WO1999061761A1

WO1999061761A1 - Arrangement for a supercharged combustion engine with crankcase ventilation

Info

Publication number: WO1999061761A1
Application number: PCT/SE1999/000769
Authority: WO
Inventors: Martin Berggren
Original assignee: Scania Cv Aktiebolag (Publ)
Priority date: 1998-05-13
Filing date: 1999-05-07
Publication date: 1999-12-02
Also published as: SE9801657D0; SE521097C2; SE9801657L

Abstract

Arrangement in supercharged combustion engine (2) with enclosed crankcase ventilation, whereby the arrangement serves to provide negative pressure in the engine's crankcase, while the engine's turbocompressor (16) driven by exhaust gases draws air in through an air filter (18) and feeds pressurized air to the engine's inlet pipe (8) via a charged air cooler (28). The feedback of crankcase gases to the inlet pipe (8) and the maintenance of negative pressure in the crankcase even during engine braking are catered for by a ventilation line (36) extending from the crankcase to a bifurcation point (40) in the air inlet duct (20) between the air filter and the compressor inlet (22). The ventilation line (36) incorporates in series a pressure regulator (44), provided with oil filter, and a two-way connection (42), one outlet (46) of which communicates with the bifurcation point (40) via the ventilation line (36), while the other outlet (48) communicates with the inlet pipe (8) via a check valve (52).

Description

Arrangement for a supercharged combustion engine with crankcase ventilation

Technical field

The present invention relates to an arrangement in a supercharged combustion engine with enclosed crankcase ventilation, in accordance with what is indicated in the preamble to patent claim 1.

State of the art

Supercharging of a piston engine is used for increasing the degree of filling of the cylinders and thereby achieves increased engine power. A mechanical pump or a compressor may be used for imparting increased pressure to the inlet air (charge air) supplied to the engine's inlet pipe. In the case of engines for heavy-duty vehicles, such as trucks and buses, turbocompressors driven by exhaust gases are now often used to provide supercharging. A charge air cooler is usually incorporated between the compressor and the engine inlet pipe in order to cool the inlet air pressurised by the compressor.

It is in practice not possible to prevent a certain quantity of combustion gas (blow-by gas) from the combustion chambers of the cylinders leaking past the piston rings and finding its way into the crankcase. In engines with enclosed crankcase ventilation, these crankcase gases are fed back to the engine inlet pipe, thereby preventing their leaking out to the surrounding atmosphere and causing air pollution.

For reasons which include the prevention of oil leakage from the crankcase via the crankshaft seals, it is desirable to maintain a negative pressure in the crankcase.

Modern trucks and buses are often provided not only with wheel brakes but also with various types of extra brake systems such as engine brake systems and/or special hydrodynamic or electrodynamic retarder devices. In its simplest form, engine braking (i.e. braking action by means of the engine) is achieved by the driver allowing the accelerator pedal to rise, advantageously in combination with changing down to lower gear. Still more effective engine braking can be achieved, however, by using some kind of exhaust brake (e.g. a settable throttle valve) which causes constriction of the exhaust gas flow during the exhaust stroke, thereby creating a counter-pressure (in the exhaust system) which the respective engine pistons have to overcome during the exhaust stroke.

With today's systems it is possible to bring about the aforesaid maintaining of negative pressure in the crankcase by placing the interior of the crankcase in communication with the negative pressure which prevails in the air inlet duct in the region between the air filter and the compressor's air inlet. In such cases a pressure regulator incorporated in the connection is used to bring about substantially constant negative pressure in the crankcase.

This known type of system does not work, however, during use of the aforesaid kind of exhaust braking, since the negative pressure between the air filter and the compressor's air inlet then becomes far too small (owing to the constricted exhaust gas flow to the turbocompressor' s exhaust gas turbine), while at the same time the gas flow in the crankcase ventilation becomes large (owing to increased blow-by gas flow past the piston rings, shaft seals in the turbo and the exhaust valve controls).

Objects of the invention

A principal object of the present invention is to provide an arrangement which ensures negative pressure in the crankcase even during engine braking (exhaust braking) in the case of a supercharged combustion engine with enclosed crankcase ventilation.

An associated further object is to provide a constructional solution which avoids any risk of crankcase gas mixed with oil being drawn into large sections of the inlet system, especially during exhaust braking, since the flow of crankcase gas into the crankcase ventilation is then particularly large. Description of the invention

The aforesaid objects are achieved, in an arrangement of the kind indicated in the introduction, by the arrangement exhibiting the features indicated in the characterising part of patent claim 1. Further developments of the arrangement may in addition exhibit the features indicated in claims 2-7.

The invention is thus distinguished by the fact that in order to ensure negative pressure in the crankcase even during engine braking, crankcase gases are led back from the crankcase to the engine inlet pipe via a ventilation line which extends from the interior of the crankcase to a connection point in the air inlet duct between the air filter and the compressor's air inlet. This ventilation line incorporates in series an oil trap, a pressure regulator and a two-way bifurcation or two-way valve, one outlet/outlet port of which is in communication with said connection point via the ventilation line, while its other outlet/outlet port is in communication with the engine inlet pipe via a check valve.

If the pressure drop in the line between the valve and the air inlet to the engine has an adapted pressure drop, a two-way valve will probably be unnecessary and a two-way bifurcation, e.g. a pipe tee, may suffice. In such cases it is advantageous to arrange a check valve at the connection point in the air inlet duct.

Particularly where engine braking is by activation of a separate exhaust brake downstream from the exhaust valves, it may be difficult and, in some cases, impossible to achieve sufficient negative pressure in the engine inlet pipe. This problem can be effectively solved, however, by means of an adjustable damper incorporated in the charge air feed connection between the charge air cooler's air outlet and the engine inlet pipe. This damper is designed to be able to be closed during towing and exhaust braking. Activation of this damper makes it possible to ensure in the engine inlet pipe a negative pressure which is sufficient to enable the crankcase gases (blow-by gases) to be led directly to the engine inlet pipe via the two-way valve. A substantial advantage of thus leading the crankcase gases directly into the cylinders is that it effectively prevents oil mixed with the crankcase gases from accompanying the latter and being deposited in the compressor and in the subsequent charge air cooler. The oil trap incorporated in the ventilation line upstream from the two-way valve is preferably an oil separating filter, which is advantageously combined with the pressure regulator to form a single unit.

Said check valve in the connection between the second outlet port of the two-way valve 5 and the engine inlet pipe may advantageously comprise one or more resilient leaf valves of the reed valve type. The purpose of this or these check valves is to ensure that no charge air leaks out from the engine inlet pipe to the ventilation line during normal operation of the engine, i.e. when no exhaust braking is taking place.

10 The arrangement according to the invention is usable in both supercharged diesel engines and supercharged Otto engines.

Brief description of the drawing

15 An arrangement according to the invention will now be described in more detail and further clarified with reference to the attached single drawing, in which: Fig.1 shows very schematically how the components and units which form part of the arrangement are arranged and connected together and are connected to a multi-cylinder combustion engine. 20

Description of an embodiment

In Fig.1 a supercharged combustion engine generally denoted by reference 2 is schematically depicted in plan view. At one end of the engine 2 there is a cooling fan 4,

25 and at the opposite other end of the engine a flywheel cover 6. On one side of the engine there is an inlet manifold 8 via which air is supplied to the engine's cylinders, and on the opposite side of the engine there is an exhaust manifold 10 which receives the exhaust gases from the cylinders and leads them to the engine's undepicted exhaust system. A larger or smaller proportion of the energy in the exhaust gases from the exhaust manifold

30 10 is utilised by their being forced to flow through the turbine section 12 of a turbocompressor 14 which is driven by exhaust gases and whose compressor section is referenced 16. The air supply system to the supercharged engine 2 depicted includes an air cleaner 18 which is provided with an air filter and through which air from the surrounding atmosphere is drawn into the air supply system's tubular air inlet duct 20 which is connected to the compressor's air inlet 22. From the air outlet 24 of the compressor 14 the pressurised air is led through a pipeline 26 connected to a charge air cooler 28 from whose air outlet 30 the compressed and cooled charge air is then led through an air supply pipe 32 to the engine's inlet manifold 8 via a constricting damper 34 incorporated in the air supply pipe. This damper is preferably a compressed air servo operated rotary damper of throttle type which can be closed during towing and exhaust braking in order to ensure in the engine inlet pipe a negative pressure sufficient to enable the blow-by gases leaking into the engine's crankcase from the cylinders to be fed back directly to the inlet manifold 8. In other words, the constricting damper 34 ensures that the pressure in the inlet manifold 8 will oscillate about atmospheric pressure. During exhaust braking, the pressure in the inlet manifold 8 is close to zero, and the opening of the inlet valves of the cylinders will cause a negative pressure which extends into the inlet pipe. It is precisely this negative pressure which can be used, during exhaust braking, to extract the crankcase exhaust gases from the crankcase via the ventilation line 36 which will now be described.

The feedback of crankcase gases from the crankcase to the inlet manifold 8 and the maintenance of negative pressure in the crankcase even during exhaust braking (engine braking) are made possible by arranging a ventilation line 36 which extends from a crankcase gas outlet 38 to a connection point 40 in the air inlet duct 20 between the air cleaner 18 and the air inlet 22 of the compressor 14. This ventilation pipeline 36 incorporates, as seen in the direction of flow, a pressure regulator, coordinated with an oil trap, and an adjustable two-way valve 42. The oil trap, advantageously in the form of an oil separating filter, is preferably combined with said pressure regulator to form a control unit 44.

The two-way valve 42 has a first outlet port 46 and a second outlet port 48. In normal operation (i.e. while exhaust braking or engine braking is not activated) the crankcase gases are led via the control unit 44 and the subsequent two-way valve 42 from the latter' s outlet 46 to the connection point 40 via the section of the ventilation line 36 situated downstream from the valve 42. Via the second outlet port 48 of the valve 42, the crankcase gases coming from the crankcase gas outlet 38 can instead be fed back directly to the inlet manifold 8 via a hose or pipeline 50 which has its downstream end connected to the inlet manifold 8 via a check 5 valve 52. This check valve prevents charge air in the inlet manifold 8 from leaking out via the pipeline 50 during normal operation of the engine 2 when no exhaust braking is taking place and the pressure in the inlet manifold 8 is significantly higher than the pressure of the crankcase gases inside the crankcase and hence in the ventilation pipeline 36. The check valve 52, which thus only allows flow in the direction from the valve 42 to 10 the inside of the inlet manifold 8, advantageously comprises one or more preloaded resilient leaf valve elements of reed valve type.

When the constricting damper 34 is closed, the two-way valve 42 is positioned so that the crankcase gases are fed back to the inlet manifold 8 via the line 50 and the check valve 15 52. The same signals as are used for controlling/positioning the damper 34 may for example be used for controlling/positioning the two-way valve 42. When the constricting damper 34 is opened, the crankcase gases are led via the outlet 46 of the valve 42 to the connection point 40 in the inlet duct 20 of the compressor 16.

20 The invention may within the scope of the attached patent claims be modified and be configured otherwise than as indicated in the embodiment described. For example, the constricting damper 34 may, instead of being placed after the charge air cooler 28, be placed before the charge air cooler, as suggested in the diagram by a "dashed" constricting damper 34b.

25

The check valve 52 described, or the line between the check valve 52 and the valve 42, may, in a further-developed embodiment, be provided with a safety valve with the object of preventing charge air being led back from the air inlet 8 into the ventilation line 26 in situations where the check valve 52 ceases to operate. This safety valve may

30 advantageously take the form of a check valve.

If the pressure drop in the line 36 between the valve 42 and the air inlet 20 has an adapted pressure drop, a two-way valve is probably unnecessary and a two-way bifurcation, e.g. a pipe tee, may then suffice. In such cases it is advantageous to arrange at the connection point 40 in the inlet duct 20 a check valve, which may with advantage be integrated with other items incorporated at the connection point 40.

Claims

Patent claims

1. Arrangement in supercharged combustion engine (2) with enclosed crankcase ventilation, which arrangement serves to provide negative pressure in the engine's crankcase, while a turbocompressor (16) driven by the engine's exhaust gases draws air in through an air filter (18) via an air inlet duct (20) and thus feeds pressurised air to the engine's inlet pipe (8) via a charge air cooler (28), characterised in that the feedback of crankcases gases from the crankcase to the inlet pipe (8) and the maintenance of negative pressure in the crankcase even during engine braking are catered for by a ventilation line (36) which extends from the interior (38) of the crankcase to a connection point (40) in the air inlet duct (20) between the air filter (18) and the compressor's air inlet (22), and that this ventilation line incorporates in series an oil trap (44), a pressure regulator (44) and a two-way bifurcation or two-way valve (42), one outlet port (46) of which is in communication with said connection point (40) via the ventilation line (36), while its other outlet port (48) is in connection with the inlet pipe (8) via a check valve (52).

2. Arrangement according to claim 1, characterised in that an adjustable damper (34) is incorporated in a charge air feed connection (32) between the air outlet (30) of the charge air cooler (28) and the inlet pipe (8).

3. Arrangement according to claim 1, characterised in that an adjustable damper (34b) is incorporated in a pipeline (26) between the air outlet (24) of the compressor and the air inlet of the charge air cooler (28).

4. Arrangement according to claim 1, 2 or 3, characterised in that the check valve in the connection (50) between the second outlet port (48) of the two-way valve (42) and the inlet pipe (8) consists of a valve unit (52) preferably comprising at least one resilient leaf valve of reed valve type, which prevents charge air outflow from the inlet pipe (8) to the two-way valve (42).

5. Arrangement according to any one of the foregoing claims, characterised in that the oil trap in the ventilation line (36) from the crankcase consists of an oil separating filter which is preferably combined with the pressure regulator to form a single unit (44).

6. Arrangement according to claim 2 or 3, characterised in that the damper is a servo-operated constricting valve (34,34b) of rotary damper type.

7. Arrangement according to any one of the foregoing claims, characterised in that instead of the two-way valve (42) it uses the two-way bifurcation with two outlets

(46,48) which consists of a permanently open two-way connection in the form of a pipe tee.

8. Arrangement according to claim 7, characterised in that a check valve is arranged in the connection between the two-way bifurcation and the air inlet duct (20), advantageously at the connection point (40).

9. Arrangement according to any one of the foregoing claims, characterised in that the combustion engine (2) is a four-stroke engine, preferably a diesel engine.