Piston ring

An oil control piston ring is described comprising a pair of axially spaced apart side rails, the side rails each having a radially outer periphery forming a rubbing face with a co-operating cylinder wall, an expander having portions which lie between the inner radially extending faces of the side rails and maintain the outer peripheral rubbing faces thereof in a spaced apart relationship characterized in that the radially inner peripheral edge of each side rail is connected by bridging members extending intermittently over at least a part of the inner circumferential length. The side rails and bridge members may be formed from a substantially flat bottomed "U-shaped" channel section.

The present invention relates to a piston ring and particularly to an 
oil-control ring for an internal combustion engine or compressor which 
comprises pistons reciprocating in an associated cylinder. 
Oil-control or oil scraper rings, as they are otherwise known, are used on 
pistons in engines to prevent or limit the passage of oil into the 
combustion chamber and so prevent excessive oil consumption. 
Multi-piece oil-control rings comprising two separate side rails which are 
held apart and urged against a cylinder wall by an expander spring are 
well known. A problem with this type of ring is that at high engine speeds 
the side rails may become unstable and vibrate resulting in high oil 
consumption. 
Another type of oil ring commonly used in an iron ring having a helicoidal 
expander spring contained in an annular groove in the rear face of the 
ring. This type of ring is expensive to produce and is difficult to make 
with an axial height of less than about 3mm. 
It is an object of the present invention to provide an oil ring which 
overcomes the above disadvantages and may be produced with an axial height 
of about 2mm or less. 
According to the present invention there is provided an oil-control piston 
ring comprising a pair of axially spaced apart side rails, the side rails 
each having a radially outer periphery forming a rubbing face with a 
co-operating cylinder wall, an expander having portions which lie between 
the inner, radially extending faces of the side rails and maintains the 
outer peripheral rubbing faces thereof in a spaced apart relationship 
characterised in that the radially inner peripheral edge of each side rail 
is connected by bridging members extending intermittently over at least a 
part of the inner circumferential length. 
Preferably, the side rails and bridging members forming the body of the 
ring may be formed from a single strip bent longitudinally into a "U 
shaped" channel section and, having portions of the bottom of the "U" 
removed to allow co-operating portions of the expander to lie between the 
side faces of the "U". 
Portions, in the form of tongues, formed from the bottom of the "U" section 
maybe bent between the side faces of the "U" to act as distance pieces to 
maintain the side faces in a spaced-apart relationship. 
Both the side rails and the expander spring may be made of steel. 
The side rails may not be parallel but may be divergent in the range of 
from 0.degree. to 20.degree. . If they diverge, the side rails may bear 
against the radial side faces of the co-operating piston ring groove in 
the piston and enhance control of the passage of both oil and gas past the 
piston ring. Furthermore, the effect of the side rails rubbing against the 
corners of the co-operating piston ring groove is to maintain the ring 
outer periphery in constant contact with the cylinder wall. 
Both the bridge members between the side/rails and the co-operating parts 
of the expander may be slotted, or otherwise perforated, to allow oil to 
drain away through the appropriated holes or slots in the co-operating 
piston ring groove in the piston. Similarly, the portions of the expander 
lying between the side rails may have appropriate slots or apertures to 
assist oil drainage. 
The body of the piston ring comprising the two side rails may be formed by 
NC techniques or other appropriate methods. The body of the piston ring 
may be formed to a desired non-circular profile. 
The rubbing faces of the piston ring body maybe treated by known techniques 
to improve, for example, the wear characteristics thereof. Such treatments 
may include nitro carburising or chromium plating, for example. 
Similarly, the sliding surface of the cylinder wall or liner maybe provided 
with a compatible coating. 
In order that the present invention maybe more fully understood an example 
will now be described by way of illustration only with reference to the 
accompanying drawings, of which:

Referring now th the drawings and where the same features are denoted by 
common reference numerals. 
A portion of the expander spring is shown at 10 and a portion of the ring 
body is shown at 12. The body 12 comprises a generally "U shaped", 
flat-bottomed channel section having a base 14, an upper side rail 16, a 
lower side rail 18 and bridge memebers 20 which are portions of the base 
14, joining the inner radial peripheries of the side rails. Intermittent 
portions of the base 14 of the "U" shaped channel are removed to leave 
apertures 22 which receive spring portions of the expander 10 as described 
below. Tongues 24 formed from the base 14 of the "U" channel are bent 
inwardly to lie between the inner faces 26, 28 of the side rails 16, 18 
and maintain the side rails in a spaced-apart relationship. Slots 30 are 
formed in the bridge members 20 for oil drainage purposes. The outer 
peripheries 32, 34 of the side rails 16, 18 form rubbing surfaces with an 
associated cylinder wall 38. The side rails 16, 18 may be parallel or may 
lie at an angle .beta. of between 0.degree. and 20.degree. to bear against 
the radial side faces 35 of the co-operating piston ring groove 36 of the 
piston `P`. The corners 37 of the groove 36, because of the divergence of 
the side rails, help to urge the peripheries 32,34 against the cylinder 
wall 38 to enhance control of oil consumption and blow by of combustion 
gases into the engine crankcase. The expander spring 10 comprises curved 
portions 42 which press against the inner faces 44 of the bridge members 
20, and spring portions 46 of generally castellated shape in plan view. 
The expander spring 10 comprises portions 48 which lie between the side 
rails 16, 18 of the body and act as spacers and base portions 50 which, at 
the edges 64 and 70, lie against the inner peripheries 52, 54 of the side 
rails in the region of the apertures 22 compressed between successive 
bridging members 20. When the piston ring 12 is compressed in the piston 
ring groove 36 for insertion into the engine cylinder, the expander 10, 
compressed by the piston ring body 12, exerts a pressure in the radial 
direction to urge the body 12 in an outwardly direction against the 
cylinder wall 38. In operation mutual sliding occurs between the axially 
extended edges 64,70 of the base portions 50 and the edges 52,54. Slots 56 
are formed in the portions 42, and which co-operate with the slots 30 for 
oil drainage. Oil drainage slots 58, 60 are also provided in the portions 
48 and base portions 50. Outwardly directed tabs 62 are formed at the 
expander circumferential ends and which abutt and lie inside one of the 
apertures 22, generally opposite the ends of the piston ring body 12.