Waste heat utilization device and control method thereof

Abstract

A waste heat utilization device includes a Rankine cycle in which an operation fluid circulates, and a control unit which controls an operation of the Rankine cycle. The Rankine cycle has a heater for heating the operation fluid using a waste fluid with a waste heat from a heat engine, an expander that expands the heated operation fluid to recover a mechanical energy, and a condenser for cooling and condensing the expanded operation fluid. The control unit operates the Rankine cycle when a waste fluid temperature is not less than a predetermined temperature and when the waste fluid is in a flowing state in the heat engine.

1 . A waste heat utilization device comprising:
 a Rankine cycle in which an operation fluid circulates, the Rankine cycle including:
 a heater for heating the operation fluid using a waste fluid with a waste heat from a heat engine; 
 an expander that expands the heated operation fluid to recover a mechanical energy; and 
 a condenser for cooling and condensing the expanded operation fluid; and 
   a control unit which controls an operation of the Rankine cycle, wherein:   the control unit operates the Rankine cycle when a waste fluid temperature is not less than a predetermined temperature and when the waste fluid is in a flowing state in the heat engine.   
   
   
       2 . The waste heat utilization device according to  claim 1 , wherein:
 the control unit sets the predetermined temperature to have a hysteresis by using a first predetermined temperature, and a second predetermined temperature which is higher than the first predetermined temperature.   
   
   
       3 . The waste heat utilization device according to  claim 1 , wherein:
 the control unit determines the flowing state of the waste fluid based on an operation state of the heat engine.   
   
   
       4 . The waste heat utilization device according to  claim 3 , further comprising:
 a rotation number detector for detecting a rotation number of the heat engine, wherein:   the control unit determines the operation state of the heat engine based on the detected rotation number.   
   
   
       5 . The waste heat utilization device according to  claim 1 , wherein:
 the waste fluid is a cooling water for cooling the heat engine; and   the Rankine cycle further includes a mechanical pump which is driven by the heat engine to send the cooling water to the heater.   
   
   
       6 . The waste heat utilization device according to  claim 1 , further comprising:
 a flow amount detector for detecting a flow amount of the waste fluid, wherein:   the control unit determines that the waste fluid is in the flowing state when the flow amount is not less than a predetermined flow amount.   
   
   
       7 . The waste heat utilization device according to  claim 6 , wherein:
 the control unit sets the predetermined flow amount to have a hysteresis by using a first predetermined flow amount, and a second flow amount which is greater than the first predetermined flow amount.   
   
   
       8 . The waste heat utilization device according to  claim 7 , wherein:
 the second predetermined flow amount is set to be greater than the first predetermined flow amount approximately by 2 L/min.   
   
   
       9 . The waster heat utilization device according to  claim 6 , wherein:
 the flow amount detector is provided adjacent to a waste fluid outlet side of the heater.   
   
   
       10 . The waste heat utilization device according to  claim 1 , further comprising:
 an electric pump for circulating the waste fluid to the heater, wherein:   the control unit determines the flowing state of the waste fluid based on an operation state of the electric pump.   
   
   
       11 . The waste heat utilization device according to  claim 1 , further comprising:
 a refrigeration cycle having a compressor for compressing and discharging a refrigerant in the refrigeration cycle, the compressor being provided to be also used as the expander or being arranged to be parallel to the expander, wherein:   the condenser is used in common in the refrigeration cycle and the Rankine cycle;   the control unit controls operation of the compressor when an operation of the refrigeration cycle is required and the waste fluid temperature is not less than the predetermined temperature; and   the control unit operates the Rankine cycle when the compressor is not operated.   
   
   
       12 . The waste heat utilization device according to  claim 11 , wherein:
 the control unit increases a discharge amount of the compressor so that a cooling capacity of the refrigeration cycle is not less than a required cooling capacity when the control unit operates the compressor.   
   
   
       13 . The waste heat utilization device according to  claim 12 , wherein:
 the control unit increases the discharge amount of the compressor so that the waste fluid temperature at an evaporator of the refrigeration cycle or a temperature of other part associated with the waste fluid temperature becomes a second target temperature which is lower than a first target temperature satisfying the required cooling capacity.   
   
   
       14 . The waste heat utilization device according to  claim 13 , wherein:
 the control unit sets the second target temperature to be lower than the first target temperature approximately by 1 to 5 degree.   
   
   
       15 . The waste heat utilization device according to  claim 1 , further comprising:
 a refrigeration cycle having a compressor for compressing and discharging a refrigerant in the refrigeration cycle, the refrigeration cycle using the condenser in common with the Rankine cycle and controlled by the control unit independently from the Rankine cycle, wherein:   the control unit simultaneously operates the refrigeration cycle and the Rankine cycle, when the operation of the refrigeration cycle is required, the waste fluid temperature is not less than the predetermined temperature, and the waste fluid is in the flowing state.   
   
   
       16 . The waste heat utilization device according to  claim 15 , wherein:
 the control unit controls a rotation number of the expander so that the sum of a first heat loss amount required for condensing the operation fluid discharged from the compressor and a second heat loss amount required for condensing the operation fluid flowing out from the expander is not more than a heat loss capacity of condensing at the condenser.   
   
   
       17 . The waste heat utilization device according to  claim 1 , wherein:
 the heat engine is an internal combustion engine for a vehicle.   
   
   
       18 . The waste heat utilization device according to  claim 17 , wherein:
 the vehicle is a hybrid vehicle or an idling stop vehicle in which the internal combustion engine is operated and stopped in accordance with a driving state of the vehicle.   
   
   
       19 . A control method of a waste heat utilization device that comprises a Rankine cycle which heats an operation fluid in the Rankine cycle by a heater using a waste fluid with a waste heat from a heat engine, expands the heated operation fluid by an expander for recovering a mechanical energy, and cools and condenses the expanded operation fluid by a condenser, the method comprising:
 determining whether a waste fluid temperature is not less than a predetermined temperature;   determining whether the waste fluid is in a flowing state; and   operating the Rankine cycle when the waste fluid temperature is not less than the predetermined temperature and the waste fluid is in the flowing state.   
   
   
       20 . The control method of a waste heat utilization device according to  claim 19 , further comprising:
 setting the predetermined temperature to have a hysteresis by using a first predetermined temperature, and a second predetermined temperature which is higher than the first predetermined temperature.   
   
   
       21 . The control method of a waste heat utilization device according to  claim 19 , wherein:
 the determining of the flowing state of the waste fluid is performed based on an operation state of the heat engine.   
   
   
       22 . The control method of a waste heat utilization device according to  claim 21 , wherein:
 the operation state of the heat engine is determined based on a rotation number of the heat engine.   
   
   
       23 . The control method of a waste heat utilization device according to  claim 19 , wherein:
 the waste fluid is a cooling water for cooling the heat engine, and the waste fluid is sent to the heater by a mechanical pump driven by the heat engine.   
   
   
       24 . The control method of a waste heat utilization device according to  claim 19 , wherein:
 the waste fluid is determined in the flowing state when a flow amount of the waste fluid is not less than a predetermined flow mount.   
   
   
       25 . The control method of a waste heat utilization device according to  claim 24 , further comprising:
 setting a predetermined flow amount to have a hysteresis by using a first predetermined flow amount, and a second flow amount which is greater than the first predetermined flow amount.   
   
   
       26 . The control method of a waste heat utilization device according to  claim 25 , wherein:
 the second predetermined flow amount is set to be greater than the first predetermined flow amount approximately by 2 L/min.   
   
   
       27 . The control method of a waste heat utilization device according to  claim 24 , further comprising:
 detecting the flow amount of the waste fluid adjacent to a waste fluid outlet side of the heater.   
   
   
       28 . The control method of a waste heat utilization device according to  claim 19 , wherein:
 the flowing state of the waste fluid is determined based on an operation state of an electric pump for sending the waste fluid to the heater.   
   
   
       29 . The control method of a waste heat utilization device according to  claim 19 , wherein:
 the waste heat utilization device further comprises a refrigeration cycle having a compressor for compressing and discharging a refrigerant, the compressor being also used as the expander or being arranged to be parallel to the expander, wherein the refrigeration cycle uses the condenser in common with the Rankine cycle,   the method further comprising:   controlling operation of the compressor when an operation of the refrigeration cycle is required and the waste fluid temperature is not less than the predetermined temperature; and   operating the Rankine cycle when the compressor is not operated.   
   
   
       30 . The control method of a waste heat utilization device according to  claim 29 , further comprising:
 increasing a discharge amount of the compressor so that a cooling capacity of the refrigeration cycle is not less than a required cooling capacity when the compressor is operated.   
   
   
       31 . The control method of the waste heat utilization device according to  claim 30 , wherein:
 the discharge amount of the compressor is increased so that the waste fluid temperature at an evaporator of the refrigeration cycle or a temperature of other part associated with the waste fluid temperature becomes a second target temperature which is lower than a first target temperature satisfying the required cooling capacity.   
   
   
       32 . The control method of a waste heat utilization device according to  claim 31 , further comprising:
 setting the second target temperature to be lower than the first target temperature approximately by 1 to 5 degree.   
   
   
       33 . The control method of a waste heat utilization device according to  claim 19 , wherein:
 the waste heat utilization device comprises a refrigeration cycle having a compressor for compressing and discharging a refrigerant in the refrigeration cycle, using the condenser in common with the Rankine cycle, and controlled by the control unit independently from the Rankine cycle,   the method further comprising:   simultaneously operating the refrigeration cycle and the Rankine cycle, when the operation of the refrigeration cycle is required, the waste fluid temperature is not less than the predetermined temperature, and the waste fluid is in the flowing state.   
   
   
       34 . The control method of the waste heat utilization device according to  claim 33 , further comprising:
 controlling a rotation number of the expander so that the sum of a first heat loss amount required for condensing the operation fluid discharged from the compressor and a second heat loss amount required for condensing the operation fluid flowing out from the expander is not more than a heat loss capacity of condensing at the condenser.   
   
   
       35 . The control method of the waste heat utilization device according to  claim 19 , wherein:
 the heat engine is an internal combustion engine for a vehicle.   
   
   
       36 . The control method of the waste heat utilization device according to  claim 35 , wherein:
 the vehicle is a hybrid vehicle or an idling stop vehicle in which the internal combustion engine is operated and stopped in accordance with a driving state of the vehicle.