Positive Crankcase Ventilation

Main Function

When the engine is working, the high-pressure combustible gas mixture and the burned gas in the combustion chamber will more or less leak into the crankcase through the gap between the piston group and the cylinder, causing blow-by gas. The components of the blow-by gas are unburned fuel gas, water vapor and exhaust gas, etc., which will dilute the oil, reduce the performance of the oil, and accelerate the oxidation and deterioration of the oil. The condensation of water vapor in the oil will form sludge and block the oil circuit; the acid gas in the exhaust gas will be mixed into the lubrication system, which will cause corrosion and accelerated wear of engine spare parts; the blow-by gas will also make the pressure of the crankcase too high and damage the crankcase. Sealed to allow oil leaks to drain away.

In order to prevent the crankcase pressure from being too high, prolong the service life of the oil, reduce the wear and corrosion of the parts, and prevent the engine oil leakage, the crankcase ventilation must be implemented. In addition, to meet increasingly stringent emission requirements and improve economy, crankcase ventilation system design must also be included in the automotive engine design process.

The installation of crankcase ventilation in the engine can solve or alleviate the above problems.

Forced crankcase ventilation

Crankcase ventilation includes natural ventilation and forced ventilation. Modern gasoline engines often use forced crankcase ventilation, also known as PCV system.

1) Natural ventilation

The natural ventilation method is to set a ventilation pipe on the crankcase, and the pipe is equipped with an air filter element. When the pressure in the crankcase increases, the gas leaking into the crankcase is discharged through the ventilation pipe.

2) Forced ventilation

The forced ventilation method guides the mixture in the crankcase to the appropriate position of the intake pipe through the connecting pipe, and returns to the cylinder for re-combustion, which can not only reduce exhaust pollution, but also improve the economy of the engine. All gasoline engines for automobiles use forced ventilation, and diesel engines for automobiles are gradually adopting forced ventilation. Mandatory ventilation can be divided into two types: open and closed.

When the engine is at full load and low speed, the open forced crankcase ventilation device produces a large amount of blow-by air, but the opening of the flow control valve is reduced. The rate is only about 75%.

The closed forced crankcase ventilation device can completely control the discharge of the crankcase, realize the complete ventilation of the crankcase, prevent the accumulation of sludge and other harmful substances, and reduce the failure and wear of the engine. Closed forced crankcase ventilation is a necessary design for gasoline engines to meet emission regulations

Part function

1. OIL SEPERATOR

The role of the oil separator is to separate the oil in the crankcase discharge from the mixture and return it to the oil sump.

2. PRESSURE CONTROL VALVE

The pressure control valve is a one-way valve whose flow section changes with the pressure difference between the two ends. It opens and closes the gas passage according to the balance between the spring force and the vacuum degree of the intake pipe.

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