Abstract:
A shift device for a transmission, which comprises a sliding sleeve, a shift fork engaging in the sliding sleeve, and an actuator that can rotate on a shaft that is disposed at an angle to the transmission shaft. In order to provide a simple and reliable control that satisfies all functional requirements, a cam having two flanks and a flattened section on the maximum radius is disposed on the shaft. On the base of the shift fork, two interacting pushrods are disposed at a fixed distance so that one pushrod rests against the one flank and the other pushrod rests against the other flank and one pushrod rests against the flattened section in at least one extreme position.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to a shift device for a transmission, consisting of a shift sleeve, displaceable in the direction of the axis of a transmission shaft, for the driving connection of transmission members, of a shift fork engaging into the shift sleeve, and of, as actuator, an element which is rotatable on a shift shaft arranged transversely to the transmission shaft and which cooperates with a foot part of the shift fork.  
         [0002]     It is known from WO 01/59331-A to adopt, as actuator a pinion which meshes with a corresponding toothing on the foot part of the shift fork, the shift shaft being driven by an electric gear motor.  
         [0003]     This has some disadvantages: the step-up of this movement transmission is constant, which, as a rule, does not correspond to the profile desired for shifting and to the characteristic of the electric motor; especially not when the shift sleeve has synchronization. There are no stops, and the toothing has no blocking action, that is to say it cannot retain the shift sleeve in the respective position. Both factors, however, are particularly important in the case of an electromotive drive. The motor is, of course, to remain currentless after a completed changeover and is even to be capable of being uncoupled in specific applications, even when changeover took place counter to the ever-acting force of a spring. Furthermore, to simplify the control, the motor is to be capable of being moved up against a stop, in order to manage without position or speed sensors.  
         [0004]     In order to remedy this, the object of WO 01/59331-A is to provide a detent disk firmly connected to the rotating element and a detent member engaging into a detent recess. Said detent member holds the rotating element after the uncoupling of the electric motor and ensures that this is possible only after a defined end position is reached. However, this remedy is highly complicated and is also not entirely satisfactory in functional terms. Due to the moments acting on the element and consequently on the detent disk (which emanate, for example, from the synchronization or from chamfers of the teeth in order to secure the sleeve against a stop), friction arises which obstructs or completely prevents the changeover. This may also occur when the two elements to be coupled are in an unfavorable relative position. The other gear in each case then cannot be engaged, and the sleeve remains set in the neutral position, which may lead to hazardous driving situations and therefore should not happen. Moreover, due to the long tolerance chain, positioning is inaccurate.  
         [0005]     The object of the invention, therefore, is to propose a simple and reliable control which satisfies all functional requirements, in particular safety requirements.  
       SUMMARY OF THE INVENTION  
       [0006]     The foregoing object is according to the invention, by means of the following:  
         [0007]     a) the rotatable element is a cam which has two flanks extending from a minimum to a maximum radius and a flattening at the maximum radius,  
         [0008]     b) two lantern wheels cooperating with the cam are provided at a fixed distance from one another on the foot of the shift fork,  
         [0009]     c) so that one lantern wheel bears against one flank and the other lantern wheels bears against the other flank and, in at least one end position, one lantern wheel bears against the flattening and the other lantern wheel bears exactly against the minimum radius.  
         [0010]     The cooperation of the cam of one member with the two lantern wheels of the other member, the two members having defined poles (one may be infinitely remote), provides a desmodromic control. In this context, the flattening is formed. Thus, one lantern wheel, together with a flattening, brings about a detention of the shift fork in an end position, and the other lantern wheel at the smallest radius gives rise to a stop. As a result, two functions, which it has been possible to fulfill only by means of two different pairs of members according to the prior art, are combined in a single pair of members, this being such that shifts can take place even counter to considerable holding forces. The lantern wheel pressing onto the flattening of the cam under the force of the coupling spring does not, of course, exert any torque on the cam. Furthermore, by the configuration of the cam shape, the step-up can be adapted to the shift requirements (in contrast to a conventional lantern wheel toothing in which the step-up must of course be constant).  
         [0011]     In a preferred embodiment, the shift fork is a two-armed lever pivotable about an axis fixed with respect to the housing and the lantern wheels are cylinders, the axes of which are parallel to the axis of the shift shaft. This affords an accurate kinematic guidance of the two members, along with low friction; the latter to an especially great extent when the lantern wheels are rotatable about their axes. Furthermore, the flanks of the cam are enveloping curves of the lantern wheels when there is a common rolling movement of cam and lantern wheels. In this case, the step-up ratio of the rolling movement can be determined by means of the configuration of one flank of the cam, that of the other flank then arising from this.  
         [0012]     In an advantageous development with a shift shaft driven by an electric motor, a shoulder is provided at the point of minimum radius on at least one flank. The electric motor can consequently be controlled automatically without path or speed regulation.  
         [0013]     In order to ensure reliable shifting, further measures may advantageously be taken: when the shift fork surrounds a shift sleeve with a large diameter, the foot part of the shift fork is appended at the lowest point of the latter, the shift force thereby being introduced symmetrically into the shift fork. When there is the risk that the shift sleeve cannot be engaged in the case of a tooth-on-tooth position, the shift fork contains an elastic element, so that the foot part can move back. When the tooth position is favorable, shifting then takes place somewhat later by means of the force of the elastic element.  
         [0014]     The invention is also concerned, particularly with regard to the power divider for motor vehicles, with an off-road gear step which can be shifted due to the axial displacement of one of its elements by means of a shift fork as a result of rotation of a shift shaft arranged transversely to the axial direction. In the case of a power divider, the problems referred to initially arise in a particularly disturbing way. They are eliminated by the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The invention is described and explained below with reference to figures in which:  
         [0016]      FIG. 1  illustrates a vertical section through a power divider having the shift device according to the invention,  
         [0017]      FIG. 2  illustrates a section according to CC in  FIG. 1 ,  
         [0018]      FIG. 3  illustrates a detail of  FIG. 2 , enlarged and varied,  
         [0019]      FIG. 4  illustrates a view according to IV in  FIG. 3 ,  
         [0020]      FIG. 5  illustrates the same as  FIG. 4  in one end position,  
         [0021]      FIG. 6  illustrates the same as  FIG. 4  in the other end position,  
         [0022]      FIG. 7  illustrates another embodiment in a view similar to that of  FIG. 4 . 
     
    
     DETAILED DESCRIPTION  
       [0023]     In  FIG. 1 , the housing of a power divider is designated as a whole by  1 , an input shaft coming from the drive unit, not illustrated, of the vehicle by  2 , a first output shaft drive-connected to the rear axle by  3  and a second output shaft drive-connected to the front axle, likewise not illustrated, by  4 . The second output shaft  4 , by means of a first toothed-belt wheel  5 , drives, below the input shaft  2 , a second toothed-belt wheel  6  which is seated on a driven shaft  7  for the drive of the front axle.  
         [0024]     To distribute the torque to the two output shafts  3 ,  4 , a differential, designated in summary by  10 , is provided. Furthermore, a control unit  11  below the differential  10  and a blocking clutch  12  for blocking the differential  10  are provided. In the exemplary embodiment shown, the blocking clutch is combined structurally with the differential  10 . It could, however, also be arranged separately, indeed even anywhere else in the power divider or in the drive train. The differential itself may also have a widely differing design within the framework of the invention.  
         [0025]      FIG. 1  and  FIG. 2  show an exemplary and particular version of the power divider. Inside a differential housing  16 , which serves here at the same time as a planet carrier, are located a sun wheel  17  connected fixedly in terms of rotation to the input shaft  2 , planet wheels  18  of the off-road gear step, which are mounted rotatably in the differential housing  16 , and first compensating wheels  21  and second compensating wheels  22 . The former ( 21 ) are connected fixedly in terms of rotation to the first output shaft  3  and the latter ( 22 ) are connected fixedly in terms of rotation to the second output shaft  4 . The differential housing  16  is surrounded by a ring wheel  19  which is axially displaceable and, in the off-road gear, is connected fixedly in terms of rotation to the differential housing  16 . This special embodiment of the differential  10  is the subject of Austrian patent 405 157 and is described in more detail there in terms of type of construction and functioning.  
         [0026]     The blocking clutch  12  is actuated by means of two ramp rings  31 ,  32  rotatable relative to one another. The first ring  31  possesses a first ramp lever  35 , and the second ring  32  possesses a second ramp lever ( 36 ), said ramp levers projecting downward and possessing rollers  39  at their free ends  37 ,  38 . Between the two rollers  39  is located a rotatable control disk  40 . During the rotation of this control disk, the rollers  39  are moved apart from one another and, via the ramp levers  35 ,  36  moved in a scissor-like manner, the rings  31 ,  32  are rotated relative to one another.  
         [0027]     In  FIG. 2, 47  is a motor output shaft of an electric gear motor, not illustrated, said motor output shaft rotating with a corresponding step-down when the motor is running. Connected fixedly in terms of rotation to this motor output shaft is a carrier shaft  48  which is slipped onto the latter in a sleeve-like manner and which is mounted on both sides in the housing  1 . The hub  49  of the control disk  40  and a cam  50  are mounted rotatably on the carrier shaft  48 . Between the hub  49  and the cam  50 , a changeover sleeve  52  is mounted fixedly in terms of rotation, but displaceably in the longitudinal direction, on the carrier shaft  48  by means of a longitudinal ball guide  51 . The changeover sleeve  52  is displaced by means of a changeover fork  53  which is actuated by a changeover magnet  54  ( FIG. 1 ) via a lever mounted in a changeover fork axis  55  ( FIG. 1 ). The changeover sleeve  52 , at its two axial ends, has first shift teeth  56  for rotationally fixed connection to the hub  49  and second shift teeth  57  for rotationally fixed connection to the cam  50 . The shift teeth  56 ,  57  are coupling teeth with a deflecting pressure angle. If only one gear shift or only one blocking clutch is to be actuated, a changeover sleeve  52  is not necessary.  
         [0028]     It can be seen in more detail in  FIG. 3  that the cam  50  cooperates in a way still to be described with lantern wheels  60 ,  61  which are arranged on the foot part  64  of a shift fork  63  which is pivotable about an axis of oscillation  62  in the housing and by means of which the ring wheel  19  is displaced in the axial direction for changeover into the off-road gear. For this purpose, a sliding block  66  is provided on each of the two sides of the ring wheel. An elastically flexible intermediate zone  65  may be provided in the foot part  64 .  
         [0029]     In the exemplary embodiment shown, the cam  50  and the lantern wheels  60 ,  61  are duplicated (cams  50 * and lantern wheels  60 *,  61 *) for reasons of lateral guidance, and the foot part  64  of the shift fork  63  is tied to the lowest point of the latter, hence in its axis of symmetry. By virtue of the latter aspect, the deformations of the two halves of the shift fork  62  are equal, so that they cannot become jammed.  
         [0030]     In  FIG. 4 , the kinematics of the cooperation of cam and lantern wheels  60 ,  61  can be seen. The lantern wheels  60 ,  61  are arranged at a fixed distance  70  from one another on the foot part  64  of the shift fork  63 . Here, they are circular cylinders (other shapes may also be envisaged, see  FIG. 7 ) with axes  71  which either are only geometric axes or are axes of rotation for the lantern wheels, on which they can rotate and thus roll on the cam  50 , in order to minimize friction. The cam is rotatable with its shaft about an axis  72  and possesses a first flank  73 , a second flank  74 , at a maximum distance from the axis  72  a flattening  75 , and at a minimum distance from the axis  72 , that is to say at a minimum radius, valleys  76 ,  77  which shoulders  78 ,  79  adjoin. The flanks  73 ,  74  are shaped in such a way that in all the middle positions, such as, for example, in  FIG. 4 , the lantern wheel  60  always bears against the flank  73  and the lantern wheel  61  always bears against the flank  74 . These flanks are therefore enveloping curves of the two lantern wheels. In contrast to a toothing, by means of a suitable shaping of the flanks  73 ,  74 , different step-ups can be implemented as a function of angle. It can also be seen directly in  FIG. 4  how, for example, a rotation of the cam  50  clockwise about its axis  72  causes a pivoting of the shift fork  63  counterclockwise about its axis of oscillation  62 .  
         [0031]     In  FIG. 5 , the cam  50 ′ is in one end position. The lantern wheel  61 ′ has run through the valley  77 ′ and reached the stop  79 ′. As a result, the electric motor driving the cam has been stopped and reversed, so that, when switched on again, it rotates in the opposite direction. In this position, the other lantern wheel  60 ′ is supported on the flattening  75 ′. Since the supporting force, illustrated by an arrow  80 , is directed toward the axis  72 ′ of the cam  50 ′, no torque is in this case exerted on the cam  50 ′. The shift fork can thus be held in the position shown without action upon the motor and without locking. If appropriate, for safety purposes, a spring, not illustrated, is provided or a coupling spring, present in any case, acts as such. The other end position of  FIG. 6  differs from that of  FIG. 5  only in that the lantern wheels  60 ″,  61 ″ have exchanged their rollers, and in that the cam  50 ″ is rotated clockwise approximately through a right angle. The shift fork is retained, here, in the other end position.  
         [0032]     The possibility of providing an elastic zone  65  in the foot part  64  of the shift fork  63  was mentioned further above. When the ring wheel cannot be engaged in the case of a tooth-on-tooth position, the elastic zone allows the cam  50  to execute its adjusting movement as far as the end position, but without the fork itself being moved in this case. Only when the teeth of the ring wheel have been displaced somewhat with respect to its counterwheel is the ring wheel engaged by means of the force stored in the elastic zone.  
         [0033]     In the variant of  FIG. 7 , the cam  150  is to a very great extent widened and thickened. It cooperates kinematically with the lantern wheels  160 ,  161  which are not cylindrical here, but bar-shaped, and are provided with suitably shaped sliding surfaces  178 ,  179 . Here, too, between the two members a desmodromic movement transmission prevails, in which the two contact surfaces  178 ,  179  are always in contact with the cam  150 .