- 1 What Is A Differential?
- 2 Need Of Differential
- 3 Components Of Differential
- 4 Construction Of Differential
- 5 Working Of Differential
- 6 Types Of Differential
- 6.1 1. Conventional Differential | Open Differential
- 6.2 2. Limited Slip Differential (Self-Locking Differential | Differential Lockout)
- 6.3 3. Non-Slip Differential
- 6.4 4. Double Reduction Type Differential
- 7 FAQ – What is a Differential
What Is A Differential?
The differential allows each rear wheel to turn at different speeds. During cornering but at the same time, it gives equal torque to each wheel when both wheels have the same traction. A system of gears in the differential arrange in such a way that it connects the propeller shaft to the rear axle. The difference in a word intends to provide relative movement to rear wheels.
Need Of Differential
The differential allows the non-steering wheels to rotate at different speeds so the car can corner without putting undue wear on the tires. The wheel on the inside of a turn moves a shorter distance compared to the outer wheel. If the axle does not allow the wheels to turn independently of each other, the tire of one wheel will be pulled across the ground.
Components Of Differential
- Drive pinion or Bevel pinion
- Ring gear or Crown wheel
- Differential case
- Differential side gear or Sun gears
- Differential pinions or Planet gears
- Axle shafts or Half shafts
- Pinion shaft or Cross pin or spider
Construction Of Differential
The figure shows the basic parts of the differential used in rear-wheel-drive cars. A small bevel gear called differential side gear is mounted on the inner ends of each axle. Two bevel gears are placed together to connect both driving and driven shafts at an angle of 90°. The differential case is connected with two-wheel axles and differential side gears.
The differential case has bearings that rotate two axle shafts. Then, two pinion gears and their supporting shaft called pinion shaft, fit to the differential case. Then, the pinion shaft meshes with two differential side gears connected to the inner ends of the axle shafts.
The ring gear moves to a flange on the differential case. The ring gear rotates the differential case. Finally, the drive pinion mounts. The drive pinion assembles with the differential housing called differential case or carrier. The driver shaft connects to the drive pinion by a universal joint and it meshes with a ring gear. Therefore, the drive pinion rotates when the driver turns the shaft. Thus, the ring gear rotates.
Working Of Differential
The input torque is mounted to the ring gear through the drive pinion, which replaces the entire differential case. The differential case is connected to both the differential side gears only through the differential pinions. Torque is transmitted to the differential side gears through the differential pinions. The differential pinions revolve around the axis of the differential case, driving the differential side gears.
While the car is on a straight road, the resistance on both wheels is equal and the ring gear, differential case, differential pinion gear, and two differential gears will replace as one unit. It results in the side gears rotating at the same speed as the ring gear makes both drive wheels rotate at the same speed. The differential pinions rotate without spinning about their axis, and both wheels turn at the same rate.
If the left differential side gear is encountered (when the vehicle runs on the curved path), the differential pinion rotates as well as a spin that allows the left differential gear to slow down, to the right differential side. This causes the outer wheel to turn faster than the inner wheel.
Types Of Differential
- Conventional Differential or Open Differential
- Limited Slip Differential (Self-Locking Differential or Differential Lockout)
- Non-Slip Differential
- Double Reduction Differential
1. Conventional Differential | Open Differential
The conventional differential shown in the figure shows the pictorial representation of the differential. The working principle is the same as described above.
2. Limited Slip Differential (Self-Locking Differential | Differential Lockout)
The standard differential works well in most situations. on very slippery road surfaces such as snowy or muddy roads, the lack of driving force, called traction force, may cause the rear wheels to slip as the standard differential will drive the wheels with the least amount of traction. If one drive wheel is on dry road and the other is on snow or mud road, the ring gear and differential case will drive the pinion gear. But, the pinion gears won’t drive both side gears.
When the pinion gears drive by the differential case, they will move around the side gear corresponding to the Wheel on a dry footpath. This results in the pinion gears driving the slipping wheel and the vehicle will not move. The standard differential transfers almost all engine power to the slipping wheel. This issue can avoid by using differential locks. Differential locks overcome traction problems by sending equal power to both wheels while allowing normal turning of the vehicle.
Limited slip differential (LSD) restricts the differential rpm between two wheels, two thrust washers, and a clutch plate which includes in the differential case shown in fig. When the resistance of the left side differential gear is greater than the wheel, the right side differential gear will rotate. It forms the teeth of the right side differential clutch member climbing the teeth of the left side differential clutch member. So, this takes two clutch members to move away from each other.
Therefore, the side gears push opposite to the thrust washers. Due to this, the rpm of the rear axle shaft gets closer to the differential case due to friction between the side gear and the thrust washers. So, it is called the limited-slip effect.
Types of Limited-Slip Differential
(I) Clutch-Plate Differential
The clutch-plate differential uses several friction discs that are similar to small manual clutch discs. The main difference between this limited-slip differential and a standard differential is placed between the clutch pack side gear and the differential case.
Clutch friction discs are made of steel covered by a friction material. The clutch plates are made of steel. The discs and the plates are alternately splined to the side gear and fit into the grooves to the differential case. Grooves in discs or plates are for better-grabbing power.
The pinion gear, side gear, and other parts are similar to a standard differential. The limited-slip differential constructs into two parts to allow for the removal of the clutch pack. Discs and plates apply by preload springs and by the mechanical pressure of the pinion gear on the side gear.
Since the pinion and side gears are beveling gears, their teeth try to come out of engagement when the differential is transmitting engine torque. This creates a pushing action on the side gears and forces them outward direction against the differential case.
The external pressure of the side gears presses the friction discs and steel plates together between side gear and case. Whenever the discs and plates press together, the splined and dogged connections (meaning tabs fit into grooves) ensure the side gear and differential case lock together.
When the vehicle is moving straight ahead, the clutch-plate differential operates similarly to a standard differential. The rear wheels and differential case turn at the same speed. The clutch packs apply but are not requires.
When the vehicle is making a turn, a higher torque due to the outer wheel rotates faster than the case and causes the clutch pack to slip. It allows the differential to operate the same as the standard differential when making turns. Discs and plates slide against each other. Discs twist with side gears, with plate case turns that allow different rotational speeds between the case and side gears. Therefore, the rear wheels rotate at different speeds.
(II) Cone Clutch Differential
This is the other version of the limited-slip differential. Instead of clutch packs, friction-lined cones are uses. The cone differential uses a cone-shaped clutch which engages a matching cone-shaped receptacle. The operation is the same as the clutch-plate differential. The Preload spring and the side gear pressures force the cone into a dished depression in the differential case.
Friction tries to lock the cone. Therefore, the side gear transfers power to the wheel with the most traction. Both the clutch-plate and the cone differential require a special limited-slip gear oil. Using ordinary gear oil in a limited-slip differential will cause discs and plates or cones to slip and vibrate during turning.
3. Non-Slip Differential
This differential is torque-controllers. Preloading the system is possible. So, the differential operates by resultant moments. Preload can adjust.
Advantages Non-Slip Differential
- Maximum traction can achieve for all grip levels
- Fuel consumption reduces.
- Tyre wear reduces.
- A comfortable driving obtain.
- Constant speed drive ensure.
- Understeer in corners reduces.
4. Double Reduction Type Differential
In final drives, there is a single fix gear reduction. This is the only gear reduction in maximum automobiles and light vehicles and some medium-duty trucks between driveshaft and wheels. Double reduction final drives are uses for heavy-duty trucks. In this arrangement, it is not necessary to have a large ring gear to achieve the required gear reduction.
The first gear reduction achieves as a single fixed gear reduction final drive through a pinion and ring gear. The secondary pinion is located on the primary ring gear shaft. The reduction of the second gear is the result of a secondary pinion that tightly couples to the primary ring gear and drives a larger helical gear that attaches to the differential case.
Double-reduction final drives may design for vehicles such as 5-ton trucks. Most commercially designed vehicles of this size use a single-reduction or double-reduction.
FAQ – What is a Differential
Q. What is a Differential?
Differential gears are a set of gears that transmit engine power to the wheels, while allowing them to rotate at different speeds. With rear-wheel-drive (RWD), the differential is between the rear wheels, which are connected to the transmission by the driveshaft.
Q. What are the types of differential?
There are four common differences used between vehicles – open, locking, limited-slip and torque-vectoring.