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Question

Difficulty: HardStarting and Charging Systems

During the engine starting cycle in an automobile, several distinct electrical and mechanical events occur in a precise sequence when the ignition switch is turned to the START position. Arrange the following operational steps of the starting system in the correct chronological order from first to last.

  1. 1Low-current electricity flows from the ignition switch through the park/neutral safety switch to energize the starter solenoid windings.
  2. 2The solenoid plunger pulls forward, moving the shift fork to slide the starter drive pinion gear into mesh with the engine flywheel ring gear.
  3. 3The internal copper contact disc in the solenoid bridges the heavy battery and starter motor terminals, closing the high-current circuit.
  4. 4High amperage flows through the motor field coils and armature, producing magnetic torque that spins the armature and cranks the engine crankshaft.
  5. 5The engine starts and spins faster than the starter motor, causing the one-way overrunning clutch to freewheel until the ignition key is released.

Answer

The correct chronological sequence begins with control current energizing the starter solenoid windings, followed by the plunger shifting the pinion gear into mesh with the flywheel ring gear, then the solenoid contact disc closing the high-current battery circuit, followed by the starter motor spinning to crank the engine, and finally the overrunning clutch freewheeling once the engine fires.
The starting system relies on a two-stage relay/solenoid operation. Turning the ignition key first energizes the low-current solenoid coils. The resulting electromagnetic pull shifts the pinion gear into the stationary flywheel ring gear. Only at the end of the plunger's travel does the contact disc bridge the large battery terminals, energizing the starter motor armature to spin the engine. Once the engine starts and rotates faster than the starter, the one-way overrunning clutch freewheels to protect the motor until the key is released.

Step-by-Step Solution

1
Identify the initial control circuit actuation.
Current flows from the battery through the ignition switch in START, passes through the neutral safety switch, and energizes the pull-in and hold-in coils of the starter solenoid.
The low-current control circuit must energize first to actuate the heavy-duty solenoid switch and mechanical shift lever.
2
Trace the mechanical motion of the solenoid plunger.
The solenoid magnetic field draws the plunger inward, pivoting the shift lever to advance the drive pinion along the armature shaft into engagement with the flywheel teeth.
The drive gear must mesh with the stationary ring gear before the motor begins high-speed rotation to avoid damaging gear teeth.
3
Identify the high-current circuit closure point.
At the end of the plunger travel, the internal copper contact plate bridges the main battery cable terminal and the starter motor feed terminal.
A heavy internal copper contact is required to handle the 150 to 300+ amperes needed by the starter motor.
4
Trace the electrical and mechanical power delivery in the starter motor.
Current energizes the armature and field windings, generating opposing magnetic fields that spin the armature shaft and deliver cranking torque through the flywheel.
High current through the starter motor windings creates the torque necessary to overcome engine compression and mechanical friction.
5
Determine the protective mechanism upon engine start.
When the engine starts running under its own power, the flywheel rotates faster than the starter pinion, causing the roller-type overrunning clutch to slip and freewheel.
Because of the gear reduction ratio (typically 15:1 to 20:1), an engine idling at 1,000 RPM would spin an uncoupled starter armature at 15,000 to 20,000 RPM, destroying it.

Key Concept

Starter solenoid dual electro-mechanical function and sequential cranking circuit operation
Estimated Time:1m 30s
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Topics

Starting and Charging Systems

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