Patent Abstract:
This invention relates to a method and system for generating energy/power in a capacitive discharge ignition system, said system comprising at least one charge winding (L) which by means of a fly wheel and via a first rectifier device (D 1 ) charges a charge capacitor (C 1 ) connected to a primary winding (P) of an ignition voltage transformer ( 30 ) in order to provide said primary winding (P) with energy for generation of a spark via a secondary winding (S) of said transformer ( 30 ), wherein a voltage control/switching unit ( 10 ) is arranged to enable output of energy (Out 21 ) from said primary winding (P).

Full Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a system and also a method for generating energy/power in a CDI system, said system comprising at least one charge winding which by means of a fly wheel and via a first rectifier device charges a charge capacitor connected to a primary winding of an ignition voltage transformer in order to provide said primary winding with energy for generation of a spark via a secondary winding of said transformer. 
       PRIOR ART 
       [0002]    Nowadays, various types of ignition systems are known and commonly used on the market, such as capacitive or inductive solutions. Most of those ignition systems have a solution including some kind of battery support, e.g. U.S. Pat. No. 6,557,537 and U.S. Pat. No. 6,082,344, which in some applications strongly can be affected, due to environmentally causes e.g. humidity and temperature, and then have drastic consequences regarding performance and/or reliability. There are also cost, environmental and life time aspects to be considered when using a battery supported solution. 
         [0003]    Ignition systems are known, without the use of battery support, and are also available on the market. However, known such systems all do show one or more disadvantages, seemingly due to accepting compromises regarding functionality to be able to eliminate battery support. It is known to, instead of battery support, use a separate small generator which however presents some disadvantages such as additional cost. Also other solutions are known, for instance, EP0727578, which shows an inductive ignition-system, wherein power is (instead of battery) taken from a primary winding to control ignition timing, i.e. control of the spark advance, but without providing any other functionality that might be desired. Further, the control circuit as such is rather complex and rather inflexible. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    The object of the present invention is to provide an improved system for generating energy/power in a CDI system, which is achieved by means of a system as defined in claim  1 . 
         [0005]    Thanks to the invention a very flexible and cost effective solution is achieved, which may bring along about the same kind of functionality as battery powered systems, but which at the same time eliminates the disadvantages related to battery supported systems. It is to be noted that the solution does not prevent usage of battery support, but as is evident provides the important technical advantage that battery support may be dispensed with. 
         [0006]    Further advantages and aspects of the invention will be evident from the detailed description below. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0007]    The invention will be described in greater detail below with reference to the appended figures, in which: 
           [0008]      FIG. 1  shows a schematic wiring diagram presenting a voltage control/switching unit according to the invention integrated in a typical CDI system wherein several triggering alternatives are depicted, 
           [0009]      FIG. 2  shows in more detail a first alternative, depicted in  FIG. 1 , of an embodiment of the voltage control/switching unit according to the invention described in  FIG. 1 , 
           [0010]      FIG. 3  shows in more detail a second alternative, depicted in  FIG. 1 , of an embodiment of the voltage control/switching unit according to the invention described in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  shows a schematic wiring diagram consisting of a voltage control/switching unit  10  according to the invention integrated in a somewhat simplified form of a typical CDI system. 
         [0012]    A brief description of the typical CDI system used in this example follows. The CDI system comprises of an iron core T 1  provided with four conventionally arranged windings, L, T, P and S, which are magnetised by means of one or several magnets integrated in the flywheel which at the rotation of the flywheel will sweep past the end portions of the iron core T 1 . The variant with several magnets could be used for providing (from a general point of view) a more powerful generator which in addition to the function as ignition voltage generator also could be used for other purposes, for example fuel injection systems or handle heating on chain saws. The relative magnet movement induces a voltage in the windings L, T, P and S according to the following. 
         [0013]    In a so called charge winding L, there is induced a voltage which is used for the spark generation, as such. The charge winding L is via one of its end points  1  connected via rectifier devices D 1  to a charge capacitor C 1 , in which the energy will be stored until the spark will be activated, and to a thyristor Q 1 . The other end point  2  of the winding L is connected to earth. 
         [0014]    A so called trigger winding T is connected with a first end point  7  to earth and a second end point  8  to an input terminal In 11  of an ignition control unit M 1  and delivers to this input terminal information about the position and velocity of the flywheel and preferably also power supply to the control unit M 1 , e.g. to the processor thereof. It could be noted that the control unit M 1  may comprise of an only slightly modified version of a known, conventional control unit. 
         [0015]    The third winding P constitutes the primary winding and the fourth winding S the secondary winding of a transformer  30  for generating ignition voltage to a spark plug SP 1 . The end point  4  of the third winding P as well as the end point  5  of the fourth winding S is connected to earth. 
         [0016]    In a conventional way an output terminal Out 11  on the control unit M 1  is activated when the ignition voltage should be delivered to the spark plug. The switching device (the thyristor) Q 1  having a trigger electrode of which is connected to the output terminal Out 11  creates a current path to earth which results in the connection of the voltage over the capacitor C 1  to the primary winding P. Initially a voltage transient is then generated in the secondary winding S due to the very high voltage derivative in the connection point  12  at the anode of the thyristor Q 1 . Immediately thereafter the state in the transformer  30  changes into a damped self-oscillation in which the energy transits between the inductor P and the capacitor C 1  through the switching device Q 1 . 
         [0017]    The description above is simplified, and it is evident for the skilled person to foresee other both resonant and non-resonant circuits for spark generation without departing from the scope of the invention. 
         [0018]    According to the invention there is a voltage control/switching unit  10 , that controls output of power, at Out 2 l, from the primary winding P which power may be used to drive a device (e.g. a sensor and/or a solenoid) externally of the ignition system. In the embodiment shown in  FIG. 1  the voltage control/switching unit  10  is shown to have two input terminals In 21  and In 22  and one output terminal Out 21 . A first input terminal In 22  is connected to the output terminal In 12  on ignition control unit M 1 , and the second input terminal In 21  is connected to the capacitor C 1  and to the end  3  of the primary winding P via a connection point  11 . The switching unit  10 , is significant in that the switching (to the off mode) is only performed during a part of a complete revolution of the flywheel, and in such a way that the switching unit  10  is switched off for a desired time period (e.g. 100 μs) for not disturbing the generation of the spark. Hence, a signal to In 21  or In 22  or both terminals In 21  and In 22  together, initiates or affects the switching unit  10  to switch off during a part of a revolution of the flywheel, before or in connection with, the said control unit (M 1 ) initiating said spark, to not negatively affect said generation of spark. The rest of the time, the unit  10  is in its “on mode”, whereby an output of about 0,5-2 W is obtained at Out 2 l, at a flywheel speed of as low as 2000 rpm. 
         [0019]    An optional connection  9 , connecting the ignition control M 1  and the voltage control/switching unit  10 , enables a feedback and information about the charge/load level of a charge capacitor  14 , described in  FIG. 2 , and the connection  9  can also be utilized for a change of the switch frequency etc. over the rpm. 
         [0020]    The operation and method of the switching unit  10  according to the invention, and described in  FIGS. 1 and 2 , is such that the switching is managed/controlled by information from the in-signal on input terminals In 21  and In 22 , either together or separately, dependent on specific needs/desires. For example if the system is set to be triggered by any in-signal and there is provided an in-signal to the input terminal In 22  from the ignition control unit M 1 , based on information from the micro-processor therein, the switch control  19  will be controlled to switch off at a, regarding this kind of application, short period of time before the ignition control unit M 1  will control the opening of the thyristor Q 1 , which starts the current flow through the primary winding P and generates the spark in SP 1 . Shortly after termination of the spark the control unit M 1  will again close the thyristor Q 1  and also activate the switch control  19  to be set in the on mode. 
         [0021]      FIG. 2  shows in more detail a first embodiment of the voltage control/switching unit  10  according to the invention, that is indicated in  FIG. 1 , as one of the options to trigger/control the voltage control/switching unit  10 . The voltage control/switching unit  10  is shown to comprise a switch control  19 , a diode  13 , a switch element  15  and a charge capacitor  14 . The anode side of the diode  13  is connected to the input terminal In 21  and the cathode side is connected to a first connector  16  of the switch element  15 . A second connector  18  of the switch element  15  is connected to the output terminal Out 2 l and to the charge capacitor  14 . 
         [0000]    The switch control  19 , which controls the switching of the voltage control/switching unit  10 , is connected to a connector  17  of the switch element  15  and to the input terminal In 22 . For a skilled person it is evident that the switch element  15  may comprise various components available on the market e.g. a thyristor, a Triac etc. The purpose of the switch control  19  is to control that the switch element  15  is switched off during a desired (e.g. preset in the CPU of the control unit M 1 ) period of time, e.g. 100 μS, starting at or immediately before the generation of spark. In this embodiment the switching signals In 22  are controlled by software and/or hardware and a CPU in the ignition control M 1 , which normally implies conventional TTL-signals, e.g. a pulse signal at In 21  some μS before the initiating of the spark to put the switch element  15  in the off mode and a duration of about  100  μS to switch back to the power generating mode. A purpose of the charge capacitor  14 , connected between the output terminal Out 21  and earth, is to stabilize the output from terminal Out 21 , to provide energy to the external device when the switch element  15  is off. 
         [0022]      FIG. 3  shows in more detail a second embodiment of the switching unit  10  according to the invention, depicted in  FIG. 1  as one of the options. The switching unit  10  comprises, of a Triac or thyristor or other suitable switching element  21 , a spark initiation detection unit  25 , the capacitor  14  and the switch control  19 . Whereof one power terminal  22  of the Triac  21  is connected to the input terminal In 21  (which is corresponding to the diode  13  in  FIG. 2 ) and a second power terminal  23  is connected to the output terminal Out 21 . The capacitor  14 , connected between the output terminal Out 2 l and earth, is stabilizing the outgoing voltage of the output terminal Out 21 , i.e. supplying power during the off mode of the control/switching unit  10 . The switch control  19 , which controls the switching of the switching unit  10 , is connected to the gate  24  of the Triac  21  (which is corresponding to the switch element  15  in  FIG. 2 ). The spark initiation detection unit  25 , which is integrated in the switch control  19 , is connected via a connection S 21  to the input terminal In 21  which means, according to this example, that the voltage control/switching unit  10  is connected to the CDI system via the connection In 21  only. 
         [0023]    The operation and method of the switching unit  10  shown in  FIG. 3 , is such that the switching is managed/controlled by information from the in-signal on the input terminal In 21 , which is given by the voltage transient (amplitude and/or pulse-form) in the primary winding P created when initiating the spark generation which is detected by the spark initiation detection unit  25 , which in turn generates a signal to the switch control  19 , whereby the switch control  19  immediately switches off the voltage control/switching unit  10 . The core of the switch element in this embodiment is the Triac  21  that switches off during a certain period of time, e.g. in the range of  80 - 120  μS. In this embodiment the signal to switch off is not generated before the start of generation of the spark but a short time (e.g. ≦ 5  μS) after the start, due to the use of a detection unit  25 . Accordingly the specific period of time in the off mode starts immediately after the generation of spark is initiated. When the generation of spark is ended the voltage control/switching unit  10  is switched back to the power generating mode. 
         [0024]    It is evident that in conformity with other known spark generating CDI systems the switching may preferably be controlled by the amplitude or pulse-form of the primary winding P, wherein the signals and current flow is caused by the magnetism of the passing flywheel. Accordingly, e.g. the detection of a negative pulse on the primary winding P may be used to cause an immediate interrupt i.e. an immediate switch off of the voltage control/switching unit  10  or possibly, if desired, with a preset delayed or premature triggering. Hence, a very flexible means of controlling due to the fact that the control unit  10  may be flexibly set with a great variety of (desired) triggering parameters. 
         [0025]    In preferred embodiments intended to be used primarily in connection with small engines (e.g. chain saws) the components of a system according to the invention may be chosen within a wide range to provide the functionality as intended by the invention. However, there are some basic requirements, e.g. that there is a charge winding L that is sufficiently powerful to generate needed energy, i.e. within the range of 1-15 mWs. 
         [0026]    Summarized, one advantage of the switching unit  10  according to the invention is the ability to utilize the primary winding for generation of an electrical power, and this in alignment with a very low impact on the performance of the CDI system, i.e. the sparking generation, and regarding burn-time, ignition voltage, energy and the peak power. The generated energy/power can be used for supplying of internal or external units e.g. sensors, solenoids. 
         [0027]    The invention is not limited by the embodiments described above but may be varied within the scope of the appended claims. For instance the skilled person realizes that several external units may be connected to Out 21  and that for instance at a higher rpm, which produces a higher output then could be arranged for connecting a further external device, e.g. fuel mixture meter, battery charging, sensors or other small power demanding devices. Further, the skilled person realizes that many other evident modifications, may be made within the scope of protection, e.g. using a further winding (or several), in series with the primary winding, to achieve the desired voltage. 
         [0028]    Regardless of form of embodiment, the switch unit  10  can also be used for limiting output power. This can be implemented as a voltage control device which then will regulate output voltage by switching unit  10  on/or off as a reaction to variations in both output load and engine rpm.

Technology Classification (CPC): 5