Fastener and driver assembly

There is disclosed an improved fastener and driver assembly which assures sufficient depth of engagement between the drive socket of the fastener and the working portion of the driver bit to provide efficient torque transfer from the driver to the fastener. The assembly includes a fastener having a recessed drive socket which is multi-lobular in cross-section, having an inner surface formed by alternating and smoothly joined flutes and lobes. The assembly also includes a driver for imparting rotational torque to the fastener which includes a head portion having a tip end and a center axis. The head portion of the driver is correspondingly multi-lobular in cross-section. The flutes are formed generally parallel to the center axis of the driver while the lobes of the head portion are tapered axially, converging toward the tip end of the head portion. This arrangement enables the driver head to enter the fastener socket to a predetermined depth, without binding, to thereby insure sufficient depth of engagement between the fastener lobes and the driver flutes to provide efficient torque transfer from the driver to the fastener.

BACKGROUND OF THE INVENTION 
The present invention is directed in general to a fastener drive system, 
and more particularly to a new and improved fastener and driver assembly 
wherein the fastener includes a drive socket and the driver includes a 
tapered bit of novel design. 
Tapered drive bits for transferring rotational torque to correspondingly 
structured fasteners are well known. Such arrangements find considerable 
application, for example, in high volume mass production assembly lines 
wherein a power tool having a tapered bit is used to drive fasteners into 
a secured position. The tapered nature of the bit enables the fastener to 
be engaged thereon with a slight friction fit such that the fastener will 
remain in mounted relation on the end of the bit until it can be engaged 
and driven. 
Prior art drive systems i.e. socketed fastener and drive bit, or socket 
driven and external fasteners driving head, have taken a wide varitey of 
forms, two of the more common being the "hex" head and "Phillips" head 
types. Most systems rely upon the use of components of similar mating 
shape with the mating portion thereon being defined by reltively planar 
surfaces. While these systems have proven satisfactory for many 
applications, in recent years multi-lobular type drive systems have been 
developed, which have proved superior for use in applications involving 
controlled high seating torques. In this regard, the multi-lobular system, 
unlike many prior art designs is possessed of high efficiency in 
converting applied force to driving torque, and these multi-lobular 
systems are also effective in reducing the radial force components which 
tend to damage the socket element of the systems. One such multi-lobular 
system is illustrated in applicant's U.S. Pat. No. 3,584,667. 
As a further matter, it is relatively common practice with respect to "hex" 
and "Phillips" type systems to employ tapered bits, in conjunction with a 
socket head fastener wherein the socket walls are parallel or only 
slightly tapered, to attain a desired degree of frictional engagement upon 
mounting of the fastener on the end of the bit. This feature is useful, in 
that the fastener will remain mounted on the bit during a moment 
preparatory to proper positioning of the fastener for driving. As an 
additional matter, use of a tapered bit serves to take up or obviate 
socket size variances that may be encountered. That is to say when a 
friction fit is obtained, the fastener is firmly engaged with the bit and 
will not "wobble" during driving. It has been proposed to apply this 
concept to multi-lobular drive systems for attainment of the same 
advantages. Unfortunately, however, these attempts have not proven totally 
successful as certain, unexpected problems have been encountered, as will 
be explained. 
More specifically, with respect to all types of drive systems, the ability 
thereof to handle applied force, and convert same to driving torque is 
dependent upon the depth of engagement of the respective male and female 
components. If insufficient depth of engagement is attained between the 
driver bit (male component) and the fastener socket wall (female 
component), the material available by the socket wall to resist the force 
being applied by the driver bit are structurally insufficient, and the 
socket wall will deform under the load. The critical nature of this factor 
will be appreciated more fully when it is also considered that often the 
drive bits are formed of hardened alloy steel, while the fastener socket 
wall is formed of much softer varieties of steel, also a consideration is 
the wide variance in dimensional tolerance that is encountered between 
fastener and driver due to many factors, such as different manufacturers 
and wear of the bit and socket forming tooling in service. These tolerance 
variations often result in interfering engagement between the fastener and 
the drive occurring before the desired minimum depth of engagement is 
realized. 
The attainment of an assured depth of engagement with multi-lobular drive 
systems has proven no problem where the surface portions of the mating bit 
and socket are disposed generally parallel to respective axis. However, 
where employment of a tapered, multi-lobular bit has been attempted, the 
results obtained have not been satisfactory, with respect to the high 
degree of uniform standards demanded by the fastener industry. More 
specifically, in inserting a tapered bit into a straight or less tapered 
socket, some measure of interference (i.e. friction of fit) will be 
attained at a certain depth of engagement. The problem is to uniformly 
attain this interference after the desired minimum depth of engagement is 
reached. 
With a tapered multi-lobular drive system, the lateral or axially extending 
portions of the bit and socket are much increased over other designs; as 
for example a "hex" system. Correspondingly, any variance in dimensional 
tolerances which might be encountered, increases the possiblity that 
surface-to-surface interference or frictional engagement will occur, 
before the discussed depth of engagement is attained. The present 
invention provides a novel solution to this problem by enabling the 
attainment of the advantage of a tapered bit, i.e. vertical mounting of 
the fastener or the bit, with a greater degree of assurance of attaining 
the minimum depth of engagement between the driver bit and the socket. 
It is therefore a general object of the present invention to provide a new 
and improved fastener drive system, wherein the fastener includes a drive 
socket, and wherein the driver, although tapered is structured for 
entering a fastener drive socket to a consistent and predetermined depth 
of engagement to assure efficient torque transfer from the driver to the 
fastener. The above mentioned object is achieved by providing a fastener 
drive system comprising, a fastener member having a drive socket, wherein 
said socket is multi-lobular in cross section and has an inner surface 
formed by alternating and smoothly joined flutes and lobes, and a driver 
for imparting rotational torque to the fastener and including a head 
portion having a tip end and a center axis. The head portion of the driver 
is correspondingly multi-lobular in cross-section having an outer surface 
formed by alternating and smoothly joined flutes and lobes for mating 
engagement in said fastener socket. More specifically the driver surface 
portions which define the base of the flutes, which it is recalled mate 
with the socket lobes are formed generally parallel to the center axis of 
the driver. On the other hand the surface portions of the bit are tapered 
axially, converging in a direction towards the tip end. As a result of 
this design the possibility of dimensional variances producing an 
undesired interfering engagement prior to attainment of the proper depth 
of engagement are substantially reduced, if not eliminated. More 
specifically, since the flute surface portions are substantially parallel 
to the bit axis attainment of premature interfering engagement along the 
interfaces with the socket lobe surfaces will not occur. As such the only 
area of possible interfering engagement is along the tapered external 
surface portion of the lobes. Since these lobe surface portions are 
external, the dimensional tolerance thereof can be controlled more readily 
to attain the desired mode of operation. Further, even if some dimensional 
variances are encountered, the likelihood of these adversely effecting the 
performance of the drive systems are materially reduced, since interfering 
engagement can occur over only a small portion of the entire surface area 
of the bit.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to FIG. 1, there is shown a fastener 12 and a driver tool or 
bit 14 constructed in accordance with the present invention. The fastener 
12 includes a head portion 16 and a shank portion 18. The head portion 16 
of the illustrated embodiment is generally conical in configuration and 
includes a spherical end surface 20. The shank portion 18 extends from the 
head portion 16 and has an external thread 22 formed therein. 
Within the head portion 16 of the fastener 12 there is formed a drive 
socket 24, which as best seen in FIG. 2, is of a multi-lobular 
configuration. That is to say, the socket 24 has an inner surface formed 
by alternating and smoothly joined concaved roots or flutes 26 and 
convexed lobes 28. The flutes 26 and lobes 28 are defined by 
semi-cylindrical or substantially semi-cylindrical surfaces which extend 
generally parallel to the center axis 30 of the fastener 12 and driver 14. 
The surfaces which define the flutes 26 and lobes 28 are oppositely curved 
with respect to one another and alternate so as to merge smoothly with 
each other. Also, as will be noted from FIG. 2, the radius of curvature of 
the flutes 26 is less than the radius of curvature of the lobes 28. 
The driver 14 includes a tip end 32 and a shank portion 34 which may be 
formed for engagement in the mounting jaws of a power tool or the like, or 
may accommodate a handle to facilitate manual operation. The portion of 
the driver 14 between the shank portion 34 and the tip end 32 defines a 
work area 36, and is that portion of the driver 14 which is utilized for 
engagement in the drive socket 24 of the fastener 12. 
As can be best seen in FIG. 3, the driver 14 is of corresponding 
muti-lobular configuration within the work portion 36, and includes an 
outer surface portion comprising first and second sets of alternating 
curved surfaces which merge smoothly to define a series of flutes or root 
portion 38 and series lobes 40. The dimension of the flutes 38 and lobes 
40 of the driver 14 are substantially similar to those of the flutes 26 
and lobes 28 of the fastener 12, albiet sized to permit interfilling 
engagement. 
One of the distinguishing features of the present invention resides in the 
surfaces defining the driver flutes 38, as best seen in FIG. 1, are 
disposed generally parallel to the center axis 30 of the driver while the 
crest, surface portion 42 of each driver lobe 40 is tapered axially along 
the tip end 32, the surface converging in a direction toward said tip end. 
More specifically, the crest surface portion 42 of the lobes 40 are 
slightly tapered with respect to the center axis 30 by an angle 44 of 
preferably 21/2.degree. to 31/2.degree.. The importance of this feature 
will be discussed more fully hereinafter. It should be noted further, that 
FIG. 1 also includes a datum line 46 which represents the location along 
the length of tip 32 or the datum diameter, which if received in the 
socket 24 will afford the minimum, desired depth of engagement. 
Referring now to FIG. 4, the driver 14 is shown engaged with the fastener 
12. As can be seen, the taper of the lobes 40 permit the driver 14 to 
enter the fastener socket 24 until an interference or frictional fit is 
attained, with the datum diameter or location 46 received within the 
socket to assume the desired depth of engagement. Because only the lobe 
crest surface 42 is tapered, the dimensions of the socket 24 and the 
degree of taper of the lobes 40 determine the depth of engagement of the 
driver 14 with the fastener 12. More specifically the dimension of the 
driver lobes 40 adjust the tip 32 are sized to permit the tip 32 to enter 
the socket 24 easily. The multi-lobular tip 32 will continue to move 
inwardly until interferring or frictional engagement is attained along 
several of the lobe crest surfaces 42. This engagement is of course the 
engagement of the lobe crese surface 42 with an axially outer surface 
portion of the socket flute 26, in which the driver tip lobe 40 is 
engaged. Due to the fact that the socket lobes 28 (shown in dotted outline 
in FIG. 4) are disposed generally parallel to axis 30, i.e. non-tapered, 
as are the root or flute surfaces 38, no interference will result along 
this interface. Accordingly since the possibility of interfering 
engagement is limited to the crest surface portion 42, dimensional 
variances are less likely to prevent the driver from reaching the desired 
depth of engagement, as indicated by datum line 46. 
As a further advantage, only one taper need be formed in producing a driver 
in accordance with the present invention in order to attain a consistent 
minimum depth of engagement. Thus, the advantages of a tapered bit are 
realized, with assurances that sufficient surface engagement between the 
drive and socket element will ensue to attain efficient torque transfer 
from the driver to the fastener even with fastener heads of reduced mass. 
As a result, stripping or reaming of the fastener drive sockets is 
precluded because the torque applied to the fastener drive socket by the 
driver will be distributed over a sufficient surface area to avoid damage 
to the fastener. 
Although the improved fastener and driver assembly herein shown and 
described is structured such that the curved surfaces defined by the 
driver lobes are tapered axially along the work portion of the driver head 
towards the tip end, it of course can be appreciated that the curved 
surfaces defined by the driver roots or flutes could be tapered with the 
lobes being parallel to the driver center axis. This alternative structure 
would also function in accordance with the principles and features of the 
present invention without departing therefrom. With the driver lobes and 
flutes thus formed, the driver could acheive the required depth of 
engagement with the fastener socket, without interference, to provide 
efficient torque transfer from the driver to the fastener. 
From the foregoing, it can be seen that the present invention provides a 
new and improved fastener and driver assembly. Due to the fact that only 
the crest lobes 42 are tapered, interference upon the insertion of the 
driver into the fastener drive socket is minimized to assure sufficient 
penetration depth of the driver for providing efficient torque transfer 
from the driver to the fastener. Furthermore, because only crest one 
surfaces 42 are tapered, forming of the driver parts to consistent 
manufacturing tolerances may be readily achieved to the ultimate end of 
providing a consistent performance of the over all drive system. 
While a particular embodiment of the present invention has been shown and 
described, modifications may be made, and it is therefore intended to 
cover in the appended claims all such changes and modifications which fall 
within the true spirit and scope of the invention, as defined by said 
claims.