Method and system for low charge detection
Methods and systems for assessing operation of a cooling system of an electric vehicle are described. In one example, a super heating temperature at an inlet of a compressor may be generated solely via a temperature sensor and a pressure sensor. The super heating temperature may be compared against a threshold super heating temperature to judge whether or not an amount of refrigerant in the cooling system is as expected.
1 . A method for operating a cooling system of a vehicle, comprising:
reducing a speed of a compressor to operate the compressor at below a threshold speed;
while operating the compressor below the threshold speed, generating an estimate of a super heating temperature of a refrigerant according to a pressure at an inlet side of the compressor and a temperature at the inlet side of the compressor; and
deactivating the compressor in response to the estimate of the super heating temperature of the refrigerant exceeding a super heating threshold temperature while operating the compressor below the threshold speed.
2 . The method of claim 1 , where the compressor is deactivated when the estimate of the super heating temperature of the refrigerant exceeds the super heating threshold temperature for a predetermined amount of time, the predetermined amount of time measured by incrementing a counter responsive to the super heating temperature of the refrigerant exceeding the super heating threshold temperature while the compressor is being operated below the threshold speed.
3 . The method of claim 2 , where the super heating threshold temperature is based on ambient temperature and the speed of the compressor.
4 . The method of claim 3 , where the super heating temperature is a present temperature of the refrigerant minus a boiling temperature of the refrigerant in a liquid state.
5 . The method of claim 1 , where the estimate of the super heating temperature is determined without data of a pressure downstream of the compressor and upstream of an expansion valve.
6 . The method of claim 1 , where the temperature and pressure sensors are downstream of a chiller and upstream of the compressor.
7 . The method of claim 1 , further comprising commanding the compressor to an adjusted speed based on a temperature difference.
8 . The method of claim 7 , where the temperature difference is a difference between a requested passenger cabin temperature and measured passenger cabin temperature.
9 . A method for operating a cooling system of a vehicle, comprising:
adjusting a speed of a compressor to operate the compressor at a reduced speed in response to a user requested temperature, where the reduced speed is less than a threshold speed;
while operating the compressor at the reduced speed, generating an estimate of a super heating temperature of a refrigerant according to a pressure at an inlet side of the compressor and a temperature at the inlet side of the compressor;
holding the speed of the compressor at the reduced speed in response to the super heating temperature of the refrigerant being greater than a super heating threshold temperature; and then
deactivating the compressor in response to the compressor being at the reduced speed and the estimate of the super heating temperature of the refrigerant exceeding the super heating threshold temperature for greater than a predetermined period of time.
10 . The method of claim 9 , where deactivating the compressor includes reducing the speed of the compressor to zero.
11 . The method of claim 10 , further comprising providing an indication of loss of refrigerant in response to the super heating temperature of the refrigerant exceeding the super heating threshold temperature.
12 . The method of claim 11 , further comprising cooling a battery and a passenger cabin of the vehicle via the cooling system while generating the estimate of the super heating temperature of the refrigerant.
13 . The method of claim 12 , where the battery is a traction battery.
14 . The method of claim 2 , further comprising:
while operating the compressor at above the threshold speed, determining the super heating temperature is less than the super heating threshold temperature; and
decrementing the counter responsive to the super heating temperature being less than the super heating threshold temperature while operating the compressor at above the threshold speed.