BACKGROUND OF THE INVENTION
[0001] 01 Hammer drills are known in which rotation of toothed surfaces against each other
causing a hammering action. Also, in United States patent 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. A further hammer drill is disclosed in United
States patent no. 6,684,964, in which the hammer action is provided by impact of facing
sets of bearings. This design suffers from increased wear and friction losses from
the impact on the bearings on each other.
SUMMARY OF THE INVENTION
[0002] 02 The present invention describes a hammer drill using a rolling hammer action.
The rolling hammer is based on a journal bearing support principal. The reciprocating
action required for hammer drilling produces high impact loading and vibration. Wear
is accelerated whenever true rolling contact or a consistent hydrodynamic lubrication
film is not maintained. This is particularly true for the sliding ramp or ratchet
design when contact is interrupted as the ramps disengage at the end of each stroke.
A similar situation occurs in the piston design when the piston reverses its direction
at both ends of its stroke.
[0003] 03 The true rolling contact provided by the proposed rolling hammer mechanism has
the advantages of providing full fluid lubrication for both the journal and true rolling
support functions that reduce friction and wear, longer service life than comparable
products, and distribution and dissipation of heat (which influences the operation
temperature), permissible speed and the load carrying capacity of the journal and
true rolling functions.
[0004] 04 The rolling hammer drill is a simple, unique and easily built mechanism. It produces
a strong single impact energy with a precise impact frequency that results in faster
removal rates and increased drill bit life regardless of size. With only minor design
changes, rolling hammer mechanism models can be built with stroke magnitudes and impact
frequencies for a wide range of applications. The unique, smooth rolling curves create
a better, lower vibration and well-shaped impact pulses for drilling holes that is
ergonomically more comfortable. Reduced uncontrolled fracturing of concrete during
drilling is another benefit. The rolling hammer drill mechanism achieves efficiency
and long life, with zero maintenance requirements and low production cost ideal for
industrial, commercial and residential applications.
[0005] 05 Therefore there is provided in accordance with an aspect of the invention, a hammer
drill with rolling contact at the contact surfaces for transmission of axial force
between a drive shaft and wave race. By using 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.
[0006] 06 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 roller bearings, mounted in a stationary
roller hub as part of the drive assembly, push the wave shaft 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 element and the wave shaft are between 0 and 90 degrees to the
tool axis. This offset makes the shearing component of the reaction force to rotate
the roller bearings inside their cavities in the roller hub, and its axial component
makes the wave shaft climb over the rotating bearing elements. The rotating bearing
elements are prevented from axial motion in relation to the roller hub, but are allowed
to rotate freely within the roller hub's cavities.
[0007] 07 These and other aspects of the invention are described in the detailed description
of the invention and claimed in the claims that follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] 08 Preferred embodiments of the invention are described, 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 of the rolling hammer drill according to the invention;
Fig. 2 is a three quarter detailed view of the roller hub assembly;
Fig. 3 is a three quarter detailed view of the wave race;
Fig. 4a is a three quarter, detail view of a portion of the wave race engaging with
the roller hub assembly;
Fig. 4b is a detailed view of a roller bearing engaged with the wave race, showing
the interaction of the lubrication film with the roller bearing and wave race;
Fig. 5a is a diagram of one revolution of the rolling hammer drill mechanism; and
Fig. 5b is an illustration of the impact frequency of the rolling hammer drill mechanism.
DETAILED DESCRIPTION OF THE DRAWINGS
[0009] 09 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.
[0010] 10 Referring to Figure 1, there is shown a roller hammer drill adaptor, 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 driver assembly 14 may be formed as an integral part
of a power tool.
[0011] 11 The driver assembly 14 includes a drive shaft 18 with one end having a hexagonal
shape in cross-section for connection into a chuck (not shown) of a conventional power
tool. At the other end of the drive shaft 18 there is a pocket with three equally
spaced roller slide cavities 43 that accept three torque transmitting rollers 45.
Torque transmitting rollers 45 engage with roller slide grooves 43, not shown in Figure
1, but shown in Figure 3a and 3c, rotationally fixing wave race 42 to drive shaft
18. The middle section of the drive shaft 18 is round in section and fits within a
bearing housing 22 that supports the drive shaft 18 within the housing 12 for rotation
relative to the housing 12. Bearing housing 22 is held in place on drive shaft 18
by shoulder 20, and may be for example use ball bearings.
[0012] 12 Housing 12 is cylindrically shaped and has a round threaded opening for roller
hub assembly 32 to be threaded into. A snap ring 34 engages a groove 36 on the drive
shaft 18 to secure the roller hub assembly 32 in place and fixed axially in relation
to the drive shaft 18, while the roller hub assembly 32 is fixed rotationally in relation
to the housing 12.
[0013] 13 The roller hub assembly 32 fits into the opening of the bearing housing and has
twelve circularly distributed cavities for position twelve roller bearings 38 as shown
in Fig. 2. Roller hub assembly 32 also has an opening for fitting bearing housing
22.
[0014] 14 As shown in Figs. 3a and 3b, the hammer assembly 16 has a face shaped to form
a wave race 42. The matching cavities 43 of the hammer assembly 16 and rollers 45
of the drive shaft 18 permit the hammer assembly 16 and drive shaft 18 to rotate together
while allowing relative axial movement between them. The working end 50 of hammer
assembly 16 is threaded with 1/2-20 UN thread.
[0015] 15 As shown in Fig. 2, roller hub assembly 32 has twelve circularly distributed cavities
for position twelve rollers 38. Housing 12 is supported on hammer assembly 16 with
needle bearings 54 that permit relative rotational movement of housing 12 in relation
to hammer assembly 16. The rollers 38 are held by retaining ring 40 in the roller
hub assembly 32.
[0016] 16 Drive shaft 18 receives torque from a source (portable drill or electric motor)
and transfers torque to hammer assembly 16 through the rollers 45. Roller hub assembly
32 stays steady in relation to the housing 12 due to the threaded connection of the
roller hub assembly 32 to housing 12. Rollers 38 are free to rotate in the cavities
in the roller hub assembly 32. Roller hub assembly 32 is held against axial movement
on the drive shaft 18 by snap ring 34.
[0017] 17 When the shaft 18 is rotated, hammer assembly 16 rotates with it. The housing
12 is held steady manually, which by virtue of the threaded connection of bearing
housing 32 in the housing 12, holds the bearing housing 32 against rotation. The rollers
38 then rotate in relation to the wave race 42. With axial compression on the drive
shaft 18 and hammer assembly 16, the waves on wave race 42 are initially located in
gaps between rollers 38. As the wave race 42 rotates, the rollers 38 ride up and down
on the waves of the wave race 42, causing axial movement of the hammer assembly 16
in relation to the drive shaft 18. The axial displacement is a function of the roller
size and wave race wave amplitude.
[0018] 18 Lubrication between wave race 42 and drive shaft 18 is provided through cavity
80 in the interior of the hammer assembly 16 which may be supplied with lubricant
through hole 82. Hole 82, shown in Figure 3b, is drilled in wave race 42 perpendicularly
to the centre axis of hammer assembly 16. Hole 82 leads out to oil reservoir 84. Reciprocating
action of the hammer assembly 16 in relation to the shaft 18 causes a vacuum effect
that sucks lubricant from reservoir 84 through opening 82 into cavity 80 and thence
along shaft 18 to the wave race 42 and bearings 38.
[0019] 19 Referring to Figure 3a, a three quarter view of the hammer assembly 16 is shown,
showing fluted raceway 41 forming the face of the wave race 42. Fluted raceway 41
is also seen in Figure 3b. Fluted raceway 41 may comprise twelve equal sinusoidal
wave cycles in 360° with an amplitude of 0.120".
[0020] 20 Referring to Figure 4a, the rolling hammer mechanism is shown in detail with parts
of the hammer assembly 16 cut away for clarity. The twelve rollers 38 are mounted
as independent journals in the stationary roller hub assembly 32, with the rotating
wave race 42 creating a hammer drill action. A consistent lubrication film is maintained
within each roller cavity through mating support geometry with continual and uninterrupted
roller rotation.
[0021] 21 Referring to Figure 4b, wave race 42 produces the rotation shown. The result is
a mechanism that has one side of each roller in true rolling contact with the wave
race, while the other side of the roller is supported by the consistent hydrodynamic
lubrication film of a journal bearing support. Force from the wave race is shown at
W. The direction of roller 38 rotation is shown at N. When a journal bearing begins
rotating, there is very little lubricant between the journal and pocket at the contact
point, h0, and rubber occurs. Therefore, much friction needs to be overcome when starting
a hydrodynamic journal bearing. When the bearing has reached sufficient speed, the
lubricant begins to wedge into the contact area, shown as the heavy black line on
the wave race and roller hub assembly. The rollers 38 of the stationary roller hub
assembly 32 are not completely surrounded by the journal of the assembly 32. The broken
lubrication film is totally restored by the wave race 42 which has partial arcs very
similar to the missing portion of the journal. Hydrodynamic lift is attained and maintained
in a continuous film of lubricant. Thus the rolling hammer drill mechanism is largely
maintenance free.
[0022] 22 The use of roller bearing engagement is to reduce friction, which generates heat
and results in loss of energy. A formula for calculating energy generated by friction
is as follows: E = K x F x A, where F = the acting force, A = the area of contact,
K = the friction coefficient and E = energy. As can be seen from the given equation,
all of the given components must be minimized to achieve the minimum energy. Acting
force is a result of pressure applied by the operator through the tool on the drilling
surface and cannot be minimized. Friction coefficient is a function of materials,
surface grade and action character (dragging or rolling). In the case of ball bearing
or roller bearing engagement, the friction coefficient is minimized because:
a) the rollers have a smoother surface than the teeth in tooth and tooth engagement;
and
b) roller bearing engagement provides rolling action as opposed to dragging in tooth
and tooth engagement.
The friction coefficient is significantly lower with roller bearing engagement than
it is with tooth and tooth engagement.
[0023] 23 Referring to Figure 5a, an illustration of one revolution of the rolling hammer
mechanism, using twelve rollers, is shown. Figure 5b is a detailed illustration of
the shape of an impact pulse of the rolling hammer mechanism which occurs at each
point where a roller engages a wave in the wave race. In Figure 5b:
A is the smooth curve at the start of the impact;
B is the smooth transition to peak amplitude;
C is the amplitude maintained to that point, followed by smooth transition to the
next cycle;
D is the smooth completion of the cycle; and
E shows that the amplitude and shape of the pulse will depend on the number of rollers
used, and the shape of the wave race. A wide variety of designs for different applications
is thus possible.
Smooth impact curves throughout the cycle results in faster drilling, improved hole
shapes, reduced operator fatigue and long life of drill bits.
[0024] 24 A person skilled in the art could make immaterial modifications to the invention
described in this patent document without departing from the essence of the invention.
1. A roller hammer, comprising:
a housing;
a drive shaft supported by bearings within the housing for rotation relative to the
housing and the drive shaft having an axis;
a set of rotating bearing elements supported within the housing and fixed in motion
relative to the housing, the rotating bearing elements being distributed in a plane
perpendicular to the axis of the drive shaft;
a hammer assembly incorporating a wave race, the hammer assembly being supported within
the housing for axial and rotational movement relative to the housing, the drive shaft
being connected to the hammer assembly to drive the hammer assembly while allowing
axial movement between the drive shaft and hammer assembly; and
the set of rotating bearing elements and the wave race facing each other within the
housing and engaging each other to impart a hammer action on the hammer assembly as
the drive shaft and hammer assembly rotate with each other in the housing under axial
load.
2. The roller hammer of claim 1 in which the rotating bearing elements are roller bearings.
3. The roller hammer of claim 1 in which the wave race has a bearing surface that follows
a sinusoidal contour.
4. The roller hammer of claim 1 in which the wave race has a smoothly undulating bearing
surface.
5. The roller hammer of claim 4 in which the smoothly undulating bearing surface comprises
equally spaced peaks and troughs.
6. The roller hammer of claim 1 in which axial forces are communicated from the drive
shaft to the wave race only through contact between the rotating bearing elements
and the wave race.
7. The roller hammer of claim 1 in which the drive shaft is the drive shaft of a power
tool.