Note: Descriptions are shown in the official language in which they were submitted.
D~6747 C-3360
CONSTANT LOAD SYNCHRONIZER WITH
PR.IMARY AND SECONDARY FRICTION SURFACES
This invention relates to synchromesh
arrangements for coaxially disposed rotary members
of a stepped-ratio -transmission, primarily for use
in motor vehicles.
Conventional synchronizers u-tilize syn-
chronizing rings which accept a force imposed upon
~hem, via a bal]sing s-truc-ture, corresponding to the
entire force exerted by the driver at the shift
lever, and thus depending on the driver's strenyth
and possible circumstances necessitating a quick
shift.
The present invention is concerned with
a synchromesh arrangam0n-t which is of a high
capacity synchronizer type, having a high ratio
of synchroniz.ing torque to synchronizing effort,
such as is described in U.S. Patent No. 4,185 r725
issuecd to Mai.na on January 29 r 1980 t and wh.ich further
allows a constant load to be applied to a primary
element while completion of shit is balked by a
secondary element until synchroniza-ti.on is achieved.
By the present invelltion, there is providecl
a synchromesh arrangement for coaxially disposed rotary
members of a stepped ratio transmi.ssion including a
hub men~er connected to rotate with a gear~ox main-
sha~t. A sliding-sleeve clutch member is formed with
axially extending in-ternal clutch teeth engaging axial
splines on the hub member~ A plurality of balls
resiliently biased towards a position of engagement
in respective detent recesses in the sliding-sleeve
clutch member provides a detent mechanism. A gear-
wheel is rotatably mounted on the mainshaft and
formed with external-engagement dog teeth for engage-
ment by the internal clutch teeth of the sliding-
sleeve clutch member. A primary synchroniæer element
is pxovided with a friction surface and connected
to rotate with the hub member. The primary syn~
chronizer is axially displaceable relative to the
hub member for interaction with fr.iction surfaces
on an intermediate ring element which in turn
reacts on a secondary synchronizer element. A cam
plate, connected to rotate with the gearwheel, is
formed with a ramp surface cooperating with a ramp
surface on the intermed.iate ring to provide an
axial force on -the cam plate which is transmitted
to the secondary synchronizer element and is
effective to provide a torque-inducing capacity
higher than that of the primary synchronizer element.
The secondary synchronizer element is
connected through a circumferential lost motion
mechanism to rotate with the hub member and includes
~alking teeth formed w~th balk chamfers -for engage-
ment by balk chamfers formed on the internal clutch
teeth whereby, on the app]ication of manual effort
~ia the slicling-sleeve clutch member, the detent
balls exert a constant Eorce in the axial direction
on the primary synchronizer element. Any surplus
axial load i5 transerred directly from the sliding~
lQ sleeve clutch member through the interengaged balk
chamfers to the secondary synchronizer element.
Thus, the friction surfaces of the primary synchronizer
element and of the intermediate element, respectively,
are brought into frictional interengagement -to thereby
produce at the intermediate ring element a synchron-
izing drag torque component which is effective, by
the action of the cooperating ramp surEaces, to pro-
duce axial movement of the intermediate ring element.
The axial movement provides a clamping action at
opposed radially extending annular friction-clutch
surfaces on the secondary synchronizer element thereby
providing an additional synchronizing drag torque
which per~orms the major contribution in bringing
the gearbox mainshaft and the rota~ably mounted
gearwheel into rotary synchronism. The interengaged
7 ~
~alk chamfers oE the balkin~ teeth. and of the internal
clutch teeth prevent dog~tooth engagement between the
sl.iding~sleeve clutch member and the gearwheel until
the gearbox mainshaft and -the gearwheel approach a
condition of rotary synchronism.
~Jith this arrangement, in the context oE a
high-capacity type of synchronizer, the synchxonizing
force to attain synchronizatlon between two coaxially
disposed rotary members is maintained at a constant
level irrespective oE the effort imposed by the
driverat the gear lever, with any excess loading on
the sliding~sleeve clutch member being -taken direct
on to the balking teeth of -the secondary synchronizer
element, whereby the synchronizer elements, in
particular the primar,y element, are pxotected -from
overloading~
Preferably/ the primary synchronizer element
is a synchro ring, and the friction surfaces o:E the
primary synchronizer element and the intermediate
ring element are Erustoconical sur~aces o~ -the
respective elements. The secondary synchronizer
element is desirably a plate~type element having Eric-
tion faces applied thereto ! since such an element
inherently has a high torque capacity.
The surfaces of the synchronizer arranye
ment which are intensely loaded may be o:E hardenecl
steel for achieving a high torque capacity~
Thus if, as is preferred, frict~on~reducing
rollers are interposed bet,ween the first and second
ramp surfaces, the ramp su~faces are des;ra~l~
hardened steel surfaces.
As an alternative friction-reducin~
expedient, a PTFE ('polytetrafluoroethylene~ inter-
layer, in the ~orm of a film or a PTFE~coated spacer,
'may be interposed between the first and second ramp
surfaces.
For high torque capacity, it is most desira~le
for the main torque~carrying fr~ction surfaces to ~e
disposed at a large radius relative to tEle main axis
of rotation (mainshaEt axis). The first and second
ramp surfaces may be disposed at a lesser radius than
the radially extending annular ~riction~clutch surfaces
of the secondary synchronizer element, at a location
radially inwardly o~ the intermediate element~ This
can provide a particularly compact and rela:tively
simple arranyement.
A significant advantage of such a synchro~
mesh arrangement is that -the primary element, which
i~ preferably of a conical seating t~pe, is protected
from overloading resulting from undue e~fort exerted
by the driver, so contrihuting to long synchxonizer
life. The excess loading is taken by the EligEler
capacity secondary synchroni~er element, desirably
a plate~type element~
A related further advantage is that, since
the primary element i5 inherently protectecl from
overloading, the system is more suitable for power
shift operation~ if required, and would allow a high
ac~uating load to be imposed on the engaging clutch
in order to effect a rapid and positive engagement
the instant synchronization is achieved~
In the drawings~
Figure 1 is a fragmentary longitudinal
s2ction illu~trating one embodiment o~ a synchromesh
arrangement in accordance with the present invention
for coaxially disposed rotary members o~ a stepped-
ratio transmission;
Figure 2 is an enlarged -fragrnentary ele-
vation, with parts broken away, illustrating details
of a sli.ainy-sleeve clutch member and hub and asso~
ciated parts o~ the synchromesh arrangement shown
in Figure l; and
Figures 3 and 4 are two views, with parts
broken away, to illustrate fllrther details o~ the
relationship between the ~l.~ding~sleeve clutch member
and the hub and a.ssociated parts which are shown in
Figure 2.
3, ~
In a specif~c synchromes~ arrangement the
actual force required to obtain synchronization within
a specified time sequence is a predetermined nominal
value which does no-t need to be exceeded~ The a.~ange-
ment which is shown in t~e drawings enahles a constantload to be applied to a primary element while the
completion of shi~t is balked by a secondary element
until synchroniza-tion is achieved.
As is shown in Figure 1 o~ the drawings, a
synchromesh arrangement lO in accordance with the
present invention includes a ~ub 12 (first rotary
element) having a longitudinally-splined connection
to a rotary mainshaft (outpu~ shaft) 14 oF a corlstant-
mesh type of gearbox, the hub 12 being located axially
between a shoulder 16 of the mainshaft and an annular
retainer 18 mounted to the mainshaft.
As is shown in Figure 2 of the drawinys,
a sliding-sleeve clutch member 20 formed with
longitudinally extending internal clu-tch tee-th 22
is slidably mounted on longitudlnally exteIIding spl.ine
teeth (axial splines) 24 formed on the hub 12.
Cîrcum~erentially spaced detent balls 26
spring-biased radially outwardl~ by respecti~e
biasing springs 28 acting on cup-like biasing plungers
30 are accommodated in an annular ~etent recess 32 of
predetermined ramp angle in the clutch member 20.
3, ~
A toothed gearw~eel 34 (:second rotar~
element) is loosely mounted on the mainshaft 14 for
rotation relat~ve thereto, th~s ~einy coa~ially
disposed with respect to the mainshaftq The year-
~ 5 wheel 34 is arranged to be dri~en ~ be~ng .in constantmesh with a ring o-~ teeth on a conventional layshaft
(not shown) that is itself dri~en in the con~entional
fashion ~y way of meshing head gears (not shown) ~y
a ~ehicle engine (also not shown). The gearwheel
34 is formed with a ring of dog teeth 36 which, as
will be described, act as one par-t of a positi~e~
engagement clutch~
Disposed axially between -the hub 12 and
the gearwheel 34 there is a primary synchronizer
element 38 in the form o-E a synchro rin~ ha~ing an
internal frustoconical friction surface 40~ To
cause the synchro ring 38 to ~e driven in a rotary
sense by the hub 12, the synchro ring includes
circumferent:ially spaced lugs 42 which extend into
respective apertures 44 in the hub. The hub 12
loca~es the synchro ring 38 radially while per-
mitting free axial displacement.
An annular intermedia-te ring 46 is also
disposed axially between the hub 12 and the gearwheel
34, at a location generally radially inwaxdly of the
synchro r.ing 38, and is formed w~th an external
7~
frustoconical frictîon surface 48 for selective
frictional engagement b~ the frustoconical friction
surface 40 on the synchro ring~ ~ first annular
ramp surface 50 on the in~ermediate ring 46 com~
prises a series of pairs of ramps, each ramp pai~r
forming a shallow circumferentially extending
V-shaped configuration.
An annular cam plate 52 is secured to the
gearwheel 34 for rotation therewith~ and is formed
with a second annular ramp surface 54 which is of
similar configuration to, and faces, the fixst annular
ramp surface 50. A series of rollers 56 retained
by a conventional roller cage is disposed between
the faciny ramp surfaces 50 and 54, with each roller
located in the diamond-shaped space between facing
ramp pairs. An annular retainer 58 is secured to the
gearwheel 34 to provide reaction for the cam plate
52, and a Belleville sprlng 60 seated on the year-
wheel biases the intermediate ring 46 axially
towards the cam plate 52, thereby mainta.ining the
rollers 56 at al] times in engagement with the
respective facing ramp pairs and also ensuring
running clearance at the interacting Eriction surfaces
of the secondary element 62.
The secondary synchronizer element 62, in
D 180574
the form of a plate~type friction clutch element,
îs provided with opposed annular friction faces
64 forming friction-clutch surfaces Eor cc>opera-tion
with corresponding annular frictlon s~lrfaces on,
respectively, the gearwheel 34 and the lnte~medi.ate
ring 46~ This secondary synchronizer element 62 is
formed with external lugs 66 which are accommodated
with circumferential play in the apertures 44 in the
hub 12~ The hub 12 locates the secondary synchronizer
lQ element 62 radially while permitting slight axial
displacement. Figure 2 illustrates the circumferen-
tial lost motion 70 available by reason of the gap
between each of the externaL lugs 66 and the circum~
ferential edge 72 of the respect;.ve aperture 44.
lS Balking teeth 74 provided with balk cham-fers
76 are formed on the external luys 66~ so providiny
radial segments oE balking teeth the balk chamfers
o~ which can selectively cooperate with corresponding
balk cham~ers 78 on -the internal clu-tch teeth 22
of the sliding-sleeve clutch member 20.
As will be described~ the foregoing elements
are effective as a constan-t-load synchromesh arrange-
ment ~or achi.eving synchronized posi-tive-clutch
engagement of the sliding-sleeve clutch member 20
with the rotary gearwheel 34, -to couple the gearwheel
34 to the gear~ox mainshaf'c L4. Figure 1 shows that
5 ~ ~
the sliding~slee~e clutch member 20 is in fact a
double~acting clutc~ member, inasmuch as a second
rotary gearwheel 80 is d~sposed on the opposite axial
side of the hub 12 from the gearwheel 34 and is
provided with synchromesh elements which are ~irtually
a mirror image o~ those provided for yearwheel 34.
The two sets of synchromesh elements, namely for the
gearwheels 34 and 80 respecti~ely, operate in a
similar manner, corresponding ko t~e description
which now follows of synchronized positive-clutch
engagement to couple gearwheel 34 to the gearbox
mainshaft 14~
By appropriate movement of a conventional
shift lever Cnot shownl connected by way of gearshift
linkage (not shown3, to a conventional striker ~ork
(also not shown) ~or the sliding-sleeve clutch member
20, this clutch member 20 is movable axially to the
left ~rom the neutral position illustrated in Figure 1
With such axial movement of -the sliding-sleeve clutch
member, the detent balls 26 are brought into contact
wi.th the primary synchroni,zer element constituted
by the synchro ring 38, and initiate energization
of the synchromesh arrangementO The ramp angles
in the detent recesses 32 are such that, i.n combi-
nation with the load exerted by -the biasing springs
12
28 on the detent balls 26, a predetermined force
~in other words, a constant load~ i~s maintained.
on the prima.ry synchronizer element 38 duri`n~ the
initial phase of displacem~nt of the slidin~
sleeve clutch mem~er 2a.
The effort applied -to -the pr.imary syn~
chronizer element 38 induces a self energizing
force on the secondary synchronizer element 62 in
a similar manner to tha. described in said U~S.
Patent No. 4,185,725~ Briefly, the frictional
interengagement of the frustoconical friction surfaces
40 and 48 induces a synchroniziny drag torque on
the int.ermediate ring 46 which causes the rollers
56 to move up-ramp to impart an axially directed
self-energizing force wpon the secondary element 62,
and this axial force is effectivP via -the friction
faces 64 of the secondary e:lement -to produce a
clamping acti.on of the secondary element between
the intermedi.ate ring 46 and the gearwheel 34 which
performs the major contribution .in bringing the
gearbox mainshaft 14 and the gearwheel 34 into
rotary synchronism.
The external balking teeth 74 on the .lugs
66 of the secondary synchronizer 62 element provide
effective blocking of the internal clutch teeth 22
12
of the sliding~slee~e clutch-member 20, preventing
further displacement o~ the clu-tch member 20 to a
gear-engagement position~ The width of the lugs 66
on the secondary element 62 i~n relation to the
apertures 44 in the hub 12 permits the circumferential
lost motion attitude in either a clockwise or counter~
clockwise direction {dependin~ on the direc-tion of
drive), so blocking further axial displacement of
the sliding-sleeve clutch men~er 20, and this lost
motion attitude is maintained as long as there exists
relative rotation of the elements requiring synchro
nization.
While the sliding-sleeve clutch member 20
is in its balked posi.tion, due to the action of the
balking teeth 74 of the secondary synchronizer
element 62, the detent balls 26 continue to exert a
constan-t force on the primar~ element 38 irrespective
o~ the equivalent force imposed by the driver, which
i5 reactecl upon the secondary element balking teeth.
Upon synchronization being achieved, the
continuing axial force acting on the in-terengaged
balk chamfers 76 and 78 effects alignment of the
halking teeth 74 into a centralized condi.tion, thereby
permitting the sliding~sleeve clutch member 20 to
proceed into a fully engaged positive-clutch posi-tion.
7 ~
14
In this position, the geaxbox mai.nshaft 14 is coupled
to the.gearwheel 34p and t~eEe~y ca~sed to rotate
at the speed a-t which the gearw~eel 34 is ~eing
driven by the layshaft, and this~ cond~tion continues
until the driver returns t~e sl~din~sleeve clutc~
mem~er 20 to its neutral posi:tion in which the
Belleville spring 60 performs a release funct~on on
the synchromesh elements.
A variant o the above descri~ed synchromesh
arrangement, still maintaining the constant load
~eature, may be provided with o~.ission of the balkiny
teeth 74 so as to eliminate mechanical inhi~i-tion of
engagement of the dog teeth 36 by the clutch teeth 2~.
In this way, the function of restraining
engagement until synchroniza-tion is achieved is left
to the discretion of the driver, who, having exerted
a load not exceeding that oE the constant load pre~
determined by the detents but suEficient in his
judgment to efEect synchronization in a desired time
sequence, will dwell at that load level accordingly
before exerting further effort to complete full
engagement.
This variant could ~e oE considerable
advantage with a manual shiet arrangement when
operating first and second gear downshift.q where
l~L
significant effort is required on large transmissIonsr
as on hea~y trucks/ to overc~me the friction between
-the sliding sur~aces of the balking chamfers 76 and 78
due to the high axial loads s-till required to achieve
synchronizat~on being sustained at those suraces to
a substantial degree beyond the stage of synchroniza-
tion.
