DUAL GENERATOR ELECTRICAL APPARATUS

Abstract: A motor vehicle electrical apparatus that has two alternating current generators (10,30) for supplying current to the electrical loads (52) on the vehicle including a storage battery (50). Both alternating current generators are connected to rectifier means (20,38) which supply direct current to the loads. The output voltage of one of the generators is controlled by a voltage regulator (54). The direct current outputs of the rectifier means is sensed (68) and the field current of the other generator is controlled (70) such that its output current (I30) is slaved to and follows the output current (I10) of the generator that is controlled by the voltage regulator.

Description: This invention relates to a dual generator apparatus wherein a pair of generators supply current to a common electrical load. The continued demand for more electrically driven accessories on a motor vehicle makes it difficult to supply all the power to the electrical loads on a motor vehicle from a single generator since there is a limit to the amount of power that can be developed by a single generator. A possible solution to the problem of supplying adequate power to the electrical loads is to use two generators instead of one. In general, dual generator electrical apparatus are known, examples being the arrangements disclosed in the US patent Nos 2,504,768; 4,539,515; 4,604,565 and 4,347,473. Further, US patent No 4,509,005 discloses a single regulator for a dual alternator apparatus and US patent No 4,661,760 discloses a regulating apparatus for a generator that senses generator current. The present invention is concerned with providing a dual generator apparatus where both generators supply current to a common electrical load and wherein only one of the generators has its output voltage controlled by a voltage regulator. The dual generator apparatus of this invention has a load proportioning control which senses the output currents of both generators. In response to the sensing of the output currents of the two generators, the apparatus controls the field current of the generator that does not have a voltage regulator such that the output current of that generator follows and is slaved to the prevailing output current level of the generator that has its output voltage controlled by a voltage regulator. It accordingly is an object of this invention to provide a dual generator apparatus wherein only one of the generators is controlled by a voltage regulator and wherein the field current of the other generator is controlled such that the output current of that generator follows and is slaved to the prevailing output current level of the generator that is controlled by the voltage regulator. To this end, a dual generator apparatus in accordance with the present invention is characterised by the features specified in the characterising portion of Claim 1. This invention provides a motor vehicle electrical apparatus that has a plurality of electrical loads including a storage battery and wherein two generators are used to supply current to the vehicle electrical loads. The output voltage of one of the generators is controlled by a voltage regulator so that the voltage applied to the electrical loads, including the storage battery, is regulated by the voltage regulator. The field current of the other generator is controlled such that the output current of this other generator is slaved to and follows the output current of the generator that is regulated by the voltage regulator. In carrying this object forward, the generators are preferably alternating current generators having output windings connected to rectifier means. The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a schematic circuit diagram of a motor vehicle electrical apparatus incorporating a dual generator apparatus in accordance with this invention; and Figure 2 is a schematic circuit diagram of a control circuit which is used in the apparatus of Figure 1. Referring now to the drawings, and more particularly to Figure 1, the reference numeral 10 generally designates an (alternating current) generator which has a field winding 12 and a (three-phase Y-connected) stator winding 14. A field discharge diode 13 is connected across field winding 12. The field winding 12 is carried by the rotor (not shown) of the generator 10 and the rotor is driven by an engine 16 of a motor vehicle as indicated by dotted line 18. The generator 10 may be of the type disclosed in US patent No 4,604,538. The stator or output winding 14 is connected to a (three-phase full-wave) bridge rectifier 20 (rectifying means) which has a positive direct voltage output terminal 22 and a negative direct voltage output terminal 24. The negative direct voltage output terminal 24 is connected to power ground identified by reference numeral 26. In Figures 1 and 2 all ground symbols, like the one identified by reference numeral 26, represent power ground. The positive direct voltage output terminal 22 is connected to a power supply conductor 28. The apparatus of Figure 1 has another (alternating current) generator 30 that includes a field winding 32 and a (three-phase Y-connected) stator or output winding 34. The generator 30 may also be of the type disclosed in the above-referenced US patent No 4,604,538. The field winding 32 of generator 30 is carried by the rotor (not shown) of the generator and the rotor is driven by engine 16 as indicated by dotted line 36. The stator winding 34 is connected to a (three-phase full-wave) bridge rectifier 38 (rectifying means) that has a positive direct voltage output terminal 40 and a negative direct voltage output terminal 42. Positive direct voltage output terminal 40 is connected to a power supply conductor 44 and negative direct voltage output terminal 42 is connected to power ground. The power supply conductors 28 and 44 are both connected to a power supply conductor 46 at junction 48. A storage battery 50 has its positive terminal connected to power supply conductor 46 and its negative terminal connected to power ground. The electrical loads on the motor vehicle are represented by resistor 52 and are connected between power supply conductor 46 and power ground, as well as by the storage battery 50. It will be appreciated that the output current of generators 10 and 30 are both supplied to power supply conductor 46 which in turn supplies current to storage battery 50 and electrical loads 52. Power supply conductor 46 therefore defines means connecting the stator or output winding 14,34 of the generators 10,30 to the storage battery 50 and electrical loads 52. The output voltage of generator 10 is controlled by a voltage regulator designated by reference numeral 54. The voltage regulator 54 has a voltage sensing means or circuit that is connected between a voltage sense lead 56 and a lead 58 that is connected to power ground. This voltage sensing means or circuit can be a resistive voltage divider. The voltage sense lead 56 is connected to junction 57 and accordingly to the positive terminal of storage battery 50. The voltage regulator 54 further has a field current energizing circuit connected between conductors 59 and 60 that includes a switching transistor. Conductor 60 is connected to field winding 12 and conductor 59 is connected to storage battery 50 via an ignition switch 62. The voltage regulator 54 may be of the type disclosed in US patent No 4,636,706 and can take other forms. The voltage regulator 54 senses the voltage between junction 57 and power ground and controls the magnitude of field current supplied to field winding 12 to maintain this voltage substantially constant. By way of example, in a 12 volt arrangement, the voltage regulator may operate to maintain the voltage between junction 57 and power ground at a voltage of about 14 volts. The voltage regulator accomplishes this by sensing the voltage between junction 57 and power ground and depending on the voltage sensed controls field current to maintain the voltage at junction 57 at a desired regulated value. The field current for the field winding 32 of generator 30 is controlled by a load proportioning apparatus which will now be described. This load proportioning apparatus comprises a current sensing means which includes a toroid 64 that is formed of magnetic material such as ferrite. The toroid 64 has a slot or gap 66 and located in the slot or gap 66 to sense the flux traversing the gap is a Hall effect device 68. The power supply conductor 28, which carries the output current of generator 10, passes through toroid 64 as does the power supply conductor 44 which carries the output current of generator 10. The output currents I10 and I30 of generators 10 and 30 flow in opposite directions as they pass through toroid 64 as indicated by the arrows in Figure 1. This causes the magnetic fields surrounding each power supply conductor 28,44 to induce bucking or opposing flux fields in the toroid 64. Accordingly, the resultant flux that traverses gap 66 and which links Hall effect device 68 will be a function of the difference in the magnitudes of output currents I10 and I30. This resultant flux will cause a voltage to be developed by Hall effect device 68 (developing means), the magnitude of which is a function of the difference in output currents I10 and I30. The voltage developed by Hall effect device 68 is applied to a load proportioning control which is illustrated in detail by the circuit in Figure 2. A part of this control is control circuit 70 that is shown as a block in Figure 1. The control circuit 70 is connected to Hall effect device 68 by a conductor 72. Control circuit 70 is connected to conductors 74 and 76 and conductor 76 is connected to one side of the ignition switch 62. Control circuit 70 has a signal ground to be described in connection with Figure 2 that is connected to power ground by conductor 78. Control circuit 70 is further connected to a conductor 80. The conductor 80 is connected to the gate G of a P-channel field effect transistor (FET) 82. This FET 82 may be an RCA type RFK 25P10 field effect transistor. The source S of FET 82 is connected to conductor 84 and the drain D is connected to one side of the field winding 32 of generator 30. The opposite side of the field winding 32 is connected to power ground. A field discharge diode 86 is connected across field winding 32. The circuit of Figure 2, which includes control circuit 70, will now be described. In Figure 2, the same reference numerals have been used as were used in Figure 1 to identify corresponding parts. In Figure 2, the arrow-like symbol identified by reference numeral 90 and all like symbols represent signal ground. Signal ground 90 is connected to power ground by conductor 78. Further, in describing Figure 2, it will be on the basis that the arrangement is a 12 volt apparatus. The Figure 2 circuit has an integrated circuit containing an operational amplifier 92 and a voltage comparator 94. The pin numbers for these devices are shown in Figure 2. This integrated circuit may be a National Semiconductor type LM 2924 device. The operational amplifier 92 amplifies the output voltage of Hall effect device 68. The Hall effect device 68 has positive voltage applied thereto by conductor 93, resistor 194 (110 ohms) and diode 96. A Zener diode Z having a breakdown voltage of 8.2 volts is connected between conductor 93 and signal ground. A capacitor C1 of 35 microfarads is connected between conductor 93 and signal ground. The positive input terminal (pin 5) of operational amplifier 92 is connected to the conductor 72 and hence to the output of Hall effect device 68 by a 75K resistor R1. Resistor R2 (75K) and capacitor C2 (0.01 microfarad) are connected between the positive input terminal of operational amplifier 92 and signal ground. Operational amplifier 92 is further connected to 150K resistors R3 and R4, 75K resistor R5 and 3K resistor R6. Resistors R3 and R4 form a voltage divider having a junction 97 connected to the negative input terminal (pin 6) of operational amplifier 92. The output of operational amplifier 92 is at junction 98 (pin 7). Operational amplifier 92 is designed for unity gain in the differential channel and high common mode rejection in the common mode channels. This allows processing the output signal of Hall effect device 68 while providing good rejection to thermal drift. The negative input terminal (pin 2) of voltage comparator 94 is connected to the output of operational amplifier 92 via a 750 ohm resistor R7. The positive input terminal (pin 3) of voltage comparator 94 is connected to junction 100 between resistors R8 (59K) and R9 (750 ohms). Also connected to voltage comparator 94 are resistors R10 (2.7M) and R11 (4.7K). The output of voltage comparator 94 (pin 1) is connected to the gate G of FET 82 by conductor 80. The voltage divider resistors R8 and R9 provide a reference voltage at junction 100 that is applied to the positive input terminal (pin 3) of voltage comparator 94. The voltage at the negative input terminal (pin 2) of voltage comparator 94 varies in accordance with variation in the output voltage of Hall effect device 68. The operation of the dual generator apparatus will now be described, first from a general standpoint and then in more detail. Fundamentally, the load proportioning control of this invention operates to sense the output current I10 and I30 of generators 10 and 30. If there is a difference, for example I10, being greater than I30, the circuit controls the field current of generator 30 such that its output current will be increased until the magnitude of I30 substantially equals I10. The current output of generator 30 accordingly is slaved to the prevailing current output of generator 10. Putting it another way, the output current of generator 30 follows or tracks the output current of generator 10. It should be apparent that the generator 30 does not have a voltage regulator like the voltage regulator 54 that regulates the output voltage of generator 10. A more detailed operation of the dual generator apparatus of this invention will now be given. Let it be assumed that generators 10 and 30 are supplying output currents I10 and I30 and that I10 is greater than I30. The flux generated in toroid 64 will be related to the difference in the current levels of I10 and I30. The net flux that is applied to Hall effect device 68 will cause it to develop an output voltage that is a function of the difference in output currents I10 and I30. This voltage is applied to operational amplifier 92 and its output will be a voltage that is a function of the difference in the output currents I10 and I30. The output voltage of operational amplifier 92 is applied to one input terminal (pin 2) of voltage comparator 94. This voltage comparator 94 compares this voltage with a reference voltage applied to pin 3 from junction 100. The circuit is arranged such that when the voltage applied to pin 2 of voltage comparator 94 is higher than the reference voltage, the output of voltage comparator 94 goes low, or in other words, connects conductor 80 to signal ground which drives the gate G of FET 82 low which in turn causes FET 82 to be biased conductive between its source and drain thereby energizing field winding 32 of generator 30 from conductor 84. With the field winding 32 energized, the output current I30 will start increasing, causing the voltage applied to the negative input terminal (pin 2) of voltage comparator 94 to start decreasing. When this voltage decreases to a point where it is less than the reference voltage (pin 3) the output of voltage comparator 94 will switch out of the low condition. A positive voltage is now applied to gate G of FET 82 from conductor 74 via resistor R11 and conductor 80 which will cause FET 82 to be biased nonconductive between its source and drain. Thus, FET 82 will be switched off when current I30 substantially equals current I10. The circuit therefore switches FET 82 on and off so as to maintain output current I30 substantially equal to I10. It will be appreciated that when current I30 increases to a point where it substantially equals I10, a flux null is created in regard to the flux that links Hall effect device 68. This shuts off FET 82. Once the field current of field winding 32 starts to decay the null in flux is disrupted. The resultant flux again increases which will again cause FET 82 to be turned on. This constant hunting for a null allows the current sensor to operate over a huge dynamic range without going into saturation and to lock on and track the existing current level output of generator 10. It should be noted that the feedback between the output of voltage comparator 94 and pin 3 (resistor R10) adds hysteresis about the current lock in point. Control circuit 70 and FET 82 therefore define controlling means for controlling the field current of the field winding 32. In the circuit as thus far described the output current I30 of generator 30 is controlled such that it follows and substantially equals output current I10. This occurs because there is a one-to-one turns ratio between the flux developed in toroid 64 and the turns of power supply conductors 28 and 44 that pass through the toroid 64. Thus, the straight conductor portions that pass through toroid 64 can be considered as one turn and there accordingly is a one-to-one turns ratio. The turns ratio can be made other than one-to-one so that the output currents I10 and I30 would not be substantially equal but rather would have a predetermined relationship or ratio. Thus, assume for example that power supply conductor 44 instead of having one turn has two turns so that there is now a two-to-one turns ratio between power supply conductor 44 and power supply conductor 28. The result of such a modification would cause a greater flux to be induced in toroid 64 by the current in power supply conductor 44 than would be induced by the same current in power supply conductor 28. The circuit would now operate such that output current I30 would still follow output current I10 but output current I30 would be less than output current I10 by a predetermined constant value that is a function of the turns ratio. It therefore will be appreciated that this invention is not limited in application to a circuit wherein output current I30 is controlled to be substantially equal to output current I10.

Claims: A dual generator apparatus for providing electrical current to an electrical load (50,52) comprising a first generator (10) having an output winding (14) and a field winding (12); a second generator (30) having an output winding (34) and a field winding (32); means (46) connecting the output windings (14,34) of the generators (10,30) to the electrical load (50,52) such that each generator supplies current (I10,I30) to the electrical load and such that the current supplied to the electrical load is substantially equal to the sum of the output currents (I10,I30) of the generators (10,30); and a voltage regulator (54) connected to the field winding (12) of the first generator (10) including voltage sensing means sensing the voltage across the electrical load, the voltage regulator (54) being operative to control the field current of the field winding (12) of the first generator (10) such that the output voltage of the first generator is regulated to a predetermined value; characterised by current sensing means (64) operative to sense the output currents (I10,I30) of the generators (10,30), the current sensing means (64) including developing means (68) for developing an electrical signal that is a function of relative magnitudes of the output currents (I10,I30) of the generators (10,30), and controlling means (70,82) responsive to the electrical signal for controlling the field current of the field winding (32) of the second generator (30) such that the output current (I30) of the second generator (30) follows the output current (I10) of the first generator (10) and such that there is a predetermined relationship between the output currents (I10,I30) of the generators (10,30). A dual generator apparatus according to claim 1, wherein the current sensing means (64) is so constructed and arranged that the output current (I30) of the second generator (30) is regulated to a magnitude that substantially equals the output current (I10) magnitude of the first generator (10). A dual generator apparatus according to claim 1 or claim 2, wherein the first and second generators (10,30) are alternating current generators, and wherein the output currents (I10,I30) of the generators are developed by rectifier means (20,38) connected respectively to an output winding (14,34) of a respective generator. A dual generator apparatus according to any one of claims 1 to 3, wherein the controlling means (70,82) comprises a semiconductor switching means (82) that is connected in series with the field winding (32) of the second generator (30). A dual generator apparatus according to any one of claims 1 to 4, wherein the developing means comprises a Hall effect device (68) that is traversed by magnetic flux that is developed by the output currents (I10,I30) of the first and second generators (10,30). A dual generator apparatus as claimed in claim 3, wherein the electrical load includes a storage battery (50), in which means (28,44,46) connect the outputs of both rectifier means (20,38) to the storage battery whereby both rectifier means (20,38) can supply charging current to the storage battery, the voltage sensing means of the voltage regulator (54) being connected to the storage battery to sense the voltage across the storage battery (50). A dual generator apparatus as claimed in claim 4, wherein the controlling means (70) is coupled to the current sensing means (64) and includes means (92,94) for causing the semiconductor switching means (82) to be biased conductive when the relative magnitudes of the output currents (I10,I30) have a first relationship and for biasing the semiconductor switching means (82) nonconductive when the relative magnitudes of the output currents of the generators (10,30) have a second relationship that is different from the first relationship. A dual generator apparatus according to claim 7 which is arranged such that the first relationship corresponds to a condition of operation where the output current (I10) of the first generator (10) is greater than the output current (I30) of the second generator (30) and wherein the second relationship corresponds to a condition of operation where the output currents of said first and second generators are substantially equal. A dual generator apparatus according to claim 7 or claim 8, wherein the semiconductor switching means is a field effect transistor (82).

Inventors: BUETEMEISTER, EARL H.
Applicants: GENERAL MOTORS CORPORATION
Application year: 1989
Main classification: H02J7
IPC codes: H02J3, H02J7