Design and assembly analysis of a gear train of a gear box report

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Transcript of Design and assembly analysis of a gear train of a gear box report

  1. 1. DESIGN AND ASSEMBLY ANALYSIS OF A GEARTRAIN OF A GEAR BOX1. NOMENCLATUREP=powerdp=diameter of pinion=helix angleBHN=brinel hardness numberE=youngs modulusEG=youngs modulus of gear materialEP=youngs modulus of pinion materialCompressive stress =Bending stress = aModule =mgear ratio = GRNo of teeth on gear =Diameter of gear =Diameter of pinion =Normal pitch =Normal pressure angle = Npressure angle = b=face widthEquivalent no of teeth on pinion =Equivalent no of teeth on gear =Y1=tooth form factorPeripheral speed = VDynamic tooth load =C = deformation factorStatic tooth load =K =load stress factorWw=wear loadX = over hangTorque =TEquivalent twisting moment =
  2. 2. ABSTRACTDifferential is used when a vehicle takes a turn, the outer wheel on a longer radiusthan the inner wheel. The outer wheel turns faster than the inner wheel that is when there is arelative movement between the two rear wheels. If the two rear wheels are rigidly fixed to a rearaxle the inner wheel will slip which cause rapid tire wear, steering difficulties and poor loadholding.Differential is a part of inner axle housing assembly, which includes thedifferential rear axles, wheels and bearings. The differential consists of a system of gearsarranged in such a way that connects the propeller shaft with the rear axles.The following components consists the differential:1. Crown wheel and pinion.2. Sun gears3. Differential casingIn the present work all the parts of differential are designed under static condition andmodeled. The required data is taken from journal paper. Modeling and assembly is donein Pro/Engineer. The detailed drawings of all parts are to be furnished.The main aim of the project is to focus on the mechanical design and contactanalysis on assembly of gears in gear box when they transmit power at different speeds at2500 rpm, 5000 rpm. Presently used materials are Cast iron and Cast steel. For validatingdesign Structural Analysis is also conducted by varying the materials for gears, Cast Ironand of Aluminum Alloy.The analysis is conducted to verify the best material for the gears in the gear boxat higher speeds by analyzing stress, displacement and also by considering weightreduction.The analysis is done in Cosmos software. Modeling is done in the Pro/Engineer.
  3. 3. 3. INTRODUCTION TO WHEELED VEHICLEDRIVE LINES3.1AXLES AND SUSPENSION SYSTEMSAutomotive drive lines and suspension systems have changed quite a bit since the firstautomobile was built. At first, automobile axles were attached directly to the main frame of thevehicle. This caused many problems. For example, the vehicle produced a very rough ride. Also,rigid construction did not work well on rough ground because sometimes one of the wheelswould not touch the ground. If the wheel off the ground was a drive wheel, the vehicle losttraction and stopped. This problem proved a need for a more flexible vehicle.The problem was corrected by using springs between the axles and the frame. The early springswere the same type used on the horse-drawn buggy. They allowed the wheels and axles to moveup and down separate from the body. The body moved very little compared to the wheels andaxles, and the ride was much smoother.Allowing the axles to move separate from the body also kept the wheels on the ground overrough roads, but this caused a new problem. The old drive train between the engine and the axlewould not work. The train had to be made to move more. This was done by adding movablejoints in the drive shaft known as universal joints. Some early vehicles used only one universaljoint on the drive shaft, while later vehicles used two universal joints on the drive shaft. Driveshafts are now usually called propeller shafts. Some long-wheel-base trucks now use as many asfour propeller shafts between the transmissionand the drive axle. These propeller shafts are connected by universal joints.Early automobiles were made up of a body, a power plant, and a running gear. The running gearwas made up of the wheels, axles, springs, drive shaft, and transmission. The transmission wasoften mounted midway between the engine and rear axle. It was connected to the engine and therear axle by drive shafts.The term "running gear" is not used any more. A new term, "chassis," is now used to identify theold running gear plus the power plant. In modern vehicles, the transmission is generally mountedon the engine and is part of the power plant.The chassis of modern vehicles, especially the frame, spring, and axles, must be very strong andyet quite flexible.
  4. 4. 3.2 INTRODUCTION TO AXLE SHAFTAn axle is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may befixed to the wheels, rotating with them, or fixed to its surroundings, with the wheels rotatingaround the axle. In the former case, bearings or bushings are provided at the mounting pointswhere the axle is supported. In the latter case, a bearing or bushing sits inside the hole in thewheel to allow the wheel or gear to rotate around the axle.Axles are an integral component of a wheeled vehicle. In a live-axle suspension system, the axlesserve to transmit driving torque to the wheel, as well as to maintain the position of the wheelsrelative to each other and to the vehicle body. The axles in this system must also bear the weightof the vehicle plus any cargo. A non-driving axle, such as the front beam axle in Heavy dutytrucks and some 2 wheel drive light trucks and vans, will have no shaft. It serves only as asuspension and steering component. Conversely, many front wheel drive cars have a solid rearbeam axle.In other types of suspension systems, the axles serve only to transmit driving torque to thewheels; The position and angle of the wheel hubs is a function of the suspension system. This istypical of the independent suspension found on most newer cars and SUVs, and on the front ofmany light trucks. These systems still have a differential, but it will not have attached axlehousing tubes. It may be attached to the vehicle frame or body, or integral in a transaxle. Theaxle shafts (usually C.V. type) then transmit driving torque to the wheels. Like a full floatingaxle system, the shafts in an independent suspension system do not support and vehicle weight."Axle" in reference to a vehicle also has a more ambiguous definition, meaning parallel wheelson opposing sides of the vehicle, regardless of their mechanical connection type to each otherand the vehicle frame or body.3.2.1 Types of Rear Axle ShaftsIn rear wheel drive vehicles, the rear wheels are the driving wheels, whereas in the vehicles withfront wheels drive the front wheels are the driving wheels. Almost all the rear axles in themodern cars are live axles, which means that these axles move with the wheels, or revolve withthe wheels and are known as live axles. Dead Axles are those axles which remain stationary anddo not move with the wheels.Rear axles / Live Axles are further classified into three types:1. Full Float axles2. Semi Float Axles3. Three quarter floating axles.
  5. 5. 3.2.2 Semi float axle:The Semi float axle is used in light trucks and passenger vehicle / buses. In the vehicles equippedwith Semi Float axle the shaft as well as the differential housing supports the weight of thevehicle . The wheel hub is directly connected to the axle shaft or is an extension of the same, theinner end of the axle shaft is splined and it is supported by the final drive unit. The outer end issupported by a single bearing inside the axle casing / axle tube. The vehicle load is transmitted toeach of the axle shafts through the casing and the bearing, this causes a bending load and atendency to shear at a point. Besides the side forces also cause end thrust and bending moment inthe axle shafts, which have to take driving torque also. The semi float axle is the simplest and thecheapest of all types, because of which it is widely used on cars. However, since axle shafts haveto support all loads, they have to be of larger diameter for the same torque transmitted to theother types of axle supporting. The axle shafts take the stress caused by turning, skidding orwobbling of the wheels. The axle shafts are flanged or tapered on the ends. When the taperedaxles are used, the brake , the brake drum and hub are pressed onto the shafts, using keys toprevent the assemblies from turning on the shafts. In some cases, the outer ends of the shaftsmay have serrations or splines to correspond with those on the drum and hub assembly. Ifin case the axle shaft breaks on the vehicle using this type of arrangement, the wheel of thevehicle will get separated from the vehicle.3.2.3 Full float axle:Full Float Axle is considered as a robust one and is used for heavy vehicles / trucks meant tocarry heavy loads. The axle shaft has flanges at the outer ends, which are connected to theflanged sleeve by means of bolts. There are two taper roller bearings supporting the axle castingin the hub, which take up any side load. Thus in case of Full Float axles , the axle shafts carryonly the driving torque. The weight of the vehicle and the end thrust are not carried by them. Theweight of the vehicle is completely supported by the wheels and the axle casing. As the axleshafts carry only the driving torque, their failure or removal does not effect the wheels. Thus theaxle shafts can be taken out or replaced without jacking up the vehicle. For the same reasonvehicle can be towed even with a broken half shaft. We can say that the axle shaft takes thewhole weight of the vehicle and absorbs all types of stresses or end thrust caused by turning,skidding, and pulling. Full Float axle is considered as the most heavy and costly axle.3.2.4 Three quarter floating axle:This is a compromise between the more robust full float axle and the simplest semi float type ofaxle. In Semi Floating axle the bearing is located between the axle casing and the hub instead ofbeing between the axle casing an