Method for controlling EGR rate (EGR) of a low pressure EGR system, system and vehicle

A system for controlling Exhaust Gas Recirculation (EGR) rate of low pressure EGR system, wherein the system comprises:

• a first calculation unit, configured to obtain a temperature of exhaust gas processed by an EGR cooler and a pressure of the exhaust gas processed by the EGR cooler;
• calculate a molar concentration of water molecules of the exhaust gas processed by the EGR cooler under a maximum humidity limit value of the exhaust gas, the molar concentration of water molecules being calculated based on the temperature of exhaust gas processed by the EGR cooler, the pressure of the exhaust gas processed by the EGR cooler, a preset maximum humidity limit value of the exhaust gas processed by the EGR cooler;
• a second calculation unit configured to obtain a temperature of a mixed gas before the mixed gas is processed by a supercharger and a compressor, and a pressure of the mixed gas before the mixed gas is processed by the supercharger and the compressor;
• calculate a molar concentration of water molecules under a maximum humidity limit value of the mixed gas before the mixed gas is processed by the supercharger and the compressor, the maximum humidity being calculated based on the temperature of the mixed gas before being processed by the supercharger and the compressor, and the pressure of the mixed gas before being processed by the supercharger and the compressor, a preset maximum humidity limit value of the mixed gas before being processed by the supercharger and the compressor;
• a third calculation unit, configured to obtain an excess air coefficient, and calculate a molar volume ratio of air according to a relative volume of nitrogen to oxygen in the air, a relative volume of carbon dioxide relative to the oxygen in the air, a relative volume of water molecules relative to the oxygen in the air, and the excess air coefficient;
• a fourth calculation unit, configured to calculate an allowable EGR rate of the exhaust gas processed by the EGR cooler under the maximum humidity limit value of the exhaust gas, according to the molar concentration of the water molecules and the molar volume ratio of the air of the exhaust gas processed by the EGR cooler under the maximum humidity limit value of the exhaust gas;
• calculate an allowable EGR rate of the mixed gas before the mixed gas is processed by the supercharger and the compressor under the maximum humidity limit value of the mixed gas, according to the molar concentration of the water molecules and the molar volume ratio of the air of the mixed gas before the mixed gas is processed by the supercharger and the compressor under the maximum humidity limit value of the mixed gas;
• a control unit configured to determine a smaller EGR rate between the allowable EGR rate of the mixed gas before being processed by the supercharger and the compressor under the maximum humidity limit value of the exhaust gas, and the allowable EGR rate of the exhaust gas processed by the EGR cooler under the maximum humidity limit value of the mixed gas;
• and take the smaller EGR rate as a maximum limit value of an EGR rate in actual working conditions.

A vehicle comprising:

• at least one processor;
• and
• a storage device storing a plurality of instructions, which when executed by the processor, causes the at least one processor to:
• obtain a temperature of exhaust gas processed by an EGR cooler and a pressure of the exhaust gas processed by the EGR cooler;
• calculate a molar concentration of water molecules of the exhaust gas processed by the EGR cooler under a maximum humidity limit value of the exhaust gas, the molar concentration of water molecules being calculated based on the temperature of exhaust gas processed by the EGR cooler, the pressure of the exhaust gas processed by the EGR cooler, a preset maximum humidity limit value of the exhaust gas processed by the EGR cooler;
• obtain a temperature of a mixed gas before the mixed gas is processed by a supercharger and a compressor, and a pressure of the mixed gas before the mixed gas is processed by the supercharger and the compressor;
• calculate a molar concentration of water molecules under a maximum humidity limit value of the mixed gas before the mixed gas is processed by the supercharger and the compressor, the maximum humidity being calculated based on the temperature of the mixed gas before being processed by the supercharger and the compressor, and the pressure of the mixed gas before being processed by the supercharger and the compressor, a preset maximum humidity limit value of the mixed gas before being processed by the supercharger and the compressor;
• obtain an excess air coefficient, and calculate a molar volume ratio of air according to a relative volume of nitrogen to oxygen in the air, a relative volume of carbon dioxide relative to the oxygen in the air, a relative volume of water molecules relative to the oxygen in the air, and the excess air coefficient;
• calculate an allowable EGR rate of the exhaust gas processed by the EGR cooler under the maximum humidity limit value of the exhaust gas, according to the molar concentration of the water molecules and the molar volume ratio of the air of the exhaust gas processed by the EGR cooler under the maximum humidity limit value of the exhaust gas;
• calculate an allowable EGR rate of the mixed gas before the mixed gas is processed by the supercharger and the compressor under the maximum humidity limit value of the mixed gas, according to the molar concentration of the water molecules and the molar volume ratio of the air of the mixed gas before being processed by the supercharger and the compressor under the maximum humidity limit value of the mixed gas;
• determine a smaller EGR rate between the allowable EGR rate of the mixed gas before being processed by the supercharger and the compressor under the maximum humidity limit value of the exhaust gas, and the allowable EGR rate of the exhaust gas processed by the EGR cooler under the maximum humidity limit value of the mixed gas;
• and take the smaller EGR rate as a maximum limit value of an EGR rate in actual working conditions.