FIELD OF INVENTION

The present invention relates to an integrated starter generator system for an internal combustion engine and particularly relates to an integrated starter generator system which serves as a power assist for internal combustion engine.

BACKGROUND OF THE INVENTION

The integrated starter generator for vehicles is disclosed in Patent document 1: JP56160792, Patent document 2: IN233001 and Patent document 3: 4290/CHE/2011.The invention in patent document 1, titled "Starting device for internal combustion engine'! discloses an integrated starter generator system in which a single permanent magnet rotary electric machine is used as a motor for an internal combustion engine during its starting phase and the same is used as a generator while the internal combustion engine is in operation. Semiconductor switches such as transistors are controlled to operate the machine either as a motor or as a generator. However, the current requirement for starting application is different from that of generation application. A high torque for cranking the internal combustion engine compels a high starting current which in turn leads to the use of thick conductors with low resistance. On the other hand, for generator application, the machine should have a large number of turns in order to supply the required voltage at low engine idling speed. Further, the voltage generated at high engine speeds should be regulated to lie within levels that will not damage the electrical loads including battery. If powerful rare-earth magnets such as NdFeB are used to create high torque which is required for starting; and if coils with sufficient number of turns are used to generate the required voltage at engine idling speed then a regulator must be use for controlling the voltage generated. Moreover, core losses will also be very high during engine operation at high speeds.

The invention in patent document 2, titled "A Power Unit for a Motorcycle" discloses an integrated starter generator which operates as a brushed DC motor during an engine starting phase wherein brushes engage with commutator segments to allow high current in the armature coils and the machine operates as a brushless synchronous generator during engine operation wherein a centrifugal mechanism moves the brushes away from the commutator segments and allows a fraction of the armature coils to generate the required voltage for supplying to electrical loads including a battery. However, the integrated starter generator described above is less reliable due to frequent brush failure as a result of arcing and heat generated during the commutator action. Also the core losses are significant at high engine speeds.

The invention in patent document 3, titled "Starter-Generator" discloses an integrated starter-generator in which a stator comprising coils is operatively connected to a crankcase, a rotor with permanent magnets is located around an outer periphery of the stator and has a first portion directly coupled with a crankshaft of the engine and a second portion is a moveable disc of a pulley for a continuously variable transmission. The moveable disc portion has a centrifugal mechanism using roller mass elements which along with an expanding plate causes the rotor to move axially along a rotational axis based on the rotor speed. Since the rotor moves axially away from the stator at high engine speeds, the flux linked with the stator coils reduces which will in turn regulate the voltage generated. Thus powerful rare-earth magnets can be used to ensure good starting characteristics while restricting core losses at high engine speeds. However, since the flux link of the rotor with the stator reduces at high engine speeds, the rotor cannot be utilized for providing power assist to the engine at high speeds. It is therefore desirable to provide an integrated starter generator system that functions as a starter, generator and as a power assist for the engine without involving high core losses.

OBJECT OF THE INVENTION

The present invention has been made in order to overcome the foregoing problems of the related arts, and provides an integrated starter generator system to assist an engine during high speed operation as well as in high load conditions and thereby improve the engine performance and efficiency The main objective of the present invention is to provide an integrated starter generator system for a vehicle which performs multiple functions including engine starting, power generation and engine power assist. To the effect, the performance of the engine can be improved with high efficiency. It is another object of the present invention to provide an improved integrated starter generator system for a vehicle which involves the use of powerful rare earth magnets without core losses at high engine speeds.

SUMMARY OF THE INVENTION

The above and other objects are achieved by providing an integrated starter generator system in accordance with the present invention. In accordance with the present invention, the integrated starter generator system comprises a first stator that includes a first set of coils, a second stator that includes a second set of coils, a rotor that includes a first portion with a plurality of permanent magnets to generate a rotational magnetic field during rotation of a crankshaft and a second portion with a centrifugal mechanism configured to axially move the rotor along the crankshaft and between said first stator and said second stator so that the rotor gets magnetically coupled either with said first stator or with said second stator based on engine speed, and a controller operatively connected to said first stator and said second stator for controlling currents in the first set of coils and the second set of coils.

Accordingly, the first stator and the second stator are connected to a crankcase of an engine and the rotor disposed concentric to both the first stator and the second stator is operatively coupled to the crankshaft of the engine. A rotational magnetic field is generated by the rotor during rotation of the crankshaft. Further, the first set of coils and the second set of coils of the first stator and the second stator respectively are connected with the controller for operating the integrated starter generator system either as an engine starter or as an electric power generator or as an engine power assist based on engine speed and electrical load. The controller calculates a engine speed by using an output provided by a speed sensor. A battery supplies electrical energy required for driving the integrated starter generator system as an engine starter, as a generator, or as a power assist for the engine based on output generated by the controller. Upon successful start of the engine, the controller switches current flow in the first stator and causes the integrated starter generator system to switch from a motoring mode to a generating mode, wherein the integrated starter generator system acts as a synchronous generator with the first set of coils of the first stator supplying current for charging the battery. An axial position of the rotor remains unchanged until speed of the engine increases beyond a predetermined value. When the speed of the engine increases beyond the predetermined value, the centrifugal mechanism causes the rotor to move axially away from the first stator. Thereafter, the rotor axially aligns with second stator and the second set of coils generates current for motoring the engine and serves as a power assist for the engine. Since the rotor moves away from the first stator, the magnetic flux presented to the rotor by the first stator reduces; as a result core losses associated with the first stator reduces. Further, the voltage generated by the first set of coils in the first stator is regulated. The controller then drives the second set of coils in the second stator for assisting mechanical power to be delivered to the engine at high speeds or at high loads. Thus, during high speed operation of the engine, the integrated starter generator system supplies additional mechanical power which not only improves efficiency of the engine but also increases power delivered. Summary provided above explains the basic features of the invention and does not limit the scope of the invention. Other objects, novel features and advantages of the invention will become more apparent to the person skilled in the art from the following details description when taken in conjunction with the accompanying drawings. Scope of the invention will be based on the claims provided.

BRIEF DESCRIPTION OF DRAWINGS

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:

Figure 1 illustrates a system diagram to depict working of the integrated starter generator system in accordance with the present invention.

Figure 2 illustrates a circuit diagram of the controller of said integrated starter generator system in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of an integrated starter generator system for a vehicle in accordance with the present invention will be described hereunder with reference to the accompanying drawings. Various features of the integrated starter generator system in accordance to the present invention will become discernible from the following description set out hereunder. 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.

Figure 1 illustrates a system diagram depicting the working of the integrated starter generator (hereinafter ISG) system installed in a vehicle. Referring to Fig.1, description is given of the working of the ISG system. Description is also given of a construction of said ISG system.

According to the present embodiment, the ISG system S is connected to an engine 10 for performing multiple functions including engine starting, electrical power generation, and engine power assist. Said ISG system S comprises a first stator 41, a second stator 43, a rotor 42 and a controller 50. The first stator 41 includes a first set of coils and the second stator 43 includes a second set of coils. While said first stator 41, and the second stator 43 is disposed in a crankcase 30 of the engine 10, the rotor 42 is axially connected to the crankshaft 20 of the engine 10, in a manner such that it is concentric to both the first stator 41 and the second stator 43. Further, as per the present embodiment, the rotor 42 has a first portion that includes a plurality of permanent magnets 44. In the present embodiment, rare-earth permanent magnets such as NdFeB (Neodymium Iron Boron) are used in the first portion of the rotor 42. However, in another embodiment ferrite magnets such as Strontium ferrite could also be used.

Further, in the present embodiment the plurality of permanent magnets 44 are located outside the first stator 41 and the second stator 43. However, in another embodiment, the first stator 41 and the second stator 43 can surround the plurality of permanent magnets 44 by providing a rotor having a smaller diameter. The rotor 42 further includes a second portion that includes a centrifugal mechanism 46. The centrifugal mechanism 46 comprises roller element masses and an expanding plate which enable the rotor 42 to move axially along the crankshaft 20 when speed of the engine 10 increases beyond a predetermined speed stored in a controller 50. The rotor 42 axially
connected with the crankshaft 20 rotates in synchronism with the crankshaft 20. Thus, when the rotor 42 rotates along with the crankshaft 20, a magnetic field is generated across the rotor 42. The first stator 41 or the second stator 42 gets linked with the magnetic field created by the rotor 42 depending on the axial position of the rotor 42. The controller 50 operatively connected to the first set of coils and the second set of coils in the first stator 41 and the second stator 43 respectively aids in controlling the working of the integrated starter generator system either as an engine starter or as an electric power generator or to assist engine power based on engine speed and electrical load. A speed sensor 60 which generates an electrical signal indicative of the rotor 42 speed is connected with the controller 50. The controller 50 calculates the rotor speed by using the speed sensor 60 signal. A battery 70 supplies the electrical energy required for driving the integrated starter generator system S as an engine starter or for assisting engine power. During operation of the integrated starter generator system S as a generator, the battery 70 will be charged through controller 50.

Figure 2 illustrates a circuit diagram of the controller 50 of said integrated starter generator system S in accordance with the present invention. Working of the integrated starter generator system S can be explained with reference to Figure 1 and Figure 2. When the engine 10 is in off condition, the rotor 42 is stationary and the magnetic field created by the first portion of the rotor 42 links the rotor 42 with the first set of coils in the first stator 41. When an engine start request is received by the controller 50, the controller 50 allows passage of current from the battery 70 to the first stator 41 by controlling a conduction angle of a plurality of first semiconductor switches (1, 2.3,4,5 & 6) disposed therein. In other words, the controller 50 excites the first set of coils in the first stator 41 to operate the integrated starter generator system S as a brushless DC motor and enables engine starting. The number of turns of coils in the first stator 41 and the second stator 43 can be varied depending on factors such as engine size, battery size, amount of power required etc. Further, the controller 50 recognizes successful starting of engine 10 by monitoring the engine speed signal generated by the speed sensor 60. Upon successful start of the engine 10, the controller 50 switches the operation of the integrated starter generator system S from a motoring mode to a generating mode. When the controller 50 recognizes that the engine 10 has started, the controller 50 changes conduction angle of the plurality of first semiconductor switches (1, 2.3,4,5 & 6) and allows passage of three phase current from the first stator 41 to the battery 70 and thus charges the battery 70. Thus, the integrated starter generator system S functions as a synchronous generator with first set of coils in stator 41 supplying current for charging battery 70. An axial position of the rotor 42 remains unchanged until the engine speed increases beyond a predetermined value stored in the controller 50. When the engine speed increases beyond the predetermined value, the centrifugal mechanism 46 causes the rotor 42 to move axially away from the first stator 41 and causes the rotor 42 to get magnetically coupled with the second stator 43. As a result, flux linkage of the rotor 42 with the first set of coils in the first stator 41 reduces and thereby the voltage generated by the first set of coils in the first stator 41 is regulated and core losses in the first stator 41 are reduced. Thereafter, the controller 50 drives the second set of coils in stator 43 to operate the integrated starter generator system S as a motor for assisting mechanical power delivered by engine 10. Thus during high speed operation of the engine 10, the integrated starter generator system S supplies additional mechanical power which will improve efficiency of the engine 10 and also increase power delivered. Further, based on vehicle operating conditions and engine load, the controller 50 causes three phase current to be supplied to the second stator 43 by controlling a conduction angle of a plurality of second semiconductor switches (11,12,13,14,15 & 16). For example, in addition to engine speed signal, the controller 50 can process additional inputs from sensors such as throttle position sensor and an engine temperature sensor. The second stator 43 thus excited supplies energy to the engine 10. Thus, the integrated starter generator system S operates in a motoring mode. As a result, additional mechanical power can be supplied to the engine 10, thereby increasing efficiency of the engine 10 and also the power delivered by the engine 10. Moreover, although flux linkage of the rotor 42 with the first stator 41 decreases when engine speed increases, as the rotor 42 moves axially away from the first stator 41, however, it is stili sufficient to maintain voltage required for charging the battery 70. As a result, both motoring and generating mode can be achieved simultaneously. Thus, by using two stators and a single rotor having a centrifugal mechanism disposed therein in accordance with the present invention, the integrated starter generator system S can be used for starting the engine 10, for generating electricity for charging battery 70, for assisting engine power delivery, and for regulating generated voltage during speed change, while ensuring reduced core losses in both the stators. In the present embodiment, the integrated starter generator system S operates in starting mode when a engine rpm is in the range of 0-6000 rpm, in generating mode above 1000 rpm and in power assist mode above 4000 rpm. In another embodiment, in order to facilitate the integrated starter generator system S to operate either as a motor or as a generator, the integrated starter generator system S can include Hall Effect sensors in the first stator 41 and the second stator 43. Alternatively, in another embodiment, the integrated starter generator system S can be made to function without sensors by including the controller 50 in a manner such that it senses coil voltages of the first stator 41 and the second stator 43.

Further, in another embodiment, instead of a single controller driving coils in the first stator 41 and the second stator 43, two separate controllers can be provided for driving the coils in the first stator 41 and the second stator 43. The two controllers are interconnected to recognize the mode of operation of the integrated starter generator system so as to suitably control currents in the first set of coils and the second set of coils of the first stator 41 and the second stator 43 respectively. The present invention has been explained in relation to its essential and preferred embodiments, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed. The scope of the invention can be extended to two-wheeled vehicles such as motorcycle, scooter, three-wheeled vehicles, four wheeled vehicles and stand-alone power units. Although the preferred embodiment uses the position estimate to display information to the user, other applications like visual or audible navigation assistance, vehicle-to-vehicle communication or vehicle-to-ground station communication are possible. While the present invention has been shown and described with reference to the foregoing preferred embodiments, it will be apparent to those skilled in the art that changes in form, connection, and detail may be made therein without departing from the spirit and scope of the invention as defined in the appended claims:We Claim:

1. An integrated starter generator system (S) comprising:a first stator (41) that includes a first set of coils, a second stator (43) that includes a second set of coils, said first stator (41) and said second stator (43) being disposed in a crankcase (30) of an engine (10); a rotor (42) axially connected to a crankshaft (20) of the engine (10) and disposed concentric to said first stator (41) and said second stator (43), said rotor (42) comprising a first portion that includes a plurality of permanent magnets (44), and a second portion that includes a centrifugal mechanism (46) to move said rotor axially along the crankshaft (20) and between the first stator (41) and the second stator (43) so as to magnetically couple said rotor (42) either with the first stator (41) or the second stator (43) based on engine speed; and a controller (50) operatively connected to the first set of coils and the second set of coils for controlling currents in the first set of coils and the second set of coils of the first stator (41) and the second stator (43) respectively.

2. The integrated starter generator system (S) as claimed in claim 1, wherein the plurality of permanent magnets (44) is made of a rare earth material. The integrated starter generator system (S) as claimed in claim 1, wherein the centrifugal mechanism (46) includes a plurality of roller mass elements and an expanding plate operativeiy connected to each other. The integrated starter generator system (S) as claimed in claim 1, wherein the controller (50) includes a plurality of first semiconductor switches (1, 2, 3, 4, 5 & 6) for controlling currents in the first stator (41). The integrated starter generator system (S) as claimed in claim 1, wherein the controller (50) includes a plurality of second semiconductor switches (11, 12, 13, 14, 15 & 16) for controlling currents in the second stator (43).