U.S. patent number 3,802,286 [Application Number 05/335,458] was granted by the patent office on 1974-04-09 for chain tensioning device.
This patent grant is currently assigned to Joh. Winflhofer & Sohn. Invention is credited to Adam Biedermann, Gerhard Winklhofer, Hermann Zollner.
United States Patent |
3,802,286 |
Winklhofer , et al. |
April 9, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
CHAIN TENSIONING DEVICE
Abstract
A chain tensioning device in which a plunger axially movable in
a cylinder carries a chain engaging head and is biased outward of
the cylinder cavity by a compression spring. One of two guide
elements engaging each other for threaded movement substantially
about the cylinder axis is secured to the plunger while the other
guide element is fixedly fastened to one part of a unidirectional
ratchet coupling, the other coupling part being fastened to the
cylinder. The engaged coupling permits the plunger and chain
engaging head to move outward of the cylinder cavity while
preventing movement of the plunger toward a retracted position. An
operating shaft is accessible outside the cavity for manual
disengagement of the ratchet coupling and rotation of the second
guide element to move the plunger into its retracted position
against the compression spring. A manually releasable locking
device locks the plunger in the retracted position.
Inventors: |
Winklhofer; Gerhard (Krailling,
DT), Zollner; Hermann (Munich, DT),
Biedermann; Adam (Puchheim, DT) |
Assignee: |
Joh. Winflhofer & Sohn
(Munich, DT)
|
Family
ID: |
5839155 |
Appl.
No.: |
05/335,458 |
Filed: |
February 26, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Mar 16, 1972 [DT] |
|
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2212818 |
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Current U.S.
Class: |
474/111 |
Current CPC
Class: |
F16H
7/08 (20130101); F16H 2007/0872 (20130101); F16H
2007/0812 (20130101); F16H 7/0829 (20130101); F16H
2007/0857 (20130101); F16H 2007/0806 (20130101); F16H
2007/0859 (20130101); F16H 2007/0891 (20130101); F16H
7/0836 (20130101) |
Current International
Class: |
F16H
7/08 (20060101); F16h 007/08 () |
Field of
Search: |
;74/242.11S,242.13A |
References Cited
[Referenced By]
U.S. Patent Documents
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3626776 |
December 1971 |
Staudinger et al. |
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Foreign Patent Documents
Primary Examiner: Gerin; Leonard H.
Claims
What is claimed is:
1. A tensioning device for an elongated, flexible, power
transmitting element comprising, in combination:
a. a cylinder member having an axis and defining a cavity
therein;
b. mounting means for mounting said member on a stationary
support;
c. a plunger member received in said cylinder member for axial
movement inward of said cavity into a retracted position, and
outward of said cavity away from said retracted position;
d. an engaging head mounted on said plunger member outside said
cavity for joint axial movement with said plunger member;
e. yieldably resilient means interposed between said members and
biasing said plunger member away from said retracted position
thereof;
f. a first guide element secured to said plunger member;
g. a second guide element rotatable in said cavity about said axis
and engaging said first guide element for relative helical movement
of said guide elements, whereby said second guide element is
rotated about said axis in one direction during said outward
movement of said plunger member;
h. ratchet means on said second guide element for limiting inward
movement of said plunger member under axial pressure applied to
said head to a substantially constant maximum distance in all axial
positions of said plunger member spaced from said retracted
position;
i. operating means outside said cavity for manually turning said
second guide element in a direction opposite to said one direction
and for thereby moving said plunger member into said retracted
position thereof; and
j. manually releasable locking means for locking said plunger
member in said retracted position against axially outward
movement.
2. A device as set forth in claim 1, wherein said ratchet means
include a uni-directional coupling engageable to secure said second
guide element to said cylinder member against relative angular
movement in said opposite direction while permitting said angular
movement in said one direction.
3. A device as set forth in claim 2, wherein said operating means
include a shaft member extending axially outward of said cavity in
a direction away from said head, said shaft member being fixedly
fastened to said second guide element.
4. A device as set forth in claim 3, wherein said cylinder member
has an end wall transverse to said axis, said shaft member passing
axially and rotatably through said end wall, and abutment means
limiting axial movement of said shaft member relative to said
cylinder member to a distance sufficient for disengaging said
coupling.
5. A device as set forth in claim 4, wherein the portion of said
shaft member outside said cylinder is formed with a key-receiving
recess.
6. A device as set forth in claim 3, wherein said locking means
include a resilient arm projecting from said shaft member radially
relative to said axis, and abutment means on said cylinder member
engaging said arm and thereby limiting angular movement of said
second guide element under the force of said yieldably resilient
means, said arm being sufficiently resilient to permit deflection
of the same when said shaft member is being turned manually.
7. A device as set forth in claim 3, wherein said second guide
element is formed with a helical, elongated groove, and said first
guide element engages said groove for longitudinal movement
therein, a portion of said second guide element bounding a
laterally enlarged pocket communicating with one longitudinally
terminal portion of said groove, said portion of said second guide
element jointly with said first guide element constituting said
locking means, said first guide element being received in said
pocket when said plunger member is locked in said retracted
position, and being released from said pocket by movement of said
shaft member axially inward of said cavity.
8. A device as set forth in claim 2, wherein said locking means
include a locking member, said cylinder member and said head
constituting a pair of cooperating elements, said locking member
being mounted on one of said cooperating elements, essentially
consisting of reslient material, and lockingly engaging the other
cooperating element under the resilient force thereof in said
retracted position of said plunger member.
9. A device as set forth in claim 2, wherein said head, said
plunger member, and said one guide element jointly constitute a
plunger assembly, and said locking means are operatively interposed
between said assembly and said cylinder member for releasably
locking said plunger member in said retracted position.
10. A device as set forth in claim 2, wherein said locking means
include a locking member mounted on said cylinder member and
resiliently engaging said second guide element for impeding
movement thereof relative to said cylinder member.
11. A device as set forth in claim 2, wherein said plunger member
has a central bore and is formed with an elongated, helical, first
groove about said axis radially open toward said bore, wall
portions of said plunger member bounding said groove and
constituting said first guide element, said second guide element
being tubular about said axis and carrying at least one radial
projection received in said groove, additional wall portions of
said plunger member bounding an elongated second groove extending
in a radial plane relative to said axis, respective longitudinally
terminal portions of said first and second grooves communicating
with each other for sequential longitudinal movement of said
projection in said first and second grooves, said additional wall
portions in cooperation with said projection constituting said
locking means.
12. A device as set forth in claim 1, wherein said second guide
element is formed with a helical, elongated groove, and said first
guide element engages said groove for longitudinal movement
therein, respective edge portions of said second guide element
laterally bounding said groove, said ratchet means including a
plurality of ratchet teeth on the edge portion bounding said groove
in an axial direction away from said head, said ratchet teeth
projecting into said groove and being spaced in the direction of
groove elongation for receiving said first guide element
therebetween during said inward movement of said plunger member
under said axial pressure.
Description
This invention relates to tensioning devices for transmission
belts, chains, and like elongated, flexible, power transmitting
elements, and particularly to an improvement in the tensioning
device for the timing chain of an internal combustion engine
disclosed in the German Pat. application No. 1,775,273, published
on May 27, 1971.
The known device includes two telescopically engaged members,
hereinafter referred to as a cylinder and a plunger, which are
movable relative to each other in the direction of their common
axis, the plunger being biased outward of the cylinder cavity by a
compression spring. Two guide elements engaged for relative
threaded movement about the common axis of the cylinder and the
plunger are fixedly fastened to the plunger and to one of two
ratchet elements respectively, the other ratchet element being
fixedly fastened to the cylinder to prevent relative threaded
movement of the guide elements in a direction that would permit
movement of the plunger inward of the cylinder cavity.
When the device is arranged on a suitable fixed support with the
axis transverse to the direction of movement of the chain to be
tensioned, the tensioning head is held in resilient engagement with
the chain by the compression spring, and is moved outward of the
cylinder in steps corresponding to the spacing of the ratchet teeth
as the chain stretches to keep the chain in tensioned
conditions.
Ultimately, the chain becomes too long to permit proper operation
even with the aid of the tensioning device, and must be replaced.
The tensioning device, for cooperation with the new chain, must be
restored to the original condition, that is, the plunger and the
head must be retracted inward of the cylinder. This cannot be done
in the known device without partly disassembling the same. The
compartment, normally oil-filled, which houses the timing chain of
most internal combustion engines, and in which the tensioning
device is mounted, is downwardly open to the oil sump of the engine
in the crankcase, and a small part removed from the chain
tensioning devie during partial disassembly may accidentally drop
into the sump and be very difficult to recover. Yet, it may cause
serious damage to the engine unless removed.
The object of the invention is an improvement in the known device
which permits the engaging head of the device to be retracted for
cooperation with a newly installed chain without removing anything
from the device.
It is another object to provide a locking device, manually
releasable, which holds the engaging head in the retracted
condition and out of the way of the old chain being removed and the
new chain being installed until tensioning engagement of the head
with the chain is again required.
With these objects in view, the invention provides a tensioning
device for a chain or other elongated, flexible, power transmitting
element which includes a cylinder arranged for mounting on a
stationary support and a plunger received in the cylinder for axial
movement inward of the cylinder cavity into a retracted position,
and outward of the cavity away from the retracted position. A chain
engaging head is mounted on the plunger outside the cavity for
joint axial movement. The plunger is resiliently biases away from
the retracted position and is secured to a first guide element. A
second guide element is rotatable in the cylinder cavity and
engages the first element for relative helical movement of the
guide elements substantially about the cylinder axis, whereby the
second guide element is rotated about the axis in one direction
during the outward movement of the plunger. A ratchet device on the
second guide element limits inward movement of the plunger under
axial pressure applied to the chain engaging head to a
substantially constant maximum distance in all axial positions of
the plunger spaced from the retracted position. Operating means are
accessible outside the cylinder cavity for manually turning the
second guide element in a direction to move the plunger into its
retracted position. A manually releasable locking device permits
the plunger to be locked in the retracted position.
Other features, additional objects, and may of the attendant
advantages of this invention will readily be appreciated as the
same becomes better understood by reference to the following
detailed description of preferred embodiments when considered in
connection with the appended drawing in which:
FIG. 1 shows a chain tensioning device of the invention in
side-elevational section on its axis;
FIG. 2 illustrates the device of FIG. 1 in bottom plan view;
FIG. 3 shows another tensioning device of the invention in section
on the line III--III in FIG. 4;
FIG. 4 is a sectional view of the device of FIG. 3 taken on the
line IV--IV;
FIG. 5 illustrates yet another tensioning device of the invention
in a view corresponding to that of FIG. 1;
FIGS. 6, 7, and 9 show modified details for use in the device of
FIG. 5;
FIG. 8 is a side-elevational, sectional view of yet another
modification of the device of FIG. 5;
FIG. 10 illustrates a further tensioning device of the invention in
section on the line X--X in FIG. 11;
FIG. 11 shows the device of FIG. 10 in section on the line
XI--XI;
FIG. 12 is a view of an additional tensioning device of the
invention in front-elevational section on its axis;
FIG. 13 illustrates the device of FIG. 12 in fragmentary section on
the line XIII--XIII; and
FIG. 14 shows the device of FIG. 12 in section on the line
XIV--XIV.
Referring initally to FIGS. 1 and 2, there is shown a chain
tensioning device for tensioning the timing chain of an internal
combustion engine. It includes a cushion 1 of oil-resistant,
synthetic rubber which engages the moving chain to be tensioned
when the device is installed in its normal operating condition. The
cushion 1 is backed by a metal frame 51, and the chain engaging
head formed by the cushion 1 and frame 51 is fixedly fastened to a
plunger 2 having the approximate shape of an inverted, tall,
cylindrical cup. The plunger 2 is coaxially received in a cylinder
3 integrally cast with two mounting lugs 52 which permit the device
to be installed on a stationary engine part, such as the cylinder
block or the timing chain cover.
A guide spindle 4 having approximately one turn each of steeply
pitched, dual threads is a strip of glass-fiber reinforced plastic
twisted about the common axis of the plunger 2 and cylinder 3. It
engages a matingly threaded guide nut 53 which is a suitably shaped
axial portion of an otherwise cylindrical tube 5 fixedly and
coaxially fastened to the transverse top wall of the plunger 2 and
depending therefrom. The tube 5 partly envelops the spindle 4, and
the tube 5 together with the inner, axial wall of the plunger 2
bounds an annular space in which an axial portion of a helical
compression spring 6 is received.
The spring is axially confined between the afore-mentioned
transverse wall of the plunger 2 and a crown wheel 7 fixedly and
coaxially fastened to the end of the spindle 4 remote from the
cushion 1. The spring 6 normally holds the wheel 7 in conforming,
locking engagement with a complementary, annular crown wheel 8
fixedly fastened to the bottom wall of the cylinder 3. The wheels
7, 8 have each a crown of radial ribs or ratchet teeth closely
similar in cross section to saw teeth so that the two wheels
constitute a uni-directional ratchet coupling which permits
relative angular displacement of the spindle 4 and the cylinder 3
in one direction under an applied torque sufficient to overcome the
locking force of the spring 6.
An operating shaft 9 coaxially and fixedly attached to the spindle
4 and the wheel 7 rotatably extends through central bores of the
wheel 8 and of the cylinder bottom outward of the cylinder 3. The
portion of the shaft 9 accessible outside the cylinder 3 has a slot
54 in an axial plane which permits the shaft 9 to be turned
manually by means of an inserted tool or ket. A split, spring-metal
washer 10 carrying two integral, diametrically opposite,radial
locking arms 10' is secured on the exposed part of the shaft 9
against rotation by an integral projection 11 of the washer 10
which engages the slot 54. In the illustrated position of the
apparatus, the washer 10 is axially spaced from the outer, radial
end wall of the cylinder 3 a distance slightly greater than the
engaged axial height of the teeth on the wheels 7, 8. The rounded
heads 12 of two rivets inserted in the bottom wall of the cylinder
3 abuttingly engage the resilient arms 10' and prevent
counterclockwise rotation of the spindle 4 and the shaft 9 from the
position shown in FIG. 2 under the pressure exerted by the spring 6
which tends to drive the plunger 2 out of the cylinder 3.
A nipple 55, better seen in FIG. 4, normally is supplied with
lubricating oil during operation of the tensioning device, and the
oil is discharged through a duct 56 leading from the cavity of the
plunger 2 to an orifice in the cushion 1. Restricted throttling
passages in the nippe 55 and the duct 56 prevent sudden relative
motion of the plunger 2 and the cylinder 3 when the device is
filled with non-compressible oil, this dash-pot effect being
analogous to that of a liquid-filled automotive shock absorber.
The apparatus of FIGS. 1 and 2 is operated as follows:
The cylinder 3 is mounted by means of the lugs 52 on an internal
combustion engine (not shown) in the normally oil-filled
compartment which houses the valve timing chain and the cooperating
sprockets on the crankshaft and the camshaft of the engine. A new
timing chain, properly installed, is spacedly adjacent the face of
the cushion 1 which is directed obliquely upward in the view of
FIG. 1.
Oil under pressure is fed to the timing chain compartment through
the nipple 55, the interior cavity of the cylinder 3 and the
plunger 2, and the duct 56, so that a film of fresh lubricant is
maintained between the timing chain and the cushion 1, and
oscillations of the plunger assembly are damped. The oil is
returned to a pump from the compartment in a conventional manner,
not relevant to this invention. Flutter of the chain may move the
cushion 1 inward of the cylinder 3 over a maximum axial distance
corresponding to one tooth spacing of the wheels 7, 8 against the
return pressure of the spring 6 in all positions of the plunger 2
except the illustrated fully retracted position.
As the chain stretches, the cushion 1 moves axially away from the
cylinder 3, and the resulting relative axial motion of the tube 5
and the spindle 4 causes the latter to turn counterclockwise, as
viewed in FIG. 2. The slope of the saw teeth on the crown wheels 7,
8 is sufficiently shallow to permit stepwise rotation. Flutter in
the chain cannot compress the spring 6 because of the ratchet
effect of the crown wheels 7, 8 by an amount greater than that
determined by the circumferential length of one tooth on the wheels
7, 8.
When stretching of the chain can no longer be compensated for by
the advancing cushion 1, the chain needs to be replaced, and the
chain tensioning device must be restored to its original,
illustrated condition to permit removal of the old chain and
installation of a new one. For this purpose, a key, such as a flat
steel bar, a screwdriver, or the like, is inserted into the slot
54, and the shaft 9 is pushed inward of the cylinder 3 until the
teeth of the wheel 7 clear those of the wheel 8, and the washer 10
abuts against the outer bottom face of the cylinder 3. The plunger
2 may now be retracted by manually turning the shaft 9 in a
direction which is clockwise, as viewed in FIG. 2, the manually
applied force being sufficient to deflect the arms 10' as they move
over the rivet heads 12 into the illustrated position in which the
plunger 2 is axially locked against the force of the spring 6 until
the arms 10' are again moved counterclockwise over the heads 12 to
release the spring 6 after installation of the new timing
chain.
During replacement of the timing chain, the tensioning device of
the invention remains in the fully assembled condition, and no
loose parts can be dropped into the non-illustrated sump at the
bottom of the timing chain compartment.
Except as specifically set forth, the embodiments of the invention
described hereinbelow with reference to FIGS. 3 to 14 are closely
similar in structure and operation to the chain tensioning device
illustrated in FIGS. 1 and 2, and identical elements are provided
with the same numerals, and may not again be described.
The two guide elements which connect the plunger 2 with a ratchet
coupling in the apparatus illustrated in FIGS. 3 and 4 are a
cylindrical sleeve 13 and a pin 14 respectively, the pin projecting
from the plunger 2 into a groove or slot 13' in the sleeve 13. The
groove extends in one helix turn about the common axis of the
sleeve 13, the plunger 2, and the cylinder 3. The compression
spring 6 is radially confined in the sleeve 13.
The operating shaft 15 which rotatably and axially slidably passes
through the transverse end wall at the bottom end of the cylinder
carries a radial flange 16 which limits axial movement of the shaft
15 inward of the cylinder cavity as described above with reference
to the spring washer 10. The ratchet coupling which may be
disengaged by axial movement of the shaft 15 is constituted by an
integral rim of teeth 17 on the aforementioned end wall of the
cylinder 3 and a second, conforming rim 19 on another flange 18
attached to the shaft 15. The set screws which fixedly attached the
flanges 16, 18 to the shaft 15 in a conventional manner have been
omitted from the drawing. The flange 18 is fixedly fastened, as by
soldering (not shown), to the lower, annular edge of the sleeve
13.
As is better seen in FIG. 4, wall portions of the sleeve 13 bound a
lateral or axial pocket 20 at the lower end of the slot 13'. When
the plunger 2 is moved to its fully retracted position by means of
the shaft 15 and a suitable key inserted in a tool-receiving
transverse slot of the shaft, as described above, the pin 14 is
axially aligned with the pocket 20. When the shaft 15 is released,
the spring 6 causes the pin 14 to be retained in the pocket 20,
thereby locking the plunger 2 in the retracted position until it is
released manually by again moving the shaft 15 axially and turning
the shaft until the pin 14 is out of alignment with the pocket
20.
In the several modified tensioning devices illustrated in FIGS. 5
to 9, a flanged shaft 15 substantially identical with that
described with reference to FIGS. 3 and 4 is fixedly fastened to a
guide spindle 4 identical with that shown in FIG. 1 and cooperating
with a guide nut on a tube 57 fixedly fastened to the plunger 2,
the nut having been omitted from FIGS. 5 to 9 since its structure
and operation will be adquately understood from FIG. 1 and the nut
54 shown therein. FIGS. 5 to 9 particularly illustrate the locking
devices which hold the plunger assembly including the plunger 2,
the tube 57 and the chain-engaging head on the plunger in the
retracted position of the plunger during installation of a new
timing chain as described above.
The rubber cushion la on the frame 51 of the chain-engaging head
illustrated in FIG. 5 has a hook-shaped, resilient lip portion 21
which conformingly engages a hook-shaped projection 22 of the
cylinder 3' in the fully retracted position of the plunger assembly
shown in FIG. 5. The lip portion 21 is readily disengaged manually
after installation of the chain to be tensioned so that the spring
b can 6 can the cushion la axially into the chain-engaging
position.
The cushion 1b illustrated in FIG. 6 is dimensioned so as to expose
a face of the frame 51 which is obliquely inclined toward the axis
of the device in a direction away from the cylinder 3. A spring
clip 23 attached to the cylinder 3 engages the oblique face of the
frame 51 in the fully retracted condition of the plunger assembly
and may be disengaged either by direct manipulation of the clip 23,
or by merely turning the shaft 15 with a force sufficient to slip
the frame 51 out from under the clip 23.
Since the plunger assembly cannot move axially when the two guide
elements are prevented from relative threaded movement, it is
sufficient angularly to secure the shaft 15 and associated elements
to lock the plunger assembly in the retracted position. The
embodiment illustrated in FIGS. 1 and 2 employs a locking device
based on this mode of operation. Others are shown in FIGS. 7 and
8.
A radial bore in the cylinder 3a shown in FIG. 7 is provided with a
fixedly fastened, internally threaded sleeve 58 having a restricted
radially inner orifice, and outwardly closed by a threadedly
adjustable plug 59. A helical compression spring 60 in the sleeve
58 biases a steel ball 24 outward of the restricted orifice of the
sleeve 58 and into a conforming recess 61 of the flange 18' on the
shaft 15. The click stop arrangement constituted by the
spring-loaded ball 24 can lock the plunger assembly of the
apparatus of FIG. 7 in the retracted position, yet can readily be
released by merely turning the shaft 15.
The apparatus of FIG. 8 has a rubber cushion 1c in its
chain-engaging head which is merely illustrative of the wide
variety of modifications that may be applied to the individual
elements of the chain tensioning apparatus of the invention. The
plunger assembly of the device shown in FIG. 8 is held in the
retracted position by means of a leaf spring 25 fixedly fastened in
the cavity of the cylinder 3 to the transverse bottom wall of the
latter. One end portion 25' of the spring 25 is offset angularly
from the remainder of the spring for frictional, braking engagement
with the cylindrical outer circumference of the flange 18 on the
shaft 15.
In the modified apparatus shown in FIG. 9, the locking device
releasably locking the plunger assembly in the retracted position
is interposed between the plunger 2b and cylinder 3b. A bore in the
cylinder 3b is provided with a click stop not significantly
different from that described with reference to FIG. 7 and
including a steel bearing ball 26 which is spring biased inward of
a radial bore 27 of the plunger 2b.
The synthetic rubber cushion 1d of the tensioning apparatus
illustrated in FIGS. 10 and 11 is a portion of a chain-engaging
head otherwise constituted by an integral, trough-shaped part 62 of
a tubular plunger 2". The cushion is vulcanized to a brass liner 63
in the trough 62 which upwardly closes an axial bore of the plunger
2"0 and is formed with a throttling passage 64 communicating with
the bore. Two helical grooves 29 in the wall of the bore extend
each in about one turn about the common axis of the plunger 2' and
the cylinder 3" in which the plunger is axially movable.
The grooves 29 are slidably engaged by respective short,
cylindrical pins 28 projecting in opposite diametrical directions
from a plastic sleeve 30 coaxial with the plunger 2". A helical
compression spring 6' is axially interposed in the central bore of
the sleeve 30 between the liner 63 and a bottom wall 32 of the
sleeve 30 which projects radially and carries a rim of ratchet ribs
engaging a corresponding rim 33 of ratchet ribs integral with the
lower, transverse end wall of the cylinder 3". An operating shaft
34 integrally injection-molded with the sleeve 30 and its bottom
wall 32 is accessible outside the cylinder cavity as described with
reference to the other tensioning devices of the invention, and
carries a separately attached flange 65.
Wall portions of the plunger 2", in addition to the helical grooves
29, also bound a circumferential groove 31 which extends in a
radial plane relative to the plunger axis immediately adjacent the
liner 63. When the plunger 2" is in the illustrated, retracted,
axial position, it may be turned by means of the shaft 34 to locate
the pins 28 in the groove 31, and thereby to lock the plunger 2" in
the retracted position.
FIGS. 12 to 14 show a chain-tensioning device of the invention
which is somewhat similar to that described above with reference to
FIGS. 3 and 4. A guide pin 14' projects radially inward from the
plunger 2 into a generally helical groove or slot 38 in a guide
sleeve 35 coaxially received in the plunger 2 and enveloping the
compression spring 6. A lateral pocket 20' at the lower
longitudinal end of the slot 38 permits the plunger 2 to be locked
in its retracted position as described above with reference to
FIGS. 3 and 4. The edge of the sleeve 35 upwardly bounding the slot
38 is smoothly helical, and the lower edge carries projecting
ratchet teeth 37.
An operating shaft 36 projects axially from the bottom wall of the
cylinder 3 in which the plunger 2 is movably received. The shaft 36
is axially secured by a radial flange 41 outside the cylinder
cavity and an integral flange 42 in the cavity. Notches 39 in the
flange 42 are engaged by lugs of the sleeve 35 which secure the
sleeve against axial and angular movement relative to the shaft 36.
A sealing ring 40 in the bottom wall of the cylinder 3 extends
about the shaft 36.
During movement of the plunger 2 outward of the cylinder 3, as the
associated timing chain stretches, the guide pin 14' normally is
held in contact with the smooth edge of the slot 38 by the spring
6, and the sleeve 35 is gradually turned as the plunger 2 follows
the stretching timing chain. During flutter of the chain, the axial
pressure exerted by the chain on the cushion 1 can push the plunger
2 inward of the cylinder 3 only until the pin 14' is received
between two ratchet teeth 37, the shape of the teeth being such
that no significant circumferential force is exerted by the pin 14'
on the sleeve 35. The slot 38 and the pin 14' thus combine the
guide function of the elements 4, 53 in FIG. 1 with the
uni-directional coupling function of the ratchet-toothed crown
wheels 7, 8.
When it becomes necessary to replace the timing chain, a
screwdriver or other key inserted into the slotted, accessible end
of the shaft 36 permits the sleeve 35 to be turned, and the plunger
2 to be retracted thereby until the pin 14' is received in the
pocket 20'. The wall of the pocket merges so gradually with that of
the slot 38 that axial movement of the shaft 36 is not needed for
disengaging the pin 14' from the pocket 20' after installation of a
new timing chain. Manual turning force also is sufficient to
dislodge the pin 14' from between two teeth 37 without axial
movement of the shaft 36.
Frictional engagements between the plunger and the cylinder has
been found sufficient in the several embodiments of the invention
to prevent rotation of the plunger about the common axis when the
plunger is retracted by means of the operating shaft. During normal
operation, the angular position on the plunger assembly relative to
the cylinder is secured by the chain engaging the rubber cushion 1
of the head. If necessary and desired, an axial rib on the cylinder
may engage a corresponding groove in the plunger or vice versa to
prevent rotation of the plunger in the cylinder. The problem, if
any, is non-existent in a cylinder cavity and plunger of
non-circular cross section, and such a device is specifically
contemplated as a variation of the several cylindrical plungers
illustrated.
The term "plunger," as employed in this specification and the
attached claims does not exclude a suitably shaped piston combined
with a piston rod projecting axially from the cylinder cavity and
carrying the chain-engaging head.
It should be understood, therefore, that the foregoing disclosure
relates only to preferred embodiments of the invention, and that it
is intended to cover all changes and modifications of the examples
of the invention herein chosen for the purpose of the disclosure
which do not constitute departures from the spirit and scope of the
invention set forth in the appended claims.
* * * * *