Automobile Mechanic Motor Vehicle - Transmission System PDF

Automobile Related Theory for Exercise 2.1.92 Mechanic Motor Vehicle - Transmission System Major systems and its components Objectives: At the end of this lesson you shall be able to define heavy vehicles specify various components and its purpose identify major m...

Automobile Related Theory for Exercise 2.1.92 Mechanic Motor Vehicle - Transmission System Major systems and its components Objectives: At the end of this lesson you shall be able to define heavy vehicles specify various components and its purpose identify major manufacturers and products. Introduction power and single line, dual line air brakes. ABS brakes are anti lock brakes which prevents skiding of vehicles. Any road vehicle combination of road vehicles with a gross vehicle weight rating (GVWR) of 4,500 kg or more The steering system is a group of parts that transmit the is considered a heavy vehicle. Further to classify that movement of the steering wheel to the front wheel, and there are heavy commercial and heavy passenger sometimes the rear, wheels. The primary purpose of the vehicles on roads. Passenger vehicles given due steering system is to allow the drive to guide the vehicle. importance to passenger safety, where as commercial When a vehicle is being drive straight ahead, the steering vehicles are built keeping the load and torque aspects. system must keep it from wandering without requiring Being a life line of the economy, these vehicles are an the drive to make constant corrections. The steering integral part of the commercial activity of any country system must also allow the drive to have some road feel and these vehicles are usually deployed in the long haul (feedback through the steering wheel about road surface distance and in transportation of materials at the ports conditions). For maximum tire life, the steering system as also in the extraction of natural resources like iron or should maintain the proper angle between the tires both coal etc. during turns and straight-ahead driving. The drive should be able to turn the vehicle with less effort, and with proper Major components of heavy vehicles and their control. Power steering provide this facility. purpose (Fig 1) 4 Chassis and frames 1 Engine A vehicle frame or chassis, is the main structural element It is a power pack of any automobile vehicles where in of a motor vehicle to which all other components are which the power is developed by means of combustion fastened. Another term for this design is body-on-frame of a fossil fuel. In heavy vehicles the major fuel is high construction. It has to hold carry and support the whole speed diesel oil. Simply we can say diesel. All most all vehicle to move smoothly. the engines are now a day’s internal combustion engines. Few decades ago the external combustion engines were Also it has to deal with static and dynamic loads, without also exist in practice. The engines are capable of propel undue deflection or distortion. larger loads with considerable speed. So that the These include constructions are heavier when compare with the Weight of the body, passengers, and cargo loads. passenger cars and other utility vehicles. Vertical and torsional twisting transmitted by going Present days popular engines are as under over uneven surfaces. NA engines- Natural aspirated engines Transverse lateral forces caused by road conditions, TC engines- Turbo charged engines side wind, and steering the vehicle. Torque from the engine and transmission. TCAC engines- Turbo charged after cooled engines Longitudinal tensile forces from starting and CRDI engines- Common rail diesel injection engines acceleration, as well as compression from braking. 2 Power trains Sudden impacts from collisions. Power trains are arranged in such a way that the Three important classifications are C frame and box transmission is conducted smoothly from engines to frames. wheels. Wherein which we have various types of 5 Suspension system clutches, various types of gear boxes, propeller shaft, The purpose of the complete suspension system is to differentials and final drive and axles. In an axle there isolate the vehicle body from road shocks and vibrations are single, double and multi axles are fitted to serve which would otherwise be transferred to the passengers various purpose. and load. I must also keep the tires in contact with the 3 Control systems road, regardless of road surface. A basic suspension system consists of springs, axles, shock absorbers, arms, The brakes should be sturdy and efficient to stop the roads, and ball joints. The spring is the flexible component vehicles with heavy loads speed. So that the of the suspension. Basic types are leaf springs, coil manufacturers go with various brakes such as servo, springs and torsion bars. 1 2 Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.92 With independent suspension, the wheels can move 11 HVAC System independently of each other, which reduces body It is used for making the drive cabin comfortable for movement.This prevent the other wheel being affected driving. It deals about A.C compressor and other A.C by movement of the wheel on the opposite side, and this components and Heater. reduces body movement. When a wheel strikes a bump, there is a reaction force, and energy is transferred to the 12 Major manufacturers in India spring which makes it oscillate. Oscillations left 1 Tata motors uncontrolled can cause loss of traction between the wheel and the road surface. 2 Ashok Leyland Shock absorbers dampen spring oscillations by forcing 3 Mahindra & Mahindra oil through small holes. The oil heats up, as it absorbs 4 MAN-Trucks India ltd. the energy of the motion. This heat is then transferred through the body of the shock absorber to the air. When 5 Eicher motors a vehicle hits an obstruction, the size of the reaction force 6 Volvo motors depends on how much unsprung mass is at each wheel assembly. Sprung mass refers to those parts of the 7 Premier motors vehicle supported on the springs. The includes the body, 8 Swaraj Mazda the frame, the engine, and associated parts. Unsprung mass includes the wheels, tires, brake assemblies and 9 Benz motor suspension parts not supported by the springs. Products Vehicle ride and handling is improved by keeping Passengers segment unsprung mass as low as possible. Wheel and brake units that are small and light follow the road contours Goods segments without a large effect on the rest of the vehicle. Different products in goods segments are 6 Electrical system a 2-axle vehicles, The heavy vehicle has the following electrical systems: b Multi axle vehicles, a Storage system (Battery) c Tippers, b Starting system d Tankers, c Charging system (Alternations) e Special purpose vehicles (Concrete mixture, scooter d Lighting system and Accessories carries, car carrier etc..) e HVAC system 13 Name plate-Constructional differences and their merits 7 Storage system Motor name plates enables installation and maintenance It provides the DC power source for the various system personal to quickly understand and recognize exactly used in the vehicles. It deals about batteries generally find the procedure. Name plates primarily sever an 24v battery system is used for heavy vehicles. informative function. 8 Starting system  Frame size It is used to start the vehicle.It deals about starter, starter,  Design letter relays, sharring switch, solenoids etc.  Service factor 9 Charging system  Full load efficiency It deals about the alternators, voltage controllers etc. It is used to charge the battery source.  Certification code 10 Lighting system and Accessories  Manufacturer serial number The vehicle requires many light during night travel and  Symbols and logos day travel. The lighting system deals about head lights,  Manufacturer, name and address tail light,stop light, brake light, cabin light, fog light, pairing light TVM Indicator lights, number plane light, reverse  Rated horse power light etc.. It also deals about wiper, washer, horn, uses, circuit breakers, instrument cluster, GSP etc.. Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.92 3 Automobile Related Theory for Exercise 2.1.93 - 96 Mechanic Motor Vehicle - Transmission System Clutch Objectives: At the end of this lesson you shall be able to state the principle of clutch state the need for a clutch in a vehicle list out different types of clutch state the function of the clutch state the various types of clutch actuation systems explain the function of mechanically operated clutch. Principle of clutch It should damp vibrations and shocks during operation. The clutch works on the principles of friction. When two It should not slip under high torque transmission. friction surfaces are brought in contact with each other and pressed, they are united due to the friction between Torque transmission by clutch depends upon the: them. The friction between the two surfaces depends - size of the clutch plate upon the area of the surfaces, pressure applied upon then and co-efficient of friction of the surface materials. - coefficient of friction The two surfaces can be seperated and brought into - spring pressure, and contact when required. One surface is considered as driving member and the other as driven member. The - number of clutch plates used. driving member is kept rotating when the driven member Types of clutch actuation is brought in contact with the driving member, it also starts rotating, when the driven member is seperated from the Types Features Advantages driving member, it does not revolve. This is the principle of a clutch operation. Mechanical Pedal effort is Less maintenance Actuation transmitted by and easy to repair. Need for a clutch linkage to While shifting gears, the speed of the sliding sleeve and withdrawl bearing the respective gear on the main shaft should be Hydraulic Pedal effort is Less pedal effort to synchronized to avoid gear collision noise. This is Actuation transmitted engage & achieved by disconnecting the transmission of power through fluid disengage and from the engine flywheel to the gearbox shaft with the to withdrawl clutch help of the clutch. The clutch is used to connect and bearing. disconnect transmission of power from the engine flywheel to the gearbox drive shaft. Working of a clutch (Single plate, dry, coil spring type) Different types of clutches (Figs 1 & 2) They are:  Cone clutch  Dog clutch  Single plate clutch with coil spring  diaphragm clutch  Multi-plate dry wet clutches  Semi-centrifugal clutch  Fully centrifugal clutch  Fluid coupling. Function of the clutch The clutch should connect and disconnect the power from the engine to transmission smoothly and gradually without affecting the other components. 4  The clutch plate (Fig 3) consists of a torque plate (10), and the clutch lining (11) made of frictional material, is fixed on the torque plate (10) by rivets (12). Damper springs (13) are fixed in the torque plate to dampen shocks during clutch operation. A clutch consists of driven and driving components. A clutch cover (1) is mounted on the flywheel (2) by a set of screws. In the clutch cover, a pressure plate (3) presses the clutch plate (4) against the flywheel (2) by Operation of a single plate hydraulic clutch (Fig 4) the pressure of springs (5). The clutch plate hub(4) is In light and heavy vehicles with a single dry plate the splined on the gearbox drive shaft (6). The clutch plate spring force becomes excessive and it becomes difficult (4) rotates along with the flywheel (2), and power is for the driver to release the clutch. So a hydraulic transmitted to the drive shaft (6). mechanism is added to the transmission which minimizes When the clutch pedal is pressed, the withdrawal bearing the force required by the driver to operate the clutch. (7) pushes the withdrawal plate (8) through the linkages. When the clutch pedal is pressed, hydraulic fluid from The withdrawal plate (8) pushes the clutch finger (9). the master cylinder reaches slave or servo cylinder. As The clutch finger (9) swivels and moves the pressure the fluid is under pressure it actuates the slave cylinder plate (3) away from the flywheel (2). The springs (5) are push rod which releases the clutch release fork, thereby compressed. Now the pressure plate (3) does not exert disengaging the transmission. pres-sure on the clutch plate (4) and the clutch plate (4) does not transmit power from the flywheel (2) to the drive shaft (6). Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.93 - 96 5 Function of different types of clutch Objectives: At the end of this lesson you shall be able to state the function of - multi-plate clutches - dry clutches - wet clutches state the functions of a semi-centrigual clutch state the functions of a fully centrigual clutch state the functions of fluid coupling. Cone clutch (Fig 1) This type of clutch is used in constant mesh gearboxes with and without a synchronized unit. Diaphragm spring type (Figs 3, 4 & 5) When the clutch is engaged the friction surfaces (4) of the male cone (2) on the clutch shaft (1) engage with the female cone (3) on the flywheel (5) due to the force of the spring. When the clutch pedal is pressed the male cone slides on the splines of the clutch shaft against the spring force. It gives more frictional area and is simple in construction. It is practically absolute and the same principle/device is used in the synchronizer unit in a synchromesh gearbox. Dog clutch (Fig 2) This type of clutch is used to lock two shafts together or to lock a gear to a shaft. When the sleeve (2) slides on a splined shaft (1), its internal teeth (5) match with the dog clutch (3) teeth of the driving shaft, (4) and the clutch is engaged. In this type there is no possibility of a slip as both the shafts revolve exactly at the same speed. 6 Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.93 - 96 In some modern vehicles, instead of using coil springs a conical dish-shaped steel plate diaphragm spring (1) is used. It exerts force on the pressure plate (3) to press the clutch plate (4) firmly for engaging the clutch. It does not have release levers. The slots start from the centre of the diaphragm to form a number of release fingers (2). It requires very little pedal effort to disengage the clutch, and it works noise-free. Multi-plate clutch (Figs 6 & 7) Fluid coupling consists of two half shells fitted with interior fins (7) which rotate from the hubs. These units are mounted very close to each other with their open ends, so that they can turn independently without touching each other. A housing (5) surrounds both units to make a complete assembly. Inside, the assembly is filled with 80% of fluid. The driving unit impeller (1) is linked to the crankshaft (2) and gets the oil into motion when the crankshaft (2) rotates. The driven impeller (3) is mounted on the driven shaft (4). Due to the movement of the oil, the impeller (3) rotates and transmits torque to the driven shaft (4). To transmit more torque, instead of using a bigger flywheel and clutch plate, two or three small clutch discs Fly wheel are used to increase the frictional area. The pressure The flywheel mounted on the engine crank shaft large plates (2) and clutch plates (1) are alternatively arranged ring gear is attached the fly wheel. The fly wheel is bolted on the clutch shaft (3) and compressed by a number of to a cover which carries a pressure plate, pressure pressure springs (4). This type works in the same way springs and releasing levers. The entire assembly of the as a single plate clutch does. fly wheel and the cover rotate all the times, when an These clutches may be dry or wet. When the clutch is automatic transmission is used the torque converter operated dry it is called a dry clutch, but where the oil is assembly acts as the fly wheel. used in the clutch it is called a wet clutch. The flywheel stores energy during the power stroke are The wet clutches are generally used along with or as a supplies it to the crank shaft during the idle stroke i.e part of automatic transmission. suction, compression and exhaust the size of the flywheel depends upon the number of cylinder and general These types of clutches are mostly used in scooters, construction of the engine. motorcycles, heavy commercial vehicles, earth moving machines, race cars etc. Dual-mass flywheel Fluid coupling (Fig 8) This is intended to damp torsional vibrations which are generated by the periodic cycle of Fluid coupling enables the driver to use the clutch and the four strokes and the firing order in the gear with less skill and fatigue than the conventional crankshaft and a conventional flywheel. clutch. Wrong clutch engagements or selection of improper gear will not produce any sound. Any sudden At certain rotational speeds torsional vibrations can result load is cushioned and absorbed by the fluid coupling so in gearbox noises (gearbox rattling) and body droning. that dynamic stresses or breakages of the gear teeth of the mechanism and final drive are reduced. Fluid coupling The conventional flywheel mass of an internal combusion is used with the epicyclic gearbox as the output shaft engine consists of the crankshaft-drive components, the (drive shaft) is always in motion. flywheel and the clutch. In the diagram (Fig 9) the speed fluctuations of the engine and the gearbox at full load are plotted against time. Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.93 - 96 7  Primary flywheel Secondary flywheel Inner damper Outer damper Operating principle Dividing the flywheel mass into the primary mass on the engine side and the secondary mass on the gearbox side increases the mass moment of inertia of the rotating gearbox parts. In this way, the resonant range is below The vibrations of the engine ouput and gear box input the engine’s idle speed and thus not in the engine’s have virtually identical amplitudes and frequencies. In operating range. the event of superpostion (resonant range), this results The diagram (Fig 12) shows that the vibration curves of in gearbox noises and body droning. the engine output and gearbox input are clearly far Design (Fig 10) removed from each other. In this way, the torsional vibrations generated by the The conventional flywheel mass is divided into the engine are isolated from the gearbox, and gearbox primary flywheel (crankshaft drive, primary flywheel) rattling and body droning no longer occur. and the secondary flywheel mass (secondary flywheel, clutch). Advantages A torsional-vibration damper connects the two flywheel Reduction of gearbox and body noises (rattling, masses. The function of this damper is to isolate the chattering, droning). flywheel-mass system of the engine from the gearbox Protection of power-plant components. and the drive train. A clutch disc without a torsion damper can therefore be used for the clutch. Lower synchromesh wear. The dual-mass flywheel (Fig 11) consists: Clutch disc does not requires a torsion damper. Throw out bearing Fig 11 A throw out bearings is a part of an automobile clutch system. It is provided between the clutch release fork and clutch finger / diaphragam spring. It is a thrust bearing with the inner race contacting the clutch deactivation finger. It is used to release the pressure plate by applying thrust force while pressing the clutch pedal to disengage the engine power from flywheel to clutch disc. 8 Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.93 - 96 Automobile Related Theory for Exercise 2.1.97 Mechanic Motor Vehicle - Transmission System Gear shifting mechanism Objectives: At the end of this lesson you shall be able to state the various types of gear shift mechanism state reasons for the gear slip. The gear shift lever is located either on the steering column or on the floor board (Fig 1) To engage the gear, the gear shift lever, moves the selector rods 1 & 2. The gear shift forks 3 & 4 are fixed on the selector rod. The shifting forks 3 & 4 sit in the slot of the sliding dog clutch or gear. When the selector rod moves, the shifting fork also moves and pushes the respective sliding dog clutch or gear to engage the respective gear. When the selector shaft is moved, it forces the pin (6) into a groove cut in the opposite rail and the lock or spring loaded ball (7) hold selector shaft in locking position. Gear slip The following are the reasons for the gear to slip. Wrong adjustment of gear lever/selector rod. Weak lock spring. Worn out locking ball/pin. Excessive end float of gear. 9 Automobile Related Theory for Exercise 2.1.98 Mechanic Motor Vehicle - Transmission System Gearbox Objectives: At the end of this lesson you shall be able to state the need for a gearbox state the various resistances in vehicles motion calculate gear ratios state the different types of gearboxes describe the various components and their functions in a sliding mesh gearbox describe the various components and their functions in a constant mesh gearbox and its advantages state reasons for gear noise. Gearbox (Manual transmission) Linear velocity ‘V’ remains the same for both the gears. A gearbox is used to get different torques and speeds So, T1 X N1 = T2 X N2 which are required to overcome the following resistances. Road resistance T xN Air resistance N = 1 1 = 10 x 50 = 25 2 T 20 Gradient resistance 2 Load on vehicle Here the r.p.m.of gear (2) is half of gear (1). So torque By engaging different gears, engine torque is increased will be double. while speed is decreased. In the top gear the r.p.m and It means in higher gear the torque is less and in lower torque of the engine and gearbox remain the same. gear the torque is more. Simple gear train Different sets of gears are used in the gearbox to achieve When there is only one gear on each shaft it is known as different speeds and torques. Simple gear train. When the distance between turn shaft Compound gear train is small, it is used. When there are more than one gear on a shaft it is called When a small gear (1) (Fig 1) drives the bigger gear (2) as compound gear train. When the distance between the r.p.m. of the bigger gear (2) is reduced in proportion the driver and driven has to be bridged over by of the gear tooth. For example: Gear (1) is having 10 intermediate gears and at the same time high gear ratio teeth and gear (2) is having 20 teeth. Assuming gear (1) or small gear ratio is required then the advantage of rotates at 50 r.p.m. intermediate gears is intenstified by providing compound gears on intermediate shaft. Power train (Fig 2) The drive shaft (1) along with the gear (2) is always rotating at the engine r.p.m. The shaft (1) drives the countershaft gear (3), (4) ,(5) & (6) which are fixed on the countershaft. The gears (7) & (8) on the main shaft (9) get power from the countershaft’s respective gear, when engaged. To get the desired r.p.m or the torque the respective gear, on the main shaft (7) or (8) is engaged with the countershaft gears (7) and (8) are splined on the mainshaft and when these gears are No.of teeth on driven engaged with the countershaft gears, power is Gear ratio (or) speed ratio = transmitted to the main shaft (9). To get the reverse speed No. of teeth on driver the idler gear (6) is used in between the main shaft and the countershaft gears. 10  To achieve reverse speed, the mainshafts (1) gear is Gear selection slided on the main shaft, to engage with the idler gear The selection of gear depends upon the speed if the (4). vehicle it to be driven. For example the speed and To slide the gear on the shaft the shifter forks (7) directly appropriate gear selection of a vehicle is given below: sit on the main shaft’s (1) gear. The shifter forks are connected to the gear shift lever through the selector Gear selection Speed in Km/h rods 8). st I gear 15 In this type of gearbox, spur gears are always used, nd II gear 30 because the gear is slided on the shaft to engage with the countershaft gear. rd III gear 45 Constant mesh gearbox (Fig 5) IVth gear 65 Vth gear on top gear 80 Types of gear boxes Sliding mesh gearbox Constant mesh gearbox Synchromesh gearbox Sliding mesh gearbox (Figs 3 & 4) In this gearbox the gears of the mainshaft (1) are always in mesh with the corresponding gears of the countershaft (2). But power is not transmitted unless the dog clutch (3) or (4) engages with the particular gear on the main shaft (1). The main shaft is splined. In between the splined main shaft and gears, bushes (5) are provided. The fixed dog clutch (6) is splined on the main shaft gear (1). Therefore the gear and the fixed dog clutch both rotate freely without transmitting power. The dog clutch can slide along and revolve with the main shaft. When In this gearbox, the gears are mounted directly on the the sliding dog clutch (3 or 4) is engaged with the main shaft (1). The gear is slided on the main shaft with respective gear’s fixed dog clutch, power is transmitted the help of the shifter yoke mechanism (7) to engage from the gear to the main shaft through the sliding dog with the countershaft (2) gear. The gears on the clutch clutch (4) and fixed dog clutch (6). shaft (3) and countershaft (2) are fixed. The idler gear is In this type of gearbox, helical gears are used. always in mesh with the countershaft’s gear. Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.98 11 Advantages Static The power transmission is smooth when helical gears A seal used between two parts that do not move in are engaged because more than one tooth in contact at relationship to each other, such as the pan and oil pump- a time. to-case gaskets. Easy to engage Dynamic Less wear of gears in comparison to the sliding mesh A seal used between two parts that do move in gearbox because gears are always in mesh and gear relationship to each other. This movement is either a shifting is done through the sliding dog clutch. rotating or reciprocating (up and down) motion. The seal of a clutch piston an example of this of seal. Gearbox troubles Positive Gear noise A seal that prevents all fluid leakage between two parts. The following are the causes for noise in the gearbox. Non positive Wrong adjustment of gear shifting fork. A seal that allows a controlled amount of fluid leakage. Misalignment between gearbox and engine. This leakage is typically used to lubricate a moving part. Gearbox not lubricated. Three major types of rubber seals are used in manual Excessive backlash between gears/worn out gears. automatic transmission. They are ‘O’ ring, Lip seal and the square cut seal. Normally an ‘O’ ring is installed in a Gearbox bearings damaged/worn out pitted grooves cut into the inside diameter of one of the parts Gear teeth broken / worn out to be sealed. ‘O’ ring is compressed between the inner Bearings part and the groove ‘O’ ring, seal forms a tight seal between the two parts. When a component slides over or rotates around another part, the surfaces that contact each other are called Lip seals (Fig 6) are used to seal parts that have axial or bearing surfaces. rotational movement. Lip seals are used around input and output shafts to keep fluid in the housing and dirt A bearing is a device placed between two bearing out. Lip seals are also commonly used as shaft seals. surfaces to reduce friction and wear. Sliding bearings are used at following conditions: Low rotating speed Very large bearing surfaces Low use applications Sliding bearings composed of a relatively soft bronze alloy, many are trade from steel with bearing surface bonded. Square cut seals Rolling bearings/antifriction bearings such as roller bearing, ball bearings etc,. are used in high speed It is similar to an ‘O’ ring, however, a square-cut seal can applications, high load with relatively small bearing withstand more axial movement than an ‘O’ ring can. surfaces, and high use. Square-cut seals have a rectangular or square cross section. They are designed this way prevent the seal In gear box gear rotating on c fixed shaft can have more from rolling in its groove, when there are large amounts than one bearing surface, it is supported and held in place of axial movement. by the shaft in a radial direction with the help of the bearings. Metal sealing ring (Fig 7) The metal sealing rings are used at the places in which Bushes some leakage is acceptable metal sealing rings are used Bushes are cylindrically shaped and held in place by in transmission at pressurized. Ring seals are made of press fit. Since bushes are typically made of a soft metal, cast iron, nylon or teflon. they are act like a bearing and support many of the Teflon seals rotating parts. It takes the radial load. Some transmission use teflon seals instead of metal Thrust washers seals. Teflon provides for a softer sealing surface, which It s fitted with roller bearings. Thrust bearings/washer’s results in less wear on the surface that it rides on and are used limit the end play and also reduce the friction therefore a longer-lasting seal. Teflon seals are similar between two rotating parts. Roller bearings are used in in appearance to metal seals except for the hook-end combination with flat thrust washers to control end play type. The ends of locking end teflon seals are cut at an of a shaft or the gap between a gear and its drum. angle (Fig 8). 12 Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.98 TYPES OF GEARS Spur gears Helical gears Rack & pinion Worm gears Teeth are straight and Teeth are at an angle to the Teeth are parallel to the Teeth are at an angle parallel to the gear axis. gear axis. axis of the gears. with the axis and are curved. Only one tooth in More than one tooth in Only one tooth in contact. More than one tooth contactact at a time contact at the same time in contact. No axial thrust is produced Axial thrust is produced No axial thrust is produced Axial thrust is produc- while transmitting torque. while transmitting torque. while transmitting torque. ed while transmitting Hence it is often used for torque. reverse gear in transmission It transmits torque for It transmits torque for It converts rotary motion It transmits torque at parallel and non-coplanar parallel and non-coplanar into linear motion and right angle for shaft shaft vice versa. parallel and non- coplanar shaft Drawback: Clicking noise Drawback: Due to axial during teeth contact thrust gear will move front and back Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.98 13  Spiral bevel gears Spur bevel gears Herring bone gears Teeth are curved. Teeth are straight. Teeth are straight at an angle and opposite. More than one tooth in contact. Only one tooth in contact. More than one tooth in contact. Produces axial thrust. Produces axial thrust. Although teeth are inclined, the shaft does not produce axial thrust. It neutralises the axial thrust. Used to transmit torque at 90°. Used to transmit torque at 90°. Used to transmit torque for parallel axis and coplanar axis. Synchromesh gearbox Objectives: At the end of this lesson you shall be able to explain the need of synchromesh action in a gearbox list out the different types of synchromesh gearboxes explain each type of synchromesh gearbox explain the function of a synchromesh unit explain power flow in different gear positions explain the advantages of a synchromesh gearbox over-sliding mesh and constant mesh gearboxes. Synchromesh are used for easy gear shifting when a vehicle is in motion. With synchromeshing action, gears can be changed without using double declutching. An unskilled driver can also change gears with less danger of gear clashing as in the case of in-sliding mesh and constant mesh gearboxes.. Synchronising action (Figs 1,2 & 3) A synchroniser unit has a synchroniser sleeve (1), hub (2), a set of blocking rings (5), conical cup (8) provided on the blocking ring. Correspondingly a cone (9) shape is provided on gears (6) and (7) to suit the matching of the cup (8) and cone (9). Gears (6) and (7) rotate in mesh with the countershaft gear whereas the hub (1) rotates at the main shaft’s speed. Whenever any particular gear is to be engaged, the sleeve (1) is pushed towards the gear, and it further pushes up (8). The first cup (8) makes contact with the 14 Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.98 cone (9) of the gear (7) and due to friction between the The cones will be pressed together and the friction cone and the cup’s blocking ring (5) and gear (7) start between them will tend to bring about synchronising. rotating at the same speed. Further movement of the It needs minimum pressure to press the cones together. sleeve (1) engages the dog teeth of the sleeve (1) with Once the gear is engaged, the springs (3) will press the dog teeth of the blocking ring (5) and gear (7). As at against the fingers (4) and hold the gear in position. this stage the blocking ring and gear are rotating at the same speed. This engagement is carried out smoothly Baulk ring synchromesh (Fig 5) without double declutching and without causing any clashing noise. Types of synchromesh gearboxes The various types of synchromesh gearboxes are given below: baulk type baulk ring type multi and double cone type porche type Baulk type (Fig 4) This type of synchroniser unit is mostly used to engage the IV gear from III and vice versa. In this dog clutch sleeve (1) is free to slide on the splines on the hub. The hub (2) is fixed to the main shaft; when the clutch sleeve is moved to the right its internal splines engage the dog teeth to the 3rd gear (4), and when it is moved to the left its splines engage with the dog teeth of the 4th gear (5). The synchronising action is provided by the baulk rings (6 & 7) which are having internal cones to engage with the external cones formed on gears. Multi and double cone synchronisers This type is mostly used for heavy commercial vehicles. This type is provided with three slipping surfaces in the cone assembly. In this type the torque will be three times more than the other types. Porsche synchroniser In this type the cone (1) and the main shaft (2) rotate at In this type the gear on the end of the clutch shaft drives the same speed. the lay shaft. Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.98 15 It consists of a three-armed spider. Gear ratios Jeep vehicle This synchroniser is used to change the top gear with a Ist gear 2.798:1 positive drive between the top gear and the main shaft. IInd gear 1.151:1 It is designed to obtain uniform pressure between the Top or IIIrd gear 1:1 ring and the sleeve. Reverse gear 3.798:1 The above two synchronisers are not widely used in Indian vehicle. hence figures are not given. Power flow in different gear positions is shown by figures below and also briefly discussed. The synchromesh gearbox and power flow in different gears. Power flow in Neutral Introduction Neutral position (Fig 7) A 3-speed all helical gear, synchromesh gearbox (transmission) of a passanger car is shown in Fig 6. In the neutral position there is no flow of power from engine-clutch primary shaft transmitted to the gearbox main shaft. This condition helps to start the engine and run it without movement of the vehicle. Secondly, the main shaft and lay shaft second speed It has 3 forward speed and one reverse speed for gears are in constant mesh but the second speed and selection. This is closed as manually operated selective high speed dog clutch is not engaged. Also the main type because te driver can select the required gear ratio shaft second speed gear is not splined or keyed to the by shifting the gear by the operation of the gear shift main shaft but it simply rotates on it without transferring lever. any power. Construction The black line with arrow shows the power flow from the clutch shaft to the countershaft through the main drive The gearbox shown in Fig 6 here consists of the following gear and countershaft gears which are in constant mesh. main parts. Case and extension of housing All gears are revolving but no power is being transmitted. Rotating parts including bearings Power flow in first or low gear Shift mechanism First or low gear (Fig 8) Details The power flow in first or low gear is shown in the figure. The case houses all parts of the gearbox and serves as By shifting the reverse and low sliding gear towards the a container for the gear oil. left and making it mesh with countershaft (Layshaft low The rotating parts consist of te main and lay shafts, its gear, First gear) position is obtained. The ratio is 2.798:1. bearings, gears, dog clutches and synchroniser The clutch primary shaft drives the countershaft through mechanism. the main drive gear and countershaft drive gear. The case cover carries a selector and shifter mechanism The flow of power (shown in black line arrow) goes from and seals the gearbox housing against water and dirt. the countershaft to the main shaft, through countershaft low gear to the reverse and slow sliding gear (I gear) which is splined to the gearbox main shaft and then to the U-joints and to the rear wheels. 16 Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.98  Power flow in the top gear is shown in the figure. The synchroniser sleeve is moved to the left so that its teeth could mesh with the teeth on the hub of the main drive gear after the second speed gear is released out of engagement. Now a direct drive engagement takes place locking the main shaft to the clutch shaft. Speed of main shaft = speed of clutch = 1:1 shaft No power is transmitted through the other revolving gears in the system. The power flow the line (arrow) shows the direct drive through the synchroniser mechanism to the gearbox main shaft. Speed of main shaft = 1/2.798 of clutch shaft speed. Reverse gear position (Fig 11) All forward shifting is accomplished by action of the mechanism synchroniser. Second gear position (Fig 9) In this gear, the synchroniser mechanism stands in neutral position. The clutch shaft and the main shaft are seperated from the drive. By operating the gear shift lever the reverse and low sliding gear is moved to the right and is engaged with The first engagement is released out by shifting the first the reverse idler gear. This engagement causes the and reverse sliding gear out of mesh and bringing the change of direction of rotation of the reverse gear which system to neutral position. in turn transfers the drive to the main shaft. Now the The synchroniser sleeve is then moved to the right so main shaft rotates in the reverse direction. The drive is that its teeth are meshed with the teeth on the hub of the then transmitted to the road wheels at the rear through second gear after synchronisation. The synchroniser hub U-vehicle moves in the reverse direction. is internally splined to the main shaft. Hence the power The power flow is from the clutch shaft main gear, flows through clutch shaft main drive gear to the counter countershaft gears, the reverse idler and then to reverse shaft second speed gear which turns the main shaft. and low sliding gear and then to te main shaft. Speed of main shaft = 1/1.151 of clutch shaft speed. Speed of main shaft = 1/3.798 of clutch shaft. Top gear or high gear position (Fig 10) Advantages of synchromesh gearbox over sliding and constant mesh gearboxes. It requires less force to change the gears. In sliding mesh gear boxes, the gear wheels themselves move on the shaft to mesh with each other which is eliminated in the synchromesh gearboxes, thereby increasing the life of the gears. The constant mesh and sliding mesh gearbox requires double declutching while changing the gears which is not needs in a synchromesh gear boxes. An unskilled driver can operate the synchromesh gear boxes as compared to constant mesh and sliding mesh gearboxes since double declutching is not required for this. Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.98 17 Synchromesh gearbox troubles Objective: At the end of this lesson you shall be able to list out the various troubles and their causes in a synchromesh gearbox. Common troubles and remedies in a synchromesh gearbox Trouble Causes Remedies Hard gear shifting Synchronising unit damaged or springs Replace the unit or re-install improperly installed after service springs correctly Gear locked in one gear Synchronising unit stuck Free the sticking units. Replace the damaged parts. Gear slip Synchroniser worn out or defective Repair/replace Noise from gearbox in neutral Bearings worn out or dry Lubricate/replace. position. Fill gear oil to correct level. Insufficient lubricant in the gear box. Check and realign. Gear box misaligned with engine. Transmission noisy in gear Clutch friction disc defective. Replace/set right. Replace the Synchroniser worn out or damaged. Replace the worn out or damaged Gears worn out or damaged part Gear clash during shifting Synchroniser defective. Repair or replace. Clutch free play too much. Adjust clutch pedal free play. Gear shifting linkage out of adjustment. Readjust again. 18 Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.98 Automobile Related Theory for Exercise 2.1.99 - 103 Mechanic Motor Vehicle - Transmission System Layout of driveshafts Objectives: At the end of this lesson you shall be able to draw a layout of drive lines draw a layout of front wheel drive draw a layout of rear wheel drive. Drive line types Drive line In transmission system there are two types of drive lines The drive line represents the universal joints, drive shaft are adopted. One is front wheel drive and the other one and other parts transmitting engine torque to the driving is rear wheel drive line to transmit the engine torque to wheels or rear driving axle. The purpose of the drive line the driving wheels as shown in Fig.1. is to transmit engine torque smoothly to the driven parts in the driving axle. Front-wheel drive line Front wheel drive has the engine and driveline located between the front driving wheels. A typical front wheel power train is illustrated schematically in Fig 2. A key point to observe with front wheel drive is that the power flow leaves the transaxle (transmission and axle) housing to enter the driveline to rotate the front driving wheels. Power train of an automobile with rear-wheel drive: A manual transmission shown in the above Fig. 4 is a transmission that the driver must shift by hand or manually. It is an assembly of gears and shaft that Rear wheel drive line: The purpose of the rear wheel transmits power from the engine to the final drive or drive drive line is the same as the front wheel drive line; the axle. difference is location. The rear wheel driveline is located between the transmission and the rear axle housing as illustrated in Fig 3. The power flow will leave the transmission to enter the drive line. The drive line torque will then enter the rear driving axle to rotate the driving wheels. 19 All wheel drive, 4WD, free wheeling and transfer case Objective: At the end of this lesson you shall be able to differentiate all wheel drive and 4 wheel drive. All wheel drive (Fig 1) of them cannot be switched off. All wheel drive is used in special application like race and sports cars. These These system are sometimes called full - time four wheel systems can be used in high gears and high speed drive. All - wheel -drive systems are designed to function applications. on all types of surface, both on-and off-road, and most 20 Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.99 - 103 Front - Wheel - Drive (Transaxle and CV joint) Objectives: At the end of this lesson you shall be able to describe transaxle function describe the transaxle powerflow. Introduction FWD car has transaxle either manual or automatic (Fig 1). Most of the transaxle mounted sideways and a few have been mounted longitudinally (Fig 2&3). Manual transaxles have three parallel paths for power flow. Transverse transaxles shifted through two cables or rods. One moves a selector other moves shifht fork back and forth Fig (4&5). Transaxle differential allows wheels to turn at different speeds when rounding corners. Differential side gears is transmitted power to front axles through axles shaft. Fig 1 TO ENGINE TORQUE CONVERTOR PLANETARY GEARS AND CLUTCHES DRIVE CHAIN TO FRONT AXLE DIFFERENTIAL Transaxle power flow (Fig 6 &7) Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.99 - 103 21  Front wheel final drive In front wheel drive vehicles the transaxle is transmit the power from engine to the front wheels through drive shaft. Transmission (Gearbox) and final drive (Differential assembly) are enclosed in one casing is called transaxle. Fixed gears for first, second and reverse on input In front wheel final drive no propeller shaft is required, in shaft. which transmission main shaft pinion gear is directly connected to the ring gear of differential assembly. Fixed gears for third, fourth, fifth on intermediate shaft. Note: The engine is fitted at front side of the Engine is mounted sideways. vehicle. Axle run parallel to input shaft Drive shafts are connected to the differential assembly Axle shafts and CV joint boots (Fig 8 & 9) through constant velocity joints. Front wheel differential (Fig 10) In front wheel drive vehicles differential is attached with transmission. It is used to differ the front wheels speeds left and right side to make a smooth turn while maneovering during turns. It consists of sun gears and star gears. The friction of differential gears similar to the rear wheel differential. The only difference is the transaxle shafts (drive shafts) having the constant velocity joints at the juncture of wheel hubs. 22 Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.99 - 103 Transmission/Transaxle designs Pot joints permit diffraction angles upto 22° The internal components of a transmission or transaxle and axial displacement upto 45 mm. consist of a parallel set of metal shafts on which meshing Post joints are situated at the final-drive end. gear sets of different ratios are mounted. By moving the shift lever, gear ratios can be selected to generate Fixed constant-velocity joints different amounts of output torque and speed. Ball joints The gears are mounted or fixed to the shafts in a number These consist of the ball star, ball shell, ball cage and of ways. They can be internally splined or keyed to a balls (Fig 13) shaft. Gears can also be manufactured as an integral or “clustered” part of the shaft. Gears that must be able to freewheel around the shaft during certain speed ranges are mounted to the shaft using bushings or bearings. The shafts and gears are contained in a transmission or transaxle case or housing. The components of this housing include the main case body, side or top cover plates, extension housings and bearing retainers. The metal components are bolted together with gaskets providing a leak-proof seal at all joints. The case is filled with transmission fluid to provide constant lubrication and cooling for the spinning gears and shifts. Types of constant velocity joints The ball shell and ball star have curved tracks, on which Sliding constant - velocity joints the balls run. Ball joints permit diffraction angles upto 38° Tripod joints (Fig 11) in their normal version and upto 47° in their special version. They do not permit any axial displacement. Ball joint as fixed constant-velocity joint Double joints Two universal joints are combined to form a single joint (Fig 14). In order to ensure fault-free operation, the shaft ends to be connected are centered on the inside of the joint. These can be used in the case of independent suspension both on powered front axles (front - wheel drive) and on powered rear axles (rear-wheel drive) Tripod joints permit diffraction angles upto 26° and axial displacement upto 55 mm. The tripod star is always towards the final drive end. Pot joint (Fig 12) They are used in commercial vehicles. Double joints permit diffraction angles upto 50°. They do not permit any axial displacement. Flexible discs Flexible discs are resilient, maintenance-free joints. They permit only small diffraction angles and linear variations. They are installed in the derivation primarily as flexible elements for damping vibrations and noises. Flexible discs are permanently connected with the body or frame. There are the following different types: These are ball joints, the balls of which are guided by a Hardy discs cage run on straight tracks of the ball and the ball shell. Silentbloc joints Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.99 - 103 23 Rear wheel drive - Propeller shaft Objectives: At the end of this lesson you shall be able to state the function of the propeller shaft state the need for centre bearing state the hotchkiss drive state the torque tube drive. Functions of propeller shaft (Fig 1) Hotchkiss drive (Fig 2) It has two longitudinal rear leaf springs (1). The front end of the spring (1) is connected to the frame with the pin and the rear end is connected to the frame by a bracket and shackles. The gearbox (2) and the rear axle (3) are connected by an open propeller shaft (4), through the universal joint and the slip joint. Whenever the torque resistance of the rear axle changes i.e while driving fast The propeller shaft (1) connects the gearbox (2) and final or applying the brake, the springs get deflected and this drive (3). The pinion shaft of the differential is connected helps to damp the shock. The slip joint accommodates to the propeller shaft (1). One universal joint (4) is used variation in length between the gearbox (2) and the rear in between the propeller shaft and the pinion shaft of the axle (3). differential. Another universal joint (4) with one slip joint (5) is also used between the propeller shaft (1) and the Torque tube drive (Fig 3) gearbox (2). The propeller shaft rotates at high speed and bears a heavy torque. So it is made of strong steel tube. In some vehicles a solid propeller shaft is also used. Vehicles having a larger wheel base use two propeller shafts. Whenever the distance between gearbox and rear axle is very large (example-passenger buses) more than one propeller shaft is used for torque transmission. Centre bearing is used to connect the two propeller shafts. In this type of drive the propeller shaft (1) is enclosed in Types of drives the tube (2). The tube (2) is fastened to the differential housing (3). The other end of the tube (2) is connected Two types of drives are used: to the gearbox by a flexible joint (4). Only one universal Hotchkiss drive joint is used in this drive. To provide strength, brace rods are connected between the torque tube (2) and the Torque tube drive differential housing (3). In this drive or torque bar springs can be used. Universal and slip joints Objectives: At the end of this lesson you shall be able to state the need for a universal joint state the function of a universal joint state the constructional features and function of the different types of universal joints state the need for a slip joint. Need and function of universal joint ups and downs on a road, the angle between the gearbox and the rear axle changes. The universal joint In any vehicle the gearbox and the rear axle are at accommodates this variation in angle and permits smooth different levels. A universal joint provides a flexible transmission of torque from the gearbox to the rear axle. connection. It allows the propeller shaft to transmit torque from the gearbox to the rear axle. Similarly due to the 24 Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.99 - 103 Types of universal joints joint assembly is fixed to the companion flange (7). Whenever the angle between the gearbox and the rear Cross-type or spider and two yoke type axle changes, the ball accommodates this variation by Ball and trunnion type moving in the ‘U’ channel. Cross-type universal joint (Figs 1 & 2) Slip joint (Fig 4) A cross-type universal joint has a spider (4). At the four ends of this, needle roller bearings (6) are fixed with When the vehicle is moving, the rear suspension spring bearing caps (7). Two yokes (1) and (2) at 90° to each compresses and expands because of the ups and downs other are pivoted to the spider (4). on the road. As a result, the length and the angles Ball and trunnion type universal joint (Fig 3) between the gearbox and rear axle varies. To accommodate this change in length, slip joints are used. In this type of joint a ball head (1) is fixed at the end of the propeller shaft by a pin (2). At both the ends of the The joint yoke (1) has internal splines matched with pin two steel balls (3) with roller bearings (4) are fixed. external splines of the propeller shaft (2). Whenever The centering button (5) and a button spring (6) keep there is any change in length the joint yoke (1) moves on the pin (2) in the centre. The propeller shaft and universal the shaft (2) and adjusts the length. Rear axle assembly Objectives: At the end of this lesson you shall be able to state the various types of axle housings state the various types of rear axles. Parts of rear axle assembly Types of axle housings The rear axle assembly consists of the following units: Split type (Fig 1) Axle housing Banjo type (Fig 2) Axle shaft In the split type housing (1) two halves are bolted to the differential housing. Hub, brake and wheel Banjo type housing (2) is welded and made into a single Differential and CWP piece. The differential carrier is bolted to the housing. Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.99 - 103 25 Power is transmitted from the final drive to the wheel the axle shaft takes only a partial load of the vehicle but hub through the two axle shafts. The axle shaft’s inner the full driving thrust. end has external splines which sit in the sun gear’s splines. Fully floating axle (Fig 5) Types of rear axles Three types of rear axles are used depending upon the mounting of the hub. Semi-floating axle (Fig 3) In this type of axle, the hub (1) is mounted on the axle housing (4) on two taper roller bearings (3). The axle shaft (2) takes only the driving thrust. The vehicle’s load is taken by the axle housing (4). In this type of axle the hub (1) is directly fitted on the axle Both semi floating and 3/4 floating axles cost of axle is shaft (2). The axle shaft rests on the bearing (3) in the less but load carrying capacity is less. Axle shaft bend axle housing (4). In this, the axle shaft takes the vehicle on excess load. Bearing life is poor. Fully floating axle load as well as the driving thrust. used heavy taper roller bearing and carries high load. Three quarter floating axle (Fig 4) Axle shaft gives good life. Cost of full float axle is high. In this type of axle, the hub (1) is mounted on the axle housing (4) at one end by the bearing (3). The other end of the hub (1) is connected to the axle shaft (2). As such Final drive Objectives: At the end of this lesson you shall be able to state the function of the differential state the internal parts of differential state the need for the differential. Final Drive (Differential) - function 3 Double reduction type The final drive serves two purposes. Internal parts of differential (Figs 1 & 2) It transmits power at a right angle. The final drive consists of a pinion (1) crown wheel (2) and a differential cage (3). Inside the cage the spider- It increases the torque by reducing the speed. cross (4) with planetary gears (5) are assembled. Also Types of differential two sun gears (6) are assembled on both sides of the planetary gears (5). The sun gears (6) have internal 1 Conventional splines in which the axle shaft’s (7) spline end sits. 2 Power or Non-slip 26 Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.99 - 103  To examine differential action, raise the rear axle assembly till both wheels clearly ground and support them on two jacks. Rotate RHS wheel by 1 turn in forward direction. You will observe LHS wheel runs in opposite direction by 1 turn. While taking a LHS turn the outer wheel has to travel longer distance and turn several turn etc. compared to left wheel. This is how the differential turns is achieved between the inner and outer wheels. The crown wheel is fixed on the cage (3). The axle shaft’s Limited slip differential splined end is fixed to the sun gears and the other end is bolted to the wheel hub. A limited slip differential (LSD) in a type of differential that allows its two output shafts to rotate at different speed When the vehicle is moving straight, (Fig 3) the power is but limit the maximum difference between the two shaft. transmitted from the pinion (1) to the crown wheel (2) and to the cage (3). When the cage (3) is rotating the Working of a Limited Slip Differential spider (4) also rotates along with the star gears (5). The Limited slip differentials(LSD) are used in automobile to sun gears (6) are pushed by the star gears, and power overcome the traction difference problem of drive wheels. is transmitted to the axle shafts(7). During a straight line A vehicle fitted with a standard differential moves straight, run the star gears (5) do not rotate on their axis. and one drive wheel is on a surface with good traction Need for the differential and the other wheel is on a slippery track. In a standard differential the left and right axle rotations are completely When the vehicle makes a turn (Fig 4), the inner wheel independent. Since one wheel is on a slippery track, the has more grip on the road than the outer wheel. So the standard differential will make that wheel spin in respective inner sun gear (6) offers more resistance. At excessive speed, while the good traction wheel will that time, the star gears (5) rotate on their own axis and remain almost dead. This means high power supply to move the inner sun gear slowly and allow the outer sun the slippery wheel and low power flow to the good traction gear to rotate faster. So the outer wheel travels more wheel. So the vehicle won't be able to move. distance in the same time. Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.99 - 103 27 One way to overcome this problem is to limit the Space between the side gears is fitted with a pre-load independency or relative motion between the left and spring. Pre load spring will always give a thrust force right axles. Limited slip differentials are introduced for and will press clutch pack together. this purpose. One of the most commonly used LSD Separating action of Bevel gears (Fig 6) technology is clutch-pack based. Constructional Features of LSD The basic components of a standard differential are shown below. It has got pinion gear, ring gear, case, spider gears and side gears. Apart from its basic components a Limited slip differential has got a series of friction and steel plates packed between the side gear and the casing. Friction discs are having internal teeth and they are locked with the splines of the side gear. So the friction discs and the side gear will always move together. (Fig 5) Spider and side gear are bevel gears. It has got one specialty. When torque is transmitted through a bevel gear system axial forces are also induced apart from the tangential force. The axial force tries to separate out the gears. Side gear and axle are 2 separate units. The side gear has got a small allowance for axial movement. So during high torque transmission through spider-side gear arrangement, a high separating thrust force is also transmitted to the clutch pack. This force presses and locks the clutch pack assembly against wall of the casing. Since one wheel is on a high traction surface, the torque transmitted to it will be higher. So the thrust force developed due to the bevel gear separation action also will be high at that side. Thus clutch pack at high traction wheel side will be pressed firmly and clutch pack will be locked. So power from the differential casing will flow directly to high traction axle via clutch pack assembly. On the other hand clutch pack on the low traction wheel side is not engaged yet, so power flow will be limited to that side. So the vehicle will be able to overcome the Steels plates are having external tabs and are made to traction difference problem. fit in the case groove. So they can rotate with the case. If any of the clutch pack assembly is well pressed, the However while taking a turn the LSD can act like a normal frictional force within them will make it move as a single differential. In this case thrust force developed due to solid unit. Since steel plates are locked with the case bevel gear separation action won't be that high. So the and friction discs with the side gear, in a well pressed plates in clutch pack will easily overcome frictional clutch pack casing and the clutch pack will move together. resistance and will be able to slip against each other. Or motion from the casing is directly passed to the Thus the right and left wheel can have different speed corresponding axle. just like an open differential. Four wheel drive Objectives: At the end of this lesson you shall be able to explain the necessity of a four wheel drive explain the purpose of the transfer case explain the operations of a four wheel drive explain the shifting mechanism in the transfer case. Necessity of a four wheel drive condition, the vehicle cannot be pushed. Therefore, power is transmitted to other wheels also through the In the four wheel drive mechanism, there is provision to transfer case. supply power to all the four wheels, whenever it is needed. When the vehicle is moving on sand, slushy Purpose of transfer case ground, traction between wheels and road is lost and The transfer case is mounted in the back of the main the drive wheel tends to slip on the ground. In this transmission. It is sometimes called auxiliary gearbox. 28 Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.99 - 103 The transfer case can transmit engine power either only shaft (2) goes to the main shaft (9). The main shaft’s to the rear wheels of the vehicle or to all the four wheels sliding gear (5) engages with the high range gear (3) according to the driving requirements. (Fig 2) and power is transmitted to the front wheel’s drive output shaft (11) and the rear wheel’s output shaft (10) The transfer case can also provide low or high speed through the idler gears. (Fig 2) transmission. A low speed transmission drive is mostly used when moving with the heavy load requiring high traction torque. Operation of transfer case (Four wheel drive) The transfer case consists of a main shaft (9) on which the low range gear (4) and the high range gear (3) are fixed. These gears rotate freely on bushes. The sliding gear (5) slides on the main shaft. An idler gear shaft (1) is fixed between the main shaft and the rear differential drive shaft (10) and the front differential drive shaft (11). A clutch locking drive gear (12) is fixed on the front differential drive shaft (11). During neutral position, (Fig 1) the sliding gear (5) and clutch drive gear (12) are not engaged with their respective gears and power is not supplied to the front and rear wheels. When the lever is shifted to engage the low range four wheel drive position, the drive from the primary gear shaft (2) goes to the main shaft (9). The main shaft’s sliding gear (5) engages with the low range gear (4) (Fig 3) and transmits the drive to the output shafts of the front and rear drive shafts (10 & 11) through the idler gears. When power is to be supplied to the rear wheels only, the front drive clutch gear is kept in neutral position and the sliding gear (5) on the main shaft is engaged to low or high range gears (4) or (3), depending upon the requirements. In this condition, power flows only to the rear axle. When a vehicle is driven over slushy ground the drive wheels tend to spin without moving the vehicle. In this position, the clutch drive gear to front wheels is engaged. Now power will be supplied to all the four wheels. When the lever is shifted to engage a high range four wheel drive position, the drive from the primary gearbox Automobile: Mechanic Motor Vehicle (NSQF Level - 5): R.T. Exercise 2.1.99 - 103 29 Shifting mechanism in four wheel drive To shift between H4 and L4 or L4 and H4 the The transfer case is provided with a shift mechanism to vehicle should be stationary. operate the four-wheel drive mechanism. Purpose of a transfer case A gear shifting lever is provided in the driver’s cabin and it is connected to a clutch locking drive gear of the first Vehicles equipped with a transfer case (4WD & AWD) gear through a shifting rod and fork. Similarly another for better on slippery surfaces, giving them the ability to lever is provided to engage the sliding gear (5) with low accelerate more efficiently, when purchasing a vehicle range or high range gears, and is connected with the its important to ask yourself if you will be travelling with sliding gear through the shifting fork and rod. your vehicle on snowy, wet, sandy or rocky roads. If so considering a vehicle with four-wheel or all-wheel drives Differential & transfer case may be tight for you. Four wheel drive and all-wheel drive Vehicles are equipped with at least one differential and vehicles are ideal for off-roading and the needed traction some also have a transfer case. Each need to work with adverse weather conditions. efficiently in order transfer torque from the transmission Maintaining the differential & transfer case to the wheels. A four-wheel drive (4WD) and an all-wheel drive (AWD) vehicle, however, needs a ransfer case in Transaxle oils, differential fluid and gear oils should be addition to differentials on each axle. While both operate changed between 30,000 - 60,000 miles by a certified similarly, there is a difference between transfer case and technician. Clean, fresh oil provides better protection of differential. the differential and well-lubricated parts as with any component on the vehicle ensure the best performance. Differential Transfer case fluid should be replaced every 30,000 miles As part of the front and/or rear axle assembly, the to remove any debits or contaminants and to better differential is designed to drive wheels while allowing lubricate components. This is highly recommended for them to rotate at different speeds when turning by trucks that two loads and utilize four wheel drive providing proportional rpms between the left and right frequently. wheels. The power from both the engine and Symptoms of trouble in the differential transmission is directed through the differential and out to the wheels. Wiring or whining noises when decelarating. Transfer case A howl or whine during acceleration over high or low speeds. The transfer case is located between the transmission and front and rear differentials via the driveshafts, Rumbling whining at speeds over 20 miles per hour creating a two-wheel drive (2WD) or four-wheel drive but changes while turning. vehicle. On a four-wheel or all-wheel dirve (AWD) vehicle, it directs power to two or four wheels. When the transfer Frequent clunking sound every few feet or when case engages the front shaft, which feeds power to the starting to move. front wheels, the vehicle then becomes a four-wheel Vibration that increases with speed. drive. All-wheel drive vehicles receive power through the transfer case at all times. Each vehicle has a different Transfer case will need to be inspected unable to or have setup. Pick-up trucks have two-wheel and four-wheel trouble switching from two wheel drive to four wheel drive drive options, some crossovers have an option of all- or the vehicle shudders when turning. wheel or two-wheel drive, while some SUVs have an Neglecting any maintenance service on vehicle is unwise option of all-wheel drive. Performace vehicles also are in any situation. Spent differential fluid after time, available in 2-wheel or all-wheel drives. Four wheel and becomes dirty and contaminated. Continuing to drive with all-wheel drive options offer better traction and unclean fluid is risky as it may result in undue wear or maneuverability for steep roads. components leading to permanent damage. Avoiding The transfer case with its neutral, high and low ratio mainteance on the transfer case may