US2875737A - Tools operated by an internal combustion engine - Google Patents

Description

March 3, 1959 E. UECKERT 2,875,737 I TOOLS OPERATED BY- AN INTERNAL COMBUSTION ENGINE Filed Aug. 14, 1956 2 Sheets-Sheet 1 March 3, 1959 UECKERT 2,375,737

TOOLS OPERATED BY AN INTERNAL COMBUSTION ENGINE Filed Aug. 14, 1956 2 Sheets-Sheet 2 Fig.3

United States Patent TOOLS OPERATED BY AN INTERNAL COMBUSTION ENGINE Ernst Ueckert, Mannheim, Germany, assignor to Knorr- Bremse G. in. b. H., Munich, Germany Application August 14, 1956, Serial No. 604,033 Claims priority, application Germany May 19, 1956 3 Claims. ('Cl. 123 -7) This invention relates to tools operated by'an internal combustion engine, and is more particularly, but not exclusively, concerned with tools which comprise'a working piston which is freely movable in the cylinder, and which piston is moved during the'striking stroke by the pressure of combustion gases and which is moved by compressed air during the return'stroke. The compressed air is controlled by a slide valve which is reversed by the varying pressure in the combustion chamber and which is constructed as a valve open towards the combustion chamber, as is the mixture inlet valve. In addition to the two valves, an ignition device is also situated in the combustion chamber of the tool. Ignition is initiated by a switching device, preferablyby a contact breaker, which is operated by an auxiliary piston.

One object of the invention consists in eliminating the tendency to'misfiring which is present with tools of this kind and in preventing burning and sticking of the slide valve.

A second object of the invention consists in improving the ignition arrangement with regard to accurate maintenance of the time of ignition, in preventing the slide valve from being thrown violently by the combustion pressure against its seating and in preventing the latter from being burned by the hot combustion gases.

A third object of the invention consists in improving the cooling of such a tool by surface cooling of the working cylinder independently of whether the working piston is in motion or not.

A forth object of the invention is a further improvemerit of the cooling arrangements consisting in the employment for cooling purposes of used return stroke air which constitutes by far the greatest amount of compressed air supplied to the tool.

The above mentioned objects are accomplished by measures set forth in particular in the appended claims.

For a better understanding of the invention and to show how the same may be carried into eifect, reference will now be made to the accompanying drawings in which:

Figure 1 shows the tool operated by an internal combustion engine at the instant of ignition,

Figure 2 shows the position in which the working piston has completed its striking stroke, the slide valve for control of the return stroke air having been already reversed,

Figure 3 shows the cooling arrangement at the instant when the hammer operated by an internal combustion is stopped, and

Figure 4 shows the arrangement of cooling air apertures through while the air is blown on to the cylinder from the outside.

Arranged with a tight fit in a cylinder 1 is a stepped piston 2 whose stroke is limited at the top by a collar 3 and at the bottom by an anvil 4. Connected to the anvil 4 in non-positive manner is a tool 5 which can, for example, be a chisel. The cylinder 1 is closed at its underside by a guide member 6 so that a sealed-oft chamber 7 is formed.

Situated in the upper portion of the cylinder 1 is a combustion chamber 8 whichi's' closed by a cylinder head 9. A sparkingplug 10 projectsihto the combustion chamher 8. Situated in the cylinderhead 9 is a mixture inlet valve 11 and a' control slide valve 12. Both comprise, at their sides facing the combustion chamber, a sealing face 13 with which they come to bear tightly against the cylinder head 9. The mixture inlet valve 11 is brought by a spring 14 into its sealing position. Its travel is limited in the opening sense by abutting of theannular disc 15 against a projection not shown or againsta projection of the cylinder 1'. Travel of the control slide valve 12 is limited by' the sealing face 13 on a collar portion of the valve 12 an'd'by a projection in the cylinder 1. An annular groove is formed on the control slide valve '12, which groove 16 can establish communication between annular s aces 17 and 18 and also between annular spaces 18 and" 19. The annular space 17 communicates by way of a starter slide 20 to a compressed air inlet 21, the annular space 18 by way of a duct 22 to the chamber 7 below the working piston 2, and the annular space 19 by way of a throttle point 23 to the exhaust duct 24. The diameter of the, throttle point 23 in proportion to the large diameter of the working piston 2, measured at the collar 3, is 1:10 to 1:15, the pressure of the compressed air supplied from the outside amounting to 2 to 3 kgl/cm and the hammer carries out approximately 1,200 blows per minute. The duct 22 is also taken into a space 25 below an auxiliary piston 26, which aleaf spring 27 tends to displace in opposition to the air pressure prevailing the space 25. Such a displacement has the effect that the breaker contact 28 is opened. The contact 28 is arranged in the primary circuit of an ignition coil (not shown) in whose secondary circuit the sparking plug 10 is situated. The primary circuit is supplied from an ignition current generator which, like the compressed air source, is separate from the tool and is therefore not illustrated. The starter slide 20, during the first part of its travel, under the eifect of turning a handle 44 in the counterclockwise direction opens up not only the access of air to the annular space 17 but also by way of a nonreturn valve 29 and an annular space 34 to a fuel container 30. At a further part of its travel, it opens a ballvalve 31 so that the fuel can issue under the effect of the air pressure hearing thereon by way of ar-iserpipe 32 to above a nozzle 33 and mix with the compressed airsituated in an annular space 34. The mixture passes into a mixing chamber 35 which communicates with an inner space 36 of the mixture inlet valve 11.

Let the position shown in Figure 1 be considered first of all in order to illustrate the method of operation of the tool operated by an internal combustion engine. The working piston 2 has mov'ed'into its upper end position under the eifect of the pressure effective in the space 7. Situated in the combustion'chamber is a fuel-air mixture, which, even after the mixture inlet valve is-clo'sed, maintains the rotational movement which was imparted to the said mixture' owing to th'e'on'e-sided'position of the said valve. Since the'influence of thespring 14 had already closed the mixture inlet valve 11 at the beginning of the upward stroke, and since the slide valve 12 was sealed by a cylindrical sealing portion 39 even when the sealing face 13 was lifted away, itwas possible for a pres sure to build up in the combustion chamber 8 which, owing to the converted kinetic energy of the working piston 2, is still above the value imposed by the cross-sectional ratio of the stepped working piston 2 and the pressure in the chamber 7. The ratio of the large diameter of the working piston to the smallest diameter of the said piston is between 1.1 and 1.2. Acting in opposition to this pressure is the pressure of the compressed air supplied at 21 and which bears against the end face 40 of the relatively small-diameter upper portion 41 of the slide valve 12. Since the pressure in the chamber 8 is higher than the pressure on the end face 40 and the associated end face 42 is greater than the end face 40, there is produced an upwardly directed force which reliably brings the control slide valve 12 into the illustrated position. In this position, the annular space 18 is connected by way of the annular space 19 to the discharge ducts 24, so that the space 7 is vented. The air flowing through the duct 24 cools the cylinder 1. The throttle 23 delays this outflow so long that even if the slide valve 12 is reversed prematurely it is ensured that the working piston 2 is brought into its end position when the auxiliary piston 26 is pushed downwards by the leaf spring 27 owing to the drop in air pressure in the space 25, and opens the breaker contact 28 and thus releases a spark at the sparking plug 10. Owing to the rotary movement of the introduced charge, the latter is ignited progressively and uniformly so as to produce smooth, knock-free combustion. The mixture situated in the chamber 8 is burned and drives the working piston 2 downwards onto the anvil 4 which transmits to the tool the blow which it itself receives. When the piston 2 has freed exhaust slots 43, the used gases flow out at high speed, so that the pressure in the combustion chamber 8 drops quickly. The excess pressure prevailing in the mixing chamber 35 opens the mixture inlet valve 11, which allows fresh mixture to flow into the chamber 8 driving the burned gases before it (Figure 2). Under the influence of the pressure bearing against the end face 40, the slide valve 12 moves into the position shown in Figure 2, and connects together with annular spaces 17 and 18, and as a result compressed air is admitted into the duct 22. The auxiliary piston 26 moves into the position corresponding to closure of the breaker contact 28, and the chamber 7 is filled with compressed air, whereby the working piston 2 is driven upwards so that the operation described hereinbefore can proceed once more.

By partly releasing the operating handle 44, first of all the ball valve 31 is completely closed and the opening 48 is partly closed, whereby supply of fuel to the nozzle 33 is cut off, and then the hammer operates merely with compressed air and with a substantially reduced striking force. If the handle 44 is completely released, the starter slide 20 moves into its right-hand end position in which the supply of air to the annular space 18 and to the fuel container 30 ceases, whereby the working piston 2 is stopped. This position isshown in Figure 3. The effect of the non-return valve 29 causes the pressure in the fuel container 30 to be maintained for a certain time so that the supply of fuel can be provided instantaneously once more after short working pauses. When the working piston 2 stops, compressed air flows through an aperture 45 opened in the right-hand end position of the starter slide 20, to the exhaust duct 24 and cools the cylinder 1. This supply of fresh air replaces the cooling effect of the used return stroke air. In addition, as long as compressed air is applied at 21, the cylinder 1 will be cooled both when operating and in the stopped condition, with cooling air which is directed along outer surface of the cylinder wall from a plurality of apertures 4 47 formed around the periphery of the cylinder and supplied via a bore 46. The smallest cross-section of the bore 46 amounts to approximately a quarter to a third of the smallest cross-section which determines throughflow through a slot 48.

I claim:

1. A tool operated by an internal combustion engine comprising a working cylinder, a main piston freely movable in the cylinder, a combustion chamber at one end of the cylinder, at non-return valve for admitting a combustible mixture into the combustion chamber, a conduit for applying compressed air against that end of the piston that is remote from the combustion chamber thereby to move the piston towards the combustion chamber, an inlet for compressed air, an outlet duct, a throttling device in the outlet duct, a slide valve operable in dependence upon the pressure in the combustion chamber for controlling flowof compressed air from the inlet to the conduit and from the conduit to the outlet duct, an ignition device arranged at the periphery of the combustion chamber, a contact breaker having contacts that open to operate the ignition device, an auxiliary piston operating the contact breaker, an auxiliary cylinder in which the auxiliary piston is located, a duct connecting the auxiliary cylinder with said conduit whereby the auxiliary piston is moved in one direction when there is high pressure air in said conduit, and a spring urging the auxiliary piston in the direction opposite to said one direction to open said contacts.

2. A tool operated by an internal combustion engine comprising a working cylinder, a piston freely movable in the cylinder, a combustion chamber at one end of the cylinder, an inlet device which serves to admit combustible mixture into the combustion chamber, a conduit for applying compressed air against that end of the piston that is remote from the combustion chamber thereby to move the piston towards the combustion chamber, an ignition device in the combustion chamber, a slide valve for controlling compressed air flow through the conduit, ducts in the wall of the working cylinder, means for feeding air to these ducts for cooling the working cylinder, Outlets distributed around the outer periphery of the working cylinder and directed along the outer surface of the cylinder, and means for supplying the outlets with air for cooling the cylinder independently of whether the working piston is operating or not.

3. A tool as set forth in claim 2, wherein the feeding means conveys to said ducts the return stroke air exhausted from the working cylinder via said conduit and said slide valve when the piston is working, and wherein the inlet cross-section for the cooling air supplied to said outlets amounts to between a quarter and one third of the inlet cross-section for the return stroke and combustible mixture forming air.

References Cited in the file of this patent FOREIGN PATENTS Sweden Ian. 8, 1935

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