FR3100946A1 - Oil-cooled electric machine - Google Patents

Abstract

The invention relates to an electric machine comprising: - a rotor (ROT) bathed in a dielectric cooling liquid, - a casing (CAR) comprising at least one bearing housing (LP) receiving a bearing (RB) at the end of the rotating shaft (AT) of the rotor (ROT), characterized in that said bearing housing (LP) comprises a receptacle (REC) capable of collecting dielectric cooling liquid sprayed into the housing (CAR) by bubbling said rotor ( ROT), and in that said bearing housing (LP) comprises at least one through channel opening axially between the outer ring (BER) of said bearing and a sidewalk (TRO) internal to said bearing housing (LP). Figure for the abstract: Figure 2

Description

Oil-cooled electric machine

The present invention relates generally to the field of electrical engineering and relates more specifically to an electrical machine cooled by a dielectric coolant liquid such as oil.

In an oil-cooled sealed electric machine, dynamic seals are inserted on both sides of the machine, around the rotating shaft, to ensure the sealing of the machine. The bearings around the machine shaft also need lubrication. In order to cool the active parts of the machine, which are the rotor and the stator, and to lubricate the bearings and seals of the machine, with the same oil, a generally expensive oil circuit is created.

For example in the patent WO2018206890, oil circulation channels and injectors are positioned in the casing of the machine, in order to spray oil on the bearings and on the active parts of the machine. This type of cooling system requires a pump, a strainer, injectors and a circulation circuit which significantly increase the cost of the electric machine.

One of the aims of the invention is to remedy at least some of the drawbacks of the prior art by providing an electric machine cooled by a dielectric liquid, which is inexpensive while ensuring good cooling of the active parts of the machine and a good lubrication of bearings and dynamic joints of the machine.

To this end, the invention proposes an electric machine comprising:

- a rotor comprising a rotating shaft, a lower part of said rotor bathed in a dielectric cooling liquid,

- a stator fixed to an internal wall of a casing of the machine and surrounding said rotor, the casing comprising at least one substantially cylindrical bearing housing receiving via a bearing one end of said rotating shaft, said bearing being held in position in said bearing housing by on the one hand a retaining ring integral with an outer ring of said bearing, said retaining ring being brought into abutment against an axial end surface of said bearing housing, and by the other starts from a circular shoulder of said rotating shaft against which an inner ring of said bearing is brought into abutment,

characterized in that an upper angular portion of a substantially cylindrical part of said bearing housing comprises a receptacle capable of collecting dielectric cooling liquid projected into the casing by bubbling from said rotor, and in that said upper angular portion comprises at least a channel passing radially through said substantially cylindrical part, said channel emerging axially between the outer ring of said bearing and an internal annular peripheral sidewalk of said bearing housing.

Thanks to the invention, the active parts of the machine are cooled by the oil projected by the rotor when the latter rotates, and the bearings of the machine are also lubricated by the oil projected by the rotor during its operation. This saves circulation channels, a pump, a strainer dedicated to this circulation, and injectors. The machine according to the invention is therefore less expensive, more compact and simpler to manufacture than in the prior art.

Advantageously, in said machine according to the invention, said channel opens into a space of at least 2 mm (millimeters) made between said internal annular peripheral sidewalk of said bearing housing and said bearing, and in which a dynamic seal is arranged around said rotating shaft in the space delimited by said internal annular peripheral sidewalk. This space allows a good circulation of the oil all around the bearing and the dynamic seal.

Also advantageously, said retaining ring comprises a recess, said recess being located radially between the outer ring of said bearing and an inner cylindrical surface of said bearing housing. This characteristic of the invention allows the flow of lubricating oil towards the lower part of the housing, without flooding the space between the bearing and the dynamic seal.

Advantageously, said recess is located angularly closer to a horizontal plane encompassing the axis of said rotating shaft, than to a vertical axis intersecting the axis of said rotating shaft. This makes it possible to keep a reserve of lubricating oil at the level of the bearing, at the time of a new start of the electric machine.

According to a variant embodiment of the invention, said receptacle and said bearing housing of said casing are made in a single piece obtained by molding. This variant allows easy assembly of the electric machine.

Preferably, said receptacle is formed of a separate part interposed axially between an internal wall of said casing and said retaining ring, said part comprising a weir forming said channel and molded in a lower part of said part, said lower part of said part being inserted into a corresponding recess formed in said substantially cylindrical portion of said bearing housing. This embodiment of the invention allows easier production of the walls of the casing, the bearing housings of the machine according to the invention being very little modified in this embodiment compared to the bearing housings of the prior art.

Advantageously, said receptacle is formed of a separate piece interposed axially between an internal wall of said casing and said retaining ring, said piece having the shape of a deformed crown section, the outer periphery of said crown being offset axially with respect to the internal periphery of said crown, said internal periphery of said crown being attached to said external periphery of said crown by a corresponding annular section, said external periphery of said crown being in abutment against said retaining ring, said annular section conforming to the surface of said upper angular portion of said substantially cylindrical portion of said bearing housing, a weir forming said channel being molded in said annular section and in said inner periphery of said crown, said inner periphery of said crown being inserted into a corresponding recess formed in said portion substantially cylindrical of said bearing housing, said piece further comprising retaining elements in the form of radially and axially extending walls at the longitudinal ends of said annular section. In this embodiment of the machine according to the invention, the receptacle is simple to manufacture and is easily mounted on the corresponding bearing housing.

Preferably, said receptacle is made of plastic. It is thus easy to produce by molding and inexpensive.

The invention also relates to an electric or hybrid vehicle comprising an electric traction machine according to the invention, in which said casing of said electric machine comprises an exchanger in its lower part incorporating a network of coolant channels connected to a circuit of cooling connecting other equipment of said vehicle including the radiator located at the front of said vehicle, said cooling liquid being glycol water. This exchanger allows the cooling of the dielectric cooling liquid located in the casing of the machine, in particular when the temperature of said dielectric cooling liquid is greater than a high temperature threshold.

Preferably, in said vehicle according to the invention, said dielectric cooling liquid is oil, said electric machine is oil-tight and comprises an oil reservoir in a lower part of said casing provided with a heating resistor, said vehicle comprising means for activating said heating resistor when the temperature of the oil in said reservoir is below a low temperature threshold, during a start-up phase of said vehicle. This heating of the oil on start-up allows the machine to operate correctly in very cold weather, as the oil at low temperature does not allow the bearings and dynamic seals of the machine to be properly lubricated, and induces significant viscous friction on the rotor. .

Advantageously, in said vehicle according to the invention, said electric machine is sized for a nominal speed not exceeding 9000 revolutions per minute and does not include an internal oil projection circuit. This dimensioning makes it possible to maintain good efficiency for the electric machine, the friction of the oil on the rotor inducing significant losses at very high speeds.

The electric or hybrid vehicle according to the invention has advantages similar to those of the electric machine according to the invention.

Other characteristics and advantages will appear on reading a preferred embodiment described with reference to the figures in which:

shows in longitudinal section an electric machine cooled by a dielectric liquid according to the invention, in this preferred embodiment,

represents an enlargement of FIG. 1 at the level of a bearing of the electric machine according to the invention, in this preferred embodiment,

represents a part of the machine according to the invention forming a receptacle, in this preferred embodiment,

represents a rotating shaft of the machine according to the invention, with the position of said part relative to other elements fixed on the shaft, in this preferred embodiment.

According to a preferred embodiment of the invention represented in FIG. 1 , an electric machine ME according to the invention comprises a sealed casing CAR in which is fixed a stator STAT, a substantially hollow cylindrical assembly, formed of sheets comprising windings of wires of copper. The stator STAT is fixed by screws or by shrinking to the substantially cylindrical internal wall of the housing CAR. By "substantially" in this application, is meant "apart from a few variations", for example with bumps or holes added with respect to a shape thus defined, or with a difference within a range of 10% with respect to a direction or a position thus defined.

In the stator STAT is housed a rotor ROT, an assembly of laminations and windings or magnets surrounding a rotating shaft AT. The ends of the rotating shaft AT are held in bearings, in particular ball bearings, mounted on the rotating shaft AT and housed in substantially cylindrical bearing housings LP formed in the substantially flat walls of the housing CAR. In particular the ball bearings are housed in a cylindrical internal part of the bearing housings.

On the enlargement of a part of Figure 1 located at the level of a bearing housing LP, visible in Figure 2 , the ball bearing RB housed in the cylindrical internal part of the bearing housing LP comprises an outer ring BER and a BIR inner ring. The outer ring BER is secured to a retaining ring BR at the axial end of the outer ring of the bearing RB facing the rotor ROT. It should be noted that in this application the axial direction refers to the rotating axis AX of the rotor ROT, the radial and ortho-radial direction are also defined with respect to this axis AX.

In a known manner, the CAR casing is for example designed in two parts, a bottom wall in which the ROT rotor is inserted, and a lid closing the CAR casing, the wall of which is visible in FIG . When the cover of the housing CAR is closed on the bottom wall of the housing CAR, an axial end surface SEA of the bearing housing LP located on the side of the rotor ROT, presses against the retaining ring BR in the direction of the rotor ROT, participating to the stressing of the ball bearing RB. The axial end surface SEA extends on a plane orthogonal to the axis AX of the rotor ROT. The ball bearing RB is held in position by a circular shoulder EP on the rotating shaft AT, which exerts a force in the opposite direction to the rotor ROT on the inner ring BIR of the ball bearing RB.

The lower part of the ROT rotor is bathed in a dielectric cooling liquid, which in this preferred embodiment of the invention is OIL oil. The terms lower and upper, or top and bottom in this application refer to a vertical axis V along which the electric machine ME is positioned. This axis is directed in the opposite direction to the direction of the force of gravity. The NO level of the OIL oil in the lower part of the ME electric machine is located at the level of the lower winding of the ROT rotor.

When the electric machine ME is in operation, the rotational movement of the rotor ROT brings the oil OIL over the entire cylindrical surface of the rotor ROT, which makes it possible to cool the rotor windings. The OIL oil is also projected by the rotor ROT onto the cylindrical internal surface of the stator STAT, thus cooling the stator windings. As it falls, the projected oil which reaches the rotating shaft AT of the rotor ROT lubricates the ball bearings only very slightly. Another part of the projected oil, while falling, is trapped in a receptacle REC arranged on an upper surface of the bearing housing LP. A channel crossing this upper part of the bearing housing LP brings the oil thus trapped into the space located between the ball bearing RB and a dynamic joint JD extending the wall of the housing CAR to seal the electrical machine ME at the level of the output. of the rotating shaft AT. The oil thus effectively lubricates the RB ball bearing and the JD dynamic seal.

More precisely, the receptacle REC is open at the top, its lower part matching an upper angular portion of the substantially cylindrical part of the bearing housing LP except at the level of the channel formed by a recess EV in the bearing housing LP and which opens between the outer ring BER of the ball bearing RB, and an internal annular peripheral sidewalk TRO of the bearing housing LP. This space ESP between the sidewalk TRO and the outer race BER of the ball bearing RB extends axially for at least 2mm, the ball bearing RB not being fully pressed into the bearing housing LP. This ESP space preferably extends axially over 4 to 6 mm.

The internal annular peripheral sidewalk TRO of the bearing housing LP delimits, in the wall of the housing CAR, a space in which the dynamic seal JD is housed hermetically closing the axial end of the electric machine ME at the level of the ball bearing RB.

In this preferred embodiment of the invention, the receptacle REC is a part represented in FIG. 3 and assembled on the bearing housing LP, for example clipped or screwed thereto. This part, for example made of molded plastic material, has the shape of an angular section of a flat crown having been axially deformed. In particular, the outer periphery PE of this ring section is offset axially with respect to the inner periphery PI of this ring section. The walls of these outer PE and inner PI peripheries of the receptacle REC are connected by an annular surface SA matching the upper surface of the bearing housing LP on which it is placed. The wall of the outer periphery PE is pressed against the retaining ring BR, the wall of the inner periphery PI is inserted into the recess EV formed radially in the substantially cylindrical part of the bearing housing LP. The receptacle REC also comprises retaining elements ER closing the angular ends of the part, these angular elements extending radially along the outer peripheral wall PE and axially over the width of the annular surface SA. Thus the external peripheral wall PE, the annular surface SA, the retaining elements ER and the wall of the casing CA against which the receptacle REC is held form the walls of an accumulation tank for the projected oil which falls by gravity into the CAR housing. Radial channels CAN made in the internal peripheral wall PI of the receptacle REC form a spillway allowing the oil to descend to lubricate the ball bearing RB and the dynamic seal JD.

The position of the receptacle REC with respect to the ball bearing RB on the rotating shaft AT and with respect to the dynamic joint JD is shown in FIG. 4 , without the casing CAR of the electric machine ME. The position sensor target CC is therefore located outside the casing CAR of the electric machine ME. A recess OR made in the retaining ring BR, allows the oil flowing between the dynamic joint JD and the ball bearing RB, to flow into the lower part of the housing CAR. When the rotating shaft AT is mounted in the electric machine ME, this recess OR is located radially between the outer ring of the ball bearing RB and the inner cylindrical wall of the bearing housing LP. In order to leave a reserve of oil when the electric machine ME stops in the space between the dynamic joint JD and the ball bearing RB, the recess OR is located angularly closer to a horizontal plane (therefore orthogonal to the axis V) encompassing the axis AX of the rotating shaft AT, than the vertical axis V passing through the axis AX of the rotating shaft.

In addition, to facilitate proper lubrication and proper cold operation of the ME electric machine, a heating resistor is placed in the lower part of the CAR casing. This heating resistor is connected to a circuit controlled by a computer connected to a temperature sensor. This temperature sensor indicates the temperature of the OIL oil, or the ambient temperature. When the temperature raised is below a low temperature threshold, for example -10°C (degrees Celsius), the computer supplies power to the circuit connected to the heating resistor, which then heats the OIL oil.

In order to cool the oil OIL during operation of the electric machine ME, so that it does not exceed a high temperature threshold, for example 40° C., a heat exchanger ECH is integrated into the casing CAR of the electric machine. ME. This ECH exchanger is for example made up of a glycol water circuit machined in the lower part of the electrical machine ME, and connected to a cooling circuit.

In particular when the electric machine ME is an electric traction machine of an electric or hybrid vehicle, the exchanger ECH is connected to the main cooling circuit of the vehicle, which cools the power electronics of the vehicle and is connected to the radiator located at the front of the vehicle.

The oil being in direct contact with the rotor increases the mechanical losses at high speed. Preferably, the electric machine ME is therefore sized to operate nominally on a speed threshold of up to 9000 revolutions per minute at the most. This maximum rated speed can be set a little lower, for example 8000 revolutions per minute Thus the vehicle using the ME electric traction machine does not require an internal oil projection circuit including an oil pump.

Although in this embodiment only one REC receptacle is shown, alternatively each bearing housing of the electric machine ME is provided with a REC receptacle. Other variants are also possible. For example, as a variant, the receptacle REC and the bearing housing are cast from a single piece obtained by molding. In another variant, a single CAN channel is molded in the part forming the REC receptacle.

Claims (10)

Electric machine (ME) comprising:
- a rotor (ROT) comprising a rotating shaft (ET), a lower part of said rotor (ROT) bathed in a dielectric cooling liquid (OIL),
- a stator (STAT) fixed to an internal wall of a casing (CAR) of the machine (ME) and surrounding the said rotor (ROT), the casing (CAR) comprising at least one substantially cylindrical bearing housing (LP) receiving via a bearing (RB) one end of said rotating shaft (AT), said bearing (RB) being held in position in said bearing housing (LP) by, on the one hand, a retaining ring (BR) integral of an outer ring (BER) of said bearing (RB), said retaining ring (BR) being brought into abutment against an axial end surface (SEA) of said bearing housing (LP), and on the other hand by a circular shoulder (EP) of said rotating shaft (AT) against which an inner ring (BIR) of said bearing is brought into abutment,
characterized in that an upper angular portion of a substantially cylindrical part of the said bearing housing (LP) comprises a receptacle (REC) capable of collecting dielectric cooling liquid (OIL) projected into the casing (CAR) by bubbling of the said rotor (ROT), and in that said upper angular portion comprises at least one channel (CAN) passing radially through said substantially cylindrical part, said channel (CAN) emerging axially between the outer ring (BER) of said bearing and a peripheral sidewalk (TRO) inner ring of said bearing housing (LP). Electrical machine (ME) according to Claim 1, in which the said channel (CAN) opens out into a space (ESP) of at least 2 mm provided between the said internal annular peripheral sidewalk (TRO) of the said bearing housing (LP) and the said bearing. (RB), and wherein a dynamic seal (JD) seal is disposed around said rotating shaft (AT) in the space delimited by said sidewalk (TRO) inner annular device. Electric machine (ME) according to claim 1 or 2, characterized in that said retaining ring (BR) comprises a recess (OR), said recess (OR) being located radially between the outer ring (BER) of said bearing (RB) and an inner cylindrical surface of said bearing housing (LP). Electric machine (ME) according to Claim 3, characterized in that the said recess (OR) is situated angularly closer to a horizontal plane encompassing the axis (AX) of the said rotating shaft (AT), than to a vertical axis ( V) intersecting the axis of said rotating shaft (AT). Electric machine (ME) according to any one of Claims 1 to 4, characterized in that the said receptacle (REC) and the said bearing seat (LP) of the said casing (CAR) are produced in a single piece obtained by moulding. Electric machine (ME) according to any one of Claims 1 to 4, characterized in that the said receptacle (REC) is formed of a separate piece interposed axially between an internal wall of the said casing (CAR) and the said retaining ring (BR ), said part comprising a weir forming said channel (CAN) and molded in a lower part of said part, said lower part of said part being inserted into a corresponding recess (EV) formed in said substantially cylindrical part of said bearing housing (LP ). Electric machine (ME) according to any one of Claims 1 to 4, characterized in that the said receptacle (REC) is formed of a separate piece interposed axially between an internal wall of the said casing (CAR) and the said retaining ring (BR ), said part having the shape of a section of a deformed crown, the external periphery (PE) of said crown being axially offset with respect to the internal periphery (PI) of said crown, said internal periphery (PI) of said crown being attached to said outer periphery (PE) of said ring by a corresponding annular section (SA), said outer periphery (PE) of said ring bearing against said retaining ring (BR), said annular section (SA) conforming to the surface of said upper angular portion of said substantially cylindrical part of said bearing housing (LP), a weir forming said channel (CAN) being molded in said annular section (SA) and in said inner periphery (PI) of said ring, said inner periphery (PI) of said crown being inserted into a corresponding recess (EV) formed in said substantially cylindrical part of said bearing housing (LP), said part further comprising retaining elements (ER) in the form of walls extending radially and axially at the longitudinal ends of said annular section (SA). Electrical machine (ME) according to Claim 6 or 7, in which the said receptacle (REC) is made of plastic material. Electric or hybrid vehicle comprising an electric traction machine (ME) according to any one of Claims 1 to 8, in which the said casing (CAR) of the said electric machine (ME) comprises an exchanger (ECH) in its lower part incorporating a network of coolant channels connected to a cooling circuit connecting other equipment of said vehicle, including the radiator located at the front of said vehicle, said coolant being glycol water. Electric or hybrid vehicle according to Claim 9, in which the said dielectric cooling liquid (OIL) is oil, the said electric machine (ME) is oil-tight and comprises an oil reservoir in a lower part of the said casing. (CA) provided with a heating resistor, said vehicle comprising means for activating said heating resistor when the temperature of the oil in said reservoir is below a low temperature threshold, during a start-up phase of said vehicle .