U.S. patent number 3,585,974 [Application Number 04/803,164] was granted by the patent office on 1971-06-22 for valve actuating mechanism.
Invention is credited to Robert L. Weber.
United States Patent |
3,585,974 |
Weber |
June 22, 1971 |
VALVE ACTUATING MECHANISM
Abstract
The invention contemplates a valve-actuating system wherein
purely longitudinal displacement is achieved upon relative rotation
of members in coaxial, helically cammed relation. A number of
different embodiments are disclosed whereby the desired rotation is
effected, and illustrative employments are described for valve
actuation derived from various cam structures, including a cam with
spring-loaded follower, and a desmodromic cam, as well as
block-mounted and overhead camshaft forms thereof.
Inventors: |
Weber; Robert L. (New Canaan,
CT) |
Family
ID: |
25185746 |
Appl.
No.: |
04/803,164 |
Filed: |
February 28, 1969 |
Current U.S.
Class: |
123/90.12;
74/110; 123/90.27; 123/90.6; 251/229; 123/90.14; 123/90.28;
123/90.61; 251/250; 123/90.24 |
Current CPC
Class: |
F01L
1/46 (20130101); F01L 1/12 (20130101); F01L
1/181 (20130101); F01L 1/30 (20130101); F01L
1/04 (20130101); F01L 1/146 (20130101); F01L
1/026 (20130101); Y10T 74/18992 (20150115) |
Current International
Class: |
F01L
1/12 (20060101); F01L 1/04 (20060101); F01l
001/04 (); F01l 001/30 (); F01l 001/32 () |
Field of
Search: |
;123/90,90.14,90.24,90.27,90.28,90.6,90.61 ;74/110
;251/229,249,250 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Smith; Al Lawrence
Claims
What I claim is:
1. Valve mechanism, comprising a valve body having a seat and a
valve member and stem guided by said body for axial reciprocation
between open and closed relation with said seat, a first sleeve
member carried by said body and having a guide bore for said stem,
a second sleeve member having a part in helically cammed axial
overlap with said first sleeve member and with a part connected to
said stem, and actuating means including reciprocating
rack-and-pinion means for rotary reciprocation of said second
sleeve member, whereby rack reciprocation imparts axial
reciprocation to said valve member with respect to said seat.
2. Valve mechanism according to claim 1, in which the pinion of
said rack-and-pinion means is carried by said second sleeve
member.
3. Valve mechanism according to claim 1, in which the pinion of
said rack-and-pinion means is an external formation of said second
sleeve member.
4. Valve mechanism according to claim 1, in which said
rack-and-pinion means is so positioned that rack-and-pinion action
takes place within the axial extent of helically cammed engagement
between said sleeves.
5. Valve mechanism according to claim 1, in which said
rack-and-pinion means is so positioned that the rack-and-pinion
reaction vector is offset from the valve-reciprocation axis and is
oriented in substantially the direction of the nearest tangent to
the locus of helically cammed engagement between said sleeves.
6. Valve mechanism according to claim 1, in which said valve and
stem are free to rotate in the connection thereof to said second
sleeve member.
7. Valve mechanism according to claim 1, in which the connection
between said stem and said second sleeve member includes
longitudinally adjustable means, whereby, for a given rack stroke,
adjustment may be made for the degree of valve-seat engagement at
the valve-closed position.
8. Valve mechanism according to claim 1, in which said helically
cammed overlap includes a threaded engagement between said sleeve
members.
9. Valve mechanism according to claim 1, in which said helically
cammed overlap includes plural antifriction elements riding matched
inner and outer helical race grooves in the region of axial overlap
of said sleeve members.
10. Valve mechanism according to claim 1, in which said actuating
means includes a driven rotary cam, and cam-follower means
including the rack of said rack-and-pinion means.
11. Valve mechanism according to claim 10, in which said follower
means includes a follower element with an adjustably securable
connection to said rack, whereby adjustment at said connection
provides adjustment of the degree of valve-seat engagement at the
valve-closed position.
12. Valve mechanism according to claim 10, in which said body
includes guide means for the nonrotatable guided longitudinal
reciprocation of said rack.
13. Valve mechanism according to claim 10, in which said body
includes guide means for the rotatable guided longitudinal
reciprocation of said rack, the teeth of said rack being a
formation of revolution about the axis of rack reciprocation.
14. Valve mechanism according to claim 13, in which said body
includes means for the rotatable guided reciprocation of the
element of said cam-follower means which rides said cam, and in
which the net contact region between said cam and said
follower-element is offset from the guide axis for said
element.
15. Valve mechanism according to claim 10, in which said cam is of
the desmodromic variety.
16. Valve support and actuating mechanism for the poppet valve of
an internal-combustion engine, comprising an elongated guide
bushing adapted to be secured to an engine, said bushing having a
bore for the rotatable longitudinally reciprocated guidance of the
stem of a poppet valve, a sleeve axially overlapping part of said
bushing, the overlapping portions of said sleeve and bushing having
helically cammed engagement, said sleeve including connection means
for the removable connection of the tail of a poppet-valve stem
thereto, said sleeve having external pinion-tooth formations for
actuated engagement by mating driver teeth external to the valve
axis.
17. Mechanism according to claim 16, in which the said pinion-tooth
formations are helically pitched in the direction opposite to the
pitch of said helically cammed engagement.
18. Mechanism according to claim 16, in which the helical lead of
said pinion-tooth formations is substantially equal in magnitude
but opposite in direction to that of said helically cammed
engagement.
19. Mechanism according to claim 16, in which said bushing includes
at one end a first elongated generally cylindrical adapter-mount
portion for reception in a mounting bore of an engine frame, a
radial shoulder intermediate the helically cammed and adapter-mount
portions of said bushing for limiting the insertion-mounting of
said bushing in the engine frame, and locating and locking means
off the axis of said bushing and serving to retain the axial and
angular position of the bushing when inserted in the engine
frame.
20. Mechanism according to claim 16, in which the helical lead of
said pinion-tooth formations exceeds the magnitude and is opposite
in direction to that of said helically cammed engagement.
21. Mechanism according to claim 20, in which the helical lead of
said pinion-tooth formations is in the range of substantially
35.degree. to 45.degree..
22. Mechanism according to claim 20, in which the helical lead of
said pinion-tooth formations is substantially 41.degree. to
42.degree..
23. Mechanism according to claim 20, in which the helical lead of
said cammed engagement is in the range of substantially 25.degree.
to 35.degree..
24. Mechanism according to claim 20, in which the helical lead of
said cammed engagement is substantially 29.degree..
25. In combination, an internal-combustion engine including a cam
shaft and having a cylinder and inlet and exhaust ports
communicating with said cylinder, inlet and exhaust poppet valves
having guided support in said engine for opening and closing said
ports, and valve-actuating mechanism driven by said cam shaft for
actuating said valves and for the random angular indexing of said
valves with each actuating cycle thereof; said mechanism
comprising, for each valve, reciprocating cam-follower means
tracking a part of said cam shaft and a connection from said
cam-follower means to its valve, said connection including two
overlapping sleeves in helically cammed engagement, one of said
sleeves being referenced to the engine frame and the other of said
sleeves including means independent of said helically cammed
engagement and responding to cam-follower reciprocation to
rotationally reciprocate said other sleeve, the valve stem being
freely rotatably connected to said other sleeve.
26. In combination, an internal-combustion engine including a cam
shaft and having a cylinder and inlet and exhaust ports
communicating with said cylinder, inlet and exhaust poppet valves
having guided support in said engine for opening and closing said
ports, and valve-actuating mechanism driven by said cam shaft for
actuating said valves and for the random angular indexing of said
valves with each actuating cycle thereof; said mechanism
comprising, for each valve, reciprocating cam-follower means
tracking a part of said cam shaft and a connection from said
cam-follower means to its valve, said connection including means
referenced to the engine frame and responding to cam-follower
reciprocation to impart to its valve a reciprocating cycle that is
both angular and axial; said connection including a helical-track
ball bearing on the axis of valve actuation, said bearing
comprising inner and outer elements having matched helical ball
races in their overlapping adjacent surfaces, balls in said races,
one of said elements being fixed to the engine frame, the other of
said elements having a rotary-reciprocating driven connection to
said cam-follower means, the valve-stem connection being made to
said other element, with the valve freely rotatable.
27. The combination of claim 26, in which said ball bearing
includes retainer means retaining adjacent balls in spaced relation
in the ball complement of each race.
28. The combination of claim 27, in which a single retainer serves
balls of all races.
29. In combination, an internal-combustion engine including a cam
shaft and having a cylinder and inlet and exhaust ports
communicating with said cylinder, inlet and exhaust poppet valves
having guided support in said engine for opening and closing said
ports, and valve-actuating mechanism driven by said cam shaft for
actuating said valves and for the random angular indexing of said
valves with each actuating cycle thereof; said mechanism
comprising, for each valve, reciprocating cam-follower means
tracking a part of said cam shaft and a connection from said
cam-follower means to its valve, said connection including means
referenced to the engine frame and responding to cam-follower
reciprocation to impart to its valve a reciprocating cycle that is
both angular and axial; said connection including matched inner and
outer helically splined elements with the helix axis on the axis of
valve actuation, one of said elements being fixed to the engine
frame, the other of said elements having a rotary-reciprocating
driven connection to said cam-follower means, the valve-stem
connection being made to said other element, with the valve freely
rotatable.
30. In combination, an internal-combustion engine including a cam
shaft and having a cylinder and inlet and exhaust ports
communicating with said cylinder, inlet and exhaust poppet valves
having guided support in said engine for opening and closing said
ports, and valve-actuating mechanism driven by said cam shaft, said
valve-actuating mechanism including cam-follower means for each
valve and tracking a part of said cam shaft, preloaded spring means
independent of the valve closing forces and acting between the
engine frame and said cam-follower means for assuring cam-tracking,
and means including a helically cammed sleeve referenced to the
engine frame and connected to its valve, said sleeve having a
rotary reciprocating driven connection to said cam-follower
means.
31. The combination of claim 30 in which the direction of preload
of said spring means biases said cam-follower means in the
valve-opening direction.
32. In combination, an internal-combustion engine comprising spaced
parallel cam shafts in synchronized relation, complementary
desmodromic cams on said cam shafts, a reciprocating follower
tracking a pair of complementary cams on said cam shafts, a valve
having an elongated stem, valve-stem guide means, a rotatable
sleeve connected to said valve stem and in helically cammed
engagement with said valve-stem guide means on an axis concentric
with the axis of valve-stem guidance, and means connecting said
sleeve to said follower to impart to said sleeve cyclical
oscillations about the sleeve axis in accordance with
reciprocations of said follower.
33. In combination, an internal-combustion engine comprising a cam
shaft having a pair of desmodromic cams, a reciprocating follower
tracking both said cams, a valve having an elongated stem,
valve-stem guide means, a rotatable sleeve connected to said valve
stem and in helically cammed engagement with said valve-stem guide
means on an axis concentric with the axis of valve-stem guidance,
and means connecting said sleeve to said follower to impart to said
sleeve cyclical oscillations about the sleeve axis in accordance
with reciprocations of said follower.
34. As an article of manufacture, a unitary valve-stem guide and
longitudinal actuator, comprising an elongated guide member having
at one end means for secure removable attachment to an engine frame
and including at the other end a generally cylindrical projection,
elongated valve-stem guide means extending through said member in
concentric relation with said projection, and a sleeve carried
concentrically about said projection and having a helically cammed
rotary and longitudinal displacement relation to said
projection.
35. The article of claim 34, in which said sleeve has external
helical threads of helix-advance direction opposed to that of said
cammed relation.
36. The article of claim 34, in which the end of said sleeve
projects axially beyond said projection and includes means for the
selective attachment of a valve stem.
37. The article of claim 36, in which said sleeve comprises a first
sleeve part in helically cammed relation to said projection and a
second sleeve part in threaded longitudinally adjustable relation
to said first sleeve part and at the axially projecting end
thereof, said selective attachment means being on said second
sleeve part.
38. The article of claim 34, in which plural splines establish the
said helically cammed engagement.
39. The article of claim 34, in which plural balls in plural
corresponding helical races in said projection and within said
sleeve establish the said helically cammed engagement.
40. In combination, an internal-combustion engine including a
cylinder head and comprising a cam shaft with a pair of cams and
journaled for rotation in said head, intake and exhaust port and
valve structure in said head on opposite sides of said cam shaft,
an intake-valve actuator including a rotary sleeve connected to its
valve on a valve-actuating axis, an exhaust-valve actuator
including a rotary sleeve connected to its valve on a
valve-actuating axis, said axes being inclined toward each other on
opposite sides of said cam shaft, each sleeve being externally
helically threaded, and rack followers meshing with said respective
sleeve threads and tracking said cams in opposite directions but
substantially in a plane common to the axis of cam shaft
rotation.
41. Valve mechanism, comprising a valve body having a seat and a
valve member and stem guided by said body for axial reciprocation
between open and closed relation with said seat, a first sleeve
member carried by said body and having a guide bore for said stem,
a second sleeve member having a part in helically cammed axial
overlap with said first sleeve member and having a part connected
to said stem, and actuating means including reciprocating driving
means connected for rotary reciprocation of said second sleeve,
whereby rotary reciprocation imparted to said second sleeve member
imparts axial reciprocation to said valve member with respect to
said seat.
42. Valve mechanism according to claim 41, in which said actuating
means includes a cam-and-follower mechanism determining the
reciprocation imparted to said second sleeve member.
43. Valve mechanism according to claim 42, in which said actuating
means includes fluid-pressure operated means between said
cam-and-follower mechanism and said second sleeve member.
44. Valve mechanism according to claim 41, in which said actuating
means includes fluid-pressure operated means determining the
reciprocation imparted to said second sleeve member, and recycling
program means including pressure-fluid reversing valve means in
controlling relation with said fluid-pressure operated means.
45. Valve mechanism according to claim 42, in which said actuating
means includes a belt in positive direct-driving relation with said
second sleeve member.
46. Valve mechanism according to claim 42, in which said second
sleeve member has a toothed periphery, and in which said actuating
means includes means having a reciprocating geared engagement to
said toothed periphery.
47. Valve mechanism according to claim 46, in which said
last-defined means includes a pinion gear.
48. Valve mechanism according to claim 46, in which said
last-defined means includes a sector gear and in which an arm
effectively integral with said gear is part of said
cam-and-follower means.
49. Valve mechanism comprising a body element having an elongated
guide bore, a valve element including a stem supported in said bore
and slidably guided thereby for longitudinal and rotary motion, and
valve-actuating mechanism referenced to said element and including
a linear-reciprocating to rotary-reciprocating coupling wherein a
rotary-reciprocating output element is guided for
rotary-reciprocation on and axial reciprocation along the axis of
said guide bore, said mechanism including a linear-reciprocating
input element reciprocable on an axis angularly offset from the
guide-bore axis, said angular offset being in the range
intermediate a direction parallel to and a direction normal to the
guide-bore whereby thrusts imparted to said output element and
occasioned by reciprocation of said input element are necessarily
characterized by a combination of axial and rotary-reciprocating
thrust components, and an axially retaining interconnection between
said output element and said valve stem.
50. The mechanism according to claim 49, in which said
interconnection is characterized by freedom for relative rotation
of said valve element and of said output element.
51. The mechanism according to claim 49, in which said
valve-actuating mechanism includes between said input and output
elements an interconnection member freely rotatable on the
linear-reciprocation axis of said input member.
Description
This invention relates to an improved motion-translating mechanism
having particular utility when embodied in valve-actuating
mechanism of internal-combustion engines.
The poppet valve used in most of today's internal-combustion
engines has survived many attempts to improve upon its simplicity
and dependability. There have been numerous innovations in valve
mechanisms and in methods of actuating the valve, but because of
high cost, inadequate reliability, excessive complexity, or a
combination of these factors, few improvements have reached the
stage of mass-production, and none of these few has long survived
the test of the marketplace.
Despite the apparent triumph of the poppet valve, the valve area
still plagues today's high-compression engines, as a major trouble
source; in contrast, design considerations for other engine parts,
such as pistons, rods, crankshaft, camshaft, cam followers, heads
and block have become fairly well understood and stabilized.
Advances in metallurgy have made it possible to achieve a high
degree of operating reliability, provided reasonable care is given
to proper lubrication.
Much of the serious trouble begins in the so-called valve train,
i.e. the system of push rods, rocker arms, valve guides, springs,
valves, etc. Chiefly, the trouble lies in mechanical wear of the
valve stem in its guide, due to an actuating force component which
is other than purely axial. Such nonaxial component is attributable
to several factors, including "angularity" in force transmission
from the rocker arm to the valve stem, and deliberate off-axis
contact between the valve stem and its actuator (to impart indexed
valve rotation for better seating). In operation, the valve-seat
bore will depart from concentricity with the valve-guide bore, and
the valve stem may eventually depart from concentricity with the
seat face on the valve member.
After 5 to 10,000 miles, the average production engine has begun to
wear significantly in its valve trains, for one of more of the
above-noted reasons, because current design cannot help but put
some side thrust on the valve stem, for every actuating stroke.
Such wear impairs the ability of the valve to seat squarely, and
heat-dissipation is adversely affected, with rapid deterioration in
performance and accelerated wear of the valve, the valve guide and
other engine parts such as pistons, rings and cylinders.
It is, accordingly, an object of the invention to provide an
improved valve-train movement which will eliminate or very
substantially reduce engine problems of the character
indicated.
It is a specific object to provide a valve-train mechanism which is
inherently free of side thrust on the valve stem, for a
longitudinally reciprocating valve system; stated in other words,
it is an object to provide such mechanism in which purely axially
oriented reciprocating forces are generated for valve
actuation.
Another object is to achieve the foregoing objects with a
construction in which a net indexing rotational increment is
imparted to the valve for each actuation thereof, thus reducing any
tendency to form a localized "hot spot" in the area of valve-seat
engagement.
Still another object is to provide an improved valve-actuating
mechanism which inherently assures full and uniform valve seating
for very extended periods of engine operation, as compared with
systems in use today.
A further object is to provide an improved valve-actuating
mechanism which inherently absorbs, by direct reaction to the
engine block or cylinder head, a major fraction of
valve-accelerating and decelerating forces, thus reducing wear in
cam and follower parts of the valve train.
It is in general an object to achieve the foregoing objects with a
basically simple structure, which lends itself to economic
mass-production, adjustment, servicing and replacement (if ever
necessary), which may use standard valves, which inherently
requires relatively low actuating forces, which is equally
adaptable to conventional cam-and-spring-return and to desmodromic
or other cam-actuating techniques, and which involves minimum
modification of other parts of the engine.
Other objects and various further features of novelty and invention
will be pointed out or will occur to those skilled in the art from
a reading of the following specification in conjunction with the
accompanying drawings. In said drawings, which show, for
illustrative purposes only, preferred forms of the invention:
FIG. 1 is a simplified fragmentary sectional view of an
internal-combustion engine incorporating valve-actuating mechanism
of the invention, utilizing a single block-mounted cam and
spring-loaded follower to derive valve-actuating displacements;
FIG. 2 is a generally similar but more fragmentary view to
illustrate the invention in the context of a desmodromic
cam-and-follower system for deriving valve-actuating
displacements;
FIG. 3 is an enlarged fragmentary view, partly broken away and in
section, for better illustration of one embodiment of
valve-actuating mechanism;
FIG. 4 is a view similar to FIG. 3 to illustrate another
embodiment;
FIG. 5 is a longitudinal sectional view, partly broken, to
illustrate alternate cam-follower mechanism usable with either of
the mechanisms of FIGS. 3 and 4;
FIG. 5A is a fragmentary view in elevation, taken from the aspect
designated 5A-5A in FIG. 5;
FIG. 6 is a fragmentary view similar to FIGS. 3 and 4 to illustrate
a modification;
FIG. 7 is a simplified diagram schematically illustrating a further
embodiment;
FIGS. 8 and 8A are respectively simplified front and side
elevations schematically illustrating a still further
embodiment;
FIGS. 9 and 10 are simplified views in elevation, partly broken and
in section, and schematically illustrating two further embodiments
of the invention;
FIG. 11 is a view similar to FIG. 1 to illustrate an
overhead-camshaft employment of the invention;
FIG. 12 is a simplified view in perspective to illustrate a
modified desmodromic-cam employment of the invention;
FIG. 13 is a simplified fragmentary side view, taken at a section
through the camshaft, to illustrate schematically the
cam-and-follower parts of FIG. 12; and
FIGS. 14 and 15 are similar simplified diagrams respectively
depicting pressure-fluid operated embodiments of the invention.
Briefly stated, the invention contemplates a valve-actuating system
wherein purely longitudinal displacement is achieved upon relative
rotation of members in coaxial, helically cammed relation. A number
of different embodiments are disclosed whereby the desired rotation
is effected, and illustrative employments are described for valve
actuation derived from various cam structures, including a cam with
spring-loaded follower, and a desmodromic cam, as well as
block-mounted and overhead camshaft forms thereof.
Referring to FIG. 1 of the drawings, the invention is shown in
application to a four-cycle internal-combustion engine comprising a
block 10 having a cylinder bore 11 for guided reception of a piston
12. A pin 13 connects piston 12 to a rod 14, the other end of which
is carried at a crank 15 of a crankshaft 16, journaled on a drive
axis 17. A head 18 closes the outer end of the cylinder 11 and
supports a spark plug 19, as well as gas porting such as the inlet
passage 20, and guide means 21 for orientation of a poppet valve
22; valve 22 is shown in open position to permit the downstroke of
piston 12 to draw combustible mixture into cylinder 11. A camshaft
23 is journaled (by means not shown) on an axis fixed in relation
to the drive axis 17 and is driven at one-half drive shaft speed by
a suitable synchronizing connection, suggested at 24. In the form
shown, the face 25 of a cam follower 26 tracks the profile of a cam
27 on camshaft 23. Follower 26 includes an elongated shank which is
guided in a fixed bushing 28 and which is resiliently urged by
spring loading at 29 to maintain the tracking relationship.
In accordance with the invention, the conventional tappet and
rocker-arm relation between cam follower 26 and valve 22 is
completely replaced by mechanism whereby cam-follower reciprocation
is translated into rotary reciprocation of two members, coaxial
with each other and with the stem 30 of valve 22; a helically
cammed relation between the two coaxial members imparts
straight-line actuation of the valve stem, i.e. free of side or
lateral thrust reaction on the valve stem.
In the form of FIG. 1, one of the two relatively rotatable members
is basically a sleeve or nut 31, and the other is the valve-stem
guide 21, the latter being shown insertably fitted in a suitable
receiving bore in the cylinder head 18 and held by a key pin 32 and
a radial shoulder 33 as a fixed part of the cylinder-head assembly.
Plural balls 34 ride corresponding helical raceways or grooves in
axially overlapping adjacent cylindrical surfaces of members
21--31, so that rotary reciprocation of sleeve 31 effects
corresponding but purely axial reciprocation of sleeve 31 and of
valve stem 30, carried therewith. Rotary reciprocation is imparted
to sleeve 31 by reaction to the thrust of a rack 35, connected by
an elongated push rod 36 to follower 26; rack 35 meshes with
helical threads 37 on the otherwise cylindrical periphery of sleeve
31. The angle .alpha. characterizes the effective inclination of
the valve-stem axis with respect to the rack-reciprocation axis as
viewed in FIG. 1; this angle and other related factors will be
discussed in greater detail below, in connection with FIG. 3. It
will be understood that rack 35 and rod 36 may be provided with
greater support as necessary, as for example that indicated at boss
36' for rod 36; and boss 36' may serve the added function of a
frame reference for the upper end of spring 29 in the event that
the teeth of rack 35 are straight or substantially straight, the
dashed outlines in FIG. 1 behind the inlet 20 may be taken as
schematic suggestion of guide means on the valve body for the
nonrotatable guided longitudinal reciprocation of rack 35.
The connection of valve 22 to sleeve 31 is preferably such as to
permit relatively free relative rotation of these parts. In the
form shown, this is achieved in the context of a light frictional
resistance, occasioned by a preloaded spring 38. The reduced tail
39 of valve stem 21 passes freely through a central opening in an
end wall 40 of sleeve 31, and spring 38 is compressed between wall
40 and a retaining washer or snap ring 41, carried at the end of
tail 39; if desired, washers may be provided immediately adjacent
the respective faces of wall 40, as shown.
In operation, the valve 22 is open when follower 26 is tracking the
low point of cam 27. With ensuing camshaft rotation, follower 26
and rack 35 are displaced upwardly, to lift sleeve 31 and to
develop clockwise rotation thereof (as viewed upwardly along the
valve-stem axis); it will be understood that such rotation is the
reacting result of the described helically cammed relation between
members 21--31. Valve-seating occurs just prior to tracking the
high part of cam 27; spring 38 thus resiliently loads the
valve-seated relation. Upon tracking the downslope of cam 27,
sleeve 31 commences its return stroke before unseating valve 22; by
the time valve 22 is unseated, sleeve has already begun to rotate
in the opposite (counterclockwise) direction. The cycle is
completed when the valve is fully open, as shown.
It will be appreciated that since torsional friction characterizes
the otherwise freely rotatable relation between valve 22 and sleeve
31, there will be a tendency of valve 22 to track the angular
oscillation of sleeve 31, but that in the course of a plurality of
valve cycles, there is a net unidirectional progression of valve
rotation, even though sleeve 31 rotates just as much in each
direction of rotary oscillation. The detailed explanation of such
net unidirectional rotation (or indexing) of valve 22 is not yet
completely understood, but it is believed in part to be
attributable to the fact that upstroke displacement of valve 22 is
shorter than that of sleeve 31, so that angular acceleration of
valve 22 begins more gently on the upstroke as compared with more
sudden acceleration at commencement of the valve downstroke.
Similarly, angular deceleration of the valve is more gentle at the
end of the downstroke than it is at the end of the upstroke. The
very substantially larger valve-seating area at 42 determines
abrupt achievement of zero rotational speed for valve 22 at the end
of its upstroke, but this is to be compared with the relatively
small torsional forces available to accelerate rotation of valve 22
as it begins its downstroke. The net result is to develop more
counterclockwise than clockwise rotation in valve 22, in the long
run, so that the valve and its seat may be self-burnishing and
assure prolonged accurate seating, with well-distributed
heat-dissipation over the entire seat 42, and free of "hotspot"
development.
In the form shown, precise adjustment of the timed seating of valve
22 is available through adjustment of the effective length of rod
36, between follower 26 and rack 35. For this purpose, rack 35 is
shown threadedly engaged to one end of rod 36, with a lock nut 35'
to hold the position. The other end of rod 36 is similarly
threadedly engaged to follower 26 and is locked by nut means
43.
The arrangement of FIG. 2 is generally similar to FIG. 1, except
that positive cam actuation develops both the upstroke and the
downstroke of the follower 45. Follower 45 is shown with parallel
forks 46-46' piloting on the camshaft 47 which carries a flat cam
plate having a cam groove 48. A cam-follower roll 49 on follower 45
tracks the radially inner wall of grove 48 to generate upstroke
movement, and it tracks the radially outer wall of groove 48 to
generate downstroke movement. The other end of follower 45 is
provided with a rack 50 (suitably guided by means not shown) to
drive a valve-actuating sleeve 51 in the manner discussed in FIG.
1, except that since rack 50 is in front of sleeve 51 (as
distinguished from FIG. 1, where rack 35 is behind sleeve 31), the
helical outer rack-drive threads on sleeve 51 are shown with the
opposite direction of helical advance; by the same token, the
direction of helically cammed engagement between valve-stem guide
52 and sleeve 51 is the opposite of that shown between members
21--31 in FIG. 1. The net result of recycled cammed actuation of
the valve 53 of FIG. 2 is the same as in FIG. 1, except that
positive actuation of both strokes in FIG. 2 assures greater
fidelity of valve programming under high-speed conditions, and the
net rotation for incremental indexing of the valve about its axis
will, of course, be the opposite of that in FIG. 1.
FIG. 3 is an enlarged sectional view to illustrate an adjustable
feature embodied in the valve-actuating mechanism within the
coaxial structure of the sleeve 55 and valve-stem guide member 56.
FIG. 3 also serves to illustrate the relation of angles involved in
rack-pinion engagement and in the helically cammed engagement,
respectively.
An adjustable feature within sleeve 55 employs an auxiliary sleeve
55' threaded in a counterbore at the open or tail end of the sleeve
55. Auxiliary sleeve 55' is shown with a reduced aperture in an
end-closure wall 57, and the reduced tail 58 of the stem 59 for
valve 60 extends through this aperture. As washer 61 seats against
the shoulder defining the reduced end 58, and a spring washer 62
retains the assembly with resilient loading which, it will be
recalled, is used to assure seating. Preferably, angularly
registering cutouts or slots (not shown) in members 61--57, are
provided to permit "breathing" or venting air that must be
displaced during reciprocating of the valve actuator. Adjustment of
the threaded advance of auxiliary sleeve 55' within the primary
sleeve 55 will be seen to develop precise control of valve-stem
location, so that valve 60 may seat with the desired slight
resilient loading via spring 62. Once the adjusted position is
determined, a lock nut 65 is set against sleeve 55 to secure the
adjustment.
FIG. 3 serves the additional purpose of illustrating presently
preferred angular relationships in my valve-actuating mechanism,
for the case of ball coupling between members 55 --56. The angle
.alpha. will be recognized as the angle between the reciprocating
rack 66 and the valve-stem axis, and the rack teeth have tangential
engagement with the helical threads on the outer surface of sleeve
55; the angle .alpha. is thus the complement of the angle of
helical advance for these threads. The angle .alpha. preferably
exceeds the angle .beta., which is the angle of advance for the
helix which determines cammed action between the inner and outer
members, namely the grooved part 67 of the valve-stem guide 56 and
the bore of sleeve 55. Preferably, the latter engagement utilizes
plural equally angularly spaced like helical grooves or raceways
68, and plural balls are received in each of these raceways. The
plural balls will be understood to support the relatively rotatable
members throughout the course of the actuating stroke and to assure
concentricity of positioning and of the actuating thrusts.
FIG. 4 illustrates a modification wherein the rack-actuating axis
70 will be understood to be in a plane above the plane of the paper
and therefore on the side of the sleeve 71 opposite to that
displayed for the rack 66 and sleeve 55 in FIG. 3. The helical
raceway progression within sleeve 71 is therefore shown in the
opposite direction to that displayed in FIG. 3. In the modification
of FIG. 4, a thin retaining sleeve 72 is positioned in the annular
space between valve-stem guide 73 and the sleeve 71. This retainer
is apertured at predetermined angular and axial spacings so as to
retain spaced balls in the various raceways, and thus to assure an
economy of balls as well as independent action of all balls in the
various and respective race relationships. These results are
achieved without sacrifice of the coaxial relationships discussed
above whereby no off-axis thrust component is introduced in the
actuation of the valve 74.
In a specific illustrative embodiment of the FIG. 4 arrangement, as
applied to a small-horsepower Briggs and Stratton engine having a 1
-inch diameter intake valve and a 7/8-inch diameter exhaust valve,
each having a lift of 0.165 inch, the actuating rack travel is
0.220 inch, the angle .alpha. is about 41.degree.--42.degree. and
the angle .beta. is about 29.degree..
FIG. 5 illustrates a modified rack structure wherein the rack
member 75 is cylindrical and is formed with like circumferential
grooves, contoured as rack teeth over the entire rack length. As
shown, the rack 75 is a sleeve carried in the upper end of rod 76
forming part of the cam-follower structure. Rod 76 includes a
circumferential shoulder 77 defining a stop for location of a coil
spring 78, preloading the rack sleeve 75 against adjustable lock
nuts 79 at the threaded upper end of rod 76. Preferably, the
assembly of rack 75 and rod 76 is preassembled to a suitably bossed
portion 80 of the cylinder head. The lower end of rod 76 may thus
be guided by and project through boss 80, and a pin 81 retains
spring-preloading means 82 within the cylinder-head structure. The
cam follower itself is shown merely as a rod 83 suitably guided in
the engine block 84 to ride its particular actuating cam 85, and it
will be understood that upon assembly of the cylinder head to the
block, the follower rod structures 76--83 will align, as shown,
preferably with slight compressionally loaded relief (at 86) of the
shoulder 77 from the cylinder head. Rotation of cam 85 lifts the
rod structure against the loading of spring means 82 and drives
rack 75 through the further resilient loading 78. Rack 75 will be
understood to engage a valve-stem-actuating sleeve 87 which is
threaded in accordance with principles already discussed, and the
spring means 78 will be available for slight further compression
once the valve has attained its fully seated position. Spring means
78 will thus be understood to obviate the need for particular
spring preloading within the concentric valve-actuating structure,
as at 38 in FIG. 1.
FIG. 5A illustrates a preferred offset relation, to the extent
identified .DELTA., between the axis of follower rod 83 and the
centerline of the cam 85. This offset is such that an asymmetrical
part of the end face of follower 83 is always unsupported by
contact with the cam 85. In operation, this necessarily means a
predominant torsional friction or drag to impart slight incremental
rotation of the follower rod 83 for each cycle of the cam. Such
rotation achieves a desired uniform burnishing of the cam follower
end face and at the same time transmits a measure of consistent
incremental rotation to the rod 76 on which the rack 75 is mounted.
Thus, wear of the rack teeth is never localized at any one angular
position but is rather well-distributed about the full periphery of
tooth engagement with the sleeve 87.
FIG. 6 illustrates a modification in which the sleeve 90, which is
driven by a rack on the axis 91, is itself engaged to the valve
stem guide member 92 by means of elongated splines, as at 93.
Splines 93 mate with corresponding grooves as at 94 in the bore of
sleeve 90. With proper lubrication, a film of oil thus spreads
torsional reaction leads over a very extensive area, thus avoiding
stress concentrations in any part of the valve-actuating cycle and
contributing to long life, with an assured concentric thrust
development at all times. The structure is simplified by omission
of the antifriction elements, and the angles .alpha. and .beta. may
approach equality, as suggested in the drawing.
FIGS. 7 to 9 illustrate several different alternative organizations
for developing the desired valve-actuating thrusts. In FIG. 7, the
externally threaded sleeve 95 for actuating the valve 96 is driven
by meshing teeth 97 of a sector 98 journaled for pivotal action at
99 and deriving oscillating torques from follower arm 100
integrally formed with the sector 98. Sector teeth 97 may be
straight, parallel to the pivot 99, and mesh tangentially with the
external threads on sleeve 95. Cam 101 on an overhead cam shaft 102
drives arm 100 against a suitable loading spring 103.
In the arrangement of FIGS. 8 and 8A, an elongated pinion 105
meshes with the helically threaded exterior of the sleeve 106 for
actuating valve 107, and it will be understood that suitable means
(not shown) may be employed to translate cam actuation into driven
rotary reciprocation of the pinion 105. The teeth of pinion 105 are
shown straight and they mesh tangentially with the external tooth
formations on sleeve 106. The angle .alpha. already identified thus
becomes the angle between the pinion axis and a radial plane normal
to the valve-stem axis.
In the arrangement of FIG. 9, the helically threaded sleeve 110 is
driven by a toothed belt 111 which serves the function of the rack
of the various forms discussed above. The belt 111 has tooth
formations meshing with the helix of sleeve 110 throughout the full
circumferential extent of helical wrap or overlay shown in the
drawing. This leaves generally tangentially projecting opposite
ends of the belt 111. One of these ends may be spring-tensioned
with reference to a frame part and the other end may be drawn in
accordance with a cam-derived profile, but in the form shown the
belt 111 is continuous, being laid over suitable pulleys or pinions
112--113, one or both of which may be driven in accordance with the
rotary reciprocating motion necessary to achieve the desired cycle
of valve actuation. In the form shown, the phantom outline shown at
114 suggests completion of the continuous belt 111 on the back side
of sleeve 110 and in clearance relation therewith.
FIG. 10 illustrates a further embodiment of the invention in which
twin overhead cam shafts 115--116 are provided with complementary
cams 117--118 for desmodromic actuation of a shuttled follower 119;
cam shafts 115--116 are synchronously driven at the same speed, as
suggested by the meshed l:l gear train G.sub.1 --G.sub.2 --G.sub.3.
Follower 119 may be a rod with circumferentially grooved rack-tooth
formations 120 in mesh with the helical threads on the outside of a
valve-stem actuating sleeve 121, for operating the valve 122 in
accordance with principles already discussed. The virtue of the
system of FIG. 10 is that not only is all valve actuation achieved
by mechanisms carried by the cylinder head, but the actuation is
positive in both stroke directions so that end play or mechanical
hysteresis can be reduced to a minimum, thus assuring enhanced
efficiency at high speeds of operation.
FIG. 11 is an enlarged sectional view to illustrate another
overhead-camshaft actuating system of the invention. The drawing
illustrates application to both the intake valve 125 and the
exhaust valve 126 serving the same cylinder 127 of an engine which
may be of the familiar "V" variety. A single overhead camshaft 128
is suitably journaled in the cylinder head and it carries, in
suitably spaced pairs, an intake actuating cam 129 and an exhaust
actuating cam 130. A timing belt 123 is shown connecting the
camshaft 128 for 2:1 synchronized drive from the main camshaft;
belt 123 may also serve a similar overhead camshaft for valves in
the other bank 124 of the "V" arrangement of cylinders.
The follower mechanism for both cams 129--130 may be generally
similar, and therefore detailed discussion of the
exhaust-valve-actuating follower 131 will suffice. Follower 131 is
shown to be generally cylindrical and guided within an elongated
bore in a boss or other formation 132 in the cylinder-head casting.
Follower 131 may be cupped, with a relatively thick closure wall to
serve as a cam follower proper, and with a hollowed bore to receive
and locate a preloading spring 133. A threaded plug 134 at the
outer end of the guide bore for the cam follower provides frame
reference for the preloading adjustment. The guide structure 132
will be understood to be locally cut away, as at a window opening
designated 135 for the case of the intake-valve-actuating
structure. Through the window 135, the threaded periphery of the
sleeve 136 may have meshing access to the circumferential
rack-tooth formations 137 on the follower 138 which tracks cam 129.
By virtue of the similarity of actuating mechanisms for valves
125--126, similar access and meshing relationship will be
understood to apply for the sleeve 139 and the rack-tooth
formations 140.
In the arrangement of FIG. 11, the preloading spring 141 for the
exhaust-valve actuating structure will be seen to supply the
desired resilient loading of the valve-seated position, and
auxiliary sleeve 142 within the main sleeve 139 affords adjustment
of this seated relationship. Similar adjustment and preloading are
of course available for the intake-valve actuating mechanism, and
it will be noted that access for either or both of these
adjustments is very simply achieved by removing the hollow bolt
structure 143 which surrounds the spark plug 144 and which retains
a shroud or closure pan 145, against sealing gaskets, over the
entire assembly.
FIG. 12 is a schematic illustration of another desmodromic
cam-actuating system, representing an alternative drive for the
sleeve 150 of actuating mechanism for a valve 151. In FIG. 12, a
single follower rod 152 is provided at its outer end with a rack
portion 153 and at its inner end with two like cam-follower rolls
153--154 mounted at diametrically opposite sides of the camshaft
155 and on opposite faces of the follower rod 152. In the vicinity
of cam-following engagement, rod 152 is cut out at 156 to define
spaced elongated parallel piloting walls for guided location on the
periphery of the camshaft 155; each follower rod 152 is located
axially between an upstroke cam 157 and a downstroke cam 158 which
are respectively in constant contact with the follower rolls
153--154. Preferably, the camshaft is characterized by an elongated
cylindrical bore 159 having radially ported connection, as at 160,
in the regions between pairs of cams 157--158. Such passages
provide a means of freely circulating lubricant to assure smooth
desmodromic cam action. To assure ready assembly of the follower
rod 152 to its camshaft, a parting line 161 suggests that rod 152
is formed of two like abutting elongated halves, secured together
by screws at suitably spaced locations 162-162' in the vicinity of
cam-follower contact.
FIGS. 14 and 15 are very schematic illustrations of pressure-fluid
operated systems for concentric valve-actuating mechanism operating
an externally threaded sleeve 165 for valve 166. In FIG. 14, a
double-acting hydraulic or pneumatic cylinder 167 with head and
tail port connections 168--169 imparts reciprocating displacement
to a rack arm on actuating axis 170. The rack arm may be merely an
end formation of a piston rod 171 and may be understood to be in
mesh with the helix formations on sleeve 165. Cyclically reversing
fluid pressures are delivered to the ports 168--169 by suitable
means merely suggested by heavy dashed lines 172--173; such means
will be understood to include actuating followers which track the
respective upstroke and downstroke cams 174--175 constituting the
pair required for operation of valve 166. Cams 174--175 are mounted
on a camshaft 176 common to all valve-actuating cams.
In FIG. 15, the double-acting pressure-operated rack actuator of
FIG. 14 will be recognized but its operation is governed by an
electrical control system involving limit switches 177--178 which
track the respective profiles of cams 174--175 to determine
alternating excitation of reversing solenoids 179--180. Solenoids
179--180 are supplied by source 181 to determine distribution (at
valve 182) of pressurized fluid in line 169 or in line 168, as the
case may be, for valve-closure and for valve-opening strokes at
166. The solenoid-operated distribution valve 182 may be of
well-known commercially available construction and is therefore not
shown in detail. The fluid system is shown to rely upon a supply
pump 183 and a pressure-fluid return system including a sump 184.
Because the fluid system of FIG. 15 has the inherent capacity to
achieve very rapid valve-actuating displacements, I indicate the
desirability of providing dashpot action, suggested at 185, to
cushion the actuating motions. A manual adjustment at 186 provides
selection of the bleed to determine dashpot action.
The description of FIGS. 14 and 15 as having fluid components will
be understood to involve a generic use of the expression. In other
words, the principles of FIG. 14 and 15 are applicable whatever the
relative compressibility of the fluid involved. Thus, these systems
may employ pressurized relatively incompressible liquids such as
oils, or they may employ pressurized more compressible fluids such
as air. Pneumatic valve operation is thus expressly contemplated by
the disclosure.
It is considered important to the invention that the essence of
rack-and-pinion contact, in the various forms disclosed, involves
primarily point contact at any single instant of time, regardless
of position in the reciprocating cycle. Point contact necessarily
follows from a tangential rack-tooth engagement at the helical
pinion teeth, assuming involute or nonslip profile design for the
meshing teeth.
From a wear standpoint, it is a matter of relative insignificance
that rack reciprocation is accompanied by axial displacement of the
helically threaded sleeve (pinion), since point-contact is always
at the essence of the engagement. Point contact applies for the
straight-rack (as in FIG. 2) forms and for the rack-of-revolution
forms (as in FIG. 5).
It will be seen that I have described improved valve-actuating
mechanism inherently capable of avoiding problems of conventional
mechanisms and making for engine constructions having substantially
extended life expectancy and materially improved operating
efficiency, particularly at high operating speeds. Specifically, my
invention points the way to elimination of the valve train as a
major problem of engine life and operation. Valve actuation becomes
virtually frictionless, and there can be no off-axis development of
valve-actuating thrusts. Servicing access and initial installation
are facilitated by using the key technique (32) to position and
retain a valve-actuating preassembly; valve-seating preload being a
matter of simple adjustment, readily accessible at the cylinder
head, as in FIG. 11 for the ends of the valve stems (at 142), or as
in FIG. 5 for the end of the cam-follower rods (at 79).
My construction enables simplification of parts and the use of
lighter-weight components, as compared to present systems. Lower
forces are needed for valve actuation, so that friction (where it
exists) necessarily involves less wear. The unitized nature of each
valve actuator permits greater flexibility to the designer as to
valve positioning, and the variety of alternate means to effect
actuating-sleeve oscillation further enhances the flexibility of
application to specific problems. Obvious advantages of increased
thermal efficiency, including avoidance of "hotspots, " flow from
the purely axial nature of all valve-actuating thrusts. From the
designer's viewpoint, my invention offers the considerable
advantage of eliminating all angularity effects which must be
accounted for in rocker-arm designs; the designer can thus rely on
the completely linear relation between force transmission and
displacement, from cam to valve. Valve reaction to the cam profile
can be more instantaneous, there being no need for
hysteresis-producing gaps or clearances in the valve train. The
light weight and lower inertia of components and lesser spring
forces of my invention mean substantial reduction of spring surge
and other elasticity effects in the valve train; these factors are
virtually completely eliminated in desmodromic versions.
Although the invention has been described in detail for the forms
shown, it will be understood that modifications may be made within
the scope of the invention as defined by the claims.
* * * * *