Positive Crankcase Ventilation: Description and Operation
Crankcase Ventilation System Description
A crankcase ventilation system is used to consume crankcase vapors created during the combustion process instead of venting them to the atmosphere.
Fresh air is supplied through a filter to the crankcase, the crankcase mixes the fresh air with the blow-by gases and then passed through a Positive Crankcase Ventilation (PCV) orifice tube (5) into the intake manifold (3).
The PCV orifice tube (5) restricts the flow rate of the blow-by gases using a 2.5 mm (0.098 inch) orifice located in the camshaft cover tube (5). If abnormal operating conditions arise, the system is designed to allow excessive amounts of blow-by gases to back flow through the crankcase ventilation fresh air tube (6) into the air cleaner resonator (1) in order to be consumed by normal combustion.
Drive Belt System Description The drive belt system consists of the following components:
^ The drive belt
^ The drive belt tensioner
^ The drive belt idler pulley
^ The crankshaft balancer pulley
^ The accessory drive component mounting brackets
^ The accessory drive components
- The power steering pump, if belt driven
- The generator
- The A/C compressor, if equipped
- The engine cooling fan, if belt driven
- The water pump, if belt driven
- The vacuum pump, if equipped
- The air compressor, if equipped
The drive belt system may use 1 belt or 2 belts. The drive belt is thin so that it can bend backwards and has several ribs to match the grooves in the pulleys. There also may be a V-belt style belt used to drive certain accessory drive components. The drive belts are made of different types of rubbers- chloroprene or EPDM-and have different layers or plys containing either fiber cloth or cords for reinforcement.
Both sides of the drive belt may be used to drive the different accessory drive components. When the back side of the drive belt is used to drive a pulley, the pulley is smooth.
The drive belt is pulled by the crankshaft balancer pulley across the accessory drive component pulleys. The spring loaded drive belt tensioner keeps constant tension on the drive belt to prevent the drive belt from slipping. The drive belt tensioner arm will move when loads are applied to the drive belt by the accessory drive components and the crankshaft.
The drive belt system may have an idler pulley, which is used to add wrap to the adjacent pulleys. Some systems use an idler pulley in place of an accessory drive component when the vehicle is not equipped with the accessory.