DESC:FIELD OF THE INVENTION

[0001] The subject matter as described herein, relates generally to an integrated starter generator for an internal combustion engine and more particularly, but not exclusively, to a crankshaft starter generator for an internal combustion engine wherein the starter generator is coupled to a crankshaft of the internal combustion engine and serves both as the starter and the generator.

BACKGROUND OF THE INVENTION
[0002] A starter motor and an electrical generator are separate components on most automobile with an internal combustion (IC) engine. An integrated starter generator (ISG) combines the starter motor and the generator into a single component as is known from US Granted Patent Publication number US 1770468. In a small IC engine, for example a motorcycle or scooter IC engine, the ISG is conventionally mounted on a crankshaft of the engine. Such ISG is also called a crankshaft starter generator (CSG). The ISG transmits rotational power from a battery to the crankshaft to start the engine and generates electric power based on rotational power from the crankshaft after the engine has started.

[0003] An ISG has several advantages which make it a preferred device to be included in a modern automobile. Firstly, the ISG reduces vehicle weight by integrating the starter motor and the generator, and by eliminating components which are redundant to the generator and the starter motor. Secondly, the ISG achieves cost reduction because a combined generator and starter motor cost less than the sum of the two devices individually. Also, administrative costs of vehicle manufacturers are reduced because only one part (ISG) instead of two (a generator and a starter motor) needs to be purchased, stored, made available as a service part, and so on. Thirdly, the ISG also causes a reduction in assembly complexity. Fewer parts go into the ISG assembly often translating into lower assembly cost. Further, due to reduced number of parts and reduced assembly steps involved, the incidents or likelihood involving mistakes are also reduced.

[0004] It is a continuous endeavour to extract optimum benefit from the ISG without increasing the cost and size of the engine. Additionally, 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 which deteriorates vehicle fuel economy. Indian Granted Patent number 212133 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. But the additional field windings increase size of the machine and will in turn increase the size of the engine.

[0005] Using ferrite magnets reduces the cost of CSG. However, ferrite magnets are not capable of producing large magnetic flux in the stator teeth of CSG. Hence, in order to achieve high cranking torque required for engine during starting mode of operation, high currents should be established in the stator coils to overcome the crankshaft inertia and take the crankshaft r.p.m to desired levels in less time. One of the ways to achieve high current is to reduce the resistance in the stator coils 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. US Patent Publication Number 6392311 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 starting torque and only a set of the coils are connected for charging the battery and thereby prevents excessive charging currents. But such a system requires a large number of semiconductor switches in the controller and increases the overall cost of the system.

[0006] Further, Japanese Patent Publication Number JP2002265659 discloses an IC 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.

[0007] Generally, three phase star configuration is adopted for coil winding of the stator core. But, in low volume capacity motorcycle or scooter IC engine, star configuration results in heat radiation loss and produces circulating currents in the coil which limits the CSG in producing high torque required to start the IC engine. In low volume capacity motorcycle or scooter IC engine, size and weight of the CSG is of utmost importance and hence, it is desirable to have an electrical machine that functions as a CSG without increasing magnet flux density and machine size, and without needing additional centrifugal mechanism or transmission gears while achieving the desired high cranking torque during engine starting and adequate charging voltage during generation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The above and other features, aspects, and advantages of the subject matter will be better understood with regard to the following description and accompanying drawings where:
FIG. 1 is a perspective view of a crankshaft starter generator according to an embodiment of the present invention.
FIG. 2 is a schematic electrical connection diagram of the stator winding with a control unit and a power source.

BRIEF DESCRIPTION OF THE INVENTION

[0009] The present invention disclosed herein is aimed at overcoming the challenges associated with the CSG without any addition to the cost or weight of the engine. Hence, it is an object of the present invention to achieve the high cranking torque in a CSG for a small engine application and to achieve the required charging voltage during generator mode of operation without any increase in size. It is another object of the present invention to disclose a retrofittable CSG with minimum design alterations for providing high cranking torque to the engine crankshaft in a cost effective manner without increasing the size of the engine.

[00010] The present invention hence discloses a CSG comprising an outer rotor with permanent magnets for connecting with an engine crankshaft, a stator for connecting with an engine crankcase and concentric with the rotor for allowing the rotor permanent magnet flux to link with stator teeth, a three phase winding on the stator for carrying currents in order to produce a torque for rotating the permanent magnet rotor during engine starting and for generating voltage in order to supply to vehicle electrical loads after engine starting. The winding has coils connected in parallel for each phase and the phases are connected in delta pattern to achieve a low line-line resistance. Hence, a large current for producing the high starting torque is achieved. The aforementioned CSG is preferably used in a small internal combustion engine installed in a two wheeled vehicle. However, it is also usable in other engine applications such as those of lawnmovers and diesel gensets.

[00011] The present subject matter and its embodiments would now be described in greater detail in conjunction with the figures in the following description. The following description provides a convenient illustration for implementing exemplary embodiments of the invention. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

[00012] Fig. 1 shows an illustrative and perspective view of a CSG for an IC engine according to the present invention. The CSG 100 comprises a rotor 20 rotatably connected with a crankshaft of the engine. The rotor 20 is provided with a plurality of permanent magnets 30 around its inner periphery in alternating north pole-south pole fashion. A stator comprising of a plurality of stator teeth 40 is supported on a crankcase of the engine. Coils 50 are wound around each stator tooth 40 for carrying electric current during starting mode of operation and for generating voltage during generating mode of operation. In assembled condition, the stator is mounted within the rotor 20 and is magnetically coupled to it. Thus, the stator and the rotor are concentric. In an embodiment, the rotor 20 is located radially outwardly of the stator. The stator teeth are separated from an inner periphery of the rotor by a small air gap. The stator teeth 40 are capable to carry the magnetic flux generated by permanent magnets 30.
[00013] The outer periphry of the rotor 20 is provided with a ferromagnetic protrusion 70. A crank position sensor 60 is mounted on the engine crankcase outside the outer periphery of rotor 20 to sense the ferromagnetic protrusion 70. The crank position sensor 60 is separated from the ferromagnetic protrusion 70 by a small air-gap. Three hall sensors 80 are located in the spacing between the stator teeth 40 for generating signals indicative of position of the permanent magnets 30 of the rotor 20.

[00014] In a preferred embodiment, the CSG 100 has twelve permanent magnet poles and eighteen stator coils. The stator coils 50 are referred by numerals 1 to 18. The voltage generated in each coil is separated in phase with the voltage generated in neighbouring coil by 120 degrees electrical angle. The consecutive hall sensors 80 are located with separation of 120 electrical degrees. In an embodiment, the permanent magnets 30 are ferrite magnets which help in cost reduction of the CSG. However, ferrite magnets are not capable of producing large magnetic flux in the stator teeth 40. Therefore, in order to achieve the high cranking torque required for engine starting, high currents need to be established in the stator coils 50. One of the ways to achieve high current in the stator coils is by reducing or lowering the resistance exhibited by the stator coils. If coils of large diameter are used for achieving the low stator coil resistance, the number of coil turns packed within each stator tooth reduces and thereby deteriorates the voltage produced during generator mode of operation.

[00015] Therefore, to achieve low stator coil resistance, the stator coils producing voltages in phase are split into three sets, each set having six coils. Referring to Fig. 1, a first set having stator coils 1, 4, 7, 10, 13 and 16 are in phase. A second set having stator coils 2, 5, 8, 11, 14 and 17 are in phase. A third set having stator coils 3, 6, 9, 12, 15 and 18 are in phase. The three sets mentioned above are separated in phase from each other by 120 electrical degrees. Each set of six coils in a phase is further split into two subsets of coils that are connected in series. Referring to Fig. 2, in the first set, a first subset has coils 1, 4 and 7 connected in series and a second subset has coils 10, 13 and 16 connected in series. The first subset and the second subset are connected in parallel to form phase R. Similarly phase Y and phase B are formed and are connected in delta to achieve a low line-line resistance which is equivalent to a single coil resistance. Further, the coils are wound in the same direction only.

[00016] Referring to Fig. 2, a thusformed delta connected stator winding 90 is connected with a controller 110 which in turn is connected with a vehicle battery 120. The controller comprises of semiconductor switches, a microcontroller and a DC link capacitor. In an embodiment, the controller 110 comprises of a plurality of semiconductor switches M1 to M6 having body diodes D1 to D6. The controller 110 also comprises of the microcontroller, signal conditioning circuit, driver circuit and power supply circuit (not shown in figure) for controlling the switches M1 to M6 based on signals of the hall sensors 80 and crank position sensor 60. The DC link capacitor 115 maintains the DC bus voltage.

[00017] During motor mode of operation, the vehicle battery 120 supplies current to the stator winding 90 in 120 degree mode BLDC (Brushless Direct Current) 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 desirable starting speed. When the crankshaft speed reaches a predetermined cranking torque indicative of successful engine start as sensed from the crank position sensor 60 signal, the controller switches the operation from motoring 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. But the controller 120 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. Hence battery charging can be achieved from engine speeds as low as the engine idling speed.

[00018] By forming a delta 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. 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 machine size is not increased and low cost ferrite magnets are used which help in downsizing the engine without increasing cost.

[00019] Although the preferred embodiment has three stator coils connected in series and further two such sets 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 are placed between the stator teeth 40, they can also be placed in slots cut out in the stator teeth face. Further the machine can also be driven in sensor-less mode wherein the back-emf is used to identify rotor permanent magnet position and thereby eliminate the need for additional hall sensors. Further the crank position sensor 60 and protrusion 70 can also be eliminated by sensing a non-uniformity in the rotor magnetic field using hall sensors 80. During starting mode of operation, the controller 110 can also drive the rotor 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 have 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
[00020] For instance, in an embodiment of a small engine in a range of 110 cc cubic capacity to about 500 cc cubic capacity, the starting torque required to overcome compression is approximately 6Nm. In such an embodiment, phase current required is 60A minimum for which the line-line resistance should be lower than 100 milliohms. According to the present invention, 75 milliohm line-line resistance is achieved with the stated winding. Hence, the present ISG is most effective for a small engine. In an embodiment, the small engine includes any IC engine less than 500 cc.

[00021] The present invention is thus briefly described. It will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the present invention.

CLAIMS:We Claim:

1. A crankshaft starter generator (100) mounted on a crankshaft of an internal combustion (IC) engine, said crankshaft starter generator (100) comprising:
a rotor (20) comprising plurality of permanent magnets (30) disposed around inner circumferential periphery;
a stator accommodated within the rotor (20), said stator comprising plurality of stator teeth (40) magnetically coupled to the plurality of permanent magnets (30); and
each of said plurality of stator teeth (40) having a stator coil (50) wound around it, said stator coil (50) wound to arrange the plurality of stator teeth (40) to a first set (R-B), a second set (R-Y), and a third set (B-Y);
wherein,
an electric current passing through the first set (R-B), the second set (R-Y) and the third set (B-Y) are configured to have a delta connected winding with a phase angle difference of 120 degrees;
the plurality of stator teeth (40) in first set (R-B) include two first subsets (R-B1, R-B2), each of said first subsets (R-B1, R-B2) is in parallel connection with each other, and wherein each of said first subsets (R-B1, R-B2) include three stator teeth having three stator coil (1,4,7 & 10,13,16) connected in series;
the plurality of stator teeth (40) in second set (R-Y) include two second subsets (R-Y1, R-B2), each of said second subsets (R-Y1, R-Y2) is in parallel connection with each other, and wherein each of said second subsets (R-Y1, R-Y2) include three stator teeth having three stator coil (2,5,8 & 11,14,17) connected in series; and
the plurality of stator teeth (40) in third set (B-Y) include two first subsets (B-Y1, B-Y2), each of said third subsets (B-Y1, B-Y2) is in parallel connection with each other, and wherein each of said third subsets (B-Y1, B-Y2) include three stator teeth having three stator coil (3,6,9 & 12,15,18) connected in series.

2. The crankshaft starter generator (100) as claimed in claim 1, wherein the controller (110) comprises a microcontroller, a signal conditioning circuit, a driver circuit, a power supply circuit and a switching circuit.

3. The crankshaft starter generator (100) as claimed in claim 1 or 2, wherein the switching circuit comprises six diode operated switches (M1, M2, M3, M4, M5 & M6) disposed to regulate the electric current passing through the stator coil (50).

4. The crankshaft starter generator (100) as claimed in claim 1, wherein the rotor (20) comprises twelve permanent magnets (30) and the stator comprises eighteen stator teeth (1 to 18).

5. The crankshaft starter generator (100) as claimed in claim 1, wherein the permanents magnets (30) are made of ferrite material.

6. The crankshaft starter generator (100) as claimed in claim 1, wherein each of three hall sensors (80) are disposed in any three consecutive spacing between consecutive stator teeth (40).

7. The crankshaft starter generator (100) as claimed in claim 1, wherein the rotor (20) comprises a ferromagnetic protrusion (70) disposed on an outer periphery of the rotor, and said ferromagnetic protrusion configured to provide the position of the crankshaft to a crank position sensor (60) mounted on an external portion of the IC engine.

8. The crankshaft starter generator (100) as claimed in claim 1, wherein said crankshaft starter generator is used in the IC engine of a two wheeled vehicle, said IC engine having a volume capacity of 110 cubic centimeters to about 500 cubic centimeters.