Abstract: An NOx absorbent is installed in an exhaust conduit of an internal combustion engine capable of fuel combustion at lean air-fuel ratios. An oxygen concentration is repeatedly or continuously decreased by, for example, switching the air-fuel from the lean air-fuel ratio to a stoichiometric or rich air fuel ratio when the exhaust gas temperature is higher than 550.degree. C. or when NOx absorbent temperature is higher than 500.degree. C. As a result, the SOx absorbed in the NOx absorbent during lean air-fuel ratio, low temperature operation is released from the NOx absorbent, and the SOx-poisoned NOx absorbent is recovered.

Abstract: An exhaust gas purification system for an internal combustion engine includes a catalyst installed in an exhaust conduit of an engine and constructed of zeolite carrying at least one kind of metal selected from transition metals and noble metals to reduce nitrogen oxides included in the exhaust gas from the engine under an oxidizing gas condition and in the presence of hydrocarbons. The system further includes means for repeating a cycle of cooling the catalyst and then stopping the cooling to allow the catalyst to rise in temperature so that the temperature rising courses of the catalyst are positively and repeatedly produced. Since the catalyst can show a higher nitrogen oxides reducing ability in the temperature rising course than in the temperature lowering course, the NOx purification rate is greatly improved due to the positive production of the temperature rising courses.

Abstract: An exhaust gas purification system includes a transition metal/zeolite first catalyst, a three-way second catalyst, and a noble metal-type third catalyst arranged in that order in the direction of exhaust gas flow in an exhaust conduit of an internal combustion engine capable of fuel combustion at lean air-fuel ratios. NOx which has not been purified by the transition metal/zeolite first catalyst is oxidized by the three-way second catalyst into NO.sub.2, which the noble metal-type third catalyst can easily decompose into N.sub.2 and O.sub.2.

Abstract: A method for purifying an oxygen excess exhaust gas by catalytically reducing nitrogen oxides contained in the exhaust gas, which comprises bringing a catalyst comprising at least one noble metal supported on a carrier composed mainly of an oxide or a complex oxide of at least one metal selected from rare earth metals and metals of the group IV A of the periodic table of elements into contact the exhaust gas.

Abstract: An exhaust gas purification system for an internal combustion engine includes an engine capable of fuel combustion at lean air-fuel ratios, a catalyst constructed of zeolite carrying at least one metal selected from the transition metals and noble metals to reduce NOx under oxidizing gas conditions and in the presence of HC. The exhaust gas purification system also includes a device for determining degradation of the catalyst, and a device for increasing the amount of HC or changing a catalyst temperature to a higher side when it is determined that the catalyst has been degraded. The NOx purification rate of the catalyst is maintained high even after the catalyst has been degraded.

Abstract: A noble metal base catalyst for decomposing a portion of NOx included in engine exhaust gas into intermediate products such as N.sub.2 O and NO.sub.2 is installed in an exhaust conduit of a lean burn engine. Further, an intermediate product decomposing means for decomposing the intermediate products produced by the noble metal base catalyst into N.sub.2 and O.sub.2 is installed downstream of the noble metal base catalyst. The noble metal base catalyst has a high thermal durability, and the noble metal base catalyst and the intermediate product decomposing means decompose NOx into N.sub.2 and O.sub.2 without a large amount of HC.

Abstract: An exhaust gas purification system for an internal combustion engine using an alcohol blended gasoline fuel includes a lean NOx catalyst capable of reducing nitrogen oxides under an oxidizing gas condition and in the presence of hydrocarbons. A bypass conduit is provided with a bypass valve so as to bypass the lean NOx catalyst. Opening of the bypass valve to cause the exhaust gas to flow through the bypass conduit is controlled in accordance with the alcohol concentration of the fuel. When the alcohol concentration is low, the bypass valve opening range is limited to a high engine speed and high engine load range, so that the exhaust gas is caused to flow through the lean NOx catalyst at low and medium engine speeds and low and medium engine loads, and the catalyst is utilized at a maximum.

Abstract: A variable compression ratio control device includes a mechanism for varying a compression ratio of an engine in response to engine driving conditions, at least between a higher stage and a lower stage, a compression ratio detecting sensor for detecting a current compression ratio, a sensor fault detecting unit for detecting a malfunction of the compression ratio detecting sensor, and a fail-safe unit for lowering and fixing the compression ratio when the sensor fault detecting unit detects a malfunction of the compression ratio detecting sensor.

Abstract: In the process for producing pitch carbon fibers by melt-spinning a carbonaceous pitch, and infusiblizing the resulting pitch fibers followed by carbonization and, additionally as needed, graphitization, the pitch fibers are subjected to infusiblization treatment following application of a dimethyl polysiloxane having a viscosity at 25.degree. C. in the range between 0.5 and 500 cSt and removing said dimethyl polysiloxane by washing prior to the carbonization.

Abstract: Provided is a process for producing pitch carbon fibers by subjecting pitch fibers obtained by melt-spinning a carbonaceous pitch to infusibilization treatment and then to carbonization treatment or both carbonization treatment and subsequent graphitization treatment, characterized in that a dimethyl polysiloxane having a viscosity at 25.degree. C. in the range of 12,000 to 1,000,000 cSt is applied to the fibers after the infusibilization treatment, and the infusibilized fibers with the dimethyl polysiloxane thus applied thereto are then subjected to the carbonization treatment or both the carbonization treatment and the subsequent graphitization treatment.

Abstract: An internal combustion engine of a lean burn type, wherein the air-fuel ratio is feedback controlled to a predetermined fixed value which is higher than a theoretical air-fuel ratio. The ignition timing is changed when the air-fuel ratio as detected by a lean sensor is off from the target air-fuel ratio, enabling quick control of the engine when the air-fuel ratio is off from the target air fuel ratio.

Abstract: In a method of and system for lean-controlling an air-fuel ratio in an electronically controlled engine, wherein the air-fuel ratio is feedback-controlled to the lean side from the stoichiometric air-fuel ratio in accordance with an output from a lean sensor generating an output signal substantially proportional to the concentration of oxygen in the exhaust gas, when it is necessary to vary a target air-fuel ratio, a target control value of an output from the lean sensor is corrected in accordance with the required variation value and the air-fuel ratio is feedback-controlled whereby the output from the lean sensor can become the corrected target control value, so that satisfactory feedback control of the air-fuel ratio can be effected even when the target air-fuel ratio is varied to a value other than the normal value.

Abstract: Disclosed is an exhaust gas recirculation system of an internal combustion engine for high altitude use. The system includes a feedback control valve for controlling the amount of exhaust gas fed back to an intake passage, and a compensating device for decreasing a set pressure level of the feedback control valve, above which set level the feedback control valve is caused to open so as to feed back the exhaust gas, when the atmospheric pressure level is lowered to less than a predetermined level. Thus, the amount of NO.sub.x formation contained in the exhaust gas can always be maintained at a low level and, furthermore, good operating characteristics of the engine can be obtained even when the engine is operated at high altitudes.