Transcript Engine Ignition

Engine Ignition
An Overview
of the
Ignition Systems Utilized
in the
Early Internal Combustion
Engines
Types
• Hot Tube Ignition
• Igniter (low tension) Ignition
• Spark Plug (high tension)
Ignition
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Hot Tube Ignition
Simplified Overview
Hot tube ignition was used on the oldest of the internal combustion engines.
Usually rather large engines. No electricity or “spark” is needed.
Air / Fuel Mixture
Piston
Closed end tube
Chimney
Figure 1
Heat source
As the air/fuel mixture is compressed, a portion of the compressed mixture is
forced into the heated closed end tube. When the temperature and pressure within
the tube reach the required point, the mixture ignites and ignites the mixture in the
cylinder. (Figure 1)
Think of a deisel engine with a glow plug
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Igniters
An igniter is simply a set of contacts or “points”. It consists of one moveable and
one fixed contact. The two contacts bodies are separated and insulated from each
other by a mica tube and washer. (Figure 2)
Igniter body / mounting bracket
Mica insulation
Fixed contact
Electrical contact
Moveable contact
Trip mechanism
Figure 2
Igniters are used in low tension ignition systems, which include:
•Battery and coil
•Low tension magneto
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Battery and Low Tension Coil
The battery and low tension coil ignition system consists of a battery, a single field
inductive coil, the igniter and a switch.
When the engine is not running, the switch should be open to prevent the flow of
current through the coil. The igniter contacts may or may not open base on the cycle of the
engine. ( Figure 3A)
Current passing through the coil for an extended period of time will cause the coil to
heat up and possibly burn out the coil.
Igniter
-
+
Battery
Switch
Coil
Figure 3A
Before starting the engine, rotate the flywheels until the igniter is in the “open” position. Close the switch
and start the engine. (Figure 3B)
Igniter
-
+
Battery
Switch
Coil
Figure 3B
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As the engine passes through the compression cycle, the engine mechanism closes the
igniter contacts just prior to the point of firing. This causes the electrical circuit to close
and current to flow through the coil. The current flowing through the coil establishes an
electrical magnetic field (EMF). (Figure 3C)
+
-
-
Igniter
+
Battery
Switch
Coil
Figure 3C
When the engine reaches the ignition cycle, the igniter is released, the contacts “snap”
open. With the contacts open, current ceases to flow through the coil. The established
EMF collapses onto the core with the reverse voltage. This reverse voltage seeks the
ground potential through the gap of the igniter contacts causing a spark. (Figure 3D)
- +
-
Igniter
+
Battery
Switch
Coil
Figure 3D
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From Fairbanks-Morse - Principles Of Magnetos
If a piece of steel is bent into a "U", to make the ordinary "magnet," the
space between the ends will be filled with invisible magnetic "lines of
force." The magnetism will be stronger at this point than anywhere else
about the magnet. If a coil of wire is moved in and out of the space
between the poles, or is revolved in this space, an electric current will be
generated in the wire, and if the ends of same are separated, a spark will
be produced between them.
N
S
Figure 4
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The MAGNETO is simply a magnet, with a coil of wire revolving
between its poles (Armature), the coil being provided with a
suitable means whereby the current generated is conducted off to
the engine igniter, the points of which are alternately opened and
closed at the proper time.
A peculiar thing about the Magneto is that the current generated
in the wire is strongest at only two points in each revolution of
the wire, and to get the best spark the igniter points in the engine
must snap when the wire is at one of these points.
N
S
Figure 5
8
The more lines of force crossed by the armature, the greater the force or
current is generated.
A
N
B
S
N
A
C
S
B
N
C
D
D
S
N
S
A
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TYPES OF LOW TENSION MAGNETOS
-
OSCILLATING
-
CONTINUOUS ROTATION
10
.
OSCILLATING MAGNETO
Igniter
Points
Figure 6A
Armature
Winding
The magneto is usually attached directly to the Igniter. The trip mechanism closes the
igniter points and pre-sets the magneto armature to the optimum position. (Figure 6B)
Igniter
Points
Figure 6B
Armature
Winding
As the trip mechanism releases, the armature (under spring tension) rotates
through the optimum lines of force. At the same time the points open. The
resulting halt in current flow collapses the field and reverse current flow causes the
spark. (Figure 6C)
Igniter
Points
Figure 6C
Armature
Winding
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CONTINUOUS ROTATION MAGNETO (Low Tension)
The continuous rotating magneto works like the oscillating magneto. The armature
rotating through the magnet field while the points are closed and opened at the
proper time.
The magneto is usually located near and attached to the drive mechanism or timing
gear. The igniter trip mechanism is a separate system. This requires that the
armature rotation must be “in time” with the Igniter. (Timing marks, crank
location, etc.)
A
B
C
D
A
Note: Many continuous rotation magnetos require a significant rotation speed
to generate sufficient current to create a spark. Therefore, many models
require starting the engine with a “battery & coil” and then switch over to the
magneto. The Fuller and Johnson early engines had a two-way switch
attached for just that purpose.
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High Tension Ignition (Spark Plug)
Buzz coil
High Tension Magneto
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These are the basic components of a buzz coil ignition
Buzz Coil Box
-
Iron
Core
+
Battery
Primary
Coil
Secondary
Coil
Spark plug
Capacitor
Trip
Contact
Buzzing
Contacts
Figure 7
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As the trip contact closes, the circuit through the primary coil is complete and the current
begins to flow. The current establishes an electrical field around the iron core causing it to
become an electro-magnet. The electro-magnet pulls on one of the buzzing contacts.
(Figure 8A)
Buzz Coil Box
-
+
+
Battery
Primary
Coil
Iron
Core
Secondary
Coil
Spark plug
Capacitor
Buzzing
Contacts
Trip
Contact
Figure 8A
As the buzzing contacts separate, the current flow through the primary coil will
cease and causing the field to collapse around the secondary coil and cause the
current to spark across the spark plug gap. (Figure 8B)
Buzz Coil Box
-
Iron
Core
+
Battery
+
Primary
Coil
Secondary
Coil
-
Capacitor
Trip
Contact
Spark plug
Buzzing
Contacts
Figure 8B
As the field collapses, the iron core will loose its magnetism. The buzzing contact will
return to its normally closed position and start the process over again The buzz coil
will continue to oscillate between these two states as long as the trip contacts remain15
closed.
High Tension Magneto
•Single Trip
•Continuous Rotation
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WICO “EK”
Figure 9
N
S
S
N
Keeper
Figure 10
17
The Wico “EK” magneto consists of the following components. (Figure 10)
Permanet Magnets
Ferris
Cores
(2)
Coils
(2)
NonFerris
Base
Points
Ferris Keeper
(Armature)
Figure 10
Electrically, the magneto looks like the following. (Figure 11)
Permanent
Magnet
Secondary
Coil
Primary
Coil
Spark plug
Capacitor
Points
Mechanical
Trip
Figure 11
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Theory of Operation
Permanent
Magnet
Secondary
Coil
Primary
Coil
When the magneto is in the normal state
(un-tripped), the keeper (armature)
channels the EMF through the ferris cores
and the magnets are in equalibrium.
(Figure 12A)
Spark plug
Capacitor
Points
Figure 12A
Mechanical
Trip
Permanent
Magnet
During the first part of the mechanical trip,
the keeper (armature) is disconnected from
the ferris cores and the EMF field is
generated around the coils. (Figure 12B)
+
Secondary
Coil
Primary
Coil
Spark plug
Capacitor
Points
Mechanical
Trip
Figure 12B
Permanent
Magnet
During the second part of the mechanical
trip, the points are opened and the field
collapses around the secondary coil and
causes a spark. (Figure 12C)
+
Spark plug
Capacitor
After the trip, the armature is returned to the
normal state and the process repeats with the
next mechanical trip.
Secondary
Coil
Primary
Coil
Points
Mechanical
Trip
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Continuous Rotation Magneto (High Tension)
•International Harvester H1
•Wico “H”
The continuous rotation high tension magneto operates the same way as the
single trip magneto only in a continuous manner. This requires “timing” to
match up to the engine mechanics, just as with the continuous rotation low
tension magnetos.
For more information check out:
http://www.old-engine.com/magneto.htm
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