Patent Description:
In order to limit the pit-stop time, which can in many cases be critical to the result of a car competition, motorsport pneumatic impact wrenches must exhibit extremely high performance in terms of speed of rotation and mechanical resistance.

Presently the socket-shaft coupling in pneumatic impact wrenches for the motorsport sector is obtained by a square profile of the wrench shaft that couples with a square hole provided on a socket connection portion. The socket is constrained on the shaft by a transverse pin, with an axis orthogonal to the shaft axis.

When this type of coupling is subjected to a high number of revolutions, even more than <NUM>,<NUM> rpm, it produces vibrations on the shaft and swinging of the socket.

This results in the operator having to manually compensate the generated vibrations and swinging to keep the wrench in axis with the nut during operations for screwing and unscrewing the wheel from its hub, with the consequent risk that the nut is not sufficiently clamped and that pit-stop times are excessive. Obviously, risks for the health of the operator handling the motorsport wrench that can arise due to prolonged use of the wrench itself must be taken in consideration. Furthermore, as they are submitted to high stresses, the socket and the socket-holding shaft are exposed to break and high wear even due to vibrations.

Socket-shaft connection assemblies are known in the prior art.

<CIT> relates to a recessed drive shaft intended for power tools. This document discloses the preamble of independent claim <NUM>.

<CIT> relates to a system for mounting vehicle wheels, in particular in motor sports, with at least one impact wrench.

An object of the invention is to improve coupling between socket and shaft of a motorsport pneumatic impact wrench.

A further obj ect is to improve clamping between socket and shaft in a motorsport pneumatic impact wrench.

Still a further object is to reduce or even overcome problems related to the use of the square profile in the socket-shaft coupling of traditional type.

Another object is to provide a socket-shaft connection assembly that fulfils the needs for efficient torque transmission and high mechanical resistance required in the motorsport sector.

Still another object is to obtain a socket-shaft coupling enabling to quickly mount and remove the socket.

According to the invention it is provided a socket-shaft connection assembly for motorsport pneumatic impact wrench comprising a socket-holding shaft, a socket, a fixing element of said socket for connecting said socket to said socket-holding shaft, characterized in that:.

Furthermore, according to the invention there is provided a motorsport pneumatic impact wrench socket.

Owing to the coupling by means of grooved profiles of the socket-holding shaft and of the socket and to conical surfaces, the torque transmission is obtained on assembly sections that are different from those enabling centering of the various assembly components. This allows to optimize the socket-shaft coupling since grooved profiles can substantially carry out the only torque transmission between socket-holding shaft and socket, thereby making such transmission relatively efficient. Furthermore, conical surfaces allow to obtain a highly precise centering, thus significantly reducing or even removing generation of swinging determined by eccentricity or axial off-set due to mounting.

The invention shall be better understood and implemented referring to the enclosed drawings which illustrate an exemplifying and non-limiting embodiment thereof, wherein:.

Referring to <FIG> and <FIG>, a socket-shaft connection assembly <NUM> for motorsport pneumatic impact wrench <NUM> comprises a socket-holding shaft <NUM>, a socket <NUM> and a fixing element <NUM> for connecting the socket <NUM> to the socket-holding shaft <NUM> along an axis X of the socket-holding shaft <NUM>. As shown in <FIG>, a retaining member <NUM> may be present, for example an O-Ring, which is arranged between the fixing element <NUM> and the socket-holding shaft <NUM> when the socket <NUM> is mounted on the socket-holding shaft <NUM>. The illustrated socket <NUM> is of the type used to screw or unscrew wheel nuts for competition cars, for example Formula <NUM>, fixed to the hub thereof by means of a single central nut, but it can be of a different type, for example for wheels fixed to the hub by means of a plurality of nuts.

The socket-holding shaft <NUM> and the socket <NUM> comprise respective grooved profiles P3, P4 (<FIG>) cooperating for torque transmission between the socket-holding shaft <NUM> and the socket <NUM> when the impact wrench <NUM> is in function.

The fixing element <NUM> is conformed to exert a force in the direction of the axis X of the socket-holding shaft <NUM> to connect the socket <NUM> to the socket-holding shaft <NUM> itself.

The centering of the socket <NUM> on the socket-holding shaft <NUM> occurs by means of a plurality of coupling conical surfaces V-B, B-A (<FIG>), obtained respectively on the fixing element <NUM>, on the socket-holding shaft <NUM> and on the socket <NUM>. The coupling conical surfaces are distinct from the grooved profiles P3, P4.

Referring to <FIG>, <FIG>, the socket-holding shaft <NUM> comprises a driving end <NUM> with which it is connected in a known way, thus not herein described, to the shaft of the pneumatic impact wrench <NUM> by which it is rotated about its own axis X. The socket-holding shaft <NUM> further comprises a socket-holding end <NUM>, arranged to receive the socket <NUM> and on which the grooved profile P3 is obtained. The grooved profile P3 comprises a plurality of teeth <NUM>, ten in number in the illustrated version, angularly equally spaced on the surface of the socket-holding end <NUM>. In non-illustrated versions, the number of teeth is other than ten. Each tooth <NUM> comprises flanks 10A, 10B that are rectilinear and tilted with respect to the tooth axis <NUM> (<FIG>) so that the tooth base <NUM>, that is closer to axis X, is larger than its tip. A tilt angle δ (delta) between two flanks 10A, 10B is for example of about <NUM>°.

Referring to <FIG>, the socket <NUM> comprises a hollow body, having an operating end <NUM> by which the car wheel nut is engaged and a connecting end <NUM> by which socket <NUM> connects with the socket-holding shaft <NUM>. The connecting end <NUM> comprises a hole <NUM> into which the socket-holding shaft <NUM> is fitted and the grooved profile P4, conformed to cooperate with the grooved profile P3 of the socket-holding shaft <NUM>, is obtained on the walls of the hole <NUM>. The grooved profile P4 comprises grooves <NUM>, ten in number in the illustrated version, arranged to receive teeth <NUM> of the grooved profile P3. Therefore, grooves <NUM> are angularly equally spaced and define a same number of projections <NUM> alternating with grooves <NUM> thereof. The number of grooves can obviously be other than ten. Grooves <NUM> comprise walls 14A, 14B that are plane and tilted by an angle γ (gamma) which is the same as the tilt angle δ (delta) of flanks 10A, 10B of the teeth <NUM> of the profile P3. The depth of grooves <NUM>, i.e. the distance between the bottom of the groove <NUM> and the crest of the projection <NUM> adjacent to the groove itself, is for instance <NUM> with a few tenths of a millimetre tolerance.

Profiles P3 and P4 have resistance sections of the tooth foot <NUM> on the socket-holding shaft <NUM> side and of the projections <NUM> on the socket <NUM> side that are equal between them. The constant section of the foot of the tooth <NUM> and of the foot of the projection <NUM> allows to have an extremely balanced mounted assembly at rotation. Furthermore, the described geometry allows a more harmonic distribution of tensions resulting in unbalanced deformations not occurring especially on the socket <NUM>.

When profiles P3 and P4 are coupled, the mutual distance between the flanks of teeth <NUM> and the walls of the grooves <NUM> is rather low in the order of <NUM>-<NUM> or lower, while the crest of teeth <NUM> remains distant from the bottom of grooves <NUM> of about <NUM>. Available clearance allows an efficient torque transmission between socket-holding shaft <NUM> and socket <NUM>, enabling at the same time to easily remove the socket <NUM> from the socket-holding shaft <NUM>, for example, to be replaced.

Referring to <FIG> and <FIG>, in order to movably fix the socket <NUM> to the socket-holding shaft <NUM>, the fixing element <NUM> comprises a threaded portion 5B, in form of threaded stem, arranged to engage into a threaded hole <NUM> (<FIG>) obtained in the socket-holding end <NUM> of the socket-holding shaft <NUM>. The threaded hole <NUM> is coaxial with axis X of the socket-holding shaft <NUM> and comprises a more internal threaded region and a stop surface <NUM> against which the fixing element <NUM> or the retaining member <NUM> can abut once mounted with the socket <NUM>. The fixing element <NUM> further comprises a head 5A arranged to interact with an inner part of the socket <NUM> to restrain the socket <NUM> on the socket-holding shaft <NUM>. The fixing element <NUM> serves substantially as a screw and the force it exerts in direction of the axis X corresponds to the clamping axial force of the fixing element <NUM> with which the socket <NUM> is constrained once mounted on the socket-holding shaft <NUM>. On the brim 5A the fixing element <NUM> has a hollow section <NUM>, for example hexagonal in section, to receive a known clamping tool, for example an Allen key. An annular recess <NUM> arranged to receive the retaining member <NUM> is provided on the head 5A in an underhead region of the fixing element <NUM>.

As indicated above, the torque transmission is implemented by grooved profiles P3 and P4. By contrast the axiality of the socket <NUM> with respect to the axis X of the socket-holding shaft is obtained by means of conical couplings. As shown in <FIG>, a first pair of coupling conical surfaces V-B is provided, one conical surface V of which is provided on the head 5A of the fixing element <NUM>, a further conical surface B1 is provided on an inner part <NUM> of the connecting end <NUM> of the socket <NUM> where the hole <NUM> ends up in a cavity <NUM> of the socket <NUM>, such cavity <NUM> being arranged to house the motorsport nut which must be screwed or unscrewed. In the section view of <FIG>, conical surfaces V and B1 of the first pair of coupling conical surfaces V-B have a same vertex angle α (alpha), which is in particular of about <NUM>°, being the vertex arranged in direction of the socket-holding shaft <NUM>. It is further provided a second pair of coupling conical surfaces B-A, a conical surface B2 of which is obtained on the socket <NUM> and a further conical surface A is obtained on the socket-holding shaft <NUM> at an inlet aperture <NUM> of the hole <NUM>. In section view of <FIG>, conical surfaces B2 and A of the second pair of coupling conical surfaces B-A have a same vertex angle β (beta), which is in particular equal to vertex angle α (alpha) of the first pair of conical surfaces V-B, for example of about <NUM>°. The vertex of angle β (beta) is arranged in direction of cavity <NUM> of the socket <NUM>. Centering is obtained by means of the two pairs of conical couplings clamped by means of the fixing element <NUM>. These conical couplings have no interference and are extremely precise. In fact, the angle ϕ (phi) (<FIG>) which, in an axial section the conical surface A of the socket-holding shaft <NUM> forms with the axis X, is of <NUM>° with +<NUM>° to +<NUM>° tolerance; furthermore, the conical surface A has a linear tolerance of <NUM> and a circularity tolerance of <NUM>. Similarly, angle β2 (beta2) (<FIG>), that the conical surface B2 forms with an axis parallel to the J axis of the socket <NUM>, is of <NUM>° with -<NUM>° to -<NUM>° tolerance; furthermore, the conical surface B2 has a linear tolerance of <NUM> and a circularity tolerance of <NUM>. Similarly, the angle β1 (beta1) (<FIG>) that the conical surface B1 forms with an axis parallel to the J axis of the socket <NUM>, is of <NUM>° with -<NUM>° to -<NUM>° tolerance; furthermore, the conical surface B1 has a linear tolerance of <NUM> and a circularity tolerance of <NUM>. Similarly, angle ψ (psi) (<FIG>) which the conical surface V forms with an axis parallel to the K axis of the fixing element <NUM>, is of about <NUM>° with +<NUM>° to +<NUM>° tolerance; furthermore, the conical surface V has a linear tolerance of <NUM> and a circularity tolerance of <NUM>.

Centering by means of pairs of conical surfaces substantially allows to reduce an axial clearance to zero, i.e. along axis X, between socket <NUM> and socket-holding shaft <NUM>.

The retaining member <NUM> is interposed between the fixing element <NUM> and the socket-holding shaft <NUM> and is housed in the annular recess <NUM> and is in contact with a stop surface <NUM> to prevent unscrewing the fixing element <NUM> itself and creating a dampening micro-effect.

As indicated above, the configuration of the socket-shaft connection assembly <NUM> allows torque transmission by means of grooved profiles P3 and P4 with no centering made therefrom. By contrast, centering is obtained by the conical pairs V-B, B-A when they are clamped by the fixing element <NUM>. Part of the torsion motion is transmitted by friction also on the centering conical pairs V-B, B-A, thereby relieving grooved profiles P3 and P4 from loads applied on teeth <NUM> and protrusions <NUM> when the high speed pneumatic impact wrench <NUM> is in function. It must be noted that <NUM>-<NUM> rpm of the pneumatic impact wrench <NUM>, corresponding to the free number of revolutions, i.e. with no engagement between socket and nut, becomes of <NUM> rpm in the working condition.

Furthermore, the socket <NUM> in the working condition is substantially aligned to the ideal axis of the nut to be screwed or unscrewed, this limiting swinging due to eccentricity or tilts with respect to the axis of the socket-holding shaft. This results in a lower rotation radial effect with a more precise engagement of the nut; the pneumatic impact wrench thus becomes more handy.

By significantly reducing swinging of the socket, return stresses on the abutting part of the pneumatic impact wrench are consequently reduced resulting, over time, in a reduced wear if compared to the traditional type of connection with square shaft. In other words, owing to the socket-shaft connection assembly <NUM> the working life of the wrench components, as well as that of the socket-holding shaft, has increased.

Furthermore, owing to the socket-shaft connection assembly <NUM>, mounting the socket <NUM> on the socket-holding shaft <NUM> is easy and quick.

With respect to the square coupling, the socket-shaft connection assembly <NUM> allows to reduce local stresses caused by torsion and to highly distribute them thus resulting in a reduction of local deformations.

The coupling symmetry, wherein the resistant sections on socket and socket-holding shaft are substantially equal, involves a propagation of tensions that is also symmetrical, thereby points of crack initiation are reduced with consequent increase of the average life of the more stressed components.

It must be noted that during a motorsport pit stop, the wheel nut is screwed in an application time of about <NUM>-<NUM> hundredths of a second and is unscrewed in <NUM> hundredths of a second, with a nominal working pressure of the supply air of the pneumatic impact wrench of <NUM> bars; the maximum torque generated by unscrewing is of <NUM>, in case of a traditional square coupling.

Owing to the socket-shaft connection assembly <NUM> it is possible to reduce or even overcome problems connected to the use of the square profile in the traditional-type socket-shaft coupling, with reduction of vibrations and swinging of the socket.

Furthermore, the experiment shows that the socket-shaft connection assembly <NUM> allows to obtain an efficient torque transmission and has a high mechanical resistance and to maintain ease of assembling and removal of sockets of traditional systems.

Furthermore, the durability of the assembly components as well as of the pneumatic impact wrench is increased.

Claim 1:
A socket-shaft connection assembly for motorsport pneumatic impact wrench (<NUM>) comprising a socket-holding shaft (<NUM>), a socket (<NUM>), a fixing element (<NUM>) for connecting said socket (<NUM>) to said socket-holding shaft (<NUM>) along an axis (X) of said socket-holding shaft (<NUM>), characterized in that:
- said socket-holding shaft (<NUM>) and said socket (<NUM>) comprise respective grooved profiles (P3, P4) cooperating for torque transmission between said socket-holding shaft (<NUM>) and said socket (<NUM>);
- said fixing element is conformed to exert a force in the direction of the axis of the socket-holding shaft (<NUM>) to connect said socket (<NUM>) to said socket-holding shaft (<NUM>);
- on said fixing element (<NUM>), on said socket-holding shaft (<NUM>) and on said socket (<NUM>) a plurality of coupling conical surfaces (V-B, B-A) are obtained for centering said socket (<NUM>) on said socket-holding shaft (<NUM>), wherein said coupling conical surfaces (V-B, B-A) are distinct from said grooved profiles (P3, P4).