Abstract:
The present invention provides an arrangement for charging energy in an energy-storing arrangement such as an ignition capacitor in electronic ignition systems. To reduce the risk of malfunction, direct-current-controlled breakers controlled by environmental conditions, normally occurring on the primary side of a transformer ( 4 ) in series with the primary winding ( 5 ) have been replaced by a frequency divider ( 2 ) controlled by environmental conditions. This frequency divider divides down a signal supplied by a signal generator ( 1 ) pulse train with a lower frequency which controls a breaker ( 7 ) connected in series with the primary winding ( 5 ) of the transformer.

Description:
FIELD OF THE INVENTION 
     The present invention provides an arrangement for charging energy in an energy-storing arrangement such as an ignition capacitor in an electronic ignition system, which energy-storing arrangement is connected to the secondary side of a transformer, the primary side of which is connected to a direct-voltage source in series with a first breaker controlled by a pulse train. 
     BACKGROUND OF THE INVENTION 
     Energy-storing arrangements of the ignition-capacitor type are used in, among other things, the functional part of projectiles in order to ignite the functional part after an ignition pulse has been received. For safety reasons, it should only be possible to charge the ignition capacitor when a number of environmental conditions have been fulfilled. One environmental condition can be that the projectile has been exposed to an acceleration pulse of a certain magnitude. Another can be that the projectile has begun to rotate. To handle the problems of environmental conditions, there is normally a number of mechanical and/or electrical breakers between the batteries for the ignition capacitors&#39; charging and the ignition capacitor itself. 
     According to GB 2 169 994 A, a first example of a charging arrangement is previously known. According to this patent document, a transformer is used to increase the battery voltage before it charges up, for example, an ignition capacitor. In series with the primary winding of the transformer, a plurality of breakers is inserted which are controlled by environmental conditions. There is also a breaker, which is controlled by a pulse train in order to generate an alternating voltage on the primary side of the transformer. The breakers controlled by environmental conditions operate with normal direct-current signals. 
     A similar charging arrangement is also known from U.S. Pat. No. 5,476,044. A breaker, which is supplied with energy from the secondary side of the transformer, opens and closes the feed of the primary side of the transformer in order to form low-voltage pulses through the primary winding of the transformer from the direct voltage from the direct-voltage source on the primary side. Environmental conditions control the breakes in series with the primary winding of the transformer. The breakers controlled by environmental conditions operate with normal direct-current signals. 
     A breaker of the type given in known charging arrangements according to the above is controlled by direct voltages. In the case of a fault in, the control electronics, a breaker can therefore be closed without corresponding environmental conditions being fulfilled. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to provide a charging arrangement where the risk of a malfunction is considerably reduced in relation to known charging arrangements with direct-voltage-controlled breakers. 
     The object of the invention is achieved by an arrangement characterized by the following, for generating the pulse train for controlling the first breaker, a signal generator and a frequency device connected to the signal generator controlled by environmental conditions of the ignition system, are included. The charging arrangement according to the invention generates the pulse train as a result of the environmental conditions which control the frequency of the pulse train which is coupled to the control of the first breaker connected in series with the primary winding of the transformer. In the charging arrangement according to the invention, therefore, it is no longer necessary to have breakers controlled by environmental conditions in series with the primary winding. The problem with malfunctions in direct-current breakers has thus been eliminated. However, this does not exclude a use of other breakers in series with the primary and secondary winding of the transformer as in GB 2 169 994 A. 
     The signal generator advantageously comprises the clock of the ignition system which normally operates within a suitable frequency range for being divided down in frequency. For example, the clock can operate with a frequency of 10 MHz, which is divided down to a frequency range of 10-100 kHz. Using the clock of the ignition system also means that the cost for a separate component as well as space can be saved. 
     According to an advantageous embodiment, a band-pass filter is coupled in between the frequency divider and the control input of the first breaker in order to attenuate signals outside a specified operating interval. The operating interval can be set to be narrow if the clock and the frequency divider operate with a great accuracy and only a specific state of environmental condition is accepted. Alternatively, the bandwidth of the band-pass filter can be increased in order to allow, for example, several specific states of environmental condition. 
     To further increase the safety in the ignition system, a second breaker is coupled in between the output of the frequency divider and the control input of the first breaker according to another advantageous embodiment. 
     According to a first further development of the embodiment with a second breaker, a control element is arranged to check the environmental conditions of the ignition system and, based on the result of the check, to control the second breaker to the closed position with approved environmental conditions and to the open position with environmental conditions which are not approved. The checking element advantageously consists of logic circuits. 
     According to a second further development of the embodiment with a second breaker, a frequency comparator arrangement is arranged to measure the frequency on the output side of the frequency divider and to control the second breaker to the closed position within frequencies which are suitable for the frequency divider and to the open position outside frequencies suitable for the frequency divider. The frequency comparator arrangement can advantageously comprise a frequency calculator for determining the frequency at the output of the frequency divider, a memory for storing frequencies which are suitable for the frequency divider and a comparator circuit for comparing the frequency found with suitable frequencies and controlling the second breaker on the basis of the result. Alternatively, the frequency comparator arrangement can comprise a first monostable multi-vibrator in series with a first D flip-flop and a second monostable multi-vibrator in series with a second D flip-flop, which first multi-vibrator is designed with a pulse length defining a lower limit frequency and which second multi-vibrator is designed with a pulse length defining an upper limit frequency for the current frequencies of the frequency divider. For determining the pulse lengths of the multi-vibrators, a resistor and a capacitor is advantageously arranged at the input of each multi-vibrator. The plausibility of the frequency of the pulse train is checked in a simple manner and the pulse train is only connected through if its frequency is determined to be plausible. 
     According to yet another advantageous embodiment, the primary side of the transformer comprises a winding with a centre tap connected to the direct-voltage source, which winding is connected symmetrically in series with the first breaker and a further breaker. This embodiment produces a symmetric feeding of the primary side of the transformer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This invention will be described in greater detail below by means of some illustrative embodiments, referring to the attached drawings, in which: 
     FIG. 1 shows a first illustrative embodiment of a charging arrangement according to the invention, 
     FIG. 2 shows a second illustrative embodiment of a charging arrangement according to the invention. 
     FIG. 3 shows a third illustrative embodiment of a charging arrangement according to the invention, 
     FIG. 4 shows a fourth illustrative embodiment of a charging arrangement according to the invention, 
     FIG. 5 shows an alternative embodiment of a frequency comparator arrangement shown in FIG. 4 used in the charging arrangement according to the invention, 
     FIG. 6 illustrates the functions of multi-vibrators used in the frequency comparator arrangement according to FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to the illustrative embodiment shown in FIG. 1, a signal generator  1 , a frequency divider  2  and a band-pass filter  3  are arranged on the primary side of a transformer  4  with a primary winding  5  and a secondary winding  6 . The signal generator can be provided with a clock in an ignition system in which the charging arrangement is included. The output of the band-pass filter  3  is connected to the control input of a breaker  7  which is connected in series with the primary winding  5  of the transformer. There is also a direct-voltage source or battery  8  in series with the primary winding of the transformer. On the secondary side of the transformer there is a rectifier circuit  14  for converting alternating voltage transferred through the transformer. The rectifier circuit  14  comprises a bridge circuit with four diodes  9 ,  10 ,  11  and  12 . An ignition capacitor  13  included in the ignition system is coupled to the bridge circuit  14 , in the manner shown, in series with a diode  15  and a resistor  16 . 
     The following description provides the basic operation of the charging arrangement. From the signal generator  1 , a signal, for example of the order of magnitude of 10 MHz, is output to the frequency divider  2 . The frequency divider  2  is supplied with information about the environmental condition by inputs  17 . The information can consist, for example, of a digital code of ones and zeros. For codes which represent acceptable environmental conditions, the frequency of the incoming signal is divided to a frequency within the pass band of the band-pass filter  3 , for example of the order of magnitude of 10-100 kHz. Any signals, the frequency of which lies outside the pass band of the band-pass filter is attenuated in such a manner, that the breaker  7  is not closed. This arrangement forms an alternating voltage in the transformer  4  which is rectified in the rectifier circuit  14  on the secondary side before it charges up the ignition capacitor  13 . After that, the energy stored in the ignition capacitor  13  can be utilized for igniting, for example an electrical detonating cap. 
     FIG. 2 shows a modification of the embodiment according to FIG.  1 . The components which correspond to those in the embodiment described with regard to FIG. 1 are given the same reference designations and will not be described any further. To produce a symmetrical feeding of the primary side from the battery  8 , the primary winding  5  is provided with a centre tap to which the battery  8  is connected. Two breakers  7  and  7 ′ controlled from the frequency divider  2  via the intermediate band-pass filter  3  and  3 ′ are connected in series with and symmetrically with respect to the primary winding  5 . An inverter  32  is inserted in series with one of the band-pass filters, in this case filter  3 ′. With frequencies within the frequency range of the filters  3 ,  3 ′, the breakers  7 ,  7 ′ will be opened and closed in opposite phase. 
     In the illustrative embodiment shown in FIG. 3, a checking element  18  and a second breaker  19  are introduced. The checking element  18  senses the code at inputs  17  of the frequency divider  2  and controls the breaker  19 . The checking element can be constructed of a number of logic circuits of conventional type, not shown. It can be noted, that the environmental conditions which control the checking element  18  do not need to be identical with the environmental conditions which control the frequency divider. On the secondary side, charging circuits can be constructed in accordance with FIG.  1 . It can be pointed out, however, that other alternative embodiments are conceivable for all illustrative embodiments described in this text. 
     The embodiment proposed in FIG. 4 includes a frequency comparator arrangement  20  and a breaker  19 . The arrangement  20  can comprise a frequency calculator  21  for determining the frequency at the output of the frequency divider  2 , a memory  22  for storing frequencies suitable for the frequency divider which will allow the ignition capacitor to be charged and a comparator circuit  23  for comparing the frequency found with stored frequencies and controlling the breaker  19 . When the detected frequency and the frequency stored in the memory correspond, the pulse train is coupled through to the breaker  7  in series with the primary winding  5 . 
     To check that the output frequency from the frequency divider  2  lies within an approved interval, a single check circuit according to FIG. 5 can alternatively be used. The circuit comprises two retriggerable monostable multi-vibrators  24 ,  25 , two D flip-flops  26 ,  27 , a first resistor  28  and a first capacitor  29  at the input of the multi-vibrator  24  and a second resistor  30  and a second capacitor  31  at the input of the multi-vibrator  25 . The check circuit is connected through clock input  33  to the output of the frequency divider  2 . The clock input  33  is connected to multi-vibrators  24 ,  25  and the clock inputs of D flip-flops  26 ,  27 . A direct voltage V cc  feeds components included in the check circuit in the manner shown in FIG.  5 . When a multi-vibrator is triggered at the input by the output signal of frequency divider  2 , a pulse is generated at the output of the multi-vibrator, the length of which is determined by the resistor  28  and the capacitor  29  for the multi-vibrator  24 , and the resistor  30  and the capacitor  31  for the multi-vibrator  25 . If an additional trigger pulse comes within a time corresponding to the pulse length, the output continues to be high for a time corresponding to the pulse length calculated from the last triggering time. This means that if the time of the period of the output signal is shorter than the pulse length of the multi-vibrator, the output from the multi-vibrator will be constantly high. Otherwise, the output signal is low at the triggering time. 
     The pulse lengths of the multi-vibrators  24  and  25  are then selected in such a manner that the multi-vibrator  24  provides a pulse which corresponds to the shortest period which is acceptable whilst multi-vibrator  25  provides a pulse which corresponds to the longest period which is acceptable for the output signal from the frequency divider  2 . If the frequency of the output signal from the frequency divider is to be accepted, it is a requirement, that the output signal from the multi-vibrator  24  should be low whilst the output signal from the multi-vibrator  25  should be high at each triggering time. 
     The table shown in FIG. 6 relates to the output signals from the multi-vibrators  24  and  25  at the triggering time for the case where the output signal frequency is too low, acceptable and too high. By sampling the output signals from both multi-vibrators  24 ,  25  at the positive edge of the output signal from the frequency divider it is therefore possible to check that the output signal of the frequency divider is within an acceptable frequency interval. This sampling is done with the aid of the D flip-flops  26 ,  27 , which are triggered at the positive edge and then read in the values at the outputs of the multi-vibrators  24 ,  25 . F high  therefore signals that the frequency is too high and F low  signals that the frequency is too low. The value read in lies at the output of the D flip-flop until the next positive edge triggers the flip flop again. A conventional logic circuit, not shown, can form the control signal for breaker  19  on the basis of these two signals. Another alternative is also to use a breaker in series with the breaker  19  and to let the D flip-flops each control a breaker. 
     The charging arrangement described above is not limited to the illustrative embodiments described but a plurality of modifications are possible within the scope of the invention as defined in the patent claims following.