Engines and Power Trains Midterm 3

Conductors

Substances that are capable of transmitting electric current, heat, or sound. Have less than 4 electrons in outer shell (best are gold, silver, copper)

Insulators

Substances that are poor conductors of electric current (more than 4 electrons in outer shell)

Circuit

Continueous conductor that provides a path for the flow of electrons away from and back to the generator

Volt

Unit in which electrical pressure is measured (electrical generator forces electrons to move from atom to atom, like a pump)

Current 

Amount of electrical charges flowing past a point (1 Ampere is equal to 6.28 biliion billion electrons per second)

Resistance

Opposition to flow in an electrical circuit (1 ohm is the amount of electrical resistance overcome by 1 volt to cause 1 amp of current to flow)

How is resistance affected by the size of the wire?

Resistance is proportional to the length and diameter of the wire being used in the circuit.

Large diameter = less resistance; vice versa

Longer wires = more resistance; vice versa

How does temperature affect resistance

Temperature increases = resistance increases

Resistance formula

R = (rho*length)/area

Electrical Power

the work done per time by a current (I) under pressure (V) or E. (unit of measurement = W)

Watts(W)

Watts = Volts(V) * Amps(A)

Horsepower

The power required to raise 33,000 lbs one foot in one minute (1hp = 746 watts)

Alternating Current (AC)

Current that reverses its direction at a given frequency (60 Hz)

Direct Current (DC)

Electric current which flows in only one direction (used in all automotive and mobile equipment electrical systems)

Semi-conductors

Composed of elements with exactly 4 valence electrons in outer shell. Used in devices that control electrical current

Diodes

A device that will allow current to pass in only one direction

Standard diode

Always produce a simple one-way flow of electrons

Zener diodes

reverses the flow of current above a certain voltage

Transistors

Devices that use a small electrical current to control a larger current

Capacitors

Devices that store electrons. Used to protect other components from voltage spikes, and as a filter to smooth out voltage to a constant level

Resistors

Devices that reduce voltage output by resisting the flow of current in the circuit

Static charge

Type of force that causes electrons to leave an atom, this is done by friction

Magnetic fields

• A bar magnet generates lines of force which come out of the North pole and enter the south pole

• These lines of force are heavily concentrated at the poles

• Thus, magnetic force is greatest at the poles

Electromagnetism

• Electrical current generates its own magnetic field

• As the current flow through the conductor is increased, so is the intensity of the magnetic field

Right Hand Rule

Fingers point at the direction of the electric field and the thumbs point at the direction of the current

Conductors in Magnetic Fields

If two parallel conductors are:

• Carrying current in opposite directions, their magnetic field will repel them

• Carrying current in the same direction, they will be attracted.

In the case of two or more parallel conductors carrying current in the same direction:

The magneitc field between the conductors is cancled out and the conductors form a single magnetic field of greater strength

If the conductor is formed into a single loop:

It’s magnetic field is the same as a straight conductor

If the conductor is formed into many loops (coil):

It’s magnetic field is the equivalent os the sum of all the loops

Electromagnetic induction

When a conductor is moved across a magnetic field, voltage is induced in the conductor. Because voltage has polarity (direction), it will cause current to flopw in a given direction (electrical generation)

How batteries produce current

Produce current through a chemical reaction between the lead plates (Anodes and Cathodes) in the cell and electrolyte

What are the negative lead plates of a battery?

Anodes (Lead = Pb)

What are the positive plates of a battery

Cathodes (Lead Peroxide = PbO2)

Besides the lead plates, what also produces current in the battery 

Electrolytes (H2SO4)

When does the battery become discharged?

When the electrolytes are exhausted and the plates become sulfated

What does it look like for the Anode plate (negative) to become sulfated? 

Pb + SO4 = PbSO4 + 2e-

What does it look like for the Cathode plate (positive) to become sulfated?

PbO2 + SO4 + 4H + 2e- → PbSO4 + 2H2O

How are batteries recharged?

Batteries are recharged by passing DC in opposite direction of the dicharge, reversing the process

What is the chemical reaction process of the battery being recharged?

2PbSO4 + 2H2O → Pb + PbO2 + 4H+ + 2SO4

Note how the H2 SO4 electrolyte has been restored during the charging reaction

Each cell in a lead acid battery is composed of:

• lead (-) plates; anodes

• lead peroxide (+) plates; cathodes

• electrolyte, a mixture of 2/3 water and 1/3 sulfuric acid

• separators, insulating plates that keep the anode and cathode from shorting out

How do you determeine the amount of voltage produced by a battery?

Batteries are made up of one of more cells ina a plastic or rubber case, connected in a series

[Each cell produces about two volts, so → Voltage = # cells * 2]

Does temperature affect the specific gravity of a battery electrolyte?

• Temperature effects the density/specific gravity of all liquids including battery electrolytes

• As temperature decreases, the density/specific gravity increases and vice versa

  • Cold Battery → Greater Charge

  • Hot Battery → Weaker Charge

What is used to check the specific gravity of each cell in a battery?

Hydrometer; most hydrometers include a thermometer to correct the specific gravity reading to (80 deg F)

Functions of a charging system:

Recharges the battery

• During starting: the battery supplies the entire electrical load

• During peak operation: the battery helps the generator/alternator supply enough current

Provides the current during operation

• During normal operation: the generator/alternator is able to supply all the current that is needed

What is a DC charging system?

Use a generator and a regulator to produce and control electrical power

What are the two major components of a generator?

Armature: a rotating wire conductor loop

Magnetic poles: A stationary magnetic field

When the armature is rotated within the field produced by the magnetic poles, we have:

relative motion between a magnetic field and a conductor, so voltage is generated in the wire loop

What is a commutator?

Used with the generator; a split metal ring, with one hald connected to each side of the wire loop

What do brushes do?

They make contact with the commutator and connect to wires that carry the current to the load and back again

What type of current does a generator produce?

Produced AC current because the flow of the current reverses as it rotates within the fixed magnetic field

What converts the generator’s AC current to DC current

The commutator and brushes

How do brushes contribute to the AC to DC current change

The brushes are fixed relative to the magnetic poles. So, as the current swaps direction in the armature, it also swaps brushes with left = positive and right = negative

What are some factors that affect generator output?

• Strength of the magnetic field

• The number of wire conductor loops on the armature

• The speed of the armature

What are some other generator system components?

• Cutout relay

• Voltage regulator

• Current Regulator

What is a cutout relay?

disconnects the generator when the system is not in operation (to prevent battery discharge)

What is a voltage regulator?

Cuts the power to the field circuit when there is low demand on the generator

What is a current regulator?

cuts power to the field circuit when there is too much demand on the generator

What is an AC charging system?

Uses an alternator and a regulator to produce and control electrical power

What are AC charging systems composed of?

• Alternator

• Voltage/current regulator (controls voltage and current output by regulating the field circuit)

• Bridge rectifier (converts AC to DC using diodes)

• Ignition switch

• Battery

• Load

How does an alternator differ from a generator?

• In an alternator, the conductor (stator) is stationary and the magnetic poles (rotor) rotate

• An alternator rectifies AC to DC using diodes rather than a commutator

Since the conductors are stationary, how does this benefit the circuit?

It can be connected directly to the charging circuit instead of passing through a commutator and brushes

Components of an alternator:

• Rotor: consists of a wire coil wrapped around an iron core mounted on a shaft

  • The ends of the coil are attached to two slip rings on the shaft

  • DC current flows through the coil via the brushes and slip rings (generating a multi-pole magnetic field)

• Stator: is an iron frame that carries three sets of windings (one for each phase)

• Recitifier: composed of six diodes connected to each phase in sets of two

What is the purpose of a starting circuit?

• It is to safely and efficiently crank the IC engine

• Modern automative engine simply require much energy. Modern energy systems quickly start engine while keeping operator safe. 

What are the starting circuit components?

• Battery: Supplies energy

• Starter switch: Activates the circuit

• Solenoid or magnetic switch: Engages the starter motor

• Starter motor: Drives the flywheel to crank the engine

What are the components of a starting motor?

• Field frame assembly

• Armature

• Drive mechanism

• Solenoid

How does a starter work?

• Coverts electrical energy to mechanical work (it is the reverse of a generator)

• The armature forms its own magnetic field when energized by current from the battery

How was the current passed from the battery to the armature?

The current is passed through a commutator and brushes (just like the generator)

So far, what is comprised of the starter motor

The starter motor is comprised of the:

• Pole pieces

• armature

• commutator

• brushes

What are the types of motor circuits

• Series-wound

• Parallel-wound

• Series-parallel wound

• compound wound

What are the different types of switches?

• Magnetic

• Manual

• Solenoid

• Series-parallel

Are manual switches often used?

No, because of the high current hazard and long electrical path

How do magnetic switches work?

Close the circuit between the battery and the starter when an electromagnet and can be mounted on the starter or in some other location

How do solenoid switches work?

Perform the same function as the magnetic switch but also pushes the pinion gear into mesh with the flywheel so they have to be mounted on the starter

What do the starter drives do?

• Connects the starting motor to the flywheel so that the crankshaft can be turned

• Accomplished by moving the starter pinion gear into mesh with the flywheel when the starter motor is engaged

What are the types of starter drives

• Inertia drives

• electromagnetic drives

What is inertia drive?

Utilizes the weighed pinion gear on a spiral shaft to engage the flywheel

What is electromagnetic drive?

Shifted in and out of engagement with the flywheel by the action of the solenoid plunger acting on the pivoting fork in the starter

What is the purpose of an ignition system

To create (high voltage) spark to ignite the air/fuel mixture in the spark ignition engines

What are the ignition circuit components

• Ignition coil

• Condensor

• Distributor and breaker points

• Spark plugs

What are the two parts of an ignition circuit?

• Primary circuit: low voltage from battery

• Secondary voltage: high voltage used to fire the spark plugs

What is expected from an ignition system

• Must convert the low voltage to high voltage to fire engine

• Accurately time the high voltage sources

• Deliver the voltage to the correct spark plug at the appropriate time

What are the components of the primary circuit?

• Ignition switch: controls opens/closes the circuit

• Coil primary winding: composed of a few turns of heavy wire, it generates a magnetic field of the coil

• Distributor contact/breaker point: opens and closes the primary circuit during operation

• Condenser: Prevents arcing at the points and helps collapse the magnetic field in the coil rapidly

What are the components of a secondary circuit?

• Coil secondary winding: composes of many turns of fine wire multiples the voltage induced by the magnetic field of the primary winding

• Distributor rotor: transfers the high secondary voltage to the distributor cap

• Distributor cap: distributes the high voltage to the correct spark plug

• Spark plugs: ignite the air-fuel mixture to the cylinder

How does the system work

Before the points open:

• When the ignition switch is turned on, current flows from the battery through the primary winding of the coil

• The current while passing, produces a magnetic field

• Then passes through the closed points to ground

After the points open:

• As the engine is turned over by the starter, the distributor shaft is turned

• A cam on the shaft opens the point

• Once open, the flow of current on the primary circuit stops, collapsing the magnetic field

• As it collapses, a voltage is induced on the primary and secondary winding of the coil

What happens in the primary circuit

The current flow is stopped and is absorbed by the condensor instead of going to ground through the points

What happens on the secondary circuit?

• Secondary winding is composed of many more turns of wire than the primary thus more voltage 

• High voltage runs from the coil to the distributor, where it is directed to ground through the appropriate spark plug

What is the purpose of ignition advanced systems?

• In order to get the greatest power and efficiency fro combustion, the spark must come at a specific time

• As the speed of the engine increases, so does the amount of advance required

What is a centrifugal/mechanical advanced system

the most common type, used to increase advance as the engine speeds up

composed of counterweights and springs pinned to the breaker cam

as the engine speed increases, the weights are pulled and the breaker cam and rotor are moved forward

What is a vacuum advanced system?

• Under high manifold vacuum conditions, less fuel and air are being delivered to the cylinder

• The lean mixture burn slower than rich full load mixtures thus efficiency is improved with increase advance

• Uses diaphragm connected to manifold vacuum

Describe a modern solid state ignition system

• There has been a steady reduction in the number of moving parts in ignition systems

• First to be replaced was the breaker points and afterwards the distributors all together