The present invention relates to a drive assembly for an electric vehicle, which assembly is comprised of an electric motor mounted to engage with a wheel of the vehicle, to drive the rotation of this wheel when the motor is powered with electrical energy.
Electric motors are now commonplace and their use has now extended to practically all spheres of activity, including the field of transport and notably motor cars. Their excellent efficiency and therefore their low level of fuel consumption, their low noise levels, their compactness, etc., makes them increasingly attractive in an incessantly growing number of applications.
However, certain significant drawbacks still remain despite the appreciable progress that has been made with respect to certain performance aspects. This is particularly the case with the problems connected with the heating up of the motors, particularly in applications requiring prolonged operation and/or high powers. Furthermore, in most electric motors, the rotors are subjected to significant electromagnetically induced heating. The motor shaft may reach very high operating temperatures. Some of the heat energy is removed by conduction, by point contacts with the rolling bearing, from the heart of the motor to the outside of the casing and also by radiation. The hotter things are around the rotor, the lower this heat loss. This leads to a natural increase in rotor temperature.
In electric vehicle drive assemblies like the one depicted for example in
Patent Application WO 2004/107535 proposes a rotary electric machine, notably for a motor vehicle, provided with means of cooling and of removal to the outside of the heat produced in the machine. The cooling and removal means comprise at least a device comprising a heat-transfer fluid capable of absorbing heat from the surroundings through a first state change, and of returning the heat to the surroundings in a further state change, and a path for the circulation of this fluid between a heat production zone and a heat removal zone. This concept can be used for alternators, starters or alternator-starters for motor vehicles. Furthermore, the installations are aimed in particular at removing the heat produced by the rectifier device, notably the diodes. The alternators described are also fitted with fans positioned in such a way as to generate a circuit of cooling air.
That document describes ways of installing a heat pipe that are specific to alternators or to alternator-starters and cannot be reapplied directly to electric vehicle drive assemblies.
In order to alleviate these various disadvantages, the invention provides various technical means.
First of all, a first object of the invention is to provide a vehicle drive assembly that encourages effective removal of the heat energy generated during operation.
Another object of the invention is to provide a drive assembly for a vehicle moving around under conditions that promote the life of the seal at the interface between the wheel and the motor and avoids potential premature deterioration of this seal.
To achieve this, the invention provides an electric vehicle drive assembly that includes an electric motor mounted to engage with a wheel of the vehicle, to drive the rotation of the latter when the said motor is powered with electrical energy, the electric motor comprising a rotor mounted with the ability to rotate in a stator through the interposition of an internal rolling bearing near the wheel and of an external rolling bearing some distance from the wheel, and a magnetic assembly provided with a portion mounted on the stator and a portion mounted on the rotor, and designed to drive the rotation of the said rotor, the rotor of the motor being provided with a heat pipe comprising at least one condensation zone for condensing and at least one evaporation zone for evaporating a heat-transfer liquid, the evaporation zone of the heat pipe extending axially inside the internal rolling bearing.
The solution advantageously provides a drive assembly the motor of which comprises one or more heat pipes extending axially from the zone of the rolling bearing and of the seal (evaporation zone near the wheel) towards the condensation zone provided at the output of the motor, on the opposite side from the wheel. The heat pipes serve to collect heat energy from a hot zone and transmit it to the other side, to a cold zone.
The present solution makes it possible to cool not only the magnetic part of the motor but also the portion of the shaft internal to the rolling bearing adjacent to the wheel and internal to the seal.
This solution also makes it possible to improve the removal of heat energy from the hottest zone of the rotor by associating with the rotary assembly a heat exchange means that is reliable and performs well.
The present solution is particularly advantageous as a means for the internal cooling of motor rotors, particularly high performance ones, used for example in electric vehicle drive systems.
According to one advantageous embodiment, the assembly comprises a coupling zone provided with an adaptor and the heat pipe extends through a seal provided between the motor and the adaptor.
According to another advantageous embodiment, the axis of the heat pipe is coaxial with the axis of the rotor.
Advantageously, the condensation zone is located in the zone more or less corresponding to the external rolling bearing of the motor.
Advantageously also, the heat pipe is conical, the wider portion being on the same side as the evaporation zone.
According to another alternative form of embodiment, the heat pipe comprises a reservoir of heat-transfer liquid provided in the region of the evaporation zone.
According to yet another embodiment, the axis of the heat pipe makes an angle (alpha) with respect to the axis of rotation of the rotor.
According to yet another embodiment, a plurality of heat pipes are distributed circumferentially along the periphery of the rotor of the motor.
The invention also provides an electric motor for a drive assembly as mentioned hereinabove, comprising a heat pipe the evaporation zone of which extends axially inside the internal rolling bearing of the motor.
All the embodiment details are given in the description which follows, supplemented by
As shown schematically in
In the absence of any force other than gravity, the return of liquid by capillarity allows the heat pipe to be used in almost any position.
A heat pipe is a reliable system requiring little or no maintenance, lightweight and with low mechanical inertia, and is passive, having the ability to transmit high levels of thermoflux with a small temperature difference and the thermal conductivity of which is several hundred times higher than the thermal conductivity of a copper bar. The heat pipe can operate in all positions (inclined, horizontal) and can be fitted to existing motors.
The active material of the heat pipes, the one that evaporates and condenses, is chosen according to the temperature at which the heat pipe is to operate. Use is made for example of water, ether or alcohol.
The heat pipes are preferably cylindrical in shape, consisting of a tube with good thermal conductivity, if possible made of metal. Copper, which is a very good conductor, is one of the materials used.
The heat pipes may also include a simple hole, which may be blind or open, with heat-transfer liquid, this assembly being hermetically sealed after air has been evacuated.
Various types of heat pipe arrangement are described in what follows for installing a drive assembly according to the invention in the electric motor.
Various solutions to encourage the removal of heat from the motor in general, but also from the region of the seal 20, are set out in what follows.
As shown in the cross section of the motor in
The evaporation zone 2 is provided in the zone that is to be cooled, i.e. under the internal rolling bearing 12 and the seal 20, the removal of heat energy taking place at the inlet to the rotor where there were, for example, machined or added-on fins 4 to encourage cooling.
The cross section through the motor of
As shown in the cross section of the motor of
Thanks to the axial component of centrifugal force, the conical shape encourages the return of the heat-transfer fluid to the evaporation zone and thereby improves the efficiency of the system. The cone angle, which takes account of the speed of the motor and the diameter of the drive shaft is advantageously comprised between 0.3 and 2 degrees. In this embodiment, the use of a contact compound and of a position retaining system are not needed.
The evaporation zone 2 of the heat pipe is inside the rotor 14, making it possible to maintain an acceptable temperature radially on the inside of the rolling bearing 12 and of the seal 20. Heat energy is removed at the inlet to the rotor 14 to which is grafted an element that encourages cooling, such as machined or added-on fins 4.
The axial component of centrifugal force which is caused by the inclined position of the heat pipe encourages the return of heat transfer fluid and improves the efficiency of the system. The heat pipe is held in its housing by, for example, a washer or a locking ring. The thermal connection between heat pipe and shaft is afforded by a special high temperature contact compound.
Another embodiment shown in the installation diagram of
The figures and the descriptions thereof given hereinabove illustrate the invention rather than limiting it. In particular, the invention and its various alternative forms have just been described in conjunction with one particular example comprising a drive assembly in which the motor is connected to the wheel at the radially external portion of the wheel.
Nevertheless, it is obvious to a person skilled in the art that the invention can be extended to other embodiments in which, as alternatives, the motor engages with a wheel at a connection point situated at some other radial position, or even at the centre of the wheel.
The reference signs in the claims are entirely nonlimiting. The verbs “comprise”, and “include” do not exclude the presence of elements other than those listed in the claims. The word “a/an” or “one” preceding a component does not exclude there being a plurality of such components.
Number | Date | Country | Kind |
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1103555 | Nov 2011 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB2012/002121 | 10/16/2012 | WO | 00 | 5/20/2014 |