Abstract:
A method and device for joining assembled hollow shafts which consist of a tube and several attachable parts such as cams, flanges, bearing sleeves, pulse generating devices, toothed gears and chain gears slid on to the tube, wherein the tube, inside the attachable parts, is radially plastically expanded in individual portions by applying internal pressure in such a way that the attachable parts are secured to the tube by a permanent press fit, wherein the attachable parts and the tube are individually positioned and fixed relative to one another and wherein the tube is sequentially plastically expanded in individual portions associated with the individual attachable parts.

Description:
TECHNICAL FIELD 
     The invention relates to a method of and device for joining assembled hollow shafts and attachable parts. In particular, the invention relates to radially plastically expanding portions of the tube by applying internal pressure in such a way that the attachable parts are secured to the tube by a permanent press fit. The hollow shafts may be, for example, tubular camshafts or driveshafts. The attachable parts may be, for example, cams, flanges, bearing sleeves, trigger discs, toothed gears or chain gears which are slid onto the hollow shafts. 
     BACKGROUND OF THE INVENTION 
     In such hollow shaft assemblies, the drive elements, such as the cams and driving pinions of a camshaft, are each produced as individual elements with through-apertures. The drive elements are then slid on to the hollow shaft or tube. Thereafter, a probe member is slid into the tube. The probe member comprises individual operating regions which are axially associated with the drive elements. Each operating region includes a probe portion which is delimited by two annular seals. A hydraulic medium can be applied in the operating region at a high pressure of up to 3000 bar, for example. As a result, the tube is plastically expanded in the respective longitudinal portion, thus securing the drive elements on the hollow shaft. The deformation of the drive elements preferably takes place in the purely elastic range. 
     U.S. Pat. No. 4,750,250 discloses, in general, a method and a device for simultaneously fixing a plurality of drive elements such as cams, gearwheels and bearing bushes on a hollow shaft in one operation. The problem of holding the drive elements in an accurate position relative to the hollow shaft, particularly with respect to angular accuracy, however, is not satisfactorily addressed. 
     U.S. Pat. No. 5,195,239 describes a method and a device for positioning all of the drive elements on a hollow shaft. In this case, too, after all the drive elements have been positioned, all the drive elements are jointly joined on the hollow shaft by simultaneously expanding the hollow shaft in the individual portions associated with the drive elements. The drive elements are positioned with respect to their axial and angular positions by electromagnetic forces. Given the magnetic properties of the drive elements and of the hollow shaft, however, the accuracy of this method of positioning raises concerns. Moreover, the device in which the hollow shaft is held has a horizontal axis which is very difficult to automate. 
     U.S. Pat. No. 5,054,182 discloses methods and devices for joining a shaft of the above-mentioned type, wherein all the drive elements are first slid on to a hollow shaft and wherein the hollow shaft is then inserted into an overall device which comprises a divisible die for each individual drive element. Each divisible die holds the respective element in a predetermined axial and angular position relative to the hollow shaft and the remaining drive elements, respectively. Various embodiments disclose part axes in a horizontal position and part axes in a vertical position. These devices are very difficult to automate. In addition, they are totally unsuitable for shafts with different designs because each joint type requires its own set of die inserts. The overall device has to be newly set up for the axial positions of the individual divisible dies. 
     The above-mentioned methods have common disadvantages in that, because of the large number of operating portions of the probe, the number of possible faults which might occur is increased, and it is not easy to immediately identity the source of the fault. If the hydraulic pressure curve is indicating any malfunction while the probe is being operated, the entire assembled shaft has to be regarded as a reject. 
     If different hydraulic pressures have to be applied to different individual portions of the hollow shaft, for example for a spur gear flange on the one hand and for cams on the other hand, this can only be achieved by means of a highly complicated probe design. 
     Within a relatively short time, the unavoidable wear of the annular seals at the probe, which seals delimit the operational portions in pairs, leads to the need to replace the annular probe seals. This is a complicated operation. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and device which, while featuring a simplified design for the device, are suitable for automating the process to a considerable extent. In the present method, the attachable parts and the tube are individually positioned and fixed relative to one another. The tube is then sequentially plastically expanded in individual portions associated with the individual attachable parts. A device according to an embodiment of the invention provides one single positioning and fixing unit for the attachable parts and one single holding and positioning device for the tube. By applying the present method wherein the drive elements are positioned individually on the hollow shaft and thereafter secured one after the other, the device is greatly simplified in that only one single positioning and fixing device is required for the drive elements. The positioning and fixing device is reloaded sequentially. The design of the probe is also simplified in that it only requires one single operating portion. If operating portions of different lengths are required, it is relatively easy to provide different probes which comprise one operating portion each and which are alternatively placed into the required position. Faults are also more readily detectable. For example, if, as a result of a leakage at the probe, the joining operation does not result in a proper pressure build-up, the respective fault can be identified immediately. The joining operation can then be repeated without there necessarily occurring any assembly rejects. 
     According to one method, the attachable parts are individually positioned and fixed in space. For each attachable part, the tube is moved into an associated, predetermined axial and angular position, and an individual tube portion axially associated with the attachable part is plastically expanded. The respective device is designed in such a way that the positioning and fixing unit is fixed in space, and the holding and positioning device for the tube, with reference to the tube axis, is axially and rotatingly drivable relative to the positioning and fixing device. This embodiment has a considerable advantage in that the positioning and fixing device for the attachable parts, particularly cams, can be held in a stationary condition, which, at the same time, greatly facilitates automatic loading of the positioning and fixing device, while all the relative positions of the parts relative to one another can be controlled by axial and rotational movements of the tube in space. The respective control processes can be carried out by a NC control unit. The relative positions of the attachable parts relative to one another on the tube are highly accurate because of the identical positioning of the holding and fixing device. During the entire process, the clamping condition of the tube remains unchanged. 
     According to a first embodiment of the method, the joining stages for all the attachable parts on one tube take place in one single common device (joining station). This is particularly advantageous for small production runs. With the clamping conditions of the tube in a chuck remaining unchanged, this leads to the greatest possible positional accuracy of the attachable parts relative to one another. 
     According to a second embodiment of the method, there is provided a plurality of devices (joining stations), wherein in each joining station only one single attachable element is positioned on the tube and joined therewith. The number of joining stations corresponds to the number of attachable parts for a shaft, with the overall system, optionally, being provided with a reserve station. To ensure that the angular accuracy continues to be maintained, the clamping conditions of the tube, in this case, too, should remain unchanged. For this purpose, the tube is associated with a chuck which, in each one of the stations, can be fixed in accurate angular positions and at accurate heights by means of clamping and stopping faces at the chuck in a receiving or holding device. 
     In another embodiment, each station comprises a tool changing unit by means of which a tube provided with an additional attachable element can be replaced by a tube which has yet to be provided with the respective attachable element. As already mentioned, the handing-over and clamping operations take place directly at a freely transferable chuck associated with the tube. The tool changing unit is preferably arranged at the holding and positioning device for the tube. 
     In a further embodiment, workpiece transporting units of the pallet type are provided and are guided on a transport track from station to station. They are stopped at the individual stations by a stopper which can be slid into the transport path. The transporting units are clamped in by a clamping mechanism in accurate positions relative to the position in the transport path and relative to the vertical alignment of the tube. Such workpiece transporting units can preferably also be used in an individual station, so that the processes of entering workpieces into the station and removing same from the station can be automated. 
     In another embodiment, the workpiece transporting units of the pallet type also carry, in a die, a complete set of attachable parts for a complete hollow shaft, such as a camshaft, with the number of parts in the die being reduced by one from station to station. 
     For example, in a particular station, after one of the transport units has been moved in and fixed, first a newly moved-in tube on the transport units replaces a tube which is already located in the station and has been provided with the respective attachable part. The tube partially equipped with attachable parts, in each station, stays behind by one station relative to the transport unit into which it was first inserted before entering the first station. 
     The transport units are moved in identical phases from station to station. Accordingly, the joining operations take place in identical phases in all stations. 
     Equipping the transport units with a complete set of parts is greatly advantageous in that for the complete system, equipping can take place in one single equipping station. This equipping operation can be carried out manually, but with large production runs it can also be carried out automatically. In the case of manual equipping, the equipping station can be followed by an automatic checking station for correctness and completeness of equipment. The transport units preferably run on a closed loop. Behind the last joining station, the completed hollow shaft is ejected, with the clamping mechanism in the chuck preferably not being released, i.e. the chuck leaves the plant together with the hollow shaft. In this way, the chuck can possibly facilitate subsequent operations such as straightening, cutting to lengths and measuring. The chuck can again be clamped into the respective receiving devices in the operating stations by means of a high-speed clamping mechanism. 
     In another embodiment, the attachable elements preferably do not leave their transport plane from station to station when they are removed from the pallet-type transport unit and inserted into the positioning and fixing device. In this way, the transport means for the attachable elements in the stations can be simplified in such a way that they can only be moved in one plane along two axes. In this embodiment, the elements can only be deposited in the station, whereas they are lifted out of the station by controlling the positioning mechanism for the tube after the joining operation. 
     It is particularly advantageous that the individual joining stations are designed identically and can be used universally. Of course, the stations should be programmed in such a way that the attachable element in the highest position on the tube is joined in the first joining station and from there, the elements are joined in stages descendingly down to the attachable element in the lowest position on the tube in the last joining station. 
     The tube expanding probe is preferably adjustable between two levels. When inserting the attachable element into the positioning and fixing unit, the free probe end with the operating portion is withdrawn downwardly. Subsequently, after the attachable element has been inserted and fixed, the free probe end is moved forward into the positioning and fixing unit in such a way that the operating portion is positioned inside the attachable element. In order to ensure an accurate axial position at the probe end, the free probe end, for the purpose of being moved forward, is temporarily centered in a guide which can be tensioned and which does not prevent the probe from being slid through. As soon as the probe has been slid into the attachable element and is still centered and held therein, the lower open end of the tube is lowered from above, introduced into a centering device, and guided over the probe end. When the tube surrounds the probe, the probe fixing device is opened, so that the tube, as far as necessary, can be slid downwardly on to the probe. Thereafter the tube is firmly clamped in at its lower end, with the probe centering itself via the sealing rings on both sides of the operating portion inside the tube. The attachable element, which can be fixed by a pneumatic mechanism, is able to expand radially during the subsequent hydraulic expanding operation and thus center itself on the tube. 
     Other advantages and features of the invention will also become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of this invention, reference should now be made to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of examples of the invention. 
       In the drawings: 
         FIG. 1  shows an inventive joining station
         A) in a side view   B) in an end view   C) in a plan view.       
         FIG. 2  shows a pallet for attachable parts with the tube holding device in the form of a detail
         A) in a side view   B) in a plan view.       
         FIG. 3  shows a horizontal transporting unit for attachable parts in the form of a detail
         A) in a side view   B) in a plan view.       
         FIG. 4  shows a positioning and fixing device for attachable parts in the form of a detail. 
         FIG. 5  shows a probe holding device in the form of a detail in a side view. 
         FIG. 6  shows a complete system with eight individual joining stations according to  FIG. 1  in a plan view. 
         FIG. 7  shows an inventive shaft assembly in a partial illustration
         A) in a longitudinal section   B) in a cross-section through a cam.       
         FIG. 8  shows an inventive probe head. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Below, the three illustrations of the joining station according to  FIG. 1  will be described jointly. Three axes of movement have been given the reference symbols x, y, and z. A rack  90  is shown comprising a workpiece transporting unit  10  which is horizontally transportable in the direction of arrow P. The workpiece transporting unit  10  includes a pallet  11  and a stand  15 . The pallet workpiece transporting unit  10  runs on a transport track  13  extending inside the device. In particular, it is possible, here, to provide one groove at the pallet  11  at the groove edge extending parallel relative to the direction of movement and two bores at the opposite edge extending parallel relative to the transport direction. The receiving mechanism is loaded from one side by a 90° prism extending parallel relative to the transport direction and, from the other side, by two tapered pins positioned in the same horizontal plane, so that the pallet  11  is fixed in an accurate horizontally aligned position and in an accurate position on its transport path. On a base plate  12  of the pallet, there is positioned a die  14  which serves to accurately position a complete set of attachable elements for a hollow shaft such as a camshaft. On the base plate  12 , there is arranged an accurately vertically aligned stand  15  to whose upper end there is secured a holding and clamping device  16  for an individual chuck  17 . The chuck  17  comprises outer engaging devices which are positioned in the holding device  16  in a play-free and angularly accurate way. A tube  18  is firmly clamped into the chuck  17  and maintains the tube  18  firmly clamped in position during the entire joining process in accordance with the invention. 
     The rack  90  is provided with a further stand  19  in which a numerically controlled tube holding and positioning device  20  is vertically movable by means of a linear driving motor  21 . In the tube holding and positioning device  20 , there is provided a second chuck  23  which can be of the same type as the chuck  17 , and a second holding device  22 . However, the second holding device  22  deviates from the first holding device  16  in that it is provided with a numerically controlled rotary drive  24  which is able to move the holding device  22  and thus the chuck  23  into any rotational position inside the rack  90 . A further tube  18 ′ is clamped into the chuck  23 . The tube  18 ′ in the chuck  23  has already been equipped with an attachable part and, in this case, is replaced by the tube  18  in the stand  19 . 
     Between the two chucks  17 ,  23 , there is provided a workpiece changing device  25  which is secured to the tube holding and positioning device  20  and which comprises two radially opposed gripping arms  26 ,  27  and a rotary head  28 . By rotating the rotary head 90°, the workpiece changing device built in the design of the standard tool changing device is able, simultaneously, to embrace both chucks  17 ,  23  which are then released from their holding devices  16 ,  22 , and by continuing to rotate the rotary head  28  by 180°, the chucks can be exchanged relative to one another until they are again taken over by the holding devices  16 ,  22 . Thereafter, the rotary head  28  can be rotated back by 90°, so that the tube in the position of the first chuck  17  can be replaced by another tube by transporting the pallet  11  further and moving in a further pallet. The tube in the position of the second chuck  23  can then undergo the stages and movements required for a joining operation. 
     In addition, the rack  90  is provided with a horizontal transport unit  30  with a three-prong gripper  32  ( FIGS. 3A and 3B ) which comprises a first transverse guide  33  for a carriage  31  with a gripper  32  extending transversely to the direction of transport. The transverse guide  33  is secured to a slide  34 , as well as a longitudinal guide  35  for the slide  34  moving in the transport direction. The gripper  32 , in turn, comprises a vertical guide  36 . The gripper  32  and the guides  33 ,  35 ,  36  can be used for numerically controlling the individual attachable elements, removing the attachable elements from the holding device  16  in the die  14  and moving them into a positioning and fixing unit  40  whose center is positioned underneath the axis of the second chuck  23 . 
     Underneath the fixing unit  40 , there is arranged a probe holding and guiding device  60  in which there is held a hydraulic pressure agent probe  64  and which can be moved axially into two positions. Furthermore, the probe holding and guiding device  60  comprise a gripping unit  65  by means of which the probe  64  can be temporarily fixed when a tube is slid on. However, the gripper  65  is opened again immediately, so that, depending on the predetermined position of the attachable element on the tube, the latter can be moved downwardly significantly beyond the probe  64 . For the purpose of inserting the attachable element into the fixing device  40 , the probe  64  is moved axially into its lower position, so that the inserting movement is not obstructed. Subsequently, and prior to lowering the tube, the probe  64  is moved into its second higher position, with the operating portion of the probe coming to rest inside the attachable element. 
     The two illustrations of  FIG. 2  will be described jointly below. They show, in the form of an enlarged detail, the workpiece transporting unit  10  with the pallet base plate  12 , the die  14  bolted on to the base plate  12 , the stand  15  also bolted to the base plate  12 , as well as the holding device  16  attached to the stand. The holding device  16  is intended for a chuck. The die  14  is provided with twelve recesses  37  into which there can be inserted individual cams whose angular positions roughly correspond to those of said recesses  37 , as well as hexagonal recesses  38  into which a cylindrical bearing sleeve can be inserted, for example. These different recesses  37 ,  38  can be numerically controlled by the above-mentioned gripper  32 . Underneath the holding device  16  there is provided an oil catching dish  39  which is able to catch oil dripping from the tube equipped with at least one attachable element, so that the oil is not lost or reaching the transport track. As already mentioned, the holding device  16  is arranged in such a way that the chuck  17  can be held in an accurate position with regard to the angle of rotation. The chuck  17  can also be held rectangularly relative to the base plate  12  and, consequently, relative to the rack  90 , with the pallet  11  being clamped in. 
     The two illustrations of  FIG. 3  will also be described jointly below. They show a gripper head  32  which is arranged at a carriage  31  which can be moved on a rail or transverse guide  33  in the direction of the Y-axis. The transverse guide  33  is held in a slide  34  which, in turn, is movable on a longitudinal (slide) guide  35  along the X-axis. The gripper head  32 , in turn, is movable in a vertical guide  36  at the carriage  31  in the direction of the Z-axis. The gripper  32  comprises three radially adjustable prongs  29 . If necessary, the adjustability of the gripper head in respect of height in the direction of the Z-axis can be eliminated if the prongs  29  can be opened to such an extent that they laterally approach the attachable parts and centrally enclose and grip same. 
     The two illustrations of  FIG. 4  will also be described jointly below. The positioning and fixing unit  40  shown in  FIG. 1  in its entirety only comprises a base plate  52  on which there are mounted several clamping devices and holding devices. The clamping and holding devices can be pneumatic devices. A first pair of cylinder housings  41 ,  42  with holding jaws  43 ,  44  serves to hold and fix one of the attachable parts, such as a cam. At the front ends of the pairs of jaws  43 ,  44 , there are provided rollers  45 ,  46 ,  47 ,  48  with vertical roller axes, so that a cam placed on to an annular disc such as a carrying ring  49  is centered on the axis  50  when the holding jaws  43 ,  44  are closed. The cylinder housing  41  of the holding jaw  44  is adjustable by means of a slide  51  relative to the plate  52  in the direction of the X-axis. For this purpose, there is provided an adjusting crank  53 . On the other hand, the cylinder housing  42  of the holding jaw  44  is arranged firmly on the base plate  52 . The cylinder unit  41  acts at a higher pneumatic pressure than the cylinder unit  42 , so that the jaw  43  constitutes a fixed stop and the jaw  44  a resilient stop. 
     When the attachable part (i.e., cam) has been placed on to the carrying ring  49  and is substantially centered on the axis  50 , two clamping jaws  55 ,  56  with semi-circular recesses are moved forward towards each other, with said semi-circular recesses being gripped at their top ends. The resulting conical introducing aperture makes it possible to thread the tube accurately into the through-aperture of the attachable part, such as the cam, when the tube is subsequently lowered. 
     When the tube has been moved in and fixed, and before the subsequent operation of expanding the tubular portion inside the attachable part, two measuring scanners  57 ,  58  contact the attachable part for the purpose of recording the deformation of same as a function of time during the expanding operation. It should be noted that, on the one hand, a permissible amount of elastic deformation should not be exceeded in order to avoid crack formations in the attachable part. On the other hand, the remaining elastic deformation should be such that it is possible to assume a sufficiently high plastic deformation of the tube portion to ensure a fixed and firm fit of the attachable part. 
       FIG. 5  shows the probe holding and guiding device  60  in the same view as in  FIG. 1   a . In a cylinder housing  61 , there is provided an actuating cylinder  62  which is movable in the direction of the Z-axis and which is adjustable between an upper position as illustrated and a second lower position. At the actuating cylinder  62 , there is provided a clamping device  63  which clamps in a probe member  64  shown in dashed lines only. The lower probe member  64  shown in a broken-off condition at the lower end is followed, at the lower end, by a pressure agent supply for a hydraulic medium. The upper end of the probe member, which is also shown broken off, is followed by an axially delimited operating portion which, between two annular seals, comprises an exit aperture for a hydraulic medium. At the upper end of the cylindrical housing  61 , there is provided an adjustable clamping device  65  which centers the probe axis  70  accurately on the above-mentioned axis  50  of the positioning and fixing unit  40  without obstructing the axial mobility of the probe between two said positions. The clamping device  65  preferably opens as soon as the operating portion of the probe has been moved into the attachable part and before the tube is subsequently, from above, slid over the probe end and introduced into the through-aperture of the attachable part. At the lower end of the housing  61 , there is provided a light barrier element  66  which cooperates with a corresponding reflector  67  which is secured to the probe member  64 . The light barrier element  66  and reflector  67  are configured to form a functional stop if the probe member is incorrectly displaced downwardly by an incorrectly threaded-on tube. 
       FIG. 6  is a plan view of a system with eight complete joining stations  80  which are positioned inside an infinite rectangular conveying track system or transport loop  81  which comprises rotary stations  82  at the respective corner points. The conveying track system can comprise conveyor belts or roller tracks. At one of the shorter ends of the track system  81  there is arranged an equipping station  83  in which workpiece transporting units are equipped with a complete set of attachable parts and with a tube clamped into a chuck. In accordance with the illustration, it can be a station wherein equipping is carried out manually, but the station can easily be automated. On the transport path moving counter-clockwise, there follows a checking station  84  for checking the results of the equipping operation, which checking station  84  is preferably automated. A number of workpiece transporting units  10  are indicated in front of the equipping station  83  and the above-mentioned checking station  84 . After a workpiece transporting unit has been rotated in the rotary station  82   1 , the workpiece transporting unit passes the first four joining stations  80   1 ,  80   2 ,  80   3 ,  80   4  which are integrated into the transport path. The tube is moved into each of the joining stations  80   1  to  80   4  via the tool changing device and equipped with a first or additional attachable part and, via the tool changing device, again placed into the same or the subsequent workpiece transporting unit  10  for the purpose of continued transport. After having been transported transversely through the two subsequent rotary stations  82   2 ,  82   3 , the tube is equipped with an additional attachable part in each of the four subsequent joining stations  80   5  to  80   8 . It is also possible, for example, for pairs of attachable parts to be joined in the individual stations directly one after the other at identical rotational angles relative to the tube. Finally, in an ejecting station  85 , the finish-equipped and joined shaft assembly (i.e., camshaft) is removed from the system and placed onto a transfer belt  86 . Finally, the empty workpiece transporting units  10  are returned via a fourth rotary station  82   4  into the equipping station  83 . 
       FIG. 7  shows part of an inventive shaft assembly in the form of a camshaft  100 . Two cams  101 ,  101 ′ are secured on the tubular member  18  in identical circumferential positions in accordance with the inventive method. A needle bearing  102  is loosely slid on between the two cams  101 ,  101 ′. At the end of the shaft  18  a friction bearing  103  and a gear  104  are included which are secured in accordance with the inventive method. A cover  105  is inserted into the open end of the shaft. The attachable parts  101 ,  101 ′,  103 ,  104  have been slid on and secured by plastic deformation of the tube  18  one after the other. Of course, the attachable parts  101 ,  101 ′,  103 ,  104  are only representative of the type of parts and overall assembly process contemplated by the present invention. They are provided as examples only and are not meant to be limiting. 
       FIG. 8  shows the upper end of the probe member  64  with a bolted-on probe head  68 . An inner bore  69  with an axis  70  passes through both probe member  64  and probe head  68 . The bore  69  ends in the probe head  68  in the form of a blind bore. Between two collar portions  71 ,  72  on the probe head  68 , there is positioned a plurality of sleeves which fix a pair of annular seals  73 ,  74  which are kept at a distance from one another by a spacing sleeve  75 . The length of the sleeve  75  defines the operating range of the probe. A radial bore  76  starts from the central bore  69  and passes through the sleeve  75 . A hydraulic pressure agent flows through the radial bore  76  into the operating range sealed inside the tube by the annular seals  73 ,  74 . The probe member  64  and the probe head  68  are connected to one another by a threaded connection  77 . The sleeve  75  and the annular seals  73 ,  74  are tensioned relative to the collar  72  by threaded tensioning mechanism  78 . 
     From the foregoing, it can be seen that there has been brought to the art a new and improved method of and device for joining assembled hollow shafts. While the invention has been described in connection with one or more embodiments, it should be understood that the invention is not limited to those embodiments. Thus, the invention covers all alternatives, modifications, and equivalents as may be included in the spirit and scope of the appended claims.