WO2018185667A1

WO2018185667A1 - Electric machine for a vehicle

Info

Publication number: WO2018185667A1
Application number: PCT/IB2018/052308
Authority: WO
Inventors: Venkata RAGHUNATH KUMAR RACHABATTUNI; Samraj JABEZ DHINAGAR
Original assignee: Tvs Motor Company Limited
Priority date: 2017-04-05
Filing date: 2018-04-04
Publication date: 2018-10-11
Also published as: TWI782005B; TW201838291A; CN110612654A; CN110612654B; EP3607638A1

Abstract

The present subject matter discusses about the electric machine and core saturation sensing setup, and the method of detecting the core saturation. The present subject matter proposes that an auxiliary winding with at least one tooth is wound around at least one of the stator tooth along any one phase of the phases of the machine. The ends of the wire are given to the signal conditioning circuit which filters the signal from noises. The filtered signal is given to an ADC (analog to digital converter) pin of the controller to digitalize the signal value.

Description

ELECTRIC MACHINE FOR A VEHICLE

TECHNICAL FIELD

[0001] The present invention discusses about the electric machine and core saturation sensing setup, and the method of detecting the core saturation.

BACKGROUND

[0002] An electric machine is usually composed of stator and rotor. The rotor for different machines are constructed differently, based on machine topology. Induction machine's rotor is either wound rotor with slip rings or a squirrel cage type. Switched reluctance machine's rotor is usually a salient pole type, without magnets. Permanent magnet based machine's rotor is usually composed of rotor laminations encircling the magnets.

[0003] When it comes to the stator construction, stator is constructed by stacking the lamination sheets either LASER cut, or stamped. These sheets are usually of the same shape and size all through the length. This forms the extruded look of the stator along the length. The winding is usually done around the stator teeth to result in the desired winding pattern.

[0004] An internal combustion engine for a vehicle is usually provided with a starter motor which is used for starting the engine from zero speed. The starter motor takes energy from an energy storage medium such as a battery. Additionally, the engine is also equipped with a magneto arrangement which is used for generating power to charge the battery.

[0005] Integrated starter generator (ISG) is a specialized machine associated with the internal combustion engine. The ISG is used for starting the engine by letting the engine rotate till the ignition is provided, and then be able to generate power from the induced voltage above a threshold speed of the engine operation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The detailed description is described with reference to the accompanying figures. The same numbers are used throughout the drawings to reference like features and components. [0007] Fig. 1 illustrates a left side view of an exemplary two-wheeled vehicle, in accordance with an embodiment of the present subject matter.

[0008] Fig. 2 illustrates a typical cross section of an electrical machine in accordance to an embodiment of the present invention.

[0009] Fig. 3 illustrates a perspective view of a typical tooth of the electrical machine in accordance to an embodiment of the present invention.

[00010] Fig. 4 depicts a block diagram of a control system for assisting an internal combustion engine of a vehicle during starting and during high speed operations in accordance to an embodiment of the present invention.

[00011] Fig. 5 illustrates a flow diagram depicting method for reducing the losses and for increasing the startability of the electrical machine, in accordance to an embodiment of the present subject matter.

DETAILED DESCRIPTION

[00012] The present invention describes a machine which is beyond ISG in terms of functionality. This invention is also designed to provide assistance to the engine under high load conditions at high speed so that vehicle and engine operation can be performed to reduce C02 and NOx emissions.

[00013] Further, the present invention can be realized with the help of multiple machine topologies, such as Induction machine, switched reluctance machine (SRM), and BLDC (brush less direct current) machine. Induction and switched reluctance machines are operated with corresponding power electronic controllers that regulate the torque based on the input conditions such as present speed of rotation.

[00014] While induction machine and SRM do not have the speed limited by induced back-emf (electro motive force), BLDCDs speed range suffers due to this induced voltage. This is the voltage induced in the winding coils due to the rate of change of flux in the coils caused by presence of rotating magnets. This voltage limits the current flow into the machine, limiting the possible torque at speeds above zero depending on the supplied voltage.

[00015] When a machine is designed for starting and power assist operations, requirements are conflicting. Starting requires high torque constant, and power assist requires high speed/power operation and in turn low torque constant.

[00016] In the present invention, the electrical machine, for example, the BLDC machine is designed with startability of the engine as the primary target. However, for such designs, the no-load speed of the machine is greatly limited by the back- emf.

[00017] Considering the BLDCDs speed limitation, the BLDC machine is constructed with less number of turns so that the induced voltage is less and hence the speed band is wider. This requires more current to be passed to the motor coils during starting operation.

[00018] But when the high current is passed through the stator coils, the magnetic field produced may saturate the stator core material above a certain current threshold.

[00019] The present invention proposes that an auxiliary winding with at least one tooth is wound around at least one of the stator tooth along any one phase of the phases of the machine. The ends of the wire are given to the signal conditioning circuit which filters the signal from noises. The filtered signal is given to an ADC (analog to digital converter) pin of the controller to digitalize the signal value.

[00020] The voltage induced in the coil is proportional to the rate of change of the flux linkage in the coil area. The proportionality constant depends on number of turns in the auxiliary winding given by equation below.

Phi = j v(t) * dt + C

[00021] By adding the voltage value captured in the controller over time, the current flux in the stator tooth/teeth is determined. In an embodiment, the stator teethDs magnetic flux density is determined based on the stator teeth geometry for the given electrical machine computed as below.

Phi

Area

[00022] When the controller realizes that the B value is beyond the predetermined threshold, the controller limits the current into the electrical machine to the value of current just before the threshold is reached.

[00023] The zero offset C from the integration can be used to identify the magnetD s position with respect to the tooth in a permanent magnet based machine. In an alternative embodiment, the stator includes a temperature sensor which is used to limit the current based on a predetermined temperature.

[00024] ISG application benefits from this invention because of the feasibility to use thicker conductors with less strands. This lets the machine to be operable at high speeds (due to less induced voltage) and also produces more torque at starting (due to the more current that can be given to the motor). Its applications to ISG is not a limitation & can be used for other applications. Any motor usage can derive benefit from this invention which may be used for a electric vehicle or hybrid vehicle etc.

[00025] In an embodiment, the present subject matter provides an electrical machine with one or more electrical phases. The electrical machine is capable of identifying magnetic flux saturation and limiting current to pass through for reducing the losses and for increasing the startability of the electrical machine. The electrical machine includes a stator having a stator core and a plurality of teeth disposed around a periphery of the stator core. Each tooth of said plurality of teeth is wound with conducting wire of predetermined thickness to form a winding. A rotor that is capable of rotating by interacting with a magnetic field produced by the stator upon receiving electrical energy from at least one power source is provided. The rotor is separated from said stator by an air gap. The plurality of teeth includes at least a first set of teeth corresponding to at least a first phase of said one or more electrical phases. The first set of teeth includes an auxiliary winding wound at least around one tooth of said first set of teeth. In an embodiment, the rotor is disposed inside said stator. In an alternative embodiment, the rotor is disposed outside said stator.

[00026] In an embodiment, the magnetic field is perpendicular to an axis of rotation of said rotor. While, in an alternative embodiment, the magnetic field is parallel to an axis of rotation of said rotor.

[00027] In an embodiment, the auxiliary winding includes at least one turn of conducting wire wound around said at least one tooth. The rotor includes a plurality of permanent magnets that are arranged facing the plurality of teeth of said stator.

[00028] In one embodiment, the present invention includes a control system for identifying magnetic flux saturation and limiting current to pass through for reducing the losses and for increasing the startability. The control system includes an electrical machine with one or more electrical phases, including a stator having a stator core and a plurality of teeth disposed around a periphery of said stator core. Each tooth of said plurality of teeth is wound with conducting wire of predetermined thickness to form a winding. A rotor is capable of rotating by interacting with a magnetic field produced by the stator upon receiving electrical energy from at least one power source. The rotor is separated from said stator by an air gap, wherein said plurality of teeth includes at least a first set of teeth corresponding to at least a first phase of said one or more electrical phases. The first set of teeth includes an auxiliary winding wound at least around a tooth of said first set of teeth.

[00029] In an embodiment, at least one energy storage device is provided. The energy storage device is capable of supplying energy to said electrical machine when said electrical machine is operating as a motor, and for storing energy generated by said electrical machine when said electrical machine is operating as a generator.

[00030] Further, in an embodiment, the present subject matter describes a machine controller including at least one microcontroller. The machine controller including a signal conditioning circuit, said signal conditioning circuit is capable of receiving a voltage output from at least one end of said auxiliary winding. The at least one microcontroller is capable of receiving a conditioned signal from said signal conditioning circuit and detects a magnetic flux of said stator core and compares with a predetermined threshold value of magnetic flux. In an embodiment, the signal is conditioned by scaling down the voltage and filtering noise. The conditioned signal achieved as a result is nothing but a scaled down voltage. The machine controller limits the flow of current through the electrical machine when the magnetic flux of said stator core is greater than the predetermined threshold value of magnetic flux.

[00031] In an embodiment, the microcontroller of the control system includes a pulse width modulation circuit that limits the current through the machine by actuating one or more power electronic switches of said machine controller. In one embodiment, the signal conditioning circuit is low pass filter, and the threshold frequency for filtering is more than the maximum electrical frequency of the electrical machine.

[00032] Further, in an embodiment, the electrical machine is capable of achieving a peak torque at operating current being limited to about 50 Nm to52 Nm both during starting of the vehicle and during providing power assistance to the powertrain e.g. an internal combustion engine during running of the vehicle.

[00033] In an embodiment, the present invention describes a method for identifying magnetic flux saturation and limiting current to pass through for reducing the losses and for increasing the startability. The method incudes the steps of operating an electrical machine to start an internal combustion engine of a vehicle. The method further includes the step of sensing the voltage induced across an auxiliary coil wound at least around a tooth of a first set of teeth of a stator of said electrical machine, by a signal conditioning circuit of a machine controller. In an embodiment, the method includes determining magnetic flux across said tooth of said stator based on at least the sensed voltage, by the machine controller. The determined magnetic flux is then compared against a predetermined threshold value of magnetic flux. In an embodiment, the method further includes limiting the flow of current through the electrical machine, by said machine controller when the magnetic flux of said stator core is greater than the predetermined threshold value of magnetic flux.

[00034] These and other advantages of the present subject matter would be described in greater detail in conjunction with the figures in the following description.

[00035] Fig. 1 illustrates a left side view of an exemplary two-wheeled vehicle, in accordance with an embodiment of present subject matter. The vehicle 100 has a frame assembly 105, which acts as the structural member and as skeleton of the vehicle 100. The frame assembly 105 includes a head tube 105 A through which a steering assembly is rotatably journaled. The steering assembly includes a handle bar assembly 111 connected to a front wheel 115 through one or more front suspension(s) 120. A front fender 125 covers at least a portion of the front wheel 120. Further, the frame assembly 105 includes a main tube (not shown) extending rearwardly downward from the head tube 105 A. A fuel tank 130 is mounted to the main tube 105A. Furthermore, a down tube (not shown) extends substantially horizontally rearward from a rear portion of the main tube. In addition, the frame assembly includes one or more rear tube(s) (not shown) that extends inclinedly rearward from a rear portion of the down tube. In a preferred embodiment, the frame assembly 105 is mono-tube type, which extends from a front portion F to a rear portion R of the vehicle 100.

[00036] In one embodiment, a power unit 135 is mounted to the down tube. In an embodiment, the power unit 135 includes an IC engine. The fuel tank 130 is functionally connected to the power unit 135 for supplying fuel. In a preferred embodiment, IC engine is forwardly inclined i.e. a piston axis of the engine is forwardly inclined. Further, the IC engine 135 is functionally coupled to a rear wheel 140. A swing arm 145 is swingably connected to the frame assembly 105 and the rear wheel 140 is rotatably supported by the swing arm 145. One or more rear suspension(s) 150, which are connecting the swing arm 145 at an angle, sustain both the radial and axial forces occurring due to wheel reaction. A rear fender 155 is disposed above the rear wheel 145. A seat assembly 160 is disposed at a rear portion R of the step-through portion defined by the frame assembly 105. In an embodiment, the seat assembly 160 includes a rider seat 160A, and a pillion seat 160B. Further, the pillion seat 160B is positioned above the rear wheel 145. Further, the vehicle 100 is supported by a centre stand (not shown) mounted to the frame assembly 105. A floorboard 165 is mounted to the down tube and is disposed at the step-through portion. The floorboard 165 covers at least a portion of the power unit 135. The vehicle 100 is employed with an auxiliary power unit (not shown) supported by the frame assembly 105, for example, an energy storage device such as battery. Additionally, the vehicle 100 is provided with at least one set of foot rest(s) 180 for the rider/pillion to rest their feet.

[00037] Fig.2 illustrates a cross-section of an electrical machine with respect to an embodiment of the present invention. In an embodiment, the electrical machine is an outer rotating BLDC machine. In an embodiment, the outer rotating BLDC machine acts as an integrated starter generator (ISG). The electrical machine 101 of the present subject matter includes a rotor 104, which further includes a back iron 106 and a plurality of magnets 108 that are disposed on the inner surface of the rotor 104. In an embodiment, the back iron 106 rotates along with the rotation of the rotor 104. In an embodiment, the plurality of magnets 108 is permanent magnet.

[00038] Further, the back iron 106 can be made out of any one of iron, silicon steel, which is either made as one full block of iron or silicon steel. Alternatively, the back iron 106 is made as layers of iron or silicon steel with plurality of electrical insulation layers in between. In an embodiment, the plurality of magnets 108 can be any one of arc type magnets and flat magnets. Further, in one embodiment, the plurality of magnets 108 is disposed adjacently to each other circumferentially, without any gap. Alternatively, the plurality of magnets 108 can be disposed adjacently to each other circumferentially with circumferential air gap between two adjacent magnets of the plurality of magnets 108.

[00039] Further, the electrical machine 101 includes a stator 102 having a centrally provided stator core 118 around which a plurality of stator teeth 112 are circumferentially disposed forming a plurality of stator slots 114 therebetween. In an embodiment, the plurality of stator slots 114 is further filled with plurality of winding 116. In an embodiment, the stator 102 is enclosed within the rotor 104 and radially separated by an air gap 110. In an embodiment, each tooth of the plurality of stator teeth 112 includes a stem portion. In one embodiment, the stem portion of the tooth of the plurality of stator teeth 112 is provided with equal width on both ends of the stem portion, i.e., at a first end that is towards the stator core 118 and a second end that is away from the stator core 118. In an alternative embodiment, each slot of the plurality of stator slots 114 is formed to have equal width at both ends, i.e., at an end that is closer to the stator core 118 and at an end that is away from the stator core 118, which is achieved by two adjoining tooth of the plurality of stator teeth 112 having different widths at both its ends. In another alternative embodiment, each of the tooth of the plurality of stator teeth 112 and the each of the slot of the plurality of stator slots 114 are formed in such a manner that the width of the tooth and the slot at both the ends are not equal. In one embodiment, the stem portion of the each of the tooth of the plurality of stator teeth 112 ends, with a head portion facing the rotor 104, and has a width that is wider than the stem portion.

[00040] Fig. 3 illustrates a perspective view of a typical tooth 112 of the electrical machine 101 in accordance to an embodiment of the present invention. In an embodiment, Fig. 3 represents one of the stator tooth 112 with primary winding 310 and an auxiliary winding 306. The auxiliary winding 306 is represented by single strand of wire 306 around the tooth 112. In an embodiment, the stator tooth 112 has a head portion 302 and a stem portion 308. The head portion 302 faces the inner surface of the rotor 104. In an embodiment, the stem portion 308 is less in thickness as compared to the head portion 302. In an embodiment, a side surface 304 of the head portion 302 separates the two adjoining stator teeth 112. In an embodiment, each of the stator tooth 112 is wound with one or more primary winding 310. In an embodiment, the electrical machine 101 enables the primary winding 310 with increased thickness, which results in less number of primary winding 310. This lets the electrical machine 101 to be operable at high speeds (due to less induced voltage) and also produces more torque at starting (due to the more current that can be given to the motor). In an embodiment, the application of the electrical machine 101 of the present invention as ISG is not a limitation for other applications. Any motor usage can derive benefit from this invention.

[00041] Further, in an embodiment, the present subject matter provides the electrical machine 101 with one or more electrical phases. The electrical machine 101 is capable of identifying magnetic flux saturation and limiting current to pass through for reducing the losses and for increasing the startability of the electrical machine 101. The electrical machine 101 includes a stator having a stator core and a plurality of teeth disposed around a periphery of the stator core. Each tooth 112 is wound with conducting wire of predetermined thickness to form the primary winding 310. In an embodiment, the auxiliary winding 306 includes at least one turn of conducting wire wound around the tooth 112 and along any one phase of the phases of the electrical machine 101. The ends of the wire of the auxiliary winding 306 are given to a signal conditioning circuit (shown in Fig.4) which filters the signal from noises.

[00042] Fig. 4 depicts a block diagram of a control system 400 for assisting an internal combustion engine of a vehicle 100 during starting and during high speed operations in accordance to an embodiment of the present invention. In an embodiment, the control system 400 includes a machine controller 402, which further includes at least one microcontroller 404, and a signal conditioning circuit 406. In an embodiment, the machine controller 402 is an ISG controller 402, which is powered by an energy storage device, for example, battery controls the electrical machine 101 to operate effectively both during the starting of the vehicle by providing a boost voltage to the electrical machine 101 , and during running operation of the vehicle by providing a voltage from the battery 410. In an embodiment, the microcontroller 204 is capable of processing the signals received from the auxiliary winding 306 by a signal conditioning circuit 406. In an embodiment, the signal conditioning circuit 406 is capable of receiving a voltage output from at least one end of the auxiliary winding 306. At least one microcontroller 404 is capable of receiving a conditioned signal from the signal conditioning circuit 406 and detects a magnetic flux of the stator core and compares with a predetermined threshold value of magnetic flux. In an embodiment, the signal is conditioned by scaling down the voltage and filtering noise. The conditioned signal achieved as a result is nothing but a scaled down voltage. The machine controller 402 limits the flow of current through the electrical machine 101 when the magnetic flux of said stator core is greater than the predetermined threshold value of magnetic flux.

[00043] In an embodiment, the microcontroller 404 of the control system 400 includes a pulse width modulation circuit (not shown) that limits the current through the machine 101 by actuating one or more power electronic switches (not shown) of the machine controller 402. In one embodiment, the signal conditioning circuit 406 is a low pass filter, and the threshold frequency for filtering is more than the maximum electrical frequency of the electrical machine 101 , for example, an integrated starter generator (ISG) 101.

[00044] Fig. 5 illustrates a flow diagram depicting method 500 for reducing the losses and for increasing the startability of the electrical machine 101 , in accordance to an embodiment of the present subject matter. In an embodiment, at step 502, the method 500 involves operating the machine 101 to start the engine. In an embodiment, at step 504, the method 500 involves sensing the voltage induced across the auxiliary winding 306 of the machine 101 in order to determine the magnetic flux. Further, in an embodiment, the method 500 involves allowing the current into the electrical machine 101 to increase, before determining whether the magnetic flux induced is more than a predetermined threshold value of magnetic flux at step 508. In an embodiment, if the determined magnetic flux is not greater than the predetermined threshold magnetic flux, then the method 500 involves allowing the current to the electrical machine 101 to increase further. However, in an embodiment, if the determined magnetic flux is identified to be greater than the predetermined threshold value, the method 500 involves limiting the current to the electrical machine 101 by limiting the voltage at step 510. After limiting the current to the electrical machine 101 at step 510, the method 500 further loops back to step 504 for again sensing the voltage induced across the auxiliary winding 306. [00045] Many modifications and variations of the present subject matter are possible in the light of above disclosure. Therefore, within the scope of claims of the present subject matter, the present disclosure may be practiced other than as specifically described.

Claims

We claim:

1. An electrical machine (101) with one or more electrical phases, said electrical machine (101) capable of identifying a magnetic flux saturation and a limiting current to pass through for reducing the losses and to improve the startability of said electrical machine (101), said electrical machine (101) comprising:

a stator (102) having a stator core (118) and a plurality of stator teeth (112) disposed around a periphery of said stator core (118), each tooth of said plurality of stator teeth (112) is wound with a conducting wire of a predetermined thickness to form a winding; and

a rotor (104) capable of rotating by interacting with a magnetic field produced by said stator (102) upon receiving electrical energy from at least one power source, said rotor (104) separated from said stator (102) by an air gap (110),

said plurality of stator teeth (112) includes at least a first set of teeth corresponding to at least a first phase of said one or more electrical phases, and said first set of teeth includes an auxiliary winding (306) wound at least around one tooth of said first set of teeth.

2. The electrical machine (101) as claimed in claim 1, wherein said rotor (104) is disposed inside said stator (102).

3. The electrical machine (101) as claimed in claim 1, wherein said rotor (104) is disposed outside said stator (102).

4. The electrical machine (101) as claimed in claim 1, wherein said magnetic field is perpendicular to an axis of rotation of said rotor (102).

5. The electrical machine (101) as claimed in claim 1, wherein said magnetic field is parallel to an axis of rotation of said rotor (104).

6. The electrical machine (101) as claimed in claim 1, wherein said auxiliary winding (306) comprises at least one turn of conducting wire wound around said at least one tooth.

7. The electrical machine (101) as claimed in claim 1, wherein said rotor (104) having a plurality of permanent magnets (108) that are arranged facing the plurality of stator teeth (112) of said stator (102).

8. A control system (400) for identifying magnetic saturation and limiting current to pass through for reducing the losses and for increasing the startability, said control system (400) comprising: an electrical machine (101) with one or more electrical phases, including a stator (102) having a stator core (118) and a plurality of stator teeth (112) disposed around a periphery of said stator core (118), each tooth of said plurality of stator teeth (112) is wound with a conducting wire of a predetermined thickness to form a winding, and a rotor (102) capable of rotating by interacting with a magnetic field produced by said stator (102) upon receiving electrical energy from at least one power source, said rotor (104) separated from said stator (102) by an air gap (110), wherein said plurality of stator teeth (112) includes at least a first set of teeth corresponding to at least a first phase of said one or more electrical phases, and said first set of teeth includes an auxiliary winding (306) wound at least around a tooth of said first set of teeth;

at least one energy storage device for supplying energy to said electrical machine (101) when said electrical machine (101) is operating as a motor, and for storing energy generated by said electrical machine (101) when said electrical machine (101) is operating as a generator; and

a machine controller (402) including at least one microcontroller (404), said machine controller (402) including a signal conditioning circuit (406), said signal conditioning circuit (406) capable of receiving a voltage output from at least one end of said auxiliary winding (306), said at least one microcontroller (404) capable of receiving a conditioned signal from said signal conditioning circuit (406) and detects a magnetic flux of said stator core (118) and compares with a predetermined threshold value of a magnetic flux, and said machine controller (402) limits the flow of current through the electrical machine (101) when the magnetic flux of said stator core (118) is greater than the predetermined threshold value of magnetic flux.

9. The control system (400) as claimed in claim 8, wherein the microcontroller (404) includes a pulse width modulation circuit that limits the current through said electrical machine (101) by actuating one or more power electronic switches of said machine controller (402).

10. The control system (400) as claimed in claim 8, wherein the signal conditioning circuit is low pass filter, and the threshold frequency for filtering is more than the maximum electrical frequency of the electrical machine (101).

11. The control system (400) as claimed in claim 8, wherein the electrical machine (101) is capable of achieving a peak torque at operating current being limited to about 50 Nm to 52Nm both during starting of the vehicle and during providing power assistance to the powertrain during running of the vehicle.

12. A method for identifying a magnetic flux saturation and a limiting current to pass through for reducing the losses and for increasing the startability of a electrical machine, said method comprises:

operating an electrical machine (101) to start an powertrain of a vehicle;

sensing the voltage induced across an auxiliary winding (306) wound on at least a tooth of a first set of a plurality of stator teeth(l 12) of said electrical machine (101), by a signal conditioning circuit (406) of a machine controller (402);

calculating a magnetic flux across said tooth of said first set of a plurality of stator teeth (112) based at least on the sensed voltage, by said machine controller (402);

comparing the calculated magnetic flux against a predetermined threshold value of magnetic flux; and

limiting the flow of current through said electrical machine (101), by said machine controller (402) when the magnetic flux of said stator core (118) is greater than the predetermined threshold value of magnetic flux.