Abstract:
An apparatus ( 30 ) and method for forming of a vehicle&#39;s driveshaft ( 32 ) is provided which makes use of a PMF process. The coil device used in the PMF apparatus is assembled around the shaft from two or more coil sections ( 40, 41, 43; 42, 44, 45 ) firmly attached to one another, and which may be disassembled from one another to allow to remove the formed driveshaft ( 32 ).

Description:
[0001]     This is a Continuation-In-Part of International Patent Application No. PCT/IL2005/000087, filed Jan. 25, 2005, and published as WO 2005/070583, which in turn takes priority from Provisional Patent Application No. 60/538,500 filed Jan. 26, 2004. 
     
    
     FIELD AND BACKGROUND OF THE INVENTION  
       [0002]     The invention relates to an apparatus and method for forming of a vehicle&#39;s driveshaft having an elongated shaft and two coupling end parts. This is achieved, in accordance with the invention, by a pulsed magnetic force (PMF) process.  
         [0003]     A vehicle&#39;s driveshaft, having the general structure as outlined above, is commonly manufactured by welding ends of a cylindrical shaft to coupling end parts. Conventional welding is a time consuming and relatively expensive process.  
         [0004]     Furthermore, the workpieces are typically heated in this process and therefore at times cooling installations need to be included.  
         [0005]     A known way of rapid “cold” joining or welding of workpieces to one another is by the use of a PMF process. By this technology, a very short and intense electric pulse is discharged through a coil and this discharge induces eddy currents in a workpiece which yield magnetic repulsion between the electric coil and the workpiece. This repulsion then deforms the workpiece proximal to the forming coil causing its surface to rapidly move and impinge on another workpiece whereby it either pressure joins, and with higher energy surface welds to the other workpiece.  
         [0006]     A particular application of this process is in joining or surface welding of a tubular workpiece onto a cylindrical one contained therein by inducing inward radial deformation of the tubular workpiece. PMF processes and some specific applications thereof are disclosed in the following U.S. Pat. No.: 3,654,787 (Brower), U.S. Pat. No. 3,961,639 (Leftheris), U.S. Pat. No. 4,170,887 (Baranov), U.S. Pat. No. 4,531,393 (Weir), U.S. Pat. No. 4,807,351 (Berg et al.), U.S. Pat. No. 5,353,617 (Cherian et al.), U.S. Pat. No. 5,442,846 (Snaper) and U.S. Pat. No. 5,824,998 (Livshitz et al.).  
         [0007]     A specific application of the PMF process for the purpose of joining components for a vehicle&#39;s driveshaft is described in U.S. Pat. No. 5,981,921.  
         [0008]     There are some specific problems in the realization of the PMF process for forming a driveshaft in that the end pieces radially protrude beyond the circumference of the shaft. In order to utilize the PMF process, the forming coil should be brought into close proximity to the deformed workpiece and in this case this means that the forming coil needs to be closely fitted around the shaft. After joining or surface welding of the shaft and the coupling end part, it is not possible, with the prior art methods, to release the coil turnover and the driveshaft. This is the reason, that the PMF process has not yet found a true application in practice in the field of forming of driveshafts.  
       SUMMARY OF THE INVENTION  
       [0009]     In accordance with the invention an apparatus and method for forming a driveshaft is provided. In accordance with the invention, the above noted problems are overcome by providing an apparatus and utilizing a method in which the forming coil is assembled around the shaft from two or more coil sections which are firmly attached to one another. This forming coil is associated with a current generating unit such that through current discharge from said unit a PMF is produced to cause pressure joining or surface welding of the two driveshaft components.  
         [0010]     In the following, the term “joining” will be used to jointly denote both joining of two workpieces, which means bringing their juxtaposed surfaces into very close proximity in a manner so that they pressure impact with one another, as well as surface welding which means in effect a molecular interaction between their juxtaposed surfaces of the two workpieces. In fact, whether joining or welding is achieved in the PMF process depends, to a large extent, on the amount of PMF energy and of the exact working parameters. The artisan will be able to define whether joining or surface welding is required and also to define the exact parameters needed to achieve either joining or welding. For parameters to achieve welding, reference is made to U.S. Pat. No. 5,824,998, which is incorporated herein by reference. As stated, the term “joining” should be construed as referring to either or both of joining and welding.  
         [0011]     In accordance with the invention there is provided a novel apparatus and method for forming a driveshaft of the kind having a shaft and two coupling end parts of radial dimensions larger than those of the shaft.  
         [0012]     The apparatus comprises one or two forming assemblies for forming one end or two ends of a driveshaft, respectively; the one or two forming assembles comprising each a holder and a forming unit. The holder is a adapted to receive and hold a driveshaft end part pre-assembly which after joining will form the end part of the driveshaft. The pre-assembly consists of two components, of which one is an end section of an elongated shaft that defines an axis, and the other is a coupling end part member, either the shaft end section or a portion of the end part member having a generally cylindrical shape with an axial cylindrical cavity that accommodates an axial cylindrical portion of the other snugly fitted therewith, the end section and said portion defining together a cylindrical joining section of the two components. The forming unit comprises a forming coil device that defines a forming space which can accommodate said joining section and comprises a current generating unit that is associated with the forming coil device, for generating a current pulse within the forming coil unit thereby to yield a PMF sufficiently strong to yield joining the two parts of the joining section. The forming coil device is assembled from two or more coiled sections which are firmly attached to one another at attachment faces thereof, which can be disassembled to permit release of the so formed driveshaft end part.  
         [0013]     The method for forming a driveshaft in accordance with the invention comprises: (a) providing a shaft, the shaft defining an axis, and a coupling end part member; either the shaft end section or a portion of the end part member having a generally cylindrical shape with an axial cylindrical cavity and the other having an axial cylindrical portion that can fit within said cavity, and fitting said cylindrical portion into said cavity to define together a joining section with an external cylindrical shape cavity can accommodate of the other snuggly fitted therewithin and defining together a cylindrical joining section of the two components; (b) fitting a forming coil device around said joining section, the forming coil device being assembled from two or more coil sections firmly attached to one another at attachment faces thereof and being associated with a current generating unit; (c) generating an intense current pulse through said forming coil device to generate a pulsed magnetic force (PMF) sufficient for joining the two parts of the joining section; and (d) disassembling the forming coil device to free the so formed end section of the driveshaft. Steps (a) and (d) may either be performed simultaneously for the two ends of the shaft to simultaneously join two coupling end part members one to each end of the shaft Alternatively, these steps may be performed in sequence by first carrying out steps (a) to (d) for joining one coupling end part member to one end of the shaft and then repeating these steps for joining another coupling end part member to the other end of the shaft.  
         [0014]     An apparatus for simultaneous forming of the two end parts of a driveshaft will comprise two forming assemblies. Where the apparatus comprises a single forming assembly, first one end will be formed, the shaft will then be reversed and the other end will then be formed.  
         [0015]     In accordance with one embodiment of the invention, the forming coil is connected directly to a current discharge circuitry. In accordance with this embodiment, the coil device is comprised of two or more, typically three or more coil sections of which two are end section connected each to one pole of the current discharge circuitry. In the case of three coil sections, for example, two are such end sections and one is an interconnecting section. In accordance with one embodiment, a coil of this kind is formed from a dielectric, non-electrically conducting material with an inner layer made of an electrical material. The dielectric material there serves as a structured element. An example of such a material is epoxy glass. The conducting layer may be made of copper as well as any other suitable method substance. Typically, the conducting layer extends also to the attachment faces and serves as the electrical link between the different sections.  
         [0016]     The different sections may be held together by a reinforcing structure, may be connected to one another by the use of screws and bolts and in general by any other suitable means.  
         [0017]     In accordance with another embodiment, the forming coil device is an independent coil device being an inductive association with a primary coil which is in turn connected to a current discharge circuitry, whereby a current pulse discharged through the primary coil induces the generation of a forming current pulse within the forming coil. In accordance with the one preferred embodiment, a forming unit comprises a primary coil connected to a current discharge circuitry for generating an intense current pulse, and two or more inserts, each of which constitutes a section of a forming coil device accommodated within an opening defined by the primary coil, the opening being of a diameter sufficient to permit the coupling end part to pass therethrough, and defining in turn a forming space to accommodate said joining section; the inserts being made of or having at least outer, inner and radial faces being made of an electrically conducting layer and being attached to one another at attachment faces with an electrically insulating layer between them. The inserts, in accordance with this embodiment, are typically a trapezoidal cross-section with the broad base facing outwards and the narrow base facing inwards juxtaposing the joining section.  
         [0018]     The method in accordance with the above preferred embodiment, comprises: fitting a forming coil device adjacent said joining section, the forming coil device comprises a primary coil connected to a current discharge circuitry for generating an intense current pulse, and two or more inserts, each of which constitutes a section of a forming coil device accommodated within an opening defined by the primary coil, the opening being of a diameter sufficient to permit the coupling end part to pass therethrough, and defining in turn a forming space to accommodate said joining section; the inserts being made of or having their external layer made of an electrically conducting layer and being attached to one another at attachment faces with an electrically insulating layer between them; generating an intense current pulse through said primary coil to induce a forming current in the inner face of the forming coil device to generate a pulsed magnetic force (PMF) sufficient for joining the two parts of the joining section; and disassembling said inserts and removing the primary coil by axially moving either the primary coil or the formed driveshaft end.  
         [0019]     In accordance with one preferred embodiment, it was found that superior joining is achieved by the use of an auxiliary device which is temporarily fitted together with the end part member to yield together a body having axial symmetry.  
         [0020]     After formation of the joins between the shaft and the end part member, the auxiliary device is removed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:  
         [0022]      FIG. 1A  is a schematic longitudinal section through a prior art vehicle driveshaft.  
         [0023]      FIG. 1B  is a longitudinal section of the vehicle driveshaft of the invention.  
         [0024]      FIG. 1C  shows the end section of the shaft overlapping the end recess of the end part prior to constriction to form the driveshaft of  FIG. 1B .  
         [0025]      FIG. 2A  is a partial longitudinal cross-section of an apparatus of the invention with a driveshaft to be formed therewith.  
         [0026]      FIG. 2B  is a view from the direction of arrow II in  FIG. 2A .  
         [0027]      FIG. 3A  is a schematic longitudinal cross-section of an apparatus in accordance with another embodiment of the invention with the driveshaft to be formed therewith.  
         [0028]      FIG. 3B  is a cross-section through lines III-III in  FIG. 3A .  
         [0029]      FIG. 4  shows a typical fork-shaped driveshaft end piece.  
         [0030]      FIG. 5  is a partial view of an apparatus of the invention adapted for joining an end piece of  FIG. 4 .  
         [0031]      FIG. 6  shows a coil device structure in accordance with another embodiment of the invention.  
         [0032]      FIG. 7  is a view similar to  FIG. 1C  illustrating use of an intermediate driver element according to a further feature of the present invention.  
         [0033]      FIG. 8  is a view similar to  FIG. 3A  illustrating use of an intermediate driver element according to a further feature of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]     Reference is first being made to  FIG. 1A , which shows a prior art driveshaft.  
         [0035]     The driveshaft  1  consists of a tubular shaft  2  and two coupling end parts  3  and  4 , one at each end of shaft  2 . The two ends  2 A and  2 B of shaft  2  are sealed each in a respective recess  3 A and  3 B of end parts  3  and  4 , respectively, and welded to it by conventional welds  3 B and  4 B, respectively.  
         [0036]     In distinction from prior art driveshafts, driveshaft  6  made in accordance with the invention, shown in  FIG. 1B  (where like elements were given the same reference numeral with a prime indication), is formed by welding the shaft  2 ′ to the coupling end parts  3 ′ and  4 ′ by the use of a PMF process. The ends  2 A′ and  2 B′ are constricted and sealed in recesses  3 A′ and  4 A′, the constriction being achieved through a PMF process such as that will be described below. Through the PMF process ends  2 A′ and  2 B′ also become welded to respective recesses  3 A′ and  4 A′.  
         [0037]     As will also be appreciated, while the shaft shown herein is a tube, in other embodiments of the invention it may be a solid, elongate cylindrical mass.  
         [0038]      FIG. 1C  shows the end  2 A′ of shaft  2 ′ overlapping the recess  3 A′ of end part  3 ′ prior to PMF application. There is a gap between these two workpieces such that ratio of h as the length l of the overlapping portion typically meet the formula h/l=0.1- 0.5.  
         [0039]      FIGS. 2A and 2B  show a forming coil device generally designated  8  accommodating a driveshaft pre-assembly consisting of an end part member  10  having flange portion  12  and an end section  11  of tubular shaft. The coil device  8  is a single wind coil formed by three coil sections  14 A,  14 B and  14 C each of which is constituted from respective dielectric body  15 A,  15 B and  15 C and with respective conducting layers  16 A,  16 B and  16 C.  
         [0040]     Layers  16 A,  16 B and  16 C may typically be made of copper or any other high conductive material. The dielectric body  15 A,  15 B and  15 C may, for example, be made of epoxy glass or any other suitable dielectric material which has the property of being able to resist strong and abrupt forces (the PMF process causes very strong radial forces on the forming coil). Each of the layers  16 A,  16 B and  16 C extend over attachment faces  17  by which the different coil sections are attached to one another. This ensures electrical contact between the conducting layers in the different coil sections whereby all conducting layers constitute together a single wind coil. At their other end conducting layers  16 A,  16 B terminate in two respective protruding conductor sections  18 A and  18 B linked to a discharge circuit  19  consisting of a capacitor battery  20  and a switch  21 . Bodies  15 A,  15 B and  15 C may comprise respective cooling channels  21 A,  21 B and  21 C having inlets and outlets, that is inlet  22  and outlet  23 , respectively, and transfer of a cooling fluid (a gas or liquid) therethrough. The different coil sections may be held together by a variety of means such as for example an external holding structure or any other suitable fixing arrangement as may be known per se.  
         [0041]     As can be readily appreciated, after joining of a tubular section  10  to the end section  11  of the shaft, the coil device is disassembled to free the formed driveshaft end section.  
         [0042]     Reference is now being made to  FIG. 3A and 3B  showing an apparatus, generally designated  30 , with a driveshaft pre-assembly  31  consisting of a shaft  32  and two end part members  33 , one at each end of shaft  32 . In the apparatus of this embodiment, the two end parts of the driveshaft are formed simultaneously.  
         [0043]     Pre-assembly  31  is mounted between two holders  35  having a stepped protrusion  36  with an inner section  37  fitted within the lumen of shaft  32 , an intermediate section  38  and an outer flange  39 . In this way, the pre-assembly is firmly held in a firm pre-assembly arrangement.  
         [0044]     The apparatus comprises two forming assemblies  40  and  41  each including a multi-wind primary coil  44  and  45 , respectively, which are interconnected by a lead  46  and linked at their respective ends  47  to a current discharge circuitry  48  including a capacitor battery  49  and a switch  50 . The primary coils  44  and  45  are coaxial with shaft  32 . Two crescent shaped field shapers  42  and  43  are fitted within the space defined by the primary coils  44 , 45  and constitute together a forming coil device  51  also coaxially with the shaft  32 . The two field shapers  42  and  43  define together a forming space  52  fitted around the portions of the pre-assembly which are to be joined to one another. Holes  55  may be formed in the field shaper sections  42 , 43  for both cooling and current concentration. The ends  56  and  57  are insulated to avoid electric contact between the two inserts.  
         [0045]     In operation, a very short and intense electric pulse is actuated by the discharge circuitry  48  which then passes through primary coils  44 , 45  inducing an oppositely directed current in field shapers  42  and  43  and this current circulating in each of the field shapers causes a magnetic repulsion between the field shapers and the pre-assembly portions contained within the forming space thereby causing the two to pressure join, and with higher energies to surface weld, to one another. In this embodiment, both joins are formed simultaneously. It is appreciated that it is possible, in accordance with other embodiments, to separate the primary coils  44  and  45  and provide each with an independent current discharge circuitry having each an independent ignition arrangement. Alternatively, coils  44  and  45  may also be in a parallel electrical conductor (i.e. both to the same discharge circuitry).  
         [0046]     In the specific embodiments of the apparatus shown in  FIGS. 3A and 3B , field shapers  43  are fixed onto a pole  60  while field shapers  42  are linked to an opening mechanism  61 . At the end of the operation, primary coils  44  and  45  can be moved axially to permit removal of field shapers  42 . After such removal, the so formed driveshaft may be removed.  
         [0047]     When the coupling end part member has a significant axial asymmetry close to the portion which is to be joined or welded, for example, a fork-shaped end part as is typically the case with driveshafts end parts, the electromagnetic field generated by the PMF process, may become irregular near the asymmetrical end piece portion, which may cause non-uniformity of the joins. In order to overcome this problem, an auxiliary device may be used, aimed at temporal restoring the axial symmetry of the coupling end part member. The insert is preferably produced from a material similar in electromagnetic properties to the coupling end part member.  
         [0048]      FIG. 4  shows a typical driveshaft coupling end part member which consists of a cylindrical joining portion  71  and a fork connector portion  72 .  
         [0049]     In  FIG. 5  the axial asymmetry of fork  70  is compensated for by the use of an auxiliary device  75 , which in this case constitutes an integral part of the holder  31 .  
         [0050]     When the pre-assembly is fixed on holder  31 , the fork  72  combines with the auxiliary device  75  to induce a combined body with an axial symmetry. When the driveshaft is unloaded from the apparatus, the auxiliary device stays connected to a holder  31 .  
         [0051]     A coil assembly useful in an apparatus in accordance with another embodiment of the invention is shown in  FIG. 6 . Two forming coil members  81  and  82 , form part of structures  83  and  84 , respectively, shown herein in an exploded view but which in use are placed proximal to one another with a distance between them of about 2 mm or less.  
         [0052]     Structure  83  is a closed loop conductor constituted by a planar conductive strip, but for coil member portion  81 . Structure  84  is constituted from a similar planar conductive strip, ending, however, at open ends  85  and  86  connected to a discharge circuitry (not shown).  
         [0053]     In use, when current is discharged through conductor structure  84 , current progresses along arrows  90  and this causes a counter current in the direction of arrows  91  in conductor structure  83 . This yields an overall circular current around forming space  95  defined by two coiled sections  81  and  82 . Placed in this forming space  95 , is the portion to be joined of the driveshaft pre-assembly with the coupling end part facing towards the interior of conductor structures  83  and  84 .  
         [0054]     Turning finally to  FIGS. 7 and 8 , since the technique of PMF forming is based upon induced electric eddy currents within the workpiece, the energy efficiency of the technique is much lower for metals having relatively poor electrical conductivity (such as Steel, Titanium and Nickel alloys) than for those with high conductivity. In order to improve the efficiency of the technique, certain implementations of the present invention employ a driver element, formed from metal with a higher electrical conductivity than the workpieces, deployed around at least part of the joining region. The presence of this driver element reduces the energy required for a given welding effect. This feature will now be illustrated with reference to  FIGS. 7 and 8 .  
         [0055]      FIGS. 7 and 8  are generally similar to  FIGS. 1C and 3A , respectively, and employ the same reference numerals for equivalent elements. As seen in  FIG. 7 , the workpiece is here modified by addition of a driver element  99  deployed in close overlapping relation with at least part of the region of overlap of end  2 A′ and recess  3 A′. Driver element  99  is formed from a metallic material with electrical conductivity higher than that of the recessed element, and most preferably, from a high-conductivity metallic alloy such as an Aluminum or Copper alloy. Driver element  99  preferably extends around the entire circumference of the cylindrical joining region, and most preferably also overlaps substantially the entire length l of the joining region. The element may be implemented as a solid metal collar, or may be flexible foil wrapped around the joining region. The total thickness of driver element  99  is preferably in the range from 0.3 mm to 2 mm, and its width (i.e., the dimension parallel to the axis of the shaft) is preferably in the range from 1 mm to 30 mm. After welding, driver element  99  may remain as part of the joined structure, or may be removed (e.g., peeled off) by any suitable mechanical or other technique.  
         [0056]      FIG. 8  shows a forming device similar to that of  FIG. 3A , with equivalent elements labeled similarly. In this case, field shapers  42  and  43  have been modified to allow space of driver element  99 . In all other respects, the structure and operation of the device of  FIG. 8  is essentially the same as that of  FIG. 3A  described above.  
         [0057]     It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the scope of the present invention as defined in the appended claims.