The starter consists of the following components.
1.Magnetic switch
2.Armature
3.Yoke sub-assembly
4.Brush and brush holder
5.Reduction gear
6.Overrunning clutch
7.Pinion gear and helical spline
1.Magnetic switch
The magnetic switch operates as a main switch of the current flowing to the motor and controls the pinion gear by pushing and pulling it.
The pull-in coil is wound up with thicker wire than the hold-in coil, and its magnetomotive force of the pull-in coil is also greater than that of the hold-in coil.
2.Armature and ball bearing
The armature generates a motor’s revolving force, and the ball bearing supports the high speed revolution of the armature.
3.Yoke sub-assembly
The yoke sub-assembly produces the magnetic field required for the motor to operate. It also works as an outer case of the field coil, the pole core and a passage of the lines of magnetic force. The field coil is connected to the armature coil in series.
4.Brush and brush holder
The brushes are pressed against the armature commutator by the brush springs, allowing the current to flow from the coil to the armature in fixed direction. The brushes are made of copper-carbon, which has excellent conductivity and abrasion resistance characteristics. The brush springs repress the excessive revolution of the armature and stop the armature revolution just after the starter stops by pressing the brush.
Weakened brush springs or worn brushes may lead to insufficient electrical contact between the brushes and the segments of the commutator. The resulting excessive electrical resistance at the contact points will reduce the supply of current to the motor, impeding torque build-up.
5.Reduction gear
The reduction gear transmits the revolving force of the motor to the pinion gear and increases torque by slowing the motor speed as well. The reduction gear reduces the revolution of the motor at a reduction ratio of 1/3-1/4, and it has an overrunning clutch built-in.
6.Overrunning clutch
The overrunning clutch transmits the motor rotation to the engine via the pinion gear.
In order to prevent the starter breakage by its high-speed revolution arising from engine start, the overrunning clutch is a one-way type with rollers.
7.Pinion gear and helical spline
The pinion gear and the ring gear transmit the revolving force of the starter to the engine by securely engaging with each other. The pinion gear is chamfered for excellent engagement. The helical spline converts the revolving force of the motor to the driving force of the pinion and supports the engagement and the disengagement of the pinion gear as well.