Technical Field

This invention relates to a tool suitable for tightening two screw-threaded fasteners simultaneously to the same torque.

Tools of the aforesaid kind are known, as shown in British Patent Specification No. 723,036 comprising a motor-driven input shaft and a differential drive mechanism connecting the input shaft to each of two output shafts which are adapted to tighten one of said fasteners so that the output torques are always substantially equal. These known tools have been designed for production line use and are generally large and supported on a fixed frame to which work is delivered for the threading of the pairs of screw-threaded fasteners. Such tools can alternatively be made freely movable by suspending them on a balanced gantry hoist, but they are still cumbersome to use.

There is a particular need for a tool to tighten pairs of fuel injector fasteners evenly to the same torque in order to avoid mechanical distortion and uneven sealing. A tool of the aforesaid kind is suitable for production line assem¬ bly of injectors, but would not be suitable for service or "field" use, both because of its size and weight and because it would be too costly for intermitent limited use. An object of the present invention is to provide a tool of this general kind which is suitable for service use.

Disclosure of the Invention

According to the invention, a tool suitable for tightening two screw-threaded fasteners simultaneously to the same torque comprises a housing, an input shaft, a differential

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gear mechanism within the housing coupling the input shaft to a pair of parallel output shafts that extend perpendic¬ ular to the input shaft and rotate in the same sense with rotation of the input shaft and carry, or are adapted to carry, fastener engaging means at their free ends outside the housing, characterised in that the input shaft is jour¬ nalled at both ends in opposite walls of the housing and carries hand-operating means at one end externally of the housing whereby it can be rotated, the output shafts are each journalled in a single bearing in a wall of the hous¬ ing, the differential gear mechanism comprises a pair of bevel gears rotatably mounted on the input shaft and each meshing with a respective bevel gear fixed to the end of one of the output shafts within the housing, and hand-grip means is provided externally of the housing for use by an operator in steadying the tool when rotating the ^* hand-operating means.

It will be appreciated that a tool according to the invent¬ ion is a hand-tool of inherently simple and compact design, . comprising a differential gear mechanism enclosed in a hous¬ ing provided with a hand-grip, and having hand-operating means and a pair of projecting fastener tightening shafts drivingly connected through the differential gear mechanism with the hand-operating means located to one side of the shafts for ease of use.

Preferably, the hand-operating means comprises a hub with a plurality of radially projecting spokes so that after runn¬ ing down a pair of fasteners, the operator can always conveniently engage his fingers with a spoke to give a final sharp tightening twist irrespective of their angular position.

If the final torque setting of the fasteners is critical, the hand-operating means may comprise a connector such as a hexagonal nut for engagement by a torque spanner.

Preferably, the hand-grip is located opposite the fastener tightening shafts, so that a thrust can be applied along the line of the shafts to hold them in engagement with the fasteners.

Description of the Drawings

The invention will now be described by way of example with reference to the accompanying drawings in which

Figure 1 is a section through a tool according to the invention on a plane through the axis of the input shafts;

Figure 2 is a view along the axis of the input shaft of the tool of Figure 1 with the left-hand half of the housing and parts of the differential removed;

Figure 3 is a view showing the hand-operating means of the tool of Figure 1; and

Figure 4 is a view showing alternative hand-operating means to that in Figure 3.

Best Mode of Carrying Out the Invention

The illustrated tool comprises a housing 1 formed from a pair of similar castings 2 that are held together by screws 3. An input shaft 4 extends through the housing 1 along an axis perpendicular to the plane of abutment of the castings 2, and is journalled each end in plain bearings 5 in the base wall portion 6 of each casting 2.

The input shaft 4 carries a differential gear mechanism within the housing 1 comprising a pair of bevel gears 7 rotatably supported one each side of the shaft 4 on a hub 8 that is integral with the shaft 4 and has a diametral tapped hole 9 through it. A screw 10 is inserted through a cen¬ tral bore in each gear 7 and is threaded into the hole 9. Each gear 7 meshes with a bevel gear 11 rotatably mounted on the shaft 4 each side of the gears 7 a second bevel gear 12 is formed integrally with each gear 11, and these double . gears 11, 12, are restrained axially between the base wall portions 6 via a spacing sleeve 13 and washers 14 adjacent each portion 6.

Each gear 12 meshes with a gear 15 that is fixedly connected to one of a pair of output shafts 16 that project from the housing 1 parallel to one another and perpendicular to the input shaft 4. A spigot 17 is formed integrally with each gear 15 and projects through a plane bearing 18 in a thick¬ ened side wall portion 19 of a respective one of the cast¬ ings 2. The end of each spigot 17 externally of the housing is received in a recess 20 formed in an enlarged end 21 of each shaft 16, and a grub screw 22 connects the spigot and shaft together. Washers 23 are provided on a spigot 17 either side of the wall portions 19. Each shaft 16 and gear 15 lies on the same side of the respective gear 12 as the other (the left-hand side in Figure 1) so that rotation of the input shaft tends to rotate both shafts 16 in the same sense for simultaneous tightening. The gear ratio of each pair of gears 12, 15, is the same even though the sizes are different to fit compactly within the housing 1.

The outer end of each shaft 16 is provided with a coupling 24 for a detachable nut socket 25 (Figure 2) .

Hand operating means 26 is connected to one end 27 of the input shaft 4 that projects from the housing 1. This pro¬ jecting end 27 is the right-hand end as seen in Figure 1 so

that clockwise rotation of the operating means 26 (as viewed in Figure 3) will serve to rotate the output shafts 16 in the appropriate sense for nut tightening. This arrangement would be suitable for a right-handed operator, but would need to be modified for a left-handed operator by providing an input shaft with the projecting end 27 at the left-hand end in Figure 1 to receive the operating means 26 at this end.

The hand operating means 26 comprises a hub 28 carrying five equi-angularly spaced spokes 29 that project radially from the hub. A boss 30 projects axially and is formed with a central tapped hole 31 that engages the threaded end 27 of the input shaft 4. It will be appreciated that the spoked 29 can be conveniently gripped by the operator and turned to tightened nuts in use.

^• Alternatively, the hand operating means may comprise a spoked wheel, as shown in Figure 4, having spokes 32 and carrying a knob 33 near its outer periphery that may be used by an operator when running down nuts, the spokes being used to give a final tightening twist.

A hand-grip 34 is provided to allow the operator to steady the tool with his free hand when in use. This is produced by indentations 35 along the top of the housing either side of the plane of the input and output shafts 4, 16, so as to form a raised ridge 36 therebetween that is aligned with . said plane (see Figure 2) . The operator can then press down on the tool with his free hand to hold the sockets 25 in place on a pair of nuts being tightened.

A tool used for tightening pairs of fuel injector nuts would have the spacing of the two output shafts equal to that for injector nuts. It will be appreciated that in operation the differential gear mechanism will operate to tighten both

nuts down equally, any differential tightening of one nut relative to the other causing a reaction that transfers more of the applied torque to the other nut until the forces on both are balanced again. Thus the nuts are tightened simul¬ taneously to the same torque level and distortion of the injector and gas leakages are thereby avoided.

An advantage of the hand operation is that excessive over¬ tightening of the injector nuts is avoided. The dimensions of the gears 12 and 15 in fact assists in this respect by reducing the overall gear ratio, although the dimensions of these gears is selected primarily in relation to the size of the gear assembly 7, 8, 10, in order to produce a compact mechanism.