At present, the wheel end bearings of automobiles are maintenance-free, which means that the design life should be at least equal to that of automobiles. However, design life and actual life are two different things after all. After all, the service life of bearings will change due to different operating environments. If the rule of K 15 is applied, when the working temperature of the bearing increases by 15 degrees, the service life of the bearing will be halved. For example, the design life of bearings is 200,000 kilometers, and the ideal working temperature is 30 degrees.
Then when the working temperature rises to 45 degrees, the actual life of this bearing will be reduced to 654.38+ 10,000 kilometers. Of course, there are many factors that affect the life of bearings, such as lubrication, load bearing, shaft hole fit, environmental cleanliness, sealing conditions and so on. The change of these parameters will directly affect the actual life of bearings. Therefore, in real life, we can see that the wheel end bearings of some cars will run for hundreds of thousands of kilometers, and some may be broken after 60,000 to 70,000 kilometers.
Why is the automobile wheel end bearing maintenance-free?
Ball bearings and needle bearings are rolling bearings. Compared with the sliding bearing (bearing bush) used on the crankshaft, the amount of wear produced during work is greater, because the friction surface of the sliding bearing will be isolated by pressure oil (so-called oil film) during work, and the oil plays the role of supporting and separating two frictional metal surfaces. Therefore, the wear is very low, as long as the oil is changed regularly, because running in the environment of high temperature and high load (impact when the piston moves up and down) has a great influence on the lubricating medium oil.
Therefore, it is necessary to replace the lubricating medium regularly at the parts where the sliding bearing (hydrostatic pressure) is used, and it is not necessary to replace the bearing bush (the burning of the bearing bush is accidental). But the wheel end bearing of a car is different. The running condition of family cars is single, the load is not large (although family cars are generally more than one ton, they can be completely ignored on the mechanical level), and the rotation speed is low. Although the current peak engine speed can approach 6000 rpm, it exceeds 1000 rpm after passing through the gearbox and tail gear (transmission ratio = gear ratio * tail gear ratio).
Therefore, the running environment of wheel end bearing is far more ideal than crankshaft bearing, so the design life of wheel end bearing is at least 6.5438+0.5 million kilometers. Of course, design life and actual life are two different things. The design life of an engine is generally1.5-25 thousand kilometers, but the actual life can even reach several million kilometers. Manufacturers are conservative about the design life of products. In other words, as long as there is no problem with the sealing of the wheel end bearing, the internal grease can maintain its lubricating ability for a long time.
Therefore, the wheel end bearing of an automobile does not need maintenance, because disassembly will inevitably destroy the seal, which is similar to the fact that many waterproof watches lose their geomantic omen when they change their batteries. After all, the small wheel end bearing is different from the big truck, and the load is also very different. Therefore, the bearings used for large trucks (generally needle rollers, the linear load is stronger than the point load) also need to be disassembled and buttered regularly. But the wheel end bearing of the car is light and sealed. As long as it is not subjected to violent impact, the bearings of the original car generally do not break.
What will cause damage to the wheel end bearing?
The main reasons that may affect the service life of rolling bearings are as follows
1. Operating temperature.
2. Clean environment.
3. Load (impact).
Lubrication.
Generally, you don't need to care too much about the running temperature of a wheel end bearing, because a car will be tested according to the market environment before it is put on the market, and secondly, the speed of the wheel end bearing of the car can be controlled (within 2000 rpm, pay attention to the wheel end rather than the engine speed), so it is difficult to break through the upper temperature limit when running. Generally speaking, environmental cleaning and lubrication have little influence on automobile bearings. After all, the relatively sealed design can still isolate most of the dust and moisture. It should be noted that after wading, try to run for a period of time before turning off the fire and evaporating water as much as possible.
After all, water may seep into the bearing, leading to emulsification of lubricating oil (emulsification is the most inevitable state change after oil contacts water), thus losing its lubricating ability. In fact, the most likely cause of bearing damage is collision, for example, the car often hits the pit, or frequently pushes against the curb, and the tire side collides with a hard object. These methods are most likely to cause damage to the wheel end bearing. In the final analysis, wheel end bearings are most afraid of hard impact, which easily leads to deformation of bearings and balls.
This is also the reason why the engine crankshaft chooses sliding bearing (bearing bush) instead of rolling bearing. Rolling bearings are very afraid of impact, and the lubrication effect of grease is very poor under high temperature and high speed conditions. It is not because of the lame shape of the crankshaft that the rolling bearing cannot be sleeved. Now many friends have this wrong cognition. In fact, rolling bearings can be divided into integral bearings and split bearings. As shown in the above picture, it is actually a split bearing, which can be divided into upper and lower parts and can be used for various rotating shafts with strange shapes. Therefore, the crankshaft of automobile engine doesn't need rolling bearings, not because it can't be sleeved, but because it can't bear the frequent up-and-down impact of the piston at high speed, and it is not easy to solve the lubrication problem.