The exhaust gas system (28) has a heat exchanger (32) arranged between the thermal heating device (30) and the catalytic converter (29). An exhaust gas pipe from the IC engine is led to the catalytic converter and bypasses the heat exchanger. The thermal device is a burner. The catalytic converter is preheated by the burner for the rapid attainment of the converter operating temperature and/or to maintain the operating temperature. The heat output of the burner is set at a level greater than is necessary just to heat the catalytic converter.
