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.

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.

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.