Motor Technology Design Flaws: Where Is It Reflected?


Posted May 24, 2019 by Aggisxjetl

The Eaton Char-lynn Motor has a detailed analysis to see how much it affects.
 
motor technology is an important indicator of the performance of automobiles. Most consumers who choose to import and joint venture models value foreign advanced motor technology. In fact, Mercedes-Benz BMW has a fatal flaw in the motor of the world* car. The Eaton Char-lynn Motor has a detailed analysis to see how much it affects.

  

The process of producing power from the motor is carried out in the cylinder. First, the cylinder sucks the mixture (air containing fuel) or air through a negative pressure, compresses the gas into the combustion chamber, ignites the mixture to cause thermal expansion, and the high pressure generated by the expansion pushes the piston downward to provide power to the automobile. If there is a gap in the cylinder, during the compression and combustion of the mixture, part of the compressed and burned gas can be squeezed out of the gap, which accelerates the cylinder pressure and reduces the force pushing the piston.

  

1. Is there really a gap in the cylinder?

  

The cylinder is a cylinder with the top and surrounding cylinders sealed, and the bottom piston structure is "sealed" by the piston ring. The piston ring is an open ring. For the convenience of installation and to prevent thermal expansion, the piston ring must have a gap that can be extended. The piston ring will not be stuck due to the increase of the outer diameter during thermal expansion. The gap is about 0.1-0.2. Millimeter. In order to reduce the "leakage" caused by the piston ring notch, the designer used the corresponding leak proof design.

  

(1) blind cavity design

  

Since the piston ring has a gap, it will leak, and the designer uses a double-ring (diesel is three-ring) design to reduce gas leakage. Specifically, two piston rings are installed on the piston, and the openings of the two piston rings are shifted by 180°, and the gap between the two piston rings is called a blind cavity. Although the gas can still leak through the gap of the upper piston ring notch - the blind cavity - the lower piston ring gap, the leakage has been significantly reduced, so the current motor basically adopts this design. When the motor is working, the piston ring can rotate with the up and down movement. The opening of the two piston rings can be less than 180°. If it is too close, the effect of the blind cavity will be affected and the gas leakage will increase.

  

(2) Oil seal design

  

It is generally believed that motor-filled oil is only used to lubricate parts. Textbooks and manufacturers say that even oil-changing mechanics emphasize the lubrication of oil when selling *oil. In fact, the role of oil is not just that. The gap between the piston ring and the gap between the piston ring groove can cause gas leakage, and the designer is to close the gaps and gaps by the viscous nature of the oil. A fluid mechanics concept is introduced here: non-Newtonian fluids. The viscosity of the fluid and the stress (shear force) of the fluid are correlated. Designers use the viscosity of the oil to close the gaps and gaps in the piston by utilizing the principle of non-Newtonian fluids to prevent gas leakage.

  

There have been companies that used non-Newtonian fluids to design motor additives (remember that many years ago, the United States imported "Licardo") added very fine metal particles to the oil to increase the sealing performance of the gap, thereby saving fuel and Improve the purpose of power. Consumers can also use this principle to select a higher viscosity oil (such as W30), and can also improve the power output of the motor under the premise of ensuring the lubrication function.

  

2. What impact does the gap affect?

  

A four-cylinder (four-stroke) motor is widely used at present, and it is used as an example to analyze how the piston ring notch affects the work of the motor.

  

Analyze in the order of 1-3-4-2 firing. The working sequence of the cylinder is “intake-compression-work-exhaust”, each stroke pushes the crankshaft to rotate 180°, and each of the four cylinders is cycled once (that is, four strokes per cylinder) to push the crankshaft to rotate 720° (two ring). From the perspective of the pressure inside the cylinder, the notch mainly affects the compression and the work stroke: when the stroke is larger than the pressure outside the notch, the in-cylinder gas leakage can occur; during the working stroke, the pressure inside the cylinder is always higher than the gap. Pressure, so there is gas leakage throughout the journey.

  

(1) Degree and time of gap leakage

  

When the stroke is reduced, the pressure inside the cylinder is gradually increased. Only when the pressure is greater than the pressure outside the cylinder and the stress of the oil is overcome, the mixture will leak out. When the power stroke is performed, the pressure inside the cylinder is always higher than the pressure outside the cylinder, so there is gas leakage throughout the stroke.

  

The relationship between stroke and time associated with air leakage can be analyzed in three dimensions.

  

A, the length of the leak stroke

  

*The line shows the continuity of each cylinder from the beginning to the end of compression, that is to say, the gas leakage is from the beginning of the contraction stroke to the end of the power stroke, so the time for the gas in the cylinder to leak outward is the sum of the time of the two strokes. .

  

B. Overlap of the leaking stroke

  

The second line shows the other cylinder stroke states with the *row cylinder stroke. For example, when one cylinder is compressed, the two cylinders are doing work, and when one cylinder is working, the three cylinders are compressing..., so that two cylinders are simultaneously in the same time period. Leaking through the gap.

  

C, continuity of air leakage

  

* The cylinder strokes of the row and the second row are during the continuous cycle without any interruption, but continuously throughout the motor operating time. As soon as the motor is started, there are two cylinders that are leaking from start to finish.

  

Through the above analysis, it can be judged that the gas leakage in the cylinder caused by the piston ring notch is really serious.

  

However, it is too early to rely solely on the above analysis, and the conclusions that must be obtained through actual testing by scientific methods will be more reliable.

  

(2) Measuring cylinder leakage method

  

The cylinder sealing test was introduced in the second section of Chapter 2 of the Automotive Testing Technology and Equipment published by the Machinery Industry Press in 2009. The test contains three items: cylinder compression pressure detection, cylinder air leak rate detection and crankcase helium rate detection.

  

The basic conditions of the first two tests are based on the contraction stroke of the cylinder, and there is no pressure change including the power stroke and gas leakage in the cylinder. In the previous analysis, we have noticed that the gas pressure in the cylinder is much higher than the cylinder pressure during the whole period of the power stroke. That is to say, the gas leakage caused by this period is the key factor affecting the fuel consumption and output torque of the motor. .

  

At present, the final compressor pressure of most motors is about 8-12 kg/cm?, according to the pressure unit, 1 kg/cm?=98 kPa, 10 kg/cm? about 1000 kPa (about 1 Mpa); when entering the power stroke, The rapid expansion of the ignited mixture can increase the pressure in the cylinder to more than 100 kg/cm (about 10 MPa). The test parameters recorded in the book are to detect the cylinder leakage rate under the pressure condition of 0.4Mpa. The set pressure parameter is about half lower than the actual pressure of the cylinder in the compression stroke, and it is even less able to reflect the excessive pressure when the power stroke is performed. If the gap area is constant, the greater the pressure per unit time, the more gas is leaked, so the above detection method cannot reflect the actual leakage of the cylinder.

  

It seems that such detection technology does not truly and comprehensively reflect the seriousness of the leakage of the piston ring gap, and it also creates a illusion that the "pocket is very limited".

  

3, closed piston ring

  

Several closed piston rings are described here.

  

(1) lapped piston ring

  

There is currently a lapped piston ring that blocks the vertical passage of gas leakage down.

  

This type of piston ring is mostly used in diesel motors and has the advantage of blocking vertical passages for gas leakage. However, the horizontal notch of the piston ring can still allow high pressure gas to pass through the gap inside the piston ring and then leak through the horizontal notch below. The lap-type piston ring reduces the gas leakage rate to some extent by extending the leakage passage, but the gap is not completely closed.

  

(2) Fully closed piston ring

  

There are many patents on the China Patent Online for fully closed piston rings. The patent number is 200720120873.1 (Applicant Chen Yuchuan) as an example.

  

The inventor has improved the interface design of the piston ring to prevent the upper gas from leaking downward and inside. This design is more advanced than the lapped piston ring, completely closing the "notch" at the piston ring interface. Look at the situation after the end of the piston ring is combined.

  

When the piston ring is installed in the working position, the two ends are completely closed, and the reserved expansion gap is completely closed to the inner and inner passages, leaving only a very small (completely fitting) joint gap. The use of such a fully closed piston ring can limit the gas leakage in the cylinder of the motor contraction stroke and the power stroke, and is basically not affected by the change of the position of the two piston ring notches on the piston, which is very beneficial to improve the fuel economy of the motor. Sex and motivation.

  

4. Long-term effects caused by gaps

  

The large leakage of gas in the cylinder caused by the piston ring notch is only the beginning of the problem, because everything written in the previous section is premised on the new motor. As the mileage of the car increases, the cylinder wall and the outer side of the piston ring are continuously worn, the piston ring gap is also increased, and the amount of gas leaking is constantly increasing. The "Cylinder Leakage Rate Reference Diagnostic Parameter Standard Value" described in "Car Detection Technology and Equipment" is specified as follows:

  

When the new car leaves the factory, the cylinder leakage rate of the motor is basically at a "good" level; after a certain number of kilometers, the cylinder leakage rate may remain at the "normal" level; as the number of kilometers continues to extend (15-20 million kilometers or more), the cylinder The leak rate will become a "poor" or "poor" level. Usually the repair union replaces the piston ring for you when the piston ring notch length is more than 0.5mm. Because the cylinder wall is also subject to wear, even if a new piston ring is replaced, the gap gap is relatively large, and it is difficult to reach the new car level. I remember that a few friends who opened a BMW car felt that the power was seriously degraded when they drove to about 200,000 kilometers. When they went to the 4S shop for maintenance, they were asked to replace the motor. The reason is here. After the car has traveled 200,000 kilometers, the motor overhaul is basically carried out. The main job is to replace the piston ring.

  

Now everyone knows more about the impact of the piston ring notch on motor performance. In fact, things can't be like this. You can slide up and take a closer look at the schematic view of the fully closed piston ring.

  

In addition to the fact that the fully closed piston ring can substantially block the leakage of gas through the gap of the piston ring joint, a more important advantage is that it remains sealed when the outer edge of the piston is worn. The expansion gap A of the piston ring gradually increases with the wear of the outer edge, and the joint gap can remain unchanged. Therefore, the sealing property of the piston ring remains unchanged; only after the wear to the expansion gap coincides, the gap will be generated and the gas will leak downward. . If the joint has sufficient extension margin, the motor of a car can maintain the power level and fuel consumption level of the new car while driving 50-100 million kilometers.

  

Many foreign or joint venture vehicles use the motor opening (overhaul) mileage as an important indicator of motor performance, which caters to the psychological needs of Chinese consumers for “durability”.

  

I hope that Chinese auto companies can also design motors that are not overhauled for 500,000 kilometers or even 1 million kilometers, and they also have the dual advantages of no increase in fuel consumption and no decline in power.

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Last Updated May 24, 2019