Abstract:
A fault detection method is disclosed for a motor vehicle charging system including a generator and an electrical component coupled to receive electrical current from the generator. In one embodiment, the method comprises sensing a first voltage at an output of the generator and sensing a second voltage at the electrical component and, if the first voltage and the second voltage differ by more than a predetermined amount, reducing or suspending output of electrical current from the generator. One advantage of the method disclosed herein is in its ability to diagnose a fault in an electrical connection at the output of a motor vehicle generator, where the fault manifests itself as a high resistance connection.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to motor vehicle charging systems and, more particularly, to the detection of faults in such systems. 
     2. Description of the Related Art 
     In a motor vehicle charging system, the connection between the power output terminal of an alternator and the power distribution system of the vehicle can occasionally be faulty. Such a faulty connection can be due to improper connection at the vehicle assembly plant, corrosion of the connection due to aging, loosening of the connection over time, or other factors. 
     A faulty connection which results in a completely “open” circuit at the output of the alternator will become quite readily apparent to the driver of the vehicle as his battery loses charge. However, faulty connections which result, not in an open circuit but in a high resistance connection or an intermittently open circuit, may not as readily manifest themselves to the driver of the vehicle. Thus, a system and method for diagnosing these classes of faulty connections at the output of an alternator will prove advantageous. The charging system can take appropriate action in its operation, and the driver can be made aware of the fault and have the vehicle repaired. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to diagnose faults at the output of an alternator. More particularly, an object of the invention is to diagnose faults which manifest themselves as a high-resistance condition or an intermittently open-circuit condition. 
     In one aspect, the present invention provides a fault detection method for a motor vehicle charging system including a generator and an electrical component coupled to receive electrical current from the generator. The method comprises the step of sensing a first voltage at an output of the generator. The method further comprises the step of sensing a second voltage at the electrical component. In addition, the method comprises the step of comparing a difference of the first voltage and the second voltage to a predetermined voltage, the predetermined voltage indicative of a high resistance connection between the output of the generator and the component. If the difference is greater than the predetermined voltage, the method includes the step of reducing or suspending output of electrical current from the generator. 
     Another aspect of the present invention provides a fault detection method for a motor vehicle charging system including a generator and an electrical component coupled to receive electrical current from the generator. The method comprises sensing a first voltage at an output of the generator and sensing a second voltage at the electrical component. If the first voltage and the second voltage differ by more than a predetermined amount, the predetermined amount being a function of an output current of the generator, the method includes reducing or suspending output of electrical current from the generator. 
     In a third aspect, the present invention provides a fault detection method for a motor vehicle charging system including a generator, a voltage regulator operatively coupled to the generator, an electrical component coupled to receive electrical current from the generator and a powertrain controller. If the charging system has an operational fault, the method comprises providing a fault indicating signal from the voltage regulator to the powertrain controller indicative of the operational fault. If the signal intermittently indicates the operational fault, the method also includes providing a first charging system control signal from the powertrain controller to the voltage regulator to limit or suspend output of the generator. 
     Designs according to the present invention provide the capability to diagnose alternator output connection faults which manifest themselves in a high-resistance, but not fully open circuit, condition. In doing so, the present invention provides advantages over alternative designs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a motor vehicle charging system  10  according to one embodiment of the present invention. 
     FIG. 2 is a schematic diagram of voltage regulator  16  of FIG.  1 . 
     FIG. 3 is a flowchart showing a fault diagnosis routine performed within voltage regulator  16 . 
     FIG. 4 is a graph containing two traces illustrative of an intermittently faulty connection between alternator output terminal  21  and conductor  23  in charging system  10 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a charging system  10  according to one embodiment of the present invention is illustrated. Alternator  14  is a device which generates electrical energy in a motor vehicle. Alternator  14  is coupled to the vehicle&#39;s engine (not shown) to rotate along with engine rotation. Connected to alternator  14  is voltage regulator  16 . Regulator  16  is responsible for trying to keep the output voltage of alternator  14  in regulation. Battery  19  is charged by current received from output  21  of alternator  14 . Regulator  16  and alternator  14  are preferably physically coupled such that they form one unit which is installed on the engine when the engine is assembled. 
     Alternator  14  comprises a three-phase stator  141 , as is contained in alternators known to the art. Stator  141  has three windings, the outputs of which are connected to rectifier  143 . Rectifier  143  takes the three-phase alternating current power output from stator  141  and converts the power to direct current power for use by the motor vehicle. Rectifier  143  is preferably a six-diode full-wave bridge rectifier, well-known to those skilled in the art. 
     The output  20  of rectifier  143  is coupled to output terminal  21  of alternator  14 . Further, output  20  of rectifier  143  is coupled to provide power for field coil  147 . 
     Engine controller  18  is preferably a microprocessor-based device which contains sufficient microcomputer resources (memory, throughput, registers, inputs, outputs and the like) to perform the functions ascribed to it herein. Engine controller  18  has responsibility for a number of engine management functions including idle control and fuel injection control, as are many engine controllers known to the art. 
     In the present invention, engine controller  18  further has responsibility for determining the voltage to which regulator  16  should control the output of alternator  14 . 
     Connecting regulator  16  and alternator  14  are three circuits. Field circuit  22  is the means by which regulator  16  controls the voltage output from alternator  14 . Regulator  16  modulates the voltage on field circuit  22  to control field current in field coil  147  of alternator  14 . Stator circuit  24  is a means by which regulator  16  verifies proper operation of alternator  14 . Through stator circuit  24 , regulator  16  can monitor whether alternator  14  is producing a voltage output. B+ circuit  26  is the third signal connecting alternator  14  to regulator  16 . 
     Connecting regulator  16  and engine controller  18  are two circuits. Load indicator circuit  28  provides a pulse-width-modulated signal from regulator  16  to engine controller  18 . The duty cycle of that signal is proportional to the duty cycle of the voltage at circuit  22  (i.e., the circuit which sinks current through field coil  147 ). The signal on load indicator circuit  28  provides engine controller  18  with a measure of the mechanical torque applied to the engine by alternator  14 . It will be recognized by those skilled in the art that the torque applied to the engine by alternator  14  is a function of the current flowing though field coil  147 . 
     Load indicator circuit  28  has a second function as well. If voltage regulator  16  detects a fault in the charging system, voltage regulator  16  pulls load indicator circuit  28  LOW continuously (that is, a 0% duty cycle). This indicates to engine controller  18  that a fault has occurred in the charging system. In a preferred embodiment of the present invention, load indicator circuit  28  has a duty cycle (percentage of time in the HIGH state) in the range of 6% to 97% during normal (non-fault) operation of alternator  14 . The signal on load indicator circuit  28  preferably has a frequency of 125 Hz. 
     Regulator control circuit  30  is a means by which engine controller  18  can provide a command to regulator  16  indicating the voltage level at which regulator  16  should control alternator  14 . The signal provided by engine controller  18  to regulator  16  on regulator control circuit  30  is pulse-width-modulated, the duty cycle of the signal being a function of the desired voltage command from engine controller  18  to regulator  16 . Preferably, the duty cycle of the signal is generally proportional to the desired voltage command from engine controller  18  to regulator  16 . Also preferably, the frequency of the signal on regulator control circuit is 125 Hz. 
     Charging system warning lamp  25  is connected between ignition switch  33  and engine controller  18 . Engine controller  18  illuminates warning lamp  25  in the event that engine controller  18  learns from voltage regulator  16  via load indicator circuit  28  that a fault has occurred in the charging system. The vehicle&#39;s driver is thus informed of the malfunction in his charging system. 
     The interior of regulator  16  will now be described with additional reference to FIG.  2 . Regulator  16  includes integrated circuit (IC)  42 . IC  42  is known as an “Externally-Controlled Integral Alternator Regulator” (ECIAR) chip and is manufactured by Motorola Corporation. 
     Field terminal  44  is connected to the collector of Darlington transistor  48 . Darlington transistor  48  is the means by which current is modulated in the field coil of alternator  14  for control of the output voltage of alternator  14 . The base of Darlington transistor  48  is connected to pin “FD” of IC  42 . Pin “FD” turns Darlington transistor  48  ON and OFF. 
     Regulator  16  contains recirculation diode  47 . By examination of FIGS. 1 and 2, it is apparent that recirculation diode  47  is connected across field coil  147 . The purpose of recirculation diode  47 , as is known in the art, is to clamp the voltage across field coil  147  as field coil  147  is turned ON and OFF by regulator  16 . Clamping of the voltage by recirculation diode  47  prevents large swings in field current as field coil  147  is turned ON and OFF. Recirculation diode  47  is also called a “flyback diode” by some people in the art. 
     Stator terminal  51  of regulator  16  is connected to ground via resistor  53  and to pin “STA” of IC  42  via resistor  55 . As has been previously mentioned, stator terminal  51  is connected to one winding of the stator of alternator  14 . Unless an alternating voltage (characteristic of the output of one phase of three-phase alternator  14 ) is seen at pin “STA”, a fault is indicated. 
     Load indicator terminal  57  of regulator  16  is connected via resistor  59  to pin “LI” of IC  42 . Pin “LI” has the ability to sink current, thereby being able to pull load indicator terminal  57  LOW. In this way, pin “LI” can create a pulse-width-modulated load-indicating signal at load indicator terminal  57 , which is read by engine controller  18 . The signal at pin “LI” is essentially contemporaneous with the signal at pin “FD”, which drives field coil  147  via Darlington transistor  48  as discussed above. Pin “LI” also has the ability, previously discussed, to hold load indicator terminal  57  LOW continuously. In this way, regulator  16  indicates to engine controller  18  that a charging system fault has been detected by regulator  16 . 
     Terminal  60  of regulator  16  is connected via resistor  62  to pin “RC” of IC  42 . As has been previously mentioned, terminal  60  is an input to regulator  16  for the voltage command from engine controller  18  on circuit  30 . The signal fed via terminal  60  to pin “RC” is also used to “wake up” IC  42 . IC  42  goes into a quiescent state when the vehicle is not being operated and the charging system is not needed. IC  42  “wakes up” when it sees the pulse width modulated signal provided from engine controller  18  on circuit  30 . 
     Terminal  64  of regulator  16  is connected via a voltage divider comprising resistors  66  and  68  to pin “SNS” of IC  42 . Terminal  64  is also connected to battery  19 , in order for regulator  16  to sense the voltage of battery  19 . 
     Terminal  45  of regulator  16  is connected via a voltage divider comprising resistors  70  and  72  to pin “AR” of IC  42 . Terminal  45  is also connected to output  20  of rectifier  142 , in order to sense the output voltage of alternator  14 . 
     One skilled in the art will also recognize that a microprocessor can be substituted for IC  42  within regulator  16 . Such a microprocessor can be programmed with software and provided with appropriate microcomputer resources (inputs, outputs, registers, memory and the like) to perform the functions of IC  42 . 
     A faulty connection between terminal  21  and conductor  23  can manifest itself in a high electrical resistance at that connection. This, in turn, manifests itself in a relatively high voltage drop across that connection. Thus, to diagnose a high-resistance connection, voltage regulator  26  performs the routine illustrated in FIG.  3 . At step  302 , voltage regulator  26  measures the voltage at the positive terminal of battery  19 . At step  304 , voltage regulator  26  determines whether the charging system is operating “within regulation” by comparing the voltage at battery  19  to a regulation threshold (typically 13.5 volts). If the battery voltage is below that threshold, it is inferred that the alternator is operating at “full field” (i.e., Darlington transistor  48  is fully “ON” to try to increase the output of the alternator). In this case, the output current of the alternator is likely to be quite high, with a correspondingly high voltage drop across the connection between terminal  21  and conductor  23 . In order to prevent false indications of a high-resistance fault, the fault detection routine of FIG. 3 returns to step  302  under this circumstance. 
     If, alternatively, the answer at step  304  is NO, the voltage at output  20  of rectifier  143  is measured (step  306 ). At step  308 , the two measured voltages are compared. If they are greater than a threshold voltage, it is determined that a high-resistance connection exists between output terminal  21  and conductor  23 . This determination can be made because given Ohm&#39;s law, a higher resistance between output terminal  21  and conductor  23  will cause a greater voltage drop across that connection. The threshold voltage may be, for example, about 0.5 to 0.7 volts. The difference in voltages with an open circuit fault between output terminal  21  and conductor  23  would, by contrast, be (for example) about 5 volts. 
     If the difference of voltages is greater than the threshold voltage at step  308 , the current output from alternator  14  is suspended or limited, in view of the faulty connection, at step  310 . The suspension or limitation can be performed by engine controller  18  reducing the commanded voltage on regulator control circuit  30 . Also, a dedicated signal can be provided between engine controller  18  and voltage regulator  16  (either via a dedicated wire or multiplexed on regulator control circuit  30 ) through which engine controller  18  can command voltage regulator  16  to suspend generation of output current. 
     It should be noted that in normal operation of alternator  14 , the voltage at output  20  of rectifier  143  undergoes significant fluctuation, up to about 3 volts. This is at least in part due to the output current from alternator  14  being the result of rectification of three alternating current waveforms produced by stator  141 . In order to allow the present invention to operate with greater precision and to avoid false indications of a faulty connection (i.e., “false positives”), the voltage threshold used at step  308  can be a function of the output current of alternator  14 . Thus, for a given resistance which would indicate a faulty connection between output terminal  21  and conductor  23 , the threshold voltage for detecting that fault will be larger for a larger output current. 
     To further ensure against “false positives”, the algorithm of FIG. 3 can be modified to require that at step  310 , the difference of voltages must be above the threshold for at least a predetermined time before taking action to limit or suspend the output current of alternator  14 . 
     To prevent engine controller  18  from permanently suspending or limiting current output from alternator  14  in the event of a “false positive”, engine controller  18  can periodically re-enable normal operation of alternator  14 . Engine controller  18  would do this by resuming its normal voltage commands to voltage regulator  16  on regulator control circuit  30 . If the fault reappears, engine controller  18  would again limit or suspend the output of alternator  14 . Engine controller  18  could retry enabling normal voltage commands to voltage regulator  16  a predetermined number of times and then conclude that the suspension or limitation of output should be permanent (until a vehicle repair is made). 
     A fault at the connection between output terminal  21  and conductor  23  can also be in the form of an intermittent open circuit fault. Such an intermittent open circuit fault can be caused by a loosened fastener coupling conductor  23  to output terminal  21 . An intermittent open-circuit fault can produce the waveforms shown in FIG.  4 . The lower trace shows the voltage at output  20  of rectifier  143 , while the upper trace shows the signal on load indicator circuit  28 . When the voltage at output  20  of rectifier  143  rises in view of the intermittent open circuit (indicated as point “A” on the graph), voltage regulator  16  recognizes the rise and holds the signal on load indicator circuit  28  LOW. The voltage at output  20  of rectifier  143  rises in the event of the intermittent fault because voltage regulator  16  attempts to control the output of alternator  14  to ensure that the voltage at the positive terminal of battery  19  is at the predetermined target voltage. When the intermittent open-circuit fault no longer exists (indicated at point “B”), the signal on load indicator circuit  28  resumes its normal function. With an intermittent fault such as this, engine controller  18  could retry enabling alternator  14  a predetermined number of times. If the fault recurs beyond this number of times, a final determination that a fault exists could be made. Engine controller  18  could permanently limit or suspend the output of alternator  14 , illuminate fault indication lamp  25  and set a diagnostic code in memory to log the fault for retrieval by repair personnel. 
     While a faulty connection between output terminal  21  and conductor  23  has been discussed herein, any faulty connections between output terminal  21  and battery  19  can equivalently be diagnosed by systems according to the present invention. For example, the output of alternator  14  may be provided to a junction box, from which it is then provided to battery  19 . A faulty connection to the junction box in such a configuration can be diagnosed by the present invention. 
     Various other modifications and variations will no doubt occur to those skilled in the arts to which this invention pertains. Such variations which generally rely on the teachings through which this disclosure has advanced the art are properly considered within the scope of this invention. This disclosure should thus be considered illustrative, not limiting; the scope of the invention is instead defined by the following claims.