1 Overview of limited slip differential

The differential is one of the important parts of the automobile drive axle, as shown in Figure 1, it is equivalent to a torque divider, which transmits the input torque to the left and right drive half shafts, and allows the two half shafts to rotate at different speeds .

The main problem faced by the current differential is how to ensure that the vehicle can conduct power stably under the following three conditions to ensure a good passability of the vehicle.

(1) Ensure the normal operation of the vehicle under normal conditions (road), and avoid reducing the handling stability of the vehicle due to problems such as uneven road or different tire pressure.

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(3) When encountering muddy or soft roads with low adhesion coefficient, it can provide power in time to get rid of difficulties.

Ordinary differentials can only meet the first two conditions mentioned above. In case three, when one wheel falls into a slippery road, the evenly distributed torque characteristic of the differential makes it a short-term obstacle to normal driving on muddy roads. plate. With the continuous development of the automotive field, more and more researches on differentials have been made in the machinery industry. In order to make up for the shortcomings of traditional differentials, limited-slip differentials have emerged and are widely used in off-road vehicles.

The limited slip differential is an improvement of the ordinary differential, which means that the difference in the speed of the driving wheels on both sides can fluctuate within a certain range, so as to ensure that the vehicle is in a straight line, turning, or encountering a muddy road. A new differential that can get enough driving force. At present, limited slip differentials mainly include active control, passive control (including torque induction and speed induction) and manual control.

Manual control refers to changing the torque distribution ratio of the middle differential or half-axle differential through the driver's manual operation, mainly various manual differential locks [1].

In the passive control differential, the torque-sensing type determines the differential limit torque method according to the input torque. There are mainly variable transmission ratio differentials and Torson differentials; the speed-sensing type is with the limit The difference in the rotational speed of the left and right axle shafts of the slip differential passively limits the differential differential.

The active control differential is a controllable differential based on the passive control differential. The active control differential can control the torque in real time according to the contact between the wheels and the road surface.

The limited slip differential can ensure that the vehicle meets the driver’s requirements for passability, power, and safety during the driving process, guarantees a good running state of the vehicle, and to a certain extent solves the problem of The tires are slipping and idling, and the traditional differential cannot transmit enough power to the other wheel, resulting in the dilemma that the driving force generated by the vehicle cannot drive the vehicle.

This article mainly takes the domestic and foreign demand for limited-slip differentials and the current research status as the background, and conducts research and theoretical comparative analysis on the variable transmission ratio differentials and the Torson differentials in the limited-slip differentials. Provide reference for further research work.

2 Torson differential

The Torson differential completes the differential function through a unique and sophisticated mechanical design and effectively improves the ultimate grip. The internal structure of the Torson differential is very different from the traditional differential. Its core component is a special gear meshing system, including left and right half shafts, helical gears, left and right half shaft transmission worms, spur gears, differential housings, etc. The working principle of the Torson differential is realized by using the driving characteristics between the worm gear and the worm. When the worm gear is rotated, the worm can be easily driven. On the contrary, when the gear is rotated, the worm cannot be driven. A set of synchronous gears are welded to both ends of the helical gear to complete the basic differential function, as shown in Figure 2. Show.

(2) When turning, perform differential operation according to the speed of the wheels on both sides to provide power for the wheels on both sides to ensure the unequal distance travel of the wheels.

When the vehicle turns (right), in order to ensure the normal driving of the vehicle, the rotation speed of the left wheel needs to be higher than that of the right wheel. At this time, the left wheel drives the left worm to accelerate rotation, and the corresponding gear rotates accordingly. In addition, because the rotation speed of the right worm is slow, there is a rotation speed difference with the housing. That is to say, from the perspective of the housing, the right worm is reversing, so the right helical gear will rotate in the reverse direction. Synchronous gears fixed at both ends will ensure that the speed of the helical gears is the same at all times, which brings about a precise proportional wheel differential speed.

When the tire encounters a slippery road, the wheel on the slippery side starts idling, and the speed of the helical gear will immediately increase. With the help of the synchronization gear, the other side gear will synchronize the high speed to the side gear, but the side helical gear cannot The speed continues to be transmitted to the left worm (the worm wheel cannot drive the worm), so the entire mechanism is stuck. The left and right wheels return to the same driving speed, and a large amount of torque is output to the high-grip side again, and the body becomes stable and starts to drive normally.

Due to torque load considerations, three sets of synchronous helical gears are usually assembled. Other differential structures require a short response time before being completely locked. Torson’s full-time meshing design achieves even slight and short grip. Any imbalance will be locked quickly.

3 Variable transmission ratio limited slip differential

In recent years, different scholars have improved the specific structure of the limited slip differential, among which the variable transmission ratio differential (variable ratio differential) is an improved form of the limited slip differential. The improved variable transmission ratio differential can determine the transmission ratio change rule according to the actual situation within the entire circle of the planetary gear, relying on the barrier effect of the variable transmission ratio transmission to increase the locking coefficient, and does not change the overall structure of the drive axle , And finally realize the differential speed, changing the dilemma that ordinary differentials cannot transmit power on slippery roads. At the same time, the problem of the limited-slip differential transmission ratio change range is small, the change period is short through the variable transmission ratio differential has been further solved.

Because the speed ratio of the traditional variable transmission ratio differential is changed to one cycle, the transmission ratio is difficult to meet the requirements of the vehicle for off-road performance. Zhong Wang Xiaochun et al. proposed a three cycle variable transmission ratio limited slip differential, which greatly improves The traction of the vehicle is reduced.

Zhongjia Jumin proposed a new transmission form, which breaks through the limit of the number of teeth and the circumferential pitch, and makes the ratio of the number of teeth of the planetary gear and the half shaft gear to 1:2, which can maximize the amplitude of the change of the transmission ratio (to ± 40%), this new transmission form can obtain the maximum transmission ratio variation range, thereby obtaining a large locking coefficient. The test results show that the theoretical and actual locking coefficients can reach 2.33 and 3.15, and the off-road performance of the vehicle is significantly improved.

Zhong Zhang Xueling proposed a new type of non-circular planetary gear differential, which automatically adjusts the output torque distribution through the transmission gear ratio effect to achieve anti-skid, thereby improving the cross-country passability of the vehicle. In addition, the author designed a variety of differential transmission schemes based on the proposed new-type inter-axle non-circular planetary gear differential structure for selection. The experiment has been completed in the differential prototype of a certain model, and the result proves the new differential. The transmission torque of the original differential is increased by 1.7 times.

Zhong Jia Jumin proposed a new type of non-circular planetary gear differential for off-road vehicle transfer cases. The non-circular central gear has the same shape, the planetary gears have the same shape, and the phase difference is 90°. Three sets of double planetary gears are used to achieve load sharing. , It can realize the variable ratio distribution of the torque of the two output shafts, which is equivalent to increasing the locking coefficient of the differential, which is expected to improve the cross-country passability of the vehicle.

4 Comparative analysis

The Torson differential has no time delay in the process of realizing the differential, and the response is fast. When the differential needs to be realized, the driving wheel produces a torque difference. The Torson differential can respond quickly in a short time and change the torque to change Adjust the wheel difference. In addition, compared with the traditional differential, the Torson differential does not have a multi-disc clutch, so there is no maintenance problem, and it is reliable and durable. However, it needs to be clear that the processing accuracy and manufacturing process requirements of the Torson differential are very high, so its manufacturing cost is also very high, and it can only be used on mid-to-high-end models at present. In addition, the weight of the differential is relatively large, which affects the center of gravity and acceleration speed of the vehicle to a certain extent, and is less used in China.

Compared with Torson differentials, variable transmission ratio differentials have been widely studied in China. Because their manufacturing costs are relatively easy to accept compared with Torson differentials, and to a certain extent, it can realize the difference of off-road vehicles. Therefore, in the application of domestic vehicles, the variable transmission ratio limited slip differential is relatively widely used.

5 Conclusion

This article analyzes the practical problems that differentials generally need to be solved, gives the classification of limited slip differentials, and uses Torson differentials and variable transmission ratio limited slip differentials as examples to carry out structural analysis and principle explanations. Finally, a comparative analysis of the two limited slip differentials is carried out. It is believed that with the development of the automotive industry, the design and development of automotive differentials will also be further developed.