Integrated Starter Generator

A BAS mounted external to the engine
One of the newest technologies to emerge is the ⚡ integrated starter generator ⚡ (ISG). Although this system can be used in conventional engine-powered vehicles, one of the key contributors to the Hybrid's fuel efficiency is its ability to automatically stop and restart the engine under different operating conditions. A typical Hybrid vehicle uses a 14 kilowatt (kW) electric induction motor or ISG between the engine and the transmission. The ISG performs many functions such as fast, quiet starting, automatic engine stops/starts to conserve fuel, recharges the vehicle batteries, smoothes driveline surges, and provide regenerative braking. The ISG is a three-phase AC motor. At low vehicle speeds, the ISG provides power and torque to the vehicle. It also supports the engine, when the driver demands more power. During vehicle deceleration, ISG regenerates the power that is used to charge the traction batteries. The ISG can also convert kinetic energy from AC to DC voltage. When the vehicle is traveling downhill and there is zero load on the engine, the wheels can transfer energy through the transmission and engine to the ISG. The ISG then sends this energy to the HV battery for storage. FIGURE. A BAS mounted external to the engine. An ISG can be mounted externally to the engine and connected to the crankshaft with a drive belt. This design is called a belt alternator starter (BAS). In these applications, the unit can function as the engine's starter motor as well as a generator driven by the engine. Both the BAS and the ISG use the same principle to start the engine. Current flows through the stator windings it generates magnetic fields in the rotor. This will cause the rotor to turn, thus turning the crankshaft and starting the engine. In addition, this same principle is used to assist the engine as needed when the engine is running.

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Starter Control Circuit Components

Solenoid-operated starter has the solenoid mounted directly on top of the motor
Magnetic Switches The ⚡ starter motor ⚡ requires large amounts of current (up to 300 amperes) to generate the torque needed to turn the engine. The conductors used to carry this amount of current (battery cables) must be large enough to handle the current with very little voltage drop. It would be impractical to place a conductor of this size into the wiring harness to the ignition switch. To provide control of the high current, all starting systems contain some type of magnetic switch. There are two basic types of magnetic switches used: the solenoid and the relay. FIGURE. Solenoid-operated starter has the solenoid mounted directly on top of the motor. Starter-Mounted Solenoids. A solenoid is an electromagnetic device that uses the movement of a plunger to exert a pulling or holding force. In the solenoid-actuated starter system, the solenoid is mounted directly on top of the ⚡ starter motor ⚡. The solenoid switch on a starter motor performs two functions: It closes the circuit between the battery and the starter motor. Then it shifts the starter motor pinion gear into mesh with the ring gear. This is accomplished by a linkage between the solenoid plunger and the shift lever on the starter motor. In the past, the most common method of energizing the solenoid was directly from the battery through the ignition switch. However, most of today's vehicles use a starter relay in conjunction with a solenoid. The relay is used to reduce the amount of current flow through the ignition switch and is usually controlled by the powertrain control module (PCM). This system will be discussed later in this chapter. When the circuit is closed and current flows to the solenoid, current from the battery is directed to the pull-in and hold-in windings. Because it may require up to 50 amperes to create a magnetic force large enough to pull the plunger in, both windings are energized to create a combined magnetic field that pulls the plunger. Once the plunger is moved, the current required to hold the plunger is reduced. This allows the current that was used to pull the plunger in to be used to rotate the starter motor. FIGURE. The solenoid uses two windings. Both are energized to draw the plunger, then only the hold-in winding is used to hold the plunger in position. When the ignition switch is placed in the START position, voltage is applied to the S terminal...

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Starter Drives

Starter drive pinion gear is used to turn the engine's flywheel
The starter drive is the part of the starter motor that engages the armature to the engine fly-wheel ring gear. A starter drive includes a pinion gear set that meshes with the flywheel ring gear on the engine's crankshaft. To prevent damage to the pinion gear or the ring gear, the pinion gear must mesh with the ring gear before the starter motor rotates. To help assure smooth engagement, the ends of the pinion gear teeth are tapered. Also, the action of the armature must always be from the motor to the engine. The engine must not be allowed to spin the armature. The ratio of the number of teeth on the ring gear and the starter drive pinion gear is usually between 15:1 and 20:1. This means the starter motor is rotating 15 to 20 times faster than the engine. The ratio of the starter drive is determined by dividing the number of teeth on the drive gear (pinion gear) into the number of teeth on the driven gear (flywheel). Normal cranking speed for the engine is about 200 rpm. If the starter drive had a ratio of 18:1, the starter would be rotating at a speed of 3,600 rpm. If the engine started and was accelerated to 2,000 rpm, the starter speed would increase to 36,000 rpm. This would destroy the starter motor if it was not disengaged from the engine. FIGURE. Starter drive pinion gear is used to turn the engine's flywheel. FIGURE. The pinion gear teeth are tapered to allow for smooth engagement. The most common type of starter drive is the overrunning clutch. The overrunning clutch is a roller-type clutch that transmits torque in one direction only and freewheels in the other direction. This allows the starter motor to transmit torque to the ring gear but prevents the ring gear from transferring torque to the starter motor. FIGURE. Overrunning clutch starter drive. In a typical overrunning-type clutch, the clutch housing is internally splined to the starter armature shaft. The drive pinion turns freely on the armature shaft within the clutch housing. When torque is transmitted through the armature to the clutch housing, the spring-loaded rollers are forced into the small ends of their tapered slots. They are then wedged tightly against the pinion barrel. The pinion barrel and clutch housing are now locked together; torque is transferred through the starter motor to the ring gear and engine. FIGURE. When the armature...

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