An Overview of Drivetrain

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Transcript of An Overview of Drivetrain

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An overview on Drivetrain

What is drivetrain?The drivetrain of a motorized vehicle is the group of components, excluding the engine or drive motors, that deliver power to the driving wheels.Common components of automotive drivetrain includesDriveshaft/Propeller shaftTransmissionGearboxDual Clutch TransmissionContinuously Variable TransmissionElectrically Variable TransmissionInfinitely Variable TransmissionClutchDifferential Torque ConverterAxleTransfer case

Front AxleFront DifferentialTransmissionTransfer CaseRear DriveshaftRear DifferentialFront DriveshaftRear AxleHow it worksIn general, power from the engines crankshaft is transferred to the clutch. The clutch controls the amount of power delivered to the rest of the driveline, this is done either manually(pedal/hand control) or automatically (torque converter).

The power transmitted from the clutch is then used to drive the transmission of the vehicle. The transmission controls the ratio of torque and speed between the engine and the axle.

Power is then transmitted through the driveshaft to the differential, which controls the balance of power given to each driving wheel. ClutchesWhen disengaged the clutch will spin independently of the wheels speed, and when it is engaged, the engine wheel speed is a direct function of engine RPM. Most clutches in vehicles are dry meaning there is no lubrication present in the disks. This is done to reduce power losses in friction and windage. Power sport clutches are almost always wet, and allow for you to ride the clutch.

Some clutches actuate based on the speed on the engine solely. These centrifugal clutches use rotational inertia to engage the clutch at a preset engine RPM. When the engine RPM drops below this threshold, the clutch disengages itself. This allows a machine to be in a neutral gear, without a gearbox.

ClutchesAnother type of performance clutch is the slipper clutch. These clutches prevent engine braking from hindering speed when the vehicle decelerates prior to cornering. They will slip, and allow the drive wheel to spin at a faster rate than the engine. The slip in the clutch allows for the rear suspension to remain unloaded by wheel hop or chatter. In extreme cases the slipper clutches prevents the rear wheels from locking up if the engine seizes.

CVT(continuously variable transmission)The CVT is a type of transmission that relies on centrifugal power, much like the centrifugal clutch, to transfer power from the engine to the rest of the drivetrain. Many CVT systems work without a clutch, and are tuned to not engage until a certain engine RPM is reached. This allows for vehicles to have their engine turning, without the wheels moving. CVTs are designed to operate the engine at a single RPM, keeping artificial load on it, forcing it to produce maximum torque.

CVTThe tuning of the internal hardware of the CVT is a process that can change the operation of the system completely. The CVT is made up of two pulleys, a primary (driving) and secondary (driven) pulley. The primary pulley has the following;Sheave(diameter and angle)Ramp profileWeightSpringThe secondary pulley has the following;Sheave(diameter and angle)Helix angleSpringBelt tension

Changing any of these parts will affect the function of all the others, and for the most part they cannot be changed independent of one another.

Sequential TransmissionMost motorcycles and four wheel performance vehicles utilize a sequential transmission to change the gear ratio between the engine and wheels. They are ideal for race applications because there is no need to operate the clutch during upshift and downshift operations, only when starting from a standstill. In a 5-speed sequential gearbox, there are 5 sets of shifting gears, each set has a fixed gear and a moveable gear. Each shift causes the shifting drum to advance a set number of degrees. When the shifting drum moves, a movable gear is shifted in the gear assembly, which changes the overall drive ratio.

Engine InputGearboxOutput

8Single speed gear reductionsIn addition to the gearing of the transmission, power sports vehicles use a gear reduction between the output shaft of the transmission and the rear wheel drive differential. This can be in the form of a pulley system, chain reduction, or gearbox.

Planetary Gear TrainA planetary gear set utilizes multiple contact points to transmit power more efficiently than a normal gear set. The planetary gearbox can also be utilized for the construction of a multiple ratio gearbox, which is done by locking the rotation of the four different parts. The use of one-way clutch, or brake stops the rotation of the part, and the path that power is transmitted changes, changing the ratio.Ring GearPlanet CarrierSun GearPlanet Gears

Mechanical DifferentialsDifferentials control the power distribution given to the left and right drive wheels. There are many types but the most common areSpool (Locked Differential) The axles are locked together; wheels always spin at the same rate. Both wheels receive equal engine power.

Open Differential The wheel with the least load receives the majority of the engine power.

Limited Slip Differential Clutch packs and a preload spring force power to travel to each axle, not equally in most cases.

Torsen (Torque Sensing) Differential Applies more torque to the wheel with highest load, when the other wheel is slipping. In other cases it acts like an open differential.

Electronic TCS Uses anti-lock braking systems to prevent wheel spin, power transfer between wheels in also controlled electronically.

Self-Locking Differential An open differential that can be manually locked and unlocked via cockpit controls.Torque sensing differentialsThe Torsen Differential has a built in capability to automatically adjust torque sent to the left and right driving wheels.

In a situation where one wheel rotates faster than the other, the differential will sense the difference and automatically accommodate, so that the wheel with lower grip will not absorb all of the engines torque.

At the moment where one wheel has zero grip, the axle will act as if it is locked, like a spool.

Drive ShaftsTo transmit power from the transmission to the wheels, or across the length of the car between transfer cases. In almost all cases, the shafts are not straight, and need to be misaligned for packaging purposes. The two ways to misalign a driveshaft is with a Constant Velocity Joint(also Tripod), or Universal Joint.The CV Joint has a higher efficiency than the U-Joint, but is more costly to manufacture and cannot withstand axial loads, where as the U-Joint can be designed to handle axial stresses.

Splined CV Joint