Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT (ORIGINAL) Name of Applicant: Illinois Tool Works Inc. Actual Inventors: David Collinson and John Mallet Address for Service: DAVIES COLLISON CAVE, Patent Attorneys, I Nicholson Street, Melbourne, Victoria 3000. Invention Title: "Drive system for threaded fasteners" Details of Associated Provisional Application No.: 2009901248 24 March 2009 The following statement is a full description of this invention, including the best method of performing it known to us: C:\NRPortbl\DCC\PLB\2776877_1. DOC - 18/3/10 C:\NRonblDCCPLB\2T765%7_ .DOC.I8a3/2010 DRIVE SYSTEM FOR THREADED FASTENERS The present invention relates to a drive system for threaded fasteners and more particularly to a threaded fastener having a head with an internal drive recess, and a driver bit for 5 engagement in the drive recess. A drive system in widespread use is the Phillips cross drive having an internal recess of cruciform section within the head of a screw or other threaded fastener, and a driver bit of complimentary shape. The detailed design of the recess and complimentary bit is such that 10 the driver bit tends to "cam out" of the recess and may then break or wear at an unacceptable rate. "Cam out" occurs when the bit lifts out of the drive recess in the fastener under the effect of the torque being transmitted. As the bit "cams out", less surface area becomes available to transmit the torque which results in an increased load on the reduced available surface area. As the material of the bit and fastener can only 15 withstand a certain maximum load, once past this limit, deformation of the available surfaces starts and continues until the surfaces are deformed to such an extent that driving can no longer occur, with the bit being thereafter unusable. Also, depending on the depth of the drive recess, a wobbling effect may be experienced when using the drive, the shallower the depth the greater will be the wobbling effect. 20 The wobbling effect and "cam out" is increased in the Phillips drive when thick corrosion resistant coatings are applied to the fastener as these have the effect of reducing the depth of the drive and which results in increased wobble and "cam out". All of these effects tend to be exacerbated in high torque applications and in screws having a low profile head such 25 as are used in steel frame applications where the protrusion of the head has to be minimised to allow for the fixing of cladding to the frame. Although "cam out" can be avoided by using an internal straight-sided drive such as a hexagon drive or a six lobed drive such as the Torx drive, a straight-sided drive is still 30 prone to a wobbling effect which is a function of the clearance between the recess and the complimentary drive bit.
H gp nero em Rob C'G xw 1 I I.dcun2t{7/2I I5 -2 The present invention in its preferred embodiments relates to a drive system in which "cam out" and wobble are substantially eliminated and which is capable of use even with screws having a low profile head. According to a first aspect of the present invention, there is provided a threaded fastener 5 having a head with a driving recess, the recess being of generally cruciform shape in cross section transverse to the axis of the fastener to provide four driving segments uniformly spaced around the axis of the fastener, each segment having a driven face extending axially for engagement by a corresponding driving face of a driver of complimentary form engageable within the recess, a trailing face opposite the driven face, and a peripheral surface between the 10 driven and trailing faces, wherein the peripheral surfaces of pairs of segments which are diametrically opposed converge towards the inner end of the recess at an included angle of between about 30 and 300, the driven face extends parallel to a plane through the axis of the fastener, and the trailing face is inclined to the driven face such that the space defined between the driven and trailing faces is wedge-shaped tapering from the outer end of the recess to the 15 inner end of the recess at a taper angle of from about 2 to 100 and wherein each driven face lies in close proximity to the plane and its associated trailing face is further to the rear of the plane, whereby when the driver of complimentary form is engaged within the recess with driving ribs of the driver located in the segments, the ribs of the driver will be wedged between the peripheral surfaces of the diametrically opposed segments and the opposed driven 20 and trailing faces of each segment. Advantageously the included angle between the peripheral surfaces of the pairs of opposed segments is between about 30 and 150, with approximately 7 to 80 being especially preferred. Advantageously the taper angle of the trailing face to the driven face of each segment is about 5'. 25 Preferably the respective driving faces of each pair of driven faces are parallel to a common plane through the axis of the fastener and the two common planes associated with four segments intersect at right angles one to the other. According to a second aspect of the invention, there is provided a driver having a driving 3 portion engageable in the recess of a fastener according to the first aspect, wherein the driving portion is of complimentary form to that of the recess and is of rucirorm cross-section to provide four driving ris uniformrly spaced around the axis of the duver each driving rib being, engageable within respective one of the iving segments of the recess and having a 5 peripheral surface engageable with the peripheral surface of the segment a driving face engagea ble with the driven face of the segment and a trilng face cngagebl with thetrailing face of ie segment whereby he opposed peripheral surfaces of each pair of diametrically opposed driving ribs will be wedged between the oppod peripheral edges of each pair of diametrically opposed segments, with the driving and trailing faces of each rib wedged 10 between the drive-n and training faces of the segment According to a third aspect of the invention. there is provided a driver hi a dn ving portion of complementary form to the recess of a fastener according to the first aspect, for driving engagement within the recess. Ar enthodiment of the invention will now be described by way of example only with reference 15 to the accompanying drawings in whec: 'igne I is a perspective view of a driver bit of a drive system in accordance with one embodiment of the invention; Figure 2 is a perspective view to an enlriged scale showing the driving ortion of the bit; Figure 3 is an end view of the driving portion; 20 Figure 3A is an end view corresponding to Figure 3 but marked to show cross sectional references for other Figures: Figure 4 is a side view of the driving portion; Figure 5 is a transverse section taken on line V-V of Figure 4; Figure 6 is a transverse section taken on line VI-V of Figure 3A; 25 Fgure 7 is an axial section of a driving rib taken on line VII-VII of Figure 3.A; Figure 8 is a side view of a threaded fastener; C WnRPnblDCC\LtB\775%7_L.DOC-18V3/2010 -4 Figure 8A is a side view to an enlarged scale of the head portion of the fastener; Figure 9 is a plan view of the fastener from the head end; Figure 10 is an axial section of the head portion taken on line X-X of Figure 9; Figure 11 is a transverse section of the head portion taken on line XI-XI of Figure 5 8A; and Figure 12 is an axial section of the head portion taken on line XII-XII of Figure 9. The drive system of the preferred embodiment will initially be described with reference to the design of a driver bit 2 and it is to be understood that the design of the recess in the 10 head of the screw or other threaded fastener will be of complimentary form to that of the bit for co-operation with the bit. With reference to Figures 1 to 7, the basic form of the driving portion of the bit 2 is of a cruciform cross-section to provide four driving ribs 4 equi-angularly spaced around the 15 longitudinal axis 0-0 of the bit. The peripheral surfaces 6 of the four driving ribs 4 lie on an imaginary frustoconical surface which tapers towards the outer end of the bit. Accordingly, the opposed peripheral surfaces 6 of each pair of opposed driving ribs 4 will incline in a longitudinal direction towards the outer end of the bit. When the bit is engaged in a cruciform recess of complimentary form in the fastener, the engagement of the 20 longitudinally inclined peripheral surfaces of the bit 2, with correspondingly inclined peripheral surfaces of the cruciform recess in the fastener will provide a wedging action of the bit within the recess. The taper angle is important in providing an effective wedging action which assists in 25 preventing wobble and also to prevent the "cam out" effect discussed earlier. The included angle a (see Figure 6) between the peripheral surfaces 6 of each pair of opposed driving ribs 4 (thereby corresponding to the included angle of the imaginary frustoconical surface on which they lie) is between about 30 and 15*. An included angle a of less than about 30 will provide an insufficient wedging effect for the prevention of wobble. The size of the 30 included taper angle a is also a factor in avoiding "cam out", as large taper angles are a factor inducing "cam out". Although we have determined that "cam out" is unlikely to occur even with an ineladed tapmer angle ofup to about 30 a taper angle of that order could be difficult to accommodate within sole existing screw heads while retaining sufficient volume and ticnes of metal within the head to properly withstand the driving torque, As such, we have deterined that an upper imait of the included taper angle a of around 15' should be 5 suitable lor most existing sizes of screw head, In a particularly preferred forn the included taper angle is around 74' An ange ofthis order provide an effective wedgng action and is able readily to be accommodated even in screws with Iow profile heads, With reference now to Figures 3 and 5, each driving rib 4 has a leading face 8 in the direction of normal driving rotation of the bit (and which thereby foris the driving face) and a trualing 10 face 10M in relation to two mutual pe 1 rpendicular axkal reference planes A A BB which intersect at the longitudinal axis 0-0 of the bit, the driving face 8 of each of the ribs 4 is flat and parallel to one or other of these planes. The diving faIe 8 of the rib wil: enage a corresponding driven fce in the recess and which is likewise flat and parallel to one or other of two corresponding reference planes which intersect at the longiudira axis of the fastener. 15 Rt will also be seen from Figures 3 and 5 that in relation to its associated plane of reference (A A or B--B), the rib 4 is not generally synmetrical about that plane but, rather, the driving f'ac 8 is slightly forward of the plane whereas the trailing face 1 has a greater projection to the rear of the reference plane. The significance of this is that n relation to the recess in the head of the fastener, tne proxiinity of the corresonding driven face in the recess to its aoctoed axial 20 reference plane allows for adequate thickness of material in the head forwardly of that plane for effective torque transmission, even in screws within lowx profile heads. [he more substantial offset of th trailing face of the rib 4 to the rear of the axial reference plano ensures that the rib has sufficient strength for effective torque transmissior In contrast, with a driving rib of the same width but with is driving and traii ng Paces arranged approximately symmetrically in 25 relation to the axial reference plane, the increased ftorwards projection of the driving face relative to the reference plane which would occur in that situation would result in a reduction in the material ofthe C.\RPotnb\DCC\PLB\277$796 I DOC.IMM/20 10 -6 fastener head forwardly of its associated driven face and in the case of a low profile screw for example, the reduction in the volume of material in advance of the driven face could be such that under high torque conditions the head could shear from the shank of the fastener. 5 When considered in transverse section (Figure 5), the trailing face 10 of the rib 4 inclines away from the reference plane at the root or inner end of the rib and then merges with the driving face 8 of the next rib via a curvature of large radius. This ensures that the root portion of the rib has good torsional strength for the required torque transmission. 10 When considered in axial cross-section (see Figure 7), the trailing face 10 of the rib 4 inclines towards the associated reference plane, and thus towards its associated driving face 8, in an axial direction towards the outer end of the bit. Accordingly, when considered in axial section each driving rib 4 is wedge-shaped tapering towards its outer end as is clearly shown in Figure 7. The corresponding recess in the fastener will be 15 similarly wedge-shaped provided by a corresponding inclination in a longitudinal direction of a trailing face relative to the driven face. Accordingly, the driving rib 4 becomes wedged within the corresponding recess and the effect of the wedging action is to lock the axial driving face 8 of the rib 4 firmly against the axial driven face of the recess to ensure that no wobble occurs. 20 The taper angle @ required to achieve this wedging action is not significant and is in the range of from about 20 to 100 with around 50 being especially preferred. A taper of more than about 100 is likely to be difficult to accommodate in a fastener having a conventional head size. 25 A threaded fastener for driving by the driver bit 2 is shown in Figures 8 to 12. Although the particular fastener shown is in the form of a self-drilling screw with a head of relatively low profile, this is given only by way of example only and it is to be understood that the drive system of the invention is applicable to a broad range of threaded fasteners. It will 30 be seen the that head 20 of the fastener has a recess 22 of complimentary form to that of the driving portion of the bit 2 and thereby of a cruciform cross-section to provide two C:\NR rblDCCPLB\275%7 .DOC-183/20O10 -7 pairs of diametrically opposed segments 24 equi-angularly spaced around the longitudinal axis 0-0 of the fastener. The opposed peripheral surfaces 26 of each pair of opposed segments 24 are engaged by those 6 of the driving ribs 4 and incline at a taper angle a (see Figure 10) equivalent to that of the bit 2 to provide the wedging action for the bit 5 previously discussed. Each segment 24 has a leading face 28 in the normal direction of driving rotation which thereby forms the driven face of the segment, and a trailing face 30. In relation to two mutually perpendicular axial reference planes A-A, B-B which intersect at the longitudinal axis of the fastener, the driven face 28 of each of the segments 24 is flat and parallel to one or other of these planes. As described in relation to the design of the 10 bit, the driven face 28 is slightly forwardly of the plane whereas the trailing face 30 has a greater projection to the rear of the reference plane whereby the driven and trailing faces 28, 30 of the segment 24 are engaged respectively by the driving and trailing faces 8, 10 of the rib 4 of the bit. 15 When considered in axial section (Figure 12) the trailing face 30 of the segment 24 inclines towards the driven face 28 whereby the segment 24 is wedge-shaped tapering towards the inner end of the fastener for co-operation with the wedge-shaped rib 4, the taper angle P of the recess corresponding to that of the ribs of the drive bit. 20 The overall taper of the driving portion of the bit (the frustoconical taper) and the corresponding taper of the recess 22 of the fastener, and the taper of each of the ribs 4 and the corresponding taper of each of segments 24 are at relatively shallow angles which provide for an effective wedging action which eliminates wobble and "cam out". The shallow taper angles also allow for a greater thickness of corrosion resistant coatings on 25 the fastener without reducing the depth of the drive to any practical extent. The wedging action provided by the tapers also remove the tendency of the bit to slip out of the recess if the load during driving is not applied directly along the axis of the screw. As "cam out" is avoided, the load per available surface area on the driving faces of the 30 driver bit does not change and therefore deformation of the driving surfaces is significantly reduced.
H gg\irnteosen\NRPorlbl\DCCGW~PO9493 I - doc-2 I1172015 -8 The cross-sectional area of the driving portion of the bit is relatively large in relation to the required depth of penetration into a corresponding recess in the fastener head. As a result the recess does not need to be especially deep and a recess of adequate depth can be accommodated even in low profile heads to provide a high torque drive without being of a 5 depth which might cause the head to shear. Likewise, the relatively large cross-sectional area of the driving portion ensures that it will not shear at the junction with the fastener head. It is envisaged that the drive system will be produced in a range of different drive sizes (four, for example). The basic geometry for each size will be as described herein with the size variations occurring to increase the strength of the drive and fastener to withstand a required 10 torque. Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. 15 The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates. 20 While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation. It will be apparent to a person skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the present invention should not be limited by any of the above described 25 exemplary embodiments.