FORM-2
THE PATENTS ACT, 1970
( 39 of 1970 )
fR©VKt©IWt/COMPLETE
SPECIFICATION
SECTION 10


TITBE
" A N" IMPROVES©*? H* IGNITION SYSTEM ft)R 2 OR 3 WHEELED VEHICLES
APPLICANT
BAJAJ AUTO LIMITED, of Akurdi, Pune 411 035, State of Maharashtra, India, an Indian Company.

?

IMPROVEMENT IN IGNITION SYSTEM OF 2 OR 3 WHEELED VEHICLES
This invention relates to an improved ignition system for 2 or 3 wheeled vehicles. This mventionTrelates to improvement in ignition system used for providing spark for igniting the air-fuel mixture in engines used in 2 or 3 wheeled vehicles. This invention particularly relates to the ignition system employing igniter. For the simplicity of the explanation, such vehicles are termed as 'vehicles' in this patent application.
In the engines used in these vehicles, the mixture of air and fuel, commonly called as charge, is ignited in the combustion chamber at predetermined time with the help of a spark produced at the tip of the spark plug. The electrical energy for providing the spark is generated by magneto. The instant at which the spark is produced in combustion chamber is controlled by the electrical components comprising of the magnetic pick-up coil in the magneto, ignition coil (HT coil), igniter, etc. The spark needs to be produced at the instant, which produces optimum power. In general, this instant necessarily should be such that after initiation of the spark, peak pressure of the charge inside combustion chamber takes place at the instant when the piston just crosses top dead center position. In common terms, this instant is known as ignition timing of the engine. The ignition timing is dependant on the design characteristic of the engine like cylinder volume, power out put desired at various speeds, design of the combustion chamber and so on. Engine performance parameters like emissions, fuel efficiency, power, torque etc. depend very much on this ignition timing. In order to improve the performance of engine, it is well established that variable ignition timing helps to a large extent. In known designs of the ignition system, various means of varying the ignition timing are employed. The ignition timing is varied by combination of signals of engine RPM and signals of position of throttle opening by an Optical or Sliding Switch or micro switch or potentio metric provided on RH side of handle bar or a suitable other location. This type of arrangement is hereinafter referred to as Throttle Position Sensor. The ignition system of the vehicles is very well known to the people and does not need further detailed explanation.
The above mentioned known systems of varying the ignition timing through Throttle Position Sensor have some disadvantages as mentioned below.
One of the disadvantages of the known system of variable ignition timing using the Throttle Position Sensor is that if the dust or any particle falls in the path of sensing, the system malfunctions.
Yet another disadvantage of the known system is that in case of short circuit in the system, the Throttle Position Sensor can get permanently damaged and the system malfunctions.
Yet another disadvantage of the known system is that in case of any stray lights/ reflection from any object containing the infrared content may lead to malfunction of the system.
Yet another disadvantage of the known system is that in case of Sliding Switch or micro switch or potentio metric type of sensing, due to constant wear and tear, the contacts wear out and the system fails.
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In order to avoid above difficulties, we have designed an improved ignition system, which uses Magnetic Throttle Position Sensor.
One of the objectives of the improved ignition system using the
Magnetic Throttle Position Sensor is that if the dust or any
particle falls in the path of sensing the system still operates
properly«
Yet another objectives of the improved ignition system using the Magnetic Throttle Position Sensor is that in case of short circuits in the power source of the ignition system, the Throttle Position Sensor is not affected permanently and system function properly once the short circuit is removed.
Yet another objectives of the improved ignition system using the
Magnetic Throttle Position Sensor is that in case of any stray
lights/reflection from any object containing the infrared
content, there is no effect on the system.
Yet another objectives of the improved ignition system using the Magnetic Throttle Position Sensor is to improve the reliability/life of the sensor considerably by eliminating sliding contact for sensing.
The invention provides an improved ignition system for 2 or 3 wheeled vehicles comprising a magneto, an igniter, a magnetic-pulsar coil, an ignition coil, a magnetic throttle position sensor arranged to work in sequence for generating spark at the tip of a spark plug, said magneto being capable of generating electrical energy required to start said igniter, said magnetic pulsar coil being inductive type sensor capable of sensing engine speed generates the electrical energy required to start the igniter (2). Magnetic pulsar coil <3) , which is inductive type sensor senses engine speed (RPM) and sends signal to the igniter <2>. The igniter provides the required outputfor ignition-timing angle as per the speed of the vehicle engine RPM and engine load condition sensed by the throttle position sensor (6). Ignition coil (4) generates the high voltage required to provide spark at the tip of the spark plug (5) to ignite the charge in the combustion chamber at the time determined by igniter <2>.
Fig. 2 illustrates a block diagram of the improved ignition system as per the invention. In this system, magneto (1) generates the electrical energy required to start the igniter (2). Magnetic pulsar coil (3), which is inductive type sensor senses engine speed (RPM) and sends signal to the igniter <2). The igniter provides the required output for ignition-timing angle as per the speed of the vehicle engine RPM and engine load condition sensed by the magnetic throttle position sensor (7). Ignition coil (4) generates the high voltage required to provide spark at the tip of the spark plug (5) to ignite the charge in the combustion chamber at the time determined by igniter (2).
In the improved ignition system as per the invention, the igniter (2) gets signals not only about the engine RPM, but also gets, engine load data in the form of throttle position through the Magnetic Throttle Position Sensor (7) as shown in Figure 2.
The Magnetic Throttle Position Sensor (MTPB) (7) as mounted on chassis or similar part of vehicle employed in ignition system as per the invention essentially comprises of reed switch assembly is assembled on holder magnet assembly <11>. JThe Reed Switch ^ Assembly (8) assembled on„Jao.l_der for reed swijbchZgJLJSMj 1 y1' (!£*>■* "» YfilTHTolder Magnet Assembly (11) is rot ably assembled on^p^fw447) , which is welded, to Holder reed switch Assembly (10) an^*w^}in position by the spring (14), Washer (13) and Circlip (I "2 > .""""On © lug of the spring (14) engages with holder magnet Assembly (11) and the another lug is connected to holder reed switch Assembly (10). The dimensional aspects of the complete system are so designed to maintain a predetermined radial gap between magnet Assembly (9) and reed switch Assembly (S). 0~ring (15) and (16) are provided to prevent external dust from going between rotational assembly including holder magnet assembly (11). The bolder magnet Assembly (11) is welded to throttle plate (IS), which is provided with a hold to assemble the throttle cable (20) through cable adjuster (19). When the throttle is fully closed, the angular relationship between the reed switch Assembly (8) and magnet Assembly (9) is maintained at predetermined angle (01). When the throttle is rotated by a predetermined angle (02) the edge of the magnet Assembly (9) goes out of center axis (c) of reecj ©witch Assembly (8). The throttle cable (20) is s branch of the main throttle cable (not shown) in which the other branch is assembled to the carburetor (not shown) in a conventional manner. The signal cables (not shown) of the magnetic throttle position •sensor (7) is connected to the igniter Assembly (2).
With reference to fig.3, the diagram shows two typical ignition timing graphs engine speed vs. ignition timing. The map MAPI represents ignition timing with the magnet Assembly (9) and reed Bwitch Assembly (8) are in 01 position as illustrated in fig 4B. The map MAP2 represents ignition timing when the magnet Assembly (9) and reed switch Assembly (S) are greater than 02 position as illustrated in fig.4C.
When the throttle is fully closed i.e. the 01 position, (i.e. position A mentioned in figure 4A,4B and 4C where the resistance between the leaves of the reed switch assembly (S) is zero) the magnetic throttle position sensor's (7) output is "in closed condition and the igniter (2) outputs the MAP 1 graph of ignition timing. When the edge of the magnet Assembly (9) is just above the central axis of the reed switch Assembly (8) i.e. greater than 02 position (i.e. position A mentioned in figure 4A, 4B and 4C where the resistance between the leaves of the reed ©witch assembly (8) is infinite), the magnetic throttle position sensors' (7) output gets opened and the igniter (2) outputs the MAP 2 graph of ignition timing.
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Embodiment:-
The description and the illustrations given above are for Magnetic Throttle Position Sensor (MTPS) mounted on the chassis or any other suitable vehicle part and operated through a branch of the main throttle cable assembly snd the other branch i, carburettor body (30), throttle shaft assembly (25), spring (27), screws (32) and switch bracket assembly (29).
The Magnet Assembly (33) is assembled snugly on to the throttle shaft assembly (25) of the carburettor. The lug (26) of the throttle shaft assembly (25) ensure retention of magnet assembly (33) in place. The throttle cable is connected to hole in the throttle shaft assembly (25), The reed switch assembly (34) is snugly fitted on to reed switch holder assembly (28), which is fastened to the carburettor body (30) using 2* screws (32). One lug of the spring (27) engages with carburettor body (30) and the another lug is connected to throttle shaft assembly (26). Here, also the lugs of the reed switch bracket assembly (29) retain the reed switch assembly (34) is place. The shape of the reed switch bracket assembly (29) and the throttle shaft assembly (25) is so designed that at idling condition, there is a predetermined angular relationship (0.1) between reed switch assembly (34) and magnet Assembly (33). While opening the throttle through the throttle cable (3.1), the magnet assembly (33) rotates along with throttle shaft assembly (25). Also after predetermined angular position 02, the edge of the magnet assembly goes out of the central axis of reed switch assembly.

Basic function of the MTPS mounted directly on the carburettor is same as explained to with reference to MTPS as shown in Figure 4A, 4B and 4C.
Yet another method of mounting of the Magnetic Throttle Position Sensor (MTPS) is the magnet assembly can be slided over reed switch assembly in a linear fashion instead of angular positions explained above.
WE CLAIM:
1. An improved ignition system for 2 or 3 wheeled vehicles comprising a magneto (1), an igniter (2), a magnetic pulsar coil (3), an ignition coil (4), a magnetic throttle position sensor (7) arranged to work in sequence for generating spark at the tip of a spark plug (5), said magneto (1) being capable of generating electrical energy required to start said igniter (2), said magnetic pulsar coil (3) being inductive type sensor capable of sensing engine speed (RPM) and sends sending signals to said igniter (2). which being capable of providing the required output for adjusting ignition-timing angle as per the speed of the engine RPM and engine load condition sensed by said magnetic throttle position sensor (7); said igniter coil (4) being capable of generating high voltage required to provide spark at the tip of said spark plug (5) to ignite the charge contained in the combustion chamber at a predetermined time selected by said igniter (2)/
2. An improved ignition system as claimed in claim 1 wherein said magnetic throttle position sensor (7) essentially comprises a reed switch assembly (8), a magnet assembly (9), and a first holder (10) for said reed switch assembly, a second holder (11) for said magnet assembly, a circlip (12), a washer (131a torsion spring (14), a pair of O-rings (15 and 16), a pin (17), a throttle plate (18),(a£)feable adjuster (19) and a throttle cable (20); the said sensor being mounted on chassis or similar part of the vehicle.
3. An improved ignition system as claimed in claim 1 or 2 wherein said magnet assembly assembly (9) is assembled on a holder (11) and said reed switch assembly (8) assembled on a holder (10); said holder for magnet assembly (11) is^raMJy^ assembled on said holder for reed switch assembly; said pin (17) is welded on said reed switch assembly holder (10); said magnet assembly holder (11) being integral with throttle plate (18) provided with a hole to assemble throttle cable (20) through cable adjuster (19) is mounted on said pin (17) and held in position by a torsion spring (14), washer (13) and a circlip (12); one lug of the torsion spring (14) is connected to magnet assembly holder (11) and the other lug is connected to said reed switch assembly holder (10); said pin (17) is so designed and located as to maintain a predetermined gap between said magnet assembly (9) and a reed switch assembly (8), a pair of O-rings (15 and 16) is adapted to prevent the entry of external dust between the rotational assembly and of the magnet assembly holder (11).
4. An improved ignition system as claimed in claim 1 to 3 wherein said throttle cable (20) is a branch of main throttle cable, the other branch being connected to carburettor.
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5. In improved igmtion system as claimed in claim 1 wherein said magnetic throttle position sensor essentially comprises a magnet assembly (33), a reed switch assembly (34), a reed switch holder assembly (28), a carburettor body (30), a throttle shaft assembly (25) with lug (26), a spring (27), screws (32) and a reed switch bracket assembly (29), throttle cable (31), said sensor is mounted on the carburettor of the vehicle employed. 6 An improved ignition system as claimed in claim 1 and 5 wherein said magnet assembly (33) is assembled to a throttle shaft assembly (25) with lug (26) and said reed switch assembly (34) is fixed to reed switch holder assembly (28); and said reed switch holder assembly (28) is fixed to carburettor body (30) through reed switch bracket assembly (29) with the help of screw (32); one lug of the spring (27) engages with carburettor body (30) and the another lug is connected to throttle shaft assembly (26); the said throttle shaft assembly (25) being operable by a throttle cable (31).
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7. An improved ignition system as claimed in any of the preceding claims, wherein the angular relationship and radial gap between the reed switch assembly (8) or (34) and magnet assembly (9) or (33) is maintained at a predetermined angle and value respectively, when the throttle is fully closed.
8. An improved ignition system as claimed in the preceding claims, the edge of the magnet assembly (9) or (33) is so located that it goes out of eentef central axis (C) of reed switch assembly (8) or (34) respectively, when the throttle is rotated by a predetermined angle.
9. An improved ignition system for 2 or 3 wheeled vehicle substantially as herein described and as illustrated in the drawings accompanying this complete Specification.