Abstract:
A device for actuating a gearwheel of a transmission device. The gearwheel rotates on a shaft and can be shifted by way an engagement mechanism that includes at least one actuator that is arranged at least partially inside the shaft. The actuator can be actuated by a pressure medium to fix the gearwheel to the shaft. The actuation force required for engaging or disengaging the gearwheel can come from within the shaft. The actuator is a piston-cylinder unit which is either rotationally fixed to the shaft or rotationally fixed relative the shaft. When the actuator is rotationally fixed relative to the shaft, the active connection between the actuator and the gearwheel, which is to be shifted, includes a drive decoupling unit between the actuator and the shaft.

Description:
This application is a National stage completion of PCT/EP2007/060818 filed Oct. 11, 2007, which claims priority from German patent application serial no. 10 2006 049 281.1 filed Oct. 19, 2006. 
     FIELD OF THE INVENTION 
     The invention concerns a device for actuating a gearwheel designed as a loose wheel of a transmission device. 
     BACKGROUND OF THE INVENTION 
     Step-down transmissions known from practice, such as dual clutch transmissions, automated manual transmission, manual transmissions or suchlike, are usually made with gearwheels mounted to rotate on a shaft, which engage with other gearwheels connected in a rotationally fixed manner on another shaft, thereby forming so-termed paired gearwheels. By alternate rotationally fixed connection of the gearwheels mounted to rotate on the shaft, the gearwheel pairs can be engaged in the force flow of a step-down transmission by means of appropriate shift elements such as synchronizers, claws, clutches or frictional elements, to produce the various gears of the step-down transmission. 
     In relation to the shaft on which the gearwheels are mounted to rotate, or loose wheels of a step-down transmission are arranged, the shift elements provided for engaging the gearwheel pairs are actuated mechanically, hydraulically, pneumatically or magnetically from the outside or from inside. 
     From DE 43 25 964 A1 it is known, in the case of gearwheels that rotate on a shaft, to connect them in a rotationally fixed manner to the shaft by means of a hydraulically actuated shift sleeve. For this, the shift sleeve is supplied with pressure medium that passes through the transmission shaft by hydraulic conduits. 
     The hydraulic actuation of the shift sleeve provided for fixing the gearwheels made as loose wheels requires, in the axial extension of the shaft, structural space between gearwheels arranged on the shaft and to be actuated, and because of this the reduction of the need for structural space, attempted by actuating from the inside of a transmission shaft outward, is not achieved to the desired extent. 
     In addition, a piston space associated with the shift sleeve is disadvantageously sealed relative to its surroundings by so-termed contact sealing devices, so that during the movement of the piston relative to the cylinder undesirably large friction forces are produced because of the sometimes high actuation pressures. In turn these friction forces lead to an increase of the actuation forces that have to be applied to actuate the piston. Moreover, the sealing action of a contact seal deteriorates with increasing operating time because of friction, and in some circumstances this compromises the functionality of such control means. In addition, further friction losses occur in the area of lubrication oil inlets provided between a housing and the transmission shaft, for the reasons already stated these are undesired. 
     From DE 102 06 584 A1 hydraulically actuated shift elements are known by means of which gearwheels mounted to rotate on a shaft can be connected in a rotationally fixed manner to the shaft. The shift elements are actuated by two hydraulic actors located inside the shaft and connected in a rotationally fixed manner to it, both of these actors being supplied with oil by a non-rotating oil supply unit. 
     Disadvantageously, it is very elaborate and expensive to seal and mount such an oil supply unit relative to its surroundings, and the oil supply unit must be arranged coaxially with respect to the shaft. If several actors are arranged in the shaft and are to be hydraulically actuated, then a complex oil supply and outlet system has to be provided. 
     Another design, known from DE 102 06 584 A1, comprises two actuators which, when a transmission is operating, have a connection rod that rotates together with the shaft, whose rotation speed is decoupled relative to a non-rotating housing. To actuate the gearwheels, made as loose wheels, both electromagnetic and hydraulic actuators are proposed, such that in each case one shift element is connected by a connection rod to one actor and rotates with the speed of the shaft, whereas a cylinder housing of a piston-cylinder unit is static relative to the shaft and the connection rod. 
     Owing to the high relative rotational speeds that occur during the operation of a transmission device, between a piston connected to the connection rod and the cylinder housing, either complex and costly sealing of the piston space delimited by the piston and the cylinder housing is necessary, this being affected by friction and wear, or the piston space will be characterized by substantial amounts of leakage that cause large pressure and oil losses. 
     From DE 102 25 331 A1 a change-under-load transmission with central synchronization is known, in which loose wheels on a transmission shaft can be actuated by a hydraulic actuator actuated hydraulically and arranged at least partially inside the transmission shaft. In the case of this actuator, a connection rod coupled to a piston is connected in a rotationally fixed manner to the shaft, whereas a cylinder housing of the actuator, made as a piston-cylinder unit, is fixed to the housing. 
     The disadvantage here, however, is that the drive decoupling between the connection rod and the cylinder housing is achieved by a corresponding connection between a piston and the connection rod, for example a slide or roller bearing, and the seal between the piston spaces separated from one another by the piston, which is necessary for proper functionality, is achieved only with considerable cost and complexity. 
     Thus, the purpose of the present invention is to make available a device for actuating a gearwheel made as a loose wheel of a transmission device, which is characterized by little demand for structural space and whose functionality is ensured with low sealing cost and complexity along with low frictional forces. 
     SUMMARY OF THE INVENTION 
     In the device according to the invention for actuating a gearwheel of a transmission device made as a loose wheel, the gearwheel being mounted to rotate on a shaft and being able to be actuated, by means of an engaging device which comprises an actuator operated by a fluidic pressure medium and which is arranged at least partially inside the shaft, to an engaged condition in which the gearwheel is connected in a rotationally fixed manner to the shaft and such that the gearwheel can be acted upon from inside the shaft outward by the actuation force required for its engagement or disengagement, the at least one actuator is made as a piston-cylinder unit arranged completely inside the shaft and connected in a rotationally fixed manner to it. 
     A device made with an actuator of such type is of compact and lightweight structure, and compared with designs known from the prior art for connecting gearwheels in a rotationally fixed manner to a shaft of a transmission device, it is characterized by little demand for structural space because the actuator is accommodated completely inside the shaft. 
     In addition, compared with the known systems the cost and complexity of sealing is reduced with the device according to the invention, since the entire piston-cylinder unit is connected rotationally fixed to the shaft carrying the loose wheel, and there is no need for drive decoupling means in the area of an active connection between the actuator and preferably a shift element that actuates the loose wheel, which is usually also connected in a rotationally fixed manner to the shaft. Accordingly, piston spaces of the piston-cylinder unit that are to be acted upon by pressure medium involve no relative rotary movements between a cylinder and a piston which delimit the piston spaces of the piston-cylinder unit, and sealing is only necessary in relation to translational relative movements between the cylinder and the piston. 
     In the device the at least one actuator is made as a pneumatic or hydraulic motor, which is connected in a rotationally fixed manner to the shaft, the active connection between a motor output shaft of the motor and the gearwheel to be actuated being designed with drive decoupling means between the motor output shaft and the shaft. 
     Thus, the actuator of the device for actuating a gearwheel of a transmission device made as a loose wheel is arranged inside the shaft in a space-saving manner, so that compared with conventional transmission devices such a transmission device can be made with smaller structural space dimensions. 
     Furthermore the embodiment according to the invention of the device as described is characterized by low sealing cost and complexity, since the drive decoupling means between the actuator and the components provided for actuating the gearwheel have been moved away from the parts of the actuator acted upon by pressure medium, to an essentially pressure-free zone. The result is that in a simple manner, the actuation forces for engaging or disengaging a gearwheel are not increased to an undesired extent by friction forces caused by contact seals. 
     The device according to the invention for actuating a gearwheel of a transmission device made as a loose wheel, is also characterized by small demand for structural space, again because the actuator, preferably in the form of a pneumatic or hydraulic motor connected in a rotationally fixed manner relative to the shaft, is completely accommodated inside the shaft. 
     In addition, in the same manner as the design of the device according to the invention described above, the design of the device, in which the motor is fixed on the housing or rotationally fixed relative to the shaft, is located, in the area of the active connection between an output shaft of the motor and the gearwheel to be actuated or between the motor output shaft and the shaft, in an unpressurized zone with drive decoupling means, so that compared with systems known from the prior art the sealing complexity is reduced and the gearwheel can be changed from an engaged or disengaged condition to a disengaged or engaged condition by actuation forces as small as possible. 
     Another alternative and also space-saving embodiment of the device according to the invention for actuating a gearwheel of a transmission device made as a loose wheel, is the device in which an actuator in the form of a piston-cylinder unit is arranged inside the shaft and connected rotationally fixed to it. 
     In this last-mentioned embodiment of the device according to the invention, in the area of the active connection between a piston rod of the piston-cylinder unit and the gearwheel to be actuated, drive decoupling means are provided between the piston rod and the shaft, so that both the sealing complexity and the actuation forces for engaging or disengaging the gearwheel are as small as possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages and advantageous further developments of the invention emerge from the claims and the example embodiments whose principle is described with reference to the drawing. For the sake of simplicity, in the description of the various example embodiments the same indexes are used for components having the same structure and function. 
       The drawing shows: 
         FIG. 1 : Schematic partial longitudinally sectioned view of a transmission device comprising a first embodiment of the device according to the invention 
         FIG. 2 : Representation similar to  FIG. 1 , of a transmission device comprising a second embodiment of the device according to the invention 
         FIG. 3 : Representation similar to  FIG. 2 , in which the transmission device comprising a third embodiment of the device according to the invention; and 
         FIG. 4 : Representation similar to  FIG. 2 , of a transmission device comprising a fourth embodiment of the device according to the invention 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a partial longitudinally sectioned view of a transmission device  1  made as a step-down transmission, which comprises a device  2  for rotationally fixing a shaft  3 , in the form of a countershaft, with a plurality of gearwheels  4 ,  5 ,  6  and  7  made as loose wheels and mounted to rotate on the shaft  3 . 
     The device  2  can also be used in different transmission devices, such as automated shift transmissions, double clutch transmissions or planetary transmissions, for the automated actuation of a transmission device during gearshift operations. 
     Parallel to the shaft  3  there is a main transmission shaft (not shown), on which are arranged a plurality of gearwheels made as fixed wheels in such manner that each fixed wheel meshes with one of the gearwheels  4  to  7 . 
     The loose wheels  4  and  5  and the loose wheels  6  and  7  can be actuated alternately by means of engaging mechanisms  8  and  9  of the device  2  in such manner that the loose wheels  4  and  5  or  6  and  7  respectively are changed from a condition in which they can rotate on the shaft  3  to a condition in which they are rotationally fixed on the shaft  3 , or vice-versa, i.e. from a rotationally fixed condition to a condition in which they can rotate relative to the shaft, in order to be able to transmit a torque applied to the shaft  3 , via one of the gearwheels  4  to  7  and a respective fixed wheel meshing with the gearwheels  4  to  7 , to the main shaft of the transmission. 
     The engaging mechanisms  8 ,  9  of the device  2  have basically the same structure, so that the description below will relate essentially only to the engaging mechanism  8 . 
     The engaging mechanism  8  comprises an actuator  10  which, in the present case, is in the form of a hydraulic swing motor and is connected in a rotationally fixed manner to the shaft  3 . During the operation of the transmission device  1  the actuator  10  therefore rotates at the speed of the shaft  3 . A motor output shaft  11  of the actuator  10  is connected in a rotationally fixed manner to a spindle  12  of a spindle-nut arrangement  13  of the engaging mechanism  8 , so that drive from the actuator rotates the spindle  12  such that a nut  16 , which is engaged with the spindle  12  and is connected in a rotationally fixed manner to the shaft  3 , moves axially along the shaft  3  away from the actuator  10  or toward it. 
     In the present case the nut  16  is actively connected with two pins  14 A and  14 B that pass through the shaft  3 , in such manner that the pins  14 A and  14 B are pushed by the nut  16  along slots  15 A,  15 B of the shaft  3  in the axial direction of the shaft  3 . During the operation of the transmission device  1 , the pins  14 A and  14 B rotate, along with the nut  16  of the spindle-nut arrangement  13 , at the speed of the shaft  3  about the rotational axis of the shaft  3 . 
     To connect the gearwheel  4  or the gearwheel  5  in a rotationally fixed manner to the shaft  3  and thus change it from a disengaged to an engaged condition, at their end remote from the nut  16  the pins  14 A and  14 B are connected with a sleeve element  17  that surrounds the shaft  3 , which is connected in a form-locking manner such that it is rotationally fixed relative to the shaft  3  but can move along it in the axial direction of the shaft  3 . In addition, the sleeve element  17  is formed in the area of its circumferential surface facing away from the shaft  3  with a toothed profile  18  which, depending on its axial position, engages with a toothed profile  19  which is fixed on the loose wheel  4 , a toothed profile  20  which is fixed on the loose wheel  5  or, in a neutral intermediate position between these two toothed profiles  19  and  20 , as shown in detail in  FIG. 1 , with neither of the toothed profiles  19  and  20  so that neither the loose wheel  4  nor the loose wheel  5  is connected in a rotationally fixed manner to the shaft  3 . 
     The spindle-nut arrangement  13  and a spindle-nut arrangement  21  of the engaging mechanism  9  each constitute a drive conversion mechanism by means of which rotary drive of the actuator  10  and that of an actuator  22  of the device  2  also made as an electric motor can be converted to a translational drive movement for engaging or disengaging the loose wheels  4  to  7 . 
     To prevent spontaneous engagement of disengagement of the loose wheels  4  to  7 , the spindle-nut arrangements  13  and  21  are in this case of self-locking design, so that the nut  16  of the spindle-nut arrangement  13  and a nut  23  of the spindle-nut arrangement  21  maintain their position unless actuated by the actuator. 
     Alternatively, in other embodiments of the transmission device not illustrated in the drawing, provision is made for a shift status of a shift element, i.e. in this case the sleeve elements  11  and  40 , to be maintained by a retaining torque produced by the actuator by virtue of appropriate control of the actuators of the engaging mechanisms. 
     To actuate the loose wheels  4  to  7 , the actuators  10  and  22  are supplied, via a hydraulic rotary transfer device  24 , with the necessary hydraulic pressure from a hydraulic pump  25 . The rotary transfer device  24  is in this case connected to the pump  25  by a hydraulic line  26  and in addition comprises control valves  27  which open or block connection lines  28 A and  28 B or  29 A and  29 B, respectively between the rotary transfer device  24  and the actuator  10  or the actuator  22 , in order to pressurize the actuators  10  and  22  with pressure medium sufficiently for actuation of the loose wheels  4  to  7 . 
     The hydraulic pump, which can be arranged both outside and inside the shaft, can be powered mechanically, electrically, magnetically or hydraulically, depending on the particular application in each case. 
     By integrating the control valves  27  in the shaft  3  between the pump  25  fewer rotary oil supply connections are needed, so the device  2  can be of simple and inexpensive design. 
     By virtue of the actuators  10  and  22  made as concomitantly rotating hydraulic motors, which basically deliver a higher power density than electric motors, the device  2  is characterized by a compact and lightweight structure. This makes use of the knowledge that with a hydraulic motor large areas can be provided, upon which the pressure delivered by the pump  25  acts. In addition, owing to the transmission ratio in the spindle, a lower pressure with high volume flow can be used to actuate the motor. 
     The actuators  10  and  22  made as swing motors in this case retain the central position equivalent to the neutral shift position of the sleeve element  17  shown in  FIG. 1 , in order to support the self-locking of the spindle-nut arrangement  13  so that spontaneous engagement of the loose wheels  4  and  5  can be reliably prevented. 
     It is also possible to make the hydraulic swing motors or actuators  10  and  22  such that they retain various positions, so that an engaged loose wheel  4  or  5  can be maintained in the engaged condition without further pressurization by the pump  25 . 
     In the embodiment of the device according to the invention as shown in  FIG. 1 , drive decoupling between the motor output shaft of the actuator  10  or a motor output shaft  30  of the actuator  22  is provided in each case in the area between the spindle  12  or a spindle  31  of the spindle-nut arrangement  21  and, respectively, the nut  16  or the nut  23 , i.e. outside a pressurized zone of the device  2 , so that in a simple manner elaborate sealing means of the type known from the prior art are unnecessary. 
       FIG. 2  shows another embodiment of the device  2  according to the invention, which differs from the embodiment of the device  2  shown in  FIG. 1  both in relation to the actuators  10  and  22  and the engaging mechanisms  8  and  9 . In the embodiment of the device  2  shown in  FIG. 2  the actuators  10  and  22  are made as piston-cylinder units, which are positioned completely inside the shaft  3  and are connected in a rotationally fixed manner thereto. Pistons  33  and  34  of the actuators  10  and  22  separate piston spaces  33 A and  33 B or  34 A and  34 B which are connected respectively to the connection lines  28 A,  28 B and  29 A and  29 B, and are fixed to piston rods  35 ,  36 . 
     The piston rods  35  and  36  are fixed to respective actuation elements  37  and  38 , in which the pins  14 A,  14 B or  39 A,  39 B of the engaging mechanisms  8  and  9  engage in order to be able to actuate the sleeve element  17  and the sleeve element  40 , respectively, in the manner described earlier, along the axial direction of the shaft  3  to engage or disengage the loose wheels  4  to  7 . 
     With regard to the other functions of the device  2  in  FIG. 2 , reference can be made to the description of the device  2  in  FIG. 1 , whose functions are essentially the same. 
       FIG. 3  shows an embodiment of the device equivalent to that in  FIG. 2 , in which the actuators  10  and  22  are also made as cylinder-piston units. However, in the embodiment of the device  2  in  FIG. 3  the actuators  10  and  22  are rotationally fixed relative to the shaft  3 , so that in the area between the actuation elements  37  and  38  and the pins  14 A and  14 B and the pins  39 A and  39 B rotation drive decoupling is provided by means, in this case, of bearing devices  41  and  42  made as slide bearings, between the piston rods  35  and  36  of the engaging mechanism  8  and  9 , also rotationally fixed relative to the shaft  3 , and the pins  14 A,  14 B, and  39 A,  39 B respectively. 
     Alternatively, the bearing devices can also consist of roller bearings, to enable relative movement, as functionless as, possible between the pins rotating at the speed of the shaft  3  when the transmission device is operating, and the actuation elements of the engaging mechanisms of the device  2 . 
     Starting from the ends of the shaft  3 , the actuators  10  and  22  inside the shaft  3  are each connected in a rotationally fixed manner to a housing  43  of the transmission device  1 , so that the connections to the hydraulic pump  25  are provided without the rotary transfer device  24  shown in  FIGS. 1 and 2 , through the housing  43  of the transmission device  1  and directly to the piston spaces  33 A,  33 B and  34 A,  34 B in a simple manner. Control valves (not shown in  FIG. 3 ) for pressurizing of the piston spaces  33 A to  34 B as necessary can be arranged inside the shaft  3  or outside the shaft, depending on the particular application. 
     To increase the rigidity of the actuators, in a further development of the embodiment of the device according to the invention shown in  FIG. 3  (the further development not being shown), the actuators can be mounted in the shaft by suitable bearings at their ends engaged in the inside of the shaft, and/or the actuators can be made as hydraulic motors. 
     In the last-mentioned embodiment the rotary drive of the hydraulic motors has to be converted, for example by spindle-nut arrangements as illustrated in  FIG. 1 , into translational actuation movements for the engagement or disengagement of loose wheels arranged on the shaft. 
     In the fourth embodiment of the device  2  according to the invention, shown in  FIG. 4 , which differs from the embodiment shown in  FIG. 3  only in the arrangement of the actuators  10  and  22 , the two actuators  10  and  22  are connected in the area of their housing so that connection to the transmission housing  43  is needed on only one side. Both actuators  10  and  22  are also supplied with pressure oil from the pump  25  via that side of the transmission housing  43  to which they are connected rotationally fixed, the connection lines to the actuator  10  in this case lying outside the section plane shown and for that reason not being visible in  FIG. 4 . 
     To transmit the translational actuation movement of the actuator  10  from inside the shaft  3  to the outside, the connection between the actuators  10  and  22  comprises a so-termed free passage through which the actuation element of the engaging mechanism  8 , in which the drive decoupling is integrated, can be connected to the pins  14 A and  14 B. 
     This design makes it possible to arrange even more than two actuators connected to one another inside the shaft  3 , and thus to actuate more than four loose wheels arranged on a countershaft or suchlike. 
     Fundamentally, the device according to the invention is characterized by a compact and light structure that takes up little structural space. Furthermore, loose wheels arranged on a transmission shaft can be changed from an engaged to a disengaged operating condition or from a disengaged to an engaged one with low friction losses, so that to control the actuators the hydraulic fluid of a hydraulic system of the transmission device or a hydraulic fluid of a separate oil circuit can be used. 
     Moreover, the actuators can also be in the form of pneumatic motors or operating control cylinders and the control valves provided for the control and/or regulation of the actuators can be mechanical, electric, magnetic or hydraulic valve devices. 
     Particularly in the case of the design in which the actuators are fixed on the housing, the device according to the invention can in a simple manner be made with a leakproof, separate and efficiency-optimized high pressure hydraulic system for actuating loose wheels arranged on the shaft, since no rotary oil transfer device is needed. 
     In a further advantageous embodiment of the device according to the invention (not shown in the drawing), the device is made with only one actuator for applying the actuation force for engaging or disengaging several gearwheels arranged to rotate on a shaft, a so-termed selection actuator being associated with the actuator. By means of the selection actuator a choice can be made between the various loose wheels of the transmission device to be actuated, so that the gearwheel chosen by the selection actuator, or the shift element associated with it, is acted upon by the actuation force produced by the actuator, while the other gearwheels are not actuated by the actuator. 
     In this case the selection actuator can preferably be made as a shift magnet, a hydraulically actuated clutch, or suchlike, which produces a respective connection between the actuator of the device pressurized with a fluidic pressure medium and the loose wheel to be actuated by the device, as necessary for actuating the loose wheel or the shift element associated with it. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Indexes 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  1 
                 Transmission device 
               
               
                   
                  2 
                 Device 
               
               
                   
                  3 
                 Shaft 
               
               
                   
                  4 to 7 
                 Gearwheel 
               
               
                   
                  8, 9 
                 Engaging mechanism 
               
               
                   
                 10 
                 Actuator 
               
               
                   
                 11 
                 Motor output shaft 
               
               
                   
                 12 
                 Spindle 
               
               
                   
                 13 
                 Spindle-nut arrangement 
               
               
                   
                 14A, B 
                 Pins 
               
               
                   
                 15A, B 
                 Slots 
               
               
                   
                 16 
                 Nut 
               
               
                   
                 17 
                 Sleeve element 
               
               
                   
                 18 to 20 
                 Toothed profile 
               
               
                   
                 21 
                 Spindle-nut arrangement 
               
               
                   
                 22 
                 Actuator 
               
               
                   
                 23 
                 Nut 
               
               
                   
                 24 
                 Rotary transfer device 
               
               
                   
                 25 
                 Pump 
               
               
                   
                 26 
                 Hydraulic line 
               
               
                   
                 27 
                 Control valve 
               
               
                   
                 28A, B 
                 Connection line 
               
               
                   
                 29A, B 
                 Connection line 
               
               
                   
                 30 
                 Motor output shaft 
               
               
                   
                 31 
                 Spindle 
               
               
                   
                 33 
                 Piston 
               
               
                   
                 33A, B 
                 Piston space 
               
               
                   
                 34 
                 Piston 
               
               
                   
                 34A, B 
                 Piston space 
               
               
                   
                 35, 36 
                 Piston rod 
               
               
                   
                 37, 38 
                 Actuation element 
               
               
                   
                 39A, B 
                 Pins 
               
               
                   
                 40 
                 Sleeve element 
               
               
                   
                 41, 42 
                 Bearing device 
               
               
                   
                 43 
                 Housing