U.S. patent application number 09/768977 was filed with the patent office on 2001-05-31 for wiring harness diagnostic system.
Invention is credited to Shoemaker, Jim Milton.
Application Number | 20010002107 09/768977 |
Document ID | / |
Family ID | 22905176 |
Filed Date | 2001-05-31 |
United States Patent
Application |
20010002107 |
Kind Code |
A1 |
Shoemaker, Jim Milton |
May 31, 2001 |
Wiring harness diagnostic system
Abstract
A circuit includes a plurality of inexpensive resistors
connected at one end to the open collector outputs of an output
array of NPN output transistors which are connected to a wiring
harness or the like for selectively powering a preselected load.
The opposite ends of the resistors are connected to the base of an
NPN sense transistor. The output NPN transistors, when in the on
condition, are biased well into saturation for normal loads and
therefore provide a very low Vce (sat) when properly connected
through the harness to the intended load. In the off condition, the
output NPN transistors look essentially like an open circuit. Vce
(sat) is lower than the base turn-on voltage of the NPN sense
transistor which has a grounded emitter. The collector of the NPN
sense transistor is connected to a source of voltage through a
pull-up resistor and to an input of the microprocessor which
controls the signals to the output array transistors. The base of
each output transistor is connected to an LED to provide a visual
indication of which inputs are on and to help the technician locate
an area on the circuit board or wiring harness corresponding to a
particular function or load on the vehicle.
Inventors: |
Shoemaker, Jim Milton;
(Horicon, WI) |
Correspondence
Address: |
Deere & Company
One John Deere Place
Moline
IL
61265-8098
US
|
Family ID: |
22905176 |
Appl. No.: |
09/768977 |
Filed: |
January 24, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09768977 |
Jan 24, 2001 |
|
|
|
09240115 |
Jan 29, 1999 |
|
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Current U.S.
Class: |
324/537 |
Current CPC
Class: |
G01R 31/005
20130101 |
Class at
Publication: |
324/765 |
International
Class: |
G01R 031/26 |
Claims
1. A fault detection circuit for an electrical system having output
transistors connected to a plurality of conductive lines for
providing outputs over the lines to corresponding loads, the output
transistors switchable between first and second states, wherein in
the second states, the output transistors are in saturation with a
low collector to emitter voltage (Vce) when the lines are properly
connected to the output load, the fault detection circuit
comprising: a sensing circuit connected to the output lines; and
wherein the sensing circuit is responsive to presence and absence
of the low Vce indicative of the saturated condition.
2. The detection circuit of claim 1 including a resistor connected
between each conductive line and the sensing circuit.
3. The detection circuit of claim 1 wherein the sensing circuit
comprises a transistor having a base, and wherein the base is
connected to each of the conductive lines by a resistor.
4. The detection circuit of claim 3 wherein the voltage at the base
of the sensing circuit transistor is below turn-on voltage of the
transistor when the output transistors are in saturation.
5. The detection circuit as set forth in claim 1 including a
voltage pull-up member connected between one of the output lines
and a source of voltage, the pull-up member causing said one of the
output lines to move towards the voltage at the source when the
output transistor for that line is in the first state provided that
line is not shorted, and wherein the detection circuit is
responsive to the voltage on that line to provide a short circuit
indication.
6. The detection circuit set forth in claim 1 wherein the output
lines are connected to a transistor circuit, the transistor circuit
having a preselected output when all the output transistors are
switched on and the transistors are in saturation.
7. The detection circuit set forth in claim 6 including an output
transistor drive circuit, the drive circuit turning the output
transistors on for less than a millisecond of time to provide the
preselected output if a fault is not present in the conductive
lines.
8. The detection circuit as set forth in claim 6 wherein the
transistor circuit includes a transistor having a grounded emitter
and a base connected to the conductive lines via resistors.
9. The detection circuit as set forth in claim 8 wherein the
conductive lines are selectively disconnectable from the system,
and further including a pull-up resistor connected between a source
of voltage and the conductive lines, the pull-up resistor providing
limited current source voltage to the conductive lines to check for
faults in the system when the conductive lines are
disconnected.
10. The detection circuit set forth in claim 1 wherein the output
transistors include bases, each of the bases connected in series to
an LED for providing an indication of a switching signal to the
output transistors to thereby facilitate identification of a
portion of the electrical system corresponding to the output
loads.
11. A fault detection circuit for an electrical system on a
vehicle, the vehicle having a plurality of conditions to be
monitored, the detection circuit having switchable output
transistors connected to a plurality of conductive lines for
providing outputs over the lines to corresponding loads, the fault
detection circuit comprising: a sensing circuit connected to the
output lines and responsive to presence and absence of a
preselected output transistor condition for providing a fault
indication; a switching circuit connected to the output transistors
for switching the output transistors; and indicators connected to
the switching circuit and providing an indication of the lines over
which outputs are to be provided, the indicators facilitating
visual correlation of the conditions to be monitored with the
output lines.
12. The fault detection system of claim 11 wherein the indicators
comprise LED's connected to bases of the output transistors and
indicating when a control signal to the output transistors is
present.
13. The fault detection system of claim 11 wherein in the second
states the output transistors are in saturation and have a low
collector to emitter voltage (Vce), and wherein the preselected
transistor condition is the low Vce indicative of the saturated
condition.
14. The fault detection system of claim 13 including a transistor
circuit connected by a plurality of resistors to the output lines,
the transistor circuit having a first output when the Vce of the
output transistors is below a preselected level.
15. The fault detection circuit as set forth in claim 14 wherein
the preselected level is Vce at transistor saturation.
16. The fault detection circuit as set forth in claim 13 wherein
the switching circuit switches the output transistors to
preselected states for a time period substantially less than a
second to check for the preselected transistor output
condition.
17. A fault detection system for connecting lines of an operational
electrical circuit presenting a preselected current load, the
circuit including an output transistor with an output terminal
having an on and an off condition and connected to the current
load; the fault detection system including: a controller connected
to the transistor circuit for selectively changing the condition of
the output transistor; wherein the voltage on the output terminal
is a first level when the output transistor is in the on condition
and the current load is less than or equal to the preselected
current load, and the voltage is offset from the first level when
the transistor is in the on condition and the current load is
greater than the preselected current load; a check circuit
connected to the controller and the output line and responsive to
the voltage on the output line; and wherein the check circuit
provides a fault signal to the controller in response to the
voltage on the output line being offset from the first level.
18. The fault detection circuit as set forth in claim 17 wherein
the output transistor is in saturation when in the on condition and
is out of saturation when the current load is greater than the
preselected current load, and the check circuit is responsive to
the collector-emitter voltage (Vce) of the output transistor.
19. The fault detection circuit of claim 17 wherein the controller
periodically switches the output transistor during operation of the
electrical circuit and checks for the presence of a fault signal
without interruption of the operation.
20. The fault detection circuit of claim 17 wherein the load
comprises a low current load connected to the output terminal, the
check circuit providing a fault signal if a high current load is
connected to the output terminal or if the output terminal is
shorted.
Description
BACKGROUND OF THE INVENTION
[0001] 1) Field of the Invention
[0002] The present invention relates generally to fault detection
systems, and, more specifically, to circuitry for detecting
improperly connected or shorted wires in a wiring harness or the
like.
[0003] 2) Related Art
[0004] A typical vehicle has numerous solenoids, lamps and relays
connected by a wiring harness to a vehicle controller. An incorrect
voltage or incorrect load on a line can cause expensive damage to
electrical and electronic components and may render the vehicle
inoperable. During servicing of the vehicle or during manufacture
of the harness, the connectors may by wired incorrectly so that
battery voltage is applied directly to a semiconductor or the
semiconductor is connected to a high current sink or ground
resulting in damage to the controller or to other components in the
circuit. For example, a high current pull-in coil for an engine
enablement function such as the fuel pump drive sometimes is
incorrectly wired to the output that is meant for a low-current
hold-in coil. Fuses often are utilized in an attempt to protect the
circuit, but each fuse must be durable enough for vehicle abuse and
transients that occur during normal operation, and therefore the
fuse may fail to open before a vital component in the circuit is
damaged. Other protection methods include the use of individual
series precision current sensing resistors, one at each output of
the controller, with a series of operational amplifiers to provide
a signal to the controller. Such circuits are relatively complex,
costly and sensitive to variations in resistance. Other fault
detection circuits utilize a test power supply having a voltage
level well below the operating voltages to carry out a self-testing
procedure and allow power up only if no low impedance paths are
detected in the bus or harness. These circuits may require a
special power supply and can also be costly and complex. Some
circuits have a slow diagnostic time and cannot be used to provide
checks during routine operation of the vehicle.
[0005] Diagnosing a system with numerous input and output lines is
often tedious. Identifying a particular portion of a circuit on a
circuit board or wiring harness connection can often require
time-consuming references to a wiring diagram. As the number of
input and output functions to and from a controller increases, the
technician often finds that correlating the circuit diagram with a
particular portion of the hardware is increasingly difficult.
BRIEF SUMMARY OF THE INVENTION
[0006] It is therefore an object of the present invention to
provide an improved circuit for diagnosing wiring harnesses and
similar components. It is a further object to provide such a
circuit which overcomes most or all of the aforementioned
problems.
[0007] It is a further object of the present invention to provide
an improved circuit for diagnostic purposes which effectively
detects wiring problems. It is another object to provide such a
circuit which can detect faults quickly and which does not require
special test voltages. It is still a further object to provide such
a circuit which is sufficiently durable to operate reliably on a
vehicle or other device wherein transients and over-voltage or
under-voltage conditions occur relatively frequently.
[0008] It is another object of the present invention to provide an
improved circuit for diagnosis of wiring harnesses or the like
which is simple in construction and fast and reliable in operation.
It is another object to provide such a circuit which does not
require precision resistors or numerous operational amplifiers. It
is a further object to provide such a circuit which can quickly and
reliably check for over-voltages, wiring harness failures, and
shorts to ground or to power line and protect electronic components
before such faults cause permanent damage to the electronic
system.
[0009] It is another object of the present invention to provide an
improved circuit for on-the-go diagnosis of wiring harness
connections or the like wherein the diagnosis takes place in a very
short period of time without perceptible interruption of the normal
operation of the vehicle or other device. It is yet another object
to provide such a circuit wherein the circuit board as well as the
wiring harness connected to the circuit board can be diagnosed. It
is still another object of the invention to provide such a circuit
which is relatively inexpensive and does not require precision
resistors or a large number of operational amplifiers.
[0010] It is still another object of the invention to provide an
improved diagnostic circuit which is relatively simple and
inexpensive in construction and which facilitates easy
identification of circuit functions and circuit faults without need
for continual reference to a wiring diagram.
[0011] A circuit constructed according to the teachings of the
present invention includes a plurality of inexpensive resistors
connected at one end to the open collector outputs of an output
array of NPN output transistors which are connected to a wiring
harness or the like for selectively powering a preselected load.
The opposite ends of the resistors are connected to the base of an
NPN sense transistor. The output NPN transistors, when in the on
condition, are biased well into saturation for normal loads and
therefore provide a very low Vce (sat) when properly connected
through the harness to the intended load. In the off condition, the
output NPN transistors look essentially like an open circuit. Vce
(sat) is lower than the base turn-on voltage of the NPN sense
transistor which has a grounded emitter. The collector of the NPN
sense transistor is connected to a source of voltage through a
pull-up resistor and to an input of the microprocessor which
controls the signals to the output array transistors.
[0012] To test the connections of the harness to the NPN output
transistors, the microprocessor turns on all the output transistors
simultaneously for a very short period of time, preferably only a
few microseconds. If all the outputs are connected to the intended
loads, the Vce of each of the transistors will be less than the
base turn-on voltage of the sense transistor. If any of the outputs
is improperly connected to the source voltage or to a high current
sink, that transistor will come out of saturation and Vce will rise
above the turn-on voltage of the sense transistor. The sense
transistor then turns on to provide a signal to the microprocessor
that a fault has been detected. During operation of the vehicle,
the system continuously monitors for ground fault problems by
turning on all outputs except one for a few microseconds. If the
output that is not turned on is not shorted to ground, the voltage
on that line will rise toward source voltage and turn on the sense
transistor. Each output is checked in sequence. The microprocessor
provides a fault code if a grounded condition is detected on a line
or lines.
[0013] To provide diagnostics for a system wherein a positive
turn-on voltage is necessary for enablement of the device connected
through the harness, a similar detection arrangement is provided
which utilizes the low Vce of a PNP output transistor in
saturation. To aid in the diagnostics, each output transistor in
the output array includes a base connected in series with an input
LED so the technician can tell at a glance which inputs to the
array are on and which inputs to the array are off. The technician
therefore can determine which connections on the output array
corresponds to a particular input or output function on the vehicle
and if the output transistor on the array for that function is
operating properly by simply activating that function while looking
at the LED outputs. For example, by bouncing on the seat, the LED
for the operator presence circuit will flash to tell the technician
which line corresponds to that function. If no LED flashes when a
particular function input or output is activated, the technician
knows to look for problems in that portion of the system. The
one-to-one correspondence significantly simplifies system
troubleshooting and reduces the amount of time the technician has
to refer to the wiring schematic.
[0014] These and other objects, features and advantages of the
present invention will become apparent to one skilled in the art
upon reading the following detailed description in view of the
drawings.
BRIEF DESCRIPTION OF THE DRAWING
[0015] The single drawing figure is a schematic of a diagnostic
circuit connected to the output terminals of a output buffer
array.
DETAILED DESCRIPTION OF THE DRAWING
[0016] Referring now to the single drawing figure, therein is shown
a schematic for a portion of a vehicle circuit 10 including a cable
harness or similar multiple line element indicated generally at 12
and including a plurality of output lines 12a-12k connected through
line connectors 13 to various loads such as solenoids, relays, and
indicator lamps (not shown) on the vehicle including those for fuel
pump operation and for interlock functions such as operator
presence and parking brake operation. The lines 12a-12k are
connected to output terminals of an output buffer array 16 on a
main control board. As shown, the buffer array 16 includes a
plurality of power output transistors 18a-18k, one for each of the
output lines 12a-12k. Detailed output buffer circuits are shown
only for the first (18a) and last (18h) transistor of one array 16,
with the first power output transistor 18a being a PNP transistor
for high side switching to connect the load such as a fuel pump
solenoid or other engine enable function on line 12a to source
voltage of nominally twelve volts. The remaining transistors
18b-18h (only the circuit for 18h is shown since the circuits for
transistors 18b-18g are identical) are NPN transistors for
switching solenoids, relays and indicator lamps on lines 12b-12h to
ground. It is to be understood that the number of arrays 16 and the
combinations of PNP and NPN output transistors 18 can be varied to
accommodate different numbers of lines 12 and the switching
polarity necessary for the loads connected to those lines.
[0017] The output buffer array 16 includes inputs 22a-22h connected
to the corresponding outputs of parallel latch circuit 30 which in
turn is connected through an eight bit output bus 32 to a
conventional chip output selector 34 and microcontroller 36. The
microcontroller 36 sequentially polls various inputs and outputs
including voltage levels, fault detector circuit outputs, and
interlock switches on the vehicle via terminals 40 and reads in
these inputs and outputs eight at a time. Control signals are
provided via bus 32 to the latch circuit 30 which maintains
preselected output states depending on the signals received from
the microcontroller 36. Each of the outputs 22a-22g selectively
provides base drive current for the NPN output transistors 18b-18h
through a light emitting diode D1 connected in series with a base
current limiting resistor R1. A resistor R2 is connected between
the base of each NPN output transistor and ground. The base
resistors assure that stray currents do not bias the transistor
on.
[0018] A pull-up resistor R3 is connected between a fused voltage
source (Vbb) and the collector to pull up the voltage at the
outputs for board self-diagnostic purposes when no external output
lines 12 are connected to the board. A snubber diode D2 is
connected to the collector of each of the transistors 18b-18h and
the voltage source Vbb for protection since many of the loads on
the lines 12, such as the solenoids and relays, are inductive.
[0019] A grounded emitter inverting transistor 58 includes a base
connected by a current limiting resistor R4 to the latch terminal
22a and to ground by resistor R5. The collector of the transistor
58 is connected by a light emitting diode D3 and resistor R6 to the
base of the PNP output transistor 18a which has an emitter
connected to the voltage source (Vs). A resistor R7 is connected
between the voltage source Vs and the base to assure that the
transistor is not biased on by stray currents. A snubber diode D4
is connected in parallel with a resistor R8 between ground and the
collector of the PNP transistor 18a. The resistor R8 pulls the
output on the line 12a low when the line is disconnected from its
load, which as shown is a hold-in solenoid L1 on a fuel pump
control (or other engine enablement device).
[0020] When the latch terminal 22a goes high, the transistors 58
and 18a are turned on, and D3 provides a visual indication that the
fuel solenoid signal is present and the line 12a should be on (near
the Vs voltage level). When any of the terminals 22b-22h goes high,
the corresponding one of the transistors 18b-18h is turned on to
ground the corresponding one of the output lines 12b-12h. A visual
turn-on signal is provided by the diode D1 for that output
transistor. An LED indication can also be provided in the circuitry
connected to the terminals 40 of the microcontroller 36 so a
technician can tell at a glance which inputs are on as well as
which output lines 12a-12h are to be in the on condition.
[0021] A fault detection circuit indicated generally at 70 is
connected to the outputs 12b-12g of the NPN output transistors
18b-18h by voltage dropping resistors R11-R17, respectively. The
circuit 70 includes an NPN transistor 72 having a grounded emitter
and a collector output 74. The collector is connected through a
resistor R18 to a voltage source Vcc having a nominal voltage of
approximately five volts so that when the transistor 72 is off, the
output 74 will be high (approximately +5 volts). The base of the
transistor 72 is connected via resistors R11-R17 to the output
lines 12a-12h. When all of the NPN output transistors 18b-18h are
turned on and are in saturation, the Vce(sat) of the transistors
will be very low and on the order of 0.1 to 0.2 volts so that the
voltage at the base of the transistor 72 will be below about half a
volt and below the base-emitter turn on voltage of the transistor
72. If some of the transistors 18b-18h are turned off and some are
on (as is the case when the vehicle is in operation) or if one or
more of the output transistors is not in saturation, the voltage at
the base of the transistor 72 will rise above the turn-on voltage,
causing the output 74 to go low (approximately 0.1 volt). A pull-up
resistor R19 is connected between Vcc and the base of the
transistor 72 to make the circuit 70 more sensitive to the
condition where an NPN output transistor is not in saturation.
Since the transistors 18b-18h normally are in saturation when
turned on and properly connected to the load on the lines 12b-12g,
momentarily switching all the NPN transistors in the output array
16 to the on condition should cause the output 74 to go high (the
voltage at the base of the transistor 72 will drop below turn-on as
all of the NPN transistors go into saturation) unless there is a
fault such as an improper load, a burned out NPN transistors in the
array 16, or a short to the voltage source in one of the lines
12.
[0022] The output 74 of the transistor 72 is connected to the input
circuitry for the microcontroller 40 which senses whether the high
or low condition exists on the output. If the condition at 74 is
wrong for the given inputs to the array 16, the microcontroller can
shut down all outputs and provide a warning until the fault is
corrected. By turning on all the NPN outputs 12b-12h except one for
a short period, preferably less than 50 microseconds for a
resistive load and several hundred microseconds for an inductive
load, that single output line can be checked. The single off line
should rise toward supply voltage and cause the voltage at the base
of the transistor 72 to rise above the turn-on voltage of the
transistor which results in a low level at 74. If the low level is
detected for the particular line being tested, the microcontroller
advances the sequence to test the next one of the lines 12.
However, if at any time there is a discontinuity between the load
and the line being tested or if that line is shorted to ground, the
voltage on that line will not rise sufficiently to turn on the
transistor 72, and the microcontroller will provide a fault
indication and shut down the outputs. The test time period is so
short for each line that the normal operation of the vehicle is not
hindered during the sequencing if no faults are detected.
Therefore, ground fault tests of the outputs can be conducted at
regular intervals during vehicle operation. For example, by testing
one output each 50 milliseconds, all the outputs can be checked for
shorts in less than a second. The microcontroller 36 can shut down
operation immediately to avoid costly and time consuming component
damage.
[0023] A circuit 80 similar to the circuit 70 is connected to the
PNP output transistor line 12a. A PNP transistor 82 includes an
emitter connected to source voltage Vs and a base connected to the
line 12a by a resistor R20. The base is also connected by a pull-up
resistor R21. When the PNP output transistor 18a is off, the
voltage at the base of the PNP transistor 82 drops causing the
transistor to turn on and the level at output 84 to go to the high
condition. If the transistor 18a is on and in saturation which it
should be under normal loading, the voltage on the line 12a will
rise toward the source voltage Vs and cause the transistor 82 to
turn off which, in turn, causes the output 84 to go to the low
condition. However, if the line 12a is improperly connected to
ground or improperly connected to a high current draw component
(such as the pull-in coil for the fuel solenoid, rather than the
much lower current hold-in coil), the transistor 18a will not go
into saturation and line voltage will not be sufficient to turn off
the transistor 80. The output 84 will remain in the high condition.
A pull-down resistor 22 is connected to the collector of the
transistor 82 to assure the output 84 is low when the transistor 82
is off. A resistor R23 is connected between the collector and the
output 84 to limit output current and reduce the high condition
voltage level for compatibility with the input selection circuitry
for the microcontroller 36 which preferably operates at a voltage
much lower than Vs to keep the controller board from resetting,
even at extremely low voltages during cold starting of the vehicle.
The microcontroller 36 checks the condition at 84, and if the high
condition is found when the transistor 18a is turned on, a fault is
indicated and the outputs are shut down. By using a separate
circuit 80 for the PNP output transistor 18a, sensitivity to a
fault can be increased and the fuel pump solenoid L1 or other
positive switching engine enabling load can be checked more
frequently than the loads on the remaining lines 12b-12h. An
indicator diode (D6) is connected to the microcontroller 36 and
provides a heartbeat signal during operation as well as a coded
signal to provide a visual identification of a fault when one is
detected.
[0024] At power up of the vehicle, the circuit 10 is first checked
for major wiring errors such as Vs connected to one of the lines
12b-12h or line 12a grounded or connected to a high amperage coil
rather than to the lower amperage coil L1. All the outputs of the
array 16 are turned off, and the microcontroller checks for a low
at the output 74 and a high at the output 84 (the solenoid coils
and other external wiring on lines 12 or the resistors R3 and R8
biasing the transistors 72 and 82 into the on conditions). If the
conditions are not satisfied indicating a fault, the fault flag is
set and start-up is aborted. If the first tests are successful, the
NPN outputs 12b-12h are all turned on and the output transistors 18
should all go into saturation to turn off the sense transistor 72
and provide a high condition at 74 unless an NPN transistor is
burned out or Vs is improperly connected or shorted to one of the
outputs 12b-12h. The PNP output transistor 18a is also turned on
which should result in the transistor 82 being off and the output
84 being low, unless the line 12a is improperly connected to a high
current load such as a pull-in coil or to ground. If the preceding
tests indicate no faults, the microcontroller initiates the normal
program start for the vehicle. If not, the fault flag is set, the
routine is aborted, and vehicle operation is locked out. The
microcontroller flashes the particular code or codes associated
with the particular faults detected on the light emitting diode
D6.
[0025] During operation of the machine, the outputs 12b-12h are
tested every 50 milliseconds for a short to ground by briefly
turning on only one output line at a time and checking for the low
condition at 74 as described above. Also, the outputs 12b-12h are
checked regularly by briefly turning on all the NPN output
transistors 18b-18h except one and checking to see if the output 74
is low. If 74 is not low, the particular output line for the
transistor that is off probably is shorted to ground. The PNP
transistor output 12a is also checked as set forth above,
preferably more frequently than the NPN outputs. If a particular
test is not successful, the fault flag is set, a fault code is
flashed out on D6.
[0026] By way of example only, the following component values are
suggested:
1 R1, R6 220 ohms R2-R5, R7, R8 10 k ohms R11-R20 10 k ohms R21 1.2
k ohms R22, R23 10 k ohms
[0027] Having described the preferred embodiment, it will become
apparent that various modifications can be made without departing
from the scope of the invention as defined in the accompanying
claims.
* * * * *