The process of a deceleration starter from a stationary state to a running state is called starting. Before the starter enters the normal working cycle, it must be started by external force. The task of a modern car starter is to convert the electrical energy of the battery into mechanical energy and drive the flywheel of the engine to start the engine.
A typical starting system has three basic components, namely the battery, the ignition switch, and the starter, which are connected by wires. Among them, the starter is the core component of the starting system. The battery is a component that provides electrical energy for the starter; the ignition switch is the power distribution point of most of the electrical system of the car; the starter is the core component of the starting system, and its function is to convert the electrical energy of the battery into mechanical energy, which is then transmitted to the engine The flywheel makes the engine run.
It includes three parts: DC motor, reducer, drive gear, and electromagnetic switch. The function of the DC motor is to generate electromagnetic torque; the electromagnetic switch is coaxial with the reducer and the drive gear, and this kind of starter has no shift fork.
The DC motor is composed of armature, magnetic field (permanent magnet and field winding), electric brush and so on.
The function of the reducer and drive gear is to engage the starter pinion into the flywheel ring gear when the engine is started, and transmit the starter torque to the engine crankshaft; and after the engine is started, the starter automatically disengages the flywheel ring gear .
The function of the electromagnetic switch is to connect and cut off the circuit between the starter and the battery.
(1) Armature: A component that plays a key and pivotal role in the process of mutual conversion between mechanical energy and electrical energy of the motor. For the starter, the armature is used to generate electromagnetic torque.
(2) Magnetic pole: It is composed of iron core and field winding, and its function is to generate a magnetic field in the motor. There are generally 4 magnetic poles, and the 4 field windings form two pairs of magnetic poles and face each other. The field winding is generally connected in series with the armature winding in the circuit.
(3) Brushes and brush holders: There are 4 brushes, which are placed in a frame-shaped brush holder and kept in sliding contact with the commutator.
Two of the four brushes are positive brushes, and the current flows from the positive brush to the armature winding through the commutator, and then is grounded through the two negative brushes.
(4) Electromagnetic switch: The control mechanism of the starter is an electromagnetically operated control mechanism, whose function is to control the on and off of the motor circuit and the meshing and separation of the drive gear and the flywheel ring gear.
When the ignition switch is closed, the two coil windings (holding coil S-ground and suction coil S-M) are energized. It is worth noting that because the resistance of the pull coil is very small, the current passing through it is very large. This coil is connected in series with the motor circuit. Under the action of current, the motor will slowly rotate to facilitate the connection of the pinion and the flywheel. At the same time, the magnetic field generated in the coil attracts the iron core to push the pinion in and mesh with the flywheel ring gear. At this time, the main contact B of the heavy load is short-circuited by the short-circuit piece, that is, the short-circuit switch is closed, the main circuit of the starter is turned on, and the armature winding is supplied by the battery with a large starting current and a strong starting torque is generated; at the same time, suction The pull coil (SM) is short-circuited due to the same voltage at both ends; the holding coil (S-ground) continuously attracts the iron core to the designated position. Until the ignition switch is turned off, the holding coil (S-ground) and the pull coil (SM) are powered by the M terminal. At this time, the magnetic field generated by the pull coil (SM) is opposite to that of the holding coil (S- The magnetic field of the ground) is opposite, and the force of the two magnetic fields makes the iron core return, and the main contact B and M are disconnected. The circuit of the DC motor is cut off and decelerates to a stop.
The inspection steps of the electromagnetic switch:
First disconnect the connection between the M terminal and the motor (to prevent the motor from rotating after being energized), and connect a wire to the M terminal for grounding. Then follow the steps below to check:
① Connect the S terminal to the power supply and the M terminal to ground, and the armature should have a pulling action.
② Connect the S terminal to the power supply and disconnect the M terminal from the ground. The armature should be able to maintain the pull-in position.
③ Disconnect the S terminal from the power supply, and the armature should be able to return to its original position.
No-load performance test:
The purpose of no-load performance is to check whether there are circuit failures and mechanical failures inside the starter, clamp the starter on the vise, and connect the wires as shown in the figure above. Power-on test, see the no-load operation. Do not exceed 5 seconds each time to prevent the starter from overheating. The starter should run evenly and there should be no sparks under the brushes. The no-load current measured with a holographic multimeter at 3 seconds after starting is about 65 amperes.
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