Fault Analysis and Countermeasures of Overrunning Clutch in Domestic ZL40/50 Planetary Transmission

The domestic ZL40/50 planetary transmission adopts a roller overrunning clutch. This technology originated from imported loaders from abroad in the 1950s and 1960s and was later absorbed and improved by domestic experts. Its initial design concept was to meet the working conditions of a four-ton loader. After achieving domestic production, it was also applied to the transmission system of five-ton loaders. With the continuous introduction of new models of five-ton loaders in recent years, especially the ZL50G loader model, the overall performance of the machine has been greatly enhanced. Therefore, for the transmission system equipped with the domestic ZL40/50 gearbox, it has become extremely vulnerable. This can be seen from the common tearing of the torque converter's elastic plate at the very beginning. After increasing the thickness or quantity of the elastic plate, the overrunning clutch, which has lost its better buffering protection, has increasingly poor adaptability to working conditions. The load-bearing capacity of the rollers is significantly insufficient, and early faults occur frequently, showing an increasing trend year by year.

Common fault manifestations of the overrunning clutch assembly: slippage and seizing.

Its failure mode is manifested as follows:

1. Spring and top pin failure;

2. The cage is damaged

3. Arc indentations appear prematurely on the working plane of the inner ring CAM.

4. Excessive wear of the rollers.

At present, the domestic ZL40/50 transmission adopts a roller type overrunning clutch. According to its specific structure, it can be further divided into two types: the structure with a cage and the structure with a spring pin. Among them, those adopting the cage structure include Liugong, XCMG and Lingong, while those using the spring pin structure include Hangzhou Gear and XCMG.

The following is some analysis on its failure forms:

1. Spring pin structure overrunning clutch

The roller type overrunning clutch with a spring pin structure typically adopts 20 rollers with a diameter of Φ15, 40 small springs and pins. The wedge Angle of the rollers is generally positioned at around 6.8 to 7.2 degrees.

Due to space limitations, this structural form cannot ensure that the installation Angle axes of the spring and the top pin pass through the center of the roller. The end of the top pin and the roller undergo eccentric wear, and at the same time, the top pin is subjected to a force from the roller that deviates from the axis. During frequent squeezing and pushing processes, the top pin and the 40 small hole openings of the CAM undergo scraping friction. If the hole opening is not blunted well or the burrs are not removed thoroughly, it is easy for the mating surface of the top pin to be damaged, causing jamming. This will result in uneven spring thrust when the rollers are wedged tightly, causing the rollers to tilt and easily leading to roller jamming, which is commonly referred to as overrunning clutch seizing.

Due to the very small diameter of the 40 small springs, which is only Φ 0.3mm, when fatigue strength failure occurs, the top pins will all be embedded in the small holes and fail. Furthermore, when the cleanliness of the oil in the transmission is very poor, dirt entering the CAM hole cannot be discharged, causing the spring to fail and get embedded in the hole along with the top pin.

During the frequent overtaking and engagement of the overrunning clutch, due to the effect of centrifugal force, there is impact and friction between the rollers and the sharp corners of the CAM. The roller surface is prone to injury, and the sharp corners of the CAM are prone to damage. Due to the damage on the surface of the rollers, the working surface of the CAM bearing will be damaged when wedging. At the same time, the wear of the rollers causes the wedge Angle to continuously increase, gradually leading to slippage during overtaking.

Moreover, the oil drainage hole at the end of the top pin of the overrunning clutch is prone to damage and blockage, causing the top pin to form a cylinder effect in the small hole of the inner ring, which makes it unable to work normally and thus leads to failure.

The advantage of the spring pin structure is that it has a low requirement for synchronization during the wedging operation, and the spring pin has a certain automatic compensation capacity for the wear of the roller. The disadvantage is that the number of rollers carried during the actual wedging operation is relatively small, and the load-bearing capacity is relatively low.

2. Overrunning clutch with cage structure

The roller-type overrunning clutch with a cage structure typically uses 20 Φ13 rollers, with a wedge Angle of approximately 7°. From the perspective of theoretical calculation, under the same working condition of 20 rollers being wedged tightly, due to its small diameter, its strength is not as good as that of rollers with a diameter of Φ15. However, the cage structure has a major advantage: good synchronization during operation and a large number of rollers actually combined for work. Therefore, the actual load-bearing capacity may be even higher than that of the spring pin type. The realization of its synchronization is as follows: During the loading operation of the loader, the inner and outer rings of the clutch rotate in the same direction; When under heavy load, the inner ring's rotational speed rapidly decreases due to the resistance transmitted from the external load. Under the forced drive of the cage, the 20 rollers simultaneously enter the wedging work.

From the synchronization, it can be seen that the cage structure has very high requirements for the following two points: (1) the equal division accuracy, strength and heat treatment deformation of the cage; (2) the dimensional accuracy of the rollers

If the equal division accuracy is not high, the deformation is large or the size of the rollers is inconsistent, it will affect the number of rollers entering the wedging work. During the overtaking clutch process, the cage is subjected to frequent impacts. If stress exists simultaneously, it is particularly prone to damage and must have a relatively high strength.

Whether it is a spring pin structure or an overrunning clutch with a cage structure, the working surface of the inner ring CAM is required to have a certain depth of hardened layer to ensure hardness. The inner ring CAM is generally made of bearing steel GCrl5 material and undergoes carburizing and quenching treatment to 59 to 64HRC. If the carburized layer is too shallow and has too low hardness, arc-shaped indentations are likely to appear prematurely. If the carburized layer is too deep, although it increases the hardness, the material is prone to quenching cracking. Therefore, the requirements for heat treatment processes are relatively high.

Based on the above analysis, for the roller type overrunning clutch with a spring pin structure, the following methods can be referred to for improvement and enhancement:

"a. Change the structure of the inner ring CAM so that the center of the top pin and the spring pass through the center of the roller as much as possible. When the roller is in the overtaking state, it comes into contact with the plane of the protruding part of the CAM, eliminating the phenomenon that the sharp corners of the CAM in the original structure are prone to damage. The structure is as follows:

"b. Adjust the heat treatment process flow. Increase the hardness of the carburized layer on the CAM plane to the upper limit of 64HRC as much as possible to enhance the load-bearing capacity.

"c Control the cleanliness of the box to ensure the cleanliness of the oil.

The improved analysis proposed above only has 苁 hooks? Is the chewing container lifted? An Zhongxie? "∩ How much punishment is imposed??" "Huangjiao Abscess?" The old jurisdiction 饩銎 su xing se ji Σ si rong nai shi si si sha song yi qiang shao pa du lu? Is there a tendency to be overly frugal? "Xian Kang Mou?" Watering the mound, scraping off the sword hilt, and cutting and planting by the ladle 岵 wild sprout blowing the sword?? Chew the ultimatum to 鞒? Youdaoplaceholder0 <? Tomb 鲋? Do you want to hire a man to flirt with 嬖? "Maogao's hair is worn off?" What's the purpose? κ Jian? Gan Jian R yun braised soldier fly ソ qiang ji jie jian jian ⒄ bone tense Γ? Youdaoplaceholder0 type? "Wa?" Youdaoplaceholder0? In Jiangmu Street, is there a certain person who has fallen from Jiangmu? Chewing an ultimatum can ruin one's health? lt; BR>1 A ratchet overrunning clutch relying on magnetic reset pawl (continued on page 45)

The ratchet overrunning clutch with magnetic reset pawl is the latest product launched by Ketai Transmission Technology (Tianjin) Co., LTD. This technology was originally developed to address the reliability issue of overrunning clutches in oil pumping units in the petroleum industry. The advantages of this type of overrunning clutch are: it can transmit a large torque, and the torque value can be adjusted and designed according to the working conditions. The suction force of the permanent magnet can ensure the meshing of the pawl and the ratchet, eliminating the metal fatigue problem caused by spring return and ensuring the reliability of the pawl during long-term operation. The damage of a single pawl will not affect the reliability of the clutch. At the same time, the clutch is not sensitive to the cleanliness of the oil. As the working time increases, the synchronization of the engagement between the pawl and the ratchet improves, and the torque transmission capacity also increases accordingly.

Shortcoming: To ensure the synchronization of meshing, the error control of processing indexing is required to be particularly high. There is a certain degree of impact and noise during operation, which requires a relatively high impact strength of the bearings. Therefore, two cylindrical roller bearings are adopted for support in this structural design. As the usage time increases, the synchronization of the engagement between the pawl and the ratchet will gradually improve, and the load distribution will become more uniform.

Judging from the current usage of this product in the secondary market (accessory market), its lifespan will not be less than 6,000 hours.

2. HRD Double Cage type wedge Overrunning Clutch (DC184180C)

The HRD double cage type wedge overrunning clutch DC184180C is produced by Xiamen Hengruida Machinery Co., LTD. This clutch is a special working condition design based on the current early failure situation of the roller type overrunning clutch. On the basis of maintaining the original overrunning assembly (two shafts) universal parts, the inner ring CAM is changed to the inner ring, making the structure simpler and more reasonable. This clutch adopts a double cage structure, precisely positioning 44 wedges to achieve full synchronization and increase the torque to over 10,000 N.m. Among them, the wedge block is made of SKD11 material through nano-processing, with a dimensional accuracy of 3,000 nanometers. The working surface adopts a logarithmic helical curve to ensure its long service life. After usage analysis, its service life is over 8,000 hours. There are the following two major characteristics:

● Full synchronization

All the wedges of the clutch are forcibly positioned by double isolation rings. When meshing occurs simultaneously, their positions can be precisely maintained, allowing each wedge to be controlled and forcibly subjected to an appropriate share of the working load. This prevents individual wedges from reversing under load, causing the load to be transferred to adjacent wedges and resulting in asynchrony.

● Pre-pressure:

The preload is accomplished by the spring belt acting on the wedge, which maintains force contact with the inner and outer raceways to ensure meshing when necessary.

Compared with the traditional roller type overrunning clutch, it has the following advantages:

The wedge block has almost no friction beyond the working condition

The 44 wedges remain fully synchronized

It can ensure a constant self-locking Angle

The force is uniform and the operation is stable

It can withstand large torque and has a long service life

Under the same working conditions, the overall fuel consumption of the machine is lower.

Fault Analysis and Countermeasures of Overrunning Clutch in Domestic ZL40/50 Planetary Transmission

Zhao Lijuan and Yang Xiaobing from XCMG Research Institute

The domestic ZL40/50 planetary transmission adopts a roller overrunning clutch. This technology originated from imported loaders from abroad in the 1950s and 1960s and was later absorbed and improved by domestic experts. Its initial design concept was to meet the working conditions of a four-ton loader. After achieving domestic production, it was also applied to the transmission system of five-ton loaders. With the continuous introduction of new models of five-ton loaders in recent years, especially the ZL50G loader model, the overall performance of the machine has been greatly enhanced. Therefore, for the transmission system equipped with the domestic ZL40/50 gearbox, it has become extremely vulnerable. This can be seen from the common tearing of the torque converter's elastic plate at the very beginning. After increasing the thickness or quantity of the elastic plate, the overrunning clutch, which has lost its better buffering protection, has increasingly poor adaptability to working conditions. The load-bearing capacity of the rollers is significantly insufficient, and early faults occur frequently, showing an increasing trend year by year.

Common fault manifestations of the overrunning clutch assembly: slippage and seizing.

Its failure mode is manifested as follows:

1. Spring and top pin failure;

2. The cage is damaged

3. Arc indentations appear prematurely on the working plane of the inner ring CAM.

4. Excessive wear of the rollers.

At present, the domestic ZL40/50 transmission adopts a roller type overrunning clutch. According to its specific structure, it can be further divided into two types: the structure with a cage and the structure with a spring pin. Among them, those adopting the cage structure include Liugong, XCMG and Lingong, while those using the spring pin structure include Hangzhou Gear and XCMG.

The following is some analysis on its failure forms:

1. Spring pin Structure Roller type overrunning clutch: The spring pin structure roller type overrunning clutch typically uses 20 rollers with a diameter of Φ15, 40 small springs and pins. The wedge Angle of the rollers is generally positioned at around 6.8 to 7.2 °.

Due to space limitations, this structural form cannot ensure that the installation Angle axes of the spring and the top pin pass through the center of the roller. The end of the top pin and the roller undergo eccentric wear, and at the same time, the top pin is subjected to a force from the roller that deviates from the axis. During frequent squeezing and pushing processes, the top pin and the 40 small hole openings of the CAM undergo scraping friction. If the hole opening is not blunted well or the burrs are not removed thoroughly, it is easy for the mating surface of the top pin to be damaged, causing jamming. This will result in uneven spring thrust when the rollers are wedged tightly, causing the rollers to tilt and easily leading to roller jamming, which is commonly referred to as overrunning clutch seizing.

Due to the very small diameter of the 40 small springs, which is only Φ 0.3mm, when fatigue strength failure occurs, the top pins will all be embedded in the small holes and fail. Furthermore, when the cleanliness of the oil in the transmission is very poor, dirt entering the CAM hole cannot be discharged, causing the spring to fail and get embedded in the hole along with the top pin.

During the frequent overtaking and engagement of the overrunning clutch, due to the effect of centrifugal force, there is impact and friction between the rollers and the sharp corners of the CAM. The roller surface is prone to injury, and the sharp corners of the CAM are prone to damage. Due to the damage on the surface of the rollers, the working surface of the CAM bearing will be damaged when wedging. At the same time, the wear of the rollers causes the wedge Angle to continuously increase, gradually leading to slippage during overtaking.

Moreover, the oil drainage hole at the end of the top pin of the overrunning clutch is prone to damage and blockage, causing the top pin to form a cylinder effect in the small hole of the inner ring, which makes it unable to work normally and thus leads to failure.

The advantage of the spring pin structure is that it has a low requirement for synchronization during the wedging operation, and the spring pin has a certain automatic compensation capacity for the wear of the roller. The disadvantage is that the number of rollers carried during the actual wedging operation is relatively small, and the load-bearing capacity is relatively low.

2. Overrunning clutch with cage structure

The roller-type overrunning clutch with a cage structure typically uses 20 Φ13 rollers, with a wedge Angle of approximately 7°. From the perspective of theoretical calculation, under the same working condition of 20 rollers being wedged tightly, due to its small diameter, its strength is not as good as that of rollers with a diameter of Φ15. However, the cage structure has a major advantage: good synchronization during operation and a large number of rollers actually combined for work. Therefore, the actual load-bearing capacity may be even higher than that of the spring pin type. The realization of its synchronization is as follows: During the loading operation of the loader, the inner and outer rings of the clutch rotate in the same direction; When under heavy load, the inner ring's rotational speed rapidly decreases due to the resistance transmitted from the external load. Under the forced drive of the cage, the 20 rollers simultaneously enter the wedging work.

From the synchronization, it can be seen that the cage structure has very high requirements for the following two points: (1) the equal division accuracy, strength and heat treatment deformation of the cage; (2) the dimensional accuracy of the rollers

If the equal division accuracy is not high, the deformation is large or the size of the rollers is inconsistent, it will affect the number of rollers entering the wedging work. During the overtaking clutch process, the cage is subjected to frequent impacts. If stress exists simultaneously, it is particularly prone to damage and must have a relatively high strength.

Whether it is a spring pin structure or an overrunning clutch with a cage structure, the working surface of the inner ring CAM is required to have a certain depth of hardened layer to ensure hardness. The inner ring CAM is generally made of bearing steel GCrl5 material and undergoes carburizing and quenching treatment to 59 to 64HRC. If the carburized layer is too shallow and has too low hardness, arc-shaped indentations are likely to appear prematurely. If the carburized layer is too deep, although it increases the hardness, the material is prone to quenching cracking. Therefore, the requirements for heat treatment processes are relatively high.

Based on the above analysis, for the roller type overrunning clutch with a spring pin structure, the following methods can be referred to for improvement and enhancement:

"a. Change the structure of the inner ring CAM so that the center of the top pin and the spring pass through the center of the roller as much as possible. When the roller is in the overtaking state, it comes into contact with the plane of the protruding part of the CAM, eliminating the phenomenon that the sharp corners of the CAM in the original structure are prone to damage. The structure is as follows:

"b. Adjust the heat treatment process flow. Increase the hardness of the carburized layer on the CAM plane to the upper limit of 64HRC as much as possible to enhance the load-bearing capacity.

"c Control the cleanliness of the box to ensure the cleanliness of the oil.

The improvement analysis proposed above can only slightly increase the service life of the overrunning clutch on the current basis, but cannot fundamentally solve the problem of its insufficient load-carrying capacity. From this, we can seek other types of overrunning structures with stronger load-bearing capacity: It is not difficult to see from the design manual that, in addition to the most common roller structure, overrunning clutches also have other structural types. Such as ratchet pawl type, wedge type. The following is a brief introduction to two types of overrunning clutches that have great development potential and are expected to replace the roller type.

1. A ratchet overrunning clutch that relies on magnetic force to reset the pawl

The ratchet overrunning mechanism roller overrunning clutch with magnetic reset pawl generally adopts 20 Φ13 rollers, and the wedge Angle is about 7°. From the perspective of theoretical calculation, under the same working condition of 20 rollers being wedged tightly, due to its small diameter, its strength is not as good as that of rollers with a diameter of Φ15. However, there is a maximum for the cage structure