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Transmission system

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Automobile Transmission System Lecture notes for Diploma Mechanical engg. 5th Semester Notes.

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Transmission system

  1. 1. Transmission System in Automobile Lecture Notes By, Mr. Onkar Dixit Lecturer in Mechanical Engg. Dept. ARMIET, Sapgoan
  2. 2. The transmission is connected to the engine through the clutch. The input shaft of the transmission therefore turns at the same rpm as the engine. How Transmissions Work
  3. 3. Clutch plate
  4. 4. Single Plate Clutch
  5. 5. Diaphragm Clutch
  6. 6. Multi-plate Clutch Spigot end
  7. 7. Cone Clutch
  8. 8. Semi centrifugal Clutch
  9. 9. Centrifugal Clutch
  10. 10. Lever Ball Weight Fulcrum Stopper
  11. 11. Transfer Case/ box • A transfer case is a part of the drive train of four-wheel-drive, all-wheel- drive, and other multiple powered axle vehicles. The transfer case transfers power from the transmission to the front and rear axles by means of drive shafts. It also synchronizes the difference between the rotation of the front and rear wheels, and may contain one or more sets of low range gears for off-road use.
  12. 12. • Transfer case working principle: • The transfer case is an auxiliary transmission mounted in back of the main transmission. This is used in four wheel drive vehicles. • The transfer box enables the driver to drive in two wheel drives on highway or shift to four wheel drives for Off Road, to drive in high gear or low gear as required. • The input shaft is connected to the gear box and carries on it a neutral having axial teeth. Two input shaft gears are free to rotate on the shaft. Each of these gears have bosses on the side which have axial teeth of the same pitch as the central member on the input shaft. • Depending upon the movement of the transfer box gear level the central member and thereby the input shaft may be connected either to the small gear or to the big gear. • There are two output shafts, one going to the front axle and the second going to the rear axle. The front output shaft is smaller in diameter & is supported inside the rear output shaft, which is directly connected to the output gear.
  13. 13. Propeller shaft 1. It transmits rotary motion and power from gear box to the differential at varied angle. 2. It accommodates change in length when the rear axle moves up and down. 3. It absorbs the shocks coming on the transmission system when the vehicle starts from rest. Working of Different components, 1) Universal joint: To Transmit the power in different angular position between transmission shaft to propeller shaft and from propeller shaft to Differential. 2) Sliding joint: This serves to adjust the length of the propeller shaft when demanding from the axle movement. 3) Tubular Shaft: Withstand mainly torsional load.
  14. 14. Differential Need of differential: 1. When vehicle is taking turn, then outer wheel will have to travel greater distance as compared to inner wheel. 2. The vehicle has a solid rear axle only and no other device, there will be tendency to skid. 3. Hence wheel skidding is avoided by incorporating by mechanism i.e. differential. 4. Differential reduces the speed of inner wheel and increases the speed of outer wheel when vehicle is taking turn, at the same time keep the speed of rear wheel same when going straight ahead.
  15. 15. 1. When vehicle moves in a straight line: The power comes from propeller shaft to the bevel pinion which drives the crown wheel. Then it is carried to the differential cage in which a set of planet pinions and sun gears are located. From the sun gear it is transmitted to the road wheels through axle half shafts. In this case, the crown wheel, differential cage, planet pinions and sun gears all turn as a single unit and there is no any relative motion between the sun gear and planet pinion. The planet pinions do not rotate about their own axis. The road wheels, half shafts and sun wheels offer the same resistance to being turned and the differential gearing does not therefore operate. Both the road wheels turn at the same speed 2. When Vehicle takes a turn: The inner wheel experiences a resistance and tends to rotate in opposite direction. Due to this the planet pinions starts rotating about their own axis and around the sun gear and transmit more rotary motion to the outer side sun gear. So that outer sun gear rotates faster than the inner sun gear. Therefore the outer road wheel runs faster than the inner road wheel and covers a more distance to negotiate a turn safely.
  16. 16. Introduction and Purpose of Gear Box •Provides speed and torque conversions because of the limitations of internal combustion engines. •Also facilitates change of direction of output shaft for reversing •Automotive gearboxes are used to reduce load on the engine by manipulating torque and speed. They have the option to select one of several different gear ratios. •Once the engine has reached a number of revolutions per minute, it is advisable to increase the gear to reduce the engine rpm to reduce wear on the engine, allow more control, and greater speeds, better acceleration, and better fuel economy. •Most gearboxes are used to increase torque & reduce the speed of a output shaft. This produces a mechanical advantage •Automotive gearbox also have the provision to do the opposite ie provide an increase in output shaft speed with a reduction of torque (overdrive).
  17. 17. Types of Gear Box A. Selective gear transmission 1. Sliding mesh gear box 2. Constant mesh gear box 3. Synchromesh gear box a. Three speed b. Four speed C. Six speed B. Planetary gear transmission 1. Epicyclic gear type 2. Automatic Transmission a. Torque Converter b. Electric type
  18. 18. Constant Mesh Gearbox •All the gears are always in mesh •Gears on counter shaft are fixed to it •Gears on main shaft are free to rotate •Dog clutches can slide on the main shaft and rotate with it •Dog clutches engage with gears on the main shaft to obtain desired speed Advantages over Sliding mesh Gearbox: •Helical and herringbone gear can be used in these gearboxes and therefore, constant mesh gearboxes are quieter. •Since the gears are engaged by dog clutches, if any damage occurs while engaging the gears, the dog unit members get damaged and not the gear wheels.
  19. 19. 1. In this type of gearbox, all the gears of the main shaft are in constant mesh with corresponding gears of the countershaft. 2. The gears on the main shaft which are bushed are free to rotate. 3. The dog clutches are provided on main shaft. 4. The gears on the lay shaft are, however, fixed. 5. When the left Dog clutch is slide to the left by means of the selector mechanism, its teeth are engaged with those on the clutch gear and we get the direct gear 6. The same dog clutch, however, when slide to right makes contact with the second gear and second gear is obtained. 7. Similarly movement of the right dog clutch to the left results in low gear and towards right in reverse gear. Usually the helical gears are used in constant mesh gearbox for smooth and noiseless operation Constant Mesh Gearbox
  20. 20. Double declutching is a method of shifting gears used primarily for vehicles with an unsynchronized manual transmission, such as commercial trucks and specialty vehicles. Double clutching is not necessary in a vehicle that has a synchronized manual transmission. With this method, instead of pushing the clutch in once and shifting directly to another gear, the driver first engages the transmission in neutral before shifting to the next gear. The clutch is pressed and released with each change. The double clutching technique involves the following steps: 1. The accelerator is released, the clutch pedal is pressed, and the gearbox is shifted into neutral. 2. The clutch pedal is then released, the driver matches the engine speed to the gear speed either using the accelerator (when changing to a lower gear) or waiting for engine speed to decrease (when changing to a higher gear) until they are at a level suitable for shifting into the next gear. 3. At the moment when the revs between engine and gear are closely matched, the driver then instantly presses the clutch again to shift into the next gear. The result should be a very smooth gear change.
  21. 21. Synchromesh gearbox 1. This type of gearbox is similar to the constant mesh type gearbox. Instead of using dog clutches here synchronizers are used. 2. The modern cars use helical gears and synchromesh devices in gearboxes, that synchronize the rotation of gears that are about to be meshed
  22. 22. SYNCHRONIZERS 1. The gears on the lay shaft are fixed to it while those on the main shaft are free to rotate on the same. 2. Its working is also similar to the constant mesh type, but in the former there is one definite improvement over the latter. 3. This is the provision of synchromesh device which avoids the necessity of double- declutching. 4. The parts that ultimately are to be engaged are first brought into frictional contact, which equalizes their speed, after which these may be engaged smoothly. 5. Figure shows the construction and working of a synchromesh gearbox. In most of the cars, however, the synchromesh devices are not fitted to all the gears as is shown in this figure. 6. They are fitted only on the high gears and on the low and reverse gears ordinary dog clutches are only provided. 7. This is done to reduce the cost.
  23. 23. Construction 1. In figure A is the engine shaft, Gears B, C, D, E are free on the main shaft and are always in mesh with corresponding gears on the lay shaft. 2. Thus all the gears on main shaft as well as on lay shaft continue to rotate so long as shaft A is rotating. 3. Members F1 and F2 are free to slide on splines on the main shaft. 4. G1 and G2 are ring shaped members having internal teeth fit onto the external teeth members F1 and F2 respectively. 5. K1 and K2 are dogteeth on B and D respectively and these also fit onto the teeth of G1 and G2. S1 and S2 are the forks. 6. T1 and T2 are the balls supported by spring. These tend to prevent the sliding of members G1 (G2) on F1 (F2). However when the force applied on G1 (G2) slides over F1 (F2). 7. M1, M2, N1, N2, P1, P2, R1, R2 are the frictional surfaces.
  24. 24. Working 1. For direct gear, member G1 and hence member F1 (through spring- loaded balls) is slide towards left till cones M1 and M2 rub and friction makes their speed equal. Further pushing the member G1 to left causes it to overdrive the balls and get engaged with dogs K1. 2. Now the drive to the main shaft is direct from B via F1 and the splines. 3. Similarly for second gear the members F1 and G1 are slide to the right so that finally the internal teeth on G1 are engaged with L1. Then the drive to main shaft will be from B via U1, U2, C, F1 and splines. 4. For first gear, G2 and F2 are moved towards left. The drive will be from B via U1, U2, D, F2 and splines to the main shaft. 5. For reverse gear, G2 and F2 are slid towards right. In this case the drive will be from B via U1, U2, U5, E, F2 and splines to the main shaft.
  25. 25. Manual transmission cars use a clutch, which completely disconnects the engine from the transmission. Automatic transmission cars use a torque converter. A torque converter is a type of fluid coupling, which allows the engine to spin somewhat independently of the transmission. If the engine is turning slowly, such as when the car is idling at a stoplight, the amount of torque passed through the torque converter is very small, so keeping the car still requires only a light pressure on the brake pedal. there are four components inside the very strong housing of the torque converter: 1. Pump 2. Turbine 3. Stator 4. Transmission fluid The housing of the torque converter is bolted to the flywheel of the engine, so it turns at whatever speed the engine is running at. Torque Converter