Starting Systems and Motor Designs: Summary

The starting system is a combination of mechanical and electrical parts that work together to start the engine. The starting system components include the battery, cable and wires, the ignition switch, the starter solenoid or relay, the starter motor, the starter drive and flywheel ring gear, and the starting safety switch. The armature is the moveable component of the motor that consists of a conductor wound around a laminated iron core. It is used to create a magnetic field. Pole shoes are made of high-magnetic permeability material to help concentrate and direct the lines of force in the field assembly. The magnetic forces will cause the armature to turn in the direction of the weaker field. Within an electromagnetic style of starter motor, the inside windings are called the armature. Hie armature rotates within the stationary outside windings, called the field, which has windings coiled around pole shoes. The commutator is a series of conducting segments located around one end of the armature. A split-ring commutator is in contact with the ends of the armature loops. So, as the brushes pass over one section of the commutator to another, the current flow in the armature is reversed. Two basic winding patterns are used in the armature: lap winding and wave winding. The field coils are electromagnets constructed of wire coils wound around a pole shoe. When current flows through the field coils, strong stationary electromagnetic fields are created. In any DC motor, there are three methods of connecting the field coils to the armature: in series, in parallel (shunt), and a compound connection that uses both series and shunt coils. A starter drive includes a pinion gear set that meshes with the engine flywheel ring gear on the engine. 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. The bendix drive depends on inertia to provide meshing of the drive pinion with the ring gear. The most common type of starter drive is the overrunning clutch. This is a roller-type clutch that transmits torque in one direction only and freewheels in the other direction. The starting system consists of two circuits called the starter control circuit and the motor feed circuit. The components of the control circuit include the starting portion of the ignition switch, the starting safety switch (if applicable), and the...

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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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AC Motor Principles

AC three-phase motor used in a HEV
FIGURE. AC three-phase motor used in a HEV. A few years ago, the automotive technician did not need to be concerned much about the operating principles of the AC motor. With the increased focus on HEVs and EVs, this is no longer an option since most of these vehicles use AC motors. FIGURE. AC voltage gradually changes. It is rated at the RMS. AC voltage has a changing direction of current flow. However, this change does not occur immediately. Notice that the AC voltage sine wave indicates that in one cycle the voltage will be zero at three times. Also notice that as the current changes directions, it gradually builds up or falls in the other direction. The sine wave illustrates that the amount of current in an AC circuit always varies. The current rating is based on the average referred to as a root mean square (RMS) value. AC Motor Construction Like the DC motor, the AC motor uses a stator (field winding) and a rotor. Common types of AC motors are the synchronous motor and the induction motor. In both motor types, the stator comprises individual electromagnets that are either electrically connected to each other or connected in groups. The difference is in the rotor designs. AC motors can use either single-phase or three-phase AC current. Since the three-phase is the most common motor used in HEV and EV vehicles, we will focus our discussion on these. Note: Three-phase AC voltage is commonly used in motors because it provides a smoother and more constant supply of power. Three-phase AC voltage is like having three independent AC power sources, which have the same amplitude and frequency but are 120 degrees out of phase with each other. As in a DC motor, the movement of the rotor is the result of the repulsion and attraction of the magnetic poles. However, the way this works in an AC motor is very different. Because the current is alternating, the polarity in the windings constantly changes. The principle of operation for all three-phase motors is the rotating magnetic field. The rotor turns because it is pulled along by a rotating magnetic field in the stator. The stator is stationary and does not physically move. However, the magnetic field does move from pole to pole. There are three factors that cause the magnetic field to rotate. The first is the fact that the voltages in a three-phase system are 120 degree...

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Cranking Motor Designs

Solenoid operated Delco MT series starter motor
The most common type of starter motor used today incorporates the overrunning clutch starter drive instead of the old inertia-engagement bendix drive. There are four basic groups of starter motors: Direct drive. Gear reduction. Positive-engagement (moveable pole). Permanent magnet. Direct Drive Starters FIGURE. Solenoid operated Delco MT series ⚡ starter motor ⚡. A common type of starter motor is the solenoid-operated direct drive unit. Although there are construction differences between applications, the operating principles are the same for all solenoid-shifted starter motors. When the ignition switch is placed in the START position, the control circuit energizes the pull-in and hold-in windings of the solenoid. The solenoid plunger moves and pivots the shift lever, which in turn locates the drive pinion gear into mesh with the engine flywheel. When the solenoid plunger is moved all the way, the contact disc closes the circuit from the battery to the starter motor. Current now flows through the field coils and the armature. This develops the magnetic fields that cause the armature to rotate, thus turning the engine. Gear Reduction Starters FIGURE. Gear reduction starter motor construction. Some manufacturers use a gear reduction starter to provide increased torque. The gear reduction starter differs from most other designs in that the armature does not drive the pinion gear directly. In this design, the armature drives a small gear that is in constant mesh with a larger gear. Depending on the application, the ratio between these two gears is between 2:1 and 3.5:1. The additional reduction allows for a small motor to turn at higher speeds and greater torque with less current draw. The solenoid operation is similar to that of the solenoid-shifted direct drive starter in that the solenoid moves the plunger, which engages the starter drive. Positive-Engagement Starters FIGURE. Positive engagement starters use a moveable pole shoe. A commonly used starter on Ford applications in the past was the positive-engagement starter. Positive-engagement starters use the shunt coil windings of the starter motor to engage the starter drive. The high starting current is controlled by a starter solenoid mounted close to the battery. When the solenoid contacts are closed, current flows through a drive coil. The drive coil creates an electromagnetic field that attracts a moveable pole shoe. The moveable pole shoe is attached to the starter drive through the plunger lever. When the moveable pole shoe moves, the drive gear engages the engine flywheel. FIGURE. Schematic of positive-engagement starter. As soon as the starter drive pinion gear...

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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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Cranking Motor Circuits

The starting system of the vehicle consists of two circuits: the starter control circuit and the motor feed circuit. These circuits are separate but related. Hie control circuit consists of the starting portion of the ignition switch, the starting safety switch (if applicable), and the wire conductor to connect these components to the relay or solenoid. The motor feed circuit consists of heavy battery cables from the battery to the relay and the starter or directly to the solenoid if the starter is so equipped.

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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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