starters Flashcards
the cranking system must turn the engine over fast enough so the
heat from compression can cause combustion/ignition
a cranking system consists of
batteries cables DC motor solenoid starter drive ignition switch
the cranking motor is a powerful DC motor and has to crank the a diesel engine over at
250 rpm
cranking motor has to turn over a gas engine at
150 rpm
the gear ratio between the starter drive and the the ring gear is
20:1
a battery turns
chemical energy into electrical energy
a starter turns
electrical energy into mechanical energy
two 500amp 12 volt batteries connected in series creates
24 volts with 500 total amps
two 500 amp 12 volt batteries connected in parallel creates
12 volts with 1000 total amps
what will affect a conductors ability to conduct current
material
area
length
temperature
some manufactures may double the amount of cables used on a starter to
reduce voltage drops
the electrical formula for power is
amps x volts = watts
1HP =
746 watts
what components make up the cranking motor
Housing field coils armature commutator brushes end frames shift mechanism
the starter motor insulated circuits are made up of what components
field coils armature windings commutator brush assemblies solenoid
what is used to complete the electrical system and engage the drive motor
solenoid
four types of insulating material
varnish
mica (between commutator bars)
bakelite
plastic
how long can you crank a starter and how long will it need to cool down
can crank for 30 sec then must cool for 2 min
this protects the internal components from losing their insulating qualities
some starter housings can be part of
the ground circuit
the grounded brushes holders and the solenoid hold in windings are connected to the motor housing
some motor housings have a
ground terminal stud that is completely insulated
list the sequence of events starting from when the operator turns on the key
key turned to on position battery isolation relay energized battery group connected operator pushes start button or turns key to start mag switch energizes solenoid energizes starter drive engages cranking motor turns on engine starts
you should make sure that the components in the cranking system are designed for the same
voltage of the battery group
the field windings are wrapped around the pole shoes in the opposite directions to
create a strong stationary magnetic field
the assembly that rotates in the starting motor is called
the armature
the armature is supported by at least
2 bushings
what must there be between the stationary and rotating parts of the starter motor
an air gap
what are the two main components of the armature
armature windings
commutator
armature windings are made of heavy flat copper strips so they will have
low resistance to conduct high current flow
the laminated armature core reduces
eddy currents
the armature contains the side of two coils laid / lapped on top of each other but are separated by
insulating varnish
each end of the armature loops are connected to a
commutator bar
how dose current flow through a cranking motor
motor terminal - field windings - positive brushes - commutator bars - armature windings - negative brushes - ground
cranking motors have even pairs of brushes that match the number of
field windings and pole shoes
brushes are held in contact with the commutator bars by
spring tension
brushes are made out of
copper and carbon
what is used to electrically connect the brush to the brush holder
brush leads
when current passes through the field windings it will create
a stationary magnetic field
once current flows out of the field windings it then flows through the armature windings creating a
moving magnetic field
unbalanced magnetic force is created when the armature magnetic field is placed inside the stationary magnetic field of the field windings the armature will then be
pushed to the weak side of the stationary magnetic field
what is created when current flows from the commutator bar out the armature loop in one direction and returns to another commutator bar in the opposite direction
opposite magnetic fields
what will allow the armature to rotate smoothly and efficiently
by having several loops and several commutator bars the armature magnetic fields can be moved back into the most efficient position
why should you only crank a starter 30 seconds before letting it cool for 2 min
converting electrical energy into mechanical energy creates heat and the starter is a sealed unit
where are cranking motor usually installed
in the flywheel housing of an engine
what allows the cranking motor to be installed in several positions
the nose housing can be rotated
the starter may have up to how many motor bushings
3
the motor bushings are made of
sintered bronze
how are motor bushing lubricated
by oil saturated wicks
how can additional oil be added
by removing the oil reservoir cup plug
the starter motor should not need maintenance between
engine overhauls
what type of motor has the field windings wound in series
a series wound motor
a series wound motor will produce
high torque when the motor begins to turn
what will decrease as motor speed increases
current and torque
CEMF stands for
counter electromotive force
what dose CEMF oppose
battery voltage and will cause current and torque to decrease as speed increases
CEMF cannot exceed
battery voltage
CEMF will limit what on a free running cranking motor
cranking motor no load speed
electrical power is rated in what
watts
cranking motors can have as many as 4 poles and 4 field coils or as many as
8 poles and 8 field coils
a 12 volt cranking system should be able to deliver
9.8 volts to the cranking motor
types of motor field windings
series
parallel
series parallel
compound (shunt)
a parallel wound field coil design allows more current to flow and will produce more
torque
a compound wound field coil design will limit rotational speed by using a
shunt coil that produces a CEMF
the motor main frame contains all the rotating components and also contains the
pole shoes and field windings
heavy iron provides a path for magnetic flux lines because it has good
permeability
the commutator end housing holds one of the bushings that support the rotating armature and can also hold the
brush holder assemblies
the main frame may also have a what to support the armature
bushing
what normally holds the pinion gear that meshes with the ring gear on the flywheel
the drive end housing or the nose housing
where is the long side of the pole shoe positioned
in the direction of the armature rotation
what are field windings made of
copper ribbon
what are field windings wrapped with to prevent movement
fabric
what holds the field windings in place
the pole shoes
what components are pressed or attached to the armature shaft
laminated core
windings
commutator
how are the commutator segments insulated from each other
using mica
what is carried on the end of the armature shaft that engages the ring gear
the starter drive mechanism
what components allow current to flow from the field windings to the armature windings
brushes
commutator
where must conduction of current between the field windings and the armature take place
in a magnetically neutral region
where are the brush holders located
between the
four pole cranking motors have how many brushes riding on the commutator segments
4 brushes
2 positive and 2 negative
insulated washers and sleeves are used to isolate and protect components from
shorts and ground faults
how many bushings do heavy duty cranking motors have
3
where is the break washer located
usually between the moveable drive mechanism and a stationary member usually the center support housing
what is the break washer used for
to slow down the the cranking motor armature after engine is started
why is it important to slow down the cranking motor after the engine has started
to reduce wear and enable quicker cycling for re start
the drive mechanism transfers rotation of the
armature shaft to the flywheel through the ring gear
the drive gear should engage the ring gear before
the starting motor rotates and should be able to disengage the moment engine starts
what could happen if the starter dose not disengage the moment the engine starts
the starter could overspeed and will be badly damaged
what is the shift lever moved by to engage the starter drive
solenoid
what moves the shift lever to the disengaged position
a return spring
what dose an over running clutch protect the cranking motor from
overspeed conditions
overspeeding the armature can cause the
windings to be thrown out of their seats
the over running clutch must be able to do what when the cranking motor is turning the engine and do what once the engine starts
lock / engage
unlock / disengage
when the engine starts what will protect the armature from turning to fast
the pinion gear will turn faster than the outer shell and the rollers will turn freely
what kind of locking elements dose a sprag clutch use
banana shaped
what will allow the sprags to lock or disengage from the armature
they can tilt
what will the mesh spring do if the pinion gear teeth butt into the flywheel ring gear teeth
compress
what will reduce the chance of tooth on tooth abutment during drive engagement of the pinion gear and ring gear
they are both machined with a chamfer on the teeth
the posi-torque drive uses what style of ramp arrangement on the drive collar
dentile teeth
what are the drive collar and pinion gear assemblies held together by
the internal mesh spring
what will happen to a stalled cranking motor or slow turning motor
it will have higher than normal cranking amps and therefore overheat quickly
