What is Transfer Box | Construction and Working of Transfer Box
Transfer box is a part of a four-wheel-drive system used in four-wheel-drive or all-wheel drive vehicles. It is also called as “transfer gear case”, “transfer gearbox”, “transfer box”, ‘jockey box” or “T-case”. The function of transfer box is to distribute the torque generated in engine to all four wheels of the vehicle. The transfer box is connected to the engine, front axles and rear axles through drive shafts. This shifting mechanism is placed in the transfer case. The transfer gear box is controlled by the driver. The control is located in the vehicle compartment. It is either in the form of a transfer lever or a button.
Figure 3.37 shows the position of transfer case or transfer box in the vehicle. The front axle drive is disengaged and the transfer box is put for longer shift lever in forward position when the vehicle is running on hard surface and unleveled roads. During this stage, the shorter
shift lever will control the gear ratio such as low and high. Only low gear will be engaged when the longer shift lever is for front drive. The noise will be produced at higher speeds due to inherent resonance behaviour of spur gear train used in the transfer box.
Functions of transfer box :
(a) It receives power from the transmission and sends to both front and rear axles.
(b) The on-road transfer case coordinates the difference between rotation of the front and rear wheels.
(c) It locks the front and rear axles mechanically when required.
(d) It provides low and high range of speeds.
Types of transfer Box :
1. Gear-driven type transfer box
2. Chain-driven type transfer box
3. Housing type transfer box
4. Transfer case shift type.
Construction of Transfer Box :
- The input shaft is connected to the gear box and carries on it a member 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 lever, 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 and is supported inside the rear output shaft which is directly connected to the output gear.
- The front output shaft has fitted on it a shifter mechanism and also has splines over a small length of it, which when engage with the corresponding internal splines on the rear output shaft, connect the two shafts rotationally with each other.
Working Of Transfer Box :
When the shifter mechanism A is in the centre so that no gear is connected to the input shaft, the drive is in neutral as shown in Fig.i.
Fig.ii shows when the shifter mechanism A connects the input shaft with the big input gear, but the shifter mechanism B disconnects the front output of shaft from the rear output shaft. In this position, two-wheel drive with the high gear is obtained. In the same way Fig.iii depicts the situation with four wheel drive in low.
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