Automotive Drivetrains CLUTCHES

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

Clutch System 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 ... The engine power will transfer through the clutch to the road

System Components 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

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

Clutch Components - Flywheel 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

Flywheel Construction 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

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

Flywheel Measurements Run-out – measured with a dial indicator Parallelism – straight-edge & feeler gauge Thickness – micrometer or dial indicator

Clutch Components Input (clutch) shaft 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 – Clutch Disc Is squeezed between the flywheel and the pressure plate Transmits power from the engine crankshaft to the transmission input shaft

Facing manufactured with frictional material (may contain asbestos) Clutch Disc Construction Facing 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)

Pressure Plate (clutch cover) Clutch Components Pressure Plate (clutch cover) Squeezes clutch disc onto flywheel Can be engaged or disengaged Acts like a spring-loaded clamp

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

Clutch Components Release (throw-out) bearing Operated by the clutch linkage Presses against the pressure plate to release the clutch

Pilot Bearing (bushing) Clutch Components Pilot 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 – Hydraulic Most Commonly used today

Hydraulic Clutch Master

Hydraulic Clutch Slave

Hydraulic Clutch Slave Concentric-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