GB2449489A

GB2449489A - Vehicle in-wheel motor generators with interposed differential

Info

Publication number: GB2449489A
Application number: GB0710033A
Authority: GB
Inventors: Poramaste Jinupun; Patrick Chi-Kwong Luk
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-05-25
Filing date: 2007-05-25
Publication date: 2008-11-26
Anticipated expiration: 2027-05-25
Also published as: GB0710033D0; GB2449489B

Abstract

A vehicle power generation means 1 comprises two in-wheel electric machines 2 coupled by a differential gear assembly 3 and supported about symmetrically by a main base structure 20. Each electric machine 2 comprises a stator 4, and a rotor 5 disposed radially inward of the stator 4 and spaced by an air gap 8. Stator 4 is supported by base structure 20. The rotor comprises an inner shaft 6 and outer shaft 7 disposed coaxially by respective bearings, so that the shafts may rotate at different speeds. The electric machine 2 is preferably of switched reluctance type or induction. The electric machines 2 are supplied with power from a suitable power source such as an electric battery. The differential gear assembly 3 comprises an array of four bevel gears and a tubular rotatable housing 10. The two output gears 12 and 14 are connected with their respective axles 15 and 16 which can be coupled directly to the inner shafts of the respective rotors. The tubular housing 10 is supported through bearings by a bearing base 22, which is fixed onto the main base structure 20. The housing 10 is axially connected to the outer shaft 7 of the rotor by means of an extended hollow coupler 17. The connection arrangement to the other electric machine can be similarly achieved by the corresponding coupler 18. The electric machine 2 usually would be supplied with power from electric power source such as a battery. Alternatively, mechanical power may be applied from the wheel 24, and electric power will be generated in the machines. The invention inherits the many advantages of in-wheel motor drive systems while maintaining robustness and reliability of the differential gear. It also adds redundancy and modularity to the drivetrain. It also does not suffer from high unsprung weight currently associated with in-wheel electric drives.

Description

Intellectual Property Office DED For Creativity and Innovation

Application No. GBO7 10033.2 RTM Date:9 September 2008 The following term is a registered trademark and should be read as such wherever it occur in this document: Mitsubishi (fficp nn ooeratinq name of The Patent Office

DESCRIPTION OF INVENTION

Dual in-wheel electric machines linked by differential gear assembly Inventors: Poramoste JINUPUN & Patrick Chi Kwong LU1 Cranfield University, UK Date: 21 May2007

FIELD OF THE INVENTION

The present invention relates to power generation means for a vehicle and a method for providing power for a vehicle and is concerned particularly with two in-wheel electric machines linked by a differential gear assembly for a vehicle.

BACKGROUND OF THE INVENTION

2. Currently vehicles that are powered by electric motors generally include an electric motor that drives the wheels of the vehicle through a reduction gearbox. Typically the power is transferred from the electric motor to the reduction gearbox comprising a worm and wheel gear. The electric power for the electric motor is normally stored in an electric battery. The efficiency of this system is generally not high due to the number of gears involved, and there are also a high number of mechanical components.

3. A recent method involves an electric motor having a differential gear disposed within the rotor of the motor [European patent application EP1274161 All, which brings compactness to the system. Since the motor is the middle of the axle, this method also reduces the clearance of the axle system of the vehicle from the ground.

4. More recently in-wheel machines are used in electric drivetrain [Typical examples include US Patent 69420491. Mitsubishi has also developed the Mitsubishi In-wheel motor Electric Vehicle (M[EV) concept in which in-wheel motor is used to drive each wheel to produce an all-wheel drive system that requires no transmission, drive shafts, differential gears or other complex mechanical components. MIEV aims to control drive torque and braking force independently at each wheel. The system also allows good clearance of the vehicle as no axle is usually involved.

However, very complex control is required to ensure the motors operate cooperatively. There are extra complexity and system costs for reliability of these kinds of drivetrain.

5. The current invention will address all the above mentioned issues associated with current vehicle power means. In particular, it inherits the many advantages of in-wheel motor drive systems while maintaining robustness and reliability of the differential gear. It also adds redundancy and modularity to the drivetrain. It also does not suffer from high unsprung weight currently associated with in-wheel electric drives.

SUMMARY OF TH INVENTION

6. An object of the present invention is to provide mechanical power generation means for propelling a vehicle, the power generation means comprising two in-wheel electric machines axially linked by a differential gear assembly comprising a rotatable housing containing an array of bevel gears, and the electric machines each comprising a stator and a rotor having an inner shaft and outer shaft disposed coaxially by geanngs such as they may rotate at different speeds, the arrangement being such that in use the equal electromagnetic rotational force generated by each electric machine turns their respective wheel directly and yet cooperatively regardless of differing load conditions exerted on each wheel.

7. The two in-wheel electric machines are preferably disposed more or less symmetrically with respect to the differential gear assembly such that a "machine-gear assembly-machine" arrangement results and all units rotate on a common axis.

8. In respect of the first aspect of invention, with equal loading condition on each wheel, the inner and outer shafts of the rotors of both machines will rotate at same speed on the same axis, whilst with unequal loading conditions, the inner and outer shafts of the rotors of each machine may rotate at different speeds.

9. It will be appreciated that a suitable electric storage device will be provided for supplying electric power to the mechanical power generation means.

10. The differential gear assembly preferably comprises two output gears each connected to an end of a respective axle, and a pair of idler gears each rotatably mounted on a respective shaft, each idler gear meshing with both output gears.

11. The Iwo output gears and the two axles are preferably disposed co-axially with the rotational axis of the rotors.

12. The output gears are preferably bevel gears.

13. The idler gears are preferably bevel gears.

14. The housing structure of the differential gear assembly is preferably tubular, and comprises bearing means through which the support is provided.

15. Preferably, the inner shaft of the rotor of one of the electric machines is directly coupled to the drive end of the axle of one output gear, and the inner shaft of the rotor of the other electric machine is similarly coupled to the drive end of the axle of the other output gear, such that an "inner rotor-axle-gear-gear-axie-inner rotor" arrangement is formed.

16. Also preferably, the outer shaft of the rotor of one of the electric machines is coupled to the one end of the rotatable tubular differential gear housing by means of an extended hollow tubular coupler, and similarly the outer shaft of the rotor of the other electric machine is coupled to the other. end of the rotatable tubular differential gear housing by means of another similar coupler, such that an "outer rotor-coupler_housing_.housing_coupler outer rotor" arrangement is formed.

17. The rotatable tubular differential gear housing is preferably supported through bearings to a fixed common base.

18. Also preferably, the stator of each of the machines are joined to the same common base as in the case of the differential gear housing, in such a manner that together with the previously described arrangements of the inner and outer shafts of the machines to the differential gear assembly, the dual in-wheel electric machines can either rotate at same speed and mechanically linked upon a common axle, or can rotate cooperatively at different speeds and/or different directions upon the same common axis.

19. With respect to the first aspect of the invention, when either one, or both, of the machines are equally excited to generate electromagnetic rotational forces, it/they will rotate the inner and outer shafts of both rotors at the same speed upon a common axis provided the load is equal at both machines.

20. In normal use as a vehicle mechanical power generation means, the two electric machines will be driven by the same electrical signals and identical excitation.

21. In another use as a vehicle mechanical power generation means, only one electric machine will be driven by the electrical signals, while the other is intentionally not excited.

22. The latter case illustrates the modularity operation of the invention, with each power generation means allowing zero, one or two machines to be used for mechanical power generation for the vehicle.

23. In another use as a vehicle mechanical power generation system, only one electric machine will be driven by the electrical signals, while the other is unintentionally not excited due to signal or other failures.

24. The latter case illustrates an intrinsic redundancy of the invention.

25. The electric machine is preferably brushless type with no main unexcited magnetic flux.

26. Preferably the electric machine is of switched reluctance type or induction type.

27. This vehicle power generation means also provides significant clearance from the ground because the electric machines are embodied in the wheels, rather than between the wheels and housing the differential gear as in an prior art.

28. The rotors of the machines and the rotating parts are all close to the are axis of rotation, which result in very low unsprung weights when compared with conventional rn-wheel motor drive systems.

29. In an embodiment of the present invention the in-wheel power generation means is preferably mounted to form/integrate with the rear propulsion of a vehicle.

30. In an embodiment of the present invention the in-wheel power generation means is preferably mounted to form/integrate with the rear propulsion of a mobility aid.

31. In an embodiment of the present invention the electric machines preferably have a priinaiy operating condition as an electric motors and a secondary operating condi-tion as electric generators.

32. The term power generation means is used here within to describe both the means by which a vehicle is provided with a driving velocity and the means by which an electric current is generated by the velocity of a vehicle. It will be appreciated that in the primary operating condition the power generation means drives the wheels directly and in the secondary operating condition the power generation means generates an electric current that is stored in the storage device.

33. The second object of the invention there is to provide electric power generation means for a vehicle comprising a dual electric machine set each comprising a stator and a rotor, axially linked by a differential gear assembly comprising a rotatable housing containing an array of gears, and electric storage means, the method comprising using a rotational force on the rotors or wheels to generate an electric current and storing the electric current in the electric storage device.

34. The construction of the electric machine and the differential gear assembly used in the second aspect of the present invention is preferably substantially as specified by the first object of the present invention.

35. It will be appreciated that a suitable storage means for the electric current may be provided for storing the generated electric current.

36. The third object of the present invention is to provide breaking means for a vehicle, the method comprising the use of the electric machines and differential gear assembly as electric generators, wherein the rotational force of the rotors and rotatable housing is converted into an electric current.

37. The electric machines and differential gear assembly used in the third aspect of the present invention is preferably as specified by the first object of the present invention.

38. The present invention may include any combination of the features or limitations referred to herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

39. The following description provides specific details, by way of example only with reference to the accompanying drawing, in order to give a thorough understanding of the invention. Nonetheless, those skilled in the art would understand that the invention can be practiced without employing these specific details. Indeed, the present invention can be practiced by modifying the illustrated system and method, and can be used in conjunction with systems and techniques conventionally used elsewhere.

40. Referring to Figure 1, a vehicle power generation means (I) comprises two in-wheel electric machines (2) coupled by a differential gear assembly (3) and supported more or less symmetrically by a main base structure (20), where only one machine is shown for clarity.

41. Each electric machine (2) comprises a stator portion (4), and a rotor portion (5) disposed radially inward of the stator portion (4) and spaced by an air gap (8). Stator portion (4) is supported by base structure (20). The rotor comprises an inner shaft (6) and outer shaft (7) disposed coaxially by means of respective bearings, in such a manner that the shafts may rotate at different speeds. The electric machine (2) is preferably of switched reluctance type or induction. The electric machines (2) would be supplied with power from a suitable power source such as an electric batteiy.

42. The differential gear assembly (3) comprises an array of four bevel gears and a tubular rotatable housing (10). The two output gears (12) and (14) are connected with their respective axles (15) and (16) which can be conveniently coupled directly to the inner shafis of the respective rotors. The tubular housing (10) is supported through bearings by a bearing base (22), which is fixed onto the main base structure (20). The housing (10) is axially connected to the outer shaft (7) of the rotor by means of an extended hollow coupler (17).

The connection arrangement to the other electric machine (not shown) can be similarly achieved by the corresponding coupler (18). The electric machine (2) would be supplied with power from a suitable power source such as a battery. Alternatively, mechanical power may be applied from the wheel (24), and electric power will be generated in the machines.

43. In use the electric battery supplies the electric machine (2) with an electric current which in turn produces an electromagnetic force generated by the stator (4) and the rotor (5). This force produces a torque that rotates the rotor (5) and the differential housing (IC)) about a common axis (30). Those skilled in the art will appreciate that the design of the stator (4) and rotor (5) and the torque required will depend upon the type of vehicle driven by the power means (1).

44. The power generation means (I) may be mounted at the rear end as an electric drivetrain for a passenger vehicle, mobility aid, wheelchair, scooter or any other such wheeled vehicles.

When the vehicle is travelling in a straight line the housing (10) and the bevel output gears (12, 14) rotate but the idler bevel gears (13) will not rotate about their respective shafts.

When the vehicle travels through a bend the first axle (15) and the bevel output gear (12) will rotate at a different rotational speed to the second axle (16) and the bevel output gear (14). Due to the different rotational speeds of the bevel output gears (12, 14), the idler bevel gears (13) will rotate on their respective shafts.

45. Preferably the electric machine will be a switched reluctance motor or an induction motor Since there is no permanent magnet in these mahines, there will be no unintended induced back emf to cause uncontrolled large currents flowing in the system during fault conditions when the rotor/rotors are rotating.

46. The power generation means (1) and, in particular the electric machines (2) and differential gear assembly (3) may also be used as electric generators. The velocity of the vehicle is converted into a rotational velocity of the tubular housing (10) and the rotor portions (5) of the electric machines (2). The rotational velocity of the rotor portions (5) are used to generate an electric current in the stator portions (4). It will be appreciated that when the electric machines (2) are used as electric generators and they will provide breaking means for the vehicle. The electric power generated by the electric machines (2) could be stored in the electric battery for future use by the power means (1). There are advantages provided by using the electric machines (2) as generators, including increased range of the vehicle. p

DRAWINGS

Figure I: Dual in-wheel electric machines linked by differential gear assembly (only one electric machine is shown) Figure 2: Prior art of electric machine having a djfferential gear disposed within the rotor of the motor [European patent application EP1274161 Al]. * ** * S * * S. 55. * * *5.* * .* * * S * *S * V..

S V... * SS S. S

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Claims

I) A drive system for an electric motor vehicle, having (a) two

electric motors and each of said electric motor immerses into a vehicle wheel, (b) two drive shafts and each of said drive shaft has an inner shaft and outer shaft coaxially, (c) a first drive shaft is used on a first of said vehicle wheels and a second drive shaft is used on second of said vehicle wheels, (d) said outer shaft joins between output shaft of said electric motor and a housing of a differential gear that applies to the first of said vehicle wheels and also to the second side of said vehicle wheels, (e) inner shaft joins between said vehicle wheel and output shaft of said differential gear that applies to the first of said vehicle wheels and also to the second of said vehicle wheels, and (f) said vehicle wheels can be driven either by one or two of said electric motors therefore offers fault tolerance.
2) A drive system according to claim 1, said outer shaft is supported by bearings which are fixed on a rigid part of said vehicle.
3) A drive system according to claim 1, a space between said outer shaft and said inner shaft is fitted with bearings which allow said outer shaft and said inner shaft to be rotated independently.
4) A drive system according to claim 1, each of said electric motors is located between said vehicle wheel and said outer shaft.
5) A drive system according to claim 4, each of said electric motors has a hollow shaft.
6) A drive system according to claim 4, said outer shaft one side is fixed on said hollow shaft and another side is fixed on said housing of differential gear.
7) A drive system according to claim 4, said inner shaft one side is fixed on a hub of said vehicle wheel and another side is fixed on said housing of differential gear through said hollow shaft.
8) A drive system according to claim 1, fixing on said housing of differential gear can be done directly contact or indirectly contact.
9) A drive system according to claim 1, by means of immersing said electric motor into said vehicle wheel gains higher clearance underneath of said vehicle.

I
10) A drive system according to claim 1, said two electric motors have been fixed together indirectly through said outer shafts of said first drive shaft, said housing of differential gear, and said second drive shaft therefore said electric motors can be driven by one inverter.
11) A drive system according to claim 1, said two electric motors can be driven by separate inverter wherein need of independent control or need of increased power output for the drive system.
12) A drive system according to claim 1, frame of said two electric motors are fixed on a rigid part of said vehicle.