Magneto Assembly

Field of the Invention

This invention relates to a magneto assembly for an internal combustion engine and particularly relates to an arrangement for crankshaft position sensing in order to control engine parameters like ignition timing and fuel injection timing.

Background of the Invention:

Vehicles with an internal combustion engine generally include a magneto assembly for converting a fraction of the mechanical energy generated by the engine into electrical energy. The electrical energy generated by the magneto assembly is supplied to various vehicle electrical loads like battery, lamps and horn. In addition to electricity generation, the magneto assembly also performs the function of a flywheel in order to regulate the engine torque ripple. Conventionally the magneto assembly comprises of an outer rotor with permanent magnets and an inner stator with coils. The outer rotor is coupled with the engine crankshaft such that alternating current is produced across the stator coils when the engine is running.

Engine control system comprising ignition control and fuel injection control requires crankshaft position information. Since the rotor of magneto assembly rotates in synchronism with engine crankshaft, it is sufficient to obtain the magneto rotor position information. At least one reluctor is located on the outer periphery of the magneto rotor and a variable reluctance type sensor or a Hall Effect sensor is mounted close to the magneto rotor for sensing the passage of reluctor. The variable reluctance type sensor or Hall Effect sensor comprises a permanent magnet for generating a magnetic field. The passage of the reluctor close to the sensor varies the magnetic field which in turn is sensed by a coil in the variable reluctance sensor or by a hall sensor IC (Integrated Circuit) in the Hall Effect sensor. The signal generated by variable reluctance sensor or Hall Effect sensor is processed by an Engine Control Unit (ECU) to identify crankshaft position and engine control operations are correspondingly performed.

The conventional magneto assembly as shown in Figure 1 comprises an outer rotor
10 and a variable reluctance sensor 60. The magneto rotor 10 has permanent magnets in its inner periphery (not shown in Figure). A reluctor 20 is located on the outer periphery of the rotor 10 such that at Top Dead Centre (TDC) position of piston, the trailing edge 24 of reluctor 20 is close to variable reluctance sensor 60.

During rotation of the magneto rotor 10, the passage of leading edge 22 and trailing edge 24 introduces change in air-gap reluctance. The magnetic field generated by permanent magnet 40 is changed during the passage of reluctor 20 edges 22 and 24. The change in magnetic field produces a voltage across coil 30. The variable reluctance sensor 60 signal 50 is indicative of the crankshaft position. In this kind of construction because of additional reluctors the system cost goes up and it also leads to manufacturing complexity.

Summary of the Invention:

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.

An object of the present invention is to provide a magneto assembly which comprises at least one slot in the outer periphery of the magneto rotor. A variable reluctance type sensor or Hall Effect sensor is mounted fixedly, close to the said magneto rotor for sensing the passage of the slot.

Another object of the present invention is to provide a low cost crankshaft position sensing and is achieved without the use of additional reluctors on the outer periphery
of magneto rotor.

Another object of the present invention is to provide a magneto assembly with reduced manufacturing complexity.

Brief Description of the Drawings:

The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by
way of illustration only, and thus are not limitative of the present invention, and
wherein

Figure. 1 shows a pictorial view of a conventional magneto assembly.

Figure. 2 shows a conventional motorcycle having an internal combustion engine as the power pack.

Figure 3.3 shows a pictorial view of the magneto assembly according to one embodiment of the present invention.

Detail Description of the Drawings:

The present invention now will be described more fully hereinafter with different embodiments. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather those embodiments are provided so that this disclosure will be thorough and complete, and fully convey the scope of the invention to those skilled in the art.

The present invention is illustrated with the help of a motorcycle. Referring to Figure 2, a motorcycle comprises of a frame (101), front fork (102) attached to a pivot tube (201) of the vehicle frame, a front wheel (103) attached to these front forks (102), a handle bar (104) connected to the front forks (102), a fuel tank (105) attached so as to straddle an upper part of the vehicle frame, a seat (106) attached to the upper rear portion of the vehicle frame, a power pack having a internal combustion engine t (107) attached to the lower front section of the vehicle frame, a swing arm (108) attached to a lower rear section of the vehicle frame, suspended by a rear shock absorber (not shown) from the vehicle frame and a rear wheel attached to a rear end of swing arm (108). The intake system of the engine comprises of a fuel air metering device such as a carburettor (109), 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 (110) for covering an upper part of the front wheel (103), and a rear fender (111) for covering an upper part of the rear wheel (112). The drive from the engine (107) is transmitted from the engine to the driven wheel sprocket mounted on the rear wheel hub mounted on the rear wheel assembly. The magneto assembly (not shown in Figure 1) of the present invention is housed on the left side inside the engine (107)

Referring to Figure 3 the said magneto assembly with outer rotor (380) comprises at least one slot (370). The said slot (370) is located such that trailing edge (374) of slot (370) is located close to the variable reluctance sensor (360). The depth of the said slot (370) is calculated based on the air-gap distance between magneto rotor (380) outer periphery and sensor (360), the rotor yoke thickness and rotor (310) permanent magnet characteristics.

During rotation of the magneto rotor (310), the magnetic field created by permanent magnet (340) changes during passage of slot (370) edges (372) and (374). The change in magnetic field produces a voltage across the coil (330). The variable reluctance sensor signal (390) with the magneto rotor (380) is also indicative of the crankshaft position.
Since additional reluctors on the outer periphery of magneto rotor are not required, the associated material cost and manufacturing cost are reduced. Additional slots can be added to increase the resolution of crankshaft position information. Hall Effect sensor can also be used in place of variable reluctance sensor (360). The shape of the slot can be chosen to minimize cost and manufacturing complexity. Although a rectangular cross-section is preferred, a circular or irregular shape with sufficient width and depth will also satisfy the functional requirements. The invention being thus 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 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 claims.

We Claim:

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

Atleast one outer rotor with permanent magnets for synchronously rotating with a crankshaft of the engine;

atleast one inner stator with coils wound to generate alternating voltage based on the rotating magnetic field created by the said rotor permanent magnets;

and

at least a sensor connected with the engine crankcase and located in close proximity to the outer periphery of the said outer rotor for providing a signal indicative of the rotor position;

wherein the said outer rotor is provided with at least one slot on its outer periphery to change the magnetic field created by the said sensor.

2. The magneto assembly as claimed in claim 1, wherein the said slot on the outer periphery of the said outer rotor is preferably in the form of a hole.

3. The magneto assembly as claimed in claim 1, wherein the said sensor is preferably a variable reluctance type sensor.

4. The magneto assembly as claimed in claim1 wherein the said sensor is a Hall Effect sensor.

5. The magneto assembly as claimed in claim in 1, wherein the said slot on the said outer rotor is in close proximity to the said sensor when the piston of said engine is near a top dead centre.

6. A magneto assembly for an internal combustion engine as substantially shown and described in the specification.