Automotive Drivetrains

CLUTCHES

PurposeTo connect and disconnect engine power flow to the transmission at the will of the driver.

•Clutch systems are used to disengage the engine from the road

•When the clutch pedal is depressed, the clutch (and transmission) is disengaged from the engine

Clutch System

•With your foot off of the pedal, the clutch is engaged to the engine.

•The pressure plate holds the clutch against the flywheel, allowing power to travel through the clutch to the input shaft of the transmission ...

Clutch System

•The engine power will transfer through the clutch to the road

•Flywheel: Transfers engine power to the clutch

•Input shaft: Transfers power from clutch to the transmission

•Clutch Disk (clutch): Splined to input shaft; transfers power from engine to the input shaft

•Pressure Plate Assembly: Spring pressure tightly holds the clutch to the flywheel

System Components

Components cont:

•Release Bearing (throw-out bearing): Connected through linkage or hydraulics to the clutch pedal; Provides a way for the pressure plate to release pressure on the clutch

•Pilot Bearing (bushing) : Mounted in the tail of the crankshaft. Stabilizes the input shaft. Not always used for FWD.

•Clutch Fork (if applicable): Slides the release bearing into and away from the pressure plate assembly

Components cont:•Clutch Linkage (or hydraulic plumbing): Allows the driver to operate the clutch fork

•Clutch (bell-housing) Housing: Encloses the clutch assembly–May be integral with the transmission or removable

•Mounted on the rear of the crankshaft•Acts as balancer for engine•Adds inertia to the rotating crankshaft•Provides a surface for the clutch to contact•Usually surrounded by a ring gear for electric starter operation

Clutch Components - Flywheel

•Usually constructed of nodular cast iron which has a high graphite content

•The graphite helps lubricate engagement of the clutch

•May also be constructed from cold rolled steel

Flywheel Construction

Dual-mass Flywheel

The flywheel hub and clutch mating area are two separate components

Springs are used to dampen engine and clutch engagement oscillations

Dual-mass Flywheel

Run-out – measured with a dial indicatorParallelism – straight-edge & feeler gaugeThickness – micrometer or dial indicator

Flywheel Measurements

•Projects from the front of the transmission•Usually has a pilot which rides in a bearing or bushing in the end of the crankshaft•The clutch disc is splined to the clutch shaft

Clutch Components

Input (clutch) shaft

Clutch Components – Clutch Disc

•Is squeezed between the flywheel and the pressure plate•Transmits power from the engine crankshaft to the transmission input shaft

Clutch Disc ConstructionFacing manufactured with frictional

material (may contain asbestos)

Other surface materials include:

•paper-based•ceramic•cotton•brass

Clutch Disc Types• Rigid - used primarily for industrial/racing applications.

•Flexible - most common, everything from grandma’s cruiser to street/strip racing.

Flexible Clutch Disc

•Hub flange - in direct contact with the input shaft

•Friction ring - in direct contact with the flywheel/pressure plate.

Flexible Clutch Disc

•Clutch facing - friction material

•marcel springs - facing dampener•Torsional springs - further dampening for clutch application

•Stop pins - limits the torsional spring’s travel

•Rivets -fastens the facing material to marcel (springs)

•Squeezes clutch disc onto flywheel•Can be engaged or disengaged•Acts like a spring-loaded clamp

Clutch Components

Pressure Plate (clutch cover)

Pressure Plate - Types

Belleville/diaphragm-type Spring: uses a cone-shaped diaphragm spring for clamping force.

Multiple-Coil Springs: DUGH!

Semi-centrifugal: clamping force increases as rotational (centrifugal) force increases

Belleville/diaphragm Spring:

Spring-type Pressure Plate

Benefits and Disadvantages:Belleville/diaphragm type:

•cost effective

•uniform engagement

•limited spring pressure

Spring:•unlimited pressure capabilities

•as springs wear, pressure may become inconsistent

•Operated by the clutch linkage•Presses against the pressure plate to release the clutch

Clutch ComponentsRelease (throw-out) bearing

Clutch ComponentsPilot Bearing (bushing)

•Installed (pressed) into a machined bore in the end of the crankshaft or flywheel

•May be a bushing, ball-bearing or roller-bearing

Clutch linkage – Mechanical

Linkage-type

Clutch linkage – Mechanical

Cable-type

Clutch linkage – HydraulicMost Commonly used today

Hydraulic Clutch Master

Hydraulic Clutch Slave

Hydraulic Clutch SlaveConcentric-type

Dual-clutch Transmission Essentially an

“automatic” manual transmission

Delivered to the mainstream by Volkswagen – now being used/developed by most mfg.

Eliminates the “power sucking” torque-converter of an automatic transmission

Dual-clutch Transmission Utilizes two input

shafts – one inside of the other

Each input shaft will have a dedicated clutch or clutch pack splined to it.

A processor (computer) will engage one or the other clutches (or neither for neutral.)

Dual-clutch Transmission May use a wet or dry “clutch-pack”

Dual-clutch Transmission or conventional clutch disc design

Dual-clutch Transmission

Each of the input-shafts controls half of the transmissions gear-sets

Dual-clutch Transmission