EP0143182A1 - Two-stage exhaust turbo charger having a device to avoid lubricant losses - Google Patents

Abstract

In order to avoid loss of lubricant in the bearing housing (39) of the high-pressure stage (44, 45) of an exhaust gas turbocharger for two-stage supercharging, the interior of the bearing housing (39) is connected via a sealing air ring duct (40), lines (50, 51) connected to it and a compensating line ( 52) with the low pressure charge air line (53) in front of the high pressure compressor (44). Another conductive connection between the bearing housing (39) and the low-pressure charge air line (53) is via an oil return line to a lubricating oil tank (54) and a compensating line (54) between the lubricating oil tank (54) and the low-pressure charge air line (53).

Description

The present invention relates to an exhaust gas turbocharger for two-stage supercharging of an internal combustion engine with a device for avoiding lubricant losses according to the preamble of patent claim 1.

In the case of two-stage supercharging of internal combustion engines by exhaust gas turbochargers, the bearing of the high-pressure stage shaft is often arranged in a bearing housing between the turbine wheel and the compressor wheel, this housing serving as a collecting container for the oil escaping from the bearings, from which it enters the engine oil sump or into an oil tank separated from this flows back or is pumped there. Since it is not possible to seal the above-mentioned housing against the compressor housing and the turbine housing in such a way that oil does not enter them, the pressure in the bearing housing must always be lower than the pressures in the compressor or turbine housing. The pressure difference However, it must not be so large that the efficiency of the compressor and turbine are reduced. The pressure in the bearing housing should therefore only be as close as possible to the lower of the pressures in the compressor or turbine housing.

From there, the oil flowing out of the bearings into the bearing housing, as mentioned, either goes into the oil sump of the engine or into an oil tank separate from it, whereby ventilation must be provided in both cases. The above-mentioned requirement for the smallest possible pressure difference between the interior of the bearing housing, in which the ambient pressure prevails, and the compressor or turbine housing also follows from the fact that, if the pressure difference is too great, too much air gets into the oil reservoir in question and thus inadmissibly large amounts of oil mist are produced. that escape through the oil tank or crankcase ventilation and contribute to environmental pollution.

In addition, in the case of small pressure differences for the seal between the bearing housing and the compressor and the turbine housing, unsupported sealing rings can be used, which have a better sealing effect than supported sealing rings and are also cheaper.

In single-stage turbochargers, sealing air is often branched off from the charge air line to cool the turbine-side shaft stub and to prevent the entry of exhaust gases into the bearing housing and into the compressor. With this design, the labyrinth seal between the compressor housing and the compressor wheel is designed with a radius such that it is on the compressor wheel and essentially cancel the axial thrust acting on the turbine wheel. The air behind the labyrinth is also discharged into the environment.

Manufacturers of turbochargers strive to be able to use such turbocharger types, originally designed as single-stage turbochargers, with as few modifications as possible as the high-pressure stage of two-stage turbochargers. The most important changes and adaptations to the higher pressures upstream of the compressor and behind the turbine are measures that increase the pressure in the sealing air ducts and in the bearing housing to such an extent that the small pressure difference mentioned at the outset is achieved.

From the German utility model GM 80 26 375 from Dr. Ing.h.c. F. Porsche AG, a device is known with which lubricant losses due to the causes described at the outset are to be avoided in single-stage turbochargers for gasoline engines. For this purpose, the air space of an oil tank, in which the oil flowing out of the bearing housing is collected and which serves as an air separator, is connected to a location of the intake line between a throttle valve and the compressor. Depending on the position of the throttle valve, which serves as a power control element, there is a more or less negative pressure in the intake line in front of the compressor, which is transferred to the oil tank and the bearing housing, so that oil does not escape from the latter into the compressor housing and at the same time, the oil mist formed in the oil tank returns to the combustion chambers of the engine via the intake line and the compressor. Since the oil does not flow back into the crankcase of the engine by itself due to the negative pressure mentioned, a pump must be provided which feeds the oil back into the crankcase.

As already mentioned, this device is intended for gasoline engines that have a throttle valve in the intake line upstream of the compressor. Single or two-stage turbochargers of diesel engines do not have a throttle valve in the intake line and are therefore not suitable for the system described.

With the present invention defined in claim 1, the object of the invention is to be solved, since the prevention of lubricant losses in single-stage exhaust gas turbochargers of diesel engines is not a problem because of the pressure ratios mentioned in the introduction in the compressor, turbine and bearing housing two-stage supercharged diesel engines, where this problem arises in the high pressure stage.

The invention is described below with reference to three exemplary embodiments shown in the drawings.

• Fig. 1 einen Längsschnitt durch einen konventionellen Abgasturbolader, der durch erfindungsgemässe Massnahmen als Hochdruckstufe eines zweistufigen Abgasturboladers verwendbar gemacht werden soll,
• Fig..2 erste Mittel zur Modifikation des in Fig. 1 gezeigten Abgasturboladers,
• Fig. 3 weitere Mittel zur Modifikation des Abgasturboladers nach Fig. l,
• Fig. 4 ein Detail zu Fig. 3,
• Fig. 5 die Hochdruckstufe eines erfindungsgemässen zweistufigen Abgasturboladers mit Sperrluftkanälen, und die
• Fig. 6 zeigt, wie der in Fig. 5 mit VI bezeichnete Ausschnitt bei einem nichtmodifizierten Turbolader gestaltet ist.

In the drawings:

• 1 shows a longitudinal section through a conventional exhaust gas turbocharger which is to be used as a high-pressure stage of a two-stage exhaust gas turbocharger by means of measures according to the invention,
• 2 first means for modifying the exhaust gas turbocharger shown in FIG. 1,
• 3 further means for modifying the exhaust gas turbocharger according to FIG. 1,
• 4 shows a detail of FIG. 3,
• 5 shows the high-pressure stage of a two-stage exhaust gas turbocharger according to the invention with sealing air channels, and the
• FIG. 6 shows how the section designated VI in FIG. 5 is designed for a non-modified turbocharger.

The one-stage turbocharger shown in FIG. 1 has a compressor 1 which sucks atmospheric air through an intake line 2, compresses it and conveys it through a charge air line 3 into the working cylinders of a diesel engine, not shown. The compressor 1 is driven by an exhaust gas turbine 4 which is acted upon by the exhaust gases coming from the engine via an exhaust gas line 5. The exhaust gas relaxing in the turbine 4 exits through an exhaust pipe 6.

Compressor 1 and turbine 5 sit on a common shaft 7, which is mounted in a bearing housing 8 in bearings 9 and 10. The lubricating oil is supplied to the bearings 9 and 10 from a lubricating oil tank 11, from which a lubricating oil pump 12 presses the oil into the bearings 9 and 10 via an oil suction line 13 and an oil pressure line 14 through an oil filter 15, an oil cooler 16 and a lubricating oil supply line 17 . The oil dripping from the bearings collects in the bearing housing 8, from which it flows back into the lubricating oil tank 11 through an oil return line 18.

This lubricating oil circuit applies to larger engines with their own lubricating oil tank outside the engine crankcase. In smaller engines, the engine lubricating oil in the crankcase is usually used to lubricate the exhaust gas turbocharger. In this case, the pump 12 conveys one of the Oil supply line 17 branching, dashed oil line 19 draws part of the oil to the lubrication points of the engine, from which, as symbolized by an oil return line 20, it flows back into the crankcase of the engine symbolized by the oil tank 11.

What has been described so far is an exhaust gas turbocharger for single-stage charging of an internal combustion engine, preferably a diesel engine. In this case, the lubricating oil tank 11 is vented into the environment via a vent pipe 21. A box 22 drawn with a broken line accordingly shows the conditions in the area of the lubricating oil return flow and the lubricating oil tank ventilation in the case of a single-stage supercharging of an engine.

Two measures which make such an exhaust gas turbocharger suitable as a high-pressure stage with two-stage supercharging are shown in boxes 23 and 24 according to FIGS. 2 and 3.

The modification in box 23 compared to the training in box 22 is that the vent pipe 21 is conductively connected to the low-pressure charge air line 26 by a compensating line 25, the latter being materially identical to the intake line 2, but now between the low-pressure charger (not shown) and the one above shown high-pressure charger receives the pre-compressed charge air. Thus there is also in the oil tank 11, in the oil return line 18 and in the bearing housing 8 the pressure of the low-pressure charge air line 26 which is higher than the atmosphere, so that the pressure difference between the bearing housing 8 and the compressor 1, which now provides the high-pressure charging, is so small that the aforementioned Invention task, prevention of lubricant loss and the lowest possible air loss from the high pressure compressor is fulfilled. The pressure difference that the oil pump 12 has to be overcome is the same as when using the charger for single-stage charging.

Box 24 shows a device in the event that the supercharger lubricating oil circuit is branched from that of the engine, and it is not desirable that the associated oil tank or crankcase be pressurized. This device, shown larger in FIG. 4, sits on the bottom of a specially provided air separator vessel and consists of a level control float 27 in conjunction with an oil drain pipe 28, the upper end of which is closed by an end plate 29 and two slots 30 extending over a large part of the circumference having. The float 27 consists of a float vessel 31 and a bell 32 fastened to the underside thereof with slots 33 in the manner of the above-mentioned slots 30 in the oil drain pipe 28. The mode of operation can be seen from FIG. 4. If the lubricating oil level in the tank 11 rises above a certain level, the lower edge of the bell 32 frees the slots 30 in the drain pipe 28 and oil flows into the crankcase of the engine until the lubricating oil level has dropped again to the lowest level. The oil content separates the crankcase, in which there is essentially ambient pressure, from the space above the lubricating oil level, which is connected to the low-pressure charge air line 26 by a compensating line 28 and in which, like in the bearing housing 8, the pressure prevails after the first charging stage. A vent pipe 35 is provided for venting the crankcase.

The high-pressure exhaust gas turbocharger for two-stage supercharging shown in FIG. 5 can be obtained by modifications according to the invention from a low-pressure exhaust gas supercharger with sealing air channels for one-stage supercharging.

The broken line VI shown in FIG. 6 shows the design of the charger for single-stage charging before the modification. The sealing air symbolized by the small white arrows 36 flows from the high-pressure charge air line 37 into a sealing air channel 38 which is connected to a sealing air ring channel 40 surrounding the bearing housing 39. This sealing air ring duct 40 is delimited by an inner casing forming the bearing housing 39 and an outer housing 41. Transverse walls 42 and 43 delimit chambers separated from this sealing air ring channel 40, which are located between these transverse walls 42, 43 and the compressor 44 or the exhaust gas turbine 45, but these chambers are in conductive communication with the sealing air ring channel.

When used for single-stage charging, the sealing air ring channel, as can be seen in FIG. 6, is in conductive connection with the surroundings via ventilation ports 46 and 47, which are covered by caps 48 and 49.

In the embodiment modified according to FIG. 5 for high-pressure charging, these ventilation connections 46 and 47 are conductively connected to the low-pressure charge air duct 53 by lines 50 and 51, which open into a common equalization line 52, as a result of which such a pressure difference between the compressor 44 in the sense of the task of the invention and the interior of the bearing housing 39 sets that lubricant is prevented from escaping from the bearing housing into the compressor and / or the turbine housing.

In addition, the interior of the lubricating oil tank 54, as in the variants according to FIGS. 2 and 3, can also be connected to the low-pressure charge air line 53 by a compensating line 55, which also solves the problem of tank ventilation.

Aristatt to connect the bearing housings 8 and 39 in the embodiments according to FIGS. 2 and 3 or according to FIG. 5 with the relevant low-pressure charge air lines 26 or 53, they can also be connected to the exhaust line between the exhaust gas turbine of the high-pressure stage and that of the low-pressure stage . Since the pressures in the aforementioned exhaust gas line and in the low-pressure charge air line are of a similar magnitude, but can vary considerably depending on the operating state and application, all compensating lines should only be connected to one or the other of the two lines, preferably to the low-pressure charge air line, in order to prevent oil loss on the compressor side or in idle mode soiling of the compressor wheel by exhaust gases from the turbine.

By venting the lubricating oil tanks 11 and 54 into the low-pressure charge air line 26 and 55 in question instead of the environment, the tanks are under the same pressure as the low-pressure charge air lines, so that the pressure difference to be overcome by the oil pump is the same as when using the exhaust gas turbocharger for one single-stage charging.

Claims (6)

1. Exhaust gas turbocharger for two-stage supercharging of an internal combustion engine with a device for avoiding lubricant losses, with a low-pressure exhaust gas turbocharger and a high-pressure exhaust gas turbocharger, the bearings (9, 10) of the high-pressure exhaust gas turbocharger in a between the compressor (1; 44) and the exhaust gas turbine (4; 45 ) arranged bearing housing (8; 39) and for the lubrication of the bearings a separate or a lubricating oil circuit connected to the lubrication system of the engine is provided, further the bearing housing (8; 39) through an oil return line (18) with a lubricating oil tank (11; 54) or the crankcase of the internal combustion engine is connected and there is a ventilation device for the lubricating oil flowing back from the bearing housing into the lubricating oil tank or into the crankcase, characterized in that the interior of the bearing housing (8; 39) of the high-pressure stage by compensating lines (25; 34; 52 , 54) with the low pressure charge air line (26; 53) between the Ve rcompressor of the low pressure stage and the compressor (1; 44) of the high pressure stage or with the low pressure exhaust gas line between the exhaust gas turbine (4; 45) of the high pressure stage and the exhaust gas turbine of the low pressure stage. 2. Exhaust gas turbocharger according to claim 1, characterized in that the bearing housing (8) through an oil return line (18) with a lubricating oil tank (11) and the lubricating oil tank (11) through a compensating line (25; 34) with the low-pressure charge air line (26) . 3. Exhaust gas turbocharger according to claim 2, characterized in that before the lubricating oil tank (11) in the oil return line (18) there is an air separator vessel with a level control float (27) and an oil drain pipe (28) opening into the lubricating oil tank. 4. Exhaust gas turbocharger according to claim 2, characterized in that in front of the crankcase of the internal combustion engine, a lubricating oil tank (11) with a level control float (27) and an oil drain pipe (28) opening into the crankcase are present. 5. Exhaust gas turbocharger according to claim 1, with a sealing air ring channel (40) between the bearing housing (39) and an outer housing (41) with ventilation connection for the bearing housing, characterized in that the ventilation connection via a line (50, 51) and one of these lines receiving compensating line (52) is in conductive connection with the low-pressure charge air line (53) upstream of the high-pressure compressor (44) or with the low-pressure exhaust gas line after the high-pressure exhaust gas turbine (45). 6. Exhaust gas turbocharger according to claim 5, characterized in that the bearing housing (39) via an oil return line with a lubricating oil tank (54) and this via a compensating line (55) with the low-pressure charge air line (53) in front of the high-pressure compressor (44) in conductive connection.

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