A differential is a type of gear train consisting of three drive shafts, where one shaft’s rotational speed is the average of the speeds of the other two shafts. Differentials are commonly used in motor vehicles and enable the wheels on each end of a drive axle to rotate at varying speeds, especially when cornering.
In this reading, we’ll explore what a differential is, its diagram, function, parts, and types. We’ll also get to learn about how it works.
Let’s get started!
What Is a Differential?
A differential is a mechanism that transfers an engine’s torque to the wheels for the purpose of splitting the power, allowing the wheels to move at varying speeds. The differential has no effect when the vehicle is moving straight. The effect occurs when the vehicle is trying to make a turn, resulting in the wheel moving at a different speed.
Diagram Of a Differential
Functions of Differential In A Vehicle
- To help the engine power the wheels
- Transmit the power to the wheels as they rotate at different speed
- Act as final gear reduction in the vehicle by slowing the rotational speed of the transmission one final time before moving to the wheel
- Another function of the differential is to turn the power flow 90 degrees.
Parts Of a Differential System
The following are the major parts of a differential:
- Pinion Drive Gear: the differential part transfers power from the driveshaft (prop shaft) to the ring gear.
- Ring Gear: the ring gear transfers power to the differential case assembly.
- Spider-Gear: This component lies at the heart of the differential.
- Differential Case Assembly: this part holds the gear and drives the axel.
- Rear Drive Axle: it transfers torque from the differential assembly to the drive wheels.
Types of Differential
There are several types of differentials, each designed for specific applications and driving conditions. Here are the main types:
Open
In its simplest form, an open differential consists of two axle halves with gears on each end. A third gear connects the two axle halves, creating three sides of a square. After completing the square, a fourth gear is added to increase the strength.
The strength is increased with the ring gear added to the differential case that holds the basic core gears. This ring gear requires the wheels to be powered by connecting the drive shaft through a pinion.
An open differential improves axle cornering and is cost-effective and common. However, it distributes torque evenly between both wheels, causing the wheel with the least grip to control power transmission.
Locked
The locked type of differential is often found on a vehicle that goes off-road. It is basically an open differential with the effect of locking the axle in place to create a fixed one instead of an independent one. This effect can manually or electronically take place in the vehicle.
Locked differentials provide greater traction due to uneven torque distribution between wheels. However, they also have a disadvantage called binding, where excess torque needs releasing when wheels leave the ground or the axle is unlocked when no longer needed.
Welded/Spool
The welded differential is quite similar to the locked type, only that it has been permanently welded from an open differential into a fixed axle. The welding of the fixed axle is purposely done in order to keep both wheels spinning simultaneously. Vehicles with such differentials are meant for drifting.
The differential is not suitable for any other driving condition, as the welding already tampered with the component strength. It also increases the risk of catastrophic part failure, which may result in broken differential gears exploding through the differential casing.
Torsen
The Torsen differential uses bright gearing to produce the same effect as the limited-slip differential. However, it does not work with either clutches or fluid resistance. Instead, a layer of worm gearing is added to the traditional gear setup of an open differential.
The sets of worm gears acting on each axle provide the resistance required to enable torque transfer. Through a connected spur gear, the worm gears are constantly meshing with one another to achieve this.
The constant mesh between the two sides of the torsen helps transfer the torque immediately. This makes it more sensitive to changing roads and driving conditions. The Torsen differential is also capable of directing a high percentage of torque to one wheel, depending on the gear’s rate.
Active
The active type of differential is very similar to the limited-slip differential as it still employs mechanisms. The mechanism is used to offer the resistance needed to transfer torque from one side to another. Clutches are electronically activated instead of relying on purely mechanical force.
Active differentials use electronics to artificially change the mechanical forces the system is facing through changing driving conditions. This is why they are controllable and, hence, programmable. With sensors on such vehicles, a computer can automatically detect which wheels to transfer power to and when it should be transferred.
These types of differentials are good for performance, especially on bad roads, and help to improve cars that endure rapidly changing driving conditions. But this will be a system that can keep up their continuous adjustments to the vehicle.
Torque Vectoring
The torque-vectoring type of differential also uses an electronically enhanced system and even uses it to change the angle or vector of the vehicle. It encourages specific wheels to take more torque when needed, which improves their cornering performance.
When the opposite clutch is activated, the purely mechanically driven LSD, which would normally engage, can be used to assist with steering. While also putting more power down, overcoming the deficiencies in the LSD system.
In the corner of this differential, a multi-way LSD exerts resistance to both wheels till the axle partially locks. And also stabilizes it under braking, which is then released as the wheel speed drops and the vehicle turns in. This allows the wheels to rotate at different speeds.
How A Differential Works
If a car is making a turn to the right, the main gear may make 10 full rotations. At that time, the left wheel will make more rotations because it needs more travel, and the right wheel will make fewer rotations as it has less distance to travel.
The sun gears, which drive the axle half-shafts, rotate at a different speed related to the ring gear (one faster, one slower). This means 2 full turns each (4 full turns relative to each other), which causes the left wheel to make 12 rotations and the right wheel to make 8 rotations.
The rotation of the ring gear is the average rotation of the side sun gears. This causes the transmission in gear to prevent the ring gear from turning inside the differential when the vehicle is off. In the working of differential, the input torque is applied to the ring gear (blue), which turns the entire carrier (blue).
The carrier is connected to both sun gears only through the planet gear (green). The torque is transmitted to the sun gears through the planet gear. The planet’s gear revolves around the axis of the carrier that drives the sun’s gears.
The planet gear revolves without spinning its own axis if the resistance at both wheels is equal, which turns both wheels at the same rate. However, if the left sun gear (red) experiences resistance, the planet gear (green) spins as well as revolves. Allowing the left sun gear to slow down with an equal speeding up of the right sun gear (yellow).
Advantages
The following are the advantages of differential:
- Make it easier to maneuver, particularly in tight turns and bends.
- Turning the wheels at various speeds improves stability and keeps tires from wearing out.
- Give cars the ability to function well in a range of environments, from off-road to freeway.
- More power goes to the wheel that has a better grip, which improves stability and makes it easier to control on wet ground.
- Drivetrain components will last longer and run more efficiently with less stress.
Disadvantages
- Some vehicles are more expensive because they have more advanced differential systems, such as limited-slip or locking differentials.
- The complexity and need for maintenance and repair of differential systems may drive up the cost of vehicle maintenance.
- Sometimes a differential may transfer power to a wheel with less traction than the others, such as in muddy or slippery conditions, which will decrease the amount of traction overall.
- Excessive wheel spin from high-performance differentials might, under some situations, result in instability.