CH18 starting and traction motor systems STUDENT VERSION rev

Tài liệu học tập cơ bản khái quát về động cơ và các bộ phận trên ô tô phiên bản tiếng anh. Tài liệu này nhằm giúp chúng ta tiếp cận được cấu tạo chức năng của các bộ phận của xe. Với tài liệu này giúp các bạn sinh viên ngành cơ khí ô tô tiếp cận được những kiến thức cơ bản về ô tô và đồng thời nâng cao kiến thức tiếng anh. Bộ tài liệu này được soạn thảo bởi trường đào tạo và huấn luyện nghề ở Canada.

Chapter 18

Starting and Traction

Motor Systems

Types of Electric Motors

• Electric motors are used to start the engine

• In hybrid electric vehicles (HEVs), electric motors can used to propel the vehicle

• Smaller electric motors are DC

• Traction or drive motors are AC

Basics of Electromagnetism

• Natural magnets from magnetite

• Artificial magnets rearrange molecules to align along North and South poles

• Artificial magnets can be temporary or

permanent

• Current carrying wire generates a magnetic field

Magnetic Circuits and

• Convert electric energy into mechanical

• Use interactions of magnetic fields

• An electromagnet is fitted to a shaft

• Shaft surrounded by stationary fields

• Polarity of fields are switched

• Shaft rotation can do work

Basic Motor

Operating Principles

Operating Principles (cont’d)

• Many armature segments are used

• The number of coils and brushes differ between models

• Three styles of motor windings:

– Series motors

– Parallel or shunt motors

– Compound or combination motors

Starting System Components

• Battery

• Ignition switch

• Cable and wires

• Starter solenoid or relay

• Starter motor

• Starter safety switch

Typical Starting System

– Battery and battery cables

– Magnetic switch or solenoid

– Starter motor

Magnetic Switches

• Enables control circuit to open and close starter circuit

• Can be either a solenoid or a relay:

– Solenoid is most common

– Relays is similar to a solenoid but does not mesh starter drive gear with flywheel

Starter Drives

• Meshes armature to flywheel

• Pinion meshes with flywheel before the armature spins

• An overrunning clutch is used to prevent starter damage when the engine starts

• Pinion gear is locked

to the armature shaft

• Starting safety switch

– Prevents vehicle from starting unless in park or neutral or with clutch disengaged.

Preliminary Checks

• Check the battery and charge as needed

• Check wiring and cable connections

• Check to make sure the cables are the correct size

• Check any fusible links in the wiring

• Ensure engine has correct weight oil

Starter Solenoid Problems

• Typical complaint is a clicking noise when attempting to start the engine

• Anything that reduces current flow will

affect solenoid operation

• Solenoids can often be replaced separately

or as a starter assembly

Starting Safety Switches

• Can be checked with a voltmeter or

ohmmeter

• With transmission in park or clutch

depressed, switch should be closed

• May need adjusted if not closing circuit

Cranking Tests

• Cranking voltage test measures available voltage during cranking

– Refer to service manual for voltage

specifications – normally at least 9.6 volts

• Cranking current test measures starter

current draw during cranking

– Watch voltage and amperage and compare to specifications

Insulated Circuit Resistance Tests

• Insulated circuit contains all high current

cables and connections

• Disable or bypass the ignition

• Typical reading specifications 0.2 - 0.6 volts

• Higher readings indicated resistance in either the insulated positive or negative circuits

Control Circuit Voltage Drop

• High resistance in solenoid switch circuit reduces current flow through solenoid

windings

• Disable the ignition system

• Test between battery positive and starter switch terminal on solenoid or relay

• Normally less than 0.5 volts

Starter Drive Test

• Checks for a slipping starter drive

• Bypass or disable the ignition

• Crank engine for several seconds

• Repeat at least three times

• If engine stops cranking but starter is still spinning, the starter drive is slipping

Free Speed (No-Load) Test

• Every starter should be bench tested when removed and before being installed

• Firmly clamp starter in a vice

• Connect ammeter to battery cable and

starter to a battery

• Check current draw and motor speed

High-Voltage Motors

• Traction motors may drive vehicle or act as

a starter/generator or add power output

• HV motors can be liquid or air cooled

• Most production vehicles use AC motors

• Conversion vehicles use DC motors

Brushless DC Motors

• Similar to brushed DC motor

• Rotor and stator are reversed

• Current flow is switched to different stator windings

• May use Hall-effect sensors to monitor rotor position

AC Motors

• Has two parts, the rotor and stator

• Stator has individual electromagnets

• Rotor is the rotating magnetic field

• Current passes from stator to rotor

• Three phase AC commonly used

Rotor Sensors

• AC motors require a rotor position sensor

• Times or phases the three-phase AC

• Control system monitors position and speed

of the rotor and controls the frequency of

stator voltage

• This controls the torque and speed of the

motor

• AC supplied by an AC generator or through

an inverter connected to the battery

• Inverter changes voltage DC into voltage three phase AC

high-• Also changes AC into DC to charge the

battery pack

• Manages the flow of electricity from the

battery to the motors

• A simple controller is a potentiometer

• Controllers monitor input from sensors and controls the duty cycle of the voltage to the motor