How does the differential transmit force?

Comparison of characteristics of various differentials;

1. Open differential

The structure of Cherokee open differential is a typical planetary gear set structure, but the number of teeth of sun gear and outer ring gear is the same. In this planetary gear set, the driving wheel is a planetary carrier and the driven wheel is two sun gear. Through the transmission characteristics of planetary gear sets, we know that if the planetary carrier is used as the transmission shaft, the rotation speed and direction of two sun gear are uncertain, and even the rotation directions of two sun gear are opposite.

When the vehicle runs in a straight line, the characteristic of this differential is that the torque transmitted to the two half shafts is the same. When the driving wheel is suspended, if the transmission shaft rotates at a uniform speed, the driving force of the driving wheel with adhesion has no driving force; If the transmission shaft rotates at an accelerated speed, the driving force of the adhesive driving wheel is equal to the product of the angular acceleration and the inertia moment of the suspension wheel.

When the vehicle turns and the tires don't slip, the torque directions of the two axle shafts connected with the differential are opposite, which provides the forward driving force for the vehicle. Only the constant speed drive between the inner wheel, the planetary carrier and the inner sun gear has been replaced by the deceleration drive, and the driving feeling is that the curve acceleration is more powerful than the straight acceleration.

The advantage of open differential is that it has the best effect of changing lanes on paved roads. The disadvantage is that when one driving wheel loses adhesion, the other one has no driving force.

The application scope of open differential is that all vehicles driving on paved roads can be equipped with front axle drive and rear axle drive.

2. Limited slip differential

Limited slip differential is used to partially compensate the transmission defects of open differential on off-road roads. It is improved on the basis of open differential, and friction plates are added between the side gears of the differential case. Corresponding to the planetary gear set, a friction plate is added between the planet carrier and the sun gear to increase the resistance moment of free rotation between the sun gear and the planet carrier.

The extra torque provided by the limited slip differential is related to the power transmitted by the friction plate and the speed difference between the two driving wheels.

The LSD generated by the improved open differential structure cannot achieve 100% limited slip, because the higher the limited slip coefficient, the worse the steering characteristics of the vehicle.

LSD has the transmission characteristics and mechanical structure of open differential. The advantage is to provide a certain limited slip torque, but the disadvantage is that the steering characteristics become worse and the life of the friction plate is limited.

The application scope of LSD is pavement and light off-road pavement. Usually used for rear wheel drive. Front-drive vehicles are generally not installed, because LSD will interfere with steering, and the greater the slip limit coefficient, the more difficult it is to steer.

3. Lock the differential (mechanical lock, electric lock and pneumatic lock)

In order to ensure the driving performance of the vehicle under complex off-road conditions, the differential is locked by a certain mechanical structure to realize the synchronous rotation of the two half shafts. By analyzing the planetary gear set, the transmission mechanism of the planetary gear set is locked to ensure that the transmission ratio between the planetary carrier and sun gear and between two sun gear is 1: 1. Sun gear and planet carrier can be locked, planet carrier and planet wheel can be locked, and two sun gear can be locked.

When the locking differential is not locked, its transmission characteristics are exactly the same as those of the open differential. When locked, the transmission ratio is fixed at 1: 1.

The advantages of this differential are self-evident, and it provides the greatest driving force on off-road roads. The disadvantage is that it is extremely difficult to turn the vehicle when the differential is locked. It is possible that a single wheel bears the torque of the engine 100%, and the half axle will be deformed or broken due to excessive torque; When the vehicle turns, the two axle shafts bear opposite torques. If the tire adhesion on both sides is large, the half axle will be twisted off. In addition, this kind of differential will produce relatively loud noise when the vehicle is running.

Locking differential has all the structure and characteristics of open differential, and its application scope is the same as that of open differential when it is not locked. In the case of locking, it is only suitable for driving at low speed on unpaved roads, not on paved roads, otherwise it will damage the vehicle and turn out of control.

This differential is represented by ARB's pneumatic locking products and Eaton's electric locking products.

Four. entry, descent, and landing

Compared with the above, electronic differential system does not change the structure and characteristics of the open differential, but uses ABS or EBD system to brake the side-slip wheel unilaterally to limit the speed difference between the two driving wheels and ensure that both driving wheels have power.

Advantages: good safety and no damage to vehicles. Disadvantages: ABS and EBD systems are needed, which is expensive; In the harsh off-road environment, the reliability of electronic products is not as good as that of mechanical products; The driving force of a single wheel is not as great as that of a locking differential.

This kind of differential lock is generally only used in high-end cars and high-end SUVs due to cost reasons.

Verb (abbreviation of verb) automatic mechanical locking differential

The basic structure of this differential is the same as that of the mechanical locking differential, but the difference is that the locking and unlocking of the mechanical locking differential are completely controlled by the driver. Automatic mechanical locking differential automatically locks and unlocks according to road conditions. Its locking detection mechanism is very exquisite, and there are two detection quantities, one is the difference in rotational speed between the differential axle gear and the differential housing, and the other is the rotational speed of the differential housing.

Locking conditions: the speed of the differential case does not exceed the set value (that is, the vehicle speed is lower than the set value), and the speed difference between the speed change gear and the differential case exceeds the set value (the speed difference between the left and right wheels is too large). If both conditions are met, the differential will be locked, but steering in normal driving will not cause it to lock. During the whole locking process, the angle difference of wheel idling shall not exceed 360 degrees.

Unlocking conditions: If the speed of the differential case exceeds the set value (the vehicle speed exceeds the set value) and the torque directions of the left and right axle shafts are opposite (the vehicle turns in an open way), it will be unlocked immediately if either of them is met.

Advantages: the road driving characteristics are exactly the same as those of the open differential. Off-road pavement has exactly the same characteristics as the locking differential, and the axle shaft will not break due to steering, and its locking and unlocking process is completely automatic without manual intervention. Very high reliability.

Disadvantages: the locking noise is relatively large, and the structure is more complicated than the mechanical locking differential. Each differential can only be applied to one vehicle type and is not universal.

Applicability: it can directly replace the open differential, and can be driven both front and rear, and its applicability is not limited.

The automatic mechanical locking differential represented by Eaton products is the most suitable differential for off-road vehicles. Unfortunately, there is no product that can be directly used for small incision.

The intransitive verb Powertrax Noslip

I'm not sure what kind it belongs to. What is called more is "traction without sliding power" Functionally, it can also be called "automatic unlocking differential". It doesn't matter what the name is, it's the same product anyway.

The working principle of PowerTrax NoSlip is just the opposite of locking differential, and the design of this product is very clever. When the locking differential works, the locking operation is carried out; When PowerTrax NoSlip is working, perform unilateral unlocking operation.

PowerTrax NoSlip works in a locked state when the vehicle goes straight, and the left and right half shafts rotate synchronously with the pinion shaft through gears. When there is a rotation angle difference between the two driving wheels (the vehicle turns or one wheel slips), PowerTrax NoSlip will release the clutch of one wheel through its mechanical mechanism and cancel its power output. When the two wheels rotate by the same angle, the clutch will be engaged again. Complete a separation and reassembly operation, and the angle difference between the two wheels shall not be less than 18 degrees. When refueling the door, the wheel with a slightly faster speed separates, and when the throttle is turned off and the engine brakes, the wheel with a slightly slower speed separates. If it is used for front axle drive, the steering system of the vehicle will tend to get out of control with acceleration and deceleration. On the road surface with high adhesion (dirt road or asphalt road), if the two driving wheels slip at the same time due to excessive driving force, the PowerTrax NoSlip clutch associated with each wheel will be disengaged and engaged for 2 to 10 times, and the two wheels will alternately obtain 100% torque output from the transfer box, and the power output state of the driving wheels is not continuous, but pulsating. The greater the ground adhesion, the more. In order to withstand this high-frequency and high-torque impact, the strength of the material used to make PowerTrax NoSlip must be particularly impact-resistant, so titanium alloy is used. However, this impact torque is not considered in the design of the original car axle, which is often unbearable.

Advantages: good versatility, simple installation, no locking noise of locking differential, and no distortion of half axle due to turning on paved road.

Disadvantages: it cannot be used for full-time four-wheel drive front axle; On the flat road with high adhesion, the traction provided is less than that of the locking differential; On the road with high adhesion, the two driving wheels slip at the same time, which has a great impact on the semi-axle and is easy to break; Installing PowerTrax NoSlip will lead to greater shift impact of automatic transmission.

Applicability: it is suitable for light off-road and low adhesion road with rear axle. It is not suitable for high adhesion road surface and high power output, and it is not suitable to be installed on the front axle (even the 4-wheel drive Cherokee is easy to damage the front axle).