The present invention relates to a system for controlling the inductive loads of internal combustion engine fuel supply injectors.

As is known, for controlling internal combustion engine injectors, these must be supplied with current the pattern of which generally comprises a rapidly increasing portion, a more slowly increasing portion, a portion oscillating about a mid value, and a rapidly decreasing portion.

The EP-A-548 915 describes an internal combustion engine fuel injector control system. This circuits comprise a low-voltage supply source, and a capacitor for storing the energy required for producing a rapid current pulse in the inductive load of the injector.

The capacitor is charged by the supply source to a given voltage value, and is then connected by a first electronic switch to the injector to form a resonant circuit and transfer energy from the capacitor to the injector which thus receives the initial current pulse required for opening it.

This circuit also comprises a second electronic switch.

This circuit is connected to an electronic control unit for activating the first and second switch for predetermined time intervals and so supplying the injector with current presenting the aforementioned pattern.

It is an object of the present invention to provide a system for flexibly calculating the closing/opening times of the first and second switch so that said times are correlated with the pattern of a number of circuit quantities and with a number of injector parameters.

According to the present invention, there is provided a system as claimed in Claim 1.

The present invention will be described with reference to the accompanying drawings, in which:

• Figure 1 shows a system for controlling the inductive loads of internal combustion engine fuel supply injectors;
• Figure 2 shows a simplified electric diagram of a circuit forming part of the electronic system according to the present invention;
• Figure 3 shows time graphs of a number of quantities in the Figure 2 system;
• Figure 4 shows a detail of the Figure 1 circuit.

Number 1 in Figure 1 indicates an electronic system for controlling the inductive loads of injectors 7 of a known fuel injection system 8 of an internal combustion engine 9, in particular a supercharged diesel engine.

System 1 comprises a control circuit 100 for controlling injectors 7 and to which the injectors are connected over respective control lines 10.

System 1 also comprises an electronic control unit 12 supplied with a number of information signals (e.g. engine speed, accelerator position, etc.) from engine 9, and cooperating with control circuit 100.

With reference to Figure 2, circuit 100 comprises two input terminals 102 and 103 for connection to a supply source B consisting of a battery with a low voltage Vbatt.

More specifically, terminal 102 is connected to the anode of a diode D2, the cathode of which is connected to a first common line (actuator line) 104, while terminal 103 is connected directly to a second common line (ground) 105.

Circuit 100 also comprises a number of actuator circuits 106 connected to one another in parallel between lines 104 and 105, and each comprising an actuator L1, a coupling diode Di, a controlled electronic switch SWi (conveniently formed by a power MOSFET transistor), and a common capacitor Ci.

More specifically, each actuator Li consists of the coil of a respective injector 7, and presents one terminal connected to line 104, and the other terminal, defining node 107, connected to the anode of diode D1 which connects actuator Li to a third common line (capacitance line) 112.

The cathode of each diode Di is connected to a second node 113 in turn connected to capacitance line 112 and to a first terminal of common capacitor Ci which provides for storing energy at a higher voltage than Vbatt. The other terminal of capacitor Ci is connected to ground line 105.

Each switch SWi provides for connecting actuator Li to battery B and for transferring energy from actuator Li to capacitor Ci; is interposed between node 107 and ground 105; and presents a control input 108 connected to control unit 12 by a respective control line 56 over which control unit 12 supplies an actuator selecting signal s_i.

Circuit 100 also comprises the series connection of an electronic switch SWR (conveniently formed by a power MOSFET transistor) which provides for connecting capacitance line 112 to actuator line 104, and for recirculating the current of load Li.

More specifically, switch SWR presents a first terminal connected to capacitance line 112; a second terminal connected to actuator line 104; and a control terminal connected to a control circuit 114 (described in more detail later on) in turn connected to control unit 12 by a control line 58 over which unit 12 supplies a signal s₁ for controlling switch SWR.

Finally, capacitance line 112 is connected to control unit 12 over line 59 for permitting control unit 12 to monitor the voltage on line 112.

Control unit 12 is also supplied by a line 113a with a signal proportional to voltage Vbatt, and provides for measuring (by means of a measuring circuit not shown) the value of inductance L of actuators Li.

Circuit 100 charges capacitor Ci to an appropriate voltage value, and supplies one of actuators Li with a current Ii the pattern of which presents a high-amplitude portion with a rapid leading edge, followed by a lower-amplitude portion terminating with a rapid trailing edge.

The above pattern is achieved by controlling switches SWR and SWi as described below.

With reference to Figure 3, it is assumed to begin with that switches SWR and SWi are open (low logic level of signals s₁ and s_i), and that capacitor Ci is charged to a predetermined high value V_C (voltage V_C higher than Vbatt) so that the voltage drop between capacitance line 112 and actuator line 104 is such as to maintain a reverse bias of diode D2, and no current Ii flows in the actuators.

At instant t₀, switch SWR is closed so that actuator line 104 is brought to the voltage level of capacitance line 112.

At instant t₁, control unit 12 selects the desired actuator Li by switching respective signal s_i to high and closing the relative switch SWi.

The selected actuator Li is thus connected between capacitance line 112 and ground 105, in parallel with capacitor Ci with which it forms a resonant circuit.

The selected actuator is therefore supplied with a current pulse formed by a high-frequency sinusoid portion (the value of which is determined by the inductance of actuator Li and the capacitance of capacitor Ci) and produced by rapid discharging of the energy stored in capacitor Ci whose voltage V_C falls rapidly.

The capacitor continues discharging up to instant t₂ at which voltage V_C on line 112 approximately equals voltage Vbatt, so that diode D2 is biased directly and connects battery B to actuator line 104.

After instant t₂, the selected actuator Li is supplied by low-voltage battery B and, from this point on, injector Li is supplied with a current proportional to Vbatt/L, where L is the value of the inductance of actuator Li selected by control unit 12.

At this step, diode Di of the selected actuator continues to be reverse biased.

The current in the injector therefore increases slowly until, after a time Tbypass from instant t₁ (instant t₃), it reaches a value Ipeak.

According to the present invention, the closing time Tbypass of switch SWi is calculated by unit 12 using an electronic map M1 which supplies Tbypass as a function of Vbatt/L input values.

More specifically, map M1 supplies Tbypass values increasing alongside an increase in inductance L and alongside a fall in Vbatt.

At instant t₃, therefore, switch SWi is opened (high-to-low switching of signal s_i).

Consequently, diode Di of the selected actuator is biased directly and acts as a freewheeling diode for discharging the formerly charged actuator Li and recirculating current Ii via capacitance line 112 and switch SWR. At this step, current Ii tends to fall in proportion to -(Vd2)/L - where Vd2 is the voltage drop across diode D2, and L the inductance of selected actuator Li - until it reaches a value Ioffchop at instant t₄.

Opening time Tdelay=t₄-t₃ of switch SWi is calculated by unit 12 which presents an interpolation unit C1 for supplying Tdelay according to the equation:$$\text{Tdelay=K1+A*(L-K2)}$$ where L is the inductance of selected actuator Li expressed in µH; K1 and K2 are two experimental numeric constants; and A is an experimental gain coefficient.

At instant t₄, switch SWi is again closed, so that selected actuator Li is again charged by battery B and disconnected from capacitance line 112 by relative diode Di.

In the instants following instant t₄, the current Ii in actuator Li again increases in proportion to Vbatt/L. As of instant t₄, the current increases for a time Tonchop until it reaches value Ionchop at instant t₅ at which switch SWi is again opened.

According to the present invention, time Tonchop is calculated by unit 12 using an electronic map M2 which supplies Tonchop as a function of Vbatt/L input values.

More specifically, map M2 supplies Tonchop values increasing alongside an increase in inductance L of selected actuator Li and alongside a fall in voltage Vbatt.

Opening of switch SWi (instant t₅) again discharges actuator Li for time Toffchop.

Time Toffchop is calculated by unit 12 which presents an interpolation unit C2 for supplying Toffchop according to the equation:$$\text{Toffchop=K3+B*(L-K4)}$$ where L is the inductance of selected actuator Li expressed in µH; K3 and K4 are two experimental numeric constants; and B is an experimental gain coefficient.

As such, switch SWi is appropriately opened and closed successively to maintain a current in selected actuator Li oscillating about a predetermined medium-low value.

Switches SWR and SWi are opened successively for rapidly discharging actuator Li.

More specifically, at instant t₆, switch SWi is opened with switch SWR open. At this step, diode Di is biased directly to connect actuator Li to capacitance line 112 and again form a resonant circuit, so that actuator Li discharges rapidly into capacitor Ci, current Ii decreases in the form of a high-frequency sinusoid portion, and the energy formerly accumulated by actuator Li is transferred to capacitor Ci-whose voltage increases rapidly.

This step continues until all the current in actuator Li is discharged, and which corresponds to a first charge of capacitor Ci to voltage V₂, at which point diode Di is disabled to prevent a sign inversion of the current in the actuator (instant t₇).

Subsequently, being isolated from the rest of the circuit, capacitor Ci remains charged to voltage value V₂.

As shown in Figure 3, at instant t₈, control unit 12 again closes one or more switches SWi for time Tonric, so as to again close the circuit including battery B and each actuator Li with a closed switch SWi.

As such, each actuator Li is supplied with increasing current and, in this step, capacitor Ci remains isolated.

At instant t₉, switch SWi (or all the switches closed previously) is again opened so that, for time Toffric, as in interval t₆-t₇, energy is transferred from the actuator to capacitor C1, current Ii in actuator Li falls to zero (instant t₁₀), and the voltage of capacitance line 112 increases.

By repeating the above two steps n times, it is therefore possible to gradually charge the capacitor to the desired V_C level by first charging actuators Li simultaneously to such a value as not to activate them (and so open the injectors), and then discharging the actuator current into the capacitor.

According to the present invention, recharge time Tonric (t₉-t₈) is calculated by unit 12 using an electronic map M3 for supplying Tonric as a function of Vbatt/L input values.

More specifically map M3 supplies Tonric values increasing alongside an increase in inductance L and alongside a fall in Vbatt.

Control unit 12 also presents an electronic map C3 for supplying time Toffric.

Unit 12 also supplies the n number of recharge steps as a function of voltage V₂ of capacitor Ci at the end of the injection cycle.

The n number is calculated by unit 12 using an electronic map M4 for supplying n as a function of an input V₂ value.

Figure 4 shows a detail of control circuit 114 supervising switches of MOSFET SWR.

In particular, Figure 4 shows details of the MOSFET source and drain terminals connected respectively to line 112 and node 113.

Circuit 114 comprises a first capacitor C1 with a first terminal connected to line 112, and a second terminal connected to the cathode of a diode Dr, the anode of which is connected to node 113.

Circuit 114 comprises a second capacitor C2 connected parallel to a Zener diode Dz and presenting a first terminal connected to line 112, and a second terminal connected to the cathode of diode Dr via a resistor R.

Circuit 114 also comprises a first electronic switch SWB (conveniently formed by an optoisolator) located between line 112 and a control terminal (GATE) 115 of MOSFET SWR; and a second electronic switch SWA (conveniently formed by an optoisolator) interposed between control terminal 115 and the node 116 common to diode Dz, capacitor C2 and resistor R.

Switches SWA and SWB are controlled in complementary manner by the logic signal from control unit 12, i.e. one is always on while the other is off.

In actual use, when charging capacitor Ci as described previously, the magnetic energy accumulated by the injectors is transferred to capacitors Ci and C1 which are charged as a function of the respective capacitance values. More specifically, as the ratio of the capacitance values of capacitors C1 and Ci is less than 1, capacitor C1 is charged to a voltage V1 lower than that at the terminals of capacitor Ci, so that diode Dr is disabled, and capacitor C1 is isolated from capacitor Ci and acts as a constant voltage source with one terminal connected to the source terminal of MOSFET SWR.

Moreover, capacitor C2 is charged to a voltage Vz which is determined by Zener diode Dz, is lower than the charge voltage V1 of capacitor C1, and is higher than the threshold voltage Vgsth required for closing MOSFET SWR.

For disabling MOSFET SWR, switch SWA is opened and switch SWB closed, so that voltage Vgs between control terminal 115 and the source terminal of MOSFET SWR equals zero, thus disabling the MOSFET.

For closing MOSFET SWR, switch SWB is opened and switch SWA closed, so that voltage Vz at the terminals of capacitor C2 is applied between control terminal (GATE) 115 and the source terminal of the MOSFET which thus closes. During this step, the current supplied to MOSFET SWR is limited by resistance R, while Zener diode Dz protects GATE 115 of the MOSFET against overvoltage.

As the switching times of MOSFET SWR are not negligible, switches SWA and SWB are activated in advance with respect to the start and end of injection.

Circuit 114 therefore provides for obvious advantages by supplying MOSFET SWR at all times with sufficient voltage for rapidly closing it, and by drawing no energy from capacitor Ci for biasing optoisolators SWA and SWB.

Moreover, circuit 114 is extremely straightforward and reliable.

The system according to the present invention therefore provides for flexibly calculating, for each selected actuator Li, the control times of first and second switches SWi, SWR, by virtue of said times being correlated to the inductance L of the selected actuator Li and to the voltage Vbatt of battery B.

As such, the current supplied to each- injector 7 is regulated as a function of the inductance L of the injector coil. Since the coils of injectors 7 of system 8 invariably present differing inductance values L (due to manufacturing tolerances), each injector 7 is therefore automatically supplied with the most appropriate current value.

More specifically, an increase in inductance L makes it increasingly difficult (for known physical reasons) to inject current into actuator Li, so that time Tbypass is automatically increased to permit the current supplied to the injector to reach the predetermined Ipeak value.

Similarly, a fall in battery voltage Vbatt reduces the current gradient in interval t₃-t₂, so that time Tbypass is again increased to permit the current supplied to the injector to reach the predetermined Ipeak value.

Clearly, changes may be made to the system as described and illustrated herein without, however, departing from the scope of the present invention.

For example, the number of circuits 106 depends on the number of actuators Li and may vary as required.