Pollution sensors 'tune' running auto engines

If you think the emissions-control equipment on the 1980-model cars is complex, wait until you see the '81-model cars. New clean-exhaust systems on most 1981 cars next fall will reduce auto pollution more than any previous system. To do it, the controls will be the most complicated and costly of any used heretofore on US-built automobiles.

These systems represent the last mile for the automotive emissions engineers since the new cars will finally achieve the frequently postponed federal pollution levels ordained by the 1970 amendments to the Clean Air Act. A slight exception to this is that the 1981 oxides of nitrogen (NOx) standard has been raised from the originally mandated .4 to 1.0 gram per mile (gpm).

Since the statutory emissions standard for unburned hydrocarbons was reached with the 1980 cars, the '81 standards require only that the carbon monoxide (CO) be cut from 7 gpm in 1980 to 3.4 gpm in 1981 and NOx reduced from 2 gpm in 1980 to 1 gpm in '81.

Yet, to eliminate just this 4.6 gpm of auto pollution (about a spoonful), practically all the 1981 cars will be furnished with three-way catalytic systems while keeping the injection pumps, exhaust gas recirculation systems, the evaporative emissions controls, and other emissions paraphernalia necessary to meet the earlier standards.

Millions of 1981-model cars also will have the new throttle-body fuel injection.

Howard Kehrl, executive vice-president of General Motors, says: "These systems will represent the largest single emissions change ever made in one model year. Introducing on a massive basis all the electronics to regulate the fuel flow and the other changes that go with the oxygen sensor and the new three-way converter are really major technological changes."

The auto companies have told the federal government that the 1981 systems will add more than $200 to the cost of each car. Whether these radically different systems improve or reduce fuel economy is still not known. One thing that is certain is that the day of the backyard mechanic opening his hood and repairing or adjusting his engine is gone forever.

Lee A. Iacocca, president of Chrysler Corporation, commented on this situation when he said that taking the first pollution out of the automobile engine cost only 36 cents a gram, but now it's costing $40 a gram.

Furthermore, officials at the Environmental Protecton Agency are concerned about motorists tampering with the engines and thereby increasing emissions. They are seriously considering sealing the engine compartment. A few small openings would be used for adding oil, changing spark plugs, and making other necessary repairs.

Basically, the 1981 emissions systems developed by the US automakers are quite similar, with only minor differences. Their key element is the three-way catalytic converter which controls the emission of all three automotive pollutants -- hydrocarbons, carbon monoxide, and oxides of nitrogen. For this catalyst to function properly the engine must operate with a precise air-fuel ratio of about 14.7 parts of air to one part of fuel.

This is accomplished with an oxygen sensor in the exhaust stream which constantly monitors the exhaust gas to determine what's going into the engine.

The sensor "reports" its findings to a control module, or small computer, which then orders an electronic control system to continuously adjust the air and fuel inputs to the engine so as to get exactly the right mixture.

Also called a closed-loop system, it automatically compensates for different tolerances in the engine parts for changes in fuel composition that may call for a different fuel-air ratio, and for variations in atmospheric pressure resulting from altitude or weather changes.

To do the job precisely enough the control system, or microprocessor , also must continuously pick up information about the temperature and air pressure at several points around the engine. A half dozen sensors report such findings as frequently as 30 times a second.

Although the 1980 emissions systems are still considered to be part of the unpublicized future product, the auto companies have early versions of the '81 system on a few hundred thousand 1980-model cars. Their goal is to gradually get manufacturing and field experience with these complex systems.

A problem for the automakers is that, because of mass-production variations in their carburetors, they must aim for emission levels which are 30 to 50 percent lower than the law requires. Another problem is that the EPA now can and does make "selective enforcements audits" on any production line. If enough of the cars aren't meeting the standards at any moment, the EPA can shut down the assembly lines.

To minimize these problems, and also to improve the fuel economy, drivability , and emission control of its cars, both General Motors and Ford will be installing a throttle-body fuel-injection system on several million 1981-model cars.

The question of whether all of this is worth eliminating 4.6 grams of pollution per mile is one that buyers of the 1981 cars may have to answer.