Waste heat collecting system having expansion device

Abstract

An object of the invention is to provide a waste heat collecting system having an expansion device, in which an over expansion of refrigerant is prevented so that a loss to be caused by the over expansion is eliminated. A volume ratio of expansion for the expansion device is selected at a value, at which proper expansion of the refrigerant is achieved when the pressure difference between the high pressure and the low pressure is minimum.

1 . A waste heat collecting apparatus for a vehicle comprising: 
 an engine cooling circuit, through which engine cooling water is circulated; and    Rankine cycle having an expansion device, a condensing device, a refrigerant pump, and a heating device, which are connected in a closed circuit so that refrigerant is circulated in the closed circuit by the operation of the refrigerant pump, wherein    the heating device is disposed in the engine cooling circuit for heating the refrigerant of the Rankine cycle with the heat of the engine cooling water, so that the refrigerant is converted to high pressure and high temperature refrigerant,    the heating device is connected to an inlet side of the expansion device for supplying the high pressure refrigerant to the expansion device,    the condensing device is connected to an outlet side of the expansion device for cooling down and condensing the refrigerant from the expansion device through heat exchange with the ambient air, so that the pressure of the refrigerant at the outlet side of the expansion device depends on a condensing capacity of the condensing device,    the expansion device is of a fixed displacement type fluid machine, and an output shaft of the expansion device is driven to rotate by expansion of the refrigerant in a working chamber thereof, the expansion of the refrigerant is performed by a pressure difference of the refrigerant between the high pressure at the inlet side and low pressure at the outlet side of the expansion device, and    a volume ratio of expansion for the expansion device is selected at a value, at which proper expansion of the refrigerant is achieved when the pressure difference between the high pressure and the low pressure is minimum.    
   
   
       2 . A waste heat collecting apparatus according to  claim 1 , further comprising: 
 a refrigerating cycle having a compressor device operatively connected to and driven by an engine, a condenser, and an evaporator,    wherein the condensing device of the Rankine cycle is commonly used as the condenser for the refrigerating device.    
   
   
       3 . A waste heat collecting apparatus according to  claim 2 , wherein 
 the volume ratio of expansion for the expansion device is selected at a value between 1.5 and 2.5.    
   
   
       4 . A waste heat collecting apparatus for a vehicle comprising: 
 Rankine cycle having an expansion device; a condensing device; a refrigerant pump; and a heating device, wherein the expansion device, the condensing device, the refrigerant pump, and the heating device are connected in a closed circuit so that refrigerant is circulated in the closed circuit by the operation of the refrigerant pump, the expansion device generating a rotational driving force by expansion of the refrigerant;    an electric power generator operatively connected to the expansion device for generating the electric power when it is driven to rotate by the rotational driving force of the expansion device;    a pressure detecting device for detecting a pressure difference of the refrigerant between a pressure at a high pressure side of the expansion device and a pressure at a low pressure side of the expansion device; and    a pressure increasing means for increasing the pressure difference when the pressure difference detected by the pressure detecting device is lower than a predetermined pressure difference, so that the pressure difference becomes closer to the predetermined pressure difference.    
   
   
       5 . A rotational force generating apparatus comprising: 
 a high pressure generating device for generating a high pressure of working fluid;    a low pressure generating device for generating a low pressure of the working fluid;    an expansion device having a fixed displacement and rotating an output shaft by a pressure difference of the working fluid between the high pressure generated by the high pressure generating device and the low pressure generated by the low pressure generating device,    wherein a volume ratio of expansion for the expansion device is selected at a value, at which proper expansion of the working fluid is achieved when the pressure difference between the high pressure and the low pressure is minimum.    
   
   
       6 . A rotational force generating apparatus according to claim  5 , wherein 
 the high pressure generating device comprises a heating device for heating the working fluid with heat generated from a vehicle.    
   
   
       7 . A rotational force generating apparatus according to  claim 6 , wherein 
 the high pressure generating device comprises a heating device for heating the working fluid with heat of engine cooling water.    
   
   
       8 . A rotational force generating apparatus according to  claim 5 , wherein 
 the low pressure generating device comprises a condensing device for cooling down the working fluid by the ambient air, so as to decrease the pressure of the working fluid, and    the volume ratio of expansion for the expansion device is selected at a value, at which the proper expansion of the working fluid is achieved during the summer season, during which the pressure generated at the low pressure generating device becomes higher than the pressures in other seasons.    
   
   
       9 . A rotational force generating apparatus according to  claim 5 , wherein 
 the low pressure generating device comprises a condensing device, which is commonly used for Rankine cycle and a refrigerating cycle, and    the volume ratio of expansion for the expansion device is selected at a value between 1.5 and 2.5.    
   
   
       10 . A rotational force generating apparatus according to  claim 5 , wherein 
 a motor generator is driven by the output shaft to generate the electric power.    
   
   
       11 . A control system for an expansion device comprising: 
 an expansion device for generating a rotational driving force by expansion of high pressure and high temperature working fluid;    an electric power generator driven by the rotational driving force of the expansion device;    a pressure detecting device for detecting a pressure difference of the working fluid between a pressure at a high pressure side of the expansion device and a pressure at a low pressure side of the expansion device; and    a pressure increasing means for increasing the pressure difference when the pressure difference detected by the pressure detecting device is lower than a predetermined pressure difference, so that the pressure difference becomes closer to the predetermined pressure difference.    
   
   
       12 . A control system for an expansion device according to  claim 11 , wherein the expansion device is of a scroll type device which comprises: 
 a movable scroll to be rotated by the expansion of the working fluid, with respect to a fixed scroll, with an orbital motion; and    a crank device provided to the movable scroll for generating the rotational driving force in accordance with the orbital motion of the movable scroll, and the fixed scroll and the movable scroll are pushed to each other, as a function of the crank device, during the expansion of the working fluid.    
   
   
       13 . A control system for an expansion device according to  claim 11 , wherein the pressure detecting device comprises: 
 a pressure sensor for detecting a high pressure side pressure and a pressure sensor for detecting a low pressure side pressure of the expansion device; and    a controller for calculating a difference between the high pressure side pressure and the low pressure side pressure as the pressure difference.    
   
   
       14 . A control system for an expansion device according to  claim 11 , wherein the pressure increasing means comprises: 
 the electric power generator; and    a device for decreasing a number of rotational speed of the electric power generator.    
   
   
       15 . A control system for an expansion device according to  claim 14 , wherein 
 the device for decreasing the number of rotational speed of the electric power generator is an inverter for controlling the rotational speed of the electric power generator.    
   
   
       16 . A control system for an expansion device according to claim  14 , wherein 
 the device for decreasing the number of rotational speed of the electric power generator comprises a magnetic flux density increasing means for increasing the magnetic flux density by increasing excitation of a coil for a rotor of the electric power generator.    
   
   
       17 . A control system for an expansion device according to  claim 11 , wherein 
 the expansion device is used for Rankine cycle, and    the pressure increasing means comprises:    a condensing device provided on a low pressure side of the Rankine cycle; and    a device for increasing condensing capacity at the condensing device.    
   
   
       18 . A control system for an expansion device according to  claim 17 , wherein 
 the device for increasing condensing capacity at the condensing device comprises a blower device for blowing air to the condensing device, wherein the blower device increases the amount of the air to the condensing device.    
   
   
       19 . A control system for an expansion device according to  claim 11 , wherein 
 the expansion device is used for Rankine cycle, and    the pressure increasing means comprises:    a liquid pump for pressurizing the working fluid in the low pressure side of the Rankine side and for supplying the pressurized working pressure to the high pressure side of the Rankine side; and    a device for increasing a rotational speed of the liquid pump.    
   
   
       20 . A control system for an expansion device according to  claim 19 , wherein 
 the device for increasing the rotational speed of the liquid pump comprises an inverter for controlling a rotational speed of an electric motor for driving the liquid pump.    
   
   
       21 . A control system for an expansion device according to  claim 20 , wherein 
 the device for increasing the rotational speed of the liquid pump comprises a means for decreasing magnetic flux density of the electric motor for driving the liquid pump by decreasing the excitation for the electric motor.