Synchronizing device in a vehicle gearbox

Synchronizing device in a motor vehicle gearbox, comprising outer and inner synchronizing rings (12, 13) and a torque transmitting element (20) which transmits torque from the inner synchronizing ring to an engagement sleeve (4) in such a manner that the engaging sleeve is imparted extra force in the engagement direction.

The present invention relates to a synchronizing device in a vehicle 
gearbox, comprising a guide sleeve, intended to be non-rotatably joined to 
a shaft in a gearbox, an engaging sleeve, which is non-rotatably but 
axially displaceably mounted on the guide sleeve, an engaging ring 
provided with external engaging teeth, said ring being designed to be 
non-rotatably joined to a gear rotatably mounted on said shaft and being 
lockable relative to the guide sleeve by axial displacement of the 
engaging sleeve from a neutral position to an engaging position, in which 
internal engaging teeth on the engaging sleeve engage with external teeth 
on the engaging ring, and with synchronizing means cooperating with the 
engaging sleeve and the engaging ring, in the form of at least two 
concentric synchronizing rings, each having an individual conical 
frictional surface, said synchronizing rings being displaceable in 
engagement with corresponding conical frictional surfaces on a sleeve 
element rotationally fixed relative to the engaging ring and lying between 
said synchronizing rings. 
Synchronizing devices of the abovementioned type, so-called double 
synchronizers, are used i.a. in gearboxes for trucks to increase the 
synchronizing torque and thus reduce the shifting work and make possible 
relatively short shifting movements of the shift lever. A double 
synchronization provides an approximately 30% reduction in the shifting 
force on the shift lever compared with the corresponding single 
synchronization. In many cases the shifting force can exceed 200N on the 
shift lever in a gearbox with single synchronization and this means that 
even with a double synchronization the shifting force will be high. An 
additional reduction would therefore be desirable to eliminate the risk of 
wear-related injuries to the back and shoulders of truck drivers. 
One method is to increase the shifting distance in the shift lever to 
provide a greater mechanical advantage, but this presupposes that space is 
available so that the driver will not risk hitting his knuckles against 
parts in the cab. A long shifting distance will also create problems in 
trucks with the engine and gearbox placed under a tippable cab. Another 
method is to use a compressed air servo unit, but this is an expensive 
solution. 
The purpose of the present invention is to achieve a double synchronization 
of the type described by way of introduction, by means of which it is 
possible, while retaining a short shifting distance of the shift lever, to 
reduce, without a servo unit, the shifting force which must be applied to 
the shift lever, to a fraction of what is required for shifting in 
previously known gearboxes with double synchronization of the type 
described. 
This is achieved according to the invention by virtue of the fact that that 
one synchronizing ring is fixed rotationally relative to the torque 
transmitting element which has cam surfaces cooperating with cam surfaces 
on the engaging sleeve, said cam surfaces, upon relative rotation between 
the torque transmitting element and the engaging sleeve,--caused by 
frictional engagement between the frictional surfaces of the synchronizing 
means--creates a force acting in the engaging direction of the engaging 
sleeve. 
The invention is based on the idea of transferring a portion of the 
rotational energy of the gearbox itself to the shifting mechanism and in 
this manner creating a type of integrated servo system, which assists in 
the manually initiated and terminated shifting sequence. In principle, 
shifting, after manual initiation of the synchronizing sequence, can be 
effected entirely under the influence of the created servo system. 
However, in many cases it can be undesirable, since it can result in 
involuntary shifting. 
In a further development of the synchronizing device according to the 
invention, the torque transmitting element is axially displaceably joined 
to said synchronizing ring and is moveable away from the synchronizing 
ring against the effect of the spring force, which in a preferred 
embodiment is created by a cup spring package between a surface on the 
torque transmitting element and an opposing surface on the guide sleeve. 
Thus the force of the compressed spring package together with the angle of 
the cam surfaces determine the force acting on the engaging sleeve in the 
engaging direction, which force can be selected so that it is not quite 
sufficient to complete the shifting, but is sufficient so that the 
additional manual force required only prevents unintentional shifting.

The synchronizing device according to the invention is based on a 
previously known so-called double synchronizer, which comprises a guide 
sleeve 1, non-rotabably fixed on a shaft (not shown) in a gearbox, said 
guide sleeve having external teeth 2 engaging in a gap between the 
interior teeth 3 of an engaging sleeve 4. An engaging ring 5 with external 
engaging teeth 6 is solidly joined to a gear (not shown) rotatably mounted 
on a shaft. A synchronizing cone 7 has an external and an internal conical 
frictional surface 8 and 9, respectively, and is provided with pins 10 
extending into openings 11 in the engaging ring 5, whereby the 
synchronizing cone 7 is rotationally fixed but axially limitedly moveable 
relative to the engaging ring 5. Outer and inner synchronizing rings 12 
and 13, respectively, are arranged on either side of the synchronizing 
cone 7 and are provided with frictional surfaces 14 and 15, respectively, 
which face the frictional surfaces 8 and 9, respectively, of the 
synchronizing cone 7. In the embodiment shown, the outer synchronizing 
ring 12 is provided with keys 16, which in a known manner cooperate with a 
pair of ramps 17 on the engaging sleeve 4. In addition to the components 
described the double synchronization also comprises known spring-loaded 
keys (not shown). 
According to the invention the torque of the inner synchronizing ring 13 is 
transmitted to the engaging sleeve 4 via a torque transmitting element, 
generally designated 20, which comprises a ring 21 with a number, for 
example three, of arms or fingers 22, which are held in slots 23 in the 
guide sleeve 1 and at their ends have keys 24 which have cam surfaces 25 
oriented in a V-shape and which cooperate with corresponding cam surfaces 
26 on the ramps 17. In the example shown, the cam surfaces 25, 26 have an 
angle .alpha. of 60.degree. to the axial direction, but the angle can vary 
within the interval 40.degree.-75.degree.. 
The ring 21 is made with a number of evenly distributed teeth 27, which 
engage grooves 28 in the inner synchronizing ring 13. The ring has a 
radial flange 29 and a cup spring package consisting of two cup springs 30 
lying between the flange 29 and an opposite surface 31 on the guide sleeve 
1. 
The synchronizing device according to the invention functions as follows: 
The components are shown in FIGS. 2a and 2b in their neutral position. When 
a gear is engaged, which involves locking the gear (not shown) joined to 
the engaging ring 5 to the right in the Figures, the engaging sleeve 4 is 
displaced to the right. The outer synchronizing ring 12 is thus displaced 
under the influence of the keys (not shown) to the right and its 
frictional surface 14 will come into frictional engagement with the 
frictional surface 8, which will result in the synchronizing cone 7 being 
displaced a short distance to the right so that the inner frictional 
surface 9 of the synchronizing cone 7 will be pressed into engagement with 
the frictional surface of the inner synchronizing ring 13. The result will 
be that the synchronizing ring 13 will be rotated and with it the torque 
transmitting element 20 (see FIGS. 3a, 3b) so that initially the cam 
surfaces 25 of the keys 24 will come into contact with the cam surfaces 26 
of the ramps 17 (FIGS. 3a, 3b). The torque transmitting element 20 will be 
successively rotated relative to the engaging sleeve 4, and the 
cooperating cam surfaces 25, 26 will cause the torque transmitting element 
20 to be pressed back, compressing the cup springs 30 and the components 
will assume the position shown in FIGS. 4a, 4b. The springs 30 can be 
dimensioned so that in their compressed state they will exert a force of 
approximately 1500N in the engagement direction. 
After completed synchronization according to FIGS. 4a, 4b, release and 
engagement is effected as is illustrated in FIGS. 6 and 7, under the 
influence of the force from the spring package 30, which, in combination 
with the angle of the cam surfaces, determines how much force the driver 
must exert on the lever to complete the shifting sequence. 
During the above described sequence, the synchronization itself takes place 
in a conventional manner by the ramp 17 cam surfaces 26 proximate the 
synchronizing rings 12 coming into contact with corresponding cam surfaces 
on the blocking keys 16 of the outer synchronizing ring. 
An angle .alpha. of 60.degree. for the cam surfaces and a spring package 
with a force in the axial direction of circa 1500N has been shown for a 
certain gearbox to reduce the force and the gear lever to about 25% of the 
force supplied without the described synchronizing device according to the 
invention. 
The invention has been described with reference to components on the right 
side of the guide sleeve 1. Of course a corresponding function is obtained 
when shifting involving locking of the engaging ring 5 to the left of the 
guide sleeve 1. The ring 21 of the lefthand torque transmitting element 
has fingers (not shown) which are angularly displaced relative to the 
fingers 22 on the righthand element 20.