Do you know about drive shafts?

Our common cargo heavy trucks are basically in the form of front and rear drive, with the output torque of the engine and transmission for rotary motion, through the drive shaft to transfer this force to the rear axle, and finally through the gears in the rear axle drive shaft, transferred to the tires to form on-wheel horsepower.

The main structure of the drive shaft is composed of shaft tube, telescopic sleeve and universal joint, which seems to be a simple structure, but in fact the force it bears is not small.

The role of the telescopic sleeve is to automatically adjust the slight distance change between the transmission and the drive axle, universal joint is to ensure the flexibility of the angle between the two axes of the transmission output shaft and the drive axle input shaft, to achieve equal angular speed transmission of the two axes.

It is worth mentioning that the longer the wheelbase of the vehicle, the length of the drive shaft will follow the extension, the middle is also have to rely on the cross-joint to adjust the angle.

Cross-joint as the name implies is a cross shaft type universal joint, consisting of cross shaft, cross bearing and flange fork and other components.

In addition, there is a tubular sealing sleeve on the outside of the drive shaft, and two grease seals are set above this sealing sleeve, so that the expansion sleeve forms a completely sealed and lubricated space.

Normally, it will not be eroded by external dust, and the grease can also increase its operating strength and play a role in rust prevention.

▎Common drive shaft faults

Fault 1: The drive shaft is loose and loud

When the vehicle starts with a heavy load or accelerates, the drive shaft emits a metal impact sound, and there is a sense of looseness. After excluding the looseness of the pot angle gear and the cylindrical gear in the rear axle, it can be concluded that the driveshaft is loose. The next step is to complete the subsequent overhaul by elimination.

Generally speaking, the wear between the spline shaft and the spline sleeve of the telescopic sleeve should not exceed 0.3mm, and the amount of looseness between the cross shaft and the bearing should not exceed 0.15mm. Once the above limit of use is exceeded, the drive shaft should be replaced.

Fault 2: The connecting bolts fall off

The above-mentioned brake failure is caused by the falling off of the connecting bolt, which causes the drive shaft to lose control. It is common for the connecting bolt to fall off on large trucks, and there are many reasons for this loosening and falling off. The main reason is hard to find, and can only rely on ordinary observation and maintenance.

The most common main reason: the drive shaft shakes violently during the operation caused by the bending of the drive shaft and the dynamic balance imbalance, which leads to the loosening of the drive shaft bolts, or when tightening the drive shaft bolts, the bolts are not tightened enough, which leads to the accumulation of rotation and loosening. Another is the sudden application of gravity, and the driveshaft bolts that are not too tight will be even more overwhelmed.

After the replacement and repair, you also have to pay attention to the size of the dynamic balance of the drive shaft, the accuracy of the drive shaft must meet the requirements of use, if the two protrusions in the installation axis can not overlap, the drive shaft ends of the universal joint cross shaft is not in the same plane, can not complete the uniform rotation, it will lead to frequent failures, it should be noted that the drive shaft is not the same horizontal plane work unit, the transmission to the rear axle is an angle.

▎Precautions for the use and maintenance of the drive shaft

If it is used normally, the standard load is transported and the road conditions are good, and the drive shaft is not easy to break. The most easily damaged is the drive shaft hanger. After long-term vibration and bumps, the rubber and bracket screws of the hanger are easy to age and loosen. Once the hanger is damaged and falls off, the longer the drive shaft is, the more damaged it will be, because the transmission shaft needs the assistance of the hanger at the critical point when adjusting the height difference between the gearbox and the rear axle.

In addition to the common faults mentioned above, there are other strange faults. Usually, the maintenance of the drive shaft must not be neglected. If necessary, the drive shaft bolts should be reinforced regularly like tightening the tire screws, especially for heavy loads.

During driving, in order to protect the half shaft, use the clutch reasonably and do not start in high gear. Severe overload working conditions, low speed, large throttle, lifting the clutch violently, not only easy to damage the drive shaft, but also easy to damage the rear axle gears, half-shafts, violent impact will also lead to damage to the drive shaft universal joint cross shaft.

There are also many truckers who will add a large iron chain to the front drive shaft of the rear axle. This is to prevent the drive shaft from breaking and falling off and getting stuck on the road. If the drive shaft breaks and hits the ground when encountering uneven road surfaces, it will directly lift the rear axle of the vehicle, and even cause the rear axle to break away under heavy load, which will seriously damage the main structure of the vehicle. It seems that adding iron chains could be a good way.

▎Summary

The drive shaft is a seemingly strong "big iron rod". Everyone thinks it is stable and durable. In fact, it also has a fragile side. If it exceeds the torque and load it can bear in daily use, it will become vulnerable.