Since the engine cannot be started by itself, external power is required to generate the first combustion to start it. To start the engine, the starter rotates the crankshaft via the ring gear.
The starter is required to generate extremely large torque from the limited power from the battery and should be compact and light as well. For this reason, a DC (direct current) series motor* is used for the starter.
To start the engine, the crankshaft has to rotate faster than the minimum cranking speed. The minimum cranking speed required to start the engine differs depending on the engine’s construction and operating conditions, but it is generally 40 to 60 rpm for a gasoline engine and 80 to 100 rpm for a diesel engine.
*DC (direct current) series motor
The DC (direct current) series motor consists of the field coil and the armature coil connected in series, and it is used to generate the maximum torque when the starter begins to turn.
Type of starter
(1)Reduction type
The reduction type starter uses a compact high-speed motor.
The reduction type starter increases torque by reducing the rotational speed of the armature with the reduction gear.
The plunger of the magnetic switch directly pushes the pinion gear located on the same axis and causes it to engage with the ring gear.
(2)Conventional type
The pinion gear is located on the same axis as the armature and rotates at the same speed.
The drive lever connected to the magnetic switch plunger pushes the pinion gear and causes it to engage with the ring gear.
(3)Planetary type
The planetary type starter uses a planetary gear to reduce the rotational speed of the armature.
The pinion gear engages with the ring gear via the drive lever, as with the conventional type.
(4)Planetary reduction-segment conductor motor (PS) type
The Planetary reduction-segment conductor motor (PS) type starter uses the permanent magnets in the field coil.
The engagement/disengagement mechanism works in the same way as the planetary type.