Abstract: An off-road vehicle includes a control module which limits power source rotational speed beneath a controlled rotational speed value based both on whether a protection device such as a safety belt is engaged or disengaged and on whether the vehicle velocity is greater than or less than a velocity threshold. If the safety belt becomes disengaged while the power source is spinning above the controlled rotational speed value, the control module gradually and safely reduces power source rotational speed. If/when the safety belt becomes reengaged, the control module logic will ensure that the power source rotational speed is released from the controlled first value without immediate change in vehicle response. The invention effectively reduces safety hazards of safety belt disengagement while not creating safety hazards of its own in a wide range of discussed situations.

Abstract: An off-road vehicle includes a frame and an engine. The engine includes a cylinder block and a cylinder head, on which an exhaust passage is arranged. The cylinder head is provided with a supplementary air supply passage for mixing air into the exhaust gas discharged from the combustion chamber. Alternatively, the supplementary air supply passage can be included in the exhaust system, such as in a cylinder head mounting flange of the exhaust pipe, upstream of an oxygen sensor and first and second stage catalytic converters. The exhaust gas from the engine is further oxidized by air, which reduces the content of components such as CO and NOx in the exhaust gas, improving environmental protection.