| 摘要 |
PURPOSE:To shift spark advance at the time of normal running and at the time of acceleration by providing a negative pressure control device, which works with back pressure, in the negative pressure line leading from the negative pressure takeout port of a carburettor to a vacuum advance device of distributor. CONSTITUTION:As the back pressure in an exhaust manifold 9 becomes low during constant running, the pressure in a back pressure chamber 14 of negative pressure control device 8 sinks and, thereby, a diaphragm 13 loses its deflection and a valve 17 is closed. Thus, communication between a negative pressure chamber 16 and an atmospheric chamber 15 is shut off, and the pressure is applied directly to a vacuum advance device 6, which is set so as to give larger spark advance than that of any conventional arrangement, so that the ignition timing is sufficiently advanced and the driving feeling and fuel consuming rate are improved. The back pressure in the exhaust manifold 9 becomes high during acceleration, on the other hand, and the negative pressure to be applied to the vacuum advance device 6 as well as that in the negative pressure chamber 16 sinks and the amount of spark advance becomes small, so that the ignition timing is delayed. Generation of HC, NOx, etc. in the exhaust gas is thus reduced. |
