BACKGROUND OF THE INVENTION
1. Field of Invention
[0001] The invention relates to a roller rocker arm type valve train.
2. Description of Related Art
[0002] A roller rocker arm type valve train disclosed in
JP-A-2000-34907 is well known as the valve train employed for an internal combustion engine.
[0003] The aforementioned roller rocker arm type valve train includes an inner roller and
an outer roller (formed into a double ring structure) which are coaxially supported
at a roller pin. An outer circumferential surface of the outer roller is pressed by
a cam so as to operate a valve (intake or exhaust valve). This may reduce the friction
force generated between the rocker arm (the inner roller and the outer roller) and
the cam, thus improving the fuel consumption rate and the like.
[0004] In the valve train to which the above-described roller rocker arm is applied, an
alignment error is likely to occur in the process of manufacturing or operating conditions.
The contact surfaces of the cam and the outer roller in the axial direction are, thus,
relatively inclined to a slight degree. If the cam abuts on the outer roller in the
state where both the cam and the outer roller are inclined, the contact surface of
the outer roller tends to adapt itself to the contact surface of the cam owing to
its high support rigidity. So-called edge loads occur at each end portions of the
inner circumferential surface of the outer roller that inclines to adapt to the contact
surface of the cam and the outer circumferential surface of the inner roller in the
axial direction.
[0005] In case of a thick oil film formed between sliding contact surfaces of the rollers
under the operation condition at high speed and low oil temperature, the aforementioned
inclination of the outer roller may be covered by the thick oil film. However, in
case of a thin oil film formed under the operation condition at low speed and high
oil temperature, the inclination of the outer roller cannot be covered by the thin
oil film. The frequency of direct contact between the sliding surfaces is increased,
thus increasing the friction loss.
SUMMARY OF THE INVENTION
[0006] It is an object of the invention to provide a roller rocker arm type valve train
that prevents generation of edge loads by avoiding increase in the frequency of direct
contact between contact surfaces of the outer roller and the inner roller so as to
reduce the friction loss while maintaining fluid lubrication under an operation condition
at low speed and high oil temperature where the oil film formed between the sliding
surfaces becomes thin.
[0007] The roller rocker arm type valve train according to the invention is provided with
an inner roller that is rotatably supported at a roller pin fixed to a rocker arm
and an outer roller that is rotatably supported around the inner roller coaxially
thereto. In the roller rocker arm type valve train, an inclined surface is formed
on an outer peripheral edge of at least one of an outer circumferential surface of
the inner roller and an inner circumferential surface of the outer roller in a predetermined
range along a radial direction thereof.
[0008] In the roller rocker arm type valve train as aforementioned, the inner roller and
the outer roller are assembled into a double ring structure.
[0009] Assuming that an alignment error has occurred in the process of manufacturing or
operation conditions, and contact surfaces of the cam and the outer roller in the
axial direction are relatively inclined, in other words, the outer roller is inclined
upon its abutment on the cam, the thick oil film formed between the sliding surfaces
under the operation condition at high speed and low oil temperature may cover such
inclination of the outer roller. Accordingly, the fluid lubrication for the contact
surfaces between the outer roller and the inner roller can be maintained.
[0010] Meanwhile, if the oil film is thin under the operation condition at low speed and
high oil temperature, the inclination of the outer roller cannot be covered. Accordingly
the frequency of the direct contact between the sliding surfaces is increased, thus
increasing the friction loss.
[0011] In the roller rocker arm type valve train according to the invention, the inclined
surfaces are formed on the outer peripheral edge of at least one of the outer circumferential
surface of the inner roller and the inner circumferential surface of the outer roller
along the radial direction of the roller such that a total width of the inclined surfaces
is within a predetermined range Even if the outer roller is inclined, edge loads in
the axial direction at the end portions of the inner circumferential surface of the
outer roller and the outer circumferential surface of the inner roller are not increased,
preventing the oil film from running out. This makes it possible to maintain the fluid
lubrication under the operation condition at low speed and high oil temperature, and
to prevent increase in the friction loss owing to the increase in the frequency in
the direct contact between the sliding surfaces of the inner and the outer rollers.
[0012] The inclined surfaces formed on at least one of the outer circumferential surface
of the inner roller and the inner circumferential surface of the outer roller may
be formed as a crowning surface, a tapered surface, a chamfer surface, or an arbitrary
combination thereof.
[0013] In the roller rocker arm type valve train according to the invention, the inclined
surface is formed such that a total width of the inclined surfaces is in a range between
15% and 45% of an outer diameter of the roller.
[0014] If the width of the inclined surface which is formed on at least one of the outer
circumferential surface of the inner roller and the inner circumferential surface
of the outer roller is relatively small, the edge loads cannot be sufficiently reduced.
Meanwhile if the width of the inclined surface is relatively large, the average surface
pressure increases owing to the decrease in the contact width. There may be a concern
with respect to the direct contact between the outer and the inner rollers at the
portion other than the outer peripheral edge of the roller.
[0015] In the roller rocker arm type valve train according to the invention, the inclined
surface is formed such that the total width of the inclined surfaces is in a predetermined
range. Accordingly, the significant effect for reducing the friction loss may be obtained.
[0016] In the roller rocker arm type valve train according to the invention, the increase
in the frequency of direct contact between the outer and the inner rollers is avoided
so as to prevent generation of the edge load as well as to provide the effect for
reducing the friction loss while maintaining the fluid lubrication under the operation
condition at low speed and high oil temperature where the oil film formed between
the sliding surfaces becomes thin.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The foregoing and further objects, features and advantages of the invention will
become apparent from the following description of preferred embodiments with reference
to the accompanying drawings, wherein like numerals are used to represent like elements
and wherein:
Fig. 1 is a front view showing a structure of a roller rocker arm type valve train
according to an embodiment of the invention;
Fig. 2 is a sectional view taken along lines 2-2 of Fig. 1, showing a structure of
a main portion of the roller rocker arm type valve train according to the embodiment
of the invention;
Fig. 3 is a graph showing a relationship between an oil temperature and a friction
loss at a slide bearing;
Fig. 4 is a graph showing a relationship between a width of an inclined surface formed
on the roller and the friction force;
Fig. 5 is a sectional view corresponding to Fig. 2, showing another example of the
inclined surface of the roller rocker arm type valve train according to the invention;
and
Fig. 6 is a sectional view corresponding to Fig. 2, showing another example of the
inclined surface of the roller rocker arm type valve train according to the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0018] Fig. 1 is a front view showing a structure of a roller rocker arm type valve train
10 according to an embodiment of the invention. Fig. 2 is a sectional view taken along
lines 2-2 of Fig. 1 showing the roller rocker arm type valve train 10.
[0019] The roller rocker arm type valve train 10 is provided with a rocker arm 12 having
one end portion supported at a pivot portion 14 such that the other top portion is
moveable up and down. A pressure portion 16 at the top portion of the rocker arm 12
abuts on a cap 20 crowned on an axial top portion of a valve 18 (for example, an intake
valve or an exhaust valve).
[0020] An inner roller 22 and an outer roller 24 are attached to the center of the rocker
arm 12 in the longitudinal direction. The inner roller 22 is rotatably supported at
a roller pin 26 fixed to the rocker arm 12. The outer roller 24 is rotatably supported
around the inner roller 22 coaxially thereto. The inner roller 22 and the outer roller
24 are assembled into a double ring structure. The outer roller 24 is disposed to
be in contact with a cam 28 that presses the outer circumferential surface of the
outer roller 24. The pressure portion 16 of the rocker arm 12 then applies a pressure
force to the cap 20 crowned on the valve 18 so as to be operated.
[0021] Referring to Fig. 2, crowning surfaces 30 as the inclined surface are formed on the
outer peripheral edge of the outer circumferential surface of the inner roller 22
in a predetermined range along the roller radial direction. Chamfers 32 are further
formed at edge portions of the crowning surfaces 30, respectively.
[0022] In the roller rocker arm type valve train of the embodiment, the curvature R of the
crowning surface 30 is approximately 30 mm. The total width of the width K of the
crowning surface 30 and the width M of the chamfer 32 is 33% of the outer diameter
of the inner roller 22 with the cut amount δ of the crowning surface 30 of approximately
0.024 mm.
[0023] Operations of the roller rocker arm type valve train according to the embodiment
of the invention will be described hereinafter.
[0024] The roller rocker arm type valve train 10 includes the inner roller 22 and the outer
roller 24 which are assembled into a double ring structure.
[0025] Assuming that the axial contact surfaces of the cam 28 and the outer roller 24 are
relatively inclined owing to an alignment error that has occurred in the process of
manufacturing or operating conditions, that is, the outer roller 24 is inclined upon
its abutment on the cam 28, if the oil film formed between the sliding surfaces is
thick under the operation condition at high speed and low oil temperature, such inclination
of the outer roller 24 may be covered by the oil film. Accordingly, the fluid lubrication
between the outer roller 24 and the inner roller 22 may be maintained.
[0026] Meanwhile, if the oil film is thin in the aforementioned state under the operation
condition at low speed and high oil temperature, the thin oil film cannot cover the
inclination of the outer roller 24. The frequency of direct contact between the sliding
surfaces of the outer and the inner rollers is increased, thus increasing the friction
loss. Fig. 3 shows the experimental results representing the increase in the friction
loss as increase in the oil temperature.
[0027] In the roller rocker arm type valve train 10 according to the invention, the crowning
surfaces 30 and the chamfers 32 that form the inclined surface are made on the outer
peripheral edge of the outer circumferential surface of the inner roller 22 in the
predetermined range along the roller radial direction. If the outer roller 24 is inclined,
each edge load at the axial ends of the inner circumferential surface of the outer
roller 24 and the outer circumferential surface of the inner roller 22 is not increased,
preventing the oil film from running out. This makes it possible to maintain the fluid
lubrication under the operation condition at low speed and high oil temperature while
keeping the friction resistance as the advantageous feature of the slide bearing.
Accordingly the increase in the friction loss owing to the increase in the frequency
of direct contact between the sliding surfaces of the outer and the inner rollers
may be prevented.
[0028] If the width of the inclined surface (the crowning surface 30 and the chamfer 32)
is relatively small, the edge load cannot be reduced sufficiently. Meanwhile, if the
width of the inclined surface is relatively large, the average surface pressure is
increased owing to the decrease in the contact width. There may be a concern with
respect to the direct contact at the portion other than the outer peripheral edge.
It is preferable to form the inclined surface such that the total width thereof is
in the range between 15% and 45% of the outer diameter of the roller. Fig. 4 shows
the experimental results with respect to the influence of the change in the width
of the inclined surface (the crowning surface 30) to the friction force. The significant
friction loss reducing effect may be obtained especially when the total width of the
inclined surface (crowning surface, tapered surface, chamfer surface) is in the range
between 15% and 45% of the outer diameter of the roller.
[0029] In the roller rocker arm type valve train as aforementioned, the crowning surfaces
30 and chamfers 32 at both edge portions thereof are formed as the inclined surface.
However, the chamfers 32 do not have to be necessarily provided.
[0030] In the roller rocker arm type valve train as described above, the crowning surfaces
30 as the inclined surface are formed on the outer circumferential surface of the
inner roller 22. However, the inclined surface may be formed on the inner circumferential
surface of the outer roller 24. Alternatively, the crowning surfaces 30 may be formed
both on the outer circumferential surface of the inner roller 22 and the inner circumferential
surface of the outer roller 24, respectively by setting the cut amount δ to half.
[0031] The inclined surface may include not only the crowning surfaces 30 but also simple
tapered surfaces, chamfer surfaces, or arbitrary combinations thereof.
[0032] Referring to Fig. 5, the inclined surface may include tapered surfaces 42 and chamfers
44 formed on the outer circumferential surface of an inner roller 40 at an inclined
angle of θ and the cut amount of δ. Alternatively as shown in Fig. 6, only tapered
surfaces 48 are formed on the outer circumferential surface of an inner roller 46
as the inclined surface at an inclined angle of θ and the cut amount of δ.
1. A roller rocker arm type valve train (10) including an inner roller (22) that is rotatably
supported at a roller pin (26) fixed to a rocker arm (12) and an outer roller (24)
that is rotatably supported around the inner roller coaxially thereto, characterized in that inclined surfaces are formed on an outer peripheral edge of at least one of an outer
circumferential surface of the inner roller (22) and an inner circumferential surface
of the outer roller (24) in a predetermined range along a radial direction of the
roller.
2. The roller rocker arm type valve train according to claim 1, characterized in that the inclined surface comprises at least one of a crowning surface (30), a tapered
surface (42, 48), a chamfer surface (32, 44), and combinations thereof.
3. The roller rocker arm type valve train according to claim 1 or 2, characterized in that the inclined surface is formed such that a total width of the inclined surface is
in a range between 15% and 45% of an outer diameter of the roller.
1. Rollenkipphebel-Ventiltrieb (10), der eine innere Rolle (22), die drehbar an einer
Rollenspindel (26) gelagert ist, die an einem Kipphebel (12) befestigt ist, und eine
äußere Rolle (24) einschließt, die drehbar um die innere Rolle und koaxial zu dieser
gelagert ist, dadurch gekennzeichnet, dass schräge Oberflächen an einem äußeren Umfangsrand mindestens einer äußeren Umfangsfläche
der inneren Rolle (22) und einer inneren Umfangsfläche der äußeren Rolle (24) in einem
vorgegebenen Bereich entlang einer radialen Richtung der Rolle ausgebildet sind.
2. Rollenkipphebel-Ventiltrieb nach Anspruch 1, dadurch gekennzeichnet, dass die schräge Oberfläche mindestens eine kronige Oberfläche (30), eine kegelförmige
Oberfläche (42, 48), eine gefaste Oberfläche (32, 44) und Kombinationen davon aufweist.
3. Rollenkipphebel-Ventiltrieb nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass die schräge Oberfläche so ausgebildet ist, dass die Gesamtbreite der schrägen Oberfläche
in einem Bereich zwischen 15 % und 45 % des Außendurchmessers der Rolle liegt.
1. Train de soupape du type à culbuteur à rouleau (10) comprenant un rouleau interne
(22) qui est supporté de façon rotative au niveau d'un axe de rouleau (26) fixé sur
un culbuteur (12) et un rouleau externe (24) qui est supporté de façon rotative autour
du rouleau interne coaxialement à celui-ci, caractérisé en ce que des surfaces inclinées sont formées sur un bord périphérique externe d'au moins une
surface circonférentielle externe du rouleau interne (22) ou une surface circonférentielle
interne du rouleau externe (24) dans une plage prédéterminée le long d'une direction
radiale du rouleau.
2. Train de soupape du type à culbuteur à rouleau selon la revendication 1, caractérisé en ce que la surface inclinée comprend au moins une surface bombée (30), une surface conique
(42, 48), une surface chanfreinée (32, 44), ou des combinaisons de celles-ci.
3. Train de soupape du type à culbuteur à rouleau selon la revendication 1 ou 2, caractérisé en ce que la surface inclinée est formée de telle sorte qu'une largeur totale de la surface
inclinée est dans une plage entre 15% et 45% d'un diamètre externe du rouleau.