Gear boxes

Gearbox, types of gearbox, sliding mesh gearbox, constant mesh gearbox, synchromesh gearbox, universal joint, propeller shaft, progressive type gearbox, manual transmission, two-wheel drive, four-wheel drive, front-wheel drive, rear-wheel drive

1. GEAR BOXES By: Ratnadeepsinh Jadeja

2. Introduction Gear box is a speed and torque changing device between the engine and the driving wheels. It serves the following purposes in the transmission system of an automobile. It exchanges engine power for greater torque and thus provides a mechanical advantage to drive the vehicle under different conditions. It exchanges forward motion or reverse motion. It provides a neutral position to disallow power flow to the rest of power train. When driving power is required, It reduces the engine speed and transmits stronger torque to the driving wheels and when high running speed is desired, it transmits high speed low torque to the wheels.

3. Gear Ratios When one meshing gear rotates, the teeth of that gear cause the teeth of the other gear to move so that the other gear also rotates. The relative speed of the two meshing gears (gear ratio) is determine by the number of teeth of the two gears.  

4. Types of Gear Boxes The following types of gear boxes are used in automobiles: Selective type I. Sliding mesh II. Constant mesh III. Synchromesh Progressive type Epicyclic or planetary type

5. Selective Type Gear Boxes It is that transmission in which any speed may be selected from the neutral position. In this type of transmission, neutral position has to be obtained before selecting any forward or reverse position. Advantages of selective type gear boxes: Simple in construction. Relatively free from troubles. Light and small. Low production cost. Disadvantages: Gear ratio not being continuous but being in steps (3 to 5 steps), making it necessary to shifts gears each time when vehicle running conditions change. Noisy in operation.

6. Sliding mesh gear box (crash-type gear box)

7. Sliding mesh gear box (crash-type gear box)

8. Sliding mesh gear box (crash-type gear box)

9. Sliding mesh gear box (crash-type gear box)

10. Sliding mesh gear box (crash-type gear box)

11. Sliding mesh gear box (crash-type gear box)

12. Sliding mesh gear box (crash-type gear box)

13. Sliding mesh gear box (crash-type gear box)

14. Constant mesh gear box

15. Synchromesh gear box

16. Synchromesh gear box

17. Progressive Type Gear Boxes These gears boxes are usually used in motor cycles. In this type of transmission, the gears pass through the intervening speeds while shifting from one speed to another. There is a neutral position between two positions as shown below in the case of four speed gear box: 1 NEUTRAL 2 NEUTRAL 3 NEUTRAL 4 These gear boxes are a combination of sliding and constant mesh gear boxes. The various gear speeds are obtained by sliding the dog clutch or gear to the required position.

18. Epicyclic or Planetary Gear

19. E picyclic or Planetary Gear Box

20. Automatic Transmission Transmission in which various speeds are obtained automatically is known as automatic transmission. The driver merely selects the general car condition such as neutral, forward or reverse. Automatic transmission needs no gear change lever and clutch pedal since clutch and transmission is a combined unit and works automatically. (In semi-automatic transmission only the clutch is operated automatically) The transmission is operated hydraulically and is often known as hydraulic transmission. This transmission employs fluid coupling , torque converter and epicyclic gear arrangement. When all the different devices are combined into one unit, they perform their duties collaborately .

21. Fluid coupling/Fluid flywheel Fluid coupling is a hydraulic unit that replaces a clutch in a semi or fully automatic system, and transmits the engine torque to a transmission system. Since the coupling is a major part of the engine flywheel assembly, it is also called a fluid flywheel or fluid drive acting as an automatic clutch.

22. Fluid coupling/Fluid flywheel The efficiency of power transmission may be as high as 98 % The efficiency of the hydraulic coupling is defined as the ratio of power output to power input The ratio Wt /Wp is known as speed ratio. A fluid coupling always slips by about 2 to 4 percent when transmitting full load. It means that the turbine is always running slightly slower than the impeller and as such complete disconnection of the drive is not possible. Thus the fluid coupling is not suitable for ordinary gear box and is generally used with epicyclic gears to provide a semi or fully automatic gear box.

23. Hydraulic torque converter Hydraulic torque converter is a device used for transmitting increased or decreased power from one shaft to another. A variable torque is impressed on the driven member without the use of a gear train or clutch.

24. Advantages of automatic transmission Following are the advantages of automatic transmission: Smoother running under all conditions. Noise free gear shifting. No shock or jerky driving. Simplified driving control. Less physical and mental fatigue to the driver. Improved acceleration in hill climbing. Less wear and tear due to planetary gearing. No clutch pedal and gear lever and hence simplification of driver’s compartment. Reduced fuel consumption. Longer life.

25. Overdrive Overdrive is a device interposed between the transmission (gear box) and propeller shaft to permit the propeller shaft to turn faster (or overdrive) than the transmission main shaft. The overdrive permits the engine to operate only about 70 % of the propeller shaft speed, when the vehicle is operating in the high speed ranges.

26. Propeller Shaft

27. Universal Joint

28. FRONT WHEEL DRIVE

29. Differential