Idling System For Power Hammer

Abstract

An electric paving breaker is described which includes an electric motor, a crank and piston driven by the motor, and a ram driven by the piston which delivers energy to a tool bit to produce a hammering output. An improved idling system to prevent the piston from driving the ram unless a tool bit is in place is described.

Description

The present invention is directed to heavy-duty power tools of the type used as paving breakers and for other demolition work, and is specifically directed to an improved idling system for power hammer tools.

The tools to which this invention relates are those which generally include a source of power such as an air or electric motor, a piston connected to and driven by the power source and a ram element which is disposed between the piston and an output device. As the piston is reciprocated by the power source, energy is delivered from the piston to the ram and, as the ram reciprocates, it encounters an output means such as a chisel bit and energy is delivered to a workpiece such as pavement or concrete, etc. In the course of using such hammers, the operators commonly turn the switch controlling the power source on and hold it on as they apply the tool to various locations on the workpiece. When the tool is in contact with the workpiece, the bit, which is slidably mounted in the front end of the tool, is held in position to receive the full energy of the ram. However, as the tool is lifted and transferred to a new location, the bit slides partially out of the tool until stopped by a bit retainer. In this position, if the ram continues to be driven by the piston, the energy will no longer be taken by the workpiece, but will be applied to the front end of the tool itself. This either requires unnecessary structural strength in the front end of the tool or else the tool may be subject to premature failure.

To avoid this difficulty, it is desirable to provide an arrangement which will prevent the ram from reciprocating unless the tool bit is in position in the front of the tool and is held in its fully inward position by a workpiece. Ram catchers and rubber beat pieces which have previously been used are quickly mashed and ruined in large tools; air cushion devices have not provided adequate protection against hammering during idling. It is, therefore, the purpose of the present invention to provide an idling system, particularly for large power hammers, which will prevent the ram from reciprocating when the tool bit is not in proper position and which will not interfere with the normal operation of the tool when the bit is in its proper position relative to the ram.

Accordingly, it is an object of the present invention to provide a new and improved idling system for power hammer tools.

A further object of this invention is the provision of a new and improved hammer idling means which is more effective and more reliable than previous arrangements.

Further objects and advantages of this invention will become apparent as the description and illustration thereof proceed.

Briefly, in accord with one embodiment of this invention, a power hammer, specifically a paving breaker, is disclosed which includes an electric motor as a source of power, a gearing system for reciprocating a piston upon rotation of the motor, and a ram which is arranged to be coupled to and driven by the piston when the tool is in use. Means are provided for mounting and retaining an output bit which is driven by the ram when the tool is held against a workpiece. In specific accord with the present invention, an enclosed chamber having a check valve is provided at the bottom of the ram cylinder. In normal operation, the bit protrudes into this region, thus preventing the ram from reaching the bottom of the chamber. When the bit is removed from the tool, or when the tool is lifted from a workpiece so that the bit slides forwardly out of the normal range of the ram, the next power stroke of the ram compresses air in the chamber, slowing the ram and then opening the check valve so that the ram travels to the end of the cylinder. Means are provided to interrupt the normal coupling between the piston and the ram when the ram is at the bottom of the cylinder so that the ram remains stationary despite continued reciprocation of the piston. The ram remains in this position until it is lifted away from the bottom of the chamber by means of a tool bit being forced against a workpiece. This moves the ram upwardly in the cylinder to re-establish coupling between the piston and the ram and normal operation of the tool resumes.

In the drawing:

FIG. 1 is an elevational view of an electric paving breaker which embodies an idling system in accord with the present invention;

FIG. 2 is a schematic cross-sectional view through the tool of FIG. 1 which shows the internal mechanism of the tool;

FIG. 3 is a cross-sectional view of the forward end of the paving breaker of FIG. 1, which illustrates an idling system in accord with this invention;

FIG. 4 is a cross-sectional view corresponding to FIG. 2 but showing the parts at another point in the operation; and

FIG. 5 is a cross-sectional view similar to that of FIG. 2 but showing an alternative embodiment of this invention.

FIG. 1 illustrates generally an electric paving breaker in accord with the present invention. The tool, indicated generally at 1, includes a motor housing 2, a transmission housing 3, and a barrel 4. An output member such as a chisel bit 5 is retained on the paving breaker by means of a tool bit retainer 6.

The internal mechanism of this particular tool is shown in schematic form in FIG. 2 wherein it can be seen that this specific embodiment uses an electric motor 7 which drives a crank 8 by means of shaft pinion 9, right angle gear 10, spur pinion 11 and crank gear 12. All of these elements are, of course, supported in suitable bearings and lubricated as required. The crank 8 includes a journal portion 13 which supports the upper end 14 of a connecting rod 15. The connecting rod is coupled in a conventional manner to a piston 16 which reciprocates in the upper end of the barrel 4 upon rotation of the crank 8. At least one piston ring 17 is provided to seal the gap between the piston and the internal surface 18 of the barrel so that an air spring is created in the region 19. The air spring couples the reciprocation of the piston to a ram 20, causing it to be drawn up and then driven downwardly, producing a series of impacts on the bit 5 via a beat piece 21.

FIG. 3 illustrates the lower, or forward, end of the barrel 4. Within the barrel, the ram 20 is shown in its lowest position during working operation. In this position, the ram has just struck the beat piece 21 which transmits the energy directly to the upper end 22 of the bit 5. As previously described, this hammer makes use of the compression and expansion of the volume of air contained in the region 19 between the ram 20 and the piston. This air volume functions as a spring which permits the relatively slowly developing energy of the piston to be transferred rapidly to the ram, producing a high impact force, and which also isolates the motor and gear train from the shock loads when the ram impacts the beat piece. To allow this action to occur, a plurality of slots 23 are provided in the side of the barrel which communicate with the atmosphere and which thus prevent the development of high pressure or a vacuum ahead of the ram.

In normal operation, when the tool bit is pressed against a workpiece, the forwardmost position of the ram is that shown in FIG. 3. In this position, the region 19 between the ram and the piston is still sealed from the exhaust slots 23; thus, the upward motion of the piston reduces the pressure within chamber 19 and, in combination with the rebound energy, causes movement of the ram away from the beat piece. It is also noted that, in normal operation, the ram 20 is stopped by the beat piece just as it enters a chamber 25 at the forward end of barrel 4. Thus, air trapped within the chamber 25 does not affect the normal operation.

In front of the barrel 4, a nose piece 26 is provided to guide the tool bit 5. The nose piece is retained by a pair of roll pins, one of which is shown at 27 and by a series of bolts 28. The bolts are threaded into a retaining sleeve 29 which in turn is held within the barrel 4 by a retaining ring 30. The beat piece 21 includes a shoulder 31 which is trapped between internal shoulders 32 and 33 on the nose piece and retaining sleeve, respectively.

The retaining sleeve also includes a passageway 34 which communicates with the chamber 25 and which is closed by a check valve 35, the check valve being held closed by a spring 36. When the check valve is opened, the passage 34 communicates to the atmosphere through holes 37 and 38, in the retaining sleeve and barrel, respectively. This system permits the ram to idle under certain conditions as will now be set forth in conjunction with a description of FIG. 4.

In FIG. 4, the mechanism is shown with the tool bit 5 removed and with the beat piece 21 resting against the shoulder 32 of the nose piece. This illustrates the conditions which would apply if the tool was operated with the bit 5 removed or with the tool lifted away from the workpiece so that the bit drops to the lowest position permitted by the retainer 6. In either of these cases, the first power stroke of the piston drives the ram to and beyond the point at which it would normally encounter the beat piece 21. As the ram enters the chamber 25, air is trapped within this chamber by virtue of the close fit of the ram within barrel 4. Thus, the pressure within chamber 25 rapidly increases, slowing and stopping the ram. At some predetermined level of pressure, determined by the spring 36, the check valve 35 opens as shown in FIG. 4. This releases the air trapped in chamber 25 to atmosphere. The deceleration of the ram continues as excess pressure is relieved until finally the ram is stopped and the pressure in chamber 25 decreases to allow the valve 35 to close. At this point, the ram is below its normal operational position in the barrel 4 and the chamber 19 between the ram and the piston is now exposed to atmospheric pressure via the upper end of the slots 23. Thus, as the piston starts its next upward stroke the suction normally produced in chamber 19 simply draws air in from the atmosphere and no lifting force is applied to the ram. Since the ram receives essentially no rebound energy from the air in chamber 25 and since no lifting force is produced by the piston, the ram will remain at the bottom of the barrel 4 as the piston continues to reciprocate. Therefore, after the first, controlled motion of the ram to the front of the tool, the ram remains stationary and the front of the tool is not subjected to a continuing series of impacts which might produce serious damage.

When it is desired to resume normal operation, a tool bit must be in place within the nose piece 26. Biasing the bit against a workpiece forces the beat piece 21 into the chamber 25 and lifts the ram until it again closes the slots 23 from communication with chamber 19, thus permitting suction in chamber 19 to draw the ram upwardly and normal operation follows. In most cases, this tool is used in a vertical position with the bit pointed down; the weight of the tool exerts sufficient force on the bit to move the ram up out of the chamber 25.

FIG. 5 shows an alternative embodiment of this invention wherein the check valve 35 is replaced by a simple flapper valve 45. One end of the flapper valve is trapped between the nose piece 26 and the retaining sleeve 29 and a chamber 46 is provided in the nose piece to permit the valve to open. This embodiment operates in a manner identical to that described with regard to FIG. 4.

In the foregoing description and drawings, two specific embodiments of this invention have been illustrated and described. However, it will be clear to those skilled in the art that many changes and modifications can be made from these illustrations without departing from the essential teachings thereof. Accordingly, it is intended that the appended claims cover all such changes and modifications as may fall within the true spirit and scope of this invention.

Claims

We claim:

1. In a portable, power-operated impact tool of the type including a cylinder; a power-driven piston arranged to reciprocate in one end of said cylinder; a ram in said cylinder between said piston and the other end of said cylinder; a normally sealed air volume between said piston and said ram providing an air spring drive for said ram; at least one opening in said cylinder normally communicating the region in front of said ram to atmosphere; and means for slidably receiving a bit in said other end of said cylinder for receiving impacts from said ram; the improvement comprising a substantially closed chamber at said other end of said cylinder; said ram being prevented from entering said chamber when a bit is fully seated in said cylinder; a normally closed check valve in said chamber; said valve being set to open when air pressure in said closed chamber exceeds a predetermined level to to dissipate the kinetic energy of said ram through said check valve and limit the velocity of said ram as it traverses said chamber, and biasing means closing said valve as soon as said ram reverses its direction of movement to prevent said ram from rebounding out of said chamber.

2. An impact tool as claimed in claim 1 wherein a beat piece is provided at said other end of said cylinder for receiving blows from said ram and transmitting them to a bit seated therein.

3. An impact tool as claimed in claim 2 wherein said beat piece is arranged to extend into said closed chamber when a bit is seated in said cylinder, said beat piece being movable to a position out of said chamber.

4. An impact tool as claimed in claim 3 wherein said check valve is arranged to communicate said chamber to atmosphere upon buildup of a predetermined pressure in said chamber, whereby pressure in said chambers prevents said ram from striking the bottom of said chamber at a high velocity.

5. In a portable, power-operated impact tool of the type including a cylinder; a power-driven piston arranged to reciprocate in one end of said cylinder; a ram in said cylinder between said piston and the other end of said cylinder; a normally sealed air volume between said piston and said ram providing an air spring drive for said ram; at least, one opening in said cylinder normally communicating the region in front of said ram to atmosphere; and means for slidably receiving a bit in said other end of said cylinder for receiving impacts from said ram; the improvement comprising a substantially closed chamber at said other end of said cylinder; said ram being prevented from entering said chamber when a bit is fully seated in said cylinder; a normally closed check valve in said chamber; said valve being arranged to open when air pressure in said closed chamber exceeds a predetermined level to limit movement of said ram into said chamber, said valve being further arranged to close when the air pressure in said closed chamber is reduced to prevent said ram from rebounding out of said chamber; said region between said piston and said ram being communicated to atmosphere when said ram is in said chamber so that said ram is lifted by said piston only when a bit is seated in said cylinder.

6. An impact tool as claimed in claim 5 wherein a beat piece is provided at said other end of said cylinder for receiving blows from said ram and transmitting them to a bit seated therein.

7. An impact tool as claimed in claim 6 wherein said beat piece includes a portion extending into said closed chamber when a bit is seated in said cylinder, said portion being movable to a position out of said chamber.

8. An impact tool as claimed in claim 7 wherein said at least one opening is blocked from communication with said air volume by said ram when said beat piece is moved into said chamber by a seated bit.

9. In a portable, power-operated impact tool of the type including a driving motor, a transmission driven by said motor, a cylinder, a piston reciprocated in said cylinder by said transmission, a ram in said cylinder and coupled to said piston by a normally sealed air volume therebetween, a bit slidably disposed in the end of said cylinder for receiving impacts from said ram when said bit is fully seated in the end of said cylinder, and at least one opening in said cylinder for communicating the region in front of said ram to atmosphere, the improvement comprising a substantially closed chamber at the bit end of said cylinder; said bit, in its fully seated position, preventing said ram from entering said chamber; a check valve in the opposite side of said chamber from said ram, said check valve being positioned to open when said ram is driven into said chamber when said bit is not fully seated in said cylinder whereby said ram is prevented from striking the end of said cylinder at a high velocity by air pressure in said chamber.

10. In a portable power-operated impact tool of the type including a driving motor, a transmission driven by said motor, a cylinder, a piston reciprocated in said cylinder by said transmission, a ram in said cylinder and coupled to said piston by a normally sealed air volume therebetween, a bit slidably disposed in the end of said cylinder for receiving impacts from said ram when said bit is fully seated in the end of said cylinder, and at least one opening in said cylinder for communicating the region in front of said ram to atmosphere; the improvement comprising a substantially closed chamber at the bit end of said cylinder; said bit, in its fully seated position, preventing said ram from entering said chamber; a check valve in the opposite side of said chamber from said ram, said check valve being positioned to open when said ram is driven into said chamber when said bit is not fully seated in said cylinder whereby said ram is prevented from striking the end of said cylinder at a high velocity by air pressure in said chamber; said opening in said cylinder being positioned to communicate with said region between said piston and said ram only when said ram is in said chamber to prevent said ram from being reciprocated by said piston until said bit lifts said ram out of said chamber.

11. A portable, power-operated, heavy-duty impact tool of the paving breaker type comprising a cylinder; a power-driven piston arranged to reciprocate in one end of said cylinder; a ram in said cylinder between said piston and the other end of said cylinder; a normally sealed air volume between said piston and said ram providing an air spring drive for said ram; at least one opening in said cylinder normally communicating the region in front of said ram to atmosphere; and means for slidably receiving a bit in said other end of said cylinder for receiving impacts from said ram; a substantially closed chamber at said other end of said cylinder; said ram normally being prevented from entering said chamber when a bit is fully seated in said cylinder; a normally closed check valve in said chamber; said valve being arranged to open when air pressure in said closed chamber exceeds a predetermined level; said region between said piston and said ram being communicated to atmosphere when said ram is in said chamber; whereby operation of said piston when a bit is fully seated in said chamber causes reciprocation of said ram; operation of said piston in the absence of a bit and when a bit slides away from said chamber causing said ram to enter said chamber and remain in an idle mode.