Device for controlling inductive loads, in particular of injectors of an internal combustion engine injection system

Abstract: The control device (1) has a drive circuit (7), in turn having a number of modular circuits (10) - one for each inductor (2) - activated selectively and receiving timing signals (T), and a common circuit (11) connected to the modular circuits (10) and cooperating with the activated modular circuit (10) to supply the respective inductor (2). Each modular circuit has a first controlled switch (21, 22) connected between a first input terminal (16) and a respective first output terminal (19), and a second controlled switch (23, 24) connected between the respective first output terminal (19) and a storage capacitor (25); and the common circuit (11) has a third controlled switch (26, 27, 28) connected between the storage capacitor (25) and a respective second output terminal (20), and cooperating with the second controlled switch (23, 24) to selectively transfer energy between the storage capacitor (25) and the respective inductor (2).

Description: The present invention relates to a device for controlling inductive loads, in particular of injectors of an internal combustion engine injection system. As is known, to control the injectors of an internal combustion engine injection system, each injector must be supplied with current, the curve of which comprises a rapidly increasing portion, a more slowly increasing portion, a portion decreasing to a hold value, a portion oscillating about the hold value, and a portion decreasing to zero. To achieve such a curve, control devices are currently employed whereby the inductive loads of the injectors are connected on one side to a low-voltage supply source, and on the other side to a ground line via a controlled electronic switch. A major drawback of control devices of this sort is that, in the event of ground shorting of one of the terminals of any one of the inductive loads - e.g. due to impaired insulation of of an injector conductor, and contact between the conductor and the vehicle body - the injector and/or control device is irreparably damaged and the engine is turned off - an extremely dangerous situation when the vehicle is moving. Such a device using three switching transistors and an energy storing capacitor is known from FR-A-2538942. To eliminate the above hazard, control devices have been proposed whereby the inductive loads of the injectors are grounded on one side and connected on the other side to an internal node of the control device itself, so that, as opposed to damaging the control device and turning off the engine, ground shorting of one of the terminals of the inductive loads simply results in that particular injector being put out of use, so that the vehicle continues running minus one injector. Such control devices, however, in addition to involving complex, high-cost circuitry, normally fail to provide for simultaneously injecting different cylinders, as required for example by engine injection systems involving multiple injection of each cylinder. It is an object of the present invention to provide a straightforward, low-cost control device designed to overcome the aforementioned drawbacks. According to the present invention, there is provided a device for controlling inductive loads, in particular of injectors of an injection system of an internal combustion engine, according to claim 1 A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a block diagram of an injection system comprising a control device in accordance with the present invention; Figure 2 shows a circuit diagram of the Figure 1 control device; Figures 3 to 7 show time graphs of quantities relative to the Figure 2 control device. Number 1 in Figure 1 indicates a device for controlling the control electromagnets of injectors 3 of an injection system 4 of an internal combustion engine 5, in particular a supercharged diesel engine. In Figure 1, the control electromagnets are represented by the electric equivalents comprising inductors 2. Control device 1 comprises a timing circuit 6 receiving information signals S measured on engine 5, and generating timing signals T for controlling injectors 3; and a modular circuit 7 receiving timing signals T and for driving injectors 3 accordingly. Modular circuit 7 comprises a number of modular circuits 10, one for each inductor 2, activated selectively and receiving timing signals T as described in detail later on; and a common circuit 11 connected to modular circuits 10 and cooperating with the activated modular circuit 10 to supply respective inductor 2 as also described in detail later on. More specifically, modular circuit 7 comprises a supply line 12; a ground line 13; and a first and second connecting line 14, 15 between modular circuits 10 and common circuit 11. Modular circuit 7 also comprises a first and second input terminal 16, 17 respectively connectable to a positive pole and a negative pole of a supply source, e.g. a battery 18; and a number of pairs of output terminals, one for each injector 3. Each pair of output terminals comprises a first and second output terminal 19, 20 between which a respective inductor 2 is connected in use. More specifically, the first input terminal 16 of modular circuit 7 is connected to supply line 12, and the second input terminal 17 and the second output terminals 20 are connected to ground line 13. Each modular circuit 10 comprises a MOSFET charging transistor 21 having a control terminal connected to timing circuit 6 and receiving from timing circuit 6 a first timing signal T 1 , a drain terminal connected to supply line 12, and a source terminal connected to the anode of a charging diode 22, the cathode of which is connected to a respective first output terminal 19 of modular circuit 7. Modular circuit 10 also comprises a MOSFET discharging transistor 23 having a control terminal connected to timing circuit 6 and receiving from timing circuit 6 a second timing signal T 2 , a drain terminal connected to first connecting line 14, and a source terminal connected to respective first output terminal 19 of modular circuit 7. Modular circuit 10 also comprises a clamping diode 24 with the anode connected to second connecting line 15, and the cathode connected to respective first output terminal 19 of modular circuit 7. Common circuit 11 comprises a capacitor 25 having a first and second terminal connected respectively to first connecting line 14 and second connecting line 15. Common circuit 11 also comprises a MOSFET recirculating transistor 26 having a control terminal connected to timing circuit 6 and receiving from timing circuit 6 a third timing signal T 3 , a drain terminal connected to ground line 13, and a source terminal connected to the anode of a recirculating diode 27, the cathode of which is connected to second connecting line 15. Common circuit 11 also comprises a discharging diode 28 with the anode connected to ground line 13, and the cathode connected to first connecting line 14. The drain and source terminals of each transistor 21, 23, 26 of modular circuits 10 and common circuit 11 are connected respectively to the cathode and anode of a respective protection diode 29 operating in known manner and therefore not described in detail. Timing circuit 6 selectively activates each modular circuit 10 by supplying the control terminals of transistors 21, 23, 26 with timing signals T 1 , T 2 , T 3 , which are only supplied to the modular circuit to be activated, so that the other modular circuits 10 remain off. Furthermore, timing signals T 1 , T 2 , T 3 , control MOSFET transistors 21, 23, 26 to saturate them or to switch them off, so that each transistor acts as a closed or open switch. Operation of control device 1 will now be described with reference to one injector 3 and one modular circuit 10 - the other modular circuits - operating in the same way - which cooperates with common circuit 11 to supply respective inductor 2, and with specific reference to Figures 3 to 7 showing time graphs of timing signals T 1 , T 2 , T 3 of transistors 21, 23, 26, the voltage V C of capacitor 25, and the current flow I L in inductor 2. To begin with, timing circuit 6 opens all of transistors 21, 23, 26, so that both modular circuit 10 and common circuit 11 are off. Timing circuit 6 then closes and opens, several times in succession, the charging transistor 21 of the modular circuit 10 activated at the time, by supplying the control terminal of charging transistor 21 with a train of so-called recharging pulses, as shown in Figure 3 (RECHARGING PHASE). More specifically, when charging transistor 21 is closed (instant t 0 in Figure 3), a closed loop is formed comprising battery 18, charging transistor 21, charging diode 22 and inductor 2; and inductor 2, being supplied by battery 18 with a constant voltage, is supplied with an increasing current, which increases the energy stored in inductor 2. When charging transistor 21 is opened (instant t 1 in Figure 3), current flow in the above loop is cut off so that energy ceases to be stored in inductor 2; and the time interval t 1 -t 0 in which charging transistor 21 is closed is so calculated that the energy stored in inductor 2 is insufficient to open respective injector 3. When charging transistor 21 is opened, capacitor 25 and inductor 2 are connected to each other in series via discharging diode 28 and clamping diode 24 to form a resonant circuit, so that current flows in the loop defined by inductor 2, discharging diode 28, capacitor 25 and clamping diode 24, thus charging capacitor 25 and increasing the voltage at the terminals of capacitor 25, so that the energy stored in inductor 2 is transferred, minus any losses, to capacitor 25. As shown in Figure 6, by closing and opening charging transistor 21 several times in succession, the voltage at the terminals of capacitor 25 (which is assumed to have been precharged in previous drive cycles and therefore at an initial voltage value of other than zero) gradually increases to a predetermined value V 1 calculated to permit control of inductor 2 of injector 3; and, as shown in Figure 7, the current flow in inductor 2, as the inductor is charged and discharged, assumes a saw-tooth pattern. Timing circuit 6 then closes recirculating transistor 23 and discharging transistor 26 sequentially (instant t 2 in Figures 4 and 5) to form a further closed loop comprising capacitor 25, inductor 2, transistors 23, 26 and recirculating diode 27, and so form a further resonant circuit, so that a current flow is generated to discharge capacitor 25, reduce the voltage at the terminals of capacitor 25, and transfer all the energy stored in capacitor 25 to inductor 2, as shown in Figure 6 (RESONANT DISCHARGE PHASE). As capacitor 25 is being discharged, the current flow in inductor 2 reaches a predetermined value I 1 calculated to open injector 3 instantaneously. Upon the voltage at the terminals of capacitor 25 reaching a value V 2 equal to the voltage of battery 18 minus the threshold voltage of charging diode 22, charging diode 22 begins conducting and again connects inductor 2 in series with battery 18, which supplies inductor 2 with a constant voltage, so that the inductor is supplied with increasing current to keep injector 3 open (BYPASS PHASE). The current flow in inductor 2 therefore continues increasing, as shown in Figure 7, but at a slower rate than before. After a predetermined time interval (t bypass in Figure 7, by the end of which the current in inductor 2 has reached a predetermined value I 2 ), timing circuit 6 opens discharging transistor 23 (instant t 3 in Figure 4), recirculating transistor 26 (instant t 4 in Figure 5) and charging transistor 21 (instant t 5 in Figure 3) to form a closed loop comprising capacitor 25, inductor 2 (which combine to form a resonant circuit), clamping diode 24 and discharging diode 28, and to generate a current flow to charge capacitor 25 and discharge inductor 2 (DELAY PHASE). Discharging inductor 2 permits recharging of capacitor 25, thus reducing the number of recharging pulses required in the next drive cycle, and hence recharging time, and also reducing the time interval between one injection and the next. Rapid discharging of inductor 2 continues until timing circuit 6 closes recirculating transistor 26 (instant t 6 in Figure 5), at which point, the voltage at the terminals of capacitor 25 is at a value V 2 close to V 1 , and current flow in the loop is at a value I 3 below I 1 . When recirculating transistor 26 is closed, inductor 2 and capacitor 25 are no longer connected in series, and current, due to the energy stored in inductor 2, flows in the loop defined by inductor 2, recirculating transistor 26, recirculating diode 27 and clamping diode 24. In this phase, the current decreases at a slower rate than before (CHOPPER OFF PHASE). After a predetermined time interval (instant t 7 ), timing circuit 6 closes and opens charging transistor 21 several times in succession by supplying a train of pulses to the control terminal, and the current flow in inductor 2 assumes a saw-tooth pattern oscillating about a predetermined mean value sufficient to keep injector 3 open. More specifically, timing circuit 6 closes charging transistor 21 (instant t 7 ), so that inductor 2 is once more connected in series with battery 18 via charging transistor 21 and charging diode 22; the current flow in inductor 2 therefore increases to charge inductor 2 (CHOPPER ON PHASE) until timing circuit 6 opens charging transistor 21 (instant t 8 in Figure 3) to disconnect inductor 2 from battery 18, so that current is supplied to the loop defined by inductor 2, recirculating transistor 26, recirculating diode 27 and clamping diode 24; which current partially discharges inductor 2 (CHOPPER OFF PHASE) until timing circuit 6 again closes charging transistor 21, and the CHOPPER ON PHASE is repeated. Following injection, timing circuit 6 sequentially opens recirculating transistor 26 and charging transistor 21 (instants t 9 and t 10 in Figures 5 and 6), so that capacitor 25 and inductor 2 are once more connected in series via clamping diode 24 and discharging diode 28 to form a resonant circuit, and the discharge current of inductor 2 charges and increases the voltage of capacitor 25 (RESONANT RECHARGING PHASE). This phase continues until inductor 2 is completely discharged, thus terminating the drive cycle of injector 3; at which point, timing circuit 6 may commence a further drive cycle of another injector 3 as described above. The advantages of control device 1 are as follows. Firstly, by virtue of each inductor 2 being connected to control device 1 as described above, ground shorting of one of the terminals of inductor 2 in no way damages injector 3 or control device 1, but simply results in exclusion of injector 3, with no impairment in the operation of the other injectors 3, and without the engine suddenly being turned off. Secondly, control device 1 provides for simultaneously driving a number of injectors 3, e.g. as in the case of multiple injections in some of the cylinders of engine 5. In fact, after the DELAY PHASE, during the CHOPPER ON and CHOPPER OFF PHASES of one injector 3, capacitor 25 is again charged and capable of enabling the RESONANT DISCHARGING phase to drive another injector 3.

Claims: A device (1) for controlling inductive loads (2), in particular of injectors (3) of an injection system (4) of an internal combustion engine (5), comprising: timing means (6) generating timing signals (T) for controlling said injectors (3); drive means (7) for driving said inductive loads (2) and comprising a number of modular circuits (10), one for each inductive load (2); said modular circuits being activated selectively and receiving said timing signals (T); said drive means (7) also comprising a common circuit (11) comprising energy storing means (25); said common circuit being connected to the modular circuits (10) and cooperating with the activated modular circuit (10) to supply a respective inductive load (2); said drive means (7) also comprising a first and a second input terminal (16, 17) respectively connected, in use, to a positive pole and a negative pole of a supply source (18); and a number of pairs of output terminals, one for each injector (3); each pair of output terminals comprising a first and a second output terminal (19, 20) between which a respective inductive load (2) is connected in use; wherein each of said modular circuits (10) comprises, in combination: first controlled switching means (21, 22) connected between said first input terminal (16) and the respective first output terminal (19) of said drive means (7); and second controlled switching means (23, 24) connected between said respective first output terminal (19) and said energy storing means (25); and in that said common circuit (11) comprises: third controlled switching means (26, 27, 28) connected between said energy storing means (25) and the respective second output terminal (20) of said drive means (7); said third controlled switching means (26, 27, 28) cooperating with said second controlled switching means (23, 24) to permit selective transfer of energy between said energy storing means (25) and said respective inductive load (2). A device as claimed in Claim 1, characterized in that said drive means (7) also comprise a first and a second reference potential line (12, 13), and a first and a second connecting line (14, 15) between said modular circuits (10) and said common circuit (11); said first input terminal (16) being connected to said first reference potential line (12); and said second input and output terminals being connected to said second reference potential line (13). A device as claimed in Claim 2, characterized in that said first controlled switching means (21, 22) comprise first transistor means (21) and a first unipolar switch (22) connected to each other in series. A device as claimed in Claim 3, characterized in that said first transistor means comprise a charging transistor (21), and said first unipolar switch comprises a charging diode (22). A device as claimed in Claim 4, characterized in that said charging transistor (21) has a control terminal connected to said timing means (6) and receiving from said timing means (6) a first (T 1 ) of said timing signals, a first terminal connected to said first reference potential line (12), and a second terminal connected to an anode terminal of said charging diode (22); said charging diode having a cathode terminal connected to said respective first output terminal (19) of said drive means (7). A device as claimed in any one of the foregoing Claims from 2 to 5, characterized in that said second controlled switching means (23, 24) comprise second transistor means (23) and a second unipolar switch (24), both having respective first terminals connected together to said respective first output terminal (19) of said drive means (7), and respective second terminals connected to said energy storing means (25). A device as claimed in Claim 6, characterized in that said second transistor means comprise a discharging transistor (23), and said second unipolar switch comprises a clamping diode (24). A device as claimed in Claim 7, characterized in that said discharging transistor (23) has a control terminal connected to said timing means (6) and receiving from said timing means (6) a second (T 2 ) of said timing signals, a first terminal connected to said first connecting line (14), and a second terminal connected to said respective first output terminal (19) of said drive means (7); said clamping diode (24) having an anode terminal connected to said second connecting line (15), and a cathode terminal connected to said respective first output terminal (19) of said drive means (7). A device as claimed in any one of the foregoing Claims from 2 to 8, characterized in that said third controlled switching means (26, 27, 28) comprise third transistor means (26) and a third unipolar switch (27) connected to each other in series; said third controlled switching means (26, 27, 28) also comprising a fourth unipolar switch (28) connected between said first connecting line (14) and said second reference potential line (13). A device as claimed in Claim 9, characterized in that said third transistor means comprise a recirculating transistor (26); said third unipolar switch comprises a recirculating diode (27); and said fourth unipolar switch comprises a discharging diode (28). A device as claimed in Claim 10, characterized in that said recirculating transistor (26) has a control terminal connected to said timing means (6) and receiving from said timing means (6) a third (T 3 ) of said timing signals, a first terminal connected to said second reference potential line (13), and a second terminal connected to an anode terminal of said recirculating diode (27); said recirculating diode having a cathode terminal connected to said second connecting line (15); and said discharging diode (28) having an anode terminal connected to said second reference potential line (13), and a cathode terminal connected to said first connecting line (14). A device as claimed in Claims 6, 8, 10, characterized in that said charging transistor (21), said discharging transistor (23) and said recirculating transistor (26) are MOSFET transistors. A device as claimed in Claims 7, 9, 11, characterized by comprising a protection diode (29) connected between said first and second terminal of each of said charging, discharging and recirculating transistors (21, 23, 26). A device as claimed in any one of the foregoing Claims from 2 to 13, characterized in that said energy storing means comprise a capacitive element (25) connected between said first and second connecting line (14, 15).

Inventors: CASELLATO GIANCARLO, GROPPO RICCARDO
Applicants: FIAT RICERCHE, C.R.F. SOCIETA' CONSORTILE PER AZIONI
Application year: 1997
Main classification: F02D41
IPC codes: F02D41