DESC:FIELD OF INVENTION

The invention is related to assembly for sensing rotation of crankshaft/magneto assembly used in an engine, especially mounting arrangement of the sensing assembly including a ring magnet, which is identical to the rotor of the magneto, and a sensing element. It may be used for applications like rpm sensing, crank position sensing, commutation of magneto assembly. The magneto assembly may function as a generator or a starter or an integrated starter generator.

BACKGROUND AND PRIOR ARTS

A magneto assembly is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. In case of automobile engines, the magneto assembly is used for generating the energy required for a spark plug. The magneto assembly comprises two essential components namely a stator and a rotor. Conventionally, in case of the magneto assembly used in the automobile engines, the stator consists of a wire coil wrapped around a stator core. There are two types of coils in the stator, a primary coil wound around the core and a secondary coil wound around the primary coil. The rotor of the magneto consists of a strong permanent magnet. The rotor is connected with the crankshaft and rotates with the crankshaft.
While operating/ driving the magneto assembly, it is necessary to accurately detect the position of poles of the rotor, so that appropriate phase of the multi-phase (usually three-phase) stator can be energized at the appropriate instant. This ensures precision in driving control of the magneto assembly. Therefore, a set of identical Hall-effect sensors are mounted adjacent to the poles of the rotor, which generate signals with the passage of each pole of the rotor. These signals are processed by the control unit and used to time the activation of the stator’s phases. Conventionally, such a group of sensors is assembled in a casing, which is mounted either radially or axially in the magneto’s vicinity in the outer periphery of the rotor, on a magneto cover, or even on or inside the stator in some cases.

Generally, the sensor assembly is incorporated in the magneto assembly or in the vicinity of magneto assembly. However space availability is a constraint at this location and packaging of the sensors is difficult. This would lead to creating a bigger stator. Such a design can be seen in Japanese patent JP05390836B2. In a vehicle like a motorcycle, a scooter or a three-wheeler, where economy of space is a major issue while mounting components, the above configuration increases the size of the magneto assembly in either radial or axial direction. When the sensor assembly is mounted on the stator axially with respect to the rotor, it may lead to increase in length of the crankshaft.

Similarly, when the sensor assembly is mounted radially between the stator and the rotor, it is required to increase rotor size in radial direction, which in turn, increases overall size and weight of the magneto assembly.
It is obvious that the sensor assembly shown in the prior art is mounted in a high temperature region created due to the heat generated in the stator. Semiconductor type sensors can get affected by exposure to high temperature. Consistent high temperatures would affect life and accuracy of sensors. This would necessitate use of heat-resistant sensors and material of their mounting / packaging arrangement, which would add to the costs.
Hence, in order to achieve compactness and to have low-cost sensor assembly components, it was proposed to have a ring shaped magnet assembly, which is a miniature simulation of the rotor of the magneto, mounted outside the magneto assembly, alongwith the sensor assembly.
In known design, a similar ring magnet which is mounted outside the magneto assembly on the crankshaft. However, its position on the crankshaft is in proximity of the magneto assembly. This position being close to the magneto assembly is also in a high-temperature zone. Therefore, external cooling, using air sucked by a centrifugal fan is required. This centrifugal fan is operated coaxially with the crankshaft. It sucks in air from a hole / aperture at the cover. Drilling a hole in the cover adds to the machining time. Also, some energy is consumed in driving the fan. Thus, a separate arrangement for cooling the sensor assembly is required here.
OBJECTIVES OF THE INVENTION
To provide a solution for the mounting arrangement of a magneto position sensing assembly comprising a magnet ring and a sensor assembly.
To provide a solution for the mounting arrangement of a magneto position sensing assembly which serves for detecting pole position of the magneto’s rotor and also for detecting pulse signal representing crank position and RPM of crankshaft.
To provide a solution for the mounting arrangement of a magneto position sensing assembly where the sensor assembly is not subjected to higher temperatures.
To provide a solution for the mounting arrangement of a magneto position sensing assembly where high-temperature-resistant components are not required.
To provide a solution for the mounting arrangement of a magneto position sensing assembly that is economical.
To provide a solution for the mounting arrangement of a magneto position sensing assembly where external/forced cooling of the sensing assembly is not required.
To provide a solution for the mounting arrangement of a magneto position sensing assembly that is simple is construction and assembly as compared to prior arts.
SUMMARY OF INVENTION
A magneto position sensing assembly has a ring magnet which has plurality of north south poles, said ring magnet is mounted on the crankshaft of the engine. The rotation of this ring magnet, rotating at the same RPM as that of the crankshaft and rotor of magneto assembly, is sensed by plurality of sensors. Said sensors are preferably mounted on crankcase, which is stationary relative to the rotating crankshaft. The signals generated by the sensors are processed by the control unit for rotor pole position sensing and RPM sensing for torque control or any other application in an engine.
First aspect of this invention is that the ring magnet and sensors are mounted on a side of the crankshaft which is opposite to the side on which the magneto assembly is mounted. It may be adjacent to a clutch which is mounted on the side opposite to where magneto assembly is mounted. Further, the arrangement may also be adopted in clutchless transmission system as well. Such arrangement provides ease of packaging and prevents exposure of the sensor assembly to high temperature. This not only allows a compact magneto design, but also keeps the sensors away from high-heat zone. Thus, allowing use of less costly sensors and assembly components thereof. Further, there is no need of using additional cooling fan.
Another aspect of this invention is that the plurality of sensors comprises of at least three Hall Effect sensors. These three sensors are meant for phase sensing/ detection. A fourth sensor may also be employed for the purpose of generating pulses for ignition or fuel injection timing.
Another aspect of this invention is that the number of poles on the magnet ring is equal to that on the rotor of the magneto. While having equal number of poles ensures accuracy, however the ring magnet having number of poles which is factor of number of poles of the rotor may also serve the purpose. For e.g. If the stator has 18poles, the ring magnet can have 9 or 6 poles.
Yet another aspect of this invention is that the sensors are assembled in a casing to form a sensor assembly and the sensor assembly is mounted on the crankcase. This ensures rigidity of mounting, in addition to maintaining the sensors stationary with respect to the rotating ring magnet. The sensor casing may face the magnets on the ring magnet radially or axially, depending upon availability of space in a particular engine assembly configuration. Accordingly, the magnets of the ring magnet may be radially or axially magnetized.

In yet another embodiment, the ring magnet may be made integral with any engine part which rotates as same speed as that of crankshaft. The said engine part can be an inner race of a bearing mounted on the crankshaft.

The magneto assembly described in above embodiments may function as a generator or a starter or an integrated starter generator.

BRIEF DESCRIPTION OF DRAWINGS

REFERENCE NUMBER TABLE

No. Feature
2 Crankshaft assembly
4 Magneto
6 Clutch assembly
8 Crankshaft
10 Ring magnet
12a Sensor mounted along radial direction with respect to the ring magnet
12b Sensor mounted along axial direction with respect to the ring magnet
14a Sensor mounting bracket for 12a sensor
14b Sensor mounting bracket for 12b sensor
16 Grommet assembly
18 Ring magnet housing
22 Crankcase

Figure 1A shows a crankshaft assembly with magneto, clutch, ring magnet and sensor mounted on crankshaft.
Figure 1B shows a crankshaft assembly with magneto, ring magnet and sensor mounted on crankshaft and clutch is mounted on another shaft.
Figure 2A and 2B shows a view of a crankshaft with position sensing assembly, where sensor assembly mounted radially with respect to the ring magnet.
Figure 3A and 3B shows a view of a crankshaft with position sensing assembly, where sensor assembly mounted axially with respect to the ring magnet.
Figure 4A and 4B shows a view of a crankshaft with position sensing assembly, where sensor assembly mounted radially and axially with respect to the ring magnet.
Figure5A and 5B shows a detailed view of the ring magnet with the sensor mounted axially with respect to the ring magnet.
Figure 6A and 6B shows a detailed view of mounting of radially arranged sensor assembly on the crankcase.
Figure 6C shows a detailed view of the ring magnet with the sensor mounted radially with respect to the ring magnet.
Figure 7 shows a detailed view of the ring magnet.

DETAILED DESCRIPTION

Figure 1Aand 1B shows a crankshaft assembly (2) along with a magnet ring and a sensor assembly according to one of the embodiments of the invention. The crankshaft assembly comprises a crankshaft (8) driven by the power provided from an engine. In first aspect of the invention as shown in figure 1A, on one end of the crankshaft (8), a clutch assembly (6) is provided for engaging and disengaging power transmitted to the engine transmission. On other end of the crankshaft (8), a magneto (4) is provided. In yet another aspect of the invention as shown in figure 1B, a magneto (4) is provided on the crankshaft (8) whereas the clutch assembly (6) is mounted on another shaft parallel to the crankshaft (8). The crankshaft (8) is connected to another shaft for e.g. through a chain drive. The clutch assembly (6) enables engagement and disengagement of power between crankshaft and another shaft.

The magneto (4) comprises a rotor which rotates along with the crankshaft and a stator which encircles the rotor. The magneto assembly may function as a generator or a starter or an integrated starter generator. It is essential to detect the poles of the rotor precisely so as to energize the stator at appropriate time. To achieve this generally the magneto is provided with a sensor assembly mounted radially or axially with respect to crankshaft.

Referring to figure 1A to 7, a magneto position sensing assembly is provided with a ring magnet (10) mounted on the crankshaft. The ring magnet has identical N-S poles as that of the rotor of the magneto (4) so that while rotation of the rotor along with the crankshaft, the ring magnet will replicate exactly the same rotation as that of the rotor of the magneto. Further, a plurality of sensors(12a, 12b) is provided near the ring magnet (10) to sense the rotation of the ring magnet (10). The sensors (12a, 12b)are assembled in a casing to form a sensor assembly.

The ring magnet (10) and the sensors (12a, 12b) are positioned on a side of the crankshaft which is opposite to the side on which the magneto (4) is mounted. It may be adjacent to the clutch assembly (6) which is mounted on the side opposite to where magneto assembly (4) is mounted. As space available on magneto side is less, mounting of ring magnet (10) and sensors(12a, 12b) on side opposite to the magneto (4) facilitates packaging. Such arrangement of the ring magnet (10) and the sensors(12a, 12b) facilitates compact magneto design. When the magneto (4) operates, a lot of heat is generated which creates a high heat region around the magneto (4). Semiconductor type sensors are sensitive to heat. Positioning of the ring magnet (10) and the sensors(12a, 12b) on the side opposite to where magneto assembly (4) helps to prevent the exposure of the sensors(12a, 12b) to the high heat region. This increases a durability of the sensors(12a, 12b). Further, it also enables to use sensor assembly components such as casing, mounting bracket, etc. which are not heat resistant and usually cheaper.

In one of the aspects of the invention as shown in figure 2A and 2B, only sensors (12a) mounted in radial direction with respect to the ring magnet (10) is provided. The sensors (12a) mounted in radial direction with respect to the ring magnet (10), comprises three Hall effect sensors. The Hall effect sensors help to detect the phase change which can be used to determine crankshaft position.

In another aspect of the invention as shown in figure 3A and 3B, only sensor (12b) mounted in axial direction with respect to the ring magnet (10) is provided. The sensor (12b) tracks the rotation of the ring magnet (10). During each revolution of the ring magnet, a pulse is generated by the sensor (12b) which is equivalent to the one revolution of the ring magnet. The pulse signal represents the crank position and RPM of the crankshaft. As the RPMs of the ring magnet are equivalent to the RPMs of the crankshaft, measured RPMs are equivalent to the RPMs of the crankshaft.

In yet another aspect of the invention as shown in figure 4A and 4B, the sensors (12a) are mounted in radial reaction with respect to the ring magnet (10) and a sensors(12b) mounted in axial direction with respect to ring magnet (10). The sensors (12a) mounted in radial direction with respect to the ring magnet (10), comprises three Hall effect sensors. The Hall effect sensors help to detect the phase change which can be used to determine crankshaft position. Further, the sensors(12b) mounted in axial direction with respect to ring magnet (10) is provided for crankshaft RPM measurement. The sensor (12b) generates a pulse during each revolution of the crankshaft (8). The pulse signal represents the crank position and RPM of the crankshaft. The signals generated by the sensors (12a, 12b) are sent to a control unit (not shown) which calculates the position of the rotor with reference to the crankshaft as well as calculate the RPM of the crankshaft/ engine. Inputs with respect to crankshaft position and RPM are used by engine management systems to control ignition system timing, torque control and other engine parameters.

Referring to figure 5A to 7, the ring magnet (10)mounted within a ring magnet housing (18). The sensors(12a, 12b) are provided with a sensor casing and a sensor mounting bracket (14a, 14b).As shown in figure 6A and 6B, the sensors are mounted on the crankcase(22) using the sensor mounting bracket such that the sensors remain stationary with respect to the ring magnet (10). Mounting of the sensors (12a, 12b) on the crankcase (22) ensure rigidity of mounting.

Further, the sensor assembly is also provided with grommet assembly(16)for the passage of various cables that connect the sensors(12a, 12b)to the engine control system. The sensors may face the magnets on the ring magnet radially or axially, depending upon availability of space in a particular engine assembly configuration. Accordingly, the magnets of the ring magnet may be radially or axially magnetized.

The ring magnet (10) is provided with same number of N-S poles as that of the rotor of the magneto. Having same number of poles as that of the rotor ensures maximum accuracy. However, the ring magnet having number of poles which is factor of number of poles of the rotor may also serve the purpose. For e.g. If the stator has 18 poles, the ring magnet can have 9 or 6 poles. However, lower number of poles on the ring magnet may lead to lower precision.

The present invention would be applicable to various types of sensors that may be used to detecting crankshaft position or RPM. Further, the arrangement proposed in the invention may also be adopted in clutchless transmission systems.

It is understood that variations and modifications to the preferred embodiment will be apparent to those skilled in the art without departing the scope and the spirit of the present invention. The applicant also relies on the provisional specification and drawings annexed to the provisional specification in support of this specification. The scope of the present invention is to be determined by the following claims.
,CLAIMS:1. A magneto position sensing assembly comprises a ring magnet (10)having plurality of north south poles mounted on a crankshaft (2); and plurality of sensors(12a, 12b) to sense the rotation of the ring magnet (10); wherein the ring magnet (10) and the sensors(12a, 12b)are mounted on a side of the crankshaft (2) which is opposite to the side on which a magneto (4) is mounted.

2. The magneto position sensing assembly according to claim 1 wherein the ring magnet (10) and the sensors (12a, 12b) are mounted adjacent to a clutch (6).

3. The magneto position sensing assembly according to claim 1 wherein the sensors (12a, 12b) employed for phase sensing and detection.

4. The magneto position sensing assembly according to claim 1 wherein the sensors (12a, 12b) employed for the purpose of generating pulses for ignition or fuel injection timing.

5. The magneto position sensing assembly according to claim 3 or 4 wherein the sensors(12a, 12b) employed for phase sensing, detection and generating pulses for ignition or fuel injection timing.

6. The magneto position sensing assembly according to any of the preceding claims wherein the sensors (12a, 12b) are Hall Effect sensors.

7. The magneto position sensing assembly according to claim 1 wherein number of poles of ring magnet (10) is factor of number of poles of the rotor.

8. The magneto position sensing assembly according to claim 1 wherein number of poles of ring magnet (10) is equal to number of poles of the rotor.

9. The magneto position sensing assembly according to claim 1 wherein the sensors (12a, 12b) are assembled in a casing forming a sensor assembly provided with a mounting bracket (14a, 14b) and the sensor assembly is mounted on the crankcase (22).

10. The magneto position sensing assembly according to claim 8 wherein the sensors (12a, 12b) facing the ring magnet (10) radially or axially.

11. The magneto position sensing assembly according to claim 1 wherein the ring magnet (10) is magnetized radially or axially.

12. The magneto position sensing assembly according to claim 1 wherein the ring magnet (10) is made integral with any engine part such as an inner race of a bearing mounted on the crankshaft (2).

13. The magneto position sensing assembly according to claim 1 wherein the magneto may function as a generator or a starter or an integrated starter generator.