FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
PROVISIONAL SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Engine Safety Control Switch Circuit
INVENTOR
Name : Nationality : AddressAPPLICANTS Hole Rajendra BhikobaIndian NationalBajaj Auto Limited, Akurdi, Pune 411035,Maharashtra, India
Name : Nationality : Address : Bajaj Auto Limited Indian Company Akurdi, Pune 411035, Maharashtra, India

The following specification particularly describes the invention


>149

2005

7 DEC 2005

This invention relates to an engine safety control switch circuit.
Vehicles incorporate safety control switches, such as stop switches, to enable rapid stopping of an engine under emergency conditions. The engine stop switch is connected in the ignition circuit of the engine. These circuits are typically of the capacitive discharge ignition kind. In such a circuit, the engine stop switch has to handle a high voltage emanating from a component such as the exciter coil of the capacitive discharge ignition circuit. The voltage it handles is dependent on engine speed and ranges from about 150V to about 320V, a high voltage range.
Such stop switches are mechanical type engine stop switches which have a movable contact operated by a switch knob and fixed contacts which rub together when brought into contact to perform intended operation of the switch due to passage of AC or DC current through the closed contact point between the moveable and fixed contacts. In the case of two or three wheel vehicles, stop switches are located on vehicle parts such as the handle bar, the steering tube, the panel board or other positions of the vehicle. In positions such as the handlebar, the switch may be exposed to water, dust and dirt as sealing of such switches from the external environment is difficult. Such ingress of water, dust and dirt to the switch terminals may cause intermittent or complete malfunctioning of the switch due to the effects of short circuiting of the contacts. Where water is concerned, the entry of water into the control switch may cause electrical shock to the operator of the vehicle when the operator operates the switch. This is a hazardous situation. However, such ingress of water will not generally cause a complete loss of engine function.
While the stop switch could, in theory, be located so as to operate at a relatively lower voltage range, for example in the pulser coil circuit, from 20V to 60V, in comparison to the voltage range of the exciter coil (thus avoiding the electrical shock issue), this may also raise the difficulty of voltage drop and sudden stoppage of the engine in the case of ingress of water, dust or dirt into the switch terminal during vehicle operation. This, again, is a safety
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hazard so location of the mechanical stop switch is in the high voltage exciter coil circuit. Location of a safety control switch in the low voltage circuit is therefore avoided.
It is an object of the present invention to address the safety hazards that may be induced with prior art engine safety control switch circuits such as incorporate mechanical engine control switches. More particularly, the present invention aims to maintain operability of the engine control switch circuit and safety of a vehicle and vehicle operator even when exposed to foreign matter such as water, dust or dirt.
With this object in view, the present invention provides an engine safety control switch
circuit for a vehicle comprising:
a capacitive discharge ignition circuit having a high voltage circuit including an exciter coil
and a low voltage circuit including a pulser coil for triggering operation of an ignition means
of the vehicle ; and
a safety control switch of non-contact type for controlling operation of the engine;
wherein the safety control switch of non-contact type is connected in the low voltage circuit.
The pulser circuit may include a pulser coil and the safety control switch may
advantageously be connected in parallel to the pulser coil thereby grounding the pulser coil
and prevent an ignition triggering event.
The engine safety control switch is, most conveniently, an engine stop or kill switch which, when operated, leads to rapid stopping of the engine through deactivation of the pulser circuit, causing ignition triggering to cease and thus engine operation. If water, for example, enters the switch, the operator will not suffer electric shock of the severity expected where the stop switch is connected to handle a high voltage emanating from the exciter coil. The operator is protected because of the lower voltage of the pulser circuit to which the engine stop switch is connected, it being recalled that a typical voltage range of operation of the pulser circuit is a low 20V to 60V in comparison to the high 150V to 320V range of operation of the exciter coil. Put another way, the operating voltage-engine speed characteristic for the low voltage safety control switch always has lesser voltage value than
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the operating voltage-engine speed characteristic for the high voltage safety control switch for a given engine speed.
Any engine safety control switch of non-contact type may be employed in the engine safety control switch of the invention. In a switch of non-contact type, there is no exposure of the electrical switch path to the external environment. A particularly preferred switch is a reed switch. The reed switch may be selected to be a low capacity reed switch because of the low voltage of the pulser coil circuit. Such reed switches are of relatively low cost. The reed switch closes the low voltage circuit when a magnetic means such as a magnet or inductive coil, forming part of the switch, is moved to a predetermined position by actuation of a knob of the switch by the engine operator. As the magnetic flux is readily able to pass through non-ferromagnetic materials (such as plastic) a magnet brought into close proximity of a reed switch will be able to activate such switch even if the reeds are hermetically sealed to prevent the ingress of water or other foreign matter. The reed switch may be disconnected by moving the magnetic means away from the predetermined position, for example by the same knob mentioned earlier. Such a reed switch is resistant to the wear and tear and entry of water and dust that is so problematic with a mechanical type stop switch.
The reed switch may include contacts actuated by an inductive coil wrapped over the reed switch, the coil being energised/de-energised by a magnet located in the switch. Again, such a switch can be encased in a hermetically sealed container and remotely operated through action of the magnetic flux.
Engine safety control switch circuits according to the present invention may advantageously be used in two or three wheel vehicles though the invention may be applied to other situations.
The engine safety control switch circuit of the present invention may be more fully understood from the following non-limiting description of preferred embodiments thereof made with reference to the drawings in which:
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Figure 1 is a circuit diagram of a prior art ignition system incorporating a mechanical engine stop switch.
Figure 2 shows construction of a prior art mechanical engine stop switch indicating fixed and moveable contacts.
Figure 3 shows a prior art mechanical engine stop switch located on a handlebar of a two wheel vehicle for stopping of operation of that vehicle.
Figure 4 is a side sectional view of an engine stop switch included in an engine safety control switch circuit in accordance with a first aspect of the invention.
Figure 5 is an isometric view of the engine stop switch of Figure 4.
Figure 6 is a circuit diagram of the engine safety control switch circuit of the first aspect of the invention including the engine stop switch shown in Figures 4 and 5, the engine stop switch being in an OFF position.
Figure 7 is a circuit diagram of the engine safety control switch circuit of Figure 6 but having the engine stop switch in an ON position.
Figure 8 illustrates comparative graphs of engine speed (rpm) versus voltage for engine stop switches located in engine safety control switch circuits operated in accordance with the invention and the prior art.
Figure 9 is a circuit diagram of a circuit in accordance with a second aspect of the invention in which electric starter and engine stop switch are combined in a single switch.
Referring now to Figure 1, the engine ignition system circuit of a two wheel vehicle, such as a motorcycle or scooter, includes an engine safety control switch or stop switch S positioned in a capacitive discharge ignition (CDI) circuit and CDI assembly for operating an ignition
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means or spark plug of the engine. Switch S is located proximate the exciter coil which operates at a high voltage so switch S is also operable at high voltage. Stop switch S is located in a convenient accessible position for the rider of the motorcycle, namely the handlebar 40 as shown conveniently in Figure 3.
As shown in Figure 2, mechanical stop switch S comprises a body PI on which a knob P2 is pivoted at location P3. Body PI is provided with two fixed contacts P4 and P5. The movable contact P6 of the stop switch is also assembled on the knob P2. When the engine is not running, the knob P2 of the stop switch S is located in an OFF position and the moveable contact P6 connects both the fixed contacts P4 and P5. When the knob P2 is actuated to the ON position, the moveable contact P6 separates the fixed contacts P4 and P5 enabling the motorcycle engine to run. Such a stop switch S is prone to ingress of dust and water and constant wear and tear during operation. If water or other foreign matter enters the engine stop switch and the rider attempts to operate it, there is a real risk of electric shock because of the high voltage at the location of stop switch S. This compounds the hazards of an emergency situation that requires urgent stopping of the engine. Graph A of Figure 8 illustrates that the engine stop switch S, connected in the exciter coil circuit of one motorcycle engine, operates at voltage ranging from 150V to 280 V, a high voltage range. Graph B shows a voltage range of 150V to 310V, again a high voltage range, at the exciter coil of another motorcycle engine.
The engine safety control switch circuit of the invention again includes a high voltage circuit in which is located the exciter coil necessary for the operation of a CDI circuit. However, this circuit - as shown in Figures 6 and 7 - has engine stop switch 15 connected in parallel with the pulser coil of the circuit. The pulser coil controls triggering of the operation of the motorcycle engine ignition means or spark plug. The pulser coil, in contrast to the exciter coil, operates at 20V to 55V, a low voltage. The risk of electric shock to the motorcycle rider when operating the engine stop switch 15 is therefore much reduced compared to the prior art as shown by a comparison of Graphs A and B of Figure 8, showing the high voltage of operation of prior art mechanical engine stop switches connected in the exciter coil circuit, with Graph C for the engine stop switch of non-contact type connected in the low voltage
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pulser coil circuit. It will be observed that the voltage value for Graph C is always lower than a voltage value of Graphs A and B for a given engine speed.
The engine stop switch 15 is a non-contact switch, for example a reed switch 4, having a housing 6 on which is fixed a reed switch housing 10. Reed switch 4 is assembled in the reed switch housing 10 and includes a first contact 12 and a second contact 13. The reed switch 4 rating may be selected according to current carrying capacity and operating voltage appropriate to the application and the function that the reed switch 4 is to perform. Engine stop switch 15 is provided with a pivoted actuating knob 5. Actuating knob 5 includes a cavity 8 accommodating a magnet 9 to provide magnetic flux necessary to allow operation of the engine stop switch 15. Magnet 15 is rigidly fitted in cavity 8.
The locations of the reed switch housing 10 and actuating knob 5 are selected such that a predetermined spacing of housing 10 and knob 5 are maintained at both the ON and OFF positions of the actuating knob 5 of engine stop switch 15. As the fixed and moveable contacts P4, P5 and P6, respectively, of the mechanical engine stop switch of Figures 1 to 3 are replaced with a sealed reed switch 15, resistance to wear and tear and entry of water, dust and dirt, with their concomitant hazards of electric shock when associated with the high voltage environment of the exciter coil, are much increased in the engine safety control switch circuit of the invention.
Operation of the engine safety control switch circuit will now be described with reference to Figures 6 and 7 which include arrows showing the direction of current. In normal running, the engine stop switch 15 need not be activated. The capacitive discharge ignition circuit will operate in the usual manner with the pulser circuit triggering operation of the spark plug on a controlled intermittent basis depending upon the engine operating conditions. Figure 6 shows the circuit with the engine stop switch 15 in the OFF position. However, in an emergency condition where rapid stoppage of the engine is required by the rider of the motorcycle, the rider may depress the actuating knob 5 of the engine stop switch 15 which is thus turned ON. When turned ON, the pulser coil will be grounded and intermittent firing of the spark plug ignition means will be ceased. The engine will rapidly come to a stop.
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Modifications and variations of the engine safety control switch circuit of the invention may be understood and appreciated by the skilled reader of this disclosure. Such modifications and variations are within the scope of the present invention. For example, in known vehicles, separate switches are provided for the engine stop switch and electric start, which are normally in the vicinity of each other. These switches could be combined in a combination switch. The use of a reed switch instead of a mechanical switch facilitates the provision of such a combination electric starter/engine stop switch though a reed switch need not be employed. In such a combination switch, electric start is a function that may be further achieved by further operation of the engine stop switch relative to an ON position. Such a combination switch may have a first position in which the engine stop switch is in an ON position. In a second further position, which may be reached by further pressing the switch against the action of a biasing means such as a spring, electric start of the engine may be achieved. Figure 9 shows an engine safety control switch circuit incorporating such a combination switch which comprises an engine stop position; an engine starter position; an actuation means for moving the switch between the engine stop position and the engine starter position; and a biasing means acting against movement of the actuation means wherein movement of the actuation means against the biasing means causes movement of the switch between the stop position and the engine starter position to stop or start the engine.

(Jose M A)
of Khaitan & Co
Agent for the Applicants
Dated this 2nd day of December 2005
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