NO150027B - DRAM AND GAMBLE HAMMER WITH COMBUSTION ENGINE DRIVE - Google Patents

Description

The invention relates to a drill and chisel hammer with a percussion mechanism

and internal combustion engine, where the engine's crankshaft is connected to a crank that sets the impactor's driving piston in a reciprocating motion via a crankshaft.

Hammer drills and chisels of the above type are used above all for larger demolition areas. The internal combustion engines used for operation are usually so-called two-stroke engines. This design has the advantage over a four-stroke engine that it has a simpler structure and thus also a smaller weight with comparable performance. Two-stroke engines are therefore common for weight and price reasons in hand-operated devices and machines.

The two-stroke engine must be flushed after each working stroke

a mixture of petrol and air, i.e. that the flue gases in the cylinder are displaced by the mixture and the engine is supplied with a new, ignitable charge. In order for the mixture to flow into the cylinder, however, a pump is required. With practically all smaller two-stroke engines, the engine's crankcase is used as a flushing pump. However, this is associated with a significant disadvantage. The crankshaft and crankshaft bearings as well as the cylinder wall must be sufficiently lubricated. With the petrol-air mixture, however, the lubricating oil is washed out in a short time, so that the machine would be destroyed within a short time without countermeasures. To remedy this, two-stroke engines use a petrol-oil mixture. The oil then has the task of lubricating the drive mechanism. The petrol is the energy carrier for the combustion.

However, since the oil entering the combustion chamber only burns incompletely during the combustion of the petrol-air mixture, it appears as unpleasant, blue exhaust smoke.

Still, the efficiency of ordinary two-stroke engines is generally less than that of a comparable four-stroke engine. The lower efficiency can mainly be traced back to the flushing losses when flushing the combustion chamber. In the case of larger, stationary or in-vehicle engines, considerable energy is partly used for flushing the combustion chamber. Thus, e.g. turbo fans, rotary vane fans (Drehschieber-Geblase) or piston pumps known. For portable devices, such as e.g.

drill and chisel hammers, however, such precautions are no longer required due to weight considerations.

The invention is based on the task of providing a drill and chisel hammer with a combustion engine, where the engine achieves a high degree of efficiency by means of good flushing and the whole hammer has a favorable performance weight.

According to the invention, this task is solved by the percussion mechanism's crank being arranged in a room separated from the further parts of the hammer, which has an intake valve, and above an outflow opening is in connection with the engine's intake slot leading to the combustion chamber.

When the impactor's crankcase is separated from the hammer's other parts, this can be used as a flushing pump for the engine. As the stroke volume of the percussion mechanism for a given two-stroke engine roughly corresponds to the stroke volume of the engine, the crankcase of the percussion mechanism is very suitable as a flushing pump for the engine. The bearing of the crankshaft is usually arranged in the engine's crankcase, and the drive piston is usually lubricated by the striker. The impactor's piston rod bearings can be made without any problems with tight, grease-lubricated bearings. Lubrication of the impactor's crankcase is therefore not necessary. As the engine's crankcase in the case of a carburettor engine does not come into contact with the fuel-air mixture, or in the case of an injection engine does not come into contact with the intake air, the lubrication of the crankshaft bearings, the crankshaft bearings and the engine's cylinder sliding surfaces can be calculated according to optimal viewing points. Thus, it can e.g. dip or oil dust lubrication is used. The sucked-in fuel-air mixture must therefore not fulfill special lubrication functions. It is thus possible to operate the device without an oily two-stroke mixture, which in-

has a beneficial effect on operating costs and emissions.

The known two-stroke machines have a further disadvantage. During scavenging, part of the fuel-air mixture passes as scavenging loss through the outlet slits above the muffler into the open air. In practice, this cannot be prevented with two-stroke engines. The consequences of this are a high fuel consumption, as this fuel no longer participates in the combustion process, as well as a high proportion of unburned,

essentially poisonous gases, which escape through the exhaust pipe. With the so-called injection engines, this is prevented by flushing with clean air. As soon as the piston has covered the guide slots and the combustion chamber is thus sealed, fuel is injected using a high-pressure injection nozzle. This measure results in three advantages: With the subsequent injection of fuel, performance is noticeably increased, fuel consumption is significantly reduced and exhaust gas quality is significantly improved. The flushing with the impactor's crankcase according to the invention is suitable for carburettors as well as for injection engines.

Through the intake valve, an ignitable mixture is sucked in over a carburettor known per se, or clean air over an air filter. Although this system is particularly suitable for an internal combustion engine that works according to the two-stroke principle, can

it e.g. also with a four-stroke engine, a so-called pre-compression is achieved and thus an increase in performance. The solution according to the invention is particularly simple and requires, in relation to a known, drill and chisel hammer which is driven by an internal combustion engine, only an intake valve and a forb-injection line from the separated room's outflow opening to the engine's intake slots. The Rules of Procedure. according to the invention thus entails practically no weight gain.

In order to achieve a simple structure of the device, it is appropriate that the front side of the drive piston, which faces the crank rod, forms a wall part of the space that is separated from the other parts of the hammer. In particular, no further precautions are necessary with a pneumatic percussion mechanism, as the drive piston,

which moves back and forth in a cylinder, is already sealed against the air cushion located between the driving piston and an impact piston. The compression of the aspirated air or mixture in the separated space can be optimally determined by determining the crank stroke and residual volume within certain limits, regardless of

the drive motor.

With the help of a room separated from the other parts of the hammer, new possibilities are obtained, compared to a known device where the crank of the percussion mechanism and the crank of the drive motor are arranged in the same room. In the case of a normal two-stroke engine, the air-fuel mixture is sucked into the engine's crankcase and precompressed during the expansion phase in the crankcase's combustion chamber. Shortly before bottom dead center is reached, the overflow channels are released by the piston and the pre-compressed mixture can flow into the combustion chamber from the crankcase. When the crank is turned further, however, the pressure in the crankcase as well as in the overflow channel decreases, so that the inflow into the combustion chamber is slower. For this reason, only an incomplete flushing of the combustion chamber is possible. If, on the other hand, the scavenging pressure is increased by reducing the crankcase, there is a risk that too large a portion of the ignitable mixture flows out unburned through the exhaust gas slits as scavenging loss, which in turn leads to increased fuel consumption. In order to now optimally adapt the flushing pressure to the flushing process, it is advantageous that the percussion mechanism's crank is thus offset in relation to the engine's crank

axle that the percussion mechanism is delayed in relation to the engine with a crank displacement of from 10° to 60°. Thus, it is possible that a sufficient flushing pressure exists, until the intake or overflow slots are again covered by the piston, when the crankshaft is turned further with the bottom dead center of the engine piston as a starting point. As the percussion mechanism is connected to the crankshaft, this crankshaft displacement remains constant.

In practice, it has proven appropriate that the crank offset is 40°. Thereby, at a given position of the intake or overflow slots, there is sufficient flushing pressure until the intake or overflow slots are closed, which prevents a backflow of the flushing air and enables a significantly better flushing than can be achieved by flushing from the crankcase. On the other hand, the pressure drop between the flushing pressure and the pressure in the combustion chamber is small when the intake slits are opened, so that a flow can form in the combustion chamber and the newly inflowing mixture mostly displaces the burned gases through the exhaust gas slits.

In the following, the invention will be described in more detail by means of an example with reference to the drawings, where fig. 1 shows a drill and chisel hammer according to the invention, partly in section, fig. 2 shows the driving mechanism parts of the percussion mechanism and the engine in the top dead center position of the driving piston, following the line A - A on

fig. 1, and fig. 3 shows the drive mechanism parts in the bottom dead center position of the drive piston.

The one in fig. 1 shown hammer drill and chisel mainly consists of a general housing designated by 1. A handle 2 is attached to the rear end of the housing 1. A tool holder 3 is arranged on the side of the housing 1 which is opposite the handle 2. In the housing 1, a crankshaft for the internal combustion engine, generally denoted by 4, is rotatably mounted. Single crank rod 5 is rotatably attached to a crank pin 4a. The connecting rod 5 is again connected to a piston 6. The piston 6 is in turn guided in a cylinder 1c. At the upper end of. the crankshaft 4 is a crank generally denoted by 7 via a thread 4b connected to the crankshaft 4. A crank rod 8 for the percussion mechanism is attached to a crank pin 7a. The connecting rod 8 is on

its side connected to a drive piston 9, e.g. for a pneumatic percussion instrument. The drive piston 9 is guided in a cylinder guide 10. The impact mechanism is thus connected to the internal combustion engine. On the house 1

an intake valve generally denoted by 11 is arranged in the area of the crank 7. In the intake valve 11, a ball 11a is pressed against a valve seat 11c by means of a spring 11b. The intake valve 11

thus functioning as a non-return or one-way valve. When the drive piston 9 moves in the direction of the tool holder, air or optionally a fuel-air mixture is sucked through the intake valve 11 into a space 1a, in which the crank 7 and the crank rod 8 move. The room 1a is sealed against the other parts of the housing 1 by means of a gasket 12. The room 1a also has an outflow opening 1d. A pipeline 13 leads from the outflow opening 1d to an intake slot 1e in the cylinder 1c. When the drive piston 9 changes direction and again moves towards the handle 2, the chamber 1a is reduced and the air or fuel-air mixture sucked into it is pushed through the pipeline 13. When the piston 6 releases the intake slot 1e, the air can flow into the combustion chamber 1b. Thereby, the burnt exhaust gases, which are in the combustion chamber 1b after ignition, are displaced through an exhaust gas slot 1f. This process is referred to in the technical language as flushing. In a so-called pre-

gas engine, it is flushed with an ignitable fuel-air mixture. This in itself entails the disadvantage that a part of the mixture may escape through the exhaust gas slits 1 f and reduce the efficiency of the internal combustion engine. With the so-called injection engine, on the other hand, clean air is flushed. The fuel is sprayed through a nozzle in the combustion chamber 1 only when both the intake slot 1e and the exhaust slot 1f are closed. This in turn has a beneficial effect on the efficiency. A flywheel 14 is arranged on the lower end of the crankshaft 4, which is usual for internal combustion engines. The flywheel 14 serves, on the one hand, to equalize between the combustion engine's output and the engine's power intake during the compression phase as well as the impact work of the percussion mechanism. In addition, the flywheel is used as a generator for developing the ignition voltage and as a fan wheel for a cooling air flow which is sucked in through a cover 15 and blown past the cylinder 1c.

Of that in fig. 2 shows a section through the device, following the line A - A in fig. 1, the essential drive mechanism parts for the device are shown. The drive piston 9 is there in its top dead center position. With regard to the direction of rotation D, however, the piston 6 has already passed its top dead center position. The impactor's crankpin 7a is thus offset relative to the internal combustion engine's crankpin 4a by an angle dL>, whereby the impactor is delayed in relation to the internal combustion engine by this angle oO. Upon further turning of the crank 7, the space 1a is reduced again and the air or air-fuel mixture that is in it is ejected through the outflow opening 1d. This delay of the percussion mechanism in relation to the combustion engine has, compared to a normal two-stroke engine, where the engine's crankcase acts as a scavenging pump, the advantage that the scavenging pressure during the entire scavenging process is above the pressure in the combustion chamber, so that a backflow is prevented.

Fig. 3 shows the same drive unit parts as fig. 2, but in the bottom dead center position of the drive piston 9. The piston 6 thereby already moves away from the crank 7. Thereby, the fuel-air mixture which has flowed from the chamber 1a through the outflow opening 1d and the intake slot 1e is compressed into the combustion chamber. In this position, the percussion's power requirement is low. The energy stored in the flywheel can thus be practically completely used for the compression of the fuel-air mixture contained in the combustion chamber 1b. Thus, the phase shift between percussion and internal combustion engine also has a beneficial effect.

Claims (4)

1. Drilling and chisel hammer with hammer and internal combustion engine, where the engine's crankshaft is connected to a crank that sets the hammer's driving piston in a reciprocating movement via a crank rod, characterized in that the hammer's crank (7) is arranged in one of the hammer's other parts separate space (la) having an intake valve (11), and above an outflow opening (ld) is in communication with the engine intake slot (le) leading to the combustion chamber (lb). 2. Drill and chisel hammer according to claim 1, characterized in that the front side of the drive piston (9), which faces the crank rod (8), forms a wall part of the space (la) which is separated from the other parts of the hammer. 3. Drill and chisel hammer according to claims 1-2, characterized in that the percussion mechanism's crank (7) is so offset in relation to the engine's crankshaft (4), that the percussion mechanism is delayed in relation to the engine with an angular displacement of the crankshaft from 10° to 60°. 4. Hammer drill and chisel according to claim 3, characterized in that the angular displacement of the crankshaft is 40°.