Powertrain and Clutch System Overview

Study Notes

Powertrain

The powertrain is comprised of components that deliver forward motion to a vehicle.
Key powertrain components include the engine, transmission, driveshaft, axles, and differential
The clutch system engages and disengages the engine from the transmission, enabling the driver to start, stop, idle, and shift gears.

Clutch System Construction

The clutch system is found in different locations depending on the type of vehicle drive:
- Rear Wheel Drive (RWD)
- Front Engine
- Rear Engine
- Mid Engine
- Front Wheel Drive
Pressure Plate:
- Transmits propulsion torque to the wheels
- Pressed against the flywheel
- Contains:
  - Cover: Steel stamping or casting that houses clutch components and attaches to the flywheel.
  - Pressure Plate: Cast iron plate that provides a pivot fulcrum for the diaphragm spring.
  - Diaphragm Spring: A flat, spring-steel disc that engages and disengages the clutch, compressed between the cover and pressure plate.
  - Pivot Ring: A steel ring attached to the clutch cover that provides a fulcrum for the diaphragm spring.
  - Drive Straps: Flat, spring-steel strips that attach the pressure plate to the clutch cover and help lift the pressure plate away from the disc to disengage the clutch.
  - Release Fingers: A lever that presses on the clutch release bearing.
Two Types of Pressure Plates:
- Diaphragm Spring Clutch: Uses a diaphragm spring for engagement and disengagement.
- Coil Spring Clutch: Located in the pressure plate assembly, made of tempered-steel rods formed into a spiral that resists compression.
Friction Disc:
- Important for long service life of the clutch system
- Provides a smooth engagement and dampens engine vibrations
- Slides forward and backward on the shaft splines
- Cannot rotate the shaft.
- Contains:
  - Hub-Flange: Located between a cover plate and retainer plate; splined to fit the input shaft.
  - Torsion Springs: Located inside the damper assembly; smooth engagement and dampen vibrations.
  - Idle-Stage Dampers: Consist of small springs nestled around the hub or friction washer inside the disc.
  - Friction Material: Organic material riveted to wavy metal cushion segments, sometimes called marcels.
Components of the Friction Disc:
- Friction Material: Substances that produce friction between solid surfaces to control motion.
- Cushion Segment: Connected to the first and second annular plates; includes a radially outermost edge, a slot, a first edge, and a second edge.
- Stop Pin:
- Friction Washer: Involved in high-speed cleaning of mixed plastics.
- Idle Damper Spring (1st Stage)
- Idle Damper Spring (2nd Stage)
- Main Damper Spring (1st Stage)
- Main Damper Spring (2nd Stage)
- Hub: Carries the axle on the wheels of the vehicle.
Friction Disc and Pressure Plates:
- Friction Disc: Is sandwiched between the pressure plate and the flywheel, engaging and disengaging to control the transfer of power.
- Pressure Plate: The other side of the friction disc, provides the force that presses the disc against the flywheel.
Flywheel:
- Heavy wheel that makes an engine move smoothly
- Stores kinetic energy
- Keeps the engine at a constant speed
Crankshaft
- Mechanical component used in a piston engine
- Converts reciprocating motion into rotational motion
Pilot Bearing/Bushing:
- Supports and centers the transmission input shaft and clutch disc
Rear Main Seal:
- Keeps oil sealed inside the rear of the engine
- Located where the crankshaft connects with the transmission
Transmission Input Shaft:
- Transfers drive from the engaged engine through the clutch system into the gearbox.
Bearing Retainer:
- Separates balls in a ball bearing
- Maintains symmetrical radial spacing of the balls
- Holds the bearings together in most cases
Release Bearing:
- Also called thrust bearing, throw-out bearing
- Part of the clutch system
- Vital in smooth shifting of gears in a car
Release Fork:
- Enables smooth shifting of gears in a car
Input Shaft Seal:
- Prevents fluid from leaking past the input shaft.
Bell Housing:
- Bell-shaped extension of the engine crankcase
- Contains the flywheel and the clutch
Clutch System Function: The clutch system works by transferring torque from the engine to the transmission, enabling smooth engagement and disengagement. The pressure plate is released during gear shifting and compressed during the engagement. The friction disc is sandwiched between the flywheel and pressure plate, creating a friction surface that facilitates the power transfer.