Note: Descriptions are shown in the official language in which they were submitted.
CA 02475001 2004-07-08
ROLLING HAMMER DRILL
BACKGROUND OF THE INVENTION
O1 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
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.
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.
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
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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.
OS 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.
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.
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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
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. Sa is a diagram of one revolution of the rolling hammer drill mechanism;
and
Fig. Sb is an illustration of the impact frequency of the rolling hammer drill
mechanism.
DETAILED DESCRIPTION OF THE DRAWINGS
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.
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.
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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.
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.
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.
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.
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.
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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.
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.
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.
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".
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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.
21 Refernng to Figure 4b, wave race 42 produces the rotation shown. T'he
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 filin 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.
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
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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.
23 Referring to Figure Sa, an illustration of one revolution of the rolling
hammer
mechanism, using twelve rollers, is shown. Figure Sb 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 Sb:
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.
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.
