CA1180574A - Constant load synchronizer with primary and secondary friction surfaces - Google Patents

Abstract

CONSTANT LOAD SYNCHRONIZER WITH
PRIMARY AND SECONDARY FRICTION SURFACES

Abstract of the Disclosure A synchromesh arrangement suitable for heavy-duty applications includes a sliding-sleeve clutch formed with detent recesses of predetermined ramp angle, and spring-loaded detent balls cooperate with the respective detent recesses for constant-load energization of a ring-type primary synchronizer element. This develops a synchronizing drag torque component at an intermediate element which, by the action of a pair of ramp surfaces cooperating via rollers, thereby produces a clamping action at a plate-type secondary synchronizer element of high drag torque-inducing capacity. Any excess loading on the clutch is taken direct on to balking teeth of the secondary synchronizer element, whereby the primary synchronizer element is protected from overloading.

Description

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 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 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 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.

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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.

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A synchromesh arrangement for coaxially disposed rotary members of a stepped-ratio trans-mission, comprising a hub member connected to rotate with a gearbox mainshaft, a sliding-sleeve clutch member formed with axially extending internal clutch teeth engaging axial splines on the hub member, a plurality of detent balls resiliently biased towards a position of engagement in respective detent recesses in the sliding-sleeve clutch member, a gearwheel rotatably mounted on the mainshaft and formed with external-engagement dog teeth for engagement by the internal clutch teeth of the sliding-sleeve clutch member, a primary synchronizer element which is provided with a friction surface and connected to rotate with the hub member and is axially displaceable relative to the hub member, a secondary synchronizer element, an intermediate ring element providing interacting friction surfaces with the primary synchronizer element and with the secondary synchronizer element respectively and formed with a first ramp surface, a cam plate connected to rotate with the gearwheel and formed with a second ramp surface cooperating with the first ramp surface, with the gearwheel providing axial reaction for the cam plate, the secondary synchronizer element having a pair of opposed radially extending annular friction-clutch surfaces effective to provide a torque-inducing capacity higher than that of the primary synchronizer element, the secondary synchronizer element being connected with circumferential lost motion to rotate with the hub member, and including balking teeth formed with balk chamfers for engagement by balk chamfers formed on the internal clutch teeth, whereby on the application of manual effort via the sliding-sleeve clutch member the detent balls exert a constant force in the axial direction on the primary synchronizer element, with any surplus axial load being transferred direct from the sliding-sleeve clutch member through the interengaged balk chamfers to the secondary synchro-nizer element, such that 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 synchronizing drag torque component which is effective, by the action of the cooperating ramp surfaces, to produce axial movement of the intermediate ring element providing a clamping action at the opposed radially extending annular friction-clutch surfaces of the secondary synchronizer element to provide an additional synchronizing drag torque which performs the major contribution in bringing the gearbox mainshaft and the rotatably mounted gear-wheel into rotary synchronism, with the interengaged balk chamfers of the balking teeth and of the internal clutch teeth preventing dog-tooth engagement between the sliding-sleeve clutch member and the gearwheel until the gearbox mainshaft and the gearwheel approach a condition of rotary synchronism.

2. A synchromesh arrangement according to Claim 1, in which the primary synchronizer element is a synchro ring, and the friction surfaces of the primary synchronizer element and the intermediate ring element are frustoconical surfaces of the respec-tive elements.

3. A synchromesh element according to Claim 1 or 2, in which the secondary synchronizer element is a plate-type element having friction faces applied thereto.

4. A synchromesh arrangement according to Claim 1 or 2, in which friction-reducing rollers are interposed between the first and second ramp surfaces, and the ramp surfaces are hardened steel surfaces.

5. A synchromesh arrangement according to Claim 1 or 2, in which the first and second ramp surfaces are disposed at a lesser radius than the radially extending annular friction-clutch surfaces of the secondary synchronizer element, at a location radially inwardly of the intermediate ring element.