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The Reasons And Measures For Burnout Of CAM Bearing Sleeve Are Illustrated With Examples

The Reasons And Measures For Burnout Of CAM Bearing Sleeve Are Illustrated With Examples

2021-01-14

1. Specific phenomenon of burnout of CAM bearing bearing sleeve

The phenomenon after the burnout of the CAM bearing sleeve is mainly as follows: the inner hole of the bearing sleeve is burnt, the outer diameter is blackened, the bearing sleeve is elongated along the axial direction, the two ends of the bearing sleeve and the positioning ring are rubbed and burned, the bearing seat and the camshaft are blackened and deformed by heat, and some even cause the end bearing damage.

2. Cam bearing bearing sleeve burnout reason analysis

Usually, the main reasons for bearing sleeve damage in a short time are:

(1) improper clearance between shaft and bearing sleeve, too small or too large;

(2) bearing sleeve loss of oil or lubrication is not smooth;

(3) lubricating oil pollution or excessive scratches from foreign impurities;

④ bearing overload.

Check according to the above possible causes of damage.First, part size inspection.The parts in the accident have been damaged or seriously deformed after friction and high temperature, so the size cannot be rechecked. No abnormality was found in the inspection of the inventory parts, and all the sizes meet the requirements of the drawings.It shows that the assembly parts should be qualified, and the clearance between the shaft and the bearing sleeve is no problem.

Second, check the camshaft bearing seat shaft lubricating oil channel is smooth, the parts have no dry friction trace of lost oil, other friction pairs have no lubricating oil pollution or scratches trace of foreign bodies, lubricating oil oil is normal.

Third, whether there is overload situation.Diesel engine is an old product, which has been produced for several decades and has nearly a thousand sets. They all operate normally. If the overload reason is common, there will be many cases of camshaft bearing housing bearing sleeve burning out.However, few similar accidents have occurred since the product began to be produced, indicating that the accident was not caused by bearing overload.

Fourth, let's take a look at the camshaft bearing housing structure.

When the diesel engine works, the camshaft 1 rotates clockwise from right to left, and the camshaft gear 7 is helical gear, which produces axial force from left to right and drives the camshaft 1 and positioning sleeve 2 to move from left to right

Potential.We suspect that the positioning sleeve 2 is pressed on the end face of the bearing seat 4 and the bearing sleeve 5, and the oil outlet on the left side of the bearing sleeve is closed, so that the lubricating oil entering from hole A cannot be discharged smoothly from the left side of the bearing sleeve, and the heating of the lubricating oil causes the bearing sleeve to burn out.Inspect the end faces of positioning sleeve 2, bearing seat 4 and bearing sleeve 5 for really serious friction burn marks.

For this reason, a "cross" oil drain groove is added on the contact surface of positioning sleeve 2 and positioning ring 6. At the same time, when installing the bearing seat, check and ensure that the clearance around the sleeve and camshaft is evenly and reasonably distributed.To the end of the bench test, the bearing pedestal worked normally, and a period of time after the test of the 320 diesel engine did not happen similar accidents, the problem seems to be solved.

But soon another bench ma chine camshaft bearing burn accident again, following hot on the heels of a diesel engine bench next to the first Ⅰ column CAM shaft bearing and burn out, suggesting that previously suspected lubricating oil discharge is not smooth, cause the bearing sleeve fever burn out, must find another reason.

Comparing the two burnt out bearing sleeves of diesel engines, it is found that the severely burned part of the inner hole surface of the bearing sleeve is located on the same side surface of the cloth oil groove with the same orientation (two cloth oil grooves for each bearing sleeve) and the orientation of the cloth oil groove after the bearing sleeve is installed on the bearing seat is also basically the same .Thus, it is revealed that whether the position of the oil groove is unreasonable and the oil film cannot be formed in the bearing sleeve force direction is caused by it?Therefore, the bearing sleeve force and the formation of oil film are analyzed and checked.

The analysis shows that the distribution oil groove is set in the high pressure area with the minimum oil film thickness. When the oil enters the oil groove from the HMAX side and reaches the distribution oil groove area, the pressure is released due to the sudden increase of the space, and the oil film is destroyed. The camshaft directly contacts the bearing sleeve under the action of heavy load, resulting in the camshaft and the bearing sleeve friction heating and burning out.

Check the relevant drawings and files, there is no requirement on the installation orientation of bearing sleeve oil groove, and the installation workers at that time have no awareness of the installation orientation of bearing sleeve oil groove, so they install it at will.

There are two cloth oil grooves on the inner surface of the bearing sleeve with a distribution of 180°, and the width of the oil grooves is about 26°. If installed at will, there will be a probability of more than 30% that the cloth oil grooves will fall on the force bearing area.There has been no or very few bearing sleeve burnout accidents before, it is estimated that there are some verbal requirements uploaded down before, or the installation workers have a fixed installation habit just when the oil groove falls into the high pressure area with the smallest oil film, which is unknown.After the installation workers are replaced, the installation habits change, leading to frequent bearing sleeve burnout accidents.

Drawings combined the analysis above, the rules do not explicitly bearing oil groove in the installation position of the bearing, bearing sleeve cold fashionable cloth groove bearing is arbitrary, when oil cloth at the minimum oil film thickness in regional areas (high load), the oil film is destroyed, which may lead to a CAM shaft and the bearing sleeve friction heat and burn out.

3. Improvement measures

The first Ⅰ inline diesel engine camshaft bearing analysis and the first Ⅱ diesel engine camshaft bearing , is similar to the first Ⅰ diesel engine camshaft.To this, we can definitely say that the first Ⅰ diesel engine camshaft bearing sleeve bearing burning accident had been installed in high load bearing sleeve cloth tank area.

According to the force analysis of the camshaft in three installation states, a bearing sleeve oil groove arrangement Angle that can simultaneously meet the three installation states was selected, such as the low oil pressure area in the range of 30° as shown in Fig. 7. Relevant drawings and files were modified to clarify the installation requirements of bearing sleeve oil groove.


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