at the B terminal is 12-14V, and the current varies depending on the specifications of the alternator.

＜D terminal＞
The amount of power generated by the alternator is determined by the rotational speed of the magnetized rotor and the magnitude of the current flowing through the rotor coil (field coil) wound around the rotor. The larger the current, the stronger the magnetic force of the rotor. Since the rotor speed is determined by the engine speed (gear stage and vehicle speed) and is difficult to control, the amount of power generated is controlled by adjusting the current flowing through the rotor coil.

The current flowing through the rotor coil is controlled by the ECU (electronic control unit) applying a voltage to the D terminal that turns the transistor on and off with Pulse Width Modulation.

＜P terminal＞
The voltage generated by the alternator is input from the P terminal to the ECU, and the ECU uses the voltage value to adjust the duty cycle to achieve the target voltage value for the alternator or to detect alternator failure. You may think that the voltage at the B terminal should be input to the ECU, but since the B terminal is connected to the battery and electrical devices, the ECU cannot determine whether the alternator is normally generating power due to voltage fluctuations, so the voltage is input from a different terminal than the B terminal. The same reason why the current to the field coil is the current on the P terminal side is to supply a stable current.