Differential is used in rear-wheel drive and front-wheel drive vehicles. The difference between them is that in rear-wheel drive vehicles, it is located in the center of the rear axle. In front-wheel drive vehicles, the differential gearbox or transmission is located together in a single body. The function of the differential is to reduce the speed of the rotational movement received from the transmission, increase the torque, and transmit it to the wheels. It also enables the two drive wheels to rotate at different speeds (in turns or corners) through the use of bevel gears. Luxury or off-road vehicles use locking differentials, which lock both wheels together at low speeds, allowing them to turn at the same speed and avoid slipping. In addition to the definition of what a differential is, this page also describes the different parts and types of differentials, as well as their maintenance.
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How Does a Differential Work and What are Its Functions?
When cars move in a straight line, the wheels on both sides will turn at the same speed and amount. However, when turning right or left, the amount of wheel rotation will be different, and a system is needed to compensate for this difference. To meet this need, a car part called a differential is used. For example, when a car wants to turn right, the right wheels need to turn less than the left wheels. The differential is located between the two wheels, connected to the wheels with a half-shaft, and allows the two axles to turn at different speeds.
The function of the differential is to transmit power from the engine to the wheels. The rotational motion from the engine is transmitted to the differential by the transmission. The differential distributes this to the wheels along with the turning angle. At the same time, it allows the inner and outer wheels to turn at different speeds when turning. In a turn, a curved path will be followed, so the inner wheels need to turn less and the outer wheels need to turn faster. The differential regulates the number of wheel rotations. It regulates the engine’s rotational speed, which is first changed through the transmission and then transmitted to the differential. It changes this speed according to the turning angle and transfers it to the wheels.
Where is the Differential Located?
The location of the differential differs for front-wheel drive, rear-wheel drive, and four-wheel drive vehicles. Therefore, they need to be examined separately.
In front-wheel drive vehicles, it is located in the gearbox on the front axle. In rear-wheel drive vehicles, it is located in an area in the middle of the rear axle. In four-wheel drive vehicles, there are several differentials. There are a total of 3 differentials, including front, rear, and transfer shaft differentials.
What are the parts of a differential?
Let’s examine the parts of the differential that are used to increase the road grip of the car in turns. It is a simple structure consisting of a shaft, joints, and differential oil. The parts of the differential will be explained in detail under the headings below.
I – Differential Parts – Shaft
The shaft is the part that connects the differential to the transmission. Its flexible structure helps to maintain the position of the transmission on rough roads. For the shaft to be effective, the balance adjustment must be properly made. If this differential adjustment is not made, it may cause damage to the differential and transmission because it will not adapt to the engine speed and rotation.
II – Differential Parts – Universal Joints
The universal joint, which connects the shaft to the transmission and differential and allows the shaft to move flexibly, is found at both ends of the shaft. If the shaft consists of two parts, the number of universal joints increases to three. These joints, which must be flexible to prevent the driver from feeling the bumps and dips on the road, are generally T-shaped.
III – Differential Parts – Constant Velocity (CV) Joints
Front-wheel-drive vehicles that have standard turning angles and directional ability use constant velocity joints that can work up and down. Constant velocity joints, which are also used in high-torque vehicles, provide effective performance in large turning angles and transmit force as smoothly as possible, no matter how strong it is.
IV – Differential Parts – Differential Oil
Lubricating the differential gears and parts is one of the most important rules. Special differential oils are poured into the mechanism, and existing plugs are used to change or drain the oil. The differential must not be operated without oil. Therefore, if leakage occurs, it must be intervened. If the oil is drained, the gears will operate without oil and cause wear. Therefore, attention must be paid.
What are the types of differentials?
I – Open Differential – How does a classic differential work?
It is a differential type that sends the torque from the engine equally to both wheels. That is, the traction force on the right wheel and the traction force on the left wheel are always the same. Of course, the wheels can rotate at different speeds. Classic differentials are used in many sedans, minivans, and crossover models. It divides the power from the engine between the inner and outer wheels to work at different speeds. In an open differential, if there is a torque loss in one wheel, this decrease is naturally seen in the other wheel as well.
II – How Does a Locking Differential Work?
While the primary purpose of a differential is to allow wheels to rotate at different speeds, a locking differential is designed to do the opposite. It ensures that both wheels rotate at the same speed when necessary. When engaged, it sends equal speed from the engine to both wheels, ensuring that both wheels rotate at the same (or similar) speed. Although it may sound strange, the reason why locking differentials are often preferred can be explained as follows:
In vehicles equipped with locking differentials, if one of the wheels encounters a surface on which it cannot rotate or if it slips, the locking mechanism is activated. Then, the shaft that connects the two wheels is locked and they begin to rotate as a whole. This distributes power and torque equally to the wheels. As a result, the wheel on normal ground will turn and allow the other wheel to recover from the slip, helping the vehicle to get unstuck.
Locked differential and differential lock are often confused. However, their features are different. Locked differential is usually found in pickups and some off-road vehicles. It has limited slip feature, which prevents wheels from getting stuck in sand, mud, ice and similar surfaces by allowing them to turn at the same speed. It works like an open differential when the lock is off. Differential lock, on the other hand, is frequently seen in 4×4 vehicles and is suitable for the most challenging off-road conditions. It ensures that the wheels are completely locked and provides maximum traction on any surface. Another point to be aware of in a locked differential is that it should not be forgotten that turns cannot be safely made while it is engaged. As the inner and outer wheels turn at the same speed, road holding performance decreases, tires slip and the vehicle may skid.
III – Limited Slip Differential
Limited slip differential engages when the difference in rotation between the two wheels exceeds a certain amount and locks the axle shafts together. This eliminates the difference in speed between the wheels, providing improved traction. It functions similarly to both open and locked differentials. When the vehicle starts to slip, the limited slip differential kicks in and locks up, increasing traction.
IV – Electric Controlled Limited Slip Differential
This type of differential, which works like a limited slip differential, is more commonly seen in higher-end vehicles. It engages automatically and intervenes with precision and breadth to prevent the vehicle from sliding.
V – Dynamic Torque Control Differential
Dynamic torque control differential, which is used in continuous four-wheel drive cars, is a high-priced system that increases the weight of the vehicle. This type distributes and controls the torque going to each of the four wheels, and also increases fuel consumption to some extent.
How to Maintain a Differential?
Due to its structure, the differential, which works by combining many gears, is a crucial part that reflects the engine power to the wheels in the most appropriate way. This makes the maintenance of the differential an important issue that needs to be taken care of. Lubricating the gears and wheels in the differential prevents them from rubbing against each other and causing damage.
When and How to Maintain the Differential?
Periodically changing the differential oil and checking its level frequently is sufficient. However, the answer to the question of “When should differential oil be changed?” varies according to the type of vehicle and its usage intensity. Additionally, the mechanism should be checked for leaks to prevent differential oil from running out. If the differential oil runs out, the gears can damage each other, power will not be transmitted to the wheels adequately, and driving safety will be compromised.
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Source: Carstechnic and Btperformance