Apparatus for detecting fuel mixture ratio

Claim 1

Apparatus for optically detecting a fuel mixture ratio of mixed fuel that has two different kinds of fuel comprising: a prism, having three optical planes, one of said planes disposed to be a boundary plane with said mixed fuel; a sensor portion, comprising: (a) light emitting means mounted on another one of said planes for emitting light toward said boundary plane through said prism; (b) light receiving means, mounted on a third one of said planes, for receiving light reflected from said boundary plane through said prism and converting a magnitude of said reflected light into an electrical signal, said light emitting means and said light receiving means being relatively disposed so that said light emitting means illuminates light to said boundary plane at or near a predetermined angle at which one of said two kinds of fuel to be detected is more widely different in absolute refractive index from said prism than the other of said two kinds of fuel; and (c) detector means, connected to said light emitting means and to said light receiving means, for controlling said illuminating light from said light emitting means at a constant magnitude and for receiving said electrical signal and outputting a detected signal corresponding to said electrical signal; a distributor body, formed surrounding said two of said planes and coupled to said two of said planes of said prism at a contact zone to surround said light emitting means, said light receiving means, and said detector means; and sealing means, located at said contact zone, for sealing between said two of said optical planes and said distributor body, thereby enclosing said sensor portion.