The oil filter should have strong filtering capacity, low flow resistance and long service life. In the engine lubrication system, there are generally three types of filters. The first is the oil filter, which is installed before the oil pump to prevent large particles of impurities from entering the oil pump and early wear of the oil pump; The second is the oil strainer, which is used to filter out the impurities with large particle size (diameter between 0.05-0.1mm) in the oil. It has small flow resistance to the oil. It is generally connected in series between the oil pump and the main oil passage. It belongs to a full flow filter.

我们一般更换的机滤，就是指这种机油粗滤器；第三种是机油细滤器，用以清除直径在0.001mm以上的细小杂质，由于这种滤清器对于机油的流动阻力较大，故多做成分流式，即与主油道并联，只有少量机油流过细滤器。它一般只装备在大型柴油机上，在轿车上是没有的，绝大多数采用离心过滤式。我们在在维护保养发动机时，一般只更换机油粗滤器，就是我们常说的机油滤芯，而机油细滤器一般在二级保养时清理一次就可以了。

The machine filter we usually replace refers to this kind of oil strainer; The third is the oil fine filter, which is used to remove fine impurities with a diameter of more than 0.001mm. Because this filter has a large flow resistance to the oil, it is more component flow, that is, it is connected in parallel with the main oil passage, and only a small amount of oil flows through the fine filter. It is generally only equipped on large diesel engines, not on cars. Most of them adopt centrifugal filtration. When we maintain the engine, we usually only replace the primary oil filter, which is often referred to as the oil filter element, while the secondary oil filter is generally cleaned once during the secondary maintenance.

现在的发动机普遍使用旋装式一次性机油滤清器，也有部分车型使用的是纸芯式滤清器，其中起过滤作用的就是特制的机油滤纸。这种滤纸是一种微孔滤纸，可以过滤机油中粒度在0.05-0.1mm左右的杂质，并且对机油的流动阻力较小；为了保证小体积内有大的过滤面积，并提高滤芯的刚度，一般都折叠成纸扇形和波纹形，并与上下端盖经热固化处理而粘合在一起的。

Now the engine generally uses the rotary disposable oil filter, and some models use the paper core filter, in which the special oil filter paper plays a filtering role. This filter paper is a kind of microporous filter paper, which can filter impurities with particle size of about 0.05-0.1mm in engine oil, and has small flow resistance to engine oil; In order to ensure a large filtering area in a small volume and improve the stiffness of the filter element, it is generally folded into paper fan-shaped and corrugated shapes and bonded with the upper and lower covers after heat curing treatment.

在机油滤清器中，这种滤纸的用量是经过严格计算的，可以确保在机油的更换周期内不会发生堵塞，但也不会有太多的余量。如果超过这个周期过长，机油滤清器就会有堵塞的风险，特别是现在有些车型，机油滤清器做得很小，基本上超过机油的更换周期，它就不起多大的作用了。所以，机油和机油滤清器必须及时更换。

In the oil filter, the amount of this filter paper is strictly calculated, which can ensure that there will be no blockage during the oil change cycle, but there will not be too much margin. If the cycle is too long, the oil filter will have the risk of clogging. Especially for some models, the oil filter is very small. It basically exceeds the oil change cycle, and it will not play much role. Therefore, the oil and oil filter must be replaced in time.

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另外，在机油滤清器上还有两个重要的阀——止回阀和旁通阀。止回阀是一种单向阀，它可以让机油进入机油滤清器，但是却不可以从这里流出，它的作用是阻止发动机熄火后机油流回油底壳，保证发动机在启动后直接形成油压，尽可能的减少发动机干摩擦的时间.

In addition, there are two important valves on the oil filter - check valve and bypass valve. The check valve is a one-way valve, which allows the oil to enter the oil filter, but cannot flow out of it. Its function is to prevent the oil from flowing back to the oil pan after the engine is shut down, ensure that the oil pressure is directly formed after the engine is started, and reduce the dry friction time of the engine as much as possible

旁通阀是一种溢流阀，当机油压力过大时它就会开启，机油不经过滤清就进入主油道，它的作用是当滤纸堵塞时用来应急输送机油，防止发动机失去润滑。旁通阀的开启压力是经过精密计算的，这个压力过大或过小都会导致发动机润滑性能变差.

The bypass valve is an overflow valve. When the oil pressure is too high, it will open and the oil will enter the main oil passage without filtering. Its function is to transport the oil in an emergency when the filter paper is blocked to prevent the engine from losing lubrication. The opening pressure of the bypass valve is precisely calculated. Too much or too little pressure will lead to poor lubricating performance of the engine

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