Aged exhaust gas oxygen sensor simulator

An aged exhaust gas oxygen sensor (EGO) simulator is inserted between an exhaust gas oxygen sensor and an electronic control module for testing the response of fuel control and emission systems to various amounts of exhaust gas oxygen sensor aging/degrading. The sensor signal is input to a summing amplifier where a delay signal is added. Positive and negative summing amplifier outputs go through vernier and decade controls, which add delay, and then to a variable gain inverter. The difference signal is integrated and output to the summing amplifier as the delay signal and output to a ground offset control for shifting the waveform up and down before going out to the control module. The vernier and decade controls add delays to mimic an aged/degraded exhaust gas oxygen sensor.

FIELD OF THE INVENTION 
The present invention relates generally to an exhaust gas oxygen sensor 
(EGO), and, more particularly, to a device for testing the response of 
fuel control and emission systems to various levels of EGO aging. 
BACKGROUND OF THE INVENTION 
Modern vehicles must control exhaust emissions to meet air quality 
standards. An exhaust gas oxygen sensor monitors exhaust emissions and 
inputs exhaust data to an electronic control module that can vary the 
fuel/air mixture to help keep emissions within the required parameters. As 
an exhaust gas oxygen sensor ages, its output varies causing exhaust 
emissions to rise, sometimes above a target level. It is desirable to have 
a tool for development and production calibration of the electronic 
control module to identify the exhaust gas oxygen sensor threshold signal 
degradation that will cause exhaust emissions to exceed the target level. 
Accordingly, it will be appreciated that it would be highly desirable to 
have a tool that would mimic the signal of an aged or otherwise degraded 
exhaust gas oxygen sensor. 
SUMMARY OF THE INVENTION 
The present invention is directed to overcoming one or more of the problems 
set forth above. Briefly summarized, according to one aspect of the 
present invention, an aged exhaust gas oxygen sensor simulator is inserted 
between an exhaust gas oxygen sensor and an electronic control module for 
testing the response of fuel control and emission systems to various 
levels of exhaust gas oxygen sensor aging. The simulator comprises input 
means for receiving a sensor signal from the exhaust gas oxygen sensor, a 
summing amplifier adding the sensor signal and a delay signal and 
producing a summed signal at its output, a variable gain inverter having 
an input and an output, a first control means connecting the summing 
amplifier output to the variable gain inverter input for simulating a rich 
to lean transition, a second control means connecting the summing 
amplifier output to the variable gain inverter input for simulating a lean 
to rich transition, and an integrator receiving the variable gain inverter 
output and delivering the delay signal to the summing amplifier and the 
electronic control module. 
The simulator adds delays to the exhaust gas oxygen sensor signal to mimic 
transitions of the air/fuel mixture from rich to lean and from lean to 
rich. A feedback signal is summed with the sensor signal to produce a 
delayed signal output which mimics an aged or degraded sensor. The 
simulator includes an impedance matching network to prevent distortion of 
the sensor signal when the simulator box is connected. 
These and other aspects, objects, features and advantages of the present 
invention will be more clearly understood and appreciated from a review of 
the following detailed description of the preferred embodiments and 
appended claims, and by reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1-2, an exhaust gas oxygen sensor signal simulator delay 
box 10 is inserted in series between an exhaust gas oxygen sensor (EGO) 12 
and a control module 14 to mimic the characteristics of aged or degraded 
EGO sensors. The front panel of the simulator box 10 is divided into three 
sections with the left section having decade and vernier control knobs 16, 
18 for controlling rich to lean fuel mixture transitions. A right hand 
section has decade and vernier control knobs 20, 22 controlling lean to 
rich fuel mixture transitions, and a center section has a control switch 
23 and a ground offset vernier control knob 24. For the present invention, 
the decade control knobs 16, 20 have three active positions. 
Referring to FIGS. 1, 2 and 4, the simulator 10 includes a mode switch 26, 
preferably located on the front panel of the box, that, in a normal mode, 
electrically removes the simulator and, in an aged mode, inserts the 
simulator between the sensor 12 and control module 14. Thus, in the normal 
mode, a sensor signal from the exhaust gas sensor 12 is routed directly to 
the control module 14. In the aged mode, the sensor signal is input to an 
operational amplifier 28 configured as a unity gain follower with 
resistors 30, 32 connected between ground and the noninverting input of 
the amplifier 28. The sensor signal is input at the junction of the 
connected resistors 30, 32. Amplifier 28 and resistors 30, 32 match the 
impedance sensor 12 would see if connected to the control module 14 
thereby acting as a buffer to prevent distortion of the input signal. 
The output of amplifier 28 is connected to the inverting input of 
operational amplifier 34 through resistor 36. A delay signal is also input 
to the inverting input of amplifier 34 through resistor 38. The 
noninverting input of amplifier is grounded through resistor 40. Feedback 
resistors 42, 44 are also connected to the inverting input of amplifier 34 
while the output of amplifier 34 is connected through diode 46 to resistor 
42 and through diode 48 to resistor 44. Diodes 46, 48 are connected with 
opposing polarities to the output of amplifier 34 so that when amplifier 
34 functions as a summing amplifier its inputs through resistors 36 and 38 
are summed so that a positive output causes diode 46 to conduct producing 
a voltage across potentiometer 50, on the other hand, a negative output 
causes diode 48 to conduct creating a voltage drop across potentiometer 
52. 
Potentiometer 50 is preferably a wire wound resistor with a movable tap for 
adjusting effective resistance. The tap is moved by turning the vernier 
control knob 18. Similarly, potentiometer 52 has a tap that is moved by 
turning the vernier control knob 22. The tap on potentiometer 50 connects 
potentiometer 50 to resistors 54, 56 and 58 which, in turn, are connected 
to the inverting input of operational amplifier 60. Selection of one of 
the resistors 54, 56, 58 is accomplished by turning decade resistor knob 
16 to the 1, 2 or 3 position. Values of the resistors are in powers of ten 
so that the second resistor 56 is ten times the value of the first 
resistor 54, and the third resistor 58 is ten times the value of the 
second resistor 56 and a hundred times the value of the first resistor 54. 
A resistance network contains resistors 62, 64 and 66 connected in 
parallel to the noninverting input of amplifier 60. The values of the 
resistors 62, 64, 66 are the same the values of the resistors 54, 56 and 
58, respectively. Selection of one the resistors from among the network is 
accomplished by turning decade resistor knob 16 to position 1, 2 or 3. 
Position 1 selects resistor 62 along with resistor 54 while position 3 
selects resistor 66 along with resistor 58. 
Resistance network 68 is identical to the resistance network containing 
resistors 54, 56 and 58 and connects the tap for potentiometer 52 to the 
inverting input of amplifier 60. Resistance network 70 contains resistors 
the same as resistors 62, 64 and 66 that are selected in the same manner 
except that decade resistor knob 20 is turned to select from among 
resistors in network 70. Resistor 72 is grounded on one end and connected 
to the noninverting input of amplifier 60 along with resistance network 70 
and one of the resistors 62, 64 or 66. Feedback resistor 73 completes the 
circuit in which amplifier 60 is configured as a variable gain inverter. 
There are two sets of controls for the simulator, one set for rich to lean 
transitions and one set for lean to rich transitions. To allow for 
independent delays of 1 ms to 1250 ms, each control set has two controls, 
a decade switch for which only the 1, 2, and 3 settings are used, and a 
vernier control which is adjusted from 0.0 to 0.92. The relationship 
between .tau. in milliseconds and the decade (D) and vernier settings 
(.alpha.) is 
##EQU1## 
with values as indicated in the following table 1. 
TABLE 1 
______________________________________ 
Decade Setting 
Vernier Setting 
Milliseconds 
______________________________________ 
D .alpha. .tau. 
1 0.fwdarw.0.92 
1.fwdarw.12.5 
2 0.fwdarw.0.92 
10.fwdarw.125 
3 0.fwdarw.0.92 
100.fwdarw.1250 
______________________________________ 
The output from amplifier 60 is input through resistor 74 to the inverting 
input of operational amplifier 76. Resistor 78 is connected between the 
noninverting input of amplifier 76 and ground. A capacitor 80 is connected 
to the inverting input and output of amplifier 76 thereby configuring it 
as an integrator. The output from integrating amplifier 76 is input 
through resistor 38 to the inverting input of amplifier 34 to be summed 
with the output of input amplifier 28. 
The output of integrating amplifier 76 is input through resistor 82 to the 
inverting input of amplifier 84 which is configured as a summing 
amplifier. Also connected to the inverting input, to be summed with the 
input to resistor 82, is an input to resistor 86. Resistor 86 is also 
connected to the tap of potentiometer 88 that has one end grounded to 
provide a ground offset signal to shift the waveform up and down within a 
-1 v to +1 v window. The other end of potentiometer 88 is connected 
through resistor 90 to switch 23 that can switch between a ground position 
and positive and negative supply voltages to simulate an exhaust gas 
oxygen sensor failure. Grounded resistor 92 is connected the noninverting 
input of summing amplifier 84. A feedback resistor 94 is connected between 
the summing input and output of amplifier 84. The output of amplifier 84 
goes out to mode switch 26, which, in the aged mode, delivers the output 
to the control module 14. 
Operation of the present invention is believed to be apparent from the 
foregoing description and drawings, but a few words will be added for 
emphasis. The electronic simulator box is capable of independently slowing 
the rich to lean and lean to rich response rates of the sensor signal. 
Vernier control potentiometer 50 and decade control resistors 54, 56 and 
58 slow the rich to lean response rate, while vernier control 
potentiometer 52 and decade control resistor network 68 slow the lean to 
rich response rate. Rich to lean transitions are identified from the 
trailing edge of the sensor signal waveform and lean to rich transitions 
by the leading edge. 
HEGO is an acronym for heated exhaust gas oxygen sensor and has a normal 
signal level of 0 v to +1 v. A HEGO produces a high output for a rich 
exhaust air/fuel (A/F) ratio and a low output for a lean exhaust A/F 
ratio. One common mode of HEGO failure is a uniform shift in signal 
voltage transfer function in the negative direction, called characteristic 
shift downward (CSD) as is known in the art. CSD causes the HEGO's lean 
voltage to be as low as -1 v and the rich voltage to be as low as 0 v. The 
ground offset control of the aged exhaust gas oxygen sensor simulator box 
is used to shift HEGO waveform up and down within this -1 v to +1 v 
window, thus simulating a CSD failure mode or correcting the waveform of a 
HEGO which is experiencing CSD. 
It can now be appreciated that there has been presented a simulator which 
slows the lean to rich and/or rich to lean response rates of the exhaust 
gas oxygen sensor feedback signal independently from 1 to 1250 ms. This 
introduces shifts in the fuel control system away from stoichiometry, 
causing NO.sub.x, CO and HC emissions to change. The simulator box is 
wired in series between the exhaust gas oxygen sensor and the electronic 
control module. The sensor signal is modified by varying the response rate 
and/or by imparting a DC ground offset. There are two sets of controls 
(vernier pot and decade resistance switch) which independently vary the 
lean to rich and rich to lean response rates and a third set of controls 
(vernier pot and polarity switch) for varying the ground offset. A switch 
allows bypassing of the device completely. 
While the invention has been described with particular reference to an 
automobile fuel and emission system, it is apparent that the simulator is 
easily adapted to other fuel and emission systems. As is evident from the 
foregoing description, certain aspects of the invention are not limited to 
the particular details of the examples illustrated, and it is therefore 
contemplated that other modifications and applications will occur to those 
skilled in the art. It is accordingly intended that the claims shall cover 
all such modifications and applications as do not depart from the true 
spirit and scope of the invention.