Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to a detent mechanism
and, more particularly, it relates to a mechanism
wherein shiftable gears in a transmission are held
by a detent againstunintentional movement.
It is well known to provide a transmission
in which gears or gear selection mechanisms are
selectively slidable into and out of engagement. The
sliding movement is usually provided by a shift rail
which may either be fixed and provide support for
the selection mechanism or alternatively may be
rigidly connected to the selection mechanism and
slidably mounted in a transmission case.
It is clearly desirable that the selection
mechanisms be freely slidable to ensure smooth and
convenient change of gear ratio. Howover, it is
also necessary to provide suitable means for pre-
venting unintentional movement of the selection
mechanism, due for example, to shock forces on the -
transmission or the forces generated between meshing
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gears.
- A detent mechanism is commonly employed to
`~ prevent unintentional movement and usually comprises
a plug biased into engagement with the shift rail by
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means of a; spring. Clearly the spring force must
be sufficient to prevent unintentional movement
of the selection mechanism but at the same time
must allow smooth gear shifting. Where transmis-
sions are used in arduous conditions or to transmit
large torques both these conditions cannot be met
- 30 because of the large forces imposed upon the selec-
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tion mechanisms. Consequently an unsatisfactory
compromise is reached.
It is an object of the present invention
to obviate or mitigate the above disadvantages.
According to the present invention there
is provided a change speed transmission having a
clutch control operable upon a clutch to interrupt
power transmission to the change speed transmission,
a ratio selection mechanism movably mounted on sup-
port means for movement into a required speed
ratio, detent means operable between the selection
means and the support means, biasing means for bias-
ing the detent means into engagement with both the
support means and the selection mechanism, and con-
trol means operable by the clutch control to vary
the bias of the biasing means and thereby vary the
holding force of the detent means upon interruption
of the power transmission. -
Embodiments of the present invention will
now be described by way of example only with re-
ference to the accompanying drawings, in which~
; Fig. 1 is a sectional view through part
of a change speed transmission:
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Figure 2 is an end elevational view, with parts thereof
broken away, and showing a further embodiment of a transmission;
Fig. 3 is a view of a fragment of the transmission shown
in Fig. 2.
Referring now to Fig. 1 a transmission for a vehicle or
the like, includes a transmission gear 10 and a shift member 11
in the form of the shift fork as can best be seen in Fig. 2
which engages the gear 10 for shifting the gear along its longi-
tudinal axis. A shift member 12 is shown in Fig. l, to control
a second gear which forms part of a set of gears, each of which
are shiftable for setting the transmission in the desired speed
ratio.
A cylindrical shift rail 13 is included in the transmission
and pilots the shift forks 11 and 12 which can slide along the
longitudinal axis of the rail 13. A connector 14, which is only
fragmentarily shown, extends from a control member movable by
operator to each of the forks 12, 13 so that the operator can
move the links or slide the shift members 11 and 12 on the rails
13. The operator therefore aan actuate the connectors 14 ;
to move the shift members 11 and 12 along the rail 13 and there-
by shift the gears, such as the gear 10, in the transmission or
gear set.
Movement of each of the shift members 11 and 12 is controll~
ed by a detent member 16. The members 16 are movably disposed
on the shaft rail 13 to move in a radial direction. The shift
rail 13 has a cylindrical pocket 19 through which the cylindrical
detent member 16 can extend and slide radially of the longitudinal
axis of the shift rail 13 for movement into and out of engage-
ment with the shift members 11 and 12. The radially outer ends
17 of the detent members 16 are hemispherically formed, and are
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selectively disposed in one of several hemispherically-formed
pockets 18 in the shift members 11 and 12. The pockets 18 are
spaced along the longitudinal axis of the rail 13, The members
11 and 12, and thus the detent members 16 can be selectively dis-
posed in any one of the several pockets 18 to thereby hold the
shift members 11 and 12 and thus the gears 10 in a selected ;~
position. Fig. 1 shows the detent members 16 in the engaged
and thus securing position so that the detent members 16 are
shown operatively associated with and thus securing the rail 13 ~ -
with the shift members 11 and 12.
Fig. 1 further shows that the shift rail 13 has a hollow
cylindrical interior 21 which snugly slidably receives two spaced-
apart piston members 22 and 23. The piston members 22, 23 are
yieldingly urged apart by a compression spring 24. The ends 26 ;
of the piston members 22 and 23 are conically shaped, and the
inner ends 27 of the detent members 16 are likewise conically
shaped. Thus the two conically-shaped configurations are in
conformity and sliding contact such that when the piston members
22 and 23 are moved away from each other and into contact with
- ~ 20 the detent members 16, then the detent members 16 are urged ra-
dially outwardly into securing position with the shift members 11
and 12, respectively. The force of the spring 24 is insufficient
to prevent slip of the detent members relative to the shift -
; members 11 and 12 which can therefore be shifted, under the in-
fluence of the links 14, along the rail 13.
Where a gear set or transmission assembly relies only upon
the force of a spring to hold the gears in their desired selected ~- -
position, it is common to have the gears inadvertently move out
; of that set position, since the spring holding the detent members
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is not sufficient for that purpose. A hydraulic system, gener- 7
ally designated 31, and shown somewhat schematically in the low- '~
er portion of Fig. 1 includes a hydraulic pump 32 connected with
a hydraulic line 33 which has a section 34 extending to the shift
rail interior 21 at a location between the pistons 22 and 23,
Thus the pistons22 and 23 will be subjected to the pressure de-
livered by the pump 32,
A valve 36 controls the hydraulic pressure at the interior
21 of the shift rail 13, and includes a shiftable spool 37 which
10 slides in a cylindrical passageway 38 under the control of a
clutch member or actuator in the form of a vehicle clutch pedal
39, A link 41 connects the spool 37 to the pedal 39. The valve
36 controls hydraulic pressure in the line 34, by controlling the
flow of hydraulic fluid from the passageway 33 into the housing 38
and thus to a line 42. When the spool 37 is in the position shown
in Fig, 1 the clutch pedal 39 is being depressed by the operator
to operate the clutch and there is no pressure in the shift rail
interior 21. Thus the shift members 11 and 12 can be shifted,
if desired. When the pressure on the pedal 39 is released, the
20 spool 37 will return upwardly under the influence of a compres-
sion spring 43 to prevent flow to the line 42. When the conduit
33 is thus closed off, then the pressure from t,he pump 32 will be
directed to the shaft rail interior 21 adjacent the pistons 22 ,~ -
and 23, The force on the detent members 16 is increased and
movement of the shift members 11 and 12 is prevented,
Figs. 2 and 3 show another embodiment of the invention
which utilizes the arrangement of the detent member operatively
associated between a shift rail and the shift members and includ-
es the hydraulic system which secures the detent member in the
30 locking position. Fig, 2 shows shift rail 46 on which the
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shift member 47 is slidably mounted, and it will here be seen that
the member 46 is in the nature of a fork having its ends 48 spac-
ed apart to engage on opposite sides of the section of the gears
10, as shown and indicated in connection with Fig. 1. The shift
rail 46 is of a solid cylindrical shape, and has circular grooves
49 formed therein and spaced apart along the axis of the shift
rail 46. A detent member 51 is slidably mounted in a cylindrical ~-
bore 52 extending in a shank 53 in the shift member or fork 47.
Thus, the detent member 51 may slide radially toward and away
from the shift rail 46. The member 51 has a rounded nose or end
54 which engages one of the grooves 49 when the shift member 47
is adequately aligned with the grooves 49, to hold the shift mem-
ber or fork 47 in a position axially on the rail 46. A plug 56
: is shown in the bore 52, and a compression spring 58 is disposed -:
in contact with the detent member 51 to urge the detent member
into contact with the shift rail 46.
The hydraulic system 31 described in Fig. 1 can also be
utilized in this embodiment. In this instance fluid is transmitt- -
ed through a flexible hydraulic line 57, such as of a nylon or
rubber tubing, is in hydraulic fluid-flow communication with
the shift member 47 to extend to the bore 52 and into the
interior 59 of the detent member 51 through a flow passageway
61 in the detent member 51. Hydraulic pressure in the hollow
interior 59 will force the detent member 51 into a secure
position against the shift member 47 to axially fix it relative
to the raii 46. Again, when the operator depresses the clutch
pedal 39, that is when he wants to shift the gears 10, then the
hydraulic pressure in the line 57 is relieved and the operator
can then move the shift member 47 along the rail 46 by simply
overcoming the force of the spring 58. The spring 58 does not
prevent movement but indicates to the operator when the shift
s member 47 has been placed in a desired gear engag-
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ing or shifted position.
In summary, both embodiments utilize the force of a compres-
sion spring and also hydraulic pressure with the hydraulic pres-
sure being under the control of the operator and subject to the
action of the clutch.
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