What are the structural hotspots of a starter armature?

　　 Starter armature The entire armature is moved by the magnetic force of the magnetic poles, causing the drive gear to mesh with the flywheel ring gear. The armature of the starter is offset from the magnetic pole by a certain distance under the action of the return spring, and the commutator is relatively long. The starter housing is equipped with an electromagnetic switch. Its magnetizing coil is controlled by the starter switch S. The movable contact is the contact bridge. The upper end of the contact bridge is longer, and the lower end is shorter, so the starter circuit can be connected in two stages. The starter has three magnetic field windings, of which the main magnetic field winding with fewer turns is made of flat copper bars, and the other two fine wire windings are the series auxiliary magnetic field winding and the parallel auxiliary magnetic field winding (also called the holding coil). The starter one-way clutch generally uses a friction plate clutch.

　　The working process of the starter armature is divided into two stages. The series auxiliary excitation winding mainly works in the first stage, and in the second stage it is almost short-circuited due to being connected in parallel with the main excitation winding; the parallel auxiliary excitation winding works in both stages, which not only increases the magnetic force attracting the armature, but also limits the no-load speed.

　　(1) Engaging

　　When the starter switch S is turned on, the electromagnet generates suction to attract the contact bridge. However, due to the pawl resting against the workpiece, the contact bridge can only close at the upper end, and the series and parallel auxiliary magnetic field winding circuits are connected. The current circuit is: positive pole of the battery → static contact → upper end of the contact bridge → parallel auxiliary magnetic field winding → ground, ground → negative pole of the battery. Positive pole of the battery → static contact → upper end of the contact bridge → series auxiliary excitation winding → armature, armature → ground, ground → negative pole of the battery. The generated electromagnetic force overcomes the counteracting force of the return spring, attracting the armature to move to the left, and the starter drive gear meshes with the flywheel ring gear.

　　At this time, due to the large resistance of the series auxiliary magnetic field winding, the current flowing through the armature winding is small, and the starter rotates at a lower speed, so the armature rotates at a low speed and moves to the left, so the gear meshing is softer, which is the first stage of connecting the starter.

　　(2) Fully engaged

　　After the armature moves so that the small gear is fully engaged with the flywheel ring gear, the disc fixed on the commutator end face lifts the pawl to make the baffle trip, so that the lower end of the contact bridge closes, and the main magnetic field winding of the starter is connected. The starter drives the crankshaft to rotate at the normal working torque and speed, which is the second stage of connecting the starter.

　　During the starting process, the friction plate clutch engages and transmits torque. After the engine starts, the clutch disengages, and the crankshaft torque cannot be transmitted to the starter shaft. At this time, the starter is in a no-load state, the speed increases, the counter EMF in the armature increases, and therefore the current in the series auxiliary magnetic field winding decreases. When the current is small enough that the magnetic force of the magnetic pole cannot overcome the counteracting force of the return spring, the armature moves back to its original position under the action of the return spring, so the drive gear disengages, and the pawl returns to the locked position, preparing for the next action. The starter will not stop rotating until the starter switch S is turned off.

　　The starter armature can protect the flying car and counterattack capability from power limitations, so a high-power starter can be made. Its disadvantages are that it is not suitable for working in an inclined position, the structure is complex, and the transmission ratio cannot be large. In addition, when the friction plate is worn, the friction will be greatly reduced, so it needs to be adjusted frequently.