Lubricating system for aircraft drive
A lubricating pump having a first stage and a second stage; the first stage in turn has an intake connectable hydraulically to a tank of lubricating fluid, and a delivery outlet connectable hydraulically to a lubricated member; the first stage compresses the lubricating fluid from the tank to a pressure for supply to the member; the second stage in turn has an inlet connectable hydraulically to a casing housing the member, and an outlet connectable hydraulically to the tank; the second stage feeds the lubricating fluid in the casing back into the tank; the second stage is a Roots type, and has a first and a second rotor rotating about respective axes to feed the lubricating fluid from the inlet to the outlet; and the first and second rotor are operated by the first stage.
1. A lubricating system ( 2 ) for lubricating a drive ( 3 ) powering a helicopter rotor, said lubricating system ( 2 ) comprising:
a lubricating pump ( 1 );
a tank ( 4 ) of lubricating fluid; and
a casing ( 9 ) housing a lubricated member of said drive ( 3 );
said lubricating pump ( 1 ) comprising:
a first stage ( 5 ) comprising an intake ( 6 ) hydraulically connected to said tank ( 4 ) and a delivery outlet ( 7 ) hydraulically connected to a number of nozzles ( 8 ) for feeding said lubricating fluid into said casing ( 9 ) and onto said lubricated member, said first stage ( 5 ) compressing, in use, said lubricating fluid from said tank ( 4 ) to a pressure to supply to said lubricated member housed within said casing ( 9 ); and
a second stage ( 10 ) comprising an inlet ( 11 ) hydraulically connected to an opening ( 12 ) defined by said casing ( 9 ) and an outlet ( 13 ) hydraulically connected to said tank ( 4 ), said second stage ( 10 ) feeding said lubricating fluid in said casing ( 9 ) back into said tank ( 4 );
said second stage ( 10 ) being a Roots type comprising a first rotor ( 31 ) and a second rotor ( 32 ) rotating, in use, in opposite directions to feed said lubricating fluid from said inlet ( 11 ) to said outlet ( 13 );
said first rotor ( 31 ) and said second rotor ( 32 ) both being operated by said first stage ( 5 );
said first rotor ( 31 ) comprising a number of first lobes ( 33 ) and said second rotor ( 32 ) comprising a number of second lobes ( 34 ) such that said first and second lobes ( 33 , 34 ) having conjugate profiles in constant contact with one another;
said first stage ( 5 ) comprising a third rotor ( 35 ) and fourth rotor ( 36 ) connected functionally to said first and second rotors ( 31 , 32 ), respectively;
one of said third and fourth rotors ( 35 , 36 ) being powered and rotating, in use, the other one of said third and fourth rotors ( 35 , 36 );
said lubricating pump ( 1 ) further comprising:
a first shaft ( 37 ) fitted with and connecting said first and third rotors ( 31 , 35 );
a second shaft ( 39 ) fitted with said second and fourth rotors ( 32 , 36 ); and
a housing ( 20 ) housing said first and second stages ( 5 , 10 );
said housing ( 20 ) comprising:
a first end body ( 21 ) and a second end body ( 22 ) defining respective axial ends of said housing ( 20 );
a first plate ( 23 ) and a second plate ( 25 ) interposed axially between said first and second end bodies ( 21 , 22 ) and separating said first and second end bodies ( 21 , 22 ) in a fluid tight manner;
said first end body ( 21 ) having a first cavity facing said first plate ( 23 ) and housing said first and second rotors ( 31 , 32 );
said second end body ( 22 ) having a second cavity facing said second plate ( 25 ) and housing said third and fourth rotors ( 35 , 36 ).
2. The lubricating system as claimed in claim 1 , wherein said first stage ( 5 ) is of a volumetric type pump.
3. The lubricating system as claimed in claim 1 wherein said first and third rotors ( 31 , 35 ) are angularly integral with said shaft ( 37 ).
4. The lubricating system as claimed in claim 1 wherein said third and fourth rotors ( 35 , 36 ) define respective gears ( 35 , 36 ) meshing with each other.
5. The lubricating system as claimed in claim 1 , wherein a head of said first stage ( 5 ) is greater than the head of said second stage ( 10 ).
6. The lubricating system as claimed in claim 1 , wherein said first and second stages ( 5 , 10 ) are designed so that, in use, lubricating fluid flow through said second stage ( 10 ) is greater than flow through said first stage ( 5 ).
7. The lubricating system as claimed in claim 6 , wherein t, in use, lubricating fluid flow through said second stage ( 10 ) is at least 1.5 times of the flow through said first stage ( 5 ).
8. The lubricating system as claimed in claim 1 , wherein said shaft ( 37 ) extends through said first and second plate ( 23 , 24 , 25 ).
9. The lubricating system as claimed in claim 1 , wherein said first stage ( 5 ) comprises a first casing ( 26 ) defined between said second end body ( 22 ) and said second plate ( 25 ), and wherein said second stage ( 10 ) comprises a second casing ( 27 ) defined between said first end body ( 21 ) and said first plate ( 23 );
said first lobes ( 33 ) and said second lobes ( 34 ) define with said second casing ( 27 ) a number of chambers ( 40 ) varying cyclically in volume, in use, and inside which said lubricating fluid is fed from said inlet ( 11 ) to said outlet ( 13 ).
10. The lubricating system as claimed in claim 9 , wherein each of said first and second lobes ( 33 , 34 ) has a cycloid-shaped profile cooperating with said lubricating fluid.
11. The lubricating system as claimed in claim 1 , wherein said tank ( 4 ) is arranged above said intake ( 6 ) of said first stage ( 5 ), and wherein said opening ( 12 ) is arranged below said tank ( 4 ) and above said intake ( 6 ).
12. A drive for powering a helicopter rotor in combination with a lubricating system according to claim 1 .