Positive Crankcase Ventilation Valve

PCV is the abbreviation of Positive Crankcase Ventilation (forced crankcase ventilation) in English, which means crankcase (or oil pan) active ventilation control system in Chinese. Positive Crankcase Ventilation valve consists of valve body, valve, valve cover and spring, which cannot be decomposed. Its main function is: the gas in the crankcase is introduced into the intake manifold through the PCV valve, and a small amount of air is directly entered into the intake manifold by the air filter element through the PCV valve, which avoids freezing at the throttle valve. Insufficient combustion and worsening emissions. Prevent blow-by gas from entering the atmosphere and prevent oil deterioration.

Introduction

At the end of the engine's working combustion process, some unburned mixture leaks from the piston rings into the crankcase under high pressure, a leakage known in the industry as "blowby". These blow-by gases can escape into the atmosphere from the crankcase and cause pollution. These escaping air mixtures are not excluded, but also dilute the oil in the crankcase, causing the oil to deteriorate and cause premature wear of engine parts. Since the 1960s, California has taken the lead in requiring cars to be equipped with a PCV system, which has become a must for cars.
Most gasoline engines are equipped with PCV valves (forced crankcase ventilation) to facilitate engine ventilation, but contaminants in the blow-by gas can deposit around the PCV valve and may clog the valve. If the PCV valve is blocked, the polluted gas will flow into the air filter reversely, pollute the filter element, reduce the filtering capacity, increase fuel consumption, increase engine wear, and even damage the engine. Therefore, regular maintenance of the PCV is necessary to remove contaminants around the PCV valve.

Device

PCV device is mainly composed of ventilation hose and PCV valve. Generally, one breather hose connects the air filter to the valve cover, and the other connects the PCV valve to the intake manifold. The PCV valve is composed of a plunger valve and a spring, which is located on one side of the intake manifold. The vacuum degree of the intake manifold determines the degree of opening, closing and opening of the PCV valve, and the degree of opening, closing and opening of the PCV valve. Determines the amount of blow-by gas mixture that is re-injected into the intake manifold for combustion.
In other words, when the engine speed is normal or the speed is relatively slow, the air flow is small, the blow-by gas is also small, the PCV valve opening is small or even closed, so the blow-by gas that is forced to be sucked into the combustion is relatively small or even no. When the engine is accelerated or the rotational speed is relatively high, the airflow is large, the blow-by gas is also large, and the PCV valve opening is large, so more blow-by gas is forced to be sucked into the combustion.

Work process

The earliest positive crankcase ventilation system used was an open system, which only added a ventilation pipe with a PCV valve between the intake pipe and the crankcase. The working process is as follows: under the action of the intake vacuum, the fresh air from the outside enters the crankcase through the vents that are connected to the atmosphere at the oil filler cap, etc. After mixing with the blow-by gas in the crankcase, it is sucked into the intake system through the PCV valve. into the combustion chamber to burn. This system has a simple structure and is easy to install and maintain. However, under certain operating conditions, all crankcase blow-by gas cannot be sucked into the intake system. All the blow-by gas is sucked into the intake system, and part of the blow-by gas is discharged into the atmosphere from the oil filler cap, thus causing pollution to the environment. Improvements to the open system resulted in a closed crankcase ventilation system. This system seals the crankcase on the basis of the open system, and adds a ventilation pipe connected to the crankcase between the air filter and the carburetor (the throttle body for the EFI engine). The air filter and ventilation pipe enter the crankcase to mix with the blow-by gas, and enter the cylinder through the PCV valve for combustion under the action of the vacuum in the intake pipe. When the engine is working under heavy load, after the excess blow-by gas enters the intake manifold through the ventilation pipe, it mixes with the engine intake air and enters the cylinder for combustion. The closed system does not allow blow-by gas to be discharged into the atmosphere, but can also use fresh air for crankcase ventilation, and is widely used in the world.

Working principle

The PCV valve is a metered control valve. Installed between the engine crankcase ventilation system and the intake system. The PCV valve is controlled by the degree of vacuum to adjust the flow rate of the oil fume generated by the crankcase ventilation system into the intake system. When the engine is running at high speed, the flow rate is higher than that at low speed. At the same time, when the engine flashes back, the PCV valve should be able to cut off. Ventilation prevents crankcase explosion.

Function

Every car has an exhaust pipe to discharge the exhaust gas from the engine combustion, but there is no way to discharge 100% of the exhaust gas, and a small part of the combustion exhaust gas will still be drilled into the oil pan through the gap between the piston and the cylinder wall , Once the oil and gas entering the oil pan accumulates too much and cannot be eliminated, air pressure will form, which will not only dilute the oil, cause poor lubrication system parts, but also cause serious consequences such as abnormal oil consumption. Therefore, the oil and gas in the oil pan must have a discharge pipeline. In the past, before the legislative control of automobile exhaust pollution, pipes were connected from the oil pan to allow the oil and gas to be directly discharged into the atmosphere. The older the car is, the more serious the oil and gas leakage will be, and the more exhaust gas will be discharged from the oil pan, causing serious air pollution.
Since the 1960s, California has taken the lead in requiring cars to be equipped with a PCV system, so PCV can be said to be the oldest smoke pollution control system. It has a control valve that is connected to the intake pipe of the engine and the oil pan at the other end, so that after the engine starts to run, the vacuum generated by the intake air can suck out the oil and gas in the oil pan and let it flow with the fresh air. Into the cylinder to burn to solve the pollution problem.

Inspection Method

With the engine running at idle speed, remove the PCV valve from the cylinder head cover hose and check if the PCV valve is clogged. If you put your hand on the PCV valve interface, your fingers can feel a strong vacuum suction.
Another inspection method is to remove the crankcase intake pipe from the air filter after refitting the PCV valve, cover the nozzle with a piece of tissue paper, and wait until the pressure in the crankcase decreases (after about 1MIn). , it should be obvious that the tissue paper is sucked towards the nozzle. In addition, after the engine is stopped, remove the PCV valve and shake it by hand to check. If a "click" sound is heard, it means that the PCV valve is flexible and usable.

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