GB2295931A

GB2295931A - Fuel injector driver with raised initial current

Info

Publication number: GB2295931A
Application number: GB9603567A
Authority: GB
Inventors: Garry Brown; Thomas Richard Brock
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1992-08-22
Filing date: 1993-07-22
Publication date: 1996-06-12
Anticipated expiration: 2013-07-22
Also published as: GB2295931B; GB9603567D0

Abstract

A switch mode fuel injector circuit comprises a main switch 14, a recirculation switch 20, and a current detector 18. The solenoid 16 current is regulated by the control circuit 24 such that an initial peak current period (figure 2) is followed by a holding current period. The recirculation switch 20 may be opened to increase current decay at the end of the peak current period and at the end of the holding current period, and it may be closed before the main switch at the beginning of the hold phase. The control circuit 24 determines whether the solenoid current has exceeded a given level, or has not reached a desired level within a fixed time, and turns off switches 14 or 20, or both. The recirculation switch 20 may be located in the solenoid branch (figure 5). <IMAGE>

Description

Fuel InJector Control This invention is a divisional application divided from the applicant's co-pending application GB 9315167.8 and relates to solenoid actuation systems which include switch mode circuits to control the current level in the actuation means, and has particular application in fuel injector control systems.

The present invention provides a solenoid actuator control system having a charge circuit and a recirculation circuit with a common section forming part of each, a power supply for creating a potential difference across the charge circuit, solenoid actuation means in the common section, charge switch means for opening and closing the charge circuit, current measuring means for measuring the current in the charging circuit and in the recirculation circuit, and control means for switching the system from a charge mode to a recirculation mode and back in response to signals from the current measuring means to regulate the current through the solenoid actuation means, the control means being arranged to adopt a peak mode holding the current in the solenoid actuation means between a peak high level and a peak low level during an initial period and then to adopt a hold mode holding the current in the actuation means between a hold high level and a hold low level, wherein the control means is arranged to enter hold mode after a predetermined period from initiation of an actuator pulse.

The circuit may also comprise recirculation switch means for opening and closing the recirculation circuit.

Preferably the control means is arranged to enter hold mode on expiry of a first predetermined period if the current in the actuation means has reached a predetermined level within that period, and to enter hold mode on expiry of a second predetermined period if the said predetermined level has not been reached within one of said periods.

More preferably the control means is arranged to enter hold mode immediately if the said predetermined level is reached during the second time period.

Desirably the recirculation switch is arranged to be closed before the charge switch after the control means has switched from peek mode to hold mode thereby to slow down the current decay rate.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Fig.l is a diagram of a fuel injector control system according to a first embodiment of the invention; Fig.2 is a graph showing the current through the injector actuation means of the system of Fig.l as a function of time during nominal operation; Fig.3 is a graph similar to Fig.2 showing the current during different operation when the current in the injector actuation means rises less quickly; Fig.4 is a graph similar to Fig.3 showing the current during different operation when the current in the injector actuation means rises still less quickly; and Fig.5 is a diagram of a fuel injector control system according to a second embodiment of the invention.

Referring to Fig.l, in the first embodiment of the invention the fuel injector supply system comprises a charge circuit 10 and a recirculation circuit 12. The charge circuit 10 comprises a power supply, a charge switch 14 in the form of a MOSFET, a fuel injector actuation means in the form of an injector coil 16, a current sensor 18 and an earth connection connected in series in that order.

A recirculation switch 20 in the form of a MOSFET and a diode 22 are connected in series across the injector coil 16 and the current sensor 18. The diode prevents the current flow from the supply through the recirculation switch 20 to earth so current can therefore only flow through the recirculation switch 20 by flowing around the loop comprising the recirculation switch 20 the diode 22 the injector coil 16 and the current sensor 18.

That loop forms the recirculation circuit 12, and the injector coil 16 and current sensor 18 are in a common section 17 forming part of the charge circuit 10 and the recirculation circuit 12.

A control circuit 24 including a clock 26 is connected to the charge switch 14, the recirculation switch 20 and the current sensor 18 and is arranged to operate the switches to control the current in the injector coil in response to the current sensor 18 and the clock 26.

The current passed through the injector coil 16 will now be described with reference to Figure 2 in which the current through an injector in normal operation is shown as a function of time. The current pattern shown is that required for a low impedance injector which requires an initial peak current to open the injector and then a lower hold current to hold the injector open for as long as is required.

When the injector is closed the charge switch 14 and the recirculation switch 20 are both open and no current flows in the injector coil 16. When it is desired to initiate an injector pulse a command signal is produced in the engine management system which closes both the switches 14, 20 and triggers the clock 26 at time to and the current I through the injector coil 16 rises rapidly. When the current sensor 18 detects that the current reaches a peak high level I4 the control circuit 24 opens the charge switch 14. That prevents any further current from flowing through the charge circuit 10 but a current does continue to flow through the injector coil 16 and current sensor 18 round the recirculation circuit 12.

The current in the recirculation circuit falls off because there is no power supply to maintain it. When the current falls to a peak low level I3 the charge switch is closed again and the current I rises again.

The charge switch 14 keeps switching on and off to maintain the current I between the peak high and peak low levels I4, I3 until a time td at the expiry of a period Tpeak from the initial closing of the charge switch 14, when it is assumed that the injector is fully open. At that point the charge switch and the recirculation switch are both opened and the current I drops rapidly until the current sensor detects that it has reached a hold high level 12. The recirculation switch then closes so that the current I drops less rapidly until it reaches I. Then the charge switch 14 and recirculation switch 15 are both closed until the current rises to the hold high level 12.

The current is held between I1 and I2 by the control unit 24 switching the charge switch 14 on and off for a hold period T-hold, which expires at time tp The complete length of the pulse from to to tp is determined by the engine management system and is dependent on the speed of the engine and the amount of fuel required.

At time tp both switches 14, 20 are opened and the current I falls rapidly to zero, allowing the injector to close and ending the injection pulse.

If the current reaches I3 before the desired injector opening time td then the injector is functioning normally and the control circuit operates as described above. If the current reaches I3 at a time t1 after the expiry of the desired peak current time at td but before expiry of a maximum injector opening time at t, m as shown in Figure 3 then the control circuit 24 opens both of the switches on the expiry of that time period and enters hold mode, which is maintained until the end of the injector pulse period at tp when both of the switches 14, 20 are opened.

Referring to Figure 4, if at time tm the peak high current I4 has not been reached the control circuit goes to hold mode at trn and this is maintained until the end of the injector pulse at tp.

Because the required injector pulse can sometimes be very short it is possible that tp is before the expiry of T-peak, or before the peak high current I4 has been reached. In that case the switches 14, 20 still both open at tp.

Referring to Figure 5 in a preferred embodiment of the invention all of the components which are the same as those in Figure 1 are indicated by the same reference numeral preceded by 1. The only difference is that the recirculation switch 120 is in the common section 117 of the circuit between the injector coil 116 and the current measurer 118. This enables the inclusion of additional safety features to protect the circuit.

Because the injector coil 116 is remote from the rest of the circuit there is a length of wire from the top of the injector coil, i.e. the side thereof nearest the supply, to the charge switch 114 and another length of wire from the bottom of the injector coil, i.e. the side thereof nearest to earth, to the recirculation switch 120 which can be shorted causing damage to the circuit, in particular to the current measurer 118, or cause the injector to be held on for long periods which is obviously undesirable for example after an accident.

The control circuit 124 is therefore arranged to detect certain irregularities in the current measured by the current measurer 118 and operate at least one of the switches 114, 120 to break any short circuit which may have been created.

The clock 126 and the current measurer 118 can be used to monitor the generation of the system to check for its correct operation and take precautionary measures such as switching off the current to the injector coil 116 if any problems are detected.

If the bottom of the injector coil 116 is shorted to ground the current sensor 118 will not sense an increase in current after the switches 114, 120 are closed at the start of an injection pulse. The control circuit 124 is therefore arranged to measure the time taken from to for the current to reach 12. If this exceeds a predetermined period the control circuit opens the charge switch 114.

Although 12 is used as the measured current in this case, 13, or another suitable current level could equally be used.

If the top of the injector coil is shorted to ground the current sensor would not detect a rise in current after to. However the current in the charge switch would rise very quickly because there would be little impedance in the circuit. Therefore a current limiting device 128 is connected between the charge switch 114 and the supply to cut off the circuit if the current through it is high enough to damage the recirculation switch 114.

If the bottom of the injector coil 116 is shorted to the supply the current will rise much more quickly after to than usual because of the low impedance in the circuit.

The control circuit is therefore arranged to turn off the recirculation switch 120 if the current reaches I3 before a predetermined time tx Again, current levels other than I3 could be used in this check.

The control circuit 124 is also arranged to check the current I in both peak mode and hold mode to determine whether it reaches any of a number of check levels which would indicate a malfunction. In peak mode the check current levels are set above the peak high current I4 and below the peak low current 13. In hold mode the check levels are set above the hold high level I2 and below the hold low level Il. If any of the check levels are reached the current to the injector coil 116 is cut off or some other precautionary action taken. Alternatively only one check level may be used in each mode.

Claims

1. A solenoid actuator control system having a charge circuit and a recirculation circuit with a common section forming part of each, a power supply for creating a potential difference across the charge circuit, solenoid actuation means in the common section, charge switch means for opening and closing the charge circuit, current measuring means for measuring the current in the charging circuit and in the recirculation circuit, and control means for switching the system from a charge mode to a recirculation mode and back in response to signals from the current measuring means to regulate the current through the solenoid actuation means, the control means being arranged to adopt a peak mode holding the current in the solenoid actuation means between a peak high level and a peak low level during an initial period and then to adopt a hold mode holding the current in the actuation means between a hold high level and a hold low level, wherein the control means is arranged to enter hold mode after a predetermined period from initiation of an actuator pulse.

2. A solenoid actuator control circuit according to claim 1 further comprising recirculation switch means for opening and closing the recirculation circuit.

A solenoid control system according to claim 1 or claim 2 wherein the control means is arranged to enter hold mode on expiry of a first predetermined period if the current in the actuation means has reached a predetermined level within that period, and to enter hold mode on expiry of a second predetermined period if the said predetermined level has not been reached within one of said periods.

4. A solenoid actuator control system according to claim 3 wherein the control means is arranged to enter hold mode immediately if the said predetermined level is reached during the second time period.

5. A solenoid actuator control system according to claim 2, or either of claims 3 or 4 when dependent thereon, wherein the recirculation switch is arranged to be closed before the charge switch after the control means has switched from peek mode to hold mode thereby to slow down the current decay rate.

6. A solenoid actuator control system substantially as described herein with reference to the accompanying drawings.