Mee404 lecture 03

Mee404 lecture 03

• 1.
  MEE 7101 AUTOMOBILE ENGINEERING Preparedby: Deepak Sharma (Asst. Prof.) Department of Mechanical Engineering IET, GLA University Mathura Lecture: 3 GEAR BOX & THEIR TYPES
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  Functions of agear box in an Automobile 1. An automobile is able to provide varying speed and torque through its gear box. 2. To provide high torque at the time of starting, vehicle acceleration, climbing up a hill. 3. To provide more forward speeds by providing more than one gear ratios. In modern cars, five forward gears and reverse gear is provided. 4. Gear box provides a reverse gear for driving the vehicle in reverse direction.
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  Types Of GearBox (a) Selective type gear boxes : (i) Sliding mesh gear box (ii) Constant mesh gear box (iii) Synchromesh gear box
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  Sliding Mesh GearBox 1. It is simplest type of gear box out of the available gear boxes. 2. In this type of gear box, gears are changed by sliding one gear on the other. 3. This gear box consists of three shafts; main shaft, clutch shaft and a counter shaft.
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  Sliding Mesh GearBox  In a four speed gear box (which includes one reverse gear), the counter shaft has four gears which are rigidly connected to it.  Clutch shaft has one gear and main shaft has two gears.
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  Sliding Mesh GearBox The two gears on the main shaft can slide in the horizontal direction along the splines of the main shaft.  The gears on the counter shaft cannot slide. The clutch gear is rigidly fixed to the clutch shaft.
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  Sliding Mesh GearBox
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  Constant Mesh GearBox  In this gear box, all gears on the main transmission shaft are constantly connected to corresponding gears on countershaft or lay shaft.  In addition, two dog clutches are provided on the main shaft. One dog clutch is between the second gear and cutch gear and another is between the first gear and reverse gear.  Splines are out on main shaft so that all the gears are feed on it.
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  Constant Mesh GearBox
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  Constant Mesh GearBox  Dog clutches can also slide on main shaft and rotate with it. However, all the gears on countershaft are rigidly fixed to it.  Top or 3rd speed gear is obtained when the left dog clutch is slided to left to mesh with clutch gear by using the gear shift lever.  In this case, main shaft rotates at the same speed as that of clutch gear or engine crankshaft speed which is the maximum speed. Speed ratio obtained is 1 : 1.
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  Constant Mesh GearBox Second gear is obtained when dog cutch (left side) meshes with second gear. In this condition clutch gear rotates the drive gear on countershaft and countershaft drives the second gear on the main shaft. All other gears on main shaft are free, so they do not move.
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  Constant Mesh GearBox In the same manner, first gear is obtained when right hand side dog clutch meshes with first gear. Reverse gear is obtained when right side dog clutch meshes with reverse gear on main shaft.
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  Advantage of ConstantMesh Gear Box • Since all the gears are in constant mesh, wear and tear of gears and any possible damage of gears do not occur in engaging and disengaging gears. • Also, any sound are not generated in engaged/disengaged.
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  Synchromesh Gear Box This type of gearbox is similar to the constant mesh type gearbox.  Instead of using dog clutches here synchronizers are used.  The modern cars use helical gears and synchromesh devices in gearboxes, that synchronize the rotation of gears that are about to be meshed
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  Synchromesh Gear Box Its working is also similar to the constant mesh type, but in the former there is one definite improvement over the latter.  This is the provision of synchromesh device which avoids the necessity of double-declutching.  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
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  Video on ManualTransmission
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  Traction and Tractiveeffort
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  Relation between enginespeed and vehicle speed
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  Assignment-2 1. What arethe function of gear box? 2. Write on notes on different types of gearbox? 3. Write precise notes on the working of constant mesh gear box? 4. Write any five difference between constant mesh gear box and sliding mesh gear box? 5. Explain the working of synchromesh gear box? 6. What is the importance of synchronising device in synchromesh gear box?