METHOD AND DEVICE FOR DRIVING A TURBOCHARGER

Abstract

In a method for driving a turbocharger with the aid of induction air which is fed to the turbine inlet, the compressed air which exits at the compressor outlet is guided into a turbine auxiliary inlet of the turbine, which turbine auxiliary inlet opens downstream of the turbine inlet into the turbine chamber at a point, at which the pressure in the driven state of the turbine is lower than the pressure of the air which is compressed by the turbocompressor.

Description

This invention relates to a method of driving a turbocharger comprising a turbine and a turbo compressor, with a housing which includes a turbine chamber having a turbine inlet and a turbine outlet, and a compressor chamber having a compressor inlet and a compressor outlet, and with a rotor having a turbine wheel arranged in the turbine chamber and a compressor wheel arranged in the compressor chamber, the method including the step of driving the rotor by means of charge air supplied to the turbine inlet. The present invention relates furthermore to a device for implementing the method.

To develop and manufacture turbochargers, specific measurement and test purposes including, for example, high-speed balancing operations, make it necessary for the rotor of the turbocharger to be brought to its maximum operating speed or a similarly high speed. For this to be accomplished, it is known from DE 10 2009 013 432 A1 to apply charge air to the turbine of the turbocharger, supplying in this manner the necessary propulsive power to the rotor. The charge air conventionally used is compressed air which may be drawn, for example, from a network of compressed air. The amount of compressed air needed for driving is considerable, the more so since compressed air is, as a rule, cold, that is, at room temperature, and the enthalpy difference in the turbine is correspondingly small. Compressed air as carrier of energy is comparatively expensive, and the energy efficiency of the drive of the turbine using compressed air is unfavorable. Therefore, accelerating a turbocharger rotor to maximum operating speed by means of charge air incurs considerable expense.

In a method of the type referred to and described in DE 10 2011 054 236 A1, the compressed air exiting at the compressor outlet is fed to the turbine inlet and admixed, by means of a jet pump, to the charge air for driving the turbine wheel, which is fed in the form of a jet to the turbine inlet at a pressure higher than the air arriving from the compressor and at a higher flow rate. In this way, added use is made of the compressed air supplied from the compressor side of the turbocharger for driving the turbocharger, and the amount of charge air needed is correspondingly lower. Admixing by means of a jet pump requires the pressure of the air arriving from the compressor to be below the pressure of the charge air only by an amount enabling the jet pump to ensure admixing by mixing the jet. The fulfillment of this condition depends on the respective configurations of turbine and compressor of the turbocharger and is not always guaranteed. Accordingly, this method is limited to applications in which the pressure differential between the pressure of the charge air and the pressure at the outlet of the compressor is not very high.

RU 2 023 248 C1 discloses a method of testing a supercharge turbo compressor in which high-pressure air generated by a starter compressor is fed to a swiveling nozzle arranged in the first stage of a two-stage ejector disposed downstream from the turbine, the first stage being provided with a diffuser. To perform a variety of tests, the nozzle is capable of swiveling into the direction of travel of the medium for generating a pressure below atmospheric in the gas discharge end of the turbine, or into the opposite direction for generating a pressure above atmospheric in the gas discharge end of the turbine.

Moreover, GB 611 528 A discloses a test arrangement in which a turbine to be tested is driven by compressed air and coupled to a compressor, providing the possibility for the compressed air at the compressor outlet to be used for driving the turbine by heating it and feeding it to the turbine inlet for augmenting the air supply.

RU 2 348 910 C1 discloses a method of testing turbochargers in which gas is injected to an inlet of the turbine and to an inlet of the compressor, causing the compressor to be set in rotation by the turbine. No provision is made for returning the compressed air to the inlet of the turbine.

It is an object of the present invention to provide an improved method of the type initially referred to, which reduces the demand for charge air for driving the rotor of the turbocharger.

According to the present invention, this object is accomplished by the method recited in claim 1. An advantageous device for implementing the method is recited in claim 2.

In the method of the present invention, the compressed air exiting at the compressor outlet is directed to a turbine auxiliary inlet which opens downstream from the turbine inlet into the turbine chamber at a site where the pressure in driven condition of the turbine is lower than the pressure of the air compressed by the compressor.

With the method of the present invention, added use is made of the compressed air supplied by the compressor of the turbocharger for driving the rotor by feeding it to the turbine auxiliary inlet. It will be understood, of course, that the air supplied by the compressor cannot be sufficient for driving the rotor because losses occur in both the turbine and the compressor which have to be compensated for by an external energy supply in the form of charge air. In addition, a surplus of energy is needed to accomplish a short-time acceleration of the rotor to a high rotational speed. In contrast to a drive using exclusively charge air, the method of the invention requires a considerable smaller amount of charge air for driving the rotor, since the energy stored in the air arriving from the compressor can be reclaimed for driving the turbine. In principle, the charge air supplied is only required to cover the energy losses in the turbine and the compressor and the losses in the rotor bearings. It is hence possible to reduce the consumption of charge air considerably by the method of the invention which affords relative ease of implementation. This then also results in a corresponding cost reduction for the drive of the turbocharger.

The method of the invention affords the further advantage of being largely independent of the turbocharger configuration and the pressure of the charge air. The pressure of the charge air in the turbine inlet is reduced in the turbine chamber to about atmospheric pressure in the turbine outlet. By suitable selection of the site of the auxiliary inlet between turbine inlet and turbine outlet, the pressure at the mouth of the auxiliary inlet can be therefore adjusted such as to be below the supply pressure of the turbo compressor by an amount sufficient to achieve a pressure differential for the air arriving from the turbo compressor which is beneficial for driving the turbine.

To implement the method of the invention, a device for driving a turbocharger comprising a turbine and a turbo compressor is suitable, with a housing which includes a turbine chamber having a turbine inlet and a turbine outlet, and a compressor chamber having a compressor inlet and a compressor outlet, with a rotor having a turbine wheel arranged in the turbine chamber and a compressor wheel arranged in the compressor chamber, and with a source of charge air adapted to be coupled to the turbine inlet, with the turbine chamber having a turbine auxiliary inlet which opens downstream from the turbine inlet into the turbine chamber at a site where the pressure in driven condition of the turbine is lower than the pressure of the air compressed by the compressor, and wherein the compressor outlet is adapted to be coupled to the turbine auxiliary inlet by a line in order to direct the compressed air exiting at the compressor outlet into the turbine auxiliary inlet.

The device of the present invention affords ease and economy of manufacture and convenience in handling. For increased efficiency, added provision may be made for guide vanes in the turbine inlet and/or in the turbine auxiliary inlet.

The method of the invention is suitable for utilization in connection with complete turbochargers and also turbocharger core assemblies. In turbocharger core assemblies the housing is composed of a center casing accommodating the rotor bearings and constituting a component part of the turbocharger, and of a turbine casing and a compressor casing which are attached to the center casing, forming, respectively, the turbine chamber and the compressor chamber with associated inlets and outlets. The method of the invention is not considered limited to an application to turbochargers but may also find a useful application in similarly constructed assemblies, for example, gas generator assemblies of small gas turbines, in order to drive these for balancing purposes or other requirements.

The present invention will be explained in more detail in the following with reference to an embodiment illustrated in the accompanying drawing. The drawing shows schematically a turbocharger with a connected charge air drive constructed in accordance with the invention.

Represented in the drawing is a turbocharger 1 comprising a turbine 2 and a turbo compressor 3. The turbocharger 1 includes a housing 4 defining a turbine chamber 5 and a compressor chamber 6 and a bearing casing 7 arranged therebetween. The housing 4 accommodates a rotor 8 having a shaft 9 carried in the bearing casing 7. Mounted on the shaft 9 in the turbine chamber 5 are a turbine wheel 10 and in the compressor chamber 6 a compressor wheel 11. On the motive fluid inlet side, the turbine chamber 5 is provided with an annular turbine inlet 12 which surrounds the turbine wheel 10 and opens radially into the turbine chamber 5, with the possibility for guide vanes 13 being arranged in its mouth. At the front end of the turbine wheel 10, the turbine chamber 5 opens into a coaxial turbine outlet 14. Between the turbine inlet 12 and the turbine outlet 14, the turbine chamber 5 includes an annular turbine auxiliary inlet 15 which opens into the turbine chamber 5 and may have on its mouth a nozzle ring 15 with guide vanes. The compressor chamber 6 has at its front end a central compressor inlet 17 and an annular compressor outlet 18.

To drive the turbocharger 1, for example, for measurement purposes, the compressor outlet 18 is connected to the turbine auxiliary inlet 15 by means of a line 20. In addition, a line 21 connects the turbine inlet 12 to a charge-air reservoir 22 to which charge air is delivered by a motor-powered compressor 23. Arranged in the line 21 is a valve 24 for controlling the supply of charge air. The pressure of the charge air is considerably higher than the maximum pressure which the compressed air supplied from the turbo compressor 3 reaches in the compressor outlet 15 at maximum operating speed.

When it is desired to drive the rotor 8 and accelerate it to a speed corresponding preferably to the maximum operating speed, the valve 24 opens, directing charge air into the turbine inlet 12. The charge air entering from there into the turbine chamber 5 drives the turbine wheel 10, setting the rotor 8 in rotation. With the speed of the rotor 8 increasing, the output of the turbo compressor 3 increases, too, and with it the pressure of the compressed air in the volumetric flow fed to the turbine auxiliary inlet 15. A pressure differential develops on the turbine auxiliary inlet 15 between the pressure of the compressed air and the pressure in the turbine chamber 5 which at this point has already dropped to a low pressure. The pressure differential becomes greater with the speed, generating an air stream of high flow velocity which drives the turbine wheel 10. The turbine speed continues to increase until it reaches a value at which an equilibrium is present at which the energy supplied with the charge air from the charge-air reservoir 22 corresponds to the energy losses in the turbine 2, in the turbo compressor 3 and in the rotor bearings. When it is desired to increase the rotor speed still further, it is necessary to increase the supply of charge air by suitable control of the valve 24. Conversely, the rotor speed may be lowered by reducing the supply of charge air.

Overall, by introducing the compressed air supplied by the turbo compressor 3 into the turbine 2, the necessary amount of charge air and hence the expenditure of energy and cost for a measurement and test operation of the turbocharger 1 are significantly reduced.

Claims

1. A method of driving a turbocharger (1) comprising a turbine (2) and a turbo compressor (3), with a housing (4) which includes a turbine chamber (5) having a turbine inlet (12) and a turbine outlet (14), and a compressor chamber (6) having a compressor inlet (17) and a compressor outlet (18), and with a rotor (8) having a turbine wheel (10) arranged in the turbine chamber (5) and a compressor wheel (11) arranged in the compressor chamber (6), the method including the step of driving the rotor (8) by means of charge air supplied to the turbine inlet (12), wherein the compressed air exiting at the compressor outlet (18) is directed to a turbine auxiliary inlet (15) which opens downstream from the turbine inlet (12) into the turbine chamber (5) at a site where the pressure in a driven condition of the turbine (2) is lower than the pressure of the air compressed by the turbo compressor (3).

2. A device for driving a turbocharger (1) comprising a turbine (2) and a turbo compressor (3), with a housing (4) which includes a turbine chamber (5) having a turbine inlet (12) and a turbine outlet (14), and a compressor chamber (6) having a compressor inlet (17) and a compressor outlet (18), with a rotor (8) having a turbine wheel (10) arranged in the turbine chamber (5) and a compressor wheel (11) arranged in the compressor chamber (6), and with a source of charge air adapted to be coupled to the turbine inlet (12), comprising a turbine auxiliary inlet (15) which opens downstream from the turbine inlet (12) into the turbine chamber (5) at a site where the pressure in a driven condition of the turbine (2) is lower than the pressure of the air compressed by the turbo compressor (3), and by a line (20) adapted to couple the compressor outlet (18) to the turbine auxiliary inlet (15) in order to direct the compressed air exiting at the compressor outlet (18) into the turbine auxiliary inlet (15).

3. The device according to claim 2, wherein guide vanes (13) are arranged in the turbine inlet and/or in the turbine auxiliary inlet.

4. The device according to claim 2, wherein the supply of charge air is controllable by a valve (24).