Patent Application
20060283612
The present disclosure relates generally to a tool assembly, and more specifically to a hammer assembly having a two part body comprising an upper housing member and a lower housing member.
Hydraulic hammers are used on work sites to break up large hard objects before such objects can be moved away. Hydraulic hammers may be mounted to back hoes or excavators, or may be hand-held. Typically, the hammer assembly is powered by either a hydraulic or pneumatic pressure source. During a work or power stroke, high fluid pressure is applied to a first shoulder of a piston, thereby driving the piston in a forward direction. The piston then strikes a work tool, which is driven in the forward direction thereby causing a work tip of the tool to strike the rock, concrete, asphalt or other hard object to be broken up. During a return stroke, fluid pressure is applied to a second shoulder of the piston in order to return the piston to its original position.
The work tool, also known as a tool bit, is retained within a sleeve, commonly referred to as a front head. When the tool is driven forward, the kinetic energy of the tool is transferred to the object to be broken up. However, if full contact with the object to be broken up does not occur, a proportion of the energy is transferred to the front head. If no contact takes place with the object to be broken up, then all of the energy may be transferred to the front head. Consequently, the front head is subject to cyclical loading which tends to pull it away from the cylinder of the hammer assembly. Conventionally, external tie rods are used to tie the front head to the cylinder. The tie rods increase the overall diameter of the hammer assembly and add to the complexity of manufacture. Tie rods typically have to be replaced at regular service intervals, since they are subject to fatigue failure and failure of a tie rod can cause irreparable damage to the entire hammer assembly.
At least some of the disclosed embodiments may overcome one or more of the abovementioned drawbacks.
In accordance with a first aspect of the present disclosure, there is provided a tool assembly comprising a housing defining a chamber and a reciprocating piston arranged in the chamber for cyclical movement in a work stroke and a return stroke. The housing includes a lower housing member, an upper housing member and engaging structure which permits the engagement of the upper housing member with the lower housing member by relative rotation of the upper and lower housing members, each of the lower and upper housing members defining a portion of the chamber.
In accordance with a second aspect of the present disclosure, there is provided a method of assembling a tool assembly, comprising: providing a lower housing member defining a lower chamber; providing an upper housing member defining a upper chamber; providing a work tool housed in one of the lower and upper chambers; engaging the lower housing member and the upper housing member by relative rotation of the upper and lower housing members to form a tool assembly defining a single chamber comprising the lower and upper chambers; and applying a prestressing force to urge the lower housing member away from the upper housing member.
With reference to
The piston 18 includes a work portion 26 and a load portion 28. Pressurized fluid is advanced by a first hydraulic pressure source 30 against the work portion 26 to serve as a drive structure and urge the piston 18 towards the work tool 20 during the work stroke. Similarly, pressurized fluid is advanced by a second hydraulic pressure source 32 against the load portion 28 to serve as a return structure to return the piston 18 during the return stroke.
The hydraulic circuit is not described further, since it will be apparent to the skilled person that any suitable hydraulic arrangement may be used to provide pressurised fluid to the piston 18, such as the arrangement described in U.S. Pat. No. 5,944,120.
Near the end of the work stroke, the piston 18 strikes the work tool 20. The work tool 20 includes a tip 46. A tool retention member 80 retains the work tool 20 and limits the movement of the work tool 20 in the general direction of arrow 22. Removing the tool retention member 80 allows a variety of work tools 20 with different configurations of the tip 46 to be attached to the tool assembly 10. As the piston 18 strikes the work tool 20, the force of the piston 18 is transmitted through the work tool 20 to the tip 46 in the general direction of arrow 22. Moreover, this force is applied to a hard object such as rock, concrete, or asphalt in order to break up the hard object. The tool retention member does not form part of the present disclosure but is described in more detail in our co-pending application Ser. No. 11/______ (Attorney Docket No. 08350.3434 filed concurrently herewith).
With reference to the embodiments of FIGS. 1 to 4 the upper and lower housing members 12, 14 are connected by an engaging structure 50. In the illustrated embodiment the engagement structure 50 includes four lugs 52 provided equidistantly about the circumference of a plug portion 54 of the upper housing member 12. These are shaped such that as the plug portion 54 is inserted into a socket portion 56 of the lower housing member 14 the lugs 52 can pass between four projections 58 formed on the internal wall 60 of the socket portion 56. The upper housing member 12 is then rotated by 45 degrees relative to the lower housing member 14 so that the lugs 52 engage beneath the projections 58. It is to be understood that other forms of mutually engaging protrusions may be envisaged, and the shape and number of lugs and protrusions can be varied and are not limited to those shown in the figures. A stop (not illustrated) may be formed on the internal wall 60 of the socket portion such that upon rotation of the upper housing member 12 one of the lugs 52 comes into contact with the stop to indicate that sufficient rotation has taken place.
Prestressing structure in the form of four jacking screws 70 are provided to urge the upwardly facing mating surfaces 72 of the lugs 52 against the downwardly facing mating surfaces 74 of the projections 58. The screws 70 engage in threaded apertures 76 provided equidistantly around the perimeter of a circular flange 78 of the upper housing member 12. The jacking screws 70 engage with an upwardly facing bearing surface 79 formed on the upper end of the lower housing member 14.
Although embodiments have been described with reference to lugs and projections, it is to be understood that other forms of mutually engaging protrusions may be provided. For example the upwardly facing mating surface on the upper housing member may be provided on a helical protrusion which forms a male thread and engages with the downwardly facing mating surface of a corresponding helical protrusion on the lower housing member, serving as a female thread. In another example the engaging structure may be a bayonet coupling in which two or more pins are provided on the plug of the upper housing member, the pins engaging with two or more L-shaped slots provided on the internal surface of the socket.
Although an embodiment has been described in which the plug portion 54 is formed on the upper housing member 12 and the socket portion 56 is formed on the lower housing member 14, the engaging structure may be reversed, so that the plug portion is formed on the lower housing member 14 and the socket portion is formed on the upper housing member 12.
Although the prestressing structure described above comprises four jacking screws 70, the number, type and position of the jacking screws may be varied. Moreover other prestressing structure may be used, such as springs or other resilient elements which urge the upper and lower housing members apart. In the case of corresponding helical protrusions on the upper and lower housing members the prestressing structure may be the elastic or plastic deformation of the threads under a tightening torque on the housing members.
The upper and lower housing members 212, 214 are connected by an engaging structure 250. In the illustrated embodiment the engagement structure 250 includes four lugs 252 provided equidistantly about the circumference of a plug portion 254 of the upper housing member 212. These are shaped such that as the plug portion 254 is inserted into a socket portion 256 of the lower housing member 214 the lugs 252 can pass between four projections 258 formed on the internal wall 260 of the socket portion 256. The upper housing member 212 is then rotated relative to the lower housing member 214 so that the lugs 252 engage beneath the projections 258. It is to be understood that other forms of mutually engaging protrusions may be envisaged, and the shape and number of lugs and protrusions can be varied and are not limited to those shown in the figures. A stop (not illustrated) may be formed on the internal wall 260 of the socket portion such that upon rotation of the upper housing member 212 one of the lugs 252 comes into contact with the stop to indicate that sufficient rotation has taken place.
An annular bearing surface 300 is provided on the internal wall 260 of the socket portion 256. A piston sleeve 302 is provided around the piston and bears at one end against the bearing surface 300. The other end of the piston sleeve 302 bears against a valve sleeve 304 which is held against an accumulator housing 306. The accumulator housing 306 and its associated accumulator cover 308 are secured to an upper bearing surface 314 of the upper housing member 212 by tension screws 310. The valve sleeve 304 has a resilient deflector flange 312 which deflects to provide a biasing compression force when a torque is applied to the tension screws 310, as described below. The tension screws may be necked down, and may form part of a Bellville type interface.
The operation of the embodiment of the tool assembly shown in FIGS. 1 to 4 will be described. In use, the jacking screws 70 are tightened to a predetermined torque to prestress the engaging structure and establish a known contact stress between the upwardly facing mating surfaces 72 of the lugs 52 and the downwardly facing mating surfaces 74 of the projections 58.
In the embodiment shown in
In at least some of the embodiments, under the cyclical action of the piston 18, 218 and tool 20, 220, which act to pull the upper 12, 212 and lower 14, 214 housing members apart, the contact stress varies cyclically, but remains in compression throughout the cycle, thereby reducing the risk of fatigue failure. In contrast the tie rods of the prior art hammer systems are subject to cyclical tensile stresses and have a much greater risk of fatigue failure.
The upper housing member 12, 212 is a precision component which contains the hydraulic components of the hammer system and requires substantial machining, while the lower housing member 14, 214 is a lower precision component which requires minimal manufacturing. By manufacturing the two housing members 12, 212, 14, 214 as separate components and joining them by the engaging structure 50, 250, the lower housing member can be made more economically and does not have to be manufactured to the high tolerances required by the upper housing member. The two housing members 12, 212, 14, 214 when joined, offer the advantages of a single housing 11, 211 in that the tool assembly 10, 210 is more compact than a tie rod structure and the housing 11, 211 can be cylindrical, allowing use of the tool assembly 10, 210 in narrow, confined locations such as between slabs, where the wider tie rod body would interfere with the slabs.
Although embodiments have been described with reference to a hammer assembly in which the drive means and return means are hydraulic pressure sources, the disclosed embodiments are applicable to any tool assembly having a piston movable within a chamber by suitable drive structure and return structure. The disclosed embodiments encompass pneumatic tools and other impact tools.
While the disclosed embodiments have been illustrated and described in detail in the drawings and foregoing description, such illustration and description is to be considered as exemplary and not restrictive in character, it being understood that exemplary embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected.
| Number | Date | Country | Kind |
|---|---|---|---|
| 05253698.4 | Jun 2005 | EP | regional |
