ORANGE, CONNECTICUT -- How to meet the ever more stringent automobile emissions requirements, while still maintaining the kind of performance and driveability that the auto buying public wants and deserves has become a major effort of the world's automobile industry.
For 1977, both the "Federal' U.S. requirements and the stiffer ones of the State of California have been made even more stringent, while the Federal government also has required that cars meet the same emissions standards at high altitudes as at lower altitudes.
Engineers at Saab-Scania AR of Sweden, the makers of the Saab cars, in cooperation with Bosch of Germany have found a way of satisfying the 1977 requirements while still providing good driveability and performance. The Saab system, as a natter of fact, is expected to have far reaching effects on the emissions and driveability efforts of many other car makers. Lambda Control For 1977, Saab 99 cars for sale in the Western and Rocky Mountain states will be equipped with the two-liter overhead camshaft Saab engine with a new Lambda Control system and a three-way catalyst. A problem with most catalysts currently used is that they only work to oxidize the carbon monoxide (Go) and the unburned hydrocarbons (HG) thanks to excess oxygen in exhaust. The oxygen is present either from a lean mixture or through secondary air being injected into the exhaust stream before it reaches the catalyst. The excess oxygen, however, does not make it possible to eliminate the third pollutant, nitrous oxides.(NOx). To remove NOx catalytically, a deficiency of oxygen is required. It thus seems that it would be impossible to remove all three pollutants, GO, HG and NOx through one catalyst.
But there is one possibility. Within a very narrow range of air-to-fuel ratios the oxidizing reactions for GO and 1-IC and the reducing reactions for NOx overlap. This narrow range is sometimes called the "three component window".
Precise Air-Fuel Ratio The problem is to control the engine's air-to-fuel ratio so precisely during all engine operations so that it remains within this "window'-, or as it is also called, the "stoichionetric" value -- an air-to-fuel ratio of 14.5:1. (The symbol Lambda actually indicates multiples of 14.5:1.) This is the function of the Lambda Control System.
The Saab Lambda system consists of these basic components: 1. An oxygen sensor which is mounted in the exhaust manifold and which continuously senses the oxygen content of the exhaust. 2. An electronic control unit which receives a continuous signal from the oxygen sensor and then sends a signal on the proper air-to-fuel ratio to: 3. A modulating valve which continuously adjusts the pressure in the fuel distributor to maintain the proper ratio at all times. 4. A full-throttle enrichment switch which can override the modulating valve during full throttle acceleration. 5. The three-way catalyst which at the proper air-to-fuel ratio oxidizes hyrocarbons and carbon monoxide and at the same time takes oxygen away from oxides of nitrogen. Traces of platinum and rhodium are used in the catalytic material.
System For The Future Experts at Saab note that the 1977 Saabs with the Lambda system and three-way catalyst offer both better fuel economy and better driveability than previous systems while at the same time reducing the emissions of regulated pollutants to such an extent that the basic system can probably be used for many years to come.
While the three-way catalyst and Lambda control system is used during 1977 on only those Saabs that will be sold in Western and Rocky Mountain states Saabs for the remaining states have also been modified to meet the Federal emissions requirements -- and can still do so without a catalyst or unleaded gasoline.
The compression ratio of the "Federal" 1977 Saab engines has been increased to 9.25:1 and a proportional exhaust gas recirculation system has been added together with a new type of exhaust port air-injection system that does not use an air pump. The output of the Federal cars for 1977 remains at 115 horsepower (SAE net) at 5,500 rpm and 123 ft. lbs. torque at 3,500 rpm.
For Lambda equipped cars, which do require unleaded gasoline, the compression ratio remains at 8.7:1 and the output is 110 net SAE horsepower at 5,500 rpm and 119 ft. lbs. torque at 3,500 rpm.