A DOSAGE DEVICE

Abstract: A liquid metering device for a compressed air tool includes a sealable liquid tank (2) whose lower part is connected to the compressed air inlet (3) on the tool downstream from its throttle valve, via a through-flow impeding filter element (7) that is in contact with the liquid. The filter element communicates directly with an upper tank space (8) disposed in the tank (2) above the intended maximum liquid level of the tank.

Description: A DOSAGE DEVICE The present invention relates to a liquid dosing or metering device for compressed air tools, wherein the device includes a sealable liquid tank whose lower part is connected to the compressed air inlet on the tool, downstream of its throttle valve, via a flow-restricting or flow-impeding filter element that is in contact with the liquid . Such metering devices are intended to supply a usually very small amount of liquid, normally a suitable oil, to the compressed air inlet downstream of the throttle valve in the event of an interruption in the operation of a compressed air tool. When operation is resumed, this liquid is entrained by the compressed air into the tool. It is difficult to avoid undesirable leakage of the liquid from the tank to the air inlet if there is a long interruption in operation. Moreover, it is difficult to provide, regardless of the liquid level, the desired uniform liquid dosage to the air inlet with every interruption in operation. The object of the invention is to provide a novel and advantageous liquid metering device with which the aforesaid difficulties are avoided at least to a substantial extent. To this end, it is proposed in accordance with the invention that the filter element of a device of the kind defined in the introduction also communicates directly with an upper tank space in the tank above the intended maximum liquid level in said tank. This arrangement is advantageous in that for each interruption in operation the metering device will only dispense the liquid that is already in the filter element, whereafter the pressure in the liquid tank continues to be relieved, i.e. lowered, by forcing essentially only air from the upper tank space to the compressed air inlet via the filter element. Additional advantageous features of the invention are set forth in the dependent claims. Hereinafter, the invention will be described in greater detail with reference to an exemplifying embodiment of the invention and also with reference to the accompanying drawing Fig. 1 is a partial cross-sectional view of a compressed air tool that has been provided with a liquid metering or dosing device in accordance with the invention. Fig. 2 is an axial sectional view drawn to a larger scale through a pipe having a built- in filter element utilized in accordance with the invention. Fig. 1 shows a part of a compressed air tool generally designated 1. In the illustrated case, the tool is presumed to be conventional compressed air breaker or chisel, although it could be any chosen impact or rotary compressed air tool. A small oil accommodating tank 2 has been built into the tool casing. Each time operation of the tool is interrupted, a small amount of oil will be metered out to the compressed air inlet 3 of the tool at a region thereof which is located downstream from the throttle valve (not shown) of the tool, i.e. in an area or region that is under pressure while the tool is operating but that is relieved of pressure when the tool is stopped as a result of the closing the throttle valve. Tank 2 is sealed tightly by means of a closure hood 4, and is provided with a bottom opening 5 that passes between the bottom the tank and air inlet 3. The broken line 6 indicates the oil level in the tank 2. Shown at 7 is a filter element which is in contact with the oil in the tank 2 and via which the tank communicates with the air inlet 3. The filter element 7 is made from an open-pore material, for instance a sintered material, such as sintered bronze, with pores in the range of 2-10 μm ,for instance in the range of 4-7μm. The filter element 7 thus impedes the through-flow of oil so that leakage of oil out to the inlet will be prevented when the pressures prevailing in the tank 2 and the inlet 3 are the same, but will allow air to enter the tank 2 when a positive relative pressure prevails in the inlet 3, and will allow oil and air to flow out to the inlet 3 when a relative positive pressure prevails in the tank 2. However, filter element 7, which offers less resistance to the through-flow of air than to the through-flow of oil, also communicates directly with the upper space 8 in the tank above the level 6 and above the intended maximum oil level so that when there is a positive relative pressure in tank 2, predominantly air is forced through the filter element 7 as soon the air has forced the oil present in element 7 out to the inlet 3. This ensures, as desired, that only small amounts of oil, 0.08-0.18 ml for example, will be pressed out into the inlet each time the operation of tool 1 is interrupted, and that the pressure between the tank 2 and the inlet 3 will be quickly equalised, e.g. within the space of 1-5 seconds, after such an interruption. Conversely, there will be a quick build-up of pressure in tank 2 after the throttle valve is opened, since the air is able to flow into the tank with relative ease after the oil present in the filter element has been forced out. In the illustrated example, the filter element 7 has two side surfaces 9 (Fig. 2) that are exposed to the liquid in tank 2, while a piping 10 runs between the upper tank space 8 and an upper surface 11 of the filter element 7. As a result of capillary action, the filter element 7 sucks up oil through both of the surfaces 9, and is emptied into the tank by means of in-flowing air when there is a positive relative pressure in the inlet 3, and which is emptied into inlet 3 by means of out-flowing air when there is a positive relative pressure in the chamber 2. Most advantageously, as shown most clearly in Fig. 2, the filter element7 is mounted in a relatively thick- walled pipe 12, wherein that part of the pipe which is located above the element 7 forms the aforesaid pipmg 10 and that part 13 which is located beneath the element 7 is fitted, e.g. force fitted, into the opening 5. Pipe 12 has a diagonal through-bore 14 with an inside diameter that is larger than the inside diameter of the pipe 12, wherewith filter element 7 is received in the bore 14 with a press fit for example. The invention is not limited to the described and illustarted embodiment, but can be implemented in any desired manner within the scope of the inventive concept as defined in the accompanying claims.

Claims: CLAIMS 1. A liquid metering device for a compressed air tool, wherein the device includes a sealable liquid tank (2) whose lower part is connected to the compressed air inlet (3) to the tool downstream from its throttle valve, via a through-flow impeding filter element (7) that is in contact with the liquid characterized in that filter element (7) also communicates directly with an upper tank space (8) in the tank (2) above the intended maximum liquid level in said tank. 2. A device according to Claim 1 , characterized in that the filter element (7) has at least one side surface (9) exposed to the liquid in the tank (2), and in that a tubular conduit (10) is provided between the upper tank space (8) and an upper surface on the filter element, for communication with the said upper tank space (8). 3. A device according to Claim 2, characterized in that the filter element (7) is mounted in a pipe (12) whose one end (13) is received in an opening (5) that extends between the bottom of the tank (2) and the compressed air inlet (3) of the tool, and whose other end opens into said upper tank space (8), wherein the filter element (7) comprises a porous body which is fitted in the pipe (12) and which has at least one side surface (9) exposed to the liquid in the tank via an opening in the pipe wall. 4. A device according to Claim 3, characterized in that the filter element (7) comprises a cylindrical porous body which has an outer diameter larger than the inner diameter of the pipe (12) and which is received in a bore (14) that extends diagonally through the pipe such that end surfaces (9) of the body are exposed to the liquid in tank (12) and such that a part (11) of the outer surface of said body communicates with said upper tank space (8). 5. A device according to any of Claims 1 - 4, characterized in that filter element (7) is a porous body made of sintered material, such as sintered bronze.

Inventors: KAUPPI SUNE, SAXBAECK LARS, KAUPPI, SUNE, SAXBAECK, LARS
Applicants: BEREMA ATLAS COPCO AB, KAUPPI SUNE, SAXBAECK LARS, ATLAS COPCO BEREMA AB, KAUPPI, SUNE, SAXBAECK, LARS
Application year: 1997
Main classification: B25D17
IPC codes: B25D17, F16N7