Technical Field
[0001] The present disclosure generally relates to internal combustion engines, in particular,
to a cam follower for an internal combustion engine.
Background
[0002] Various technologies are known for adjusting, for example, the opening and closing
of inlet valves and outlet valves of internal combustion engines.
[0003] Generally, a camshaft of the internal combustion engine comprises a plurality of
cams, and the opening and closing of the inlet valves and outlet valves is controlled
by a plurality of cam followers, which trace a movement of an associated cam. Such
a cam follower includes a roll that rolls on the cam. The movement of the roll on
the cam is transmitted to, for example, an inlet valve or an outlet valve by a rod
connected to the cam follower.
[0004] The present disclosure is directed, at least in part, to improving or overcoming
one or more aspects of prior systems.
Summary of the Disclosure
[0005] According to one aspect, a cam follower for an internal combustion engine comprises
a bracket, an axis mounted on the bracket and a roll rotatably mounted on the axis.
The roll extends in a longitudinal direction with a wall thickness and includes an
outer surface, an inner surface, a first end face, a second end face and a relief
chamfer extending radially inward from at least one of the first end face and the
second end face to the inner surface. The relief chamfer has a length in the longitudinal
direction and a height in the radial direction such that a ratio of the product of
the length and the height to the square of the wall thickness is greater than about
0.05.
[0006] According to another aspect, an internal combustion engine comprises a camshaft including
at least one cam and at least one cam follower. The at least one cam follower comprises
a bracket, an axis mounted on the bracket and a roll rotatably mounted on the axis.
The roll extends in a longitudinal direction with a wall thickness and includes an
outer surface, an inner surface, a first end face, a second end face and a relief
chamfer extending radially inward from at least one of the first end face and the
second end face to the inner surface. The relief chamfer has a length in the longitudinal
direction and a height in the radial direction such that a ratio of the product of
the length and the height to the square of the wall thickness is greater than about
0.05.
[0007] Other features and aspects of the present disclosure will be apparent from the following
description and the accompanying drawings.
Brief Description of the Drawings
[0008]
Fig. 1 is a schematic view of an exemplary cam follower assembly for an internal combustion
engine;
Fig. 2 is a schematic cross-sectional view of an exemplary cam follower for an internal
combustion engine;
Fig. 3 is a detailed view of a part of the cam follower of Fig. 2; and
Fig. 4 is a detailed view of a part of another exemplary cam follower according to
the present disclosure.
Detailed Description
[0009] The following is a detailed description of exemplary embodiments of the present disclosure.
The exemplary embodiments described herein are intended to teach the principles of
the present disclosure, enabling those of ordinary skill in the art to implement and
use the present disclosure in many different environments and for many different applications.
Therefore, the exemplary embodiments are not intended to be, and should not be considered
as a limiting description of the scope of protection. Rather, the scope of protection
shall be defined by the appended claims.
[0010] The present disclosure may be based in part on the realization that, when a roll
having a cylindrical body is rotatable mounted on a corresponding axis of a cam follower,
a force applied from the camshaft to the cylindrical roll may result in an application
of end pressures on the ends of the cylindrical roll. Further, if the roll is mounted
on the axis via a bushing, end pressures may also be applied to the ends of the bushing.
[0011] According to the present disclosure, the end pressures applied to the ends of the
roll and the optional bushing can be reduced or avoided by providing a recessed portion
adjacent to the ends of the roll such that the ends of the roll are not in direct
contact with the axis or the optional bushing.
[0012] Further, the present disclosure may be based at least in part on the realization
that, when a bushing is mounted between the roll and the axis, a recess formed in
the bushing can also serve to relieve the ends of the bushing and/or the associated
roll.
[0013] By providing the above-described recesses, the stiffness of the roll and/or the bushing
near the ends of the same can be reduced to reduce or avoid pressing of the ends of
the roll and/or the bushing.
[0014] Referring now to the drawings, Fig. 1 schematically shows a cam follower assembly
for an internal combustion engine. As shown in Fig. 1, the internal combustion engine
includes a camshaft 10 having a plurality of cams 12, 14, 16. A plurality of cam followers
18, 20, 22 are arranged to trace the movement of cams 12, 14, 16 by contacting the
same.
[0015] Cam 12 may operate, for example, an inlet valve arranged in an inlet of a combustion
chamber of a cylinder of the internal combustion engine via cam follower 18. Cam 14
may operate, for example, an outlet valve arranged in an outlet of the combustion
chamber via cam follower 20. Cam 16 may operate, for example, an injection device
for injecting fuel into the combustion chamber via cam follower 22. It should be appreciated
that the above example is not intended to limit the present disclosure to the configuration
shown in Fig. 1, and that one or more of cams 12, 14, 16 and cam followers 18, 20,
22 may be omitted.
[0016] Cam follower 18 comprises an operating lever formed, for example, as an oscillating
arm which may trace the stroke of cam 12 via a roll 25 supported on a bracket 26 and
transmit the same to the inlet valve via a rod 28.
[0017] In a similar manner, cam follower 20 is provided with an operating lever including
a bracket 30 and may trace the stroke of cam 14 via a roll 29 supported on bracket
30 and transmit the same to the outlet valve via a rod 32.
[0018] The stroke of cam 16 may be traced by a roll 33 mounted on a bracket 34 arranged
at the end of an operating lever of cam follower 22 and transmitted to the injection
device by a piston 24.
[0019] At their opposite ends, the operating levers are rotatably supported, for example,
on disks 36, 38, 40. The timings of the inlet valve and the outlet valve and, optionally,
the injection timing may be controlled by adjusting, for example, the positions of
disks 36, 38, 40, which may be formed as eccentrics.
[0020] Referring now to Fig. 2, cam follower 18 is shown in more detail. It should be appreciated
that the configuration of cam followers 20, 22 may be identical to the configuration
of cam follower 18.
[0021] As shown in Fig. 2, cam follower 18 includes bracket 26, roll 25, a bushing 27 and
an axis 23 mounted on bracket 26.
[0022] Axis 23 is fixedly mounted in bores of bracket 26, for example, by press fitting
or the like. Bushing 27 is mounted on axis 23. In addition, roll 25 is rotatably mounted
on bushing 27 in a known manner. It will be appreciated that, in other embodiments,
bushing 27 may be omitted, and roll 25 may be directly mounted on axis 23. Roll 25
is configured to roll on cam 12 upon rotation of camshaft 10. When camshaft 10 rotates,
movement of roll 25 is transmitted to, for example, the inlet valve of the associated
cylinder via rod 28.
[0023] During operation of the internal combustion engine, roll 25 may receive impact forces
from cam 12. This may lead to end pressures being applied to the ends of roll 25.
[0024] In order to reduce or avoid wear of the components of cam follower 18 due to these
end pressures, roll 25 includes recesses formed at the ends of the same. In the exemplary
embodiment shown in Fig. 2, the recesses are formed as relief chamfers 41, 43. This
increases the flexibility of roll 25 near the ends of the same, and reduces the end
pressures applied to roll 25 and the optional bushing 27 during rotation of camshaft
10. In particular, it reduces or avoids pressing of the ends of roll 25 against the
ends of bushing 27 (or axis 23 in case bushing 27 is omitted) at a contact interface
42 formed between roll 25 and bushing 27 (or between roll 25 and axis 23 in case bushing
27 is omitted).
[0025] Referring to Fig. 3, roll 25 and the associated bushing 27 of cam follower 18 are
shown in more detail.
[0026] As shown in Fig. 3, roll 25 includes a hollow cylindrical body having an outer surface
25a, an inner surface 25b, a first end face 25c and a second end face 25d. Roll 25
extends along a longitudinal direction parallel to axis 23 with a length 1 from first
end face 25c to second end face 25d. Further, the hollow cylindrical body of roll
25 has a wall thickness t.
[0027] Similarly, bushing 27 is formed as a hollow cylindrical body and extends along the
longitudinal direction of axis 23 with the same length 1 as roll 25. It should be
appreciated that in other embodiments a length of bushing 27 can be different from
the length 1 of roll 25. Bushing 27 also includes an outer surface 27a, an inner surface
27b, a first end face 27c adjacent to first end face 25c of roll 25 and a second end
face 27d adjacent to second end face 25d of roll 25.
[0028] As shown in Fig. 3, contact interface 42 is formed between inner surface 25b of roll
25 and outer surface 27a of bushing 27. It should be appreciated that, in case bushing
27 is omitted, contact interface 42 will be formed between roll 25 and axis 23. As
used herein, the term "contact interface" refers to the surfaces of roll 25 and bushing
27 or axis 23 that are in contact during tracing of the movement of cam 12 by cam
follower 18. Further, the term "the contact interface includes a recess" is to be
understood such that a recess is formed in one of the surfaces forming the contact
interface. In other words, this term is to be understood such that a recess is formed
in at least one of inner surface 25b of roll 25 and outer surface 27a of bushing 27,
if present.
[0029] According to the present disclosure, the end pressure at the ends of roll 25 is reduced
or avoided by providing a recessed portion of contact interface 42 adjacent to first
and/or second end faces 25c, 25d of roll 25.
[0030] In the exemplary embodiment shown in Fig. 3, the recessed portion is formed as relief
chamfers 41, 43. Each of relief chamfers 41, 43 is formed at one end of roll 25 in
the longitudinal direction and extends radially inward from the associated one of
first and second end faces 25c, 25d to inner surface 25b of roll 25. It is obvious
that relief chamfers 41, 43 are formed to extend in the circumferential direction
of roll 25, i.e., as a continuous relief chamfer that extends circumferentially.
[0031] As shown in Fig. 3, each of relief chamfers 41, 43 has an extension d in the longitudinal
direction and an extension h in the radial direction. Herein, the extension d will
be referred to as the length of the chamfer, and the extension h will be referred
to as the height of the chamfer. Each of relief chamfers 41, 43 has a size such that
a ratio of the product of the length d and the height h to the square of the wall
thickness t is greater than about 0.05. In other words, the amount of material that
is removed when relief chamfers 41, 43 are formed has a predetermined relation to
the thickness of roll 25. According to the present disclosure, a substantial amount
of material is removed in order to achieve the desired flexibility of the ends of
roll 25. It will be readily appreciated by the skilled person that many different
combinations of the length d and the height h are possible to result in the desired
amount of material. Generally, as mentioned above, the relation may be such that the
ratio of the product of the length d and the height h to the square of the wall thickness
t is greater than a predetermined value, for example, about 0.05 or about 0.1. This
may be achieved, for example, by providing each of relief chamfers 41, 43 with a length
d that is greater than about 0.25 times the wall thickness t and/or a height h that
is greater than about 0.25 times the wall thickness t.
[0032] In the embodiment shown in Fig. 3, the recessed portion of the contact interface
42 is formed as relief chamfers 41, 43 including a chamfered surface extending from
end faces 25c, 25d to inner surface 25b. It will be readily appreciated that, in other
embodiments, the relief chamfers may be formed as a step, i.e., with a rectangular
cross-section. In other embodiments, the relief chamfers may include a curved surface,
for example, a concave or convex surface extending from end faces 25c, 25d to inner
surface 25b. The relation between the height h and the length d of the relief chamfers
to the wall thickness t, however, may be the same as for relief chamfers 41, 43. The
relief chamfers may be formed by machining end faces 25c, 25d in an appropriate manner,
for example, by end milling or the like.
[0033] Turning now to Fig. 4, another exemplary embodiment of cam follower 18 is shown in
more detail. In the embodiment shown in Fig. 4, roll 25 and bushing 27 substantially
have the same configuration as in the embodiment shown in Fig. 3 such that only the
differences will be described.
[0034] In the embodiment shown in Fig. 4, a further recessed portion of contact interface
42 is formed in bushing 27. In particular, chamfers 45, 47 are formed adjacent to
end faces 27c, 27d of bushing 27 to substantially face relief chamfers 41, 43 of roll
25. As shown in Fig. 4, each of chamfers 45, 47 may have a length in the longitudinal
direction that is the same as the length d of chamfers 41, 43. Of course, in other
embodiments, the length of chamfers 41, 43 and chamfers 45, 47 may be different. Chamfers
45 and 47 may have the same or a different shape as chamfers 41, 43. Similarly, each
of relief chamfers 45, 47 may have a size such that a ratio of the product of the
length and the height of the same to the square of the wall thickness of bushing 27
is greater than about 0.05, for example, greater than about 0.1. By providing additional
chamfers 45, 47, the end pressures at the ends of roll 25 due to impact forces received
from cam 12 (see Fig. 2) can be reduced even further. It should be appreciated that,
instead of being formed as chamfers 45, 47, the recesses in bushing 27 may also be
formed as steps or curved surfaces.
[0035] While in the exemplary embodiments described so far, the recessed portion of the
contact interface included chamfers 41, 43 or similar recesses formed in roll 25,
it is also contemplated that, in case bushing 27 is present, the recessed portion
of contact interface 42 may only be formed in bushing 27. In other words, no relief
chamfers 41, 43 or similar recesses may be formed in roll 25. However, it is preferable
that such recesses are formed in roll 25 adjacent to end faces 25c, 25d to achieve
the desired flexibility of roll 25.
Industrial Applicability
[0036] The industrial applicability of the systems and methods decribed herein will be readily
appreciated from the foregoing discussion.
[0037] In particular, with the structure of the roll of the cam follower according to the
present disclosure, it is possible to reduce or avoid end pressures being applied
to the ends of the roll due to impact forces received from the associated cam. This
may improve the durability and reliability of the cam follower including the roll.
[0038] Advantageously, relief chamfers are formed in the end faces of the roll to improve
the flexibility of the ends of the same. Further, in case the roll is mounted on the
corresponding axis via a bushing, the end pressures may further be reduced by also
providing relief chamfers in the bushing facing the relief chamfers of the roll. This
may be applied both to rolls with and without a crowned profile.
[0039] It will be appreciated that the foregoing description provides examples of the disclosed
systems and methods. However, it is contemplated that other implementations of the
disclosure may differ in detail from the foregoing examples. All references to the
disclosure or examples thereof are intended to reference the particular example being
discussed at that point and are not intended to imply any limitation as to the general
disclosure.
[0040] Recitation of ranges of values herein are merely intended to serve as a shorthand
method for referring individually to each separate value falling within the range,
unless otherwise indicated herein, and each separate value is incorporated into the
specification as if it were individually recited herein. All method steps described
herein can be performed in any suitable order, unless otherwise indicated or clearly
contradicted by the context.
[0041] Although the preferred embodiments of the present disclosure have been described
herein, improvements and modifications may be incorporated without departing from
the scope of the following claims.
1. A cam follower (18, 20, 22) for an internal combustion engine, comprising:
a bracket (26, 30, 34);
an axis (23) mounted on the bracket (26, 30, 34); and
a roll (25, 29, 33) rotatably mounted on the axis (23), the roll (25, 29, 33) extending
in a longitudinal direction with a wall thickness (t) and including an outer surface
(25a), an inner surface (25b), a first end face (25c), a second end face (25d) and
a relief chamfer (41, 43) extending radially inward from at least one of the first
end face (25c) and the second end face (25d) to the inner surface (25b),
wherein the relief chamfer (41, 43) has a length (d) in the longitudinal direction
and a height (h) in the radial direction such that a ratio of the product of the length
(d) and the height (h) to the square of the wall thickness (t) is greater than about
0.05.
2. The cam follower of claim 1, wherein the relief chamfer (41, 43) extends in the longitudinal
direction with a length (d) that is greater than about 0.25 times the wall thickness
(t).
3. The cam follower of claim 1 or 2, wherein the relief chamfer (41, 43) extends in the
radial direction with a height (h) that is greater than about 0.25 times the wall
thickness (t).
4. The cam follower of claim any one of claims 1 to 3,
wherein the ratio is greater than about 0.1.
5. The cam follower of any one of claims 1 to 4, further comprising a bushing (27) mounted
on the axis (23) and rotatably supporting the roll (25, 29, 33).
6. The cam follower of claim 5, wherein the bushing (27) includes a chamfer (45, 47)
extending radially outward from one of a first end face (27c) and a second end face
(27d) of the bushing (27), the chamfer (45, 47) having a length in the longitudinal
direction and a height in the radial direction such that a ratio of the product of
the length and the height to the square of a wall thickness of the bushing (27) is
greater than about 0.05, for example, greater than about 0.1.
7. The cam follower of claim 6, wherein the chamfer (45, 47) of the bushing (27) has
a length in the longitudinal direction that is substantially the same as the length
(d) of the relief chamfer (41, 43) of the roll (25, 29, 33).
8. The cam follower of claim 6 or 7, wherein the chamfer (45, 47) of the bushing (27)
includes at least one of a stepped portion or an arcuate surface.
9. The cam follower of any one of claims 1 to 8, wherein the relief chamfer (41, 43)
is a first relief chamfer (41) extending from the first end face (25c), the roll (25,
29, 33) further including a second relief chamfer (43) extending radially inward from
the second end face (25d).
10. The cam follower of claim 9, wherein the first relief chamfer (41) and the second
relief chamfer (43) have the same configuration.
11. The cam follower of any one of the preceding claims,
wherein the roll (25, 29, 33) has a crowned profile.
12. The cam follower of any one of the preceding claims,
wherein the relief chamfer (41, 43) includes a stepped portion.
13. The cam follower of any one of the preceding claims,
wherein the relief chamfer (41, 43) includes an arcuate surface.
14. The cam follower of claim 12, wherein the arcuate surface includes a concave and/or
convex surface extending from the at least one of the first end face (25c) and the
second end face (25d) to the inner surface (25b).
15. An internal combustion engine, comprising:
a camshaft (10) including at least one cam (12, 14, 16); and
at least one cam follower (18, 20, 22) according to any one of claims 1 to 14.