GB2084251A - Damping vibrations of a compressor in an exhaust-gas turbocharger - Google Patents

Abstract

In order to damp undesirable mechanical vibrations produced by a compressor incorporated in an exhaust-gas turbocharger, which vibrations are conducted through the compressor's housing 18, at least one separating ring 22 is arranged in the compressor housing's rear wall 20 concentrically or eccentrically to rotor shaft 11, which separating ring 22 divides the rear wall 20 into a central disc 20.1 and an outer ring 20.2 and is made of a material having good vibration damping properties, e.g. a heat resistant rubber or plastics material. Alternatively two or more separating rings can be arranged on the rear wall, each either concentrically or eccentrically to the rotor shaft 11. <IMAGE>

Description

SPECIFICATION A compressor of a type incorporated in an exhaust-gas turbocharger This invention related to a compressor, of a type which can be incorporated in an exhaust-gas turbocharger, comprising a compressor housing enclosing a compressor wheel and fastened, by its rear wall, to a stator housing mounting a drive shaft.

Known high-speed compressors, more especially of the type incorporated in exhaust-gas turbochargers, produce considerable noise because the material or materials from which the compressor is made allow easy passage therethrough of any mechanical vibrations produced by the compressor during its operation.

The vibrations causing the noise are produced, for example, by the rotation of the rotor when it is in imbalance. These mechanical vibrations (or oscillations) are passed on by way of the stator components and are radiated at the compressor housing. In this respect, resonance phenomena arise at the compressor housing and the rear wall thereof.

The level of this noise, which can be very burdensome when it is in the high frequency region, is extremely difficult to reduce. One solution for reducing the level of noise, which has been used with some success, is the very fine balancing of the rotor. This solution has, however, proved extremely expensive to adopt. Moreover, the centre of balance of the rotor shifts during its operation, so that any noise reduction can only be achieved for a short time. The main cause of the increase in the level of noise during operation of the compressor is because of newly-arising imbalances at the rotor as a result of wear and ageing and also thermal distortions or eiasticplastic deformations of the rotor as a result of mechanical stresses due to centrifugal forces as well as inner moments of the bend-soft rotor.

The possibility does exist of improving the damping of the conduction of sound through the compressor between rotor and stator by an enlargement of the damping gap of the friction bearings, but this solution has only a slight value, since in the interests of a smooth shaft run, i.e. an optimising of the bearing-rotor system from the rotor-dynamic point of view, changes in the size of the bearing gap are scarcely permissible.

Finally, the level noise produced by the compressor can also be affected by a difference in the mass ratios between the compressor housing and the compressor-housing's rear wall. However, this latter solution results in a compressor of considerably higher weight, in which respect hindrances of other functions occur and an economical mass production of the compressor is hardly possible.

The problem underlying the invention is, therefore, to provide measures with which a considerable reduction in the level of noise produced by compressors, of a type incorporated in an exhaust-gas turbocharger, is achieved, in which respect not only is an economical solution for the mass production of the compressors to be found, but also the re-equipment of already existing compressors is possible with low expenditure.

In accordance with the present invention, this problem is solved in that there is provided a compressor, of a type which can be incorporated in a turbocharger, comprising a compressor housing enclosing a compressor wheel and fastened, by its rear wall, to a stator housing mounting a drive shaft, characterised in that provided in the rear wall of the compressor housing there is at least one encircling separating ring which deadens vibrations and sound conducted through the compressor housing and which connects two adjoining parts of the rear wall to one another.

As a result of the present invention, the conduction of sound through the compressor, from the rotor and the stator to the compressor housing, is considerably damped so that the level of noise radiation can be very strongly reduced.

Depending on the construction of the rear wall of the compressor housing, at frequencies of between 600 Hertz and 2000 Hertz noise damping values in the order of 12 dB at low frequencies and over 20 dB at high frequencies have been achieved. In this respect, rotors obtained from normal production and which were not finely-balanced were used.

As a result of the solution proposed by the present invention it is ensured, in an advantageous manner, that, in the production of exhaust-gas turbochargers, it is possible to use rotors having maximum production imbalance and the maximum permissible change in operating imbalance without the occurrence of severe noise, which could not previously be avoided during operation.

A further aspect of the present invention provides for the fact that, advantageously, two or more separating rings are arranged in the rear wall of the compressor housing. In this respect, the location of the mounting of each separating ring is determined by the ratio of the individual masses of each component of the rear wall to the overall mass to the rear wall and the desired pole positions of the oscillatory system. The advantage of the use of several separating rings is the fact that it provides a series-connected damping system in which, by co-ordinating the mass ratios, the pole positions can be shifted into frequency regions in which the noise radiation is particularly intensive. The design of the separating rings is to a wide extent variable and depends upon the respective constructional features of the rear wall of the compressor housing.

As a further advantageous aspect of the present invention is the fact that the or each separating ring is a flat strip element which has a force-locking adhesive connection to the adjacent parts of the compressor housing's rear wall.

Preferably the strip element is provided with projections which are in force-locking adhesive connection with adjacent parts of the rear wall.

The or each separating ring can be made of a heat and adhesion-resistant elastomer or rubber material which is bonded or vulcanised between the parts of the rear wall. Alternatively the or each separating ring may consist of a plastics material.

In this respect, in the production of the rear wall either highly heat-proof thermoplastic or polyamide materials, can be introduced into the space provided for the separating ring.

The invention will be described further, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a longitudinal section through an exhaust-gas turbocharger incorporating a preferred embodiment of the compressor of the invention; Fig. 2 is a longitudinal section through a further embodiment of a rear wall of a compressor housing of the compressor of Fig. 1; Fig. 3 is a partial view, in section, through yet a further embodiment of a rear wall of the compressor Fig. 1; and Fig. 4 is a partial plan view of a separating ring of the rear wall of Fig. 3.

Referring firstly to Fig. 1 , the illustrated exhaust-gas turbocharger comprising a stator 10, in which a rotor shaft 11 is mounted for rotation.

The rotor shaft 11 carries, on the right-hand side i.e. as viewed in Fig. 1, a turbine wheel 12 which is arranged in a turbine housing 14. Mounted on the left-hand side i.e. as viewed in Fig. 1, of the rotor shaft 11 is a preferred embodiment of the compressor of the invention comprising a compressor wheel 1 6 which rotates in a compressor housing 18. The compressor housing 1 8 is sealed off, at its rear end i.e. that end immediately opposite the stator 10, by a rear wall 20. The rear wall 20 is secured to the stator 10 by screws, only one of which screws is shown in Fig. 1.

If, because of imbalances at the turbine wheel 12 or at the compressor wheel 1 6 respectively, mechanical vibrations or oscillations arise, these are passed on by way of the stator 10 and are radiated at the compressor housing 1 8. The resonance phenomena of the system of the compressor housing 1 8 and the compressor housing's rear wall 20 are of crucial importance for the radiation, in which respect it can be stated that substantial radiation is effected by way of the compressor housing's rear wall 20.In order to counter the conduction of sound, caused by mechanical vibrations, through the compressor housing 18 and to reduce the noise radiation, inserted in a region of the rear wall 20 which is exposed on the inside and outside of the housing 1 8 is a separating ring 22 which extends concentrically to the rotor shaft axis 11 over the entire axial thickness of the rear wall 20. This separating ring 22 consists of a heat-resistant elastomer, for example of a heat-resistant rubber material, or of a plastics material, which enters into secure adhesive connection with the two adjacent metallic parts of the rear wall 20, so that a force-locking adhesive connection arises between the rear wall 20 and separating ring 22.

As a result of the separating ring 22 the compressor housing's rear wall 20 is subdivided into a central disc 20.1 and an outer ring 20.2, in which respect the separating ring 22 brings about a damping of sound, conducted through the compressor housing 18, between the central disc 20.1 and the outer ring 20.2.

In experimental constructions of the compressor of the invention very considerable lowering in the level of noise was obtained using an elastic hot adhesive. The two reference models used both showed, over a frequency curve of about 400 Hertz to 2000 Hertz, a noise abatement of about 10 dB at 400 Hertz with an improvement to about 13 dB at 1100 Hertz and a further improvement to over 20 dB at about 1700 Hertz.

The materials used for the separating ring 22 have a good material damping and good mechanical properties at a temperature of 1400C.

These properties are fulfilled by highly heat resistant rubber materials, in which respect a silicon rubber is preferred, as is also a plastics material, for example, polyamides and highly heat resistant thermoplastics.

The particular dimensions of the separation gap in the rear wall 20, which gap is filled by the separating ring 22, is governed by the material from which the separating ring 22 is made.

Fig. 2 illustrates a further embodiment of the rear wall, designated by reference numeral 30, of the compressor housing 18, which rear wall 30 is subdivided by two separating rings 32 and 33 into three parts. The aforesaid parts are respectively, a central disc 30.1 connected by way of a separating ring 32 to an intermediate ring 30.3 which in turn is connected by way of a separating ring 33 to an outer ring 30.2, The connection to the stator 10 is effected by way of the central ring 30.1, whereas the connection to the compressor housing 1 8 is effected by way of the outer ring 30.2.

As a result of the provision of two separating rings 32 and 33 in the rear wail 30 there arises a middle mass which strongly influences the resonance behaviour and which can be strongly influenced by the shaping of the intermediate ring 30.3. Through the use of such middle masses, the damping of sound conducted through the compressor housing 1 8 can be very strongly influenced, in that namely by a coordination of the mass ratios between middle mass and total mass, the pole positions of the damping course can be influenced and shifted with regard to its frequency position. In this way it is possible, with the aid of constructional measures, to reduce the noise radiation in an intentional manner, in which respect an optimisation for different constructional designs of the compressor housing and of the associated rear wall is possible.

As a result of the measures of the present invention it is also possible to convert exahust-gas turbochargers already in operation so that there is better deadening of sound conducted through the compressor housing and therewith better noise inhibition.

Since, as a result of the measures of the invention, very high damping values can be achieved, a fine balancing of the rotor i.e. the compressor wheel 16, rotor shaft 11 and turbine wheel 12, can be dispensed with. In this way considerable production advantages arise.

Although it is not shown in the drawings, an influencing of the damping of sound conducted through the compressor housing 1 8 can also be effected by separating rings arranged eccentrically to the rotor axis. This can be of advantage more especially when the cross-sectional dimensions of the compressor housing vary severely and thereby unequal mass distributions arise. Such an eccentric arrangement of the or each separating ring has, through its effect on the mass variations of the individual parts of the rear wall, a corresponding affect on the resonance phenomena in the compressor housing and the rear wall.

Illustrated in Figs. 3 and 4 is a further embodiment of the rear wall, designated by reference numeral 40, of the compressor housing 1 8 comprising a separating ring 42 provided, on its inside and its outside, with projections 43. The projections 43 engage into corresponding recesses on the end face of central disc 40.1 and outer ring 40.2 of the rear wall 40. The production of such a separating ring 42 can be effected in such a way that its component parts, produced, for example, from aluminium die cast metal, are inserted into an injection mould, in which respect a gap, corresponding to the thickness of the separating ring 42, is provided which is injected with a plastics material to form the separating ring 42. Instead of the plastics material, a rubber material can be used, which rubber material is bonded with or is vulcanised between the metal parts. Through the use of a separating ring 42 having projections 43 which extend in rib-shaped manner over portions of the inner and outer periphery of the rear wall 40, a force-locking adhesive connection is ensured.

Claims (9)

1. A compressor, of a type which can be incorporated in a turbocharger, comprising a compressor housing enclosing a compressor wheel and fastened, by its rear wall, to a stator housing mounting a drive shaft, characterised in that provided in the rear wall of the compressor housing there is at least one encircling separating ring which deadens vibrations and sound conducted through the compressor housing and which connects two adjoining parts of the rear wall to one another.

2. A compressor as claimed in claim 1, characterised in that two or more separating rings are arranged in the rear wall of the compressor housing.

3. A compressor as claimed in claim 2, characterised in that the location of mounting of the two or more separating rings is determined by the ratio of the intermediate masses of the components of the rear wail to the overall mass of the rear wall and the desired pole positions of the oscillatory system.

4. A compressor as claimed in claim 1,2 or 3, characterised in that the or each separating ring is a flat strip element which has a force-locking adhesive connection to the adjoining parts of the rear wall of the compressor housing.

5. A compressor as claimed in claim 4, characterised in that the or each strip element is provided with projections which are in forcelocking adhesive connection with the adjoining parts of the rear wall of the compressor housing.

6. A compressor as claimed in any preceding claim characterised in that the or each separating ring consists of a heat-resisting elastomer or a rubber material which Is bonded or vulcanised between the parts of the rear wall of the compressor housing.

7. A compressor as claimed in any one of claims 1 to 5, characterised in that the or each separating ring consists of a plastic material.

8. A compressor as claimed in any preceding claim characterised in that the or each separating ring is arranged eccentrically to the axis of the drive shaft.

9. A compressor of a type which can be incorporated in a turbocharger, substantially as hereinbefore described with reference to and illustrated in the accompanying drawings.