A Magneto Assembly for an Internal Combustion Engine

Field of the Invention:

This invention relates to "A magneto assembly for an internal combustion engine" and more particularly for two wheeler. ,

Background of the Invention:

Generally vehicles with an Internal Combustion Engine use a magneto assembly for generating electric power required for charging the vehicle battery and providing supply for various electrical loads like head lamp, brake lamp and AC ignition unit.

Typically a magneto assembly comprises a rotor with a plurality of circumferential permanent magnets in alternating north - south pole arrangement. The rotor is coupled to the crankshaft of the engine. A stator connected with the crankcase of the engine and aligned within the inner periphery of the rotor has laminated rotor poles carrying a stator winding. The permanent magnet rotor rotates upon rotation of the engine crankshaft and causes an alternating voltage to develop across the stator winding. The output of the stator winding is connected to a battery charging circuit and various bulbs.

The permanent magnet rotor has a tooth on its outer periphery made of a ferrous material. An externally mounted rotor position sensor like hall effect sensor or variable-reluctance type sensor is connected with the crankcase nearer to the tooth on the magneto - rotor such that a detectable signal is generated by the position sensor whenever the tooth passes it. An electric circuit' means is connected with the position
sensor to detect the rotor position signal and thereby control various engine parameters like ignition timing, fuel injection timing, etc.

Problems associated with arrangement are external rotor position sensors occupy space and increase the cost of the magneto assembly. A magneto assembly without any external rotor position sensor can reduce cost of the system and eliminate the need for a tooth on the outer periphery of the magneto rotor.

The present invention solves the noted need by providing a magneto assembly with an integrated rotor position sensor.

Summary of the Invention:

In the light of the state of the art described above, the object of the present invention is to provide a magneto assembly for an internal combustion engine, where the rotor position sensor is an integral part of the magneto assembly.

Another object of the present invention is to provide rotor position signal required for control of the engine operation without reducing the maximum power generated at different rotor speeds.

In addition, it is an object of the present invention to provide a magneto assembly with an integrated rotor position sensor which is cost effective.

Yet another object of the present invention is to provide a magneto assembly with an integrated rotor position sensor which is simple to manufacture.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

Brief Description of the Drawings:

The invention and objects and features thereof will be more readily apparent from the following description and appended claims when taken with the drawing, in which:

Fig 1 is a pictorial view of the prior art.

Fig 2 is a graph showing the pulser coil output voltage.

Fig 3 is a pictorial view of the magneto assembly with integrated rotor position sensor.

Fig 4 is a graph showing the sensor coil output voltage with high power density magnet and without high power density magnet.

Fig 5 is a graph showing the magneto capacity with high power density magnet and without high power density magnet.

Detail Description of the Invention:

For the purpose .of illustration only it will be illustrated with the help of a two wheeler motorcycle. First the whole structure of the vehicle will be roughly described. With reference to, a motorcycle comprises of a frame, front fork attached to a pivot tube of the vehicle frame, a front wheel attached to these front forks, a handle bar connected to the front forks, a fuel tank attached so as to straddle an upper part of the vehicle frame, a seat attached to the upper rear portion of the vehicle frame, an engine unit attached to the lower front section of the vehicle frame, a swing arm attached-to a lower rear section of the vehicle frame, suspended by a rear shock absorber (not shown in the drawing) from the vehicle frame and a rear wheel attached to a rear end of swing arm. The intake system of the engine comprises of a carburettor, intake duct and an air* cleaner. The exhaust system of the engine comprises of exhaust pipe and a muffler. The motorcycle is also provided with a side cover for covering a side section of the vehicle frame, a seat cover for covering a rear section of the vehicle frame below the seat, a front fender for covering an upper part of the front wheel, and a rear fender for covering an upper part of the rear wheel. The drive from the engine is transmitted from the engine to the driven wheel sprocket mounted on the rear wheel hub mounted on the rear wheel assembly.

The present invention is a magneto assembly for an internal combustion engine without any external magneto - rotor position sensor. The magneto assembly comprises a rotor connected with the crankshaft of the engine. A plurality of circumferential magnetic rotor poles in alternating north - south pole arrangement is connected with the said rotor. There is at least one magnet with power density greater than the rest of the magnetic rotor poles connected with the rotor in between the north - south pole borders. The high power density magnet is located substantially nearer to a like pole.

The magneto assembly has a stator connected with the engine. The stator has a plurality of poles for magnetic flux coupling with the magnetic rotor poles. Current coil is wound around the stator poles for generating the alternating voltage during rotation of the rotor by the crankshaft. There is a sensor coil wound around at least one of the stator poles to produce a detectable signal with reference to the -high power density magnet location in the rotor.

The high power density magnet is made of a material with remnant magnetism and permeability values greater than the other magnetic rotor poles. During rotation of the rotor by the crankshaft, the flux linked with the sensor coil wound around a stator pole changes. The flux change will be a maximum when the high power density magnet passes the sensor coil. The voltage generated across the sensor coil is proportional to the rate of change of flux linkages and hence a maximum voltage is generated when the high power density magnet passes the sensor coil. The sensor coil output can be connected to an electric circuit means to detect the position of the high power density magnet and thus the position of the crankshaft. The maximum power generated by the magneto at different rotor speeds is not reduced by the addition of the high power density magnet.

Referring to Figure 1, a magneto assembly as described in the prior art is shown. A rotor (105) can be connected with the crankshaft of the engine for rotation. There is a plurality of circumferential magnetic rotor poles (120) connected with the inner periphery of the rotor (105) in alternating north - south arrangement. A stator (101) is connected with the-engine crankcase and having a plurality of stator poles for magnetic flux coupling with the magnetic rotor poles (120). The stator poles are made of laminations to reduce eddy current losses. Current coil (125) is wound around stator poles to generate an alternating voltage upon rotation of the rotor (105) by the crankshaft. The alternating voltage is used to provide supply for lighting loads and for charging the vehicle battery.

A tooth (109) made of a ferrous material is provided on the outer periphery of the rotor which along with the pulser coil (115) acts as a rotor position sensor. The pulser coil (115) has a coil wound around a magnet. During rotation of the rotor by the crankshaft, there is a change in the*flux linked with'the pulser coil (115) when the taoth (109) passes the pulser coil. An alternating voltage is generated across the pulser coil (115) as shown in Figure 2 when the tooth (109) passes the pulser coil. The pulser coil (115) output thus provides an indication of the rotor (105) position and thereby the crankshaft position. Similarly an externally mounted hall sensor can be used to provide an indication of the rotor position. A missing tooth or a tooth pattern on the outer periphery of the rotor also provides a signal indicating the position of rotor (105). But all these embodiments require an externally mounted sensor which is cost prohibitive and occupies space.

In Figure 3, a magneto assembly with integrated rotor position sensor is shown. In addition to the plurality of magnetic rotor poles (120), a magnet 330b is connected with the inner periphery of the rotor (105) between the north - south pole borders of magnetic rotor poles (120). The magnet (330b) has power density greater than the •power density of the magnetic rotor poles (120). In the embodiment, the magnetic rotor poles are Strontium Ferrite magnets and the magnet (330b) is a Neodymium - Iron -Boron magnet. The magnet (330b) has remnant magnetism and permeability values greater than that of the magnetic rotor poles (120). The magnet (330b) is located nearer to a like pole (North Pole in Fig 3)- A sensor coil (325) is wound around at least one of the stator poles. During rotation of the rotor (105) by the crankshaft an alternating voltage is generated across the sensor coil (325) as shown in Figure 4. The voltage generated is proportional to the rate of change of flux linked with the sensor coil (325). The change in the flux will be a maximum when the magnet (330b) passes the stator pole with the sensor coil (325). Therefore, the alternating voltage will have a maximum peak voltage when the magnet (330b) passes the stator pole with sensor coil (325) (the second positive voltage peak in Fig 4). The sensor coil output voltage gives an indication of the position of the magnet (330b) and thereby the rotor position. The. polarity of the maximum peak voltage depends on the magnetic polarity of the magnet (330b) and the direction of rotation of the rotor (105).

The radial length of the magnet (330b) can be lesser than the radial length of the magnetic rotor poles (120). To maintain the same air gap between the rotor poles and stator poles, the magnet (330b) with lesser radial length is attached to a projection (330a) that is connected to the inner periphery of the rotor (105). The projection (330a) is made of a high permeability material. Since the radial length of the magnet (330b) is less, the cost of the magnet (330b) is considerably reduced. The radial length of the magnet (330b) should at least be 30% of the radial length of the rotor magnetic poles (120). If radial length of magnet (330b) is less than 30% of the radial length of the rotor magnetic poles, then high cost magnets with flux density greater than 1.4 Tesla is required to produce detectable rotor position signal.

In Figure 4, the magneto capacity without magnet (330b) and with magnet (330b) is shown. The maximum power generated at different speeds is not reduced because of the addition of magnet (330b).
In the embodiment described, the high permeability material used for projection (330a) is a Nickel - Iron alloy.

Various modifications and adaptations may occur to those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

We Claim:

1. A magneto assembly for an internal combustion engine comprising:

a rotor connected with the crankshaft of the said engine;

a plurality of circumferential magnetic rotor poles with spaced north - south pole borders connected with the said rotor;

a stator having a plurality of stator poles connected with the said engine for magnetic flux coupling with said magnetic rotor poles;

at least one magnet connected with the said rotor in between the said north -south pole borders of the
said magnetic rotor poles substantially nearer to a like pole and having power density greater than the said magnetic rotor poles;

at least one current coil wound around the said stator poles for generating alternating voltage upon rotation of the said rotor by the said crankshaft; and

a sensor coil wound around at least one of the said stator poles to generate a rotor position signal when the said magnet passes the said stator pole with the said sensor coil.

2. A magneto assembly as claimed in claim 1 wherein the said magnet has a radial length lesser than that of the said magnetic rotor poles.

3. A magneto assembly as claimed in claim 2 wherein the said, magnet is connected to a high permeability material that is in turn connected with the said rotor to minimize flux leakage.

4. A magneto assembly as claimed in claim 3 wherein the said high permeability material is a Nickel Iron alloy.

5. A magneto assembly as claimed in claim 2 wherein the said radial length of the magnet is at least 30% of the radial length of the said magnetic rotor poles.

6. A magneto assembly as claimed in claim 1 wherein the said magnet is a rare earth magnet.

7. A magneto assembly as claimed in claim 6 wherein the said rare earth magnet is a Neodymium-lron-Boron magnet.

8. A magneto assembly as claimed in claim 1 wherein the said magnet is preferably circumferential.