Organic rankine cycle waste heat recovery system

Abstract

A Rankine cycle for recovering waste heat from an engine includes a Rankine cycle circuit having a pump, a heat exchanger, an expansion device, a cooling device and a bypass circuit. The bypass circuit selectively provides a flow path for working fluid to bypass the expansion device, and includes a flow control valve actuated by a working fluid pressure differential to selectively open or close the bypass flow path. The expansion device includes a drive member directly coupled to a front end accessory drive (FEAD) of the engine such that a rotational speed of the expansion device is dictated by engine speed and the expansion device is free from separate speed control. The expansion device provides torque to the FEAD via the drive member when the system is in a waste heat recovery mode thereby reducing engine load and improving fuel economy.

What is claimed is: 
     
         1 . A Rankine cycle system for recovering waste heat from an engine of a vehicle, the system comprising:
 a Rankine cycle circuit through which a working fluid circulates, the circuit including:
 a pump for circulating the working fluid in the circuit; 
 a heat exchanger thermally coupled to a heat source associated with the engine and adapted to transfer heat to the working fluid; 
 an expansion device configured to selectively receive the working fluid from the heat exchanger and expand the working fluid to generate work; 
 a cooling device configured to receive the working fluid from the expansion device and cool the working fluid; and 
 a bypass circuit selectively providing a flow path bypassing the expansion device, the bypass circuit including a flow control valve actuated by a working fluid pressure differential to selectively open or close the flow path bypassing the expansion device; 
   wherein the expansion device includes a drive member directly coupled to a front end accessory drive of the engine such that a rotational speed of the expansion device is dictated by engine speed and the expansion device is free from separate speed control.   
     
     
         2 . The system of  claim 1 , wherein when the working fluid is directed to flow through the expansion device in a waste heat recovery mode of the Rankine system, the expansion device provides torque to the front end accessory drive via the drive member thereby reducing an overall load on the engine and improving fuel economy. 
     
     
         3 . The system of  claim 2 , wherein when the Rankine system is in a non-waste heat recovery mode of operation, the flow control valve is actuated so as to provide the flow path bypassing the expansion device for the working fluid thereby minimizing a parasitic load of the expansion device while not controlling a rotational speed of the expansion device. 
     
     
         4 . The system of  claim 1 , wherein the expansion device is directly coupled to a belt wrap of the front end accessory drive and includes an absence of a clutch. 
     
     
         5 . The system of  claim 4 , wherein the expansion device comprises a scroll expander and the drive member comprises a pulley, the scroll expander having a scroll shaft coupled to the pulley, which is directly coupled to the front end accessory drive. 
     
     
         6 . The system of  claim 1 , further comprising a discrete low temperature radiator circuit fluidly coupled to the condenser and configured to reject heat from the working fluid flowing through the condenser, the low temperature radiator circuit including a low temperature radiator. 
     
     
         7 . The system of  claim 1 , wherein the Rankine circuit further comprises a recuperator configured to reduce the temperature of the working fluid downstream of the expander. 
     
     
         8 . The system of  claim 1 , wherein the bypass circuit comprises:
 a low pressure reference control line fluidly coupled to the circuit proximate an outlet of the expansion device and to one side of the flow control valve; and   a high pressure reference control line fluidly coupled to the circuit proximate an inlet of the expansion device and the flow control valve such that the low and high pressure reference control lines provide oppositely acting forces on the flow control valve.   
     
     
         9 . The system of  claim 8 , wherein the bypass circuit further comprises:
 a bypass flow line coupled at one end to the flow control valve and at another end to the circuit proximate to the expander outlet, the bypass flow line together with the flow control valve providing the flow path bypassing the expansion device;   wherein the high pressure reference control line is coupled to the bypass flow line downstream of the coupling to the flow control valve such that flow of working fluid from the heat exchanger is in fluid communication with the flow control valve and the bypass flow line via the high pressure reference control line.   
     
     
         10 . The system of  claim 9 , wherein the bypass circuit further comprises an electronically controlled valve positioned in the high pressure reference control line between the coupling of the high pressure reference control line to the flow control valve and to the bypass flow line. 
     
     
         11 . The system of  claim 10 , wherein the electronically controlled valve is configured to be controlled to i) block flow of the working fluid through the high pressure reference control line to the bypass flow line thereby reducing bypass flow through the flow control valve; and ii) allowing the working fluid to flow through the electronically controlled valve to the bypass flow line and at least substantially bypassing the flow control valve. 
     
     
         12 . The system of  claim 11 , wherein the heat source comprises exhaust gas and the heat exchanger comprises a vapor generator; and wherein the system further comprises an exhaust gas bypass circuit having an exhaust bypass valve, the exhaust bypass circuit configured to selectively provide an exhaust flow path bypassing the heat exchanger. 
     
     
         13 . The system of  claim 12 , further comprising a controller in communication with at least the pump, the exhaust bypass valve, the electronically controlled valve and one or more temperature and pressure sensors in communication with the Rankine circuit proximate an exit of the heat exchanger. 
     
     
         14 . The system of  claim 13 , wherein the controller is configured to:
 receive signals from the one or more temperature and pressure sensors indicative of a temperature and pressure, respectively, of the working fluid exiting the vapor generator; and   compare the signals to one or more predetermined thresholds indicative of whether the working fluid exiting the vapor generator comprises i) a sufficient or ii) an insufficient temperature and pressure for the Rankine system to enter a waste heat recovery mode.   
     
     
         15 . The system of  claim 14 , wherein the controller is further configured to command the electronically controlled valve to close when it is determined that there is a sufficient temperature and flow to enter the waste heat recovery mode, thereby actuating the flow control valve to block the working fluid bypass flow path and force the working fluid exiting the vapor generator to flow through the expansion device. 
     
     
         16 . The system of  claim 14 , wherein the working fluid flowing through the expansion device in the waste heat recovery mode is converted to shaft power and drives the pulley thereby providing torque to the front end accessory drive and reducing an overall load on the engine. 
     
     
         17 . The system  claim 14 , further comprising an attemperator in communication with the circuit proximate an exit of the vapor generator and configured to be controlled to selectively inject cooling fluid into the circuit to control a superheat value of the working fluid upstream of the expander. 
     
     
         18 . A method of utilizing a Rankine cycle system for recovering waste heat from an engine of a vehicle, the system including a Rankine cycle circuit for circulating working fluid through a heat exchanger thermally coupled to a heat source from the engine, through an expansion device downstream of the heat exchanger, and through a condenser downstream of the expansion device, the method comprising:
 determining, at a controller of the vehicle, a pressure and a temperature of the working fluid in the circuit between the heat exchanger and the expansion device;   determining, at the controller, whether the system enters a waste heat recovery mode based on the determined temperature and pressure; and   commanding a bypass valve in a bypass circuit of the Rankine cycle circuit that bypasses the expansion device to actuate a flow control valve to i) allow the working fluid to flow through the bypass circuit when the system does not enter the waste heat recovery mode thereby bypassing the expansion device; ii) block the working fluid from flowing through the bypass circuit thereby directing the working fluid to flow through the expansion device; and iii) modulate a pressure of the working fluid at an inlet to the expansion device to optimize thermodynamic cycle efficiency;   wherein the expansion device includes a drive member directly coupled to a front end accessory drive of the engine such that a rotational speed of the expansion device is dictated by engine speed and the expansion device is free from separate speed control.   
     
     
         19 . The method of  claim 18 , wherein commanding the bypass valve to actuate the flow control valve to direct the working fluid to flow through the expansion device provides for the expansion device inputting torque to the front end accessory drive via the drive member thereby reducing an overall load on the engine and improving fuel economy; and
 wherein commanding the bypass valve to actuate the flow control valve to allow the working fluid to flow through the bypass circuit provides for minimizing a parasitic load of the expansion device while not controlling a rotational speed of the expansion device.