ABDULLAH AFTABIME-278REPORT ON DRIVE TRAIN

DRIVE TRAIN The drivetrain of a motor vehicle is the group of components that deliver power to the driving wheels. This excludes the engine or motor that generates the power.

FunctionThe function of the drivetrain is to couple the engine that produces the power to the driving wheels that consume this mechanical power. This connection involves physically linking the two components, which may be at opposite ends of the vehicle and so requiring a long propeller shaft or drive shaft. The operating speed of the engine and wheels are also different and must be matched by the correct gear ratio. As the vehicle speed changes, the ideal engine speed must remain approximately constant for efficient operation and so this gearbox ratio must also be changed, either manually, automatically or by an automatic continuous variation.

Components SPROCKETS CHAIN DIFFERENTIAL DRIVE SHAFTS CV JOINTS.

SPROCKETS

General Overview:A sprocket or sprocket-wheel  is a profiled wheel with teeth, cogs, or even sprockets that mesh with a chain, track or other perforated or indented material. The name 'sprocket' applies generally to any wheel upon which radial projections engage a chain passing over it. It is distinguished from a gear in that sprockets are never meshed together directly, and differs from a pulley in that sprockets have teeth and pulleys are smooth. The sprocket interfaces with the differential and the drive chain. Size and tooth count of the sprocket will influence the acceleration of the car and the transitions between the gears of the transmission during dynamic events.

How it WorksSprockets take the linear force from the drive chain and produce rotational energy to spin the differential. The diameter of the sprocket helps produce a moment arm to produce the torque on the differential.

SPECIFICATIONS

Material:Standard Carbon Steel, with or without hardened teeth.Stainless Steel (Specify grade where applicable)Special materials such as alloy steel, bronze, etc., state preference and alternative where appropriate. Hardening Recommendations:Hardened teeth substantially increases sprocket life. Degree of hardness This is governed by these conditions:1. Rockwell “C” 35 to 50 pinion or driver.2. Rockwell “C” 25 to 40 larger diameter or driver sprockets.

Induction or flame hardening will be used as best suited to theindividual application. The diameter and pitch of the sprocketgovern the method used.Caution should be used to avoid “file hardness” (RockwellC 62 and above) as it is not recommended for sprockets dueto brittleness.Depth of hardening should be limited so as to provide caseonly on the wear surfaces with a tough resilient core to absorbshock.

Brinell, Rockwell and Scleroscope HardnessNumbers with Corresponding TensileStrength

SPROCKET CALCULATIONS: Horsepower: Equals 33,000 foot pounds per minute, or 550 foot pounds per second.HP = Working Load × T × P × R.P.M. /396,000.Where : T = number of sprocket teethP = chain pitch Chain Working Load:When the horsepower input is known and the chain working load is desired, this can be calculated as follows:Working Load = HP x 33,000/Ft. Per Min.or = HP x 396,000/T × P × R.P.M. Chain Speed :Can be determined from the following formula:Chain Speed = T × R.P.M./ Kwhere T = number of sprocket teethConstant K (Pitches of Chain Per Foot) PITCH 3⁄8" 1⁄2" 5⁄8" 3⁄4" 1" 11⁄4" 11⁄2" 13⁄4" 2" 21⁄2" 3"K 32 24 19.2 16 12 9.6 8 6.85 6 4.8 4

Factor of Safety: Is determined as follows:F.S. = Chain Ultimate Strength/Chain Working Load Shaft Torque: Ordinarily is greater for the driven shaft than for the driving shaft due to the difference in sprocket sizes and R.P.M. Torque is usually expressed in inch pounds.Torque( Driving Shaft) = HP × 63,000/R.P.M

(Torque(Driven Shaft)= Working Load × RWhere a crank arm is used the load transmitted by the armcan be determined as follows:Crank arm Load = Driven Shaft Torque/ror = Chain Working Load × R/r Catenary Tension: Imposed by reason of the weight of chain can be approximated as follows:Catenary Tension = W × L/28 × S + (W × S)where W = weight of chain (lbs. per ft.)S = chain sag (feet) = 2% to 3% of shaft centers approx.L = Shaft centers in feet.• Number Single Double Triple Quadruple• 25 0.08

Chain Length Calculation:The following equation may be used to determine the chain length required for any two-sprocket drive. L = 2C + (N + n)/2 + A/Cwhere:C = Shaft Center Distance in pitches,L = Length of chain in pitches,N = Number of teeth in larger sprocket,n = Number of teeth in smaller sprocket,π = 3.1416,A = Value from table below tabulated for values of N-n,P = Pitch of chainCalculation of shaft centersThe following formula is useful in determining theapproximate centers in inches for chain lengthsin pitches already determined.

Manufacturing Processes for Sprocket In most cases, the manufacturing process to be

used greatly lies on the facility available. Though, hobbing remains one the best methods that could be used, in this work universal milling machine was used.

Differential (mechanical device)

A differential is a gear train with three shafts that has the property that the angular velocity of one shaft is the average of the angular velocities of the others, or a fixed multiple of that average.

Overview:In automobiles and other wheeled vehicles, the differential allows the outer drive wheel to rotate faster than the inner drive wheel during a turn. This is necessary when the vehicle turns, making the wheel that is traveling around the outside of the turning curve roll farther and faster than the other. The average of the rotational speed of the two driving wheels equals the input rotational speed of the drive shaft. An increase in the speed of one wheel is balanced by a decrease in the speed of the other.When used in this way, a differential couples the input shaft (or prop shaft) to the pinion, which in turn runs on the crown wheel of the differential. This also works as reduction gearing to give the ratio. A differential consists of one input, the drive shaft, and two outputs which are the two drive wheels, however the rotation of the drive wheels are coupled by their connection to the roadway. Under normal conditions, with small tyre slip, the ratio of the speeds of the two driving wheels is defined by the ratio of the radii of the paths around which the two wheels are rolling, which in turn is determined by the track-width of the vehicle (the distance between the driving wheels) and the radius of the turn.

TYPES OF DIFFERENTIALS:There are three different types of differentials used in the Vehicles. OPEN DIFFERENTIAL LIMITED SLIP DIFFERENTIAL LOCKING DIFFERENTIAL

OPEN DIFFERENTIAL:

ADVANTAGES :It is light weight.Easy to maintain.

DRAW BACKS: The wheel of least resistance will receive all of engine torque.The wheel of greater resistance will receive less torque .

CONCLUSION:Using this type will not help in driving the vehicle on the slippery surface because the wheel over slippery region will have low resistance and more torque ,so that will slip and vehicle will not move in straight direction.

LIMITED SLIP DIFFERENTIAL:

ADVANTAGES: When the slip or low resistance is detected it will send power to both tyres.It is reliable in slip conditions. DRAW BACKS OF IT:It has more weight.It is costly.It is not easy to maintain.

LOCKING DIFFERENTIAL:It has three types MECHENICAL LOCKER:It uses springs to lock.

ELECTRICAL LOCKER:It uses electro-magnet for locking.

AIR LOCKERIt uses air for locking

ADVANTAGES OF LOCKING DIFFERENTIAL:

A locking differential provide increased traction compared to a "open" differential by restricting each of the two wheels on an axle to the same rotational speed without regard to available traction or differences in resistance seen at each wheel.A locking differential is designed to overcome the chief limitation of a standard open differential by essentially "locking" both wheels on an axle together as if on a common shaft. This forces both wheels to turn in unison, regardless of the traction (or lack thereof) available to either wheel individually.A locked differential can provide a significant traction advantage over an open differential, but only when the traction under each wheel differs significantly.

DRAW BACKS OF IT:Because they do not operate as smoothly as standard differentials, automatic locking differentials are often responsible for increased tire wear. Some older automatic locking differentials are known for making a clicking or banging noise when locking and unlocking as the vehicle negotiates turns. This is annoying to many drivers. Also, automatic locking differentials will affect the ability of a vehicle to steer, particularly if a locker is located in the front axle. Aside from tire scuffing while turning any degree on high friction (low slip) surfaces, locked axles provoke under-steer and, if used on the front axle, will increase steering forces required to turn the vehicle. Furthermore, automatically locking differentials can cause a loss of control on ice where an open differential would allow one wheel to spin and the other to hold, while not transferring power. An example of this would be a vehicle parked sideways on a slippery grade. When both wheels spin, the vehicle will break traction and slide down the grade.

CONCLUSION: Limited-slip differentials are considered a compromise between a standard differential and a locking differential because they operate more smoothly, and they do direct some extra torque to the wheel with the most traction compared to a standard differential, but they are not capable of 100% lockup.Traction control systems are also used in many modern vehicles either in addition or as a replacement of locking differentials . One example is  electronic differential lock(EDL). This EDL is not in fact a differential lock, but operates at each wheel. Sensors monitor wheel speeds, and if one is rotating more than 100 RPM more than the other (i.e. slipping) the EDL system momentarily brakes it. This transfers more power to the other wheel, but still employs the open differential, which is the same as on cars without the EDL option.

DRIVE SHAFTS• A drive shaft is a mechanical component for transmitting torque and rotation, usually used

to connect other components of a drive train that cannot be connected directly because of distance or the need to allow for relative movement between them.

Design and Analysis of Drive Shaft AssumptionsThe shaft rotates at a constant speed about itslongitudinal axis.The shaft has a uniform, circular cross section. The shaft is perfectly balanced, i.e., at every cross section, the mass center coincides with the geometric center.All damping and nonlinear effects are excluded.The stress-strain relationship for steel material is linear& elastic; hence, Hooke’s law is applicable for the material.Acoustical fluid interactions are neglected, i.e., the shaft is assumed to be acting in a vacuum.

Selection of Cross-Section

The drive shaft can be solid circular or hollow circular.Here hollow circular cross-section was chosen because:The hollow circular shafts are stronger in per kg weight than solid circular.The stress distribution in case of solid shaft is zero at the center and maximum at the outer surface.While in hollow shaft stress variation is smaller.In solid shafts the material close to the center arenot fully utilized.

Design Specifications

1. Starting Torque (Nm) =Max. Engine Torque x 1st Gear Ratio2. I-M.I., mm4 = Moment Of Inertia= (П/64) (Do4-Di4)3. J-POLAR M.I., mm4=(П/32) x (O.D.4 - I.D.4)4. Z-Section Modulus, mm3= (П/16) x ((O.D.4-I.D.4) / O.D.)5 Torsional Shear Stress/mm2= (Starting Torque x D) / (2xJ)

Design Criteria for material selection:

Torsional Shear Stress < Shear Strength of materialIf Torsional Shear stress is exceeding Shear strength of material then next Diameter of shaft is chosen.B. Critical Speed Calculation:Critical Speed, RPM = (30/П) x SQRT (g / δmax)Where, δmax is maximum static deflection of drive shaft.Max.Deflection, δ, mm = (5 x M x g x COSϴ x L3) / (384 xE x J) by Rayleigh Reitz MethodWhere M is mass of tube.

Constant-velocity joint:

Constant-velocity joints  allow a drive shaft to transmit power through a variable angle, at constant rotational speed, without an appreciable increase in friction or play. They are mainly used in front wheel drive vehicles, and many modern rear wheel drive cars with independent rear suspension typically use CV joints at the ends of the rear axle half shafts and increasingly use them on the prop-shafts (drive shafts).Constant-velocity joints are protected by a rubber boot, a CV gaiter, usually filled with molybdenum disulfide grease. Cracks and splits in the boot will allow contaminants in, which would cause the joint to wear quickly.

TYPES OF CV JOINTS Tracta joints The Tracta joint works on the principle of the double tongue and groove joint. It comprises only four individual parts: the two forks (a.k.a. yokes, one driving and one driven) and the two semi-spherical sliding pieces (one called male or spigot swivel and another called female or slotted swivel) which interlock in a floating (movable) connection. Each yoke jaw engages a circular groove formed on the intermediate members. Both intermediate members are coupled together in turn by a swivel tongue and grooved joint. When the input and output shafts are inclined at some working angle to each other, the driving intermediate member accelerates and decelerates during each revolution. Since the central tongue and groove joint are a quarter of a revolution out of phase with the yoke jaws, the corresponding speed fluctuation of the driven intermediate and output jaw members exactly counteract and neutralize the speed variation of input half member. Thus the output speed change is identical to that of the input drive, providing constant velocity rotation.

Tracta joint

Rzeppa joints:A Rzeppa joint consists of a spherical inner shell with 6 grooves in it and a similar enveloping outer shell. Each groove guides one ball. The input shaft fits in the center of a large, steel, star-shaped "gear" that nests inside a circular cage. The cage is spherical but with ends open, and it typically has six openings around the perimeter. This cage and gear fit into a grooved cup that has a splined and threaded shaft attached to it. Six large steel balls sit inside the cup grooves and fit into the cage openings, nestled in the grooves of the star gear. The output shaft on the cup then runs through the wheel bearing and is secured by the axle nut. This joint can accommodate the large changes of angle when the front wheels are turned by the steering system; typical Rzeppa joints allow 45°–48° of articulation, while some can give 54°. At the "outboard" end of the driveshaft a slightly different unit is used. The end of the driveshaft is splined and fits into the outer "joint". It is typically held in place by a circlip .

Rzeppa joint:

Weiss jointsIt consists of two identical ball yokes which are positively located (usually) by four balls. The two joints are centered by means of a ball with a hole in the middle. Two balls in circular tracks transmit the torque while the other two preload the joint and ensure there is no backlash when the direction of loading changes.Its construction differs from that of the Rzeppa in that the balls are a tight fit between two halves of the coupling and that no cage is used. The center ball rotates on a pin inserted in the outer race and serves as a locking medium for the four other balls. When both shafts are in line, that is, at an angle of 180 degrees, the balls lie in a plane that is 90 degrees to the shafts. If the driving shaft remains in the original position, any movement of the driven shaft will cause the balls to move one half of the angular distance. For example, when the driven shaft moves through an angle of 20 degrees, the angle between the two shafts is reduced to 160 degrees. The balls will move 10 degrees in the same direction, and the angle between the driving shaft and the plane in which the balls lie will be reduced to 80 degrees. This action fulfills the requirement that the balls lie in the plane that bisects the angle of drive. This type of Weiss joint is known as the Bendix-Weiss joint.

Tripod joints:These joints are used at the inboard end of car drive-shafts.This joint has a three-pointed yoke attached to the shaft, which has barrel-shaped roller bearings on the ends. These fit into a cup with three matching grooves, attached to the differential. Since there is only significant movement in one axis, this simple arrangement works well. These also allow an axial 'plunge' movement of the shaft, so that engine rocking and other effects do not preload the bearings. A typical Tripod joint has up to 50 mm of plunge travel, and 26 degrees of angular articulation. The tripod joint does not have as much angular range as many of the other joint types, but tends to be lower in cost and more efficient. Due to this it is typically used in rear wheel drive vehicle configurations or on the inboard side of front wheel drive vehicles where the required range of motion is lower.

Tripod joints:

Double Cardan:Double Cardan joints are similar to double Cardan shafts, except that the length of the intermediate shaft is shortened leaving only the yokes; this effectively allows the two Hooke's joints to be mounted back to back. DCJs are typically used in steering columns, as they eliminate the need to correctly phase the universal joints at the ends of the intermediate shaft (IS), which eases packaging of the IS around the other components in the engine bay of the car. They are also used to replace Rzeppa style constant-velocity joints in applications where high articulation angles, or impulsive torque loads are common, such as the drive-shafts and half-shafts of rugged four wheel drive vehicles. Double Cardan joints require a centering element that will maintain equal angles between the driven and driving shafts for true constant velocity rotation. This centering device requires additional torque to accelerate the internals of the joint and does generate some additional vibration at higher speeds

Double Cardan:

Thompson coupling:The Thompson constant velocity joint (TCVJ), also known as a Thompson coupling, assembles two cardan joints within each other to eliminate the intermediate shaft. A control yoke is added to keep the input and output shafts aligned. The control yoke uses a spherical pantograph scissor mechanism to bisect the angle between the input and output shafts and to maintain the joints at a relative phase angle of zero. The alignment ensures constant angular velocity at all joint angles. Eliminating the intermediate shaft and keeping the input shafts aligned in the homo-kinetic plane greatly reduces the induced shear stresses and vibration inherent in double cardan shafts. While the geometric configuration does not maintain constant velocity for the control yoke that aligns the cardan joints, the control yoke has minimal inertia and generates little vibration. Continuous use of a standard Thompson coupling at a straight-through, zero-degree angle will cause excessive wear and damage to the joint; a minimum offset of 2 degrees between the input and output shafts is needed to reduce control yoke wear. Modifying the input and output yokes so that they are not precisely normal to their respective shafts can alter or eliminate the "disallowed" angles.

Thompson coupling

Malpezzi joints:This joint consists of a cage with a spherical inner with a shaped mouth. The input shaft fits on the center of a sphere with two rectangular grooves. To assemble it, the spherical driving ball is inserted in the cage by matching the two grooves with the narrowest part of the cage's mouth, rotated 90°. Then two steel blocks are inserted in the grooves and locked in place with a bolt running through the cage's side.This joint was extensively tested for possible automotive application but proved to be unable to cope with the articulation needed for such a use. It was widely used in Italy in agriculture, as it was better suited than a Cardan joint to rotate at high speed and cheaper than a Rzeppa joint. By the early '90s, with the appearance on the market of Rzeppa joints produced in Asia, its production became uneconomic and it was discontinued.

Malpezzi joints