FIELD OF THE INVENTION

The present invention relates generally to electric motors specially a squirrel cage induction motor for hybrid and electric vehicle.

BACKGROUND AND PRIOR ART

Most motors used in Electric and Hybrid Cars today use or rely on permanent magnets. These permanent magnets are made from neodymium, a rare earth mineral. These motors are also known as synchronous motors which have stationary magnetic field on the rotor.

The induction motor technology is a very common and inexpensive method which is being used in different appliances. Induction motors have a rotating magnetic field on the rotor. In a squirrel cage motor, this field is created because the motion of the stator field relative to the shortened rotor cage induces currents in the rotor. These currents generate the rotor field, which interacts with the stator field to create torque.

Introduction to hybrid/electric vehicles in India is in very much premature or developmental stage. This is new trend picking up very fast. Till now squirrel cage induction technology is not used to develop a motor suitable for automotive usage, especially for Hybrid and Electric vehicles especially in India.

Moreover, a book named "Electrical and Electronic Principles and Technology"
by "John Bird" states that the squirrel cage induction motor has very poor starting torque and must be started off-load or very lightly loaded. It further states that also on starting, the current can be four to five times the normal load current, due to the motor acting like transformer with secondary short circuited. But the mentioned comments in the book have been overcome in the present invention to meet application requirement.

US 6967419 titled "Motor for hybrid vehicle" discloses a motor for hybrid vehicles which comprises a rotor with magnets mounted on a peripheral section of a drive plate provided between a crank shaft of an internal combustion engine and a transmission; and a stator provided facing this rotor in the radial direction. As a result, it is possible to rotate the rotor about the same axis as the crank shaft and to assist the drive of the engine as well as regenerating part of the kinetic energy of the vehicle. The base section of the rotor is integrally formed with the drive plate by press-forming so that a reduction in the number of parts and weight is achieved. This motor is provided for a hybrid vehicle in which miniaturization of the drive system and transmission system can be achieved while maintaining driving performance.

US 6965186 titled "Electric motor for hybrid vehicles" describes an electric motor for a hybrid vehicle which has a rotor disposed and coupled between an internal combustion engine and a transmission, the rotor being coupled to the crank shaft of the internal combustion engine and via a plate to the transmission. The objective of this motor is to provide an electric motor for a hybrid vehicle which prevents excess increase in the cost of producing the rotor and which enables securing a desired performance easily. It comprises of a rotor disposed and coupled between an internal combustion engine and a transmission, the rotor being coupled, at one end thereof in a direction of a rotation axis, to a crank shaft of the internal combustion engine and at an opposite end, to the transmission via a drive plate; a through hole provided in the rotor so as to extend there through in the direction of the rotation axis; a fastening hole provided in an end face of the crank shaft and in the drive plate, each facing and being in communication with the through hole; and a fastening member inserted in the through hole and in each of the fastening holes such that the rotor is fixed between the crank shaft and the drive plate.

US 4562397 titled "Squirrel-cage induction motor" discloses a induction motor comprising a stator having a stator core and stator windings divided into first and second coils with different numbers of poles, and a squirrel-cage rotor including a rotor core and a plurality of rotor conductors embedded in the vicinity of the surface of the core. The number of the rotor conductors is the same as the average number of poles of the first and second stator coils, where conductors are arranged equidistantly along the periphery. This induction motor, with the construction of a squirrel - cage rotor, permits a variable speed operation without using any special device.

US 4920293 titled "Squirrel-cage induction motor" whose one of the objective is to provide a squirrel-cage induction motor comprising a fixed first stator, a movable second stator and a braked motor interlocked through a gear mechanism with the second stator to shift the second stator easily and rapidly relative to the first stator according to the characteristics required by load.

It's another object is to provide a motor capable of being incorporated into an automatic control system, comprising a fixed first stator, a movable second stator, and a braked motor for shifting the second stator relative to the first stator, in which the second stator can manually be operated. Therefore, the present invention provides a squirrel-cage induction motor comprising a squirrel-cage rotor, a fixed first stator, a rotatable second stator, a segmental gear mounted on the circumference of the second stator, a braked motor interlocked through a gear mechanism including the segmental gear with the second stator to turn the second rotor, and a control circuit which operates conditions required by load to provide a command signal representing an angle of turning the second stator in the normal or reverse direction to drive the braked motor so that the second stator is turned through the angle specified by the command signal through the gear mechanism by the braked motor.

WO2011025918 titled "Multiple Induction electric motor and vehicle" discloses a novel electric motor and vehicle that stores electrical power, provides a first and second direct current power input from the stored electrical power, separately produces first and second synchronized variable frequency alternating current control signal from the first and second current power inputs respectively. It also discloses a process and system for turning a shaft. The disclosed invention claims for basic principle of induction motor. But the present invention discloses Special induction motors for automotive industry designed to meet IC engine performance.

SUMMARY

The present invention discloses a type of squirrel cage induction motor for application in electric and hybrid vehicles. The speciality of the motor of the present invention is that it takes less voltage and produces higher torque and speed. It uses a low cost technology but on the other hand highly reliable and maintenance free.

This motor works along with engine and helps to minimize fuel consumption by maintaining optimum load on engine. During heavy load and in the regions where Engine is not efficient, motor will assist engine and improve the engine performance. During braking, idle running or under-loading this machine acts as generator and recover power.

The novel and key features of the proposed motor is as follows. The motor is designed for a speed range of 1000 to 8000 rpm, input of 28 - 72 volts, frequency from 20 Hz to 300 Hz which produces an output as desired by engine for optimum performance. The motor also includes inbuilt temperature sensor and speed sensor to make them compatible with controllers. It is flexible to meet various characteristics of IC engines for smooth operation.

The advantages of the disclosed motor are as follows: (a) Regenerative braking - AC system which can take back energy from braking as it gives out. This helps to recover lot of battery power which is not possible with DC machines; (b) favorable torque -AC induction motor torque which can be well matched with IC engines which are not possible in present system. This helps in longer life of transmission system; (c) no maintenance is required with induction motors; (d) AC motor controller is more user friendly and self controlled by driver based on his style of driving. With other machines, it is not possible since they are matched with motor characteristics; (e) AC controller which is simple to move the vehicle forward and backward, this is not the case with the existing system.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of the invention will become apparent from the following description of embodiments as illustrated in the accompanying drawings. The following drawings are only examples and it may be noted that it is possible to apply the same principle and construct other types of motors.

Figure 1 illustrates an isometric view of the induction motor EVM90V1 of the present invention.

Figure 2 illustrates sectional view of the induction motor EVM90V2 and EVM90V3 of the present invention.

Figure 3 illustrates sectional view of the induction motor CEV132-V1 of the present invention.

Figure 4 illustrates sectional view of the induction motor BEV132-V2 of the present invention.

Figure 5 illustrates a graph showing characteristics of typical torque v/s speed and current v/s speed of a normal induction motor.

Figure 6 illustrates flux linkage for optimum performance.

Figure 7a and 7b illustrates the existing and new improved motor showing the difference in the conductor position.

Figure 8a and 8b illustrates the existing and the new improved motor showing the difference in the arrangement of stator frame.

Figure 9a, 9b, and 9c illustrates the existing and the new improved motor showing the difference in the bearing used in the motor.

Figure 10 illustrates the arrangement of the stator and rotor in the electric vehicle motor.

Figure 11a and lib illustrates the mounting of the existing motor and new motor on the electric vehicle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 illustrates a typical cross sectional view of 3 phase AC squirrel cage induction motor EVM90V1 disclosed. The induction motor has two main parts such as a stationary stator assembly 7 and a moving rotor assembly 8. The body 9 of the motor is made up of aluminium or steel or cast iron or plastic material which includes a shaft 3. There are two covers for the motor namely drive end cover 1 which covers the shaft extension region and drives the load and non-drive end cover 2 which covers the opposite region. Sensing elements for temperature and speed are one of the special features of this type of induction motor. The normal bearing 5 is located at the other end of the shaft 3. The induction motor also includes sensor Bearing (BRG) 4, bearing cap 6, eight Mild Steel Inserts (M.S.Inserts) 10, Cable holder/gland 11, fan 12, and circup 13 as its structural components.

In a typical example, the rotor is designed to run in the speed range of up to 8000 rpm. The stator is supplied with an input voltage up to 72 Volts. The rotating magnetic field cuts the rotor windings/bars and which in turn rotates to produce the mechanical power.

Figure 2 illustrates sectional view of the induction motor EVM90V2 and EVM90V3 of the present invention. This view shows the drive end cover/flange 1, non-drive end cover 2, sensor BRG 4, normal bearing 5 , bearing cap 6, eight M.S.Inserts 10, stator assembly 7 , rotor assembly 8, shaft 3, key way 14 and four fixing studs 15 of the motor.

Figure 3 illustrates sectional view of the induction motor CEV132-V1 of the present invention. This view shows the drive end cover/flange 1, non-drive end cover 2, shaft 3, sensor BRG 4, normal bearing 5 , bearing cap 6, stator assembly 7, rotor assembly 8, body 9, three Cable holders/glands 11, key way 14, four fixing studs 15, oil seal 16, and an eye bolt 17 of the motor.

Figure 4 illustrates sectional view of the induction motor BEV132-V2 of the present invention. This view shows the drive end cover/flange 1, non-drive end cover 2, shaft 3, sensor BRG 4, normal bearing 5, bearing cap 6, stator assembly 7, rotor assembly 8, body 9, five Cable holders/glands 11, key way 14, oil seal 16, two eye bolts 17, two O-rings 18, Outlet/inlet plug 19 and an outer shell 20 of the motor.

Outer shell is a part which holds winding in place while the motor is in operation. This also protects the winding from external factors in automotive application. Outer shell is having different shapes and material to meet the best fit to specific application.

Typical Torque v/s Speed and Current v/s Speed characteristics of normal Induction motor is shown in Figure 5. The motors designed for Vehicle application are having characteristics matching the application and engine requirements at various speed ranges. Typical flux distribution in induction motor is shown in Figure 6.

In the present invention the number of parallel paths selected is same as number of poles. By doing the series joints in the overhangs are avoided, reducing the failures and increases the reliability.

Figure 7 illustrates the existing motor and new improved motor showing the difference in the conductor position where Figure 7a shows the position of the conductor in the existing motor 71 and Figure 7b shows the position of the conductor in the new improved motor 72. Since the vehicle motors are battery operated, the operating voltage is very low (of the order of 28 to 72V). Hence the rated current of the motor becomes too high. This requires high cross section of the winding conductors and very difficult to bring to the terminal box 73 as shown in Figure 7a. The procedure employed in the current development is to bring directly the conductors outside 72 through a separate opening made on the end cover and left as flying leads 74 as shown in Figure 7c. These leads go to the controller of the vehicle. The arrangement is shown in Figure 7b and 7c. In other words, the provision of a terminal box is eliminated.

Figure 8 illustrates the existing and new improved motor showing the difference in the stator frame. Figure 8a shows the existing motor having stator frame 81 which is used as housing for the wound stator. Wherever dimensional limitations are there for mounting in vehicles, this stator frame is eliminated. Alternatively, spigot 85 is created on the stator stack 84 and end covers 82 are placed on this and held together by 4 studs 83 running from one end cover to the other. The arrangement is shown in Figure 8b.

Figure 9 illustrates the existing and new improved motor showing the difference in the arrangement of the sensor bearing. Figure 9a shows the isometric view of the existing motor's bearing and Figure 9b shows the new improved motor's sensor bearing. Wherever closed loop control of the motor operation is used an encoder or tacho generator 94 mounted on the non-driving end of the motor is used to get the speed feedback signal as shown in Figure 9c. Here in electric vehicle motors "sensor bearing" is used. This bearing has a sensor 91, 92 inside and gives the speed feedback signal from the leads 93 coming out of the bearing. This reduces the overall size and number of components in the system. Sensor bearing arrangement is shown in Figure 9b and 9c.

Figure 10 illustrates the arrangement of the rotor and stator in the electric vehicle motor. In some cases due to the space constraint for mounting the motor, more power is required in a small diameter and long motor is preferred. However there are practical difficulties in manufacturing such very long motor. Therefore a novel method is adopted where 2 stators 101, 102 are made independently and housed in the same housing, one after the other. Similarly 2 rotors are used for each of the stator i.e., rotors 103,104 for stator 101 and rotors 105,106 for stator 102 (which means 4 rotors 103,104,105 and 106 in a single motor). The arrangement is shown in Figure 10.

Figure 11 illustrates the mounting of the motor of the existing and new improved motor. Figure 11a shows the front view 111, side view 112 and bottom view 113 of the existing motor and Figure lib shows the front view 121, side view 122 and bottom view 123 of the new improved motor. Standard practice of mounting the motor is a loose hole in the motor feet and tapped hole on the mounting surface. In some cases for accurate positioning of the motor, a tapped mounting hole is put on the motor itself. The details are shown in Figure 11a and lib.

Salient design features of vehicle motor:

• The motors for Vehicle application are designed such that the flux linkage is optimum to produce maximum torque with minimum current.

• Proper care in the slot combination, slot design, linkage path is taken and worked out very carefully.

• The vehicle motor is designed with shallow rotor bars to get maximum torque.

• The base frequency is chosen such that throughout the operation zone of the motor the efficiency is maximum.

• Winding connection is chosen to have no joints in the winding.(4 parallel star for 4 pole motor).

• Stamping thickness is chosen such that the core losses are minimum at all frequencies.(0.5 mm up to 75 Hz, 0.35mm for more than 75Hz.).

Typical ratings and specification of few motors are given below as example towards this development.

WE CLAIM

1. A 3-Phase AC squirrel cage induction motor for hybrid and electric vehicles with increased reliability where the motor produces maximum torque with minimum current using optimum flux linkage, the design optimizes slot combination, slot design and linkage path, the base frequency is chosen such that throughout the operation zone of the motor the efficiency is maximum, the stamping thickness is chosen such that the core losses are minimum at all frequencies comprising a stator and rotor assembly 7, 8 mounted on a shaft 3, all being housed in a body 9 having two covers characterized in that two stators 101,102 are mounted side by side, two rotors each 103,104 and 105,106 are provided for each of the stator 101,102, the conductors for making the connection with the controller of the vehicle being brought outside the motor through a separate opening 74 a spigot 84 is being provided on the stator stack and end covers being placed on the spigot 84, the covers being held together by a fastening means, the bearing used in a sensor bearing.

2. A 3-Phase AC squirrel cage induction motor as claimed in claim 1, wherein the fastening means in a stud 83.

3. A 3-Phase AC squirrel cage induction motor as claimed in claim 1, wherein the motor is mounted through the tapped mounting hole provided on the motor itself.

4. A 3-Phase AC squirrel cage induction motor as claimed in claim 1, wherein there are two covers for the motor including a drive end cover 1 and a non-drive end cover 2.

5. A 3-Phase AC squirrel cage induction motor as claimed in claim 1, wherein a normal bearing 5 is located at the other end of the shaft 3.

6. A 3-Phase AC squirrel cage induction motor as claimed in claim 1, wherein the induction motor includes a sensor 4, bearing cap 6, eight M.S.Insert 10, Cable holder/gland 11, fan 12, and circup 13 as its structural components.

7. A 3-Phase AC squirrel cage induction motor as claimed in claim 1, wherein:

a. The rotor is designed to run in the speed range of up to 8000 rpm;

b. The stator is supplied with an input voltage up to 72 Volts; and

c. The rotating magnetic field cuts the rotor windings/b ars and which in turn rotates to produce the mechanical power.

8. A 3-Phase AC squirrel cage induction motor as claimed in claim 1, wherein one embodiment has a drive end cover 1, non-drive end cover 2, sensor BRG 4, normal bearing 5, bearing cap 6, eight M S Insert 10, stator assembly 7, rotor assembly 8, shaft 3, key way 14 and four fixing studs 15 of the motor two eye bolts 17, two O-rings 18, Outlet/inlet plug 19 and an outer shell 20 of the motor.

9. A 3-Phase AC squirrel cage induction motor as claimed in claim 1, wherein the number of parallel paths selected is same as number of poles such that the series joints in the overhangs are avoided, reducing the failures and increasing the reliability.

10. A 3-Phase AC squirrel cage induction motor as claimed in claim 1, wherein in one embodiment the stator frame 81 which is used as housing for the wound stator is eliminated wherever dimensional limitations exist for mounting in vehicles, an alternatively a spigot 84 is created on the stator stack 85 and end covers 82 are placed on this and held together by 4 studs 83 running from one end cover to the other.

11. A 3-Phase AC squirrel cage induction motor as claimed in claim 1, wherein in one embodiment a different arrangement of the sensor bearing is used to reduce the overall size and number of components in the system such that wherever closed loop control of the motor operation is used an encoder or tacho generator 94 mounted on the non-driving end of the motor is used to get the speed feedback signal where in electric vehicle motors a "sensor bearing" is used having a sensor 91, 92 inside and responsible for giving the speed feedback signal from the leads 93 coming out of the bearing.

12. A 3-Phase AC squirrel cage induction motor as claimed in claim 1, wherein in one embodiment a different arrangement of the rotor and stator in the electric vehicle in situation where more power is required in a small diameter and long motor is preferred where two stators 101, 102 are made independently and housed in the same housing, one after the other, two rotors are used for each of the stator i.e., rotors 103, 104 for stator 101 and rotors 105, 106 for stator 102 (which means 4 rotors 103,104,105 and 106 in a single motor).

13. A 3-Phase AC squirrel cage induction motor as claimed in claim 1, wherein in one embodiment a new improved motor with a front view 121, side view 122 and bottom view 123 is used where the practice of mounting the motor is a loose hole in the motor feet and tapped hole on the mounting surface but alternatively some cases for accurate positioning of the motor, a tapped mounting hole is put on the motor itself.

14. A 3-Phase AC squirrel cage induction motor as claimed in claim 1, wherein a winding connection is chosen to have no joints in the winding. (4 parallel star for 4 pole motor).

15. A 3-Phase AC squirrel cage induction motor as claimed in claim 1, wherein the vehicle motor is designed with shallow rotor bars to get maximum torque.