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| What
is a converter lock up clutch anyway? |
The
short answer to this question is: Whenever the converters clutch disc
is in its engaged position, a direct drive connection exists between
the engine and the input shaft of the transmission. That's converter
clutch lock up! We'll try to keep this explanation as simple as possible
but this section contains the following topics that need to be covered
to help will understand how this system operates.
- The driving
parts and their relationship to each other.
- The driven
parts and their relationship to each other.
- How driving
and driven sections connect and disconnect from each other
While section one
described all the parts of the converter, this section will
be limited to only those six components that directly make up the
converter lock up clutch system. The converter lock up clutch system
is made up of six major components: the engines crankshaft,
the flexplate (sometimes called a flywheel), the engine side
converter front cover (#3),
the clutch disc, the converter turbine and finally the
transmissions input shaft/drum assembly. Three of the six components
make up the driving section and three make up the driven
section. The driving and driven sections are always
the same parts whether the converter is working in hydraulic coupling
mode (normal converter action) or locked up clutch mode. The position
of the clutch disc inside the torque converter determines which mode
of operation the converter is operating in. When hydraulically pushed
away from the engagement surface it's in normal hydraulic coupling
mode. When the clutch disc is hydraulically forced to the engagement
surface, it's locked up or in direct drive mode. |
| The
Driving Section |
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Most of you
are already familiar with the engines crankshaft and flexplate (flywheel)
so I won't spend any time trying to explain these parts. The flex
plate (flywheel) is bolted directly to the end of the engines crankshaft.
The transmissions torque converter is bolted directly to this flexplate
creating a single driving mechanism. These three components,
crankshaft, flex plate and the converter are physically connected
to each other by bolts therefore always act as a single
unit. They will always turn at exactly the same speed. For
this discussion, we are not interested in the whole converter shell,
just the forward shell portion where the converters clutch disc
will interact. We have cut a converter apart at the central weld
to help clarify the relationship of the parts.
Picture #1
below a side view of a fully assembled converter, engine side to the
right, transmission side to the left. This
converter has two pieces that make up its outer shell.
These two sections are held together
by a central circumferential weld. We cut this circumferential weld
off using a lathe, then split this converter so we could show both
sides of the converter shell in picture #2.
The piece on the left in picture #2, is
the pump section of the converter which engages into the transmission.
The piece on the right in picture #2
is the converters front cover
piece that bolts to the flexplate (note the bolt bosses). Picture
#3 is
a view of the inside of this front cover. Picture #3
also shows the surface where the converter clutch disc engages when
in the locked position. The engines crankshaft, flexplate
and the converter front cover (picture #3)
make up the driving section of the converter
clutch system.
If you wish
an explanation of the pump section of the converter shell, see component
#6 in the first part of this technical write up. This section is
only interested in the front cover.
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| The
Driven Section |
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The three
driven components are: the converter clutch disc, the
converter turbine assembly and the transmissions input
shaft/drum assembly. The driven components are always
physically connected together so they act as a single unit
at all times. This is done using splined bores, hubs and shafts
that physically connect all three components together. These spline
connections allow for slight fore and aft movement between these
components.
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The picture
at left shows the three components that make up the driven section.
- Left end
is the Clutch Disc.
- Middle is
the Turbine assembly.
- Right end
is the transmissions input shaft/drum assembly.
These three
components are connected by splined areas on each component and
always act as one unit. What one component does, the other will
also do. They always turn at exactly the same rpm.
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The picture at the right is the same assembly as above only this
view is showing the clutch disc end clearly. Note the friction material
that engages with the inside surface of the front cover shown above
in picture #3 above.
When this clutch disc is hydraulically forced up against the inside
of the converter cover (picture #3).
This creates a direct mechanical connection between
the driving section and this driven section.
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The
pictures at left are views of both sides of the turbine assembly.
They clearly show the input shaft/drum assembly where it connects
by splines to the turbine.
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Up until this point, the pictures of the driven section have shown
the input shaft/drum assembly engaged to the splines of the turbine
(like the two pictures above). We have shown them this way to help
clarify how they spline together. However, the input shaft/drum
assembly is actually part of the transmission not the converter.
When it's installed in the transmission, you can't see the drum
assembly, just a small section of the splines of the input shaft
(see the picture directly to the right). When the torque converter
gets installed, it's placed over this shaft, where it engages the
turbine. The picture at right is viewing the inside of the transmissions
bell housing area.
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The
two pictures at the left illustrate how the clutch disc (left picture)
and the turbine (right picture) spline together. This spline connection
allows for the fore and aft movement of the clutch disc This movement
is necessary for the clutch disc to engage or disengage from the
converter cover.
The clutch disc is allowed to move because it's riding on the outside
hub splines of the turbine assembly (red arrow in the middle picture
above). These turbine splines mate to the inside splines of the
clutch disc dampening spring assembly (red arrow in the left picture
above). You now know how the driven parts connect to each other.
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The converter
clutch disc is designed to move slightly
fore and aft, while the turbine and input shaft/drum assemblies
are designed to be held in relatively fixed positions. The clutch
discs movement is controlled by fluid flowing directly from the
transmissions internal hydraulic pump. The direction of movement,
whether for or aft, is determined by which side of the disc this
hydraulic fluid is directed to. If the fluid is directed to the
rear side of the disc, it will move forward slightly to engage,
with force, against the inside of the converter cover. When this
disc is forcefully engaged in this forward position, it "locks"
the drive and driven assemblies together as one, creating a direct
drive from the engine to the transmission. This action is basically
the same as releasing the clutch pedal in a manual transmission
equipped car. When hydraulic fluid is routed to the front side of
the clutch disc, the disc moves slightly to the rear. This rearward
disc movement causes the drive and driven assemblies
to become physically disengaged from each other, returning the torque
converter to its normal fluid coupling operation.
During
fluid coupling (standard converter) operation, the driving
and driven sections are physically separate by a small gap between
the clutch disc and the converter cover. During this type
of converter operation, power is transmitted from the driving
section, through the converter to the driven section by a
fluid coupling action between the converter pump and the turbine
(the clutch disc is always spline connected to the input shaft but
it just goes along for the ride).
During
converter clutch lock up operation, the driving and
driven sections are physically connected when the clutch
disc is forced forward against the converter cover. During this
type of operation, power is transmitted directly from the driving
section to the driven section by the physical direct connection
at the clutch disc and the converters front cover (then the hydraulic
coupling is not used and the turbine just goes along for the ride).
When
the disc is in its engaged position, the input shaft/drum assembly
of the transmission will always be turning at the exact same speed
as the engines crankshaft thereby eliminating any heat production
inside the torque converter. When this is properly understood and
used correct it can have tremendous advantages in controlling heat
build up inside the torque converter!
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