Abstract:
A motor vehicle gearbox which includes at least two parallel primary and secondary shafts, respectively connected in rotation to an engine, and through a main transmission, to a wheel. The primary shaft bears a first idler gear to a second stationary pinion borne by the secondary shaft. The first idler is capable of being jaw clutched on the primary shaft for transmitting engine power to the wheel. A self-disengaging control selectively accelerates or brakes the primary shaft which bears the idler so as to synchronize them before linking them in rotation. A self-disengaging accelerator accelerates the primary shaft if its speed is less than that of the idler, and a self-disengaging brake brakes the primary shaft if its speed is greater than that of the idler.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a motor vehicle gearbox. 
     The invention relates more particularly to a motor vehicle gearbox of the type which is provided with at least two parallel shafts, the primary and secondary, respectively linked in rotation to a vehicle engine and, via a transmission, to at least one vehicle wheel, and of the type in which one of the shafts supports at least one first idler pinion engaging with a second fixed pinion supported by the other shaft, the first pinion being capable of being linked in rotation to the shaft which supports it to transmit motive power from the engine to the vehicle wheel. 
     DISCUSSION OF THE BACKGROUND 
     There are known numerous gearboxes which permit the establishment of various gear reduction ratios by interlocking of idler pinions on their shafts. 
     In the case, for example, of a gearbox with two parallel shafts, when a user initiates the change from a first gear reduction ratio to a second gear reduction ratio by means of a gear shift lever, the first idler pinion corresponding to the first ratio is “released” from the first shaft supporting it before the second idler pinion corresponding to the second ratio is in turn interlocked on the first shaft. Since the operation is extremely fast, the first shaft continues to turn at a speed close to that which it had when the first idler pinion was interlocked thereon. The second idler pinion, which for its part is driven by a second fixed pinion of the other shaft with which it is engaged, turns at a speed substantially different from that of the first shaft by virtue of a different gear reduction ratio. 
     To ensure that it can be interlocked on the first shaft, the second idler pinion must be brought beforehand to a speed of rotation substantially equal to that of the first shaft. 
     This is the function conventionally assigned to devices known as synchronizers. 
     Each idler pinion is coupled to an axially declutchable device, generally operated by an axially movable band driven by the displacement of an operating fork parallel to the shaft supporting the idler pinion. 
     Once clutched, the device permits the idler pinion to be frictionally in rotation to its shaft in such a way that it progressively leads to an adequate speed of rotation without transmitting a large torque at the same time. 
     In a second step (the pinion and shaft turning at the same speed), the device then permits the idler pinion to be linked to the shaft by means, for example, of a toothed coupling, thus establishing a gear reduction ratio of the gearbox. 
     Such a device is advantageous in that interlocking of the idler pinions on their shafts can be facilitated thereby. In fact, since the majority of interlocking devices are provided with toothed couplings, it is important that the idler pinions be synchronized beforehand with their shaft(s) before being interlocked, in order to limit tooth wear and to guarantee noiseless operation of the interlocking device. 
     On the other hand, the devices provided with synchronizers have the disadvantage of using a synchronizer based on idler pinions, thus considerably increasing the axial space requirement and weight of the gearbox. 
     In addition, in the case of a so-called robotized gearbox, or in other words a gearbox in which the different members are shifted by pilot-controlled actuators, these actuators being operated by an electronic control unit on which the vehicle operator acts, the use of synchronizers is particularly difficult. In fact, compared with a conventional operating system with selection fingers and forks, operation of the synchronizers by actuators is particularly inappropriate, since the actuators occupy considerable space. 
     SUMMARY OF THE INVENTION 
     To remedy these disadvantages, the method according to the invention no longer comprises bringing the pinion to be interlocked to a speed close to that of the shaft on which it must be interlocked, but instead comprises bringing the shaft on which it must be interlocked to a speed close to that of the pinion to be interlocked. 
     With this objective the invention proposes a gearbox of the type described hereinabove, characterized in that it is provided with controlled declutchable means permitting the primary shaft to be accelerated or braked selectively in order to synchronize the speed of the idler pinion with that of the shaft supporting it before linking it in rotation to the said shaft, and being capable of accelerating the primary shaft as long as its speed is lower than that of the idler pinion and of braking the primary shaft as long as its speed is higher than that of the idler pinion. 
     According to other characteristics of the invention: 
     the declutchable means for accelerating the primary shaft are provided with means for temporarily linking the primary shaft in slipping rotation to the secondary shaft; 
     the means for linking the primary shaft in rotation to the secondary shaft are provided with a first toothed gear coaxial with the primary shaft, which gear engages with a second toothed gear supported by the secondary shaft and linked in rotation thereto, the second gear being capable of being temporarily linked in rotation to the primary shaft via a slipping device for coupling of acceleration; 
     the controlled declutchable means for braking the primary shaft are provided with means for temporarily linking the primary shaft in slipping rotation with the gearbox case; 
     the means for linking the primary shaft in rotation to the gearbox case are provided with a fixed frustoconical bearing surface of the gearbox case, coaxial with the primary shaft, to which the primary shaft can be linked temporarily via a slipping device for coupling of braking; 
     the slipping devices for coupling of acceleration and of braking are provided with a common contact wheel, which is linked in rotation to the primary shaft by splines, which is provided with two oppositely disposed annular frustoconical bearing surfaces, and which is capable of being driven slidingly along the primary shaft 
     toward a first active extreme axial position in which a first annular frustoconical bearing surface cooperates by friction with a complementary annular frustoconical bearing surface of the said first toothed gear, to accelerate the primary shaft, 
     or toward a second, opposite active extreme axial position in which a second annular frustoconical bearing surface cooperates by friction with the fixed, annular and complementary frustoconical bearing surface of the gearbox case, to brake the primary shaft, 
     by passing through an indexed intermediate axial rest position; 
     the annular bearing surfaces are frustoconical; 
     the annular frustoconical bearing surfaces are plane, and the contact wheel is a clutch disk covered with a friction lining material; 
     the slipping devices for coupling of acceleration and coupling of braking comprise an electromagnetic clutch, in which two radial cages coaxial with the primary shaft, supported respectively by the first toothed gear and by the fixed frustoconical bearing surface of the gearbox case, are capable of cooperating selectively in slipping manner with two ends of a rotor in two portions integral with the primary shaft to accelerate or brake respectively the primary shaft when a magnetic flux is established between a rotor portion and a clutch cage; 
     the electromagnetic clutch is a metal-powder clutch; 
     the gearbox is provided with a motorized pump, in which a fixed case supporting axial pistons is integral with the gearbox case, in which a control plate is linked in rotation to the primary shaft of the gearbox, and which is capable of operating selectively as a hydraulic motor or hydraulic pump to accelerate or brake respectively the primary shaft; 
     the gearbox is a robotized gearbox which is provided with automated control means acting on the declutchable means for acceleration and braking of the primary shaft, and automated means for interlocking the idler pinions on the shafts supporting them. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages of the invention will become clear from reading the detailed description hereinafter, which will be understood by referring to the attached drawings, wherein: 
     FIG. 1 is a schematic view in section through a longitudinal central plane passing through the axes of the two shafts of a gearbox constructed according to the invention, provided with a noninterlocked idler pinion and a coupling device with contact wheel, illustrated in a rest mode; 
     FIG. 2 is a view similar to FIG. 1, the coupling device being illustrated in an active mode of acceleration of the primary shaft; 
     FIG. 3 is a view similar to FIG. 1, the coupling device being illustrated in an active mode of braking of the primary shaft; 
     FIG. 4 is a view similar to FIG. 1, the idler pinion being interlocked and the coupling device being illustrated in an inactive mode; 
     FIG. 5 is a schematic view in section through a longitudinal central plane of a gearbox constructed according to a variant of the invention and provided with a device for coupling by friction clutch; and 
     FIG. 6 is a schematic view in section through a longitudinal central plane of a gearbox constructed according to another variant of the invention and provided with a device for coupling by electromagnetic clutch. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Throughout the description, identical reference numbers denote identical or similar elements. 
     In known manner, a gearbox  10  is provided with a case  12  which supports in rotation two longitudinal parallel shafts, the primary  14  and the secondary  16 . Primary shaft  14  receives motive power from an engine (not illustrated) of the vehicle, while secondary shaft  16  is capable of transmitting the motive power to at least one wheel  18  of the vehicle via a transmission  20 . An idler pinion  22  supported by primary shaft  14  is capable of being interlocked with a fixed pinion  24  of the secondary shaft to transmit the motive power from primary shaft  14  to secondary shaft  16 . Gearbox case  12  is provided with case end  26 , which is provided with controlled declutchable means  28  for acceleration or braking of primary shaft  14 . 
     According to a first embodiment, controlled declutchable means  28  are provided with a toothed gear  40  integral in rotation with one end of secondary shaft  16 , the said gear engaging with a toothed gear  42 , which is supported in rotation by end  26  of gearbox case  12  and which is coaxial with primary shaft  14 . Toothed gears  40  and  42  are permanently engaged, and so toothed gear  42  is indirectly driven in rotation by wheel  18  of the vehicle. 
     Controlled declutchable means  28  are also provided with a coupling device  30 , in which a contact wheel  32 , provided with a hub  50 , is linked in rotation to the primary shaft by splines  34 . Contact wheel,  32  is capable of being driven slidingly along the primary shaft, and is provided on two oppositely disposed faces with a first annular frustoconical bearing surface  36  and a second annular frustoconical bearing surface  38 . An axial sliding gear wheel  48  cooperating with a hub  50  of contact wheel  36  permits its axial sliding movements along splines  34  of primary shaft  14  to be controlled. 
     Coupling device  30  is also provided with a fixed annular frustoconical bearing surface  44 , supported by the end  26  of the gearbox case and coaxial with primary shaft  14 , which passes therethrough. Annular frustoconical bearing surface  44  is disposed facing first annular frustoconical bearing surface  36  of contact wheel  32 . 
     Coupling device  30  is also provided, facing second annular frustoconical bearing surface  38  of contact wheel  32 , with an annular frustoconical bearing surface  46 , which is supported by toothed wheel  42  and consequently is coaxial with primary shaft  14 . 
     In this way, contact wheel  32  of the coupling device is, in an intermediate rest position illustrated in FIG. 1, disposed axially between annular frustoconical bearing surfaces  44  of end  26  of the gearbox case and  46  of toothed gear  42 , but is not in contact with the said regions. 
     In fact, gearbox  10  illustrated in FIG. 1 is in a neutral position in which idler pinion  22  of primary shaft  14  is not interlocked with fixed pinion  24  of secondary shaft  16 . This configuration corresponds to a state in which the vehicle is stopped or is in an intermediate state in which another idler pinion (not illustrated) supported by primary shaft  14  is interlocked on the primary shaft and in which idler pinion  22 , for example, will subsequently be interlocked on primary shaft  14  to engage a different gear reduction ratio. 
     In this state, contact wheel  32  occupies an intermediate position along splines  34  in which it does not cooperate with any of the elements of coupling device  30 . Toothed gear  42  is then driven at a speed proportional to that of wheel  18  by the fact of its engagement with toothed gear  40  of the secondary shaft and of transmission  20 . 
     The view of FIG. 2 illustrates a state in which secondary shaft  16  is turning at substantially greater speed than primary shaft  14 . In this state the vehicle operator has released the aforesaid idler pinion (not illustrated), declutched and initiated engagement of the gear reduction ratio corresponding to idler pinion  22 . Primary shaft  14  slows, while the secondary shaft is driven by wheel  18  of the vehicle. 
     In this case, to achieve interlocking of idler pinion  22  on primary shaft  14  and to cause it to engage with fixed pinion  24  of secondary shaft  16 , by sliding its hub  50  longitudinally along shaft  14 , it is necessary to bring it beforehand to a sufficiently high speed of rotation that teeth  52  of idler pinion  22  and  54  of fixed pinion  24  can cooperate noiselessly. 
     For this purpose, controlled sliding gear wheel  48  first moves hub  50  of contact wheel  32  toward the left, such that its annular frustoconical bearing surface  38  cooperates by friction with annular frustoconical bearing surface  46  of toothed gear  42 . In this way, contact wheel  32  is driven in slipping rotation by toothed gear  42 , the speed of which is linked to that of secondary shaft  16 . Contact wheel  32  then drives primary shaft  14  via splines  34 , and brings it progressively to a speed of rotation sufficient to permit interlocking of idler pinion  22  on shaft  14  to engage with fixed pinion  24  of secondary shaft  16 , as will ultimately be seen with reference to FIG.  4 . 
     The configuration described with reference to FIG. 3 illustrates the case in which primary shaft  14  is turning at substantially greater speed than secondary shaft  16 . 
     To achieve interlocking of idler pinion  22  and to permit engagement of idler pinion  22  with fixed pinion  24 , it is necessary to brake primary shaft  14 . This operation is performed by moving sliding gear wheel  48  axially toward the right, such that annular frustoconical bearing surface  36  of contact wheel  32  cooperates by slipping friction with fixed annular frustoconical bearing surface  44  of end  26  of the gearbox case. In this way, a braking torque is applied to hub  50  of contact wheel  32 , and it progressively brakes primary shaft  14 , thus permitting interlocking of pinion  22  and engagement thereof with fixed pinion  24 , as described with reference to FIG.  4 . 
     FIG. 4 illustrates the last phase of interlocking of idler pinion  22  on primary shaft  14  in such a way that it engages with fixed pinion  24  of secondary shaft  16 . 
     In this configuration, primary shaft  14  has been brought to an adequate speed of rotation via coupling device  30 . Sliding gear wheel  48  of coupling device  30  is then driven in such a way that contact wheel  32  once again occupies, as described with reference to FIG. 1, an intermediate rest position between annular frustoconical bearing surfaces  46  of toothed gear  42  and fixed frustoconical bearing surface  44  of end  26  of the gearbox case. 
     The primary shaft then turns, by virtue of its inertia, at an adequate speed, and a device (not illustrated) moves idler pinion  22  axially toward the left in such a way that it is brought integrally into rotation with primary shaft  14  and that its teeth  52  engage with teeth  54  of the fixed pinion of secondary shaft  16 , thus permitting transmission of the motive power originating from the engine (not illustrated) to secondary shaft  16  to drive the vehicle. 
     This embodiment is particularly advantageous, since it permits simple synchronization of primary shaft  14  with secondary shaft  16  to be achieved. 
     Thus, a single device  28 , situated at the end of gearbox  12 , for example, or in another place of gearbox  12 , permits synchronization of all of the idler pinions of the gearbox to be achieved. In fact, such a device is applicable both to idler pinion  22  of primary shaft  14  (as has been described) and to idler pinions that would be supported by the secondary shaft, since the nature of the operation performed by device  28  is synchronization of the speeds of the primary and secondary shafts to correspond closely to the chosen gear reduction ratio. 
     Device  28  also permits the compactness and weight of the gearbox to be greatly influenced, since the conventional synchronizer devices associated with each idler pinion become superfluous. In fact, a single device  28  controls all synchronization operations of the gearbox via an appropriate logical control unit, which adequately directs the movements of contact wheel  32  via sliding gear wheel  48 . 
     FIG. 5 illustrates an alternative embodiment of the invention. In this embodiment, the operating principle of controlled declutchable means  28  is similar to that described with reference to FIGS. 1 to  4 , but the cooperating surfaces are substantially different. Coupling device  30  in this case comprises a friction clutch, contact wheel  32  comprising a clutch disk covered on its two faces with friction lining, plane annular bearing surfaces  44  of end  26  of the case and  46  of toothed gear  42  being plates, made of ground steel, for example. 
     In fact, contact wheel  32  is provided with two plane annular bearing surfaces  38  and  36  designed to cooperate with complementary plane annular bearing surfaces  44  and  46 . Such a design favorably influences the manufacturing costs, since it eliminates the need for construction of frustoconical surfaces, which are generally costly to machine. 
     As an alternative (not illustrated), the clutch comprising coupling device  30  can advantageously comprise an electromagnetic clutch in which contact wheel  32  comprises a rotor and in which toothed gear  42  and end  26  of the gearbox case are each provided with a cage coaxial with primary shaft  14 , these cages being able to be traversed by an electromagnetic flux, which drives the rotor formed by wheel  32 . The two radial cages are supported respectively by the first toothed gear ( 42 ) and by the fixed bearing surface ( 44 ) of the case ( 12 ) of the gearbox ( 10 ), and are capable of cooperating selectively in a slipping manner with two ends of the wheel ( 32 ), which forms a rotor in two portions and which is integral with the primary shaft ( 14 ) to accelerate or brake respectively the primary shaft ( 14 ) when a magnetic flux is established between a portion of the wheel ( 32 ) forming a rotor and a cage of the clutch. 
     The electromagnetic clutch under consideration can also be a powder-type electromagnetic clutch, the electrical power consumed by such a device then being much smaller than that consumed by a conventional electromagnetic clutch. Such a device has the advantage that it can be controlled simply by a logical control unit, which ensures synchronization of primary shaft  14  with secondary shaft  16 . 
     FIG. 6 illustrates a final embodiment of the invention in which controlled declutchable means  28  are provided with a motorized pump  56 , which is disposed at end  26  of the gearbox case and which is linked in rotation to primary shaft  14 . In this configuration, declutchable means  28  receive power not from secondary shaft  16  but from the engine which, for example, supplies a hydraulic compressor. Motorized pump  56  is provided, for example, with axial pistons (not illustrated), and it can operate selectively as a hydraulic motor to accelerate primary shaft  14  or as a hydraulic pump to brake primary shaft  14 . 
     This variant is particularly advantageous, since it permits synchronization of primary shaft  14  with secondary shaft  16  to be achieved by hydraulic means, the power of which is furnished, for example, by a hydraulic compressor supplied by the vehicle engine. Such declutchable means can therefore be controlled by an extremely simplified logical control unit involving very few electronic components. These declutchable means are particularly suitable to an automatic robotized gearbox in which the hydraulic control unit generally has a predominant place. Such a robotized gearbox can include automatic control means acting on the declutchable means for acceleration and braking of the primary shaft ( 14 ), and automated means for interlocking of the idler pinions ( 22 ).