Waste heat recovery system

Abstract

The waste heat recovery system of an engine includes a Rankine cycle, a first bypass passage, a first valve and a control unit. The Rankine cycle allows a working fluid to circulate therethrough. The Rankine cycle has a first heat exchanger, a second heat exchanger, an expander and a condenser. The first heat exchanger exchange heat between the working fluid and the engine or a first intermediate medium exchanging heat with the engine. The first bypass passage allows the working fluid to pass therethrough. One end of the first bypass passage is located at an upstream side of the condenser and the other end is located at a downstream side of the condenser. The first valve opens and closes the first bypass passage. When temperature of the engine or the first intermediate medium is lower than a first predetermined value, the control unit opens the first valve.

1 . A waste heat recovery system of an engine comprising:
 a Rankine cycle allowing a working fluid to circulate therethrough, the Rankine cycle having:
 a first heat exchanger for exchanging heat between the working fluid and the engine or a first intermediate medium exchanging heat with the engine; 
 a second heat exchanger for exchanging heat between the working fluid and an exhaust gas of the engine or a second intermediate medium exchanging heat with the exhaust gas of the engine; 
 an expander for expanding the working fluid to recover mechanical energy; 
 a condenser for condensing the working fluid; 
   a first bypass passage connected to the Rankine cycle for allowing the working fluid to pass therethrough, wherein one end of the first bypass passage is located at an upstream side of the condenser and the other end of the first bypass passage is located at a downstream side of the condenser with respect to flow direction of the working fluid;   a first valve for opening and closing the first bypass passage; and   a control unit for controlling operation of the waste heat recovery system, wherein when temperature of the engine or the first intermediate medium is lower than a first predetermined value, the control unit opens the first valve.   
     
     
         2 . The waste heat recovery system according to  claim 1 , wherein the one end of the first bypass passage is located at a downstream side of the expander and the other end of the first bypass passage is located at an upstream side of the first heat exchanger. 
     
     
         3 . The waste heat recovery system according to  claim 2 , further comprising:
 a pump provided for pumping the working fluid, wherein the other end of the first bypass passage is located at an upstream side of the pump;   a second bypass passage connected to the Rankine cycle for allowing the working fluid to pass through the second bypass passage, wherein one end of the second bypass passage is located at the upstream side of the pump and the downstream side of the expander and the other end of the second bypass passage is located at a downstream side of the pump and the upstream side of the first heat exchanger; and   a second valve for opening and closing the second bypass passage, wherein the second valve opens when pressure of the working fluid at the upstream side of the pump is higher than pressure of the working fluid at the downstream side of the pump.   
     
     
         4 . The waste heat recovery system according to  claim 3 , wherein the second valve is a check valve. 
     
     
         5 . The waste heat recovery system according to  claim 2 , further comprising a pump for pumping the working fluid, wherein the other end of the first bypass passage is located at a downstream side of the pump. 
     
     
         6 . The waste heat recovery system according to  claim 5 , further comprising:
 a third bypass passage connected to the Rankine cycle for allowing the working fluid to pass through the third bypass passage, wherein one end of the third bypass passage is located at the upstream side of the pump and the downstream side of the one end of the first bypass passage and the other end of the third bypass passage is located at the downstream side of the pump and the upstream side of the other end of the first bypass passage; and   a third valve for opening and closing the third bypass passage,   wherein when the temperature of the engine or the first intermediate medium is lower than the first predetermined value, the control unit opens the third valve,   wherein the expander, the first bypass passage, the first heat exchanger and the second heat exchanger cooperate to form a first closed circuit, and   wherein the pump and the third bypass passage cooperate to form a second closed circuit.   
     
     
         7 . The waste heat recovery system according to  claim 6 , wherein the one end of the third bypass passage is located at the upstream side of the condenser. 
     
     
         8 . The waste heat recovery system according to  claim 6 , wherein the first closed circuit and the second closed circuit are in communication with each other so that the working fluid is allowed to circulate between the first closed circuit and the second closed circuit. 
     
     
         9 . The waste heat recovery system according to  claim 1 , further comprising:
 a pump for pumping the working fluid;   a motor generator for driving the pump and converting the mechanical energy generated by the expander into electric power; and   a clutch provided between the expander and the motor generator,   wherein the one end of the first bypass passage is located at a downstream side of the second heat exchanger and an upstream side of the expander and the other end of the first bypass passage is located at an upstream side of the pump.   
     
     
         10 . The waste heat recovery system according to  claim 1 , wherein when the temperature of the engine or the first intermediate medium is a second predetermined value that is higher than the first predetermined value or higher, the control unit opens the first valve. 
     
     
         11 . The waste heat recovery system according to  claim 6 , wherein when the temperature of the engine or the first intermediate medium is a second predetermined value that is higher than the first predetermined value or higher, the control unit closes the first valve and the third valve. 
     
     
         12 . The waste heat recovery system according to  claim 1 , further comprising a fourth valve connected to the Rankine cycle at the upstream side of the condenser and a downstream side of the expander for cutting off the circulation of the working fluid through the condenser, when the temperature of the engine or the first intermediate medium is lower than the first predetermined value, the control unit closes the fourth valve.