The invention relates to an element which generates a magnetic field in order to fasten a compressor wheel to a turboshaft of an exhaust-gas turbocharger, having a basic body and a thread.
The power which is generated by an internal combustion engine depends on the air mass and the fuel quantity supplied to the internal combustion engine. In order to increase power, it is necessary to supply the internal combustion engine with an increased quantity of combustion air and fuel. The increase in power is brought about in an induction engine by increasing the cubic capacity or by increasing the rotational speed. However, increasing the cubic capacity basically gives rise to relatively heavy internal combustion engines which have relatively large dimensions and are therefore more expensive. Increasing the rotational speed entails considerable problems and disadvantages, in particular in relatively large internal combustion engines.
A technical solution which is often used for increasing the power of an internal combustion engine is supercharging. This refers to the precompression of the combustion air by means of an exhaust-gas turbocharger or else by means of a compressor which is driven mechanically by the engine. An exhaust-gas turbocharger is composed essentially of a compressor and a turbine which are connected to a common shaft and rotate at the same rotational speed. The turbine converts the energy of the exhaust gas which is usually wasted by being expelled from the exhaust pipe into rotational energy and drives the compressor. The compressor sucks fresh air in and feeds the precompressed air to the cylinders of the engine. An increased fuel quantity can be supplied to the relatively large air quantity in the cylinders, as a result of which the internal combustion engine outputs more power. The combustion process is also favorably influenced so that the internal combustion engine achieves a better overall efficiency level. Furthermore, the torque profile of an internal combustion engine which is supercharged with a turbocharger can be made extremely favorable.
As the exhaust gas quantity increases, the maximum permissible rotational speed of the combination of the turbine wheel, the compressor wheel and the turboshaft, which are also referred to as the rotating parts of the exhaust-gas turbocharger, can be exceeded. If the rotational speed of the rotating parts is exceeded to an unacceptable degree, they are destroyed, which amounts to a total write-off of the turbocharger. Particularly modern and small turbochargers with significantly smaller turbine diameters and compressor wheel diameters, which have an improved rotational acceleration behavior by virtue of a considerably smaller moment of mass inertia, are affected by the problem of the acceptable maximum rotational speed being exceeded. Depending on the design of the turbocharger, the turbocharger is completely destroyed even if the rotational speed limit is exceeded by only approximately 5%.
Very precise measurement of the rotational speed of turbochargers is carried out with an element which generates a magnetic field and which is arranged on the turboshaft and rotates along with it, in which case the magnetic field which is produced by the rotating element which generates a magnetic field is sensed by a sensor which generates an electrical signal which is proportional to the rotational speed of the turboshaft.
JP 10206447 A2 discloses a magnetized nut for fastening the compressor wheel to the turboshaft. A rod magnet, which is supported by a basic body, is arranged in this nut. In order to generate in the sensor a magnetic field which can be measured satisfactorily, on the one hand the rotating magnet must be as large as possible and must produce a sufficient field strength, and on the other hand all the magnets are formed from very brittle material so that they are not very suitable as an element for fastening the compressor wheel to the turboshaft since the brittle magnetic material can only absorb to a limited or insufficient degree the forces and tightening torques which occur when the compressor wheel is fastened to the turboshaft.
The object of the present invention is therefore to specify an element which generates a magnetic field in order to fasten a compressor wheel to a turboshaft of an exhaust gas turbocharger, which element generates a magnetic field strength which is as high as possible and nevertheless can absorb without damage the forces and tightening torques which occur when the compressor wheel is fastened to the turboshaft.
This object is achieved according to the invention by means of the features of independent claim 1.
In the entire basic body is composed of a magnetic material and a sleeve, which is composed of a nonmagnetic material and which has the thread which can be screwed to a corresponding thread on the turboshaft, is arranged in the basic body, the element which generates a magnetic field can generate a magnetic field with a high field strength, and in addition said element is suitable for absorbing without damage the forces and tightening torques which occur when the compressor wheel is fastened to the turboshaft. The element which generates the magnetic field according to the invention therefore combines two properties which are not available with a magnetic field-generating element according to the prior art.
In one refinement, the sleeve is embodied as a press-in sleeve. The press-in sleeve can be connected to the basic body very quickly and with little expenditure, which reduces costs and production time.
In a subsequent refinement, the basic body has an internal toothing system by means of which the sleeve is connected in a positively locking fashion to the basic body. As a result, the sleeve is permanently anchored in the basic body.
In one development, the sleeve is composed of a nonmagnetic metal. A sleeve composed of metal is very suitable for being pressed in to the basic body and it can absorb large forces and torques without damage. Alternatively, the sleeve is composed of a plastic. Modern plastics can also absorb large forces and torques without damage, and it is even conceivable to produce the sleeve in the basic body by using an injection molding method.
In a subsequent development, the sleeve is connected to the basic body by means of at least one crimped connection. A sleeve can easily be crimp-connected at the edges without a large degree of expenditure, as a result of which a secure and permanent connection of the sleeve to the basic body is also generated.
In a subsequent refinement, the sleeve is formed from austenitic steel. Austenitic steel is particularly strong and can therefore absorb particularly well the large forces and tightening torques which occur when the compressor wheel is fastened to the turboshaft.
Embodiments of the invention are illustrated by way of example in the figures, in which:
The element 17 which generates a magnetic field in order to fasten the compressor wheel 9 to the turboshaft 5 is composed of a permanent magnet 13 which forms the basic body 11 of the element 17 which generates a magnetic field. As the turboshaft 5 rotates, the magnet 13 rotates along with it about the axis of rotation of the turboshaft 5. In the process, the magnet 13 generates a change in the magnetic field strength or the magnetic field gradient in the sensor 15. This change in the magnetic field or the field gradient generates in the sensor 15 a signal which can be processed electronically and which is proportional to the rotational speed of the turboshaft 5.
A sectional illustration of the element 17 which generates a magnetic field is shown in
The thread 8, which is screwed to the corresponding thread 19 on the turboshaft 5, can be seen in the sleeve. Here too, the basic body 11 has, for example, a hexagonal cap 14 on which a screw wrench can engage. The torques and forces which arise are transmitted completely to the sleeve 10 which is formed from high-strength material. The sleeve 10 therefore absorbs all the mechanical forces, as a result of which the compressor wheel 9 is firmly secured to the turboshaft 5. The sleeve 10 is pressed against the compressor wheel 9 by means of the crimped connection 20.
On the other hand, the large-volume magnet 13, which is a component of the element 17 which generates a magnetic field, can generate a field with a high magnetic field strength, making it possible to place the sensor 15 even at a relatively large distance from the element 17 which generates a magnetic field. The magnet 13 is, for example, capable of generating a magnetic field with a field strength which can be measured through the outer wall of the compressor housing. This has the advantage that the sensor 15 can be mounted outside the compressor housing, as a result of which it is not necessary to make an intervention into the body of the compressor housing.
Number | Date | Country | Kind |
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10 2006 045 772.2 | Sep 2006 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP07/60099 | 9/24/2007 | WO | 00 | 3/26/2009 |