What is a differential?
Differential is a mechanical device used in rear axles and it's primary function is to vary the power delivered to the rear wheels when the car is negotiating a turn.
Differentials also acts as a final gear reduction, to slow down the rotational speed of the transmission before it is delivered to the wheels. Another function of a differential is to transfer power at right angle from the propeller shaft to the wheels.
Why is differential used?
When a car is negotiating a curve, the inner wheel has to cover a smaller distance compared to the outer wheel. Therefore, the inner wheel must rotate at a lower speed compared to the outer wheel.
Without a differential, both the driven wheels would rotate at the same speed. If a solid shaft is used without differential, then wheels will have to slip to accomplish the turn. Differential is not required on non-driven wheels i.e. if a car is a front wheel drive, then differential would be installed at the front axle and will not be required at the rear axle.
History of differential:
There is no clear fact about the invention of differential. Some researchers day that it was first used in China way back in 30 B.C. However, Onésiphore Pecqueur, A French mechanical engineer patented the modern day differential gear in the year 1827.
In 1874, Aveling and Porter, a British agricultural engine and steam roller manufacturer listed a 2 ton crane engine with a rear differential to permit tight cornering without disconnecting both the rear wheels.
In 1876, James Starley who was known as the father of bicycle industry invented a chain drive differential for bicycles. Interestingly, Karl Benz used this invention on his automobiles, as we can see in Benz patented Motorwagen of 1885. Power was transmitted by means of two roller chains to the rear axle.
Working of a deferential:
Differential is an integral part of a driven axle. Wheels receive power from the engine via driveshaft. The main function of a differential is to allow the wheels to rotate at different rpm while receiving power from the transmission.
The ingenious mechanism of the differential allows wheels to rotate at different rpm, while transferring power to both wheels. Lets learn a differential's construction in a step by step manner:
Case 1 (Vehicle moving in a straight direction):
Consider a vehicle moving in a straight direction. At this point, the planet gears rotate along with the ring gear but does not rotate along it's own axis. Therefore, both the sun gears rotate at the same speed, so does the wheels. In other words, the entire differential cage unit will rotate as a single solid unit.
Case 2 (Vehicle taking a right turn):
Consider a case where vehicle is taking a right turn. In this case, the planet gears play a pivotal role. The planet gears not only rotates along with the ring gear, but also rotates about it's axis. The left wheels has to rotate faster than the right wheel.
The effective combined rotation of the 2 sun gears should be equal to the planet gears i.e. peripheral velocity of the sun gears should be equal to the planet gears.
Another simple way to understand the mechanism is that the speed of the left wheel is equal to the sum of the rotational speed and the spinning speed of the planet gears. Whereas, the speed of the right wheel is the difference between the rotational speed and the spinning speed of the planet gears. This helps in making the left wheel rotate faster than the right wheel.
It is the vice-versa when a vehicle is taking a left turn. The planet gears spin in the opposite direction.
Speed reduction at the differential:
This is also one of the functions of a differential, where the speed from the transmission is reduced by having a larger ring gear compared to the pinion gear. This set-up increases the gear ratio, thus reducing the speed. This is also known as final gear ratio. If the final gear ratio is 1:5, that means the ring gear has 5 times more teeth than that of pinion gear.
Disadvantage of a standard differential:
The main disadvantage of a standard or an open differential is that it is not effective on surfaces offering different traction. Consider a situation where one wheel is moving on a slippery track (water) and the other wheel is on a rough surface. In this case, the standard differential will send the majority of the power to the slippery wheel and hence the vehicle is stuck. To overcome this problem, Limited Slip Differentials (LSD) are used.
Differential is a mechanical device used in rear axles and it's primary function is to vary the power delivered to the rear wheels when the car is negotiating a turn.
Differentials also acts as a final gear reduction, to slow down the rotational speed of the transmission before it is delivered to the wheels. Another function of a differential is to transfer power at right angle from the propeller shaft to the wheels.
Why is differential used?
When a car is negotiating a curve, the inner wheel has to cover a smaller distance compared to the outer wheel. Therefore, the inner wheel must rotate at a lower speed compared to the outer wheel.
Without a differential, both the driven wheels would rotate at the same speed. If a solid shaft is used without differential, then wheels will have to slip to accomplish the turn. Differential is not required on non-driven wheels i.e. if a car is a front wheel drive, then differential would be installed at the front axle and will not be required at the rear axle.
History of differential:
There is no clear fact about the invention of differential. Some researchers day that it was first used in China way back in 30 B.C. However, Onésiphore Pecqueur, A French mechanical engineer patented the modern day differential gear in the year 1827.
In 1874, Aveling and Porter, a British agricultural engine and steam roller manufacturer listed a 2 ton crane engine with a rear differential to permit tight cornering without disconnecting both the rear wheels.
In 1876, James Starley who was known as the father of bicycle industry invented a chain drive differential for bicycles. Interestingly, Karl Benz used this invention on his automobiles, as we can see in Benz patented Motorwagen of 1885. Power was transmitted by means of two roller chains to the rear axle.
Working of a deferential:
Differential is an integral part of a driven axle. Wheels receive power from the engine via driveshaft. The main function of a differential is to allow the wheels to rotate at different rpm while receiving power from the transmission.
The ingenious mechanism of the differential allows wheels to rotate at different rpm, while transferring power to both wheels. Lets learn a differential's construction in a step by step manner:
- Power from the transmission is transferred to a ring gear via a pinion gear.
- The crown wheel is attached to a differential cage, which contains the 'sun' and 'planet' gears.
- There are 2 sun gears which rotate in the same axis of the ring gear. There are 2 planet gears which rotate in a axis perpendicular to the ring gear.
- The planet gears are attached to the ring gear and meshed with the sun gears.
- Each wheel is connected to the sun gears independently with the help of half axle shafts. The drive from the sun gear is transferred to the wheels
Case 1 (Vehicle moving in a straight direction):
Consider a vehicle moving in a straight direction. At this point, the planet gears rotate along with the ring gear but does not rotate along it's own axis. Therefore, both the sun gears rotate at the same speed, so does the wheels. In other words, the entire differential cage unit will rotate as a single solid unit.
Case 2 (Vehicle taking a right turn):
Consider a case where vehicle is taking a right turn. In this case, the planet gears play a pivotal role. The planet gears not only rotates along with the ring gear, but also rotates about it's axis. The left wheels has to rotate faster than the right wheel.
The effective combined rotation of the 2 sun gears should be equal to the planet gears i.e. peripheral velocity of the sun gears should be equal to the planet gears.
Another simple way to understand the mechanism is that the speed of the left wheel is equal to the sum of the rotational speed and the spinning speed of the planet gears. Whereas, the speed of the right wheel is the difference between the rotational speed and the spinning speed of the planet gears. This helps in making the left wheel rotate faster than the right wheel.
It is the vice-versa when a vehicle is taking a left turn. The planet gears spin in the opposite direction.
Speed reduction at the differential:
This is also one of the functions of a differential, where the speed from the transmission is reduced by having a larger ring gear compared to the pinion gear. This set-up increases the gear ratio, thus reducing the speed. This is also known as final gear ratio. If the final gear ratio is 1:5, that means the ring gear has 5 times more teeth than that of pinion gear.
Disadvantage of a standard differential:
The main disadvantage of a standard or an open differential is that it is not effective on surfaces offering different traction. Consider a situation where one wheel is moving on a slippery track (water) and the other wheel is on a rough surface. In this case, the standard differential will send the majority of the power to the slippery wheel and hence the vehicle is stuck. To overcome this problem, Limited Slip Differentials (LSD) are used.
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