Hammer drill

#Hammer drills are known in which rotation of toothed surfaces against each other causes a hammering action. Also, in U.S. Pat. Nos. 3,149,681 and 3,133,602, rotary impact hammers with a ball on tooth engagement provide for a hammering action only in one direction of rotation. A ball on tooth engagement also tends to wear a groove in the tooth, which tends to create a wide contact area between ball and tooth. Together with the immobility of the tooth surface, the wide contact area increases friction losses and heating of the tool.

#The present invention provides a hammer drill with rolling contact at the contact surfaces for transmission of axial force between a drive shaft and hammer shaft. In the case of ball bearings, point contact is obtained. In the case of roller bearings, line contact is obtained. The area of contact is thus close to zero as opposed to a relatively large area in engagement systems using toothed surfaces. Use of point or line contact reduces heat generation and reduces energy loss due to friction.

#In some prior art products, a release clutch is used to release torque when pressure is critically increased and to prevent engagement parts from shear. In the case of a hammer drill with rolling contact, relatively low torque generators may be used where the torque does not exceed shearing stresses. The hammer drill of the present invention does not require the release clutch because it provides its function by rolling friction. When torque increases, the rotating bearing elements in the drive assembly are pushing the rotating bearing elements in the hammer assembly, thus separating the hammer assembly from the drive assembly and releasing the torque. This repetitive action also generates a hammering effect. The contact points between the rotating bearing elements are between 0 and 90 degrees to the tool axis. This offset makes the shearing component of the reaction force to rotate the rotating bearing elements inside the cavities and its axial component makes rotating bearing elements climb on each other.

#There will now be described preferred embodiments of the invention, with reference to the drawings, by way of illustration only and not with the intention of limiting the scope of the invention, in which like numerals denote like elements and in which:

#FIG. 1 is a section through a hammer drill according to the invention;

#FIGS. 2A and 2B are schematics showing relative ball positions of balls used in the hammer drill of FIG. 1;

#In this patent document, the word comprising” is used in its non-limiting sense to mean that items following the word in the sentence are included and that items not specifically mentioned are not excluded. The use of the indefinite article “a” in the claims before an element means that one of the elements is specified, but does not specifically exclude others of the elements being present, unless the context clearly requires that there be one and only one of the elements.

#Referring to FIG. 1, there is shown an adapter 10 for a hammer drill, which includes two subassemblies mounted within a housing 12. A driver assembly 14 is directly connected to the chuck of a drill or power tool (not shown) and transfers torque from drill to a hammer assembly 16. The hammer assembly 16 converts received torque into torque and axial stroke motion. The drive assembly 14 may be formed as an integral part of a power tool.

#The driver assembly 14 includes a drive shaft 18 with one end having hexagonal shape in cross-section for connection into a chuck (not shown) of a conventional power tool, and another end oblong shape in cross-section for connection with the hammer assembly 16. The middle section of the drive shaft 18 is round in section and has a step 20 for fitting a roller bearing 22 that supports the drive shaft 18 within the housing 12 for rotation relative to the housing 12. A cone shaped extension 24 covers roller bearing 22. The housing 12 is formed of a cylindrical outer case 26, a bearing housing 28 and end cup 30. Bearing housing 28 is a cylinder shaped part, and has an opening for fitting roller bearing 22 and has a round opening, partially flattened with a flat portion to create a D-shape, for positioning a bearing holder or ball holder cassette 32. A snap ring 34 engages a groove 36 on the drive shaft 18 to secure the bearing holder 32 in place and fixed axially in relation to the drive shaft 18, while the bearing holder 32 is fixed rotationally in relation to the housing 12.