GB2101240A - Synchromesh arrangements - Google Patents

Abstract

A synchromesh arrangement (10) suitable for heavy-duty applications includes a sliding-sleeve clutch (20) formed with detent recesses (32) of predetermined ramp angle, and spring-loaded detent balls (26) in hub (12) which co-operate with the respective detent recesses for constant-load energisation of a ring- type primary synchroniser element (38). This develops a synchronising drag torque component at an intermediate element (46) which, by the action of a pair of ramp surfaces (50, 54) co-operating, e.g. via rollers (56), thereby produces a clamping action at a plate-type secondary synchroniser element (62) of high drag torque-inducing capacity. Any excess loading on the clutch (20) is taken direct on to baulking teeth (74) of the secondary synchroniser element, whereby the primary synchroniser element is protected from overloading. It is suggested that the baulking teeth may be omitted in some manual-shift arrangements. <IMAGE>

Description

SPECIFICATION Synchromesh arrangements This invention relates to synchromesh arrangements for coaxially disposed rotary members of a stepped-ratio transmission, primarily for use in motor vehicles.

Conventional synchronisers utilise synchronising rings which accept a force imposed upon them, via a baulking structure, corresponding to the entire force exerted by the driver at the shift lever, and thus depending on the driver's strength and possible circumstances necessitating a quick shift.

The present invention is concerned with a synchromesh arrangement which is of a high capacity synchroniser type, having a high ratio of synchronising torque to synchronising effort, such as is described and claimed in our United Kingdom patent specification 1,583,076 (20,670/77), and which further allows a constant load to be applied to a primary element whilst completion of shift is baulked by a secondary element until synchronisation is achieved.

By the present invention there is provided a synchromesh arrangement for coaxiallv disposed rotary members of a stepped-ration transmission, 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 externalengagement dog teeth for engagement by the internal clutch teeth of the sliding-sleeve clutch mernber, a primary synchroniser 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, an intermediate ring element providing interacting friction surfaces with the primary synchroniser element and a secondary synchroniser 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 co-operating with the first ramp surface, with the gearwheel providing axial reaction for the cam plate, the secondary synchroniser element having a pair of opposed radially extending annular friction-clutch surfaces effective to provide a torque-incuding capacity higher than that of the primary synchroniser element, the secondary synchroniser element being connected with circumferential lost motion to rotate with the hub member, and including baulking teeth formed with baulk chamfers for engagement by baulk chamfers formed on the internal clurch teeth, whereby on the application of manual effort via the slidingsleeve clutch member the detent balls exert a constant force in the axial direction on the primary synchroniser element, with any surplus axial load being transferred direct from the sliding-sleeve clutch member through the interengaged baulk chamfers to the secondary synchroniser element, such that the friction surfaces of the primary synchroniser element and of the intermediate element respectively are brought into frictional interengagement to thereby produce at the intermediate ring element a synchronising drag torque component which is effective, by the action of the co-operating 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 synchroniser element, to provide an additional synchronising drag torque which performs the major contribution in bringing the gearbox mainshaft and the rotatably mounted gearwheel into rotary synchronism, with the interengaged baulk chamfers of the baulking teeth and of the internal clutch teeth preventing dogtooth engagement between the sliding-sleeve clutch member and the gearwheel until the gearbox mainshaft and the gearwheel approach a condition of rotary synchronism.

With this arrangement, in the context of a highcapacity type of synchroniser the synchronising force to attain synchronisation between two coaxially disposed rotary members is maintained at a constant level irrespective of the effort imposed by the driver at the gear lever, with any excess loading on the sliding-sleeve clutch member being taken direct on to the baulking teeth of the secondary synchroniser element, whereby the synchroniser elements, in particular the primary element, are protected from overloading.

Preferably the primary synchroniser element is a synchro ring, and the friction surfaces of the primary synchroniser element and the intermediate ring element are frustoconical surfaces of the respective elements. The secondary synchroniser element is desirably a plate-type element having friction faces applied thereto, since such an element inherently has a high torque capacity.

Such surfaces of the synchroniser arrangement as are intensely loaded may be of hardened steel, for achieving a high torque capacity.

Thus if, as is preferred, friction-reducing rollers are interposed between the first and second ramp surfaces, the ramp surfaces are desirably hardened steel surfaces.

As an alternative friction-reducing expedient, a PTFE (polytetrafluorethylene) interlayer, in the form 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 desirable for the main torque-carrying friction surfaces to be disposed at a large radius relative to the main axis of rotation (mainshaft axis). The first and second ramp surfaces may be disposed at a lesser radius than the radially extending annular friction-clutch surfaces of the secondary synchroniser element, at a location radially inwardly of the intermediate element. This can provide a particularly compact and relatively simple arrangement.

A significant advantage of such a synchromesh arrangement is that the primary element, which is preferably of a conical seating type, is protected from overloading resulting from undue effort exerted by the driver, so contributing to long synchroniser life. The excess loading is taken by the higher capacity secondary synchroniser element, desirably a plate-type element.

A related further advantage is that, since the primary element is inherently protected from overloading, the system is more suitable for power shift operation, if required, and would allow a high actuating load to be imposed on the engaging clutch in order to effect a rapid and positive engagement the instant synchronisation is achieved.

In the drawings: Figure 1 is a fragmentary longitudinal section illustrating one embodiment of synchromesh arrangement in accordance with the present invention for coaxially disposed rotary members of a stepped-ratio transmission; Figure 2 is an enlarged fragmentary elevation, with parts broken away, illustrating details of a sliding-sleeve clutch member and hub and associated parts of the synchromesh arrangement shown in Figure 1; and Figures 3 and 4 are two views, with parts broken away, to illustrate further details of the relationship between the sliding-sleeve clutch member and the hub and associated parts which are shown in Figure 2.

In a specific synchromesh arrangement the actual force required to obtain synchronisation within a specified time sequence is a predetermined nominal value which does not need to be exceeded. The arrangement which is shown in the drawings enables a constant load to be applied to a primary element whilst the completion of shift is baulked by a secondary element until synchronisation is achieved.

As is shown in Figure 1 of the drawings, a synchromesh arrangement 10 in accordance with the present invention includes a hub 12 (first rotary element) having a longitudinally-splined connection to a rotary mainshaft (output shaft) 14 of a constant-mesh type of gearbox, the hub 12 being located axially between a shoulder 1 6 of the mainshaft and an annular retainer (circlip) 1 8 mounted to the mainshaft.

As is shown in Figure 2 of the drawings, a sliding-sleeve clutch member 20 formed with longitudinally extending internal clutch teeth 22 is slidably mounted on longitudinally extending spline tteth (axial splines) 24 formed on the hub 12.

Circumferentially spaced detent balls 26 spring-biased radially outwardly by respective biasing springs 28 acting on cup-like biasing plungers 30 are accommodated in an annular detent recess 32 of predetermined ramp angle in the clutch member 20.

A toothed gearwheel 34 (second rotary element) is loosely mounted on the mainshaft 14 for rotation relative thereto, thus being coaxially disposed with respect to the mainshaft. The gearwheel 34 is arranged to be driven by being in constant mesh with a ring of teeth on a conventional layshaft (not shown) that is itself driven in the conventional fashion by way of meshing head gears (not shown) by a vehicle engine (also not shown). The gearwheel 34 is formed with a ring of dog teeth 36 which, as will be described, act as one part of a positiveengagement clutch.

Disposed axially between the hub 12 and the gearwheel 34 there is a primary synchroniser element 38 in the form of a synchro ring having an internal frustoconical friction surface 40. To cause the synchro ring 38 to be driven in a rotary sense by the hub 12, the synchro ring includes circumferentially spaced lugs 42 which extend into respective apertures 44 in the hub. The hub 12 locates the synchro ring 38 radially whilst permitting free axial displacement.

An annular intermediate ring 46 is also disposed axially between the hub 12 and the gearwheel 34, at a location generally radially inwardly of the synchro ring 38, and is formed with an external frustoconical friction surface 48 for selective frictional engagement by the frustoconical friction surface 40 on the synchro ring. A first annular ramp surface 50 on the intermediate ring 46 comprises a series of pairs of ramps, each ramp pair 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 first annular ramp surface 50. A series of rollers 56 retained by a conventional roller cage is disposed between the facing ramp surfaces 50 and 54, with each roller located in the diamond-shaped space between facing ramp pairs. An annular circlip 58 is located to the gearwheel 34 to provide reaction for the cam plate 52, and a Belleville spring 60 seated on the gearwheel biases the intermediate ring 46 axially towards the cam plate 52, thereby maintaining the rollers 56 at all times in engagement with the respective facing ramp pairs and also ensuring running clearance at the interacting friction surfaces of the secondary element 62.

The secondary synchroniser element 62, in the form of a plate-type friction clutch element, is provided with opposed annular friction faces 64 forming friction-clutch surfaces for co-operation with corresponding annular friction surfaces on, respectively, the gearwheel 34 and the intermediate ring 46. This secondary synchroniser 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 synchroniser element 62 radially whilst permitting slight axial displacement.

Figure 2 illustrates the circumferential "throw over" 70 available by reason of the gap between each of the external lugs 66 and the circumferential edge 72 of the respective aperture 44.

Baulking teeth 74 provided with baulk chamfers 76 are formed on the external lugs 66, so providing radial segments of baulking teeth the baulk chamfers of which can selectively cooperate with corresponding baulk chamfers 78 on the internal clutch teeth 22 of the sliding-sleeve clutch member 20.

As will be described, the foregoing elements are effective as a constant-load synchromesh arrangement for achieving synchronised positiveclutch engagement of the sliding-sleeve clutch member 20 with the rotary gearwheel 34, to couple the gearwheel 34 to the gearbox mainshaft 14. Figure 1 shows that the sliding-sleeve clutch member 20 is in fact a double-acting clutch member, inasmuch as a secondary rotary gearwheel 80 is disposed on the opposite axial side of the hub 12 from the gearwheel 34 and is provided with synchromesh elements which are virtually a mirror image of those provided for gearwheel 34. The two sets of synchromesh elements, namely for the gearwheels 34 and 80 respectively, operate in a similar manner, corresponding to the description which now follows of synchronised positive-clutch engagement to couple gearwheel 34 to the gearbox mainshaft 14.

By appropriate movement of a conventional shift lever (not shown) connected by way of gearshift linkage (not shown) to a conventional striker fork (also not shown) for the sliding-sleeve clutch member 20, this clutch member 20 is movable axially to the left from 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 with the primary synchroniser element constituted by the synchro ring 38, and initiate energisation of the synchromesh arrangement. The ramp angles in the detent recesses 32 are such that, in combination with the load exerted by the biasing springs 28 on the detent balls 26, a predetermined force (in other words, a constant load) is maintained on the primary synchroniser element 38 during the initial phase of displacement of the sliding-sleeve clutch member 20.

The effort applied to the primary synchroniser element 38 induces a self-energising force on the secondary synchroniser element 62 in a similar manner to that described in the said United Kingdom patent specification 1,583,076. Briefly, the frictional interengagement of the frustoconical friction surfaces 40 and 48 induces a synchronising drag torque on the intermediate ring 46 which causes the rollers 56 to move up-ramp to impart an axially directed self-energising force upon the secondary element 62, and this axial force is effective via the friction faces 64 of the secondary element to produce a clamping action of the secondary element between the intermediate 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 baulking teeth 74 on the lugs 66 of the secondary synchroniser 62 element provide effective blocking of the internal clutch teeth 22 of the sliding-sleeve clutch member 20, preventing further displacement of the clutch member 20 to a gear-engagement position. The width of the lugs 66 on the secondary element 62 in relation to the apertures 44 in the hub 12 permits the circumferential "throw over" attitude in either a clockwise or an anticlockwise direction (depending on the direction of drive), so blocking further axial displacement of the sliding-sleeve clutch member 20, and this "throw over" attitude is maintained as long as there exists relative rotation of the elements requiring synchronisation.

Whilst the sliding-sleeve clutch member 20 is in its baulked position, due to the action of the baulking teeth 74 of the secondary synchroniser element 62, the detent balls 26 continue to exert a constant force on the primary element 38 irrespective of the equivalent force imposed by the driver, which is reacted upon the secondary element baulking teeth.

Upon synchronisation being achieved, the continuing axial force acting on the interengaged baulk chamfers 76 and 78 effects alignment of the baulking teeth 74 into a centralised condition, thereby permitting the sliding-sleeve clutch member 20 to proceed into a fully engaged positive-clutch position. In this position the gearbox mainshaft 14 is coupled to the gearwheel 34, and thereby caused to rotate at the speed at which the gearwheel 34 is being driven by the layshaft, and this condition continues until the driver returns the sliding-sleeve clutch member 20 to its neutral position in which the Belleville spring 60 performs a release function on the synchromesch elements.

A variant of the above described synchromesh arrangement, stiil maintaining the constant load feature, may be provided with omission of the baulking teeth (74) so as to eliminate mechanical inhibition of engagement of the dog teeth (36) by the clutch teeth (22).

In this way the function of restraining engagement until synchronisation is achieved is left to the discretion of the driver, who, having exerted a load not exceeding that of the constant load predetermined by the detents but sufficient in his judgement to effect synchronisation in a desired time sequence, will "dwell" at that load level accordingly before exerting further effort to complete full engagement.

This variant could be of considerable advantage with a manuai-shift arrangement when operating 1 st and 2nd gear down-shifts where significant effort is required on large transmissions, as on heavy trucks, to overcome the friction between the sliding surfaces of the baulking chamfers (76) and (78) due to the high axial loads still required to achieve synchronisation being sustained at those surfaces to a substantial degree beyond the stage of synchronisation.

Claims (7)

1. A synchromesh arrangement for coaxially disposed rotary members of a stepped-ratio transmission, 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 synchroniser 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, and intermediate ring element providing interacting friction surfaces with the primary synchroniser element and with a secondary synchroniser 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 co-operating with the first ramp surface, with the gearwheel providing axial reaction for the cam plate, the secondary synchroniser 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 synchroniser element, the secondary synchroniser element being connected with circumferential lost motion to rotate with the hub member, and including baulking teeth formed with baulk chamfers for engagement by baulk chamfers formed on the internal clutch teeth, whereby on the application of manual effort via the slidingsleeve clutch member the detent balls exert a constant force in the axial direction on the primary synchroniser element, with any surplus axial load being transferred direct from the sliding-sleeve clutch member through the interengaged baulk chamfers to the secondary synchroniser element, such that the friction surfaces of the primary synchroniser element and of the intermediate element respectively are brought into frictional interengagement to thereby produce at the intermediate ring element a synchronising drag torque component which is effective, by the action of the co-operating 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 synchroniser element to provide an additional synchronising drag torque which performs the major contribution in bringing the gearbox mainshaft and the rotatably mounted gearwheel into rotary synchronism, with the interengaged baulk chamfers of the baulking teeth and of the internal clutch teeth preventing dogtooth 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 synchroniser element is a synchro ring, and the friction surfaces of the primary synchroniser element and the intermediate ring element are frustoconical surfaces of the respective elements.

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

4. A synchromesh arrangement according to any one of claims 1 to 3, in which frictionreducing rollers are interposed between the first and second ramp surfaces, and the ramp surfaces are hardened steel surfaces.

5. A synchromesh arrangement according to any one of claims 1 to 3, in which a polytetrafluorethylene interlayer is interposed between the first and second ramp surfaces.

6. A synchromesh arrangement according to any one of claims 1 to 5, in which the first and second ramp surfaces are disposed at a lesser radius than the radially extending annular frictionclutch surfaces of the secondary synchroniser element, at a location radially inwardly of the intermediate ring element.

7. A synchromesh arrangement for coaxially disposed rotary members of a stepped-ratio transmission, substantially as hereinbefore particularly described and as shown in the accompanying drawings.