Exhaust line for a motor vehicle with a closed recovery cycle for exhaust gas heat energy, and associated control method

Abstract

An exhaust line of a motor vehicle includes a heat exchanger having a first side for circulating the exhaust gases and a second side for circulating a heat exchange fluid, and a closed recovery cycle for one portion of the heat energy of the exhaust gases, in which said heat exchange fluid circulates, wherein the second side of the heat exchanger is inserted inside the closed cycle. The heat exchanger includes an intermediate wall interposed between the first and second sides of the heat exchanger. The intermediate wall comprises at least one closed cavity including a phase change material. The intermediate wall has a first exchange surface in thermal contact with the exhaust gases and a second exchange surface in thermal contact with the heat exchange fluid.

1 . An exhaust line of a motor vehicle comprising:
 a heat exchanger having a first side for circulation of exhaust gases and a second side for circulation of a heat exchange fluid;   a closed cycle for recovering a portion of heat energy of the exhaust gases, in which said heat exchange fluid circulates, the second side of the heat exchanger being inserted into the closed cycle; and   wherein the heat exchanger includes an intermediate wall interposed between the first and second sides of the heat exchanger, the intermediate wall comprising at least one closed cavity having a phase change material, the intermediate wall having a first exchange surface in thermal contact with the exhaust gases and a second exchange surface in thermal contact with the heat exchange fluid.   
     
     
         2 . The exhaust line according to  claim 1 , wherein the intermediate wall comprises a plurality of closed cavities each including an amount of a phase change material, the closed cavities being isolated from each other. 
     
     
         3 . The exhaust line according to  claim 1 , wherein the phase change material comprises one or more inorganic salts, selected from the group comprising NaOH, KOH, LiOH, NaNO 2 , NaNO 3 , KNO 3 , Ca(NO 3 ) 2 , LiNO 3 , KCl, LiCl, NaCl, MgCl 2 , CaCl 2 , Na 2 CO 3 , K 2 CO 3 , Li 2 CO 3 , KF, LiF 
     
     
         4 . The exhaust line according to  claim 1 , wherein the phase change material comprises one or more metals selected from the group comprising Sn, Pb and Zn. 
     
     
         5 . The exhaust line according to  claim 1 , wherein the phase change material has a melting temperature comprised between 100° C. and 500° C. 
     
     
         6 . The exhaust line according to  claim 1 , wherein the phase change material has a latent heat of fusion comprised between 100 and 300 kJ/kg. 
     
     
         7 . The exhaust line according to  claim 1 , wherein the intermediate wall comprises a mass of phase change material selected for allowing storage of heat energy comprised between 0.1 kWh and 10 kWh. 
     
     
         8 . The exhaust line according to  claim 1 , wherein the closed cycle is a Rankine cycle or a Hirn cycle. 
     
     
         9 . The exhaust line according to  claim 1 , wherein the closed cycle comprises a driving shaft and a member for driving into rotation the driving shaft by the heat exchange fluid. 
     
     
         10 . The exhaust line according to  claim 1 , wherein the heat exchange fluid essentially comprises water. 
     
     
         11 . The exhaust line according to  claim 1 , wherein the closed cycle is dimensioned so that the heat exchange fluid has a reference temperature at the outlet of the heat exchanger, the phase change material having a melting temperature comprised between the reference temperature and the reference temperature plus 100° C. 
     
     
         12 . The exhaust line according to  claim 1 , including:
 an upstream conduit for circulation of the exhaust gases, the upstream conduit being fluidically connected to an inlet of the first side of the heat exchanger;   a downstream conduit for circulation of the exhaust gases, the downstream conduit being fluidically connected to an outlet of the first side of the heat exchanger;   a bypass conduit connecting the upstream conduit to the downstream conduit by bypassing the heat exchanger,   a first member for orienting the exhaust gases, the first member being capable of orienting a fraction of the exhaust gases towards the heat exchanger and another fraction of the exhaust gases towards the bypass conduit, and   a second member that controls the orientation of the first member, the second member being capable of selectively controlling said fraction of exhaust gases oriented towards the heat exchanger and said other fraction of the exhaust gases oriented towards the bypass conduit.   
     
     
         13 . A method for controlling an exhaust line, including the following steps:
 providing
 a heat exchanger having a first side for circulation of exhaust gases and a second side for circulation of a heat exchange fluid; 
 a closed cycle for recovering a portion of heat energy of the exhaust gases, in which said heat exchange fluid circulates, the second side of the heat exchanger being inserted into the closed cycle; 
 wherein the heat exchanger includes an intermediate wall interposed between the first and second sides of the heat exchanger, the intermediate wall comprising at least one closed cavity having a phase change material, the intermediate wall having a first exchange surface in thermal contact with the exhaust gases and a second exchange surface in thermal contact with the heat exchange fluid; 
 an upstream conduit for circulation of the exhaust gases, the upstream conduit being fluidically connected to an inlet of the first side of the heat exchanger; 
 a downstream conduit for circulation of the exhaust gases, the downstream conduit being fluidically connected to an outlet of the first side of the heat exchanger; 
 a bypass conduit connecting the upstream conduit to the downstream conduit by bypassing the heat exchanger, 
 a first member for orienting the exhaust gases, the first member being capable of orienting a fraction of the exhaust gases towards the heat exchanger and another fraction of the exhaust gases towards the bypass conduit, and 
 a second member that controls the orientation of the first member, the second member being capable of selectively controlling said fraction of exhaust gases oriented towards the heat exchanger and said other fraction of the exhaust gases oriented towards the bypass conduit. 
   evaluating a first quantity representative of an amount of heat energy provided by the exhaust gases exiting a heat engine of the vehicle;   acquiring at least one second quantity representative of a temperature of the heat exchange fluid in closed cycle;   evaluating a third quantity representative of an amount of heat energy stored in the phase change material of the intermediate wall;   determining the fraction of the exhaust gases oriented towards the exchanger using at least the first, second and third quantities;   controlling the first member according to the determined fraction.   
     
     
         14 . The method according to  claim 13 , wherein the third quantity representative of the amount of heat energy stored in the phase change material of the intermediate wall is evaluated by:
 evaluating a fourth quantity representative of an amount of heat energy actually received by the closed cycle in the heat exchanger; and   inferring the third quantity at least from the first quantity and the fourth quantity.