Vehicle air-conditioning device
A vehicle air-conditioning device is a heat pump type vehicle air-conditioning device including an external heat exchanger that performs heat exchange between refrigerant flowing the inside thereof and outside air. With the vehicle air-conditioning device, a controller functions as a temperature-difference calculation unit that calculates the temperature difference ΔT between the refrigerant in a refrigerant flow path on the exit side of the external heat exchanger and the outside air, and in addition, the controller functions as a frost formation determination unit that determines that frost formation is caused on the external heat exchanger on the basis of the elapsed time to of a state in which the temperature difference ΔT is equal to or larger than a frost-formation temperature difference at which the frost formation may be caused on the external heat exchanger.
1. A heat pump type vehicle air-conditioning device provided with an external heat exchanger performing heat exchange between refrigerant flowing inside thereof and outside air;
an outside air temperature sensor;
an exit-side refrigerant temperature sensor; and
a vehicle speed sensor, comprising:
a controller comprising a wind speed table, configured to
calculate a temperature difference between exit-side refrigerant in the external heat exchanger and the outside air;
determine that frost formation is caused on the external heat exchanger based on an accumulated time of a state in which the temperature difference at time of a heating operation is equal to or larger than a frost-formation temperature difference at which the frost formation is caused on the external heat exchanger;
estimate a frost-formation time at which frost formation is caused, the frost-formation time being a time when water vapor at the external heat-exchanger becomes frozen, the frost-formation time being based on the temperature difference between the exit-side refrigerant and the outside air, and the frost-formation time being estimated to be shorter when the temperature difference is larger; and
determine that, in a case in which the accumulated time is equal to or longer than the frost-formation time, the frost formation that affects the heat exchangeability at the external heat exchanger is caused.
2. The vehicle air-conditioning device according to claim 1 , wherein the frost-formation time is changed by a passing wind speed of the outside air passing through the external heat exchanger.
3. The vehicle air-conditioning device according to claim 1 , wherein the frost-formation time is changed based on the temperature difference between the exit-side refrigerant and the outside air and by a passing wind speed of the outside air passing through the external heat exchanger.
4. The vehicle air-conditioning device according to claim 1 ,
wherein the controller is configured to
estimate a degree of frost formation of the frost formation caused on the external heat exchanger based on a ratio of the accumulated time relative to the frost-formation time.
5. The vehicle air-conditioning device according to claim 4 , wherein the controller is configured to estimate that the frost formation is caused on the external heat exchanger when the degree of frost formation is equal to or greater than a frost formation threshold.
6. The vehicle air-conditioning device according to claim 5 , wherein the controller is configured to
estimate the degree of frost formation for every accumulated time based on the ratio of the accumulated time relative to the frost-formation time,
calculate an integrated value by integrating the degree of frost formation estimated for every accumulated time; and
determine whether the integrated value is equal to or greater than the frost formation threshold.
7. The vehicle air-conditioning device according to claim 6 , wherein
the controller is configured to reset, in a case in which a defrosting condition is met and in which there is no frost formation, the integrated value obtained by integrating the degree of frost formation estimated for every accumulated time.
8. The vehicle air-conditioning device according to claim 2 , wherein
the frost-formation time is estimated to be shorter when the passing wind speed is faster.
9. The vehicle air-conditioning device according to claim 3 , wherein
the frost-formation time is estimated to be shorter when the passing wind speed is faster.
10. A method of operating a heat pump type vehicle air-conditioning device provided with an external heat exchanger performing heat exchange between refrigerant flowing inside thereof and outside air, comprising:
calculating a temperature difference between exit-side refrigerant in the external heat exchanger and the outside air;
calculating an accumulated time of a state in which the temperature difference at time of a heating operation is equal to or larger than a frost-formation temperature difference, the frost-formation temperature difference being a temperature difference that causes the frost formation on the external heat exchanger;
estimating a frost-formation time at which frost formation is caused, the frost-formation time being a time when water vapor at the external heat-exchanger becomes frozen, the frost-formation time being based on the temperature difference between the exit-side refrigerant and the outside air, and the frost-formation time being estimated to be shorter when the temperature difference is larger; and
determining when the accumulated time becomes equal to or longer than the frost-formation time.
11. The method of claim 10 , further comprising performing a defrosting operation when the accumulated time is equal to or longer than the frost-formation time.