Oxygen sensor signal conditioner

A method and apparatus for controlling the various functions of an internal combustion engine using a program-controlled microprocessor having a memory preprogrammed with various control laws and associated control schedules receives information concerning one or more engine-operating parameters such as manifold absolute pressure, throttle position, engine coolant temperature, air temperature, engine speed or period and the like. These parameters are sensed and then supplied to input circuits for signal conditioning and conversion into digital words usable by the microprocessor. The microprocessor system computes a digital command word indicative of a computer-commanded engine control operation and output circuitry responds to predetermined computer-generated commands and to the computed digital command words for converting them to corresponding pulse-width control signals for controlling such engine operations as fuel-injection ignition timing, proportional and/or on-off EGR control, or the like. The engine control system further includes an oxygen sensor feedback system for supplying signals indicative of the quantity of oxygen in the exhaust system of the engine back to the microprocessor for control purposes. In particular this disclosure relates to an oxygen sensor condition circuit which generates not only the bilevel output signals indicating the quality of oxygen in the exhaust system, but also generates an oxygen sensor inhibit signal which may be used in a control system to effectively disregard the output of the sensor and to apply fixed or preprogrammed conditions for controlling the air/fuel ratio. Typically the purpose of the inhibit signal is to indicate when the sensor is inoperable because of its operating temperature or its physical condition.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to a method and apparatus for controlling 
an internal combustion engine, and more particularly to a 
microprocessor-based electronic engine control system having a memory 
preprogrammed with various control laws and control schedules responsive 
to one or more sensed engine-operating parameters for generating signals 
for controlling fuel injection, ignition timing, EGR control, or the like. 
2. Statement of the Prior Art 
Many of the patents of the prior art recognize the need for employing the 
enhanced accuracy of digital control systems for more accurately 
controlling one or more functions of an internal combustion engine. 
U.S. Pat. No. 3,969,614 which issued to David F. Moyer, et al on July 13, 
1976 is typical of such systems as are U.S. Pat. No. 3,835,819 which 
issued to Robert L. Anderson, Jr. on Sept. 17, 1974; U.S. Pat. No. 
3,904,856 which issued to Louis Monptit On Sept. 9, 1975; and U.S. Pat. 
No. 3,906,207 which issued to Jean-Pierre Rivere, et al on Sept. 16, 1975. 
All of these Patents represent a break-away from the purely analog control 
systems of the past, but neither the accuracy, reliability, or number of 
functions controlled is sufficient to meet present day requirements. 
Future internal combustion engines will require that emissions be tightly 
controlled due to ever-increasing governmental regulations, while fuel 
consumption is minimized and drivability improved over the entire 
operating range of the engine. None of the systems of the prior art 
provide a method and apparatus for controlling the operation of an 
internal combustion engine over even a portion of its operating range with 
sufficient accuracy to attain minimal emissions and minimal fuel 
consumption along with improved drivability. 
Many of the systems of the prior art have attempted to utilize feedback 
from oxygen sensors located in the exhaust system for controlling various 
engine-operating conditions. These attempts were met with little success 
due to the relative unreliability of the present day oxygen sensors and 
the inability of such sensors to produce signals of significant magnitude 
on either side of stiochiometric air-fuel ratios. 
The application of the present invention permits the use of an oxygen 
sensor feedback system for control purposes by ensuring that the oxygen 
sensor signals are properly conditioned and for testing sensor temperature 
and generating an inhibit signal to inform the computing system that a low 
temperature condition exist and hence that the possibility of unreliable 
sensor readings exists.

SUMMARY OF THE INVENTION 
The system of the present invention contemplates an oxygen sensor being 
placed in the exhaust gas stream of an internal combustion engine for 
sensing the level of uncombined oxygen existing therein. The oxygen 
sensors impedance is monitored to derive an oxygen sensor inhibit signal 
when the voltage developed across the sensor exceeds a fixed level for a 
specified current applied to the sensor. In the preferred embodiment of 
the present invention, a two-sensor installation was used whereby a first 
oxygen sensor was placed in one bank of an exhaust manifold while a second 
oxygen sensor was placed in the other bank. A monitoring amplifier is 
associated with each channel and a comparator is operatively coupled to 
the output of each amplifier. A predetermined threshold indicative of 
stiochiometric operation is established at one input of the comparator and 
the amplified sensor output is applied to the other. The signal 
conditioner of the present invention also controls the current to the 
sensors for impedence monitoring and greatly enhances the feedback 
system's ability to distinguish the difference between "rich" and "lean" 
signals from those caused by sensor high impedance due to low 
temperatures, etc. Furthermore, the present invention provides means for 
optimizing the current supplied to the sensor, the inhibit threshold 
level, and a stiochiometric threshold level so as to produce properly 
conditioned signals capable of being used by said microprocessor-based 
engine control system for computing highly precise engine control 
commands. 
INCORPORATION BY REFERENCE 
This application is one of fourteen application filed on Feb. 27, 1978, all 
commonly assigned and having substantially the same specification and 
drawings, the fourteen applications being indentified below: 
______________________________________ 
Serial 
Num- 
ber Title 
______________________________________ 
881,321 
Microprocessor-Based Electronic Engine Control System 
881,322 
Feedback-Compensated Ramp-Type Analog to Digital 
Converter 
881,323 
Input/Output Electronic For Microprocessor-Based 
Engine Control System 
881,324 
Swtiching Control of Solenoid Current in Fuel 
Injection Systems 
881,921 
Dual Voltage Regulator With Low Voltage Shutdown 
881,922 
Oxygen Sensor Qualifier 
881,923 
Ratiometric Self-Correcting Single Ramp Analog To 
Pulse Width Modulator 
881,924 
Microprocessor-Based Engine Control System 
Acceleration Enrichment Control 
881,925 
Improvements in Microprocessor-Based Engine Control 
Systems 
881,981 
Oxygen Sensor Feedback Loop Digital Electronic Signal 
Integrator for Internal Combustion Engine Control 
881,982 
Improvements in Electronic Engine Controls System 
881,983 
Electronic Fuel Injection Compensation 
881,984 
Ignition Limp Home Circuit For Electronic Engine 
Control Systems 
881,985 
Oxygen Sensor Signal Conditioner 
______________________________________ 
Application Ser. No. 881,321, filed Feb. 27, 1978 now U.S. Pat. No. 
4,255,789 that application is specifically incorporated herein by 
reference. 
For a better understanding of the drawing figures in this application, 
reference is made to the same figure numbers in the above mentioned 
application Ser. No. 881,321, which includes FIGS. 1 to 34. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 2 is a block diagram of the microprocessor-based electronic engine 
control system. 
FIG. 3E is an electrical schematic diagram of the preferred embodiment of 
the oxygen sensor signal conditioning system.