Abstract:
A charging circuit for a fuel injection coil enables the controller to selectively add a pulse of increased amplitude to the beginning of an injection current pulse. Optionally, the controller can also select one of a plurality of amplitudes for the pulse and control the duration of the pulse.

Description:
This application claims priority to U.S. Provisional Application Ser. No. 60/810,027, filed Jun. 1, 2006. 

   BACKGROUND OF THE INVENTION 
   The present invention relates generally to fuel injection systems for engines. 
   Known diesel fuel injection systems include a bank of open coils and a bank of close coils. Charging circuits charge the coils to a certain current level and maintain the coil for a certain period of time. Some diesel engines are more difficult to start in very cold weather. 
   SUMMARY OF THE INVENTION 
   The present invention provides a circuit for charging coils, particularly suited for a diesel fuel injection system. In an example embodiment of the present invention, the current for some of the coils is increased for a portion of the cycle. An initial pulse is added to the normal charging level of the coils. This provides increased performance during certain conditions, for example, cold weather start-up. 
   In the example circuitry shown, the level of the pulse is optionally selectable. The controller can select one of a plurality of amplitudes for the pulse. 
   Optionally, the controller can also control the length of the pulse, by retriggering the pulse. In another optional feature, circuitry for detecting bad coils is modified to accommodate the pulse. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic of the fuel injection system according to one embodiment of the present invention. 
       FIG. 2  is a schematic of a circuit for detecting a bad coil in the circuit of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  is a schematic of an example fuel injection coil charging circuit  10  according to one embodiment of the present invention for charging open coils  12  in a diesel fuel injection system. Corresponding close coils  14  are shown and operate normally. As shown in the schematic of  FIG. 1 , the inventive feature is applied only to the open coils (even and odd); however, it is possible that it may be desirable to apply the invention to the close coils in certain situations (not shown). 
   The circuit  10  includes a microcontroller  16  (or other programmable controller or hardware control circuit) suitably programmed to perform normal control functions for the circuit  10  and suitably programmed to perform all of the functions described herein. The circuit  10  further includes a timer, in this example, a one-shot  18 . The one-shot  18  is designed to provide a pulse of predetermined length of time when enabled by the microcontroller  16  (i.e. when the microcontroller does not activate the Reset input) and when the one-shot  18  is activated on its input A. The one-shot  18  input is activated by a NAND gate  20  receiving low-active even and odd outputs from the microcontroller  16 . The one-shot  18  can also be retriggered by a peak delay signal (PKDLY) from the microcontroller  16  to a transistor T D , which can retrigger the one-shot  18  and restart the timing of the one-shot  18 . The one-shot  18  is designed to generate a pulse of a predetermined time. In the example embodiment, that pulse has a time of six hundred microseconds; however, the exact duration can be tailored for the particular application. If additional time is desired in a particular situation, the microcontroller  16  can retrigger the one-shot  18  prior to the end of the first pulse. 
   The output of the one-shot  18  is connected to four NOR gates N 1 -N 4 . The microcontroller  16  has four outputs PK 1 , PK 2 , PK 3 , PK 4 , each connected to one of the inputs of one of the NOR gates N 1 -N 4 . The output of each NOR gate N 1 -N 4  is connected to the base of two transistors T 1  and T 5 , T 2  and T 6 , T 3  and T 7 , T 4  and T 8  respectively. Each of the transistors T 1 -T 8  has a corresponding resistor R 1 -R 8  which the transistor selectively connects in parallel to Vcc. More particularly, the first four transistors T 1 -T 4  each selectively connect its corresponding resistor R 1 -R 4  in parallel with the other resistors R 1 -R 4 . Similarly, the transistors T 5 -T 8  each selectively connect its associated resistor R 5 -R 8  in parallel with the other resistors R 5 -R 8 . 
   The resistors R 1 -R 4  provide a branch of a voltage divider circuit  22  associated with the even open coils  12 , while the resistors R 5 -R 8  comprise a branch of a voltage divider circuit  20  associated with the odd open coils  12 . The voltage divider circuits  20 ,  22  each further include resistors R A  and R B , which provide a voltage input to comparators  24 ,  26 , respectively, in driver circuits for the odd and even open coils  12 , respectively. The resistors R 1 -R 4  (when activated by their associated transistors T 1 -T 4 ) are in parallel with resistor R A  in the upper half of the voltage divider circuit  20 . The resistors R 5 -R 8  (when activated by their associated transistors T 5 -T 8 ) are in parallel with resistor R A  in the upper half of the voltage divider circuit  22 . 
   Thus, it can be seen that by selectively turning on or off selective combinations of the transistors T 1 -T 4 , selective combinations of the resistors R 1 -R 4  are changing (in this case, raising) the voltage in the voltage divider circuit  22  and, consequently, the resulting voltage input to comparator  24 . Similarly, by selectively turning on or off combinations of the transistors T 5 -T 8 , selective combinations of the resistors R 5 -R 8  are provided to the voltage divider circuit  20  and selectively provide a voltage level input to the comparator  26 . Preferably, although not necessarily, the resistors R 1 -R 4  are all of different values, thus providing sixteen different possible combinations of resistors, and thus, sixteen possible voltage inputs to the comparator  24 . Preferably, the resistance values of resistors R 5 -R 8  are equal to R 1 -R 4 , respectively. Note that transistors T 1  and T 5  are turned on and off simultaneously, while transistors T 2  and T 6  are switched on and off together, as are T 3 /T 7  and T 4 /T 8 . Thus, the voltage supplied to comparator  26  should be equal to the voltage supplied to the comparator  24 . 
   The comparator  26  will compare the voltage in the odd open coils  12  to the voltage from the voltage divider circuit  22 . The comparator  26  will supply current to the odd open coils  12  until their voltage is equal to that of the voltage divider circuit  22 . When the voltage on the coils  12  decays, the comparator  26  again supplies current until it is equal to the voltage in the voltage divider circuit  22 . If this is a normal cycle, i.e. there is no extra pulse, the transistors T 5 -T 8  will be off and the voltage at the voltage divider circuit  22  at the input to comparator  26  will be the normal amount (for example, sufficient to provide  20  amps to the coils  12 ). 
   During some conditions, such as cold weather start-up, the microcontroller  16  selectively activates one or more of outputs PK 1 -PK 4 , which will ultimately turn on certain combinations of the transistors T 1 -T 8 . For example, by activating lines PK 1  and PK 2 , transistors T 1 , T 5 , T 2  and T 6  will be switched on during the one-shot  18  pulse. This will place resistors R 1  and R 2  in parallel with resistor RA of voltage divider circuit  20 , raising the voltage input to the comparator  24 . Simultaneously, this will put resistors R 5  and R 6  in parallel with resistor R A  in voltage divider circuit  22 , raising the voltage input to the comparator  26  to the same level. As will be understood, by selecting different combinations of PK 1 -PK 4 , sixteen combinations are possible. If the values of resistors R 1 -R 4  are different (and corresponding resistors R 5 -R 8  are equal to resistors R 1 -R 4 ), sixteen different voltage levels can be provided at the inputs to comparators  24 ,  26 . 
   When the pulse from the one-shot  18  is done, all of the NOR gates N 1 -N 4  (whichever combination of PK 1 -PK 4  was active) ensure that all of the transistors T 1 -T 8  are off, thus returning the voltages at the inputs to the comparators  24 ,  26  to their normal levels. The comparators  24 ,  26  then let the open coils  12  decay below their normal levels before recharging them up to their normal levels again. Note that there would likely be some hysteresis in the driver circuits. 
   If a longer pulse is desired, the microcontroller  16  can activate the peak delay (PKDLY) line, switching on transistor T D  to retrigger the one-shot  18  and restart the timing circuit inside the one-shot  18 . 
     FIG. 2  is a schematic of a circuit  30  for detecting bad coils  12 ,  14  ( FIG. 1 ). First, the bad close coil detection circuitry is as is known in the art. The forward pulse close coil signal, which indicates the beginning of a charging cycle, comes from the controller  16  ( FIG. 1 ) and initiates a one-shot  36 . The output of the one-shot  36  is connected to an input of a NOR gate N 6 . A close coil  20  amp sensor  38  (or whatever the normal fully-charged level of the close coils  14  is) sends a signal to the NOR gate N 6  when the close coils  14  reach full charge. If the close coil current level does not reach the normal full level before the one-shot  36  is done, the NOR gate N 6  goes high. If either (or both) of the inputs to the NOR gate N 7  are high, a fault is indicated at the output of the NOR gate N 7 . 
   The bad open coil detection circuitry accommodates the pulse that is added at the beginning of the charging cycle. More specifically, the RC circuit inside the one-shot  32  is selectively modified by selectively removing a resistor R 9  from the RC circuit with a transistor T 9 . The transistor T 9  is switched off while the one-shot  18  ( FIG. 1 ) is active by the PEAK signal from the one-shot  18  output ( FIG. 1 ). This puts the additional resistor R 9  in the RC circuit, thereby decreasing the time of the one-shot  32 . Note that the coils  12  are expected to charge to 20 amps (or whatever the normal charging level is) faster when the pulse is added to the beginning of the charging cycle. In the example shown it was determined to be unnecessary to offer sixteen levels of RC timing in the one-shot  32 . Instead, a single adjustment of the RC timing circuit is applied any time there is a pulse of any size. Alternatively, various resistor combinations could be added to the RC circuit similar to the way resistor combinations are added to the voltage dividers in  FIG. 1 . 
   Although a preferred embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.