Electrical Subassembly and Associated Operating Method

Abstract

Electrical subassembly and associated method of operation. An electrical subassembly is provided having a first motor and a second motor, the second motor being a reluctance motor. Each of the first motor and the second motor has a respective rotor drivingly connected to the other and is operable to generate torque, either alone or in combination with each other. The torque generated by each of the first motor and the second motor is transmittable to a vehicle drivetrain. As such, the electrical subassembly has particular application in hybrid or electric vehicles.

Description

Technical Field

[0001] The present invention relates to an electrical subassembly, in particular an electrical subassembly for use as an electric traction drive for a hybrid vehicle or an electric vehicle. Aspects of the present invention relate to an electrical subassembly, a vehicle, a method and a control device.

Background Art

[0002] Hybrid vehicles and electric vehicles typically utilize motors with permanent magnets that usually incorporate rare earth elements such as neodymium (Nd). Other types of motors are often not used for various technical reasons, which include lower torque density and problems of noise, vibration and harshness. However, motors with rare earth permanent magnets have their own drawbacks. In particular, rare earth magnets are very expensive, at least relative to the cost of other components of the electric motor (rare earth magnets can be more than twice the cost of the motor). Also, rare earth magnets have poor sustainability credentials due to the methods used in their mining and refining.

[0003] Furthermore, a permanent magnet motor generates magnetic flux at all times when the rotor within such a motor is rotating, regardless of whether current is being applied to the motor. This has potential system reliability and safety implications, as magnetically induced voltages can be generated at the electrical terminals of the motor or high currents can be generated through the motor windings. In addition, such a motor can cause no-load iron losses induced by the rotating magnetic field of the rotor, resulting in a non-zero average torque that varies as the motor rotates, a phenomenon often referred to as "cogging". The techniques employed to address cogging tend to reduce motor efficiency. In order to be able to achieve high rotor speeds, it is often necessary to apply so-called "field weakening". Otherwise, the voltage induced across the motor windings by the rotation of the rotor can exceed the supply voltage driving the motor and thus potentially prevent higher operating speeds. However, field weakening causes increased resistive losses and results in lower efficiency. Rare earth magnets are prone to demagnetization when overheated and are difficult to cool when placed within the rotor. Thus, control strategies often have to be implemented to prevent overheating.

[0004] Alternatives to permanent magnet motors include induction motors and wound rotor motors. However, these motors generate higher losses in their rotors than permanent magnet motors. These relatively higher losses are due to the motors having more windings, i.e., windings on both the rotor and the stator. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] It is desirable to develop new electric motor technologies that do not require the use of permanent magnets, particularly rare earth magnets, and / or improve efficiency over known alternatives. An object of embodiments of the present invention is to at least mitigate one or more problems associated with known devices. MEANS FOR SOLVING THE PROBLEM

[0006] According to one aspect of the present invention, there is provided an electric sub-assembly comprising: a first motor; and a second motor which is a reluctance motor, wherein each of the first motor and the second motor has a respective rotor drivingly connected to the other, and each of the first motor and the second motor is operable to generate torque, i.e., an electric sub-assembly which is a common supply source of torque is provided. Thus, the first motor and the second motor may be independently operable to generate torque, such as torque transmissible to a drive train, by the first motor alone or by the first motor and the second motor in combination with each other.

[0007] In a given embodiment, the first motor may be a reluctance motor, i.e., the electric sub-assembly may comprise a first reluctance motor and a second reluctance motor, and each of the first motor and the second motor may be operable to generate torque alone or in combination with each other.

[0008] The electric sub-assembly may form part of an electric drive unit, including but not limited to a traction drive unit for a hybrid vehicle or an electric vehicle. The electric sub-assembly can reduce the cost of the electric drive unit and / or improve the efficiency, and thus increase the attractiveness and / or feasibility of electrically driven solutions including but not limited to hybrid vehicles and electric vehicles as means of transportation.

[0009] In certain embodiments, each of the respective rotors is rotatable about a common axis, such a configuration enabling a simple and compact motor form. Each of the respective rotors may be drivingly connected to one another by a drive shaft that extends between the respective rotors for transmitting the supply of torque generated by the first and second motors. Optionally, the drive shaft may comprise a monolithic connection portion that extends between the respective rotors, enabling a simple, compact and / or robust motor form.

[0010] At least one of the respective rotors may be connected to the drive shaft such that an angular correspondence is maintained between at least one of the respective rotors and the drive shaft. Additionally or alternatively, the mechanical angle of one of the respective rotors may be offset from the mechanical angle of the other of the respective rotors. This facilitates the reduction of torque ripple and the acoustic noise resulting therefrom. At least one of the first and second motors may be one of a switched reluctance motor and a synchronous reluctance motor. The first and second motors may be made substantially the same as one another, i.e., to the same specification.

[0011] Suitably, the subassembly may comprise a control device configured to control the operation of at least one of the first and second motors. The control device may be configured to receive an input indicative of the speed and / or torque of at least one of the first and second motors. Further, the control device may be configured to control the operation of at least one of the first and second motors in response to the input. The control device may be further configured to control the operation in response to the input by using a function that associates the input with the efficiency of at least one of the first and second motors.

[0012] According to another aspect of the present invention, there is provided a hybrid vehicle or an electric vehicle comprising the above-described electrical subassembly.

[0013] According to another aspect of the present invention, there is provided a method of operating an electrical sub-assembly including the step of operating either or both of a first motor and a second motor to generate torque by the first motor alone or by the first and second motors in combination with each other, wherein the second motor is a reluctance motor and each of the first and second motors has a respective rotor drivingly connected to the other. The first motor may be a reluctance motor. Thus, torque can be generated by the first and second motors alone or in combination with each other.

[0014] The method may further include the step of selectively operating both the first motor and the second motor to generate substantially equal torque between the first motor and the second motor. Additionally or alternatively, the method may include the step of selectively operating both the first motor and the second motor to generate substantially unequal torque between the first motor and the second motor.

[0015] In a given embodiment, the method may include the step of selectively operating only one of the first motor and the second motor, for example only the first motor, to generate torque with increased efficiency compared to operating both the first motor and the second motor. Additionally or alternatively, the method may include the step of selectively operating both the first motor and the second motor to generate torque with increased efficiency compared to operating only one of the first motor and the second motor.

[0016] Optionally, the method may include the step of receiving an input indicative of the speed and / or torque of at least one of the first motor and the second motor; and selectively operating either or both of the first motor and the second motor in response to the input. The step of selectively operating in response to the input may include using a function that associates the input with the efficiency of at least one of the first motor and the second motor.

[0017] According to another aspect of the present invention, there is provided a control device for an electrical sub-assembly, the control device being configured to operate at least one of a first motor and a second motor to generate torque, either alone or in combination with each other; to receive an input indicative of the speed and / or torque of at least one of the first motor and the second motor; and to control the operation of at least one of the first motor and the second motor in response to the input by using a function that associates the input with the efficiency of at least one of the first motor and the second motor. Either or both of the first motor and the second motor may be a reluctance motor.

[0018] It should be understood that one of the features of one of the above-described aspects may be combined with one or more of the features of the other above-described aspects.

[0019] Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0021] FIG. 1 shows an electrical sub - assembly 10 according to an embodiment of the present invention. The sub - assembly 10 has a specific application for use as an electric traction device for a hybrid vehicle or an electric vehicle 100 (see FIG. 5). Thus, the sub - assembly 10 may be part of a powertrain, that is, the powertrain may include the electrical sub - assembly 10 and a drive train. As will be understood by those skilled in the art, the drive train may include one or more mechanisms for delivering mechanical power from the sub - assembly 10 to a final drive, for example, one or more drive wheels. The drive train may include one or more of a gearbox, a clutch, an axle, a transmission, and a torque converter. Other applications are conceivable.

[0022] The sub - assembly 10 includes a first reluctance motor 12 and a second reluctance motor 14. As will be understood by those skilled in the art, a reluctance motor is an electric motor that induces non - permanent magnetic poles on a ferromagnetic rotor. The rotor does not require rotor windings, and torque is generated by the motor due to the reluctance phenomenon. Each of the first motor 12 and the second motor 14 includes respective rotors 16, 18 and respective stators 20, 22. The respective rotors 16, 18 are configured to be drivingly connected to each other. As used herein, drivingly connected is understood to mean connected so as to enable torque transmission between one or more connected mechanisms. Thus, the rotation of one of the first rotor 16 and the second rotor 18 causes the rotation of the other. Each of the respective stators 20, 22 may have wound field coils for stator windings.

[0023] In a given embodiment, at least one of the first motor 12 and the second motor 14 is a synchronous reluctance motor (often abbreviated as SynRM). In a given embodiment, at least one of the first motor 12 and the second motor 14 is a switched reluctance motor (often abbreviated as SRM and sometimes referred to as a variable reluctance motor). Since a reluctance motor does not require power to be supplied to the rotor, it has a simplified design compared to more commonly used motors, such as induction motors. Therefore, a reluctance motor is at least easier to manufacture and less expensive compared to more commonly used motors. As those skilled in the art will understand, each of the motors 12, 14 can be controlled by all three-phase power electronics. However, any suitable control means, such as an asymmetric half-bridge converter, can be used.

[0024] Each of the rotors 16, 18 is drivingly connected to each other by a drive shaft 24. The drive shaft 24 is for transmitting the torque generated by either the first motor 12 or the second motor 14 to other mechanisms, that is, the drive shaft 24 forms part of a drive train. The first motor 12 and the second motor 14 are arranged relative to each other such that the respective rotors 16, 18 can rotate around a common axis 26 (such an arrangement is shown in FIG. 1). However, in a given embodiment, the first motor 12 and the second motor 14 are angularly offset such that the respective rotors 16, 18 can rotate around their respective axes. For this purpose, the drive shaft 24 may comprise one or more of a universal joint, a jaw coupling, and a rag joint. In a given embodiment, the drive shaft 24 is a monolithic connecting portion extending between the respective rotors 16, 18 or comprises a monolithic connecting portion extending between the respective rotors 16, 18. As used herein, monolithic is understood to mean an integral form. Arranging the first motor 12 and the second motor 14 such that the respective rotors 16, 18 can rotate around a common axis 26 and having a monolithic connecting portion extending between the respective rotors 16, 18 is particularly advantageous because the configuration is simple to manufacture and robust. In a given embodiment, each of the rotors 16, 18 is drivingly connected to each other by a drive belt.

[0025] In a given embodiment, to enable changing the alignment and / or distance between each of the first motor 12 and the second motor 14 (and / or between at least one of the first motor 12 and the second motor 14 and one or more other mechanisms, such as the mechanisms of the drive train), the drive shaft 24 may be grooved, i.e., the drive shaft may have a plurality of ridges or teeth that extend to surround the corresponding grooves of at least one of the respective rotors 16, 18 for meshing therewith. Thus, at least one of the respective rotors 16, 18 may have a grooved hub. The ridges or teeth may maintain the angular correspondence between at least one of the respective rotors 16, 18 and the drive shaft 24. Additionally or alternatively, the angular correspondence between at least one of the respective rotors 16, 18 and the drive shaft 24 may be maintained by keyways and key configurations. In a given embodiment, either or both of the respective rotors 16, 18 may be fixedly connected to or integrally formed with the drive shaft 24.

[0026] In use, each of the first motor 12 and the second motor 14 is operated independently of the other, that is, power can be supplied to either one or both of the first motor 12 and the second motor 14, that is, specifically to one or both of the respective stators 20, 22. Accordingly, torque is generated by either one or both of the first motor 12 and the second motor 14, either alone or in combination with each other. Thus, when operated simultaneously, each of the motors 12, 14 contributes to the total amount of torque generated. As already described, since the respective rotors 16, 18 are drivingly connected to each other, the rotation of one of the respective rotors causes the rotation of the other. Accordingly, either of the respective rotors 16, 18 rotates regardless of whether power is supplied to the respective stators 20, 22. Advantageously, this no-load (i.e., at least in one of the first motor 12 and the second motor 14) rotation does not generate the magnetic flux that occurs in a permanent magnet motor. Accordingly, when either of the respective rotors 16, 18 rotates and the corresponding motor is switched off, there is no loss and voltage at the motor terminals. This provides an improvement in efficiency and / or safety. As will be understood by those skilled in the art, this benefit is derived from one of the first motor and the second motor 14 that is exposed to no-load rotation, which is a reluctance motor, that is, the other of the first motor 12 and the second motor 14 may be provided in another manner, for example, as an induction motor.

[0027] FIG. 2 shows the efficiency of the sub - assembly 10 with respect to torque (vertical axis) and speed (horizontal axis) when only one of the first motor 12 and the second motor 14 is operating. The efficiency shown is the mechanical power output proportional to the electrical power input. The peak efficiency is shown in the plot range corresponding to the speed at which the vehicle operates frequently, which in the described embodiment corresponds to approximately 3500 rpm to 7500 rpm. Of course, when the sub - assembly 10 is part of the powertrain, the speed of one or both of the first motor 12 and the second motor 14 is proportional to the speed of the vehicle 100. However, the efficiency varies depending on the amount of torque required, for example, to provide acceleration and / or to overcome rolling resistance and air resistance. As shown in FIG. 2, lower efficiencies can be achieved with lower torque amounts.

[0028] Similarly, FIG. 3 shows the efficiency of the sub - assembly 10 with respect to torque (vertical axis) and speed (horizontal axis) when both the first motor 12 and the second motor 14 are operating (note that the scale of the vertical axis is different). The peak efficiency can be shown at a speed similar to the speed when only one of the first motor 12 and the second motor 14 is operating. However, as shown in FIG. 3, lower efficiencies can be achieved with lower torque amounts. Thus, by selectively operating each of the first motor 12 and the second motor 14 alone or in combination, relatively higher efficiencies can be achieved over a greater torque and / or speed range. This effect is illustrated in FIG. 4, which shows the peak efficiency of the sub - assembly 10 with respect to torque (vertical axis) and speed (horizontal axis) when either one or both of the first motor 12 and the second motor 14 are operating, that is, it shows the best efficiency achievable by operating either one or both of the first motor 12 and the second motor 14 for a given torque and / or speed.

[0029] The sub - assembly 10 includes a control device 110 (see FIG. 5) for controlling the operation of either or both of the first motor 12 and the second motor 14. The control device 110 controls the operation of either or both of the first motor 12 and the second motor 14 by selecting one or more control parameters. The one or more control parameters may include the voltage and current to be supplied to each of the first motor 12 and the second motor 14. Each of the first motor 12 and the second motor 14 is selectively operable by switching each of the first motor 12 and the second motor 14 on and off or by variably powering the first motor 12 and the second motor 14, that is, by providing a supply of variable current or voltage. In a given embodiment, the sub - assembly 10 may not include the control device 110. Instead, the control device 110 may be operable in communication with the sub - assembly 10 by being provided somewhere, for example, on the vehicle 100.

[0030] The control device 110 may be configured to receive an input indicative of the speed of each or both of the first motor 12 and the second motor 14 and / or the torque generated by each or both of the first motor 12 and the second motor 14. As will be understood by those skilled in the art, the torque of the sub - assembly 10 or each of the first motor 12 and the second motor 14 or the first motor 12 and the second motor 14 can be determined by a torque sensor, that is, a torque transducer. Alternatively, the torque can be derived from the current supplied to either or both of the first motor 12 and the second motor 14. The current can be determined by a current transducer. The speed can be determined by at least one of an encoder and a resolver.

[0031] The control device 110 can be configured to control each of the first motor 12 and the second motor 14 according to the speed of each or both of the first motor 12 and the second motor 14 and / or the torque generated by each or both of the first motor 12 and the second motor 14. The control device 110 can include a processor and an electronic memory. The electronic memory stores a function that associates the speed and / or torque of the first motor 12 and the second motor 14 with one or more of the control parameters. The function can be derived from efficiency - torque - speed data, as shown, for example, in FIGS. 2 to 4.

[0032] Each of the first motor 12 and the second motor 14 is substantially the same as each other, that is, each of the first motor 12 and the second motor 14 is manufactured to the same specifications, and thus can each exhibit the same operating and performance characteristics. This is particularly beneficial as it enables the electrical sub - assembly 10 to have a modular structure. The electrical sub - assembly 10 may include a plurality of motors, that is, two or more such as a third motor, a fourth motor, etc., and each motor has a respective rotor that is drivingly connected to the rotor of another motor. Each or a subset of the plurality of motors can be operable to generate torque, either alone or in combination with each other. The electrical sub - assembly 10 can include two, three, or more motors, each manufactured to the same specifications. However, in a given embodiment, the electrical sub - assembly 10 can include two, three, or more motors, each manufactured to one of two or more different specifications. By using different numbers of motors and / or motors manufactured to different specifications, improved efficiency is possible for various torque and / or speed ranges.

[0033] Disadvantages that may be associated with reluctance motors include high torque ripple (i.e., the difference between the maximum and minimum torque exhibited during one revolution of the rotor), especially when operated at low speeds, and acoustic noise resulting from the torque ripple. However, these disadvantages can be reduced by offsetting the mechanical angle of one of the respective motors 16, 18 from the other. As will be understood by those skilled in the art, the mechanical angle is the angle of the rotor with respect to the stator. The mechanical degrees in a motor are referenced to the rotation of the rotor; i.e., one revolution of the rotor is equal to 360 mechanical degrees. The offset amount depends on the design of each of the respective rotors 16, 18, but one of the respective rotors 16, 18 may be configured to be offset by 360 mechanical degrees, which is twice the number of rotor poles of each of the respective rotors 16, 18, from the other, or some other angular displacement may be advantageous for minimizing motor harmonics.

[0034] (Including any appended claims and drawings) All of the mechanisms disclosed herein and / or all of the steps of any method or process so disclosed may be combined in any combination, except combinations in which at least some of such mechanisms and / or steps are mutually exclusive. The present invention is contemplated to have particular uses in hybrid or electric vehicles and commercial vehicles, such as trucks and vans, but other uses are contemplated, including (but not limited to) hybrid or electric locomotives, off-highway and construction vehicles, marine vessels, and stationary applications.

[0035] (Including any accompanying claims and drawings) Each mechanism disclosed herein may be replaced by an alternative mechanism that serves the same, equivalent, or similar purpose, unless expressly provided otherwise. Accordingly, each mechanism disclosed is, unless expressly provided otherwise, merely an example of a comprehensive series of equivalent or similar mechanisms.

[0036] The present invention is not limited to any of the details of the foregoing embodiments. The present invention extends to any novel one or any novel combination of the mechanisms disclosed herein (including any accompanying patent claims and drawings), or to any novel one or any novel combination of the steps of any method or process thus disclosed. The claims should not be construed as merely covering the above-described embodiments, but any embodiment is within the scope of the claims.

Description of Reference Numerals

[0037] 10 Electric subassembly, 12 First motor, 14 Second motor, 16, 18 Rotors, 24 Drive shaft, 26 Shaft, 110 Control device

Claims

1. a first motor; a second motor; An electric subassembly comprising: the first motor and the second motor are substantially the same as each other, and each of the first motor and the second motor is a reluctance motor having a respective rotor drivingly connected to the other, and each of the first motor and the second motor is operable to generate torque either alone or by both the first motor and the second motor in combination with each other; one mechanical angle of each of the respective rotors is offset from the other mechanical angle of the respective rotors; each of the respective rotors is drivingly connected to each other by a drive shaft having a monolithic connecting portion extending between the respective rotors for transmitting the torque generated by the first motor and the second motor; An electric subassembly, characterized in that.

2. The electric subassembly according to claim 1, characterized in that each of the respective rotors is rotatable about a common axis.

3. The electric subassembly according to claim 2, characterized in that at least one of the respective rotors is connected to the drive shaft such that the angular correspondence between at least one of the respective rotors and the drive shaft is maintained.

4. The electric subassembly according to any one of claims 1 to 3, characterized in that the first motor and the second motor are switched reluctance motors or synchronous reluctance motors.

5. The electric subassembly according to any one of claims 1 to 4, further comprising a control device configured to control the operation of at least one of the first motor and the second motor.

6. The electric subassembly according to claim 5, characterized in that the control device is configured to receive an input indicating the speed and / or torque of at least one of the first motor and the second motor and to control the operation of at least one of the first motor and the second motor in response to the input.

7. The electric subassembly according to claim 6, further configured such that the control device controls the operation according to the input by using a function that associates the input with the efficiency of at least one of the first motor and the second motor.

8. An electric vehicle or a hybrid electric vehicle, comprising the electric subassembly according to any one of claims 1 to 7.

9. Operating one or both of the first motor and the second motor to generate torque by either the first motor and the second motor alone or the first motor and the second motor in combination with each other, wherein each of the first motor and the second motor is a reluctance motor having a respective rotor drivingly connected to the other, the first motor and the second motor being substantially the same as each other, one mechanical angle of each of the respective rotors being offset from the other mechanical angle of each of the respective rotors, each of the respective rotors being drivingly connected to each other by a drive shaft having a monolithic connecting portion extending between the respective rotors for transmitting the torque generated by the first motor and the second motor, A method of operating an electric subassembly, characterized by including the step.

10. The method according to claim 9, further including the step of operating the first motor and the second motor respectively to generate substantially equal torque between the first motor and the second motor.

11. The method according to claim 9 or 10, further including the step of operating the first motor and the second motor respectively to generate substantially unequal torque between the first motor and the second motor.

12. The method according to any one of claims 9 to 11, further including the step of selectively operating one of the first motor and the second motor to generate torque with increased efficiency compared to operating both the first motor and the second motor.

13. The method according to any one of claims 9 to 12, further comprising the step of operating the first motor and the second motor respectively to generate torque with increased efficiency as compared to operating one of the first motor and the second motor.

14. Receiving an input indicative of the speed and / or torque of at least one of the first motor and the second motor; Selectively operating either or both of the first motor and the second motor in response to the input; The method according to any one of claims 9 to 13, further comprising the above.

15. The method according to claim 14, wherein the step of selectively operating in response to the input includes using a function that associates the input with the efficiency of at least one of the first motor and the second motor.

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