What is a Differential Gear?

The vehicle differential can enable the left and right (or front and rear) drive wheels to rotate at different speeds. It is mainly composed of left and right half shaft gears, two planetary gears and a gear carrier. The function is to make the left and right wheels roll at different speeds when the car is turning or driving on uneven roads, that is, to ensure that the driving wheels on both sides make pure rolling motion. The differential is installed to adjust the difference in speed between the left and right wheels. In four-wheel drive, in order to drive four wheels, all wheels must be connected. If the four wheels are mechanically connected, the car cannot rotate at the same speed when driving on a curve. The rotation speed is basically consistent. At this time, an intermediate differential needs to be added to adjust the speed difference between the front and rear wheels.

The vehicle differential can enable the left and right (or front and rear) drive wheels to rotate at different speeds. It is mainly composed of left and right half shaft gears, two planetary gears and a gear carrier. The function is to make the left and right wheels roll at different speeds when the car is turning or driving on uneven roads, that is, to ensure that the driving wheels on both sides make pure rolling motion. The differential is installed to adjust the difference in speed between the left and right wheels. In four-wheel drive, in order to drive four wheels, all wheels must be connected. If the four wheels are mechanically connected, the car cannot rotate at the same speed when driving on a curve. In order to make the car drive on a curve The rotation speed is basically consistent. At this time, an intermediate differential needs to be added to adjust the speed difference between the front and rear wheels.

Chinese name: Differential
Foreign name: Differential
Make up: Differential case, planetary gear and side gear

Function: The two shafts rotate with each other at different speeds
Classification: Gear-type differential, non-slip differential
Application: Vehicle driving

Differential Composition

Ordinary differentials are composed of planetary gears, planetary carrier (differential case), half-shaft gears and other parts. The power of the engine enters the differential through the transmission shaft, and directly drives the planetary wheel carrier. The planetary wheel drives the left and right half shafts to drive the left and right wheels, respectively. The design requirements of the differential are: (left half shaft speed) + (right half shaft speed) = 2 (planet wheel frame speed). When the car goes straight, the speeds of the three wheels, the left and right wheels, and the planetary wheel carrier are equal and in a balanced state. When the car turns, the balance of the three is broken, causing the speed of the inner wheel to decrease and the speed of the outer wheel to increase. ^[1]

Differential principle

This adjustment of the differential is automatic. Here it involves the "minimum energy consumption principle", that is, all objects on the planet tend to consume the least energy. For example, if you put a bean in a bowl, the bean will automatically stay on the bottom of the bowl and never stay on the wall of the bowl. Because the bottom of the bowl is the lowest energy position (potential energy), it automatically chooses the static (minimum kinetic energy) instead of Will keep moving. The same thing,

3D effect When the wheels turn, they will automatically go to the lowest energy consumption state, and automatically adjust the speed of the left and right wheels according to the turning radius. ^[2]

When cornering, due to the phenomenon of slipping on the outer wheels and slipping on the inner wheels, the two driving wheels will generate additional forces in opposite directions at this time. Due to the "minimum energy consumption principle", the wheels on both sides will inevitably be caused. The speeds of the two sides are different, thus destroying the balance relationship between the three, and reflected on the half-shaft gears through the half-shaft, forcing the planetary gear to rotate, slowing down the speed of the inner half-shaft and speeding up the speed of the outer half-shaft, thereby achieving the speed of the wheels on both sides difference.

If the drive wheels on both sides of the transaxle are rigidly connected with a whole shaft, the two wheels can only rotate at the same angle. In this way, when the car turns, the outer wheels move past the inner wheels.

Differential principle diagram A large distance will cause the outer wheels to slip while rolling, while the inner wheels will roll while rolling. Even when the car is driving straight, the wheels may slip due to uneven road surfaces or uneven rolling tyres (uneven tire manufacturing errors, different wear, uneven loading, or uneven air pressure).

When the wheels slide, they not only exacerbate tire wear, increase power and fuel consumption, but also make the car difficult to steer and worsen braking performance. In order to prevent the wheels from slipping as much as possible, the structure must ensure that each wheel can rotate at different angles.

Between the shafts: Usually the driven wheels are supported on the main shaft by bearings, so that they can rotate at any angle, while the driving wheels are rigidly connected to the two half shafts respectively, and a differential is installed between the two half shafts. This type of differential is also called an interaxle differential.

Multi-axis driven off-road vehicles, in order to enable each drive axle to rotate at different angular velocities, to eliminate sliding of the drive wheels on each axle, some are equipped with an inter-axle differential between the two drive axles.

Differential action

When a car turns, the turning radius of the inner wheels and the outer wheels are different. The turning radius of the outer wheels must be larger than the turning radius of the inner wheels. This requires that the speed of the outer wheels is higher than the speed of the inner wheels when turning. The role of the differential is to meet the requirements of different wheel speeds on both sides of the car when turning! This role is the most basic role of the differential. As for the development of what is the central differential, anti-skid differential, LSD differential, Toson differentials, etc., are designed to improve the driving performance and handling performance of the car.

Differential function

When the car turns, the trajectory of the wheel is an arc. If the car turns to the left, the center point of the arc is on the left. At the same time, the arc on the right wheel is longer than the left wheel. In order to balance this difference It is necessary to make the left wheel slower and the right wheel faster. Use different speeds to make up for the difference in distance.

If the rear axle is made as a whole, the speed difference between the wheels on both sides cannot be achieved, that is, automatic adjustment cannot be made. In order to solve this problem, as early as a hundred years ago, the founder of Renault Automobile Company of France Renault designed the differential. ^[3]

Differential classification

Differentials on modern automobiles are generally divided into two types, gear type differentials and non-slip differentials, according to their operating characteristics.

Differential gear differential

Due to structural reasons, the torque distributed to the left and right wheels by this differential is equal. This

Limited slip differential This kind of differential torque sharing feature meets the normal driving of the car on a good road. But when the car is driving on a bad road, it seriously affects the passing ability. For example, when one of the driving wheels of a car is stuck on a muddy road, the car often cannot move forward (commonly known as slipping) although the other driving wheel is on a good road. At this time, the driving wheels on the muddy road slip in place, but the wheels on a good road are still. This is because the adhesion between the wheel and the road on the muddy road is small, and the road can only use this wheel to exert a small reaction torque on the semi-axle, so the torque allocated to the wheel by the differential is also small. Although the adhesion between the other driving wheel and the good road is large, due to the characteristics of the average torque distribution, this driving wheel can only be divided into the same amount of torque as the slipping driving wheel, so that the driving force is insufficient. Overcoming driving resistance, the car cannot move forward, and power is consumed on the skid drive wheels. At this time, increasing the throttle not only does not make the car move forward, but wastes fuel, accelerates the wear of the parts, and especially increases the tire wear. An effective solution is to dig out the mud under the slip drive wheel or pad dry soil, gravel, tree branches, hay, etc. under the wheel.

Differential non-slip differential

In order to improve the car's ability to pass on bad roads, some off-road vehicles and premium cars are equipped with anti-skid differentials. The characteristic of a non-slip differential is that when one side of the drive wheel is slipping on a bad road, most or all of the torque can be transmitted to the drive wheel on a good road, so as to make full use of the adhesion of this drive wheel to generate Sufficient driving force to make the car start smoothly or continue driving. In order to achieve the above requirements, the simplest method is to set a differential lock on the symmetrical bevel gear differential to make it a forced-lock differential. When the drive wheels on one side slip, a differential lock can be used to lock the differential without acting as a differential.

The anti-skid differential can overcome the ordinary bevel gear differential because the torque is evenly distributed to the left and right wheels. When driving on a bad road (muddy, snowy road, etc.), one side of the drive wheel contacts the muddy, snowy, snowy road. The road is slipping (slipping) on the spot, but the driving wheels on the other side on a good road are in a stationary state, which reduces the vehicle's passing capacity. This is because the adhesion of the driving wheels in contact with muddy, icy and snowy road surfaces to the road surface is reduced, and the road surface has a small reaction torque on the half shaft. In combination with the symmetrical bevel gear differential, it has the characteristics of equal torque distribution. The torque obtained by driving the wheels on a good road can only be equal to the torque of the driving wheels on a bad road, so the combined force of the two is not enough to overcome the driving resistance, and the car stops.

According to different structural features, there are three types of anti-skid differentials: forced lock, high friction and free wheel. Among them, there are five types of high-friction type: friction lining self-locking differential, Thorson differential, worm differential, slider cam differential, and viscous coupling differential.

The "Thosen" differential is a torque-inductive differential produced by Gleason Corporation in the United States, that is, the differential can determine whether to limit the differential effect of the differential according to the size of its internal differential torque. The structure is cleverly designed using the irreversible principle of turbine worm drive. As a new type of differential mechanism, the Torson differential has been widely used in various automobiles with its unique superior performance. ^[4]

Differential double worm differential

Double worm differential (7 photos)

The double worm differential is a product newly invented in China in 2014. It is characterized in that two worms that mesh with each other are installed in the rotor at an angle. The two worm shaft ends are connected to the output shafts on both sides. It is connected to the joint, the ring gear is installed on the rotor, the whole is fixed to the housing by the bearing, the power source is input by the ring gear, and the output shafts on both sides output power.

The two worms use a small lead angle. The size of the lead angle determines the degree of self-locking. In the worm and the turbine drive, both the worm is active and the turbine is driven. The two worms mesh, which is equivalent to each other's turbine When the lead angle is small to a certain degree, the two worms will interlock, and they can only rotate when both sides apply torque at the same time, so this is the reason for self-locking without affecting differential driving.

If used in the center differential, the diameter of the two worm pitch circles can be adjusted so that different torques can be output from the front and rear, just like the 40:60 power distribution of the front and rear.

The advantages are small size, simple processing, low cost, and full-time four-wheel drive.

LSD Differential LSD system

Speaking of AWD car drive system, people can't miss Audi Quattro. It is Audi's bold innovation and unrelenting attention that has led to more and more people.

Torsen B differential We enjoy the driving pleasure brought by AWD, and the core of the Audi Quattro AWD is the Torsen LSD differential system. Who can think of the electronic components running wild today and it still maintains the mechanical purity.

Every car must be equipped with a differential. We know the role of ordinary differentials: first, it is a set of reduction gears that converts the high speed output from the gearbox into normal speed; second, it can drive left and right The wheel speeds are different, that is, different corner speeds are output to the inside and outside wheels to maintain balance when cornering. Its drawback is that it will lose traction due to slipping when passing through wet roads. And if the limited slip function is added to the differential, it can meet the car's need for good maneuverability on rough roads. This is the Limited Slip Differential (LSD). The basic structure of an AWD system for an all-wheel-drive car is three differentials, which control the torque distribution of the front, rear, and front and rear drive shafts, respectively. These 3 differentials are not just simple differentials that are common to people. They are LSD differentials with self-locking function to ensure that the drive wheels always maintain sufficient torque output when the tires on slippery roads are slipping. The road conditions are well controlled. There are several forms of LSD differentials in the world. Today we will take a look at the Torsen self-locking differential system.

The origin of the name Torsen is derived from Torque-sensing Traction-feeling torque traction, even the brand name is derived from traction control, professional enough!

Torsen Core Torsen differential system

When there is no wheel slip during cornering, the front and rear differentials are traditional differentials, and the worm gears do not affect the difference in output speed of the half shaft. For example, when the car turns to the left, the right wheels are faster than the differential, while the left speed is low, and the worm gears with different left and right speeds can closely match the synchronous meshing gears. At this time, the worm gear is not locked, because the torque is from the worm gear to the worm gear, and power transmission in this direction is unobstructed.

Haldex multi-disc central differential

When the left wheel slips, the traditional differential will transmit power to the left wheel, so that the power of the engine can only be consumed in vain. The Tosson differential is different. At this time, the left half shaft that is rapidly rotating will drive the left worm, and the right worm will be driven by the synchronous meshing gear.

The Torsen differential is used in a full-time four-wheel drive system, and traction is distributed to each wheel, so it has good cornering and dry / wet road driving performance. The Torson central differential ensures even power distribution between the front and rear wheels. For example, when a tire encounters a road surface where friction is lacking, such as ice, the system will respond quickly, and most of the torque will be turned to the wheel with slow speed, that is, the wheel with grip.

There is no time delay in the lock-in intervention of the Toson differential, nor does it consume the total torque value. It does not have the multi-plate clutch equipped with the traditional lock-up differential, and has very little wear and tear, and can be maintenance-free.

In addition to its own performance advantages, the Toson differential also has other advantages, such as it can be matched with many commonly used transmissions and transfer cases, and it is compatible with electronic equipment such as ABS, TCS, ESP on the vehicle, which complement each other. Vehicle safety and handling services.

However, there are still two problems that are difficult to solve for the Toson differential. One is that the cost is high, so generally the Toson differential is used in high-end cars; the second is that the weight is too large, and the acceleration of the vehicle is A drag.

It has been used in automobiles as a mainstream differential for more than 20 years. However, due to its outstanding mechanical stability, it has not developed rapidly for many years. In 2011, it only developed to the third generation "Toson C". The new C-generation Torson differential is commonly used in the Audi B7-generation RS4, S8 and Q7 "Quattro" all-wheel-drive systems. The biggest change of the new Torson central differential is that the front and rear torque distribution ratio is generally controlled at 40:60, the front axle torque ratio can be changed between 15% and 65%, and the rear axle torque ratio can be between 35% and 85%. Between changes.

As the most important four-wheel-drive car manufacturer, Audi has always insisted on using the Torson differential. Except for the A3 and TT, all other Audi quattros use the Torson central differential. However, the Toson differential is not only used in Audi cars. More and more companies use the Toson differential, including Ford, GM, Toyota, Mazda, Land Rover, Volkswagen and Lexus. It's just that the front, back, and center use positions are different, and they are not the same generation.

In short, the Torson differential is a very precise and creative invention that has always maintained the characteristics of pure mechanics. Today, with the rapid and continuous introduction of various electronic equipment by major automobile manufacturers, it can still maintain its leading position in many aspects, which has to make us admire the "Thosen Differential" and its designers.

TORSEN LSD is based on the principle of worm gear and worm gear. The degree of restriction increases with the increase of relative rotation, so it is called TORQUE SENSING. Torsen differential is mainly composed of worm planet gear and differential case. Body, the front output shaft and the rear output shaft are composed of four sets of large components. The power output by the engine is directly used to drive the case of the Toson differential (the power input gear in the figure is connected to the case). The rotation of the case will drive the three sets of worm planet gears to rotate. Connected by straight teeth, and connected to the front and rear output shafts by a worm. In this way, the power can be smoothly distributed to the front and rear output shafts through the planetary gears so that the front and rear axles can be driven. It is because of the worm design of the planetary gear that it has a self-locking function. Once a wheel encounters greater resistance, the Tosson differential transmits more power to that wheel.

TORSEN LSD is based on the worm and worm principle to achieve limited sliding. The degree of limitation increases with relative rotation, so it is called TORQUE SENSING.

-Torsen Differential- the core of Torsen

From the structural view of the Torsen differential we can see the double worm gear and worm structure. It is their mutual meshing and interlocking and the transmission of torque from the worm gear to the worm gear in one direction to achieve the differential lock function. It is this property that limits slippage.

When the right wheel slips, the worm gear and worm assembly work, and traditional differentials will not transmit power to the left wheel. For the Torsen LSD differential, the fast-rotating right half-shaft will drive the right worm at this time, and the left worm will be driven by the synchronous meshing gear. When the worm drives the worm gear, they are locked, and the left and right worms are interlocked to ensure that the non-slip wheels have sufficient traction.

Thorson differential

Torsen Features of differential Torsen

-Torsen Features

Torsen LSD system The Torsen differential is a constant-speed 4WD, and traction is distributed to each wheel, so it has good curve, straight (dry / wet) driving performance. Torsen self-locking center differential ensures uniform power distribution between the front and rear wheels. Any difference in speed, such as when the front wheels meet the ice, the system will respond quickly, 75% of the torque will be turned to the slower wheels, here is the rear wheel.

The Torsen differential achieves constant-time, continuous torque control management. It continuously works without time delay, but does not involve the adjustment of the total torque output, so there is no loss of torque, and the traction control and body stability control system Compared with a greater advantage. Because there is no multi-plate clutch equipped with a traditional self-locking differential, there is no wear and tear and maintenance-free is achieved. Pure mechanical LSD has good reliability.

The Torsen differential can be matched with any transmission and transfer case, and is compatible with other vehicle safety control systems ABS, TCS (Traction Control Systems, Traction Control), and SCS (Stability Control Systems). The Torsen differential is a purely mechanical structure, which will take effect at the moment when the wheel is slipping. It has a linear locking characteristic and is a true constant-time four-wheel drive. The torque distribution is 50:50 before and after normal driving. The disadvantage is that it is very expensive.

Torsen

-Today Torsen has been produced to the 3rd generation

Torsen's new and third generation T-3 differential is the ideal intermediate differential. The T-3 still uses worm gears in the outer ring of the planetary gear, but its structure is more compact and its appearance is smaller. The torque distribution under normal conditions is 50:50, and the torque distribution before and after T-3 is 65:35. Up to 35:65 linear distribution. The T-3 dual differential system can directly provide three-way torque output of the front left, front right, and rear wheels, which is very suitable for front drive-based AWD models.

As the most important 4WD sedan manufacturer, Audi has always insisted on using Torsen differentials. More and more companies using Torsen differentials for AWD models include Ford, GM, Audi, Toyota, and Volkswagen. In today's electronic age, purely mechanical systems maintain their unique position with their solid reliability.

ELSD system

Electronic limited slip differential (ELSD). Traditional anti-skid differentials have not only improved their driving performance, but also improved their driving stability and safety. They have also shown their own shortcomings, such as increasing the fuel consumption of cars, preventing them from interacting with electronic stability program (ESP), and anti-lock braking The system (ABS) works in coordination, etc., so electronically controlled anti-skid differentials have appeared. Electronically controlled anti-skid differentials are becoming more and more widely used in mid- to high-end cars and SUVs, and are an important assembly for improving the active safety of automobiles.

Electronically controlled anti-skid differential can be divided into active anti-skid differential and four-wheel drive anti-skid differential.

The active non-slip differential includes a wet differential (V-TCS) and an active non-slip differential (LSD). The wet differential works by controlling the engine speed and the braking force of the car through an electronic control device based on the amount of slip of the driving wheels; or it controls the torque according to the speed difference between the left and right wheels, and it is optimally distributed in combination with the brake Driving wheel driving force. Active non-slip differential.

Differential maintenance program

1. The differential case must not have cracks of any nature. The contact between the case and the planetary gear pads and the differential half-shaft gear should be smooth without grooves; if there are slight grooves or wear, you can continue to use it after repairing Otherwise, it should be replaced or repaired.

2. The matching clearance between the planet gear shaft hole and the planet gear wheel shaft on the differential case must not be greater than 0.1-0.15mm, and the cooperation between the axle shaft journal and the housing hole is a clearance fit, and there should be no obvious loose feeling, otherwise it should be replaced or repaired. .

Open differential

Open differentials are most commonly used and can distribute the same size to the left and right drive axles.

Fastest differential-Ningqiang people Of torque. When the vehicle travels in a straight line, the left and right wheels are equally stressed, and there is no speed difference between the two half-shaft gears, so the planetary gear does not rotate, and the driven ring gear of the main reducer is equivalent to directly driving the two half-shaft gears. The half-shaft gear is connected to the wheel through the driving half-shaft. Therefore, after a series of power transmission processes, the wheel receives the same rotation speed as the driven ring gear of the main reducer. When the vehicle turns, the outer wheels want to get a higher speed than the inner wheels. At this time, the planetary gears are involved to allow a slight speed difference between the two half-shaft gears while maintaining the torque transmission.

Disadvantages of open differentials: If the side gears on one side are stationary relative to the other side, all the power input to the differential will be distributed to the wheels with less resistance. This is why when the wheels on one side of the car are on the ice and the other side is on the road with good adhesion, the feet are refueling. . At this point, the vehicle cannot move at all, because all the power of the engine is transmitted to the wheel with the least resistance-the wheel on the ice.

If it is a four-wheel drive vehicle with open differentials on both the front and rear axles, it is not possible to get out of sleep when encountering a single front wheel or rear wheel off the ground when off-road. The differential will actively drive the idle wheels to idle, while the wheels left on the road will not get any driving force.