Thermal protection device for a remotely regulated vehicle alternator

• US 6,414,832 B1
• Filed: 03/23/2000
• Issued: 07/02/2002
• Est. Priority Date: 03/31/1999
• Status: Expired due to Fees

• Current Assignee: Remy Incorporated (BorgWarner Incorporated)
• Original Assignee: Delco Remy Int Inc.
• Inventors: Crecelius, David R., Voss, Richard J.
• Primary Examiner(s): Patel, Rajnikant B.
• Application Number:
  US09/533,328
• Time in Patent Office: 831 Days
• Field of Search: 361/103, 361/120, 361/31, 361/106, 361/23, 361/27, 322/28, 322/24, 322/31, 322/33, 322/34
• US Class Current: 361/120
• CPC Class Codes: H02J 7/00308 Overvoltage protection
• CPC Class Codes: H02J 7/00309 Overheat or overtemperature protection
• CPC Class Codes: H02J 7/0047 with monitoring or indicating devices or circuits
• CPC Class Codes: H02J 7/14 for charging batteries from dynamo-electric generators driven at varying speed, e.g. on vehicle
• CPC Class Codes: H02P 29/02 Providing protection against overload without automatic interruption of supply protection against faults of stepper motors H02P8/36
• CPC Class Codes: H02P 9/02 Details

Abstract

The present invention provides an apparatus for reducing the allowed output current from an electrical device such as a high output capacity vehicle alternator in response to a sensed over temperature condition. In one embodiment, a thermistor is attached to the housing of an alternator to provide temperature sensing capability. As temperature exceeds a temperature set point established by a resistor bridge, op-amps, in combination with a power FET in series with the alternator field windings, act to reduce the allowed current output from the alternator in proportion to the extent the set point temperature has been exceeded. As the alternator temperature returns to below the set point, the output current restriction is reduced such that the allowed current flow is maximized without exceeding the temperature set point.

Claims

1. A thermal protection device for controlling the temperature of at least one alternator component in an alternator having an exterior housing and providing electrical output current from an output to a load, comprising:

means for sensing the temperature of the at least one alternator component and producing signals representative of said temperature;

means for variably controlling output current from the alternator, said means for variably controlling output current being operably connected to the means for sensing temperature and controlling the output current in response to said signals of said means for sensing so that as the temperature of the at least one alternator component increases the means for variably controlling output current reduces the output current of the alternator and as the temperature of the at least one alternator component decreases the output current of the alternator is increased.

2. The thermal protection device of claim 1, wherein the means for sensing temperature comprises a thermistor.

3. The thermal protection device of claim 1, wherein said means for sensing temperature is attached to the exterior housing of the alternator and the exterior housing is capable of conducting heat from the at least one alternator component to provide an exterior housing temperature proportional to the at least one alternator component temperature, so that the means for sensing temperature can sense the proportional temperature of the alternator exterior housing.

4. The thermal protection device of claim 1, wherein the means for variably controlling output current comprises a current modulating circuit.

5. The thermal protection device of claim 4, wherein said alternator comprises a field winding having a field current passing therethrough and wherein the current modulating circuit comprises:

a power transistor operably connected to the field winding of the alternator, said power transistor having a base and being controlled by a base voltage; and

an op-amp circuit connected to the base of the power transistor such that the op-amp circuit controls the base voltage of the power transistor, the op-amp circuit being operably connected to the means for sensing temperature so that as temperature of the at least one alternator component increases, the op-amp circuit reduces the base voltage of the power transistor such that the alternator field current allowed to pass through the power transistor is decreased thereby decreasing the output current.

6. The thermal protection device of claim 5, wherein the op-amp circuit comprises:

a first op-amp having first and second inputs and a variable current output being switchable between a high current output and a low current output depending on the voltage levels at the first and second inputs, said first input of said first op-amp being operably connected to the means for sensing temperature and responsive to said signals to cause said first op-amp to switch to high current output when the temperature exceeds a predetermined level;

a capacitor, said capacitor connected to the first op-amp switchable current output and capable of being charged by the high current output of the first op-amp;

a second op-amp having a first and a second input for comparing voltage and having an output switchable between a first output voltage and a second output voltage, said first input of said second op-amp connected to the capacitor and said second input connected to a first reference voltage, the output voltage operably connected to the base of the power transistor such that when the second op-amp is switched to the first output voltage, alternator field current is allowed to pass through the power transistor and when the second op-amp is switched to the second output voltage, alternator field current allowed to pass through the power transistor is decreased;

said means for sensing temperature comprising a means for providing a voltage level representative of said temperature to said first input of said first op-amp; and

means for providing a first voltage threshold connected to the second input of the first op-amp,

whereby as the temperature of the at least one alternator component increases, the voltage at the first input increases until it exceeds the first voltage threshold on the second input and the first op-amp output switches to high current output thereby passing current to charge said capacitor until the capacitor charge exceeds the first reference voltage and the second op-amp switches to the second output voltage thereby reducing the voltage at the base of the power transistor such that the alternator field current allowed to pass through the power transistor is decreased.

7. The thermal protection device of claim 6, the thermal protection device further comprising:

means for switching the first op-amp to a low current output in response to the base voltage being reduced by the second output voltage;

means for providing a second reference voltage connected to the second input of the second op-amp, the second reference voltage lower than the first reference voltage; and

a discharge path for the capacitor, connected so that when the base voltage is decreased by the second output voltage, the first op-amp current output is switched low, the capacitor is allowed to discharge until the capacitor charge reaches the second reference voltage, the second op-amp output switches to the first output voltage and the base voltage is increased and alternator field current allowed to pass through the power transistor is increased.

8. The thermal protection device of claim 5, wherein the means for sensing temperature comprises a thermistor.

9. The thermal protection device of claim 1, further comprising means for establishing a temperature set point for the at least one alternator component, such that the means for variably controlling output current does not reduce the allowed output current unless the temperature of the at least one alternator component is above the temperature set point.

10. The thermal protection device of claim 9, wherein the reduction in allowed output current is proportional to the temperature difference between the temperature set point and the temperature of the at least one alternator component, such that as the at least one alternator component temperature increases above the temperature set point, less current is allowed to be outputted by the alternator, and as the at least one alternator component temperature decreases from above the temperature set point toward the temperature set point, more current is allowed to be outputted by the alternator.

34. A method of controlling the internal temperature of an alternator by constraining the flow of output current generated by the alternator comprising the steps of:

providing the apparatus of claim 6;

comparing the voltage at the first input of the first op-amp to the voltage at the second input of the first op-amp;

switching said first op-amp to high current output when the voltage at the first input exceeds the voltage at the second input;

charging said capacitor with the first op-amp high current output;

comparing the voltage at the first input of the second op-amp with the voltage at the second input of the second op-amp; and

switching the output of the second op-amp to the second output voltage when the voltage at the first input of the second op-amp exceeds the voltage at the second input of the second op-amp.

35. The method of claim 34, wherein the rate of charging the capacitor is proportional to the difference between the voltage at the first input and the voltage at the second input.

36. The method of claim 34, further providing the apparatus of claim 7, the method comprising the additional steps of:

switching the first op-amp to a low current output in response to second op-amp switching to the second output voltage;

providing said second voltage threshold connected to the second input of the second op-amp;

discharging the capacitor;

comparing the voltage at the first input of the second op-amp to the voltage at the second input of the second op-amp; and

switching the output of the second op-amp to the first output voltage when the voltage at the first input of the second op-amp drops below the voltage at the second input of the second op-amp.

11. A thermal protection device for controlling the internal temperature of a high output capacity motor vehicle alternator by controlling the flow of output current generated by the alternator, the alternator having a housing configured to hold operable components of the alternator, the housing being capable of conducting heat generated by the operable components of the alternator so that the temperature of the housing is proportional to the internal temperature of the alternator, said device comprising:

means for sensing temperature of the housing and producing signals representative of said temperature; and

means for controlling allowed output current of the alternator operatively connected to the means for sensing temperature, so that as the temperature of the housing increases, the means for controlling allowed output current reduces the allowed output current of the alternator in response to the increased temperature of the alternator housing.

12. The thermal protection device of claim 11, wherein the means for sensing temperature comprises a thermistor.

13. The thermal protection device of claim 11, wherein the means for controlling allowed output current comprises a current modulating circuit.

14. The thermal protection device of claim 13, wherein said alternator comprises a field winding passing a field current therethrough and wherein the current modulating circuit comprises:

a power transistor operably connected to the field winding of the alternator, said power transistor having a base and being controlled by a base voltage; and

an op-amp circuit connected to the base of the power transistor such that the op-amp circuit controls the base voltage of the power transistor, the op-amp circuit being operably connected to the means for sensing temperature so that as temperature of the alternator increases, the op-amp circuit reduces the base voltage of the power transistor such that the alternator field current allowed to pass through the power transistor is decreased.

15. The thermal protection device of claim 14, wherein the op-amp circuit comprises:

a first op-amp having first and second inputs and a variable current output being switchable between a high current output and a low current output depending on the voltage levels at the first and second inputs, said first input of said first op-amp being operably connected to the means for sensing temperature and responsive to said signals to cause said first op-amp to switch to high current output when the temperature of the housing exceeds a predetermined level;

a capacitor, said capacitor connected to the first op-amp switchable current output and capable of being charged by the high current output of the first op-amp;

a second op-amp having a first and a second input for comparing voltage and having an output switchable between a first output voltage and a second output voltage, said first input of said second op-amp connected to the capacitor and said second input connected to a first reference voltage, the output voltage operably connected to the base of the power transistor such that when the second op-amp is switched to the first output voltage, alternator field current is allowed to pass through the power transistor and when the second op-amp is switched to the second output voltage, alternator field current allowed to pass through the power transistor is decreased;

said means for sensing temperature comprising a means for providing a voltage level representative of said temperature to said first input of said first op-amp; and

means for providing a first voltage threshold connected to the second input of the first op-amp,

whereby as the temperature of the alternator housing increases, the voltage at the first input increases until it exceeds the first voltage threshold on the second input and the first op-amp output switches to high current output thereby passing current to charge said capacitor until the capacitor charge exceeds the first reference voltage and the second op-amp switches to the second output voltage thereby reducing the voltage at the base of the power transistor such that the alternator field current allowed to pass through the power transistor is decreased.

16. The thermal protection device of claim 15, the thermal protection device further comprising:

means for switching the first op-amp to a low current output in response to the base voltage being reduced by the second output voltage;

means for providing a second reference voltage connected to the second input of the second op-amp, the second reference voltage lower than the first reference voltage; and

a discharge path for the capacitor, connected so that when the base voltage is decreased by the second output voltage, the first op-amp current output is switched low, the capacitor is allowed to discharge until the capacitor charge reaches the second reference voltage, the second op-amp output switches to the first output voltage and the base voltage is increased and alternator field current allowed to pass through the power transistor is increased.

17. The thermal protection device of claim 15, wherein the means for sensing temperature comprises a thermistor.

18. The thermal protection device of claim 11, further comprising means for establishing an alternator housing temperature set point, such that the means for controlling output current does not reduce the allowed output current unless the alternator housing temperature is above the temperature set point.

19. The thermal protection device of claim 18, wherein the reduction in allowed output current is proportional to the temperature difference between the temperature set point and the alternator housing temperature, such that as the alternator housing temperature increases above the temperature set point, less current is allowed to be outputted by the alternator, and as the alternator housing temperature decreases from above the temperature set point toward the temperature set point, more current is allowed to be outputted by the alternator.

20. In combination:

an alternator having an exterior housing and providing electrical output current from an output to a load;

temperature sensor operably connected to the alternator and producing signals representative of the temperature being sensed; and

a control circuit that will variably control output current from the alternator, the control circuit operably connected to the temperature sensor so that as the temperature being sensed increases, the control circuit reduces the allowed output current of the alternator and as the temperature being sensed decreases the control circuit increases the allowed output current of the alternator.

21. The combination of claim 20, wherein the temperature sensor comprises a thermistor.

22. The combination of claim 20, wherein said temperature sensor is attached to the exterior housing of the alternator and the housing is capable of conducting heat generated internally by the alternator to provide a housing temperature representative of the temperature of the alternator housing.

23. The combination of claim 20, wherein the control circuit comprises a current modulating circuit.

24. The combination of claim 23, wherein said alternator has a field current passing through a field winding and wherein the current modulating circuit comprises:

a power transistor operably connected to the field winding of the alternator, said power transistor having a base and being controlled by a base voltage; and

an op-amp circuit connected to the base of the power transistor such that the op-amp circuit controls the base voltage of the power transistor, the op-amp circuit being operably connected to the means for sensing temperature so that as temperature being sensed increases, the op-amp circuit reduces the base voltage of the power transistor such that the alternator field current allowed to pass through the power transistor is decreased.

25. The combination of claim 24, wherein the op-amp circuit comprises:

a first op-amp having first and second inputs and a variable current output being is switchable between a high current output and a low current output depending on the voltage levels at the first and second inputs, said first input of said first op-amp being operably connected to the temperature sensor and responsive to said signals to cause said first op-amp to switch to high current output when the temperature sensed exceeds a predetermined level;

a capacitor, said capacitor connected to the first op-amp switchable current output and capable of being charged by the high current output of the first op-amp;

a second op-amp having a first and a second input for comparing voltage and having an output switchable between a first output voltage and a second output voltage, said first input of said second op-amp connected to the capacitor and said second input connected to a reference voltage, the output voltage operably connected to the base of the power transistor such that when the second op-amp is switched to the first output voltage, alternator field current is allowed to pass through the power transistor and when the second op-amp is switched to the second output voltage, alternator field current allowed to pass through the power transistor is decreased;

said temperature sensor signals comprising voltage levels representative of said temperature; and

a voltage threshold connected to the second input of the first op-amp,

whereby as the temperature sensed increases, the voltage at the first input increases until it exceeds the voltage threshold on the second input and the first op-amp output switches to high current output thereby passing current to charge said capacitor until the capacitor charge exceeds the reference voltage and the second op-amp switches to the second output voltage thereby reducing the voltage at the base of the power transistor such that the alternator field current allowed to pass through the power transistor is decreased.

26. The combination of claim 25, the op-amp circuit further comprising a discharge path for the capacitor, and wherein:

said voltage threshold is switchable between a first voltage level and a second voltage level, such that when the temperature sensed exceeds the predetermined level and the first voltage threshold is selected, the first op-amp is switched to high current output, and when the temperature sensed exceeds the predetermined level and the second voltage threshold is selected, the first op-amp is switched to low current output,

said voltage threshold being responsive to the base voltage, such that when the base voltage allows increased field current to pass through the power transistor, the first voltage threshold is selected and when base voltage is reduced such that the alternator field current allowed to pass through the power transistor is decreased, the second voltage threshold is selected; and

said reference voltage is switchable between a first reference voltage and a second reference voltage, the second reference voltage being less than the first reference voltage

said reference voltage being responsive to the base voltage, such that when the base voltage allows increased field current to pass through the power transistor, the first reference voltage is selected and when base voltage is reduced such that the alternator field current allowed to pass through the power transistor is decreased, the second reference voltage is selected,

whereby as the sensed temperature increases, the voltage at the first input increases until it exceeds the first voltage threshold on the second input and the first op-amp output switches to high current output thereby passing current to charge said capacitor until the capacitor charge exceeds the first reference voltage and the second op-amp switches to the second output voltage thereby reducing the voltage at the base of the power transistor such that the alternator field current allowed to pass through the power transistor is decreased and switching to the second reference voltage and to the second voltage threshold such that the second reference voltage on the second input of the first op-amp is decreased below the voltage on the first input of the first op-amp and the output of the first op-amp is switched to low current output and the capacitor is allowed to discharge, and such that the second reference voltage on the second input of the second op-amp is decreased below the initial voltage level on the second input of the second op-amp, so that the output of the second op-amp is maintained at the second output voltage until such time as the capacitor has discharged to a voltage lower than the second reference voltage.

27. The combination of claim 20, wherein the temperature sensor comprises a thermistor.

28. The combination of claim 20, further comprising a temperature set point, such that control circuit does not reduce the allowed output current unless the sensed temperature is above the temperature set point.

29. The combination of claim 28, wherein the reduction in allowed output current is proportional to the temperature difference between the temperature set point and the sensed temperature, such that as the sensed temperature increases above the temperature set point, less output current is allowed to be outputted by the alternator, and as the sensed temperature recedes from above the temperature set point toward the temperature set point, more output current is allowed to be outputted by the alternator.

30. A method of controlling the internal temperature of an alternator by constraining the flow of output current generated by the alternator comprising the steps of:

establishing a temperature set point corresponding to a maximum desired temperature for the alternator;

determining the temperature of the alternator;

comparing the temperature of the alternator to the temperature set point;

controlling the output current of the alternator as a function of the comparison such that as the temperature of the alternator increases, the amount of output current allowed to be generated by the alternator is reduced, and as the alternator temperature decreases the amount of output current allowed to be generated by the alternator is increased.

31. The method of claim 30, wherein the step of determining the temperature of the alternator comprises the step of using a thermistor.

32. The method of claim 30, wherein the alternator comprises an exterior housing capable of conducting heat from the interior of the alternator to provide a housing temperature proportional to the internal alternator temperature and the step of determining the temperature of the alternator comprises the steps of:

determining the temperature of the exterior housing of the alternator; and

adjusting the temperature set point to compensate for the difference between the internal alternator temperature and the temperature of the exterior housing.

33. The method of claim 30, wherein the step of controlling the output current of the alternator comprises the step of controlling the base voltage of a power transistor.