Patent Application
20220136519
The present invention relates to the field of compression devices driven by an electric machine and in particular the invention concerns a turbocharger driven by an electric machine and notably relates to a device for compressing a gaseous fluid, such as air here, by a compressor, alone or associated with a turbine to form a turbocharger, prior to sending the compressed fluid to any device and, more particularly, to the intake of an internal-combustion engine.
Indeed, as is widely known, the power delivered by an internal-combustion engine depends on the amount of air fed to the combustion chamber of this engine which is itself proportional to the density of the air.
Thus, it is usual to increase this amount of air through compression of the outside air before it is allowed into this combustion chamber when high power is required. This operation, known as turbocharging, can be carried out using any device such as a compressor alone, electrically driven by an electric machine (electrified compressor), or a compressor associated with a turbine and an electric machine to form an electrified turbocharger.
In the aforementioned two cases, the electric machine associated with the compressor can be of different types.
One is an electric machine with a small air gap and windings close to the rotor, which provides optimal guidance of the magnetic flux and optimized efficiency. This type of electric machine has the advantage of a certain compactness, which may sometimes be a problem regarding cooling thereof and requires a specific system for carrying off heat losses.
In order not to be intrusive on the air intake of the compressor, this type of electric machine is conventionally positioned on the back of the compressor in the case of an electrified compressor, or between the compressor and the turbine in the case of an electrified turbocharger, despite the presence of an unfavorable thermal environment in the latter case from being close to the turbine. Generally, the link between the compressor, the turbine and the electric machine is rigid. This type of machine can also be positioned on the compressor side, but relatively far from the air intake so as not to disturb it. The link between the compressor and the electric machine is then rigid or it is provided by a mechanical or a magnetic coupling.
This type of system is described in more detail in patents in published US patent applications and issued patents: 2014/0,373,532, U.S. Pat. Nos. 8,157,543, 8,882,478, 2010/0,247,342, 6,449,950, 7,360,361, and EP-0,874,953 or EP-0,912,821.
Another type of machine is an electric machine with a large air gap that may sometimes be several centimeters long which allows passage of the working fluid therethrough that enables integration as close as possible to the compression systems, in a significantly more favorable thermal environment.
This electric machine layout however involves the drawback of disturbing and limiting the passage of the magnetic flux between the rotor and the stator through the large air gap, and thereby contributes to limiting the intrinsic efficiency of the electric machine and the specific performances thereof (power-to-weight ratio and power density). The high losses with this type of design also require specific cooling to discharge the heat from the rotor and the stator or to limit the specific performances.
This type of electric machine is notably described in EP-1,995,429 and US published patent applications 2013/169,074 and 2013/043,745.
A third type of electric machine is a machine provided with a stator grid, which is an electric machine having a stator with stator teeth around which coils are mounted which stator teeth have large dimensions allowing passage of the air stream. This type of machine is an electric machine with a small air gap and windings positioned away from the rotor which can be arranged at the compressor intake. Such a stator grid machine is notably described in patent applications WO-2013/050,577 and FR-3,048,022.
One problem related to the electrification of compressors concerns the design of the rotor and its connection to the compressor shaft. This design is often complex (use of screws) and it is expensive to provide good coaxiality of the rotor and of the compressor shaft, as required for operation at very high rotational speeds.
Patent application FR-17/61,576 describes several electric rotor structures and structures for mounting on the shaft of a turbocharger, by adding a rotor to a shaft opening onto the compressor side. These structures provide for integration of rotors on already existing turbochargers. However, these structures are most often not readily compatible with an industrial mass production manufacturing process, considering the manufacturing tolerances and the rotor balancing operations required in order to obtain such a system.
In order to reduce the complexity of the manufacturing and assembly method, and to be compatible with an industrial mass production manufacturing process, the present invention is a compression device driven by an electric machine in which the rotor comprises a cylindrical magnet and a non-magnetic binding ring. According to the invention, the rotor is mounted on the compression shaft, and a nut is provided to axially secure the rotor and the compressor wheel of the compressor. Thus, the compression shaft extends through the rotor, which reduces the complexity of the parts to be manufactured, regarding the shape of the components or the manufacturing tolerances. Furthermore, the invention reduces the number of operations required in the manufacturing and assembly process and in particular the balancing operations which may be expensive.
The invention relates to a fluid compression device driven by an electric machine. The electric machine comprises a rotor and a stator, a compression shaft on which at least one compressor wheel is mounted. The rotor comprises a cylindrical magnet and a binding ring for retaining the magnet. The rotor is mounted on the compression shaft and a nut is arranged at the end of the compression shaft to axially secure the rotor and the compressor wheel.
According to an embodiment, the rotor comprises a means of supporting the cylindrical magnet, which is cylindrical and arranged around the compression shaft.
Preferably, the support means is a cylindrical sleeve.
According to an aspect, the cylindrical sleeve abuts against the compressor wheel and against the nut.
Advantageously, the cylindrical sleeve abuts against a system for guiding the compression shaft and against the nut.
In a variant, the compressor wheel is mounted on the cylindrical sleeve.
Alternatively, the compressor wheel comprises the support means.
According to an implementation, the outside diameter of the rotor is less than or equal to the diameter of a nose of the compressor wheel.
According to an aspect, the rotor comprises at least one non-magnetic stop on one side of the magnet.
According to an option, the binding ring is made of a non-magnetic material, preferably titanium or carbon.
According to a feature, the compression device is a turbocharger combining a turbine and a compressor, notably for an internal-combustion engine, or a microturbine.
Advantageously, the electric machine is arranged in the gas intake of the turbocharger.
According to an embodiment, the electric machine is a stator grid machine.
Furthermore, the invention relates to a method of manufacturing a compression device driven by an electric machine, the electric machine comprising a rotor and a stator, the compression device comprising a compression shaft on which at least one compressor wheel is mounted. For this method, the following steps are carried out:
a) mounting the compressor wheel onto the compression shaft;
b) mounting a cylindrical magnet onto a support means arranged on the compression shaft;
c) radially retaining the cylindrical magnet radially by a binding ring; and
d) axially securing the rotor and the compressor wheel by a nut arranged at the end of the compression shaft.
Other features and advantages of the device and of the method according to the invention will be clear from reading the description hereafter of embodiments, given by way of non limitative example, with reference to the accompanying figures wherein:
The present invention relates to a device for compressing a fluid, notably gas, driven by an electric machine. In other words, the invention relates to the assembly made up of the electric machine and the compression device. Preferably, the compression device is air compression device.
The fluid compression device comprises a shaft, referred to as compression shaft, on which a compressor wheel (also referred to as blade) is mounted.
The electric machine comprises a rotor and a stator. The rotor is mounted on the compression shaft for transmitting or drawing the torque of the electric machine to the compression shaft and the compressor wheel, and vice versa.
The rotor comprises at least:
According to the invention, the rotor is mounted on the compression shaft, and a nut is arranged at the end of the compression shaft for axially securing the rotor and the compressor wheel. In other words, the compression shaft extends through the rotor, and the assembly is secured by a nut arranged at the outlet end of the compression shaft. Thus, the rotor rests on one side against the compressor wheel and on the other side against the nut. The rotor therefore requires no fastening means, in particular a threading/tapping system, with the compression shaft (as it is the case for the embodiments described in patent application No. FR-17/61,576). Thus, the coaxiality and holding functions are disjoint, which facilitates mounting operations. Furthermore, the compression shaft is longer than the one described in the aforementioned prior application, which facilitates the design thereof. The invention thus reduces the complexity of the assembly, reduces the number of operations in the method of manufacturing and assembling the compression device, and reduces the complexity of the parts to be manufactured. The nut can also exert a preload on the rotor, the compressor and a system for guiding the compressor (bearing) with respect to a casing.
According to an embodiment of the invention, the rotor can also comprise a means of supporting the cylindrical magnet which is positioned between the compression shaft and the cylindrical magnet. The purpose of the support means is to facilitate the coaxiality of the rotor and the compression shaft. The support means has an internal bore of the same diameter as the compression shaft. For this embodiment, the support means can be cylindrical. The support means is referred to as cylindrical because it has an outer surface with at least one cylindrical portion for positioning the cylindrical magnet of the rotor. According to some embodiments, the support means can have cylindrical portions with different outside diameters.
According to a first implementation of this embodiment, the support means of the cylindrical magnet can be a cylindrical sleeve. The binding ring then exerts a radial compression of the cylindrical magnet on the cylindrical sleeve. Preferably, the cylindrical sleeve can be made of a magnetic material.
According to a first variant of this first implementation, the cylindrical sleeve can have a length equal to the length of the rotor. In this case, the cylindrical sleeve can abut on one side against the compressor wheel and, on the other side, against the nut. For this embodiment, the cylindrical sleeve can comprise a shoulder, and the shoulder can be in contact with the compressor wheel or with the nut. For the assembly of this variant, the rotor is assembled on the compression device after previously positioning the compressor wheel on the compression shaft. This variant embodiment allows each element to be made of the material that best matches the purpose thereof.
According to a second variant of this first implementation, the cylindrical sleeve can have a length corresponding to the cumulative length of the rotor and of the compressor wheel. In this case, the compressor wheel is mounted on a portion of the cylindrical sleeve. Furthermore, the cylindrical sleeve can abut on one side against the nut and on the other side against a compressor guide system (a bearing or a plain bearing for example). The cylindrical sleeve can have three cylindrical portions whose diameters may be different, one for setting the compressor wheel, one for setting the cylindrical magnet, and a shoulder between the other two portions. For this variant, the assembly is obtained by mounting the compressor wheel on the cylindrical sleeve, to provide a preliminary rotor assembly with the compressor wheel and to balance the system at once. In this assembly, the compressor wheel can be held on the cylindrical sleeve by binding, gluing, by an axial prestressing system or any similar means. One advantage of this variant is that it allows increasing the rigidity at the compressor wheel axle, which increases the values of the critical bending speeds. Indeed, the portion of the compression shaft under the compressor wheel may be a critical point for some bending modes.
According to a second implementation of the invention, the compressor wheel can comprise the cylindrical support means. In other words, the compressor wheel and the cylindrical support means make up a single monobloc piece. The support means is then an axial extension, of cylindrical shape, of the compressor wheel. The assembly of this implementation can comprise the steps of assembling the rotor on the axial extension of the compressor wheel. This implementation of the invention provides a system that has been previously assembled and balanced at once. Furthermore, this implementation of the invention limits the number of parts, and therefore the number of steps of assembling the compression device.
Preferably, the rotor according to the invention can radially comprise at most the following elements: support means (cylindrical sleeve or extension of the compressor wheel), cylindrical magnet and binding ring, all mounted on the compression shaft.
Alternatively, the rotor may have no support means, and the cylindrical magnet can be arranged directly around the compression shaft. This option allows limiting the components and therefore the steps of assembling the device.
According to an aspect of the invention, the rotor can further comprise a non-magnetic stop on at least one side of the magnet (longitudinally). This non-magnetic stop prevents magnetic losses from the magnet to the compressor wheel. The non-magnetic stop can also act as a thermal barrier by protecting the temperature-sensitive magnet. This non-magnetic stop can have the shape of a ring inserted between a shoulder of the compressor wheel and the cylindrical magnet. In other words, the non-magnetic stop can be axially interposed between the magnet and the compressor wheel.
Preferably, the electric machine can be mounted on the intake side of the compression device. For this preferred embodiment, the rotor of the electric machine can rest, on one side, against the compressor wheel and, on the other side, against the nut. Thus, mounting of the assembly is easier and the overall size is limited to the maximum. In other words, the electric machine can be adjacent to the compressor wheel on the intake side thereof.
According to an embodiment of the invention, the outside diameter of the rotor (here the binding ring) can be less than or equal to the diameter of the compressor wheel nose. The gas flow at the compression device inlet is thus not hindered by the rotor shaft.
According to an implementation of the invention, the compression device can be a turbocharger, notably for an internal-combustion engine of a vehicle. It is then a turbocharger driven by an electric machine. In this case, the compression shaft corresponds to the turbocharger shaft that connects the turbocharger turbine to the turbocharger compressor. The electric machine thus drives both the compressor and the turbine.
According to a variant of this implementation of the invention, the electric machine can be arranged in the gas (generally air) intake of the turbocharger system. This solution involves a double advantage: the electric machine can be cooled by the intake gas stream, and the intake gas is heated by the electric machine, which may be favorable for some operating modes of the internal-combustion engine.
Preferably, the electric machine can be a stator grid electric machine, i.e. an electric machine having a stator with stator teeth around which coils are mounted, and these stator teeth have large dimensions to allow passage of the air stream. Such a stator grid machine is notably described in patent applications WO-2013/050,577 and FR-3,048,022.
Moreover, the invention relates to a method of manufacturing a compression device driven by an electric machine comprising a rotor and a stator, and the compression device comprises a compression shaft and a compressor wheel. For this method, the following steps are carried out:
a. mounting the compressor wheel onto the compression shaft;
b. mounting a rotor onto a support means arranged around the compression shaft;
c. retaining the cylindrical magnet on the support means by a binding ring, which is preferably non-magnetic, the ring compressing the magnet and the support means, and the ring is substantially cylindrical,
d. axially securing the rotor and the compressor wheel with a nut positioned at the end of the compression shaft.
Advantageously, the manufacturing method can be intended for the manufacture of a compression device according to any one of the variants or variant combinations described above. For example, the manufacturing method can be intended for the manufacture of a compression device as described in connection with one of
For the first embodiment of
For the second embodiment of
For the third embodiment of
According to an embodiment of the method, the assembly made up of the compression device, or possibly the turbocharger, and the electric machine can be installed in an air loop of an internal-combustion engine.
Advantageously, the electric machine can be arranged in the air intake pipe, so that the air stream entering the compression device first flows through the electric machine. This solution has a double advantage which is the electric machine can be cooled by the intake gas stream and the intake gas can be heated by the electric machine, which can be favorable for some operating modes of the internal-combustion engine.
The manufacturing method may further comprise a step of installing the stator around the rotor.
Advantageously, the manufacturing method according to the invention can concern the electrification of a compression device or of a conventional turbocharger (equipped with a compressor wheel and a compression shaft, but initially without an electric drive). Therefore, the compressor wheel and the compression shaft can be a wheel and a shaft for which steps a) to d) described above are carried out.
In this case, the method can comprise an additional step of replacing the compression shaft with a longer compression shaft.
Besides, the invention is also suited for energy production systems such as microturbines.
The invention provides the following functional advantages of:
Creating a magnetic rotor allowing the shaft to be rotated through the generation of a rotating magnetic field by a stator comprising magnetic flux generators such as windings (three-phase windings for example);
Ensuring the mechanical strength of the rotor assembly, notably with respect to the centrifugal forces applied upon rotation, notably by use of the binding ring;
Guaranteeing good electrical performances, in terms of power as well as efficiency, to limit internal heating of the rotor (and therefore demagnetization) and to simplify cooling thereof;
Observing a high level of concentricity between the electric rotor and the turbocharger shaft to obtain a complete mechanical system (turbocharger shaft with electric machine rotor) that can be balanced with minimum unbalance;
Having a structure compatible with the assembly of the compressor wheel with the rotor on the turbocharger shaft, notably by use of the nut;
Tightening the compressor wheel with the rotor and preloading the roller bearings of the turbocharger, notably by use of the nut; and
Being compatible with an electric turbocharger mass production tooling and manufacturing method.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1901074 | Feb 2019 | FR | national |
This application is the national phase of PCT/EP2020/050746 filed Jan. 14, 2020, which claims the benefit of French Patent Application No. 19/01.074, filed Feb. 4, 2019, which are hereby incorporated herein by reference in their entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/050746 | 1/14/2020 | WO | 00 |
