Belt Drive With A Friction Wheel
Belt drive comprising a crankshaft pulley, an accessory pulley, a transmission belt wound on the crankshaft pulley, an accessory pulley, a water pump friction pulley and a friction wheel having a friction surface co-operating with the friction pulley and a back of the transmission belt at a section of the belt that is wound around the crankshaft pulley; the friction wheel is made of metal and has a knurled friction surface, the friction pulley comprises a soft friction annulus with the friction surface of the friction wheel.
1 . A belt drive comprising: a first pulley rotatable about a first fixed axis and connected to a crankshaft of an IC engine; at least a second rotatable pulley; a transmission belt wound on said first and second pulleys and having a belt back; a friction pulley connected to an engine accessory and rotatable about a second fixed axis parallel to said first axis; and a friction wheel, which is rotatable about a third axis parallel to said first and second axes and has a friction surface co-operating with said friction pulley and a back of said belt at a section thereof that is wound around said first pulley, said friction pulley comprising a friction annulus softer than, and co-operating with, said friction surface of said friction wheel, characterized in that said friction wheel is made of metal and said friction surface is knurled.
2 . A belt drive as claimed in claim 1 , characterized in that said friction wheel is made of pressed steel.
3 . A belt drive as claimed in claim 1 , characterized in that the friction surface of the friction wheel has a knurled pattern formed by at least one sheaf of rectilinear impressions inclined with respect to the friction surface generatrices.
4 . A belt drive as claimed in claim 3 , characterized in that said knurling pattern includes two mutually inclined sheaves of rectilinear impressions intersecting each other to form adjacent rhombuses.
5 . A belt drive as claimed in claim 4 , characterized in that the two sheaves are inclined in opposite directions with respect to the generatrices of the friction surface.
6 . A belt drive as claimed in claim 3 , characterized in that each impression forms with the generatrices of said friction surface an angle ranging from 15° to 75°.
7 . A belt drive as claimed in claim 6 , characterized in that said angle ranges between 15° and 45°.
8 . A belt drive as claimed in claim 6 , characterized in that said angle is 30°.
9 . A belt drive as claimed in claim 5 , characterized in that the impressions of the respective sheaves mutually intersect to form an angle of 60°.
10 . A belt drive as claimed in claim 2 , characterized in that said impressions have, in cross-section, a profile including two flanks which are smoothly connected with a top line.
11 . A belt drive as claimed in claim 10 , wherein said flanks form with the top line rounded transition areas.
12 . A belt drive as claimed in claim 11 , characterized in that said transition areas have a curvature radius greater than 0.05 mm.
13 . A belt drive as claimed in claim 11 , characterized in that said transition areas have a curvature radius of about 0.1 mm.
14 . A belt drive as claimed in claim 10 , characterized in that the cross-section profile of said impressions includes a rounded a bottom line, said flanks being flex-shaped and smoothly connected to said bottom line.
15 . A belt drive as claimed in claim 10 , wherein the ratio A/P between a width A and a pitch P of said impressions ranges from 0.15 to 0.5.
16 . A belt drive as claimed in claim 15 , wherein said ratio A/P is about 0.25.
17 . A belt drive as claimed in claim 10 , wherein the ratio A/D between width A and depth D of said impressions ranges from 5 to 10.
18 . A belt drive as claimed in claim 17 , wherein said ratio A/D is about 7.5.
19 . A belt drive as claimed in claim 16 , characterized in that said pitch P, width A and depth D of said projections are about 1.2, 0.3 and 0.04 mm, respectively.
20 . A belt drive as claimed in claim 10 , characterized in that said impressions have a substantially V-shaped profile in cross section.
21 . A belt drive as claimed in claim 20 , characterized in that the ratio A/D between width A and depth D of said impressions ranges from 0.5 to 10.
22 . A belt drive as claimed in claim 10 , characterized in that said impressions have a substantially rectangular profile in cross section.
23 . A belt drive as claimed in claim 20 , characterized in that the ratio A/D between width A and depth D of said impressions ranges from 1 to 10.
24 . A belt drive as claimed in claim 1 , characterized in that at least one between said friction annulus and said back is embossed.
25 . A belt drive as claimed in claim 24 , characterized in that at least one between said friction annulus and said back comprises an antiwear surface layer.
26 . A belt drive as claimed in claim 25 , characterized in that said antiwear surface layer comprises a fabric.
27 . A belt drive as claimed in claim 26 , characterized in that said fabric is a cotton/polyester knitted fabric.
28 . A belt drive as claimed in claim 26 , characterized in that said fabric comprises fibres made of polymeric material with high thermal resistance and high toughness.
29 . A belt drive as claimed in claim 26 , characterized in that said antiwear surface layer comprises an anti-abrasive layer external to said fabric.
30 . A belt drive as claimed in claim 29 , characterized in that said anti-abrasive layer comprises a polytetrafluoroethylene-based compound.
31 . A belt drive as claimed in claim 1 , characterized in that said friction annulus is made of elastomeric material.
32 . A belt drive as claimed in claim 31 , characterized in that said friction annulus has a hardness of 85 to 99 Shore A.
33 . A belt drive as claimed in claim 32 , characterized in that said friction annulus has a hardness of about 94 Shore A.
34 . A belt drive as claimed in claim 1 , characterized in that said third axis is mobile for decoupling said friction pulley from said belt.