Tire Rack's Recommended Installers are your installation solution. You can drop-ship
to their location, too!
Your are here: Articles | How Your Car Works > Automotive Starting System
|
|||||||||
AUTOMOTIVE
|
|
The only function the starting system provides is to crank the engine fast enough
to run. The vehicle's ignition and fuel systems provide the spark and fuel for the engine
operation, but they are not considered components of the basic starting system. |
|
Starting System - Design and Components
-
A typical starting system has six basic components and two distinct electrical circuits. These components are:
-
battery
-
ignition switch
-
battery cables
-
magnetic switch (either an electrical relay or solenoid)
-
starter motor
-
starter safety switch
-
The starter motor draws a great deal of electrical current from the battery. A large starter motor might require 250 or more amperes of electrical current. This electrical current flow through the large cables that connect the battery to the starter and ground. The driver controls the flow of this current using the ignition switch normally mounted on the steering column. The battery cables are not connected to the switch.
The system has two separate circuits:
-
The control circuit.
-
- The control circuit allows the driver to use a small amount of battery current to control the flow of a large amount of current in the starting circuit. The entire circuit usually consists of an ignition switch connected through normal-gauge wire to the battery and the magnetic switch (solenoid or relay).
-
The starter circuit.
-
- The starter circuit carries the high current flow within the system and supplies power for the actual engine cranking. Components of the starter circuit are the battery, battery cables, magnetic switch or solenoid, and the starter motor.
-
Battery and Cables
-
- Many of the problems associated with the starting system can be solved by troubleshooting the battery and its related components.
- The starting circuit requires two or more heavy-gauge cables. One of these cables connects between the battery's negative terminal and the engine block of transmission case. The other cable connects the battery's positive terminal with the solenoid.
- On vehicles equipped with a starter relay, two positive cables are needed. One runs from the positive battery terminal to the relay and the second from the relay to the starter motor terminal.
-
Magnetic Switches
-
-
A solenoid is an electro mechanical device that uses the movement of a plunger to exert a pulling or holding force. As shown in the picture, the solenoid mounts directly on top of the starter.
-
|
-
Relays are the second major type of magnetic switch used. It is very similar to the solenoid. However, it is not used to move the drive pinion into mesh. It is strictly an electrical relay or switch.
-
Starter Motor
|
-
-
The starter motor converts the electrical energy from the battery into mechanical energy for cranking the engine. The starter is a special type of electric motor designed to operate under great electrical overloads and to produce very high horsepower.
-
-
-
All starting motors are generally the same in design and operation, though their appearance will vary between manufacturers.
-
Starter Motor Drive Mechanisms
|
-
A starter drive includes a pinion gear set that meshes with the flywheel on the engine's crankshaft.
|
- To prevent damage to the pinion gear or the flywheel's ring gear, the pinion gear must mesh with the ring gear before the starter motor rotates. To help ensure smooth engagement, the end of the pinion gear is tapered. Also, the movement of the armature must always be caused by the action of the motor, not the engine. For this reason, starter drive assemblies include an overrunning clutch.
Overrunning Clutch
|
- The overrunning clutch, part of the drive mechanism, performs a very important job in protection the starter motor. When the engine starts and runs, its speed increases. If the starter motor remained connected to the engine through the flywheel, the starter motor would spin at very high speeds, destroying the starter motor.
- To prevent this, the armature must disengage from the engine as soon as the engine turns faster than the starter has cranked it. However, with most starter designs the pinion remains engaged until electricity stops flowing to the starter. In these cases, an overrunning clutch is used to disengage the starter.
- The overrunning clutch housing is splined to the starting motor armature shaft. The drive pinion turns freely on the armature shaft within the clutch housing. When the clutch housing is driven by the armature, the spring loaded rollers are forced into the small ends of their tapered slots and wedged tightly against the pinion barrel. This locks the pinion and clutch housing solidly together, permitting the pinion to turn the flywheel and, thus crank the engine.
- When the engine starts, the flywheel spins the pinion faster than the armature. This releases the roller, unlocking the pinion gear from the armature shaft. The pinion then overruns the armature shaft freely until being pulled out of the mesh without stressing the starter motor. The overrunning clutch is moved in and out of mesh by the starter drive linkage.
- With that said, if you just think of it like this: When you are cranking the engine, the starter motor is driving the vehicles engine. When the engine starts running on its own, the engine becomes the driving unit and the starter becomes the driven unit. The flywheel at this point drives the overrunning clutch in a reverse direction (see image) allowing it to free wheel. If this did not happen the flywheel would turn the starter at the speed of the engine and even at idle speed that would mean the starter would turn up to 1000 RPM or more. That would destroy the starter motor.
Other readers found these articles interesting as well.
Your are here: Articles | How Your Car Works > Automotive Starting System
Automotive Combustion Chamber Automotive Fuel Injection
Copyright © 2011, [Know-yourcar.com]. All rights reserved.