Automotive Ignition System

When the first gasoline internal combustion engine was designed and constructed, one of the issues it had was that the crankshaft needed to be turned in order to start the engine. The solution was found by using a crank handle and moving the crankshaft by hand to find the precise point for the first impulse or spark to start the engine.

 

Subsequently, the issue was solved through the construction and use of a motor (i.e., starter) which was mounted on the ground and was started with a button. By using electric current, the motor rotated the crankshaft and was kept on until the engine started. In this way, it was possible to discontinue the use of a crank handle.

 

Now, there are modern starting motors that function magnetically by either a button on the dashboard or when the ignition or contact key is turned.

The starting system is designed to give the engine crankshaft the movement necessary to create the first live spark or the expansion or force that initiates the functioning of the engine.

 

The starter consumes a great deal of power because it creates the mechanical energy needed to move the crankshaft and overcome the enormous resistance to the compression of the mixture in the combustion chamber.

 

A fully charged battery can be discharged in just a few minutes when the starter is on. It is estimated that the starter has a consumption of 400 to 500 amps of current and that is why the battery can be completely discharged in such a short time. It is therefore not advisable to hold the ignition switch on for too long.

Since an engine is unable to start on its own, the crankshaft must be rotated by an external force to compress the air-fuel mixture and to start the combustion. The starter is mounted on the cylinder block and pushes against a drive gear when the ignition switch is turned on, engaging the flywheel and turning the crankshaft.

The starter is an electric motor with a pinion and a device for guiding the pinion onto the sprocket wheel. On the exterior, the armature, pole pieces and field coils are similar to a generator. The field coils are connected in a series, functioning as a motor due to a current that is applied in sequence, and because of its high torque, from the beginning overcomes the resistance imposed by the engine.

 

The transmission ratio between the gear and the pinion is approximately 20:1. With this high ratio, the pinion cannot be permanently attached to the gear, since the engine reaches a rotation frequency that is too fast for the smaller electric motor. Therefore, a special release is needed such that the main engine separates from the motor when the rotation frequency exceeds a certain speed.

The internal framework of a starter motor (or, simply, the starter) is similar to an electric motor. It is mounted on the top of the crankcase of the engine, so that the pinion at the very end of its axle engages with the gear ring on the periphery of the flywheel. This way when the small electric engine turns, the combustion engine also turns and the car can be started. Sprocket size depends on the speed of the electric starter.

 

The starter is basically composed of three assemblies:

 

1. Magnetic control or Solenoid assembly

2. Starter motor assembly

3. Bendix drive assembly

 

The parts that make up the starter are similar to a generator, the difference being in the field coils and armature. There is also another very noticeable difference: the starter consumes power. Both work based on the principles of magnetism and electromagnetism.

 

Starter parts include the following:

 

1. magnetic core

2. return spring of the solenoid magnetic core

3. collar connecting the lever discharge mechanism

4. Bendix spring and axle assembly

5. horn for the rear end of the armature shaft

6. stop ring for the remote or Bendix drive

7. drum discharge clutch mechanism

8. damping spring of the drive mechanism return

9. pole pieces or assemblies of field coils and their cores

10. armature

11. brush holder assembly

12. copper brushes

13. front cover, including horn and felt

14. through bolts with snap rings

15. hull or housing

 

The housing or hull is made of soft iron, and the wire in the armature and field coils is a particularly thick type of copper. The brushes are also made of copper, and the remaining parts are similar to a generator.

 

Information Courtesy of Soporte Técnico Automotriz

 

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