Abstract: Whether discharge of high-concentration, unburned fuel is indicated or not is determined based on air-fuel ratio AF, calculated air-fuel ratio AFc and exhaust temperature thco (S110, S112, S114). If it is determined that high-concentration, unburned fuel would be discharged (“no” in any of S110, S112, S114), amount of fuel addition per one addition is decreased in PM regeneration control (S116). Therefore, in a state where high concentration HC is to be discharged to the downstream of an exhaust purifying filter, the amount of fuel addition at one time is immediately decreased, so that discharge of high-concentration HC to the outside can be prevented, and generation of white smoke can reliably be prevented.

Abstract: A temperature of a catalyst disposed in an exhaust system is raised to a target bed temperature by supplying an unburned fuel component to the catalyst. A learned value is updated based upon a catalyst bed temperature under a temperature increase control and the target bed temperature so that the learned value corresponds to a difference between the respective temperatures. Whether the learned value is out of a proper range or not is determined whenever the learned value is updated. Abnormality is determined when determination that the learned value is out of the proper range is made over several successive updates of the learned value.

Abstract: Whether discharge of high-concentration, unburned fuel is indicated or not is determined based on air-fuel ratio AF, calculated air-fuel ratio AFc and exhaust temperature thco (S110, S112, S114). If it is determined that high-concentration, unburned fuel would be discharged (“no” in any of S110, S112, S114), amount of fuel addition per one addition is decreased in PM regeneration control (S116). Therefore, in a state where high concentration HC is to be discharged to the downstream of an exhaust purifying filter, the amount of fuel addition at one time is immediately decreased, so that discharge of high-concentration HC to the outside can be prevented, and generation of white smoke can reliably be prevented.

Abstract: A welded steel product having a low sensitivity to weld cracking, produced by welding a base steel material comprising at least one member selected from the group consisting of rare earth metal, Ca, Ba, Te and Se using a welding material comprising at least one member selected from the group consisting of rare earth metals, Te and Se, and having a weld metal containing at least one rare earth metal in an amount of 0.0005 to 0.10% and at least one of Te and Se in an amount not more than 0.10%.

Abstract: A free cutting graphitic steel comprising:Si: from more than 1.5 to 2.3%Mn: 0.1 to 0.7%S: not more than 0.015%One or both Al and Ti: 0.015 to 0.1% in totalRare earth: 0.01 to 0.2% andSpheroidized graphite: 0.20 to 0.90% with the balance being iron and unavoidable impurities,Said spheroidized graphite being distributed at a ratio of more than particles 50/mm.sup.2.