Internal combustion engine with secondary air pump for catalyst

Abstract

A secondary air pump for a small internal combustion engine for supplying secondary air to the exhaust system of the engine upstream of a catalyst element. The air pump includes a thinly-profiled pump housing attached to the crankcase of the engine, an inlet in fluid communication with the atmosphere, and an outlet in fluid communication with the exhaust system of the engine upstream of the catalyst element. First and second impellers within the pump housing and are driven by the crankshaft and camshaft of the engine, respectively, and cooperate with one another and with the pump housing to define a plurality of moving working spaces which convey air from the inlet to the outlet during running of the engine.

1 . An internal combustion engine, comprising: 
 an engine housing;    first and second shafts rotatably supported by said engine housing; and    an air pump, comprising: 
 a pump housing;  
 an inlet in fluid communication with the atmosphere;  
 an outlet in fluid communication with an exhaust system of said engine;  
 first and second impellers disposed within said pump housing and driven respectively by said first and second shafts, said impellers cooperating with one another and with said pump housing to define a plurality of moving working spaces which convey air from said inlet to said outlet upon rotation of said first and second impellers.  
   
   
   
       2 . The internal combustion engine of  claim 1 , wherein said first and second impellers each include a plurality of lobes in meshing cooperation with one another.  
   
   
       3 . The internal combustion engine of  claim 2 , wherein said first shaft drives said second shaft at one-half the speed of said first shaft, and said second impeller includes twice the number of said lobes as said first impeller.  
   
   
       4 . The internal combustion engine of  claim 2 , wherein said first shaft drives said second shaft at one-half the speed of said first shaft, and said first impeller includes two said lobes and said second impeller includes four said lobes, whereby four of said working spaces convey air from said inlet to said outlet for each rotation of said second shaft.  
   
   
       5 . The internal combustion engine of  claim 1 , wherein said first shaft is a crankshaft, said crankshaft in timed driving relationship with said second shaft.  
   
   
       6 . The internal combustion engine of  claim 1 , wherein said second shaft is a camshaft, said camshaft in timed driven relationship with said first shaft.  
   
   
       7 . The internal combustion engine of  claim 1 , wherein said pump housing is formed at least in part by said engine housing.  
   
   
       8 . The internal combustion engine of  claim 1 , wherein said exhaust system of said engine comprises: 
 an exhaust passage in fluid communication with said air pump outlet;    a catalyst element disposed within said exhaust passage downstream of said air pump outlet; and    a muffler associated with said exhaust passage.    
   
   
       9 . The internal combustion engine of  claim 1 , further comprising a one-way valve associated with said air pump outlet.  
   
   
       10 . An internal combustion engine, comprising: 
 an engine housing;    a crankshaft rotatably supported by said engine housing;    an additional shaft driven from said crankshaft and rotatably supported by said engine housing;    an exhaust system including an exhaust passage and a catalyst element; and    an air pump, comprising: 
 a pump housing including an inlet in fluid communication with the atmosphere and an outlet in fluid communication with said exhaust passage at a location upstream of said catalyst element; and  
 first and second impellers disposed within said pump housing and driven respectively by said crankshaft and said additional shaft, said impellers each including a plurality of lobes in meshing cooperation with one another to define moving working spaces which convey air from said inlet to said outlet upon rotation of said first and second impellers.  
   
   
   
       11 . The internal combustion engine of  claim 10 , wherein said additional shaft is a camshaft, said camshaft in timed driven relationship with said crankshaft.  
   
   
       12 . The internal combustion engine of  claim 11 , wherein said crankshaft drives said camshaft at one-half crankshaft speed, and said second impeller includes twice the number of said lobes as said first impeller.  
   
   
       13 . The internal combustion engine of  claim 11 , wherein said crankshaft drives said additional shaft at one-half crankshaft speed, and said first impeller includes two said lobes and said second impeller includes four said lobes, whereby four of said working spaces convey air from said inlet to said outlet for each rotation of said additional shaft.  
   
   
       14 . The internal combustion engine of  claim 10 , wherein said pump housing is formed at least in part by said engine housing.  
   
   
       15 . The internal combustion engine of  claim 10 , wherein said pump housing further comprising a one-way valve associated with said air pump outlet.  
   
   
       16 . An internal combustion engine, comprising: 
 an engine housing;    first and second shafts rotatably supported by said engine housing; and    an air pump, comprising: 
 a pump housing;  
 an inlet in fluid communication with the atmosphere;  
 an outlet in fluid communication with an exhaust system of said engine; and  
 means within said pump housing for conveying air from said inlet to said outlet upon rotation of said first and second shafts.  
   
   
   
       17 . The internal combustion engine of  claim 16 , wherein said first shaft is a crankshaft and said second shaft is a camshaft, said camshaft in timed driven relationship with said crankshaft.  
   
   
       18 . The internal combustion engine of  claim 16 , wherein said exhaust system of said engine comprises: 
 an exhaust passage in fluid communication with said air pump outlet;    a catalyst element disposed within said exhaust passage downstream of said air pump outlet; and    a muffler associated with said exhaust passage.    
   
   
       19 . The internal combustion engine of  claim 16 , further comprising a one-way valve associated with said air pump outlet.