BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, feature and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which:
FIG. 1 is a schematic view showing a fuel vapor treatment system according to an embodiment of the invention;
FIG. 2 is a flow chart of purge control;
FIG. 3 is a flow chart of a concentration detection routine;
FIG. 4 is an operating waveform diagram to show the operating states of the respective parts of the fuel vapor treatment system;
FIG. 5 is a diagram to show the operating states of the respective parts of the fuel vapor treatment system when a shutoff pressure Pc is measured;
FIG. 6 is a diagram to show the operating states of the respective parts of the fuel vapor treatment system when a pressure P0 by an air flow is measured;
FIG. 7 is a diagram to show the operating states of the respective parts of the fuel vapor treatment system when a pressure P1 by an air-fuel mixture flow is measured;
FIG. 8 is a diagram to show a method for determining with reference to the convergence value of the pressure P0 by the air flow whether the behavior of change in the pressure P1 by the air-fuel mixture flow is substantially identical to the behavior of change in the pressure P0 by the air flow; and
FIG. 9 is a diagram to show the operating states of the respective parts of the fuel vapor treatment system in a period of purging.