PowerPoint for

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PowerPoint for
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Chapter 53
Clutch Fundamentals
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Contents

• Clutch principles
• Clutch construction

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Automotive Clutch

• Used to connect and disconnect the engine and
  manual transmission or transaxle
• Allows the driver to control power flow between
  the engine and transmission or transaxle

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Drive Trains
Front-WheelDrive Vehicle
Rear-WheelDrive Vehicle
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Clutch Principles

• Vehicles with manual transmissions require a
  clutch
• Power flow from one unit to another can be
  controlled with a drive disc and a driven disc

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Clutch Theory
Clutch is disengaged

• Clutch is engaged

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Simplified Clutch
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Basic Clutch Parts
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Clutch Action (Disengaged)

• When driver presses the clutch pedal, clutch
  release mechanism pulls or pushes on the clutch
  fork
• Fork moves the release bearing into the center of
  the pressure plate
• Pressure plate face pulls away from the clutch
  disc
• Clutch disc and transmission input do not turn

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Clutch Action (Disengaged)
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Clutch Action (Engaged)

• When driver releases the clutch pedal, spring
  pressure inside the pressure plate pushes forward
  on the clutch disc
• This locks the flywheel, disc, pressure plate,
  and transmission input together
• Engine rotates the transmission input

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Clutch Action (Engaged)
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Clutch Construction

• Components
• pilot bearing
• flywheel
• clutch disc
• pressure plate
• release bearing
• clutch housing (bell housing)
• clutch release mechanisms
• clutch start switch

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Pilot Bearing

• Pressed into the end of the crankshaft
• Supports the end of the transmission input shaft
• Made of a solid bronze bushing, roller or ball
  bearing
• Prevents the transmission shaft and clutch disc
  from wobbling when the clutch is released

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Flywheel

• A mounting place for the clutch
• The pressure plate bolts to the flywheel face
• Flywheel face is precision machined to a smooth
  surface, where it contacts the clutch disc
• Normally made of iron for good wear and heat
  dissipation

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Clutch Disc

• Consists of a splined metal hub and a round metal
  plate covered with friction material (lining)
• Splined to the transmission input shaft
• Disc is free to slide back and forth on the shaft

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Clutch Disc
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Clutch Disc Torsion Springs

• Help absorb some of the vibration and shock
  produced by clutch engagement
• Small coil springs located between the clutch
  disc hub and the friction disc

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Clutch Disc Facing Springs

• Flat, metal springs located under the discs
  friction material
• Springs have a light wave (curve)
• allow the friction material to flex inward
  slightly during clutch engagement
• flexing smoothes engagement

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Clutch Disc Friction Material

• Made of heat-resistant substances
• Grooves cut in the material aid cooling
• Rivets are commonly used to bond the friction
  material to both sides of the metal body of the
  disc

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Pressure Plate

• Spring loaded device
• Locks or unlocks the clutch disc and the flywheel
• Clutch disc fits between the flywheel and
  pressure plate
• Two basic types
• coil spring
• diaphragm spring

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Coil SpringPressure Plate
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Components

• Small coil springs
• clamp clutch disc between face and flywheel
• Face
• large ring that contacts the clutch disc
• Release levers
• allow the release bearing to move the face
• hinged inside the pressure plate

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Centrifugal Action

• Semi-centrifugal pressure plate uses weighted
  release levers or rollers to increase clamping
  pressure on the clutch disc
• As speed increases, their outward thrust acts on
  the release levers
• Extra force keeps the clutch from slipping, and
  allows the use of lighter springs, reducing pedal
  effort

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Diaphragm Spring Pressure Plate

• Uses a single diaphragm spring instead of several
  coil springs
• Diaphragm spring is a large, round disc of spring
  steel which rides on a pivot ring part way in
  from the outer edge
• Pushing in on the center of the spring bends the
  outer edge away from the engine, releasing the
  clutch disc

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Diaphragm Spring Pressure Plate
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Release Bearing

• Usually a ball bearing and collar assembly that
  reduces friction between the pressure plate
  levers and the clutch fork
• A few imported vehicles use a graphite bearing
• ring shaped block of graphite presses on a
  smooth, flat plate on the clutch release levers

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Release Bearing
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Clutch (Bell) Housing

• Bolts to the rear of the engine
• Encloses the clutch assembly
• Made of aluminum, magnesium, or cast iron
• Transmission bolts to the back of the clutch
  housing

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Clutch Assembly

• Diaphragm clutch with a hydraulicrelease
  mechanism

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Hydraulic Clutch Release Mechanism

• Uses a simple hydraulic circuit to transfer
  clutch pedal action to the clutch fork
• Components
• clutch cylinder
• hydraulic line
• slave cylinder

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Clutch Cylinder

• Produces hydraulic pressure for the system
• Mounted to the firewall or cowl
• Push rod links the clutch pedal and the cylinder
  piston
• Most systems use brake fluid

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Clutch Cylinder
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Slave Cylinder

• Uses hydraulic pressure to cause clutch fork
  movement

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Clutch Linkage Mechanism

• Uses levers and rods to transfer motion from the
  clutch pedal to the clutch fork
• A bellcrank may be used to reverse the movement
  of the clutch pedal
• A release rod transfers motion to the fork and
  allows adjustment

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Clutch Linkage Mechanism
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Clutch Cable Mechanism

• Uses a steel cable inside a flexible housing to
  transfer pedal movement to the clutch fork
• One end usually has a threaded sleeve for clutch
  adjustment

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Clutch Cable Mechanism
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Automatic Clutch Adjuster

• Removes play from the clutch cable as components
  wear
• Pedal has a quadrant and pawl device
• Spring inside applies light tension on the cable
  to take up extra slack
• If there is too much play when the clutch is
  released, the pawl will ratchet over the quadrant
  teeth, taking up slack

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Automatic Clutch Adjuster
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Clutch Start Switch

• Prevents the engine from cranking unless the
  clutch pedal is depressed
• Safety device that keeps the engine from starting
  while in gear
• Usually mounted on the clutch pedal
• May control current from the ignition switch to
  the starter solenoid or may be an input to the
  engine computer

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Clutch Installation

• Rear wheel drive transmission

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Clutch Installation

• Front wheel drive transaxle