Patent Application
20200412206
The present invention relates to an electric machine, in particular to an electric machine that can be used in an electrically-assisted compression device for compressing a working fluid such as a liquid fluid or a gaseous fluid.
It more 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 the compressed gaseous fluid to any device and, more particularly, to the intake of an internal-combustion engine.
The invention can notably prove to be relevant in the transport sector (motor or heavy-load transport for example), the aerospace sector, the power generation sector or the food industry, the petroleum industry, the construction sector or the medical/paramedical sector.
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 the engine, which amount of air is proportional to the density of the air.
Thus, it is usual to increase the 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 mechanism 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 several 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 and requires a specific system for carrying away heat losses.
In order not to be intrusive to the air intake of the compressor, this type of electric machine is conventionally positioned on the back of the centrifugal 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 unfavourable thermal environment in the latter case, 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 cause disturbance.
This type of systems is described in more detail in patents and published applications: US-2014/0,373,532, U.S. Pat. Nos. 8,157,543, 8,882,478, US-2010/0,247,342, U.S. Pat. Nos. 6,449,950, 7,360,361, EP-0,874,953 or EP-0,912,821.
The cooling systems disclosed in these patent and applications provides external cooling of the stator, which may make the system more complex in the design and integration thereof.
Another type of machine is an electric machine with a large air gap that may sometimes be several centimeters long, to allow passage of the working fluid therethrough. This permits enabling integration as close as possible to the compression systems, in a significantly more favorable thermal environment.
However, this large air gap involves a drawback regarding passage of the magnetic flux between the rotor and the stator, and therefore a limitation for the intrinsic efficiency of the machine and the size of the stator for the same power output.
This type of electric machine is notably described in patents and published applications EP-1,995,429, US-2013/169,074 or US-2013/043,745.
A new type of machine has recently appeared. It is a machine provided with a stator grid, which is described in more detail in patent applications FR-3,041,831 (WO-2017/050,577) and FR-3,048,022. This electric machine, referred to as “stator-grid” machine, comprises a rotor and a stator. The stator comprises radial passages circumferentially arranged along the stator, magnetic flux generators housed in these radial passages and a stator bearing receiving the rotor. The magnetic flux generators are coils for example. The radial passages comprise fluid circulation galleries facing the magnetic flux generators. Furthermore, the radial passages are separated by radial teeth, also referred to as “stator teeth”.
This machine affords the advantage of providing a better compromise in terms of cooling and electrical performance than the other two types of machines. However, under some operating conditions, the cooling induced by the fluid flow through the circulation galleries may prove insufficient when the fluid flow rate is set to reach an overall system performance goal, without correlation of the need for intrinsic cooling of the machine.
For all these electric machines, cooling of the stator is a major challenge for improving the lifetime of the electric machine, increasing its operating range and improving its efficiency. However, this cooling should not, in return, impact the maximum output power. Similarly, cooling should not significantly impact the cost or the size of the system. Moreover, the performance of the electric machine is very important in the performance of an electrified compressor and, a fortiori, in the case of an electrified turbocharger.
Similar problems appear for all types of electric machines.
Moreover, with electrified turbocharging system type solutions, using stator-grid electric machines may appear limiting when the rate of flow through the electric machine is high. It may generate a high pressure drop likely to reduce the overall performance of the system.
In order to meet the aforementioned requirements, the present invention relates to an electric machine comprising a rotor, a stator, an outer casing and a cooling system for cooling the stator, the rotor and the stator being coaxial along a longitudinal axis with the stator comprising magnetic flux generators. The stator cooling system comprises at least two fluid circulations. At least a first circulation extends longitudinally within the stator and at least a second circulation is positioned around the periphery of the stator. Thus, the electric machine is provided with an effective cooling positioned as close as possible to and on either side of the magnetic flux generators, without impacting the magnetic flux or the iron losses. Furthermore, this cooling induces no significant extra cost or major change in the size of the system. This cooling is simple and it does not use a closed fluid loop that would require adding pumps and other equipments, and cause fluid consumption. Finally, it allows limiting the pressure drop generated by the machine on the fluid, by not passing all of the working fluid through the stator grid.
The invention also relates to a compression device equipped with such an electric machine and to a turbocharger electrified with this type of electric machine.
The device according to the invention relates to an electric machine comprising a rotor, a stator, an outer casing and cooling of the stator, the rotor and the stator being coaxial along a longitudinal axis, the stator comprising magnetic flux generators, in that the cooling of the stator comprises at least two fluid cooling circulations, at least a first circulation extending longitudinally within the stator and at least a second circulation positioned around the periphery of the stator.
Advantageously, the stator comprises radial passages circumferentially arranged along the stator with the radial passages being delimited by radial teeth, the magnetic flux generators being housed in the radial passages, the radial passages forming at least a first fluid passage facing the magnetic flux generators.
Preferably, the fluid is air, and more preferably air at ambient temperature taken from the ambient medium.
According to an embodiment of the invention, at least a second circulation is arranged between the magnetic flux generators and the outer casing.
According to a variant of the invention, the inlet to the at least the second circulation is radial from the at least first circulation.
Alternatively, the inlet of the at least second circulation is axial.
According to an embodiment of the invention, the outlet of the second circulation is radial.
Alternatively, the outlet of the second circulation is axial.
Advantageously, the second circulation comprises, at the outlet thereof, a substantially radial orientation of the fluid flow for mixing the fluids circulating in the at least two circulations.
Advantageously, the at least the second circulation comprises an active or passive flow regulation positioned at the inlet or at the outlet of the at least second circulation.
Preferably, the at least the second circulation comprises fins at the level of the at least second circulation, and preferably fins extending from one end to the other of the section, orthogonal to the direction of flow of the fluid, of the at least second circulation.
The invention also relates to a compression device for a gaseous or liquid fluid, comprising compression with an intake for the fluid to be compressed, an outlet for the compressed fluid, the compression of the fluid being carried by a compressor shaft and housed between the intake and the outlet, and an electric machine according to one of the above features, the electric machine being positioned upstream, in relation to the direction of flow of the fluid, from the compression.
Moreover, the invention also relates to an electrified turbocharger device comprising an expansion device and a compression device, according to one of the above features, the expansion device and the compression device being fastened to the same rotating shaft, thus allowing common rotation of the expansion device and the compression device.
Other features and advantages of the system 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 invention relates to an electric machine comprising a rotor, a stator, an outer casing and stator cooling means of a cooling device. The rotor and the stator are used to generate an electric current (“generator” mode of the electric machine) or to drive the rotor in rotation from an electric current (“motor” mode of the electric machine). The purpose of the outer casing, which is also simply referred to as casing, is to protect the internal equipments of the machine, including the rotor and the stator, against external aggressions (splash water for example) and to protect the user from electrical hazards and from the so-called “rotary machine” risks related to the electric machine. The rotor and the stator are coaxial, along a longitudinal axis, which allows rotation of the rotor in the stator. The stator comprises magnetic flux generators, coils for example. When the electric machine operates in “motor” mode, the magnetic flux generators create a magnetic flux driving the rotor, equipped with magnetic receivers such as permanent magnets, in rotation. When the machine operates in “generator” mode, the rotation of the rotor and, therefore, of its permanent magnets generates an induced electric current in the magnetic flux generators (thus operating as a receiver).
The cooling means or device is used to cool the machine so that it can operate over optimal temperature ranges. Thus, the life of the electric machine and the efficiency thereof are increased. The performance of the electric machine is also improved.
The cooling means comprises at least two fluid circulation means or devices.
At least a first circulation means or device extends longitudinally in the stator (within the stator). The fluid thus passes completely through the stator in the longitudinal direction, making it possible to capture a large part of the thermal losses of the electric machine stator, possibly by means of the stator grid.
At least a second circulation means or device is positioned around the periphery of the stator. When the rotor is positioned in the stator, at least a second circulation means or device is then positioned outside the stator, between the stator and the outer casing. This second circulating fluid flow passes as close as possible to the magnetic flux generators, which improves cooling thereof and therefore increases the performance and the efficiency of the electric machine. If possible, only a wall separates the second circulating fluid flow from the magnetic flux generators, the wall preventing direct contact between the fluid and the magnetic flux generators.
The at least two circulation operates in open circuits. Thus, no pump, pipe and secondary equipment required for closed-loop circulation is necessary. When the at least two fluid circulations are separated only by the magnetic flux generators, i.e. when the fluid circulation means or device are located on either side of the magnetic flux generators to pass as close as possible to the magnetic flux generators, the efficiency of the cooling is improved.
This configuration of the cooling with at least two fluid circulations is particularly interesting. It allows increasing the fluid passage section in relation to a configuration where only one or the other fluid circulation is used, without increasing the air gap. By increasing the passage section, the fluid flow rate can thus be increased without inducing additional pressure drops. On the other hand, in a configuration where only one of the two fluid circulations is used, the increase in the fluid passage section would be greater and would require a more significant increase in the overall size of the machine. As a result, the flow of fluid passing through the machine would then be limited because of the pressure drops.
Increasing the flow of fluid in the electric machine allows its intrinsic cooling to be improved. Furthermore, by dividing the fluid circulation into at least two parts, one inside the stator and at least another part on the outer periphery thereof, and more particularly if the circulating flow passes on either side of the magnetic flux generators, the cooling effectiveness is improved. It is then possible, for the same machine size, to increase its power or, for a machine of same power, to make it more compact. Furthermore, the temperature reduction of the flux generators allows reduction of their resistance and therefore the Joule losses, which further improves the efficiency.
This cooling is particularly relevant when a compressor for example is used downstream from the electric machine. Indeed, increasing the flow rate reaching the compressor inlet without impacting the pressure drops in the electric machine allows the compressor performance to be improved. A compression device electrified by such a machine, and a fortiori an electrified turbocharger device, thus represents a significant performance gain by synergy between the gains obtained on the electric machine and those obtained by the compression means.
Here, the present invention concerns all types of electric machines, including machines with a stator grid and machine with a large air gap.
According to an embodiment of the electric machine according to the invention, the stator can comprise radial passages circumferentially arranged along the stator which are cylindrical or substantially cylindrical. The radial passages can be delimited by radial teeth, and magnetic flux generators can be housed in the radial passages. The radial passages thus form at least a first fluid passage facing the magnetic flux generators (coils for example). In this case, the electric machine is a stator-grid electric machine.
The cooling comprises at least two circulations as defined above which is particularly suited to a stator-grid electric machine. Indeed, the stator-grid electric machine is designed to allow a significant flow of fluid within the stator. At least a second circulation, located on the periphery of the stator which is preferably between the magnetic flux generators and the outer casing, allows further improvement in cooling, for example, during an operation inducing a strong current in the magnetic flux generators, and therefore significant Joule losses. This additional cooling also makes it possible to improve the life of the electric machine, as well as the efficiency of the electric machine by reducing the temperature and therefore the resistance of the flux generators.
Moreover, since the flow rate is already high in the stator due to the configuration of the stator-grid machine, the passage section of the second circulation can be reduced, which limits space constraints. With this second circulation, it is possible to reduce the passage section within the stator, which limits space constraints and the amount of materials used in the stator. This provides a reduction in the cost of the system as well as a reduction in iron losses in view of the electric machine comprising less ferric material.
Preferably, the fluid can be air which is preferably air taken from the ambient medium. There is therefore no need for consumption of a dedicated fluid, which on the one hand reduces the cost of the cooling and, on the other, avoids the use of pumps, tanks, pipes and other secondary equipments that would impact the cost and involve risks of failure.
According to a variant of the invention, at least a second circulation can be located between the magnetic flux generators and the outer casing. Thus, fluid circulation is as close as possible to the magnetic flux generators which provides improved cooling.
Preferably, at least a second circulation can be an annular space, for example between the outside diameter of the magnetic flux generators and the inside diameter of the outer casing.
This at least second circulation can also be a set of longitudinal spaces of circular section, in form of inserted tubes or bores in a metallic mass. These spaces are preferably evenly distributed around the magnetic flux generators in order to carry off the thermal energy as homogeneously as possible.
According to an embodiment of the machine according to the invention, the shape of the stator, the rotor and the outer casing can be cylindrical, substantially cylindrical or annular. The inlet to the second circulation can be radial from the first circulation. In this case, the flow passing into the machine is partly diverted. Part of the flow continues longitudinally and passes through the stator, and the diverted part enters at least a second circulation radially. The flow distribution is achieved passively via the pressure difference upstream/downstream from the electric machine. This configuration allows the design of the machine to be simplified with a single air inlet instead of two separate inlets.
Alternatively, the inlet to at least a second circulation can be axial. In this case, the electric machine has two separate air inlets. The fluid inflows through these two air inlets may or may not come from the same fluid stream upstream from the electric machine. The axial inlet is interesting because it allows reduction of pressure losses in relation to a radial inlet.
According to a variant of the system according to the invention, the outlet of at least a second circulation can be radial. The junction of the flows leaving at least a first circulation and at least a second circulation can thereby occur before the fluid leaves the electric machine which homogenizes the outlet flow.
Alternatively, the outlet of at least a second circulation can be axial. In this case, the electric machine has two separate air outlets. These two air outlets may or may not join in the same fluid stream downstream from the electric machine. The axial outlet is interesting because it allows reduction of pressure losses.
Advantageously, at least a second circulation can comprise, at the outlet thereof, a means for providing a substantially radial orientation of the fluid flow for mixing the fluids circulating in at least two circulations. The function of this substantially radial orientation is to orient the circulating fluid flow to impart a rotational motion thereto, referred to as pre-rotation, about the longitudinal axis of the electric machine. This function is particularly interesting when a compressor is used downstream, in the direction of circulation of the fluid, from the electric machine. Indeed, the pre-rotational motion of the fluid allows the operating range of the compressor to be modified by increasing the use area thereof, notably towards low flow rates and high compression ratios. The compression ratio is the ratio of the compressor outlet pressure to the compressor inlet pressure. This substantially radial orientation can for example be blades or parts substantially or partly resembling blades. It can also be circular parts as for example a circular rotating part and a circular stationary part with at least one of the two parts being perforated so that, during rotation, the perforation opens more or less so as to be alternately totally open, partly closed, totally closed, partly open, totally open, etc.
Advantageously, at least a second circulation can comprise an active or passive flow regulation means or device positioned at the inlet or at the outlet of at least a second circulation. This regulation allows or prevents circulation in the second circulation. This improves operation of the machine by avoiding passage when it is not relevant. When useful, in particular in case of high flow rates or in order to modify the orientation of the flow downstream from the electric machine, either control of the flow regulation provides a suitable opening (active flow regulation), or the pressure drop generated in this flow regulation causes part of the flow to pass into the second circulation (passive flow regulation). The passive flow regulation has the advantage of having a low cost and it requires no control. The passive flow regulation can for example be one or more calibrated openings, calibrated holes for example. It can also consist of a relevant orientation at the inlet to the second circulation, which generates a suitable pressure drop causing the fluid to pass into the first circulation up to a given flow rate. On the other hand, the active system provides flow regulation and more suitable operation. It can be an “on-off” valve, a regulation valve of ball valve type or a set of blades for example.
Preferably, at least a second circulation can comprise fins at the level of the second circulation. The fins increase the heat exchange surface area and thus improve cooling of the machine.
Preferably, fins can extend from one end to the other end of the section and be orthogonal to the direction of flow of the fluid, of the second circulation. For example, when the stator and the outer casing are cylindrical, the fins can extend from the outside diameter of the stator to the inside diameter of the outer casing. Thus, the heat exchange surface area is improved.
The invention also relates to a compression device for a gaseous or liquid fluid, comprising a compression with an intake for the fluid to be compressed and a compressed fluid outlet. The fluid compressor is carried by a compressor shaft and housed between the intake and the outlet. The device comprises an electric machine according to at least one of the above features. The electric machine can then be positioned upstream, in relation to the direction of flow of the fluid, from the compressor. Using an electric machine as described above allows the performance of the electric compressor to be improved, through improved performance of the electric machine, increased flow rate at the compressor inlet and modification of the operating range of the compressor to increase the use area thereof, notably to low flow rates and high compression ratios, using pre-rotation for example. Pre-rotation, in the opposite direction, also allows the operating range of the compressor to be extended to high flow rates.
The invention further relates to an electrified turbocharger device comprising an expansion means or device and a compression device as described above. The expansion means or device and the compression device are then fastened to the same rotating shaft, thus allowing common rotation of the expansion means or device and of the compressor. The improvements brought to the electrified compressor with one of the above features allow the performance of the electrified turbocharger to be improved.
The electric machine comprises a rotor 3 and a stator 12. Stator 12 is stationary. Rotor 3 and compression means 15 rotates by a common action induced by rotating shaft 1. The magnetic field induced in electric machine 10 can generate the rotation of rotor 3 which drives rotating shaft 1, which itself drives the compression means 15. Under certain conditions, upon deceleration of the compression means, the operation can be reversed so that the rotation of compression means 15 drives rotating shaft 1, which in turn causes the rotation of rotor 3, thus generating electricity within electric machine 10.
Furthermore, for
The electric machine of
Axis xx is the longitudinal axis about which rotor 3 and shaft 1 rotate. Rotor 3 is fixedly mounted on rotating shaft 1 which provides common rotation of shaft 1 and rotor 3. The stator which consists of stator grid 4 and magnetic flux generators 5, surrounds the rotor and is stationary. An air gap is located between the rotor and the stator.
A guiding system 2 is used to bear the forces, notably the mass of the electric machine, and to support bearings, which by way of non-limitative example, enable connection between rotating shaft 1 and a fixed frame (not shown).
A fluid circulates in the electric machine. This fluid is air for example, preferably taken from the ambient medium. The fluid circulation is an open-loop circulation.
In
A second circulation flow F2 is diverted from first circulation flow F1A/F1B and is sent to an inlet ER2, which is a radial inlet here, prior to passing through at least a second circulation. This second circulation is an annular section between magnetic flux generators 5 and outer casing 6. Preferably, this second circulation is close to the outside diameter of magnetic flux generators 5, which optimizes cooling thereof. This second part of the circulation flow then joins the first part of the flow, generated by flows F1A, F1B and F2, by leaving through radial outlet SR2. The flow leaving the electric machine thus is the flow reconstituted by flows F1A, F1B and F2.
It is also possible to integrate a circulation flow orientation means (not shown) on radial outlet SR2. This orientation means allows both mixing the flows from second circulation flow F2 and from the two parts of first flow F1A and F1B passing through the air gap and the stator which imparts a pre-rotation, about the axis of rotation, thereto. This pre-rotation of the flow is particularly interesting when a compression device, a fortiori a turbocharger device, is positioned behind the electric machine. Indeed, this pre-rotation of the flow at the compression device inlet allows the efficiency thereof to be increased. This pre-rotation can for example be induced by blades or pieces of blades.
In
This embodiment also comprises flow regulation means 7 positioned at radial inlets ER2 of second circulation flow F2 passing into at least a second circulation means. These flow regulation means 7 control or block passage of the fluid into the circulation means for passage of flow F2. They can notably open or shut a passage section in “on-off” mode, or open a passage section in a controlled manner, thus providing a more or less large flow passage section according to need. Without limitation, the flow regulation means can be a simple calibrated hole allowing passage of flow F2 under certain pressure/flow rate conditions (passive system), an “on-off” valve (active or passive system), or a regulation valve (active system) such as a ball valve for example.
For
For
The outlet of flow F2 remains radial and it is provided with a flow regulation means 7 on radial outlet SR2. The flow regulation means 7 may or may not comprise an outlet flow orientation means for controlling a pre-rotation of the flow.
In
The invention is particularly relevant, inter alia, for other applications such as turbines, notably of microturbine or turbogenerator type.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1852012 | Mar 2018 | FR | national |
Reference is made to International Application No. PCT/EP2019/054849, filed Feb. 27, 2019, which claims priority to French Patent Application No. 18/52.012, filed Mar. 8, 2018, the contents of which are incorporated herein by reference in their entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/054849 | 2/27/2019 | WO | 00 |
