Vehicular heat management system

A vehicular heat management system, comprising:

• a compressor;
• a condensing heat exchanger;
• an expansion valve;
• an evaporation heat exchanger;
• and
• a control part configured to, when a refrigerant superheat degree on a discharge side of the evaporation heat exchanger is lowered to a predetermined lower limit value or less, control, step by step, at least two devices directly involved in the increase and decrease of the refrigerant superheat degree to increase the refrigerant superheat degree until the refrigerant superheat degree exceeds the lower limit value,
• wherein the evaporation heat exchanger includes a plurality of evaporation heat exchangers,
• the expansion valve on the upstream side of one of the plurality of evaporation heat exchangers is an electromagnetic expansion valve (EXV),
• the control part is configured to, when a refrigerant superheat degree on the discharge side of an electromagnetic-expansion-valve-side evaporation heat exchanger is lowered to the lower limit value or less, control the compressor and the electromagnetic expansion valve to increase the refrigerant superheat degree until the refrigerant superheat degree exceeds the lower limit value,
• the plurality of evaporation heat exchangers includes a chiller for cooling a battery,
• the control part is configured to, when a refrigerant superheat degree on the discharge side of the chiller is lowered to the lower limit value or less, control a rotation speed of the compressor and an opening degree of an electromagnetic battery-cooling expansion valve to increase the refrigerant superheat degree until the refrigerant superheat degree exceeds the lower limit value, and
• when the refrigerant superheat degree on the discharge side of the chiller is lowered to the lower limit value or less, the control part is configured to:
• firstly reduce the opening degree of the battery-cooling expansion valve to induce an increase in the refrigerant superheat degree on the discharge side of the chiller in a first step;
• secondly reduce the rotation speed of the compressor to induce an increase in the refrigerant superheat degree on the discharge side of the chiller in a second step;
• and
• thirdly completely turn off one of the battery-cooling expansion valve and the compressor to limit a refrigerant flow toward the chiller to induce an increase in the refrigerant superheat degree on the discharge side of the chiller in a third step, so that the refrigerant superheat degree on the discharge side of the chiller exceeds the lower limit value.