Drive circuit for inductive loads, particularly for fuel injectors

Claims

1. An improved fuel injector drive circuit, said drive circuit having

a switch series-connected to an inductive load, said load having first and second terminals;

a first current recirculating branch, having nodes connected to said first and second terminals of said load, for maintaining a predetermined load voltage and enabling a fall in load current at a first predetermined rate from a peak current and having a plurality of series-connected Zener diodes;

a second current recirculating branch parallel-connected to the load, for enabling a fall in load current at a second predetermined rate from a predetermined maximum hold current;

a logic control unit responsive to said load current for opening and closing said switch and said branches, so that the load is supplied with current rising to said peak current, and then falling at said first predetermined rate and oscillating between said predetermined maximum hold current and a predetermined minimum hold current; the improvement comprising

means, connected to said first branch, for varying said predetermined load voltage supplied across the load to a lower predetermined load voltage when said load current reaches a predetermined amount from said peak current, said supplied voltage varying means having a transistor having emitter and collector terminals connected to said second terminal of the load and between a predetermined pair of connected Zener diodes, a base terminal of said transistor coupled to an output of a comparator having a first input connected to a reference voltage source, and a second input connected to a load current sensing element for short-circuiting a predetermined subset of said series-connected Zener diodes;

whereby said fall in load current from said peak current occurs at said first predetermined rate and is then slowed when said load current reaches said predetermined amount from said peak current.

3. The circuit as in claim 2 wherein said first branch comprises a plurality of series-connected Zener diodes generating said predetermined bias voltage and said first branch bias voltage decreasing means comprises means for short-circuiting a subset of said Zener diodes to decrease said predetermined bias voltage.

4. The circuit as in claim 3 wherein said first recirculating branch comprises a transistor having a base terminal connected to said first node, an emitter terminal connected to said Zener diodes and a collector terminal connected to a third node of said first recirculating circuit, said third node connected to said second reference potential line.

5. The circuit as in claim 4 wherein said first recirculating branch comprises a resistive means connected between said collector terminal and said third node, said collector terminal further connected to said switch.

6. The circuit as in claim 3 wherein said short-circuiting means comprises a transistor having emitter and collector terminals connected between said load and said switch, and a predetermined pair of connected Zener diodes, a base terminal of said transistor connected to a second switch for turning on said transistor when said current through said load reaches said predetermined amount less than said peak value, said second switch connected to an output of a comparator having a first input connected to a reference voltage source, and a second input connected to a load current sensing element.

7. The circuit as in claim 6 wherein said inductive load comprises a fuel injector.

8. A circuit for driving an inductive load, said circuit comprising

a switch connected in series with said inductive load between first and second reference potential lines;

a recirculating branch having a first node connected to said first reference potential line, and a second node connected between said switch and said inductive load, said branch having a plurality of series-connected Zener diodes generating said voltage across said load to enable a fall in load current through said load after said current reaches a peak value;

means, responsive to said load current and connected to said switch and to said first reference potential line in parallel to said load, for controlling said switch so that said load current oscillates between first and second hold values after said current falls from said peak value; and

means, responsive to said controlling means and connected to said branch, for short-circuiting a subset of said Zener diodes to decrease said voltage across said load when said current through said load reaches a predetermined value after said current falls from said peak value;

whereby said fall in current through said load is slowed when said current reaches said predetermined value from said peak value.

9. The circuit as in claim 8 wherein said recirculating branch has a third node connected to said second reference potential line and a transistor having a base terminal connected to said first node, an emitter terminal connected to said Zener diodes and a collector terminal connected to a third node of said recirculating circuit, said third node connected to said second reference potential line.

10. The circuit as in claim 9 wherein said recirculating branch comprises a resistive means connected between said collector terminal and said third node, said collector terminal further connected to said switch.

11. The circuit as in claim 8 wherein said short-circuiting means comprises a transistor having emitter and collector terminals connected between said load and said switch, and between a predetermined pair of connected Zener diodes, a base terminal of said transistor connected to a second switch for turning on said transistor when said current through said load reaches said predetermined value, said second switch connected to an output of a comparator having a first input connected to a reference voltage source, and a second input connected to a load current sensing element.

12. The circuit as in claim 11 wherein said inductive load comprises a fuel injector..Iadd.

13. A device for controlling an electronic fuel injector that has a solenoid and a solenoid-controlled fuel valve, said solenoid having first and second terminals, said device comprising:

a first supply terminal coupled to said first terminal of said solenoid;

a second supply terminal;

a control circuit having an input terminal for receiving a fuel-injector control signal, a sensing input terminal, a first control output terminal, and a second control output terminal;

a sensing element having a first terminal coupled to said sensing input terminal of said control circuit and having a second terminal;

a solenoid drive switch having a control terminal coupled to said first control output terminal of said control circuit, said drive switch serially coupled to said sensing element, the series combination of said drive switch and said sensing element being coupled between said second terminal of said solenoid and said second supply terminal; and

a first variable voltage controller having first and second regulator terminals respectively coupled to said first and second terminals of said solenoid, said variable voltage controller having a control terminal coupled to said second control output terminal of said control circuit..Iaddend..Iadd.14. The device of claim 13, further comprising:

said control circuit having a third control output terminal; and

a second voltage controller having first and second regulator terminals respectively coupled to said first and second terminals of said solenoid, said second voltage controller having a control terminal coupled to said third output terminal of said control circuit..Iaddend..Iadd.15. The device of claim 13 wherein said control circuit comprises:

a maximum-hold-current reference terminal; and

a comparator having a first input terminal coupled to said sensing input terminal, a second input terminal coupled to said maximum-hold-current reference terminal, and an output terminal coupled to said second control

output terminal..Iaddend..Iadd.16. The device of claim 13 wherein said first variable voltage controller comprises:

a plurality of diodes that are serially coupled between said first and second terminals of said solenoid, said diodes having their cathodes directed toward said second terminal of said solenoid; and

a switch having a control terminal coupled to said control terminal of said first voltage controller, said switch coupled in parallel with one or more of said diodes..Iaddend..Iadd.17. A device for driving an inductive load, comprising:

a drive switch coupled to said inductive load;

a first voltage regulator coupled to said inductive load; and

a control circuit coupled to said voltage regulator and to said drive switch, said control circuit being connected to receive an input signal, and in response to said input signal, said control circuit being operable to,

close said drive switch such that a charge current flows through said inductive load,

open said drive switch when said charge current rises to a peak level,

control said voltage regulator to adjust the voltage across said inductive load such that a discharge current that flows through said inductive load falls at a first rate,

detect when said discharge current falls to a first predetermined value, and

in response to said detection, control said voltage regulator to adjust said voltage across said inductive load so as to decrease the rate at which said discharge current falls..Iaddend..Iadd.18. The device of claim 17 wherein said control circuit is further operable to:

detect when said discharge current falls to a second predetermined value that is less than said first predetermined value; and

in response to said latter detection, control said switch such that a hold

current flows through said inductive load..Iaddend..Iadd.19. The device of claim 17 wherein said control circuit is further operable:

to control said voltage regulator to limit said voltage across said inductive load to a first voltage level substantially immediately after opening said drive switch; and

in response to detecting said discharge current falling to said first predetermined value, to control said voltage regulator to reduce said voltage across said inductive load to a second voltage level that is less than said first voltage level..Iaddend..Iadd.20. The device of claim 17, further comprising:

a second voltage regulator coupled to said inductive load and said control circuit; and

in response to said discharge current falling to said second predetermined value, said control circuit operable to activate said second voltage regulator and alternately open and close said drive switch such that said hold current oscillates between said first and second current levels..Iaddend..Iadd.21. The device of claim 17, further comprising:

a regulator transistor having a control terminal coupled to said control circuit, said regulator transistor coupled across said inductive load; and

in response to said discharge current falling to said second predetermined value, said control circuit operable to activate said regulator transistor and alternately open and close said drive switch such that said hold current oscillates between said first and second current levels..Iaddend..Iadd.22. The device of claim 17 wherein said first voltage regulator comprises:

a plurality of serially connected reverse-biased diodes coupled across said inductive load; and

a switch having a control terminal coupled to said control circuit, said

switch coupled across one or more of said diodes..Iaddend..Iadd.23. An inductive load drive circuit, comprising:

a switch series-connected to an inductive load, said load having first and second terminals;

a first current recirculating branch, having nodes connected to said first and second terminals of said load, for maintaining a predetermined load voltage and enabling a fall in load current at a first predetermined rate from a peak current;

a logic control unit responsive to said load current for opening and closing said switch and said branches, so that the load is supplied with current rising to said peak current, and then falling at said first predetermined rate and oscillating between said predetermined maximum hold current and a predetermined minimum hold current; and

means, connected to said first branch, for varying said predetermined load voltage supplied across the load to a lower predetermined load voltage when said load current reaches a predetermined amount from said peak current;

whereby said fall in load current from said peak current occurs at said first predetermined rate and is then slowed when said load current reaches said predetermined amount from said peak current..Iaddend..Iadd.24. The drive circuit of claim 23, further comprising a second current recirculating branch parallel-connected to the load, for enabling a fall in load current at a second predetermined rate from a predetermined maximum hold current..Iaddend..Iadd.25. A circuit as claimed in claim 23 wherein said first recirculating branch comprises a number of series-connected bias voltage elements, and said supplied voltage varying means comprise means for short-circuiting a predetermined subset of said bias voltage elements..Iaddend..Iadd.26. A circuit as claimed in claim 25 wherein said bias voltage elements comprise a plurality of series-connected Zener diodes, and said short-circuiting means comprise a transistor having emitter and collector terminals connected to said second terminal of the load and between a predetermined pair of connected Zener diodes, a base terminal of said transistor coupled to an output of a comparator having a first input connected to a reference voltage source, and a second input connected to a load current sensing element..Iaddend..Iadd.27. A circuit for driving an inductive load, said circuit comprising:

a switch connected in series with said inductive load between first and second reference potential lines;

a first recirculating branch having a first node connected to said first reference potential line, and a second node connected between said switch and said inductive load, said first branch providing a fall in current through said load after said current reaches a peak value;

a second recirculating branch connected between said switch and said first reference potential line in parallel with said inductive load, said second branch enabling a fall in current through said load;

a logic unit for controlling said switch and said branches so that said load is supplied with current rising to said peak value, and then falling to and oscillating about a lower hold value; and

means connected to said first branch for controlling said first branch so that said fall in current through said load is slowed after said current reaches a predetermined amount less than said peak value..Iaddend..Iadd.28. The circuit as in claim 27 wherein said first branch comprises a plurality of series-connected bias voltage elements for generating a predetermined bias voltage across said load to enable said fall in current through said load, and said controlling means for short-circuiting a subset of said bias voltage elements to decrease said bias voltage across said load when said current through said load reaches said predetermined amount less than said peak value so that said fall in current through said load is slowed after said current reaches said predetermined amount less than said peak value..Iaddend..Iadd.29. The circuit as in claim 28 wherein said bias voltage elements comprise Zener diodes connected in series, and wherein said short-circuiting means comprises a transistor having emitter and collector terminals connected between said load and said switch, and a predetermined pair of connected Zener diodes, a base terminal of said transistor connected to a second switch for turning on said transistor when said current through said load reaches said predetermined amount less than said peak value..Iaddend..Iadd.30. The circuit as in claim 27 wherein said first recirculating branch has a third node connected to said second reference potential line..Iaddend..Iadd.31. A circuit for driving an inductive load, said circuit comprising:

a switch connected in series with said inductive load between first and second reference potential lines;

a recirculating branch having a first node connected to said first reference potential line, and a second node connected between said switch and said inductive load, said branch providing a voltage across said load to enable a fall in load current through said load after said current reaches a peak value;

means, responsive to said load current and connected to said switch and to said first reference potential line in parallel to said load, for controlling said switch so that said load current oscillates between first and second hold values after said current falls from said peak value; and

means, responsive to said controlling means and connected to said branch, for decreasing said voltage across said load when said current through said load reaches a predetermined value after said current falls from said peak value;

whereby said fall in current through said load is slowed when said current reaches said predetermined value from said peak value..Iaddend..Iadd.32. The circuit as in claim 31 wherein said branch comprises a plurality of series-connected bias voltage elements generating said voltage across said load and said voltage decreasing means comprises means for short-circuiting a subset of said bias voltage elements to decrease said voltage..Iaddend..Iadd.33. The circuit as in claim 31 wherein said bias voltage elements comprise Zener diodes connected in series and wherein said short-circuiting means comprises a transistor having emitter and collector terminals connected between said load and said switch, and between a predetermined pair of connected Zener diodes, a base terminal of said transistor connected to a second switch for turning on said transistor when said current through said load reaches said predetermined value..Iaddend..Iadd.34. The circuit as in claim 31 wherein said recirculating branch has a third node connected to said second reference potential line..Iaddend..Iadd.35. A method of driving an inductive load, comprising:

causing a charge current to flow through said inductive load;

allowing said inductive load to discharge when said charge current becomes equal to a peak value such that a discharge current that decreases at a first rate flows through said inductive load;

causing said discharge current to decrease at a second rate when said discharge current becomes equal to a first value, said second rate less than said first rate; and

causing a hold current to flow through said inductive load when said discharge current becomes equal to a second value that is less than said first value..Iaddend..Iadd.36. The method of claim 35 wherein said causing a hold current to flow through said inductive load comprises maintaining said hold current between said first and second values..Iaddend..Iadd.37. The method of claim 35 wherein said causing a hold current to flow through said inductive load comprises causing said hold current to oscillate between said first and second values..Iaddend..Iadd.38. A method of driving an inductive load, comprising:

coupling a first charge voltage across said inductive load such that a charge current flows through said inductive load;

uncoupling said charge voltage from across said inductive load when said charge current attains a peak level;

after said uncoupling, regulating a discharge voltage across said inductive load such that a discharge current flows through said inductive load, said discharge current decreasing at a first rate until said discharge current attains a first current level, said discharge current thereafter decreasing at a second rate that is less than said first rate; and

when said discharge current attains a second current level, alternately coupling a second charge voltage across said inductive load and regulating said discharge voltage such that a hold current, that is between said first and second current levels flows through said inductive load.

.Iaddend..Iadd.39. The method of claim 38 wherein said regulating comprises:

limiting said discharge voltage to a first voltage level until said discharge current attains said first current level; and

limiting said discharge voltage to a second voltage level that is less than said first voltage level when said discharge current attains said first current level..Iaddend..Iadd.40. The method of claim 38 wherein said first and second charge voltages are equivalent..Iaddend..Iadd.41. The method of claim 38 wherein said alternately coupling and regulating comprises alternately coupling said second charge voltage across said inductive load and regulating said discharge voltage such that said hold current oscillates between said first and second current levels..Iaddend..Iadd.42. The method of claim 38 wherein said regulating comprises:

coupling a first number of reverse-biased diodes across said inductive load until said discharge current attains said first current level; and

coupling a second number of reverse-biased diodes across said inductive load when said discharge current attains said first current level, said second number less than said first number..Iaddend.