Patent Document

BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a method and system for battery-based activation of a voltage regulator. The present invention more particularly relates to a voltage regulation method and system that is activated based on a battery voltage signal. 
     2. Description of the Related Art 
     Voltage regulation systems for controlling the field current of a diode-rectified alternating current generator, which supplies the electrical loads on a motor vehicle, generally are well known to those skilled in the art. One known type of voltage regulator senses the voltage applied to the battery, and if this voltage is higher than a desired regulated value, a transistor that controls field current is switched off. When generator voltage drops below the regulated value, the field controlling transistor is switched on. The transistor is repetitively switched on and off in response to sensed voltage changes to thereby cause the output voltage of the generator to be maintained at a predetermined, desired regulated value. 
     In another type of known voltage regulator, the field current is pulse-width modulated at a constant frequency to maintain the output voltage of the generator at a desired regulated value. In this type of regulator, the pulse width is a function of the difference between actual generator output voltage and a desired voltage. Examples of this type of regulator are disclosed in U.S. Pat. No. 2,976,473 to Shaw et al. and U.S. Pat. No. 4,275,344 to Mori et al. British Patent No. 1,392,096 also discloses pulse-width control of field current, and in that patent, the voltage reference takes the form of a cyclic staircase waveform. 
     Another example of a voltage regulator that employs pulse-width modulation of generator field current is disclosed in U.S. Pat. No. 4,636,706 to Bowman et al., the contents of which are incorporated herein by reference. According to Bowman et al., the regulator disclosed in that patent utilizes a digital apparatus that includes an up-down counter which responds to the relative magnitudes of the actual output voltage of the generator and the desired regulated output voltage of the generator. When the actual output voltage of the generator is below the desired regulated value, the counter is incremented or counted up, and when the actual output voltage is above the desired regulated value, the counter is decremented or counted down. The instantaneous count in the counter is used to determine the on time of a semiconductor switch that is connected in series with the field winding of the generator. The instantaneous count thus determines the pulse-width of the voltage that is applied to the field. Whenever actual output voltage exceeds the desired regulated value, the field controlling semiconductor switch is biased off. Thus, during the time that the actual output voltage is above the desired regulated value, the field is not energized and the counter is decremented. When actual output voltage then drops below the desired regulated value, the field is energized at the pulse-width represented by the magnitude of the count in the counter, and the counter is incremented. 
     Regardless of which type of voltage regulator is implemented, it is desirable to turn off the voltage regulator associated with an engine whenever the engine is not running. This prevents the energy stored in the engine&#39;s battery from being drained by the regulator&#39;s circuitry. 
     The voltage regulator, however, must be reactivated when the engine is started (i.e., when the generator begins to turn). One conventional way of reactivating the voltage regulator is to wire a vehicle&#39;s ignition switch or other circuitry associated therewith to an activation input terminal (i.e., the lamp input) of the voltage regulator. In particular, this wiring is performed so that the voltage regulator gets “strobed on” by closure of the ignition switch. This wiring arrangement, while generally effective, does require an electrical connection from the ignition switch or its associated circuitry to the voltage regulator. However, this added connection has some disadvantages. Since the connection extends out from where the regulator and/or generator is mounted, the connection remains relatively unprotected and susceptible to damage. The connection can be inadvertently disconnected, cut or otherwise rendered inoperative. The soldering techniques that are typically used to effect the added connection also can fail. If any of these events occur, the voltage regulator typically cannot become activated. As a result, no voltage regulation is provided and/or the generator fails to generate current. In the automotive context, this translates into added costs associated with repair and/or warranty work. 
     Consequently, there is a need in the art for a method and/or system capable of activating a voltage regulator in such a way that no external connection to an ignition switch is required, thereby reducing the likelihood that the voltage regulator will fail to become activated in response to the starting of the engine. 
     Another conventional technique for activating a voltage regulator avoids the external connection to the ignition switch by using the residual magnetism in the vehicle&#39;s generator. In particular, one or more of the phases from the generator is connected to the lamp input (or another suitable input) of the voltage regulator and the residual magnetism from the associated winding is used to activate the voltage regulator when the generator begins to turn. The residual magnetism, however, can dissipate over time (e.g., through diode leakage in the bridge rectifier of the generator). This dissipation can result in turn-on problems for the generator. Similar problems arise when road salt or other contaminants invade the bridge rectifier of the generator. The residual magnetism-based arrangement therefore tends to be unreliable in some respects. In addition, disassembly of the generator and re-assembly requires the voltage regulator to be “flashed,” since there is no residual magnetism left in the windings after re-assembly of the generator. Such an arrangement also requires “flashing” when it is initially assembled. 
     Consequently, there is a need in the art for a method and/or system adapted to minimize or eliminate one or more of the shortcomings set forth above. In particular, there is a need in the art for a method and/or system adapted to activate a voltage regulator without requiring a connection to an engine&#39;s ignition switch or related components, and also without requiring the presence of residual magnetism in the windings of the generator during an engine start. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to overcome one or more of the foregoing and other problems. 
     One advantage of the present invention is that unlike in conventional systems, it requires no additional connections external to the regulator. Another advantage is that no additional electrical inputs are required for regulator activation. The present invention provides a method adapted to activate a voltage regulator in response to a battery signal. This method begins by taking a measurement of the voltage signal provided by the battery. When the value of the battery voltage signal is below a threshold reference value indicative of when an engine is being started, then an activation signal is generated. The activation signal is applied to a voltage regulator to thereby commence regulation. 
     In a preferred embodiment, a field current through a field winding of a generator is strobed. Once strobing has begun, if the engine is rotating (and hence also the generator), the generator will produce an output (due to the active field current) and regulation begins. 
     A system for battery-based activation of a voltage regulator is also presented. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 illustrates a motor vehicle charging system in accordance with the present invention. 
     FIGS. 2A-2B are timing diagrams showing generation of an activation signal according to the invention. 
     FIG. 3 is a flow chart showing the inventive method of activating a voltage regulator of the present invention. 
     FIG. 4 is a timing diagram showing a battery voltage corresponding to a startup interval of an internal combustion engine (with starter). 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a motor vehicle electrical charging system  10  according to of the present invention. Charging system  10  includes a voltage regulator  11  having a (i) voltage regulation unit  12  and (ii) a battery voltage detection circuit  14  that is adapted to activate voltage regulation unit  12  in a manner to be described hereinafter. Voltage detection circuit  14  generates an activation signal, designated S 15 , on node  15 . The signal S 15  is applied to a “LAMP” input of regulation unit  14 , designated a “L” in FIG.  1 . Charging system  10  also has an alternating current (AC) generator  16 . Generator  16  may be a multiphase AC generator of a conventional type, and is shown, for example purposes only, having a three-phase delta-connected stator winding  18  and a rotatable field winding  20 . Generator  16  may be of the type disclosed in the U.S. Pat. No. 3,538,362 to Cheetham et al. with the exception that the generator in FIG. 1 has a delta-connected stator winding rather than the Y-connected stator winding shown the Cheetham et al. patent. It will be understood, however, that voltage regulation unit  12  and voltage detection circuit  14  of this invention can be used with generators that have either delta or Y-connected stator windings or various combinations thereof, having more or less than three phases (although 3-phase is common). 
     Field winding  20  is part of a rotor assembly (not shown) that is rotatably driven by an engine  22 , which may be included, for example, in a motor vehicle (also not shown). Engine  22  is shown connected to an idle speed control  24  which controls the idle speed of engine  22 . Generator  16  typically is driven at a higher speed than the speed of engine  22  by a belt and a pulley arrangement in a well known manner. 
     In the illustrated embodiment, the output terminals of stator winding  18  are connected to respective AC input terminals of a three-phase full-wave bridge rectifier, designated by reference numeral  26 . As also illustrated, bridge rectifier  26  may include three positive diodes  28  which have their cathodes connected to a direct current (DC) voltage output terminal  30 . As further illustrated, bridge rectifier  26  may also have three negative diodes  32 , the anodes of which are connected to a grounded direct current (DC) output terminal  34  of bridge rectifier  26 . A voltage that is developed at junction  36  is a pulsating voltage (AC), and the frequency of the voltage pulses developed at junction  36  is a function of generator and engine speed. When the generator  16  is not rotating, it does not generate an output voltage and the voltage at junction  36  is substantially zero. 
     Connected to charging system  10  is a storage battery  38 . The negative side of battery  38  is grounded and the positive side of battery  38  is connected to a junction  40 . Battery  38  will be assumed to be a 12-volt storage battery in the description of this invention, though it is understood that the invention is not limited in this regard. Battery  38  is charged by a circuit that includes a conductor  42  that connects DC voltage output terminal  30  of bridge rectifier  26  to junction  40 . Battery  38  and generator  16  feed various electrical loads, not illustrated, on the motor vehicle, that are electrically connected between junction  40  and ground. 
     Voltage regulation unit  12  controls an electrical current through field winding  20  to regulate the voltage appearing between junction  40  and ground to a desired regulated value. As mentioned above, in describing this invention, it will be assumed that the system is a 12-volt system and that the desired regulated voltage that is to be maintained between junction  40  and ground is about 14 volts (e.g., 13.6 volts). This desired regulated voltage typically will vary with temperature. Though the foregoing exemplary voltages are used in the description, it is understood that the invention may be practiced using different voltages. For example, 42-volt systems will fall within the spirit and scope of the present invention, with corresponding reference values being selected for such system. Voltage regulation unit  12  may comprise conventional apparatus known in the art, having an activation input terminal (e.g., as in Bowman et al. described above). 
     The current through field winding  20  may be controlled by a switch, such as a semiconductor switching device, which may take the form of a metal oxide semiconductor (MOS) field effect transistor  44 , although other switching devices may obviously be used. In the illustrated embodiment, transistor  44  may be N-channel enhancement mode type of transistor. Transistor  44  is shown having a gate terminal “G” connected to conductor  46 , a drain terminal “D” connected to junction  48  and a source terminal “S” connected to a first side of field winding  20 . A second side opposite the first side of field winding  20  is connected to ground. Junction  48  is connected to positive DC terminal  30  of bridge rectifier  26  via a conductor  50 . It should be understood that in some embodiments, switch  44  is included in regulator  11  (this arrangement is not specifically shown). A field winding discharge diode  52  is connected across field winding  20 . 
     When transistor  44  is biased into a conductive state (i.e., conductive between its drain D and source S), current will flow through field winding  20  originating from positive direct voltage output terminal  30 , through conductor  50  to junction  48 , through the drain D and source S electrodes of transistor  44  and then through field winding  20  to ground. Transistor  44  is switched on and off, in a manner known in the art, in order to maintain the voltage at junction  40  at the desired regulated value, which for exemplary purposes has been assumed to be about 14 volts (e.g., 13.6 volts). Of course, nodes  30  and  40  are electrically connected and will assume substantially the same voltage. 
     Since voltage regulation unit  12  consumes some energy, it may conventionally be turned-off when engine  22  is turned off. This prevents battery  38  from being drained by voltage regulation unit  12 , especially if engine  22  remains off for a long period of time. As long as engine  22  remains off, voltage regulation unit  12  remains off. When engine  22  is to be restarted, there is consequently a need to activate voltage regulation unit  12 . Prior art arrangements may use a connection from one or more of stator windings  18  to activate voltage regulation unit  12  using residual magnetism in the stator windings  12 , or use a connection from the ignition switch of the vehicle (or associated circuitry such as a lamp circuit) to activate voltage regulation unit  12 . As indicated above, however, such arrangements suffer from certain disadvantages. Charging system  10  avoids those disadvantages by providing a voltage regulator  11  having a battery voltage detection circuit  14 . 
     Battery voltage (e.g., B+) is always available to the regulator. When the battery voltage is used for activation, then no additional connections will be required. As will be described in greater detail hereinafter, voltage detection circuit  14  processes the battery voltage (i.e., the level thereof in one embodiment) to activate the regulator to begin regulation, and thus requires no additional external electrical connections. Voltage detection circuit  14  is preferably integrated with voltage regulation unit  12  to make regulator  11 . Regulator  11  may be, and preferably is, colocated with the generator  16 . An integrated unit may be preferred since it makes protection of the electrical connection between voltage regulation unit  12  and voltage detection circuit  14  more economical and minimizes the likelihood of failure of a connection and any repair or warranty costs associated therewith. Voltage detection circuit  14  alternatively can be implemented as a separate unit from voltage regulation unit  12  and/or generator  16 , if such a design is deemed acceptable or more desirable. 
     FIGS. 2A-2B are timing diagrams showing, in greater detail, the generation of an activation signal based on detection of a transient signal on the battery voltage line B+. FIG. 2A specifically shows a voltage range, between a first, upper level, designated V 1 , and a second, lower level, designated V 2 . The predetermined range defines a range in which an output voltage level of battery  38  is expected to fall if the battery  38  is in a normal, healthy condition, but when the generator  16  is not operating, plus an additional safety or guard band. For example, a standard battery operating voltage may lie, for the 12-volt battery  38  described above, between about 11.9 and 12.3 volts. On the upper end, the threshold V 1  may be about 12.6 volts, the level above which is indicative of the generator  16  generating power. On a lower end, the threshold V 2  may be defined to be about 11.6 volts, slightly less than the lower level referred to above indicative of a starter motor being added as a lead, for example. 
     By way of reference, when the engine  22 , and generator  16  are being operated, and the generator  16  is being suitably regulated by voltage regulator  11 , the output is maintained at a level above the range described above, such regulated voltage being designated V REG  in FIG.  2 A. This allows, during active running of the engine and generator, of an at least small trickle charging current to flow through the storage battery  38 . 
     Thus, at some time t 0  when the engine  22  is not running (and thus the generator  16  is also not being operated), the voltage level of the battery  38 , namely the voltage level at junction  40  (designated signal S 40 ), may lie within the above-described predetermined range V 1  to V 2 . Voltage detection circuit  14  is configured to detect when a voltage level of signal S 40  assumes a level that is indicative of an engine being started or other starting condition, and generate an activation signal S 15  in response thereto. In a conventional vehicle, when the user turns on the ignition, and keys to the “start” position, electrical current is drawn from storage battery  38  in order to run a conventional starter motor (not shown). This results in a momentary drop in the battery voltage level, as a large amount of electrical current is drawn from the storage battery  38 . This voltage transient is therefore indicative of an attempt to start engine  22 . The lower threshold V 2  is selected, in one embodiment, so as to detect such an event. Thus, in FIG. 2A, at time t 1 , a start attempt has been made, as indicated by a drop in the battery voltage S 40 , below the lower threshold level V 2 . 
     As shown in FIG. 2B, voltage detection circuit  14  is operative to detect the above-described transition of the battery voltage level S 40  below threshold level V 2  at time t 1 , and generate the activation signal in an asserted state, as shown in exemplary fashion by a pulse  54 . 
     FIG. 3 is a flowchart diagram illustrating the method according to the present invention. In step  56 , the voltage regulator unit  12  of voltage regulator  11  is deactivated. This may have in-fact occurred when the vehicle was last turned off, when the engine  22  was stopped. The method then proceeds to step  58 . 
     In step  58 , the voltage detection circuit  14  determines whether there is a transient signal on the battery S 40  line indicative of a start attempt. As shown above, in connection with FIG.  2 A and FIG. 2B, this may, in one embodiment, be simply a threshold detection (i.e., when the battery voltage level falls below a threshold level, V 2 ). However, other characteristics of the starting event (i.e., connecting the battery to the engine starter) may be observed and detected. For example, certain characteristic current draws, or the like, may also be looked for by circuit  14  in determining whether the starter has been connected as a load in an attempt to start engine  22 . In further embodiments, other approaches for starting engine  22  may also be expected, and accordingly, circuit  14  may be suitably configured to detect these approaches. For example, the vehicle may be “jump started” wherein the battery from another vehicle is used (as shown), the vehicle may be push-started or the like. In any event, if no transient is detected (“NO”), in step  58 , the method branches back and step  58  is again performed. This “loop” is continued until a desired transient signal is detected. Thus, if the answer is “YES,” then the method branches to step  60 . 
     In step  60 , circuit  14  activates voltage regulator unit  12 . In one embodiment, a pulse, such as pulse  54  in FIG. 2B, is generated and is applied to an activation input such as a “LAMP” input designated “L” in the figures. The “LAMP” input on voltage regulation unit  12  is so designated because in conventional systems, a lamp circuit may be provided that (i) illuminates a warning lamp when the charging system is not working properly when the ignition is on, and (ii) generates an activation signal when the ignition is keyed on that is provided to the “LAMP” input of a voltage regulation unit for activation. Of course, this prior art arrangement has shortcomings inasmuch as the battery would be subject to drain even when there is no desire to start the engine, such as when the vehicle operator is just listening to the radio or the like, and, additionally, there requires a separate connection from the lamp circuit to the lamp input on the voltage regulation unit, which, as noted above, is subject to failure, among other things. The description of a “LAMP” input, however, in voltage regulation unit  12  is exemplary only and not limiting in nature, only an activation input of some kind is required. 
     Once activated, the voltage regulation unit will perform a start procedure wherein the switch  44  is, in one embodiment, strobed in a predetermined manner in order to produce electrical current through field winding  20 . In one embodiment, such predetermined manner involves strobing at a 30% duty cycle, which may last over a predetermined period of time (e.g., between about 3 to 5 seconds), and which preferably cycles at a predetermined frequency (e.g., selected from the range of between about 200 hz to about 400 hz). The combination of the predetermined period of time and frequency of the strobing may be selected to provide a desirable starting current in field winding  20 . Thus, if engine  22  is actually turning, thereby turning the generator, then such field current may be expected to be sufficient to allow generation of electricity at the output of generator  16  (i.e., at the output of junction  30 ). However, if the engine/generator are not turning, then there will be no effect. While the ON time and OFF time of the duty cycle will vary depending on the type of transistor  44  being used, the desired starting current in field winding  20 , and like considerations, an exemplary combination of ON and OFF times is an ON time of about 10 milliseconds and an OFF time of about 30 milliseconds. 
     With continued reference to FIG. 3, when the battery voltage exceeds the first, upper threshold V 1 , then this condition is indicative of the engine and generator rotating to produce electricity. In decision block  62 , this is considered to be a valid “start” condition, meaning that an operator is attempting to start engine  22 . The method then branches to step  64 , wherein normal regulation via voltage regulation unit  12  is commenced. However, if, after an initial start up procedure, as described above (e.g., 3-5 seconds) does not result in the battery voltage, S 40 , surpassing the upper level V 1 , then this means that no such “start” condition is being initiated. Control, accordingly, returns to step  56 , wherein the voltage regulator unit  12  is deactivated (to minimize battery drain). 
     In an alternate embodiment, strobing circuitry  13  (best shown in FIG. 1) may be provided if strobing of the activation signal S 15  is desirable. Exemplary situations where strobing may be desirable include situations where voltage regulation unit  12  is not equipped with its own strobing circuitry and where the voltage regulation unit  12  and/or transistor  44  are of the type that require a strobed activation signal. Strobing circuitry  13  may be connected to the activation signal S 15  and arranged so that the activation signal S 15  is strobed before it is applied to the activation input (“L”) of voltage regulation unit  12 . This is shown in exemplary fashion, in dashed-line format, as activation signal  54   s  (strobed) in FIG.  2 B. 
     Voltage regulation unit  12  may be configured to continue operation on its own after an activation signal has been applied for a limited duration, and regulation of the generator output has commenced. Accordingly, the output of detection circuit  14  or strobing circuitry  13  (when used) may be configured to have a limited duration consistent with the timing requirements of voltage regulation unit  12 . 
     In other embodiments, further features are implemented to minimize or eliminate false starts, and/or minimize battery drain. For example, an unhealthy battery may always be below the lower threshold level V 2  (best shown in FIG.  2 A). In addition, the operator of the vehicle may turn the headlamps on while the engine is off, thereby bringing down the battery voltage below the lower threshold V 2 . In either case, it may be undesirable to turn “on” the voltage regulator. Therefore, in alternate embodiments, the present invention provides filtering mechanisms, and counting mechanisms to prevent the voltage regulator unit  12  from, in-effect, being “activated” all the time, or for the duration of the above-described false conditions, or other false conditions. Thus, circuit  14  may be further configured to keep a count of the number of “failed” attempts at commencing regulation (i.e., those attempts where the field current was strobed on, but that, due to the engine/generator not rotating, the battery voltage S 40  did not exceed the upper threshold V 1 ). After a predetermined number of failed “start” attempts (e.g., five in one embodiment), a predetermined delay may be invoked (e.g., 5 seconds). Selection of the count value allows for such number of successive iterations through the voltage strobing start-up procedure before the above-mentioned deferral time, thereby reducing the drain on battery  38 , which is especially important if battery  38  has already been substantially discharged and therefore whose voltage is already low. 
     In addition, in a still further embodiment, circuit  14  is configured to filter spurious voltage transients, and reject the same as amounting to noise not indicative of an attempt to turn on a starter motor to start engine  22 . For example, extremely short duration “spikes” may be filtered, to avoid recognizing a successful starting operation when such starting operation has really not been initiated at all by the operator. 
     FIG. 4 shows the level of a starter  66  output on junction  40  during the start up procedure indicated above. As shown in FIG. 4, current through the field winding  20 , coupled with rotation of the generator rotor, will result in an output on DC output  30  of generator  16 , which is coupled to junction  40 , and shown as signal S 40  in FIG.  4 . Initially, field current is passed through field winding  20 , and the accompanying rotation results in a relatively large voltage, as shown in FIG. 4 (e.g., approximately 23.6 volts for one half of one cycle). Feedback of this increased voltage level to voltage regulation unit  12  will cause it, as is well known, to adjust the level of field current applied through field winding  20 . As shown this process, after 5-6 cycles, results in maintaining a regulated voltage output, for example, approximately 13.6 volts in FIG.  4 . 
     While the present invention has been described with reference to certain preferred embodiments and implementations, it is understood that various modifications and variations will no doubt occur to those skilled in the art to which this invention pertains. These and all other such variations which basically rely of the teachings through which this disclosure has advanced the art are properly considered within the scope of this invention. 
     The preferred embodiment was chosen and described on order to best explain the principles of the invention and its practical application. The preceding description is intended to enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims.

Technology Category: h