CA1118689A

CA1118689A - Internal combustion engine driven drilling and chipping hammer

Info

Publication number: CA1118689A
Application number: CA000333220A
Authority: CA
Inventors: Peter Gloor
Original assignee: Hilti AG
Current assignee: Hilti AG
Priority date: 1978-08-14
Filing date: 1979-08-03
Publication date: 1982-02-23
Also published as: FI71818B; PL117394B1; GB2027629A; NO150027C; DK149510B; IE48460B1; PL217730A1; NO792624L; IT7923950A0; DK149510C; DE2835570C2; CS208125B2; SE7906633L; IE791469L; MX147430A; SE436989B; NL7904806A; GB2027629B; FI71818C; JPS5531590A

Abstract

ABSTRACT OF THE DISCLOSURE
In a drilling and chipping hammer, an internal combustion engine drives a crankshaft which, in turn, drives a percussion piston. The hammer includes a housing divided into two separate spaces, one communicating with the percussion mechanism and the other communicating with the internal combustion engine. Air or a fuel-air mixture is supplied through a valve in the housing into the percussion mechanism space. As the percussion piston is driven during one part of its reciprocating movement it draws the air or fuel-air mixture into the percussion mechanism space.
During the other part of its reciprocating movement, the percussion piston forces the air or fuel-air mixture from the space through a flow passageway into the combustion space in the engine.

Description

111~t;8~3 The present invention is directed to a drilling and chipping hammer with a percussion mechanism and an internal combustion engine drive with the engine connected to a crankshaft with a crank at one end which drives the percussion mechanism in a reciprocating motion over a connecting rod.
Drilling and chipping hammers of this type are used primarily in heavy drilling and breaking operations.
With an internal combustion engine serving as the drive for the hammer, a so-called two-cycle engine is usually employed.
On a comparitive output basis, such an engine has the advantage of a simple assembly over a four-cycle engine and, further, is of a lower weight. As a result, two-cycle engines are standard with manually operated drilling and chipping hammers for weight as well as cost reasons.
Following each power stroke, the combustion chamber in two-cycle engine must be scavenged with a fuel-air mixture so that any exhaust gases within the chamber are displaced by the mixture and a new combustible charge is provided. To maintain a flow of the fuel-air mixture into the combustion chamber, a pump is required. With practi-cally all small two-cycle engines, the engine crankcase is used as a scavenger pump. Such an arrangement, however, causes a considerable drawback. The crankshaft and connecting rod bearings as well as the cylinder walls must be kept sufficiently lubricated. Without taking any countermeasures, the scavenging of the lubricating oil by the fuel-air mixture would destroy the tool within a short period of time. To avoid this problem in twb-cycle engines the fuel~air mixture usually includes a mixture of gasoline ~' ~

1~18689 and oil~ The gasoline functions as the energy source for the internal combustion engine.
Since oil is present within the combustion cham~er, it is only incompletely burned and ends up as a bothersome blue exhaust smoke.
In most cases the efficiency of a conventional two-cycle engine is lower than that of a comparable four-cycle engine. The lower efficiency can be traced mostly to scavenger losses occurring in the combustion chamber. With large size, stationary or vehicular-mounted ~ngines, a considerable input is used in scavenging the combustion chamber. In such units, turboblowers, rotary disc blowers or even reciprocating pumps are used. In portable units, such as drilling and chipping hammers, such devices cannot be used because of their weight.
The primary object of the present invention is to provide a drilling and chipping hammer using an internal combustion engine as its power source where an effective scavenging action is afforded which develops a high efficiency while maintaining an optimal unit weight for the hammer.
In accordance with the present invention, the hammer housing is divided into a percussion mechanism space and an engine space with the two spaces separated from one another. An inlet valve in the housing admits air or a fuel air mixture into the percussion mechanism space and a flow passageway conducts the air or fuel-air mixture into the combustion chamber in the engine without passing through the engine space.
With the percussion mechanism space separated ~ . _ , . . .

111868'~

from the rest of the hammer mechanism, it can be used as a scavenyer pump Eor the internal combustion engine. Since for any given two-cycle engine the percussion stroke volume about matches that of the engine, the percussion mechanism space is most suitable as an engine scavenger pump.
Genera~ly, the crankshaft bearing is located in the engine space and the percussion piston is usually lubricated by the percussion mechanism. The connecting rod bearings can be equipped with sealed lubricated bearings. Consequently, no lubrication of the percussion mechanism space is required.
Since the engine space is not contacted by the fuel-air mixture (in the case of a gasoline engine) or with drawn-in air (in the case of a fuel injection engine), the lubrication of the crankshaft bearings, the connecting rod bearings and the other working surfaces associated with the engine can be accomplished in an effective manner using a splash or oil mist lubrication method. Accordingly, the fuel-air mixture does not have to provide any special lubricating function.
Therefore, it is possible to operate a drilling and chipping hammer embodying the present invention without adding oil into the two-cycle fuel-air mixture and such a factor has a favorable effect on the operating costs and the waste gases.
Known two-cycle engines have another drawback.
During the scavenging operation, part of the fuel-air mixture is released along with the scavenged losses from the combustion chamber through the exhaust muffler into the ambient atmosphere. With two-cycle engines this effect usually cannot be avoided. Furthermore, a high fuel consumption results because a certain amount of the fuel is lost to the combustion process and a high percentage of ~1~8~89 unburned and mostly toxic gases escape with the exhaust.
In so~called injectlon engines, this problem is avoided by using pure air for the scavenging action. During operation, as soon as the engine piston covers the exhaust openings, fuel is injected by means of a high-pressure nozzle. Such operation results in three advantages: (1) because of the delayed fuel injection a measurable boost is gained in the engine performance, (2) fuel consumption is appreciably reduced, and (3) the quality of the waste gases is substantially improved. The scavenging action according to the invention utilizing the percussion mechanism space is suitable for both gasoline and injection engines.
An inlet valve is provided through which a fuel-air mixture is drawn in through a known carburetor or pure air is drawn in through an air filter. Though this system is particularly suitable for a two-cycle engine, it can also be used for a four-cycle engine to produce a so-called charge for increasing performance.
The present i~vention provides a particularly simple arrangement and, in comparison with known combustion engine driven drilling and chipping hammers, it requires only an inlet valve and piping to connect the outlet from the percussion mechanism space with the inlet openings into the combustion chamber. As a result, there is practically no increase in weight of the drilling and chipping hammer.
To simplify the arrangement of the hammer, the end face of the percussion piston joined to the connecting rod acts as a movable wall and seals the percussion mechanism space from other parts of the hammer. Therefore, particularly with a pneumatic percussion mechanism, no ~, additional sealing action is required because the percus-sion piston reciprocating in a cylinder is sealed against the air cushion located between the piston forming a portion of the percussion mechanism space and the piston effecting the actual percussion action. The compression of the air or fuel-air mixture drawn into the percussion mechanism space can be optimized by establishing, indepen-dently from the engine drive, a crank stroke and dead space within specified limits. In comparison with known units, where the end of the crankshaft with its drive crank extends into the percussion mechanism space, new possibi-lities open up since this space can be separated from the reminder of the hammer components. In a conventional two-cycle engine, the fuel-air mixture is drawn into the engine crankcase and is precompressed therein during the expansion phase in the combustion chamber. Just before reaching the bottom dead centre, the inlet openings are uncovered by the piston and the precompressed mixture is free to flow into the combustion chamber. As the crankshaft continues to rotate, howev~r, the pressure within the engine crankcase drops so that the flow into the combustion chamber is reduced. Accordingly, only an incomplete scavenging of the combustion chamber is possible. If, however, the scavenging pressure is increased by a reduction in the space, there is the danger that too much of the fuel-air mixture escapes unburned through the exhaust openings as scavenging losses with an increase in fuel consumption. Accordingly, for adjusting the pressure to optimize the scavenging process, it is advantageous if the connection from the crank to the percussion mechanism is angularly offset relative to the .

1~18689 connection from the engine to the crankshaft so that the percussion piston lags behind the engine piston in an angular range of 10 to 60. The effect of such an arrange-ment is that as the engine piston moves from the dead centre position a sufficient scavenging pressure is still present until the engine piston again covers the inlet or outlet openings from the combustion chamber. Because the percussion mechanism is coupled with the crankshaft, -the angular offset relationship remains constant.
From practical experience, the angular offset has been established as 40. Accordingly, with given inlet and exhaust opening positions, the effect of a sufficient scavenging pressure lasts until the closure of such openings, so that a back blow of the scavenging air is prevented and an improved scavenging is afforded as compared with conven-tional crankcase scavenging. On the other hand, the pres-sure gradient between scavenging and combustion chamber pressures effective upon the opening of the inlet openings is so minimal that a flow can develop into the combustion chamber with the fresh inflowing mixture displacing the exhaust gases mostly through the exhaust openings.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure.
For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.
IN THE DRAWING:

Figure 1 is a side view, partly in section, of a drilling and chipping hammer embodying the present inven-tion;
Figure 2 is a cross-sectional view taken along the line A-A in Figure 1 showing the upper dead-centre position of the percussion piston in the percussion mechan-ism as compared to the engine piston; and Figure 3 is a view similar to ~'igure 2, however, showing the percussion piston in the bottom dead-centre position.
In Figure 1 a drilling and chipping hammer is I illustrated having a housing 1. A handle 2 is attached to ¦ the right or rear end of the housing 1. At its front or left-hand end, the housing 1 supports a tool holder 3. A
crankshaft 4 of an internal combustion engine is rotatably supported within the housing 1. A connecting rod 5 is rotatably mounted on a crank web 4a of the crankshaft 4.
The connecting rod at its end spaced from the crank web 4a is secured to a piston 6 of the internal combustion engine.
The piston 6 is displaceably mounted within a cylinder lc mounted on the housing. As viewed in Figure 1, a crank 7 is attached to the upper end of the crankshaft 4 by a thread 4b. A connecting rod 8 is mounted at one end on a crank pin 7a secured to the crank 7. Connecting rod 8 forms a part of the percussion mechanism a~d is connected to a piston 9 such as is used in a pneumatic percussion mechanism. Piston 9 is reciprocally mounted in a sleeve 10. Located in the housing 1, adjacent the crank 7, is an inlet valve 11. Inlet valve 11 includes a ball lla biased against a valve seat llc by a spring llb. If the piston 9 1118~89 moves toward the tool holder 3, either air or a fuel-air mixtu-re can be drawn into a space la through the inlet valve 11. Crank 7 and connecting rod 8 are located within the space la. The interior of the housing is constructed so that a seal 12 separates the space la from the remainder of the interior of the housing. Space la has an outlet opening ld. A pipeline 13 extends from the outlet opening ld to an inlet opening le in the cylinder lc opening into the combustion chamber lb in the engine. When piston 9 reverses direction and moves toward the handle 2, the end face of the piston 9 forms a movable wall in the space la and the volume within the space is reduced and the air or fuel-air mixture drawn into it is ejected into the pipeline 13. When the piston 6 moves rearwardly toward the handle and uncovers the inlet opening le into the combustion chamber, then the air or fuel-air mixture in the pipeline 13 can flow into the combustion chamber lb. Therefore, the waste gases resulting from ignition in the combustion chamber lb are displaced through an exhaust opening lf.
Technically, this operation is known as scavenging. With an internal combustion engine, a fuel-air mixture is used in the scavenging operation. The drawback in such a scavenging operation is that a part of the fuel-air mixture can also escape through the exhaust opening lf causing a reduction in the efficiency of the engine. Where so-called fuel injection engines are used, however, the scavenging action is effected with air alone. Fuel is injected into the combustion chamber lb through a nozzle only after both the inlet opening le and the exhaust opening lf are closed.
Such an arrangement has a positive effect on the engine ~18689 efficiellcy. A flywileel 14 is positioned on the lower end of the crankshaft 4 as viewed in Figure 1. Such a flywheel 14 is standard on internal combustion engines. The fly-wheel 14 serves as a compensator between the internal combustion engine power output and the engine power input during the compression cycle and the percussion mechanism operation. Further, the flywheel is used to generate ignition voltage and also as a fan wheel for a cooling air flow drawn in through a screen 15 in the housing 1 and conveyed over the cylinder lc of the engine.
In Figure 2, the sectional view taken along the line A-A in Figure 1, the drive and driven components of the hammer are illustrated. The percussion mechanism piston 9, shown in full line, is located in its upper dead-centre position. The engine piston 6, however, shown in dashed lines, hàs already passed its upper dead-centre position. Accordingly, the crank pin 7a connected to the percussion mechanism is offset relative to the internal combustion engine crank web 4a by an angle 0~ so that the percussion mechanism lags the internal combustion engine by the angle OC. As the crank 7 continues to rotate, the volume of space la is reduced as the end face of the piston 9 moves toward the right-hand end of the housing and the air or fuel-air mixture previously drawn into the space is forced through the outlet opening ld into the pipeline 13.
In comparison with conventional two-cycle engines in which the engine crank housing serves as a scavenger pump, the advantage of the lagging action of the percussion mechanism relative to the engine is that, during the entire scavenging process, the scavenging pressure exceeds combustion engine 111~3689 pressure so that back-flow is prevented.
In Figure 3, the same components are illustrated as in Figure 2, however the percussion mechanism piston 9 is in its bottom dead-centre position. Accordingly, engine piston 6 has already moved past its bottom dead-centre position. In this arrangement, the fuel-air mixture which has entered the combustion chamber lb through the pipeline 13 from space la is compressed. At this position, the percussion mechanism output consumption is low so that the stored energy of the flywheel can be used fully for compressing the fuel-air mixture in the combustion chamber lb. In this way, the phased or angular displacement between the percussion mechanism and the engine affords an equally positive effect.

As stated above the angle 0~ may be between 10 and 60, but in practice the preferred range is in the region of 40.

Having described what is believed to be the best mode by which the invention may be performed, it will be seen that the invention may be particularly defined as follows:
A drilling and chipping hammer comprising a housing, a percussion mechanism located within said housing, an internal combustion engine mounted on said housing and including an engine piston, an engine crankshaft located in said housing, a first connecting rod connected at one end to said engine piston and at the opposite end to said crankshaft, a crank connected to said crankshaft at a position spaced from said first connecting rod, said percussion mechanism including a reciprocal percussion ~ - 10 -lil8689 piston, a second connecting rod located within said housing and attached to said crank and to said percussion piston for transmitting the reciprocating action to said percussion piston from said crankshaft for effecting a percussion application stroke and a return stroke, wherein the improve-ment comprises means Eor dividing the interior of said housing into a percussion mechanism space containing said crank and said second connecting rod and an engine space containing said first connecting rod with said percussion mechanism space sealed from said engine space and said crankshaft extending from said engine space into said percussion space, said engine including a combustion chamber separated from said engine space by said engine piston, an inlet valve mounted in said housing for selectively supplying one of air and a fuel-air mixture into said percussion mechanism space during the percus-sion application stroke of said percussion piston, and means forming a flow passageway for conveying the one of air and fuel-air mixture from said percussion mechanism space to said combustion chamber during the return stroke of said percussion piston.
The invention further comprises such a drilling and chipping hammer wherein said second connecting rod being connected to said crank angularly offset relative to the connection of said first connecting rod to said crank-shaft so that said engine piston leads said percussion piston by an angle in the range of 10 to 60 and preferably in the region of about 40.

While specific embodiments of the invention have been shown and described in detail to illustrate the appli-cation of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from s~ch principles.

~,''

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A drilling and chipping hammer comprising a housing, a percussion mechanism located within said housing, an internal combustion engine mounted on said housing and including an engine piston, an engine crankshaft located in said housing, a first connecting rod connected at one end to said engine piston and at the opposite end to said crank-shaft, a crank connected to said crankshaft at a position spaced from said first connecting rod, said percussion mechanism including a reciprocal percussion piston, a second connecting rod located within said housing and attached to said crank and to said percussion piston for transmitting the reciprocating action to said percussion piston from said crankshaft for effecting a percussion application stroke and a return stroke, wherein the improvement comprises means for dividing the interior of said housing into a percussion mechanism space containing said crank and said second connecting rod and an engine space containing said first connecting rod with said percussion mechanism space sealed from said engine space and said crankshaft extending from said engine space into said percussion space, said engine including a combustion chamber separated from said engine space by said engine piston, an inlet valve mounted in said housing for selectively supplying one of air and a fuel-air mixture into said percussion mechanism space during the percussion application stroke of said percussion piston, and means forming a flow passageway for conveying the one of air and fuel-air mixture from said percussion mechanism space to said combustion chamber during the return stroke of said percussion piston.

2. A drilling and chipping hammer, as set forth in Claim 1, wherein said second connecting rod is connected to an end face of said percussion piston and said end face forming a displaceable wall in said percussion mechanism space.

3. A drilling and chipping hammer, as set forth in Claim 2, wherein said second connecting rod is connected to said crank angularly offset relative to the connection of said first connecting rod to said crankshaft so that said engine piston leads said percussion piston by an angle in the range of 10-60°.

4. A drilling and chipping hammer, as set forth in Claim 3, wherein the angular offset is 40°.

5. A drilling and chipping hammer, as set forth in Claim 4, wherein a flywheel is mounted on the opposite end of said crankshaft from said crank.

6. A drilling and chipping hammer, as set forth in Claim 5, wherein said flywheel includes a fan for cooling said internal combustion engine.

7. A drilling and chipping hammer, as set forth in Claim 1, wherein said dividing means includes a fluid-tight seal for sealing said percussion mechanism space from said engine space so that the one of air and fuel-air mixture in said percussion space cannot leak into said engine space.