U.S. patent application number 09/875649 was filed with the patent office on 2002-07-11 for mechanical lash adjuster apparatus for an engine cam.
Invention is credited to Pierik, Ronald J..
Application Number | 20020088415 09/875649 |
Document ID | / |
Family ID | 25366137 |
Filed Date | 2002-07-11 |
United States Patent
Application |
20020088415 |
Kind Code |
A1 |
Pierik, Ronald J. |
July 11, 2002 |
MECHANICAL LASH ADJUSTER APPARATUS FOR AN ENGINE CAM
Abstract
A rocker assembly has a first arm for following a first or
opening camshaft lobe, a second arm for following a second or
closing camshaft lobe, and a pivot axis of the rocker arm
therebetween. A captive roller follower on the first arm follows
the first lobe, and a slider on the second arm follows the second
lobe. An eccentric pivot pin for the rocker assembly is rotatable
to change the location of the pivot axis of the rocker assembly
with respect to the captive roller and the slider, to adjustably
set mechanical lash among these components after installation of
the rocker arm assembly into a variable valve mechanism of an
internal combustion engine.
Inventors: |
Pierik, Ronald J.;
(Rochester, NY) |
Correspondence
Address: |
Delphi Technologies, Inc.
P.O. Box 5052
Mail Code 480414420
Troy
MI
48007
US
|
Family ID: |
25366137 |
Appl. No.: |
09/875649 |
Filed: |
June 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09875649 |
Jun 6, 2001 |
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09755345 |
Jan 5, 2001 |
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6386161 |
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Current U.S.
Class: |
123/90.16 ;
123/90.15 |
Current CPC
Class: |
F01L 13/0021 20130101;
F01L 1/30 20130101; F01L 2013/0073 20130101; F01L 13/0026
20130101 |
Class at
Publication: |
123/90.16 ;
123/90.15 |
International
Class: |
F01L 001/34 |
Claims
What is claimed is:
1. A pivot pin disposable in first and second bores in first and
second elements, respectively, for pivoting of the second element
relative to the first element about a pivot axis, said pin
comprising first and second cylindrical elements having first and
second axes, respectively, said first and second axes being
parallel and offset from each other, such that rotation of said
pivot pin in said first and second bores changes the location of
said pivot axis with respect to said first element.
2. A pivot pin in accordance with claim 1 wherein said first
element is a frame and said second element is a rocker
assembly.
3. A rocker assembly pivotable about a pivot axis for following a
valve-opening cam lobe and a valve-closing cam lobe of a variable
valve mechanism in an internal combustion engine, the mechanism
having a frame for pivotably supporting the rocker assembly,
comprising: a) a first arm; b) a first follower on said first arm
for following said valve-opening cam lobe; c) a second arm disposed
at an included angle from said first arm; d) a second follower on
said second arm for following said valve-closing cam lobe; and e) a
pivot pin disposable in said frame and disposed in said rocker
assembly for pivoting of said rocker assembly about said pivot axis
with respect to said frame, said pin having first and second
cylindrical elements having first and second axes, respectively,
said first and second axes being parallel and offset from each
other, such that rotation of said pivot pin in said frame and said
rocker assembly changes the distance between said pivot axis and
said valve-opening and valve-closing cam lobes.
4. A rocker assembly in accordance with claim 3 wherein the
diameter of said first cylindrical element is greater than the
diameter of said second cylindrical element.
5. A rocker assembly in accordance with claim 3 wherein the
diameter of said second cylindrical element is greater than the
diameter of said first cylindrical element.
6. A rocker assembly in accordance with claim 3 wherein one of said
first and second cylindrical elements is a cylindrical pin
insertable through an off-center longitudinal bore in the other of
said cylindrical elements.
7. A variable valve mechanism for an internal combustion engine,
comprising a rocker assembly pivotable about a pivot pin having a
pivot axis for following a valve-opening cam lobe and a
valve-closing cam lobe of the variable valve mechanism in an
internal combustion engine, said mechanism having a frame for
pivotably supporting said rocker assembly, said pivot pin being
disposable in first and second bores in said frame and said rocker
assembly, respectively, for pivoting of said rocker assembly
relative to said frame about said pivot axis, said pin having first
and second cylindrical elements having first and second axes,
respectively, said first and second axes being parallel and offset
from each other, such that rotation of said pivot pin in said first
and second bores changes the location of said pivot axis with
respect to said frame and to said cam lobes.
8. An internal combustion engine comprising a variable valve
mechanism including a rocker assembly pivotable about a pivot pin
having a pivot axis for following a valve-opening cam lobe and a
valve-closing cam lobe, said mechanism having a frame for pivotably
supporting said rocker assembly, said pivot pin being disposed in
first and second bores in said frame and said rocker assembly,
respectively, for pivoting of said rocker assembly relative to said
frame about said pivot axis, said pin having first and second
cylindrical elements having first and second axes, respectively,
said first and second axes being parallel and offset from each
other, such that rotation of said pivot pin in said first and
second bores changes the location of said pivot axis with respect
to said frame and to said cam lobes.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a Continuation-In-Part of a pending U.S.
patent application, Ser. No. 09/755,345 filed Jan. 5, 2001.
TECHNICAL FIELD
[0002] The present invention relates to valve train systems for use
on internal combustion engines; more particularly, to devices for
controllably varying the lift and/or timing of valves in such
engines; and most particularly, to means for controlling the lash
between the camshaft lobes and a two-arm rocker arm in a valve
train system having cam lobes for both opening and closing an
individual valve.
BACKGROUND OF THE INVENTION
[0003] Devices for controllably varying the degree of lift and the
timing of opening and closing valves in internal combustion engines
are well known. See, for example, U.S. Pat. No. 5,937,809 issued
Aug. 17,1999 to Pierik et al., and U.S. Pat. No. 6,019,076 issued
Feb. 1, 2000 to Pierik et al., the relevant disclosures of which
are herein incorporated by reference. Such a device is referred to
in the art as a Variable Valve Mechanism (VVM). Such devices
commonly employ a rocker assembly which pivots with or about a
shaft or pin as a part of the apparatus train. Typically, the
rocker assembly has a first bearing element, for example a roller,
which follows the profile of a cam lobe during rotation of a
camshaft.
[0004] Conventional variable valve mechanisms typically include
many component parts, such as link arms, joints, pins, and return
springs, and are thus relatively complex mechanically. Return
springs are used typically to maintain the roller in contact with
the input cam lobe and to reduce mechanical lash as the input cam
lobe rotates from a high lift position to a low lift position. The
use of such return springs negatively impacts the durability of the
VVM and also may limit the operating range of the mechanisms,
thereby limiting the operation of the intake valve throttle control
system to a correspondingly-limited range of engine operation.
[0005] It is known to provide a second cam lobe per valve in place
of return springs for closing the valve, and to employ a two-armed
rocker assembly having appendages in contact with both the opening
lobe and the closing lobe at all times. The angular orientation
between the eccentrics of the opening and closing lobes on the
camshaft defines the rotational angle through which the valve is
open. Typically, the surface of the opening lobe is followed by a
roller mounted on the first rocker arm, and the surface of the
closing lobe is followed by a slider mounted on the second rocker
arm. Such an arrangement provides positive control of the rocker
assembly, and thus of the associated valve, at all positions of the
camshaft and obviates the need for return springs.
[0006] A practical problem can arise in manufacturing and
assembling such a two-lobe system. The stack-up of machining and
mounting tolerances among the rocker, the roller, the pivot shaft
for the rocker, the two cam lobes, and the camshaft mounting in the
engine head can be formidable. Ideally, the roller and slider are
just lightly in contact with the base circles of their respective
cam lobes during the non-lift portions of the rotational cycle. If
this lash relationship is too tight, i.e., zero or negative
clearance, the valve may not open or close properly, or the rocker
assembly may be stressed and distorted. If the lash relationship is
too loose, the rocker assembly may clatter or chatter undesirably
against the cam lobes, and the valve may not open fully or
precisely in time.
[0007] What is needed is a simple means whereby the valve train
components may be manufactured and assembled with loose tolerances
and then the lash relationship of the cam followers to the cam
lobes may be easily and precisely adjusted and retained after the
valve train is assembled.
[0008] It is a principal object of the present invention to provide
improved apparatus and method for setting the lash relationship of
cam followers to cam lobes in a two-cam, two-follower valve
train.
[0009] It is a further object of the invention to provide such a
system wherein the setting may be conveniently and accurately done
after the valve train is assembled.
SUMMARY OF THE INVENTION
[0010] Briefly described, a rocker assembly in accordance with the
invention has a first arm for following a first or opening camshaft
lobe and a second arm for following a second or closing camshaft
lobe, the arms being designated with respect to a pivot axis of the
rocker arm therebetween. Preferably, the first arm is provided with
a captive roller follower and the second arm is provided with a
captive sliding follower or slider. These elements are so selected
for economy because opening of the valve is more mechanically
demanding than is closing it. The pivot axis of the rocker
assembly, the surface of the roller at the contact point with the
opening lobe, and the surface of the slider at the contact point
with the closing lobe, taken together define a triangle in space
which must fit exactly into the space requirements of the valve
train assembly of each valve in a multi-cylinder engine. An
eccentric pivot pin for the rocker assembly is rotatable to change
the location of the pivot axis of the rocker assembly with respect
to the captive roller and the slider, thus to adjustably set
mechanical lash between these components and their respective cam
lobes after installation of the rocker assembly into a variable
valve mechanism of an internal combustion engine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] These and other features and advantages of the invention
will be more fully understood and appreciated from the following
description of certain exemplary embodiments of the invention taken
together with the accompanying drawings, in which:
[0012] FIG. 1 is an elevational view of a variable valve mechanism
for a double-lobe camshaft substantially as disclosed in the parent
application, Ser. No. 09/755,345, having some components omitted
for clarity, wherein the relative positions of the rocker assembly
pivot axis, roller, and slider are fixed and not adjustable;
[0013] FIG. 2 is an elevational view of a rocker assembly in
accordance with the invention, showing an eccentric pivot pin for
the rocker assembly; and
[0014] FIGS. 3 through 5 are isometric views of three separate
embodiments for eccentric pivot pins as shown in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] Referring to FIG. 1, there is shown a portion of a variable
valve mechanism 10, including an input camshaft 12 on which are
mounted valve-opening cam lobe 14 and valve-closing cam lobe 16.
The cam lobes are disposed in a predetermined angular relation
relative to each other and relative to central axis A of input
shaft 12. The paired lobes 14,16 (only one pair shown) are spaced
along the length of input shaft 12. Each respective pair of cam
lobes 14,16 is associated with a corresponding variable valve
mechanism 10 and with a corresponding cylinder of an internal
combustion engine (not shown). For purposes of clarity, a single
variable valve mechanism 10 is discussed hereafter.
[0016] Opening cam lobe 14 and closing cam lobe 16 rotate as
substantially one body with input shaft 12. The lobes are, for
example, affixed to or integral with shaft 12 which is received
within and extends through rotary bearing mounts disposed on the
head of the engine.
[0017] Output cam 18 is oscillatably disposed on shaft 12 for
actuation of a valve stem, tappet, or roller finger follower (none
shown) in known fashion via contact with eccentric surface 20. Cam
18 is pivotably connected to link 19 which is an elongate arm
member pivotably coupled at a first end to output cam 18 and at a
second and opposite end to rocker assembly 22. Rocker assembly 22
is coupled, for example, by pins 24, to link 19 and to a frame
member (omitted for clarity) about which it pivots upon axis B. The
frame member may be independently rotated to various positions
about shaft 12 to advance or retard the timing of valve opening, as
disclosed in the incorporated reference patents. Rocker assembly 22
may be thought of as comprising two arms 26,28. First arm 26
carries roller 30 which followingly engages valve-opening cam lobe
14 along eccentric surface 32 and is pivotably pinned to link 19 as
discussed above. As shaft 12 and lobe 14 rotate, roller 30 causes
assembly 22 to pivot about axis B, thus causing, via link 19,
output cam 18 to oscillate about shaft 12.
[0018] Rocker assembly 22 further includes a following slider pad
34 disposed on second arm 28 which slidingly engages valve-closing
cam lobe 16 along eccentric surface 36. Lobes 14,16 are so shaped
and oriented, and arms 26,28 are so oriented with respect to axis B
that followers 30,34 are substantially in contact with eccentric
surfaces 32,36, respectively at all times during rotation of shaft
12. Thus the action of rocker assembly 22 is fully controlled at
all times and does not require use of return springs to assure
proper motion. (In practice, the lash adjustment of the system
optimally provides for a rest clearance of about 0.001"between
slider 34 and surface 36.)
[0019] As noted above, there is little room for error in the
manufacture and installation of the components shown in FIG. 1, or
of the receiving engine head and VVM mounting components as well.
Assembly 22 must have roller 30 and slider 34 positioned accurately
with respect to axis B such that they just touch surfaces 32,36,
respectively. It is a principal object of the invention to provide
apparatus and method whereby the position of the slider may be
adjusted post-assembly to achieve the required degree of accuracy
and optimal amount of lash.
[0020] Referring to FIG. 2, rocker assembly 22 is substantially as
configured in FIG. 1. However, pivot pin 24 is replaced with an
improved pivot pin, shown as 24a,24b,24c in FIGS. 3-5 and as
discussed below. The improved pivot pin has at least two
cylindrical sections 38,40. The first cylindrical section 38 has an
axis 42 coaxial with the axis of the mounting frame (not shown) for
rocker assembly 22. The second cylindrical section 40 has an axis
44 coaxial with pivot axis B of rocker assembly 22. Axes 42 and 44
are parallel but not coaxial; the axes are offset by a
predetermined amount. Thus, by rotating the improved rocker pivot
pin with an appropriate tool such as a hexagonal wrench applied to
hexagonal socket 46 in the end of the pivot pin, the distance of
axis B from cam lobes 14,16 is changed, thus changing the lash
between the lobes and their followers. The amount of change in
clearance or lash is a function of the angle through which the pin
is rotated and the eccentricity of the pin (distance between axes
42 and 44). The eccentricity needed can be determined at the design
stage after an analysis of the stack-up of manufacturing variances
of the components of the VVM 10.
[0021] There are several variations in configuration of an improved
pin having two offset cylindrical sections. The diameters of the
sections can be of various sizes, depending upon the desired
arrangement of components. For example, the designer may choose to
have the smaller diameter in the supporting frame for the rocker
assembly and the larger diameter in the rocker assembly, or vice
versa.
[0022] Referring to FIG. 3, an improved pin 24a has two relatively
large diameter first sections 38a,38b separated by a relatively
small diameter second section 40a. Pin 24a is useful where frames
(not shown) on either side of rocker assembly 22 have large
diameter bores for receiving the relatively large diameter sections
38a,38b, and assembly 22 has a relatively small diameter bore for
receiving section 40a of pin 24a.
[0023] Conversely, referring to FIG. 4, an improved pin 24b has two
relatively small diameter first sections 38c,38d separated by a
relatively large diameter second section 40b. Pin 24a is useful
where frames (not shown) on either side of rocker assembly 22 have
small diameter bores for receiving the relatively small diameter
sections 38c,38d, and assembly 22 has a large diameter bore for
receiving section 40b of pin 24b.
[0024] Referring to FIG. 5, the desired eccentric adjustment may be
obtained through use of either single or multiple cylindrical
bushing(s) 48 disposed in either the frame bore or the rocker
assembly bore. Bushing 48 has an off-center bore 50 for receiving a
cylindrical pin 52 substantially equivalent to prior art pin 24,
disposable in either the corresponding assembly bore or frame bore
to form an equivalent eccentric pin 24c. As in use of pins 24a and
24b, by rotating bushing 48 as by a hexagonal wrench, the
mechanical lash in a VVM 10 may be adjusted.
[0025] It should be understood that in all embodiments in
accordance with the invention, known means are to be employed for
restricting further rotation of the eccentric pin after lash
adjustment is complete, as by staking, set screws, clamps, and the
like.
[0026] While the invention has been described by reference to
various specific embodiments, it should be understood that numerous
changes may be made within the spirit and scope of the inventive
concepts described. Accordingly, it is intended that the invention
not be limited to the described embodiments, but will have full
scope defined by the language of the following claims.
* * * * *