Evaporative emission leak detection system and detection method for engines

An evaporative emission leak detection system for engines, which is characterized in that the detection system comprises a fuel tank, a carbon canister, a diagnostic instrument and a pressure detector. The carbon canister is separately in fluid communication with the fuel tank and the intake system of the engine, a fuel tank isolation valve is provided between the carbon canister and the fuel tank, and a carbon canister control valve is arranged between the carbon canister and the engine and used to control the fluid communication between the carbon canister and the engine. The diagnostic instrument comprises an intake and a vent, wherein the intake is connected to the atmosphere, while the vent is connected to the carbon canister;

• a booster assembly, a check valve assembly and a pipeline switching assembly are provided and the first and second ventilation pathways connecting the intake and the vent are formed inside the diagnostic instrument, wherein the first ventilation pathway directly connects the intake with the vent, while the second ventilation pathway sequentially connects the intake with the booster assembly, the check valve and the vent;
• the pipeline switching assembly switches between the first ventilation pathway and the second ventilation pathway within the diagnostic instrument based on detection demands to achieve air connectivity between the intake and the vent. The diagnostic instrument further comprises a shell housing the intake, the vent, the first chamber and the second chamber, wherein the first and second chambers are separately connected to the intake, the vent is connected to the second chamber, and the first chamber is connected to the second chamber and the vent through the first pipeline. The booster assembly is fixed to the shell and located on the side of the first chamber away from the first pipeline;
• the check valve assembly is connected to the shell, arranged within the first chamber and positioned between the booster assembly and the first pipeline;
• the pipeline switching assembly is located inside the second chamber and used to control the fluid communication between the first pipeline and the second chamber, so that the air pressurized by the booster assembly can pass through the check valve, the first pipeline and the second chamber and finally leave the shell through the vent, when the first pipeline is connected to the second chamber.