FR2532711A1 - Transmission for automobile vehicle. - Google Patents

Abstract

The transmission comprises a gear box 10 controlled by a lever 11 and a complementary transmission device C situated upstream of the gear box and able to assume at least two operating positions under the action of the control means E. The transmission comprises first means S1 which are sensitive to the position of the lever 11, second means S2 which are sensitive to the speed of the vehicle and prevention means P, actuated by the abovementioned sensitive means S1, S2, which are suitable for preventing the control of a change in operating position of the complementary transmission device C if the lever 11 does not occupy a determined position or if the speed of the vehicle is greater than a determined limit.

Description

Transmission for motor vehicle The invention relates to a

  transmission for a motor vehicle of the kind that includes a gearbox controlled by a gear shift lever, and an additional transmission device, located downstream of the gearbox, capable of assuming at least two operating positions under

the action of control means.

  The invention aims, above all, to make the

  transmissions of the genus in question as they

  meet the various requirements of the

  practical, and in particular such as their conditions of use

tion are improved.

  According to the invention, a transmission for a motor vehicle of the kind defined above is characterized in that it comprises first means sensitive to the position of the control lever of the gearbox, second means sensitive to the speed of the vehicle and

  means of prohibition, activated by the above-mentioned

  sensitive yen; suitable for preventing the ordering of a change

  operating position of the additional transmission device, the assembly being arranged so that such a change in operating position is only authorized when the gearbox control lever occupies a determined position and the vehicle speed is below a certain limit,

  any change in the operating position of the device

  additional transmission is prohibited when

  these two conditions are not met.

  The additional transmission device can comprise a transfer box capable of taking at least two operating positions corresponding to two speed ranges, for example a "road" range and a "field" range, the change of position of the transfer box being able to be performed using a

  control device for this transfer box; the pre-

  miers means sensitive to the position of the gearbox control lever are then arranged in such a way that authorization to change the position of the transfer box can only be granted when the gearshift lever is on the neutral position N Ces

  first sensitive means can be formed by a con-

  electric touch capable of closing (or opening) when

  the gearshift lever is in the neutral position N The means of preventing the shifting of the position

  of the transfer case can be made up of a dis-

  positive locking erasable locking finger, consisting of a piston rod of a pressurized fluid cylinder controlled by a solenoid valve itself controlled by the above electrical contact. The transfer box is advantageously equipped with

  synchronization devices and speed limit pre-

  determined, above which any change in posi-

  Operation of the transfer box is prohibited,

  is chosen so that the life of the devices

  synchronization is satisfactory.

  Speed sensitive means may include

  take a rotary detector mounted on a rotating shaft

  of the transmission, in particular mounted on an intermediate shaft

  diary of the transfer box; this rotary detector is combined with electronic threshold means capable of supplying, on their output, a voltage signal, for example intended for controlling solenoid valves, depending on whether the vehicle speed is lower or higher than the

predetermined limit.

  The additional transmission device may include a differential mechanism equipped with dog clutch means; one operating position corresponds to the non-clutched differential, while the other operating position corresponds to the clutched differential; the control means for acting on this complementary transmission device are formed by the means for

dog clutch control.

  In this case, the first means sensitive to the position of the gearbox control lever can be arranged so as to allow the change

  operating position for two specific positions

  born (for example) of the gearshift lever of the gearbox, for example for the first position and reverse reverse The clutch control means can be constituted by a spus pressure fluid cylinder

  the means of prohibition then include an electro-

  valve, controlled by electrical contacts. The complementary transmission device can

  understand, in combination, the transfer case and the different

  rentiel equipped with interconnection means.

  In this case, the first means sensitive to the po-

  position of the gearbox control lever may

  can be combined with means sensitive to the position of the transfer box control device so that clutching of the differential is not authorized

  only when the transfer case is in the "field" position.

  The complementary transmission device can

  include a mechanism for driving an auxiliary socket

  liar or propeller, equipped with a dog clutch device; the authorization or the prohibition of the interconnection of the auxiliary drive or propeller is obtained in a manner similar to that of the control of the differential interconnection.

  The invention consists, apart from the arrangements

  tions set out above, in certain other provisions which will be more explicitly discussed below in connection with

  of a particular embodiment described with reference

  Reference to the attached drawings, but which is in no way limiting. Figure 1 of these drawings is a diagram of the

  transmission according to the invention.

  Figure 2 is a more detailed schematic view

from the transfer case.

  Figure 3 is a partial section of the box

  transfer illustrating the locking means.

  Figure 4, finally, is a detailed section of the

  differential clutch control.

  Referring to the drawings, and more particularly

  Rement in Figure 1, we can see a transmission for a motor vehicle, schematically shown which

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  has a gearbox 10 controlled by a lever

  11 gear change This lever 11 can be com-

  manually ordered by a driver; a return linkage 12 can be provided to act on another lever 13 which more directly controls the changes in speed.

ports of the box.

  The transmission includes a transmission device

  complementary mission C, located downstream (in the direction of transmission of the rotational movement) of the 1 o gearbox 10, and capable of assuming at least two operating positions under the action of the control means. This additional transmission device C may include a transfer box 14, schematically represented in FIG. 1, capable of taking two operating positions corresponding to two speed ranges, for example a "road" range identified by the letter R and a "range". terrain ", identified by the letter T. As will be indicated below, the device

  additional transmission may include independent

  especially from the transfer case 14, or in combination with

  this box, another mechanism with two operating positions

  operation, in particular a differential mechanism equipped

  dog clutch means; a first function position-

  then corresponds to the non-clutched differential, tan-

  say that the other operating position corresponds to the

clutch differential.

  The transmission comprises first means Si sensitive to the position of the lever 11 for controlling the gearbox, second means 52 sensitive to the

  vehicle speed and prohibition means P ac-

  tiated by the above sensitive means Si, 52, own

  to prevent the command from a change of operating position

  operation of the complementary transmission device C, the assembly arranged so that such a change

  position of the complementary device C is not self-

  that when the control lever 11 occupies a determined position and the vehicle speed is less than a predetermined limit; every change

  of operating position of device C is inter-

  said when these two conditions are not met.

  When the device C comprises a transfer box 14, the first sensitive means Si are arranged so that authorization to change the position of the transfer box 14 can only be granted when the gear shift lever 11 is in the neutral position N. The first sensitive means Si then include a 1 o electrical contact 15 capable of closing when the lever It is in the neutral position; as shown in Figure 1,

  the contact 15 is controlled by the auxiliary lever 13.

  It is clear that a reverse operation could be provided with a command by opening the contact 15 when the lever 11 is in the position N.

  The means of prohibiting P from a change of position

  operation of the transfer case 14 include a locking device 16 with erasable blocking finger 17 constituted by a piston rod of a jack 18

  with pressurized fluid, in particular a hydraulic cylinder.

  Alternatively, a pneumatic cylinder could be used.

  The cylinder 18 is of the single-acting type and, in the absence of fluid pressure, the locking finger 17 is held in the locking position by a spring 19 acting on the piston; when the pressurized fluid is admitted against the opposite face of the piston, the latter is pushed back and the finger 17 is erased The erasing position of the finger 17 corresponds to that shown in FIG. 1, for which a slide 20 a for controlling the transfer case can be moved using a lever 20, this

  which allows to drive, through a

  chette 21, the sliding pinion 22 of the transfer box

  14 This box 14 is advantageously equipped with

  synchronization devices 23, with additional cones, to facilitate the transition from the "road" R range to the

range "field" T or vice versa.

  In the locked position, the finger 17 projects across the path of the slide 20 a.

  position of the slide shown in FIG. 1, corres-

  corresponding to the "field" range of box 14, the doiat 17, if

  came in blocking position would constitute a stop for the ex-

  end of the slide and would prevent return to posi-

  "road" position R. If the slide 2 Oa occupied the "road" position, the finger 17, in the blocking position, would cooperate

  with a notch 24 provided in the slide and preventing

  would cost the displacement of the slide 20 a towards the position

  "terrain" T and therefore the change of position of function-

box 14.

  The supply of pressurized fluid to the jack 18, and therefore the control of the finger 17 is provided by a solenoid valve 25 When the winding 26 of this solenoid valve is energized, as shown in the

  Figure 1, this solenoid valve is open and ensures the ar-

  supply of pressurized fluid to the jack 18, from a pressure source 27 The pressure source comprises a reservoir of liquid 28, a pump 29 discharging pressurized fluid into the pipe 30; the pump 29 can be driven by a belt cooperating with a pulley 31, the belt being driven by the vehicle engine An oleopneumatic pressure accumulator 32

  is planned at the start of line 30.

  When the winding 26 of the solenoid valve 25 is no longer energized, the slide of this solenoid valve passes into a position for which the fluid chamber of the jack 18 is connected to the liquid reservoir 28 in such a way

  so that the finger 17 goes into the locked position.

  The electrical circuit for controlling the winding 26 and the solenoid valve 25 is connected between earth and the output 33 of threshold electronic means 34 such

  that a Schmitt seesaw, via the

  tact 15 The electronic threshold means 34 have a power supply terminal 34 a connected to a positive terminal 35 of a power source, for example an accumulator,

  and have another terminal 36 connected to ground.

  These threshold electronic means 34 are combined

  with the sensitive second means 52 comprising a detector

  rotary tor 37 formed by a toothed wheel 38 mounted on a rotating shaft of the transmission, in particular on an intermediate shaft of the transfer case (see Fig 2) and by a fixed magnetic detector 39 The output of the detector 39 is connected to

  an input of electronic means 34.

  When the signal supplied by the detector 39 remains below a determined limit, corresponding to a determined speed of the vehicle, the electronic means 34 supply, at their output 33, a voltage signal

  sufficient for controlling solenoid valves such as 25.

  When the vehicle speed exceeds the predetermined limit, the electronic means 34 switch and the output 33 switches to zero or too low voltage

  for controlling solenoid valves such as 25.

  The vehicle speed limit for which

  the voltage signal on output 33 switches is before

  carefully chosen equal to or close to 8 km / hour.

  The operation of the transmission described

previously is as follows.

  If the gear shift lever 11 is at

  -Neutral point N contact 15 is closed.

  If, in addition, the vehicle speed is lower than the predetermined limit, for example 8 km / hour, the

  voltage signal present on the output 33 of the electrical means

  34 is sufficient for controlling the electro-

  valve 25 This solenoid valve 25 therefore assumes the position of

  groove shown in Figure 1 for which the pressurized fluid is admitted into the cylinder 18, and the finger

blocking 17 is deleted.

  It is then possible to move the lever 20 of the transfer box 14 to pass from the "road" position

to "ground" or vice versa.

  On the other hand, if one of the two conditions mentioned above is not fulfilled, that is to say if the gear shift lever 11 is not in position N, or if the vehicle speed is higher at the predetermined limit, for example 8 km / hour, finger 17 passes

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  in the locked position and prohibits any change of position

  operation of the gearbox 14.

  This provides effective protection of the transfer box 14 and the transmission as a whole against misuse. The presence of a synchronization device 23 in the transfer box 14 thus becomes possible and

  ensures easier and smoother control.

  The complementary transmission device C may include other mechanisms, independently of

  or in combination with the transfer case 14.

  The complementary transmission device C can, in fact, comprise a differential mechanism 40

  (Fig 2) equipped with clutch means 41 of the differential.

  An operating position corresponds to the differential

  not clutched, while the other operating position-

  This corresponds to the clutch differential.

  In the representation of the drawings, the difference

  tiel and the differential clutch means are shown in combination with the transfer box However, it is clear that a transmission according to the invention may not include a transfer box between the gearbox 10 and the differential 40 The advantages

  provided by the invention would subsist.

  The clutch 42 control means may comprise a jack 43 with pressurized fluid, in particular a hydraulic jack of the single-acting type intended to drive the clutch 41 itself, which, in known manner, ensures rotation lock of the differential housing 44 with respect to an output shaft 45 of this differential Consequently, the other output shaft 46 of the differential will also be

  locked in rotation relative to the housing 44.

  The single-acting cylinder 43 has a spring

  reminder 47 (fig 2) controlling the declutching of the differential

  when the fluid chamber of the cylinder 43 is connected

  at the exhaust, that is to say at the reservoir 28.

  An indicator light 48 can be provided (fig 1)

  intended to indicate if the differential is clutched or not.

  This indicator light 48 is connected in series between earth and the positive terminal of a DC voltage source, with a contact 49 suitable for being controlled by an inclined ramp 50 linked in translation to the dog clutch 41 When the dog clutch 41 occupies the corresponding position. to the clutch differential, the contact 49 is closed (for example) and the indicator light 48 is on When the differential is not clutched, the clutch 41 has moved back relative to the position shown in FIG. 1, and the contact probe 49 is less depressed by the ramp 50 which has retreated, the contact 49 is then open (for example) and the

LED 48 is off.

  The first sensitive means Si are arranged

  in order to authorize the change of position of function-

  nement of the differential and dog clutch means for two positions (for example) determined by the lever 11 of

  shifting These two positions will be the posi-

  tion 1 euet the on position "AR" l For this, an electrical contact 15 a is provided which is capable of closing when the lever 11 is in the on position "A Rl" As visible in FIG. 1, the contact 15 a is placed way to cooperate

  with the auxiliary lever 13 Another contact 15 b is pre-

  seen to close when the lever It is in position "the" in FIG. 1, this contact 15 b cooperates directly with the

lever 11.

  The second sensitive means 52 are the same as those described above. The predetermined speed limit

  above which any change in position of function

  operation of the differential and the dog clutch means is prohibited is chosen, preferably, equal to the speed limit adopted for the control of the transfer box 14, which simplifies the installation However, one could provide, if necessary, a limit of different speed for prohibiting or authorizing interconnection, this

  which would involve electronic means with a full threshold

mentally ill 34.

  The prohibition means P suitable for preventing the control of a change in the operating position of the differential and the clutching means comprise a solenoid valve 25 a, similar to the solenoid valve 25, the control winding 26 a of which is connected, on one side, at an output 51 of the threshold electronic means 34 When the winding 26 a is energized, the solenoid valve 25 a takes the position shown in Figure 1 and ensures the admission of pressurized fluid into the means of

  control 42 of the differential clutch When the reel

  26 a is no longer energized, the drawer of the elect

  solenoid valve 25 has dropped and placed in communication the fluid chamber of the jack 43 with the reservoir 28 so that

  that the declutching is controlled by the spring 47 (fig 2).

  An input terminal 51 a, threshold means 34, is

  connected via contact 49 to the posi-

  tive of the DC voltage source Inside the means 34, the terminal Sa and the output 33 are connected, by

  example, at the two inputs of an "OR" door, (not shown

  whose output is connected to output 51 So, a

  signal of sufficient voltage to control the electro-

  valve 25 a will be obtained at output 51 if the speed of the

  vehicle is less than the predetermined limit (8 km / h.

  for example) or if the differential is clutched (contact

49 closed).

  The other end of the winding 26 a is connected

  to earth via a switch

  request 52 that the driver must close when he wants to

  hold the differential clutch The contacts 15 a and 15 b are connected, in parallel, between this switch 52

  and said other end of the winding 26 has the

  tacts 15 a, 15 b thus form an "OR" gate since the supply circuit of winding 26 a will be closed

  depending on whether contact 15 a or contact 15 b is closed.

  It is clear that we could, depending on the case

  of species, authorize a change of position of function-

  additional device C for other posi-

  lever 11; it would then suffice to provide sensitive means, for example electrical contacts,

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  judiciously arranged to ensure authorizations.

  In the example envisaged, the differential equipped

  a dog clutch is combined with the transfer box 14.

  An electrical contact 53 is then provided connected in series between said other end of the winding 26 a and a point f common to the two branches in parallel containing

  contacts 15 a and 15 b This electrical contact 53 consists of

  kills a means 53 sensitive to the control lever 20 of the box

  transfer Contact 53 is arranged so as to close

  sea when the lever 20 occupies the "ground" position T (shown in FIG. 1) The contact 53 is open when the lever 20 occupies the "road" position R It can thus be seen that the control of the dog clutch is only possible when the transfer box 14 is in the "field" position T. The operation of the transmission device comprising in combination the transfer box 14 and the differential 40 fitted with the clutch means 41 is

the following.

  Regarding the order of the trans-

  fert 14, it remains identical to what has been described previously.

  cedent A change of position of the transfer box 14 is only possible if the lever It is in position N

  and the vehicle speed lower than the predefined limit

finished.

  The differential clutch is controlled

under the following conditions.

  When the gear shift lever is in the ie on or reverse position, one of the contacts 15 a, 15 b is closed If, in addition, the control lever 20 of the

  transfer case is in position T ("field") the

  while electric 53 is also closed Finally, if the speed of the vehicle is lower than the predetermined limit, for example 8 km / hour, the electric voltage on the terminal

  51 is sufficient to control the solenoid valve 25 a.

  When all these conditions are met, if the driver wishes to clutch the differential, he

  just close the switch 52; the electric circuit

  feed plate of the winding 26 a then closes and the solenoid valve 25 a passes into the open position shown in FIG. 1 The fluid under pressure is

  admitted into the fluid chamber of cylinder 43 and the crabo-

  differential level is established The indicator light 48 comes on A sufficient voltage signal, introduced by closing the contact 49, is maintained on output 51 in the event that the sufficient voltage signal disappears on output 33 (overshoot of the speed limit of

8 km / hour for example).

  O If the driver of the vehicle moves the lever 11 to the 2 nd or 3 rd or neutral position N, the supply circuit

  the winding 26 a is interrupted The electro-

  valve 25 a is no longer energized and its slide valve moves to the position which connects the cylinder's fluid chamber

  43 with the tank 28 The clutch is then ordered

  die by spring 47 (fig 2), forming return means

dog 41.

  Naturally, if the driver of the vehicle

  hates to declutch the differential, he just has to open

switch 52.

  When the differential clutch control is possible, which supposes that the control lever 11 is either in position 1 e, or in the on position "AR", it is impossible to modify the operating position of the transfer case which is on the

"field" position.

  The differential clutch is allowed as long as

* vehicle speed remains below the pre-

  determined (8 km / hour for example) However, when the dog clutch has been carried out, it remains maintained even if the speed exceeds the predetermined limit of 8 km / hour

  thanks to the information given by the contact 49 of crabo-

  tage, electronic means 34, information that allows

  maintain on output 51 the suf- ficient voltage signal

  fisante for the excitation of the solenoid valve 25 a same-

  when this voltage signal disappears on output 33

  when exceeding the speed limit.

25327 11

  It is thus seen that a transmission conforming to the

  vention is protected against false operations or against use in bad or dangerous conditions for this transmission Fatigue harmful to the equipment, and which can lead to breakage of part,

are thus avoided.

  The complementary transmission device C

  may include other mechanisms, for example a mechanism

  nism 54 (fig l), or drive clutch of an auxiliary socket

  such as a power take-off, or a drive train

  vice, in the case of an amphibious vehicle This mechanism 54 is similar to the dog clutch means 41 and allows, by

  a translation of coupling or uncoupling in rotation

  tion a shaft driven by the engine of the vehicle, and either an auxiliary socket, a propeller or any other

organ to be driven in rotation.

  The control of the translational movement of the

  canism 54 can be ensured by a hydraulic cylinder 43 b with single effect, similar to the cylinder 43 A contact 49 b can cooperate with a ramp 50 b, linked in translation to the dog clutch 54 so as to control the ignition or extinction of a

  indicator light 48 b for clutching of the drive mechanism

  xiliary. A line 55 is connected to the fluid chamber of the jack 43 b This line 55 is connected to the outlet orifice of a solenoid valve 25 b similar to the solenoid valve 25 a; the control winding 26 b of this solenoid valve is connected between the positive voltage terminal of a DC voltage source and ground,

  via a control switch 56.

  The return port to the reservoir 28 of the solenoid valve

  26 b is directly connected to this tank via

  diary of a pipe 57 The inlet for pressurized fluid, of the solenoid valve 26b, is connected

  by the pipe 58 at the outlet port of the valve valve 25 a It can thus be seen that the pressurized fluid cannot be

  admitted into the fluid chamber of the cylinder 43 b only if the solenoid valve 25 a is in the excited position

  which ensures the admission of pressurized fluid into the

  nalisation 58; in other words, starting the mechanic

  auxiliary drive linkage by moving the dog clutch

  54 will only be possible when the differential 40 is itself

  same interconnection The mounting of the solenoid valve 25 b downstream and in series with the solenoid valve 25 a on the discharge pipe

  of the pump 29 makes it possible to obtain this result.

  The operation of the auxiliary plug or propeller drive mechanism results immediately

1 o of the previous explanations.

  As long as the solenoid valve 25 a is not energized, that is to say as long as its output and therefore the jack 42 and

  line 58, are connected to reservoir 28, the clos-

  contact 56 while causing the solenoid valve 25 b to operate, will not allow the admission of pressurized fluid into the jack 43 b since the line 58 is not connected to the pump discharge 29 It will therefore not be possible to command the drive of the

  auxiliary mechanism, plug or propeller even if the conduct-

tor closes switch 56.

  On the other hand, when the differential clutch 40 is ensured, that is to say when the solenoid valve 25 a is open and occupies the position shown in FIG. 1, the pressurized fluid is admitted into the pipe 58,

as well as in the jack 42.

  If the driver then wishes to activate the device

  auxiliary device, it suffices to close the switch 56.

  The declutching of the differential 40 obtained by re-

  fallen from the solenoid valve 25 a and placing the line 58 in communication with the reservoir 28, causes the auxiliary drive mechanism to unclutch (socket

  force or propeller) whatever the position of the

switch 56.

  Again, the information transmission device

  vention is protected against false operations or against

  improper use detrimental to the longevity of the parts.

  Referring to Figure 3, we can see a detailed representation of part of the transfer case

2.532711

  14 and means of prohibiting the change of position

  of this transfer box We have designated by the same references

  digital references, in this FIG. 3, the elements having functions identical to elements already described with

  reference to figure 1 The description of these elements does not

will therefore not be resumed.

  Figure 4 is a partial detail-ei representation, dog clutch means and the differential J again, we used the same reference numerals to designate the elements playing roles identical to

  elements already described with reference to Figures 1 and 2.

  It therefore does not seem useful to repeat their description.

tion.

Claims (11)

  1 Transmission for motor vehicle comprising   a gearbox (10) controlled by a shift lever   gearbox (11), and a complementary transmission device (C) located downstream of the gearbox, capable of assuming at least two operating positions   operation under the action of control means (E), character-   terrified by the fact that it comprises first means (Sî) sensitive to the position of the gearbox control lever, second means (52) sensitive to the   vehicle speed and prohibition means (P), ac-   tioned by the above sensitive means (55, 52), own   to prevent the command from a change of operating position   operation of the additional transmission device   (C), the assembly being arranged so that such a change-   operating position is only allowed when the gearbox control lever (11)   occupies a determined position (N; le, AR) and that the vi-   vehicle size is less than a specified limit,   any change in the operating position of the device   tif of additional transmission (C) being prohibited   when these two conditions are not met.   2 Transmission according to claim 1, in   which the complementary transmission device comprises   takes a transfer case (14) capable of taking   at least two operating positions (R, T) correspond   laying on two speed ranges, for example a "road" range (R) and a "field" range (T), the change of position of the transfer box can be carried out using a control device (20) of this transfer box, characterized in that the first means (51) sensitive to the position of the control lever (11) of the gearbox (10) are arranged so that the authorization of a change of position of   the transfer box (14) can only be granted when   the shift lever is in the posi- neutral (N).   3 Transmission according to claim 2, charac- 25327 1 1   terrified by the fact that the first sensitive means (Si) are formed by an electrical contact (15) capable of closing (or opening) when the change lever   is in neutral (N) position.   4 Transmission according to claim 3, characterized in that the means for prohibiting (P) the change of position of the transfer box (14) comprise a locking device (16) with erasable locking finger (17), constituted by a cylinder piston rod (18) for pressurized fluid controlled by a solenoid valve (25) itself controlled by the above-mentioned electrical contact O Transmission according to any one of   Claims 2 to 4, characterized in that the   transfer case is equipped with synchronization devices   tion (23) and that the predetermined speed limit,   above which any change in position of function-   transfer box (14) is prohibited, is chosen   so that the lifetime of the syn-   chronization (23) is satisfactory.   6 Transmission according to any one of the res-   previous indications, characterized in that the   speed sensitive means (52) includes a sensor   rotary tor (37, 38, 39) mounted on a rotary shaft of the transmission, in particular mounted on an intermediate shaft of the transfer box (14), this rotary detector being combined with electronic threshold means (34) suitable for supplying, on their output (33), a voltage signal, for example intended for the control of solenoid valves, depending on whether the vehicle speed is lower or higher than the predetermined limit.   7 Transmission according to any one of the res-   above, in which the   complementary transmission (C) includes a different mechanism   ferential (40) equipped with clutch means (41)>, an operating position of this differential mechanism corresponding to the non-clutched differential, while   the other operating position corresponds to the different   dogged clutch, the control means to act on this additional transmission device being formed   by the dog clutch control means (42), charac-   terrified by the fact that the first means (Si) sensitive to the position of the control lever (11) of the gearbox (10) are arranged so as to allow the change   operating position of the different mechanism   rentiel (40) for two determined positions (for example) of the gear shift lever (1 l), for example for   position l and reverse position (AR).   8 Transmission according to claim 7, in which the clutch control means (42) comprise a jack (43) with pressurized fluid, characterized by   the fact that the first means (Si) sensitive to the posi-   tion of the control lever (11) of the gearbox includes two electrical contacts (15 a, 15 b) capable of closing when the control lever (11) of the gearbox occupies one of the determined positions (i or AR), while the means of prohibition (P) specific to   prevent the command from a change of operating position   operation of the dog clutch means, comprise an electro   valve (25 a) controlled by the above contacts (15 a,   b), for supplying the jack (43).   9 Transmission according to the whole claim   tion 8 and any one of claims 2 to 5,   characterized in that the first means (Sl) sensitive to the position of the control lever (11) of the   gearbox are combined with means (53; 53) sens-   sibles-au position du-control device (20) of the transfer box (14) so that clutching of the differential is only allowed when the box   transfer is in "field" position (T).   Transmission according to any one of the res-   dications 7 to 9, characterized in that it is   arranged in such a way that when the interconnection of the different   rentiel (40) has been carried out, it remains maintained even if the   vehicle speed exceeds the predetermined limit, no-   especially thanks to information given by a dog clutch contact (49), information which makes it possible to maintain a signal of sufficient voltage for the excitation of   the solenoid valve (25 a) for controlling the dog clutch.   11 Transmission according to any one of the res-   dications preceding, characterized in that the predetermined limit of the speed of the vehicle, above which any change in the operating position of the additional transmission device is prohibited; is around 8 km / hour.   12 Transmission according to claim 7 or according to all of claim 7 and any one   of claims 8 to 11, wherein the device   additional transmission (C) includes in addition   differential gear (40) equipped with dog clutch means, a drive mechanism (54) of an auxiliary socket   or a propeller, characterized in that it comprises   takes a jack (43 b), for controlling the mechanism (54) for driving the auxiliary socket or the propeller,   this jack (43 b) being itself controlled by an electro-   valve (25 b) mounted downstream of and in series with the electric   solenoid valve (25 a) for controlling the differential clutch   on a pressurized fluid pipe.