Gearbox Transmission Transaxle

 Gearbox 

The gearbox is an important part of an automobile with a mechanical device. It is utilized to increase the output torque and change the speed variation of the vehicles by the gear ratio. This means that the gearbox allows the engine to run at different speeds.

 

Why is a gearbox necessary in an automobile?

The gearbox is necessary to regulate both the power output and the speed range of the engine relative to the vehicle speed.

In the automobile, a gearbox is fitted after the clutch unit and it provides the driver can increase the driving torque and speeds to cop-up with the road and load condition. 

The necessity of gear gearbox variation of resistance to the vehicle motion at various speeds and variation of tractive effort of the vehicle available at various speeds.

 

Construction and gear arrangement of the gearbox.

The construction of the gearbox consists of the following two units -

•  Gearbox housing, containing are shafts such as layshaft (counter gear shaft), input shaft, output shaft, main shaft, the following shaft which carry the gear, bearings and gears and gear pinion etc.
•  The top cover contains selective mechanisms, gear fork, gear shifting lever, oil seal and other supportive parts.
• The gear arrangements of the gearbox a bigger gear is driven by smaller gear, having half the number of gear teeth. Beings this torque of the driven gear is increased to double with half speed. It takes advantage of increased torque.

Gearboxes with different speed gears

The gearboxes are designed to provide different speed gears as follows-

A three-speed gearbox provides three-speed gear speed 1st first, 2nd second and top gear ( 3th third gear), third forward  With one reverse gear. The three-speed gearbox using a sliding mesh of gearbox is the oldest type of gearbox used in an automobile.

A four-speed gearbox provides first (1st), second (2nd), third (3rd) and top gear (4th) four forward gear and one reverse gear. 

A five-speed forward gears and with reverse gear. The fourth and fifth forward gearbox uses the synchromesh gears unit with the manual gearboxes. This is commonly used nowadays also.

Transmission system 

Those parts of the vehicle which transmit the engine power to the wheel, such as clutch, gearbox, universal joints, propeller shaft, differential and axle shaft are included in the transmission system. The variation of speed ratio and forward and reverse motion. obtained through the transmission system.

Unit of the transmission system

The transmission system consists of the following main unit: 

• The Clutch unit consists of the clutch assembly or fluid clutch.
• The transmission unit consists of the gearbox, transfer case, overdrive,
• Driving axle unit consisting of final drive, differential half-shaft, axle shaft.
• Driveline unit consisting of the propeller shaft and universal joints.

Transmission & Transaxles 

The mechanism which transmits power from the engine crankshaft to the road wheels is called transmission or transaxle and sometimes it is ais also called a gearbox.

The main function of transmission or transaxle in the automobile powertrain or drivetrain,  they provide the torque and speed determined by the gear ratio accordion to that road and load condition. It provided reverse so that vehicle can move backwards and neutral position which is used for engine starting purposes without turning the drive wheels.

Types of transmission or transaxle

 

The transmission or transaxle is basically into two categories they are manual and automatic transmission or transaxle.

The manual transmission or transaxle are conventionally operated shifting gear manually or by hand. 

Automatic transmission and transaxle shift gears automatically. Without driver inputs.

Difference between transmission and transaxle :

The transmission is used in rear-wheel-drive vehicles, which is mounted on a longitudinally after engine clutch then transmission output shaft power flow through the driveline via differential and axle shaft to the road wheel all in a single line. In the same way work on both manual and automatic transmission functions. Usually, this type of transmission is used on the rear-wheel-drive vehicle, truck, bus picks up truck etc. 

The transaxle is a combination of transmission and rear axle as a single unit. The transaxle is to front-mounted gear and shaft. It is attached to a front-mounted transversely engine and drives the front wheels. The transaxle includes a final drive and differential into a single assembly. The vehicle comes with a transaxle in both manual and automatic options but it is mainly used on light-duty passenger vehicles.

Nowadays in Indian vehicles, manual transmission and transaxle are five-speed with a fifth forward gear. fifth and sixth forward gear called overdrive, with synchromesh gearboxes.

Synchromesh gearbox

Synchronizers mechanisms are used in manual transmission or transaxle (gearbox), in which gear speeds are obtained through synchronising units. A device that facilitates the meshing of two gear by causing the speed of both gears to coincide at the same time. These devices ensure that gears and sliding sleeves about to mesh rotates at the same speed. The results are a smooth engagement.

The advantages of the synchronizing mechanisms:

• To prevent gear clash during gear shifting.
• Noise and jerk are eliminated.
• A smooth meshing is possible.
• Double declutching is not required.

The advantages of the transaxle are :

• Extremely rigid engine and drive components. 
• Misalignment is avoided 
• Unit is compact 
• Better riding quality
• Better comfort facilities.

Purpose of Overdrive : 

The purpose of overdrive is to cause the propeller shaft to turn faster or over than the speed of the engine crankshaft. In simple words said that the output shaft is faster than or overdrive in the input shaft. This allows a lower engine speed to keep the vehicle moving at its desired road speed.

The overdrive is fitted to the rear of the extension part of the transmission and transaxle in between the gearbox and propeller shaft or (driving shaft).

Advantages of overdrive:

• The overdrive permit for an engine lowers Speed to maintain the car at high speed.
• When the vehicles are moving at steady ( stable fixed) speed or do not require as much power to keep them moving.
• Better fuel economy and reduced engine wear result, with less noise and vibration.

Gear Ratio

The number of revolutions of driving gear required to turn a driven gear through one complete revolution for a pair of gears, ratio is found by driving the number of teeth on the driven gear by the number of teeth on the driving gear.

" The ratio of tuning speed of the two gears"

• The first gear ratio of the vehicle first gear ratio is about 4:1. The crankshaft turns four times to turn the output shaft once.

• The second gear ratio is about 2.4:1. The input shaft turns 2.4 times to turn the output shaft once.

• The Third gear ratio is about 1.5:1. The one and a half turn engine crankshaft only one turn of the output shaft.

• The fourth gear or direct drive gear ratio is about 1:1. The once turns of input and output shaft.

• The fifth gear or override ratio is 0.8:1. The output shaft turns one complete revolution while the counter gear turns only 0.8. ( a little more than three quarters) revolution. The output shaft turns faster than overdrive the input shaft

• The reverse gear ratio is about 3.5:1. The output shaft turns in the reverse direction because of the reverse idler gear.