Abstract: If a demanded power exceeds a predetermined threshold, where the threshold is based on a catalyst temperature, power from a power storage unit is supplied to a wheel.

Abstract: Pistons for internal combusion engines are described. The pistons comprise a crown component and a skirt component wherein the crown component consists of an iron or nickel based alloy annular portion having fitted directly therein a ceramic insert, the crown component being joined to the skirt component by an annular composite laminated member of steel and aluminium alloy the steel of the laminated member being energy beam welded to the annular portion of the crown component and the aluminum alloy of the laminated member being energy beam welded to the skirt component there being after welding a sealed, hollow, annular chamber disposed at the junction between the crown component and the skirt component. Embodiments are described having ceramic inserts of silicon nitride and including combustion bowls.