EXHAUST-GAS TURBOCHARGER

Abstract

An exhaust-gas turbocharger (1), having a shaft (2) on which are arranged a compressor wheel (3) and a turbine wheel (4), a bearing housing (5) in which are arranged a compressor-side bearing arrangement (6) and a turbine-side bearing arrangement (7) for the shaft (2), an oil inflow line (8) and an oil outflow line (9), and an additional oil accumulator (10) for the bearing arrangements (6, 7) of the shaft (2). The oil accumulator (10) is a pressure accumulator arranged in a branch line (11) of the oil inflow line (8), and a controllable valve (13) is arranged between the oil accumulator (10) and the opening-in point (12) of the branch line (11) into the oil inflow line (8).

Description

The invention relates to an exhaust-gas turbocharger according to the preamble of claim 1.

An exhaust-gas turbocharger of said type is known from EP 2 054 597 B1.

For the supply of lubricant to the bearings of the shaft, said exhaust-gas turbocharger utilizes the engine oil pump of the internal combustion engine on which the turbocharger is mounted.

As a result of the lengths of the lines or ducts, the viscosity of the lubricant, manufacturing tolerances and other influences, however, there is a delay in the build-up of pressure, and therefore a delayed supply of lubricant to the bearing system of the exhaust-gas turbocharger, during an engine start.

A similar problem can also occur during the stopping of the engine when the exhaust-gas turbocharger overruns on account of its mass inertia. In both cases, the bearing arrangement runs through the mixed friction phase, wherein furthermore, during a renewed engine start, the lubricant remaining in the exhaust-gas turbocharger is heated by the residual heat.

This has the result that the viscosity of the lubricant falls and the lubricating properties are degraded yet further.

The described problems can, in extreme applications such as for example in hybrid applications or a very high number of start/stop cycles, lead to damage to the bearing arrangement of the exhaust-gas turbocharger and therefore to failure of the overall system.

Therefore, in the generic exhaust-gas turbocharger according to EP 2 054 597 B1, an additional oil accumulator is provided which, in said document, is referred to as an emergency oil tank and extends in the axial direction over all the radial bearings. Since gravitational force is used to provide an oil supply in said system, the emergency oil tank is arranged above the radial bearings and at a small radial distance from said bearings.

Tests carried out within the context of the invention have however shown that, specifically in the extreme applications mentioned above, an additional oil supply of said type which is based on gravitational force is often not sufficient.

It is therefore an object of the present invention to provide an exhaust-gas turbocharger of the type specified in the preamble of claim 1, which always permits a sufficient supply of oil to the bearing arrangements of the charger shaft at a standstill and during the start-up of the exhaust-gas turbocharger.

Said object is achieved by means of the features of claim 1.

The additional oil accumulator of the exhaust-gas turbocharger according to the invention is designed as a pressure accumulator. To avoid mixed friction states during a start/stop cycle of the exhaust-gas turbocharger, lubricant is supplied in a dosed fashion to the bearing arrangement thereof by means of said pressure accumulator.

For this purpose, during engine operation, a partial quantity of the lubricant in circulation is extracted and temporarily stored in the pressure accumulator as pressurized lubricant. For this purpose, use may be made of a hydraulic accumulator such as is known from the field of hydraulics.

By means of a controllable valve on the pressure accumulator and preferably a further simple check valve in the inflow line for the lubricant, it is possible for lubricant to be supplied in a dosed fashion to the bearing arrangements during the starting and stopping of the engine.

It is possible here for the check valve in the inflow line to be exchanged for a controllable valve, in particular check valve, or a pressure differential valve.

If a pressure differential valve is used, the pressures on both sides of the valve are utilized to generate a movement of the valve in order to realize a build-up or dissipation of pressure in the inflow line and/or in the pressure accumulator and during start/stop cycles.

If a controllable valve, in particular check valve, is used, the pressure signals of the inflow line and of the accumulator system are evaluated and linked by means of an actuation strategy in such a way that a uniform pressure build-up takes place in the bearing system.

Here, it is possible according to the invention for the system to be designed as an external or internal system.

As an internal system, it is possible here for the components of the pressure accumulator, of the valves and of a control device to be integrated in the bearing housing of the exhaust-gas turbocharger.

Further details, advantages and features of the present invention will emerge from the following description of an exemplary embodiment on the basis of the drawing, in which:

FIG. 1 shows a perspective, cut-away illustration of an exhaust-gas turbocharger showing the basic components not illustrated in FIG. 2, and

FIG. 2 shows a schematically simplified illustration of an exhaust-gas turbocharger according to the invention.

An exhaust-gas turbocharger 1 according to the invention illustrated in FIG. 2 has not only the components illustrated in said figure but also the components shown in FIG. 1, specifically a shaft 2, a compressor wheel 3, a turbine wheel 4 and a bearing housing 5. A compressor-side bearing arrangement 6 and a turbine-side bearing arrangement 7 for mounting the shaft 2 are arranged in the bearing housing 5.

The exhaust-gas turbocharger 1 according to the invention self-evidently also has all the other conventional components of modern turbochargers, but these are not of importance for the description of the present invention.

According to FIG. 2, the exhaust-gas turbocharger 1 also has an oil inflow line 8 and an oil outflow line 9 which are hydraulically connected to the engine oil circuit of the engine on which the exhaust-gas turbocharger 1 is mounted.

The exhaust-gas turbocharger 1 according to the invention also has an additional oil accumulator 10 which is designed as a pressure accumulator and arranged in a branch line 11 of the oil inflow line 8. As shown in FIG. 2, a controllable valve 13 is inserted between the oil accumulator 10 and the opening-in point 12 of the branch line 11 into the oil inflow line 8. The controllable valve 13 can be opened and closed by means of a control device 14, wherein the control device 14 for this purpose uses pressure signals from the inflow line and from the pressure accumulator 10, said pressure signals being symbolized in FIG. 2 by the dashed line DS.

Also provided in the oil inflow line, upstream of the opening-in point 12, is a simple check valve 15 which may also be replaced with a controllable valve.

By actuating the valves 13 and 15, the pressure accumulator 10 can be charged with pressurized lubricant when sufficient oil pressure has been built up by the oil pump of the engine.

During start/stop processes, it is then possible, by means of the lubricant temporarily stored in the pressure accumulator 10 and the actuation of the valves 13 and 15, for lubricant to be supplied in a targeted fashion to the bearing arrangements 6 and 7 of the exhaust-gas turbocharger 1 in order to prevent the non-ideal bearing conditions resulting from insufficient lubrication, as explained in the introduction.

In addition to the above written disclosure of the invention, reference is hereby explicitly made to the diagrammatic illustration thereof in FIGS. 1 and 2.

LIST OF REFERENCE SYMBOLS

• 1 Exhaust-gas turbocharger
• 2 Shaft
• 3 Compressor wheel
• 4 Turbine wheel
• 5 Bearing housing
• 6 Compressor-side bearing arrangement
• 7 Turbine-side bearing arrangement
• 8 Oil inflow line
• 9 Oil outflow line
• 10 Oil accumulator/pressure accumulator
• 11 Branch line
• 12 Opening-in point
• 13 Valve
• 14 Control device
• 15 Check valve
• DS Pressure signal

Claims

1. An exhaust-gas turbocharger (1), having

a shaft (2) on which are arranged a compressor wheel (3) and a turbine wheel (4),

a bearing housing (5) in which are arranged a compressor-side bearing arrangement (6) and a turbine-side bearing arrangement (7) for the shaft (2),

an oil inflow line (8) for supplying oil to the bearing arrangements and an oil outflow line (9), and

an additional oil accumulator (10) for the bearing arrangements (6, 7) of the shaft (2),

wherein the oil accumulator (10) is a pressure accumulator arranged in a branch line (11) of the oil inflow line (8), and

wherein a controllable valve (13) is arranged between the oil accumulator (10) and an opening-in point (12) of the branch line (11) into the oil inflow line (8).

2. The exhaust-gas turbocharger as claimed in claim 1, including a control device (14) for opening and closing the controllable valve (13) as a function of received pressure signals (DS) from the inflow line (8) and the oil accumulator (10).

3. The exhaust-gas turbocharger as claimed in claim 1, wherein a check valve (15) is arranged in the oil inflow line (8) upstream of the opening-in point (12) of the branch line (11).

4. The exhaust-gas turbocharger as claimed in claim 1, wherein a controllable valve is arranged in the oil inflow line (8) upstream of the opening-in point (12) of the branch line (11).

5. The exhaust-gas turbocharger as claimed in claim 1, wherein a pressure differential valve is arranged in the oil inflow line (8) upstream of the opening-in point (12) of the branch line (11).

6. The exhaust-gas turbocharger as claimed in claim 1, wherein the oil accumulator (10) and the valves (13, 15) and also the control device (14) are integrated into the bearing housing (5).

7. The exhaust-gas turbocharger as claimed in claim 1, wherein the oil accumulator (10) and the valves (13, 15) and also the control device (14) are an external system.