US3521497A - Gearing arrangement for rotary and reciprocable hammer drill - Google Patents

Description

July 21, 1970 P. SCHMUCK 3,521,49?

GEARING ARRANGEMENT FOR ROTARY AND RECIPROCABLIL'. HAMMER DRILL Filed July D, 19GB United States Patent Office 3,521,497 Patented July 21, 1970 3,521,497 GEARING ARRANGEMENT FOR ROTARY AND RECIPROCABLE HAMMER DRILL Peter Schmuck, Mauren, Liechtenstein, assignor to Hilti Aktiengesellschaft, Schaan Furstentum, Liechtenstein Filed July 9, 1968, Ser. No. 743,374 Claims priority, application Germany, July 24, 1967,

H 59,672 Int. Cl. F16h 25/12; B2Sd 9/00 U.S. Cl. 74-22 1 Claim ABSTRACT F THE DISCLOSURE BACKGROUND OF THE INVENTION In known hammer drills, wherein the drill is both rotated and axially reciprocated by a driving motor, preferably an electric motor, the output torque of the driving motor is divided into two work functions, one effective to rotate the drill and the other effective to reciprocate the drill along the drill axis. The drive movement is transmitted from the motor driving shaft, which carries a driving pinion, to a single first gear engaging the driving pinion. The axial reciprocation of the drill is effected by this single gear and, through another gear or another gear train engaging the first gear, the drill is rotated. In these arrangements, both partial forces or partial torques must be transmitted by only that single tooth of the driving pinion which happens to be in engagement with the lirst or output gear.

To attain good drilling eiciency, a relatively larg driving power or torque must be applied in these hammer drills, while the weight and the volume of the drills, and thus of the driving motor, must be kept as small as possible. For this reason, the drive shaft of the motor must rotate at very high angular velocities. However, due to the fact that the angular velocity of the drill and the beating frequency of the hammer effective to reciprocate the drill axially, must be smaller, by multiple, than the r.p.m. of the motor drive shaft, a large gear reduction ratio of the transmission is necessary. To attain this large gear reduction ratio with the fewest possible gears, the motor driving pinion must be as small as possible or must have the fewest possible teeth. This results in an undercut tooth form which is very unfavorable with respect to bending strength.

During operation of such a hammer drill, the gears, and especially the driving pinion, are under such a heavy strain, due to the beating of the hammer and, for example, by sudden jamming of the drill, that, as a result of this unfavorable tooth form of the driving pinion, tooth breakages at the driving pinion occur and, as a consequence, tooth breakages occur, at least in part, in other gears of the gear reducing arrangement.

SUMMARY OF THE INVENTION This invention relates to hammer drills of the type in which the drill is both rotated and axially reciprocated and, more particularly, to an improved gearing arrangement for such a hammer drill and which avoids the disadvantages of prior arrangements.

In accordance with the invention, this objective is obtained by dividing the power required for the drives of the two work functions into two partial forces or torques immediately at the driving pinion of the motor. These two partial forces or torques are then directed into two different force or torque paths by two gears directly engaging the driving pinion of the motor and each included in a respective different one of the two drives. With this arrangement, only one of the two partial torques or forces must be transmitted by the then engaged tooth of the driving pinion, whereby the strain on the teeth of the driving pinion is greatly reduced.

Advantageously, the two gears directly engaging the motor driving pinion are arranged exactly or approximately diametrically opposite each other. Thereby, the bending moments acting on the shaft of the driving pinion through the teeth of the latter are, for the most part, equalized. An additional safety factor .against tooth breakage is thereby obtained.

An object of the present invention is to provide an improved gearing arrangement for a hammer drill of the type including two drives, one rotating the drill and other axially reciprocating the drill.

Another object of the invention is to provide such a gearing arrangement in which the two partial torques are provided directly at, or immediately at, the driving pinion of a motor driving the drill.

A further object of the invention is to provide such a gearing arrangement in which each of the two drives includes a respective gear, and these two gears are directly engaged with the driving pinion.

Still another object of the invention is to provide such a gearing arrangement in which the two gears directly or immediately engaged with the driving pinion are arranged substantially diametrically opposite each other.

A further object of the invention is to provide such a gearing arrangement in which the strain on the teeth of the motor driving pinion is greatly reduced.

A further object of the invention is to provide such a gearing arrangement in which bending moments, acting on the shaft of the driving pinion through the teeth of the latter, are substantially equalized.

Another object of the invention is toprovide such a gearing arrangement providing a greatly increased safety factor against breakage ofgear teeth.

For an understanding of the principles of the invention, reference is made to the following description of a typical embodiment thereof as illustrated in the acompanyng drawing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing, the single figure is an elevation view, partly in section, illustrating an exemplary embodiment of a hammer drill incorporating the gearing arrangement of the present invention.

DESCRIPTION 0F THE PREFERRED EMBODIMENT The hammer drill illustrated, solely by way of example, in the drawing includes a casing 1 to which is secured an electric motor 2 for driving the drill. Motor 2 includes an antifriction bearing 3 rotatably supporting its output or driving shaft 4 t0 which is secured a driving or output pinion 5. Pinion 5 meshes directly with two gears, a gear 6 and a gear 7.

Gear 6 is secured to rotate with a shaft 10= rotatably mounted in axially spaced antifriction bearings 8 and 9. Shaft 10 has secured to rotate therewith a conical or bevel pinion 11 which meshes with a bevel gear 13, the bevel pinion 11 being integral with or fxedly secured to the upper end of shaft 10. Bevel pinion 13 is fixed to a cylinder or cylindrical sleeve 12 which is rotatably supported by an antifriction bearing 14. Bevel gear 13 thus transmits the rotation of bevel pinion 11, gear 6 and driving pinion to sleeve 12.

1 Sleeve 12 has an outer end 15 in which is non-'rotationally secured a tool holder 16 which is rotatably supported in an antifriction bearing 18 mounted in a sleeve 17 secured to casing 1 of the hammer drill.

vTool holder 16 has a bore extending completely axially therethrough lfor longitudinal guiding and rotational entrainment of the drilling tool 19. For this purpose, the bore and the drill are formed with mating polygonal cross sections, such as hexagonal cross sections, for example. The mating shank of drill or drilling tool 19 is axially displaceable in tool holder 16, and the end 19a of tool 19 extends into the bore 12a of cylinder or cylindrical sleeve 12. A pivoted holding strap 20 is provided to restrain tool 19 from falling out of the tool holder, and lthis strap can be pivoted out of the way for changing the tool 19.

VWhen the hammer drill is in operation, a hammer 21, designed as a pneumatic piston, beats on the inner end 19a of drill 19, the hammer 21 being axially reciprocable in the cylinder or cylindrical sleeve 12. Hammer 21 is operated, through the medium of an air cushion 22, by a drive piston 23 axially reciprocated in cylinder bore 12a. Through the medium of piston 23 and air cushion 22, axial reciprocation is imparted to hammer 21 in a known manner, and the kinetic energy of hammer 21 is transmitted, as a sudden impact, to drill 19 as hammer 21 strikes the inner end 19a of the shank of tool 19.

Drive piston 23 is reciprocated by means of a connecting rod 26 which has one end pivotally connected to piston 23 by means of a pin or bolt 24- extending diametrically of piston 23. The other end of connecting rod 26 is articulated on a crank pin 25a of a chank shaft 25 rotatably supported in bearings 27 and 28. Gear 7, meshing directly with driving pinion 5, is ixedly secured to crank shaft 25.

In the usual manner, a switch 30 is mounted in handle 29 of the hammer drill for the purpose of starting and stopping the hammer drill.

What is claimed is:

-1. In a hammer drill of the type driven by a motor having: a driving pinion, and including two drives, one rotating the drill and the other reciprocating the drill along the drill axis, a gearing arrangement comprising, in combination, two gears each meshing directly with said driving pinion and each included in a respective different one of said drives; one of said drives including crank means directly driven by one of said two gears; the other of said drives including a rotatable sleeve and reduction gearing means connecting the other of said two gears to said r0- tatable sleeve.

References Cited UNITED STATES PATENTS 3,161,241 12/1964 Allen et al 74-22 WESLEY S. RAT LIFF, JR., Primary Examiner U.S. Cl. X.R.

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