Conventional type
1.Construction differences between the conventional type and the reduction type (figure on the left)
2.Engagement/disengagement of the pinion gear
(1)Magnetic switch
The construction of a magnetic switch of the conventional type is basically the same as that of the reduction type. However, this type pulls the plunger to engage and disengage the pinion gear, whereas the reduction type pushes the plunger to do it.
(2)Drive lever
The drive lever transmits the movement of the magnetic switch to the pinion gear. The pinion gear engages and disengages with the ring gear by this movement.
(3)Drive spring
The drive spring is built in the drive lever or in the magnetic switch. The drive spring of the conventional type operates in the same way as the return spring of the reduction type.
3.Speed reduction mechanism
Since the conventional type can obtain enough torque to start the engine by the large-type armature, the speed reduction mechanism is not necessary for this type. For this reason, the armature is connected directly with the pinion gear.
4.Brake mechanism
(1)General
Some conventional types are equipped with a brake mechanism, which stops the revolution of the motor if the engine failed to start. The brake mechanism also controls a high speed of the motor just after the engine starts.
A part of conventional type starters and reduction type starters other than those that have a brake mechanism are not so equipped for the following reasons:
The armature is lightweight, and inertia force is low.
A pressure of the brush is large.
The speed reduction gear causes friction.
However, there are some large-sized starters (24V-type) which are equipped with an electrical brake mechanism.
(2)Operation
The brake spring and the lock plate push the armature against the commutator end frame to produce braking effect.
Planetary type
1.Construction differences between the planetary type, the reduction type and the conventional type (figure on the left)
2.Engagement/disengagement of the pinion gear
Drive spring
The drive spring is built in the magnetic switch. The drive spring operates in the same way as the reduction type and the conventional type.
The magnetic switch and the drive lever operate in the same way as the conventional type.
3.Speed reduction mechanism
(1)Construction
The planetary carrier has three planetary gears. The planetary gears engage with the sun gear on the inner side and with the internal gear on the outer side. Normally, the internal gear is fixed and does not revolve.
(2)Characteristics
Reduction ratio of the planetary type is 1:5, and the armature is smaller and its speed is faster than that of the reduction type. In order to achieve quiet operation, plastic material is used for the internal gear. The planetary type has a dumping device, which absorbs excess torque, to avoid the internal gear breakage.
(3)Operation
When the sun gear is driven by the armature, the planetary gear revolves along with the internal gear and then the planetary carrier revolves. As a result, the speed of planetary carrier with the planetary gear reduces, causing torque to pinion gear to increase.
Damping Device:
PS (Planetary reduction-Segment conductor motor) Starter
1.Field coil
Instead of the field coils used in the conventional starter, the PS (Planetary reduction-Segment conductor motor) starter uses two types of permanent magnets: the main magnets and the interpolar magnets.
The main and interpolar magnets are arranged alternately inside the yoke. This allows the magnetic flux generated between the main and interpolar magnets to be added to the magnetic flux generated by the main magnets. In addition to increasing the amount of magnetic flux, this construction shortens the overall length of the yoke.
PS (Planetary reduction-Segment conductor motor) Starter
2.Armature
Instead of the round-shaped conductor wires used in the conventional starter, the PS (Planetary reduction-Segment conductor motor) starter uses square-shaped conductors. In this type of construction, square-shaped conductors can achieve the same conditions as those achieved by winding numerous round-shaped conductor wires, but without increasing the mass. As a result, the output torque is increased, making the armature coil more compact. Because the surface of the square-shaped conductors that are used in the armature coil functions as a commutator, the overall length of the PS starter is shortened.