U.S. patent number 3,568,780 [Application Number 04/843,669] was granted by the patent office on 1971-03-09 for free-piston-type percussion device with air pump.
This patent grant is currently assigned to Kaiichi Kikai Seisakusho Co., Ltd.. Invention is credited to Susumu Matsuo.
United States Patent |
3,568,780 |
Matsuo |
March 9, 1971 |
FREE-PISTON-TYPE PERCUSSION DEVICE WITH AIR PUMP
Abstract
A tool cylinder is provided in parallel with an air pump
cylinder. Each cylinder is separated by its respective piston into
an upper and a lower chamber each of which communicates
pneumatically through an upper and a lower opening with its
counterpart in the other cylinder. The openings are open and closed
by the relative position of the pistons. A constant volume of air
is sealed tightly in the chambers. When the pump piston is actuated
upwardly by an external rotary power source, highly compressed air
is supplied on the head of the free-piston while a negative air
pressure is produced in the lower chambers. The combination of this
high pressure above and low pressure below causes the free-piston
to be forced abruptly downward. At the lower dead point of the
free-piston it hits a chisel and opens an upper portion of the
lower opening thus allowing the high pressure in the upper chamber
of the tool cylinder to escape to the lower chamber of the pump
cylinder. A lower buffer or cushion chamber of relatively large
volume is formed in the tool cylinder and it absorbs a part of the
downward energy of the free-piston. The free-piston is pushed back
by this cushion chamber to a position where a lower portion of the
lower opening is opened. At this time, the pump piston is moving
downward and thus provides a positive pressure in the lower chamber
and a negative pressure in the upper chamber. The free-piston is
driven upward by these positive and negative pressures and its own
inertia and closes the upper opening, thereby forming an upper
buffer chamber in the tool cylinder. The upward movement of the
free-piston is absorbed by the upper buffer chamber and the
free-piston then falls by its weight to a position where the upper
opening is opened, to complete the cycle.
Inventors: |
Matsuo; Susumu (Shizuoka-ken,
JA) |
Assignee: |
Kaiichi Kikai Seisakusho Co.,
Ltd. (Osaka, JA)
|
Family
ID: |
11994334 |
Appl.
No.: |
04/843,669 |
Filed: |
July 22, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Mar 15, 1969 [JA] |
|
|
44/19256 |
|
Current U.S.
Class: |
173/201;
60/537 |
Current CPC
Class: |
B25D
11/125 (20130101); F02F 7/006 (20130101) |
Current International
Class: |
B25D
11/00 (20060101); B25D 11/12 (20060101); F02F
7/00 (20060101); B25d 011/02 (); B25d 011/12 () |
Field of
Search: |
;173/13,116
;60/62.6 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Purser; Ernest R.
Claims
I claim:
1. A free-piston type percussion device with air pump,
comprising:
an air pump cylinder which slidably supports a piston therein, said
piston being driven reciprocally up and down in a regular manner by
a rotating power source of constant velocity;
a tool cylinder housing the said free-piston which on its downward
work stroke supplies an impart force to a chisel;
means for combining said cylinders adjacent to and in parallel with
each other;
upper and lower opening means for connecting the internal cavities
of said cylinders near their tops and bottoms;
an upper buffer means of small volume provided in the upper portion
of said tool cylinder by positioning the upper face of said upper
opening slightly below the head cover of said tool cylinder, said
buffer means preventing said free-piston from striking said
cylinder head cover at its upper dead point; and
a lower buffer means of large volume provided at the lower portion
of said tool cylinder by positioning the lower face of said lower
opening far above the lower end of said tool cylinder, said lower
buffer rebounding said free-piston after it strikes said chisel and
reaches its lower dead point to a position sufficient to open at
least a lower portion of said lower opening, said lower opening and
said two pistons being in such relationship with each other that
said free-piston opens an upper portion of said lower opening at
its lower dead point and allows the pressure in said upper chamber
of said tool cylinder which forced said free-piston on its downward
stroke to escape to said lower chamber of said pump cylinder and in
such a relationship with each other that said pump-piston opens an
upper portion of said lower opening at its lower dead point and
allows the pressure in said lower chamber of said tool cylinder
which forced said free-piston on its return stroke to escape to
said upper chamber of said pump cylinder, and said opening and said
two pistons being in such a relationship with each other that said
free-piston reaches its upper dead point after it closes said upper
opening and said pump-piston reaches its upper dead point without
closing said upper opening so as to discharge the air compressed in
said upper chamber of said pump cylinder through said upper opening
to said upper chamber of said tool cylinder thereby forcing said
free-piston downward.
Description
BACKGROUND OF THE INVENTION
There have been known air actuated percussion devices employing a
free-piston, for use in crushing rock, and breaking up the surface
of concrete roads and packed gravel roads. Air pressure for such
known devices is generally supplied by means of a hose from a air
compressor located remote therefrom and thus the work must be
performed by dragging the hose over the area to be crushed.
Further, the driving power of such air compressor must be
considerably greater than is necessary for the work done by such
device because of the considerably large efficiency loss due to
thermal and pressure losses in sending the air through a long hose.
To eliminate or minimize these disadvantages, i.e., the thermal
loss and leakage loss, special consideration must be given to the
design of the air compressor. This becomes particularly significant
when the power or air discharge pressure of the compressor is in
excess of 10 kg/cm.sup.2.
Accordingly, an air compressor whose discharge pressure is within a
range of 4 to 8 kg/cm.sup.2 is conventionally used to avoid the
necessity of special considerations in design of the compressor.
However when such a relatively low-power compressor is used, the
output power of the device used in combination with such compressor
is limited to a certain level and in some cases this level is not
sufficient to perform the desired work.
SUMMARY OF THE INVENTION
The present invention relates to a novel, powerful and efficient
percussion device adapted for use in a road crusher or a rock
borer. The device comprises a tool cylinder housing a free-piston
therein and an air pump cylinder provided in parallel with the tool
cylinder and housing a pump-piston therein. These cylinders
communicate with each other through at least a pair of openings
provided one at each end of each cylinder.
The pump-piston of the air pump cylinder is driven reciprocally at
a constant rate by a rotating source of power and the reciprocating
pump-piston acts upon the air sealed within these cylinders as a
power transmitting medium thus alternately setting up two different
conditions in the upper and lower chambers of the tool cylinder:
one being for the work stroke of the free-piston wherein it
transmits impact power to a tool such as chisel with its movement
from one upper dead point to the other lower dead point and the
other being for the return stroke of the free-piston to its
original position.
The primary object of the present invention is to provide a novel
percussion device which essentially eliminates the disadvantages
encountered in the conventional device, and the present invention
eliminates these disadvantages of the prior percussion device which
utilizes a hose, a free-piston driven by compressed air and an air
compressor located remote from the piston cylinder by employing a
pair of parallel pump and tool cylinders provided as a unit and
driving the pump piston directly by a rotating source of power.
Further, according to the present invention, the percussion energy
applied to a tool such as chisel at the end of the work stroke of
the free-piston, i.e., at the lower dead point of the piston, is
remarkably increases by discharging from the upper chamber of the
pump cylinder air which has been highly pressurized by the upward
movement of the pump-piston to the upper chamber of the tool
cylinder whose free-piston is near the upper dead point and is
about to start the work stroke and by simultaneously introducing
the strong negative pressure in the lower chamber of the pump
cylinder to the lower chamber of the tool cylinder, so that the
difference in pressure between the upper and lower chambers of the
tool cylinder is multiplied thereby causing the free-piston to be
abruptly forced downward and thus transmitting extremely intense
force to the chisel. Accordingly, another object of the present
invention is to provide a novel high-power percussion device.
Furthermore, according to the present invention, the power required
by the air pump for the work to be done by the chisel is
considerably lower than that of the conventional device and thus a
device of the same output power can be made considerably more
compact. The pump and tool cylinders of the present invention are
provided in a parallel construction with at least a pair of
openings connecting them, thus minimizing the relatively large
efficiency loss which is unavoidable in the conventional device
using a hose to carry compressed air to the tool cylinder. Another
object of the present invention is to provide a highly efficient
and compact percussion device.
The structural features of the present device wherein the tool and
pump cylinders are combined as a single unit makes it possible to
mount the present percussion device on a truck thereby increasing
the mobility of the device. Further, the work area of the device
can be readily extended by mounting it on a swing arm extending
from the truck or on other suitable installations by shortening the
length of both cylinders.
According to a further feature of the present invention, the upper
chamber of the pump cylinder is adjacent to the upper chamber of
the tool cylinder and compressed air at an increased temperature
due to the adiabatic compression in the upper chamber of the pump
cylinder is fed into the upper chamber of the tool cylinder to
force the free-piston downward. Here it then expands adiabatically
so that the upper chamber of the pump cylinder is cooled by the
expansion of the high-pressure air thus preventing any thermal
accumulation in the chamber. Thus the present device maintains a
relative low temperature even in continuous operation over a
prolonged period of time.
In addition, in the present device, a constant quantity of air is
sealed in the cylinders and reciprocates between these cylinders as
a power transmitting medium, and consequently little mechanical
and/or fluid noise is produced in operation. If a mere drop of
lubrication oil is supplied between each piston and its cylinder
wall every several minutes, it will form fine particles and create
an oil film between them. Since pyrolysis of the oil is effectively
prevented by the low temperature at which the cylinder is
maintained this oil film provides very effective lubrication.
BRIEF EXPLANATION OF THE DRAWING
These and other objects and advantages of the present invention
will become apparent from the description of a preferred embodiment
with reference to the drawings in which:
FIG. 1 is a cross-sectional side view of an embodiment of the
percussion device of the present invention in which the pump-piston
is at its upper dead point;
FIG. 2 is a similar view to FIG. 1 except that the pump-piston is
at its lower dead point;
FIG. 3 is a cross section taken along a line 3-3 in FIG. 1;
FIGS. 4 a, 4 b, 4 c, 4 d, 4 e, 4 f, show schematically the relative
operations of the pump-piston and the free-piston of the present
invention; and
FIG. 5 is a cyclic chart corresponding to FIGS. 4 a to 4 f.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring now to the drawings, particularly, to FIGS. 1 through 3,
cylinder block 1 resembles a figure eight in cross section (FIG. 3)
and it is provided with pump cylinder 12 slidably housing
pump-piston 11 and tool cylinder 22 slidably housing free-piston
21. These cylinders are disposed parallel to each other. Upper end
12 a of pump cylinder 12 is sealed by head cover 13 and upper end
22 a of tool cylinder 22 is sealed by head cover 23. These upper
ends are maintained at substantially the same height. Lower end 22
b of tool cylinder 22 sealed by cover 24 is positioned below lower
end 12b of pump cylinder 12 sealed by crankcase 14. The interiors
of both cylinders 12 and 22 communicate with each other at the
upper and lower portions thereof through upper and lower openings 3
and 4 which are provided in wall portion 2 of the cylinder block 1,
which portion separates the cylinders 12 and 22 from each
other.
Upper face 3 a of upper opening 3 is positioned some what lower
than upper end 22 a of tool cylinder 22 and thus upper air cushion
chamber 25 is formed beneath head cover 23 when the head of
free-piston 21 passes above the upper face 3 a of upper opening
3.
The volume of chamber 25 is very small because the distance between
upper end 22 a of tool cylinder 22 and upper face 3 a of upper
opening 3 is short. On the pump cylinder side the upper face of
opening 3 inclines upwardly to form face 3' as shown in FIG. 1.
Instead of or together with such formation the head of pump-piston
11 may be provided with downwardly inclined head surface 11' as
shown in FIG. 1. Inclined face 3' of opening 3 and/or inclined head
surface 11' ensures the opening 3 is never closed completely even
when pump-piston 11 reaches its upper dead point. The diameter of
upper opening 3 is selected in such a way that the lower ends of
pistons 11 and 21 at their respective upper dead points are always
below lower face 3 b of upper opening 3 (FIG. 1). Further, the
position of lower face 4 b of lower opening 4 corresponds
substantially to lower end 12 b of pump cylinder 12 and therefore
it is positioned far above lower end 22 b of tool cylinder 22. With
this positioning, when the lower end of the free-piston 21
continues downward beyond the position of lower end face 4 b of
lower opening 4, lower air cushion chamber 26 of very large volume
is formed above cover 24 within the tool cylinder. The vertical
width of the lower opening 4 is made larger than that of upper
opening 3 so that, even though there is a large difference in
position between lower end 12b of the pump cylinder and lower end
22 b of the tool cylinder, the heads of both pump-piston 11 and
free-piston 21 at their lower dead points are positioned below
upper face 4 a of lower opening 4 thus opening the top part 4' of
lower opening 4 (FIG. 2). As explained hereinafter, this is a
significant point in that it allows the pistons 11 and 21 to serve
as a slide valve for reversing the positive and negative pressure
conditions in the upper and lower chambers in tool cylinder 21. And
the vertical width of upper opening 3 is made shorter than that of
lower opening 4 because of the necessity of making the area of
upper opening 3 smaller and the area of lower opening 4 larger. Why
this necessity exists will be explained hereinafter.
Crankcase 14 supports crank 15 which is driven by external power
transmitted through end portion 16 projecting from airtight crank
case 14. Crank 15 is rotated at a constant velocity (e.g. at a
given velocity between 100 and 1200 r.p.m.). Thus, crank 15 drives
the pump-piston 11 reciprocally in the conventional manner through
connecting rod 17.
Shocker 27 which is struck by free-piston 21 on its downward work
stroke is mounted slidable in its axial direction on cover 24 which
further has mounted thereupon stay 29 which supports chisel 28
which indirectly through shocker 27 receives the impact force from
free-piston 21.
From the foregoing description, it will readily be understood that
cylinder block 1 which includes the pump cylinder block and the
tool cylinder block can be suitable modified, that the driving
power to rotate crank 15 may be supplied from an internal
combustion engine, a fluid pressure motor or an electric motor, and
that shocker 27 may be done away with so that free-piston 21
directly strikes the shank of chisel 28. Although so far in this
specification the lower opening 4 has been described as being
divided into two parts, these of course may be combined into one
opening if there is no adverse effect on the strength of wall
portion 2 of cylinder block 1.
When crank 15 is rotated, pump-piston 11 regularly and alternately
performs first and upward stroke wherein the air in the upper
chamber of pump cylinder 12 is compressed and a negative pressure
is created in the lower chamber, and next a downward stroke wherein
the air in the lower chamber is compressed and a negative pressure
is created in the upper chamber. Thus in tool cylinder 22 which
communicates with pump cylinder 12 through the upper and lower
openings 3 and 4, the pressure is respectively positive and
negative in the upper and lower chambers during the upward stroke
of pump-piston 11 and respectively negative and positive during the
downward stroke. Thus to simplify, the free-piston is forced to
move downward when the pressure is positive in the upper chamber
and negative in the lower and completes its work stroke by hitting
shocker 27. Subsequently, it moves upward on its return stroke when
the pressure become negative in the upper chamber and positive in
the lower chamber. As will be already understood, the terms "upper
chamber" and "lower chamber" refer to the spaces in the cylinder
above and below the piston which separates them in such a manner
that when the volume one of them is increased by the movement of
the piston, the other is decreased correspondingly. In the
illustrated embodiment, the chambers of the cylinders 12 and 22 are
separated respectively by the pistons 11 and 21.
Accordingly, when pump-piston 11 at its upper dead point, it is
clear that free-piston 21 has completed its work stroke or is near
the end of the stroke. The cycles of the pistons 11 and 21
subsequently to the above situation are explained with reference to
FIGS. 4 a to 4 f. Free-piston 21 compresses the large volume of air
in air cushion chamber 26 as it travels downward reaching its lower
dead point. At this point the top of free-piston 21 has moved below
top part 4' of lower opening 4 connecting the upper chamber of tool
cylinder 22 and the lower chamber of pump cylinder 11 and thereby
allowing the positive pressure in the upper chamber of the tool
cylinder which performed the work stroke to escape to the lower
chamber of the pump cylinder which is under negative pressure FIG.
4 b.
However, because of the effect of the compressed air in lower air
cushion chamber 26, the free-piston is at the next moment started
on its return stroke. The reaction of chisel 28 against the
percussion force transmitted through shocker 27 aids the air
cushion in sending free-piston 21 on its return stroke. Although
lower opening 4 is for an instant closed by free-piston 21 during
its return stoke, it is soon again opened so that the lower chamber
of the tool cylinder and the lower chamber of the pump cylinder are
connected.
The pump-piston travels downward compressing the air released from
the upper chamber of the tool cylinder into the lower chamber of
the pump cylinder. The compressed air in the lower chamber of the
pump cylinder exerts through the large lower opening 4 a force
which tends to raise the free-piston.
At the same time, a negative pressure is produced in the upper
chamber of the pump cylinder and through the upper opening 3 this
pressure acts to suck the free-piston into the upper chamber of the
tool cylinder. FIG. 4 b shows the pump-piston on the downward
stroke from the upper dead point at the position where the driving
means has advanced 60.degree.. FIG. 4 c shows the situation after
another 60.degree. from the preceding condition. At this time,
free-piston 21 is on its return stroke being acted upon by the low
positive pressure below and the negative pressure above.
When pump-piston 11 is at its lower dead point, the top part 4' of
lower opening 4 is opened and the upper chamber of the pump
cylinder communicates with the lower chamber of the tool cylinder
and the air in the lower chamber of the tool cylinder which has
been acting to raise free-piston 21 escapes to the upper chamber of
the pump cylinder which is under negative pressure (FIG. 4 d).
By the time the pump-piston 11 reaches it lower dead point, the
free-piston has generally already closed the upper opening 3 and
sealed upper buffer chamber 25 of the tool cylinder with its head.
Accordingly, the free-piston compresses the air in upper buffer
chamber 25 as it thereafter continues on its return stroke moving
upward to its upper dead point by its own inertia. Hence the
velocity of the free-piston is lowered considerably.
When, after reaching the lower dead point, pump-piston 11 starts on
its upward stroke, lower opening 4 is closed for an instant and
immediately reopened so that the lower chamber of the pump cylinder
communicates with the lower chamber of the tool cylinder. The
negative pressure produced in the lower chamber of the tool
cylinder and even tends to brake the return stroke of the
free-piston moving under its own inertia (FIG. 4 e).
The free-piston compresses the air in the buffer chamber 25 and
reaches its upper dead point. Since buffer chamber 25 has less
volume than lower buffer chamber 26, the compressed air in chamber
25 merely prevents the impingement of the piston head onto head
cover 23 and does not have sufficient cushioning effect to force
the free-piston downward. And the ever increasing pressure in the
upper chamber of the pump cylinder acts as a side pressure upon the
free-piston through upper opening 3 and assists the free-piston in
its tendency to remain near the upper dead point at its residual
moment (FIG. 4f).
When the pump-piston reaches the upper dead point and the air in
the upper chamber of the pump cylinder is compressed to the maximum
degree, the free-piston switches to the work stroke and upper
opening 3 is opened by the downward movement of the piston under
its own weight. For this reason, the highly compressed air in the
upper chamber of the pump cylinder is discharged through upper
opening 3 to the head of the free-piston and the discharged air
expands abruptly in the upper chamber of the tool cylinder. At this
time, since a negative pressure in the lower chamber of the
pump-cylinder is supplied through lower press opening 4 into the
lower chamber of the tool cylinder, the free-piston 1 hits shocker
27 intensely through its fast and abrupt work stroke toward its
lower dead point (FIG. 4 a ).
Thus, in the present invention which uses a certain predetermined
volume of air sealed in the pump and tool cylinders as a force
transmitting medium, the pump-piston driven reciprocally by a
constant rotating power source causes the free-piston to perform
intermittent and nonuniform reciprocal strokes. The relationship
between the two cylinders can be represented diagrammatically as in
FIG. 5. When pump-piston 11 is at position A, B, C,..... F, A' or
B' the position of free-piston 21 in cylinder 22 becomes
respectively point, a, b, c, ......., f, a' or b'.
Although the present invention is described with reference to the
preferred embodiment hereinbefore described, it should be
appreciated that the illustrated embodiment can modified and a
percussion device capable of producing an intense percussion force
and workable with minimized noise without any leakage of the medium
air may be obtained by designing the pump cylinder in such a way
that its diameter is larger than that of the tool cylinder and that
the air volume to be exhausted to the tool cylinder by the action
of the pump-piston is made larger by 10-- 30 percent than that of
the free-piston so that the free-piston is actuated with a
sufficient volume of excess air, by determining the rotation of the
crank of the air pump according to the mass of the free-piston, the
length of the stroke thereof and other suitable factors, and/or by
selecting the areas of the upper and/or lower openings, the
positions thereof and the degree of opening thereof in relation to
the movements of the pistons, in connection with the above various
factors.
* * * * *