ELECTRIC MACHINE COOLED WITH A DIELECTRIC HEAT TRANSFER FLUID

Description

[0001] The present invention relates generally to the fields of electrical engineering and automobiles and more specifically concerns an electrical machine for an electric or hybrid motor vehicle.

[0002] Electric machines for electric or hybrid vehicles, and in particular the motors providing torque to the transmission system of such a vehicle, require an efficient cooling system.

[0003] A known cooling system for an electric motor, such as that described in document CN201355790, makes it possible to cool at least part of the active parts of an electric motor, using a dielectric heat transfer liquid of the oil type. A cooling circuit injects the liquid onto the upper part of the stator of the motor, the liquid flows by gravity towards the lower part of the stator and is collected via holes located in the lower part of the motor, in a reservoir.

[0004] Such a cooling system has a disadvantage in certain engine architectures on an electric or hybrid vehicle. Indeed, when moving such a vehicle, with such a system the liquid would be displaced in the oil tank during acceleration, braking or cornering of the vehicle, so that the liquid would rise through the holes in the lower part of the engine, and would flood part of the air gap between the rotor and the stator. This would result in a loss of engine performance and emulsion of the liquid, detrimental to good cooling of the engine and good lubrication of the rotor shaft bearings.

[0005] Document US6065297 describes a liquid cooler for building air conditioning, in which an attempt is made to ensure good circulation of the oil in the circuit despite relatively small pressure differences between points in the circuit. In particular, the oil evaporates in certain parts of the circuit and is deposited at different points in the circuit. An orifice in the compressor wall sucks in the cooling gas. The orifice opens into a pipe with a non-return valve which opens into the cooler's oil reservoir.

[0006] Document FR1233384 discloses a check valve, the valve body of which is housed eccentrically and is attacked in the middle by a lever biased by a spring.

[0007] Document FR1396629 describes an automatic drain valve, particularly for emptying water from a boat.

[0008] GB2062361 describes an electric drill provided with a means for preventing water from entering and remaining in the drill housing.

[0009] 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 for an electric or hybrid motor vehicle cooled by a dielectric heat transfer liquid, which does not have any loss of performance due to turns, acceleration or braking of the vehicle.

[0010] To this end, the invention proposes an electric machine for an electric or hybrid motor vehicle, comprising a casing capable of protecting the active parts of said electric machine, a cooling system comprising means for spraying a heat-transferring dielectric coolant onto at least part of said active parts, a reservoir capable of collecting by gravity said coolant flowing through at least one orifice in a wall separating said active parts and said reservoir, said machine being characterized in that it comprises at said at least one orifice, a flap fixed to said wall and capable of covering said at least one orifice, an elastic means capable of opening said flap under the effect of gravity of said coolant,and a non-return means capable of keeping said flap closed when a force exerted on said coolant in said reservoir brings said liquid against said flap.,

[0011] Thanks to this invention, the coolant does not rise into the casing, which would flood the rotor and create emulsion. This preserves the machine's performance.

[0012] According to the invention, said flap, said elastic means and said non-return means are formed from the same membrane made of elastic material fixed on either side of said at least one orifice and in which said flap is made, the edges of the fixed portion of said membrane covering the edges of said flap, the edges of said flap forming a descent towards said reservoir.

[0013] This implementation of the invention has the advantage of being inexpensive and simple to manufacture.

[0014] Said membrane is preferably made of silicone, which has the advantage of having high resistance to high temperatures and having deformation as a mechanical characteristic.

[0015] Advantageously, said membrane comprises concave outer edges capable of being elastically fixed to the edges of said at least one orifice. Thus, the membrane is simple to install, since it simply needs to be clipped onto the wall at the level of the coolant flow orifices. This installation also does not require modification of an existing casing of an electrical machine according to the prior art.

[0016] According to an unclaimed alternative, said flap is arranged under said wall and is of larger dimensions than those of said orifice, said non-return means comprising a return spring fixed on a pivot connection connecting said flap to said wall. This alternative has the advantage of being usable on large oil flow orifices, the flap being rigid in this alternative implementation.

[0017] Advantageously, in this alternative, said shutter is fixed by said pivot connection to a frame fixed on the edges of said orifice to said wall by clips. Thus, it is possible to benefit from the invention without modifying the existing casing of an electrical machine according to the prior art.

[0018] Preferably, said shutter and said frame are made of plastic, which has the advantage of being inexpensive to produce.

[0019] Other characteristics and advantages will appear on reading a preferred embodiment described with reference to the figures in which: there figure 1 represents an electrical machine according to the invention, the figure 2 represents in detail the lower part of the electric machine of the figure 1 , there figure 3 represents in section a membrane used in said lower part, the figure 4 represents a relief view of said membrane, and the figure 5 represents an alternative embodiment of the invention, in detail in the lower part of an electric machine according to the invention.

[0020] According to a preferred embodiment of the invention shown in figure 1 , an electric machine ME according to the invention comprises a casing CA protecting the active parts of the machine such as its stator STA and its rotor ROT. The electric machine ME is intended to provide torque to the wheel of an electric or hybrid vehicle, and therefore requires an efficient cooling system.

[0021] To do this, it includes in particular a cooling circuit OC capable of circulating oil from an oil reservoir OT, to the active parts of the electric machine ME, here to the rotor windings. The oil is sprayed at the outlet of the oil circuit OC, by injectors fixed in the flat walls of the casing CA on either side of the electric machine ME, opposite the rotor windings of the electric machine ME. Other injectors at the outlet of the oil circuit OC spray the oil onto the bearings RO of the rotor shaft, these bearings being fixed in housings of each of the flat walls of the casing CA on either side of the electric machine ME.

[0022] The oil sprayed by these different injectors flows by gravity towards the lower part of the electric machine ME, then through holes TR located in the lower wall of the casing CA, into the oil reservoir OT. A pump OP located on the cooling circuit OC, sucks the oil from the oil reservoir OT and reinjects it towards the active parts of the electric machine ME. In this embodiment of the invention, three flow orifices TR are distributed regularly on the lower wall of the casing CA, but alternatively a single central flow orifice TR is used, which reduces the risks of oil rising.

[0023] In order to prevent oil from rising into the air gap of the ME electric machine, MB membranes, visible on the figure 2 , cover the TR ports while allowing oil to flow through the MB membranes. One of these MB membranes, made of a flexible material such as silicone or any equivalent material resistant to temperatures between -40°C (degrees Celsius) and 120°C, is visible in detail on the figures 3 et 4 . It comprises a flexible flap V which lowers towards the oil reservoir OT under the weight of the oil flowing from the active parts of the electric machine ME. The flap V is made by a cut in the membrane MB, or by molding at the same time as the membrane MB. In the vertical direction relative to the electric machine ME, that is to say in the direction of flow of the oil in nominal mode, the section of the flap is made at an angle. Thus the edges of the flap V form a slope allowing the flow of oil into the reservoir, but are blocked against the corresponding edges of the rest of the membrane MB when the oil is pushed against the membrane MB from the oil reservoir OT, which prevents it from rising in the air gap. Alternatively, the edges of the flap V are not made in a regular bevel but form a more irregular descent, for example in steps, towards the reservoir OT.The MB membrane also has rail-shaped edges allowing it to be clipped onto the edges of the CA housing wall at the TR ports.

[0024] According to an alternative embodiment shown in figure 5 , a plastic frame is clipped onto the edges of the TR orifices. On one edge of the frame located in the tank, a rigid V2 flap, also made of plastic, is fixed by a LP pivot connection. The plastic used for the V2 flap and the frame can withstand a temperature between -40°C and 120°C. A tarable return spring keeps the V2 flap in contact with the frame. Said spring is wound around a central rod, said rod connects the flap and the frame by a hinge connection.

[0025] Thus the return spring allows the opening of the flap V2 and the passage of the oil towards the reservoir OT when it flows from the active parts of the machine ME, when the vehicle is traveling at constant speed, on a straight road. The flap V2 is of larger dimensions than the orifice TR, so during a turn or sudden acceleration / deceleration, the oil contained in the reservoir OT is pressed against the flap V2 which is blocked by the edges of the wall of the casing CA and prevents the oil from rising into the air gap.

[0026] Other variant embodiments of the invention are of course conceivable, for example a dielectric heat transfer liquid other than oil can be used.

Claims

1. Electric machine (ME) for an electric or hybrid motor vehicle, comprising a casing (CA) designed to protect the active parts (ROT, STAT) of said electric machine (ME), a cooling system comprising means for spraying a dielectric heat-transfer cooling liquid onto at least one part of said active parts, and a reservoir (OT) designed to collect by gravity said cooling liquid flowing through at least one orifice (TR) in a wall separating said active parts and said reservoir (OT), said machine (ME) being characterized in that it comprises, at said at least one orifice (TR), a flap (V) fastened to said wall and designed to close off said at least one orifice (TR), an elastic means designed to open said flap (V) under the effect of the gravity of said cooling liquid, and a non-return means designed to keep said flap (V) closed when a force exerted on said cooling liquid in said reservoir (OT) brings said liquid against said flap (V), said flap (V), said elastic means and said non-return means being formed from one and the same membrane (MB) of elastic material that is fastened on either side of said at least one orifice (TR) and in which said flap (V) is produced, the edges of the fixed portion of said membrane (MB) covering the edges of said flap (V), the edges of said flap (V) forming a descent towards said reservoir (OT).

2. Electric machine (ME) according to Claim 2, characterized in that said membrane (MB) is made of silicone.

3. Electric machine (ME) according to either of Claims 2 and 3, characterized in that said membrane (MB) comprises concave outer edges designed to be fastened by elasticity to the edges of said at least one orifice (TR).