Engine Operation Interrupt Using Ambient Oxygen Sensing

1. Field of the Invention

The invention relates to operation of an internal combustion engine as a function of ambient gases.

2. Prior Art

Not every combustion process, including that which takes place within an internal combustion engine, goes to completion. One product of incomplete combustion is carbon monoxide. Carbon monoxide, when inhaled in sufficient quantities, can have an undesirable effect on the human body. Even though emission control devices have been installed in U.S. automobiles since 1975, idle operation in an enclosed space can cause a condition which results in elevated concentrations of carbon monoxide in the air of the enclosed space. The present invention is aimed at preventing reduced concentrations of oxygen in the ambient.

U.S. Pat. No. 4,221,206 teaches the use of two carbon monoxide (CO) detectors, one electrical and the other electromechanical, and deactivating a vehicle engine only when the signals from both CO detectors signal the presence of CO above a predetermined amount. Such a system may cause undesirable interruption of engine operation when the vehicle is moving as a result of temporarily high CO concentrations originating from passing nearby exhaust gas sources such as heavy-duty vehicles, tractors, or earth moving machinery. It would be desirable to obviate sudden disablement of a moving vehicle triggered by an extraneous event such as being near an exhaust pipe of a heavy-duty vehicle or any other chance source emitting a relatively high concentration of carbon monoxide in the exhaust gas.

FIG. 3 shows, schematically, the time evolution, after initiation of vehicle idling operation in an enclosed space (e.g., a garage), of: (a) the A/F ratio of the engine; (b) the width of the fuel pulse injected sequentially to each engine cylinder; (c) the oxygen concentration in the enclosed space; and (d) the rate of emitted CO as well as the resulting concentration of CO in the enclosed space. After a few seconds following ignition, the A/F ratio is maintained at the stoichiometric value by the feedback controlled fuel metering system. Under this condition, and for a properly functioning three-way catalyst, the production rate of CO is very small (and constant) and its concentration in the enclosed space rises only very slowly.

As time passes, oxygen is depleted from the air in the enclosed space. Consequently, less fuel is required to keep the A/F ratio at stoichiometry, and the width of the fuel pulse will continuously be decreased by the control system. After a certain time T.sub.1 has elapsed, the width of the fuel pulse reaches the minimum value specified by the design of the fuel metering system. At that point, the A/F ratio begins to drift into the rich region and the rate of tailpipe CO production rapidly increases for two reasons: first, the concentration of CO in the gas emerging from the engine increases, and, secondly, the efficiency of the three-way catalyst rapidly decreases to zero as the A/F becomes richer and richer. The engine will continue idling until, at time T.sub.2, the A/F becomes so rich (e.g., A/F=6) that combustion cannot be maintained. Even though engine operation terminates at this time, the oxygen level may have reached an undesirably low level for occupants in the vehicle passenger compartment. It would be desirable to have a system which would avoid such an oxygen depletion.

This invention includes a system for the interruption of the operation of an idling and stationary motor vehicle equipped with an internal combustion engine, including the step of sensing when the oxygen level in the surrounding ambient decreases below a predetermined value. The method includes also recognizing an idling condition and interrupting the engine operation when there are simultaneous signals signifying both the predetermined level of oxygen and the idling condition of the engine.

FIG. 1 is a block diagram of a system in accordance with the embodiment of this invention;

FIG. 2 is a logic flow diagram showing the sequence of events in accordance with an embodiment of this invention;

FIG. 3 is a graphic representation versus time of, in FIG. 3A the air/fuel ratio, in FIG. 3B the width of fuel pulse, in FIG. 3C the percent of oxygen, and in FIG. 3D the percent of carbon monoxide; and

FIG. 4 is a graphic representation of typical characteristics showing the sensitivity characteristics of the sensor suitable for use in an embodiment of this invention.

Referring to FIG. 1, an electronic engine control system 10 includes an ambient oxygen sensor 11 which is coupled to a comparator 12. Comparator 12 also has an input from a setpoint voltage V.sub.o source 13. If the output of oxygen sensor 11 is less than setpoint V.sub.o source 13, the output of comparator 12 is a set voltage V.sub.1 (signifying "low" oxygen concentration in the ambient). An idling decision comparator 14 has a first input from an rpm sensor 15 and a second input from a setpoint S.sub.o source 16. Idling decision comparator 14 determines if the output from the rpm sensor 15, S, is less than S.sub.o. If S is less than S.sub.o, a set output S.sub.1 (signifying engine idling) is sent from comparator 14. The outputs of comparators 12 and 14 are applied to an activation decision block 17 wherein it is determined if the outputs from comparators 12 and 14 are in a set condition. If this is the case, an activation signal from decision block 17 is applied to a block 18 wherein the engine control system ignition is turned off.

Referring to FIG. 2, a logic flow diagram shows the sequence of events for operation of the apparatus of FIG. 1. The sequence of events starts at a block 20 and then goes to a decision block 21 where it is asked if the engine is running. If yes, logic flow goes to a decision block 22 where it is asked if the engine is idling. If yes, logic flow goes to a decision block 23 where it is asked if the oxygen level is low. If yes, logic flow goes to a decision block 24 where it is asked if switch N is set to a "1" state, i.e., it is on. If yes, logic goes to a block 25 where the ignition pulse voltage is turned off. Logic flow then goes to a block 26 wherein the switches N and M are set to "2". Designating switch N =2 and M =2 means that the ignition voltage is off. When the switch conditions are N =1 and M =1, the ignition voltage is on. Logic flow from block 26 goes to an end block 27.

Returning to block 21, if the engine is not running, logic flow goes to decision block 23. At block 22, if the engine is not idling, logic flow goes to end block 27. At block 23, if oxygen is not low, logic flow goes to a decision block 28 wherein it is checked to see if switch M is in a off, i.e., a "2" condition. If not, logic flow goes to end block 27. If YES, logic flow goes to a block 29 wherein the ignition pulse voltage is turned on. Logic flow from block 29 goes to a block 30 wherein switches N and M are set equal to "1" indicating that the ignition voltage is on. Returning to block 24, if switch N is not equal to "1", logic flow goes to end block 27.

Referring to FIG. 2, if desired, an optional decision block can be inserted after decision block 22. Decision block 31 is coupled to receive the NO output of decision block 22. At decision block 31, it is asked if the vehicle transmission is in neutral or park. If NO, logic flow goes to N block 27. If YES, logic flow goes to decision block 23 wherein it is checked to see if oxygen is low. This optional decision block 31 may be useful in a case where the accelerator is depressed so that the engine is operating at a relatively high rpm and is not idling, but the transmission gear is in neutral or park. The logic flow from start block 20 to end block 27 can be repeated at some convenient rate.

Engine operation can be terminated in a number of ways. As discussed above, the ignition pulse voltage to the spark plugs may be turned off. Alternatively, voltage pulses to the fuel injectors may be discontinued, the fuel pump may be turned off, or the ignition switch may be turned off. One way of turning off the ignition switch would be to put an additional secondary switch in series with the main ignition or start switch. The secondary switch is then interrupted.

If desired, the vehicle may be equipped with the capability to detect whether the vehicle is moving or not. If such is the case, the above-described engine idle check may be replaced with a vehicle-not-moving check. Still further, it may be desirable to have a sub-routine that keeps track of the duration of vehicle idling or stationary nonmovement when the oxygen level is high. Then, when a low oxygen level is detected, engine operation is not terminated unless vehicle idling or stationary condition was occurring for a preset minimum duration of time.

An embodiment of this invention can use an oxygen sensor to monitor the oxygen concentration in the atmosphere ambient to the vehicle, and to provide a signal to the car computer to turn off the engine when the oxygen concentration drops to a preset level. The oxygen sensor can be one of several types, for example, a solid-state sensor based on an oxygen pumping principle with ZrO.sub.2 electrochemical cells. A single cell can be used or, if desired, a double cell sensor. The latter device is more accurate because it is less sensitive to temperature and absolute pressure variations. An advantageous location for the oxygen sensor is under the vehicle hood.

The setpoint, signifying the condition for turning the engine off, should be about 18% of oxygen in the ambient and within a range of 16-20%.

As discussed, a signal from an electronic engine module can be used to signify idle engine operation. Additionally, one can use the output of the oxygen sensor. Consequently, in this scheme, the engine operation is terminated when the oxygen sensor indicates an oxygen level below a predetermined value and the engine is idling.

It is conceivable that when the engine is automatically turned off according to the above sequence of events, the driver may attempt to restart the engine. In this case, the engine control computer may be set so that the engine cannot be restarted until signals from the oxygen indicates an absence of the low oxygen condition. Conversely, engine operation is not inhibited when there is an adequate oxygen condition.