Fuel injection control device

Claim 1

A fuel injection control device, comprising: an after treatment device which is provided in an exhaust passage of an internal combustion engine and purifies exhaust gas by the action of a catalyst; exhaust gas temperature detection means for detecting an exhaust gas temperature passing through said after treatment device; a fuel injector for a catalyst, which is employed to raise the exhaust gas temperature by supplying fuel to said catalyst; and control means for controlling a fuel injection quantity injected by said fuel injector for a catalyst, said control means executing an exhaust gas temperature increase control by conducting fuel injection for a catalyst with said fuel injector for a catalyst and raising the exhaust gas temperature when the exhaust gas temperature detected by said exhaust gas temperature detection means is less than an activity temperature of the catalyst in said after treatment device, wherein when executing said exhaust gas temperature increase control, said control means determines a target injection quantity of said fuel injection for a catalyst based at least on the difference between the exhaust gas temperature which is considered as a target and an actual exhaust gas temperature detected by said exhaust gas temperature detection means and also determines an upper limit value of injection quantity of fuel injection for a catalyst based at least on the actual exhaust gas temperature detected by said exhaust gas temperature detection means, conducts control such that the actual injection quantity of fuel injection for a catalyst becomes said upper limit value when said target injection quantity is equal to said upper limit value or higher, and conducts control such that the actual injection quantity of fuel injection for a catalyst becomes said target injection quantity when said target injection quantity is less than said upper limit value.