CRANKCASE VENTILATION IN A SUPERCHARGED INTERNAL COMBUSTION ENGINE

Abstract: Supercharged internal combustion engine with crankcase ventilation, comprising a first evacuation conduit (46) for evacuating blow-by gas from the engine crankcase (3) to its intake conduit (20) downstream of the throttle (26), and a second evacuation conduit (43) for evacuating blow-by gas from the crankcase to the engine intake conduit (24) on the suction side of the compressor (23). Each evacuation conduit is connected to an individual oil separator (29, 40), a pressure regulator (42, 25) and a non-return valve (44, 47). Each non-return valve is arranged to permit free gas flow in the direction from the crankcase, but to prevent or limit flow in the opposite direction.

Description: Crankcase ventilation in a supercharged internal combustion engine The present invention relates to a supercharged internal combustion engine, comprising a cylinder block, a cylinder head, a crankcase containing oil, an air intake conduit communicating with intake channels in the cylinder head, said intake air conduit being connected to a charge unit and having a throttle downstream of said charge unit, a first evacuation conduit joining the crankcase to the intake air conduit at a point downstream of the throttle for evacuation of blow-by gases from the crankcase, a second evacuation conduit which connects the crankcase to the intake air conduit at a point on the suction side of the charge unit and communicates with a first pressure regulator arranged to maintain an at least approximately constant pressure in the crankcase, and means for separating oil out of the evacuated blow- by gas. It is a known fact that it is not possible to achieve piston ring seals between the pistons and the surrounding cylinder walls in an internal combustion engine, which, in normal engine operation (not engine braking), provide a 100% sealing-off between the combustion chambers and the engine crankcase. A certain amount of combustion gases, so-called blow-by gases, almost always leaks past the piston rings and into the engine crankcase. To avoid excessively high overpressure developing in the crankcase due to the blow-by gases, the crankcase must be ventilated, diverting these gases so that only a low overpressure is permitted in the crankcase. It is desirable to ventilate a crankcase to atmospheric pressure, but for environ- mental reasons the simplest and cheapest solution is not acceptable, viz. ventilating the crankcase directly to the surrounding atmosphere. Rather, the blow-by gases must be returned to the engine combustion chambers, and this is effected by mixing them with intake air in the intake manifold. The simplest solution is to connect the evacuation conduit from the crankcase to the intake manifold at a point before the charging unit, since there is atmospheric, or essentially atmospheric, pressure from the intake air filter up to the charging unit. The problem has, however, been that, despite the use of some form of oil separator, a certain amount of oil missed accompanying the blow-by gases out of the crankcase and into the charging system. The oil is collected in the charging system and, depending of the amount of oil and the temperature, the functioning of the charging system can be disturbed. One method of avoiding the problem of oil collecting in the charging system is to connect the evacuation conduit after the throttle, but there, especially at low load, there prevails a pronounced sub-atmospheric pressure and this is undesirable for several reasons. It is also not possible to evacuate the crankcase gases to this loca- tion when the engine is supercharged. A known method of solving this problem, at least to a certain extent, is to arrange two evacuation conduits, one before the charging unit and one after the throttle. The evacuation conduit after the throttle is connected to the intake manifold via a constriction and a non-return valve, which prevents flow in the direction from the intake mamfold. The problem is, however, that it is difficult to achieve balance in such a system both for suction engines, which always have sub-atmospheric pressure in the intake mamfold, and supercharged engines, which have sub-atmospheric pressure in the intake manifold at low load and overpressure at high load. In a known crankcase ventilation system for supercharged engines, the evacuation conduit to the intake manifold before the charging unit contains a pressure regulator disposed to maintain an essentially constant pressure approximately corresponding to atmospheric pressure in the crankcase. At high load, gas flows through this last-mentioned evacuation conduit to the intake manifold on the suction side of the turbo unit. Since there is overpressure in the intake mamfold downstream of the throttle, the non-return valve in the other evacuation conduit is closed so that no air can be forced back into the crankcase. At low load and sub-atmospheric pressure in the intake manifold downstream of the throttle, the blow-by gas flows from the crankcase via the non-return valve and the constriction to the intake manifold, but at the same time, under certain operating conditions, air is sucked via the pressure regulator from the intake mamfold up- stream of the charging unit to the intake mamfold downstream of the throttle. This exchange between hot gas flowing in one direction and cold air flowing in the other direction results in condensation and risk of frost blockage in cold weather. To avoid this it is known to use a heating coil with hot coolant around the evacuation conduit upstream of the throttle but such an installation is expensive. The purpose of the present invention is to achieve a supercharged internal combustion engine with pressure-regulated crankcase ventilation, whereby the above described disadvantages are removed. This is achieved according to the invention in an internal combustion engine of the type described by way of introduction by virtue of the fact that the first evacuation conduit communicates with a second pressure regulator arranged to maintain said essentially constant pressure in the crankcase, and that both evacuation conduits are coordinated with valve means, disposed to limit or prevent gas flow in the direction from the intake conduit towards the crankcase. By virtue of the invention there is achieved a pressure-regulated crankcase ventilation both for suction engine operation (low load) and for supercharging (high load). At suction engine operation, practically all of the crankcase gas flows through the first evacuation conduit to the intake manifold downstream of the throttle, since the valve means in the second evacuation conduit prevent or limit the flow of fresh air in the opposite direction, i.e. to the crankcase. When the intake manifold is charged with overpressure, then practically all the crankcase gas will go through the other evacuation conduit to the intake mamfold on the suction side of the charge unit, since the valve means in the first evacuation conduit prevent or limit the flow from the intake manifold to the crankcase. The valve means in the evacuation conduits can either be simple check valves which completely block flow towards the crankcase, or valves, which prevent a high flow in the direction from the crankcase and a limited flow (calibrated leakage) in the opposite direction. The advantage of the latter solution is that the risk of creating unacceptably low pressure in the crankcase when engine braking is eliminated. Since in this case there is no combustion producing blow-by gases, and the sub- atmospheric pressure in the intake manifold after the throttle is at a maximum when the throttle is closed, the sub-atmospheric pressure will otherwise cause gas to flow in the opposite direction, i.e. from the crankcase past the piston rings into the com- bustion chamber and out through the exhaust manifold. Under unfavourable conditions, this reversed gas flow could lead to the crankcase pressure being so low that air would be sucked via the crankshaft seals into the crankcase from the surrounding atmosphere since the sealing lips of the seals are turned to seal against overpressure in the crankcase and not against overpressure on its outside. This could result in sucking in cont-iminants which could cause damage to bearings, pistons and cylinder linings. The flow of air from the surrounding atmosphere to the crankcase through the calibrated leakage through the valves provides freedom to select a pressure in the intake manifold which is so low that the engine does not produce any natural blow-by gas, which occurs when the average pressure above the piston is lower than the average pressure below the piston, which can occur, as mentioned above, during engine braking in combination with extremely low intake pressure. Despite the fact that the engine does not produce any blow-by gas by itself, the pressure regulators can regulate the crankcase pressure by means of the apparent blow-by amount of air via the evacuation conduits. By the airflow into the crankcase via the evacuation conduits, a higher total flow is obtained through the oil separation means, which produces more complete oil sepa- ration. Furthermore, the increased blow-by gas velocity produces a higher heating effect in the gas, which improves the cold properties in the means for oil separation, in the pressure regulators and in the associated hoses and pipes. The invention will be described in more detail below with reference to examples shown in the accompanying drawings, where Fig. 1 shows a schematic cross section through a turbo-charged internal combustion engine with a previously known crank- case ventilation system, and Fig. 2 shows a corresponding engine with a crankcase ventilation system according to the invention. The Figures illustrate a cross section through one cylinder of a multi-cylinder (e.g. four or six cylinders) straight engine with a cylinder block 1, a cylinder head 2 and a crankcase 3 containing lubricant. A crankshaft 4 mounted in the crankcase is joined via connecting rods 5 to pistons 6 in cylinder 7. In the cylinder head 2 there is combustion chambers 8, into which intake conduits 9 and exhaust conduits 10 open. The gas exchange in the combustion chambers 8 is controlled by intake and exhaust valves 11 and 12, respectively, which are driven by camshafts 13 and 14, respectively. A sparkplug 15 projects into each combustion chamber 8. Valves and camshafts are enclosed in a space delimited by the cylinder head 2 and a valve cover 16, said space 17 communicating with the crankcase 3 via channels 18 in the cylinder head 2 and the cylinder block 1. An intake manifold 19 is securely screwed to the cylinder head 2 and has branch conduits 20 opening into intake channels 9 in the cylinder head. The manifold 19 is connected via a conduit 21 with a charge air cooler (not shown) to the outlet from a compressor 23 driven by an exhaust turbine 22, the inlet to the compressor 23 be- ing connected to an intake air conduit 24 with an air filter 25. The supply of air to the combustion chambers 8 is regulated by a throttle 26. The interior of the crankcase 3 communicates via an opening 27 with a container 29 provided with baffles 28. The container forms an oil separator, which is intended to separate and return the oil in the oil mist which unavoidably follows the blow-by gas out through the opening 27 in the crankcase. The oil separator 29 can be of a type known per se, mounted in a plastic container fixed to the outside of the crankcase. In the known engine shown in Fig. 1 the oil separator has an outlet 30 connected to a conduit 31 which splits into two branches 32 and 33, one 32 of which is connected to the intake manifold 19 downstream of the throttle 26 and the other 33 of which is connected to the intake air conduit 24 between the air filter 25 and the compressor 23. The branch 32 communicates with the intake conduit 20 via a non-return valve 34 and a constriction 35, while the branch 33 communicates with the intake air conduit 24 via a pressure regulator 36 disposed to maintain a practically constant pressure slightly below atmospheric pressure in the crankcase. When the engine at low load works as a suction engine with sub-atmospheric pressure in the intake manifold 19 downstream of the throttle 26, blow-by gas flows primarily through the branch 32, which means that not any or very little oil will be collected upstream of the throttle 26. When the engine at high load is supercharged so that overpressure prevails in the intake manifold 19 downstream of the throttle 26, the non-return valve 34 closes so that blow-by gas flows through the branch 33 to the intake air conduit 24, but since the air velocity is high, the oil mist will be drawn with the intake air into the combustion chamber without oil being deposited in the charging system. Under certain operating conditions, as was mentioned above, intake air can be sucked from the intake air conduit 24, through the branch 33 with its pressure regu- lator 36 to the intake conduit downstream of the throttle 26. This alternating flow of warm blow-by gas and cold intake air in the branch 33 increases the risk of freezing in cold weather, and therefore some form of heating of the branch 33 is usually arranged. The constriction 35 must also be serviced regularly to prevent clogging. Fig. 2 shows a solution according to the invention which avoids the above mentioned problems at the same time as it is simple and inexpensive. In addition to the oil separator 29 communicating directly with the crankcase 3, there is an additional oil separator 40, which is joined to the valve cover 16 and communicates with the space 17 and thus also with the crankcase 3 via the channels 18 in the cylinder head 2 and the block 1. The outlet 41 of the oil separator 40 opens directly into a pressure regulator 42, which is disposed to maintain a largely constant pressure slightly below atmospheric pressure in the space 17 and thus consequently in the crankcase 3 as well. The pressure regulator 42 communicates with the intake air conduit 24 at a point between the air filter 25 and the charge unit via a conduit 43 containing a non- return valve 44, which permits free flow of crankcase gas in the direction towards the intake conduit 24. The non-return valve 44 can be of the conventional type which completely blocks the flow in one direction or of a type which permits free flow in one direction and a limited flow in the opposite direction. In the present case the latter type is preferable since when there is a negative blow-by flow, i.e. flow from the crankcase to the combustion chamber, which can occur during heavy engine braking for example, it permits a limited flow of fresh air to the crankcase. The outlet 30 to the oil separator 29, communicating directly with the crankcase, is connected to a pressure regulator 45, which, like the pressure regulator 42, is disposed to maintain essentially constant pressure slightly below atmospheric pressure in the crankcase 3. A conduit 46 joins the pressure regulator 45 to the intake conduit 20 downstream of the throttle 26 and contains a non-return valve 47, which can be of the same type as the non-return valve 44, i.e. a valve which permits free flow of crankcase gas from the crankcase but prevents or limits flow in the opposite direction. At low load, when the compressor 23 does not supercharge, there is sub-atmospheric pressure in the intake conduit 20 downstream of the throttle 26 and blow-by gas flows now via the oil separator 29, the pressure regulator 45 and the conduit 46 to the intake conduit 20. Please note that the conduit 46 lacks a constriction corresponding to the constriction 35 in the previously known system shown in Fig. 1, thereby reducing the number of locations in the engine requiring regular service. At high load, when the compressor 23 supercharges, overpressure prevails in the intake conduit 20, and blow-by gas flows now via the channels 18, the chamber 17, the oil separator 40, the pressure regulator 42 and the conduit 43 to the air intake conduit 24. If the valve 47 is a pure non-return valve, there will be no airflow to the crank- case 3 via the conduit 46, but preferably the valve 47 is a valve which permits a limited calibrated airflow from the intake conduit 20 to the crankcase 3. This increases the gas velocity through the oil separator 40, improving oil separation and increasing the temperature in the pipes and hoses. This is of particular advantage in a straight engine with a hot and a cold side, with the cold side at the front of the vehicle. By separating the oil separation in two oil separators 29 and 40 and placing the oil separator 40 connected to the valve cover 16, optimally short conduits are achieved, further reducing the risk of freezing.

Claims: Claims 1. Supercharged internal combustion engine, comprising a cylinder block (1), a cylinder head (2), a crankcase (3) containing oil, an air intake conduit (19, 21, 24) communicating with intake channels (9) in the cylinder head, said intake air conduit being connected to a charge unit (23) and having a throttle (26) downstream of said charge unit, a first evacuation conduit (46) joining the crankcase to the intake air conduit at a point downstream of the throttle for evacuation of blow-by gases from the crankcase, a second evacuation conduit (43) which con- nects the crankcase to the intake air conduit at a point on the suction side of the charge unit and communicates with a first pressure regulator (42) arranged to maintain an at least approximately constant pressure in the crankcase, and means (29) for separating oil out of the evacuated blow-by gas, characterized in that the first evacuation conduit (46) communicates with a second pressure regulator (45) arranged to maintain said essentially constant pressure in the crankcase (3), and that both evacuation conduits (43, 46) are coordinated with valve means (44, 47), disposed to limit or prevent gas flow in the direction from the intake conduit (19, 21, 24) towards the crankcase (3). 2. Internal combustion engine according to Claim 1, characterized in that the valve means (44, 47) are non-return valves, which prevent flow in the direction from the intake conduit (19, 21, 24) towards the crankcase (3). 3. Internal combustion engine according to Claim 1, characterized in that the valve means (44, 47) are non-return valves, which permit a high flow in the direction from the crankcase (3) towards the intake conduit (19, 21, 24) and a limited flow in the opposite direction. 4. Internal combustion engine according to one of Claims 1-3, characterized in that the means for separating oil out of the evacuated blow-by gas comprise first and second oil separators (29, 40) to which the first and the second evacuation conduits (46 and 43, respectively) are connected. 5. Internal combustion engine according to Claim 4, characterized in that the first evacuation conduit (46) is joined to an oil separator (29), which communicates directly with the crankcase (3), while the second evacuation conduit (43) is connected to an oil separator (40), which communicates with a space (17) defined between the cylinder head (2) and a valve cover (16), said space in turn communicating with the crankcase (3).

Inventors: MOREN MATS, MOREN, MATS
Applicants: MOREN MATS, VOLVO PERSONVAGNAR AB, MOREN, MATS
Application year: 2000
Main classification: F01M13
IPC codes: F01M13