DESC:FIELD OF THE INVENTION
[0001] This invention relates to an improved electrical machine used as starter-generator of an internal combustion engine.
BACKGROUND
[0002] A single electrical machine functioning as a motor for starting an internal combustion engine and as a generator for charging a vehicle battery is known from US1770468. However, such a machine uses brushes and commutator segments, which degrade durability, and requires complicated gearing system to connect with the engine crankshaft.
DISCUSSION OF THE PRIOR ART
[0003] US 3902073 A titled “Starter generator electrical system utilizing phase controlled rectifiers to drive a dynamoelectric machine as a brushless dc motor in the starter mode and to provide frequency conversion for a constant frequency output in the generating mode” discloses a starter-generator electrical machine that is driven as a brushless electric motor during starting operation using cycloconverters. Nevertheless, the machine has excitation winding which increases the size of the machine and constant frequency output is not required for driving the vehicle electrical loads.
[0004] US 4219739 A titled “Starter motor-alternator apparatus” discloses a starter-generator electrical machine which works as a brushed DC motor during starting operation and works as a separately excited synchronous machine during generator mode of the operation. However, such a machine requires a mechanism to separate the brushes and commutator segments.
[0005] US 5132604 A titled “Engine starter and electric generator system” discloses a starter-generator electrical machine that is connected with an engine crankshaft through a transmission means that in turn can be switched between two speed reduction gear ratios. An actuator mechanism sets the speed reduction gear ratio differently for starting and generating modes. Nevertheless, the actuator mechanism and speed reduction gears increase the size and complexity of the engine.
[0006] High magnetic flux is required during engine starting but during generation mode of operation and particularly at high rotor speeds, the high magnetic flux results in high core losses that deteriorates vehicle fuel economy. Indian patent publication 343/CAL/1999 [Patent No.:212133] titled “Starter generator” discloses an electrical machine with permanent magnets and additional field windings to control the air-gap flux suitably for starting and generating modes of operation. Yet, the additional field windings increase the size of the machine and will in turn increase the size of the engine.
[0007] US 6392311 A titled “Starter generator for internal combustion engine” discloses an electrical machine operating as a starter-generator wherein all the coils of the machine are supplied with current during a starting mode to achieve the required high torque and only a set of the coils are connected for charging the battery and thereby prevents excessive charging currents. Nonetheless, such a system requires a large number of semiconductor switches in the controller and increases the overall cost of the system.
[0008] Japanese application no. 20020265659 titled “Engine provided with generator/motor, and its controller discloses an engine with a continuously variable transmission (CVT) wherein the moveable pulley of the CVT acts as a rotor of an electrical machine which starts the engine and also functions as a generator for charging the vehicle battery. During generation operation, as the crankshaft speed increases, the pulley moves axially away from the stator of the electrical machine and thereby achieves the required reduction in magnetic flux to limit the core losses. But, such a machine needs a CVT system or a centrifugal mechanism to achieve the flux regulation and might not be able to supply to large electrical loads during generator mode of operation.
[0009] An electrical machine that functions as a starter-generator without increasing magnet flux density and machine size and which does not require additional centrifugal mechanism or transmission gears while achieving the desired high torque during starting and adequate charging voltage during generation is the need of the hour. Low cost ferrite magnets can be used to minimize cost and also to minimise core losses. But high currents need to be established in the stator coils to achieve high torque during starting mode of operation. The stator coil resistance needs to be low which in turn will increase the coil diameter. With large diameter coils, the number of turns that can be packed within the stator tooth reduces which deteriorates voltage generation during generator mode of operation. To achieve the high starting torque with low cost permanent magnets and to achieve the required charging voltage during generator mode of operation without increasing machine size is the need of the hour.
[00010] Indian granted patent IN203814 discloses a coil winding arrangement for a multiphase electric motor or generator wherein each phase comprises at least two sets of coils that are connected in parallel and each set has coils wound on different teeth of the stator such that coils of different sets are wound in circumferentially separated regions of the stator. Although a starter-generator with such a design can achieve high starting torque owing to reduced effective line-line resistance, an imbalance in back-emf generated in each set of circumferentially separated coils due to rotor unbalance will lead to circulating currents along parallel connected sets of coils and increases copper losses. The imbalance in the stator coil currents can also lead to rotor vibrations which if matches with the resonant frequency of the connecting members will in turn lead to irritating noise. Thus, there is a need for an improved multi-phase electric machine with parallel-connected sets of coils that is capable of addressing the aforementioned and other problems in the prior art and at the same time should be capable of generating equal back-emf.

SUMMARY OF THE INVENTION
[00011] An electrical machine used as starter-generator of an internal combustion engine comprising a rotor with permanent magnets for connecting with an engine crankshaft, a stator for connecting with an engine crankcase and concentric with the rotor to allow the rotor permanent magnet flux to link with stator teeth, and a three phase winding on the stator for carrying currents in order to produce a torque for rotating the rotor during engine starting. Also, the electrical machine is used for generating voltage in order to supply to the vehicle electrical loads after engine starting. The stator has stator windings having sets of coils connected in parallel in each phase and the phases are preferably connected in delta connection to achieve a low line-line. Also, the windings permits a large current for producing the high starting torque. The coil winding further comprises sets of coils connected in series in each parallel set of coils to generate equal back-emf by distributing coils in each parallel set along the stator circumference.
[00012] The stator teeth are divided two or more sequential regions. The coils connected in series are wound to two or more sets of teeth of said plurality of teeth of the stator, wherein at least one teeth of said two or more sets of teeth are selected from each sequential region of said two or more sequential regions.
[00013] The coils connected in series of the each parallel set of coils are selectively wound to the teeth of the stator and the teeth are selected distributively along the circumference of the stator for said selective winding. In other words, the two or more coils of each parallel set of coils is wound to two or more sets of teeth of the plurality of teeth of stator. At least one teeth of the two or more sets of teeth are selected from each sequential region of said two or more sequential regions. This enables distribution of coils circumferentially about the stator circumference.
[00014] It is an aspect of the present subject matter that the electrical machine is capable of providing high starting torque. It is an advantage that effective line-line resistance is reduced.
[00015] It is a feature of the present subject matter that the electrical machine provides a balance in back-emf generated in each set of circumferentially separated coils.
[00016] It is yet another advantage that circulating currents along parallel-connected sets of coils is reduced. It is a further advantage that the copper losses are reduced.
[00017] It is an additional feature that any rotor imbalances due to unbalances back-emf are also reduced.
[00018] It is a feature that the coils connected in series of the each parallel set of coils are selectively wound to the teeth of the stator and the teeth are selected distributively along the circumference in a sequence.
[00019] It is a feature that the coils connected in series of the each parallel set of coils are selectively wound to the teeth of the stator and the teeth are selected distributively along the circumference in a non-sequential manner.
[00020] It is yet an additional feature that smooth startability of the engine is attained.
[00021] It is yet another additional feature that the rotor vibrations are also reduced. It is an advantage that the noise of the system is also reduced.
[00022] It is another advantage that the electrical machine is compact.
[00023] It is yet another advantage that optimal number of semiconductor switches thereby improving cost of the system.
[00024] The present subject matter is for a two-wheeled or a three-wheeled compact vehicle.
BRIEF DESCRIPTION OF THE DRAWINGS
[00025] Figure 1 shows the pictorial front view of the electrical machine, in accordance with an embodiment of the present subject matter.
[00026] Figure 2 shows an electrical connection diagram of the stator winding with controller and vehicle battery, in accordance with one embodiment of the present subject matter.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[00027] Figure 1 shows the front view of the electrical machine 100. The electrical machine 100 comprises an outer rotor 20 for connection with an engine crankshaft (not shown). The rotor 20 has plurality of permanent magnets 30 disposed around its inner periphery in alternating North Pole – South Pole fashion. A stator 40 comprising plurality of stator teeth 40T disposed concentric with the rotor 20, are separated from the rotor 20 by a small air-gap and the stator 40 is connected with an engine crankcase (not shown). The stator teeth 40T carry the magnetic flux generated by permanent magnets 30. Further, stator coils 50 are wound around the stator teeth 40 for carrying electric current during starting mode of operation and for generating voltage during generating mode of operation. A crank position sensor 60 is mounted on the engine crankcase outside the outer periphery of rotor 20 to sense a ferromagnetic protrusion 70 provided on the outer periphery of rotor 20. The crank position sensor 60 is separated from the protrusion 70 by a small air-gap. Also, three hall sensors 80 are located in the spacing between the stator teeth 40 for generating signals indicative of rotor permanent magnets 30 position. The stator teeth 40T disposed circumferentially about the stator 40 are divided into two or more sequential regions A, B, C. Each sequential region A, B, C includes two or more teeth that adjacent to each other.
[00028] In the preferred embodiment, the electrical machine 100 has 12 permanent magnets 30 and 18 stator coils 50. So, in this implementation, the stator teeth 40T are divided in three sequential regions A, B, C. Sequential region A includes teeth 1-6 that are in sequence when moving clockwise along the circumference of the stator 40. Similarly, sequential region B includes teeth 7-13 and sequential region C includes teeth 14-18. The voltage generated in each coil of the stator coils 50 with the voltage generated in the neighbouring coil will be separated in phase by 120 degrees electrical angle. The consecutive hall sensors are located with 120 electrical degrees separation. The stator coils 50 are numbered 1 to 18.
[00029] In an embodiment, the permanent magnets 30 are low cost ferrite magnets. In order to achieve the high starting torque required for engine starting, high currents need to be established in the stator coils 50 because the ferrite magnets will not be capable of producing large magnetic flux in the stator teeth 40. In order to allow high currents, the resistance exhibited by the stator coil 50 has to be low. If large diameter coils are used for achieving the low stator coil resistance, the number of turns that can be packed within each stator tooth reduces and thereby deteriorates the voltage produced during generator mode of operation.
[00030] To achieve low stator coil resistance, the stator coils 50 producing voltages in phase are split into two sets of coils each. As depicted in Figure 2, which is the inter connection of coil windings connected in delta, wherein coils 1, 4, 7, 10, 13 and 16 are in phase RB. Similarly, coils 2, 5, 8, 11, 14 and 17 are in phase YR and coils 3, 6, 9, 12, 15 and 18 are in phase BY. Hereinafter, for the sake of convenience, a particular tooth 40T of the stator 40 are referred with the respective stator winding reference numeral For example, a tooth having the stator winding 1 is referred to as tooth 1. The windings coils arrangement is hereinafter referred to as stator winding 90. The three collections of coils, viz. YR, RB, and BY, mentioned above are separated in phase from each other by 120 electrical degrees. Each phase YR, RB, and BY is split into required sets of symmetrically wound coils and is connected in parallel. In other words, each phase RB, RY, and BY includes two or more parallel sets of coils P1, P2, P3, P4, P5, and P6. Further, each parallel set of coils P1, P2, P3, P4, P5, and P6 includes two or more series set of coils that are symmetrically disposed about the stator 40. The two or more series set of coils are connected in series. In the present implementation, the coils 1, 13 and 7 are one parallel set P1 of phase RB that are connected in series and the coils 10, 4 and 16 are another parallel set P2 of the phase RB that are connected in series. Both these parallel sets P1, P2 are connected in parallel to form phase RB. The series set of coils connected in series within each parallel set of coils are selectively wound around different teeth that are selected distributively along the circumference of the stator, as depicted in Figure 1.
[00031] The two or more coils (1, 13, 7), (10, 4, 16), (2, 14, 8), (11, 5, 17), (12, 6, 18), (3, 15, 9) of the each parallel set of coils P1, P2, P3, P4, P5, P6 are wound to two or more sets of teeth 40TS of the plurality of teeth 40T, wherein at least one teeth of the two or more sets of teeth 40TS are selected from each sequential region of said two or more sequential regions A, B, C. In the Figure 1, the set of teeth 40TS that is marked includes the teeth 3, 15, 9. However, two or more sets of teeth 40TS are present that are not marked viz. teeth 1, 13, 7 form one set of teeth 40TS (not marked), the teeth 10, 4, 16 form one set of teeth 40TS (not marked).
[00032] For example, the coils 3, 15, and 9 are selectively wound to set of teeth 40TS including teeth 3, 15, 9 of the stator 40. The teeth 3 is from a first sequential region A, the teeth 9 is from a second sequential region B, and the teeth 15 is from a third sequential region C. Thus, due to the distributive disposition of coils circumferentially of the stator of each parallel set P1, P2, P3, P4, P5, and P6, the back-emf generated in each set is less prone to variation due to rotor unbalance. Similarly, phase YR and phase BY comprises two or more parallel set of coils P3, P4, P5, and P6 each and each parallel set includes two or more coils connected in series that are circumferentially disposed. The phases RB, YR and BY are connected in delta to achieve a low line-line resistance, which is equivalent to a single parallel set coil resistance.
[00033] In the present case, each phase RB, YR and BY has two parallel sets of coils (P1, P2), (P3, P4), (P5, P6). The six parallel set of coils P1, P2, P3, P4, P5, P6 has three coils connected in series (1, 13, 7), (10, 4, 16), (2, 14, 8), (11, 5, 17), (12, 6, 18), (3, 15, 9). In one embodiment, the three series connected coils (1, 13, 7), (10, 4, 16), (2, 14, 8), (11, 5, 17), (12, 6, 18), (3, 15, 9) of each parallel set of coils P1, P2, P3, P4, P5, P6 are wound to set of teeth 40TS with three teeth. Each teeth of the set of teeth 40TS are each selected from the three sequential regions A, B, C. For example, the three series connected coils 3, 15, 9 are connected are wound to one set of teeth 40TS includes three teeth 3, 15, 9. Also, the three teeth 3, 15, 9 are selected from the sequential regions A, B, C. This provides the teeth to be distributed around the stator circumference to ensure that back-emf generated in each parallel-connected set will be equal. In another implementation, the number of parallel sets of coils in each phase can vary. Also, the number of coils connected in series in each parallel set can also vary.
[00034] In an embodiment, the two or more coils connected in series of the each parallel set of coils P1, P2, P3, P4, P5, P6 are wound to two or more teeth that are selected distributively about said stator 40 circumference in a non-sequential pattern. For example, in the present implementation, the coils 1, 7, and 13 are connected in series. However, the coil 1 is connected to one interjunction R and other end is connected to coil 13. Similarly, other end of coil is connected to coil 7, which is connected to interjunction B. Referring to Figure. 1, moving in clockwise direction from coil 1 towards coil 18, the coils 1, 7, and 13 are in sequence, which is a physical sequence. However, the electrical connection of coils 1, 7, and 13 is non-sequential as the sequence of electrical connection is 1, 13, and 7, which is different from the physical sequence. For example, flow of current in the parallel set P1 is from coil 1 to coil 13 and then to coil 7 or vice-versa.
[00035] The coils 1, 13, 7 of the parallel set of coils P1 are wound to two or more teeth 40T of plurality of teeth 40T of the stator selected distributively along the circumference of the stator 40. The teeth are selected distributively, as in, the stator windings (as show in Figure. 1) selected are distributed along the circumference of the stator 40. In the current implementation, the teeth 1, 7, 13 are distributed along the circumference of the stator 40. In an embodiment, the selected teeth are substantially equidistant. In another embodiment, the selected teeth may not be equidistant. In yet one embodiment, the selected teeth may be distributed symmetrically.
[00036] Therefore, parallel sets of coils that are having sets of coils connected in series are distributively provided along the circumference of the stator to generate equal back-emf due to distribution of the coils around the stator 40 circumference. Additionally, any circulating currents that may be formed are reduced due to creation of equal back-emf. Also, it is advantage that the copper losses are reduced. Further, this enables flow of higher currents that provides higher torque for rotation of crankshaft. This rotation of crankshaft improves startability of the internal combustion engine. This electrical machine 100 is applicable in compact vehicles, having a tightly packed layout, such are two-wheeled or three-wheeled vehicle with improved performance.
[00037] Also, the teeth 40T that are selected distributively provide a balanced electromagnetic structure. This balanced electromagnetic structure further reduces any vibrations and associated noises that may arise due to imbalance.
[00038] The interjunction of phases R, Y, and B are connected to a control means to enable the operation of the electrical machine 100 as motor and to charge the battery 120.
[00039] Referring to Figure 2, the delta-connected stator winding 90 is connected with a controller 110, which in turn is connected with a vehicle battery 120. The controller 110 comprises semiconductor switches M1 to M6 having body diodes D1 to D6. The controller 110 also has a microcontroller, signal conditioning circuit, driver circuit and power supply circuit (not shown in figure) for controlling the switches M1 to M6 based on hall sensors 80 signals and crank position sensor 60 signal. The controller also has a DC link capacitor 115 for maintaining the DC bus voltage.
[00040] During motor mode of operation, the battery 120 will supply currents to the stator winding 90 in 120 degrees mode Brushless Direct Current (BLDC) motor driving pattern. Since the line-line resistance is small, high stator coil currents are set-up, which, results in large torque that can accelerate the engine crankshaft to a starting speed. When the crankshaft speed reaches a predetermined speed indicative of successful engine start as sensed from the crank position sensor 60 signal, the controller 110 switches the operation from motor mode to generating mode wherein the stator winding 90 generated voltage is supplied to the battery 120 through switches M1 to M6 and diodes D1 to D6. The switches M1 to M6 are driven in a phase-controlled manner to maintain the battery charging voltage within predetermined limits. Since the stator winding 90 is in delta configuration, the voltage generated at low speeds will be very less and insufficient for charging the battery directly. However, the controller 110 uses the winding 90 inductance along with semiconductor switches M1 to M6 and body diodes D1 to D6 to form boost converter configuration that can boost the stator voltage to a high value required for charging the battery. Therefore, the battery 120 can be charged even during low speed of engine such as engine idling speed.
[00041] By forming a delta-connection of the stator winding 90 with phase coils having low resistance due to parallel coil connections, high phase currents are set-up during BLDC motoring mode of operation. Since each collection of coils connected in series are connected in parallel and are capable of generating equal back-emf due to distribution of the coils around the stator 40 circumference, circulating currents are reduced and hence reducing copper losses. The balanced electromagnetic structure further reduces vibrations and associated noises. Further, boost charging by the controller 110 ensures adequate battery charging voltage even during low engine operating speed. Since no additional shunt regulator is used for charging voltage regulation, high charging efficiency is achieved with minimum cost. The electrical machine 100 size is not increased and low cost ferrite magnets are used which help in downsizing the engine without increasing cost. The electrical machine 100 can be compactly packaged in the engine without affecting any compact layout of the engine as the
[00042] Although the preferred embodiment has three stator coils connected in series in each parallel set and further two such parallel sets are connected in parallel to form a single phase, each coil in the phase can be connected in parallel to form a very low phase resistance and result in much higher phase currents depending on engine cranking requirements. Although the hall sensors 80 are placed between the stator teeth 40, they can also be placed in slots cut out in the stator teeth face. The machine can also be driven in sensor less mode wherein the back-emf is used to identify rotor permanent magnet position and thereby eliminating the need for additional hall sensors. Further, the crank position sensor 60 and protrusion 70 can be eliminated by sensing non-uniformity in the rotor magnetic field using hall sensors 80. During the starting mode of operation, the controller 110 can also drive the rotor 20 in a reverse direction momentarily and then rotate in forward direction to take advantage of the machine inertia and thereby overcome the cranking load, particularly with engines having large compression pressure. The machine can also be used to supplement the engine power to form a hybrid mode of operation depending on vehicle user requirements.
[00043] The improved electrical machine of the present invention can be used in all vehicles with internal combustion engines, especially in compact two-wheeled and three-wheeled vehicle, and in other applications with engines like lawn movers and diesel generator sets.
,CLAIMS:I/We claim:
1. An electrical machine (100) capable of functioning as motor and generator, said electrical machine (100) being functionally coupled to a crankshaft of an internal combustion engine, said electrical machine (100) comprising:
a rotor (20) with plurality of permanent magnets (30) disposed circumferentially, said rotor being connected to the crankshaft;
a stator (40) including plurality of teeth (40T) disposed circumferentially about said stator (40) and said plurality of teeth (40T) are facing the rotor (20), said plurality of teeth (40T) are divided into two or more sequential regions (A, B, C); and
a stator winding (90) wound to said plurality of teeth (40T) of said stator (40), and said stator winding (90) includes three phases (RB, RY, and BY) connected in a delta connection, wherein
each phase (RB, RY, and BY) of the stator winding (90) is provided with two or more parallel sets of coils (P1, P2, P3, P4, P5, P6), each parallel set of coil (P1, P2, P3, P4, P5, P6) of said two or more parallel sets of coils (P1, P2, P3, P4, P5, P6) includes two or more coils ((1, 13, 7), (10, 4, 16), (2, 14, 8), (11, 5, 17), (12, 6, 18), (3, 15, 9)) connected in series, and
said two or more coils ((1, 13, 7), (10, 4, 16), (2, 14, 8), (11, 5, 17), (12, 6, 18), (3, 15, 9)) of said parallel set of coils (P1, P2, P3, P4, P5, P6) are wound to two or more sets of teeth (40TS) of said plurality of teeth (40T), wherein at least one teeth of said set of teeth (40TS) are selected from each sequential region of said two or more sequential regions (A, B, C).
2. The electrical machine (100) of claim 1, wherein said two or more teeth (40T) are circumferentially symmetrically spaced about said stator (40).
3. The electrical machine (100) of claim 1, wherein said rotor (20) comprises plurality of permanent magnets (30) disposed around inner circumferential periphery.
4. The electrical machine (100) of claim 1, wherein said stator (40) comprises plurality of stator teeth (40T) magnetically coupled to the plurality of permanent magnets (30).
5. The electrical machine (100) of claim 1, wherein said two or more coils ((1, 13, 7), (10, 4, 16), (2, 14, 8), (11, 5, 17), (12, 6, 18), (3, 15, 9)) of each said parallel set of coils (P1, P2, P3, P4, P5, P6) are wound to said two or more sets of teeth (40TS), wherein the electrical series connection is in non-sequential pattern.
6. The electrical machine (100) of claim 1, wherein said permanent magnets (30) are ferrite magnet type.
7. The electrical machine (100) of claim 1, wherein said stator winding (90) of the electrical machine (100) is connected to a controller 110 for operating the electrical machine as motor and generator.
8. The electrical machine (100) of claim 1, wherein said stator (40) is provided with one or more hall sensors (80) placed between the stator teeth (40T).
9. The electrical machine (100) of claim 1, wherein the number of sequential regions (A, B, C) is equal to at least a number of coils in each parallel set (P1, P2, P3, P4, P5, P6).
10. The electrical machine (100) of claim 1, wherein said electrical machine (100) is mounted to the crankshaft the internal combustion (IC) engine of a two wheeled vehicle, said IC engine having a volume capacity of 110 cubic centimetres to about 500 cubic centimetres.