Crankcase ventilation system

In an internal combustion engine, a crankcase ventilation system (CVS) is a one way, pressure-sensitive passage which allows the natural build up of gases to escape from the crankcase in a controlled manner. In an internal combustion engine, a crankcase ventilation system (CVS) is a one way, pressure-sensitive passage which allows the natural build up of gases to escape from the crankcase in a controlled manner. Blow-by, as it is often called, is the result of combustion material from the combustion chamber 'blowing' past the piston rings and into the rotating assembly's housing. Turbocharged engines are additionally complicated by exhaust leakage from the turbocharger shaft, and in some cases, the valve stem seals. These blow-by gases, if not ventilated, inevitably condense and combine with the oil vapor present in the crankcase, forming sludge or causing the oil to become diluted with unburnt fuel. Excessive crankcase pressure can furthermore lead to engine oil leaks past the crankshaft seals and other engine seals and gaskets. Therefore, it becomes imperative that a crankcase ventilation system is used. This allows the blow-by gases to be vented through a PCV (positive crankcase ventilation) valve out of the crankcase. Ventilation typically leads to the intake manifold, allowing the gases to be recirculated before exiting through the tail pipe. This method greatly reduces emissions and is known as a closed-loop CVS. Conversely, an open-loop CVS vents directly to the atmosphere through a filter. From the late 19th century through the early 20th, blow-by gases from internal combustion were allowed to find their own way out to the atmosphere past seals and gaskets. It was considered normal for oil to be found both inside and outside an engine, and for oil to drip to the ground in small but constant amounts. The latter had also been true for steam engines and steam locomotives in the decades before. Even bearing and valve designs generally made little to no provision for keeping oil or waste gases contained. Sealed bearings and valve covers were for special applications only. Gaskets and shaft seals were meant to limit loss of oil, but they were usually not expected to entirely prevent it. On internal combustion engines, the hydrocarbon-rich blow-by gases would diffuse through the oil in the seals and gaskets into the atmosphere. Engines with high amounts of blow-by (e.g., worn out ones, or ones not well built to begin with) would leak profusely via those routes. The first refinement in crankcase ventilation was the road draft tube, which is a pipe running from a high location contiguous to the crankcase (such as the side of the engine block, or the valve cover on an overhead valve engine) down to an open end facing down and located in the vehicle's slipstream. When the vehicle is moving, airflow across the open end of the tube creates a draft that pulls gases out of the crankcase. The high location of the engine end of the pipe minimises liquid oil loss. An air inlet path to the crankcase, called the breather and often incorporated into the oil filler cap, meant that when a draft was generated at the tube, fresh air swept through the crankcase to clear out the blow-by gases. The road draft tube, though simple, has shortcomings: it does not function when the vehicle is moving too slowly to create a draft, so postal and other slow-moving delivery vehicles tended to suffer rapid buildup of engine sludge due to poor crankcase ventilation. And non-road vehicles such as boats never generated a draft on the tube, no matter how fast they were going. To remedy this situation manufacturers located the breather air filter in the air stream coming from the engine radiator fan, the manufacturers also modified the breather to incorporate an air scoop to direct the air into the breather filter so that the engine could be ventilated while the car or truck was standing still. The draft tube discharged the crankcase gases, composed largely of unburnt hydrocarbons, directly into the air. This created pollution as well as objectionable odors. Moreover, the draft tube could become clogged with snow or ice, in which case crankcase pressure would build and cause oil leaks and gasket failure. During World War II a different type of crankcase ventilation had to be invented to allow tank engines to operate during deep fording operations, where the normal draft tube ventilator would have allowed water to enter the crankcase and destroy the engine. The PCV system and its control valve were invented to meet this need, but no need for it on automobiles was recognized. In 1952, Professor A. J. Haagen-Smit, of the California Institute of Technology at Pasadena, postulated that unburned hydrocarbons were a primary constituent of smog, and that gasoline-powered automobiles were a major source of those hydrocarbons. The GM Research Laboratory (led by Dr. Lloyd L. Withrow) discovered in 1958 that the road draft tube was a major source—about half—of the hydrocarbons coming from the automobile. The PCV system thus became the first real vehicle emissions control device. Positive crankcase ventilation was first factory-installed on a widespread basis by law on all new 1961-model cars first sold in California. The following year, New York required it. By 1964, most new cars sold in the U.S. were so equipped by voluntary industry action so as not to have to make multiple state-specific versions of vehicles. PCV quickly became standard equipment on all vehicles worldwide because of its benefits not only in emissions reduction but also in engine internal cleanliness and oil lifespan. In 1967, several years after its introduction into production, the PCV system became the subject of a U.S. federal grand jury investigation, when it was alleged by some industry critics that the Automobile Manufacturers Association (AMA) was conspiring to keep several such smog reduction devices on the shelf to delay additional smog control. After eighteen months of investigation by U.S. Attorney Samuel Flatow, the grand jury returned a 'no-bill' decision, clearing the AMA, but resulting in a consent decree that all U.S. automobile companies agreed not to work jointly on smog control activities for a period of ten years.