FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)

"OIL COOLED BRUSHLESS DIRECT CURRENT MOTOR (BLDC)
FOR ELECTRIC VEHICLES"
ELECTROTHERM (INDIA) LTD, an Indian Company, of 72, Palodia, Via Thaltej, Ahmedabad 382 115, India
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present invention relates to electric vehicles, wherein the brushless DC motors (BLDC motor) are widely used. More particularly, the invention is directed to the constructional improvements in BLDC motor by providing oil coolant which leads to enhanced cooling effect while the motor is running on overload condition*.
BACKGROUND OF THE INVENTION
The need for electric vehicles is emerging very fast as personal transportation for short distance coverage. Generally, the electric vehicles are fitted with brushless DC motors (BLDC motors) as a prime source for driving the vehicle, especially Permanent Magnet Brushless Direct current Motor (hereinafter referred to as PMBLDC Motor) is used. The motor is usually a hub motor mounted directly inside the rear wheel rim (the rim is attached to rotor). The PMBLDC motor used in most of the electric vehicles is cooled by natural flow of air while the vehicles move on the road. However, the cooling is insufficient in high powered motors hence the overheating damages the motors.
Presently, the electric vehicles are being operated in urban and rural areas where the probability of meeting high gradient and overload conditions is high. Under these conditions, the stator coil windings in the motor get heated resulting in increase in temperature inside the motor. Secondly, the BLDC motors are fitted with the MOSFET inverters which also increase the temperature inside the motor.
Thirdly, the entire assembly of the existing electric vehicle is completely sealed to prevent the entry of water into the motor when the vehicle is driven through knee deep water on roads. The sealing of the said assembly also aids the temperature rise in the motor and affect the layout and operation of the coil windings, hall sensor and circuits. Since the bulk of the heat is generated on the stator and the stator is enclosed by enveloping rotor, there is no effective method of dissipating the heat to the surroundings. Hence, there arises a need to improve the existing BLDC motor that can provide

enhanced cooling effect while the motor is running on overload conditions. Normal AC, DC & BLDC motors have rotor disposed on shaft and stator outside, hence the motor is cooled efficiently by natural cooling or fan.
It is known that, the major amount of heat transfer takes place through convection and only very small amount of heat passed by the axle using conduction. However, the convection coefficient of heat transfer of air is very low and therefore the heat transfer is slowed, hence affecting the performance and efficiency of the motor. This problem is further compounded when motor is completely sealed against water entry.
The above mentioned problem is aggregated as the power of the motor is increased. The cooling by natural convection is insufficient as the surface area is not increased in proportion to power. Due to the constant temperature increase, frequency of failure of sensors fitted inside the motor also increases. Additionally, the temperature inside the motor increases up to 195°C, resulting in damage to the motor and the performance degrade of the conventional electric vehicles. Therefore, there arises a need to select a medium wherein which convection coefficient of heat transfer is very high.
Hence, considering the above mentioned problems, there is a need to provide an improved BLDC motor with enhanced cooling effect in overload conditions. Specifically, the BLDC motor needs to be constructed in order to effectively cool the stator windings, halls sensors and circuits without allowing any external water ingress & without allowing leakage of cooling medium.
OBJECT OF THE INVENTION
The primary objective of the present invention is to provide an improved BLDC motor having enhanced cooling effect in overload condition.
The secondary objective of the present invention is to provide an oil cooled BLDC motor.
Yet another objective of the present invention is to incorporate the oil cooled BLDC motor in electric vehicle.

SUMMARY OF THE INVENTION
Accordingly, the present invention relates to an oil cooled brushless direct current electric motor for electric vehicles, said motor comprising a stator assembly comprising a stator with slots provided with stator coil windings; a rotor assembly encapsulating the stator assembly; and a pair of motor covers being configured circumferentially with the rotor assembly on both sides, so as to create a space between the motor cover and stator-rotor assembly, wherein the said space is filled with coolant oil for being distributed over the coil windings by means of one or more internal fins radially spaced and provided on the motor cover, on inside.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 illustrates a perspective view of an electric motor of electric vehicles in accordance with an aspect of the present invention.
Figure 2 illustrates a perspective view of the motor in accordance with an aspect of the present invention.
Figure 3 illustrates a sectional view of the motor in accordance with an aspect of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, the present invention is relates to an oil cooled brushless direct current electric motor for electric vehicles, said motor comprising: a stator assembly comprising a stator with slots provided with stator coil windings; a rotor assembly encapsulating the stator assembly; and a pair of motor covers being configured circumferentially with the rotor assembly on both sides, so as to create a space between the motor cover and stator-rotor assembly, wherein the said space is filled with coolant oil for being, distributed over

the coil windings by means of one or more internal fins radially spaced and provided on the motor cover.
In one aspect of the present invention, the stator assembly is secured to a axle via a first supporting structure.
In another aspect of the present invention, said rotor assembly comprises a plurality of permanent magnets circumferentially distributed facing the stator assembly.
In yet another aspect of the present invention, each of the said motor cover is secured to the axle via a ball bearing and at least two oil seals.
In still another aspect of the present invention, the said oil seals are disposed adjacently with a circlip provided in-between the oil seals.
In one aspect of the present invention, comprising a breather tube having one end being exposed outside and other end being disposed into the space between the motor cover and the stator-rotor assembly.
In another aspect of the present invention, the motor cover is extended and secured to the axle, the extended portion of the motor cover comprises a third oil seal disposed on one end of a brake plate.
In still another aspect of the present invention, the motor cover is provided with at least one oil filling hole to allow coolant oil to be filled in the space formed between the motor cover and the stator-rotor assembly.
In yet another aspect of the present invention, the coolant oil is synthetic or mineral based or semi synthetic.

Reference will now be made in detail to the presently preferred aspects of the present invention, examples of which are illustrated in the accompanying drawings.
Figure 1 illustrates a perspective view of an electric motor of electric vehicles in accordance with an aspect of the present invention.
The present invention relates to the oil cooled brushless DC (BLDC) electric motor for electric vehicles being operated by an electronic control unit (ECU). The electric vehicles are two wheelers or three wheelers or four wheeled vehicles. The motor is a brushless permanent magnet type motor operating on direct current (DC). The motor comprises a stator assembly and a rotor assembly encapsulating the stator assembly.
The stator assembly (interchangeably referred to as stator) comprises a stator core with slots provided on the circumference of the stator. The stator is secured to a axle with the slots extending along the axis of the axle. The slots include windings of an electrical conductor such as copper wire or any other conducting material. The windings are configured to produce three-phase or multiphase electrical current when pulsed voltage input is given by ECU. The stator is secured to the axle via a first supporting structure. In one aspect, the first supporting structure is web shaped and made of any material such as cast iron, steel and so on. In another aspect, the first supporting structure is made of any other material and of any shape. As the stator is secured to the axle, the axle also remains static.
The rotor assembly or rotor comprises a rotor core made of material that has relatively high permeability to magnetic flux. The rotor includes a plurality of permanent magnets or permanent magnet clusters, the clusters refer to plurality of permanent magnets arranged in a group. The permanent magnets are disposed circumferentially along the inner perimeter of the rotor core.
Further, the motor is partially filled with coolant oil or any lubricating substance for providing lubrication to the stator coil windings. The coolant oil having good dielectric

properties, good thermal conductivity, and high flash point is filled in the motor. In one aspect, the coolant oil is synthetic or mineral based or semi synthetic.The motor also comprises a pair of motor covers being configured circumferentially with the rotor assembly on both sides. In one aspect, the motor covers are engaged with the rotor on both sides thereby when the rotor rotates, the motor covers also rotate along with the rotor. Each of the motor cover is provided with one or more fins or scoops on the inner side facing the stator-rotor assembly. In one aspect, the fins are arc-shaped disposed radially with space between the fins. The fins are disposed as cast or welded with equal or unequal spaces between them. In addition, each of the motor covers is provided with at least one oil filling hole to allow the coolant oil to be stored in the space formed between the motor cover and the stator-rotor assembly.
Also, each of the motor covers is secured to the axle via at least two oil seals, a first oil seal and a second oil seal. In one aspect, the oil seals are approximately 'C shaped and made of rubber material. In another aspect, Che oii sesis are made of any material ancf of any shape. The oil seals are being secured to the'rotor and placed adjacent to each other. The first oil seal is disposed facing the stator-rotor assembly so as to prevent the coolant oil passing out through the axle. The second oil seal is disposed facing opposite to the first oil seal so as to prevent the entry of water and dust particles into the motor cover. The oil seals are secured to the axle via a fastening means such as a circlip which is disposed between the oil seals. The circlip is made of semi-flexible metal ring (e.g. spring steel) or any other material well known in the art.
Further, the motor cover is extended, in particular, the brake drum is extended and prevented with a third oil seal (also referred to as oil seal brake plate) disposed on one end of the brake plate. The purpose of the oil seal in brake plate is to guide any oil leaked inadvertently through oil seals in the cover to flow out through tapering provided on the brake plate and holes therein. Thus, the oil seal brake plate prevents the .oil entering into the brake shoes as the leaked oil may render brakes ineffective due to lowered coefficient of wet friction compared to dry friction.

Additionally, the motor comprises a breather tube provided through a hole in the axle. The breather tube is circular or oval in cross-section or any other hollow cross section and made of rubber, thermoplastic or thermosetting material or any material known in the art. One end of the breather tube is disposed into the space formed between the motor cover and the stator-rotor assembly, whereas the other end is exposed into the outside atmosphere. The excess pressure due to oil vapor is released through the breather tube thereby avoiding pressure increase inside the motor.
Figure 2 illustrates a perspective view of the motor in accordance with an aspect of the present invention.
As shown in the fig.2, the coolant oil is filled in the space formed between the motor covers and the stator-rotor assembly. The space is partially filled with the coolant oil that is being distributed by the fins (shown in the fig.2).
During the operation of the motor, the rotor on which the permanent magnets are fixed rotates due to interaction with the magnetic field generated by current passing through stator windings. Due to current, the coil windings get heated and the temperature rises inside the motor. The temperature rise is controlled by circulating fluid through the coil windings using the coolant oil stored. As the motor cover is engaged to the rotor, the motor covers also rotate with the rotor. The internal fins on the motor cover carry and distribute the coolant oil to the coil windings that are located on the upper surface, thereby cooling the heated coil windings and reducing the temperature inside the motor. Thus the heat transfer takes place effectively by means of the coolant oil. Further, the coolant oil is filled into the motor via the oil filling holes shown in fig.2.
Figure 3 illustrates a sectional view of the motor in accordance with an aspect of the present invention.
As illustrated in fig.3, the first and second oil seals are placed adjacent to each other with the circlip provided between them. The first oil seal is disposed facing the stator-rotor

assembly so as to prevent the coolant oil passing out through the axle. The second oil seal is disposed facing opposite to the first oil seal so as to prevent the entry of water and dust particles into the motor cover. Further, the third oil seal or the oil seal brake plate is provided on end of the brake plate to prevent to the coolant oil entering the brake shoes.
At overload conditions, when the temperature inside the motor rises or when current drawn by the motor increases above an average limit, the motor needs to be effectively cooled. The cooling effect of the motor is achieved by splashing the motor with coolant oil filled inside the motor. The coolant oil is distributed over the stator coil windings thereby reducing the maximum heat at a high rate. The splashing of the coolant oil is achieved by the internal fins for splashing the coolant oil onto the coil windings results in reduction of heat, and thereby cooling the motor.
During the circulation and the heat transfer, the coolant oil vapors causing increase of pressure in the motor. The breather tube (shown in fig.3) allows the excess pressure to flow out; thereby maintaining the pressure inside the motor which will prevent oil leakage through the oil seals. Further, the process of lubricating the coil windings using the coolant oil controls the temperature increase caused during gradient or overload conditions. Especially, the temperature increase is controlled and maintained within the range of 60-100 degree Celsius which is feasible for motors. Moreover, the oil seals prevent the oil entering out and also prevent water entering inside the motor, improving the life span of the motor.
In preferred aspects, the number of oil seals can be increased as they are replaceable and low cost involving low maintenance cost. In further aspects, the number of internal fins can be increased or decreased depending on the need and application of the motor and manufacturer's design. Also, the fins can have various shapes depending on the.need. In further more aspects, the number or size of oil filling holes can be varied based on the size and power consumption of the motor.
• 1 8 NOV 2009

The herein-described electric motor has been provided with constructional improvements and the motor is proven to be simple and cost effective. The present design can be implemented into production with little additional cost to the product and has no additional maintenance requirements. The present design is a low cost solution which can be retrofitted into existing electric or hybrid electric vehicles equipped with brushless DC motors, or easily integrated into new models.
The advantages of the disclosed invention are thus attained in an economical, practical, and facile manner. While preferred aspects and example configurations have been shown and described, it is to be understood that various further modifications and additional configurations will be apparent to those skilled in the art. It is intended that the specific aspects/ embodiments and configurations herein disclosed are illustrative of the preferred and best modes for practicing the invention, and should not be interpreted as limitations on the scope of the invention.
ADVANTAGES OF THE INVENTION
1. Improves the cooling effect in BLDC electric motors for electric vehicles.
2. Temperature and pressure inside the motor is maintained.
3. Adding few constructional modifications to achieve better cooling effect.
4. Increases the efficiency and life span of the motor.
5. Simple and Cost effective.
6. Less maintenance cost involved.

We claim:
1. An oil cooled brushless direct current electric motor for electric vehicles, said motor
comprising:
(a) a stator assembly comprising a stator with slots provided with stator coil windings;
(b) a rotor assembly encapsulating the stator assembly; and
(c) a pair of motor covers being configured circumferentially with the rotor assembly on both sides, so as to create a space between the motor cover and stator-rotor assembly, wherein the said space is filled with coolant oil for being distributed over the coil windings by means of one or more internal fins radially spaced and provided on the motor cover.

2. The motor as claimed in claim 1, wherein the stator assembly is secured to a axle via a first supporting structure.
3. The motor as claimed in claim 1, wherein said rotor assembly comprises a plurality of permanent magnets circumferentially distributed facing the stator assembly.
4. The motor as claimed in claim 1, wherein each of the said motor cover is secured to the axle via a ball bearing at least two oil seals.
5. The motor as claimed in claim 1, wherein the said oil seals are disposed adjacently with a circlip provided in-between the oil seals.
6. The motor as claimed in claim 1, comprising a breather tube having one end being exposed outside and other end being disposed into the space between the motor cover and the stator-rotor assembly.