Exhaust gas treating system for internal combustion engine

Claim 1

An exhaust gas treating system for an internal combustion engine having an exhaust pipe and a catalytic reactor, having a catalyst therein, disposed in said exhaust pipe for oxidizing engine exhaust gases passing therethrough, said system comprising a burner chamber communicating with said exhaust pipe upstream of said catalytic reactor, ignition means disposed in said burner chamber for effecting combustion of an air-fuel mixture supplied thereto, an air-fuel mixture supply passage communicating with said burner chamber for supplying said burner chamber with said air-fuel mixture, said air-fuel mixture supply passage having a venturi portion provided with a nozzle communicating with a float chamber, an air pump communIcating with said air-fuel mixture supply passage and driven through an electro-magnetic clutch for forcibly supplying air thereinto, a by-pass passage having an inlet intersecting said air-fuel mixture supply passage between said air pump and said venturi portion and an outlet communicating with said burner chamber, a fuel shut-off valve associated with said nozzle for selectively shutting off the supply of fuel into said air-fuel mixture supply passage, and a control circuit for controlling the operations of said electromagnetic clutch, said fuel shut-off valve and said ignition means for controlling the temperature of said air to be delivered to said catalytic reactor, said control circuit including a d.c. voltage source, an ignition switch connected to said d.c. voltage source, first and second thermostatic switches connected in parallel to said d.c. voltage source through said ignition switch, said first thermostatic switch being connected to said fuel shut-off valve and said ignition means, and a relay including first and second stationary contacts connected to said d.c. voltage source through said first and second thermostatic switches respectively, a solenoid coil connected to said first thermostatic switch, and a movable contact associated with said solenoid coil and connected to said electro-magnetic clutch, said first thermostatic switch being closed to energize said fuel shut-off valve, said ignition means and said electro-magnetic clutch for effecting combustion of said air-fuel mixture supplied to said burner chamber to heat the air to be delivered to said exhaust pipe upstream of said catalytic reactor when said temperature of said catalyst is below a lower limit of a predetermined range, said second thermostatic switch being closed to energize only said electromagnetic clutch for supplying said air into said catalytic reactor through said burner chamber for thereby decreasing the temperature of said catalyst when said temperature of said catalyst is beyond an upper limit of said predetermined range, and said first and second thermostatic switches being simultaneously opened to de-energize said fuel shut-off valve, said ignition means and said electro-magnetic clutch when said temperature of said catalyst is within said predetermined range.