Abstract: An EGR control system for a direct injection spark ignition engine operated at a plurality of the combustion modes comprising stratified-charge combustion and premix-charge combustion. The system includes a flow rate control valve equipped at the EGR passage to regulate flow rate of the exhaust gas to be recirculated which is operated when the one combustion mode is determined to be changed to another of a plurality of the combustion modes, thereby ensuring an EGR amount that is neither deficient nor excessive for the combustion mode, while preventing misfire from happening and preventing the degradation of drivability, fuel economy and emission performance from occurring. Alternatively, the system includes an actuator for regulating an opening of a throttle valve or a second EGR control valve installed in a branch passage and a passage switching valve for switching the EGR passage and the branch passage.

Abstract: A process for producing an aluminum nitride sintered body is disclosed, comprising mixing an aluminum nitride powder with (a) a calcium compound and (b) a copper compound, and, if desired, (c) a yttrium compound as sintering aids; molding the mixture; and sintering the molded article in a non-oxidative atmosphere. The resulting sintered body has a high density (3.10 g/cm.sup.3 or higher) and a high thermal conductivity (110 W/mK or higher) even by sintering at a low temperature (1500.degree. to 2000.degree. C.).

Abstract: A positioning member is installed on a pinion of a steering gear in such a manner that its U-shaped bend forms an alignment mark. A yoke of a steering shaft joint has a slit which forms an alignment mark. The U-shaped bend is insertable into the slit only when the pinion and the steering shaft are properly aligned.