Friction gear transmission systems or components – With lubrication
Reexamination Certificate
2000-09-12
2001-10-23
Herrmann, Allan D. (Department: 3682)
Friction gear transmission systems or components
With lubrication
C476S010000, C476S014000, C476S042000
Reexamination Certificate
active
06306060
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the supply of cooling fluid to the rollers of hydraulically actuated roller assemblies. It relates especially, but not exclusively, to the supply to rollers that must rotate at high speed and under high loading from two opposed surfaces which contact the roller at opposite ends of a diameter, so squeezing the roller between them. The invention thus relates particularly to the rollers used in the variators of the toroidal-race rolling traction type.
2. Discussion of Prior Art
This invention has particular, though not exclusive, application to continuously-variable-ratio transmissions (“CVT's”) of the toroidal-race rolling-traction type, and in particular to roller-control units of the kind by which the orientation of the traction-transmitting rollers may be controlled hydraulically, by means of the direct connection of the carriage of each roller to a piston, movable within a hydraulic cylinder connected to a controlled source of variable fluid pressure.
In such variators, the cooling of the discs and rollers and of the traction fluid is always an important consideration. As is well understood in the art, the fluid must always be present in the form of a thin film between the rollers and the toroidal races of the discs, to prevent metal-to-metal contact, so that traction is transmitted between discs and rollers by way of shear generated within the thin film. In practice the waste heat generated within the film, in an instant during which it is transmitting traction, is quickly dissipated an instant later when that particular volume of fluid will have moved clear of the “nip” between race and rollers. As to the discs, the heat conductivity of the hardened steel they are made of is not particularly high. However, the total area of each disc is high compared with the areas of instantaneous contact with its co-operating rollers, and the location of those areas of contact tends to change frequently because the ratio transmitted by the variator is also continually changing. Conventional lubrication techniques are therefore usually sufficient to prevent overheating of the discs.
With the rollers it is different, however: the heat input is always concentrated at the circumference. The concentration of the heat input is aggravated by the fact that the roller rim is, in practice, rounded to a cross-radius, so that the instantaneous “contact” between roller and race, by way of the intervening film of traction fluid, tends to be small when measured in a direction parallel to the roller axis.
British patent application number GB-A-2282196 discloses a roller assembly for a CVT in which cooling fluid is provided to the roller surface via a hollow roller support stem. The fluid is passed through a single outlet positioned opposite the roller outer surface and bathes the roller in cooling fluid.
International application no. PCT GB 97/37156 discloses, as shown in
FIG. 1
of the accompanying drawings, an improved arrangement for the supply of cooling fluid to rollers in a CVT system. A roller assembly
10
comprises a roller
12
with bearings
14
,
16
, mounting the roller
12
for rotation on a central shaft
18
in a supporting carriage
20
. The roller assembly
10
is secured to a hollow stem
22
which in turn is supported in spherical joint
24
within a piston
26
positioned within a cylinder
28
. The cylinder and piston between themselves define a chamber having two portions
30
a
,
30
b
. Movement of the piston
26
is achieved by varying the pressure of hydraulic fluid supplied to each chamber
30
a
,
30
b
in a manner well known to those skilled the art and therefore not described in detail herein. Cooling fluid is supplied from a source thereof
32
to passage
34
extending along the stem
22
and thence to a pair of outlets
36
before being sprayed onto the surface of roller
12
. Before passing into passageway
34
the lubricating fluid enters a chamber
38
into which the proximal end
40
of the piston/stem assembly
26
,
34
extends. As a consequence of this arrangement, it will be appreciated that lubricating fluid pressure will act against proximal end
40
and this might affect the accurate positioning of the roller assembly
10
. A small movement effect will also be present due to the existence of surfaces
42
within passageway
34
. In this arrangement, the hydraulic fluid used to control the piston position is supplied to chamber
30
a
,
30
b
from the same source
32
as that used to supply lubrication fluid to the roller.
Whilst the above-discussed arrangements provides a perfectly adequate roller control system, problems can arise in connection with the efficient supply of cooling fluid to the roller, particularly when its flow path is through the roller actuation piston. In such cases a small bore supply is often used and multiple bends are encountered before the fluid reaches the roller. The combination of these two features can cause undesirable pressure losses and reduce the effectiveness of the cooling system.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a roller control unit which reduces and possibly eliminates the problems associated with the above-mentioned control unit.
Accordingly, the present invention provides
a roller control unit for a continuously-variable-ratio transmission comprises:
a cylinder having a cylinder wall; and
a piston, within the cylinder and being axially translatable therealong;
a chamber, formed by said cylinder and piston for receiving hydraulic fluid which, in operation causes said piston to move between first and second axially displaced positions; and
a lubrication supply passage, for supplying lubrication to a roller connected to said piston for movement therewith; characterised in that said lubrication supply passage comprises a chamber formed between said piston and cylinder wall and one or more radially extending passageways through said piston, each having a first end in fluid communication with said chamber and having a second end in communication with said roller.
Preferably, said chamber comprises a recess in the cylinder wall.
Conveniently, said chamber comprises an annular recess.
Advantageously, the control unit further includes seal means in said cylinder wall at each axial end of said chamber and acting between the cylinder wall and said piston.
Alternatively, the chamber may comprise a recess in the outer surface of the piston.
Conveniently, the alternative chamber may comprise an annular recess.
In the alternative arrangement, the roller control unit further includes seal means at axially displaced positions on the piston and acting between the piston and the cylinder wall.
Preferably, the piston comprises a hollow piston having a cavity therein in which one or more of the second ends of said one or more passageways are in fluid communication therewith.
Communicatively, the roller control unit further includes a roller support stem having an axially extending lubrication supply duct and in which said duct includes a first end in fluid communication with said cavity for receiving lubrication fluid therefrom.
Preferably, the cavity comprises an open ended cavity having an open end and said unit further includes a plug fixed relative to said cylinder and extending into said open end of said piston, thereby to define said cavity between itself and an end face of said piston.
Advantageously, said plug is a sliding fit within said cavity and, in operation, said piston slides over said plug thereby to define a cavity of variable volume.
Advantageously, said chamber is formed at least in part by said plug.
In a preferred arrangement the chamber comprises two portions, said first portion being bounded by the cylinder and piston and the second portion being bounded by said cylinder, piston and a plug fixed relative to said cylinder and extending into an axially extending cavity within said piston.
REFERENCES:
patent: 3828618 (1974-08-01), Sharpe et al.
patent: 5564993 (1996-10-01), Robinson
patent:
De Freitas Andrew Damian
Dutson Brian Joseph
Herrmann Allan D.
Nixon & Vanderhye P.C.
Torotrak (Development) Limited
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